MUNICIPAL SLUDGE
MANAGEMENT
AND DISPOSAL
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MUNICIPAL SLUDGE MANAGEMENT--1975
The EPA Research and Development Representative in your
Federal Region has requested that this copy of the "Proceedings
of the 1975 National Conference on Municipal Sludge Management
and Disposal" be sent to you. The Conference, which was held at
Anaheim, California, was cosponsored by the Office of Research
and Development of the U.S. EPA and Information Transfer, Inc.,
Rockville, Maryland.
Enclosed for your information is a copy of the Organization
Chart for the Office of the EPA's Assistant Administrator for
Research and Development. The research and development program
on treatment, processing, and disposal of municipal wastewater
sludge is conducted by the Ultimate Disposal Section (Wastewater
Research Division) in Cincinnati's Municipal Environmental Research
Laboratory. Headquarters' coordination is carried out by the
Waste Management Division in Washington, D.C.
Mr. Don Ehreth (phone: 202/426-0265) and I (phone 513/684-7645)
will be pleased to respond to your questions about the program.
/ ^Joseph B. Farrell, Ph.D.
Chief, Ultimate Disposal Section
'Wastewater Research Division
Municipal Environmental Research Laboratory
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ASSISTANT ADMINISTRATE FjR f£ C-'VO t D[V£LQP"£',T
Dr. Wilson k. Tallev ':*/) 7^5-2630
ASSOCIATE ASSISTANT AC" I N I STPAK ?
Carl q. Cerber (202) 75&-OI72
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OFFICE OF MOMITORING L TECHNICAL SUPPORT
Deputy Asilslant Administrator:
Albert C. TrdkyusVi, Jr." (202) ^26-2202
Deputy: H. Matthew Bills* (202) 1.26-2202
PROGRAM OPERATIONS jT
RtGIONAL SERVICE', STAFF
(202) U6-23I/
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(202) 1.26
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LABORATORV, Cincinndli
Director; Dwlght G. Bdllin
(511) 684-7301
ENVIRONMENTAL MONITORING & SUPPORT
1919) ^9-2106
ENVIRONMEHTAL MOHITOMSC- i SUPPORT
LABORATORY, Loi Vojan
Oi rector: Dr. Del hert S Bur tn«
(702) 736-2969, t* 201
OFFICE OF Irlt PI'.IHC ! [1 ' L
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Dr. Struhcn J. Cjg-^ f202) 755-^57
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Director- Dr. Aig-cv, J ^cL
HEALTH EFFECTS RESEARCH LABOPATORV,
C.ncmnat t
(513) 68J-7401
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EHVIHOHMENTAL RESEAflCh L«hCPAT" i3 r ,
D i rector: Dr. Tfi.
OFFICE OF AIR, L^NO, fc UATER USE
Dr. Thoui Murphyi (;C2) 1-25-2260
Deputy] Lawrence Gray* (202) Ii26-397
-------
Albe/t. Roy (Dr.)
Deputy Assistant Administrator*
Office of Health and Ecological Effects
613..WSMW** -RD 683
Altshuller, A. Paul (Dr.)
Director,* Environmental Sciences
Research Laboratory
Research Triangle Park,
North Carolina 27711
Ballinger, Dwight C.
Director,* Environmental Monitoring
and Support Laboratory,
Cincinnati, Ohio 45268
Earth, Delbert S. (Dr.)
Director,* Environmental Monitoring
nnd Support Laboratory,
P. 0. Box 15027
Lae Vegas, Nevada 89114
Bartsch, A. F. (Dr.)
Director,* Environmental Research
Laboratory,
200 SW 35th Street
Corvallis, Oregon 97330
Bills, H. Matthew
Deputy,* Office of Monitoring &
Technical Support
3100G WSM** R 680
Mr. Francis T Mj/o
Director,* Municipal Environmental
Research Laboratory
Cincinnati, Ohio 45268
Burchard, John K. (Dr.)
Director,* Industrial Environmental
Research Laboratory
Research Triangle Park,
North Carolina 27711
Cauley, William A.
Director,* Technical Support Division
3100B WSM** RD 680
Cortesi, Roger S.
Director,* Criteria Development and
Special Studies Division
W613F. WSM** RD 683
Daly, Phyllis A.
Director,* Office of Planning
and Review
W915 WSM** RD 675
Duke, Thomas W. (Dr.)
Director,* Environmental Research
Laboratory
Sabine Island,
Culf Breeze, Florida 32561
Duttweiler, David W. (Dr.)
Director,* Environmental Research
Laboratory
Athens, Georgia 30601
Engel, Ronald (Dr.)
Director,* Health Effects Division
W609B WSM** RD 633
Frietsch, William
Director,* Program Operations Staff
3702F WSM** RD 682
Gage, Stephen (Dr.)
Deputy Assistant Administrator,
Office of Energy, Minerals, & Industry
635 WSMV** RD 681
Garner, R. John (Dr.)
Director,* Health Effects
Research Laboratory
Cincinnati, Ohio 45268
Gerber, Carl R.
Associate Assistant Administrator,
Office of Research & Development
911 WSMV.1** RD 672
Gray, Lawrence
Deputy,* Office of Air, Land, and
Water Use
3702C WSM** RD 682
Hall, Clinton W.
Director,* Energy Coordination
Staff
W647A WSM** RD 681
Knelson, John H. (Dr.)
Director,* Health Effects
Research Laboratory
Research Triangle Park,
North Carolina 27711
Lederman, Peter B. (Dr.)
Director,* Industrial and
Extractive Processes Division
627 WSMW** RD 681
Mastracci, Michael
Director,* Regional Services Staff
3100C WSM** RD 680
McErlean, Andrew T. (Dr.)
Director,* Ecological Effects Division
W611 WSM** RD 683
Mount, Donald I. (Dr.)
Director,* Environmental Research
Laboratory
6201 Congdon Boulevard
Duluth, Minnesota 55804
Murphy, Thomas (Dr.)
Deputy Assistant Administrator?
Office of Air, Land, and Water Use
3702B WSM** RD 682
Neuschatz, Alan
Director,* Office of Financial and
Administrative Services
3812C WSM** RD 674
Princiotta, Frank
Director,* Energy Processes Division
631 WSMV.1** RD 681
Rausa, Gerald
Director,* Program Operations Staff
W635 WSM** RD 681
Robeson, Ross K.
Director,* Program Operations Staff
3100F V.'SK** RD 680
Rosenkranz, William A.
Director,* Waste Management Division
37021 WSM** RD 682
Schneider, Eric D. (Dr.)
Director,* Environmental Research Laboratory
P. 0. Box 277
West Kingston, Rhode Island 02982
Shearer, S. David (Dr.)
Director,* Environmental Monitoring
and Support Laboratory
Research Triangle Park
North Carolina 27711
Stephan, David G. (Dr.)
Director,* Industrial
Environmental Research Lab.
Cincinn.il 1
Talley, Wilson K. (Dr.)
Assistant Administrator
for Research 6 Development
W9I1 WSM** RD 672
Trakowski, Albert C.
Deputy Assistant Administrator*
Office of Monitoring £,
Technical Support
3100 I WSM** RD 680
Wright, Darwin R.
Director,* Agriculture and
Non-Point Sources Management
Division
3702E WSM** RD 682
Wiser, Herbert L. (Dr.)
Office of the Principal Science
Advisor*
W923 WSM** RD 676
Galegar, William C.
Director,* Robert S. Kerr Environmental
Research Laboratory
P. 0. Box 1198
Ada, Oklahoma 74820
Shobe, Randall V.1. (Dr.)
Director,* Technical Information Division
3809H WSM** RD 680
Stanley, Thomas W.
Director,* Monitoring Technology Division
3809D WSH** RD 680
* Acting
** The address for all Waterside Mall (WSM) offices is:
401 M Street, S.W.
Washington, D. C. 20460
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PECCEEDINCS CE THE 197<5
Ml K SII CONFERENCE CN
MUNICIPAL SELDCE
MANACEMENT AND DISPOSAL
AUGUST 18-20,1975
Anaheim, California
Sponsored by:
The Office of Research and Development
United States Environmental Protection Agency
Environmental Quality Systems, Inc.
Information Transfer, Inc.
-------
Printed in the United States of America
Library of Congress Catalog No. 75-39534
Copyright© 1975
by
Information Transfer, Inc.
1160 Rockville Pike
Rockville, Maryland 20852
All Rights Reserved
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CONTENTS
Every thing Is Connected to Everything Else 1
The Honorable George E. Brown, Jr., United States Congress
Everything You Wanted To Know About Sludge
But Were Afraid To Ask 4
Harold Bernard, Environmental Quality Systems, Inc.
Impact of Industrial Wastewater Pretreatment
on Sludge Management 14
Charles Ris, George Rey and Thomas Short,
United States Environmental Protection Agency
For California—A Model Industrial Waste Ordinance 19
Paul C. Soltow, Jr., Bay Area Sewage Services Agency
Institutional Problems of the Small Treatment Plant 23
E.J. Martin, Richard DuBois and Harold Bernard,
Environmental Quality Systems, Inc.
Regional Wastewater Solids Management Program
Los Angeles—Orange County Metropolitan Area 26
David Burack, Los Angeles-Orange County Sludge Program
Computer Evaluation of Sludge Handling and Disposal Costs 30
Robert Smith and Richard G. Eilers,
United States Environmental Protection Agency
Urban Sludge Disposal or Utilization
Alternatives—Soico-Economic Factors 60
Albert Montague, United States Environmental Protection Agency
Sludge Management Alternatives for Coastal Cities 65
Terry Bursztynsky and John Davis, Engineering-Science, Inc.
By-Product Solids Management Alternatives
Considered for Philadelphia 73
Elmer F. Ballotti and Thomas E. Wilson, Greeley and Hansen
Sludge Disposal Alternatives for Boston 80
George D. Simpson, Havens and Emerson, Ltd.
Alternatives for Disposal for the Metropolitan
Denver Sewage Disposal District No. 1 86
William J. Martin, Metropolitan Denver Sewage
Disposal District No. I and Jerry D. Boyle,
C//2-M Hill, Incorporated
Energy Conservation Practices in Municipal Sludge Management 91
G. Wade Miller, Public Technology, Incorporated
Updating the 1974 Pittsburgh Conference 101
Darwin R. Wright, United States Environmental Protection Agency
in
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IV
Summary of the ASCE Seminar on Sludge Disposal
C. Michael Robson, MCA Engineering Corporation
The Past, Present, and Future Prospects of Burning
Municipal Sewage Sludge Along With Mixed Municipal Refuse H5
Elbridge M. Smith and Allan R. Daly, Roy F Weston, Inc.
High Energy Radiation in Sludge Treatment—Status and Prospects 124
J.B. Farrell United States Environmental Protection Agency
Management of Municipal Wastewater Treatment Residuals 134
Edward H. Bryan, National Science Foundation
Pyrolysis of Sewage Sludge 139
Robert A. Olexsey, United States Environmental Protection Agency
Sludge Pyrolysis for Energy Recovery and Pollution Control 146
F. Michael Lewis, Stanford Research Institute
A Sludge Policy for the 70'S 153
L. Russell Freeman, United States Environmental Protection Agency
Ecological Impact of the Disposal of Municipal
Sludge onto the Land 156
James Schmid, Dennis Pennington and
Jack McCormick, Jack McCormick & Associates, Inc.
Plant Uptake of Heavy Metals from Sewage Sludge Applied to Land 169
Rufus L. Chaney, United States Department of Agriculture and
Michael C. White and Paul W. Simon, Maryland Environmental Service
Effects of Sewage Sludge or Effluent Application to Soil on the
Movement of Nitrogen, Phosphorus, Soluble Salts and Trace Elements to Ground waters 179
A.L. Page and P.P. Pratt, University of California
Environmental Effects of Sludge Disposal in Sanitary Landfills 188
Bruce R. Weddle, United States Environmental Protection Agency
Engineering Study and Field Demonstration Trials
for Sand Dune Stabilization 200
George D. Ward, George D. Ward and Associates
Potential Health Impacts of Sludge Disposal on the Land 204
Gory J. Love, Edythalena Tompkins and Warren A. Galke,
United States Environmental Protection Agency
FDA's Overview of the Potential Health Hazards Associated with the
Land Application of Municipal Wastewater Sludges 214
G.L. Braude, C.F. Jelinek and P. Corneliussen
Food and Drug Administration
A Summary of Observations on Thermophilic Digester Operations 218
George T. Ohara and James E. Colbaugh, City of
Los Angeles' Hyperion Treatment Plant
Utilization of Methane from Sludge Digestion 222
Surinder K. Kapoor and Donald Newton, Greeley and Hansen
Processing, Economicsand Sale of Heat Dried Sludge 235
Gerald Stem, United States Environmental Protection Agency
Composting Raw Sludge 245
E. Epstein and G.B. Willson, United States Department of Agriculture
Potpourri 249
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MUNICIPAL SLUDGE
MANAGEMENT AND DISPGSAE
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"EVERYTHING IS CONNECTED TO
EVERYTHING ELSE"
The Honorable GeorgeE. Brown, Jr.
United States Congress
(36th. C.D.—California)
Washington, D. C.
I am glad to be here today with such a distinguished
group of specialists in the esoteric field of sludge man-
agement and disposal. My presence is apparently a con-
cession to the fact that with such a diversity of expertise
as is represented here, it might have been difficult to
find a speaker with a sufficiently broad background to
encompass all of these specialties. Under these circum-
stances it is appropriate to call on a politician, who is
sometimes defined as one who knows less and less about
more and more, until finally he knows nothing about
everything.
I welcome this opportunity, because I have a genuine
interest, both personal and legislative, in your problems.
I also have some very serious reservations about the
kinds of technological developments which characterize
our society, developments which have, in the course of
solving certain kinds of problems, brought on other
problems of an even more serious nature. Your meeting
here reflects that situation; for you are called upon to
find new solutions to those second-order problems
created by the nature of our technological growth.
I am especially pleased to see that your program and
your participants reflect a multi-disciplinary and multi-
institutional approach to the problems you are address-
ing. It is my sincere hope that gatherings of specialists,
such as this one, will move us towards solutions to real
problems. That is, after all, the major reason for having
it. But I continue to be skeptical. Let me explain why.
The current dilemma with sludge disposal has come
about as we developed from a rural, thinly settled, fairly
unspecialized society toward an urban, densely settled
and highly specialized society. We simultaneously grew
away from our frugal and thrifty beginnings to become
the most affluent and thriftless society in the world. The
growth of industry and continental markets, and the ex-
istence of hugh inventories of cheap energy and other re-
sources, lead to a new emphasis on material consump-
tion and a new disregard for conserving and recycling
materials, and minimizing waste. Inevitably this has led
to the necessity of meetings such as this, to seek solu-
tions to the problem of disposing of a resource that has
been labeled waste. Not only has our system mis-labeled
this resource, for much of it is not only useable, but in-
creasingly valuable, but the system has diluted and dis-
persed it so as to make its recovery and use many times
more difficult.
We have developed an enormous, highly specialized,
single purpose waste disposal system which has, at least
until quite recently, been regarded as largely uncon-
nected with other systems in the society. Largely hidden
from public view, the waste disposal system has at-
tracted little public attention or interference, except on
the infrequent occasion of a major breakdown.
As the system expanded by orders of magnitude,
formerly adequate waste disposal and dispersal
methods became inadequate. Land, air, rivers and even
oceans proved too small in capacity to absorb the by-
products of a profligate society without harmful side-ef-
fects on human and other life. And now we have entered
the era of the legislative solution, seeking by law and
regulation to control the excesses of our every-growing
and more prosperous society.
As a corollary to the problem of over-abundant waste,
we face another growth problem—that of inadequate
supplies of materials and energy. Dramatic increases in
the prices of oil, natural gas, fertilizers and chemicals
derived from hydrocarbons, and a host of other things
and processes based on them, have now forced us to
change our perspective on what constitutes waste, and
how it can be re-cycled, re-used, and beneficially dis-
posed of in natural systems.
None of this is new to the members of this audience. It
is part of your daily environment, and the cause for con-
ferences such as this one.
As we enter the era of increased Federal legislation,
and corresponding legislative action at state and local
levels, we find that in the usual course such legislation
can frequently be categorized as single-purpose, crisis-
response legislation. It is designed by its authors to solve
one problem at a time, and not to deal with the multitude
of inter-connected issues that surround any important
social problem. Such is the nature of the legislative pro-
cess.
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EVERYTHING IS CONNECTED
Legislators are aware of this failing, if such it is and
usually include in such legislation a suitable number of
catch-all clauses which have as their purpose the direct-
ing of the administrators in the executive branch to per-
form all necessary related duties and functions required
to solve the particular problem. There are many ex-
amples of such legislation.
The technical community has sometimes contributed
to this legislative failing by not developing, synthesiz-
ing, and publicizing broadly adequate solutions to socio-
technical problems, and forcefully channelling such pro-
spective solutions into the legislative process on a con-
sistent basis. Frankly, the narrow reach of most scien-
tific and technical fields, at least in comparison to the
scope of the problems facing us, has contributed to this
failing. I see developing within the scientific and tech-
nical community, however, a growing awareness of the
importance of integrative mechanisms which will bring
together not only the knowledge specialties, but the total
knowledge component, with the action components of
society into new forms of problem-solving systems. Per-
haps this conference is an example of such develop-
ments.
Which brings me to one of my major concerns, which
is reflected in the title of my remarks, "Everything is
connected to everything else." Most of you will recog-
nize that I have stolen this from Barry Commonor, who
cites it as one of the four rules for solving environmental
problems.
I am fearful that you, as specialists, will seek to devise
another specialized approach to the management and
disposal of municipal sludge, and leave the larger prob-
lems, the problems caused by the "connections with
everything else", for others to solve. You would be justi-
fied in opting to solve your own problems first, but I be-
lieve that you would be neglectful of your full responsi-
bilities if you did not at least ask the question—Does the
solution to my problem create problems for someone
else? Could a different solution help to solve someone
else's problem? Clearly, these are difficult and
complicated questions that may be impossible to fully
answer, but they are not irrelevant questions.
Your conference has a genuine cross-section of ex-
perts who can and probably will, address the entire
range of issues that relate to sludge management and
disposal. Each speaker will have a small, but important
piece of the puzzle contained in their presentation. If you
are fortunate, you will leave here this week with some
real solutions to your problems, at least theoretically.
And then you will encounter a whole new set of difficul-
ties. You may find that the public will not accept your
solution, or that the solution requires the development of
complicated inter-connections with other economic
sectors, such as agriculture or energy. Or you may find
that the economics of your solution do not impress those
who hold the purse strings. Whatever difficulties you
encounter, they will be accentuated by the fact that you
will be a specialist, attempting to communicate with
others who do not share your experiences or expertise.
This situation is not unique to waste management. But
I'm optimistic that the opposition to certain sludge dis-
posal methods, especially land disposal, will be on
grounds that should be surmountable. The ease with
which you can sell your disposal technique will vary with
special circumstances, but I can assure you that certain
trends, already well underway nationally, will continue
to restrict some of your options and will tend to highlight
the importance of those remaining options that are not
precluded by law.
These trends include a continued increase in energy
prices, thus changing much of the economics of the past
in such divergent areas as incineration and fertilizer
costs. There will be a continued effort to reduce air pollu-
tion emissions. There will be a continued effort to reduce
the release of pollutants into the water systems. Finally,
and perhaps most importantly, there will be increasing
need for and effort to reduce the amount of metals and
other persistent chemicals released into the air, land,
and water.
Given the nature of the restraints being forced upon
sewage plant operators, it is unfortunate that the Envi-
ronmental Protection Agency does not yet have ade-
quate research results to set standards for acceptable
methods of sludge disposal. It is especially disappoint-
ing that regulations for the control of heavy metals are
not yet established, especially since the main sources of
these metals are industrial, and fairly easily con-
trollable. You will be hearing more about this as your
conference goes along. I hope that the results of your
discussions move up rapidly towards the promulgation
of guidelines for fully acceptable methods of sludge
disposal.
Eventually, and probably fairly soon, the combination
of forces which I have dealt with here only briefly will
force a situation where we will be controlling the quality
of our wastes much more carefully in order to fully re-
claim those constitutents having value for use in energy
or fertilizer production, with true, unusable wastes
being the only remaining sludge. Such a situation might
even lead to sewerless communities that compost their
own domestic wastes, and recycle or specially treat in-
dustrial wastes. Such communities would, of course,
have to be far more integrated and aware of wastes than
are today's cities and towns, and would in all likelihood,
have to become better integrated with regular agricul-
tural practices. In such a community the motto, "Every-
thing has value" would be practiced. Such a community
could have animals recycling agricultural and animal
wastes back to new food, while the people could recycle
much of the remainder of the wastes back to energy pro-
duction for the food or industrial cycle from which it
came.
Many of our colleagues who have returned recently
from Mainland China describe a society which, in a
primitive way, contains many of the features which I
have mentioned. While I am not ready to advocate that
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EVERYTHING IS CONNECTED
we adopt the Chinese system or life-style, I think we can
learn from them how to maximize the use of limited re-
sources. And all societies, including our own, are now
forced to recognize the fact that there are real limits to
resources and to the carrying capacity of both the planet
Earth, and our own little piece of that planet.
The Chinese, and many other more primitive societies
have learned how to close the loop of natural cycles. In
many cases they are learning after centuries of failing to
do so. On a limited scale, and in certain isolated situa-
tions, small groups in our country are seeking to develop
"closed loop" styles of living—systems which might be
described as relatively self-sufficient, low-throughput
types of systems.
Such systems tend to be smaller rather than larger.
Our fascination with bigness may have reached the end
of the line. The book, Small is Beautiful has become a
best seller. The gigantic, all-encompassing centrally-
planned and directed system, whether it be a Social Se-
curity computer, such as we have seen revealed in all of
its weaknesses in the past few days, or a continental or
global economic or governmental system, may carry
such a heavy weight of problems that these problems
constitute a built-in self-destruct system.
Perhaps this is the next great challenge to face us in
building a new human culture—the challenge to create,
with our unsurpassed scientific and technological
abilities, a new emphasis on networks of small, closed-
loop, largely self-sufficient, self-defining and self-di-
recting communities, including economic and social en-
tities, and all other forms of human organizations and
activities.
If such is indeed the case, then you here today are
among those who must accept a major responsibility to
help "close the loop." The linear approach of passing
our wastes out to somewhere else, to some mythical
"away", is no longer practicable. But in order to close
the loop, to do your job of waste management, you must
convince the people who are sending their wastes away
to take them back.
These people, quite rightly, want assurances that
what you are bringing back is safe and useful. Some of
your speakers will be telling you that it may not be safe.
It is especially not safe if the slduge you wish to bring
back is contaminated with heavy metals, and these
heavy metals then enter the biological chain. But this
problem can be, and will be solved. It can be solved by
source controls, and by consistent sludge test and moni-
toring procedures, prior to land application, just as we
test and monitor drinking water before it enters the
domestic supply system.
But, even with assurances of safety and healthful-
ness, there remains a complex problem of community
acceptance of recylced sewage sludge. How do we ad-
dress that problem?
The average citizen does not know how his community
works. He may know where the sewer goes, but most
likely he will only be aware of the tax bill and the sewer
connection charge. Even elected officials, who are
among the few mandated generalists in our society, are
seldom aware of the details of community infra-struc-
tures such as waste disposal systems. And elected offi-
cials are highly unlikely to oppose an angry, even though
uninformed, constituency over a waste disposal issue.
And the people are leary of sludge and sludge disposal
sites.
A recent example from our Nation's Capitol may be in-
structive. The National Park Service began applying
municipal sludge to the area along the Mall near the
Washington Monument. Since the White House is just
across the street and in need of soil conditioner, the Park
Service offered to supply the need from their sludge. The
deal seemed closed, until some higher official got wind
of the proposal, so to speak, and it was suddenly off. The
White House will use artificial fertilizer, but not sewage
sludge. So much for leadership.
I must say, before closing, that your work will continue
to have strong support in the Congress. In handling the
EPA Office of Research and Development authorization
bill this year, under our new House jurisdictional ar-
rangements, I found that one of the few areas receiving
increases above the President's recommended budget,
by insistence of the Committee on Science and Tech-
nology, was that of solid waste disposal, and particularly
the matter of sludge disposal research and development.
I expect the Committee and the House to continue their
favorable attitude toward this subject.
I am personally extremely well disposed toward in-
creased research and development, particularly so
where it recognizes the importance of some of the para-
meters which I have tried to sketch. The importance of
research and development is implicit in Berman's Rule,
enunciated by your distinguished keynote speaker at
last year's conference, who said "While we can do as
much planning and discussing of numerous alternatives
as we care to, while we can develop all types of "sys-
tems" approaches, and while we can develop "models"
to our hearts content, no one solution will ever solve all of
our municipal sludge problems. Rather, a series of ap-
proaches are required which I am confident, will even-
tually lead to the gradual elimination of the seemingly
gigantic problem which faces us today."
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EVERYTHING YOU WANTED TO KNOW ABOUT
SLUDGE BUT WERE AFRAID TO ASK
Harold Bernard
Environmental Quality Systems, Inc.
Rockville, Maryland
INTRODUCTION
This paper supplies an overview for the remainder of
papers in the Proceedings. It indicates the impact on
sludge volumes and characteristics of legislation, of
sources of wastewater, sewage treatment, and agrono-
my practices. The paper describes the uniqueness of
sludge characteristics and its dependence on its imme-
diate past history. Sludge is placed in a perspective with
other industrial practices and natural occurrences that
similarly impact on the environment.
Impact of Population
Figure 1 is a Bureau of Census map of the United
States, showing the location of municipalities of 10,000
people and greater. Therefore, the map also depicts the
location of sewage treatment plants of about one mgd or
greater, on the assumption that municipalities of this
size must have a sewage treatment plant. The significant
density is around the Mississippi River and increases as
you go east with other pockets of density along the West
Coast, in the Los Angeles area, San Francisco, San
Diego, and in the upper northwest extremities of the
country. The Bureau of Census has projected about a two
percent increase in population annually. Forthat reason,
we don't feel that the population increase will have a sig-
nificant impact on the quantity of sludge that will be gen-
erated over the next decade.
Impact of Legislation
The sections of the Federal Water Pollution Control
Act Amendment of 1972 and their associated impacts are
indicated in Table 1 and described as follows:
1. Section 301 establishes effluent limitation for both
publicly owned and non-publicly owned treatment
wastes. It may be expected that by 1977-1978,
municipal sludges resulting from application of
secondary treatment to all publicly owned treat-
ment works will be significantly increased. Efflu-
ent limitations at the best available technology
stage will produce significant amounts of non-pub-
lic or industrial wastes, sludges, and process resi-
dues by 1983-1985.
Section 306 establishes "the national standards of
performance for various industrial categories."
Originally in PL 92-500, 27 major categories of in-
dustry were included. The Environmental Protec-
tion Agency couples the promulgation of national
standards of performance with effluent guidelines
for these 27. As time passed, additional listing of
industrial categories was promulgated. The EPA
has plans to continue promulgating the effluent
guidelines and national standards of performance
and it is likely that at some point in time virtually
every category of industrial waste will be covered.
The National Pollution Discharge Elimination Sys-
tem will ensure that these provisions are enforced.
The end result will be to significantly increase
sludges and process residues, initially from the 27
primary categories and as time passes into the
1980's and early 1990's, from every industrial cate-
gory.
Section 307 establishes toxic and pretreatment ef-
fluent standards. The net effect of the requirement
of this section in locations where publicly owned
treatment works accept industrial wastes will be
increases of sludges and other process residues
from industrial and other establishments which
have installed new treatment works to meet pre-
treatment requirements or to eliminate the dis-
charge of toxic and hazardous materials to the
sewer systems and subsequently to the publicly
owned treatment works. These residues will re-
quire programs for disposal of sludges and other
residues in urban areas, particularly where land
space or space for additional sludge treatment and
ultimate disposal including incineration is limited.
Section 402 of the Act establishes the National Pol-
lutant Discharge Elimination System (NPDES) and
associated permit scheme which will be operated
on a continuous basis either by the EPA or by each
of the states as they become eligible to exercise the
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EVERYTHING YOU WANTED TO KNOW ABOUT SLUDGE
15,000,000
10,000,000
5,000,000
2,500,000
1,000,000
500,000 ONE DOT EQUALS 10,000 PERSONS
250,000 OUTSIDE UMANIZED AREAS
50,000 US DEPARTMENT OF COMMERCE BUREAU OF THE CENSUS
Figure 1: Population Distribution — 1970 Census.
requirements of this section of the Act. The permit
scheme constitutes an enforcement mechanism
updated on a regular basis and will require atten-
tion, by state, Federal and local regulatory agen-
cies, to discharges, whether public or private, to
the nation's waters. In the past, the enforcement
of water pollution control requirements has not
TABLE 1
Sections of PL 92-500 That Impact on
Production of Sludges
EFFLUENT LIMITATIONS
NATIONAL PERFORMANCE STANDARDS
(EFFLUENT GUIDELINES)
NPOES - PERMIT REQUIREMENTS
TOXIC AND PRETREATMENT REQUIREMENTS
LIMITATIONS ON OCEAN DISCHARGE
POTENTIAL RESIDUES FROM TREATMENT OF
NON-POINT SOURCES
been nearly as consistent or continuing as this sec-
tion of the Federal law requires. As a result,
sludges and process residues resulting from addi-
tional treatment as described above, will receive
continuous attention. Also, sludges and process
residues which may have been disposed of properly
in the past will result in even greater quantities.
The enforcement of PL 92-500, including Section
309, the continuing capability for civil suits, and
additional criminal penalties will significantly im-
prove the pollution abatement picture in the United
States over the coming years and of course, will
contribute substantially to the production of addi-
tional sludges and process residues.
5. Very large sludge quantities are currently being
discharged to the ocean environment, particularly
from the east coast into the New York Bight. Sec-
tion 403 of the Act requires the establishment of
ocean discharge criteria. The Administrator of the
EPA acting through this section and also through
Section 405 of the Act relating to the disposal of
sewage sludge has in recent months been taking an
increasingly harder position against any disposal
of sludges or process residues to the ocean envi-
ronment. This factor alone may as much as double
the requirement for land space or other techniques
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EVERYTHING YOU WANTED TO KNOW ABOUT SLUDGE
for the disposal of sewage sludge within a very
short time, over the next five years.
6. Section 404 of the Act requires permits for the dis-
posal of dredged or silt material. Section 403 limits
the alternatives for the disposal of this material as
time passes.
7. The analysis of alternative treatment techniques
and the "ultimate disposal of sludge in a manner
that will not result in environmental hazards" are
requirements for projects before they receive pub-
lic funds (Section 201).
8. Other requirements of PL 92-500 will also affect the
production of sludges and process residues. In-
creasing attention is required for control of drain-
age from mine sources. Additionally, require-
ments are placed, for the first time, related to
nonpoint sources of pollution. It is clear that as
time passes, and the point sources are controlled,
non-point sources will assume increasing impor-
tance , particularly in those watersheds where point
sources of pollution have been completely elimi-
nated through recycle or high degree of treatment,
and in those areas where advanced waste treat-
ment is being used now or will be used in the near
future for the control of nutrients. Control of pol-
lution from construction activity particularly land
stripping, strip mining activities, logging practices
and other potential non-point sources of pollution
must be reviewed on a continuing basis for produc-
tion of process residues.
In summary, the nation will see larger increases in
residues from the treatment of wastewaters than from
any increases due to population growth. For example, it
was estimated that in 1973 there was slightly under five
million dry tons of municipal sludge (see Table 2). In
1975, that figure will increase only slightly. We have
seen how sludge quantities will change, but what of
sludge characteristics. Sludge varies from one com-
munity to another and even in the sewage treatment
plant from one day to another. About 10 to 15 years from
now, when the fishable-swimmable and "no discharge"
sections of PL 92-500 become effective, sludge quanti-
ties will have doubled.
TABLE2
Impact of 1977,1983,1985
Goals of PL 92-500
1973
1977
1983
1985
1990
4.7 MILLION TONS
SECONDARY TREATMENT REQUIRED
5 MILLION TONS
"FISHABLE SWIMABLE"
BEST PRACTICABLE WASTE TREATMENT
TECHNOLOGY
NO DISCHARGE
8.0 MILLION TONS
10 MILLION TONS
Sludge Variability
The factors affecting the variability of sludge are indi-
cated in Table 3. One of the factors to which little atten-
tion is paid is the source of the water itself. The source of
water supply determines, to a large extent, the quantity
and quality of inorganic dissolved solids in the sewage
water. The source of the actual sewage would also play
an important role. For example, household wastes, from
a community such as New York City, which is a relatively
old city with small industries, and without residential
garbage, would be very different from a community such
as Anaheim, which is a relatively new 20-year-old com-
munity which has little industry and almost every house-
TABLE3
Factors in Variability of Sewage Source
WATER SUPPLY
HOUSEHOLD WASTES
COMMERCIAL ESTABLISHMENTS
INDUSTRIAL WASTES
RAW
TREATED
COMBINED SEWERS
INFILTRATION
hold has a garbage disposal unit. Commercial establish-
ments, both number and type, will impact on the sewage
characteristics. The type of industry, whether or not it
requires pretreatment, will have an impact on the char-
acteristics of sewage. Combined sewers would have a
tremendous impact. In the community described later in
the proceedings, the daily dry weather flow, even with
some infiltration, is about 3 to 3'/2 million gallons; the
wet weather flow is well over ten million gallons, all flow-
ing through the sewage treatment pla'nt.
The various factors perhaps, explain why sewage
treatment plants differ in solids generated per capita as
indicated in Table 4. In a comparison of four plants, the
minimum/maximum values between the four plants
vary by a factor of almost four. As mentioned before, the
type and variability of the sources will significantly im-
pact on both the quantity and the character of the sew-
age, and therefore, the residues. The sewage treatment
-------
EVERYTHING YOU WANTED TO KNOW ABOUT SLUDGE 7
TABLE4
Solids Generation Rates* From Four Plants
Plant
l
2
3
4
Minimum
0.338
0.137
0.201
0.140
Maximum
0.491
0.146
0.296
0.270
*lbs/cap/day (multiply by 0.454 for kg/cap/day)
process itself, such as activated sludge, trickling filter or
chemical treatment, will generate completely different
types and quantities of sludge. Tables 5 and 6 indicate
the quality and quantity of sludges generated by the
various types of treatment plants. Different days in the
same plant, depending upon the character of the opera-
tion on that particular day, as well as the character of the
sewage being received, will produce different residue
characteristics. For example, lime treatment for the re-
moval of phosphorous, would increase residue volumes
by approximately one and a half percent of the volume of
wastewater treated. Recalcination and recirculation
drastically reduces that quantity. Alum or sodium alumi-
nate would add about one pound of alum per four pounds
TABLES
Factors in Variability of Sludge Produced by
the Type of Sewage Treatment
PRIMARY TREATMENT
% OF SEHAGE VOLUME
ACTIVATED SLUDGE PROCESSES AND VARIATIONS-% OF SEWAGE VOLUME
TRICKLING FILTER
CHEMICAL TREATMENT
OF SEWAGE VOLUME
LIME TREATMENT
98% PHOSPHORUS REMOVAL
SLUDGE 1.5* OF WASTEWATER VOLUME
RECALCINATION
ALUM OR SODIUM ALUMINATE TREATMENT
80-90% PHOSPHORUS REMOVAL
4 LBS. OF SLUDGE/LB. OF ALUM
IRON TREATMENT
80-90% PHOSPHORUS REMOVAL
SLUDGE 2.5 LBS./LB. OF Fe
DENITRIFICATION TECHNIQUES
REFRACTORY ORGANICS REMOVAL TECHNIQUES
800 2500 LBS./MG. WITHOUT REGENERATION
DISSOLVED SOLIDS REMOVAL TECHNIQUES
TABLE6
Estimated Dry Sludge (D.S.) Production
For Various Wastewater Processes
Primary sludge
Waste activated sludge
Trickling filter sludge
Extended aeration waste sludge
Aerated lagoon sludge
Filtration sludge
Algae removal sludge
Chemical addition to clarifiers*
Ibs./MG
1,000
700
650
830
830
125
125
450
+3
*Based on application rate of 80% alum and 20% Fe
of sludge produced, or about 25 percent of the character-
istics of the sludge will be composed strictly of the alum
that was added to treat the sewage for the phosphorous
removal. Iron denitrification techniques also add dif-
ferent quantities of additives and create different char-
acteristics in the sludge. As noted (in Table 7) in the
22,000 sewage treatment plants in the country, ten per-
cent of them are collection systems only, another ten
percent are primary treatment with sedimentation, and
TABLE 7
The Number and Type of Municipal Wastewater
Treatment Facilities in the United States and the
Population Served by Each
Type of Treatment Process
Population
Served
Number of
Plants
Collection System Only - No Treatment 2,890,676 2.404
Minor Treatment - Screening and
Chlorination Only
Primary Treatment - Sedimentation
Intermediate Treatment - Chemical
Secondary Treatment - Biological
Secondary - Activated Sludge
Secondary - Extended Aeration
Secondary - Trickling Filter
Secondary - Effluent to Land
Secondary - Oxidation Pond
Secondary Filter
Secondary - Miscellaneous
Tertiary - Physical, Chemical
Total 154,945,105 22,054
the other 80 percent vary between intermediate treat-
ment and secondary treatment of various types. Tertiary
treatment, using physical chemical treatment concepts,
now only makes a small contribution to the overall
sludge generation picture, consisting of only 800 out of
780,135
37,904,943
6,780,241
2,506,245
47,561,508
3,963,602
29.688,917
410,444
7,680,982
1,606,110
10,798,203
2,373,698
72
2.714
70
1,980
1,831
2,694
3,523
144
5,031
309
1,245
809
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8 EVERYTHING YOU WANTED TO KNOW ABOUT SLUDGE
the 22,000 plants. Their impact will increase as "best
practical" and "best available treatment" concepts are
instituted.
As noted previously, quantities and sludge character-
istics vary between treatment plants using the same con-
cept. Table 8 compares the variability of some heavy
metals in sludges in three activated sludge plants and
between activated sludge and a trickling filter plant. The
quality of the influent varies between the plants. Re-
moval rates or percentages are also different. In all like-
lihood, operational characteristics also affect the quanti-
ties and characteristics of sludges removed.
TABLES
Fate of Metals Through Sewage Treatment Process
Bryan, Ohio, Activated Sludge
Metal
Chroml urn
Copper
Nickel
21 nc
Influent Sewage, (mg/1) Final Effluent, (mq/l)
Average
0.8
0.2
0.05
2.2
Range Average Range
0.6-1.1 0.2 0.2-0.3
0.2-0.3 0.1 0.04-0.1
0.03-0.1 0.05 0.03-0.1
1.4-3.0 0.2 0.2-0.3
Percent
Immobilized
1n Sludge
__
—
—
—
Grand Rapids, Michigan, Activated Sludqe
Chromium
Copper
Nickel
Zinc
Chromium
Copper
Nickel
Z1nc
3.6
1.4
2.0
1.5
O.B
0.2
0.03
0.3
0.7-5.6 2.5 1,0-3.3
0.7-2.4 1.6 0.4-2.9
1.3-3.4 1.8 1.0-2.5
0.6-2.5 0.8 0.6-1.2
Richmond, Indiana, Activated Sludge
0.2-2.1 0.2 0.01-0.5
0.1-0.4 0.07 0.04-0.2
0.01-0.1 0.02 0.01-0.03
0.1-0.5 0.1 0.1-0.2
40
16
12
58
82
73
78
85
Rockford, Illinois, High-Rate Trickling Filter
Chromi urn
Copper
Nickel
Zinc
1.8
1.4
0.9
2.7
0.5-2.9 1.2 0.6-1.5
0.6-3.3 1.0 0.5-3.6
0.2-1.9 0.9 0.5-1.4
1.2-3.4 1.3 0.8-1.7
37
23
8
53
Table 9 indicates further impact on ranges of trace ele-
ments due to sludge handling. Undigested sludge is
quite different than secondary digested sludge. Vacuum
filter cake sludge also has a different constituency be-
cause of the removal of dissolved solids in the liquid
TABLE9
Range of Trace Elements Found in Sewage Sludge
In Relation to Treatment Process
Element
Mercury
Chromium
Copper
Nickel
Zinc
Cadmium
lead
Arsenic
Undigested Liquid
Sludge f)
1.2
66
200
44
900
6
150
3
3.4
7,800
- 1,740
740
8,400
166
- 26,000
16
Secondary Digester
Sludge b)
2 -
22 -
260 -
14 -
1,120 -
2 -
240 -
4 -
56
9,600
10,400
1,440
16,400
1,100
12,400
18
Vacuum Filter
Cake c>
0.6-
28 -
84
12
480 -
2
80
2.8 -
27
10,600
2,600
2,800
9,400
480
3,000
11
As mentioned at the outset, and as shown in Table 10,
the industrial contributions will add a tremendous
amount of residues that must be considered in an overall
municipal sludge management concept. In the top two
categories of "inorganics" and "iron and steel", the
smaller number indicates the tonnage that can be recy-
cled back to the respective industry. The difference is
that tonnage which must be considered for disposal into
the environment. As you can see, the net tonnage of
residue that must be disposed of in 1977 and 1983 from
the ten industries will be approximately 13 million tons.
As mentioned previously, in 1977, municipal sludge will
be only about five million tons, so there will be about two
and a half times more industrial residue to be expected
in the next several years than from the municipal area.
TABLE 10
National Generation of Wastewater Sludge
From the Major Industrial Sectors (in 10" tons)
Inorganics
Iron and steel
Pulp and paper
Meat products
Petroleum refining
Textiles
Organics
Plastics & synthetics
Fruits & vegetables
Electroplating
TOTAL
NET TOTAL
(Tons 1.1 kkg)
1971
"•07/14.6
3'47/1.8
1.08
0.42
0.69
0.19
0.21
0.14
0.05
0.04
23.34/16.4
1977
26'°722.3
6'85/3.1
2.24
0.92
0.85
0.52
0.41
0.24
0.07
0.07
38/25"
1983
32.00
729
8.03
75
13
3.41
1.09
1.02
0.74
0.48
0.32
0.11
0.07
47/34
13
a } From 6 treatment plants
b ) From 22 treatment plants
c ) From 14 treatment plants
As indicated in Table 6, the actual treatment concepts
given to the sludge will have a tremendous impact on the
characteristics of the sludge. Figure 2 indicates the po-
tential unit processes and sludge handling systems that
can be given to the sludge such as stabilization, condi-
tioning, dewatering, heat drying, reduction, and then
the final disposal methods such as disposal onto land,
land reclamation, power generation, etc. There are ap-
proximately a quarter of a million combinations one can
synthesize with just these eight unit processes that make
up a sludge disposal or sludge treatment system.
Operations within the same treatment plant vary over
a tremendous range, as shown in Table 11 for the Calu-
met Treatment Plant of the Metropolitan Sanitary Dis-
trict of Greater Chicago. The various constituents, am-
monia, phosphorus, chromium, cadmium, copper, etc.,
vary over a range from double to almost an order of mag-
nitude.
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EVERYTHING YOU WANTED TO KNOW ABOUT SLUDGE
TABLE 11
Sludge Variability
Composition of Digested Sludge from the
Calumet Treatment Plant,
Metropolitan Sanitary District
Component
Total N
Amnoniun-N
P
K
Cr
Cd
Cu
Pb
Hn
Hi
Zn
In solids
C
H
N
Concentration , ppm
1000
500
700
150
10
10
30
15
7
1
72
-
22
3
3
- 3500
- 2000
- 1550
- 175
- 50
- 35
- 45
- 33
15
3
- 292
- 27%
- n
- 3.5*
In addition to the variables within the treatment plant,
disposal onto the land adds an additional 20 variables.
These are indicated in Table 12. Metal uptake usually
increases with pH. The type of soil, the clay fractions in
the soil, the organic fractions in the soil, and in the
sludge, affect uptake. Permeability of the soil or the resi-
dence time of the sludge leachate in the soil affects up-
take. Soil temperature, the previous soil moisture, the
TABLE 12
Factors Affecting Uptake of Heavy Metals
TYPE OF SLUDGE
pH OF SOIL AND SLUDGE
TYPE OF SOIL
CLAY FRACTIONS
ORGANIC FRACTIONS
PERMEABILITY
CLIMATE
SOIL TEMPERATURE
SOIL MOISTURE
PLANT TYPE
PLANT AGE
FORM OF HEAVY METAL
INTERFERENCE OF OTHER HEAVY METALS
TOTAL QUANTITY OF HEAVY METALS
PAST HISTORY OF APPLICATION
EXCHANGE CAPACITY OF SOIL
AGE OF METAL (FORM?)
PRESENCE OF HYDROUS OXIDES
LABORATORY METHOD
existing soil moisture, the plants being cultivated on the
land will have a unique impact on the uptake and trans-
port characteristics of the sludge. The plant age, the
sludge age, the form of the heavy metal, whether it's an
oxide, or a carbonate, what other heavy metals are
present, will all have an impact or interfere with the up-
take of metals. The total quantity of metals that exists in
the sludge and in the soil at the time of sludge applica-
tion, the actual age of the metal, whether the land is
seeded immediately, or whether the sludge is aged for a
week or two before the seed is applied, will determine
uptake. The actual laboratory method that one used to
indicate the removal or uptake of metals will affect ap-
parent uptake analyses.
One method gives a low estimate of uptake. One ex-
tracts even the constituents that were tied very tena-
ciously to the soil before the sludge was applied, so the
analyses actually indicates an over-conservative amount
of metals taken up by the plant. The impact of these vari-
ables is illustrated in Table 13 which indicates the range
of constituents in the soil and in the sludges, varying
from 0.1 to 40 micrograms per gram, in the soil, and 0.1
to about five in the plants. Table 14 illustrates the fate of
five metals in various crops grown in untreated soil and
soil treated with sludge. It is not necessary to dwell on
any particular sludge, but important to indicate the tre-
mendous variation one can expect.
TABLE 13
Total Concentrations of Trace Elements Typically
Found in Soils and Plants
Cone, in Soils (M-^/g)
Cotrenon Range
Cone. In Plants (M-g/g)
Normal
Toxic1-/
As
B
Cd
Cr
Co
Cu
Pb
Mn
Mo
Ni
Se
V
Zn
6
10
0.06
100
8
20
10
850
2
40
0.5
100
50
0.1 -40
2 -100
0.01-7
5 -3000
1 -40
2 -100
2 -200
100 -4000
0.2 -i
10 -1000
0.1 -2.0
20 -500
10 -300
0.1 -5
30 -75
0.2 -0.8
0.2 -1.0
0.05-0.5
4 -15
0.1 -10
15 -100
1 -100
1
0.02-2.0
0.1 -10
15 -200
>75
>20
>50
50-100
>10
>200
]_/ Toxicities listed do not apply to certain accumulator plant species
In applying sludge to the land, one is always con-
cerned about the fate of the bacteria and the virus usual-
ly inherent in sludge. The observed distance of travel,
time of travel, and whether or not bacteria or virus will
survive, is shown in Tables 15 and 16. The viruses have a
longer lifetime than bacteria, surviving up to 27 weeks.
One must also place survival in the context of time of
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10 EVERYTHING YOU WANTED TO KNOW ABOUT SLUDGE
UPG^TYPEl THICKENING |STA^LI^T!gN|cavPIT10NING|DEWATERINGJHEATPRYINGl REDUCTION l_ _P>NAl i
"™ | "lending { Reduction (Stabilization J |~ {"stabilization | Disposal 1
PRIMARY
FILTER >RE5S
DRYING BEDS
ROTARY
VACUUM FILTER
FLASH OH VEII
IMULTIPLE HtABTMl INCINEBATIOM
LAMP RECLAM
fOWER
GENERATION
ElUTRIATION I \HORIZONTAL EIITfH/ \ TRAY OBVER I I WET AIM O»IOATION| iSANITAHYJ.ANgfll.lJ
HEAT TREAT, j
CYLINDRICAL
SCBEtN
S'RAV DHYER
I OCEAN DISPOSAL I
Figure 2: Unit Processes—Sludge Processing and Disposal.
TABLE 14
Trace Element Composition of Crops Grown on Soil
Treated with Sludge at an Average Rate of
66 M. Tons/Ha/Year for 19 Years
TABLE 15
Summary of Reported Distances of Travel of
Pollution in Soil and Groundwater
Treatment
Untreated
Treated
Untreated
Treated
Untreated
Treated
Untreated
Treated
Untreated
Treated
Untreated
Treated
Untreated
Treated
I/
Noture of Pollution
Pollutant
Observed
distance of
travel a )
Time of
travel
Cr Cu Mo Nl Zn
Leeks
0.71 5.7 0.50 2.0
0.54 16.0 1.10 7.0
Globe Beet Tops
0.85 8.5 0.45 3.2
1.0 10.0 0.65 16.5
Globe Beet Roots
0.3 11 0.1 1.65
0.8 18 0.25 13.0
Potato Tops
1.70 4.2 0.37 1.7
3.0 8.2 1.0 5.2
Potato Roots
0.09 9.5 0.40 0.25
0.03 9.5 0.27 0.57
Carrot Tops
0.41 8.2 0.58 1.28
0.88 9.9 0.84 3.0
Carrot Roots
0.03 6.3 0.12
0.06 4.6 0.12
Leeks, beets, and potatoes are means
plots. Carrots were grown on soil 7 years after treatments
discontinued.
travel in the
46
135
169
>505
102
250
90
120
30
27
47
99
34
42
of 2
vero
terrestial environment. For example, in the
27 weeks, mentioned above, the bacteria moved
feet. If the land is larger than this, the survival
only 65
charac-
teristicsof the bacteria or virus maybe inconsequential.
Sewage polluted trenches
intersecting ground water
Polluted trenches inter-
secting ground water
Sewage in bored latrines
intersecting ground water
Sewage in bored latrines
lined with fine soil
Sewage in bored latrines
intersecting ground water
Sewage in bored latrines
intersecting ground water
Coliform organisms in-
troduced into soil
Sewage effluents on
percolation beds
Sewage effluents on
percolation beds
Sewage polluted
ground water
Introduced bacteria
Chlorinated sewage
Coliform bacteria
Coliform bacteria
Coliform bacteria
Anaerobic bacteria
Coliform bacteria
Coliform bacteria
Coliform bacteria
Coliform bacteria
Coliform bacteria
Bacteria
Bacteria
Bacillus prodigiosus
Fungi
a) For bacteria, the distance observed was the (
65 feet
232 feet
10 feet
50 feet
10 feet
35 feet
80 feet
regressed to 20 feet
50 meters
400 feet
150 feet
o few meters
69 feet
300 feet
ixtent of travel.
27 weeks
_
-
37 days
9 days
..
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EVERYTHING YOU WANTED TO KNOW ABOUT SLUDGE 11
TABLE 16
Survival Times of Organisms
Organism
Ascaris ovoa )
B. Typhoso
Cholera vibrios
Col i form
Endomoeba
histolytica >
Hookworm larvae >
Leptospira
Polio virus
Salmonella typhi
Shigella
Tubercle bacilli
Typhoid bacilli
Type of
Medium application
Soil
Vegetables
Soil
Vegetables
Spinach, lettuce
Non-acid vegetables
Grass
Tomatoes
Vegetables
Soil
Soil
Soil
Polluted water
Radishes
Soil
Tomatoes
Soil
Soil
Sewage
AC
AC
AC
AC
Sewage
Sewage
AC
AC
Infected feces
AC
Infected feces
Infected feces
AC
AC
AC
Survival time
up to 7 years
27 - 35 days
29 - 70 days
31 days
22 - 29 days
2 days
14 days
35 days
3 days
8 days
6 weeks
15-43 days
20 days
53 days
74 days
2-7 days
6 months
7-40 days
a^ Unlikely to move in the unsoturated zone
b) Artificial Contamination
Sludge accounts for only 7.5 dry tons of the total quantity
of residues generated. As can be seen, the other resi-
dues far outweigh the 7.5 tons for the sanitary sludge.
The industrial wastewater sludge, for example, is 35
million tons per year and is of much greater significance
than the municipal sludge. Industrial process residues
produce six times as much as the municipal sludges.
Mining waste is mostly overburden. Another viewpoint
is to compare sludge with sediment runoff as shown in
Table 17. Within the three billion tons of soil that erodes
annually is found three million tons of nitrogen, 4.5 mil-
lion tons of phosphorus, and 45 million tons of potassi-
um. The 5 to 7.5 million tons of municipal sludge (com-
posed of from three to six percent nitrogen) in orders of
magnitude less than that being contributed to the envi-
ronment from the erosion of sediment.
The nutrient and metal contributions from fertilizer
shown in Table 18 were obtained from the Department of
Agriculture publications. Normal agronomy practices
TABLE 17
Nutrients in Sediment Runoff
3 BILLION TONS OF SOIL ERODES ANNUALLY
3 MILLION TONS OF NITROGEN
Sludge in Perspective
Constituents in sludges should be placed into per-
spective with other residues and with other operations
that contribute the same constituents to our environ-
ment.
Figure 3 shows the percentage of municipal sludges
related to residual generation from other sources.
4.5 MILLION TONS OF PHOSPHOROUS
45 MILLION TONS OF POTASSIUM
TABLE 18
Plant Nutrients Applied to the
Land from Fertilizers
Figure 3: Estimated Industrial Versus Other Residual (Aug. 1970-
1974( (Dry Weight in Million Tons Per Year).
NITROGEN
PHOSPHATE
POTASSIUM
COPPER
IRON
MANGANESE
ZINC
MOLYBDENUM
9 MILLION TONS/YEAR
2.5 MILLION TONS/YEAR
3.5 MILLION TONS/YEAR
2500 TONS/YEAR
3300 TONS/YEAR
11,000 TONS/YEAR
15,000 TONS/YEAR
80 TONS/YEAR
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12 EVERYTHING YOU WANTED TO KNOW ABOUT SLUDGE
apply the same constituents to the land for which we ex-
press concern in municipal and industrial sludges. The
differences are obviously the concentration of consti-
tuents that are applied to the soil.
Figure 4 indicates the quantity of nitrogen that can be
contributed to the terrestrial environment by rainout.
These vary from about 3.5 kg per hectare per year in the
industrial northeast and around the Great Lakes, Chica-
go, and Minneapolis area, to about one kg/hectare/year
in the southwest. Source of nitrogen and phosphorus
content in the top one foot of soil also varies from about
.04 percent to about .3 percent in the various parts of the
.3 kg/no/yr
.5 kg/ho/yr
2.0 kg/ho/yr
1.0 kg/ha/yr
1.0 kg/ho/yr 1.5 kg/ho/yr 2.0 kg/ha/yr
1.5 kg/ho/yr
1.0 kg/ho/yr
1.0 kg/ho/yr
Source:
Personal Communication, Joy H. Gravens, Regional Forester
USDA-FS, Eastern Region, Milwaukee, Wise. (Aug. 1974).
1.0 kg/ho/yr
1.5 kg/ha/yr
Figure 4: Nitrogen (NH4 —N and N03 —N) in Precipitation.
Highly Dtveria
Insufficient Dot
Figure 5: Percent Nitrogen (N) in Surface Foot of Soil.
-------
EVERYTHING YOU WANTED TO KNOW ABOUT SLUDGE 13
m^mim
-MlW%m^i$K
[J 0.20-0.:
Figure 6: Phosphorus Content in the Top One Foot of Soil.
Mils*
Figure 7: Predicted pH of precipitation over the eastern United States,
1965-1966.
country, as shown in Figures 5 and 6. The pHof the rain-
out also varies considerably throughout the nation (Fig-
ure 7). Metals tend to leach faster in an acid soil environ-
ment.
In summary, I would again like to indicate that your
sludge is unique. It will have different characteristics
than anybody else's and will probably vary daily. Your
environment is also different than anybody else's. You
cannot use field data and laboratory data from other in-
vestigators per se; you can use other data as guidance to
direct your particular solution(s).
In additon, it is unlikely that national guidelines will
be useful. Such guidelines will have to be overly con-
servative and may require inordinately high acreage to
dispose of the sludge. Any guidelines should permit
flexibility to take into consideration the broad variability
in sludges, the environment and various acceptable
controls.
REFERENCES
1. Environmental Impact of the Disposal of Wastewa-
ter Residuals, National Commission on Water Quality,
to be published January, 1976.
2. Bureau of the Census, 1970, Census of Population,
U.S. Department of Commerce, Washington, D.C.,
August, 1973.
-------
IMPACT OF INDUSTRIAL WASTE WATER
PRETREATMENT ON SLUDGE MANAGEMENT
Charles Ris and George Rey
United States Environmental Protection Agency
Washington, D. C.
and
Thomas Short
United States Environmental Protection Agency
Ada, Oklahoma
INTRODUCTION
It is easy to say, "Yes, there is an impact on sludge
management practice resulting from pretreatment of in-
dustrial wastewater." It is, however, significantly more
difficult to describe and critique the nature of this im-
pact for an audience that is made up of those involved in
sludge management, those that produce the industrial
pollutants and those that regulate and monitor the en-
vironment. A moment of thought on the triad just men-
tioned is an underlying reality which has significant
bearing on pretreatment and its effect on residue man-
agement and or .... perhaps the inverse that is residue
control and its relationship to the need for pretreatment.
With the implementation of a pretreatment strategy
for industrial sources the institutional considerations of
industrial or private sector motives and economies are
linked with those of the local"public authority and the in-
stitutions of state or Federal government. Figure 1 por-
trays the initial and very basic options which the Indus-
Figure 1: Joint Is An Option.
trial discharger must consider knowing that one option
will transfer the water pollution problem to the munici-
pal sector with strings attached. Such a linking of "ways
and means" for the purpose of improving our environ-
ment is always a challenge to those charged with turning
complex strategies into realistic and workable solutions.
Before exploring the relationships between residue
control practices and the pretreatment of industrial ef-
fluents, it is well to consider the terminology of pretreat-
ment. In its rudimentory form pretreatment implies a
need to:
1. make the industrial waste similar in characteristic
to that used as a design norm for a municipal waste
treatment facility; or
2. to render the industrial wastewater "compatible"
with an existing control system capability to as-
simulate.
Other terms that are pertinent to the topic and fre-
quently confused in environmental jargon include:
• Assimulate- to make similar
• Reuse to use again
• Residue something that remains after
• Disposal orderly placement or distribution
• Dump - to get rid of irresponsibly
It is interesting, now, to reference a concept. With an
understanding of the above terms and study of Figure 2
it can be rationalized that: to reuse residues (to an opti-
mum degree) would avert the need for their disposal
thereby eliminating the need to dump. To achieve reuse,
however, requires the assimilation of a residue into a
proper environment. The question remaining, there-
fore, is what is the proper environment for the residue
especially an industrial one.
Although, in theory, it may be possible to completely
avert the need for disposal of residues from the treat-
ment of industrial wastewater, the current but limiting
state-of-the-art does not yet justify the practicality in
many cases, particularly for small and medium volume
discharges.
The current assessment by some individuals is that to
eliminate the discharge of pollutants (toward "zero dis-
charge") would be a severe economic requirement. Such
conclusions have been made, in many cases, by ignoring
the impact future technology will or could have in alle-
viating the economic penalty of basic pollution control.
14
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IMPACT OF INDUSTRIAL WASTEWATER PRETREATMENT 15
Figure 2: The Basin Cycle.
and/or in addition may not have included proper credits
for resource recovery. It is a contention that the net cost
of pollution control solutions via the route of water reuse
and residue recovery could well be at an acceptably low
cost and in some cases actually profitable; after all the
majority of industrial pollutants are in fact lost products
or raw materials, both of which have an inherent greater
economic value than the heterogeneous constituents of
domestic sewage residues.
Experience to date with the EPA Industrial Pollution
R&D program, coupled with a few basic principles of
chemistry and environmental considerations leads one
to the following qualitative technological forecast con-
cerning the pollution control techniques that will or are
evolving in the near term. Table 1 is a summary of this
forecast for selected residue classes by major chemical
constituent. The assigned numbers 1-3 indicate the
probability of the designated technological approach
establishing itself as commercially viable and environ-
mentally acceptable, during the next decade. Table 1
suggests that the residues listed below domestic sludge
contain the potential to be managed in an environmen-
tally desirable way at no net cost to an industrial opera-
tion. This is to say that the recovery value of the residue
ingredients should generate sufficient income to offset
the cost of recovery or reconstitution operations. Those
listed above domestic sludges will in all probability be
difficult to reuse in a significant manner that would re-
sult in a net profit over the cost of their stabilization and/
or disposal. Although there have been a few success
stories with reuse of brines the base line reference used
is the domestic organic sludges from sewage treatment
plants which are envisioned as resulting in a net cost to
produce by-products or reuse in any effective manner.
The forecasts themselves are fairly optimistic in that
they project that with the proper technological solution
TABLE 1
Industrial Residue Classes and
Technology Forecast'
Probable Practicable
Residue Technology
>
'
a* o
wo
=> IU
aj ae
•v- o
t/» t-
(Da.
RESIDUE CLASS
1.
2.
3.
4.
5.
6.
NaCl 2(2)
Na2S04/S03
CaCl2/S03
B1ox-0rqanic Sludges (Domestic)
PHnary SS Sludges (Domestic)
CaS04
3(2)
2
3
1
2
-
3
1
3
1
1(2)
1
1
2
2
3
7. B1ox-0rqan1c Sludges
(Che*. Ind.)
8. Red Muds
9. P04-Sl1mes (F-)
10. Primary SS Sludges (Food Ind.)
11. Fe(S04)2-(S04)3
12. FeCl2-Cl3
13. Cl-0rgan1cs
14. Cr/Zn/Cu/Pb-Cd-Hg
(l)Dlsposal to land or oceans
(2)p0tent1al solution probability (1 high, 3 low)
the majority of significant residue chemical classes
should result in the reuse of the polluting constituents
rather than their disposal.
On the municipal front we find considerable anxiety
overthe cost and adequacy of sludge management prac-
tices. In addition, we know that depending upon the dis-
posal technique selected there may be limitations
needed to control the quality of the sludge. If land appli-
cation is under evaluation certain cover crops could not
successfully be cultivated and harvested in the presence
of large quantities of metals. On the other hand, other
crops are more tolerant to the presence of metals.
There is an ever-present complexity cause by a variety
of factors which ultimately justifies the selection of one
residue management practice over another. The impact
of applying pretreatment for the purpose of controlling
sludge quality to meet a design norm is concealed in a
residue is a quantity of material that remains after a long
chain of conveyances and treatment.
-------
16 IMPACT OF INDUSTRIAL WASTEWATER PRETREATMENT
Pretreatment: Past and Present
The use of pretreatment as a strategy and as a specific
pollutant control technique is certainly not new to the
practice of water pollution control. The universal reason
for its use has essentially been for the purpose of pre-
venting the discharge of pollutant materials which
threaten the safety and are otherwise detrimental to the
efficient operation of a treatment works. The specific
technologies used were for the purpose of rendering the
industrial fraction similar to the norm (domestic waste-
waters) either through partial or near complete removal
of certain pollutants. The overall purpose for instituting
pretreatment was predicated on maintaining some level
of aggregated water quality in a receiving body of water.
Only, in specific instances can we show that the need for
pretreatment resulted from a particular residue man-
agement problem. In fact the similar presence of a pollu-
tant and its impact on residue control in one city need not
have the same impact in an other system. This inconsis-
tency of impact is easily understood when one considers
the varied and complex criteria governing the fate of a
pollutant and the use of alternative residue control
practices.
We experience considerably more anxiety over resi-
due stabilization and assimilation into our environment
than we do about the new frontier of recovery and reuse.
The "use it again" option, however, is in its infancy and
is a visible research frontier. In the interim there is con-
cern over the "fate and effects" that residues will or
could have on the environment. There is an expanding
data base suggesting that unstabilized residues (i.e.,
raw sludges) discharged in the past to our ultimate sinks,
the land and sea, have detrimental environmental im-
pacts. In other words, we are now realizing the true cost
of past dumping practices.
Having referenced the past philosophy for pretreat-
ment, the nation is now exposed to a supplemental con-
dition for pretreatment as the result of Public Law
92-500, the most recent water pollution control legisla-
tion. In this law, a supplemental or minimum level of
pollution control is required; that is a level of control that
can be achieved by the use of available, practicable and
economically achievable technology. The rigorous exer-
cise of developing guidelines and standards to meet this
criteria is no doubt familiar to all. One of the guidelines
and standards to be developed under the PL 92-500 pro-
gram are the industrial pretreatment guidelines and
standards.
It is difficult to estimate at this-point what impact new
pretreatment standards will have on residual manage-
ment practices because the exact nature of the regula-
tions relative to policy, procedures, and numerical limi-
tations is still under review by EPA. It is interesting to
speculate that when the regulations are ultimately set
forth, the impact on sludge management can be pre-
dicted only after taking account of the physical and
chemical effects of a treatment system followed by the
proper factoring of the sludge management practice. In
addition a new wrinkle is introduced via the PL 92-500
logic because not only is the old philosophy of pretreat-
ment for "incompatibles" emphasized but it is pro-
posed that regulations be developed to prevent the dis-
charge of pollutants which will "pass through" a public-
ly owned treatment works (POTW).
Relationship of Pretreatment and Residues to
Other Environmental Concerns
It is necessary to divorce the discussion from the un-
certainty of Federal standards and look at the relation-
ships between residue management, pretreatment and
the entire environmental control picture. Perhaps one of
the more useful viewpoints from which to consider the
issues is that of the research technologist. By training he
is an engineer, by experience he is seeking new and bet-
ter ways of achieving a goal, and by discipline he is hope-
fully unprejudiced by institutional limitations.
In the industrial technology research program of EPA
there is an underlying policy of minimizing inter-media
pollutant transfer in the development of control tech-
nology for the industrial source. This basic premise ac-
knowledges that the fate of pollutants is transferable
from media to media as shown in Figure 3, impling that
there is a driving force to move residues from media
control activities toward the land media or oceans; these
sinks containing the potential for ultimate disposal by
their inherent capacity for containing and assimilating
matter.
The media "relative sensitivity" rating values of 1, 2
and 3 indicate the relative difficulty to confine, control or
clean up an emission into the media; one (1) being the
most difficult, and three (3) the least difficult. The most
visible form of this pollutant shifting trend is the residue
or sludge which in most cases is destined for land
disposal.
Figure 3: Inter-Media Fate of Pollutants.
-------
IMPACT OF INDUSTRIAL WASTEWATER PRETREATMENT 17
In addition to the macro scope of environmental con-
trol we find that pretreatment has a unique place in the
sequence of regulatory initiatives and in addition is a
control option for other water quality problems. If pre-
treatment is to ascend from the status of a local option to
a national strategy it must prove to be a reasonable equi-
lizer between the industrial state-of-the-art for pollution
control and that of the municipal sector. Its wide spread
use as a national or local control mechanism must not
significantly effect: (1) the desirability of maintaining a
positive overall environmental impact, and (2) the vi-
ability of having combined industrial and municipal sys-
tems. The same criteria is curiously relevent to the selec-
tion of a residue control practice and the related need for
pretreatment (see Figure 4).
Impact Considerations - A Case Study
In further discussing the relationships we will take ad-
vantage of a case study that was initiated by the Office of
Research and Development of EPA. The investigation,
currently about 70 percent complete, was intended to
elucidate on the impacts of implementing a Federal pre-
treatment program in a large metropolitan/industrial
area. The City of Buffalo, New York, was entertaining
similar thoughts of a study and the EPA and the city
initiated a grant project to answer questions of mu-
tual interest.
The only disappointment to date is that one of the sig-
nificant inputs to the study, the pretreatment regula-
tions, are still not firm. There is, however, valuable in-
PffMFMMFAS
OPTUM
formation in the form of trends that are visible and will
be integrated into the discussion as appropriate.
Consider a situation where a municipal treatment sys-
tem serves a significant number of industrial customers.
The community is potentially subject to a number of
water pollution strategies dealing with secondary treat-
ment, pretreatment, user charges, and cost recovery. In
making adjustments to the existing industrial and muni-
cipal complex so as to comply with regulatory require-
ments, the objective is to maintain a favorable cost ef-
fectiveness, economic achievability, technical viability,
and an over-all positive environmental impact. Realizing
that residue disposal practices may dictate criteria for
pretreatment or that pretreatment for other reasons may
effect sludge management, the following considerations
are pertinent.
1. What is the significance of industrial wastewaters
in the municipal system?
Quantity/Quality
-630 industrial sources (many industries still discharge
to waterway)
-23 MGD industrial/180 MOD total
-industrial contribution
13% by flow
25% by BOD
13% by SS
26% by PO
ph 0.9-1210
COD loadings of 152,000 Ibs./day
SLUDGE MNJAGEMENT
EEWTERING
BIO-STABILIZATION
INCINERATION
LAND APPLICATION, DISPOSAL
OCEAN DISPOSAL
REUSE
SUPPLY
HEALTH HAZARDS
SLUG DISCHARGE
POLLUTANT EDUCTION
POLLUTANT DISCHARGE PROHIBITION
ABEAWIEE PLANNING
POSITIVE ENVIRONMENTAL
IMPACT
COST BENEFIT
ECONOMIC ACHIEVABILITY
TECHNICAL VIABILITY
ENFORCEMENT PROVISIONS
dATER
INADEQUATE QUALITY
INCOMPATIBILITY
;TRIAL PASSTHROUGH OF
Figure 4: Pretreatment—A Control Option.
-------
18 IMPACT OF INDUSTRIAL WASTEWATER PRETREATMENT
Elements #/Day mg/l(180mgd)
Crj 877 0.6
Zn 619 0.4
Cu 383 0.3
Ni 140 0.09
Cn 57 0.04
Pb 55 0.036
Cd 8 0.009
Hg 0.3 0.0002
As 0.02 0.00001
Revenues (Anticipated under new ordinance)
-industrial contribution
17% of capital costs
27% of O&M
2. Given the technological control limits to be achieved,
what changes in current POTW and industrial discharge
practice are needed?
Control limits are yet to be determined ... (Is it second-
ary treatment or is it secondary plus an added degree
of control for the industrial wastewaters based on se-
lected incompatibles? Will the industrial limits be
based on concentration or a quantity of pollutant?)
3. Is there a need for pretreatment of industrial waste-
waters because of problems in disposing of the sludge?
To be determined ....
Current practice (primary treatment) includes sludge
digestion and incineration. The municipal system will
be upgraded to secondary treatment with FeCl3 as-
sisted precipitation in primary tanks for PC>4 control.
No operational problems currently exist relative to in-
cineration or stack gas emissions. Study efforts will
continue to evaluate the effect of an increase in metal
content in the sludges and the continued viability of
incineration.
4. Is an absolute industrial pretreatment strategy the
best alternative to achieve new levels of control for the
combined municipal and industrial wastewater.
To be determined . . .
It is realized the initial problem, that is to control the
incompatible characteristics of industrial wastewa-
ters, can be accomplished at two sites - the industrial
site and the POTW. To choose either location arbitrar-
ily would not give proper emphasis to technical and
economic achievability and long term viability. A sig-
nificant judgement point occurs when the degree of
control, purpose of control (technology standard, wa-
ter quality standard) and discharge permit are ref-
erenced.
Research Needs
Each of the topics, pretreatment and sludge manage-
ment, have inherent research needs. In the pretreat-
ment area, the desire to regulate incompatible and pass
through industrial pollutants has stressed our under-
standing of the relationship of the industrial point source
and the POTW.The specific research needs can be iden-
tified with the following items:
1. Chemical reactions in a POTW;
2. Completeness and consistency of operating data
for industrial compatibility;
3. Concept of combining industrial and municipal
wastes to take advantage of favorable reactions;
4. Identification of inhibiting, toxic and pass through
pollutants;
5. Impact of localized and or regional implementation
of a pretreatment strategy.
In analyzing the current pressures for adequate
sludge management, we find an immediate concern for
the economic achievability of technologies together with
a growing interest in the fate and health aspects of pollu-
tant assimilation into the environment. For the long term
there is little doubt that new information on the fate and
health aspects of pollutants will inturn generate new
control requirements at which point the cycle of effect
and control begins anew.
CONCLUSIONS
The pressure for environmental imporvements, as
partially stimulated by Federal regulatory programs, is
focusing more and more attention to the situation of area
wide or even combined industrial and municipal point
source control. The situation is both existing in many
metropolitan areas and is preserved as a future option
through areawide and comprehensive planning pro-
grams of EPA. Although the actual mixing of industrial
and municipal wastewaters and integration of subse-
quent control systems is not the only way to achieve
areawide management of point sources, it is the most
perplexing in terms of making adjustments or changes to
meet new regulations.
The current concerns for adequate sludge manage-
ment practices as prejudiced by the presence of indus-
trial components and the more basic concern for the de-
gree of industrial incompatibility relative to technology
standards are examples of current topics requiring the
attention of the research community and equitable
analysis from those that write the laws, develop the
regulations and ultimately enforce the programs.
It is worthy to consider that the two mandates of the
1970's, economic achievability and resource conserva-
tion , are two factors which show signs of significantly in-
fluencing both research and implementation of pro-
grams dealing with industry and its relationship with the
environment.
-------
FOR CALIFORNIA—A MODEL
INDUSTRIAL WASTE ORDINANCE
Paul C. Soltow, Jr.
Bay Area Sewage Services Agency
Berkeley, California
Control of industrial wastes entering municipal sew-
age collection and disposal systems has been a concern
of engineers for many years. The probelm has been
made more acute in recent times through the simultane-
ous growth of industries, increasingly strict receiving
water requirements for waste dischargers and much
more sensitive and sophisticated municipal waste treat-
ment processes. Passage of Public Law 92-500, the Fed-
eral Water Pollution Control Act Amendments of 1972,
made control of industrial wastes a major element in the
nation's goal of "Clean Water". Construction grant
funding is contingent upon establishment of effective in-
dustrial waste regulations.
The national emphasis toward better industrial waste
controls did not find California industries and municipal
waste dischargers unprepared. Substantial efforts have
been made toward better industrial waste control and
treatment by the California Water Pollution Control As-
sociation (CWPCA). In the fall of 1973, a Uniform Ordi-
nance Subcommittee was formed of members of the
CWPCA's Industrial Waste Committee to explore the
feasibility of uniform practice in industrial waste control.
The subcommittee was composed of members from
regulatory agencies, public sewerage agencies and in-
dustrial associations.
Work on the Uniform Ordinance was assisted by the
Bay Area Sewage Services Agency (BASSA), a nine-
county regional agency created by the California legisla-
ture to develop and implement water quality manage-
ment plans for the San Francisco Bay region. As part of
its regional services program, BASSA has undertaken a
source control program to assist local and subregional
entities in surveillance, planning and education. The
Model Ordinance is a vital component of this program.
Early work of the Uniform Ordinance Subcommittee im-
mediately recognized the need for regional uniformity in
industrial waste control. Industrial waste regulations
varied from one neighboring jurisdiction to another even
though treated effluents were being discharged into the
same receiving body after similar degrees of treatment.
Furthermore, many jurisdictions were in the process of
revising or updating their own existing regulations to
conform to new state and Federal requirements for con-
struction grants. The Subcommittee felt that timely
preparation of a model ordinance suitable for direct
adoption or adaptation by local agencies with as few
changes as necessary, would be a valuable public serv-
ice, with the following benefits:
• Establishment of uniform practices for enforcement
and to facilitate disposal of waste pollutants.
• Promotion of greater efficiency among regulatory
and municipal agencies in carrying out industrial
source control programs.
• Provision of a basis of equity and fairness to indus-
try and private wastewater dischargers who must
comply with regulations which can vary from com-
munity to community.
• Elimination of undesirable relocations of industries
from one jurisdiction to another.
As a basis for the model, the Subcommittee took a
draft ordinance being considered by the East Bay Dis-
chargers Authority—a joint powers subregional agency
comprised of the cities of San Leandroand Hayward, and
the Castro Valley, Oro Loma and Union Sanitary Dis-
tricts—and added critical review and comment from all
parts of the region. This included recommendations of
Federal and state regulatory agencies, industry, cities
and special districts. In writing the model ordinance, ef-
forts were made to incorporate latest state and Federal
regulations. All provisions are designed with flexibility
to meet Federal and state industrial cost recovery re-
quirements.
Response to the model ordinance has been enthusias-
tic and widespread since its presentation at the April
1974 convention of the California Water Pollution Con-
trol Association, where through the subsequent months,
demand for the document both within and outside Cali-
fornia has necessitated a second printing. Comments
have been received from many agencies and individuals,
which will be considered in a future revision of the Model
Ordinance. Acceptance of the ordinance by local agen-
cies has been encouraging. In the Bay Area, the large
19
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20 A MODEL INDUSTRIAL WASTE ORDINANCE
East Bay Dischargers Authority and its agencies, and
several other dischargers in the region have adopted the
model ordinance with minor changes.
Highlights of the Model Ordinance
Prohibitions
Prohibited hazardous, toxic and incompatible wastes
are wastes which can cause any of the following: fire or
explosion; flow obstruction or plant damage; endanger
life; create nuisance; pollute air; interfere with treat-
ment processes; prevent effluent or sludge reclamation;
adversely affect receiving waters; cause local agency's
treatment works to be in violation of any statute or regu-
lation; or overload collection or treatment facilities.
Storm and cooling waters are also prohibited except un-
der special permit issued by the local agency. Special
permission is also required for discharge of radioactive
wastes and wastes from holding tanks. Garbage grinder
usage is limited to shredding of food wastes prepared for
consumption on the premises or under special permit.
Garbage grinders shall not be used for shredding plas-
tic, paper products, inert materials or garden refuse.
Effluent Limitations
Limitations are placed upon wastewater discharges to
assure control of toxic or hazardous materials while con-
tin uing to provide an acceptable level of public service to
all segments of the community. Limits for heavy metals
are based upon ocean water discharge requirements and
allow for a 10:1 dilution (or removal) in the community
collection and treatment process (see Table 1).
TABLE 1
Effluent Limitations
Allowable Concentration mg/1
Arsenic
Cadmium
Copper
Cyanide
Lead
Mercury
Nickel
Silver
Total Chromium
Zinc
2.0
0.01
1.0
0.2
0.5
3.0
Other prohibitions include temperature, oil and
grease, pH, chlorinated hydrocarbons and phenols, as
shown in Table 2.
Provisions are included for effluent limitation under
Public Law 92-500 to apply in instances where these are
more stringent than the Model Ordinance.
Compatible Pollutants
Treatment plants are designed to meet the needs of
the communities served. Fundamental to waste treat-
ment processes is the disposal of so-called "compatible
pollutants". These are defined in the Model Ordinance
as biochemical oxygen demand (BOD); suspended
solids; pH (greaterthan 6.0); fecal coliform bacteria; and
TABLE2
Other Limitations
Temperature
Oil and grease (vegetable origin)
Oil and greaae (petroleum origin)
Chlorinated hydrocarbons*
Phenolic compounds*
Limits
150°F (65.5°C.) max.
300 mg/1 max.
100 mgl/1 max.
0.02 mg/1 max.
1.0 mg/1 max.
other pollutants identified in NPDES permit if compati-
ble to local treatment.
Determination of Wastewater Volume
User charges are applied against the total amount of
water used from all sources unless discharged to com-
munity sewers. The total amount of water used from
public and private sources is determined by means of
meters installed and maintained at the expense of the
user and approved by the Agency.
For users where significant portions of water received
from metered sources do not flow into the community
sewer user charges are applied against net volume dis-
charged into the sewer.
For users where it is unnecessary or impractical to in-
stall meters, wastewater volume may be determined
upon estimated prepared by the Agency. These are
based upon rational determinations in consideration of
such factors as number of fixtures, population equiva-
lent, annual production of goods and services or other
determinants of water use.
Administration
Application of source control management to a waste
treatment system must rely upon effective administra-
tive procedures. Fundamental to the Model Ordinance's
approach is a system of permit for major wastewater dis-
chargers and a practical reporting system. Emphasis
should be placed upon development of a spirit of coop-
eration among industrial users and a sense of awareness
of the problems of municipal waste treatment.
Figure 1 shows the permit process which begins with
the user completing a permit application questionnaire.
The local agency determines if the user is a major con-
tributor, that is, if the industry meets any of the follow-
ing criteria: (1) flows in excess of 50,000 mgd; (2) flows in
excess of five percent of treatment plant design capacity
or capability to treat; (3) discharges toxic pollutants in
toxic amounts; or (4) have a significant impact, either
singly or in combination with other industries, upon the
collection or treatment system.
Wastewater Discharge Permits
Discharge permits may contain the following: (1) rates
and charges; (2) average and maximum waste constitu-
ents and characteristics; (3) limits on flow rate and time
of discharge or requirements for flow regulation and
equalization; (4) inspection and sampling facilities; (5)
monitoring programs; (6) discharge reports; (7) mainte-
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A MODEL INDUSTRIAL WASTE ORDINANCE 21
DETERMINATION OF;
INDUSTRIAL
USERS
PERMIT
APPLICATION
QUESTIONNAIRE
Major contributing industry.
(Flows exceed 50,000 mgd or
5% of plant capacity, contain
toxic pollutants or signifi-
cantly impact local system or
plant.)
OTHER USERS NOT DEFINED ABOVE
DISCHARGE PERMIT
Specifies rates and charges; avg.
and max. constituents and charact-
eristics; flows and times;
inspection, sampling, monitoring,
reports, mass emission rates,
other.
NON PERMIT USERS
User charges based on class and
volume or fixed charge.
Figure 1: The Wastewater Discharge Permit Process for Industrial Source Control.
nance of plant records; (8) mass emission rates; (9) other
conditions as may be appropriate.
Permits are issued to specific users for specific opera-
tions. Permits cannot be reassigned, transferred, sold,
moved to new premises or applied to a changed opera-
tion.
Permits are issued for specified periods of time not to
exceed five years. Permits may be revoked for the fol-
lowing reasons: (1) incorrect or improper reporting of
waste constituents and characteristics; (2) failure to re-
port significant changes in operations or wastes; (3)
refusal of access to premises for inspection or sampling;
and (4) violation of permit conditions. Monitoring facili-
ties may be required to be built at the user's expense for
inspection sampling and flow measurement. Local agen-
cy representatives shall be provided reasonable access
at all times for purposes of inspection or sampling.
Users shall make wastewater acceptable before dis-
charging to sewers. Facilities required to pretreat waste-
water to acceptable levels shall be provided and main-
tained at the user's expense. Plans showing pretreat-
ment facilities and operating procedures must be ac-
ceptable to the local agency before construction, but re-
view of such plans and operating procedures does not re-
lieve users from the responsibility of modifying the
facility as necessary to produce effluents acceptable un-
der the provisions of the Model Ordinance. All subse-
quent changes in pretreatment facilities or methods of
operation shall be reported to the local agency.
Every user shall provide protection from accidental
discharge of prohibited materials or other wastes. De-
tailed plans showing facilities and operating procedures
to provide protection shall be submitted to the local
agency for review, and must be acceptable before con-
struction.
Information and data on users obtained from reports,
questionnaires, permit applications, permits and moni-
toring programs and from inspections shall be available
to the public or other governmental agency without re-
striction unless users specifically request and demon-
strate that the release of such information would divulge
information, processes or methods which would be detri-
mental to the user's competitive position.
User Charges and Fees
Users are classified by assignment to a "User Classifi-
cation" category according to the principal activity con-
ducted on the premises based on typical wastewater con-
stituents and characteristics. The purpose of classifica-
tion is to facilitate regulation if discharges based on con-
stituents to provide effective means of source control,
and to establish a system of user charges and fees to in-
sure equitable recovery of the local agency's cost.
Wastewater constituents and characteristics may in-
clude, but not be limited to the following: suspended
solids, BOD, COD, oil and grease, and chlorine demand.
User classification charges may be adopted for each
category based upon charges for average wastewater
constituents and characteristics. The charges for each
wastewater constituent and characteristic established
by the local agency and set forth in the local agency's
schedule of charges and fees which may include: (1) user
classification charges; (2) fees for monitoring; (3) fees
for permit applications; (4) appeal fees; and (5) charges
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22 A MODEL INDUSTRIAL WASTE ORDINANCE
and fees based on wastewater constituents and char-
acteristics including industrial cost recovery provisions
of the Federal Act.
Users who are not required to obtain Wastewater Dis-
charge Permits must pay applicable user charges as
established by the Agency. These shall be determined
by multiplying user classification charge by the waste-
water volume. The local agency may elect to set a fixed
unit charge for certain user classifications based on
wastewater constituents and characteristics. The mini-
mum charges should be based upon typical average
strength of domestic wastewater.
Enforcement
Enforcement effort should be directed toward practi-
cal correction of waste discharge problems with em-
phasis placed upon prevention rather than punishment.
Local authorities must consider sanctions such as termi-
nation of service, misdemeanor penalties, civil dam-
ages, etc. in the overall context of the laws under which
their individual agencies operate. The severest criticism
of the early version of the Model Ordinance came from
legal counsel from special districts whose organic acts
differed on matters of enforcement and penalties.
Accidental discharges in violation of the Model Ordi-
nance must be reported immediately by the user to en-
able possible countermeasures to be taken. Appropriate
followup should be made, including advising plant em-
ployees of permit requirements and accidental dis-
charge prevention measures.
When a discharge of wastewater has taken place, in
violation of the Ordinance, or the Wastewater Discharge
Permit, the local agency may issue an order to cease and
desist, and direct that those persons not complying with
such prohibitions, limits, requirements, or provisions to:
(1) comply forthwith; (2) comply in accordance with a
time schedule set forth by the Agency, or (3) take appro-
priate remedial or preventive action in the event of a
threatened violation.
Abatement of violating circumstances relies upon
court action, assessment of charges for local agency re-
pair costs, civil damages not to exceed $6,000 for each
day in which violations occur. Any misrepresentation of
facts or interference with collection monitoring or in-
spection data is an ordinance violation subject to its
penalties. Following notice and hearing, the local agen-
cy may terminate service.
SUMMARY
The Model Ordinance Subcommittee encouraged by
the response to its efforts is in the process of preparing
an updated version of the Model Ordinance which
should be available later this year. Many members of the
Subcommittee consider the Model Ordinance an essen-
tial first step toward development of a broadly based in-
dustrial waste code capable of easy adoption by ref-
erence by local agencies. Questionnaire and permit
forms have been prepared in a convenient booklet
format to assist Model Ordinance users. Copies of the
Ordinance and other information may be obtained from
the Bay Area Sewage Services Agency, Hotel Clare-
mont, Berkeley, California 94705.
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INSTITUTIONAL PROBLEMS OF THE SMALL
TREATMENT PLANT
E.J. Martin, RichardDuBois and Harold Bernard
Environmental Quality Systems, Inc.
Rockville, Maryland
INTRODUCTION
This is a real problem. It happened in a real com-
munity. For obvious reasons the names of the commun-
ity and the involved state are omitted. Some people here
may recognize the problems as their own. The story be-
gins some eight or nine years ago when the community
started to grow and the existing plant became over-
loaded. At that time, the treatment plant had a capacity
of about one mgd. In the middle 50's, as with all com-
munities, they really started to grow and the plant soon
became undersized. The community engaged a consult-
ing engineer. In this case, a local consulting engineer
that actually lived in the community. The consulting en-
gineering firm designed the plant on the basis of the re-
quirements of the Clean Water Act of 1965 and the vari-
ous state laws of that time period. Unfortunately, soon
after the plant was placed in operation, the Water Pollu-
tion Control Act and Amendments of 1972 (PL 92-500)
became the national law and the environmental laws of
the State also changed dramatically. In addition to the
limitation of the design due to the laws of the time, the
plant also had some unique design problems; the opera-
tors had operational limitations in regard to the new unit
operations planned for the enlarged plant and the state
and EPA played various roles to compel compliance of
performance for both the original design and the new
legislation.
The Problem
As mentioned, the plant was a one mgd. It included
activated sludge with some digestion capabilities. The
engineer designed the new plant to be a six mgd acti-
vated sludge plant with what he thought was also future
capacility to include some phosphorus removal. The de-
sign replaced digestion with wet oxidation. The en-
gineering report was submitted to the community about
the end of 1967. By the time the city approved the design
it was well into 1968. Construction did not actually start
until 1969. The plant went into operation in 1971, and
about a year later, in 1972, PL 92-500 became the na-
tion's law with its "best practical treatment" and its
"best available treatment" concepts.
Since this plant was located in the Great Lakes Basin,
"best practical treatment" required extensive removal
of phosphorus. PL 92-500 also required sewer infiltration
reduction programs, industrial surveys and sewerage
treatment cost participation (described in detail by Mr.
Charles Ris in a subsequent paper) determination of
compatibility of industrial wastewater sources with the
municipal treatment plant, and a fair share charge for
the industrial contributors. Negotiations were initiated
in 1972, between the community, the state, and the Fed-
eral government (and are still continuing in 1975) for the
plant to be upgraded in accordance with PL 92-500 and to
correct difficult sludge handling problems. Table 1 indi-
cates the chronology just mentioned.
TABLE 1
Plant Chronology
EXISTING PLANT A/S WITH DIGESTION 1 MGD
1966 CLEAN WATER ACT
1967-8 ENGINEERING FIRM SUBMITTED ENGINEERING REPORT
TO CITY WHICH WAS ACCEPTED
1969 CONSTRUCTION STARTED
1971 PLANT WENT INTO OPERATION 6 MGD
1972 PASSAGE OF 92-500
BPT
BAT
INFILTRATION REDUCTION
INDUSTRIAL SURVEYS
PERMIT NEGOTIATIONS
1975 EPA
OEPA
23
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24
INSTITUTIONAL PROBLEMS
There are real villans and heros in this episode, some-
times changing roles as you will see. As mentioned pre-
viously, the new plant was designed as a six mgd waste
activated sludge plant with phosphorus removal capa-
bility. Sludge is recycled back to the primary tanks,
periodically withdrawn to a concentration tank. It is then
pumped to the wet oxidation unit for heat processing.
The heat treated sludge is decanted in a small storage
vessel, and then applied to a new vacuum filter with the
filtrate going back to the head end of the plant, and the
sludge being disposed of in a sanitary landfill. However,
as the plant was designed for phosphorus removal, and
due to the new requirements of PL 92-500, the state is re-
quiring that the community reduce its phosphorus con-
centration in the effluent from about three milligrams
per literto about 0.3 milligrams per liter. Unfortunately,
the existing plant already has fantastic sludge disposal
problems stemming from many sources, but principally
related to the sludge handling system. Because the com-
munity already had received a construction grant from
the Federal government and the state, it now had a very
low priority for receipt of any additional funds for up-
grading the plant. Consequently, there probably is no
chance of the city getting additional funding for many
years. In addition, the Federal government is withhold-
ing $175,000 of the remaining original construction
grant funds until the plant is upgraded as they specified.
The design engineer thought he was designing a plant
on the basis of requirements existing in 1968-69, and
those that he could reasonably project. Besides not
being able to project the requirements of PL 92-500 into
the design of the new plant, the designer also did not
provide adequate flexibility in the sludge handling pro-
cess system in the plant. Only one new filter was added
to an existing 15 year old vacuum filter. About a year
after the new plant went into operation, the old filter
went out of operation. Because of the age, parts became
increasingly difficult to get, and it finally became too ex-
pensive to keep running.
There is also only one wet oxidation unit, which is
sized very close to the existing operating conditions of
the plant. Moreover, the afterburners on the off-gas sys-
tem were improperly designed. They provided a gas
temperature of only 800°F instead of the 1400° to 1800°F
necessary to eliminate all odors. Moreover, the boiler
feedwater sub-unit supplier did not conduct adequate
boiler feedwater analyses. As a result the heat exchange
units frequently corroded, plugged up or malfunctioned.
In addition, the same personnel that operated the one
mgd activated sludge plant were available to operate
this plant with little or no training in the areas of boiler
feedwater control and pressure vessel operation. They
could not properly cope with the needs of the thermal
units or their peculiar sludge handling requirements.
This inadequate training resulted in many problems de-
veloping with the boiler feedwater supply and the wet
oxidation units. The result was that these two units
caused the sludge handling portion of the plant to be in-
operative about 75 percent of the time.
As mentioned previously, sludge storage is inade-
quate. Treated sludge lies around the outside of the
buildings until it is loaded onto a truck to be hauled to a
sanitary landfill. Odors abound around the treatment
plant and the neighborhood. The local residents con-
tinually decry the odorous atmosphere around the plant
and the neighborhood even when the thermal units
operate, so there is a reluctance to operate these units
even when they perform as designed. Due to the odor
and because the thermal units are inoperative most of
the time the sludge is recycled to the head end of the
plant. The entire treatment plant must then be operated
as an extended areation plant, and the one vacuum filter
that is in operation must handle the entire sludge re-
quirements. In addition, the high wet weather flow di-
verted to the plant is about ten mgd (as compared with
the dry weather flow of about three mgd). This creates a
flushing effect which from a plant operators point of view
may really be "heaven sent". It momentarily solves all
sorts of sludge problems.
On top of the sludge problem indicated, the state and
EPA are insisting on phosphorus removal and odor re-
duction. This is in spite of the fact that increasing phos-
phorus removal will add 50 percent to the existing sludge
handling problem and really make the remaining units
undersized and probably compound the plant operation,
sludge dewatering and odor problems.
It should be emphasized that the community does
wish to comply. It wishes it had a well operated plant
without the aforementioned problems. It will initiate a
wastewater survey for the fair share contribution from
the industries just as the Federal law 92-500 indicates it
should. The city also wishes to incur no additional capital
investments, and sorely wishes to minimize plant oper-
ating costs concomitant. They also wish to obtain addi-
tional sources of revenue. As this is an election year the
city would like to be able to announce a reduction in resi-
dential sewerage charges. And of course they would like
to receive the $175,000 EPA is still withholding so it can
make some of the costly modifications. The municipality
did resolve its odor problem rapidly. They are now using
masking agents at an annual cost of more than $20,000,
and will probably continue to do so through the critical
warm weather or until the forthcoming elections.
In summary, almost all of the problems mentioned
above stem from those problems associated with the
sludge handling system and unit operations, as indi-
cated in Table 2. If the various sludge handling unit
operations were designed correctly and they were oper-
ated satisfactorily there would be fewer problems.
The solutions to the various treatment plant ills and
the conflicting requirements between the state's desires
and the city's ability to comply (at least through the eyes
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INSTITUTIONAL PROBLEMS 25
TABLE 2
Sludge Related Problems
1. NO REPLICATION OF SLUDGE HANDLING EQUIPMENT
2. INADEQUATE STORAGE
3. INADEQUATE THICKENING
4. MAKESHIFT SLUDGE TRANSFER
5. QUESTIONABLE CAPACITY OF SLUDGE FILTERS
6. USE OF ACTIVATED SLUDGE SYSTEM FOR SOLIDS STORAGE
7. ONE HEAT TREATMENT UNIT WITH ASSOCIATED PROBLEMS
a. Boiler heat exchanger coils continually
corrode
b. Afterburner is inadequately sized and
combustion temperature is too low
creating odors
c. Solids separator (oxidized sludge) source
of problems
d. Scaling on inside of pressure vessel
e. Inadequate training of personnel
f. Inadequate assignment of personnel by plant
to operate unit
g. System sized too closely to plant needs
h. Inadequate heat treated sludge storage
TABLE 3
Short Term Solutions to Plant Problems
1. HEAT TREATMENT UNIT (HTJ) MANUFACTURER PLANT TRAINING
AT NO COST
PLANT ASSIGNED ONE OPERATOR TO BECOME INTIMATELY FAMILIAR
WITH UNIT
CHEMICALLY TREAT SLUDGE AND USE THE ONE VACUUM FILTER TO
MAXIMUM CAPACITY
4. USE HTU AS STANDBY
5. SHIP SLUDGE OFF-SITE TO LANDFILL OPERATION THAT HAS PERMIT
(AT 3.54 PER GALLON WET OR $4.5/CU.YD. FOR SOLID)
RECYCLE WASTE SLUDGE TO PRIMARY SYSTEM AND OPERATE
SYSTEM AS AN IXTENDED AERATION PLANT
7. NO LIME ADDITION FOR PHOSPHOROUS REMOVAL
8. NEGOTIATE WITH STATE FOR
A. PLANNING FUNDS
B. TIME EXTENSION ON P REMOVAL
C. CONSTRUCTION GRANT
TABLE4
Long Term Solutions to Plant Problems
1. INDUSTRIAL SURVEY
2. INFILTRATION SURVEY
3. LABORATORY EXPANSION
4. UPGRADE PERSONNEL
5. OBTAIN PERMANENT OFFSITE SLUDGE DISPOSAL ARRANGEMENTS
A. TO LANDFILL
B. TO FUTURE REGIONAL TREATMENT PLANT
6. REDESIGN SPECIFIC UNITS IN THE PLANT
7. REPLICATE CRITICAL UNITS
8. MEET ALL FEDERAL AND STATE REGULATIONS
of the community) resolved themselves into short term
and long term solutions, as indicated in Tables 3 and 4.
The principal sludge treatment method suggested re-
volves around recirculating the sludge to the plant,
chemical treatment, and dewatering with the one
vacuum filter that is available. The thermal units would
be used as a back-up when the vacuum filters were down
for maintenance or repairs.
Off site disposal was considered for both concepts be-
cause of the nature of the heat treatment equipment, the
inflexibility of the sludge transfer system, inadequacy of
sludge storage, the odor problems, and the fuel costs as-
sociated with the operation of the heat treatment unit.
However, it was necessary to dewater to the maximum
extent possible. At costs of 3.5 cents/gal or 4.5 cents/
C. Y., annual sludge disposal costs could vary from about
$120,000 for a sludge with six percent solids to $16,500
for a sludge with 30 percent solids. The relative success
achieved with chemical addition to the highly oxidized
(recirculated) sludge made that operation relatively
simple, provided a 30 percent solids cake and made
offsite disposal of the dewatered sludge attractive.
SUMMARY
Given a reasonable time and some cooperation from
the U.S. Environmental Protection Agency and the State
Environmental Protection Agency, I am sure that every-
body's concerns about compliance and the proper per-
formance from this plant will be satisfied.
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REGIONAL W ASTEWATER SOLIDS
MANAGEMENT PROGRAM
LOS ANGELES-ORANGE COUNTY
METROPOLITAN AREA
David Burack
Los Angeles- Orange County Sludge Program
Whittier, California
I am grateful for a chance to tell you about a major
sludge study which is just getting off the ground in the
Southern California area. Perhaps those of you with
similar problems will be interested in the conduct of this
study. You might wish to provide information which will
help us in our task.
Lately there has been a lot of talk about the ultimate
disposal of wastewater solids originating in the Southern
California coastal area. The two horns of the dilemma
are familiar to all of us.
On the one hand, restrictions regarding sludge dis-
posal are becoming more stringent. In California, in ad-
dition to P.L. 92-500 and the Marine Protection, Re-
search and Sanctuaries Act, we have the State's "Water
Quality Control Plan for Ocean Waters of California."
This plan prohibits, outright disposal of sludge to the
ocean as a long-term solution.
On the other hand, Federal requirements to upgrade
municipal wastewater treatment plants and projected
growth patterns will result in a substantial increase of
wastewater solids.
Restrictions on disposal plus increase in production
equals one big problem.
Sludge processing and disposal projects, now under
way or in the planning stages in the Los Angeles region,
appear likely to provide immediate short-term solutions
to this problem.
For the long-term solution, a Step 1 grant under Sec-
tion 201 of P.L. 92-500 has been secured for a basinwide
wastewater solids management program, to be con-
ducted under a Joint Powers Agreement by the three
major wastewater agencies in the region, with as-
sistance of the State of California and the United States
Environmental Protection Agency.
The Program will study all feasible alternative solu-
tions to the long-term disposal of wastewater solids ori-
ginating in Los Angeles and Orange Counties.
Figure 1 shows the study area, which includes all of
Los Angeles and Orange Counties. The area is 120 miles
long in its greatest extent and runs 30 to 80 miles in from
the ocean. All together, this is an area of about 4,800
square miles with a population of 8.5 million. We also in-
tend to look at potential reclamation or disposal sites and
conveyance routes beyond these boundaries.
The dimensions of the problem now and in the future
are shown in Figures 2 and 3. The three major waste-
water agencies now generate about 1,200 tons of sludge
per day on a dry solids basis (Figure 2). Of this, about
700 tons is discharged to the ocean, either in sludge-only
or sludge-plus-effluent ocean outfalls. About 180 tons
goes to landfills or is composted and sold to nurseries
and home gardeners. The balance of the 1,200 tons are
organics removed during anaerobic digestion.
If and when state and Federal requirements are met,
the solids disposal picture will change drastically
(Figure 3). By 1985, our estimates indicate an increase of
100 tons over present production, due to population
growth. Of the total 1,300 ton input, 100 tons will still go
to the ocean even with full secondary treatment, 800 tons
will go the land, with the balance volatiles lost during
digestion.
From 700 tons to sea ... to 800 tons to land. Here
comes the sludge, all right. Can we compost it? Can we
pyrolize it with garbage and possibly get some energy or
metals credits? Or are we going to face a worse uphill en-
vironmental battle than now with ocean dumping? These
are just some of the questions our Program hopes to
answer.
Figure 4 shows the organization of the program. The
State Water Resources Control Board representative
chairs the Policy Board. Other members include a repre-
sentatives from: (1) Region IX, EPA; (2) Los Angeles
County Sanitation Districts; (3) City of Los Angeles; and
(4) Orange County Sanitation Districts.
The three local agencies mutually agreed that the San-
itation Districts of Los Angeles County would act as lead
agency. The lead agency provides the routine adminis-
trative functions required by the Policy Board and the
Project Manager.
The Project Manager is directly responsible to the
Policy Board and has overall responsibility for the con-
duct of the study and preparation of the final project re-
26
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INSTITUTIONAL PROBLEMS 27
STUDY AREA
Figure 1: Study Area.
REGIONAL WASTEWATER SOLIDS MANAGEMENT PROGRAM
LOS ANGELES-ORANGE COUNTY METROPOLITAN AREA
PRESENT CONDITIONS
Figure 2: Present Conditions.
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28 INSTITUTIONAL PROBLEMS
V
REGIONAL WASTEWATER SOLIDS MANAGEMENT PROGRAM
IDS ANGELES ORANGE COUNTY METROPOLITAN AREA
AFTER SECONDARY
CIRCA 1985
Figure 3: After Secondary (Circa 1985).
POLICY BOARD
STATE WRCB (CHAIR!
EPA
LACSO
CITY OF LA
OCSD
STAFF REVIEW
COMMITTEE
STATE WRCB
EPA (CHAIR.)
LACSO
CITY OF L A.
OCSD
STAFF (6)
PROGRAM
DIRECTION
LEAD AGENCY
L A C S D
STEP I GRANT RECIPIENT
PROJECT MANAGER
TASK MANAGERS
Figure 4: Organization of Regional Wastewater Solids Management Program, Los Angeles—Orange County Metropolitan Area.
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INSTITUTIONAL PROBLEMS
29
port. The Project Manager is assisted by a Staff Review
Committee, which is comprised of representatives from
the participating agencies and has his own staff of four
technical and two clerical personnel.
Also serving in an advisory capacity will be many in-
terested individuals and organizations. We aren't sure
yet how these groups will mesh with the overall pro-
gram, hence, the drawing is not complete.
Figure 5 shows the meat of the program, the series of
tasks to be considered during the study. These tasks will
be performed by the participating agencies or by outside
contracts. The Project Manager is responsible for as-
signing and scheduling tasks, in addition to personnel
and budget items. Each task group will have a desig-
nated task manager, whose activities will be coordinated
by the Project Manager and his staff. As indicated, dis-
posal or recycling alternatives to be studied and evalua-
ted are:
• Recycling of wastewater solids for agricultural uses,
reclamation of soils, and use as soil supplement.
• Disposal of wastewater solids to land, i.e., sanitary
landfills, evaporation basins, and spreading on
dedicated land.
• Disposal of wastewater solids to ocean.
• Incineration and pyrolysis processes for volume re-
duction and resource recovery.
• Conditioning, dewatering and composting.
In conjunction with these alternatives, transportation
and processing of solids and disposal of industrial
sludges will also be studied.
A wastewater solids management system ultimately
will be selected, based on the evaluation of various dis-
posal and recycling alternatives, consistent with identi-
fiable constraints. The system may be a combination of
various sludge handling, disposal, or recycling methods,
and may be regional or local in concept.
The schedule for the study presently covers a three-
year period, with completion expected in 1978. The work
REGIONAL WASTEWATER
SOLIDS MANAGEMENT PROGRAM
LOS ANGELES - ORANGE COUNTY
METROPOLITAN AREA
TASKS:
PROJECT DEVELOPMENT
RECYCLE TO LAND
DISPOSAL TO LAND
DISPOSAL TO OCEAN
INCINERATION A PYROLYSIS
SOCIAL, ECONOMIC a INSTITUTIONAL STUDIES
WASTEWATER SOLIDS MANAGEMENT
TRANSPORTATION STUDIES
EVALUATION OF ALTERNATIVES Ok
SELECTION OF SYSTEM FOR IMPLEMENTATION
DISPOSAL OF INDUSTRIAL SLUDGES
Figure 5: Series of Tasks to be Considered During the Study.
involved is now estimated to cost two million dollars.
However, it is likely that this estimate will increase sig-
nificantly when the detailed work program is submitted,
especially since the question of disposal of industrial
sludges, not now included in the plan of study, will be
considered in depth.
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COMPUTER EVALUATION OF SLUDGE HANDLING
AND DISPOSAL COSTS*
Robert Smith and Richard G. Filers
United States Environmental Protection Agency
Cincinnati, Ohio
INTRODUCTION
Treatment and disposal of sludges produced in muni-
cipal wastewater treatment plants can account for as
much as 60 percent or as little as 20 percent of the total
cost of treatment. Careful consideration should, there-
fore, be given to selecting the sludge treatment and dis-
posal scheme which meets the site-specific constraints
at a minimum cost. Some factors which determine the
scheme selected are the nature of the sludges produced,
ultimate disposal options available, the local cost of elec-
trical power or fuel oil, and the subjective preference of
the designer orthe community officials. Thus, it can be
seen that many of these factors are site specific and some
are difficult to quantify. In this report, a digital computer
program which is capable of examining the cost and per-
formance of a wide variety of alternative sludge handling
schemes is described, and the results of sample calcula-
tions are presented. This computer program can be used
as a management tool to narrow the range of sludge
treatment and disposal options when the site-specific
conditions are known.
For example, in rural communities the least-cost
method of sludge disposal might be lime stabilization
followed by application of the sludge to the land. How-
ever, in some localities the land might be wet for several
months of the year necessitating undesirable storage of
the sludge. The computer program is capable of esti-
mating the cost of this method, but the subjective and
aesthetic factors associated with storage of the sludge
cannot be quantified. In urban communities, the land
available for sludge spreading might be far from the
treatment plant and transportation charges could equal
the cost of more complex treatment and disposal at the
plant site.
*This report has been reviewed by the Municipal Environmental Re-
search Laboratory, U.S. Environmental Protection Agency, and ap-
proved for publication. Mention of trade names or commercial
products does not necessarily constitute endorsement or recommenda-
tion for use.
Another option might be to reduce the mass of the or-
ganic sludge economically by the use of anaerobic di-
gesters. Anaerobic digesters have the added advantage
of producing methane gas which can be either sold or
used in the plant for heating or to supply internal com-
bustion engines. The internal combustion engines can
be directly coupled to air blowers or water pumps or can
be used to drive electrical power generators. However,
anaerobic digesters have been known to fail as a result of
toxic substances being introduced with the raw waste-
water or as a result of improper charging. For this and
other reasons, anaerobic digesters are sometimes not in-
cluded as part of the treatment scheme.
To demonstrate the capability of the program a large
number (261) of alternative sludge treatment and dis-
posal schemes are considered in this report and the cost
is estimated for each treatment scheme. The basic com-
putational program used is called the Executive pro-
gram; and the details of this program have been pub-
lished previously. The Executive program contains a
subroutine for each of the liquid and sludge treatment
processes. It contains the rate and mass balance rela-
tionships necessary to generate the effluent stream vec-
tors when one or more influent stream vectors are sup-
plied together with certain decision variables. The sub-
routine also sizes all structures and equipment and esti-
mates the capital and operating and maintenance costs
associated with the process. The stream vector is a list of
parameters which fully characterize the stream. The
definition of each component of the stream vector is
shown in Table 1 along with the values used for the raw
wastewater. The Executive program contains the neces-
sary logic to call each subroutine needed in a way which
allows for solution of all stream vectors when the pro-
cesses used and the interconnecting piping network are
supplied as input to the program. When recycle streams
are involved an iterative procedure is followed until the
components of all stream vectors converge. Equipment
and structures associated with each process are sized
within the subroutine, and the construction and operat-
ing and maintenance costs are both estimated.
30
-------
HANDLING AND DISPOSAL COSTS 31
TABLE 1
Contents of the Stream Vector
(I designates the stream number)
Row
So.
1
2
3
5
6
7
8
9
10
11
12
13
14
15
16
17
FORTRAN
Variable Name
SMATX (1,1) I
SMATX (2,1) Q
SMATX (3,1) SOC
SMATX (4,1) SNBC
Nominal Value
for
Plant Influent
SMATX
SMATX
SMATX
SMATX
SMATX
SMATX
SMATX
SMATX
SMATX
SMATX
SMATX
SMATX
SMATX
(5,1) SON
(6,1) SOP
(7,1) SFM
(8,1) SBOD
(9,1) VSS
(10,1) TSS
(11,1) DOC
(12,1) DNBC
(13,1) DN
(14,1) DP
(15,1) DFM
(16,1) ALK
(17,1) DBOD
Parameter Definition
Stream Number
Volume Flow, mgd 10.
Solids Organic Carbon, rag/1 53.8
Solid Nonbiodegradable Carbon
mg/1 15.
Solid Organic Nitrogen, mg/1 5.
Solid Organic Phosphorus, mg/1 .8
Solid Fixed Matter, cg/1 60.
Solid BOD, mg/1 72.5
Volatile Suspended Solids, mg/1 115.
Total Suspended Solids, ng/1 175.
Dissolved Organic Carbon, mg/1 72.5
Dissolved Uonbiodegradable Carbon,
mg/1 11.
Dissolved Nitrogen, mg/1 20.
Dissolved Phosphorus, cig/1 9.
Dissolved Fixed Matter, mg/1 500.
Alkalinity, mg/1 250.
Dissolved BOD, mg/1 115.
Two basic types of municipal wastewater treatment
plants are considered in this report; primary sedimenta-
tion plants and activated sludge plants. In the primary
sedimentation plant, the sludge stream to be treated is
the underflow stream from the primary settler. In the
activated sludge plant, two sludge streams must be
treated; the underflow stream from the primary settler
and the waste activated sludge (WAS) stream which is
split off the underflow stream from the final clarifier.
When the cost is expressed as dollars/dry ton of sludge
solids, the mass flow in one or both streams is being used
as the basis.
The next section of this report outlines the basis for
computing the mass and concentration of sludge pro-
duced in liquid handling processes. Following sections
describe the content of the subroutines which charac-
terize the individual sludge handling processes. Finally,
the alternative sludge handling schemes considered are
identified and the estimated cost for each scheme is
given.
Although the Executive program is capable of sizing
and estimating the cost of any size plant all example
computations discussed in this report will be for plants
having a design capacity of ten mil gal/day.
The FORTRAN method of writing mathematical equa-
tions is used in this report. An explanation of the FOR-
TRAN method is given in the Appendix.
Estimaton of Sludge Production
The Executive program was used to make all per-
formance and cost calculations given in this report. The
stream vector selected for the raw wastewater stream is
shown in Table 1.
The primary settler subroutine (PRSET) used in the
Executive program assumes that the fraction removed
(FRPS) has the same value for all species of suspended
solids. For example, the fraction of inorganic suspended
solids removed equals the fraction of organic suspended
solids removed. The value of FRPS is 0.6 for all computa-
tions. The overflow rate (GPS) expressed as gal/day/sq
ft of surface area needed to accomplish the specified re-
moval rate (0.6) is found from the following relationship:
FRPS = 0.827(2.71828**(GPS/2780)) (1)
Therefore, it can be seen from equation (1) that the re-
quired primary settler overflow rate to achieve 60 per-
cent removal of suspended solids is 868 gpd/sq ft. Since
the assumed concentration of suspended solids in the
raw wastewater is 175 mg/1, the production of primary
sludge is 875 Ib/mil gal treated with no recycle of WAS
to the primary settler. The primary sludge is 66 percent
volatile. When WAS is not returned to the raw wastewa-
ter stream entering the primary settler, the concentra-
tion of primary sludge is taken as five percent; when it is
returned, the concentration of the sludge stream from
the primary settler is taken as three percent.
The model used for the activated sludge process is de-
scribed in Reference 2. The mixed liquor suspended
solids concentration (MLSS) held in the aerator is set at
2000 mg/1. The required concentration of BOD in the
final effluent stream is always set at 13 mg/1.
Thus, when the BOD load on the activated sludge pro-
cess is increased by recycle streams, the size of the aera-
tor and final clarifier are increased to achieve the same
BOD quality in the final effluent stream. As shown in
Reference 2, the fraction of the MLSS which escapes in
the final effluent stream is a function of the hydraulic
detention time, the MLSS, and the hydraulic overflow
rate for the final clarifier. The aerator volume (VAER)
expressed in mil gal is calculated from the following
relationship where Q is the volume flow in mil gal/day
(mgd), BODIN is the concentration (mg/1) of BOD in
the primary effluent stream and BODOUT is the concen-
tration of BOD in the final effluent stream (13 mg/1).
VAER = Q*(BODIN- BODOUT)/
(MLSS/1000)/BODOUT/24 (2)
When no recycle streams are returned to the primary
settler, the value for the activated sludge process influ-
ent volume flow (Q) is 9.97 mgd. The value for BODIN is
144.1 mg/1, and the value for BODOUT is 13 mg/1.
VAER can be calculated from equation (2) as 2.095 mil
gal, and the corresponding value for hydraulic detention
time is five hours.
The sludge retention time (SRT) at this operating
point is 3.32 days. The volatile sludge wasted is 757
Ib/mil gal of plant flow, and the total wasting rate is 935
Ib/mil gal. Thus, the WAS is 80 percent volatile. With no
recycle streams, the total sludge production is 875 Ib/mil
gal for primary sludge and 935 Ib/mil gal for WAS for a
total of 1810 Ib/mil gal.
-------
32 HANDLING AND DISPOSAL COSTS
Production of sludge in the activated sludge process is
difficult to estimate because it depends on the nature of
the feed stream as well as the operating policy used.
Vosloo3, using the data reported by Hopwood and
Browning4 and Wuhrmann5, developed the following
relationship:
Ibsludge/lb BOD applied = 1/(1 + 0.05*SRT) (3)
This relationship is plotted in Figures 1 and 2. Similar
data collected at the Hyperion Plant in Los Angeles was
reported by Bargman and Borgerding6. These data
points are plotted in Figures 1 and 2. The data reported
by Vosloo and the data points from Hyperion are both for
settled municipal wastewater. Sludge production at Hy-
perion was somewhat less than that reported by Vosloo,
but the scatter in the data is great.
The Executive program was used to generate similar
sludge production data and these computed points are
also shown in Figures 1 and 2. In general, this calculated
data agrees well with the estimates made by Vosloo. To
generate the data, the value of BODOUT was varied
from 40 mg/1 (corresponding to an SRT of 0.87 days) to
five mg/1 (corresponding to an SRT of 13 days). The
value used for MLSS was 2000 mg/1. All of the com-
puted data reported are around the design point cor-
responding to 3.3 days SRT.
Lime Stabilization
Sludges which are not biologically digested or incin-
erated are stabilized by the addition of lime. The target
pH for stabilization is 11.5, and the estimated dose to
achieve it is 212 Ib of lime (CaO)/ton of dry solids.
When dewatering is effected by vacuum filters or cen-
trifuges, a sludge holding tank with a minimum deten-
tion time of three days is used. Therefore, only the cost
of lime slaking and feeding equipment is added when
lime stabilization is required. When no dewatering is
provided or dewatering is achieved in sand drying beds,
a sludge holding tank with a detention time of three days
is provided to mix lime into the raw sludge.
0)
CO
•o
u
o
9
•a
o
M
o.
to
W
ti
on
.o
O Hyperion
Q Executive Program
F/M, (Ibs of BOD applied/day) / (Ib of MLSS In aerator)
Figure 1: Estimation of Sludge Production in the Activated Sludge Process.
-------
HANDLING AND DISPOSAL COSTS 33
to
OHyperion
D Executive Program 5
SRT, (Ibs of MLSS In aerator) / (Ib of MLSS produced/day)
Figure 2: Estimation of Sludge Production in the Activated Sludge Process.
The cost of lime slaking and feeding equipment was
taken from Reference 7. Estimates of man-hours for
operation and maintenance were developed by W.F.
McMichael and reported in an in-house memorandum 8-
Relationshipsfor estimating the cost of lime slaking and
feeding are shown in Figures 3 and 4. For example, a
ten-mgd primary sedimentation plant produces 8,834 Ib
of raw primary sludge per day and used 936 Ib of lime fc
stabilization at a cost of $25 per ton. Therefore, the lime
cost is $11.74/day or 0.117 cents/1000 gal of water
treated. Lime slaking and feeding equipment is sized for
the peak diurnal flow. The following relationship be-
tween average daily flow and peak diurnal flow is used:
QP = 1.78*QA**0.92
QP = peak diurnal flow, mgd
QA = average daily flow, mgd
Construction cost for slaking and feeding equipment
is about $20,300 and the cost of the sludge holding tank
with a three day detention time is about $49,600. Add-
ing 36 percent for interprocess piping and other ancillary
costs gives a total capital cost of $95,400. Amortizing this
amount at six percent over 25 years results in a cost of
$20.45/day or 0.204 cents/1000 gal treated. Operation
and maintenance costs for the sludge holding tank and
the lime addition facilities total 0.335 cents/1000 gal.
Adding the cost of lime and debt service gives a total
treatment cost of 0.657 cents/1000 gal for lime stabiliza-
tion of primary sludge.
Gravity Thickening
The gravity thickener subroutine considers two in-
fluent and two effluent streams. The first influent
stream is the sludge stream to be thickened. The second
influent stream is the wash water normally split off the
final effluent stream. The first effluent stream is the
thickened sludge stream and the second effluent stream
is the supernatant normally returned to the head end of
the liquid handling train. A total of five decision para-
meters are necessary to specify the size and
performance of the thickener.
The first decision parameter is the recovery factor
(TRR), which is defined as the fraction of the sludge
mass in the first influent stream which exists in the first
effluent stream. The second decision parameter is the
sludge concentration in the thickened sludge stream.
The third decision parameter is the hydraulic overflow
rate (GTH) expressed as gal/day/sq ft of surface area
and the fourth decision parameter is the solids loading
rate (GSTH) expressed as Ib of sludge solids/day/sq ft of
surface area. Since the basic sizing parameter for the
thickener is the surface area the fifth decision parameter
-------
34 HANDLING AND DISPOSAL COSTS
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1,000.
100,000.
10,000.
Lime Addition Rate, Ibs/day
Figure 3: Construction Cost for Lime Slaking and Feeding in January 1971 Dollars.
is the excess capacity factor applied to surface area. operated with wash water the wash water ratio (WRT) is
If the thickener is to be operated with no wash water found which will make both GTH and GSTH equal the in-
the surface area is taken as the greater of the two values put values. WRT is defined as the ratio of volume flow in
for surface area; the first is based on GTH and the the wash water stream to the volume flow in the
second is based on GSTH. If the thickener is to be thickened sludge stream.
un-
-------
HANDLING AND DISPOSAL COSTS 35
M
(0
01
M
I-J
o
§
PB
I
10,000. 10
1,000. 10
g
100.
100.
1,000.
Lime Addition Rate, Ibs/day
10,000.
Figure 4: Operation and Maintenance Labor Man-Hours Required for Lime Slaking and Feeding.
The concentration of sludge solids in the supernatant
stream is found from a mass balance relationship. The
ratio of organic to total solids in both effluent streams is
found by assuming that solids entering the process in the
two influent streams are thoroughly mixed. The same
assumption is used to find the ratio of organic to total
dissolved matter in both effluent streams.
Cost estimating relationships for sedimentation given
in Reference 20 are used to estimate construction cost
and operating and maintenance cost using the computed
value for surface area as the independent parameter.
The value used for GTH is 700 gpd/sq ft in all cases.
The concentration of raw primary sludge from the pri-
mary settler is taken as five percent with no recycle of
-------
36
HANDLING AND DISPOSAL COSTS
WAS andthree percent when WAS is recycled. The con-
centration of WAS is taken as one percent. When pri-
mary sludge is gravity thickened alone, the value for
GSTH is 16 Ib/day/sq ft and the sludge is thickened to
eight percent. When primary sludge and WAS are
mixed before being thickened the value for GSTH is
eight Ib/day/sq ft and the mixture is thickened to four
percent. When WAS is returned to the primary settler
influent, the three percent sludge in the settler under-
flow is thickened to six percent with a value of eight
Ib/day/sq ft for GSTH. When WAS is gravity thickened
alone, the value for GSTH is six Ib/day/sq ft, and the
sludge is thickened to two percent.
When wash water is added to the incoming sludge the
concentration of the diluted sludge stream can be found
from the following formula:
Diluted sludge concentration, % =
GSTH/GTH/0.0833 (4)
If the diluted sludge concentration exceeds the concen-
tration of the incoming sludge no wash water is added
and the value for WRT is zero. The concentration of sus-
pended solids in the overflow stream can then be calcu-
lated simply as the product of the diluted sudge concen-
tration and the factor (1-TRR). For example, using a
value of 0.9 for TRR it can be seen from equation (4) that
the dil uted concentration for primary sludge will be 2740
mg/1 and the suspended solids in the overflow will be
274 mg/1. Similiarly, for a mixture of primary and WAS
the diluted sludge will have a concentration of 1372
mg/1 and the overflow will contain 137 mg/1 suspended
solids. For gravity thickening of WAS the diluted sludge
will be 1030 mg/1 and the overflow will contain 103 mg/1
suspended solids.
Air Flotation Thickening
The sludge handling schemes discussed in this report
use air flotation thickening only for WAS and the basic
sizing parameter is GSTH. If no polymers are used, the
recommended value for GSTH is ten Ib/day/sq ft. When
a dose of ten Ib of polymer/ton of dry solids is used, the
recommended value for GSTH is 30. In computing the
cost of air flotation thickening, it is assumed that poly-
mers are used at a cost of $0.45/lb.
A secondary sizing parameter is GTH and its maxi-
mum allowable value is 1150 gpd/sq ft. The concentra-
tion of suspended solids in the influent sludge stream
necessary to satisfy values for GSTH and GTH simul-
taneously is given by the following relationship:
Influent sludge concentration, mg/1 =
GSTH*1000,000/GTH/8.33 (5)
Therefore, if a value of 30 is used for GSTH, GTH will not
exceed 1150, unless the solids concentration of WAS is
less than 3131 mg/1. It is assumed that the thickened
WAS is four percent solids. The fraction of influent sus-
pended solids which escape in the overflow stream is ex-
pressed by TRR. No dilution water is added to WAS.
Therefore, if the concentration (mg/1) of unthickened
WAS is called TSS1, the concentration of thickened
sludge is called TSS3, and the concentration of suspend-
ed solids in the overflow is called TSS4, the following re-
lationship can be used to find TSS4:
TSS4 = (1-TRR)*TSS3/(TSS3/TSS1-TRR) (6)
Using40,000mg/1 for TSS3, 10,000 mg/1 for TSS1, and
0.95 for TRR the value for TSS4 can be computed as 164
mg/1. The value assumed for TRR in the calculations re-
ported here is 0.95.
The excess capacity factor used for the flotation
thickener is determined by the assumed operating hours
per week and the commercially available sizes. It is as-
sumed that weekly operating hours are related to the de-
sign capacity of the plant as follows; less than two mgd,
40; two to five mgd, 80; 5-20 mgd, 100; over 20 mgd, 168.
For example, if a one mgd plant produces 893 Ib
WAS/day and operates the flotation thickener 40 hr/wk
the required size is (893/30)*( 168/40) or 125 sq ft. The
next larger commercially available size is 150 sq ft, so
the excess capacity factor is 150/125 or 1.2. Construc-
tion, operating, and maintenance costs for flotation
thickeners are given in Reference 9.
Anaerobic Digestion
The Executive program contains two subroutines for
anaerobic digestion: the first (DIG) represents a com-
pletely mixed anaerobic digester; the second (DIG2)
represents the second-stage anaerobic digester, which
is treated as a thickener with no wash water added. The
relationships used to represent the first-stage com-
pletely mixed digester are taken from the work of
McCarty 10- A full discussion of the model for the first-
stage digester can be found in Reference 2. The
anaerobic destruction of biodegradable organic solids
and dissolved material is represented by a Monod type
of rate equation with no recycle of active solids. The con-
centration of biodegradable dissolved and particulate
organics entering the digester is known from the influent
stream vector. Dissolved and solid biodegradable or-
ganic material are assumed to be destroyed at equal
rates. If F equals the concentration (mg/1) of biode-
gradable material (expressed as carbon in the effluent
stream from the first-stage digester), then F is calcu-
lated as follows:
F = K2/(K1*TD 1) (7)
Kl = 0.28/2.71828**0.036*(35 T) (8)
K2 = 700.*2.71828**0.10*(35 T) (9)
T = digester temperature, °C
TD = hydraulic detention time, days
The TD used for the first-stage digester is 15 days, and
the temperature of the digester is set at 30°C. Therefore,
the value for F is 463 mg/1 as carbon. The value for F
does not depend on the concentration if biodegradable
carbon in the influent stream. Using the stream vector
shown in Table 1, we can see that the concentration of
biodegradable carbon entering the anaerobic digester is
-------
HANDLING AND DISPOSAL COSTS 37
11,124 mg/1 when unthickened primary sludge is di-
gested. Therefore, about 96 percent of the
biodegradable carbon in the influent stream is destroyed
by anaerobic digestion. The corresponding reduction in
volatile solids is 66 percent, and the reduction in dry
solids is 44 percent. Nitrogen released by destruction of
organic solids is assumed to leave the digester is dis-
solved form.
The standard cubic feet (scf) of methane produced is
found by assuming that 5.61 scf are produced per pound
of COD destroyed and that the ratio of COD to carbon is
taken as 3.5. Therefore, in the example cited, 36,771 scf
of methane is produced per day. Since 359/12 scf of
methane plus carbon dioxide must be produced per
pound of carbon digested, the production of carbon
dioxide is 19,311 scf/day. Thus, about 15 scf of digester
gas is produced per pound of volatile solids destroyed,
and the gas is 66 percent methane.
The second-stage digester is treated as a thickener
with a detention time of 15 days. The concentration of
dry solids in the thickened sludge stream is taken as five
percent. The solids recovery factor (TRR) is the fraction
of entering solids that leave the second-stage digester in
the thickened sludge stream. TRR is set at 0.81. There-
fore, if the concentration of solids in the effluent from the
first stage digester is 28,135 mg/1, the concentration of
solids in the overflow stream is 9,823 mg/1. The concen-
tration of dissolved species is assumed to be the same in
both effluent streams.
Aerobic Digestion
Although the physical and biological principles in-
volved in aerobic digestion are well known, design rela-
tionships are not well established in terms of the capa-
city of equipment and structures for a specified degree of
treatment with a known feed stream. A sketch of the
aerobic digestion process is shown in Figure 5.
Several operational alternatives are available in de-
signing the process. For example, it can be designed to
handle WAS alone or raw primary sludge can be added
to the aerobic digester. In larger plants it is common
practice to install a settler after the aerator to separate
the solids from the supernatant and return them to the
aerator. The supernatant is commonly returned to the
main plant. Aerobically digested sludge is often dis-
posed of on the land either directly or after being dewa-
tered on sand-drying beds. Centrifuges or air flotation
can be used to thicken aerobically digested sludge.
The basic design variable for the aerator is either TA
(aerator volume/average influent flow volume) or SRT
(sludge mass/average sludge wasting rate). The aerator
is sometimes sized using pounds of volatile solids fed per
day per lOOOcu ft of aerator capacity as the principal de-
sign variable. Several laboratory studies have been
made to relate the percent of volatile solids destroyed to
TA or SRT. The best known and most widely quoted data
of this sort are reported by Jaworski, Lawton, and Roh-
IS2 - primary sludge
OS2 - supernatant
OS1 - digested sludge
Figure 5: Diagram of the Aerobic Digestion Unit Process.
Hch11, and are shown plotted on semi-log paper in
Figure 6. One of the fundamental problems in using this
kind of data is to estimate the fraction of the volatile
solids that is essentially nonbiodegradable. Another re-
lated problem is to estimate the shape of the curves
shown in Figure 6 when the mix of primary sludge and
WAS is varied. Information which would allow for this
kind of design is not available.
The data shown in Figure 6 are for a mixture of pri-
mary sludge and WAS in the proportion of 1.75 to 1.0. It
can be seen that when the temperature is 20°C the di-
gestion process is almost complete after 15 days, even
though primary sludge represents the greater propor-
tion. On the other hand when the temperature is 15°C,
about ten percent of the biodegradable volatile solids re-
mains at 30 days of TA.
In the Executive program, the subroutine AEROB is
used to represent aerobic digestion. The process can be
designed with or without a final settler depending on the
input value for the parameter XAFS; without settler if
XAFS = Oand with settler if XAFS = 1. The aerator is
sized using a specified TA. When WAS is digested
alone, the TA specified is ten days. When raw primary
sludge and WAS are aerobically digested in the same
basin, the TA is set at 20 days. Regardless of the nature
of the feed stream, it is assumed in AEROB that all bio-
logically degradable material is fully degraded within
the process.
The stream vector used classifies solid and dissolved
pollutants as organic or inorganic and further classifies
the organic constituents as biodegradable or nonbiode-
gradable. Solid constituents (mg/1) of WAS are classi-
fied as MLASS (active solids), MLBSS (biodegradable
volatile solids), MLNBSS (volatile nonbiodegradable
solids), MLDSS (volatile debris solids), and MLISS (in-
organic solids). To compute the fraction of the volatile
solids that is not degraded in the aerobic digester, the
assumptions contained in Reference 2 are used. Some of
these assumptions are; the ratio of BOD to volatile sus-
pended solids is 0.84, and the yield coefficient repre-
senting production of active solids from MLBSS is 0.65.
The fraction of MLASS remaining after cell lysis is 0.18.
The compaction ratio representing the concentration of
-------
38 HANDLING AND DISPOSAL COSTS
100.
so
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a
(0
T>
O
CO
O
>
60
(1)
o
•H
M-l
O
a)
00
a)
4J
§
o
10.
1.
10 15 20 25
Aerobic Digester Detention Time, days
Figure 6: Aerobic Digestion Performance as Reported by Jaworski.
30
solids in the WAS divided by the mixed liquor
suspended solids concentration (MLSS) is URSS with a
value in the range of three to five.
Using these assumptions, the concentration of non-
biodegradable material which enters the aerobic diges-
ter in the WAS stream can be calculated as follows:
Nonbiodegradable solids in WAS, mg/1 =
URSS*(MLASS*0.18 + MLBSS*0.84*0.65
*0.18 + MLNBSS + MLISS + MLDSS) (10)
A similiar relationship can be used for finding the con-
centration of nonbiodegradable material which enters
the aerobic digester in the raw primary sludge stream.
To make this calculation it is assumed that the ratio of
volatile suspended solids to solid nonbiodegradable or-
ganiccarbon (SNBC) is 2.13, the concentrations (mg/1)
of particulate and dissolved BOD are designated as
SBODandDBOD, and the concentration (mg/1) of inor-
ganic material is designated as SFM. The relationship
for primary sludge is as follows:
Primary nonbiodegradable solids, mg/1 =
2.13*SNBC + (SBOD + DBOD)*0.65
*0.18 + SFM
-------
HANDLING AND DISPOSAL COSTS 39
As an example, consider a one mgd plant that has a
raw wastewater suspended solids concentration of 175
mg/1. Assume that the primary settler removes 60 per-
cent of the solids, that the solids removed are 66 percent
volatile, and that 72 percent of the volatiles is biodegrad-
able. The massof sludge in the primary sludge stream is
therefore, 875 Ib/day. The mass of volatile sludge is 577
Ib/day and the mass of biodegradable sludge is 416
Ib/day. The mass of biodegradable sludge remaining
after aerobic digestion can be found by multiplying 416
Ib/day first by 0.84 to convert to BOD, by 0.65 to find the
microorganism yield, and by 0.18 to convert the micro-
organism yield to debris solids. Thus, the mass of bio-
degradable solids remaining after aerobic digestion is 41
Ib/day. When this amount is added to the nonbiodegrad-
able mass (875-416 = 459 Ib/day) it can be seen that 500
Ib/day of sludge remains after aerobic digestion. The re-
maining sludge is 41 percent volatile and the reduction
effected is 43 percent.
The solids remaining after aerobic digestion of the
WAS can be calculated similiarly. At the design point
used for the computations, the 2000 mg/1 of mixed li-
quor is divided as follows: 638 mg/1 for MLASS, 621
mg/1 for MLBSS, 223 mg/1 for MLNBSS, 104 mg/1 for
MLDSS, and 414 mg/1 for MLISS. Using equation (10)
with a value of five for URSS it can be seen that the con-
centration of solids remaining in the WAS stream after
aerobic digestion will be 4585 mg/1 representing a 54
percent reduction in WAS solids. The remaining solids
are 55 percent volatile. The amount of WAS produced
in a one mgd plant was 861 Ib/day. Therefore, about
396 Ib/day of WAS remains after aerobic digestion. A
detailed accounting of these calculations is shown in
Table 2.
When the concentration of primary sludge is five per-
cent and the concentration of WAS is one percent it can
be seen that if the TA is set at 20 days and both sludge
TABLE2
Inventory of Sludge Entering and Leaving
the Aerobic Digester
I. PRIMARY SLUDGE
1. nonvolatile
2. volatile
a. biodegradable
b. nonbiodegradable
II. WASTE ACTIVATED SLUDGE
1. nonvolatile (MLISS)
2. volatile nonbiodegradjt>le CtLN'B
3. volatile debris solids (MLDSS)
4. active solids (MLASS)
5. biodegradable volatile solids
(MI.BSS)
TOTAL AMOUNT 0" SLUDGE FROM AEROBIC DIGESTER
Reduction in sludge solids
Reduction in volatile solids
293
577
416
161
179
96
45
276
298
202
41
161
179
96
45
50
896
497.
67%
streams are aerobically digested the size of the digester
will be 33,200 cu ft. If WAS had been digested alone the
size of the aerator with a TA of ten days would have been
13,800 cu ft.
At least one principal supplier of aerobic digesters
recommends the use of the parameter 0.05 Ib of sludge
solids/day/cu ft of digester volume. If the mass of
primary sludge and WAS to be digested is 1740 Ib/day
as shown in Table 2 the aerobic digester volume would
be 34,800 cu ft using this method. If WAS only is di-
gested the size of the digester would be 17,300 cu ft.
When the parameter TA is used to size the digester, pre-
thickening of the sludge will have a significant effect on
the digester size.
When a final setter is used it is sized for an overflow
rate in the range 100 to 150 gpd/sq ft. Therefore, when
primary sludge and WAS are digested in a one mgd
pi ant the surface area of the settler will range from 83 to
125 sq ft with a diameter of 11 to 13 ft.
Diffused air is preferred over mechanical aerators for
supplying oxygen to the aerobic digestion process be-
cause it minimizes problems associated with the chang-
ing level in the aerator. When no settler is provided the
contents of the aerator are allowed to settle periodically
and the supernatant is removed by decantation. The
minimum amount of air needed to keep the solids in sus-
pension is 20 std cu ft of air per minute (scfm) for each
lOOOcuft of aerator volume. Thus, if the size of the aera-
tor is 34,800 cu ft the air supply must be at least 696
scfnl. Oxygen needed for biological activity can be esti-
mated by noting that one pound of oxygen must be sup-
plied for each pound of COD destroyed. The ratio of COD
to volatile solids can be estimated as 1.5. Therefore,
since it is shown in Table 2 that a total of 840 Ib/day of
volatile solids or 1260 Ib/day of COD are destroyed it fol-
lows that the oxygen demand will be 1260 Ib/day. Nitri-
fication of ammonia nitrogen is also likely to occur in the
aerobic digester, and this also demands oxygen. The
concentration of ammonia nitrogen in the influent
sludge streams might average 20 mg/1. Nitrogen is also
released when the sludge solids are degraded. Organic
material normally contains about 7.5 percent nitrogen.
Therefore, if 840 Ib/day of volatile solids are degraded
the ammonia nitrogen released will be about 63 Ib/day.
The ammonia nitrogen entering with the sludge streams
will be only about 2.1 Ib/day giving a total of 65.1 Ib/day
of ammonia nitrogen to be oxidized. Since about 4.6 Ib of
oxygen are required to oxidize one pound of ammonia ni-
trogen this will increase the oxygen demand by 300
Ib/day for a total demand of 1560 Ib of oxygen/day. If the
oxygen transfer efficiency is five percent the air supply
for biological activity will be about 1250 scfm. Notice that
this is almost twice the amount needed to keep the solids
in suspension. In the subroutine AEROB the air supply
is computed both ways and the larger value is used for
sizing the blower installation.
Phosphorus released as a result of destruction of or-
ganic material is assumed to leave the digester in the
-------
40
HANDLING AND DISPOSAL COSTS
dissolved state. Organic material is assumed to contain
one percent phosphorus. When a final settler is used in
the process the recycle pumps can be sized by writing a
mass balance for volatile solids (VSS) around the control
volume shown by the dashed rectangle in Figure 5. Let Q
equal the influent volume flow and QR equal the return
flow in mgd. Let FR equal the fraction of the influent VSS
destroyed and URSS equal the compaction ratio. If the
mixed liquor volatile solids concentration is MLVSS the
following equations will express the mass balance for
VSS:
Q*VSS + QR*MLVSS*URSS =
(Q + QR)*MLVSS + FR*Q*VSS (12)
Solving for the ratio QR/Q, we find:
QR/Q = (1 - (1-FR)*VSS/MLVSS)/(URSS-1) (13)
Using the data in Table 2 it can be seen that the value for
VSS will be 12,150 mg/1 and the value for FR will be
0.667. Thus, if MLVSS is estimated as two percent and
URSS as 1.5 the ratio QR/Q will have a value of 1.6.
The concentration of solids in the sludge stream from
the aerobic digester is estimated as four percent when
primary sludge and WAS are combined and 2.5 percent
when WAS is digested alone. The supernatant stream is
assumed to have a suspended solids concentration of 200
mg/1 and a total BOD concentration of 100 mg/1; 50
mg/1 dissolved and 50 mg/1 in the form of particulate.
These assumptions are applied whether or not a final
settler is provided.
For a more thorough discussion of the aerobic diges-
tion process, including a study of the time-dependent
aspects, see Reference 12.
Elu (nation
A recognized way of reducing the chemical demand
for sludge conditioning before vacuum filtration is elu-
triation or sludge washing. The subroutine ELUT is used
in the Executive program to calculate mass balances
around the elutriation process, to size the equipment,
and to estimate the cost. The subroutine ELUT is very
similiar to that for gravity thickening. The principal dif-
ference is that the wash water rate (WRE) is supplied as
input. WRE is defined as the volume flow (mgd) of the
wash water stream (usually secondary effluent) divided
by the volume flow of the feed sludge stream.
Values are supplied as input for the design parame-
ters hydraulic overflow rate (GE, gpd/sq ft) and the
solids loading rate (GES, Ib/day/sq ft). The required
surface area for the elutriation basin is computed using
each of the design parameters, and the larger area is se-
lected for cost estimation. The solids recovery (ERR) and
the concentration of solids in the underflow stream are
supplied as inputs, and the stream vectors for the two ef-
fluent streams are computed in a manner identical to
that used for the gravity thickener. The solids concen-
tration in the thickened sludge stream is usually set at
six percent, and the ERR is estimated as 76 percent.
Vacuum Filtration
The size of a vacuum filtration installation is ex-
pressed as square feet of filtering area, which is deter-
mined by using two principal parameters; (1) the
vacuum filter loading rate (VFL) expressed as gal/hr/sq
ft of water removed from the sludge; and (2) operating
hours perweek. In small plants, the number of operating
hours/week is usually determined by the smallest com-
mercially available vacuum filter equipment. In inter-
mediate plants (for example, ten mgd) the filter is
commonly operated only seven hr/day, five days/week,
since one-half hour is allowed each day for both startup
and cleanup.
Traditionally, vacuum filter performance has been ex-
pressed as filter yield (F) with the dimension of Ib dry
solids filtered/hr/sq ft of filter area. Using vacuum filter
performance data gathered before 1957 McCarty
showed that the performance could best be described in
terms of VFL 13. F is related to VFL by the following
simple mass balance relationship given by McCarty.
F = VFL*8.33/100/(1/SF—1/SC) (14)
SF = solids concentration of feed sludge, %
SC = solids concentration of sludge cake, %
McCarty found that when the sludge is to be disposed of
at a land fill the value for VFL averaged 6.2 gal/hr/sq ft,
but when it was to be incinerated the value more closely
approximated four gal/hr/sq ft.
McCarty also found that the solids content of the
sludge cake correlated well with the solids concentration
of the feed sludge stream. The following relationship
was found:
SC= 100 —88/SF**0.123 (15)
If the solids content of the cake is found from equation
(15) and substituted into equation (14), then F can be ex-
pressed adequately by the following equation:
F = VFL*0.07856*SF**1.1667 (16)
Thus, it can be seen that filter yield is almost directly
proportional to the concentration of the feed sludge
stream. Performance data collected by McCarty are
shown plotted as a function of feed sludge concentration
in Figure 7. A line with a slope of 1.1667 is shown in
Figure 7 using a value of 6.2 gal/hr/sq ft for VFL. It can
be seen that the line fits the data reasonably well. A
couple of the data points collected by McCarty involved
the use of lime and ferric chloride but the use of chemi-
cals had no clear effect on the relationships found.
Since 1957, however, the use of polymers for sludge
conditioning prior to vacuum filtration has come into
practice and there is evidence that higher filter yields are
possible with the addition of polymers. Current esti-
mates of F which can be reliably used for sizing vacuum
filter installations are given by equipment manufactur-
ers and by data contained in Reference 15. The data
given in Reference 15 is plotted in Figure 8. Yields
achieved with and without the use of polymers are shown
but the yields expected when polymers are used are sig-
-------
HANDLING AND DISPOSAL COSTS 41
nit'icantly higher. The points marked with tails represent
performance with polymers. The line corresponding to a
value of 9.0 for VFL is shown by the solid line, and it ap-
pears to be a reasonable fit for the yield achievable with
polymers. This line is used to size vacuum filters in the
calculations presented here. The same relationship is
used whether or not the sludge is to be incinerated. For
example, if equation (16) is used with a value of 9.0 for
VFL it can be seen that when the concentration of sludge
to be filtered is five percent the filter yield will be 4.6
Ib/hr/sq ft and when the sludge is gravity thickened to
eight percent before vacuum filtration the yield will be
eight Ib/hr/sq ft. Therefore, since the amount of sludge
produced in a ten mgd primary plant is 8,750 Ib/day and
the filtering time is 35 hr/week the size of the vacuum
filter installation must be at least 219 sq ft when the
sludge is thickened and 380 sq ft when it is not. The
doses of sludge conditioning chemicals used prior to
100.
cr
03
01
•H
M
01
O
cd
. in
6_ ::;::::::::::::::::: ; ^ ^
EE = = EEEEEE;EEEE;;E;; i ODigested Elutriated
I ; ------:-:::::::• j A Raw Activated S ludgG
:__ = = = :::::::::::::: V Primary and WAS Dige
: : :::::::::::::::•.: •#• Raw Chemical Sludge
3_ 1 || |I[||||[[|]|[|||||||||||||||||||||||||H|||M|||H
2.5 E--E; = ~ = = EEEEE;;;E; ;:;;;;:: :; EEE;:;;::;:;;:: ;;: ; EEE;;:E
o. 10 :J - i'i"£i" —
9. EEE = EEEEEE|EE;;;E;;;;;;;;;;;; ; ,, iEEEEE;EE;;;E;;E, ;;;;;;: [EEEE;;E
8. EEEEEEEE|:::::::::::::±::::; :: EE: :: :i:| :::± :::::| : :| :E: J i:
"llll'l 1 lilllliii
= 11;!!!
;=;=:Eii;;:::::::;: ::::::;:: : ;=;;;;;;;;;;;! !;.,: 1;::;
: = = - = = = ::::::::::::: ::::::::: ::::: :j 1 :::::::::::: :::i:::::
2. ---j'
1.9. :;-~:::::::::::::::| ,::::::::: i :::::::::::::::::::: :::::::::
i. i. ;;ja::::::::::;;:::; ::;;::::;; ; :::::::::;;::;:,:;:;;!; :;::::;;:
1 1.9 2 2.9 3 4967
1.
sted and Elutriated ] •--
8 9 10 1.5 22. 4
10. 50.
Feed Sludge Solids Concentration, %
Figure 7: Vacuum Filter Performance as Reported by McCarty.
-------
42 HANDLING AND DISPOSAL COSTS
t-l
0)
•H
o
30. "H
8_
7
6
5
4_
2.5
2
1.5
10. 10
9
8.
7
6
5
4
3
2,5
1.5
1. 1
\
--
:;:::::::::::::::: O Raw Primary
Digested Primary
;EEEEE;EEE;E;;;;;;; d Digested Elutriated 1
::=; = ::::::::::•::., V Digested Elutriated ]
--
J~-C ---. |.
IliMJJiJM:::!; ;;!: ii !M!::J;;; iii: ;:; ilji II
jjr::::::::;;;:;; ;;;; ;:::;;;;;; ;;,, , :;:;.;;;;
1.5 2 2.5 3 4 567
:: mi:::;::::::::::: :::: : : :
^rimary ;;; ;; 1 •'• -.-----, • ;; ;
WAS !|i Mii 1 IE IEEE ; i ;;; E
'rimary and WAS E::; |;: J; :::: : :: 1
::: -- --"•••: ::::::::: :|: : :::: : : ::
•:: :-:::::::::::::::::: :::: ::::: :::::: t
in l/fl I' /f jffHtti ' n 1 1 Pi
t _..-iai . — ..
;;;; IEEEEEEEEEEEE;;;;;; ;;;;; : ;EEE; i; ::
8 9 10 1.5 2 2.5 3 5
10. 50.
Feed Sludge Solids Concentration, %
Figure 8: Vacuum Filter Performance as Reported in the Technology Transfer Manual.
vacuum filtration, as shown in Table 3 must be inter-
preted in the following way. Ferric chloride is used with
or without lime but polymer is never used with ferric
chloride. Estimated costs reported here assume that
lime and ferric chloride are used in all cases.
Centrlfugation
In principle, a centrifuge used to dewater sludge is
analogous to a gravity thickener except that the force of
gravity is increased by as much as 3000 times by rotation
of the bowl. A sketch of the solid-bowl, scroll-conveyer
centrifuge considered in this report is shown in Figure 9.
The cylindrical settling volume (sometimes called the
pool) in the centrifuge, which is analogous to the liquid
volume in the gravity thickener, has a length (L) and a
depth of (i"2 —rj). Thus, it can be seen that the shallow
depth of the settling volume is another major advantage
over the gravity thickener. Feed sludge flows into the
-------
HANDLING AND DISPOSAL COSTS 43
TABLE3
Estimated Chemical Conditioning Dosage
for Vacuum Filtration
CaO Dose FeCl3 Dose Polymer Dose Cao + FeCl3
$/ton
1. Primary Sludge
2. Limed Primary (212 Ib CaO/ton)
3. Digested Primary Sludge
4. Digested/Elutriated Primary
5. Raw (Primary + WAS)
6. Limed (Primary + WAS)
7. Digested (Primary + WAS)
8. Digested/Elutriated (Primary + WAS)
9. Aerobically Digested WAS +
Anaerobically Digested Primary
Ib/ton
176
0
240
0
200
0
372
0
Ib/ton
42
42
76
68
52
40
110
125
372
110
Ib/ton
5
5
20
9
18
5
36
24
36
5.01
2.81
7.86
4.56
5.98
2.68
12.02
8.38
12.02
Polymer
$/ton
1.65
1.65
6.60
2.97
5.94
1.65
11.88
7.92
11.88
Cost, $/lb: CaO, 0.13; FeCl3, 067; Polymer, .33.
L -
B-
D-
P-
S -
CK —
Bowl length
Beach length
Bowl diameter
Pool depth
Scroll pitch
Beach angle
U)B— Bowl speed
60S— Scroll speed
Figure 9: A Solid Bowl Scroll Conveyer Centrifuge.
centrifuge through the center of the scroll shaft. The
centrate overflows from the machine over the weirs lo-
cated at the end opposite the beach end. Dewatered
sludge is scrolled up onto the beach and out of the ma-
chine.
Parameters of interest to the process designer are: (1)
the design capacity (gpm) for each size centrifuge
operating on each type of sludge; and (2) the percent re-
covery and percent sludge cake solids achievable with a
recommended polymer dose. Recovery is defined as the
percentage of the solids entering the machine which
leave the machine in the sludge cake.
It has been shown by Vesilind 16 and others that the
two principal machine variables which determine per-
formance are rotational speed and sludge retention time
(defined as pool volume/feed sludge flow rate). Operat-
ing characteristics show that as the pool volume is in-
creased, recovery increases but the percent of cake
solids decreases. Current practice is to operate the cen-
trifuge to achieve recoveries in the 85 to 95 percent
range, but this can be done only when cationic polymers
are added to the feed sludge stream.
Performance and sizing relationships used in this re-
port are based on a specific line of four centrifuges. A
fifth larger centrifuge is available but its use was not
considered in this report. The nominal feed rate for the
largest of the four centrifuges is given in Table 4 for
seven sludge types. For each sludge type the nominal
feed rates for the three smaller centrifuges are a fixed
fraction of the nominal feed rate for the largest. For ex-
ample, the smallest centrifuge has a feed rate which is
0.275 times the feed rate for the largest; the next larger
size has a feed rate which is 0.350 times the largest feed
rate, and the next larger size has a feed rate which is
0.590 times the largest. This relationship between feed
rate and the centrifuge size is demonstrated in Figure 10.
-------
44
HANDLING AND DISPOSAL COSTS
TABLE4
Performance Capabilities of a Typical
Dewatering Centrifuge
1. Raw Primary Sludge
2. Limed Primary (270 Ib/ton)
3. Digested Primary Sludge
4. Primary + WAS
5. Limed (Primary + WAS)
6. Digested (Primary + WAS)
7. Aerobically Digested WAS
+ Anaerobically Digested
Pr iitiar y
P-5400
Nominal Feed Rate
gal/minute
90
160
100
80
160
80
80
The polymer dose, the percent recovery, and the per-
cent dry solids in the dewatered stream are shown in
Table 4 for the seven sludge types. These three variables
are assumed to depend only on the sludge type and are
supplied as input to the Executive program subroutine
(CENT) for sludge centrifugation.
The type of sludge to be centrifuged is identified by
supplying the nominal feed rate (gpm) for the largest
centrifuge. The minimum number of centrifuges in the
installation (usually two) is also supplied as input to-
gether with the operating hours/week. Since the volu-
metric amount of sludge to be centrifuged is known and
the operating hours/week are specified, the required
design capacity per centrifuge can be calculated. The
size of centrifuge with sufficient capacity is then selected
from the set of four sizes. If the minimum number of the
largest size centrifuge cannot handle the feed stream the
number of centrifuges is increased until a sufficient
number is found. Finally, each centrifuge installation is
tested to make sure that all of the sludge can be centri-
fuged with 24 hr/day operation when one centrifuge is
out of operation. If this criterion is not met, the number
of centrifuges is increased until it is.
When the number and size of centrifuges in the instal-
lation are established, the construction cost is estimated
from relationships given in Reference 20. The cost of
polymer is computed from the specified dose and the
cost per pound of polymer. Other elements of operation
and maintenance cost are computed as functions of the
annual tonnage of sludge processed according to rela-
tionships given in Reference 20.
Sludge Drying Beds
Sludge drying beds considered in this report are un-
covered and are assumed to be located in a moderate cli-
Polymer Dose
Ib/ton
Cake Solids, %
32
30
25
19
30
22
21
% Recovery
90
90
90
90
90
85
85
mate. Sizing relationships used were taken from the
work of Haseltine17 who found that, after ambient air
conditions, the concentration of dry solids in the sludge
applied to the beds is the most important factor in esti-
mating the bed area required. The moisture content of
the sludge removed from the beds is also important in
estimating the bed size but it is of secondary importance
compared to the concentration of the feed stream. Hasel-
tine collected sludge drying bed performance data from
14 plants and derived the following relationship between
gross bed loading (FB) and the solids concentration (SF)
of the feed stream:
FB = 0.96*SF— 1.75 (17)
FB = Ib dry solids applied/sq ft/30 days
SF = dry solids concentration of feed
sludge, percent
A linear regression through the data collected by Hasel-
tine has the following slightly different form. The cor-
relation coefficient was 0.70.
FB = 0.694*SF —0.107 (18)
In an effort to take into consideration the moisture
content of the sludge cake removed from the drying
beds, Haseltine next plotted the product of FB and the
solids concentration of the sludge removed (SC) versus
SF. He found the following relationship:
SC*FB = 35.*SF — 50 (19)
A linear regression performed on the data reported by
Haseltine has the following form:
SC*FB = 29.84*SF — 33.3 (20)
The correlation coefficient was 0.838 indicating a better
fit than the relationship between FB and SF.
The discovery made by Haseltine that the allowable
bed loading depends primarily on SF is the same con-
clusion reached by McCarty 13 with regard to vacuum
-------
HANDLING AND DISPOSAL COSTS 45
a
a.
0)
a)
c
00
•H
CO
0)
o
Centrifuge Size Number
Figure 10: Design Flow Rates for Fi\e Standard Centrifuge Sizes.
-------
46 HANDLING AND DISPOSAL COSTS
filters. McCarty concluded that the area of filter re-
quired to dewater a given mass of sludge solids is best
expressed as a moisture removal rate. Data reported by
Haseltine was analyzed using this concept and the re-
sults are shown in Figure 11. The regression line
through the data points is shown below.
1/FB = 2.139*(1/SF —1/SC) —0.00189 (21)
If the small constant (0.00189) is neglected, the moisture
removal rate for sludge drying beds can be deduced from
the constant 2.139 as 5.6 gal/sq ft/30 days. Therefore,
the volume of sludge which can be dewatered on one sq
ft of vacuum filter area in one hour is about the same as
can be dewatered on one sq ft of sludge bed area in 48
days. Put another way, if the vacuum filter operates 35
hr/week, the ratio of sludge bed area required to equiva-
lent vacuum filter area is 241. Equation (21) is used in
the Executive program to size the sludge drying beds.
For example, if five percent primary sludge is anaero-
bically digested in a single-stage, completely-mixed di-
gester, the concentration of the digested sludge is 2.8
percent. If the moisture in the sludge cake is set at 35
percent, the required sludge bed loading is computed
from equation (21) as 1.431bof dry solids/sq ft/30 days.
The amount of sludge to be dewatered in a ten mgd
primary plant over a 30 day period is about 148,000 Ib.
Therefore, the area of the sludge beds can be calculated
F = Filtration Rate, Ib. dry solids/30 days/sq ft £J
'-ttP-'-J^^r''
$
U-+4-
.4+3
t;:
S, = Percent total solids in sludge feed
I . . i i i i i i , ,, i i! i i i i i i i I I I I I M I I f-(-p
3E
tt^mf
&MW-
tftr
S = Percent total solids in filter cake g
*-» 4
Figure 11: Haseltine Sand Drying Bed Data Correlated According to McCarty.
-------
HANDLING AND DISPOSAL COSTS 47
as 148,00071.43 = 103,500 sq ft. If a second-stage diges-
ter is provided to thicken the sludge to five percent, the
required area is only 45,000 sq ft.
Multiple Hearth Incineration
The subroutine for multiple hearth incinerators used
in the Executive program (MHINC) is based on the
model developed by Rocketdyne and described in Ref-
erence 18. The sizing parameter used is Ib of dry solids
fed/hr/sq ft of hearth area with a value of 2.0. The num-
ber of individual incinerators installed and the operating
hours per week are inputs to the Executive program.
Since the pounds per day of dry solids to be incinerated
are known from the mass balance calculations, the
hearth area for each individual incinerator can be calcu-
lated. A list of 59 standard incinerator sizes is included in
the subroutine and the program finds the smallest in-
cinerator with sufficient hearth area. For example, a ten
mgd primary plant generates about 9,845 Ib of dry solids
per day, including sludge-conditioning chemicals. If the
installation is to be made up of two incinerators both
operating 35 hr/week, the hearth area needed for each
incinerator is 492 sq ft. The next larger size incinerator
has 510 sq ft of hearth area, is 10.75 ft in diameter, and
has eleven hearths. Thus, the installation will consist of
two 510 sq ft hearth area incinerators.
The subroutine next proceeds to calculate the fuel re-
quirements. A sketch showing the principal heat losses
and inputs is shown in Figure 12. Heat losses consist of
the following eight components:
1. Heating and evaporation of water associated with
the sludge
2. Enthalpy of the ash
3. Heat for calcining of calcium carbonate
4. Heat for decomposing Fe(OH)
5. Radiation and convection losses
6. Heat associated with discharged cooling air
7. Enthalpy of gaseous combustion products
8. Heat for temperature cycling
The heat balance is based on incineration of one pound of
dry volatile solids (DVS) for which the higher heat value
is taken as 10,000 Btu/lb.
The largest single heat loss is due to evaporation of the
water in the feed sludge. In the example cited above, the
sludge to be incinerated is 71 percent water and the dry
solids are 60 percent volatile. Therefore, to incinerate
one pound of DVS, 4.1 Ib of water must be evaporated.
Operation of the incinerator is controlled to hold the
temperature of the exhaust gas stream at 800°F. There-
fore, since the enthalpy of water vapor at 800°F is 1,404
Btu/lb, the heat required to evaporate the water asso-
ciated with the sludge cake is 4.1*1,404 or 5,756 Btu/lb
of DVS.
A small amount of heat is lost in the ash discharged
from the incinerator. The temperature of the ash is taken
as400°Fand the specific heat of the ash is assumed to be
0.2 Btu/lb. The temperature of the feed sludge and the
Figure 12: Principal Heat Inputs and Losses from a Multiple Hearth
Incinerator.
ambient air is taken as 60°F. Therefore, the heat lost in
the ash is (400-60)*0.2*0.67 = 46 Btu/lb of DVS.
When digested primary and WAS are vacuum filtered
before incineration 200 Ib of lime and 150 Ib of ferric
chloride per ton of DVS are often used to condition the
sludge. Since, in the example cited, there are 1.67 Ib of
dry solids per Ib of DVS, 0.167 Ib of CaO and .125 Ib of
ferric chloride are added for each Ibof DVS. When one Ib
of CaO is added to the wet sludge 1.79 Ib of CaC03 will
be formed. Similiarly, one Ib of ferric chloride added to
the sludge results in 0.66 Ib of Fe(OH)3. Heat required to
calcine one Ib of calcium carbonate is 761 Btu, and the
heat required to convert ferric hydroxide to Fe203 is 227
Btu/lb of Fe(OH>3. Therefore, the heat consumed in cal-
cining the carbonate is 227 Btu/lb of DVS and the cor-
responding heat consumed by the iron is 19 Btu/lb DVS
giving a total of 246 Btu/lb DVS.
The amount of heat lost by convection and radiation
depends on the surface area of the incinerator (SAREA),
which can be estimated from the hearth area (FHA)
as follows when both SAREA and FHA are expressed
as sq ft.
SAREA = 64.03*FHA**0.51 (22)
The temperature difference between the incinerator
shell and the ambient air is taken as 100°F. The heat
transfer coefficient (HC) is expressed as a function of
wind velocity (WV. mph) as follows:
HC= 1.735*(1 + 0.374*WV) (23)
Heat lost by convection and radiation (QTRAN, Btu/hr)
is then calculated as follows:
QTRAN = 100*SAREA*(1.279 + HC) (24)
In the cited example, it is assumed that the incinerators
are housed and the wind velocity is zero. Therefore, the
heat loss is 1.125 X 106 Btu/hr. Converting this to Btu/lb
DVS by dividing by the average incineration rate for
volatile solids gives an estimate of 952 Btu/lb DVS.
If the fuel value (10,000 Btu/lb DVS) is reduced by the
losses resulting from water in the sludge cake (5,756
-------
48
HANDLING AND DISPOSAL COSTS
Btu/lb DVS), the loss in the ash (46 Btu/lb DVS), the loss
due to conditioning chemical (246 Btu/lb DVS), and the
loss through radiation and convection (952 Btu/lb DVS),
the amount to be lost in the products of combustion and
the discharged cooling air must be 3,000 Btu/lb DVS.
In order to consider the heat loss in the cooling air the
following relationship between the cooling air blower
capacity and the incinerator hearth area is used.
Blower capacity, scfm = 3.102*FHA (25)
Therefore, in our example, the blower capacity is 1,582
std cu ft/min for each incinerator or a total of 3,164 scfm.
Since the incineration rate is 23.4 Ib DVS/min, the rate
at which cooling air is supplied is 10.1 Ib cooling air/lb
DVS. If the cooling air is discharged at 325°F, the heat
lost in the cooling air is (325-60)*0.24 = 63.6 Btu/lb of
air or 642 Btu/lb DVS. The amount of cooling air recy-
cled to the combustion air inlet varies between 60 to 80
percent. Since the heat lost in the discharged cooling air
is small, it is assumed that the fraction recycled is 70 per-
cent and that the loss is 30 percent of the cooling air dis-
charged to the atmosphere is 193 Btu/lb DVS. Thus, the
heat lost in the combustion products must equal 2,807
Btu/lb DVS.
Combustion is represented by the following chemical
equation.
(FC/12)C + (FH2/2)H2 + (F02/32)02
+ (FS/32)S + (FN2/28)N2 + (X/32)02
+ 3.31 (X/28)N2 —»A(CO2) + B(H20)
+ D(S02 + E(N2) (26)
In this equation the F's are the mass fractions of carbon,
hydrogen, oxygen, sulfur, nitrogen and oxygen in the
fuel and A, B, C, & D are moles of combustion gases.
Chemical symbols identify the elements. For example,
p£/\2 is the moles of carbon in a unit mass of the fuel.
The symbol X represents pounds of combustion oxygen
supplied per Ib of fuel. Since air is assumed to consist of
23.2 percent oxygen and 76.8 percent nitrogen by mass,
3.31 Ib of nitrogen are associated with each Ib of oxygen.
Values used for fuel mass fractions are shown below.
carbon, C
hyarogen, HZ
oxygen, 02
nitrogen, N-
sulfur, S
MW
12
2
32
28
32
Dry Sludge Fuel Natural
Solids
.55
.06
.35
.03
.01
Oil
.86
.11
.00
.00
.03
Gas
.67
.22
.01
.10
.00
Digester
Caa
.50
.12
.38
.00
.00
If the moles of carbon, hydrogen, oxygen, sulfur, and ni-
trogen on one side of the equation are set equal to the
number of the other, the following relationships are
obtained.
Fc/12 = A (carbon) (27)
FH2/2 = B (hydrogen) (28)
F02/32 + X/32 = A + B/2 + D (oxygen) (29)
Fs/32 = D (sulfur) (30)
3.31 (X/28) + FN2/28 = E (nitrogen) (31)
Using equations (27-30) the mass of oxygen needed to
combust a unit mass of fuel can be found as follows.
X = 32[Fc/12 + FH2/4 + Fs/32] — F02 (32)
Substituting the mass fraction values for the four fuel
types into equation (32), the mass of oxygen needed to
combust a unit mass of each fuel can be calculated with
the following result.
Dry Volatile Sludge Solids
Fuel Oil
Natural Gas
Digester Gas
If the fraction of excess air used is represented by
EX AIR, the mass of gaseous combustion products re-
sulting from combustion of a unit mass of fuel can also be
found from equations (27-31) as follows.
1.6071b 02/lb fuel
3.2031b02/lbfuel
3.537 Ib02/lb fuel
1.913 Ib02/lb fuel
Sludge Solids
2.017
0.54
0.02
i.607*EXAIR
5.32*(1 + EXAIR) + .03
Fuel
Oil
3.153
0.99
0.06
Natural
Gas
2.457
1.98
.00
Digester
Gas
1.833
1.08
.00
Values (Btu/lb/°F) for the average specific heat of
combustion gases at constant pressure over the
temperature range of 60 to 800°F are:
C02
H20
S02
N2
.239
.467
.175
.254
.233
The average specific heat for water does not include
the heat of vaporization at the base temperature (60°F).
Thus, if the higher heating value for the fuel is used, an
additional term must be included to provide for 1060
BTU/lb of water for vaporization. Using these estimates
for the enthalpy and mass of combustion products, the
enthalpy of the combustion products is expressed as
follows:
BTU/lb DVS = 2113+ 1223*EXAIR
(33)
The recommended range for EXAIR is 0.5 to 1.5. In the
example, the enthalpy of the combustion products must
equal 3,000 Btu/lb DVS minus the heat lost in the cool-
ing air (193 Btu/lb DVS) or 2807 Btu/lb DVS. From
equation (33) it can be seen that this will occur when
EXAIR has a value of 0.567.
From this type of calculation it can be seen that the
moisture and volatile content of the feed sludge cake
must be held within relatively narrow limits if the use of
auxiliary fuel, on one hand, and overheating of the incin-
-------
HANDLING AND DISPOSAL COSTS
49
erator, on the other hand, are to be avoided. This is
shown graphically for the example used in Figure 13. It
can be seen from the graph that when the volatile frac-
tion is 0.6 the sludge moisture content can be as high as
71.2 percent before auxiliary'fuel is needed. Similarly,
when the volatile fraction is 0.6, the exhaust products
will exceed 800°F if the moisture content is less than
66.2 percent.
To illustrate the computation of auxiliary fuel oil
needed, notice that if the moisture content of a 60 per-
cent volatile sludge increases from 71 percent to 75 per-
cent about 0.23 Ib of water is added /lb DVS for each per-
centage point. Thus, about 25.8 lb or 3.5 gal (7.5 Ib/gal)
of fuel oil is needed for each ton of dry solids per per-
centage point of added moisture. In t-he example used
about 4.9 tons/day of dry solids are incinerated and the
Percentage of Excess Combustion Air
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No Fuel Required
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Percentage of Moisture Content of Incinerator Feed
Figure 13: Determination of the Percentage of Incinerator Excess Combustion Air from the Moisture Content of the Sludge.
When auxiliary fuel is needed to keep the stack gas
temperature at 800°F, the type of fuel can be specified in
the subroutine by setting TYPE equal to one for fuel oil,
two for natural gas, and three for digester gas. Since the
auxiliary fuel is burned with zero excess air, the net heat
generated by the addition of auxiliary fuel is simply the
higher heat value of the fuel minus the heat lost in the
combustion products. The higher heat value for fuel oil is
taken as 19,000, 21,000, and 12,000 btu/lb for fuel oil,
natural gas, and digester gas, respectively. From the
mass of combustion products produced and the average
specific heats given, the net heat produced from the
combustion of one pound of fuel oil is 15,019 Btu/lb,
15,581 Btu/lb for natural gas, and 8,967 Btu/lb for
digester gas. Since 1,404 Btu are required to raise the
temperature of water to 800°F, one pound of fuel oil is
required for each 10.7 pounds of water which enters with
the sludge cake.
auxiliary fuel oil used will be about 17.2 gal/day/per-
centage point. If the cost of fuel oil is taken as $0.30/gal
and the moisture content is increased from 71 percent to
75 percent the annual cost for auxiliary fuel will be
$7,535. This corresponds to a cost of about $4.20/ton of
dry solids incinerated.
Auxiliary fuel is also needed for thermal cycling of the
incinerator. In the model devised by Rocketdyne, a char-
acteristic heatup time in hours (CYT) was found as a
function of FHA. CYT is expressed as a discontinuous
linear relationship covering the range from zero to 3,000
sq ft of effective hearth area. This relationship is con-
tained in the Executive program and when FHA is
known the value for CYT can be found. In the case of the
incinerator having a hearth area of 510 sq ft, the value for
CYT is 25.24 hr.
Two basic types of thermal cycles exist. The first is the
cold cycle which is used when the incinerator tempera-
-------
50 HANDLING AND DISPOSAL COSTS
ture is reduced to ambient level for inspection and main-
tenance and is then brought back up to operating level.
The second, called a hot cycle, is employed when the
temperature is reduced to 1200°F and the incinerator is
allowed to "soak" while not in service. Both cycles con-
tain periods for heatup and periods for soaking. The rate
of fuel useage is estimated as 1,913 Btu/hr/sq ft of
hearth area for raising the temperature and 315 Btu/hr/
sq ft of hearth area for maintaining the incinerator at the
soak temperature. The cold cycle contains heatup
periods totaling 5/9 CYT and soak periods totaling 4/9
CYT. The heatup period for the hot cycle is 1 /9 CYT but
the soak period can be of any duration.
To calculate the fuel needed for thermal cycling, the
operating hours per week (HPWK) and the number of
startups per week (SPER) are supplied as inputs to the
subroutine. Typical values are five for SPER and 35 for
HPWK. Using these values the annual heatup hours for
hot cycles is 5*52*(l/9)*25.24 or 729 hr/yr for each in-
cinerator. Thus, the fuel requirements for two incinera-
tors will be 1,422 X 106 Btu/yr and taking the cost of fuel
oil at $0.30/gal the annual cost for fuel will be $3,800/yr.
The standby or soak hours can be calculated as (7/9)*
(52*7*24 — 52*35) or 5,379 hr/yr per incinerator. The
heat requirement is 1,728 X 10^ Btu/yr, and the cost of
fuel oil is $4,600/yr. It is also assumed that each incin-
erator will be shut down for inspection and maintenance
twice each year. The total heatup time is (10/9)*CYT and
the soak time is (8/9)*CYT for each incinerator. There-
fore, the total heat requirement for two cold cycles is
30.96X 10^ Btu/yr for each incinerator. If fuel oil is used
the annual cost for two cold cycles for each of two in-
cinerators will be $165/yr. Thus, in this example, the
total cost of thermal cycling is $8,565/yr. This corre-
sponds to $4.80 per ton of dry solids incinerated.
Hauling and Spreading Liquid Sludge
The work of McMichael 19 was used as the basis for
calculating the cost of hauling and spreading liquid
sludge on the land. The principal design parameter is
tons of dry solids spread/acre/yr and the value used is
15. A lagoon is provided to store liquid sludge when the
ground is unsuitable for spreading. The liquid volume of
the lagoon is calculated from a specified detention time
(lagoon volume/annual volume of sludge produced)
taken to be 0.25 yr in this report. It is assumed that the
liquid sludge is transported from the plant site to the
spreading site by truck. The three standard truck capaci-
ties recognized in the subroutine are 1200 gal, 2500 gal
and 5500 gal. The truck size is supplied as input and for
the results reported in this report the truck size used was
2500 gal. The useful life of the truck is also supplied as
input and for the 2500 gal truck this was set at six years.
Finally, the round trip hauling distance is supplied to the
subroutine in miles. The assumed distance for this re-
port was ten miles.
The average road speed for the truck is estimated at 25
mph and it is assumed that 15 minutes are required to
load and to unload the truck. Therefore, the maximum
number of trips per year can be calculated as 2080
working hr/yr divided by the average time per trip
(10/25+ 0.5) or 23 lltrips/yr. The amount of limed pri-
mary sludge produced in a ten mgd plant is about 7.66
million gal/yr. Using a 2500 gal truck the number of
truck trips needed per year is 3066 and it can be seen that
at least two trucks will be required. The cost of two 2500
gal trucks is $72,800 and the amortization cost assuming
six percent interest and a useful truck life of six years is
$14,800/year.
Annual operating hours for hauling, assuming one
driver pertruck, is found by multiplying the annual trips
(3066) by the time per trip (0.9 hr) or 2759 hr/yr in this
case. Wages for the driver are taken from data published
U.S. Dept. of Labor for Water, Steam, and Sanitory Sys-
tems Non-Supervisory Workers and 15 percent is added
for overhead. The hourly wage used in this report is
$4.35/hr or $5/hr with overhead. Maintenance and fuel
costs forthe trucks are taken as $0.475/mile for the 5500-
gal truck, $0.425 for the 2500-gal truck, and $0.305/mile
forthe 1200-gal truck. Therefore, in the example the an-
nual cost of operating the two trucks is $13,795 for
wages, $13,030 for mileage, and $14,800 for amortiza-
tion. The total cost of sludge hauling is $41,625/yr and
since 1780 tons of dry solids are transported per year the
hauling cost is about $23/ton.
Since it is assumed that land is not depreciated by ap-
plication of sludge, the cost of land is taken as the
interest charges only. The land needed to dispose of
1780 dry tons/yr will be 119 acres. If the land cost is
taken as $1000/acre and the interest rate as six percent
the land cost will be $7140/yr. The construction cost for
the lagoon is about $35,000 and the amortization cost will
be $2700/yr when the life of the lagoon is 25 yr and the
interest rate is six percent. Operating and maintenance
cost for the lagoon is about $530/yr. The cost of remov-
ing 445 ton/yr of sludge from the lagoon at $13/ton is
$5785/yr. The total cost of sludge hauling and spreading
for this example is $57,780/yr or about $32/ton.
Estimated Costs for Alternative
Sludge Treatment Schemes
The twelve sludge treatment processes described in
this report can be arranged into a large number of
feasible treatment schemes. The particular scheme
adopted is likely to depend on the site constraints, the
cost, and the preference of the plant designer. When the
design of a specific plant is being considered and the de-
sign variables are known, the Executive program can be
used as a tool to narrow the range of alternative schemes
by calculating the cost of candidate schemes. To demon-
strate the capability of the Executive program for this
use, design variables for ten mgd primary and activated
sludge plants have been arbritrarily assigned values to
show the range of costs to be expected.
A logical grouping of the possible alternative sludge
treatment schemes is shown in Table 5. The processes
-------
HANDLING AND DISPOSAL COSTS 51
n:
IV
Vl;
vn:
TABLES
Enumeration of Sludge Handling
and Disposal Schemes
Treat and Dispose of Prinary Sludge Separately (1-42)*
Treat ana Dispose of WAS** Separately (43-51)
Treat Coabinad Prinary and HAS with Croup II Schemes (52-60)
Return KAS to Primary Settler and Use Group I Schemes (61-10?)
Gravity Thicken Combined Prinary and 1JAS (103-123)
Gravity Thicken Prinary and HAS Separately and Mix (124-lii)
Gravity Thicken Primary, Air Flotation Thicken WAS and Mix (lij
Aerobically Digest '.-AS, Anaerobically Digest Primary,
Mix and Land Dispose with or without Dewatering on
Sand Drying 3eds (166-189)
Aerobicelly Digest '.;AS, Anaerobically Digest Primary,
Mix, Debater by Vacuum Filter or Centrifuge and Dispose
:o Land or Incinerate (190-213)
5ame as IX Except WAS is Gravity Thickened (214-237)
5ane as IX Except WAS is Air Flotation Thickened (23S-261)
Identifying numbers for individual schemes shown in T-'biii
\aste activated sludge
used in each scheme, the type of sludge treated in each
process, and the cost of sludge handling as compared to
the total plant cost are shown in Table 6. Note that many
of the schemes enumerated in Tables 5 and 6 might be
eliminated on qualitative grounds. For example, the use
of large incinerators near population centers could pose
the threat of an air pollution nuisance. Inadvertent
dumps of toxic chemicals could make the use of anaero-
bic digestion unpractical. Some experience has shown
that when aerobically digested WAS is mixed with
anaerobically digested primary sludge before applica-
tion to the land, a severe odor problem can occur. There-
fore, some schemes in Groups VIII-XI may be unpracti-
cal because of this potentially undesirable odor problem.
With these qualifications the treatment schemes
listed in Table 6 can be used as a rough screening of al-
ternative sludge handling methods on the basis of cost.
Table 6 contains an estimate of the mass of dry sludge
solids processed, the costs of treating and disposing of
the sludge, and the total costs for plants using 261 dif-
ferent sludge treatment and disposal schemes. All cost
estimates are adjusted to January, 1974 dollars.
In schemes 1-42, primary sludge is treated separately
and the cost estimates are for primary sedimentation
plants. In all other schemes, the cost estimates are for
conventional activated sludge plants. However, in
schemes 43-51, primary sludge and WAS are treated
separately. For this reason, the cost estimates for the en-
tire plant are not given, and the amount of sludge shown
and the costs for treating it are for WAS only. In schemes
61-102, waste activated sludge was returned to the pri-
mary settler influent stream. An MLSS concentration of
2000 mg/1 could not be held in the aerator while still
achieving the 13 mg/1 target concentration for BOD in
the final effluent stream. It was necessary, therefore, to
reduce the demand MLSS level to 1750 mg/1. For all
other schemes, the MLSS level was 2000 mg/1 and the
BOD concentration of the effluent stream was 13 mg/1.
In Table 6 the kind of sludge treated in each process is
identified by symbols such as P, for primary sludge, A
for WAS, (P+A) fora mixture of primary and WAS, and
(P/A)to indicate that the process is used twice; once for
primary sludge and once for WAS.
The mass of sludge processed per million gallons of
wastewater treated is found by adding the dry sludge
solids mass flow (Ib/day) in the primary settler under-
flow stream to the dry solids mass flow in the final settler
underflow stream and dividing by ten.
Most estimates for construction and operation and
maintenance costs were taken from Reference 20. Addi-
tional cost relationships that were used are given in the
text of this report and in Reference 1.
TABLE6
Cost Estimates for Alternative Sludge
Treatment and Disposal Schemes
Case Number
1
2
3
4
5
6
7
Mass of Sludge Pro-
duced by Liquid Hand-
ling Processes ,
Ib/mg
883
941
894
894
946
939
947
Capital Cost for
Complete Plant,
millions of dollars
1.829
1.847
2.306
2.899
1.978
3.747
2.196
Total Treatment Cost
for Complete Plant ,
cents/1000 gallons
9.10
8.76
9.83
11.32
9.71
11.79
9.65
Capital Cost for
Sludge Handling
Processes, millions
of dollars
0.203
0.211
0.696
1.296
0.362
1.142
0.573
Total Treatment Cost
for Sludge Handling,
cents/1000 gallons
2.16
1.79
2.92
4.43
2.79
4.90
2.70
1 Sludge Handling Cost,
dollars/ton dry
solids
48.98
38.12
65.45
99.21
59.19
104.42
57.12
1
Lime Stabilization
P
P
P
P
P
[Gravity Thickening
P
P
Ovir Flotation
Thickening
"irst Stage
\naerobic Digestion
nBecond Stage
Anaerobic Digestion
Aerobic Digestion
Elutriation
Vacuum Filtration
P
P
P
1
Centrifugation
P
P
V-l
Q
0
jj
H
in
Incineration
P
P
ILand Spreading of
I.inuicl Sludoc
P
P
-------
52 HANDLING AND DISPOSAL COSTS
TABLE 6 (Continued)
w
1
0)
in
5
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
Mass of Sludge Pro-
duced by Liquid Hand-
ling Processes ,
Ib/mg
948
1007
1000
883
884
932
932
941
941
992
992
895
974
895
974
915
915
936
1022
936
1022
964
964
948
1034
948
1034
974
974
995
1086
995
1086
1025
1025
895
901
901
914
916
916
929
Capital Cost for
Complete Plant,
millions of dollars
2.782
2.044
2.604
2.O23
2.104
2.243
2.230
2.015
2.049
2.252
2.246
2.587
2.368
3.028
2.781
2.443
2.864
2.504
2.608
2.923
3.001
2.475
2.877
2.440
2.404
2.872
2.811
2.265
2.679
2.518
2.632
2.930
3.020
2.496
2..S92
-
-
-
-
-
-
-
Total Treatment Cost
for Complete Plant,
cents/1000 gallons
11.13
9.92
11.23
9.20
8.75
9.10
9.22
8.81
8.70
9.28
9.30
10.17
9.65
11.92
11.13
10.46
11.96
10.14
10.35
11.60
11.76
10.37
11.80
9.69
9.79
11.49
11.24
9.79
11.28
10.21
1O.46
11.66
11.84
1O.46
11.88
-
-
-
-
-
-
-
Capital Cost for
Sludge Handling
Processes , millions
of dollars
1.167
0.417
0.986
0.405
0.490
0.629
0.618
0.386
0.423
0.626
0.623
0.980
0.756
1.426
1.175
0.835
1.26O
0.897
1.001
1.320
1.398
0.867
1.274
0.821
0.782
1.257
1.194
0.643
1.062
0.899
1.013
1.315
1.405
0.877
1.277
0.405
0.896
0.929
0.437
1.201
1.184
O.2O2
Total Treatment Cost
for Sludge Handling,
cents/1000 gallons
4.20
2.96
4.29
2.27
1.84
2.19
2.31
1.85
1.74
2.33
2.35
3.27
2.74
5.03
4.23
3.55
5.07
3.24
3.45
4;71
4.87
3.46
4.91
2.95
2.84
4.56
4.31
2.85
4.35
3.27
3.52
4.73
4.91
3.52
4.95
4.06
3.93
3.79
3.15
4.81
4.68
1.70
Sludge Handling Cost,
dollars/ton dry
solids
88.72
58.94
85.90
51.59
41.71
47.11
49.71
39.40
37.14
47.09
47.56
73.22
56.30
112.46
87.05
77.81
110.96
69.41
67.69
100 . 83
95.44
71.98
101. 9O
62.33
55.05
96.29
83.34
58.60
89.43
65.89
64.89
95.11
90.57
68.77
96.58
90.86
87.39
84.31
69.17
105.23
102.26
36. 8O
Lime Stabilization 1
P
A
A
A
Gravity Thickening
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
A
Air Flotation
Thickening
A
A
A
First Stage
Anaerobic Digestion
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
p
P
P
P
p
p
p
P
p
P
P
P
P
p
P
Second Stage
Anaerobic Digestion
P
P
P
P
p
p
P
p
P
p
p
P
p
P
P
P
Aerobic Digestion 1
A
A
A
A
Elutriation 1
P
p
P
p
P
P
p
p
Vacuum Filtration
p
p
p
P
P
p
p
P
p
P
P
P
p
p
p
P
P
Centrifugation 1
P
P
P
P
p
P
p
P
P
P
Sludge Drying Beds
P
P
P
P
A
A
Incineration
P
P
P
p
P
p
P
P
P
P
P
P
p
p
Land Spreading of
Liquid Sludnc |
P
P
P
P
A
A
A
A
A
-------
HANDLING AND DISPOSAL COSTS 53
TABLE 6 (Continued)
Case Number
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
Mass of Sludge Pro-
duced by Liquid Hand-
ling Processes ,
Ib/mg
929
929
1779
1792
1793
1823
1827
1827
1866
1868
1868
1754
1898
1678
1678
1925
1903
1900
19O1
1957
1932
1754
1760
1782
1913
1898
1900
2062
2062
1821
1923
1821
1923
1911
1911
1794
2269
1794
2269
2088
2088
1 Capital Cost for
Complete Plant,
millions of dollars
-
-
3.423
4.368
4.453
3.471
4.116
4.712
3.305
4.547
4.574
3.575
3.523
4.627
5.490
3.858
4.715
4.040
4.916
3.655
4.671
3.983
5.031
4.205
4.312
3.716
3.796
3.981
4.003
5.282
4.359
5.927
4.993
4.399
5.006
4.617
4.849
5.237
5.476
4.600
5.202
1 Total Treatment Cost
for Complete Plant ,
cents/1000 gallons
-
-
16.92
18.38
18.07
16.48
16.54
18.95
15.37
18.73
18.39
17.89
15.74
18.07
20.52
17.73
19.61
17.07
19.42
16.76
19.32
18.26
18. 06
16.30
16.88
15.59
15.31
15.81
16.01
19.35
16.99
22.38
19.21
17.93
20.24
17.94
18.40
20.00
20.62
18.30
20.60
Capital Cost for
Sludge Handling
Processes, millions
of dollars
1.028
1.005
0.496
1.452
1.540
0.536
1.199
1.799
0.347
1.611
1.641
0.416
0.315
1.565
2.432
0.706
1.571
0.851
1.734
0.471
1.497
0.836
1.886
1.135
1.163
0.518
0.599
0.779
0.8O3
2.140
1.279
2.789
1.917
1.251
1.863
1.553
1.748
2.177
2.379
1.457
2.063
Total Treatment Cost
for Sludge Handling,
cents/1000 gallons
4.11
3.97
5.18
6.65
6.35
4.72
4.81
7.23
3.54
6.94
6.61
5.24
2.98
5.83
8 '.28
5.13
7.02
4.35
6.71
4.05
6.63
5.65
5.42
4.04
4.26
2.86
2.57
3.06
3.26
6.74
4.70
9.77
6.93
5.31
7.63
5.70
6.08
7.77
8.31
5.71
8.02
Sludge Handling Cost,
dollars/ton dry
solids
88.53
85.69
58.31
74.25
70.92
51.82
52.70
79.22
37.95
74.40
70.83
59.86
31.49
69.50
98.75
53.31
73.88
45.79
70.63
41.40
68.67
64.46
61.67
45.43
44.55
30.17
27.07
29.73
31.65
74.03
48.91
107.40
72.17
55.63
79.89
63.56
53.65
86.62
73.29
54.77
76.85
Lime Stabilization
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
Gravity Thickening
A
A
A
A
A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
Air Flotation 1
Thickening 1
A
A
A
First Stage
Anaerobic Digestion
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
Second Stage
Anaerobic Digestion
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
Aerobic Digestion
A
A
P+A
P+A
P+A
P+A
P+A
P+A
Elutriation
P+A
P+A
P+A
P+A
Vacuum Filtration
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
Centrifugation
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
Sludge Drying Bods
A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
Incineration
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
Land Spreading of
Liquid Sludoc
A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
-------
54 HANDLING AND DISPOSAL COSTS
TABLE 6 (Continued)
14
0>
U)
6
91
92
93
94
95
96
97
98
99
100
101
102
103
1 04
1OS
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
Mass of Sludge Pro-
duced by Liquid Hand-
ling Processes,
Ib/mg
1922
2254
1922
2254
2062
2062
2O75
2462
2075
2462
2269
2269
1970
1993
1994
2224
2197
1970
1973
2142
2142
1998
2294
1998
2294
2143
2143
2156
2516
2156
2516
2340
2340
1970
1993
1994
2224
2197
1970
1973
2142
2142
Capital Cost for
Complete Plant,
millions of dollars
4.364
4.314
4.980
4.936
4.165
4.761
4.385
4.645
4.992
5.263
4.332
4.926
3.3O9
3.844
4.739
3.543
4.619
3.503
3.588
3.768
3.789
4.164
4.094
4.783
4.719
3.949
4.548
4.173
4.425
4.783
5.046
4.113
4.708
3.352
3.886
4.782
3.586
4.663
3.546
3.631
3.811
3.833
Total Treatment Cost
for Complete Plant,
cents/1000 gallons
17.17
16.98
19.46
19.19
17.19
19.48
17.42
17.96
19.47
20.13
17.56
19.84
14.96
16.34
18.77
16.47
20.20
14.80
14.51
14.99
15.19
16.39
16.18
18.52
18.22
16.37
18.66
16.61
17.16
18.49
19.19
16.73
19.01
15.13
16.51
18.94
16.64
20.36
14.97
14.67
15.16
15.36
Capital Cost for
Sludge Handling
Processes , millions
of dollars
1.173
1.109
1.794
1.736
0.968
1.570
1.190
1.440
1.802
2.O62
1.131
1.730
0.319
0.872
1.774
0.550
1.637
0.524
0.611
0.788
0.813
1.193
1.114
1.817
1.744
0.975
1.580
1.201
1.448
1.816
2.074
1.139
1.739
0.363
0.915
1.817
0.594
1.681
0.567
0.654
0.832
0.857
Total Treatment Cost
for Sludge Handling,
cents/1000 gallons
4.44
4.26
6.74
6.48
4.45
6.75
4.69
5.24
6., 74
7.42
4.82
7.11
3.04
4.45
6.90
4.55
8.29
2.90
2.6O
3.09
3.29
4.50
4.28
6.64
6.33
4.48
6-. 78
4.72
5.27
6.62
7.32
4.85
7.14
3.21
4.62
7.07
4.71
8.46
3.07
2.77
3.26
3.46
Sludge Handling Cost,
dollars/ton dry
solids
46.24
37.80
70.13
57.53
43.21
65.50
45.21
42.59
65.05
6O.30
42.54
62.73
30.88
44.71
69.25
40.92
75.52
29.51
26.41
28.91
3O.78
45.05
37.32
66.48
55.25
41.84
63.33
43.87
41.93
61.46
58.21
41.48
61.08
32.60
46.40
70.93
42.42
77.03
31.22
28.12
30.47
32.34
Lime Stabilization
P+A
P+A
P+A
P+A
P+A
P+A
II
Gravity Thickening
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P/A
P/A
P/A
P/A
P/A
P/A
P/A
P/A
P/A
Air Flotation 1
Thickening |
First Stage 1
Anaerobic Digestion 1
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
Second Stage
Anaerobic Digestion
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
1 Aerobic Digestion
Elutriation 1
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
Vacuum Filtration 1
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
Centrifugation
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
Sludge Drying Beds
P+A
P+A
P+A
P+f
Incineration
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
!Land Spreading of
Liquid Sludoc
P+A
P+A
.P+A
P+A
P+A
P+A
-------
HANDLING AND DISPOSAL COSTS 55
TABLE 6 (Continued)
VI
0
in
n
u
133
134
135
136
137
138
139
140
141
142
L43
L44
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
Mass of Sludge Pro-
duced by Liquid Hand-
ling Processes,
Ib/mg
1998
2294
1998
2294
2143
2143
2156
2521
2156
2516
2340
2340
1922
1959
1960
2170
2144
1922
1927
2092
2095
1965
2245
1965
2245
2095
2095
2107
2463
2107
2463
2289
2289
1791
1793
1867
1870
1827
1828
1888
1889
1972
1 Capital Cost for
Complete Plant,
millions of dollars
4.207
4.137
4.826
4.763
3.992
4.591
4.216
4.338
4.826
5.091
4.157
4.752
3.553
4.292
5.191
3.897
4.835
3.808
4.010
4.116
4.139
4.690
4,391
5.319
5.020
4.320
4.923
4.525
4.798
5.139
5.423
4.473
5.072
4.198
4.313
4.325
4.423
4.471
4.570
4.231
4.302
4.365
1 Total Treatment Cost
for Complete Plant ,
cents/1000 gallons
16.55
16.34
18.68
18.39
16.53
18.82
16.77
16.40
18.66
19.36
16.89
19.17
16.48
17.69
20.13
17.87
21.07
16.48
15.81
16.22
16.43
17.96
17.27
20.35
19.32
17.73
20.03
17.86
18.48
19.74
20.53
18. Ol
20.30
17.90
17.30
17.99
17.57
18.59
18.17
17.65
17.39
17.75
Capital Cost for
Sludge Handling
Processes , millions
of dollars
1.237
1.158
1.860
1.789
1.019
1.623
1.245
1.493
1.860
2.119
1.183
1.783
0.589
1.344
2.249
0.931
1.877
0.855
1.056
1.160
1.186
1.743
1.433
2.376
2.067
1.370
1.977
1.576
1.847
2.194
2.476
1.523
2.126
1.281
1.397
1.388
1.486
1.554
1.653
1.285
1.358
1.397
Total Treatment Cost
for Sludge Handling,
cents/1000 gallons
4.66
4.44
6.81
6.50
4.65
6.95
4.89
5.43
6.79
7.48
5.01
7.31
4.63
5.87
8.32
6.02
9.23
4.65
3.97
4.39
4.60
6.14
5.43
8.53
7.49
5.91
8.22
6.04
6.67
7.93
8.72
6.20
8.50
6.17
5.57
6.20
5.78
6.87
6.44
5.84
5.58
5.87
Sludge Handling Cost,
dollars/ton dry
solids
46.73
38.76
68.16
56.69
43.40
64.88
45.42
43.15
63.00
59.51
42.89
62.49
48.26
59.95
84.94
55.48
86.18
48.42
41.29
42.02
43.94
62.55
48.42
86.88
66.76
56.48
78.52
57.36
54.22
75.36
70.87
54.19
74.28
68.95
62.20
66.48
61.80
75.20
70.47
61.94
59.10
59.61
Lime Stabili3ation
P+A
P+A
P+A
Gravity Thickening
P/A
P/A
P/A
P/A
P/A
P/A
P/A
P/A
P/A
P/A
P/A
P/A
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
A
A
P
P
P/A
Air Flotation
Thickening
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
First Stage
Anaerobic Digestion
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P
P
P
P
P
P
P
P
P
Second Stage
Anaerobic Digestion
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
Aerobic Digestion
A
A
A
A
A
A
A
A
A
Elutriation 1
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
Vacuum Filtration
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
Cent rifugat ion
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
Sludge Drying Beds 1
P+A
P+A
P+A
P+A
P+A
P+A
Incineration
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
Land Spreading of
Liquid Sludnc |
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
-------
56
HANDLING AND DISPOSAL COSTS
TABLE 6 (Continued)
Case Number 1
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
Mass of Sludge Pro-
duced by Liquid Hand-
ling Processes ,
Ib/mg
1974
1926
1927
1878
1878
1960
1961
1914
1915
1974
1975
2065
2066
2015
2O16
1823
1960
1823
1960
1954
1954
1896
2049
1896
2049
2055
2055
1912
2O58
1912
2058
2059
2059
1993
2147
1993
2147
2159
2159
1891
2036
1891
Capital Cost for
Complete Plant,
millions of dollars
4.414
4.544
4.562
4.430
4.457
4.563
4.568
4.703
4.716
4.484
4.513
4.624
4.628
4.764
4.776
4.952
4.825
5.584
5.448
4.681
5.292
4.950
5.100
5.574
5.722
4.875
5.484
4.870
4.907
5.496
5.529
4.691
5.300
5.011
5.169
5.633
5.790
4.945
5.552
4.939
4.759
5.419
Total Treatment Cost
for Complete Plant,
cents/1000 gallons
17.65
18.56
18.27
17.99
17.85
18.06
18.10
18.68
18.71
18.21
18.06
18.29
18.32
18.92
18.94
19.35
19.12
21.62
21.21
19.37
21.75
19.53
19.94
21.57
22.03
19.89
22.26
19.25
19.41
21.40
21.50
19.39
21.76
19.75
20.19
21.80
22.28
20.14
22.51
19.23
18.85
21.01
Capital Cost for
Sludge Handling
Processes , millions
of dollars
1.446
1.598
1.617
1.514
1.543
1.626
1.633
1.787
1.801
1.539
1.571
1.656
1.661
1.819
1.832
2.042
1.912
2.678
2.539
1.772
2.386
2.041
2.193
2.668
2.818
1.969
2.581
1.930
1.966
2.560
2.592
1.752
2.364
2.073
2.231
2.698
2.854
2.007
2.617
2.006
1.823
2.489
Total Treatment Cost
for Sludge Handling,
cents/1000 gallons
5.77
6.75
6.45
6.27
6.12
6.28
6.32
6.96
6.99
6.40
6.25
6.41
6.44
7.11
7.. 13
7.63
7.40
9.91
9.50
7.66
10.05
7.82
8.24
9.87
10.34
8.20
10.58
7.45
7.61
9.60
9.71
7.60
9.98
7.96
8.40
10.01
10.50
8.35
10.73
7.45
7.O6
9.23
Sludge Handling Cost,
dollars/ton dry
solids
58.52
70.14
67.00
66.80
65.26
64.12
64.50
72.72
73.06
64.94
63.36
62.16
62.43
70.57
70.79
83.77
75.58
108.79
96.97
78.50
102.95
82.52
80.48
104.17
100,95
79.82
103.00
77.98
74.00
100.47
94.39
72.82
96.98
79.87
78.27
100.49
97.83
77.42
99.44
78.83
69.46
97.63
Lime Stabilization I
Gravity Thickening
P/A
P
P
A
A
P
P
P/A
P/A
P
P
P
P
P
P
P
P
P
P
P
P
P
P
A
A
A
Air Flotation
Thickening
A
A
A
A
A
A
First Stage
Anaerobic Digestion
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
p
P
P
P
p
P
P
P
P
p
P
P
P
P
P
P
P
Second Stage
Anaerobic Digestion
P
P
p
p
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
p
P
P
P
P
Aerobic Digestion
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Elutriation
P
p
P
P
P
P
•P
P
P
Vacuum Filtration
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
Centrifugation
P+A
P+A
P+A
P+A
P+A
P+A
P+/
P+A
Sludge Drying Beds
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
^
Incineration
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
Land Spreading of
| . Liquid Sludnc
P+A
P+A
P+A
P+A
P+A
P+A
P+A
-------
HANDLING AND DISPOSAL COSTS 57
TABLE 6 (Continued)
Case Number
217
218
219
220
221
222
823
224
225
226
227
228
229
23O
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
Mass of Sludge Pro-
duced by Liquid Hand-
ling Processes ,
Ib/mg
2036
1969
1969
1969
2130
1969
2130
2065
2.065
1988
2141
1988
2141
2075
2075
2074
2236
2074
2236
2172
2172
1850
1989
1850
1989
1933
1933
1924
2080
1924
2080
2025
2O25
1942
20B9
1942
2089
2035
2O35
2O25
1865
2025
Capital Cost for
Complete Plant,
millions of dollars
5.208
4.772
5.222
4.881
5.026
5.340
5,459
4.829
5.264
4.838
4.838
5.304
5.276
4.708
5.147
4.936
5.090
5.385
5.518
4.899
5.322
5.099
4.932
5.597
5.4O4
4.916
5.386
5.055
5.216
5.535
5.674
4.970
5.426
5.003
5.030
5.489
5.492
5.010
5.470
5.113
5.061
5.583
Total Treatment Cost
for Complete Plant,
cents/1000 gallons
20.34
19.44
21.18
19.27
19.63
20.74
21.06
19.43
21.10
19.09
19.12
20.68
20.57
19.17
20.87
19.47
19.86
20.91
21.30
19.67
21.30
19.88
19.54
21.70
21.10
20.06
21.87
19.96
20. 4O
21.51
21.91
20.05
21.80
19.75
19.89
21.42
21.42
20.38
22.15
20.17
19.78
21.69
Capital Cost for
Sludge Handling
Processes, millions
of dollars
2.275
1.839
2.292
1.948
2.094
2.410
2.529
1.897
2.334
1.874
1.870
2.342
2.311
1.742
2.185
1.972
2.124
2.423
2.549
1.934
2.360
2.186
2.017
2.687
2.491
2.004
2.477
2.144
2.307
2.626
2.766
2.060
2.518
2.061
2.085
2.550
2.550
2.068
2.531
2.171
2.164
2.644
Total Treatment Cost
for Sludge Handling,
cents/1000 gallons
8.56
7.67
9.41
7.49
7.86
8.97
9.30
7.66
9.34
7.21
7.24
8.82
8.70
7.30
9.00
7.60
7.99
9.05
9.40
7.80
9.44
8.16
7.82
9.98
9.39
8.34
10.16
8.24
8. 7O
9.80
10.21
8.34
10.10
7.95
8.08
9.62
9.62
8.58
10.36
8.37
8.13
9.89
Sludge Handling Cost,
dollars/ton dry
solids
84.12
77.91
95.66
76.17
73.87
91.15
87.36
74.26
90.52
72.60
67.70
88.75
81.28
70.43
86.81
73.32
71.49
87.31
83.90
71.91
87.01
88.23
78.71
107.94
94.42
86.36
105.17
85.73
83.65
101.92
98.24
82.42
99.81
81.88
77.39
99.12
92.13
84.35
101.82
82.70
87.26
97.71
Lime Stabilization
Gravity Thickening 1
A
A
A
A
A
A
A
A
A
P/A
P/A
P/A
P/A
P/A
P/A
P/A
P/A
P/A
P/A
P/A
P/A
P
P
P
P
P
P
P
P
P
Air Flotation
Thickening |
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
First Stage
Anaerobic Digestion
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
Second Stage
Anaerobic Digestion
p
P
P
p
P
p
P
P
p
P
p
p
P
p
P
P
p
P
p
P
P
Aerobic Digestion
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Elutriation
p
P
P
P
P
P
P
P
P
P
P
p
p
P
Vacuum Filtration
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
Cent rifugat ion
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+f
Sludge Drying Deds
Incineration
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
P+A
Land Spreading of
Liquid Sludnc |
-------
58
HANDLING AND DISPOSAL COSTS
TABLE 6 (Continued)
Case Number
259
260
261
•O
1 C
83
Mass of Sludge
duced by Liquic
ling Processes,
Ib/mg
1865
2128
2128
in
VI
rf
W H
Capital Cost fc
Complete Plant,
millions of dol
5.735
5.059
5.505
p
0 P w
§ 0
Total Treatmenl
for Complete P3
cents/1000 gal]
22.16
20.36
22.08
8
o
U 'rl
Capital Cost fc
Sludge Handlinc
Processes , mil.
of dollars
2.790
2.118
2.566
•p «
u) O>
8C u)
•a c
,,S5
Total Treatmenl
for Sludge Hanc
cents/1000 gal'.
10.33
8.56
1O.29
p
8
rn b*
Sludge Handlin
dollars/ton dr1
solids
94.64
80.54
96.78
O
•rl
•p
Lime Stabiliza
%
•H
C
Gravity Thicke
P
P
P
Air Flotation
Thickening
A
A
A
stion
First Stage
Anaerobic Dige
P
P
P
stion
Second Stage
Anaerobic Dige
P
P
P
o
•rl
Aerobic Digest
A
A
A
Elutriation
P
c
0
•H
Vacuum Filtrat
P+A
Cent rifugat ion
P+A
P+A
m
•8
a
Sludge Drying
Incineration
P+A
P+A
VI
0
Land Spreading
Liquid Sludqc
P primary sludge treated
A waste activated sludge treated
P+A mixture of primary sludge and WAS treated
P/A primary sludge and WAS treated separately with the process indicated
Except for centrifuges, which were amortized over a
ten year period at six percent interest, capital costs for
equipment and structures were amortized over 25 years
at six percent interest. Capital cost is defined as the con-
struction cost plus the costs of yardwork, land, engineer-
ing, legal-fiscal-administrative services and interest
during construction. Total treatment cost is defined as
the sum of amortization and operation and maintenance
costs.
The cost for treating and disposing of sludge ex-
pressed as dollars per ton of dry solids is also included in
Table 6. This figure ranges from about $30 per ton for
anaerobic digestion followed by dewatering on sand dry-
ing beds to over $100 per ton when the sludge is dewa-
tered by vacuum filtration or centrifugation and then in-
cinerated. The cost of treating and disposing of sludge
approaches 60 percent of the total treatment cost for the
entire plant. Therefore, it can be seen that the method
selected for sludge handling has a significant effect on
the total cost of treatment.
REFERENCES
1. Eilers, R.G., and Smith, R., "Executive Digital
Computer Program for Preliminary Design of Wastewa-
ter Treatment Systems," NTIS-PB 222 765, (March
1973).
2. Smith, R., "Preliminary Design and Simulation of
Conventional Wastewater Renovation Systems Using
the Digital Computer, "NTIS-PB 215 409, (March 1968).
3. Vosloo, P.B.B., "Some Factors Relating to the De-
sign of Activated Sludge Plants," Journal of the Insti-
tute/or Water Pollution Control, Vol. 69,. N. 5, p. 486,
(1970).
4. Hopwood, A.P., and Downing, A.L., "Factors Af-
fecting the Rate of Production and Properties of Acti-
vated Sludge in Plants Treating Domestic Sewage,"
Journal of the Proceedings of the Institute for Sewage
Purification, p. 435, (1965).
5. Wuhrmann, K., "Effects and Interactions of Some
Operating Parameters in the Activated Sludge System,''
Schweiz.Z. Hydrol., Vol. 26, p. 218, (1964).
6. Bargman, R.D., and Borgerding, J., "Characteri-
zation of the Activated Sludge Process," EPA Environ-
mental Protection Technology Series, EPA-R2-73-224,
(April 1974).
7. Black and Veatch Consulting Engineers, "EPA
Process Design Manual for Phosphorus Removal," EPA
Technology Transfer Series, (October 1971).
8. McMichael, W.F., "Manpower Required for Lime
Addition," EPA Internal Memorandum, (May 17,1972).
9. McMichael, W.F., "Cost of Dissolved Air Flotation
Thickening of Waste Activated Sludge at Municipal
Sewage Treatment Plants," NTIS-PB 226 582/AS,
(January 1974).
10. McCarty, P.L., "Kineticsof Waste Assimilation in
Anaerobic Treatment," Developments in Industrial
Microbiology, Vol. 7, p. 144, (1966).
11. Jaworski, N., Lawton, G.U., and Rohlich, G.A.,
"Aerobic Sludge Digestion," Third Biological Waste
Treatment Conference, Manhattan College, (1963).
12. Smith, R., Eilers, R.G., and Hall, E.D., "A
Mathematical Model for Aerobic Digestion," NTIS-PB
222 029 (February 1973).
13. McCarty, P.L., "Sludge Concentration—Needs,
Accomplishments, and Future Goals," Journal of the
Water Pollution Control Federation, Vol. 38, p. 493,
(1966).
14. McCarty, P.L., "Design Factors for Sewage
Sludge Vacuum Filters," Master of Science Thesis,
Massachusetts Institute of Technology, (1957).
15. Roy, F. Weston Inc., "EPA Process Design
Manual for Upgrading Existing Wastewater Treatment
Plants," EPA Technology Transfer Series (October
1971).
16. Vesilind, P.A., "Estimation of Sludge Centrifuge
Performance," Journal of the Sanitary Engineering
-------
HANDLING AND DISPOSAL COSTS 59
Division, Proceedings of the American Society of Civil
Engineers, Vol. 96, No. SA3, p. 805, (1970).
17. Haseltine, T.R., "Measurement of Sludge Drying
Bed Performance," Sewage and Industrial Wastes, Vol.
23, No. 9, p. 1065, (1951).
18. Unterberg, R., Sherwood, J., and Schneider,
G.R., "Computerized Design and Cost Estimation for
Multiple Hearth Sludge Incinerators," NTIS-PB 211
264, (July 1971).
19. McMichael, W.F., "Cost of Hauling and Land
Spreading of Domestic Sewage Treatment Plant
Sludge," NTIS-PB 227 005/AS, (July 1973).
20. Patterson, W.L., and Banker, R.F., "Estimating
Costs and Manpower Requirements for Conventional
Wastewater Treatment Facilities," NTIS-PB 211 132,
(September 1971).
APPENDIX
FORTRAN Method of Writing Mathematical Equations
The use of the FORTRAN mode of expression has sev-
eral advantages. First, all expressions can be written
using ordinary typewriter symbols on a single line.
Second, ambiguity and misunderstanding can be
avoided when the simple rules are understood. Third,
when a computer program is being described, the vari-
able names used in the digital computer program can be
used thus making the computations performed better
understood by the reader.
FORTRAN provides five basic operations: addition,
subtraction, multiplication, division, and exponentia-
tion. Each of the operations is represented by a distinct
symbol as follows:
Addition +
Subtraction —
Multiplication *
Division /
Exponentiation **
In writing FORTRAN expressions, using the opera-
tions shown above, the following rules must be
observed:
1. Two symbols of operation must not appear next to
each other. Thus, A*—B is not a valid expression
but A*(—B) is valid.
2. Parentheses must be used to indicate groupings
just as in ordinary mathematical notation. Thus,
(X + Y)3 must be written (X + Y)**3 to convey the
correct meaning. Again, A—B + C and A—(B + C)
are both legitimate expressions, but they do not
mean the same thing.
3. When the hierarchy of operations in an expres-
sion is not completely specified by the use of paren-
theses, the sequence of operations is as follows: All
exponentiations are performed first, then all mul-
tiplications and divisions, and finally all additions
and subtractions.
4. When the order of consecutive multiplication and/
or division or addition and/or subtraction is not
specified by the use of parentheses, the operations
are performed from left to right. Thus, A/B/C
would be taken to mean A/(B*C) not (A*C)/B.
Also, A—B+C would mean (A—B) + C not
A—(B + C).
FORTRAN also provides for the use of certain com-
mon mathematical functions such as the following:
Square Root SQRT (X)
Natural Logarithm ALOG (X)
Exponential (ex) EXP (X)
Trigonometric Sine SIN (X)
Trigonometric Cosine COS (X)
Absolute Value ABS (X)
-------
URBAN SLUDGE DISPOSAL OR
UTILIZATION ALTERNATIVES
SOCIO-ECONOMIC FACTORS
Albert Montague
Uni'ed States Environmental Protection Agency,
Region III
Philadelphia, Pennsylvania
The ability for rural cities to handle sludge generated
in their municipal wastewater treatment facilities, using
land application or incineration methods has on the
whole been a relatively simple matter. As a matter of in-
terest there have been instances where sludges being
treated in drying beds had somehow vanished. The
dryed sludge apparently being taken by some organic
farmer. Resistance by neighboring communities to ac-
cept this natural resource has for the most part been
minimal, at least in rural areas. Therefore, rural com-
munities have in general had a high degree of success in
utilizing sludge.
The receptiveness of neighboring areas to readily ac-
cept municipal wastewater treatment residue is, in my
opinion, due to the socio-economic relationship which
these outlying communities share with their rural city
counterparts. Another important consideration is the
availability of land in these outlying areas, which in
many instances are abundant when compared to large
metropolitan areas.
This same climate of receptiveness and cooperation
apparently has not developed for many large metropoli-
tan areas. Therefore, the rapport which many major
cities share with their suburban and rural communities
is in this regard less certain. The ability for a major
metropolitan area to effectively handle its sludge and
hopefully have society make full use of its value, perhaps
in the reclamation of strip mines for their enhancement
and increased productivity by upgrading soil conditions,
while using the backhaul capability of empty coal rail-
cars, has been extremely difficult to implement. Thus,
fostering the practice of disposal and not utilization. This
situation can be attributed to two main factors. One is
the technical concern, i.e., potential health hazards of
bringing a wastewater treatment by-product which may
contain a host of materials some of which may be toxic or
pose a health threat. The other is characteristic of human
nature, namely not wanting the waste materials from a
community which in general is removed socially, eco-
nomically, and politically from the potential receptor.
The latter factor may, from a psychological standpoint,
affect the public's technical concerns of a land applica-
tion system to the degree that their concerns may be ex-
aggerated when weighed against the information and
experience which has been gained, in the handling of
municipal sludges which have been effectively stabi-
lized.
A host of treatment systems have been examined that
deal with the final sludge processing step. Incineration
and various heat treatment techniques have been a
favored approach for some time. But with current and
future costs of natural fuels escalating at rates never be-
lieved possible, it is abundantly clear that incineration
and other energy intensive systems will not prevail
unless they are found to be cost-effective and not energy
intensive. Concurrently we must also remain mindful of
satisfying emission requirements so that we can main-
tain or improve applicable air quality standards. This
requirement may in some instances prove to be both
technically difficult and costly.
As for land spreading, the application of sludge in a
liquid state appears to be one of the most attractive al-
ternatives from an economical and environmental stand-
point except when one compares it with the cost of ocean
disposal for coastal megalopoli and the out of sight out of
mind philosophy associated with this practice. Further-
more, the degradative effects and environmental
stresses which we have monitored from ocean dumping
these materials are vividly illustrated when one
examines the effects it has rendered on the marine en-
vironment in the New York Bight and Philadelphia's
sludge dumping site. There is every reason to believe
that the resulting effects which society has witnessed by
this disposal method may ultimately result in the demise
of this practice. The method has an inherent shortcom-
ing, namely the inability to control or manage the fate of
these materials once the sludge has been discarded into
the marine eco-system. The aforementioned shortcom-
ing does not apply however to land application tech-
niques, since prudent management practices can easily
be implemented using this approach, thereby controlling
the degree of environmental stress.
60
-------
URBAN DISPOSAL OR UTILIZATION ALTERNATIVES 61
It is generally known that sludges from municipal
sewage treatment plants vary markedly in both organic
and inorganic content. This is obviously due to the vari-
ability and composition of the wastewater. The inherent
characteristics of sludge are the result of three major
considerations:
1. The domestic water supply system including the
water supply source, treatment and conveyance
system;
2. The compounds associated with industrial and do-
mestic wastewaters;
3. Storm water and subsurface inflow into the collec-
tor system.
The composition of municipal wastewaters is basically
dependent on the proportion and nature of the com-
munity's lifestyle and industrial base.
The residential diet has been shown to affect waste-
water and sludge characteristics. For example, the daily
normal digestion and excretion of zinc is expected to be
approximately ten mg/person. The concentration of
zinc in various food products have been detected from
levels of less than one ppm in fruits to as much as 2300
ppm in oysters. It has also been established that today's
automobile tires are manufactured from a variety of
materials. Unfortunately one of these is zinc and, be-
cause of its inherit impurities, cadmium. Under normal
use and wear it is naturally expected that these automo-
bile tire materials and other heavy metals some of which
may come from auto exhausts, automobile brake linings,
the scrubbing of air pollutants, etc. would during
periods of precipitation be scoured off road surfaces and
into the municipal sewer system (Table 1). If the collec-
tor system is of the combined sewer type, significant
quantities of these materials and associated metals will
ultimately find their way into the municipal wastewater
treatment facilities and the sludges generated therein.
The fact that many of these heavy metals build up in the
sludge, coupled with the degree of accumulation makes
any final handling method considerably more difficult to
manage from an environmental standpoint (Table 2).
In some cases, relatively high quantities of heavy
metals were found to be accumulating in wastewater
treatment plant sludges in a number of cities throughout
our nation. This excess was and still is in some cases ap-
parently thought to be due primarily by in'dustrial dis-
charges. However, as a result of a two-year compre-
hensive study dealing with sources of metals in New
York City and a subsequent report published by New
York City's Department of Water Resources, it was
clearly shown that at least in a megalopolis of this size
complete control of all industrial contributors would not
result in any significant gain in the reduction of heavy
TABLE 1
Heavy Metals Loading Intensities
(Lb/CurbMile)
ZINC
COPPER
LEAD
NICKEL
MERCURY
CHROMIUM
San Jose- I
San Jose- 1 1
Phoenix- I I
Milwaukee
Baltimore
Atlanta
Tulsa
Seattle
1.4
.28
.36
2.1
1.3
.11
.062
.37
.49
.020
.058
.59
.33
.066
.032
.075
1.85
.90
.12
1.51
.47
.077
.030
.50
.19
.085
.038
.032
.077
.021
.011
.028
.20
.085
.022
-
.023
.019
.034
.10
.14
.029
.047
.45
.011
.0033
.081
Arithmetic
Means
.75
.21
.68
.060
.080
.12
-------
62 URBAN DISPOSAL OR UTILIZATION ALTERNATIVES
TABLE2
Contents of Trace Elements in 57 Sewage
Sludges from Locations in Michigan, U.S.A.
Element
Hg
Cd
Cr
Cu
As
Ni
Pb
Zn
0.1
2
22
84
1.6
12
80
72
Range
wg/g—
56
1100
30,000
10,400
18
2800
26,000
16,400
Mean
5.5
74
2031
1024
7.8
371
1380
3315
Median
3.0
12
380
700
7.5
52
480
2200
1-10
49
28
0
0
48
0
0
0
No.
10-100
4
20
19
1
9
33
2
1
Samples Within Range
100-1000
0
8
18
42
0
15
43
9
1 000-1 000(
0
1
18
13
0
9
10
44
) >1 0,000
0
0
2
1
0
0
2
3
metals into the municipal wastewater treatment system.
According to the authors it is claimed that approximately
91 percent of the copper, 94 percent of the zinc, 84 per-
cent of the cadmium and 80 percent of the chromium
would still get into the sewer system if 100 percent con-
trol were placed on these industrial discharges. Only in
the case of nickel would a zero discharge by industry re-
sult in a significant reduction 38 percent of the current
level. These findings should be corroborated by at least
two other comprehensive surveys of this or greater mag-
nitude.
If heavy metals continue to be a source of concern and
frustration as related to our handling of municipal
sludges and for that matter all sludges, it may be neces-
sary that our society make some major changes in its life-
styles so that we can effectively control the movement of
these materials. Perhaps we may have to give up tires
having zinc derivatives, chromate compounds in cooling
towers, copper sulfate as an algicied, etc.
One method which holds great promise in partially re-
solving the ultimate step in processing sludge, currently
confronting large urban centers is that of land spreading
stabilized sludge. Providing of course that suburban and
rural communities become receptive and would permit
these urban centers the opportunity to prove its full
worth. A process which allows for man's utilization of
this natural resource if prudent management practices
are followed during the entire effort.
Small or relatively low applications of sludge contain-
ing an abundance of micronutrients such as boron, zinc,
copper, manganese, etc., would normally be sufficient
to satisfy most or existing soils which are deficient in
these minerals. However, large applications of these
materials when the concentration of these micronu-
trients are found to be high could promote deficiencies in
growth yields and/or toxicities. Therefore, limits of ap-
plication exist and must be defined so that the soil-plant-
sludge inteface is not upset. It is essential that we realize
the full beneficial value of the sludge from its fertilizer
and soil conditioning standpoint. While sludge in a
liquid state contains both major and minor nutrients for
plant growth, it may not be a balanced fertilizer or a wide
variety of crops and soils.
Sludge composition will undoubtedly change depend-
ing on factors previously enumerated and the methods of
stabilization. Sludges are normally low in potassium, of
medium value in available nitrogen and high in phos-
phorous. It may be inappropriate to compare it to com-
mercial fertilizers from a handling standpoint because of
the volumes which are needed to achieve the same nu-
trient objectives. Nevertheless, if arrangements can be
implemented where the sludge is delivered and applied
on fields at no cost to the farmer, liquid sludge can be
utilized in a manner that is economical, suitable as a
fertilizer supplement and excellent as a soil conditioner.
As a result of the addition of organic matter which is
rather abundant, in the sludge, to the soil, it has been
shown that the sludge amended soils have in many cases
improved significantly with regard to; ability to hold
moisture, humus content, soil fertility and improved soil
structure. Thus making the sludge far more valuable as a
soil conditioner than that as a fertilizer.
This factor makes sludge a very effective material for
the reclamation of marginal lands which may have been
depleted of organic matter through misuse. In fact, the
application of sludge on strip mined areas for purposes
of reclamation has in a number of instances resulted in
the growth of vegetation where none could develop, due
to previous mining practices. A significant increase in
the ph value was also noted with regard to surface runoff
during periods of precipitation. Another benefit is the
effective control of soil erosion and sediment transport
-------
URBAN DISPOSAL OR UTILIZATION ALTERNATIVES
63
because of the ground cover which is formed during this
reclamation process. The disposal of sludge which can
be used as resource by society is inexcusable.
A number of different treatment techniques have
amply demonstrated that significant reductions can take
place with respect to bacterial concentrations. Although
it also has been shown that some of these processes pro-
vide conditions which are hostile to these organisms,
they are by no means lethal (Table 3).
to land environs has on the whole demonstrated the vi-
ability of this approach and that the risks to public health
are slight if appropriate handling and management tech-
niques are employed.
Finally and of major importance is the issue of cost.
This factor has been found to vary considerably depend-
ing on the method of analysis, area of study, etc.. Un-
fortunately some of these efforts, in my opinion, appear
to be compiled in a subjective rather than objective man-
TABLE3
Bacteria in Sewage Sludge
(Per 100 ml)
Fecal coli
(x 106)
Salmonella
Pseudomonas
Raw Primary
Trickling filter
Raw WAS ^
Raw WAS
(thickened) - B
Raw WAS - C
Anaerobic digested
primary
Aerobic digested WAS
Anaerobic digested WAS
Iron primary
Lime primary
pH 9.0
Lime primary
pH 11.5
11.4
11.5
2.8
20
2.0
0.39
0.66
0.32
32
32
0.014
460
93
74
9,300
2,300
29
150
7.3
460
1,500
<3.0
46,000
110,000
1,100
2,000
24,000
34
100,000
1,000
21,000
24,000
<3.0
(a)
Waste activated sludge
The potential for contamination of groundwater by
pathogenic microorganisms is dependent on the ability
of pathogens to survive and move through the soil sys-
tem. Many factors govern their pathways and compli-
cate the assessment of their movement through the soil
mantle. Unfortunately, there is a dearth of information
on this subject. Nevertheless, the information that is
available regarding the effects of sludge land spreading
practices and that also of applying wastewater effluents
ner and are thus misleading. A rigorous cost analysis is
beyond the scope of this paper. However, some efforts
that deserve mention will be briefly cited.
One analysis in particular was done for Metropolitan
Sewer Board of the Twin Cities area. Nearly 300 pro-
cessing combinations were considered which were
initially pared down to 59. Based on this rigorous cost
analysis, land spreading of sludge was listed as the most
cost-effective candidate. Obviously each situation from a
-------
64 URBAN DISPOSAL OR UTILIZATION ALTERNATIVES
cost analysis standpoint, for municipalities, is unique
and what applies to one community may not be appli-
cable to another. One other study although not as recent,
but appropriate nevertheless, if the listed values are ex-
trapolated to reflect inflationary trends, also shows the
economic advantages of landspreading sludge in a
liquid state (Table 4).
TABLE4
Comparative Costs of Suldge Disposal (1970)
(Presented in English Units)
Method
Estimated cost,
$/dry short ton
Incineration
Wet-air oxidation
Multiple-hearth
Fluidized-bed
Drying: fertilizer sale
Lagooning
42-50
30-57
30
Pumping
Trucking 5% sludge
Trucking 10X sludge
Disposal at sea
Pumping
Barging 5% sludge
Barging 10% sludge
Land appl ication
Landfill
Heat-dried sludge
Dewatered sludge
Liquid sludge
Strip-mine reclamation
7-49
18
12
11
12
9
25
50
25
15
16
The final sludge processing method which is eventual-
ly selected, has based on past experiences been influ-
enced to a large degree by elements which are socio-
political. This fact effectively dilutes the environmental-
economic analysis and associated recommendations.
If we are to make significant progress in effectively
managing our environment. We must make these latter
elements which "really" influence the ultimate decision
aware of the advantages and disadvantages of the op-
tions that are currently available.
The following recommendations are offered in the
hope that we can effectively correct the current
situation:
1. Develop an active public awareness program on the
benefits and liabilities of the proposed sludge process-
ing system, whether it be landspreading of sludge for
cropland and/or reclamation purposes, power genera-
tion, ocean disposal, incineration, etc.
2. A realistic program in controlling heavy metals into
our wastewater collection systems not only focusing on
industry, but commercial uses where it is humanly
practicable.
3. A sincere effort on the part of our leadership to ap-
ply those techniques which have been sufficiently de-
veloped and/or demonstrated and to highlight the pit-
falls of those systems or approaches that failed to
achieve either the performance or objectives under
consideration.
4. That a research and demonstration effort which is
meaningful in scope and commensurate with current
environmental construction grant expenditures be
implemented.
-------
SLUDGE MANAGEMENT ALTERNATIVES
FOR COASTAL CITIES
Terry Bursztynsky and John Davis
Engineering-Science, Inc.
Berkeley, California
INTRODUCTION
For many years the principal goal of wastewater treat-
ment has been production of clear, high quality effluent
water, whereas treatment and disposal of sewage solids
removed from the aqueous stream has been considered a
secondary activity of rather less concern. It has since be-
come apparent that sewage sludge disposal must be-
come an integral part of an overall land, air and water re-
source management plan. In Southern California, the
problem of solids disposal has become a particularly
serious concern in coastal communities, since these
communities support the greatest part of the State's
population and their traditional solution of ocean dis-
posal is being blocked by regulatory action. The search
for a more acceptable method of disposal for sewage
sludge has to be conducted against a background of in-
creasing public awareness of not only marine pollution,
but also degradation of air quality and inappropriate
land-use practices.
Recognizing the seriousness of the problem the
Southern California wastewater agencies and state and
Federal agencies concerned with environmental protec-
tion have conducted or are presently conducting a num-
ber of investigations of alternative sewage sludge man-
agement practices. Recently a well-funded study of the
problem was commenced by a group of wastewater
agencies and is expected to report its findings in approxi-
mately two years. In 1973-74 Engineering-Science, Inc.
in association with J.B. Gilbert and Associates con-
ducted a pilot study of the sludge disposal problem
under a contract with the Washington Environmental
Research Center of the Environmental Protection
Agency.
The object of the pilot study was to compile regula-
tions effecting the choice of sludge management options
to develop an evaluation and comparison method for
sludge management alternatives and to apply the sys-
tem to the three largest wastewater dischargers in the
Los Angeles area. The evaluation method should permit
an equitable comparison of the advantages and disad-
vantages of different sludge management options yet
satisfy the public's need to follow and understand the
method.
This paper presents a summary of the findings of the
study. Its conclusions are not based on extended or ex-
haustive evaluations; however, until the present more
detailed study is completed they do provide some illumi-
nation of the problem and some of its possible
solutions1.
The Sewage Sludge Disposal Problem
In Southern California
The average daily production of wastewater sludges
by California coastal communities as reported in 1973
was 1,251 metric tons. The sludges result from treat-
ment, principally primary, of 69 m^/sec [1,575 mgd] of
raw municipal wastewater. Table 1 summarizes present
wastewater flow and sludge production rates in coastal
California.
TABLE 1
Present Sludge Production (1973)
Area
San Francisco Bay
Area counties
Los Angeles County
Orange County
San Diego County
Other
Total
JFLlow,
m /sec
19. 6
34.3
7. 1
5. 1
3.0
69. 1
Sludge production,
metric tons dry
solids/day
485
528
95
95
48
1,251
Total sludge
production, %
38
42
8
8
4
100
Reference: 1973 EPA Needs Survey
The wastewater flow treated by the three largest dis-
chargers (City of Los Angeles, Los Angeles County Joint
Outfall Facilities and Orange County) in the Los Angeles
basin in 1973 was 40.8 3/sec [931 mgd] average daily
dry-weather flow. The mass of sewage sludge generated
by these three agencies was 48 percent of the total
sludge tonnage generated by all of the California coastal
communities.
On the basis of projections of coastal agencies in Cali-
fornia, general adoption of secondary treatment will re-
sult in production of 4,000 metric tons of sludge each day
65
-------
66 ALTERNATIVES FOR COASTAL CITIES
by 1995, approximately a threefold increase over the
present rate and two-thirds of which is attributable to the
higher level of treatment. In Southern California it is
estimated that production will be 405 metric tons [445
short tons] of sludge daily at the City of Los Angeles Hy-
perion Plant. The Joint Works of Los Angeles County
will produce 1,062 metric tons [1,168 short tons], and the
County Sanitation Districts of Orange County will reach
315 metric tons [347 short tons] daily.
The basic characterization of sewage sludges and
their constituents has often been reported and will not be
repeated here. However, it is worth noting that the rela-
tive portions of total raw sewage flow representing in-
dustrial waste at the Joint Treatment Plant, Hyperion
and Orange County are 35, 12 and 25 percent, respec-
tively. Source control of industrial wastes will reduce the
amounts of heavy metals and toxicants reaching treat-
ment plants, but source control will take several years to
implement and will never eliminate the problem of toxic
material in sewage sludges. In terms of treated sewage
sludge, Table 2 presents the changes to be expected in
sludge characteristics from the most commonly used
unit processes. Sludge processing unit performance
characteristics are shown in Table 3.
TABLE2
Changes in Sludge Constituents
Through Basic Processing
Constituent
Percentage of
original water
content
Percentage of
original solide
content
Percentage of
original organic
toxicants
Percentage of
original inorganic
toxicants
Percentage of
original organic
matter
Raw
sludge
100
100
100
100
100
Digested sludge
100
60
Decreased by
undetermined
amount
100
30 to 40
Digested and
dewatered
47
40 to 58
Decreased by
undetermined
amount
Estimated
80 to 95
28 to 35
Raw dewatered Supernatant, ccntrate,
and Incinerated filtrate or off-gas
0 43 to 100
30 to 40 60 to 70
Varies with process
efficiency
0 Undetermined
Undetermined Undetermined
0 Varies with process
efficiency
TABLE3
Sludge Processing Unit Performance
Process
Thickening
Gravity
Flotation
Treatment
Aerobic
digestion
digestion
Incineration
Feed
Primary
WAS
Primary t WAS
Digested primary
Digested primary
«, WAS
Primary t WAS
WAS with chem.
WAS without chem.
Primary, thickened
Primary tt WAS,
thickened
Primary fi WAS,
Primary, dewatered
Primary & WAS,
dewatered
Total
pe
1-3
0.5-1
2
2-5
2-3
2
0.5-1.5
0.5-1.5
5-8
4-5
4-5
25
25
Total
rccnt wt
5-8
2-3.5
4-5
5-8
5-7
4-5
3.5
3-5
2-4
2-5
2-3
100
100
Volume
pe
50-60
50-60
50-60
50-60
65
65
60
10
10
0
0
75-85
75-85
Solids
rcent
98 +
98 +
98 +
98 +
98 +
95 +
95 +
95 +
60-65
50-60
40-60
50-60
30-40
30-40
Weto
Heat
Any, thicke
98 +
98 +
Lime stabili-
zation
Dewatering
Drying beds
Pressure fil-
tration
Centrifuge
Primary, thickened
Primary b WAS,
thickened
Any, digested
Any, lime stabili-
zation
Primary & WAS, con-
ditioned
Digested, conditioned
Digested, conditioned
Digested
Digested, conditioned
Digested
5-8
4-5
2-5
4-8
2-3
2-3
2-5
5-6
2-5
2-5
2 5
5-8
4-5
40
40
35
25
25-37
30-40
18-21
20-25
90
0
0
50
50
85-90
90
80-90
60-75
75-85
95 +
110
110
98 +
98+
90 +
90--95+
98 +
55
90-95
98 +
Sewage Sludge Disposal Criteria
Sewage sludge management practices may have an
impact on many environmental elements. Ocean dispos-
al of sludge obviously may affect water quality, land
disposal of sludge may affect groundwater quality or soil
productivity and sludge incineration will affect air
quality.
The diversity of potential impacts of sewage sludge
disposal is reflected by the plethora of governmental
regulations that constrain the selection of choices with
respect to sludge disposal. Tables 4, 5, 6, 7, and 8 sum-
marize the relevant regulations and multi-media sludge
disposal criteria applicable in coastal Southern Cali-
fornia.
The Alternative Evaluation System
The need to systematically evaluate and quantify en-
vironmental impacts of alternative courses of action has
spawned a variety of evaluation systems, the best-
known of which are the U.S.G.S. Matrix, the Battelle En-
vironmental Evaluation System, the Georgia Institute of
Ecology's Optimum Pathway Matrix and the U.S. Bur-
eau of Reclamation's method 2'5. The U.S.G.S. Matrix is
an inventory or checklist of factors that can be useful for
selecting criteria relevant to an alternative. The Battelle
-------
ALTERNATIVES FOR COASTAL CITIES 67
TABLE4
Summary of Regulatory Authority Affecting Sewage Solids Disposal
Disposal System
Incineration
Incinerator ash disposal
to land
Incinerator ash disposal
to water
Pollutant emissions to
2
W
PS
PS
M,
< «
California State
Resources Bo
PS
x
c
3
6
W
O
O
OOQ
r
.
PS
S
0,
c
3
O
U
00
C
a
O
-
-
PS
CO
Of— *
. Tl O
California State
Water Resour
Control Boarc
Regional Water
Quality Contn
Board
PS PS
PS PS
~o
L*
0}
•>£
State Solid Wast
Management 1
N
-
-
c
o
•« 2 i*
California State
Department o
Public Health
California Coas
Zone Conserv
Commission
L PS
L PS
PS
^
c
3
Los Angeles Co
Engineer
PS
-
-
£ c
§1
Los Angeles Co
Regional Plar
Commission
Department of
City Planning
Los Angeles
P P
-
c
V
14
R]
Orange County
Planning Dep:
-
-_i
Orange County
Flood Contro!
District
PS
-
atmosphere
Land Disposal
Landfill of dewatered
solids
Land disposal of liquids
Ocean Disposal
Ocean discharge of sludge
Ocean discharge of liquid
was to
Reclamation-reuse
Pollutant emie8ions to
atmosphere
Use of processed packaged
soil conditioner
PS
PS
PS PS PS PS
PS
PS
F
PS
PS
PS
F
PS
N
L
L
L
L
P
P
PS
PS
PS
PS
PS
P
P
P
P
PS
PS
Use of raw or digested
sludge for soil condi-
tioning
PS PS
PS
PS
KEY TO LETTER CODE: P - Agency issues permits but not numerical standards
PS - Agency Issues permits which Include emission standards
N ~ Agency approves new disposal sites that have proved need and necessity
L - Agency has broad statutory authority but does not issue permits
F - Agency has a prohibition policy
2. opacity
3. particulate
matter
4. beryllium
5. mercury
6. nuisance
7. equipment
8. oxides of nitrogen
TABLES
Summary of Emission and Equipment Criteria
Relating to Sewage Solids Disposal to the Atmosphere
Parameter
1. Ringelmann
Federal
Environmental
Protection Agency
none
California Air Los Angeles Air
Resources Board -Pollution Control District
shall not be
2 Nu. 1 for more
than 3 minutes
Orange County Air
Pollution Control Dist.
shall not be
i No. 1 for more
than 3 minutea
-------
68
ALTERNATIVES FOR COASTAL CITIES
TABLE6
Summary of Regulatory Agency Disposal
Criteria Relating to the Eand
California State
Water Resources
Control Board
California Regional
Water Quality
Control Boards
Los Angeles
County Engineer
Orange County
Flood Control
District
1. Solid Waste
Z. Liquid Waste
Standards for land disposal of solid waste are adopted by all agencies on a case basis in
general conformance to disposal site classifications set forth in Subchapter 15,
Chapter 3, Title 23 of the California Administrative Code and presented in Appendix 2.
All agencies establish standards for land disposal of liquid waste on a case-by case basis.
TABLE?
Summary of Liquid Waste Disposal Criteria
for Discharges to the Ocean
Parameter
Liquid Waste
Grease and oil
5 Day 20° BOD
Suspended solids
Setteable solids
Floating participates
(dry wt. }
Turbidity
pH
Fecal coliform
Arsenic
Cadmium
Total chromium
Copper
Lead
Nickel
Silver
Zinc
Mercury
Aldrin
Dieldrin
Benzidine
FFD
DDE
DDT
Endrin
Cyanide
Total chlorinated hydro-
carbons
Polychlorinated biphenyls
Toxaphene
Phenolic compounds
Total chlorine residual
Ammonia (as N)
Toxicity Concentration
Raw sludge, digested
sludge, digester supernatant
all untreated
Units
mg/1
mg/1
mg/1
ml/1
mg/1
JTU
„ units
No/100
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
./J'g/l
^ug/1
yug/1
yUg/1
,-g/l
iA.0/1
mg/1
^g/1
^ug/1
>*g/l
mg/1
mg/1
mg/1
tu
Federal California
Environmental State Water
Protection Resources
Agency _ _ Control Board
30 3 454
30(3) 45(4)
none
none
n&ne
within .the limits
ml 200t3' 400<4'
none
0.32(7)
non
non
non
non
non
o.1W
c s(5) (7)
-> * ->
i.s'7'
0.6<6' <7>
»-*7
0.1<7)Q
none
10(7)
1.0
none
none
none
none
none
50 (1) 90 (2)
Percentile Per cent Lie
10
none
50
0. 1
1.0
50
6.0 to 9.0
none
0.01
0.02
0. 005
0.2
0..1
0. 1
0.02
0.3
0. 001
none
none
none
none
none
none
none
0. 1
2. 0
none
none
0.5
1.5
40
1.5
expressly
10
none
75
0.2
2.0
75
none
0.02
0. 03
0.01
0.3
0.2
0.2
0. 04
0.5
0. 002
none
none
none
none
none
none
none
0.2
4.0
none
none
1.0
2.0
60
2.0
prohibited
California
Regional Water California Coastal
Quality Control Zone Conservation
Bnard Cnmmiflflinn
50
Percentile
-o
rt
o
CQ
o
IH
O
U
(0
U
3
O
to
01
f-jf
cu
rt
o
a
to
-------
ALTERNATIVES FOR COASTAL CITIES
69
TABLES
Summary of Ocean Discharge Criteria
for Solid Wastes
Parameter
Units
Federal Environmental
Protection Agency
Cal. Regional
Water Resources
Control Board
Cal Regional
Water Quality
Control Boards
Cal. Coastal Zone
Conservation
Commission
Solid Waste
Mercury fc mercury mg/kg
compounds
Cadmium & cadmium mg/kg
compounds
Total organohalogena mg/kg
Oil and grease none
Wastes Containing
(a) Arsenic
(b) Lead
(c) Copper
(d) Zinc
(e) Selenium
(f) Vanadium
(g) Beryllium
(h) Chromium
(i) Nickel
(j) Oxygen consuming or
biodegradable matter
(k) Materials on any EPA
list of toxic pol-
lutants
0.75'
0.61
1.5
3.0
limiting permis. cone. "
no visible sheen when
material is added to
water in the ratio of
1:100 -waste to water
limiting permis. cone. *
5 o
o
3c
2solid phase
-liquid phase
that concentration of waste material or chemical constituent in the receiving water which, after
reasonable allowance for initial mixing in the mixing zone, will not exceed 0.01 of a concentration
shown to be toxic to appropriate sensitive marine organisms in a bioassay carried out in accordance
with approved EPA procedures or 0.01 of a concentration of waste otherwise shown to be detrimental
to the marine environment.
identification of all relevant evaluation factors; these
factors were then divided into four groups: economics,
environmental factors, feasibility factors and perform-
ance factors. The economic evaluation is relatively
straight-forward because the cost of the labor and ma-
terials necessary to construct and operate the alternative
sludge management systems can be expressed in mone-
tary terms. Factors in the other three groups reflect non-
monetary values and can only be evaluated in a subjec-
tive manner.
In order to determine the relative importance of each
factor in the eyes of the individuals affected by the alter-
native courses of action it is necessary to sample opinion
by interviews or questionaires. Every effort should be
made to poll an appropriate sample in order that the im-
portance values or weights assigned each factor reflect a
typical cross-section of public opinion. Because of
limited interests and time, a sampling of only wastewa-
ter treatment agencies and regulatory agencies along
coastal California was obtained during this study. Table
9 shows the averaged results of a sampling of 40 agen-
cies with a response of 15 agencies.
While the public is best qualified to weigh the indivi-
dual factors, only experts can provide a consistent and
fair rating of an alternative with respect to any factor
with the exception of aesthetics. The evaluation system
recognizes the subjective nature of most of the ratings,
TABLE9
Environmental Evaluation Values3
Environmental ,
Factors
Water Quality
Air Quality
Land Quality
Flora and Fauna
Aesthetics
Public Health
Community Impact
Resource
Conservation
ralues
9
8
6
6
6
9
6
5
Feasibility
Factors
Financ ial
Feasibility
Public
Acceptability
Land Use
Compatibility
Ease of Imple-
mentation
Values
9
8
7
6
Performance
Factors
System
Effectiveness
Reliability
Adaptability
Calamity
Resistance
Permanence
Values
9
8
5
6
6
^ased on a scale of 1 to 10; averaged results of survey; disposal and
regulatory agencies
but it is felt that alternatives should be consistently rated
among the same factors. A graduated and defined scale
was used to define rating numbers from zero (worst
case) to ten (best case or maximum benefit to the en-
vironment). The rating of an alternative with respect to a
certain factor can then be multiplied by the previously
assigned importance value or weight of that factor. The
weighted ratings can be summed within each evaluation
factor group and a score with respect to environmental
factors, feasibility and performance obtained for each
alternative.
Sludge Management Alternatives for
Southern California
The alternatives evaluated for the major Los Angeles
area dischargers included: (1) ocean disposal; (2) pro-
-------
70 ALTERNATIVES FOR COASTAL CITIES
cessingfor sale; (3) local landfilling; (4) landfilling at re-
mote sites; (5) evaporation ponds in Antelope Valley; (6)
reclamation of land in Antelope Valley; and (7) incinera-
tion . In each case appropriate treatment, such as anaero-
bic digestion and sometimes centrifuge dewatering, was
assumed for primary and secondary level wastewater
treatment sludges.
Ocean Disposal
Each of the three dischargers has in operation sepa-
rate wastewater treatment facilities and ocean outfalls.
Each discharger was considered a separate entity dis-
posing of sludge locally with regionalization offering no
advantages but containing a possible disadvantage in
discharging a greater mass of sludge within a limited
geographical area.
Processing for Sale
Los Angeles County composts dewatered digested
sludge on their property and sells it for less than the ac-
tual costs of composting. Orange County sells dewatered
digested sludge prior to composting. Envisioning a glut
on the market where all dischargers produce this ma-
terial , the sale price of compost to commercial packagers
will drop significantly and for purposes of analysis was
assumed to be zero.
Centrifuge centrate, which is estimated at 85 percent
by volume of the feed liquor would be discharged back to
the wastewater treatment system. Wastewater treat-
ment facilities would be incrementally larger to accomo-
date this waste and an incremental rise in effluent con-
stituents may be noticed.
Local Landfilling
Each of the three dischargers has several sanitary
landfills, of Class II or better, located within 35 miles of
their facilities and at least one major landfill within 20
miles. The disposal of dewatered sludges to a sanitary
landfill can be considered as a solution to a solid waste
disposal problem.
Remote Landfilling
It was assumed that it may become necessary to truck
dewatered sewage sludges 100 to 130 miles to an inland
disposal site.
Antelope Valley Evaporation Ponds
Doubts concerning the handling of sewage sludge
centrate led to the development of common pipeline
transport and disposal facilities to pump digested
sludges to the high desert in the Antelope Valley to take
advantage of an evaporation rate of six ft/yr.
Evaporation ponds based upon a design loading of
three ft/yr would dry the sludge to 40 percent solids after
which the sludge would be placed in a local landfill. Fed-
eral land for the ponds was assumed available at no
charge.
Antelope Valley Soil Reclamation
Digested sludge would be pumped to a 40 million gal-
lon storage lagoon in Antelope Valley. Based upon the
Lahontan Regional Water Quality Control Board's appli-
cation limit of two Ib/acre of total nitrogen per day,
76,000 acres would be needed to accommodate the sew-
age sludge. To utilize the reclaimed soil as farmland, 271
million gallons/day of irrigation water would be needed.
This quantity of water does not appear to be available;
and the use of sewage sludge on currently productive
land is not recommended6'7; therefore, no farming
disposal system exists in the Southern California coastal
area. Because the transport of treated wastewaters for
irrigation appeared infeasible, this alternative was
dropped.
Incineration
A separate multiple-hearth incinerator with air-pollu-
tion control equipment was assumed for each treatment
facility complex. Vacuum filters would dewater raw
sludges to 35 percent solids, sufficient to maintain com-
bustion, and incinerator ash would be trucked to a local
landfill.
Comparison of Alternatives
Preliminary cost estimates for southern California
conditions were based upon annualized capital, operat-
ing and maintenance costs and reclamation revenue and
included the entire processing train for each alternative,
with credit given for existing facilities. Table 10 shows
combined costs for the three agencies.
The relative ranking of the alternatives with respect to
environmental considerations, feasibility and perform-
ance together with the principal difficulty associated
with each alternative is shown in Table 11. Figure 1 com-
pares graphically the characteristics of the alternatives.
Weighted ratings forthe alternatives are included in Ap-
pendix A.
The comparative ranking of alternatives demonstrates
that the least-cost solution for municipalities with exist-
ing ocean outfalls is ocean disposal at $3.4 million an-
naually. The next best solution, at over double the an-
nual cost, is composting. Incineration and local land-
filling are within $1 million annually of each other at
TABLE 10
Costs of Alternatives
Alternative
Cost, $/metric ton
dry solids
Ocean Disposal
Processing for sale
Local landfill
Remote landfill
Evaporation and landfill
Soil Reclamation
Incineration
20
25
44
48
58
30
-------
ALTERNATIVES FOR COASTAL CITIES
71
TABLE 11
Non-Monetary Evaluation
of Alternatives
Ranking
Alternative mental bilitv
Processing for 1 1
sale
Local landfill 2 2
landfill
Soil reclamation - unranked -
Incineration 3 4
mance Problem s
environment
6 Unpredictable market for
soil amendments
5 Dwindling capacity of
acceptable sites
venience community
pipeline transport
Unavailability of supple-
3 Adverse effects on air
quality
_1 3OO
I!
O< 250
0:0:
UJ
250
~.
•:•:
V
•'.•
ALT. 5
LT. 4 ~~
?j ALT 5
—
5 10 15 20 25
TOTAL ANNUAL COST, million dollar*
Figure 1: Comparison of Alternatives.
$11.8 and $12.8 million, while the remote disposal
schemes in the Antelope Valley or remote landfills are
the most expensive at $19 or $25 million annually.
The best environmental rating was achieved by com-
posting for sale, followed by local landfilling and in-
cineration. The most detrimental environmental ratings
were achieved by remote disposal options. In terms of
feasibility for implementation, composting for sale and
local landfilling scored best, followed by ocean disposal
and incineration. Again, the poorest alternatives were
remote disposal.
Performance rating, which measures simplicity and
continuity of operation along with proven dependability,
rated the remote disposal options the highest followed
closely by incineration, ocean disposal and local landfill,
while the poorest alternative was composting for sale.
The low rating of composting for sale was influenced by
expected limitation in the market's ability to absorb
compost.
CONCLUSIONS
Based upon the evaluations of the original seven alter-
natives, it would appear desirable to select composting
for sale for each of the major agencies. Environmental
risks are minimized and in fact some benefits are reali-
zed with composting. The system has very good public
acceptability, land use compatibility, ease of implemen-
tation and financial feasibility. The performance rating
could be substantially upgraded by allowing excess
sludge production above market capacity to be buried at
a local landfill. To a large extent this is the system being
employed at Los Angeles and Orange Counties and indi-
cates that natural selection processes of public pressure,
economic considerations and environmental awareness
have been at work.
It should be noted however that ocean disposal re-
mains the least cost option by a wide margin. It would be
a misallocation of resources to abandon ocean disposal
entirely unless it is clearly demonstrated that its envi-
ronmental impact is greater than that of the more costly
alternatives.
REFERENCES
1. An Analysis of the Sewage Sludge Disposal Prob-
lem in Southern California, Engineering-Science, Inc.
and J.B. Gilbert & Associates, 1974.
2. Whitman, IraL., etal., "Design of an Environmen-
tal Evaluation System," Batelle-Columbus Laboratories
report to the Bureau of Reclamation, U.S. Department of
the Interior, 1971.
3. Dee, Norbert, et al., "An Environmental Evalua-
tion System for Water Resource Planning," Water Re-
sources Research, 9, No. 3 pp 523-535.
4. Odum, E.P., et al., Optimum Pathway Matrix
Analysis Approach to the Environmental Decision Mak-
ing Process, Institute of Ecology, University of Georgia,
Athens, Georgia, 1971.
5. "Guidelines for Implementing Principles and
Standards for Multi-Objective Planning of Water Re-
sources," by the U.S. Bureau of Reclamation, review
draft, December 1972.
6. Recycling Treated Municipal Wastewater and
Sludge through Forest and Cropland, Eds. Sopper,
W.E. and Kardos, L.T., Penn State University, Uni-
versity Park and London, p. 95, 1973.
7. Recylcing Municipal Sludges and Effluents on
Land, U.S. Environmental Protection Agency, July
1973.
-------
72
ALTERNATIVES FOR COASTAL CITIES
APPENDIX A
Evaluation Data
ALTERNATIVE
#4 Remote Landfill
UNWEIGHTED PARAMETERS
WEIGHTED PARAMETERS
Figure A-l: Evaluation of Alternatives.
ALTERNATIVE
#6 Antel ope Reclamati on
UNWEIGHTED PARAMETERS
WEIGHTED PARAMETERS
Figure A-l (Continued): Evaluation of Alternatives.
-------
BY-PRODUCT SOLIDS MANAGEMENT
ALTERNATIVES CONSIDERED FOR PHILADELPHIA
ElmerF. Ballotti and ThomasE. Wilson
Greeley andHansen
Chicago, Illinois
INTRODUCTION
The City of Philadelphia Water Department, Water
Pollution Control Division is responsible for the opera-
tion of wastewater collection and treatment for the City
of Philadelphia as well as a number of suburban com-
munities adjacent to the city. The tributary population to
the city plants is estimated to be about three million and
is projected to reach about 3,600,000 in 1990. The city
operates three plants as follows:
Estimated Flow MGD
1975 1990
1. Northeast
2. Southeast
3. Southwest
Total
170
130
175
475
250
150
245
645
By-product solids removed in the three Philadelphia
plants in 1974 amounted to about 270 dry tons per day of
raw solids not including grit, scum and screenings.
These raw solids are stabilized by anaerobic digestion,
and further processed in on-site holding basins to in-
crease their solids concentration to about ten percent.
The stabilized solids slurry are then dispersed into the
ocean at a point approximately 50 miles off shore.
After completion of the current program of expansion
and facilities improvement, it is projected that the raw
by-product solids, not including scum, grit and screen-
ings, removed in the design year 1990 will be about 518
tons per day, which is about 14,800 wet tons per day at
3'/2 percent solids. The stabilized solids quantity pro-
jected for 1990 is 332 dry tons per day which is about
9,500 wet tons per day at 3Va percent solids.
The dispersal of stabilized solids slurry at sea was ini-
tiated by the city in 1961 in an area eleven miles off shore
and moved to the present dispersal site 50 miles off
shore in May, 1973, a total one way distance of about 150
miles from the city. Since 1961, the city has arranged for
a number of studies to consider the effects of manage-
ment practices related to by-products removed from the
Philadelphia Wastewater Treatment Facilities. In 1972,
a comprehensive study of management alternatives re-
lated to by-product solids was undertaken with the re-
sults summarized in a written report dated June, 1973,
under the title, Report on Management of By-Product
Solids from Water Pollution Control Plants. After com-
pletion of the 1973 report further studies have been con-
tinuously underway to update the report findings, ex-
plore new alternatives and codify the results of addi-
tional investigations.
This presentation is a synopsis of the data, investiga-
tions, studies, discussions and other considerations
given to the concept of managementof by-product solids.
Basic Data
The by-products of water pollution control plants in-
clude screenings, grit, scum and other wastewater solids
removed as settleable solids in the primary and final
tanks. Facilities will be incorporated in the proposed ad-
ditions to the northeast, southwest and southeast plants
to process screenings, grit and scum in separate incin-
eration units. These are not considered in this presenta-
tion. In connection with the processing of the remaining
wastewater solids removed in the water pollution control
plants, a number of alternatives have been considered.
The quantities and characteristics of these solids have
been summarized, as well as the design bases used in
considering alternatives.
Based on the records maintained by the City of Phila-
delphia Water Department, the total pounds and volume
of raw solids have been estimated as shown in Table 1.
Included are estimates of the solids captured in the pri-
mary tanks, excess solids produced in the existing air
activated sludge plant at the Northeast Plant and excess
solids from the proposed new Northeast, Southwest and
Southeast oxygen activated sludge plants.
Data on physical and chemical characteristics of both
the raw and stabilized Philadelphia solids are limited.
Furthermore, it is believed that a number of the charac-
teristics will change significantly when the current pro-
gram of additions to the water pollution control plants
are completed. Table 2 presents recent data obtained on
73
-------
74 BY-PRODUCTS SOLIDS MANAGEMENT ALTERNATIVES
TABLE 1
Estimated Solids Quantities
TABLE3
Design Bases1
Description
Sewage Flow-Mgd
Raw Solids
Dry Tons Per Day
Million Gallons Per Day
At 3
-------
BY-PRODUCTS SOLIDS MANAGEMENT ALTERNATIVES 75
TABLE4
Basic Alternatives
1. Biological Processes
1. Sea dispersal of approximately 10 percent
stabilized solids at Q point His miles
off shore.
2. Sea dispersal of 12 percent stabilized
solids at a point 11*5 miles off shore.
3. Sea dispersal of 3*5 percent stabilized
solids at a point 50 miles off shore.
4. Land dispersal of stabilized solids slurry
by center pivot irrigation.
5. Land dispersal of stabilized solids slurry
by traveling gun irrigation.
6. Land dispersal of stabilized solids slurry
by solid set irrigation.
7. Land dispersal of stabilized solids slurry
by plow-in procedure.
8. Land dispersal of stabilized solids slurry
by tanker application.
9. Land dispersal of stabilized solids cake
by trenching procedures.
10. Land dispersal of stabilized solids cake
by spreading and incorporating.
11. Land dispersal of stabilized solids cake
by landfilling.
12. Land dispersal of stabilized and composted
solids cake.
2. Physical-Chemical Processes
13. Incineration of raw by-product solids.
14. Pyrolysis of raw by-product solids.
15. Heat drying of raw by-product solids.
received and considered by the city have been cate-
gorized by application as follows:
Category A Disposal
Alternatives related to disposal of by-product solids
presently stored in open lagoons on the site of the
Southwest Water Pollution Control Plant.
Category B Combination Disposal
Alternatives related to combining wastewater treat-
ment by-product solids with municipal refuse.
Category C Resource Recovery
Alternatives relatedto recovery of energy, nutrients
and other resource by-products such as metals.
Description of Alternatives
Because many of the alternatives identified differed
conceptually with regard to the overall processing of raw
by-product solids, the studies made are related to "raw"
solids. The descriptions included herein are based on
outlining the solids processing steps necessary to con-
vert the raw material to the final by-products.
Biological Processes Sea Dispersal
Sea dispersal of by-product solids comprises a two
step procedure of stabilization and hauling. The studies
were based on expanding the existing facilities for stabi-
lization by anaerobic raw solids digestion. The hauling
method considered was based on the continued use of a
pipeline to a nearby dock where stabilized solids slurry
are discharged into a barge for transporting to the dis-
persal site, approximately 50 miles from Cape May. A
number of sub-alternatives have been considered and
are described as follows:
Alternative 1. Dispersing stabilized solids slurry par-
tially dewatered to about ten percent solids in existing
lagoons, adding only the stabilization facilities required
for the projected 1990 quantities. This is referred to as
present practice.
Alternative 2. Dispersing stabilized slurry, partially
dewatered to about twelve percent solids, by adding me-
chanical solids dewatering equipment for all solids and
the additional stabilization facilities necessary for the
projected 1990 solids quantities.
Alternative 3. Dispersing unthickened (3V2 percent
solids) stabilized solids slurry, adding only the stabiliza-
tion facilities required for the projected 1990 solids
quantities. All sea dispersal alternatives include an al-
lowance tor environmental monitoring of the dispersal
site.
Biological Processes Land Dispersal
As in sea dispersal the land dispersal alternatives in-
clude the two steps of stabilization and hauling.
To estimate the cost of dispersing stabilized solids on
land with an accuracy similar to sea dispersal, it would
be necessary to identify a specific land dispersal site
since the dispersal costs are highly sensitive to such
variables as distance from Philadelphia, topography of
land, availability, location, access, etc. These considera-
tions are of paramount importance, particularly avail-
ability, since previous attempts to use Pennsylvania land
for dispersal of solids have been met with significant dis-
cussion from the general public. However, in order to
make comparisons, certain illustrative assumptions and
cost allowances have been made and are generally sum-
marized in the following herein.
Eight of the nine land dispersal alternatives con-
sidered were categorized as land reclamation or fertili-
zation, except for the landfilling alternative which is con-
sidered disposal with no additional benefits. According-
ly, it was concluded that as such, the eight alternatives
must meet the application limits stated on the proposed
(draft) U.S. EPA guidelines*. Applying these guidelines
to the Philadelphia solids, and using the modified equa-
tion included therein with the expected soils in Pennsyl-
vania, the maximum allowable loading would be 60 tons
of dry, stabilized solids per acre. The CEC value of
twelve used in the computation was based on studies
*Acceptable Methods for Utilization or Disposal of Sludges (EPA 430
(9-75) Technical Bulletin.
-------
76
BY-PRODUCTS SOLIDS MANAGEMENT ALTERNATIVES
made by the U.S. EPA at a potential site selected by the
U.S. EPA. For a 30-year project life, this would
correspond to an average loading of two tons of
stabilized dry solids per acre per year as used for the
eight land reclamation alternatives. For landfilling,
however, the solids application arrangement considered
would result in an equivalent loading of 675 tons per acre
per year.
It has been also assumed that land would be pur-
chased by the city for eight of the nine land dispersal al-
ternatives considered. Furthermore, because land avail-
ability appears to be a serious impediment and cursory
investigation indicates that only remote land dispersal
sites may be available, it has been assumed that a trans-
fer point would be located 100 miles from Philadelphia
for all cases.
Recent experiences, in other areas of the United
States, have indicated that significant adverse public re-
action can develop to odors identified as originating from
open storage lagoons and solids slurry spray irrigation
operations. For this reason, the solids slurry storage
facilities for land dispersal alternatives include costs re-
quired to cover the storage lagoons. In the case of odors
developing from spraying a solids slurry into the atmos-
phere, no countermeasure has been identified or in-
cluded. Forthis reason, alternatives based on solid slur-
ry spraying are not considered realistic and are included
only for illustrative purposes.
Solids Slurry - 31A Percent Solids
The land dispersal methods utilizing a solids slurry of
3'/2 percent solids concentration were considered to in-
corporate a pipeline from Philadelphia to a transfer point
100 miles away. Pumped slurry would be discharged into
covered storage facilities and either repumped or
trucked to the point of final application. The following
alternatives were considered:
Alternative 4. Center Pivot Irrigation
Alternative 5. Traveling gun Irrigation
Alternative 6. Solid set Irrigation
Alternative 7. Plow-in
Alternative 8. Tanker application
The first two alternatives incorporate a system of moving
sprays and the third has an immobile set of sprinkling
nozzles. The systems would include a central pumping
station at the transfer point and a piping network to the
individual application areas.
In the plow-in alternative, slurried solids would be ap-
plied by an altered moldboard plow through a flexible
hose. As a field is plowed, a layer of solids would be ap-
plied and covered with six inches of soil. A pumping sys-
tem similar to the above arrangement would be used.
Slurry spreading by tank trucks is a method which has
been popular for small scale solids dispersal operations.
The solids are delivered to private land owners onto
whose land it would be discharged as the (Water Depart-
ment owned) trucks drive across the field. While this al-
ternative eliminates the need for land purchase, it does
require arrangements with numerous farmers possibly
2000 or more that would impose a serious logistical prob-
lem which has not been completely identified as part of
these studies.
Solids Cake 20 Percent Solids
For these studies, four methods utilizing solids cake
(20 percent solids) have been considered as follows:
Alternative 9. Trenching
Alternative 10. Spreading and Incorporation
Alternative 11. Landfill
Alternative 12. Composting - Spread and Incorporate
The solids cake alternatives were based on unit train
transportation of cake to a transfer point 100 miles from
the city from which cake would be trucked to the point of
application. Since all of these alternatives require that
trucks travel across fields, none may be used on wet
ground.
For trenching operations, solids would be deposited in
shallow trenches about two feet deep and two feet wide
and two feet apart and covered with soil.
In the spread and incorporate alternative, spreading
of solids on the surface of land would be done by trucks
or wagons and incorporation would be accomplished by
plowing, discing or rotary tilling.
Landfilling is similar to trenching except that the land-
fill cavities would be larger and deeper than trenches.
The solids would be compacted and covered. Since this
method of dispersal would have high application rates,
care must be taken to prevent groundwater pollution.
For the composting - spread and incorporate alterna-
tive, it has been assumed that stabilized solids would be
chemically conditioned and dewatered by means of a fil-
ter press to a cake containing about 35 percent solids.
This cake would be transported by truck to a separate
composting plant where it would be combined with
municipal refuse and composted.
In the original studies, composting was based on the
assumption that part of the costs of mixing by-product
solids with refuse would be absorbed by the municipal
refuse supplier. Alternatively, the by-product solids
might be composted with recoverable wood chips at a
similar total cost, or composted in situ without any other
additional products. The compost would then be hauled
by truck to farm land and dispersed by the spread and in-
corporate method of application. As an alternative
means of ultimate dispersal, for which cost estimates
were not prepared, the compost could be made available
and given away at the composting site with no ultimate
dispersal costs being incurred. However, because the
total volume is great, it is doubtful that private citizens
could accomplish the total hauling project.
Physical Chemical Processes
All of the physical-chemical processes considered use
thermal energy to condition and convert, dewater or re-
-------
BY-PRODUCTS SOLIDS MANAGEMENT ALTERNATIVES 77
duce raw wastewater solids. The three alternatives
which were considered are as follows:
Alternative 13. Incineration
Alternative 14. Pyrolysis
Alternative 15. Heat Drying
For the incineration alternative, it has been con-
sidered that, prior to incineration in a multiple hearth
furnace, the waste activated sludge solids would be
thickened and combined with primary solids. The solids
mixture would then be stored in holding tanks from
which they would be fed to a low pressure heat treatment
process for conditioning before being applied to a
vacuum filter to form a 35 to 40 percent solids cake. This
auto-combustible cake would be fed to the incinerator.
The gases from the incinerator would be scrubbed and
the ash would be hauled to a landfill.
Pyrolysis is an incineration type process where burn-
ing is carried out in an oxygen deficient atmosphere and
the organic material does not lose all of its fuel value.
Pretreatment of raw by-product solids would be similar
to incineration. A product char, and possibly gases
which are condensable to oils and tars, with fuel value
could be obtained. However, volume reduction would
not be as great as with incineration and input energy re-
quirements would be higher. Pyrolysis would, of course,
sterilize the solids. At the time of the original studies
there was insufficient information available to develop
detailed construction and annual maintenance and oper-
ation cost estimates for pyrolysis.
Heat drying is similar to incineration, except that the
heating processes are stopped before the solids can be
oxidized, producing a product containing nutrients and
humus which can be marketed as fertilizer. Pretreat-
ment of raw solids would be similar to incineration. Dry-
ing systems may be designed to be flexible enough to dry
or incinerate. However, the fuel requirements of drying
would be higher than incineration, since the solids are
not burned. For these studies the costs estimated in-
clude bagging the unfortified product for distribution.
Special Category Alternatives
In addition to the biological and physical chemical pro-
cesses, a number of special category alternatives were
identified and grouped in the following categories.
Category A Disposal. Disposal methods suggested
for the removal of lagooned solids at the Southwest
Treatment Plant site to provide a pathway for the con-
struction of Highway 1-95 by the Pennsylvania Depart-
ment of Transportation have identified a number of al-
ternatives including transporting the material to other
parts of the state, other parts of the world (such as the
Bahamas), the conversion of the lagooned solids to a
building material and the conversion of the lagooned
solids to a landfill material. One such process is solidifi-
cation .
In this alternative, proprietary chemicals would be
mixed with the lagooned solids and, according to the
manufacturer, in about three days the mixture would
solidify to an inert, clean, nonpolluting product suitable
for landfill. Based on our understanding of the process,
it appears that there is no volume reduction and that
there may be a volume increase.
Category B - Combination. A number of the alterna-
tives suggested incorporate the ultimate disposal of the
treatment plant by-product solids with municipal refuse.
While the proposed alternatives are not limited to com-
bined treatment with municipal refuse, they are grouped
herein because the proposals, as outlined to the city, did
incorporate municipal refuse. The following combined
recovery process alternatives proposed by others were
reviewed and are briefly described based on data sub-
mitted with the rudimentary proposals:
1. This process would receive a wet slurry of about
3'/2 percent solids and include equipment to de-
water the slurry to 17 percent solids. This cake
would be spray dried to about 75 percent solids us-
ing the exhaust gases from the final process step
which could be fed to either a rotary kiln or a py-
rolysis unit. Refuse would be introduced at an ap-
propriate point in the flow sheet.
2. Wastewater treatment plant by-product solids
would be burned with municipal refuse in water
walled boilers to produce low pressure steam.
3. Wastewater plant by-product solids would be
mixed with wet pulped and classified refuse and
the mixture incinerated in a fluidized bed incinera-
tor. Energy recovery, and/or the recovery of met-
als, glass and paper pulp would be possible objec-
tives.
Category C - Resource Recovery. A number of alterna-
tives have been suggested that are based on receiving
wastewater treatment plant by-product solids as pri-
mary input and subjecting them to a process designed to
recover those resources in the solids that can be recycled
as useful products. The basic resources recovered in the
proposed alternatives are nutrients and metals. The pro-
jects considered based on data submitted or developed
in the studies are briefly described as follows:
1. Wet raw by-products solids would be mixed with
appropraite amount of urea and formaldehyde. The
mixture would be heat dryed, packaged and sold as
a fertilizer with a chemical composition of about
12-4-0.
2. Wet raw by-products solids would be heat dryed
using a proprietary dryer. The dried material, with
a chemical composition of about .6-4-0, would be
packaged for sale.
3. Raw by-product solids slurry at about 3'/2 percent
solids would be discharged into an acid reactor,
heated to about 450°F at a pressure of about 600
psi. It is our understanding that heavy metals, am-
monia, organics, etc., could be separated and re-
covered.
-------
78
BY-PRODUCTS SOLIDS MANAGEMENT ALTERNATIVES
Anhydrous and Liquid Ammonia Recovery: Raw
by-product solids would be stabilized by anaero-
bic digestion to produce excess methane as well as
reduce solids quantities. The system would be de-
signed to convert excess methane to anhydrous
ammonia, to concentrate digester supernatant to a
liquid ammonium phosphate and to dewater and
acid leach the solids to remove the bulk of heavy
metals.
DISCUSSION OF ALTERNATIVES
The alternatives considered for by-product solids
management have been classified as biological, physi-
cal-chemical and special category processes. The alter-
natives considered for land and sea dispersal of
stabilized solids were characterized as biological pro-
cesses since anaerobic digestion of the raw by-product
solids was the first step in each.
Based on rudimentary studies, the Anhydrous and Li-
quid Ammonia Recovery alternative appears to have po-
tential for converting the nitrogen content of the raw
solids and the energy in the volatile suspended solids
into readily usable form. Preliminary cost estimates, not
included herein, indicate that the process is cost effective
and it has been recommended for further consideration.
Based on the studies made of the 15 alternatives con-
sidered, the data shown in Table 5 present a summary,
by annual costs, of these alternatives. Further, in order
to consider the effects of energy and nutrient character-
istics of each alternative, a cost comparison was de-
veloped which considers, in addition to the annual costs,
the energy consumption and nutrient production of each
alternative. This is shown in Table 6.
Among the sea dispersal alternatives, it is clear that
some dewatering is necessary to reduce the total annual
cost of the alternative. The exact amount of dewatering
that is optimum is a function of barging costs.
TABLES
City of Philadelphia
Unit Cost of 1975 Alternatives
May, 1975
amortization
Alternative
Treat-
ment
Transpor-
tation
Total
Ultimate Amort.
Dispersal Cost
Operation and Maintenance
Treat-
ment
Transpor-
tation
Ultimate
Dispersal
Total
Total Annual
O&M Cost Cost
Sea Dispersal
1. Present Practice 12.88 0.00 0.00 12.88 6.53 13.00
2. 12% Solids, Mechanical
Dewatering 14.51 0.00 0.00 14.51 15.58 13.00
3. 3>3 Solids 12.88 0.00 0.00 12.88 6.53 44.00
Land Dispersal
4. Center Pivot Irrigation!!) 12.62 14.56 65.30 92.48 6.47 4.27
5. Traveling Gun Irrigation!!) 12.62 14.56 65.30 92.48 6.47 4.27
6. Solid Set Irrigation!!) 12.62 14.56 72.64 99.82 6.47 4.27
7. Plow-in 12.62 14.56 69.58 96.76 6.47 4.27
8. Tanker (2) 12.62 14.56 13.93 41.11 6.47 4.27
9. Trenching 14.30 0.00 65.43 79.73 25.74 7.25
10. Spread & Incorporate 14.30 0.00 65.43 79.73 25.74 7.25
11. Landfilling(3) 14.30 0.00 5.07 19.37 25.74 7.25
12. Composting with Land
Dispersal 19.24 0.00 64.84 84.08 32.76 8.95
Physical-Chemical
13. Incineration 42.43 0.00 0.00 42.43 37.68 0.79
14. Pyrolysis
15. Heat Drying 44.85 0.00 0.00 44.85 76.85 0.00
0.59
0.59
0.59
2.59
4.35
2.08
7.10
36.74
9.41
10.49
7.13
10.49
29.17
51.12
13.33
15.09
12.82
17.84
47.48
42.40
43.48
40.12
52.20
43.68
64.00
105.81
107.57
112.64
114.60
88.59
122.13
123.21
59.49
136.28
0.00 38.47 80.90
No Basis for Estimate
0.00 76.85 121.70
All costs are dollars per ton of dry raw solids. No credits for any products.
1) Not acceptable because of odor problems.
2) Severely limited because it can be applied to grass crops only.
3) Not attractive because it takes useful land out of service.
Some of the special category processes as well as the
physical-chemical processes require significant energy
to reduce and convert the by-product solids. Because the
special category alternatives require either more de-
velopmental work, combination with other projects, a
specific commitment or further study, it was not possible
to establish a common comparative base. However,
those special category processes which produce market-
able dry fertilizers were considered to be variations of
the heat drying alternative.
Among the land dispersal alternatives, it should be
noted that the costs are highly sensitive to a number of
criteria for which only rudimentary estimates could be
made at the time. The criteria which these alternatives
are most sensitive to are those involving choice of solids
application rate, number of acres of land purchased and
capital costs of land purchased. Table 7 illustrates this
sensitivity. Note, for example, the marked effect of
changing annual solids slurry application rate of 20 T/A
(as used in the original studies) to 2 T/A (based on 60
-------
BY-PRODUCTS SOLIDS MANAGEMENT ALTERNATIVES 79
TABLE6
Comparison of Alternatives on Unit Basis, Taking
Credit for Energy and Nutrients Available
Alternative
Total Annual
Cost Energy
Net
Cost
Sea Dispersal
1. Present Practice
2. 12% Solids, Mechanical
Dewatering
j. 3-l"i Solida
43.68 -2.92
64.00 -2.43
0.00
0.00
0.00 40.76
0.00 61.57
Land Dispersal
5.
6.
7.
8.
9.
10.
11.
12.
Traveling Gun Irrigation
Solid Set Irrigation
Plow-in
Tanker Application
Trenching
Spreading and Incorporate
Landfilling
Composting with Land
Dispersal
107.57
112.64
114.60
B8.59
122.13
ng 123.21
59.49
136.28
-3.70
-3.70
-3.70
-3.70
-2.86
-2.86
-2.86
-2. 54
-13.32
-13.32
-19.03
-13.32
- 8.20
- 8.20
0.00
J.60
-
-
-
-
-15
-15
0
-13
53
53
53
53
53
33
33
00
03
73.02
78.09
74.34
54.04
95.74
96.82
56.63
117.11
Physical Chemical
13.
14.
15.
Incineration
Pyrolysis
Heat Drying
60.90
Ho Basis
121.70
4.41
20.41
0.00
-13.32
0
-17
00
53
. 85.31
No Basis
111.26
All costs are dollars per ton of raw, dry*solids.
N is valued at S300/T N H3 ($365 /T N).
P is valued at S500/T P.
Energy is valued at Sl.OO/million Btu.
TABLE?
Effect of Loading Rates and Land Costs
Plow-In Alternative
Amortized Cost
Land"
Total
O & M
Total
Cost
a. 20 T/A/yr
1
2
3
b. 2
1
2
3
. @ $400/A 1
. @ $1000/A -1
. @ $3000/A 1
T/A/yr
. @ $400/A 1
. @ $1000/A 1
. @ $3000/A 1
$
$
$
$
$
2.
6,
18,
24.
61,
$184.
.46
.14
.42
.56
.41
.23
$
$
$
$
$
37
40
53
59
96
$218
.05
.73
.01
.15
.76
.84
$17.
$17.
$17.
$17.
$17.
$17.
.84
.84
.84
.84
.84
.84
$ 54.
$ 58.
$ 70.
$ 76.
$114.
$236.
.89
.57
.85
.99
,60
.68
1. This is considered the net purchase price and in-
cludes allowance for selling at a future date and
initial development of land.
T/A over project life of 30 years). The effect of purchas-
ing land at $400/acre or $3,000/acre in capital cost is
dramatic. The $l,000/acre cost, as used for these
studies, includes net purchase cost (purchase price less
present worth of future sale price) and land forming
costs.
The amount of land required for land dispersal must
be considered. At 60 T/A (2 T/A/yr. for 30 years) load-
ing rate 60,000 acres are required. Based on a utility
factor of 50 percent of any land purchased as suitable for
dispersing of solids, the total acreage required would be
about 120,000 acres. This is equal to about half the tribu-
tary area served by the Water Department. In addition,
based on these studies, it appears that most of the po-
tentially available acreage is available only in small par-
cels averaging 63 acres each. On this basis, about 2,000
farms would be included in a land dispersal project.
The management input is further complicated by the
fact that the center of operation most likely would be lo-
cated at some distance from the water department oper-
ations center. Topographic observations made from map
studies and reconnaissance level field investigations
identify the rolling irregular nature of the Pennsylvania
countryside adjacent to Philadelphia. The land features
coupled with the large number of small farms, many
angularly formed by a crisscrossing of roads and proper-
ty lines, underscore the complex nature of site selection
and site development of land tracts large enough to per-
mit a land dispersal program.
CONCLUSIONS
The studies made in connection with our work for the
City of Philadelphia indicated that the biological pro-
cesses generally ranked better than the physical-chemi-
cal processes considered from a cost, energy, and nu-
trient utilization standpoint.
A number of land dispesal alternatives utilizing
anaerobically digested solids appear to have potential as
acceptable management programs that may be effective
from a cost, energy and nutrient standpoint. However,
any land dispersal alternative requires a great deal of
land area and requires significant management input to
resolve far reaching logistical problems associated with
dispersal operations.
The significance of this problem can only be visualized
in broad terms at this time. At this time, it does not ap-
pear that a land dispersal alternative, for the total
amount of solids removed in Philadelphia, is feasible.
The sea dispersal alternative, also utilizing anaerobic
digestion as the stabilization process, has proven to be
simple, economical and easily controlled. The escalating
cost of barging to sea may require further study of alter-
natives related to optimizing barging costs, however.
Continuation of sea dispersal depends upon continued
demonstration of the fact that sea dispersal, as practiced
by Philadelphia, is not detrimental to the ocean.
Preliminary feasibility studies of the anhydrous and
liquid ammonia alternative are promising. This alterna-
tive utilizes anaerobic digestion and converts excess di-
gestion gas to the form of fertilizer commonly used for
crop fertilization in the United States. Additional studies
of the process have been recommended, including pilot
work, cost studies, equipment requirements and
product management studies. As a further area of in-
terest, it is important that studies of the means and me-
thods of improving gas production in anaerobic diges-
tion process be investigated.
-------
SLUDGE DISPOSAL ALTERNATIVES FOR BOSTON
George D. Simpson,
Havens and Emerson, Ltd.
Cleveland, Ohio
INTRODUCTION
The Metropolitan District Commission (MDC) of Bos-
ton owns and operates two major treatment plants, the
Deer Island and Nut Island Treatment Plants, which re-
ceive a combined average daily flow of about 450 mgd,
and serve a population of about 2.2 million. Both of these
treatment plants provide preparatory and primary treat-
ment, anaerobic sludge digestion, and disinfection.
Treated effluent is discharged through submerged out-
falls to Boston Outer Harbor; digested sludge is dis-
charged to the Harbor at the President Roads channel
during ebb tide, from which point sludge is carried to
sea.
This method of sludge disposal is considered inade-
quate, and the MDC has investigated alternative me-
thods of sludge management. The MDC Boston Harbor
Task Force stuided six alternatives for sludge manage-
ment in 19721 and recommended that a detailed design
study be undertaken to consider three specific methods
of sludge management: application to land; dewatering
and incineration; and wet air oxidation2. This paper pre-
sents the results of the study of these alternative me-
thods, and describes the recommended project plan and
its environmental assessment.
Alternatives were evaluated in light of four basic ob-
jectives of a good sludge management plan:
1. To stabilize organic matter and reduce the sludge
volume.
2. To recover and recycle useful elements or energy to
the greatest extent feasible.
3. To provide final disposal of residues at the lowest
total annual cost.
4. To minimize adverse impacts on the water, land
and air environments.
Preliminary Studies
Sludge Characterization
Preliminary studies included basic data such as popu-
lation, flow evaluation of the existing plants, and labora-
tory analyses of sludges collected from each plant, with
projections of sludge characteristics from the future
secondary treatment processes. Results of the analyses
and projections are shown in Tables 1 and 2. The data
shows that sludge from both plants is relatively high in
heavy metals; and that the Deer Island sludge contains
unusually high concentrations of chlorides and other dis-
solved salts resulting from sea water intrusion into the
sewer system. These factors influenced the evaluation of
alternative plans of sludge management.
TABLE 1
Population, Flows, and Sludge Quantities
,(0
n<2>
,(2)
Population Served:
Deer Is. 1,345,000
Nut Is. 625,000
AVG. Wastewater Flow, Mgd.
Deer Is. 321
Nut Is. 123
Raw Sludge Quantities^
a) Total Dry Solids, tons/day
Deer Is. 85
Nut Is. 60
B) Volatile Dry Solids, tons/day
Deer Is. 61
Nut Is. 48
1,393,000
691,000
334
141
103
75
75
59
1,430,000
757,000
347
157
202
129
149
100
1,551,000
959,000
390
210
233
169
170
127
(1) Based on Primary Treatment
(2) Based on Secondary Treatment
(3) Quantities Exclude Grit, Screenings 5 Skimmings, which for
1995 Conditions Increase the Dry Solids Mass by 7.4 Percent.
Purchased Power
At both treatment plants, all power needs are supplied
by direct engine drive or by electric generators driven by
dual fuel engines; no outside power connection is used.
Detailed cost investigations were made to determine
whether in-plant power generation was economical in
comparison with purchased power under current condi-
tions. It was found that in-plant generation at Deer
Island using digester gas as fuel is about 68 percent
80
-------
ALTERNATIVES FOR BOSTON
81
TABLE2
Sludge Characteristics*
Deer Island
Primary
Solids
TABLE3
Distilled Water and Citrate Solubility of
Selected Pollutants: Percent Soluble
of Original Pollutant Mass
Heavy Metals Concent., Mg/1:
Arsenic
Cadmium
Copper
Tot. Chromium
Lead
Mercury
Nickel
Silver
Zinc
Soluble Components; Mg/1:
Chlorides
Hardness
Sulfate
Potassium
Sodium
Boron
Volatile Solids Characteristics:
COD/VTS
TKN/VTS
P/VTS
Hexane Ext./VTS
Sulfur/VTS
BTU/VTS
SAMRT p
2 3
40 60
600 900
500 750
200 300
4 6
200 300
40 60
1000 1500
2800
1200
800
140
1700
1
1.6 1.4
0.04 0.12
0.01 0.02
0.30 0.06
0.009 0.028
11,000 11,000
2
20
300
100
200
8
200
20
800
300
200
300
95
250
4
1.6
0.04
0.01
0.30
0.009
11,000
3
30
450
150
300
12
300
30
1200
1.4
0.12
0.02
0.06
0.028
11,000
Parameter
Total Solids
Dry Cake Solids
Ash Solids
Phos
Cadmium
Copper
Total Chromium
Lead
Nickel
Silver
Zinc
Digested
Sludge
(Not Treated)
W
S
8
N/D
N/D
3
N/D
N/D
N/D
0.7
C
14
100
N/D
2
75
N/D
62
10
19
Digested
Sludge
(Treated)
W
4
6
N/D
N/D
N/D
N/D
N/D
N/D
N/D
C
17
77
N/0
2
71
N/D
61
N/D
9
Raw
Ash
(Treated)
W
1
4
. 004
N/D
N/0
17
N/D
N/D
N/0
N/D
C
5
17
31
8
6
40
N/D
12
17
4
Digested
Ash
(Treated)
W
2
4
. 006
N/D
N/D
10
N/D
N/D
N/D
N/D
C
21
48
12
28
28
54
N/D
30
10
5
Percent
Soluble
Less Than
N/D
0.02
0.01
0.3
2.0
1.8
1.2
0.01
* Yr. 1995 projected characteristics, based on laboratory analyses.
more costly than purchased power, and that generation
using fuel oil is more than twice the cost of purchased
power. At Nut Island, the present cost of in-plant gener-
ation is approximately equal to cost of purchased power,
but when capital costs of expansions to handle larger fu-
ture loads is considered, in-plant generation was found
not economical at either plant. As a result of these find-
ings, the design of alternate sludge management plans
was based on the use of varying amounts of purchased
power.
In order to predict the effects of leaching of materials
from sludge residues, a series of citrate solubility analy-
ses was performed on samples of sludge and sludge ash.
The citrate solubility test simulates a weak organic acid
environment similar to that which may be created by soil
micro-organisms in a landfill site. Effects of leaching us-
ing the citrate test were compared with leaching by
distilled water. Results are shown in Table 3; the data
shows that the organic acid leachate contains three to ten
times the concentrations of dissolved minerals then the
distilled water leachate, and indicates that the system
adopted for final disposal of sludge residue should incor-
porate facilities for recovery and treatment of leachate,
or that discharges of mineral pollutants should be con-
trolled at the source.
Recycle Waste Streams
Each of the processes considered generates certain
waste streams recycled to process. These recycle
streams may incude digester supernatant, wet oxidation
decantrate, filtrate from dewatering, centrate, thickener
overflow, and ash slurry decantrate. The cost impact of
treating recycle streams was developed for each process
considered, and the impact on main process effective-
ness was evaluated.
NOTES: » = Distilled Water Solubility
C = Citrate Solubility
Treated = Received ferric and lime conditioning chemicals
N/D = Not Detectable
Procedure: 25 gm of solvent/gm of solids, given 24 hours
of contact, shaken every hour for the first
eight hours, ashing (where applicable) at
1600'F., filtration with 0.45 filter.
The greatest impact was associated with decantrate
from the wet oxidation and heat conditioning processes,
since solubilization of organics occur in heating of
sludge. Comparative cost studies revealed that for this
application, separate pre-treatment of recycle prior to
return to process was less costly than enlarging the main
stream secondary treatment facilities to handle the total
load. The other recycled streams were assumed to be re-
turned to the plant process, with due allowance for this
load in design of the plant.
Sludge Conditioning
The relative merits of chemical conditioning and heat
conditioning of sludge prior to dewatering were ex-
amined in detail. For this application, chemical condi-
tioning using lime and ferric chloride or polyelectrolytes
was more cost-effective than heat conditioning. On a
total annual cost basis, including amortization of capital
costs and operation and maintenance charges, the heat
conditioning system was eight percent higher in cost
than the chemical system.
The high chloride content of the sludge had an im-
portant bearing in this case, since the corrosive effects of
hot sludge required the use of special alloy materials in
the heat conditioning system piping, heat exchangers
and reactors. The use of titanium or Carpenter alloys
was shown more economical than more frequent re-
placement of standard materials, but the cost of either
option weighed against heat conditioning in comparison
-------
82
ALTERNATIVES FOR BOSTON
with chemical. The greater recycle load on treatment
process was also a substantial factor in favor of chemical
conditioning.
Dewatering and Sludge Digestion
Vacuum filtration was compared with centrifugation
as means of sludge dewatering. In the circumstances of
this particular large-scale application, the study indi-
cated that vacuum filtration was the more economical.
Grit content of the sludge is relatively high, and the
abrasive effect of grit, coupled with its high corrosive
content, indicates a relatively high maintenance charge
for centrifugation. Total annual cost of centrifugation
was 16 percent higher than vacuum filtration for this ap-
plication.
Aerobic digestion was examined as a means of reduc-
ing the organic loading to the various disposal processes.
After allowances for the reduction in solids mass, for the
increased power consumption, and for the heat recovery
loss associated with the destruction of volatile solids it
was found in this instance that aerobic digestion had a
net total annual cost seven percent higher than an incin-
eration system without aerobic digestion.
Incinerators and Air Pollution Control
Alternative types of sludge incinerators were evalu-
ated, utilizing preliminary design layouts and estimates
of capital and operating cost. Multiple-hearth incinera-
tors were found to be about eight percent lower in total
annual cost for this project, and were selected for evalua-
tion.
Air pollution aspects of incineration were thoroughly
explored. High efficiency air pollution control equip-
ment, including heat recovery, was selected, and stack
emissions of particulates, sulfur oxides, nitrogen oxides,
heavy metals, pesticides, PCB's and hydrocarbons were
quantified. The latest standards of the Metropolitan
Boston Air Pollution Control District and the Federal
EPA were reviewed and compared with the projected
stack emissions. A review of stack emission tests con-
ducted on modern sludge incinerators was made, to-
gether with recent studies of emissions from such instal-
lations by EPA.
The conclusions of these studies were that the pro-
jected incinerator installation would adequately meet or
exceed all of the existing or presently proposed stand-
ards, and that incineration is a feasible alternative from
the standpoint of air pollution. This conclusion is in
agreement with recent findings of an EPA Tank Force,
which stated that: "It has been adequately demon-
strated that existing well designed and operated muni-
cipal sludge incinerators are capable of meeting the
most stringent particulate emission control regulations
existing in any state or local control agency3."
Sludge Management Alternatives
Three types of sludge management systems were con-
sidered: land application, incineration, and wet air oxi-
dation. Within each of these general methods, a number
of process variations were developed, and detailed
evaluation was made of twelve alternative systems; two
land application systems, four wet oxidation systems,
and six incineration systems. Each alternate represents
a major process sequence, so that comparison of the al-
ternatives within a given general method constitutes a
system optimization. The alternates studied are shown
schematically on Figure 1.
LAND APPLICATION ALTERNATES
INCINERATION ALTERNATES
I
WET OXIDATION ALTERNATES
| r-Gfi]
m
LEGEND
PRIMARY SLUDGE (F) - THERMAL TREATMENT
SECONDARY SLUDGE iNTii»iiATK>N?M.ui»iVY<»iD
FILL
UTILIZATION
DEWATERING
WET OXIDATION
(TV DECANT TANK
I - GRAVITY THICKENING
(B) - FLOTATION THICKENING (HJ' INCINER ATION
^^ ^-^ FLUIDIZCD ftCD
(CJ - AEROBIC DIGESTION ^-. uufiin.1 MEA.TM
i^ (j)-CONVEYANCE
QD) - ANAEROBIC DIGESTION KAIL , T«UCR, PIPE ,
• -STORAGE
Figure 1: Sludge Management Alternates.
Land Application Alternates
In establishing criteria for land application of sludge,
detailed consideration was given to: topography and soil
characteristics in the eastern Massachusetts area;
public health aspects; nutrient value of the sludge;
sludge characteristics, effects on ground and surface
waters; toxicity of sludge to soil and crops; transporta-
tion of sludge; and probable levels of revenue through
sale of crops. The topography of land in eastern Massa-
chusetts available for sludge application is relatively
rough; hilly land predominates; rural areas are charac-
terized by wooded hills interspersed with small farm
tracts in the valleys. Soils vary, but clay soils and glacial
tills of relatively low permeability predominate. Field
reconnaissance indicated that in order to obtain coherent
tracts of land of the acreage needed, total transportation
distance from the treatment plants would be about 80
miles.
-------
ALTERNATIVES FOR BOSTON
83
Three basic land application alternates were
examined. Alternate L] includes thickening, anaerobic
digestion, sterilization, pipeline transportation from the
treatment plant to the land application site storage, and
spray irrigation of sludge to croplands. Alternate 1/2 in-
cludes thickening, anaerobic digestion, sterilization,
vacuum filtration, storage, rail transportation of filter
cake to the land sites, and spreading-plowing of cake to
the croplands. Landfilling of cake was also examined un-
der this Alternate. In each case, digester gas was re-
covered for power generation.
Loading Rates. Consideration of the nutirent con-
tent, heavy metals concentration and other characteris-
tics of the sludge showed that nitrogen loadings would
be the limiting factor in establishing sludge application
rates. A nitrogen mass balance was prepared, quantify-
ing the fraction of total and soluble nitrogen forms ap-
plied which would be removed by denitrification, by crop
uptake, by fixation, by erosion, and by leaching through
the soil into the groundwater. By limiting the amount of
soluble nitrogen leached to groundwater to levels repre-
senting an increase in groundwater nitrates of less than
1 mg/1, a limiting total nitrogen application was estab-
lished. This criterion, in turn, established the permissi-
ble sludge application rates, which ranged from 5.3 to
15.2 tons of dry solids per acre per year, depending upon
whether sludge was applied as a slurry, as a dewatered
cake, or as wet oxidized residue. Later information de-
veloped for the environmental assessment report indi-
cates that the loadings might be limited to slightly lower
values by heavy metal toxicity.
Application. Evaluation was made of four methods
of sludge application to the land: spray irrigation, ridge
and furrow irrigation, subsurface injection, and spread-
ing and plowing. Because of the terrain involved, spray
irrigation by "rain guns" was selected for slurry appli-
cation over center-pivot rigs; and spreading and plowing
was selected for those alternates involving application of
dewatered sludge cake.
Public Health Considerations. Although there is no
direct evidence that careful land application of digested
sludge has caused clinical disease in humans or animals,
the literature contains many examples of survival of
pathogens, parasites and viruses after prolonged
periods of digestion and storage. Survival of pathogens
has been reported by Hinesly, et. al. after heating to
95°F., digestion for 30 days and storage for seven to
eight months4. Kenner, et. al. observed fecal coliform
survival in soils at least 21 weeks after application of di-
gested sludge5. Little data is available on the fate of
viruses in sewage treatment processes.
In the present case, where very large long-term land
application systems are contemplated, it is believed that
protection of public health should be as reliable as possi-
ble. For this reason, heat sterilization of sludge is in-
cluded as part of the process sequence.
Wet sterilization for three minutes at 121 °C and 200
psig was selected as preferable to standard pasturization
(25 minutes at 70°C, atmospheric pressure). The high
salinity of the Deer Island sludge was a distinct detri-
ment in this regard, because of the corrosive effect on
heat exchangers, and special materials of construction
were assumed for the cost analyses. Sterilization costs
amounted to about 7.5 percent to 9.5 percent of the total
capital costs of the alternate systems considered.
Sludge Transportation and Storage. Transportation of
sludge to the land application sites by pipeline, by barg-
ing, by trucking and by railroad were investigated and
compared as to total annual cost for each alternate. Pipe-
line transportation was the least cost method for
digested liquid sludge under Alternate L j; rail transpor-
tation was the least costly for handling dewatered sludge
cake under Alternate L2-
Storage of sludge is necessary over the winter season
and during periods of seed germination to prevent loss of
sludge to surface or underground waters, and to protect
crops. In the climate of eastern Massachusetts, exami-
nation of weather records indicates that storage capacity
is required for about 150 days per year. Earthen basins
with impervious linings were selected for liquid sludge
storage, and the cost of the storage facilities was in-
cluded in the evaluation.
Incineration Alternates
Six process variations were considered in the incinera-
tion alternative. These alternates were investigated to
optimize the process and to illustrate the relative bene-
fit/cost relationships of sludge thickening, anaerobic
and aerobic digestion, chemical or heat conditioning,
vacuum filtration orcentrifugation, in various configura-
tions prior to incineration. In each case, the incineration
system includes waste heat recovery and the destruction
of grit and screenings generated at the treatment plants,
as well as small quantities of prepared refuse from near-
by MDC recreational areas.
Comparison of the incineration alternatives showed
that, for this application, construction of anaerobic di-
gesters is not cost-effective; recovery of incinerator
waste heat for power generation is economical; gravity
thickening of primary sludge is not justified, but flota-
tion thickening of waste activated sludge is economically
feasible; chemical conditioning is preferred to heat con-
ditioning; multiple-hearth incinerators are more
economical than fluid-bed units; and that on-site land-
filling of ash to create new land on Deer Island would be
the most effective means of ash disposal.
The net amount of energy recovered in waste heat
boilers and generators is estimated to vary from about
3,400 KW in 1976, to 10,000 KW delivered in 1995. The
cost of power generation utilizing waste heat was calcu-
lated at about 0.86 cents/KWH (delivered to shaft) as
compared to the cost of purchased power which was
about 1.0 cents per K WH in 1973, and is currently about
3.0 cents per KWH.
-------
84 ALTERNATIVES FOR BOSTON
Wet Oxidation Alternates
Four process variations of wet air oxidation were in-
vestigated. After detailed discussions with the manu-
facturer of the process equipment, it was determined
that the evaluation would be made for alternative sys-
tems handling digested sludge or raw sludge; and that
the design would be based on overall COD reduction of
50 percent to 55 percent, at reactor conditions of 800
psig, 475°F, and 15 to 30 minutes detention period. Sys-
tem design was based on the objective of producing a
stable, inoffensive and sterile end product for final
disposal. Volatile solids solubilization of 25 percent to 30
percent was assumed for evaluation of impact of re-
cycled liquors.
For both raw and digested sludge alternates, two op-
tions for final disposal of residue were investigated:
sanitary landfill, and application to croplands. Although
the wet oxidation process destroys some organic solids,
the mineral nutrients and part of the organic solids re-
main , which have some value in application to croplands.
As mentioned, the high chloride and sulfate content of
the sludge required special consideration of construction
materials for the wet oxidation components. Use of ti-
tanium for construction of heat exchangers and reactors
was recommended by the manufacturer, and was shown
to be more economical than more frequent replacement
of other materials.
The studies showed that the digested sludge alterna-
tive utilizing landfill as the final disposal method and in-
corporating digester gas recovery was the most
cost-effective wet oxidation option. As with the incinera-
tion alternate, leachate from the landfill site would be
collected and returned to treatment.
Selection of Recommended Alternate
Cost Comparison
Capital costs of each of the twelve alternative systems
were estimated, utilizing manufacturer's quotations on
major items of equipment. Personnel requirements for
operation and maintenance were developed, integrated
with present staff schedules, and annual costs of opera-
tion and maintenance of each system were prepared for
the median year, 1987. The cost estimates included ap-
propriate credits for recovered electric power, and for
revenue from sale of crops in the case of the land applica-
tion alternatives. The most cost-effective alternate in
each of the three categories of land application, incinera-
tion and wet oxidation was then selected, and these
three systems were evaluated in detail.
Table 4 shows the comparison of the final three alter-
nates in total annual cost. Incineration is clearly the
least-cost option, being lower in capital cost than the
nearest alternative by about $7.6 million, and lowest in
total annual cost by about $1.6 million per year.
Environmental Comparisons.
In addition to cost, the three alternatives were evalu-
ated in terms of nine environmental and non-cost ele-
ments of importance: effect on treatment process, quan-
tity of residual solids, degree of resource recovery, im-
pact on land, impact on the atmosphere, impact on the
water environment, total energy required, public health
and noise impact.
In each of these areas, an evaluation matrix was pre-
pared, and the three systems rated with respect to a
number of effects within the category. Table 5 sum-
marizes this comparison in one of the categories, (Ener-
gy Required) as an illustration of the approach used. It is
of interest to note that the incineration alternate requires
only 50 X 106 KWH/Yr., about 60 percent of the total en-
ergy of the other two systems.
This rating evaluation showed that in non-cost and en-
vironmental areas, the incineration alternative rated
equal to or better than the other two in seven of the nine
categories; the land application alternate equal to or bet-
ter in three of nine, and the wet oxidation equal to or bet-
ter in one of nine.
After consideration of all of the pertinent factors, the
incineration alternate was found to be superior to the
other systems studied, and was selected as the recom-
mended method of sludge management.
TABLE4
Cost Comparison Total Annual Cost
Capital Cost Annual
Alternate Capital Cost Amortization 0§M
Proposed
Incineration
Plan $53,040,100 $3,469,500 $3,968,300
Land
Application 98,580,700 6,275,100 6,653,800
Wet
Oxidation 60,699,200 4,071,000 5,622,800
Less Savings
(1) Power
(2) Crop Revenue
-2
-2
-4
-2
,540
,240
,180
,240
,000
,000
,000
,000
(1)
(1)
(2)
(1)
Net
Annual Cost
$4,897,800
6,508,900
7,453,800
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ALTERNATIVES FOR BOSTON
85
TABLE 5
Non-Cost Environmental Impact Comparison—Energy
LAND APPLICATION
INCINERATION -
2F
WET OXIDATION
Total bnergy Demand
Recoverable Energy
Total Energy Demand
Natural Gas Energy
Requirement
Electrical Energy
Requirement
Gasoline and Diesel
Oil Requirement
Transportation
Total Average Rating
Rating Code:
Most Favorable Impact 3.
Least Favorable Impact
Recommended Project Plan
A detailed project plan was prepared for implementa-
tion of the recommended incineration system. Since the
MDC is required to have a sludge disposal system on line
by 1976, prior to construction of full secondary treat-
ment, a two-phase program was developed. The Phase I
project plan is designed to accommodate the sludge gen-
erated by primary treatment at both plants up to the
period 1980-1985, and to be on line in 1976. The Phase II
program enlarges the sludge facilities to handle the ad-
ditional sludge generated by secondary treatment, to
design year 1995.
In the Phase I project plan, anaerobic digestion will
not be expanded, but existing digesters will continue in
use at both plants up to their effective capacity. Due to
severe site limitations, sludge from the Nut Island plant
will be pumped to Deer Island for treatment and dis-
posal. For this purpose the existing submarine force
main will be extended to Deer Island, and a second pipe-
line will be built to provide standby reliability. During
Phase I, digester gas will continue to be used for electric
power generation at Nut Island, and the existing
skimmings and screenings incinerators will continue in
service.
At Deer Island, the Phase I project includes continued
service of gravity thickeners and anaerobic digesters, up
to their effective capacity, without addition of new units.
Sludge from both plants will be chemically conditioned,
vacuum filtered and incinerated at the new facility at
Deer Island. Six vacuum filters (750 s.f. each) and three
incinerators (25' dia. X 9 hearth) will be provided. Each
incinerator will be fitted with afterburner, waste heat
boiler, pre-cooler and high efficiency scrubber. A steam
turbo-generator of approximately 3,400 KW capacity
will be included for utilization of the waste heat.
Incinerator ash will be utilized for landfill to provide
additional space required at the site for future secondary
treatment. Ash leachate will be collected and recycled to
treatment.
At Deer Island, the existing dual fuel engines which
drive raw wastewater pumps will be replaced by electric
motor drives, and an outside power supply will be pro-
vided to supplement that generated onsite by digester
gas engines and waste heat recovery system. At Nut
Island, the present digester gas power generation sys-
tem will be adequate to satisfy Phase I power needs.
Under the Phase II program (commencing about
1980-85), secondary treatment will be added at both
plants, and sludge facilities will be modified to handle
the increased load. At this time digesters at both plants
will be converted to storage tanks, and all sludge will be
filtered and incinerated raw. Waste activated sludge will
be thickened in flotation units, and the mixed sludge
blended in the mixed storage tanks. Eight additional
vacuum filter and four incinerators of the same sizes will
be added, together with three turbo-generators. Total
firm waste heat power generation capacity will be about
10,000 KW Existing dual fuel engine-generators will
remain for standby service to provide backup in case of
interruption of purchased power. Alternate power
sources for standby reliability will be considered when
the Phase II program is undertaken.
The estimated construction cost of the Phase I pro-
gram is $22,016,000; and the Phase II program is esti-
mated at $24,186,000.
A full environmental assessment has been prepared,
on which a public hearing was held in April, 1975. The
USEPA is currently preparing an environmental impact
statement on the project.
For the MDC, the project is under the general direc-
tion of Mr. Francis T. Bergin, Chief Engineer, Engineer-
ing Division, and Mr. Allison C. Hayes, Director and
Chief Engineer of the Sewerage Division. Mr. Martin
Weiss, Director of Environmental Planning, was project
manager for the MDC, and the studies were conducted
by Havens and Emerson, Ltd., Consulting Engineers.
REFERENCES
1. "A Study of Alternate Methods of Sludge Disposal
for the Deer Island and Nut Island Sewage Treatment
Plants." MDC-Boston Harbor Pollution Task Force,
Pub. No. 6138, April, 1972.
2. A Plan for Sludge Management. For the Metropoli-
tan District Commission, Havens and Emerson, Ltd.
August 30, 1973.
3. "Sewage Sludge Incineration." Report No.
EPA-R2-72-040, Environmental Protection Agency,
Pub. 211,323. August, 1972.
4. Hinesley, Braids and Molina. "Agricultural Bene-
fits and Environmental Changes Resulting from the Use
of Digested Sewage Sludge or Field Crops." EPA In-
terim Report.
5. Kenner B.A., Dotson G.K. and Smith J.E., Jr.
"Simultaneous Quantification of Salmonella Species
and Preudomonas Aeruginosa," Internal Report, EPA,
National Research Center, Cincinnati, Ohio, 1972.
-------
ALTERNATIVES FOR DISPOSAL FOR THE
METROPOLITAN DENVER SEWAGE DISPOSAL
DISTRICT NO. 1
William J. Martin,
Metropolitan Denver Sewage Disposal District No. 1
Commerce City, Colorado
and
Jerry D. Boyle
CH2MHUI, Incorporated
Corvallis, Oregon
After many years of trial and error and study, the
Metro District has selected, based on environmental,
engineering, economic and social consideration, the al-
ternative which in its opinion is the most acceptable
method for the processing of sludge removed from its
wastewater treatment facilities. This method chosen for
handling and disposing of the District's sludge is to
beneficially use it for agricultural purposes.
As we see it, there appears to be three sludge disposal
methods for the industry to use. They are water, at-
mosphere and land. Since the District's treatment facili-
ties were put on-line in the fall of 1966, all three of these
sludge disposal methods have been utilized at one time
or another.
The water method for sludge disposal (this is the con-
cept that the solution to pollution is dilution) is particu-
larly inappropriate in the semi-arid climate of Colorado
where water resources are seriously limited.
Disposal via the atmosphere method is never inten-
tional, however, even inadvertent air pollution by in-
cineration or any other means is rapidly becoming social-
ly unacceptable.
The third method is the application of sludge to land.
This method is currently being used by the District.
To provide some historical background, the District
wastewater treatment facilities were initially designed
to treat 117 mgd of wastewater and to achieve an 80 per-
cent overall reduction in BOD. The original design con-
cept for the handling and disposal of sludge removed
from the processes were dewatering through dissolved
air flotation, vacuum filtration, flash drying and/or in-
cineration. The anticipated ratio of raw primary, anaero-
bically digested and undigested waste activated which
comprised the vacuum filter feed sludge were expected
to produce a filter cake solids concentration of 22 percent
to 25 percent. The chemicals required for sludge condi-
tioning prior to vacuum filtration were expected to aver-
age five percent ferric chloride and ten percent lime. If
the proposed design parameters had been realized, the
amount of water requiring evaporation at full plant capa-
city would have equalled 353 tons per day. The design
engineers involved at that time provided three flash
dryer/incinerator units each having a maximum evapor-
ative capacity of 6.5 tons of water per hour. All three
units operating at 100 percent capacity 24 hours per day
would provide a total evaporative capacity of 468 tons of
water.
Early in 1967 it became apparent that the ratio of
waste activated sludge to the total sludge mixture was
much greater than originally anticipated. The greater
quantity of the difficult to dewater waste activated
sludge had an adverse effect on the resultant vacuum fil-
ter cake solids. The dry solids averaged between 14 per-
cent and 18 percent total solids instead of the expected
22 percent to 25 percent. This sludge ratio resulted in an
increase over the original design estimate for chemicals
required for vacuum filtration by more than 100 percent.
The lower dry solids content resulted in a serious over-
load of the evaporative capability of the flash dryer/in-
cinerators. Mechanical problems and breakdowns as a
result of the overload conditions were compounded by
corrosion failures of the stainless steel components of
the dryer/incinerators which resulted from the ferric
chloride used in the conditioning of the sludge.
By the fall of 1968 the sludge handling and disposal
problem had reached crisis proportions. As a result of
mechanical problems, less than half of the evaporative
capacity of the dryer/incinerators was available for
sludge processing. Activated sludge accumulation in the
biological treatment system resulted in a rapid deterior-
ation of the final effluent quality. To minimize the scour-
ing of activated sludge from the secondary clarifiers into
the South Platte River, lagoons were constructed for the
temporary storage of the excess activated sludge. Forty
acres of lagoons representing sixty million gallons of
storage capacity provided temporary relief during the
winter months of 1968 and 1969. By the spring of 1969
anaerobic decomposition of the waste activated sludge
stored in the lagoons created serious odor problems and
serious public relations problems. Consequently, a third
alternative, land application of the vacuum filter cake,
was initiated in May, 1969.
86
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ALTERNATIVES FOR DENVER
87
Land application of the vacuum filter cake was ori-
ginally conceived to be a temporary expedient until the
dryer/incinerator units could be restored to their design
capability. The flash dryer/incinerators were operated
primarily as incinerator units between 1966 and 1968.
From 1968 until 1971 the units were operated for both
drying and incineration. The change in the operational
mode made from incineration to drying was prompted by
the desire for greater utilization of the system. As dryers
the units could be operated approximately 2,000 hours
before cleaning and major repairs were required as com-
pared to only 500 hours of operation for incineration.
The primary fuel source for the operation of the dryer/
incinerators was interruptable natural gas with No. 2
diesel as a standby or backup fuel. During the winter of
1969-1970 the natural gas service was curtailed on many
occasions and Metro did not have a sufficient allocation
of standby fuel. This limited fuel supply forced the Dis-
trict to incinerate the sludge for its caloric value as a sub-
stitute for commercial fuel.
When the dryer/incinerators were being operated as
incinerators flash fires occurred in the system when
there was insufficient moisture to utilize the BTU's
being generated in the fire box. With insufficient mois-
ture the temperature in the drying system would rapidly
increase until there was sufficient heat to ignite the
sludge resulting in a flash fire or explosion. Explosions
also occurred when slag accumulation on the walls of the
fire box would slough off and fall into the wet bottom ash
collection hopper. The hot slag resulted in creating va-
por which would expand rapidly in the 3,000°F atmos-
phere of the fire box and an explosion would result. To
minimize these explosions the units had to be shut down
periodically so that the slag formations could be removed
from the walls of the fire box. The slag removal process
required many man hours and exposed the operators to
dangerous situations.
The dryer/incinerator initially installed in 1966 met
the existing Colorado air pollution standards. In 1970
these standards were revised drastically to reduce stack
emission concentrations from stationary sources. Dur-
ing 1971 the units were operated under a temporary vari-
ance while modifications were being made to meet the
new standards. It soon became obvious that the units
could not be successfully modified to comply with the
new standards. As a result of the air pollution, mechani-
cal and energy problems the units were permanently
shut down in August, 1971.
Between May of 1969 and August of 1971 the dryer/
incinerators and the land application of filter cake were
operated concurrently.
In 1969 the District acquired 160 acres of land located
26 miles southeast of the Metro District treatment plant.
This land was part of the abandoned Lowry Bombing
Range. The land was being leased to a rancher for the
purpose of grazing cattle. The vegetation on this site was
natural pasture grass typical of the range land in Colora-
do. The vacuum filtered sludge was transported in open
13 cubic yard dump trucks equipped with special rubber
seals to prevent leakage during transport. Two methods
of sludge application were utilized at the site, one for dry
weather and the second for wet weather. The District
hired a contractor to perform the necessary work under
both modes of operation. During dry weather the sludge
was tailgated directly from the transport vehicles onto
the surface of the soil. A track vehicle equipped with a
blade was then used to spread the sludge evenly over the
surface of the soil to a depth of approximately one inch.
The sludge was then allowed to dry for 24 hours before
an industrial type rototiler (six feet wide) with a depth
capability of 18 inches incorporated the sludge into the
soil. This operation was satisfactory provided that rocks
over five inches in diameter, dense vegetation and mud
were not encountered.
During wet weather the sludge was dumped directly
onto the surface of the soil and large track vehicles with
front mount dozers were used to intermix the sludge
with the soil. A satisfactory mix was accomplished when
a ratio of five or more parts of soil were mixed with one
part of sludge. During the winter months when the soil
had frozen, the mixing of sludge and soil was extremely
difficult. Peripheral surface water channels were dug
around the site to retain the water which ran off during
snow or rain storms. Analysis of the runoff did not indi-
cate the presence of contaminants from the land applica-
tion site.
In April, 1970 the District ceased application of sludge
to the site because of concern that the high loading rates
(376 dry tons per acre) might have an adverse effect on
soil productivity and cause erosion. The site was then
seeded with Brome and Crested wheat grasses. Since
this area receives an average 13 inches of precipitation
annually and no irrigation water is available, the com-
plete revegetation process took three years. The major
problem involved in the 1969-1970 operation was vulner-
ability to adverse climatic conditions.
In 1971 the District acquired an additional 640 acres of
land at the Lowry Bombing Range and revised the land
application operation to provide for a continuous year-
round disposal of the total sludge generated by its treat-
ment facilities.
Based on earlier experience, several changes in
methodology were adopted. Metro purchased the equip-
ment necessary for the land application system and uti-
lized District personnel to operate the equipment. The
method of operation consisted of transporting the filter
cake from the treatment plant to the Lowry site in the
same type of equipment used in the previous operation.
At the land application site a ramp was constructed
which allowed the transport vehicles to transfer the
sludge directly into spreaders. The 13 cubic yard farm
manure spreaders were sized to accommodate one truck
load of sludge. The spreaders were modified to handle
the relatively wet vacuum filter cake to keep the sludge
-------
ALTERNATIVES FOR DENVER
from flowing onto the areas where it was not desired.
Special lighting was provided at the ramp to allow for 24
hour a day, seven day a week operation. A standby trac-
tor and spreader was provided for the purpose of allow-
ing the primary unit to be serviced. Sludge was spread
approximately one eighth inch deep on the surface of the
grass and usually dried within one-half hour after appli-
cation. After application of three dry tons per acre a
spike tooth harrow was used to break up any large parti-
cles . Cattle continued to graze on the pasture during this
operation.
Soil and surface water testing and monitoring at the
site indicated that there has been no contamination as a
result of the District's operation. A major advantage of
this method was that the operation did not disturb the
native grasses. Based on visual observation the grass
production at this site improved compared to the sur-
rounding area that did not receive sludge application.
Another major advantage of this type of operation was
that its cost was only one-third of the cost of drying in-
cinerator operation. Not only was this change in opera-
tion environmentally preferable, but much less expen-
sive than the previous operation.
In November of 1971 the District entered into a two
year contract with a private contractor to provide serv-
ices for land application of sludge utilizing the technolo-
gy which the District had developed. Concurrently, the
District acquired additional land for a total of 2,000
acres.
The contractor utilized larger transport vehicles and
constructed a large sludge storage hopper at the site to
store sludge from the transport vehicles until it could be
transferred into the spreaders. The spreaders used by
the contractor were also larger than those used during
the previous operations.
During the fall and winter the contractor spread the
sludge in thin layers over the grass land. Early in the
spring of 1972 the contractor experienced difficulty with
access to the field. As a result, large quantities of
vacuum filter cake were stockpiled three to four feet
deep in a depression near a dry stream bed. Subsequent
to the stockpiling of filter cake, snowstorms occurred
which covered the stockpiled filter cake. District inspec-
tors were therefore not aware of this unauthorized modi-
fication of the land application method previously
agreed upon. As the snow melted the stockpiled sludge
decomposed creating odors and people living in the area
adjacent to the site complained to the County Commis-
sioners. Another problem which occurred in late spring
of the same year after the area had dried was fire. These
fires started in the areas which had received many sur-
face sludge applications and were a result of careless
smokers and heavy equipment operating in the area.
The smoldering fires were difficult to extinguish particu-
larly during high winds.
The odor complaints resulted in a Public Hearing on
June 20, 1972. At the Public Hearing the District pro-
posed a revised method of land application to eliminate
the odor and fire hazards previously experienced. This
proposal was accepted by the County Commissioners
and implementation began in June, 1972. A revised
method consisted of applying the filter cake to the sur-
face of the soil in two to three inch layers and within six
hours of application incorporating the sludge to a depth
of ten inches using a mold board or disc plow. After
sludge incorporation the soil was tilled until a suitable
seed betf had been prepared and was subsequently
seeded with wheat or other foilage crops to provide a
vegetative cover to protect against wind and water ero-
sion. With the assistance of the Soil Conservation Serv-
ice a plan was developed to establish contours to provide
additional protection against wind and water erosion on
the entire land application site. Presently, two crops are
raised each year to provide food for the grazing cattle as
well as reduce the nitrogen and other nutrients added to
the soil.
While this method was satisfactory during dry
weather special modification had to be adapted during
winter operation. During the winter the sludge is spread
on the land by tailgating to a depth of 24 inches and in-
termixed with the soil at a rate of at least five to one. The
inclement weather site is prepared in advance by bench
and terracing the area. Sludge loadings to the inclement
weather site exceeded 300 dry tons per acre per year.
Each inclement weather site is loaded only once. Incle-
ment weather application generally takes place during
December, January and February depending upon the
severity of the winter. Since 1971 this methodology has
ensured an adequate sludge disposal capability for all of
the sludge generated by the District's treatment facili-
ties, and has received strong support from nearly all of
the area environmental groups.
In 1971 the District authorized their consulting en-
gineers, CH2M Hill to design an expansion to the central
wastewater treatment plant and to investigate various
sludge handling systems including incineration and land
reclamation. CH2M Hill recommended an agricultural
reuse system in its study report "Sewage Treatment
Plant Expansion—Predesign Study", April, 1972. This
system was recommended because it would be the most
economical method for the District and would make
beneficial use of the sludge.
Under the system proposed in the April, 1972 report,
the District would either purchase or lease 6,000 acres of
land in western Adams County approximately 25 miles
east of the central plant. The sludge would be pumped to
the site through a force main and a system of booster
pump stations. At the site dryland crops typical to the
area would be grown utilizing the sludge as a fertilizer. It
was also recommended that an anaerobic digestion sys-
tem be used to stabilize the organic materials concen-
trated in the sludge prior to agricultural reuse. The
anaerobic digestion process is highly efficient in con-
verting organic material into relatively inert humus ma-
-------
ALTERNATIVES FOR DENVER
89
terial and gases including methane and carbon dioxide.
In addition, the single stage high rate digestion process
will reduce the total organic mass of the sludge by 40 per-
cent to 50 percent.
Two public meetings were held during the winter of
1972-1973 with residents in the area of the 6,000 acre
site. The concept of utilizing the organic materials for
agricultural purposes was discussed. The residents ex-
pressed concern about the location of the project and
about its management and operation. The residents also
made several suggestions which could improve the pro-
posed system.
Because of the residents' concerns, the District au-
thorized CH2M Hill to undertake another study of using
anaerobically digested sludge for agricultural purposes.
CH2M Hill submitted a report entitled "Agricultural
Reuse Program" March,1974 which presented a revised
agricultural reuse system incorporating the residents'
suggestions.
Under the revised system, sludge treatment would be
accomplished by single step high rate digestion at the
central plant. The liquid sludge would then be delivered
from the central plant to the distribution site through a
system offeree mains and a booster pumping station.
The drying and distribution site would include approxi-
mately 600 acres of drying basins for open air drying of
the sludge, a storage area for stockpiling the dried ma-
terial prior to distribution to the users, an area for sub-
surface injection of the sludge, demonstration plots and
miscellaneous site facilities necessary for operation and
maintenance.
A 2,000 acre drying and distribution site owned by the
District was proposed for the project. Eleven sites were
identified as potential locations for a drying and distri-
bution center. These eleven sites were reduced to the
three most viable sites located 20 to 25 miles east of the
District central plant. The three sites were recom-
mended on the basis of environmental and economic
considerations.
The revised system was presented to the residents
near the proposed sites in a series of public meetings.
Meanwhile, CH2M Hill was retained to do a predesign
and site selection study for the revised system. Attempts
were made in deciding on the design and location of the
project facilities to incorporate the residents' sugges-
tions and gain public support for the reuse project. The
predesign and site selection study was presented in a
report titled "Agricultural Reuse System Predesign".
The District also authorized a more detailed study of
other sludge handling systems to investigate alterna-
tives to the agricultural reuse system. The alternatives
were analyzed on the basis of economic and environ-
mental considerations, system reliability and the ability
to incorporate the required facilities into the District's
existing facilities. Alternative sludge handling systems
were evaluated to determine the most viable method of
treating and disposing of the District's wastewater
treatment plant sludge. The following eight alternative
sludge handling systems were found to be the most vi-
able for the District.
Alternative 1 Existing System
Alternative 2 - Anaerobic Digestion - Beneficial Reuse
Alternative 3 - Filter Presses, Incinerators - Land Ap-
plication of Ash
Alternative 4 - Heat Treatment - Vacuum Filters, Land
Application
Alternative 5 - Heat Treatment - Drying Basins, Land
Application
Alternative 6 - Heat Treatment - Vacuum Filters, In-
cinerators Land Application of Ash
Alternative 7 Anaerobic Digestion Filter Presses,
Composting Fertilizer
Alternative 8 - Filter Presses - Composting, Fertilizer
Based on environmental, engineering and economic
considerations the alternatives study concluded that the
agricultural reuse system was the most desirable sludge
management system for the District. One of the most
important advantages of the system is that a former
waste material would be recovered for beneficial use.
The fertilizer or soil conditioner which would be pro-
duced from the sludge is a valuable agricultural re-
source, particularly in view of the current and projected
fertilizer shortages. In addition, the agricultural reuse
system would not depend on chemical or inert condi-
tioners for its operation and would thus be independent
of outside cost influences.
The system requires little power, compared to the
other alternatives and methane gas, a byproduct of
anaerobic digestion, would be used to heat and mix the
digesters. Outside fuel or power would be needed only to
operate the various pumps of the system and the ve-
hicles at the drying and distribution center.
The reuse system is also attractive because of its rela-
tively simple operation and inherent flexibility for final
sludge use. Because of the simplicity in operating the
system there will be comparatively low operation and
maintenance costs. As a result, it is the most economical
of all the alternatives. This system provides the flexibili-
ty for marketing liquid or air dried sludge and for using
the sludge for either subsurface injection or surface ap-
plication.
In January of 1975 the District, in cooperation with
EPA, FDA, USGS and the Colorado State Geologist's
Office, embarked on a two year $600,000 research effort
to provide information required by the EPA guidelines
for "Acceptable Methods for the Utilization or Disposal
of Sludge" and to attempt to answer the questions which
had been raised by the farm community and other regu-
latory agencies. The research effort consists of the fol-
lowing projects:
• Groundwater quality monitoring project.
• Investigation of the effects of feeding to cattle,
crops that have been grown on sludge amended soil.
• Sludge characterization project.
-------
90 ALTERNATIVES FOR DENVER
• Pathogen (virus and parasites) project.
• Nitrogen management project.
• Greenhouse and crop rotation project.
• Heavy metals monitoring project.
• Sugarbeet fertilization project.
• Mine tailing reclamation project.
• Drying basin project.
• Subsurface injection project.
In conclusion, there are two items which could have a
significant effect on all future construction. The first
item was an article which appeared in the July issue of
Water and Wastes, pp. 7:
"Steep escalations in the price of commercially
produced fertilizer may make the use of feedlot
wastes and municipal sludge imperative in the fu-
ture. Russell Train, EPA administrator, told the 5th
Annual Composting and Waste Recycling Con-
ference that the use of feedlot wastes and sludge
from municipal plants could satisfy about 6.5 per-
cent of national nitrogen requirements. Though he
admitted that this was a small increment he said it
"may mean the difference between sufficiency
and shortage. 'The Department of Agriculture has
reported that since the Phase IV price controls were
lifted in 1973, the average price of fertilizer has in-
creased from $75 a ton in mid-1973 to over $140 a
ton by fall, 1974. Anhydrous ammonia alone has al-
most tripled in price. EPA will be starting up a re-
source recovery demonstration within the next
three years in Delaware to show compost produc-
tion and facilities to enrich the product with syn-
thetic fertilizers. Another demonstration is planned
for Maine which will demonstrate a new compost-
ing technology developed by the Department of
Agriculture. Several other concepts, including
some with waste involvement, will be tested in this
fiscal year."
The second item is from the Federal Register, Grant
Regulations and Procedures - 30.420-6 Conservation and
Efficient Use of Energy:
"Grantees must participate in the National Energy
Conservation Program by fostering, promoting and
achieving energy conservation in their grant pro-
grams. Grantees must utilize to the maximum prac-
tical extent the most energy-efficient equipment,
materials, construction and operating procedures
available."
The awesome natural resource issue has provided the
catalyst for significant social and economic changes that
are occurring in our world today. Therefore, it is impera-
tive that we in the industry design and construct facili-
ties which lend themselves to change and that our goals
be established to derive the maximum benefit from the
resource which we have for so long called waste. As the
technology develops to selectively remove the precious
materials from the sludge we should not find ourselves
locked into systems which cannot be readily modified to
accommodate the new technology. We in the industry
should remove the words disposal and waste from our
vocabulary and substitute beneficial reuse and re-
sources in their place.
-------
ENERGY CONSERVATION PRACTICES IN
MUNICIPAL SLUDGE MANAGEMENT
G. Wade Miller
Public Technology, Incorporated
Washington, D. C.
INTRODUCTION
Public Technology, Incorporated is a non-profit, pub-
lic interest corporation that was organized and is spon-
sored by the so-called "Big Six" public interest groups;
the International City Management Association, Na-
tional Association of Counties, National League of
Cities, U.S. Conference of Mayors, National Governors'
Conference, and the Council of State Governments. PTI
was established in 1971 by the Big Six to act as a re-
search and development arm for local and state govern-
ments.
The primary objective of PTI is to promote the de-
velopment, introduction, and utilization of innovative
and advanced technologies in local and state govern-
ments. In accomplishing this broad objective, Public
Technology works closely with all levels of government
plus private industry.
PTI does not attempt to address itself to every city,
county, or state technologically-based problem. PTI's
overall methodology involves identification of high pri-
ority generic needs that are common to a large number of
municipalities.
Several months ago, Public Technology became aware
of such a generic need through studies conducted by
cities participating in two of our major programs. These
studies dealt with energy consumption patterns in muni-
cipal government operations. One of these studies was
conducted by the City of Indianapolis, a participant in
the Urban Consortium for Technology Initiatives pro-
gram; the second study was conducted by the City of
Nashville, a participant in the PTI operated Urban Tech-
nology System.
Before elaborating on the findings of these two im-
portant studies, a brief description of these two pro-
grams would perhaps be useful. The Urban Technology
System, funded by the National Science Foundation, is
an experiment designed to place an emphasis on the use
of technology to solve urban problems. The system con-
sists of 27 technology agents located in 27 randomly se-
lected cities and counties in the 50-500,000 population
range. These technology agents are scientists and en-
gineers by training and are placed in these municipali-
ties to address themselves to technological problems.
Each technology agent is given support by a contractual-
ly retained back-up site which may be a Federal labora-
tory, university, not-for-profit research corporation, or a
private company. The technology agent answers directly
to the mayor, city manager or chief administrative offi-
cer in a municipality, thus possessing operating flexibil-
ity and authority. The UTS network has been operational
since July, 1974.
The Urban Consortium for Technology Initiatives is
also sponsored by the National Science Foundation and
involves the 27 largest cities and six largest counties in
the Nation. The primary objective of this program is to
develop a national needs agenda for the largest U.S.
cities and counties and to bring Federal and other avail-
able resources to bear upon a number of the most critical
problems.
Municipal Inventories of Energy Consumption
In 1973, a profile of city government energy consump-
tion patterns was conducted by the City of Indianapolis.
The objectives of this inventory were to:
• determine the direct energy consumption patterns
of city operations by major end sources;
• identify those city operations which represent ma-
jor end uses of energy; and
• assist city officials in assessing the relative impacts
of potential energy supply problems on city govern-
ment operations and potential areas for energy con-
sumption.
An inventory was made of the direct consumption of
petroleum-based fuels, electricity, steam, and natural
gas by city departments and the city-county building
operations for 1972 '.
The results of this study were somewhat surprising.
The study showed that more than half of the petroleum
based fuels used in city operations were used in waste-
water treatment plants. Also, more than half of the elec-
tricity consumed by the city was used in wastewater
treatment plant operations (Figure 1). Overall, waste-
91
-------
92 ENERGY CONSERVATION PRACTICES
ENERGY
SOURCES
PERCENT OF TOTAL
CONSUMPTION
GASOLINE
20.7%
PETROLEUM,
FUELS
45.5%
10.5%
4.3%
3.9%
2.0%
MAJOR
END USES
POLICE VEHICLES
D.O.T. VEHICLES
SANITATION VEHICLES
OTHER
FUEL OIL
24.2%
23.8%
SANITATION PLANTS
.DIESEL FUEL
0.6% X.
LP GAS
0.1% "
22.0%
SANITATION PLANTS
ELECTRICITY/
41.8%
10.0%
'PUBLIC STREET LIGHTING
STEAM
6.8%
NATURAL GAS
5.9%
6.0%
3.8%
3.8%
CITY-COUNTY BUILDING
• OTHER
>.8% ^>
Figure 1: Direct Energy Consumption Patterns of City Operations In 1972.
CITY-COUNTY BUILDING
a- OTHER
& RECREATION FACILITIES
FIRE STATIONS
water treatment plant operations accounted for 45 per-
cent of direct energy consumption by major end uses
(Figure 2). It should be noted that a major portion of that
energy consumed in wastewater operations was used in
sludge incineration.
In September, 1974, the Tennessee Valley Authority
(TVA) appealed to its users to voluntarily reduce the
amount of electrical energy consumed by 20 percent.
This appeal by the TVA to its more than 2.4 million
customers was necessitated by the steadily dwindling
stockpiles of recoverable coal.
TVA provides electricity for some 160 municipal and
cooperative power systems. One of these customers, the
Nashville Electric Service, provides electric power to
-------
ENERGY CONSERVATION PRACTICES
93
SEWAGE WASTE TREATMENT PLANTS
CITY-COUNTY BUILDING
J2%
PUBLIC
STREET LIGHTING
10%
MOTOR VEHICLES.
21%'
OTHER USES
12%
Figure 2: Direct Energy Consumption by Major End Uses - 1972.
Metropolitan Nashville and Davidson County. The
Metropolitan Government of Nashville felt that possible
mandatory cutbacks or rolling blackouts could have a
catastrophic effect on the community because of its
heavy dependence on electrical power2.
Thus, on November 7, 1974, Mayor Briley of Nashville
responded to this emergency by setting into motion a
comprehensive mandatory electrical energy conserva-
tion program aimed at reducing Metropolitan Govern-
ment electrical consumption by 20 percent.
A summary of the electrical energy conservation re-
sults, as of January 15, 1975, showed an 18.24 percent
reduction of electricity energy use for the latter three
months of 1974 when compared to consumption figures
for the same period of 1973. This 18.24 percent reduction
in electrical energy demand, however, did not include
the Water and Sewer Services Department. Indeed, the
Water and Sewer Services Department showed a 14.33
percent increase during this period. The overall con-
sumption of electrical energy by this department for the
fourth quarter of 1974 amounted to 30.9 percent of total
end usage.
As a direct result of these findings, the UTS tech-
nology agent in Nashville requested that PTI furnish him
any information on methodologies which would allow his
-------
94 ENERGY CONSERVATION PRACTICES
city to reduce energy consumption in wastewater treat-
ment operations.
Sludge Disposal Costs
Pursuant to receiving the results of the Indianapolis
and Nashville studies, PTI decided to conduct an in-
formal survey to determine the extent of the energy
problem in wastewater treatment.
One of the first sources of information reviewed was
the General Accounting Office (GAO) report to the Con-
gress of January, 1974 regarding Federal research and
development programs needed to achieve water quality
goals. As part of this study, the GAO surveyed 100 large
municipalities to determine critical needs in wastewater
treatment. The three top ranked problems are:
• Inadequate treatment facilities—research needed
to reduce cost and improve secondary processes to
use less energy;
• Combined sewer and storm water discharges—re-
search needed to reduce control costs;
• Sludge handling and disposal—research needed to
reduce costs, make process easier, reduce use of
energy, and determine effects of disposal on land.
It can be noted that two of these problems deal with en-
ergy reduction and one in particular with energy reduc-
tion in sludge disposal.
Although our informal survey from this point con-
tinued to focus on wastewater treatment in general, we
began to look more closely at sludge disposal. Sludge
treatment and disposal has long been recognized by
local authorities, consulting engineers, and Federal
EPA officials as being the number one problem in
wastewater treatment today. In its 1968 publication, A
Study of Sludge Handling and Disposal3, the Federal
Water Pollution Control Administration estimated that
up to 50 percent of the capital cost and 50 percent of the
operating cost of a water reclamation facility was
devoted to solids handling. More recent estimates have
placed the operating costs even higher, in the 55 percent
to 60 percent bracket4.
Thus, in these days of rapidly escalating power costs,
potential energy shortages, and local government bud-
get deficits, it seemed only logical for PTI to inspect the
capital intensive sludge disposal process as a potential
area for energy savings and cost reduction.
OBJECTIVES AND SCOPE OF STUDY
Through a preliminary review of current literature and
several telephone calls to local officials, we soon deter-
mined that the total question of economics in sludge dis-
posal was too broad a study to attempt on a short-term
basis.
A decision was made to limit the scope of the study to
the following objectives:
1. Determination of the extent of utilization of diges-
ter gas and for what purposes;
2. Determination of the potential impact of organic
conversion (including digester gas) on national
energy demand; and
3. To obtain information on the cost/benefit tradeoffs
in digester gas utilization.
Digester Gases As Energy Source
A well known potential source of energy is the me-
thane gas produced in the anaerobic digestion process.
This gas is currently utilized for numerous purposes in
larger wastewater treatment plants throughout the
country. Use of this gas to offset operating costs is well
documented in the literature. Because of continually
changing conditions, namely fluctuations in the econo-
my, the emergence of newer sludge disposal technolo-
gies, and power costs, the "real" value of digester gas
has also continually fluctuated.
The use of digester off-gases as a fuel source can be
traced all the way back to 1895 when the street lights of a
section of Exeter, England were operated by this gas5
Although much experimentation occurred, routine
us age for plant heating, digester heating, and other uses
did not take place until the 1930's. In the 1940's, the
practice became commonplace due to technological ad-
vancements such as the development of the dual-fuel en-
gine. Development of this type of engine gave wastewa-
ter plants the capability of utilizing varying compositions
of sludge gas and other fuels, and relieved them of total
dependency on digester gas alone6.
Utilization of sludge gas became more widespread
during World War II and then began to decline in the
1950's. A number of reasons can be cited as to why this
decline occurred. The two most significant reasons
were:
• the availability of inexpensive and abundant sup-
plies of electricity, natural gas, and fuel oil; and
• the gradual shift from anaerobic digestion toward
more energy-intensive methods of sludge stabiliza-
tion.
In fact, the ready availability of energy in the late 1960's
prompted the FWPCA7to state that "many utility rates
are so low that it is uneconomical to install equipment to
develop power from digester gas."
In 1975, however, the utilization of sludge gas is again
receiving a considerable amount of attention. The ap-
parent energy shortfall, skyrocketing fuel prices, and in-
creased demands of energy resources for new and exist-
ing wastewater systems share the responsibility for this
increased attention.
A number of recent literature articles can be cited
which attest to this increased popularity. In a recent arti-
cle, Mignone8 analyzed the effects of the several dif-
ferent design parameters subject to the control of the de-
sign engineer which would increase the energy genera-
tion potential of anaerobic digesters. Adams9 described
how anaerobic gas production could be catalyzed and
thus increased through the application of powdered acti-
-------
ENERGY CONSERVATION PRACTICES 95
vated carbon. Murphy 10 estimated the volume of poten-
tial fuel available if all sewage sludge were anaerobically
digested, and described available energy conversion de-
vices. Goeppner and Hasselmann n discussed the eco-
nomic factors associated with energy production from
sewage sludge.
Thus, the trend in sludge disposal may be shifting
back toward anaerobic digestgion. Trends are hard to
predict at this point in time, however, as various alterna-
tive methodologies are being investigated. In address-
ingthe "First National Conference on Municipal Sludge
Management," Dr. J.B. Farrell of EPA noted that
"there has probably not been a more difficult time for
forecasting disposal trends 12."
Useful Facts About Digester Gas
There is an abundance of articles on anaerobic diges-
tion and gas production in literature. Information con-
cerning fuel value, gas composition, production rates,
potential uses, and energy conversion devices is readily
accessible.
The composition of digester gas is typically 60 to 65
percent methane (Crfy) with the remainder being com-
posed mainly of CO2 with traces of F^S, N2, and H2. The
fuel value of digester gas ranges from 600 to 650 Btu/ft^.
The rate of gas production is about 0.8 ft-Vcapita/day.
Six to eighteen standard cubic feet (scf) of gas are pro-
duced per pound of volatile solids destroyed.
A July, 1973 report 13 issued by the National Environ-
mental Research Center estimated that in activated
sludge plants, a maximum of two thirds of the power
needed could be generated by using sludge gas.
Using the electrical demand and gas production fig-
ures outlined in that same document, calculations have
been made which show that if all sludge were anaero-
bically digested, the energy available theoretically ex-
ceeds total plant energy demands. The NERC study esti-
mates that, if the entire U.S. population were served by
activated sludge plants, the average power consumption
would be 0.113 kwh/capita/day. Assuming a gas pro-
duction rate of 0.8 ft-Vcapita/day, with a fuel value of
640 Btu/ft^, energy availability can be calculated at
0.154 kwh/capita/day 14 It should be emphasized that
this figure is theoretical and does not account for fluctua-
tions in production rates, or energy conversion effi-
ciencies of engines and generators.
Looking at theoretical fuel values and production
figures also does not take into account potential uses,
methods of use, costs of transport if sold, and the dam-
age which the impure gas can do to engines and genera-
tors.
Digester gas is dirty. The water and F^S present in
the impure gas can and does cause operating problems
such as clogged gas lines and difficulties with control
mechanisms. The water and CO2 present in the gas
makes it harder to burn. According to a Monitor article in
a 1974 Journal of the Water Pollution Control Federa-
tion 15, the H2S normally found in digester gas can: (1)
damage metal surfaces, (2) cause pitting of engine walls,
and (3) clog piston rings.
All of the contaminants can be removed by water
scrubbing or other methods and the gas can then be
pressurized, but each of these steps involves a substan-
tial cost increment and reduces the overall
attractiveness of the gas from an economic standpoint.
Digester Gas Uses
Energy in a wastewater plant is required to: (1) raise
the temperature of the incoming sludge flow to digester
operating temperature; (2) maintain digestion operating
temperature; (3) operate various motors associated with
digestion process, such as sludge pumps and heat ex-
changers; (4) operate pumps and motors in other parts of
the plant; (5) furnish power to operate blowers in acti-
vated sludge plant; and (6) space heating for buildings.
Stated in a simple manner, the digester gas produced:
(1) can be used directly to operate equipment and thus
offset fuel oil and natural gas costs; (2) can be used to
generate electricity; or (3) can be sold for commercial or
industrial use. It is usually not practical to sell the gas if
it is possible to utilize all of it within the plant.
Technologies Involved in Use
Digester gas can be used in a direct manner to heat
boilers and produce steam. The resulting heat is then
used for space heating in plant buildings, to maintain
proper temperatures in the anaerobic digesters, and in
some cases to drive large pumps such as raw sewage
pumps. The equipment required for direct utilization of
gases is not extensive, requiring only a gas-heated boiler
or some type of heat exchanger.
The energy demands for the above listed plant opera-
tions are not great. The form of energy required to meet
the primary needs of wastewater treatment facilities is
electrical energy. Thus, the chemical potential energy
must be converted to electrical potential energy if all the
methane formed is to be utilized. This indirect gas use
requires a larger capital investment but ultimately pro-
vides greater operating flexibility.
There are presently three types of systems available to
convert chemical energy into electrical energy16: (1)
steam turbine systems; (2) gas fueled direct conversion
systems; and (3) fuel cells. Steam turbine systems are
more expensive and thus are used in larger wastewater
treatment plants which can afford a larger capital outlay.
Efficiency of a steam turbine conversion system ranges
from 12.5 to 35 percent 17.
Smaller plants generally use gas fueled (dual-fuel) en-
gines which operate on a mixture of gas and diesel oil.
The operating efficiency of the gas fueled direct con-
version system ranges from 5 to 21 percent.
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96 ENERGY CONSERVATION PRACTICES
Since digester gas is not produced continuously,
plants using the gas as a major source of energy usually
have a storage sphere which allows usage at a constant
rate. Two types of storage spheres are available; gravity
spheres and pressurized spheres. The gravity sphere
operates at a five to nine inch water column pressure.
Pressurized spheres are usually designed for 40 to 50
psig.
Plants usually have an auxiliary fuel supply on hand
for use during periods of inadequate gas production.
This auxiliary supply in a well operated plant is seldom
used, however. The plant manager of a large west coast
plant noted in a telephone interview that "our back-up
propane supply has not been used in years".
A third option for digester gas use is to sell the gas to a
commercial or industrial source. The gas may be sold in
eitherthe "sour" or "merchantable" condition. A sour
gas refers to the gas as it is produced containing the car-
bon dioxide and other impurities, and having a Btu value
of at least 600 Btu/scf. A "merchantable" gas refers to a
gas that has been cleaned, has a Btu value greater than
925 Btu/scf, greater than 95 percent methane, less than
five percent carbon dioxide, less than 1.0 grain per 100
scf hydrogen sulfide, and a moisture content no greater
than 0°F dewpoint17.
Gas is usually not sold it it can be utilized in the plant
itself. Cost of cleanup, pressurization, and transport
must be borne by either the municipality or the buyer
and these cost increments usually make the sale of the
gas economically infeasible.
Municipal Experience in Digester Gas Utilization
Information on municipal experiences with digester
gas utilization was obtained in two ways—telephone in-
terviews and a review of current literature. In addition,
PTI was able to access information gathered by the Wa-
ter Pollution Control Federation for a similar survey.
The objective of this part of the survey was to deter-
mine:
• the various uses in selected wastewater plants;
• savings realized through digester gas utilization;
• impact of the energy crisis on gas utilization prac-
tices.
Plant managers of both large and small treatment sys-
tems were contacted. The contacts in larger cities in-
cluded officials from the Los Angeles County Sanitation
Districts, The Metropolitan Sanitary District of Greater
Chicago, and the Blue Plains Wastewater Treatment
Plant in Washington, D.C. Information on operating ex-
peiences in Bloom Township, Illinois and Racine, Wis-
consin was also acquired.
The Sanitary Districts of Los Angeles County have
been utilizing the gas produced at their 340 mgd primary
treatment plant for more than 30 years. The gas pro-
duced at this plant is used to satisfy plant demands; in
addition, all excess gas (about 40 percent) is sold to an
adjacent oil refinery.
All plant heating requirements are met, digesters are
heated, and electricity generated by six large genera-
tors. The gas is also used to drive five 1100 hp reciprocal
gas engines. These engines have been in service for
more than 30 years.
As a result of the energy crisis of 1973, the Sanitation
Districts embarked on a project to equip their automo-
biles with a dual fuel system. The Districts will build
their own purification plant and will store gas for use in
emergencies. Estimates of total savings through use of
digester gas was not available.
The Metropolitan Sanitation District of Greater Chica-
go operates three major treatment works. The District
currently utilizes an estimated 70 to 80 percent of the 3 to
4.5 million cubic feet of gas produced per day to heat the
raw sludge feed, maintain digester temperature, and
heat the digestion complex buildings. The District is
currently investigating various means of utilizing the ex-
cess energy for various uses.
A 30 mgd advanced waste treatment plant has recent-
ly been completed and will use digester gas to generate
steam at 13 to 15 psi. The plant will be heated in its en-
tirety and an air conditioning system using lithium bro-
mide absorption chillers will be operated with power
produced from the digesters.
The Blue Plains Treatment Plant in Washington is
currently looking at the cost/benefits of incineration ver-
sus anaerobic digestion. A summary of the cost analysis
data is presented in the next section.
Bloom Township, Illinois buys no fuel during the
winter months other than gas for the engines that power
the blowers. Bloom Township has been using digester
gas for 23 years. Edward Meers, Manager of the Sani-
tary District, estimates a savings of $58,000 in 1972 on
fuel costs. Asked if the energy crisis had impacted the
usage of digester gas, Meers noted that natural gas is
now almost impossible to obtain during the winter
months in the midwest.
Racine, Wisconsin's treatment plant produces suffi-
cient gas to fuel the engines that drive the blowers in its
aeration system. Estimated savings are $22,00/year 18.
Other cities utilizing most or all of their digester gas
for various purposes include Philadelphia, Cleveland,
Atlanta, Tucson, and the Hyperion Plant in Los Angeles.
Cost Analysis of Sludge Handling at Blue Plains
In order to objectively determine some of the cost
tradeoffs of sludge disposal, Alan Cassel, Chief of the
Research Division of the District of Columbia's Depart-
ment of Environmental Services, was contacted con-
cerning sludge disposal alternatives under considera-
tion at the Blue Plains Wastewater Treatment Plant.
The plant, operated by the District of Columbia Gov-
ernment, services a 725 square mile area including the
entire District of Columbia and portions of Northern Vir-
ginia. Sludge processing at the present time is by
anaerobic digestion, elutriation, and vacuum filtration.
-------
ENERGY CONSERVATION PRACTICES 97
The plant was designed for 240 mgd and is currently un-
der expansion ot 309 mgd. The average daily flow at the
present time is 285 mgd. The plant serves approximate-
ly two million people in the Washington metropolitan
area.
The production and disposal of sludge is currently
being handled under an interim agreement among the
various jurisdictions pending the completion of new in-
cineration facilities. The funding of these incineration
facilities is being held up by EPA until a comprehensive
study on various methodologies for sludge processing
and disposal is completed.
Meanwhile, the plant produces 300 wet tons per day of
digested sludge as filter cake. An additional 240 tons of
primary sludge is produced due to chemical addition de-
signed to reduce the 6005 concentration of the effluent.
The digested sludge filter cake is either land filled or
composted. The primary sludge is being disposed of
mainly through burial by the trenching method.
Blue Plains' problem is hardly unique. They have dif-
ficulty in finding enough land to get rid of the sludge and
as great a difficulty in getting the various political juris-
dictions to share in the sludge disposal responsibilities.
Gas production at the Blue Plains plant is about
1,600,000 ft3/day. In winter, 310,000 ft3/day is used for
heating plant buildings, 380,000 ft3/day is used to
maintain digester temperatures in the 95°F range, and
500,000 ft-Vday is used to drive three 100 mgd. raw sew-
age pumps.
The Blue Plains plant generated electricity from the
digester gas from 1938 to 1968. In 1968, the conversion
engine wore out and was not replaced. Since electricity
was available at 0.7 cents/kwh at that time, it was not
economically feasible to purchase a new engine.
Blue Plains now pays 2.5 cents/kwh and fuel oil has
escalated in price from 12 to 14 cents/gal, to 31
cents/gal, in the same period of time. According to
Cassel, it would now be feasible to purchase a new gas
fueled direct conversion system.
In September, 1974, Cassel performed a total cost
analysis 19 on keeping twelve digesters in operation ver-
sus total incineration of raw sludge. The study is too
lengthy to be reproduced in its entirety. The results of
the analysis are summarized below. It should be noted
that the issue in question is not digestion versus in-
cineration costs, but rather a cost-benefit analysis of
keeping digestion when incinerators are installed.
All costs are based on FY 1974 operating data and
include operation and maintenance labor.
The total cost in Table 1 must be balanced against sav-
ings realized in dewatering and incineration of less raw
TABLE 1
Operation - digestion through final disposal $3,502,421
Methanol for denitrification 306,450
Total - All Costs of keeping a separate digestion process $3, 303, 871
sludge, plus the benefits associated with using sludge
gas. Table 2 tabulates the savings in cost associated with
handling less sludge through the filtration-incineration
system. The 862,000 pounds of dry solids per day is the
amount of solids to be processed if all solids were in-
cinerated. The 661,300 pounds figure is the amount to be
incinerated if digesters remain operational.
Filtration- Polymer
& ferric chloride
Fuel oil
Power
Residue Disposal
Total Savings
TABLE 2
Cost at 862.200* /day
$1,043,187
6,288,000
1,176,030
619,563
$9,126,780
$2.124.995
Coat at 661, 300* /day
$ 800,301
4,823,960
902,214
475,310
$7,001,785
Methane produced from digestion is assumed to have
a value which could reduce the fuel oil consumption.
Table 3 summarizes the methane utilization.
TABLE3
Total sludge gas production
Average use in digester heating
Amount available
BTU available (600 Btu/tt?)
Value at $2. 84/lWM Btu
($2. 84 is Btu value of oil at 40?/gal)
1,190,000 scf/day
242,373 scf/day
947,127 scf/day
568,276,200 Btu/day
$589,073
Table 4 summarizes the value of all benefits derived
from keeping digestion.
TABLE4
Savings from Table 2
Savings from Table 3
Total Savings
$2,124,995
589,073
$2,714,068
In orderto make digestion cost-effective, the value in
Table 4 must be greater than the value in Table 1. This is
not the case with the numbers used. The largest cost
with keeping digestion is the ultimate disposal of that
sludge. If a method were established to lower the $20.00
per wet ton figure, than the economics change. It is also
true that if the price of fuel oil and power increase, then
the comparative economics could change also. In
general, however, the dollar figure associated with the
methane is insignificant when compared to the other
costs of operation.
Cassel's cost analysis used a $20 per wet ton figure for
ultimate disposal. This number is higher than actual
costs at the present time. However, Cassel expects the
-------
98 ENERGY CONSERVATION PRACTICES
costs (including land costs) to escalate to that figure in
the near future. Also, he uses a 40 cents/gallon cost for
fuel oil. This figure is also high at the present time.
While this cost analysis shows that incineration in-
volves much higher overall operation and maintenance
costs, it does not address the questions of finding avail-
able land for disposal of vast amounts of sludge and the
difficulty in logistics of transport of this sludge.
Potential Impact of Byconversion on
National Energy Demand
The third objective of our study was to assess the po-
tential impact of conversion of organic wastes to energy
sources on national energy demand. Organic waste in-
cludes urban refuse, manure, agricultural crops and
food wastes, industrial wastes, and sewage sludge.
Tables 5 and 6, taken from a recent Council on Environ-
mental Quality report on Energy Alternatives 20, show
both the quantities of these wastes which are available
and the percent of various fuels potentially represented
by organic wastes.
If all organic wastes were collected, reserves could
represent two percent of total U.S. energy input.
Organic wastes, if all were converted, would represent
three to four percent of crude oil demand; six percent of
natural gas demand; or 6.8 percent of electricity gener-
ated in 1971.
It can be seen from Table 5 that 12,000,000 dry tons
municipal sewage solids were generated in 1971. This
amount is expected to increase to 14,000,000 dry tons in
1980. It should also be noted that the amount of sludge
produced is the smallest amount in the organic waste
category.
Thus, it is quite obvious that energy from sludge is not
going to impact national energy demands now or in the
future. It would appear from this data that energy from
sludge can best be used to offset operating costs in
wastewater treatment.
OVERALL CONCLUSIONS
This paper was not designed to attempt to resolve any
critical issues. The purpose was rather to attempt to
place the energy costs of wastewater treatment and
sludge disposal into a useful kind of perspective.
From the qualitative information obtained in our
desk-top study, it appears that utilization of digester gas
to offest operating costs is undergoing a revival. Also,
Source
TABLES
Quantities of Organic Waste by Source
(Dry Weight in Tons Per Year)
Reserve 1971 Resource 1971 Resource 1980
(Readily Collectable) (Total Amt. Generated) (Total Amt. Expected)
n
Urban Refuse
Manure
Logging and Wood Manufacturing
Agricultural Crops and Food
Wastes
Industrial Wastes
Municipal Sewage Solids
Miscellaneous
71. Ob
26.0
5.0
22.6
5.2
1.5
5.0
129
200
55
390
44
12
50
222
266
59
390
50
14
60
TOTAL 136.3 880 1,061
Source: Anderson, 1972: 8, 1321.
Q
Domestic, municipal, and commercial components of this waste amount to 3. 5, 1.2, and 2.3 pounds per capita
per day respectively.
Based on the 100 largest population centers in the United States.
-------
ENERGY CONSERVATION PRACTICES
99
TABLE6
Percent of Various Fuels Potentially
Represented by Organic Wastes
Reserve
(Readily
collected
now)
Resource
1971
Resource
1980
Quantity
Dry Organic
Wagtea
(10 tons
per year)
136.3
880.0
1,061.0
Percent
of Total
Energy
Input
in 1971
2
13
NA
Percent
of Crude
Oil
p
Demand
3-4
19
NA
Percent
of
Natural
Gas
Demand
6
39
NA
Percent
of 1971
Coal
£
Demand
8-9
50
NA
Percent
of 1971
Electricity
Consumption
7
44
NA
NA = Not Applicable
aAnderson, 1972: 8, 13.
Based on an average heat content for refuse of 5.260 Btu's per pound (Kasper,
1973: 7) and a 1971 U.S. energy input of 69. 0x10 Btu's (Senate Interior
Committee, 1971: 85).
CHydrogenation process at 1. 25 net barrels per ton of dry wastes (Anderson, 1972:
3) and a 1971 crude oil demand of 5. 7 billion barrels.
Conversion to methane at 5 cubic feet per pound dry waste (Anderson, 1972: 3)
and a 1971 natural gas demand of 23 trillion cubic feet.
6Coal demand of 600 million tons per year.
Based on'2,000 billion kilowatt-hours consumed.
wastewater plants, both small and large, are endeavor-
ing to utilize all of the gas rather than only a portion.
Overall conclusions of the study can be summarized as
follows:
1. Energy consumption in wastewater treatment in
general and sludge disposal in particular is a ma-
jor consumer in municipal government operations.
2. Larger wastewater plants that process sludge by
anaerobic digestion should analyze the cost-effec-
tiveness of utilizing all of its digester gas.
3. More study of energy balances in wastewater treat-
ment and sludge disposal are needed.
City managers and mayors across the country are
searching for cost reduction methods to reduce budget
deficits. Wastewater treatment has been shown to be a
significant consumer of energy. Although even substan-
tial reductions in wastewater operating costs will not
constitute a panacea, it is a good place to begin.
REFERENCES
1 City of Indianapolis Internal Memorandum from
Eugene Waltz, Technical Assistant to the Mayor to
Richard G. Lugar, Mayor of Indianapolis. October 13,
1973, p. 2.
2. The Urban Technology System Program, Metropol-
itan Government of Nashville and Davidson County;
Metropolitan Nashville's Response to an Electrical
Energy Emergency.
3. U.S. Department of Interior, A Study of Sludge
Handling, by R.S. Burd, Federal Water Pollution Con-
trol Administration, WP-20-4, 1968.
4. Advancing Environmental Control Technology, by
Albert C. Trakowski. Presented at the Second Interna-
tional Pollution Engineering Congress, Philadelphia,
Pennsylvania: October 22, 1973.
5. "MONITOR", Journal ofthe Water Pollution Con-
trol Federation, Volume 46, Number 4, April, 1974, p.
621.
6. Ibid, p. 621.
7. R.S. Burd, A Study of Sludge Handling, 1968.
8. Mignone, Nicholas A. "Anaerobic Digestion De-
sign for Energy Generation". Public Works, October,
1974, pp. 71-74.
9. Improved Anaerobic Digestion with Powdered Acti-
vated Carbon, by Nicholas A. Mignone. Presented at the
Central States Water Pollution Control Association An-
nual Meeting, Madison, Wisconsin: May 22, 1975.
-------
100 ENERGY CONSERVATION PRACTICES
10. Digester Off-Gas An Untapped Energy Source, by
Cornelius B. Murphy. Presented at the 47th Annual
Conference of the Water Pollution Control Federation,
October 7, 1974.
11. Goeppner, J. and Hasselmann, D.E. "Digestion
By-Product May Give Answer to Energy Problem",
Water and Wastewater Engineering, April, 1974 pp.
30-35.
12. "Overview of Sludge Handling and Disposal", by
J.B. Farrell. Proceedings of the National Conference on
Municipal Sludge Management. June 11-13, 1974, p. 9.
13. Smith, R. "Electrical Power Consumption for
Municipal Wastewater Treatment", EPA-42-73-281.
July, 1973, p. 42.
14. MONITOR, Journal of the Water Pollution Control
Federation, p. 621.
15. Ibid, p. 621.
16. Murphy, Cornelius B. Digester Off-Gas An Un-
tapped Energy Source.
17. Water Utilities Department, Dallas, Texas. "Spe-
cifications for the Purchase of Waste Digester Gas at the
Central Wastewater Treatment Plant". Contract Num-
ber 75-34, p. T-3.
18. MONITOR, Journal of the Water Pollution Control
Federation, p. 622.
19. Keeping Digestion at Blue Plains, Internal memo-
randum by Alan F. Cassel, Department of Environ-
mental Services, Washington, D.C.
20. Energy Alternatives: A Comparative Analysis.
Prepared for Council on Environmental Quality by Sci-
ence and Public Policy Program, University of
Oklahoma, Norman, Oklahoma, May, 1975, pp. 10-3 —
10-5.
21. Anderson, Larry L. (1972). Energy Potential from
Organic Wastes A Review of the Quantities and Sources,
Bureau of Mines Information Circular 8549. Washing-
ton: Government Printing Office.
-------
UPDATING THE 1974 PITTSBURGH CONFERENCE
Darwin R. Wright
United States Environmental Protection Agency
Washington, D. C.
INTRODUCTION
The real value of most conferences such as this sludge
management conference is the continuing dialogue
which is developed between the participants. One year
has passed since the last conference in Pittsburgh and
we felt it would be timely to report on the status of the
projects many of you heard about or read about at last
year's conference.
This paper was designed to answer the question, "I
wonder how that project we heard about last year at the
Conference ever came out?" The credit for this presen-
tation really goes to the original fourteen authors. They
have submitted brief summary comments edited to fit a
common format.
Recognizing that all papers would not necessarily
need updating, the authors were asked to report on any
other new and interesting work that they are involved in.
You are encouraged to contact the authors directly for
further information.
The following detailed comments from the authors are
in the same order as the original papers were presented
at the First National Conference on Municipal Sludge
Management.
Thickening of Sludges
Richard I. Dick
University of Delaware
Department of Civil Engineering
Newark, Delaware
In Richard Dick's presentation on "Thickening of
Sludges", thickening theory was reviewed and the inter-
action thickening with other sludge treatment and dis-
posal processes was discussed. Then economic implica-
tions of the interactions between thickening and other
sludge treatment and disposal processes were consid-
ered. This \vorkon the interactions between various pro-
cesses for sludge treatment and disposal is being con-
tinued and expanded.
The National Science Foundation has recently funded
a research project on "Process Selection for Optimum
Management of Regional Wastewater Treatment Re-
siduals" to be conducted by Professor Dick. The purpose
of the project is to study the interactions between various
components of sludge treatment and disposal processes
in order to develop a rational framework for devising
strategies for managing sludges. This will be accom-
plished by:
1. Developing cost and performance models for the
various individual processes of sludge treatment,
reclamation, and disposal.
2. Integrating the individual processes into plausible
schemes for sludge management at installations of
various sizes.
3. Optimizing the performance of the integrated
models and identifying sludge properties and de-
sign and operational variables which deserve spe-
cial consideration in developing sludge manage-
ment strategies.
4. Evaluating attributes of alternative sludge man-
agement schemes related to environmental impact
and public acceptance.
It is hoped to obtain the data required to develop the
cost and performance models from published literature,
engineering reports, and plant operational records. Pro-
fessor Dick invites those who may have such data on the
cost performance of typical sludge handling procedures
to contact him.
Anaerobic Digestor Operation at the
Metropolitan Sanitary District of Greater Chicago
Stephen P. Graef
The Metropolitan Sanitary District of Greater Chicago
Chicago, Illinois
Mr. Stephen Graef reports that no major changes have
taken place in the practice of anaerobic sludge digestion
by the Metropolitan Sanitary District of Greater
Chicago.
101
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102 PITTSBURGH CONFERENCE UPDATE
A Comparison of Diffused Air Aerobic Digestion
with Pure Oxygen Digestion of Waste Activated Sludge
David B. Cohen*
Wastewater Technology Centre
Environmental Protection Service
Burlington, Ontario
The objective of this study was to determine which
parameters have the greatest influence on the aerobic
digestion of waste activated sludge (WAS). In the first
experiment, dilute WAS (<1.0 percent TS) was aerated
with coarse bubble diffusers in an uncovered aeration
basin. In the second experiment, thickened sludge (four
to five percent TS) was oxygenated in an open tank pilot
plant. Two different ultra fine bubble oxygen diffusers
were used, a fixed diffuser (FAD) and a rotating diffuser
(RAD).
Major factors influencing aerobic digestion per-
formance were; temperature, sludge retention time,
mixing energy, solids concentration, and the initial vola-
tile fraction of the feed sludge. The high intensity mixing
oxygen diffuser accelerated solubilization of cells, which
increased oxygen respiration rates beyond the capability
of the diffused air system. Thickening of WAS had a
detrimental effect of microbial cell decay rate. This ef-
fect was overcome by the oxygen high intensity mixing
diffuser.
It was discovered that digestion performance could be
predicted by using a temperature X sludge retention
time factor. The critical factor required for good diges-
tion was 150 degree-days. Either one of these two factors
could be substituted for the other in the equation, as long
as the multiple of time and temperature exceeded the
critical value.
If the biomass temperature declined by 5°C or greater
in less than five days, nitrification ceased. A critical val-
ue of 250 degree-days was necessary to buffer the
system against such a cold temperature shock. Sludge
retention time in the digester was directly correlated
with air flotation chemical demand of the air digested
sludge. Sludge dewaterability of vacuum filtration was
improved after air digestion of dilute sludge, but ad-
versely affected by oxygen digestion of thickened
sludge, the volatile fraction of the digested sludge must
be reduced below 60 percent to avoid obnoxious odors. A
well stabilized sludge had an oxygen uptake rate below
3.0 mg 02/hr/g volatile suspended solids.
The microbial cell decay coefficient for volatile sus-
pended solids (k,j) was foundto be 0.07 days' ^compared
with 0.061 found in the literature. The highest biomass
reduction rate in the air digestion system occurred when
ecological diversity and rotifer population densities were
*David B. Cohen has presented results studied in Ontario, Canada by
the Environmental Protection Service. At the Pittsburgh Conference,
Dr. Cohen represented the Metropolitan Denver Sewage Disposal Dis-
trict No. 1. The paper presented wns Metro Denver's Experience with
Large Scale Aerobic Digestion of Waste Activated Sludge.
maximal. High biomass reduction rates were also ob-
tained in the oxygen digestion system, although pro-
tozoa and rotifers were not predominant. The organisms
responsible for pure oxygen digestion of thickened
waste activated sludge were heterotrophic mesophilic
bacteria.
Pressure Filtration - Municipal Wastewater
Solids, Cedar Rapids, Iowa
James W. Gerlich
Howard R. Green Co.
Cedar Rapids, Iowa
A detailed evaluation of pressure filtration was pre-
sented by Mr. Gerlich. At this time it is not possible to
present new data and long records of successful opera-
tion with the Passavant pressure filter, since the per-
formance of the units has changed very little. The follow-
ing points should be made. The pressure filter process,
as such, is a good one. The plant people attest to this.
When the equipment is in good mechanical condition it
performs better than anticipated in previous pilot work.
Continued structural failures of equipment have occur-
red. Most of this has been attributed to poor quality con-
trol and workmanship in the manufacturer's shop and
some to poor field service, operating instructions, main-
tenance instructions and related manufacturer's
guidance.
At this time, Passavant has just completed the third
set of new plates for one filter and are in the process of
fabricating a completely new set forthesecondfilter. In a
three year period, operation at best has only been about
50 percent capacity due to structural failures.
These structural failures were identified in engineer
reports as early as startup in 1972. Unfortunately, Pass-
avant was reluctant to consider deficiency of structure.
The facts, by Passavant observed measurements, were
that the internal support columns on the plates (eight
lines of stay-boss) were short about 4'/2 inches in the
length of the filter. Therefore the plate diaphragms were
not stable and allowed to move around. They failed by
metal fatigue at the diaphragm.
Foreign manufactured equipment of foreign tech-
nology leaves a lot to be desired. These units were manu-
factured in the United States, however, the technology
was German. Communication of technical information
is a problem for the client and for the manufacturer. In
the long run, foreign goods or technology can be a
problem.
Some of the support equipment was poorly designed.
Again, this was probably due to the limited technical in-
put at the manufacturer's level.
The reconstructed filter, with new plates, has been
doing a good job. Cakes are good, runs are short, things
are clean, and the operating personnel are happy. Only
time will evaluate how well the units last. However, a
basic structural problem as experienced should have
been solved with less time and expense.
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PITTSBURGH CONFERENCE UPDATE
103
Heat Treatment and Incineration
Dale T. Mayrose
Dorr-Oliver Incorporated
Stamford, Connecticut
Mr. Mayrose's paper covered the combined processes
of heat treatment, dewatering and incineration. No pro-
found changes or developments have occurred over the
past year which have altered Dorr-Oliver's basic recom-
mendations on sludge disposal. Dorr-Oliver is more con-
vinced that incineration is the ultimate answer to the
enormous problem of disposal of huge volumes of muni-
cipal sewage sludges.
Heat treatment has been used for many years as an al-
ternate process to aerobic and anaerobic digestion. Heat
treatment, like digestion, will reduce the volume of
sludge, but will still require the transportation of large
volumes of sludge to be disposed of by dumping on the
land or into the ocean. Dewatering by itself has also been
utilized for many years on municipal sludges. Sludges
consisting of at least 50 percent primary and 50 percent
waste activated sludge can be digested and dewatered
with centrifuges and vacuum filters to cake concentra-
tions of approximately 16 to 22 percent solids with the
use of conditioning chemicals. The same sludge, if heat
treated, can be dewatered to cake concentration in ex-
cess of 35 percent solids without conditioning chemicals.
The combination of heat treatment and dewatering re-
duces the volume of sludge. Thermal conditioning im-
proves the dewaterability of sludge which results in drier
cakes discharging from the dewatering device.
In the United States there are hundreds of sewage
treatment plants using incineration to burn dewatered
sludge. Nearly all of these plants use centrifuges or
vacuum filters to dewater chemically conditioned
sludges to cake concentration of approximately 18 to 22
percent solids. At these cake concentrations, auxiliary
fuel, usually No. 2 fuel oil, must be added to the incinera-
tor to sustain combustion. The need for conditioning
chemicals and particularly fuel oil to sustain combustion
puts a strain on the economics of incineration.
Normal domestic sewage sludges will burn in a fluid
bed incinerator at cake concentrations of approximately
35 percent solids, without the use of auxiliary fuel. There
is enough heat value in the volatile content of the sludge
to satisfy the thermal requirements necessary to evapo-
rate the water present in the sludge, incinerate the
solids, and produce a stack gas discharged at deodoriz-
ing temperatures of 1400° to 1500° F.
Each of these unit operations when considered
separately do not provide a total answer to the most eco-
nomical approach to sludge disposal. In the case of heat
treatment and dewatering, solids, although reduced in
volume, must still be disposed. Incineration alone, oper-
ating on sludge chemically conditioned and dewatered,
will require auxiliary fuel to sustain combustion.
The basis of the Pittsburgh paper was to illustrate the
economics of a sludge disposal system combining the
three operations of heat treatment, dewatering and in-
cineration: heat treatment to produce a sludge of greatly
improved dewaterability; dewatering to produce a cake
of 35 percent minimum solids concentration; and fluid-
bed incineration to reduce the organic sludge to an inor-
ganic ash without the use of auxiliary fuel or expensive
conditioning chemicals.
The only fuel required to operate the combined sludge
disposal system will be that required to operate the heat
treatment system.
Heat-treated sludge is used to preheat the cold sludge
in a sludge-to-sludge heat exchanger. The heat-treated
sludge at 400°F will preheat the cold, or nonheat-treated
sludge, to approximately 360°F. Steam is injected into
the sludge in the second section of the heat exchanger to
raise the temperature of the sludge from 360°F to 400°F.
The steam is generated by a boiler operating on fuel oil
or natural gas.
With today's energy crisis, the elimination of the fuel
required to generate steam would be a significant eco-
nomic improvement. During the last year, the use of
waste-heat boilers has been incorporated into the design
of the total sludge disposal.
The waste-heat boiler operates on the large volume of
hot stack gases at 1500°F discharging from the fluid-bed
incinerator to generate steam. The amount of steam pro-
duced in the waste-heat boiler is usually in excess of the
amount of steam required to operate the heat treatment
system. Heat recovery by the use of waste-heat boilers
has been practiced by Dorr-Oliver for many years in vari-
ous industrial processes using a fluid-bed reactor. Its ap-
plication in the municipal market with sludge incinera-
tion in relatively new. However, the technology is not
new. The design experience obtained from more
stringent or severe industrial applications is transfer-
able to the municipal market.
In Berlin, Germany, a new wastewater treatment
plant has gone into operation. This plant has been oper-
ating for approximately ten months. The solids disposal
system consists of heat treatment, vacuum filter de-
watering, fluid-bed incineration and heat recovery by
waste-heat boilers. The plant does not require condition -
ing chemicals for dewatering or fuel oil to operate the
heat treatment or incineration systems.
The solids disposal system at the Berlin wastewater
treatment plant is a wave of the future. It is a proven
economic method of sludge disposal.
Dorr-Oliver is currently exploring the possibilities of
using generated steam to operate steam turbines which
could produce electrical power to satisfy the needs of the
solids disposal system. This particular aspect is still un-
der investigation and has not yet been incorporated into
the design of any plant under consideration in the United
States. If it proves to be practical, like the application of
\\aste-heat boilers, it will make this particular approach
to solids disposal even more economically attractive.
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104 PITTSBURGH CONFERENCE UPDATE
Drying of Sludge for Marketing as Fertilizer
M. Truett Garrett, Jr.
Waste-water Division City of Houston
Houston, Texas
The sludge drying operation in the City of Houston is
continuing as reported last year. The demand for the
dried sludge is still very high.
However, in response to the energy crisis, the City of
Houston is reviewing the use of natural gas as the fuel
source. Even though natural gas is the fuel of choice, the
external demands for natural gas not only have driven
the costs up rapidly, but may also reduce the availability.
Consequently, studies have been initiated to develop
alternative fuel sources for the drying operations at the
two existing plants. Also, two new plants now in detailed
design, will be built with alternate fuel capability. Oper-
ation is expected in 1980. A third plant is in the prelimi-
nary design stage. The sludge processing system is be-
ing reviewed to determine which is the best, based upon
energy consumption.
Utilization of Digested Chemical Sewage Sludges
on Agricultural Lands in Ontario
Steven A. Black
Pollution Control Branch
Ontario Ministry of the Environment
Toronto, Ontario, Canada
Mr. Black reported on the utilization of digested
chemical sludges resulting from Ontario's phosphorus
removal program, in which approximately 100 plants
were affected by the December, 1973 deadline for phos-
phorus removal. The actual figure is 117 of which 116 are
now on line with the required phosphorus removal with
the compliance of the other being held up because of in-
plant expansion. Of the 56 plants with a December, 1975
deadline, five are already effecting necessary phos-
phorus removal and we expect the remainder to be able
to comply with the deadline.
The sludge research projects supported by the gov-
ernments of Canada and Ontario are continuing, with
some (virus, heavy metal analytical development,
sludge decomposition, application equipment) sched-
uled for completion by March 31, 1976. A new project
looking at survival of parasites in digested sludge has
been initiated. Interim reports published under the
Canada/Ontario Agreement on these projects are avail-
able from the Ministry of the Environment.
"Provisional Guidelines for Sewage Sludge Utiliza-
tion on Agricultural Lands" have been prepared by joint
ministerial committees of the Ontario Ministry of Agri-
culture and Food, Ontario Ministry of the Environment
and Ontario Ministry of Health are to be used in regulat-
ing the application of sewage sludges to agricultural
lands in Ontario. These guidelines, subject to approval,
refer to fluid sewage sludge only, and discuss the ac-
ceptable and non-acceptable levels of sludge constit-
uents such as heavy metals, nitrogen and phosphorus.
Additional information concerning these draft guide-
lines can be obtained by contacting the author.
The Economics of Sludge Irrigation
A. Paul Troemper
Springfield Sanitary District
Springfield, Illinois
The Springfield Sanitary District is currently applying
both aerobically and anaerobically digested sludge on
agricultural land at two sites. Sampling of the under-
drainage from the two sludge disposal areas has con-
tinued. Unfortunately the data for the Spring Creek
plant (the anaerobically digested sludge) does not
amount to much at this point. Pump problems made it
difficult to utilize the field. As soon as those problems
were resolved, most of the field was taken out of service
to accomodate some outfall sewer construction that ran
across the field. As a result, little worthwhile data can be
reported on this installation.
The Sugar Creek sludge application system (aero-
bically digested sludge) has been in full operation during
the entire time. A number of samples of the underdrain-
age have been collected. Results of this project will be
reported in an interim paper on the underdrainage water
characteristics at the Water Pollution Control Federa-
tion Meeting in Miami in October.
In general, based upon sampling of the underdrainage
water, the soil is very effective in removal of BOD,
suspended solids, fecal coliforms, phosphate, ammonia
nitrogen and total kjeldahl nitrogen. Data on removal of
nitrates is somewhat cloudy at this point and will require
additional data before drawing any conclusions.
Sampling of the underdrainage as well as the sludge
applied will be continued for a minimum of one addition-
al year. With the added data, conclusions with regard to
the capability of the soil to remove some of the nutrients
should be possible.
With regard to the crop grown on the areas at the
Spring Creek plant, alfalfa has been planted with the
hope that it will loosen up the soil to allow better percola-
tion of the water in the sludge. Tight soil is not a problem
at the Sugar Creek plant. Winter wheat was planted at
the end of last summer in an effort to determine how it
would react to the sludge application. The wheat crop
has been harvested, even though difficulty with horse
weed prevented complete harvest. In those areas where
the wheat was combined, it seems to be an outstanding
crop. One disadvantage with utilization of wheat as a
crop is that when the wheat stops growing in May, the
horse weeds are growing strongly and soon take over the
field. For this reason, wheat may not be a desirable crop
unless herbicides are used to control weed growth.
Orchard grass and alfalfa have also been planted
along with the wheat in this field, but no results on the
success of this crop are available at this time.
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PITTSBURGH CONFERENCE UPDATE 105
Sludge Management in Allegheny County
Richard M. Cosentino
Department of Works, Allegheny County
Pittsburgh, Pennsylvania
The project titled "Restoration of Strip Mine Lands
Using Municipal Treatment Plant Residues and Fly
Ash" was not funded by EPA. The project, which in-
volves high lime treatment of dewatered, undigested
sludge, has not yet been undertaken because of plant
construction delays. A meeting is planned with the Mc-
Candless Township Authority's consultant to discuss a
mutual project. At the present time, the possibility of
utilizing a fluid bed reactor at our transfer station does
not appear to be very likely.
However, the County has just received a grant offer
from EPA for a project titled, "Management of Residues
from the Treatment of Industrial Wastewaters". The
purpose of the study will be to develop a regional indus-
trial wastewater residue control management system for
Allegheny County, which will be consistent with recent
legislation, the needs of the economy within the County,
and one which will create the proper environmental cli-
mate to attract new industries to Allegheny County.
In addition to the study above, the County has re-
ceived a grant from the Pennsylvania Department of En-
vironmental Resources to undertake a management
study of municipal wastewater treatment plant sludges,
water treatment plant sludges, septic tank pumpings,
and spent acids. The objectives of the study will be to
determine:
1. Amount, type and dispersal of sludges in the
County.
2. Alternative methods for disposal including and un-
digested sludges and attendant problems.
3. The human and physical resources required to
operate a municipal sludge management program.
Sludge Disposal by Incineration at ALCOSAN
George A. Brinsko
Allegheny County Sanitary Authority
Pittsburgh, Pennsylvania
In this year and it appears to be true today, the prob-
lem of solids disposal is still a major issue and still re-
mains the most costly of all the processes.
Here in Pittsburgh, the odor problems were elimi-
nated by the ducting of the foul gases from the sludge
vacuum filters to the incinerators for thermal destruction
and the utilization of hydrogen peroxide to oxidize the
odor producing sulfides in the sludge. However, be-
cause of the odors, our public image has been stained
and our community relationship has been strained. The
public will not forget nor will they let us forget. Any odor
that our neighbors smell or think they smell, although it
may be coming from some other source, will result in a
rash of complaints. It will take years for us to get back in
good standing with our neighbors. The odors are gone
but the public resentment still exists.
In 1974, solids increased 37 percent to 38,946 dry tons
with a disposal cost of $65.30 a dry ton, an eight percent
increase over the previous year. Disposal costs are spi-
raling with no end in sight. The fuel adjustment charge
has caused a 55 percent increase in auxiliary fuel costs.
This coupled with new Federal and state requirements
on ash disposal due to the heavy metals has resulted in
over a 110 percent increase in ash disposal costs. There
has to be some relief from the regulatory agencies.
To counter-act the rise in auxiliary fuel costs, new and
more efficient dewatering methods have to be developed
or found. A dryer cake (around 35 percent)has to be ob-
tained to economically incinerate sewage solids. Maybe
the filter press or varnip press is the answer. Whatever
the solution maybe, less power or auxiliary fuel must be
used. A mixture of solid waste and sewage solids with
the generation of steam as a final product still appears to
be the best answer to everyone's problem. Sludge dis-
posal is a greater problem today than it was a year ago. A
greater concentrated effort has to be put forth by all to
help, if not solve, this major national problem.
Sludge Handling and Disposal at Blue Plains
Alan F. Cassel
District of Columbia Department of
Environmental Ser\'ices
Bureau of Wastewater Treatment
Washington, D.C.
Digested sludge disposal continues as before. Filter
cake is plowed into the soil. Marginal lands have been
used exclusively the past year.
Raw sludge disposal by the trenching method has
been in full operation since mid-March, 1975. Currently,
180 wet tons per day of filter cake are disposed of by this
method.
Composting raw sludge in static piles is a most prom-
ising research project ongoing at Beltsville. Dr. Elliot
Epstein will report on this project at this conference. The
finished compost product is finding widespread accept-
ance in the Washington area, particularly in large public
projects such as the Bicentennial Gardens.
Organic Recycling had operational problems with
fires and excessive wear in their dryer and associated
equipment. They have only successfully dried and pel-
letized digested sludge to date. The fibrous nature of
raw sludge has provided operation problems. They are
making equipment modifications and should be in full
operation by September, 1975. They are now a wholly-
owned subsidiary of Universal Oil Products.
EPA Region III made a decision not to build the incin-
erators at Blue Plains until one more look was taken at all
possible alternatives. The District hired Camp, Dresser
and McKee, Inc. to conduct the study. The study will be
completed by November, 1975 and hopefully a decision
will be made then.
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106 PITTSBURGH CONFERENCE UPDATE
Energy Conservation and Recycling Program of the
Metropolitan Sewer Board of the Twin Cities Area
Dale C. Bergstedt
Metropolitan Waste Control Commission
Saint Paul, Minnesota
Thermal energy conservation continues to be the
dominant mode of thought in the Commission's en-
gineering and planning. A summary of certain projects
that were reported on in Pittsburgh, follows.
Pyrolysis of refuse along with sludge cake continues
as a design project that has been carried forward by the
Rust Engineering Company under the overall direction
of our solids processing consultant, Toltz, King, DuVall,
Anderson & Associates of St. Paul. The consultants have
completed the specifications booklets and the necessary
drawings to permit advertisement of the major capital
items on a pre-buy basis. Bidding documents have been
submitted to the EPA and to the state regulatory agency
for grant approval. The intent is to purchase these major
capital items and then design the physical facilities to
the exact dimensional requirements while the equip-
ment items are being fabricated. It is anticipated that
substantial time will be saved and possibly avoid escala-
tion of costs.
Waste heat recovery is programmed in the solids
disposal expansion. The design of waste heat boilers
that will be used for generating 300 to 400 psi steam, to
operate sludge thermal conditioning facilities has been
completed. These boilers will receive incinerator gases
at 1250°F and drop the temperature to 600°F, with
further heat recovery to be accomplished in sludge
dryers.
Roll press (Impco "Vari-Nip") evaluation for sludge
dewatering has continued. We have completed one
year's investigation using this continuous roll press as a
means of dewatering conditioned raw sludges. The sys-
tem has worked well when primary sludge is fed, but it
has not yet proved cost-effective when mixtures exceed-
ing 30 percent secondary (waste activated) chemically or
thermally conditioned sludge are fed. The press delivers
cake in the range 35 percent to 40 percent solids, suffi-
cient to be autogenous in multiple hearth furnaces, and
thus eliminating the need for fuel.
On the general subject of utilization of fuels, the
MWCC has just been awarded a grant of approximately
$400,000 by the EPA for a two year study of co-incinera-
tion of solid fuels such as coal and combustible refuse
with sludge cake. In this way, it is anticipated that these
fuels will offset at least two thirds of the need for natural
gas or fuel oil in burning sludge dewatered by presently
installed vacuum filters. This project is a direct out-
growth of the coal and wood chip addition experiments
reported in last year's paper.
Sludge Management System for St. Louis
Peter F. Mattel
Metropolitan St. Louis Sewer District
St. Louis, Missouri
The solids handling systems for the three treatment
facilities of the Metropolitan St. Louis Sewer District
were discussed by Mr. Peter Mattei.
Secondary treatment is still in design, therefore, the
problems that were discussed are still the same, and the
cures which we will have with the completion of con-
struction of secondary treatment on the Mississippi
River have not been solved. A whole new program has
opened in St. Louis with the advent of Public Law No.
92-500 forcing political entities to join together in the
solving of mutual treatment and sludge handling prob-
lems. Mr. Mattei would like to participate in a discussion
of crossing political boundary lines for the purpose of
protecting the health and welfare of the people we all
serve. He is interested in finding out how other areas are
handling or solving this complex problem.
Summary of "Pretreatment and Ultimate
Disposal of Wastewater Solids Conference" -
Held May 21-22, 1974, Rutgers University
Robert W. Mason
Research and Development Branch
Region II Office - EPA
New York, New York
This paper does not lend itself to an updating, so Dr.
Mason has provided a summary of recent developments
in EPA Region II.
During 1974, 4,680,000 cubic yards of sewage sludge
corresponding to approximately 500 dry tons, were
barged into the New York Bight and dumped at a site
twelve miles off shore. New Jersey municipalities con-
tributed about 2,000,000 cubic yards of this total, the
rest coming from New York City municipalities. With the
conversion of all primary sewage plants to secondary
treatment and with the projected population growth, the
volume of the secondary sludge is expected to increase
to about 2,000 dry tons per day by the year 2000. A large
portion of the increase will occur by 1980 with the up-
grading of existing pollution control plants from primary
to secondary treatment.
Since the United States Environmental Protection
Agency (EPA), Region II, has committed itself to the
phasing out of ocean disposal of both industrial and
municipal wastes by 1981, provided a sound plan which
is environmentally acceptable can be developed, the
study of disposal alternatives is obviously a top priority
job. To answer adverse criticisms generated by the con-
tinued use of the present dumping site, two new areas
are under study by EPA. A site will be selected within
one of the two areas when the environmental impact
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PITTSBURGH CONFERENCE UPDATE 107
statement has been prepared. This should occur in Janu-
ary, 1976 and dumping transferred to the new site some-
time thereafter in 1976.
The U.S. EPA, Region II, has authorized, and through
the Interstate Sanitation Commission, is funding a study
of procedures for disposal of sludge—excluding ocean
disposal.
Phase I of the study is now complete and a report will
be issued in the middle of July. Recommendations for
the New York Metropolitan Area are primarily pyrolysis,
and to a limited extent, for selective sludges, land
disposal. Pyrolysis in multiple hearth equipment pre-
ceded by filter press dewatering of sludge is the favorite
procedure. Since pyrolysis in such equipment has not
been demonstrated, it is planned to initiate a pilot study
of the operation within the very near future. The recom-
mendation to go to pyrolysis was based on environmen-
tal impact, economic feasibility, and energy recovery.
Only a limited quantity of sludge was recommended
for land disposal. The limiting factors are the heavy
metal content of most of the area sludges as well as the
high cost of land.
As of the middle of July, Phase II of the study has been
initiated. Pyrolysis and land disposal will be examined in
depth in Phase II, the purpose being to develop, in spe-
cific terms, a recommended technical plan for sludge
management on a regional basis in the New York - North
Jersey Metropolitan area. Phase II will be completed by
June 1, 1976.
Upon completion of Phase II, comparisions will be
made between controlled ocean disposal (based on in-
vestigations concurrently being carried out by the Na-
tional Oceanic and Atmospheric Administration and the
U.S. EPA) and in-depth study of the selected alterna-
tives in Phase II. Taking into account all of these sources
of information, the Interstate Sanitation Commission
will develop a New York Metropolitan Area Sludge man-
agement plan.
The objective of EPA Project 801871, Ocean County,
New Jersey, is to demonstrate the disposal of waste-
water solids by application on coastal plain soils. Work
was started on July 1, 1973, and, with a supplemental
funding, is scheduled to terminate on October 31, 1976.
Participating in the project are the following groups:
1. U.S. Environmental Protection Agency, Region II;
and the Office of Research and Development
2. Department of Environmental Science, Rutgers
University
3. Department of Agricultural Engineering, Rutgers
University
4. Department of Soils and Crops, Rutgers University
5. New Jersey Division of Fish, Game and Shell Fish-
eries
6. New Jersey Division of Water Resources
7. U.S. Geological Survey
8. Ocean County Sewerage Authority
To date applications of liquid sludge (five percent sol-
ids) have been applied to quarter acre plots over a two-
year period. (The first year of the grant, starting July,
1972 was devoted to selection and clearing of plots,
drilling wells and establishing baseline data.) Three
loading parameters were used: 10, 20, and 40 tons/acre/
year. Crops of Rye and Midland and Bermuda grasses
were grown. Sixty-nine wells have been installed to
monitor groundwater quality. Multi-depth samplers
were also employed to define the pattern of the pollution
plume.
During 1973 and 1974 a total of 251 soil samples and
over 2,000 groundwater samples have been analyzed.
Grasses were harvested for yields, and plant tissue was
analyzed for various nutrients and heavy metals. Soils
were also analyzed throughout the period to measure the
buildup of organic matter, nutrients, and heavy metals.
While correlations between soil loadings, crop yields
and groundwater contamination were found in the two
full year's growing study, the results are still inconclu-
sive. It is evident that the study must be continued
through another full growing season (to October 31,
1975) followed by one full year (to October 31, 1976) of
measurement and analysis of all phases now under in-
vestigation.
On completion of the project it is anticipated that the
following information relating to wastewater solids utili-
zation on the land will have been developed:
1. Pollution impact on the groundwater, especially in
regard to nitrate.
2. Economical application techniques.
3. Soil and plant impact.
4. Recommended monitoring systems.
5. Suitability of wastewater solids as a soil conditioner
to increase the yield of wildlife and food plants.
6. Odor associated with applications.
SUMMARY
In summary, it is obvious that the participants from
the 1974 Pittsburgh Conference still find sludge man-
agement a complex and interesting problem. Progress is
being made towards the development and demonstra-
tion of new technology, but much more needs to be done.
In addition, problems concerned with the institutional
aspects related to Federal and state regulatory agencies
must be resolved.
The impact of the energy problem is clearly evident.
The high cost of fuel appears to indicate that better de-
watering technology is needed. Energy recovery sys-
tems through the use of waste-heat boilers and pyrolysis
units appears attractive. Land application of properly
conditioned sludges may also result in a net reduction in
energy requirements.
Much remains to be done, but it is encouraging to see
that a tremendous amount of work is being actively pur-
sued towards development of environmentally and eco-
nomically acceptable sludge management systems.
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108 PITTSBURGH CONFERENCE UPDATE
Finally, a "thank you" to all of the contributing mation on these projects or projects which you may be
authors for providing the valuable information reported conducting. The free flow of technical information is
in this paper. Interested persons are encouraged to com- vital to a successful ending in our joint fight to turn this
municate directly with both the contributing authors and waste product, sludge, into a national resource.
the participating EPA personnel to exchange any infor-
-------
SUMMARY OF THE ASCE SEMINAR
ON SLUDGE DISPOSAL*
C. MichaelRobson
MCA Engineering Corporation
Baltimore, Maryland
The "Sludge Handling and Disposal" session was in-
tended to provide information to practicing engineers in
contrast to the research orientation of much of the Con-
ference. Five speakers were invited to participate repre-
senting Federal and state agencies, the consulting en-
gineering field and equipment manufacturing. Sum-
maries of each presentation are provided, supplemented
by the information provided in the subsequent question
and answer periods.
Overview of Sludge Handling and Disposal
J.B. Farrell
National Environmental Research Center
U.S. Environmental Protection Agency
Cincinnati. Ohio
Dr. Farrell served as the keynote speaker for the ses-
sion and effectively introduced the topics to be covered
by the speakers. He pointed out that we are caught be-
tween the increasing amount of sludge and the increas-
ingly stringent controls on sludge disposal. The 4 X 10"
tons/year of sewage sludge generated in 1975 are ex-
pected to increase to 7 X 10" tons/year in the 1980's.
Much of the sludge will be more difficult to handle as
more plants are upgraded to include secondary and ter-
tiary sludges. Also, the eastern and western cities are
facing the problem of the apparent trend to phase out
ocean disposal of sludge. Stricter rules on air pollution
and heavy metals make sludge disposal even more diffi-
cult. Two other complicating factors are the rising costs
of energy and fertilizer.
Dr. Farrell divided his presentation into two parts,
sludge treatment and sludge disposal, but noted that
there was frequently a hazy distinction between the two.
Sludge treatment preceeds sludge disposal and general-
ly does not impact upon the community except for odor.
Therefore, processing choices are governed by cost and
efficiency.
*Summary of "Sludge Handling and Disposal" Session of the Second
Annual National Conference on Environmental Engineering Research,
Development and Design. Environmental Engineering Division,
ASCE, held July 21, 1975, University of Florida.
One of our primary goals today is to remove more
water from the sludge. The removal of water reduces the
energy required in the treatment process if sludge in-
cineration is to be part of the sludge disposal process.
Less water reduces hauling costs if sludge landfilling is
the disposal method. Dr. Farrell reviewed the dewater-
ing devices available in addition to the time honored
vacuum filter. These include:
• Belt Filter Presses
Carter (German-Klein)
Tail Andritz
Permutit
Smith and Loveless
Envirotech
Unimat Tromel Filterpresse (Gevman)
• Plate and Frame Filter Press
Passavant
Nichols (British-Edwards & Jones)
Envirotech (Shriver)
Dart Industries
• Centrifuges
Bird
Dorr-Oliver
Rexnord
Ingersall-Rand (Kreuger)
Sharpies
The EPA will publish a bulletin on sludge disposal in
the Federal Rgister within the next few weeks. The bul-
letin covers all means of sludge disposal, but concen-
trates on sludge utilization. The highlights of the bulle-
tin include: recommends the utilization of sludge but
tries to establish a baseline for safe use; recommends
non-agricultural use if possible; provides guidelines for
agricultural use; requires pathogen reduction for sludge
to be disposed on land with easy public access; estab-
lishes maximum loading rates for disposing sludge on
agricultural land, because of metals. If crops are to be
eaten raw, three years time must elapse between sludge
application and crop harvesting. Even if crops are
cooked or processed, the sludge must be free of indicator
organisms.
109
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110 ASCE SEMINAR SUMMARY
The question of reducing pathogens presents prob-
lems. Methods to reduce pathogens include thermo-
philic anaerobic digestion, thermophilic aerobic diges-
tion, radiation and pasteurization.
Another interesting concept was the wet oxidation
process promoted by Barber Coleman, which includes a
means of recovering metals from the sludge.
Incineration as a means of sludge disposal faces the
problems of energy conservation and particulate matter.
Our knowledge of the health effects of incinerating par-
ticulate matter must be increased to make it possible to
establish effective standards. Otherwise, incineration
may become less and less acceptable.
The energy problems associated with incineration
have directed interest in pyrolysis systems combining
sewage sludge and solid waste, such as the current study
by the Bureau of Mines. Another pyrolysis system is the
Purox system of Union Carbide. Kalinski has suggested
an interesting concept of modifying a conventional mul-
tiple hearth incinerator to act as a pyrolysis unit.
Treatment of Sludge Processing Sidestreams
A.A. Kalinski
Camp Dresser & McKee, Inc.
Boston, Massachusetts
Dr. Kalinski pointed out that sludge processing side-
streams are frequently ignored by designers. The side-
streams are merely shown by an arrow illustrating a re-
cycle back to the liquid treatment system without identi-
fying the pounds per day of the constituents of the recy-
cle flow. His awareness of the problem was intensified
by being involved in the updating of the publication, A
Study of Sludge Handling and Disposal by R.S. Euro.
The updated document entitled Handling of Municipal
Sludges and Sidestreams, soon to be published by EPA,
places great emphasis on sidestream treatment.
Subsequently Dr. Kalinski was involved in a study for
regional or subregional sludge processing facilities for
the New York—New Jersey Metropolitan Area. No
wastewater treatment plant was available for recycling
and the possible treatment of the sidestreams produced.
The required separate treatment of all sidestreams be-
fore discharge into any receiving water afforded an ex-
cellent opportunity to precisely identify all such treat-
ment costs. In addition, total energy consumption was
indicated. Such sidestream treatment costs can be a very
high proportion of many sludge processing methods and
increase the total energy requirements.
Dr. Kalinski's presentation utilized recycle streams
from three sludge treatment processes to illustrate the
unit costs of processing sludge solids. The following
points were assumed for the presentation.
Basic Assumptions: (Quantity per Million Gallons
Raw Sewage)
A. Sludge to Sludge Processing System
1 ton dry solids
TABLE 1
Effect of Recycle Stream
PROCESS
ANAEROBIC DIGESTION
HEAT TREATMENT
WET OXIDATION
RECYCLE BOD5
RANGE
(mg/l)
1000 to 3000
6000 to 10,000
—
AVERAGE
(mg/l)
2000
8000
10,000
Ib./ton
D.S.
100
400
500
Inc. Aer.
Req. (%)
8
33
40
* Ib./ton D.S. • Ib. BODs in recycle per ton of dry solids processed.
B. Primary Effluent BOD5 Without Recycle Streams
1200 pounds BODs
C. Sludge Processing Recycle Flow
6000 gallons
Table 1 illustrates the effect of recycled BOD5 on siz-
ing of the aeration tanks. It can be seen, based on the
data presented, that the activated sludge aeration would
be increased eight percent to account for anaerobic di-
gester recycle liquids, 33 percent to account for heat
treatment liquor, and 40 percent for wet oxidation recy-
cle liquor. Table 2 illustrates the effect that ammonia in
the recycle liquor would have on a treatment plant de-
signed to nitrify. The study concluded that the treatment
of sidestreams is a major expense and heat treatment
and wet oxidation are not cost effective in the treatment
of sidestreams.
Dr. Kalinski expressed concern on the effect of other
sidestreams such as incinerator scrubbers or odor con-
trol scrubbers. Incinerator scrubber water contains vola-
tilized metals such as lead and mercury in addition to
particulate matter. Odor control for off gases from a
Zimpro system required a wet scrubber, resulting in a
1000 mg/1 COD sidestream that was treated with activa-
ted carbon.
TABLE2
Effect of Recycled Ammonia
of Nitrification System
PROCESS
ANAEROBIC DIGESTION
HEAT TREATMENT
WET OXIDATION
RECYCLE AMMONIA
AVERAGE
(mg/l)
500
800
1500
Ib./ton D.S.*
25
40
75
Ib. O2/ton D.S.**
100
160
300
Ib. ammonia/ton dry solids processed
* 4 Ibs. O2/lb. ammonia nitrified
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ASCE SEMINAR SUMMARY
111
The following information evolved from the question
and answer period.
The cost of energy in the New York area was men-
tioned as five cents/kWh, which was cited as a reason for
emphasizing energy recovery.
The favored system included plate and frame filter
press dewatering to 40 percent solids, incineration and
recovery of waste heat to power portions of the process.
Studies of these systems predicted a net recovery of 100
kWh per ton of dry solids processed. The heat value of
the composited sludge was 5000 Btu per pound of dry
solids because a portion of the sludge had previously
been digested.
The study had favored pyrolysis for energy recovery
as it appeared to have a lesser air pollution problem.
However, Dr. Kalinski felt that pyrolysis systems were
five years away from being proven for application. He
foresaw incinerators being selected in place of pyrolysis
for the next five years. However, he predicted that mul-
tiple hearth incinerators would be retrofitted to pyrolysis
with few major changes.
Aerobic digestion had not been considered for sludge
processing. A 1974 University of Texas publication "Re-
covery of Energy in Waste Treatment Plants" had
shown a net potential energy recovery of 600 kWh per
ton of dry solids processed anaerobically but a net input
of 300 kWh per ton of dry solids digested aerobically.
However, aerobic digestion was favored over anaerobic
digestion in terms of total cost for plants less than ten
mgd in size.
Energy Conservation Through Incineration
F.S. Howard
Envirotech Corporation
Belmont, California
Mr. Howard opened his presentation with a definition
of sludge as provided to him by a European counterpart.
"Sludge is a substance with few attractive properties, it
is voluminous, it stinks, it is difficult to dewater on ac-
count of its colloidal character and it can be qualified hy-
genically as unreliable."
Historically, the primary concern of treatment plant
designers, regulatory authorities and municipal person-
nel centered around the liquid portion of the plant. The
solids generated in the plant were left to more or less
take care of themselves through the utilization of some
rather pedestrian methods, such as burial, spreading,
barging and dumping. As time went on, the attention
was still focused on the liquid portion with some slight
improvement in the handling of solids. Sludge digestion
and drying became more widely practiced, but grit,
screenings and skimmings were still handled expedi-
tiously by dumping out back or burying in landfill opera-
tions. Late in the 1930's a few plants built multiple
hearth incinerators and sludge burning got off to a rather
"smokey" start, burning sludge cakes vacuum filtered
with the aid of chemicals and usually requiring consider-
able auxiliary fuel to establish combustion. Still the
number of incinerators have increased and they handle
more and more sludge.
Today the impact of rising energy costs and environ-
mental concerns have caused us to review existing con-
cepts. Incinerators can be designed to meet the most
stringent air pollution standards, such as the recent de-
sign for Palo Alto, California. It can be shown that, in
many cases, the air pollution resulting from truck haul-
ing of sludge for land disposal is greater than incinera-
tion on site.
This paper was a result of practical experience and re-
search concerning the improvement of the efficiency of
sludge solids incineration. It is important to improve
combustion efficiencies and reduce auxiliary fuel re-
quirements as much as possible. To better understand
an incineration system, we must deal with the basic
components of combustion and how they might be al-
tered through plant operation and/or design to reduce
auxiliary fuel requirements; or to select more readily
available fuels such as scum, coil, paper and low grade
oils; or to make energy available for other plant functions
through waste heat recovery.
The basic areas discussed were: (1) moisture; (2) vola-
tiles; (3) excess air; (4) design and operation; and (5)
waste heat.
Moisture. When incinerating sludge cake, the major
fuel requirement is that needed to drive off the water in
the feed cake. Eachpoundof water required 1400 to 1600
Btu under normal operating conditions. Autogenous
burning is not too difficult if sufficient volatile solids and
a high solids concentration exist. However, we still need
fuel to control the furnace. As an example, for a plant in
the five to ten mgd size range, operating a vacuum filter
for dryness instead of yield would result in the cake sol-
ids content increasing from 20 percent to 25 percent with
a resultant saving of ten gph of fuel oil.
Volatiles. The volatility of incinerator feed cake can be
increased by feeding raw sludge in place of digested
sludge. Also highly volatile materials such as grease,
scum and tramp oil can be blended with the sewage
sludge to increase the cake volatility. For a five to ten
mgd treatment plant a saving of nine gph of oil could be
achieved by increasing the sludge volatility from 50 per-
cent to 75 percent.
Excess Air. Any excess air introduced to the furnace
must be heated. Therefore, excess air should be reduced
to a minimum, but operationally reasonable, level.
While 50 percent excess is a good operational level, it is
not uncommon to find 150 percent to 200 percent excess
air being used at operating facilities. Reduction of the
excess air from 150 percent to 75 percent was shown to
reduce oil requirements by six gph.
Reduction of excess air may be achieved by a control
loop, using exhaust gas oxygen levels to control the in-
duced air fan damper. An example of successful applica-
tion of this concept is the San Mateo, California Multiple
hearth incinerator installation.
-------
112 ASCE SEMINAR SUMMARY
Combined Effect. The combined improvements of
cake solids concentration increased from 20 percent to 25
percent, excess air reduced from 150 percent to 75 per-
cent and volatility increased from 50 percent to 75 per-
cent, resulted in a total oil saving of 25 gph.
Design and Operation. A good system design will in-
clude those features and controls necessary to all the
operators to cope with feed variations and combustion
requirements. Such features include providing more
rabble arms and rabble arm teeth to improve contact of
the sludge in the hearths with the flames; and providing
a means of measuring the sludge cake input and relating
it to the speed of rotation of the rabble arms.
The cost of an average sludge incinerator is approxi-
mately $2,500,000 without building. The specifications
for a sludge incinerator call for startup training and as-
sistance. This costs approximately $15,000, which is less
than one percent of the cost of the furnace. A one year
training program would result in better training and bet-
ter operation and would cost approximately $100,000 or
approximately four percent of the installed incinerator
cost.
Waste Heat Recovery. Ideally, when all the foregoing
factors have been optimized, the furnace will require
auxiliary fuel for temperature control only. Excess heat
will be available. Some designs lend themselves to in-
cluding a waste heat recovery boiler generating steam
for building heat or plant processes, such as a heat
treatment sludge conditioning system. Such systems
have been referred to as closed energy loops (CEL).
These are normally continuously operating plants.
CONCLUSION
Thermal incineration continues to gain acceptance by
providing convenient on-site reduction of sewage
sludges to sterile ash. However, in spite of this popu-
larity trend we must continually review present day de-
signs in the light of present and future environmental
and economic demands.
Most incinerator systems operating today were de-
signed and built during times of low cost fuel and semi-
stringent air pollution requirements. Today we have re-
sponded and in some cases over reacted to air pollution
control demands. A balance can soon be reached, if we
remain logical.
The fuel problem is more urgent and requires an im-
mediate review of both our present practices and future
plans. In the case of existing incinerator installation, it
has been shown how minor changes in operation and de-
sign can greatly reduce fuel consumption. Further, the
inclusion of facilities capable of producing drier sludge
cakes results in autogenous incineration with elevated
exhaust gas temperatures. The exhaust gases can then
be used to develop sufficient steam for a sludge heat
treatment system, building heat or other plant require-
ments.
Plant design incorporating these components can re-
sult in a closed energy loop system in which the sludge
volatility provides most of the energy required for sludge
reduction. The resultant sterile ash, incidentally, still
contains virtually all chemicals of fertilizer value.
DISCUSSION
The following points were discussed in the subse-
quent question and answer period.
Pulverized coal works well as a supplemental fuel.
Fairly poor grade coal may be used for this purpose. Se-
lected refuse, after removal of metal and glass, may also
be used as a supplemental fuel as it is high in volatile
material and low in moisture. Sludge cake and selected
refuse are added to the furnace at different hearth levels
due to their differing burning characteristics.
Both fluidized bed and multiple hearth incinerators
have their particular advantages under given conditions.
Highly volatile wastes might favor selection of a
fluidized bed incinerator. However, in a fluidized bed in-
cinerator all inerts go out the furnace stack and place an
additional load on the scrubber.
Multiple hearth incinerators can be converted to py-
rolysis units in the manufacturing of charcoal. Such a
conversion requires planning in the design stage.
Landspreading of Liquid Municipal Sludge
David L. Masse
Battelle Columbus Laboratories
Columbus, Ohio
Since the vast majority of active landspreading activi-
ties are not reported in the open literature, a literature
review will not yield an accurate estimate of the propor-
tion of United States sewage treatment plants which are
routinely disposing of their liquid sludges via land-
spreading. Furthermore, an examination of the most re-
cent inventory of municipal waste facilities, while pro-
viding information on sludge treatment and disposal
methods, does not yield a reliable estimate of the extent
to which landspreading is currently practiced in the
United States.
Mr. Masse reported on the results of a study per-
formed for the U.S. Environmental Protection Agency
on the State of the Art of disposal of sewage sludge by
landspreading. This report is published as EPA-670/2-
75-049, Review of Landspreading of Liquid Municipal
Sewage Sludge. An annotated bibliography is also avail-
able from the National Technical Information Service.
The paper presents the results of a mail and telephone
survey of the more than 1900 sewage treatment plants of
five Federal regions of the United States which are
greater than one mgd in treatment capacity. Field visits
to 26 plants were carried out to obtain pertinent unre-
ported data. The five Federal regions were: Region 2
New York and New Jersey; Region 3 Pennsylvania,
Maryland, Delaware, Virginia, and West Virginia;
Region 4 - Kentucky, Tennessee, North Carolina, South
-------
ASCE SEMINAR SUMMARY
113
Carolina, Mississippi, Alabama, Georgia and Florida;
Region 5 Minnesota, Wisconsin, Michigan, Ohio, In-
diana, and Illinois; and Region 9 California, Nevada,
and Arizona.
These regions were selected on the basis of the total
population involved and on the fact that they represent
the range of climate, topography, and soil conditions to
be encountered throughout the United States.
The sewage treatment plants surveyed were catagori-
zed by Federal region and plant size as shown in Tables 3
and 4.
TABLE 3
Treatment Plant Size Distribution
TABLES
Field Visits
Plant
Size,
mgd
Region
^
Total
l-ll)
Ill-Mil)
11)0
Tm a 1
247
18
12
297
27(1
26
6
102
466
41)
3
509
444
82
9
535
211
51
4
266
1,638
237
34
1,909
TABLE4
Estimated Number of PI ants Using Landspreading
Planl
Size,
mgd
Mil
III-IDO
111(1
Total
77
6
3
86
92
4
Region
5
161)
14
I
174
33
4
Total
370
27
4
401
Of this number 400 or 20 percent are estimated to be
using landspreading, with landspreading most popular
in Zone 5 and least popular in Zone 2. Most of the plants
using landspreading were in the one to ten mgd size
range, but most of all the plants are in this size range.
While the majority of the plants have practiced land-
spreading for less than ten years, several plants have
used it for sludge disposal for 30 to 40 years. Land-
spreading is typically utilized in a secondary wastewater
treatment system which digests sludge anaerobically.
Sludge is hauled for disposal on agricultural land by
means of tank trucks driven by plant personnel with a
haul distance of less than ten miles. Other types of land
used for disposal included parks, airports, gold courses,
strip mines, landfills, cemetaries, and orchards.
Visits to 26 selected plants were carried out to collect
further data (see Table 5).
Costs of operating land disposal systems are difficult
to obtain due to the cost control systems of the average
plant. However, Table 6 provides information derived
from the study. It was observed that labor costs were 65
percent to 70 percent of the overall cost.
There is presently little or no monitoring of the effect
of the sludges on the land. Springfield, Illinois was one
of the few places to monitor for metals. The city returns
the spreading area underdrainage to the plant, but there
Region
1-10
10-100
State
California
Florida
Illinois
Minnesota
Ohio
Wisconsin
Total
is little planning with respect to a loading rate. A cycling
of land disposal is caused by weather conditions.
DISCUSSION
The following points resulted from the question and
answer period.
Public acceptance of sludge landspreading is probably
better in smaller centers but has met strong opposition
in Chicago and Philadelphia.
Direct ploughing of sludge into the land has not met
with much favor due to the higher cost of equipment
and labor. Boulder, Colorado practices this method
of disposal.
The wastewater operations at the Penn State Uni-
versity Wastewater Treatment Plant cannot meet the
demand for their metal-free aerobically digested liquid
sludge. The presence of metals in the sludge makes dis-
posal more of a problem. Better control of metals in the
sewers is required, but control may be difficult in com-
bined sewer systems if storm runoff contains metals.
TABLE6
Land Disposal Costs (1972 Dollars)
Unit
$/100 gallons
S/Dry Ton
Range
1.22 to 15.00
2.33 to 61.02
Average
3.90
20.40
Treatment of Sludge for Land Disposal
Clinton R. Albrecht
Maryland Environmental Service
Annapolis, Maryland
In 1972, the District of Columbia entered into a mas-
sive construction effort at the 300 mgd Blue Plains
Wastewater Treatment Plant in order to meet new efflu-
ent standards for discharge into the Potomac River. This
construction effort eliminated the existing sludge drying
facilities and resulted in a huge sludge disposal problem
pending completion of proposed sludge incinerators. In
order to comply with discharge standards during the
construction or interim period, the addition of metal
salts to one-half of the secondary treatment units was
used to reduce the discharged BOD.5 to less than the re-
quired 100,000 pounds or 40 mg/1 600.5. One result of
this upgrading of the effluent quality was the daily pro-
duction of 240 tons per day of raw (chemically precipi-
-------
114 ASCE SEMINAR SUMMARY
tated) sludge for which no method of disposal was imme-
diately available.
The Blue Plains plant is a regional facility, receiving
approximately 50 percent of its overflow from two adja-
cent Maryland counties. The State of Maryland accepted
responsibility for disposal of raw sludge during the
period of construction of the incinerators. This task was
assigned to the Maryland Environmental Service, which
is a publically-owned, nonprofit corporation created by
the Maryland Legislature in 1971. With legislated
powers in the field of water supply, wastewater treat-
ment and solid waste treatment, MES is able to contract
for service with both public and private customers. The
Service has no regulatory powers and concentrates on
providing needed services.
In the development of methods to handle sludge, the
ideals of resource recovery and energy conservation
were emphasized. Early involvement with the
Agricultural Research Service of the United States De-
partment of Agriculture provided the research science
facilities necessary to evaluate different methods of land
disposal.
The first efforts in land disposal were a series of ex-
periments on land trenching of raw sludge conducted at
the USDA Beltsville Maryland Experimental Station in
early 1972. This served as a large-scale test to develop
all-weather procedures for hauling and incorporating
sewage sludge in the soil by trenching. This work was
more fully described in the paper by Walker in the 1974
Proceedings of the National Conference on Municipal
Sludge Management.
Composting was studied as another sludge disposal
method. Construction of a sludge composting facility be-
gan in the fall of 1972 and continued until June of 1973.
Since March, 1973, sludge has been composted on a
regular basis at Beltsville. The compost site consists of a
five-acre, crushed stone composting pad, material stor-
age areas and office complex, with control of runoff and
monitoring of groundwater. The initial method used was
open windrow composting. The sludge is transported
from Blue Plains by truck. Initially, the trucks were con-
crete mixers; later, watertight dump trucks were used.
The sludge is mixed with wood chips to bring the mois-
ture content down and to provide air voids.
Composting, which is the aerobic decomposition of
organic matter, results in the production of heat in the
piles. Temperatures in the mixture average between
120° to 140°F during the two weeks the chip sludge mix-
ture is in the windrow. After windrowing, the chip
sludge mixture is stockpiled. Temperatures in the stock-
pile reach 150° to 160°F and pathogens are substantially
eliminated. The mixture of chips and sludge is then
screened. Salvaged chips are returned to the process
and the compost is ready for distribution. This work is
more fully described in the paper by Epstein and Willson
in the 1974 Proceedings of the National Conference of
Municipal Sludge Management.
Experimental work is now being done on fixed bed
composting of raw sludge. Fixed bed composting seems
to have several advantages: higher process tempera-
tures are achieved, the energy requirement is less than
the open windrow method and there is better odor con-
trol possibility. This experimental work is now being
done under a U.S. Environmental Protection Agency re-
search grant.
In January 1975, raw sludge entrenchment site opera-
tions were started in the Maryland counties adjacent to
the District of Columbia. Raw sludge, lime stabilized to
pH 11.5 to 12.0 at 20 percent solids concentration, is
transported in sealed container trucks and the sludge is
pumped into the trenches. Every site has monitoring of
surface and groundwater as well as erosion control fea-
tures.
In 1974, the Service entered into a contract with Or-
ganic Recycling, Inc. for the dehydration of raw sludge
and processing into a commercially acceptable fertilizer.
This operation is still in the shakedown phase. Many
problems with the materials handling and air pollution
control equipment have held back full steady flow opera-
tion. However, redesign and persistence in this effort
show that it still holds great promise.
The Blue Plains Wastewater Treatment Plant sludge
disposal problem has offered a challenging opportunity
to attempt large scale sludge disposal solutions other
than incineration in a densely populated east coast
location.
Alternate methods of sludge disposal hold promise
and are consistent with resource recovery and energy
conservation. The waste engineering profession is being
called upon to evaluate all methods of sludge disposal
and weight the merits of each. The work in Maryland has
accumulated much background on several methods of
sludge disposal.
-------
THE PAST, PRESENT, AND FUTURE PROSPECTS
OF BURNING MUNICIPAL SEWAGE SLUDGE
ALONG WITH MIXED MUNICIPAL REFUSE
ElbridgeM. Smith and Allan R. Daly
RoyF. Weston, Inc.
West Chester, Pennsylvania
INTRODUCTION
The incineration of municipal sewage sludge (MSS) in
combination with mixed municipal refuse (MMR) has
long been a desirable objective of municipal plant design
to minimize the capital investment required for the ther-
mal processing of these two waste materials. MSS is
usually incombustible, even after extensive dewatering,
since there is insufficient heating value available in the
dry solids to evaporate the associated moisture. MMR,
on the other hand, is generally autogenous, producing
an excess of heat over that required to evaporate the
moisture present in the refuse. By combining the ther-
mal processing of both materials, it may be possible to
utilize the excess heat available in refuse to dry and in-
cinerate the MSS and, thus, eliminate the use of fossil
fuels that are typically used in sludge incinerators to
achieve thermal processing of the sludge. Burning MSS
along with MMR will henceforth be referred to as co-
incineration.
A number of co-incineration approaches have been
tried in the past, some are being tried now, and others
are planned for the immediate future. Under contract* to
the United States Environmental Protection Agency,
Roy F. Weston, Inc. was asked to provide a compre-
hensive evaluation of co-incineration. One phase of the
project was to assess demonstrated and experimental
co-incineration techniques. This report is based upon
that State-of-the-Art assessment.
BACKGROUND
Conventional MMR incinerators (Figure 1) simply
burn the refuse, producing a relatively inert residue with
less weight and bulk than the original refuse. Furnace
exit gas temperatures are controlled to less than 1800°F
(982 °C) by adding excess air to the furnace to prevent
slagging on the refractory walls. When MMR incinera-
tion is desired, or necessary, to reduce the bulk and
*The work upon which this publication is based was performed pur-
suant to Contract No. 68-03-0475 with the Environmental Protection
Agency.
weight of the refuse prior to ultimate disposal, the entire
cost of thermal processing and ultimate disposal of the
incinerator residue is borne by the user, who is charged a
tipping fee. That fee can be expressed in a number of
ways, but basically, although not always, should take
care of the cost of handling from that point on. Thus, the
fee charged as the refuse is received should cover all the
costs of incineration plus ultimate disposal of the residue.
When we add a steam-generating boiler to an MMR
incinerator, we can decrease the amount of excess air
required and use a smaller dust collector and induced-
draft fan, and most importantly, generate additional
revenues by selling the steam. The costs of the opera-
tion, less the steam revenues, can now be equated to a
new tipping fee, which can be, but is not always, less
than if steam revenues were not available. Steam reve-
nues are highly dependent upon the presence of a
nearby consumer willing to buy low-pressure steam on
an interruptable basis.
Conventional MSS incinerators are principally of the
multiple-hearth (Figure 2), or fluid-bed (Figure 3) type,
or may be flash-dryer systems. Each of these sludge in-
cinerators requires the use of an auxiliary fuel. Natural
gas or light oil is preferred for multiple-hearth furnaces
(MHF's). The fluid-bed furnaces (FBF's) can use almost
any fossil fuel, but again, natural gas and light oils are
preferred. Flash-dryer systems can be designed to use
any fossil fuel.
If we marry refuse and sludge incineration, we have
the potential to save a large amount of costly fossil fuel.
One estimate of the quantity of fuel required in sludge
incineration is based upon current practice in seven
cities1. On the basis of this survey, it was estimated that
50 gallons (189 liters) of No. 2 oil was required to burn
every ton (907 kg) of dry sludge solids.
If MMR can be used in place of the fossil fuel normally
required for MSS incinerators, we would have a benefi-
cial use for the refuse heat equal in value to the cost of
the fossil fuel replaced. Since refuse is a waste material
of which we have a great deal, and fossil fuel is in in-
creasingly scarce supply, this is indeed a beneficial use.
115
-------
116 BURNING WITH MIXED REFUSE
FLUE
FURNACE^
\
CHARGING CRANE
CHARGE
1 FLOOR
D
GAS CONDITIONING
CHAMBER
TIPPING
FLOOR
RECEIVING BIN
Figure 1: Continuous Feed Incinerator.
What quantities of refuse and sludge are we talking
about? Our company estimated that the domestic refuse
generation, based upon a major metropolitan area,
would be 2.74 Ibs/capita/day (1.24 kg/c/d) in 1980. To
this, we can add one Ib/capita/day (0.45 kg/c/d) of
sludge at 20 percent solids (0.20 Ibs. or 0.09 kg/c/d) for a
total of 3.74 Ibs/capita/day (1.7 kg/c/d) consisting of 41
percent combustible, 17 percent inert, and 42 percent
water.
With 203 million people in the United States of
America (1970 census), this amounts to 380,000
tons/day (345,000 tonnes/d) of which 100,000(91,000) is
MSS.
But, there is more. The 2.74 Ibs. of refuse/capita/day
(1.24 kg/c/d) represents only domestic refuse: if we add
commercial, institutional, and industrial wastes, we
could have nearly three times the domestic production,
or 1,000,000 tons/day (900,000 tonnes/d) of refuse to
dispose of. The sludge quantity of one Ib/capita/day of
MSS at 20 percent solids is based upon primary plus
secondary treatment of domestic wastewater. Inclusion
of industrial wastewaters will generate additional quan-
tities of primary and secondary sludges, and when we
add tertiary or physical treatment, we will have still
more sludge.
But, enough of this—we all recognize that we do have
a waste disposal problem in the United States.
Is co-incineration the most beneficial use of refuse? Is
it better than resource recovery or steam generation?
Frankly, we don't know—it is an alternative disposal
method, and therefore, should be included in any
shopping list of waste disposal options, possibly in com-
bination with resource recovery or steam generation.
Now, let's see where we have been, where we are, and
where we might go.
COOLING AIR DISCHARGE
FLOATING DAMPER
SLUDGE INLET
FLUE GASES OUT
RABBLE ARM AT
EACH HEARTH
DRVING ZONE
COMBUSTION ZONE
COOLING ZONE
ASH DISCHARGE
— COMBUSTION
AIR RETURN
RABBLE ARM
DRIVE
COOLING AIR FAN -
Figure 2: Multiple Hearth Sludge Incinerator.
The Past
Burd2 prepared a study of sludge handling and
disposal for the Federal Water Pollution Control Admin-
istration, which was published in May, 1968. In it, he
identified a number of installations where sludge and re-
fuse were, or had been, burned together. These in-
cinerator sites were as follows:
-------
BURNING WITH MIXED REFUSE 117
Whitemarsh Township, Pennsylvania*
Frederick, Maryland*
Waterbury, Connecticut*
Neenah-Menasha, Wisconsin*
Kewaskum, Wisconsin*
Holyoke, Massachusetts
Chicago, Illinois*
Hershey, Pennsylvania*
Burd also reported that, "A large chemical company
has successfully incinerated a thickened waste activated
sludge (2.2 percent to 2.6 percent in a boiler furnace
along with conventional fuels. However, inorganic de-
posits accumulated on the boiler tubes and eventually
forced suspension of this disposal technique."
Balakrishnan, et. al.3 in April of 1970 commented on
the disposal of refuse with sewage sludge and added the
following sites where co-incineration was reportedly
being practiced:
Watervliet, New York*
Stamford, Connecticut*
Fond du Lac, Wisconsin*
Bloomsburg, Pennsylvania*
Louisville, Kentucky*
Eberhardt,4 in May of 1966, had commented on Euro-
pean practice in refuse and sewage sludge disposal by in-
cineration. He comments, "For burning sludge, the
highest attainable degree of drying is of great impor-
tance. In view of the cost, water evaporation by means of
auxiliary fuel should, if possible, be avoided in Europe."
After describing a series of strictly sludge incinerators,
he states that, "The most economical solution for the
disposal of all waste products of a housing area is the
combustion of sludge together with refuse by using the
heat which is released by the combustion for the sludge
drying.'' He then refers to a figure showing the design of
a sludge-drying and refuse-incineration plant, where the
dry material is sold as compost for fertilizer, with the re-
mainder being burned. The design shown is very similar
to what is known in the United States as a flash-drying
system, although the design shown in Eberhardt's paper
is not attributable to the prime U.S. manufacturer of this
system. In this configuration, the dried sludge solids are
fed to the furnace immediately above the refuse feed
chute, and apparently by gravity. It is unclear whether
this co-incineration plant was simply conceptual or was
actually in operation; in any event, it is the only specific
reference to a co-incineration plant design in Eber-
hardt's paper.
Fife,5 in a paper dated January 29,1968, comments on
combined refuse and sludge incineration, listing a num-
ber of United States installations previously listed here,
and adding an installation in Essen, Germany, where
2,000 tons per day of filter press sewage sludge solids
are handled by a flash-drying system available from the
German branch of the Babcock and Wilcox Company. He
further refers to the Eastman-Kodak installation, where
ALTERNATE SLUDGE INLET
ALTERNATE SLUDGE INLET
ALTERNATE
PREHEAT BURNER
SLUDGE INLET
AMBIENT OR PREHEATED
FLUIDIZING AIR INLET
Figure 3: Fluid Bed Sludge Incinerator.
shredded refuse and flash-dried sludge are burned in a
suspension-fired boiler (which was at that time pro-
posed) and to another installation, reportedly in the
study stage, forthe City of Portland, Maine, where again
a flash-dryer system was proposed to dry the sludge
prior to burning the dried solids in a refuse incinerator.
In February of 1974, we were also aware of the follow-
ing sites where co-incineration had been tried, pro-
posed, or was in use:
Franklin, Ohio
Ansonia, Connecticut
New Albany, Indiana*
Harrisburg, Pennsylvania
We don't have the complete history of any of these 17
co-incineration installations, but we do have enough in-
formation to indicate that co-incineration has been
something less than a roaring success. Thirteen out of
the 17 listed installations have been shut down; no
longer burn sludge, or never did burn sludge along with
refuse.
Sludge was burned at the Whitemarsh Township in-
cinerator,6 but reportedly,7 the practice of co-incinera-
tion was discontinued at this site long before other prob-
lems forced the original incinerator to be shut down. As
far as we know, once the incinerator was rebuilt, there
was no further attempt to burn sludge. The MMR in-
cinerator was located at the site of a sewage treatment
plant (STP), and reportedly, the vacuum-filtered raw
sludge was mixed with the refuse prior to charging this
*Identifies an installation that has been shut down, that no longer
burns sludge, or that never did burn sludge along with refuse.
-------
118 BURNING WITH MIXED REFUSE
continuous feed incinerator. This procedure is so simple
that it has probably been tried many times, and rarely
reported.
Neenah-Menasha8was scheduled to be shut down9 at
the beginning of this year, but not because co-incinera-
tion didn't work; it did. The incinerator shut-down was
reportedly forced by the need to meet new and more
stringent air pollution regulations, and it was decided
that it was too expensive to retrofit this old incinerator
(vintage 1958). The system at Neenah-Menasha used a
Raymond flash-dryer to dry vacuum-filtered MSS. The
Combustion Engineering/Raymond flash-drying sys-
tem dried the MSS from 70 percent moisture to 15-20
percent moisture. The dried sludge was then separated
in a cyclone and conveyed to the furnace by a belt con-
veyor and apparently added to the refuse at the furnace
feed hopper. The plant consisted of two traveling grate-
type furnaces designed for a capacity of 150 tons per day.
The feed to the furnaces is reported to have been 30TPD
of garbage, 84 TPD of rubbish, and 35 TPD of dried
sludge. The spent-dryer gases from the flash-drying
system were discharged to the breeching before the
stack, and the hot gases were apparently drawn from the
residue end of the furnace.
Hershey, Pennsylvania used a Carver-Greenfield
(C-G) multiple-effect evaporator system to dry the
sludge before burning in a conventional steam generat-
ing boiler. The C-G system, which was in use from 1963
to 1972, is no longer in use 10, since extensive repairs are
required and the present sewage treatment plant will be
replaced by a regional authority plant. In the C-G drying
system, oil is added to the sludge to facilitate handling
through the triple-effect evaporator. Excess oil is then
separated in a centrifuge for reuse, and the oily sludge
solids are burned. The oil remaining in the solids re-
sulted in a significant increase in the heating value of
the sludge.
The Waterbury, Connecticut installation n consists of
two 150 TPD batch-fed circular-type MMR incinerators
equipped with a Raymond flash-drying system. The very
fibrous sludge was vacuum-filter dewatered, dried, and
charged to the incinerator along with raw MMR. The ori-
ginal STP was a primary plant, and when secondary
treatment was added, multiple-hearth furnaces were in-
stalled and the sludge is now being burned in these
MHF's. The original furnaces are in use, and the drying
system is still in existence and couldbe used if necessary.
The Holyoke incinerator 12 was started in 1965 and is
still operating. Here, vacuum-filter dewatered sludge is
dried in a rotary dryer and the dried sludge injected into
the incinerator by a high-velocity air jet. Much of the
sludge solids burn in suspension above the burning
refuse. The Holyoke installation is a good point at which
to depart from the past and enter the present, since a
similar installation has recently been constructed in
Stamford, Connecticut13, and another rotary-kiln dryer
is in use in Lulea, Sweden 14
The Present
A flow sheet for the Holyoke installation is shown in
Figure 4; note that there is a pug-mill that blends recy-
cled dried sludge with the cake from the vacuum filters
before feeding it to the rotary dryer. Dry sludge recycle
reduces the average moisture content of the dryer feed,
thereby eliminating the build-up of deposits on the dryer
walls. Note also that there is provision for auxiliary firing
at the feed end of the rotary dryer. At Holyoke, the fur-
naces are batch-fed, and the flue gases experience
periodic temperature excursions. Fuel oil is normally
used at this plant to control the temperature of the gases
entering the rotary dryer and to provide additional heat
input, since all of the sludge is dried and co-incinerated
during only 60 percent of incinerator operating cycle. At
one time, the Holyoke incinerator handled a high ton-
nage of paper waste from nearby mills, at which time no
auxiliary fuel was required. When pollution control
regulations required a reduction of coated paper waste,
it became necessary to fire auxiliary fuel, thus indicating
the need for careful planning of refuse and sludge ratios
when designing a co-incineration facility. As refuse is a
notoriously variable fuel, it is perhaps advisable to con-
sider an auxiliary fuel-use in many cases of co-incinera-
tion, even if the furnace is a continuous-feed unit. The
Stamford 13 installation was started up early in 1975 and
is very similar to the Holyoke installation.
At Lulea 14, in Sweden, there are two 360 TPD refuse
incinerators, each equipped with a rotary dryer-incinera-
tor. Waste oils are fired into the rotary drum with the ex-
haust gases passing into the refuse furnace flue up-
stream of a wet dust collector. At Lulea, the sludge is
either dried or incinerated in the rotary drum. There-
fore, the dried sludge is never burned in the MMR in-
cinerator, as is the practice at Holyoke and Stamford.
At the Eastman-Kodak Company in Rochester, New
York, dewatered sludge from the waste treatment plant
is being hauled to a steam-generating incinerator that is
suspension-fired with shredded refuse. The sludge is
dried in a Raymond flash-drying system, and the dried
sludge burned in suspension along with the shredded
refuse.
Another flash-drying system was installed in New-
burgh, New York 15, but is not now in use. The operators
report 16 that they attempted to put the system into
operation for approximately one year, but finally gave
up. They report that starting with vacuum-filtered
sludge and an initial temperature of 1700°F (927°C) the
furnace temperature would drop drastically during
operation of the flash-drying system. They were never
able to maintain proper furnace temperatures and finally
abandoned use of the system. Unusually high quantities
of excess air, due to leaks in the furnace, resulted in ex-
cess heat loss; this probably is the cause of poor dryer
performance. In earlier co-incineration attempts at New-
burgh, sludge filter cake was charged to the incinerator
feed hopper without pre-drying. The sludge cakes
-------
BURNING WITH MIXED REFUSE 119
I RAW SEWAGE
TO CONNECTICUT RIVER
DRY SLUDGE TO INCINERATOR
TO LANDFILL
Figure 4: Holyoke, Massachusetts—Water Treatment and Incinerator Flow Sheet.
dropped through the grate without burning. This ap-
proach was abandoned in favor of the flash-drying
system.
Another co-incineration installation is at Ansonia,
Connecticut17. Here, a spray dryer is used to dry thick-
ened sludge. The dried sludge can be pneumatically con-
veyed to the incinerator, where it is arranged to burn in
suspension above the second grate; however, Ansonia
generally does not burn the sludge, aslocalresidents and
the State Highway Department take most of the dried
sludge for use as a fertilizer. While the spray dryer was
designed to dry all the sludge generated by primary and
secondary wastewater treatment, difficulties in obtain-
ing sufficiently high dryer inlet temperatures restrict the
unit to handling only about half of the sludge generated
by the plant. Modifications have been made in the in-
cinerator with the objective of increasing inlet tempera-
ture and dryer capacity.
There are a number of steam-generating incinerators
in this country and abroad. Here, the appropriate means
of drying the sludge prior to burning it is to use an indi-
rect contact dryer of some kind using the steam or some
other heat-transfer fluid as the heating medium.
There are no installations in the United States incor-
porating indirect contact dryers, although one is pro-
posed for the Harrisburg, Pennsylvania 18 incinerator.
In Europe, there is an installation in Dieppe, France 19
where thickened sludge at four percent solids is ground
and then pumped to a scraped-surface, thin-film dryer
where 180°C (356°F) steam at a pressure of ten kg/cm^
(142 psig) heats the jacketed walls of the vertical vessel.
The sludge is introduced at the top of the evaporator,
and discharges from the bottom at a solids content of 52
to 55 percent. A converyor belt then delivers the dried
sludge to the MMR incinerator feed hopper.
But, do we have to dry the sludge before burning?
Why not simply spray thickened sludge into the furnace?
At Altrincham, England ^, just such a procedure was in-
corporated into the design of the plant. The plant was
-------
120 BURNING WITH MIXED REFUSE
designed to dispose of 160,000 kg (176 tons) of crude
domestic refuse per day by direct incineration through a
twin-stream system, each of the two independent incin-
erators being rated at 4,500 kg (five tons) per hour,
giving a total plant capacity of 9,000 kg (ten tons) per
hour. In addition to crude domestic refuse, the plant will
burn limited amounts of industrial and trade refuse and
approximately 109,000 liters (29,000 gallons) per day of
raw primary and humus sewage sludge at 95 percent
moisture content. The sludge was injected into the rear
of the furnace over the burn-out portion of the grate, and
the original sludge injection nozzle diameter was about
3/8ths of an inch. Later, it was determined that the mini-
mum size that was practical to prevent blockage or
plugging of the injection point was about three inches.
At the rate of sludge injection with a three inch nozzle,
however, there was insufficient heat generated within
the furnace to evaporate the moisture that would be in-
troduced; thus, sludge burning has been abandoned at
this site, and co-incineration is no longer practiced.
Another attempt to inject thickened sludge directly
into a refuse incinerator has been reported at Havant,
England 21. Special attention was given to the atomiza-
tion of the sludge, and a dual-fluid spray nozzle is
planned at this site. Tests were run with the spray nozzle
using sludge at 3.5 percent solids, but in the final de-
sign, the spray nozzles will have to handle digested,
thickened sludge at approximately seven to eight per-
cent solids. This installation is expected to be in use in
the latter part of this year.
Direct injection of thickened sludge to the furnace at
Altrincham has been abandoned, and the Havant instal-
lation is yet to start up; but we still have the possibility of
adding thickened or dewatered sludge to the refuse-fed
MMR incinerator. We previously discussed the White-
marsh Township incinerator and noted that the attempt
at this plant had been abandoned. The question was
"Why?", and we did not have an answer. One possible
answer has been reported in the European literature by
Lancoud 22. Filter-pressed sludge containing 40 percent
moisture was burned in a 200 TPD, continuous-feed,
grate-fired, steam-generating incinerator. The grate
was equipped with oscillating knives to improve com-
bustion, and the incinerator manufacturer estimated
that the feed could contain up to 20 percent pre-treated
sludge cakes, without affecting combustion. It was re-
ported that there appeared to be an excessive amount of
combustibles remaining in the residue; consequently, a
series of tests were run and it was finally concluded by
Lancoud that the sludge was not satisfactorily destroyed
by incineration due to the following:
1. Larger pieces of sludge cake move faster than re-
fuse through the furnace, thus burning time is re-
duced.
2. A crust formed on the sludge cake, hindering com-
plete combustion.
3. Poor mixing permitted sludge cakes to separate
from the refuse, with poor air contact and resulting
poor combustion.
The author suggested that the sludge cake be reduced in
size to two cm (0.79 inches) or less, that more mechanical
action be employed in the incinerator to break up crusted
cakes, and that there be improved mixing of the sludge
cakes and refuse.
Wet, damp materials such as watermelon rinds and
halves of grapefruit do have a tendency to go through
conventional incinerators without being burned. Sludge
cakes would appear to fall into this same category, and
this may well be the reason why previous attempts at
simply adding dewatered sludge to the refuse bed have
failed and been abandoned.
We have been talking about refuse incinerators that
are modified to burn sludge along with the refuse. How
about modifying a sludge incinerator to burn refuse? At
Franklin, Ohio 23, there is a FBF that is burning the resi-
due left over after resource recovery from municipal
refuse shredded under water. At Franklin, material left
over after the recovery operation is combined with thick-
ened sludge and dewatered in a cone press, with the
cake pneumatically conveyed to the freeboard of a fluid-
bed furnace. This is a rather special unit, incorporating
as it does a proprietary system for resource recovery
ahead of the furnace.
There is, in Thunder Bay, Canada 24, a fluid-bed fur-
nace that is burning wood wastes and sludge from a pulp
and paper plant. Experimentally, municipal refuse has
been burned in this furnace, and the manufacturer has
announced sale of an FBF to handle MMR.
Some experiments were also run in Lausanne, Swit-
zerland 25, where a variety of solid waste materials were
fed by gravity into a fluid-bed sludge incinerator. Re-
portedly, there were no problems, but the materials fed
were largely fine to begin with and all totally
combustible.
In Europe and the United Kingdom, there are a num-
ber of multiple-hearth furnaces burning refuse and
sludge, and at least one has been proposed in the United
States. There are three installations in Switzerland, at
Dilbendorf26, Biilach27, and Uzwil28. In the United
Kingdom, there is a MHF at Reigate29 and another at
Bowhouse 30that are similar to the Biilach unit in Swit-
zerland. The Biilach unit introduces sludge at the top
hearth and shredded refuse at a mid-hearth area. This
installation was reportedly plagued with odor problems
and has been shut down. The manufacturer has stated
that it no longer intends to offer this furnace arrange-
ment for co-incineration. In the Dubendorf and Uzwil
installations, the sludge and shredded-cleansed refuse
are introduced to the top hearth of the furnace as is
conventional practice with domestic sludge incinerators.
The Uzwil installation is considered by some Swiss au-
thorities as a model installation. The MHF as installed at
Uzwil incorporated twelve hearths, but the two top
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BURNING WITH MIXED REFUSE
121
hearths have been removed, and the refuse is now de-
posited on the original third hearth, which is now the top
hearth of the furnace.
In our country, an MHF co-incinerator has been pro-
posed for Central Contra Costa County, California 31.
Tests were performed in November of 1974 at Enviro-
tech Corporation's Brisbane, California test facility
feeding MMR and MSS together to the top hearth.
Later, sludge was fed to the top hearth and shredded re-
fuse to the third hearth of this six hearth test furnace.
The furnace was operated under reducing conditions,
thus producing a pyrolytic gas that was burned in an
afterburner to raise the off-gas temperature from
approximately 800 to 1400°F (467-760°C) to assure
complete oxidation of combustible materials in the off-
gas.
There are also a number of proprietary incinerator de-
signs under development. Among these are Union Car-
bide's Purox system32, Carborundum's Torrax sys-
tem 33, Monsanto's Landgard rotary-kiln system 34, and
a Danish installation in Kalundborg 35. All these units
have apparently been tested at one time or another with
MSS added to the MMR. The Torrax system is presently
commercially available; none have been sold in the
United States, but one is under construction in Luxem-
bourg, and another has been sold in France. Union Car-
bide has not yet decided to offer its Purox system on a
commercial basis. A 1,000 TPD Monsanto Landgard
system is undergoing start-up in the City of Baltimore.
The Future
The future of co-incineration is still uncertain, since
the final answers on so many attempts are not yet com-
pletely documented. Complete answers on those that
have been shut down are not available, and there are
competitive disposal methods that compete with the
concept of co-incineration.
As long as land is available, landfills are less expen-
sive than incineration, even after you add in the cost of
linings and leachate collection and treatment systems.
Resource recovery is another disposal method that
competes with incineration or co-incineration, but note
that resource recovery can precede or follow thermal
processing. The success or failure of resource recovery
may well depend on the market for the recovered con-
stituents. Paper is one main constituent of MMR that is
highly desirable in an incinerator operation, since it is
very combustible. The secondary market for paperstock
is highly volatile—high prices can make resource re-
covery attractive. However, we have recently experi-
enced the bottom dropping out of the secondary paper
market which of course adversely affects any plans for
resource recovery. The prices paid for materials in the
secondary markets have always fluctuated widely, and
will probably continue to fluctuate in the future.
One future co-incineration option is conventional in-
cineration with or without heat recovery, because these
units can handle raw MMR. There is no pre-processing
of the refuse, except for segregation of bulky items. Con-
ventional incineration is, therefore, an acceptable pro-
cessing step to reduce the weight and bulk of MMR prior
to ultimate disposal, and adding MSS burning provides
a beneficial use of the excess heat that is normally avail-
able in MMR.
Table 1 summarizes the effect of burning sludge in a
conventional refractory-wall MMR incinerator. The
moisture present in MSS depresses furnace tempera-
tures, but by cutting back on excess air, the furnace gas
temperatures can be held within the desirable range of
1,400-1,800°F(760°C-982°C), except for thickened
sludge feed. If we try to burn thickened sludge, we can-
not maintain adequate furnace temperatures, even with
zero excess air (theoretical combustion air require-
ments), and still handle the MMR and MSS generated in
a given region. Therefore, it is necessary to dewater the
sludge mechanically to about 20 percent solids, followed
by drying, before the sludge solids are fed to the MMR
incinerator. More intensive dewatering (i.e., pressure
filtration) is not warranted, since there is sufficient heat
available to dry and burn vacuum-filtered or centrifuged
primary and secondary sludges.
Sludge drying is an indicated processing step because
we can conveniently add a dryer circuit to the MMR in-
cinerator, and past experience indicates that sludge dry-
ing is necessary. All known past attempts to directly add
dewatered sludge to the MMR fed to the furnace have
failed—probably for reasons similar to those cited by
Lancoud 22.
Please note that the furnace temperatures reported in
Table 1 presume introduction of the dryer gases into the
MMR furnace to insure thermal destruction of any
odorous compounds that might be liberated in drying
the MSS.
Another future co-incineration option is the use of
conventional sludge incinerators modified jto handle
shredded and cleansed MMR. The refuse would, in
large part, replace fossil fuel requirements except for
startup and as a means of maintaining ignition of the
feed mixture. Furnace off-gas temperatures would be
similar to those shown in Table 1.
A third future co-incineration option involves experi-
mental furnaces. Most of the proprietary incinerator de-
signsthatare sometimes called "advanced technology"
are in various stages of development for the burning of
refuse. The outcome of these tests and prototype instal-
lations will have to be watched closely, as many of these
proprietary incinerators can be operated at highly effi-
cient combustion conditions, making large quantities of
heat available for sludge drying. The next step for these
manufacturers should be an investigation of co-incinera-
tion in full-scale equipment and for extended periods of
time.
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122 BURNING WITH MIXED REFUSE
TABLE 1
Furnace Exhaust Gas Temperatures
(Desired Temperature Range: 1,400-1,800°F (760°C-982°C)
by weight
Sludge Sol ids -
Excess Air - %
Zero
100
200
300
1*00
Base: 2.7** Ibs./c/d (1.24 kg/c/d) raw MMR
0.20 Ibs./c/d (0.09 kg/c/d) dry solids MSS
What is required for co-incineration? Certainly, ade-
quate planning and design will be necessary to insure
that sludge and refuse quantities are compatible in the
process chosen, and that they will remain so during the
life of the facility. Wide-area planning, for both refuse
and wastewater collection and processing, will be re-
quired to insure the optimum design of a co-incineration
system. And, improved communication and cooperation
between those responsible for sludge disposal and re-
fuse disposal will certainly be required if co-incineration
is to be successfully practiced.
Which system will prevail? We don't know. However,
there is enough work under way, enough installations in
existence, that co-incineration should be included as a
disposal option in any planning for solid waste and
sludge disposal. The chief beneficiary would be all of us,
since MMR can be substituted for scarce and increasing-
ly expensive fossil fuels.
REFERENCES
l.Olexsey, R.A., and Farrell, J.B., "Sludge Incinera-
tion and Fuel Conservation," News of Environmental
Research in Cincinnati, EPA-NERC-Cincinnati, May 3
(1974).
2. Burd, R.S., "A Study of Sludge Handling and Dis-
posal," FWPCA (EPA) Publication WP-20-4, NTIS No.
PB-179 514, May (1968).
3. Balakrishnan, S., et. al., "State-of-the-Art Review
of Sludge Incineration Practice," FWQA (EPA) No.
17070DIV 04/70.
4. Eberhardt, H., "European Practice in Refuse and
Sewage Sludge Disposal by Incineration," Proceedings
of ASME 1966 National Incinerator Conference, pp.
124-143, May (1966).
MMR
l*
3,05k °F
(1,679 °0
2,039 °F
(1,115 C)
1,547 °f
( 841 °C)
1,252 UF
( 678 °C)
1,055 °F
( 568 °C
45
2,898 °F
(1,592 °C)
1,951 UF
(1,066 °C)
1,485 °F
( 807 °C)
1,204 °F
( 651 °C)
1,015 °F
( 546 °C)
MMR and MSS
20
2,519 °f
(1,382 °C)
1,745 °F
( 952 °C)
1,345 °F
( 729 °C)
1,099 °F
( 593 °C)
931 °F
( 500 °C)
4
1,010 °F
( 543 °C)
777 °F
( 414 C)
635 °F
( 335 °C)
540 °F
( 282 °C)
472 °F
( 245 °C)
5. Fife, J.A., "Sewage Sludge Another Waste Dis-
posal Problem,'' Symposium on Solid Wastes, New York
Dept. of Health, Albany, N.Y., January 29 (1968).
6. Reilly, B.B., "Incinerator and Sewage Treatment
Plant Work Together," Public Works, pp. 109-110, July
(1961).
7. Memorandum from W.T. Clark, dated January 24
(1975).
8. Clinton, M.O., "Experience with Incineration of
Industrial Waste and Sewage Sludge Cake with Munici-
pal Refuse," Proceedings of the 14th Purdue Industrial
Waste Conference, pp. 155-170 (1959).
9. Verbal communication.
10. Verbal communication.
11. Nickerson, R.D., "Sludge Drying and Incinera-
tion," Journal of the Water Pollution Control Federa-
tion, Vol. 32, No. 1, pp. 90-98, January (1960).
12. Bayon, E.J., "Sludge Disposal Solution: Thicken,
Filter, Dry and Burn," The American City, June (1966).
13. Gater, D.W., "Incinerator is Part of Integrated
Waste Disposal System,"Public Works, pp. 64-67, May
(1974).
14. Bergling, S., "Combined Treatment of Refuse,
Sewage Sludge, Waste Oil and Nightsoil at Lulea, Swe-
den," International Solid Wastes and Public Cleansing
Association (LSWA) Information Bulletin No. 1, pp.
25-28, September (1969).
15. CE Raymond/Bartlett-Snow installation list.
16. Verbal communication.
17. Plant visit.
18. Pepperman, C.M., "The Harrisburg Incinerator:
A Systems Approach," Proceedings of the ASME Na-
tional Incinerator Conference, May (1974).
-------
BURNING WITH MIXED REFUSE
123
19. Tanner, R., "Gemeinsame Verbrennung von Mull
und Klarschlamm mit Abwarmeverwertung zur Sch-
lammtrocknung" (Combined Refuse and Sewage
Sludge Incineration with Waste Heat Utilization for
Sludge Drying), VGB Kraftwerkstechnik, 52 (2), pp.
140-145, April (1972).
20. Davies, G., "Altrincham Refuse and Sewage
Sludge Incineration Plant," Public Cleansing 63 (5), pp.
247-256, May (1973).
21.Munro,C.S.H. andRolfe, T.J.K., "The Incinera-
tion of Sewage Sludge with Domestic Refuse on a Con-
tinuous Burning Grate," Part of a Symposium held at
the University of York, Yorkshire, England, The Institu-
tion of Chemical Engineers Symposium Series No. 41,
pp. 01-014, April (1975).
22. Lancoud, F., "Combined Disposal of Refuse and
Sludges: Technical and Economic Considerations," 1st
International Congress on Solid Waste Disposal and
Public Cleansing, ISWA Praha 1972, Thema V, June/
July (1972).
23. Herbert, W., Flower, W.A., "Waste Processing
Complex Emphasizes Recycling," Public Works, June
(1971).
24. Limerick, J. McK., "Copeland System for Burning
Bark, Debris and Sludge Start-Ups at Great Lakes,"
Pulp and Paper Magazine of Canada, January (1972).
25. Albrecht, O.E., "Schlammverbrennung im Wir-
belschichtofen" (Sludge Incineration in Fluidized Bed
Furnaces), Chemie—Ing.—Techn., 41 (10), pp. 615-619,
May (1969).
26. Anon, "Kehricht-und Schlammverbrennungsan-
lage Region Diibendorf" (Incineration Plant for Domes-
tic Refuse and Sewage Sludge in the Dubendorf Area)
SchweizerischeZeitschriftFurHydrologie, 31 (2),
(1969), (From the Fourth International lAM-Congress,
1969, in Basel).
27. Defeche, Jean, "Combined Disposal of Refuse
and Sludges: Technical and Economic Considerations,"
1st International Congress on Solid Wastes Disposal and
Public Cleansing ISWA - Praha 1972, Thema V, pp. 3-39,
June/July (1972).
28. Rub, F., "Moeglichkeiten und Beispiele der
Kombinierten Verbrennung von Mull und Abwasser-
schlamm" (Possibilities and Examples of a Combined
Incineration of Refuse and Waste Water Sludge),
WasserLuft und Betrieb, 14 (12), pp. 484-488, Decem-
ber (1970).
29. Anon., "The Reigate Incinerator," Surveyor
(London) Vol. 138, No. 4, 130, pp. 34-35, August 6
(1971).
30. Correspondence with manufacturer.
31. Anon., "Solid Waste and Sludge = Energy Self-
sufficiency," Resource Recovery and Energy Review,
Vol. 2, No. 1, pp. 16 and 17, January/February (1975).
32. Anderson, J.E., Solid Refuse Disposal Process
and Apparatus, U.S. Patent Number 3,729,298 dated
April 24 (1973).
33. Manufacturers data.
34. Sussman, D.B., "Baltimore Demonstrates Gas
Pyrolysis—Resource Recovery from Solid Waste," U.S.
EPA Report, S.W.-75 d.i. (1975).
35. Anon., "Refuse Refineries—A Danish Develop-
ment," Environmental Pollution Management, Vol. 4,
No. 4, pp. 183 and 185, July/August (1974).
-------
HIGH ENERGY RADIATION IN SLUDGE
TREATMENT—STATUS AND PROSPECTS
J.B. Farrell
United States Environmental Protection Agency
Cincinnati, Ohio
INTRODUCTION
The fact that high energy radiation has an adverse ef-
fect on living organisms has been known since the early
days following the discovery of X-rays and radioactive
materials. This effect has been put to constructive use in
recent years and is used to pasteurize and sterilize
foods', bandages, and equipment used in medical pro-
cedures. The sources of high energy radiation utilized
have been beta rays (high energy electrons) and gamma
rays (high energy photons, emitted from the atomic nu-
cleus). The high energy electrons used in sterilization
are generated by electron accelerators. Beam energies
generated are kept below ten MeV (million electron
volts) to eliminate all danger of induced radioactivity in
the object being irradiated. As Figure 1 shows, depth of
penetration is low, and is inversely proportional to the
density of the material. This is a basic limitation of the
method, although it is offset by low cost of the electron
accelerators and the high quantity of radiation they can
focus on a small area.
The gamma rays used in sterilization are generated by
radioisotopes. Generally, "^cobalt and ^'cesium are
used. Gamma rays emitted by these radioisotopes are
low enough in energy so that there is no induced radio-
activity in the irradiated substance. As Table 1 shows,
penetration of gamma rays is much deeper than high en-
ergy electrons (beta rays). The effect on organisms is es-
sentially the same because these gamma rays form high
energy electrons within the material. The biological ef-
fects of gamma and beta rays are due to primary effects
of these electrons and secondary effects that occur when
the excited molecular species formed then react with
other molecules in the irradiated material.
Radiation sensitivity of living substances is roughly
proportional to the size of the organism and its metabolic
condition. For example, large animals are killed by an
absorbed dose of 1000 rads (one rad equals 100 ergs/g)
whereas viruses may require in excess of a megarad for a
lethal dose. Sporulating bacteria require much higher
doses to destroy them than do bacteria that do not pro-
duce spores.
The use of high-level radiation to reduce or eliminate
the pathogenic forms present in wastewater and sewage
sludge has been seriously investigated as early as the
1950's2. Interest has continued at a modest level in the
intervening years. The Metropolitan Sanitary District of
Chicago sponsored several investigations and even de-
veloped a conceptual design of a plant for treating two
mgdof wastewater or sewage sludge^. At the time, costs
appeared to be excessive, as shown, for example, by
Ballantine, et. al4 The changing world energy situation,
the increasing consciousness of people and governments
of the potential hazards from wastes, and especially, the
construction of a plant-scale sludge irradiation facility in
the Federal Republic of Germany have prompted a re-
evaluation of the potential for high energy radiation
treatment of wastes. During March 17-21, 1975, the In-
ternational Atomic Energy Agency convened in Munich
the "International Symposium on the Use of High-Level
Radiation in Waste Treatment—Status and Prospects"
to reassess the situation and give direction to further de-
velopment. The objective of this presentation is to re-
view the highlights of this symposium, particularly as
they apply to sludge, and predict the course of future
development.
State-of-the-Art
The state-of-the-art, up to the convening of the sym-
posium was well summarized by Feates and George5
They point out that the interest in irradiation of wastes
followed intensive work originally carried out on food-
stuffs and the method became feasible when large
radiation sources became available in the mid-1950's.
The effects of radiation that are of interest are the
following:
• destruction of microorganisms and parasites
• radiation-induced oxidation
• modification of molecular structure (to decrease
toxicity or enhance biodegradability)
• changes in colloid systems (to improve settling or
sludge dewatering)
Experimental work established that for sewage sludge
highly significant levels of microbial reduction occurred
124
-------
HIGH ENERGY RADIATION
125
E
£ 4
ui
O
O
OC
H
O
111
LU
WATER
456
BEAM ENERGY (mev)
Figure 1: Range of Electrons in Various Materials.
8
10
at irradiation levels under 1.0 megarad. Cost studies in-
dicated unrealistically high levels for sewage but not
necessarily for sludge. Synergistic effects on reductions
in microbial levels appeared to occur when radiation was
combined with chlorine, heat, or zinc chloride.
Radiation reduced the COD levels for aqueous solu-
tions of certain chemicals at radiation levels less than 0.2
megarad, but much higher levels were required for sig-
nificant effects with sewage. For example, Touhill, et.
at.6 found that 0.2 megarad nearly completely destroyed
cyanides and phenols, whereas Etzel and Condren7
found that, under aerated conditions, 1.0 megarad was
required to reduce the COD of a simulated wastewater
by 80 percent.
Radiation treatment evidently improves the settling
rate and filterability of sewage sludge although the ef-
fect is not large. Compton, et. al.8 found that the effect
of irradiation or filterability was about the same as two to
four percent ferric chloride but not economically com-
petitive with it.
Major Programs
The symposium revealed that, notwithstanding re-
sults with sludge that still indicate relatively high costs,
major sludge irradiation investigations are underway in
several parts of the world. This shows an optimism as to
the future of radiation processing of sludge that is
backed up by a major commitment of resources. Most
impressive are three largescale projects currently un-
derway which should provide practical information on
feasibility, effects, and economics.
Geiselbullach
For a number of years, there has been concern in
Germany and Switzerland about the transmission of in-
fection to animals grazing on pasture that has been ferti-
lized by application of liquid digested sewage sludge. As
a consequence, pasteurization (heating to 70°C for Vi
hour) has been carried out on sludges applied to lands
during the spring and summer months when animals
TABLE 1
Absorption of Gamma Rays
By Common Materials*
60
COBALT GAMMA RAYS
HALF-VALUE LAYER
(CM)
WATER 27
CONCRETE (147 LB/FT5) 13
STEEL 3.5
LEAD 1 . 8
TENTH-VALUE LAYER
(CM)
64
28
8.0
4.5
(AFTER BALLANTINE)
18
-------
126
HIGH ENERGY RADIATION
might be grazing on sludge-treated soils. Numerous
pasteurization plants have been erected in both the Fed-
eral Republic of Germany and Switzerland. The method
evidently has not been without drawbacks. There have
been reports of heat exchangers plugged by thermally
induced deposits, and an amplification of malodors by
the pasteurization process.
To increase reliability of pathogen removal and to
avoid the above-mentioned drawbacks of the pasteuriza-
tion process, a small plant for hygienization of sewage
sludge by irradiation was erected by the German Minis-
try of Research and Technology at the wastewater treat-
ment plant of the Abwasserverband Ampergruppe in
Geiselbullach, ten kilometers west of Munich. The plant
utilizes 60cobalt and has an ultimate daily capacity of
150m3 of sludge irradiated with a dose of 300krad. Cur-
rently the plant is charged with sufficient 60cobalt to ap-
ply this dose to 30 m3 per day. The experience of the
German group, which has been led by Dr. A. Suessofthe
Bayerische Landesanstalt fiir Bodenkultur and Pflan-
zenbau in Munich, is described in a series of papers pre-
sented at the symposium 9'14. A schematic diagram of
the plant is shown in Figure 2. Sludge is introduced into
the irradiation chamber and recirculated past the
^cobalt rods until the sludge has received the desired
radiation dose. The complete batch is discharged to
make way for the next sludge charge.
SLUDGE INLET
GROUND LEVEL
Lessel, et. al.9 give extremely practical information
gained by operating the Geiselbullach plant for eighteen
months, part of which is discussed below. They observed
that irradiated sludge does not develop the strong odor
that typically is generated when sludge is pasteurized. It
does not increase in volume as does pasteurized sludge
when it is heated with direct steam, and it settles better
than either pasteurized or untreated sludge. Operating
problems were encountered but easily overcome by mi-
nor design changes. Costs were slightly higher than for
pasteurization for the Geiselbullach installation. How-
ever, the authors predict costs of about three DM/m3
($23.50/dry ton, based on five percent solids sludge) for
a commercial installation of 150 m3/da (8.25 dry tons
per da), which is less expensive than pasteurization
costs.
Wizigmann and Wuersching I0 showed that the 300
krad dose in the pilot plant reduced total bacterial count
two logs, enterococcus two logs, and Enterobacteriaceae
four to five logs. Salmonella species were discovered in
16 out of 25 samples of sludge before irradiation and in
two out of 40 samples after irradiation. There were indi-
cations of regrowth after irradiation as is evidenced by
the data in Table 2. The regrowth effect is noticeable for
the enterobacterial count and exceptionally high for the
total aerobic count. The high count of the aerobic forms
is probably due to survival of bacterial spores, typically
VENT
^i(^mm$m
• W.rv'.iQfc •><•.• J .• «-a-.V! n. o.v-V
CONCRETE
SHIELDING
SLUDGE OUTLET
Figure 2: Schematic Representation of 60Cobalt Irradiation Facility at Geiselbullach (design by Sulzer Bro. Ltd., Switzerland).
-------
HIGH ENERGY RADIATION
127
TABLE2
Effect of Irradiation on Bacterial
Count in Sludge at Geiselbullach*
NUMBER OF BACTERIA PER GRAM
BACTERIA TYPE
TOTAL COUNT
SAMPLES
DIGESTED SLUDGE
2,370,000
(38)
IRRADIATED SLUDGE
Special Exit
Outlet to Bed
12,600
(26)
21,400
(16)
Drying
Bed
3,630,000
(6)
ENTEROCOCCES
SAMPLES
16,200
(38)
58
(26)
87
(16)
100
(6)
ENTEROBACTER
SAMPLES
49,500
(28)
0.1
(26)
850
(16)
93,000
(6)
* Adapted from Wizigmann and Wuersching
non-pathogenic, which multiply rapidly in a medium
from which competitive life-forms have been eliminated.
These results are not as good as predicted from bench-
scale experiments and may be due to correctable defi-
ciencies in the plant design (such as inadequate flushing
of sludge in the part of the loop outside of the radiation
zone).
Epp '' carried out studies of the effect of irradiation in
the pilot plant at 300 krad on viruses. Results show a
tenfold reduction in concentration of attenuated Polio-
virus Type 1 when capsules containing virus were in-
serted in the sludge and irradiated with 300 krads.
Under natural conditions where the virus was added di-
rectly to the sludge, there was a fourfold reduction in
virus concentration after irradiation in a limited number
of tests.
Groneman12 reported the substantial effect of irradia-
tion on two measures of sludge filterability, specific re-
sistance and compressibility. Irradiation of digested
sludge at 300 krads at Geiselbullach reduced specific re-
sistance by over 50 percent. The contrast with pasterui-
zation is marked, since pasteurization treatment doubles
specific resistance. Bench-scale experiments indicated
reductions of over 75 percent at the same level of irradia-
tion. Groneman attributed the difference to the shearing
of the sludge that occurs as the sludge is recirculated
through a centrifugal pump and piping (one pass per
minute for 288 minutes) in the pilot plant. COD of the fil-
trates was doubled by radiation treatment. Groneman
did not present data on total COD. Experiments by
Suess, et. al.13 indicated that the differences in crop
10
response were negligible between plots fertilized with
irradiated sludge or pasteurized sludge although there
was more desirable microbiological activity in the soil
with irradiated sludge.
The Geiselbullach plant, of course, is the first of its
kind and it is expected that it show some shortcomings.
As Groneman points out12, if shearing were less, the ef-
fect on settleability of the irradiated sludge could be
much more. Similarly, shortcomings in the self-flushing
characteristics of the recirculation and sludge discharge
systems may have contributed to the lower-than-ex-
pected microbiological reductions and regrowth. It is im-
portant to note that the German group is optimistic about
the future of the process, and considers it superior to the
alternative of pasteurization. There have been no com-
plaints about the use of radioactive materials at a waste-
water treatment plant, but more a feeling that the new
method has replaced inadequate technology. The Gei-
selbullach plant could be the first step in the coming-to-
age of radiation treatment of sludge.
M.I.T. Boston
Since May 1, 1974, studies on electron irradiation of
sludge have been conducted at the Massachusetts Insti-
tute of Technology with the support of the National Sci-
ence Foundation. Sinskey, et. al. 15 reported on the bio-
logical effects of irradiation, and Trump, et. al. 16 des-
cribed an ambitious project, also supported by the Na-
tional Science Foundation, to install an electron accel-
erator at Boston's Deer Island plant large enough to
treat 0.1 mgd (380 m3/da).
-------
128 HIGH ENERGY RADIATION
N2 AT 1 ATMOS.
AIR AT 1 ATMOS
-4
-5
-6
O2 AT 1 ATMOS.
I
I
_L
I
1
100 200 300 400 500 600 700
TOTAL DOSE (Krad)
Figure 3: Reduction in Total Plate Count of Raw Sludge (5% solids) Irradiated by Electron Beam in Flow System (after Sinskey, et. al.).
The results of Sinskey, et. al.l5 were preliminary in
nature, but indicated a significant synergistic effect of
oxygen. As Figure 3 shows, at doses greater than 0.3
megarad, the total plate count reduction is two logs bet-
ter when sludge is aerated prior to irradiation than when
no oxygen is present, and is three logs better when the
sludge is previously saturated with oxygen at 1.0 atmos-
phere pressure. Trump, et. al. l6 have noted that the
COD reduction that occurs when sludge is irradiated is
similarly influenced by the presence of oxygen.
The facility to be installed at Boston's Deer Island
plant is described by Trump, et. al. 16. It comprises a 50
kW electron accelerator which is capable of delivering a
dosage of 0.40 megarad to 0.1 mgd (380 nvVda) of
sludge. This is equivalent to the digested sludge output
of a community of about 400,000 people.
-------
HIGH ENERGY RADIATION
129
CABLE TO
HIGH VOLTAGE
POWER SUPPLY
CONCRETE
RADIATION
SHIELD
INCOMING
PRESSURIZED
AIR OR
OXYGEN
..ELECTRON
ACCELERATOR
INCOMING
SLUDGE
DEWATERER
^SLUDGE
WATER
COMMINUTOR
<^Ax\v/AV\Sy///A\\\\)f/l 11 f^
-------
130 HIGH ENERGY RADIATION
RADIATION AT 23°C
66°C ONLY
ADDITIVE
COMBINED
0
i
0
10 20 30 40 50 60 70 80 90 100
I I I I I
10 20 30 40 50
TIME AND RADIATION
Figure 5: Heat-temperature Synergistic Inactlvation of T4 Bacterlophage (after SMnskl, elaL).
MINUTES
KRAD
only slightly higher in cost than pasteurization at sludge
flows greater than 100 m-Vda. This quantity of digested
sludge is equivalent to a population of 100,000 in the
United States. For commercial plants, Lessel, et. al. esti-
mate that costs will actually be lower for irradiation than
for pasteurization even down to small plant sizes. Con-
flicting considerations make the choice of the most eco-
nomically desirable process less straight forward than
the graphs would indicate. For example, on the one
hand, we know that cost of fuel is escalating with time
whereas irradiation costs will doubtlessly decrease. On
the other hand, operating costs are the largest cost factor
in pasteurization, so if there are periods when pasteuri-
zation is not needed, money can be saved by periodic
shutdowns. This cost advantage is not possible with ir-
radiation, because capital makes up most of the cost of
irradiation. In the opinionof the Geiselbullach re-
searchers, irradiating makes a superior product, which
favors irradiation. Heat recovery could lower pasteuriza-
tion costs, which favors pasteurization. The economic
choice will evidently depend on specific site details, eco-
nomic factors such as fuel cost, and sociological con-
siderations such as unreasonable fears of radiation haz-
ards or unwillingness to tolerate odors of pasteurized
sludge.
Ballantine l8 has compared costs of irradiating sludge
with a 0.2 megarad dose using several different sources
of radiation. His figures, which are presented in Table 3,
are useful for pointing out the differences in the
individual components of the total costs for irradiation
when different radiation sources are used. The capital
cost, which includes source cost, is much higher for the
^cobalt and 1-^cesium than for the 3 MeV electron ac-
celerator. Source replenishment cost is higher for
-------
HIGH ENERGY RADIATION 131
0)
0.
IRRADIATION PLANT IN GEISELBULLACH
AVERAGE OF PASTEURIZATION PLANTS
I I
. COMMERCIAL IRRADIATION PLANT (ESTIMATED)
TOTAL COSTS-IRRAD.
TOTAL COSTS-PASTEUR.
^OPERATION COSTS-PASTEUR.
OPERATION COSTS-IRRAD.
30 100 150
DAILY CAPACITY (m3/DAY)
Figure 6: Comparison Between the Costs for Geiselbullach Irradiation Plant and Pasteurization Plants—DM X 0.43 = Dollars, M3 X 264 = U.S. Gal
(after Lessel, et. a].).
TABLE3
Cost Comparison of Sludge Irradiation Methods*
CAPITAL COST ($)
(SOURCE 6 SHIELDING)
AMORTIZATION
(20 YR AT 7.75%)
SOURCE REPLENISHMENT,
MAINTENANCE, LABOR
POWER (2f/KWH, 50%
EFFICIENCY)
TOTAL ANNUAL COST
$ COST/ 1000 GAL
$ COST/TON SOLIDS
5°COBALT
800,000
80,000
101,250
181,250
3.36
16.1
1 3 /
CESIUM
1,120,000
112,000
42,300
154,300
2.86
13.7
3 MeV ACCELERATOR
250,000
25,000
50,000
7,000
82,000
1.52
7.30
* (AFTER BALLANTINE)!8 150,000 GAL/DA. OF 5% SOLIDS SLUDGE AT
0.2 MEGARAD.
^cobalt than for ^cesium because the half life of ^co-
balt is considerably shorter (5 yr vs. 30 yr). The isotope
irradiation methods have negligible power costs com-
pared to the electron accelerator.
The calculated net processing cost per gallon or ton of
sludge processed is substantially lower for the electron
accelerator than for the radioisotope irradiation. This
may prove to be the case in actual practice, but it should
be understood that the effectiveness of the electron ac-
celerator has still not been demonstrated in a continuous
process on a practical scale. The poor penetrating power
of electrons from a three MeV electron accelerator re-
quires that the sludge be delivered under the electron
"gun" in thickness of the order of one or two millime-
ters. This step could be difficult to accomplish and could
increase cost to levels comparable with isotope irra-
diation.
Trump, et. al.lb have also estimated costs for their in-
stallation at Boston. Costs for this 100,000 gal/da facility
are $100,000 per year, which is equivalent to $2.74/1000
gallons or, based on five percent solids sludge, $13.207
dry ton. This is almost twice Ballantine's estimate, but
the dose is 0.45 megarad, over twice Ballantine's dose.
At this time, a dose of 0.45 megarad seems to be needed
so Trump's figures are more indicative of the true cost of
radiation treatment.
Anticipated Future Developments
A number of investigators reported at the symposium
on synergistic effects when oxygen or chlorine was
added to the sludge or wastewater when it was being ir-
radiated. Trump, et. al. 16 intend to investigate the ef-
fect of oxygen addition in their work at Boston. The pos-
sibilities for improved radiation effectiveness, although
-------
132 HIGH ENERGY RADIATION
real, may be limited by the solubility of oxygen in
sludge. The dose is applied in such a short time in elec-
tron acceleraters that the oxygen must be in solution at
the time of irradiation. A greater degree of oxygen
synergism may occur if the irradiation is done with radio-
isotopes rather than with electron accelerators. With
radioisotopes, the dose is applied over a longer time in-
terval—at least several seconds (at Geiselbullach, 4.8
hours)—so there is time for mass transfer between a
gaseous phase and a liquid phase. In addition, higher
total pressures and partial pressures of oxygen can be
maintained because the sludge is pumped through pipes
and vessels that can be made to withstand high
pressures.
In addition to these developments, which hold
promise of reducing irradiation cost, there is also the
possibility of irradiating raw sludge. This would elimi-
nate the cost of the digestion step. What could be done
with irradiated raw sludge is problematical, because it
would still be rich in unstable compounds ready to put-
refy under favorable conditions. If sludge were suffi-
ciently low in mercury, cadmium, andjiazardous organic
materials, it could perhaps go directly to the ocean. It
could be landspread by plow injection methods. Costs of
irradiation would be higher because the mass of sludge
is higher before digestion than after, and radiation dose
most likely would have to be greater. This would coun-
terbalance a substantial part of the savings generated by
eliminating digestion.
Needs-Alternatives-Prospects
In Germany and Switzerland, there has been a sub-
stantial use of sludge on agricultural land and a con-
comitant concern about its potential infection hazard.
This has led to regulations that sludge applied to pasture
or agricultural land be reduced in pathogens beyond the
level attained by digestion. Hess l9 presented new infor-
mation on the transmission of Salmonella to cattle feed-
ing on pasture after sludge spreading. Obrist20 sum-
marized the situation in Switzerland. Opinion is divided.
Veterinarians believe that elimination of pathogens is
needed but public health experts evidently do not. Until
there are more definitive indications of harm, applica-
tion of stabilized sludge to cropland after harvest and to
pasture during the winter will be permitted.
In the United States, there is extensive use of digested
sludge on pasture and agricultural lands under widely
varying climatic conditions. For the most part, public
health officials have not restricted its use. Notwithstand-
ing this lack of overt disapproval, there would probably
be much more extensive use of digested sludge than is
currently the case if the sludge were free of infectious or-
ganisms. Many more options, such as spreading liquid
sludge on highway median strips, are not being used to
the extent possible because of a reluctance to expose the
public to potential hazard. The U.S. EPA is expected to
publish for public comment a bulletin on sludge disposal
practice that will establish conditions of use and
maximum content of pathogenic organisms if sludge is
to be applied to land used as pasture or to grow food
crops. It is anticipated that environmental groups and
the general public will support and even spearhead
moves to reduce infection hazard in sludge even if the
need is not clearly established.
If a municipality is faced with the need to eliminate
pathogens to continue or adopt the practice of sludge
utilization on cropland or pasture, it can choose from a
number of alternatives. It can abandon land utilization
altogether and use some other method such as sanitary
landfill or incineration. It can utilize the sludge for recla-
mation or for growth of a non-food crop where pathogen
elimination would not be needed. If the decision is made
to utilize the sludge on cropland or pasture, there are
still alternative means for eliminating pathogens be-
sides irradiation. Farrell and Stern21 discuss the follow-
ing methods: pasteurization, thermophilic anaerobic di-
gestion, thermophilic aerobic digestion, and long-term
lagooning. Municiaplities must make their choice be-
tween irradiation and these alternative methods. Cost
will be an important consideration, but reliability of per-
formance and simplicity of operation—considerations
which favor irradiation—will have an important bearing
on the final selection.
During the next few years, regulatory agencies at the
several levels of government will become concerned
with pathogens in sludge applied to land. Codes of prac-
tice will require either pretreatment of sludges applied
to cropland and pasture to reduce pathogens or special
application procedures or practices, such as subsurface
application or application only after harvest. To give de-
sired flexibility of operation, some of the communities
affected will doubtlessly choose irradiation as a safe and
sure method for eliminating pathogens. Unless there are
some startling reductions in cost of radiation processing,
however, it is unlikely that the method will be adopted by
the majority of communities utilizing sludge on the land.
LITERATURE CITED
Literature indicated by an asterisk was presented at
the "Symposium on the Use of High-Level Radiation in
Waste Treatment," International Atomic Energy
Agency, at Munich, March 1975.
1. "Training Manual on Food Irradiation Technology
and Techniques," Technical Report Series No. 114, In-
ternational Atomic Energy Agency, Vienna (1970).
2. Ridenour, G.M., and Armbruster, E.H., "Effect of
High-Level Gamma Radiation on Disinfection of Water
and Sewage," JAWWA 48, 671 (1956).
3. Gerrard, M., "Conceptual Design of an Irradiation
Test Facility forWastewaterand Sewage Sludge," Iso-
topes and Radiation Technol. 8, No. 4, 435 (1971).
-------
HIGH ENERGY RADIATION
133
4. Ballantine, D.S., Muller, L.A., Bishop, D.F., and
Rohrman, F.A., "The Practicality of Using Atomic Ra-
diation for WastewaterTreatment," J. Wat. Poll. Contr.
Fed. 41, 445 (1969).
5. *Feates, F.S., and George, D., "Review of Work on
Radiation Treatment of Wastes," IAEA-SM 194/405.
6. Touhill, C.J., Martin, E.G., Fujihara, M.P., Ole-
sen, D.E., Stein, J.E., and McDonnell, G., "Effects of
Radiation on Chicago Metropolitan Sanitary. District
Municipal and Industrial Wastewaters," J. Wat. Poll.
Contr. Fed. 41 R44 (1969).
7. Etzel, J.E., and Condren, A.J., "Radiation Treat-
ment of Waste Waters," Trans. Amer. Nucl. Soc. 11, 56
(1968).
8.Compton,D.M.J., Black, S.J., Lierance, F.L., and
Whittemore, W.L., "Application of Ionizing Radiation
to the Treatment of Waste Waters and Sewage Sludge,"
Proc. ofSymp. on Util. of Large Radiation Sources and
Accelerators in Industrial Processing, Munich, 1969,
International Atomic Energy Agency, Vienna, p. 399
(1969).
9. *Lessel, T., Moetsch, H., and Hennig, E., "Exper-
iences with a Pilot Plant for the Irradiation of Sewage
Sludge: Design, Operation, Experience and Cost Calcu-
lations after a Period of 18 Months of Continued
Running," IAEA-SM-194/604.
10. *Wizigmann, 1., and Wuersching, F., "Experi-
ence with a Pilot Plant for the Irradiation of Sewage
Sludge: Bacteriological Studies After Irradiation of Sew-
age Sludge," IAEA-SM-194/606.
11. Epp, C., "Experience with Pilot Plant for the Irra-
diation of Sewage Sludge: Experiments on the Inactiva-
tion of Viruses in Sewage Sludge after a Radiation Treat-
ment," IAEA-SM-194/607.
12. *Groneman, A.F., "Effects of Gamma Radiation
at Pilot Plant Level as Compared to Effects of Pasteuriza-
tion on the Dewatering of Sewage Sludges,"
IAEA-SM-194/608.
13. *Suess, A., Rosopulo, A., Borchert, H., Beck, T.,
Bauchhenss, J., and Schurmann, G., "Experience with
a Pilot Plant for the Irradiation of Sewage Sludge: Re-
sults on the Effects of Different Treated Sewage Sludge
to Plants and Soil," IAEA-SM-194/609.
14. *Rosopulo, A., Fiedler, I., Staerk, H., and Suess,
A., "Experience with a Pilot Plant for the Irradiation of
Sewage Sludge: Analytical Studies on Sewage Sludge
and Plant Material," IAEA-SM-194/610.
15. *Sinskey, A.J., Shah, D., Wright, K.A., Merrill,
E.W., Sommer, S., and Trump, J.G., "Biological Ef-
fects of High Energy Electron Irradiation of Municipal
Sludge," IAEA-SM-194/302.
16.Trump. J.G., Wright, K.A., Merrill, E.W., Sin-
skey, A.J., Shah, D., and Sommer, S., "Prospects for
High Energy Irradiation of Wastewater Liquid Re-
siduals," IAEA-SM-194/503.
17. *Sivinski, H.D., "Treatment of Sewage Sludge
with Combinations of Heat and Ionizing Radiation (Ther-
moradiation)," IAEA-SM-194/303.
18. *Ballantine, D.S., "Alternative High Level Radia-
tion Sources for Sewage and Wastewater Treatment,"
IAEA-SM-194/501.
19. *Hess, E., and Breer, C., "The Sanitary Effect of
Gamma Irradiation on Sewage Sludge," IAEA-SM-194/
308.
20. *0brist, W., "Costs and Hygienic Necessity of
Sewage Sludge Pasteurization in Switzerland,"
IAEA-SM-194/507.
21. *Farrell, J.B., and Stern, G., "Methods for Re-
ducing Infection Hazard of Wastewater Sludges,''
IAEA-SM-104/102.
-------
MANAGEMENT OF MUNICIPAL WASTEWATER
TREATMENT RESIDUALS*
Edward H. Bryan
National Science Foundation
Washington, D. C.
INTRODUCTION
The Division of Advanced Environmental Research
and Technology of the National Science Foundation has
currently, about 200 active research awards in:
• Regional Environmental Management
• Weather Modification
• Environmental Aspects of Trace Contaminants
• Environmental Effects of Energy
• Earthquake Engineering
• Fire Research.
Through its other divisions within the Applied Re-
search Directorate and Research Directorate, the
Foundation supports a broad spectrum of both basic and
applied research consistent with the equally broad base
of interests that characterizes the problem of pollution.
The period leading up to the middle of the last decade
was characterized by a rather remarkable growth in pub-
lic support of scientific research. Somewhere around the
middle of the 1960's, the growth rate was estimated to be
in excess of 15 percent per year. During this period, pub-
lic confidence was high in the value of scientific research
as an investment toward the future. The change in public
perception of its responsiveness to needs of society was
expressed by Dr. Lee DuBridge in a 1969 address to the
scientific community when he said:
"... the day is past when scientists and other scholars
can sit quietly in their ivory towers unaware of and un-
concerned with the world outside their laboratories,
libraries, studies and classrooms... they must ask the
question of whether the scientific work in which they
are engaged is of sufficient importance to the progress
of knowledge and its application to be worthy of public
support."
Another way to explain what was happening in the
1960's was that problems may have been developing at a
faster rate than society's complex system of problem-
solving was able to process. This certainly was true in
*Remarks presented do not represent an official position of either the
National Science Foundation or the Federal government.
the general area of what we call "environmental pollu-
tion." With particular reference to water pollution
abatement, it is doubtful that in any year prior to 1973,
that we had installed the water pollution abatement
capacity to equal or exceed the incremental increase in
pollutant discharge.
Whatever the reason, there was a perception of a
widening gap between the rate at which problems were
surfacing and solutions emerging. Assuming that sci-
ence and technology had not lost their capability, was
there some way in which these societal institutions could
be directed toward societal needs?
In 1968, Congress amended the National Science
Foundation statute by adding support of "applied re-
search '' to its responsibilities toward basic research and
education. An implementation step taken by the Foun-
dation in 1969 resulted in the creation of a program en-
titled, "Interdisciplinary Research Relevant to the Prob-
lems of Society."
This program further evolved into the program that is
presently known as, "Research Applied to National
Needs" (RANN).
The Applied Research Directorate is the program-
matic home of RANN and the program focuses its atten-
tion on four major areas.
1. Environment
2. Energy
3. Productivity
4. Resources
Dr. Raymond Bisplinghoff, in his address to the 1972
meeting of the American Association for the Advance-
ment of Science, best described the National Science
Foundation's Program of Research Applied to National
Needs. He suggested that problem-focused research is
typically, externally motivated to satisfy the needs of so-
ciety. Its role in providing support entitles society to in-
sist that research objectives be influenced, if not totally
determined, by ultimate utility of the research-results
and that managerial responsibility for selecting research
problems lies with the sponsor. He further suggested
that research directed toward solving complex problems
134
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MANAGEMENT OF TREATMENT RESIDUALS 135
of society was likely, itself, to be complex and this was
attributable to the interlocking issues involving techni-
cal and scientific knowledge as well as social and human
values. He further indicated that a measure of the value
of research initiated be estimated before its initiation
and that emphasis be placed upon its purpose—to pro-
vide solutions to important problems.
Problem-focused research is not research that leads
only to the conclusion that more research is needed, al-
though we would expect it to open new areas for further
intellectual exploration. While we would expect it to pro-
vide opportunities for education and training, that is not
its primary objective. Its success would be measured by
its results. It seemed reasonable to expect that problem-
focused research would be in reasonable balance with
traditional basic and applied research and that not all re-
searchers would yield their prerogative for decision as to
the nature of their work nor submit to the discipline and
directed attention that are required by problem orienta-
tion toward objectives.
How each of us perceives our "world" is a complex
product of individual experiences interpreted against a
background of personal observations that have been re-
membered which, in effect, constitute a "filter" that
makes each additional event unique. With that qualifica-
tion , I suggest that the change we observed was not a so-
cietal suggestion that all scientists and scholars give up
concentrating on basic research and education, since to
assume that, would be to concede that society had de-
cided there was nothing to gain by long-range invest-
ments in a future. The action we observed may simply
have been a signal that society was interested in answers
to some short-range problems. That is, an expression of
apprehension that if some of our shorter-range problems
were not addressed and solutions found, there would be
no opportunity to exercise the longer-range options.
The goal of research supported by the Division of Ad-
vanced Environmental Research and Technology is to
provide foundations for good management decisions re-
lating to factors that affect environmental quality. Good
management may be characterized as the art of making
wise decisions on the basis of information available and
used.
The application of management principles to improve-
ment of regional environmental quality requires that we
improve our ability to predict effects of management de-
cisions. This requires improvement in our comprehen-
sion and understanding of the problem and its potential
solutions.
Rationale of the program of applied research directed
toward residuals management is conceptually based
upon fundamental resource-residuals relationships that
are common to all ecosystems and essential for sustain-
ing their vitality and viability and the assumption that
new technologies approaches can provide more feasible
solutions to both human and naturally caused environ-
mental problems. Current program of objectives are:
• To identify capabilities and limitations of known
processes for management of residuals.
• To evaluate new technological approaches for pro-
cessing and management of municipal and indus-
trial residuals.
• To achieve reconciliation of processing economies-
of-scale promised by regionalization of residuals
management with apparent collection system dis-
economies.
• To seek alternative management concepts for con-
version of residuals into products or forms that min-
imize or eliminate risk to human health or to the
life-support system upon which it is dependent.
Solid and liquid residuals from municipal and indus-
trial sources are both a threat to regional environmental
quality and a potential solution to its security as a viable
ecosystem. Program development strategy is to couple
research directed toward solutions to problems of re-
siduals management with recovery of their potential re-
source value. Objective is to maximize potential for utili-
zation of research-results.
Research Projects
In the context of these introductory remarks, there fol-
lows several briefly described research projects, cur-
rently underway or recently completed, that may be of
interest to you. The examples will include approaches to
management of municipal wastewater treatment
residual effluent and sludge, selected approaches to
management of industrial wastes and contributions to
understanding of and potential response to diffuse
sources of pollutants.
With reference to the major topic of this conference,
Dr. James L. Smith of Colorado State University is cur-
rently investigating use of land in management of waste-
water treatment residuals. The tractor-implement de-
veloped by him has the capability of injecting sludge into
soil at the rate of up to 800 gallons per minute to 40 acres
of land from a single hose-connection. Subsurface in-
jection appears to provide a technically superior and
more economical method of applying sludge to land. Ob-
jectivesof his research include determination of relative
economy of the method, esthetic and environmental ac-
ceptability and relative energy requirements. Concur-
rently, an analytical model of subsurface injection is be-
ing formulated and calibrated with field data from injec-
tion sites at Fort Collins and Boulder, Colorado and Wil-
liamsburg, Virginia. Close coupling of this research
with potential users will provide a realistic assessment of
its acceptability. Results will also provide a base for
more comprehensive environmental impact assessment
of land disposal and will provide local governments and
their consultants with information and procedures for
design of subsurface injection systems. Implementation
of the project's utilization plan included two regional
workshops held during 1974 (Boulder, Colorado and
Dallas, Texas). A site visit/demonstration was held at
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136 MANAGEMENT OF TREATMENT RESIDUALS
the Boulder injection site during the 1974 National Con-
ference of the Water Pollution Control Federation in
Denver. The eastern conference/workshop is scheduled
to be held at Williamsburg, Virginia on November 13
and 14, 1975.
Increased attention directed toward more widespread
use of land as part of a treatment-management concept
for wastewaters and their residuals has resulted in ques-
tions regarding virus removal from wastewaters by con-
ventional and advanced treatment concepts. While
treatment processes remove most if not all virus parti-
cles originally present, results from an NSF/RANN
sponsored study at the University of Texas, under the di-
rection of Dr. Bernard P. Sagik and Dr. Joseph F. Malina
showed that virus particles are incorporated as consti-
tuents of the residual sludges, are not inactivated imme-
diately, and can be released from the sludge under some
conditions.
To investigate the potential use of high-energy elec-
trons for disinfection of municipal wastewater treatment
residuals, a study was initiated at the Massachusetts In-
stitute of Technology under the direction of Dr. John G.
Trump and his colleagues, Dr. Edward W. Merrill and
Dr. AnthonyJ. Sinskey. The influence of radiation-dose,
rate of dose application, effect of availability of oxygen,
temperature effects, and the influence of competing and
synergistic substances were evaluated during an initial
phase utilizing a three MeV electron accelerator. Results
of the initial phase provided the basis for design of a re-
search facility presently under construction at the Deer
Island Wastewater Treatment Plant of the Metropolitan
District Commission of Boston. This facility will be cap-
able of in-line treatment of selected effluent or liquid
sludge under controllable conditions utilizing a 50 kilo-
watt, standard electron-source to permit delivery of
doses over the range of 100,000 to 2 million rads. Bio-
chemical and engineering data obtained from the opera-
tion of this research facility will provide the basis for
evaluation of the process including assessment of en-
ergy consumption, safety, modes of application, flex-
ibility and costs. At the dosage anticipated adequate for
disinfection of sludge (400,000 rads), this research unit
will have the capability of irradiating 100,000 gallons per
day.
In coordination with the Colorado State University re-
search, Dr. Bernard P. Sagik at the University of Texas-
San Antonio is investigating virus survival in soils being
subjected to municipal sludge application. Groundwater
and surface runoff water samples from injection sites are
being analyzed to determine the fate of viruses. Parallel
studies will utilize isotopically-labeled viruses incor-
porated into biologically active sludge and injected into
undisturbed soil cores. These will be followed for the de-
gree of viral leaching as a function of rainfall and/or irri-
gation level. Soil migration of virions will be followed by
incorporation of high levels of poliovirus vaccine into a
functional septic tank-tile field system in sandy, loam
soil of Bastrop County, Texas. Water will be pumped
from the gravel beds underlying the tile fields and from
the adjacent dry stream bed to determine the character-
istics of virion movement through soils. Soils from all lo-
cations will be examined to ascertain the possible accu-
mulation of ova, cysts and other evidence of enteric
parasites in the soil.
A study by Dr. Theodore Metcalf at the University of
New Hampshire is investigating control of virus patho-
gens by irradiation in cooperation with the research un-
derway at the Massachusetts Institute of Technology.
Objectives include comparison of concentration, absorp-
tion and magnetic separation virus assay techniques for
accuracy and reliability and application of these proce-
dures to determine the effectiveness of electron irradia-
tion for inactivation of viruses. Investigations will in-
clude determination of radiation dose for inactivation of
viruses in the presence and absence of oxygen and under
variations in pH, temperature and pressure.
A research project under the direction of Dr. Richard
Dick at the University of Delaware has just been initiated
to investigate process selection for optimum manage-
ment of regional wastewater treatment residuals. Re-
search objective is to synthesize a procedure for analysis
of cost and performance of sludge treatment processes.
Interactions between process elements for treatment
and management of sludge generated in treatment of
wastewater are being evaluated to characterize optimal
sludge management systems. Mathematical models of
the performance and cost of individual processes are
being constructed and optimal combinations of pro-
cesses and operating conditions are being identified by
integrating combinations of processes into systems for
residuals management. Fundamental sludge properties
which influence performance of treatment and subse-
quent management procedures are being used as input
variables in performance models. Operational and eco-
nomic variables are being used to build cost and per-
formance models. The combined effect of significant in-
dividual variables on overall process performance can
thus be evaluated and the models applied to a wide
variety of sludge types and local situations.
With regard to management of treated effluent, the
Foundation is supporting research on the potential utilii-
zation of wetlands for their ability to remove nutrients
from domestic wastewater that has received secondary
treatment. Research along those lines is underway at the
Universities of Michigan and Florida. The Michigan re-
search under direction of Dr. Robert Kadlec is asso-
ciated with marshlands near Houghton Lake, a headwa-
ter marsh system. Research objective is validation of a
dynamic simulation model of a peatland-marsh ecosys-
tem to determine its capability of providing advanced
treatment for effluents from domestic wastewater treat-
ment plants. Potential benefits include conservation of
effluent-contained nutrients and increased productivity
of the wetland. Secondary effluent is being obtained
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MANAGEMENT OF TREATMENT RESIDUALS 137
from the Roscommon Township treatment facility.
Simultaneously with the construction of the simulation
model, the response of the natural ecosystem to effluent
application has been studied on a small scale. Applica-
tion of effluent to a ten acre portion of the marsh has
been started to determine effects of the effluent on the
marsh and provide a first measure of the validity of the
simulation as a significant step toward evaluation of
feasibility.
In the study at the University of Florida feasibility of
utilizing cypress wetlands for conservation of water and
nutrients in effluent from municipal wastewater treat-
ment plants is being investigated by Dr. Howard T.
Odum. Cypress domes are being studied to determine
their potential utilization for management of effluent
from secondary treatment of municipal wastewater
simultaneously providing regional, greenbelts, land use
units for esthetic enhancement and wildlife protection.
Recently burned domes, those with experimental inflow
of groundwater, flowing cypress and typical acid water
domes are being characterized with respect to hydrol-
ogy, water quality and ecosystem qualities in four Flori-
da counties. Results to date indicate that cypress wet-
lands can absorb application of as much as five inches of
treated effluent per week to provide a means for qualita-
tive and quantitative regional management of water re-
sources. Ecosystem characterization of experimental
and control wetlands includes considerations of water
budget, vegetation responses, tree growth rates, nu-
trient absorption, heavy metal concentrations, microbial
activities, forest metabolism, insect grazing, and
species diversity.
Simulation using ecosystem models is being utilized
to provide better understanding of water, nutrient, and
general ecosystem functions. Feasibility and impact of
using the cypress wetlands for water management and
recycling will be estimated by including regional analy-
ses of water, economic evaluation of this land use, ef-
fects of introduction of exotic species, the relationship of
the managed systems to fire, compatible architectural
designs and public attitudes necessary for acceptance of
such projects for large-scale adoption. The final report
will present detailed results and a handbook of cypress
wetland utilization for use by planners. This project is
receiving coordinated support from the Rockefeller
Foundation which in addition is funding a study of virus
fate in wastewater used for recharge. This phase of the
study is directed by Dr. Flora Mae Wellings of the
Florida Department of Health.
With reference to industrial waste management,
placement of residuals into deep formation by use of in-
jection wells may provide a regional response to man-
agement of some wastes. Research underway at North
Carolina State University by Dr. Gerald Elkan is directed
toward determining whether biodegredation of organic
substances stored in deep formations can be utilized to
reduce their pollution potential. Dr. William Walker at
Virginia Polytechnic Institute recently completed a two-
year study of legal aspects relating to deep-well disposal
which was followed by a workshop/conference, the ob-
jective of which was to provide a definitive analysis of
deep-well disposal for substantiation of policy deter-
mination leading to effective regulation of deep-well in-
jection as a management option. A report is currently
available in draft form with final publication expected
before the end of this year.
At Washington State University, Dr. R.V. Subrama-
nian is investigating concepts of encapsulation of
hazardous wastes in polymeric resin matrices to yield
solidified products having rigid, light-weight shock-
proof structures for safe transportation and regional
management by storage with minimal danger of en-
vironmental and ecosystem contamination. Metal pro-
cessing residuals and other aqueous solutions can be
mixed with a liquid, water-extensible polymer under
conditions of high shear to form stable emulsions in
which the residuals are dispersed as small droplets in
the resin matrix. Polymerization induced by addition of a
catalyst results in droplets that become individually en-
capsulated in a shell of polymer resin. Results are ex-
pected to yield knowledge of optimum conditions for en-
capsulation, physical properties and leaching character-
istics of the solidified residuals for assessment of the en-
vironmental risk in further handling and storage.
In response to need for further insights into diffuse
sources of pollution, research is being supported at the
Smithsonian Institution's Chesapeake Bay Environ-
mental Research Center under direction of Dr. David
Correll. His research is directed at establishing relation-
ships between various agricultural land management
practices and pollutant-yield.
In cooperation with Dane County, Dr. Richard Koegel
at the University of Wisconsin is developing improved
methods for mechanical harvesting of rooted vegetation
from lakes. Coupled with the objective of developing a
more environmentally acceptable control procedure
than provided by herbicides is that of providng a re-
sponsive technological approach to nutrients entering
lake ecosystems from diffuse and discrete sources such
as agricultural and urban land drainage.
In consideration of "regionalization" of wastewater
systems to achieve "economies of scale," we are faced
with the problem of optimization of capital investment
between conduction and treatment. Dr. Donald Lauria at
the University of North Carolina has been working
toward a procedure that will permit consulting engineers
to study a wider range of options in arriving at their
recommendations in balancing these options. His
academic colleague, Dr. Daniel A. Okun, has just re-
turned from England where he studied regionalization of
water authorities in Great Britain to determine what we
can learn from those experiences. A related study was
also sponsored by the Foundation at the University of
Washington at Seattle under direction of Dr. Ralph
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138 MANAGEMENT OF TREATMENT RESIDUALS
Johnson to determine the applicability of selected Euro-
pean laws, institutions and policies to the solution of en-
vironmental problems in the United States. A seminar/
workshop is planned to be held in January 1976 at the
Foundation with Dr. Okun and Dr. Johnson to explore
the implications of their findings.
CONCLUSION
In conclusion to this brief overview of some research
being supported by the National Science Foundation,
the successful management of a region's residuals can
provide a source of materials needed to sustain the vi-
tality and viability of a region while simultaneously im-
proving its environmental quality. Deliberate action and
effort directed toward good management of residuals
will ultimately be the criterion by which a region's capa-
city to function as an ecosystem will be measured. The
level of effort directed toward solving problems relating
to environmental quality seems to be advancing toward
commitment of resources more comparable to levels as-
sociated with the creation of problems.
Nothing else is possible without achievement and
maintenance of survival standards of environmental
quality. Faced with the problem of need for response to
any problem of residuals, the only three alternative
solutions generally possible are movement away from
the accumulated residuals, movement of residuals away
to avoid their accumulation or management of residuals
within the region.
Good applied research can provide the knowledge that
is necessary to attain and maintain those levels of re-
gional environmental quality that are consistent with
other societal goals, one of which must be assumed to be
its own survival. The key to solutions to problems of en-
vironmental quality lies in successful management of so-
ciety's residuals. We cannot dispose of residuals, we can
only learn how to manage them.
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PYROLYSIS OF SEWAGE SLUDGE
Robert A. Olexsey
United States Environmental Protection Agency
Cincinnati, Ohio
INTRODUCTION
Each day, sewage treatment plants in the U.S.
produce about 13,000 dry tons of sludge of all types J.
Each day, someone must do something with all of this
sludge or it will get in the way of tomorrow's 13,000 tons.
The question to be addressed here is what to do with this
sludge.
Most of the sewage sludge produced in the United
States is disposed of directly to the land in either a land-
fill or a landspreading operation. That sludge which is
not disposed of to the land is either incinerated or dis-
posed of through ocean dumping. Since the future of
ocean disposal is, at the very least, somewhat pre-
carious, the only currently secure options that can be
planned are the land and the incineration alternatives.
The disadvantages of incineration are not difficult to
list. It is costly. It can pollute the air if not properly con-
trolled. It can consume large amounts of auxiliary fuel.
Perspective is required to foster an understanding as
to why incineration is practiced at all. Incineration has
some obvious advantages that make it attractive to
people charged with sludge disposal. Incineration is
fast. It rapidly achieves a substantial reduction in the
volume of material for ultimate disposal. Incineration is
compact, requiring minimal land area relative to the
land intensive disposal techniques. Incineration takes
place at the point of generation, thereby eliminating the
need for transporting the sludge to distant disposal
sites. Finally, incineration does not take place in some-
one's backyard. When its 10 to 15 years of useful life are
completed, the incinerator can be replaced with another
unit at the exact location as the first. The periodic search
for a new disposal site and a friendly neighborhood to ac-
cept the exported sludge is not required.
The desire to retain the option of on-site disposal and
the inadequacies of incineration have prompted a search
for disposal alternatives that retain the advantage of in-
cineration while dispensing with the disadvantages. A
candidate system is pyrolysis. The pyrolysis process will
be discussed in general here and then preliminary ex-
perimental results will be presented from a research
project funded by the Environmental Protection Agency
and conducted by the research staff of the U.S. Bureau of
Mines.
Pyrolysis
Pyrolysis is the destructive distillation of organic ma-
terials under heat and/or pressure in the absence of oxy-
gen. It is the process that is used to produce coke from
coal and charcoal from wood. In the pyrolysis process,
the organic portions of waste are reformed into lower
molecular weight compounds as typified by the follow-
ing simplified description of what happens to cellulose in
pyrolysis.
C6H10°5 + Heat - »"CH4 + H2 + c°2 + C2H4
H2°
The product compounds can be in the physical forms of a
combustible gas, tar and oil, and a solid char which also
has an appreciable heating value. The relative propor-
tions of the products that occur in each physical state as
well as the fractions of each product chemical compound
vary primarily with the amount of heat applied and
secondarily with the presence of any moisture in the
feed. Generally speaking, higher reaction temperatures
yield simpler chemical products and larger quantities of
gas at the expense of the liquid and solid product phases.
Pyrolysis of waste materials, even of sewage sludge,
is not an entirely new concept. The literature contains
references to pyrolysis experiments conducted in 1908 in
England for the purpose of recovery of nitrogen in the
form of ammonium sulfate 2.
In recent years, there has been much research activity
in the United States in the application of pyrolytic and
starved air techniques to the disposal of solid wastes.
The earliest concentrated pilot plant work in the area of
pyrolysis of waste materials for the purpose of conver-
sion to fuel was reported by the U.S. Bureau of Mines in
1970 3. This and subsequent work by the Bureau of
Mines demonstrated that any organic material yielded
similar products of gas, oil and carbon char in the pyroly-
sis process4"6.
139
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140
PYROLYSIS OF SLUDGES
Some systems for solid waste pyrolysis have pro-
ceeded to the point of full scale demonstration. Plants of
from 75 tons per day to 1,000 tons per day have been
operating or are under construction with product re-
covery ranging from oil and gas to steam and heat. A
wide variety of hardware is employed with reactors tak-
ing the form of fluidized beds, rotary kilns, shaft fur-
naces and other devices7.
The EPA-Bureau of Mines Research
While such materials as municipal refuse, scrap rub-
ber tires, rice hulls, and cow manure were being py-
rolyzed, little, if any testing had been performed on sew-
age sludge. Although the previous work had shown that
most any organic material could be pyrolyzed success-
fully, it was felt that verification of the concept for actual
sewage sludge was necessary. To this end, the Environ-
mental Protection Agency entered into an interagency
agreement with the U.S. Bureau of Mines. Under the
terms of this agreement the Bureau of Mines would con-
duct pilot-scale tests on the pyrolysis of sewage sludge
and sludge-solid waste mixtures at the Bureau's Pitts-
burgh Energy Research Center. The pilot plant equip-
ment used for the tests is the same equipment that was
employed in the previous tests with refuse, rubber tires,
and manure. A schematic of the pilot plant is presented
in Figure 1.
Basically, the pilot plant consists of a batch operated
retort heated electrically, equipment for removing tars
and oils, and equipment for cleaning, measuring and
storing gas. The retort, depicted in Figure 2, is 18 inches
in diameter and 26 inches deep and can accommodate a
charge of from 50 to 80 pounds of dried material. The tar
removal and gas cleaning apparatuses are shown in
Figure 3.
Pyrolysis occurs at temperatures ranging from 500°C
to 900°C. Depending on the test material and tempera-
ture, a test could last from six to twelve hours. In order to
ensure a smooth flow of materials through the pilot plant
sections, all materials were predried to no more than ten
percent moisture. Higher moisture contents impose a
large heat burden on the pyrolysis section due to burst
vaporization. Both quantities and qualities of product
gases are lower when larger amounts of moisture are
present in the feed.
Tests were conducted at atmospheric pressure with
primary, activated, primary-activated, and digested
sludges. This discussion will focus on the data developed
for waste activated sludge since it is the nearest to com-
pletion at this time and because it can be considered
typical for sludges.
LEGEND
1. THERMOCOUPLE
2. ELECTRIC FURNACE
3. RETORT
4. TAR TRAP
5. TUBULAR CONDENSER
6. ELECTROSTATIC PRECIPITATOR
7. AMMONIA SCRUBBER
8. ACID PUMP
STEAM
9.CARBON DIOXIDE SCRUBBER
10. CAUSTIC PUMP
11. LARGE WET-TEST METER
12. DRYING TUBE
13. LIGHT OIL CONDENSER
14. SMALL WET-TEST METER
15. GAS SAMPLE HOLDER
EXCESS GAS
IS FLARED
TO Btu AND
sp gr RECORDERS
SAMPLE COCK FOR
H2S AND NH3 TESTS
H2S04 NaOH NaOH
Figure 1: Pilot Plant Pyrolysis System.
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PYROLYS1S OF SLUDGES
141
Figure 2: Pyrolysis Retort (U.S. Department of Interior—Bureau of Mines).
Pyrolysis of Sludges Alone
Table 1 describes the energy recovered through py-
rolysis conversion in each fraction in millions of BTU per
ton of feed material for primary sludge, waste activated
sludge, and municipal refuse. The municipal refuse
used was the light fraction from shredded, air classified
refuse obtained from the Altoona, Pennsylvania, com-
post plant.
Table 2 summarizes the relative yields per fraction on
the bases of weight percent of feed, quantity per ton of
feed, and energy per ton of feed. Of significance is the
fact that, while the portion of the yield that is attributed
to the solid char is relatively insensitive to pyrolysis tem-
perature, there is a considerable shift between the liquid
and gas fraction as a function of temperature. The
greater yields of gas with higher temperature must be
considered a beneficial effect since the gas is a much
more accessible energy form than the liquid mixture of
tar, oil, and water.
Table 3 presents the analyses of the gases produced at
the two temperature extremes. Note that, while the
900°C temperature produces a much greater quantity of
gas than does the 500°C temperature, the high tempera-
ture gas has a much lower heating value than does the
500°Cgas. This is probably due to the shift in quantities
between methane and carbon monoxide at the two
temperatures.
Table 4 demonstrates that the carbon char product is
relatively unaffected by the temperature difference.
Table 5 shows that, although much less liquid is pro-
duced at 900°C much less of the liquid fraction at the
higher temperature is in the form of the valueless aque-
ous liquor. The heavy oil product is of the consistency of
a heavier petroleum distillate and has a heating value of
roughly 120,000 BTU/gal.
Feasibility of Pyrolysis of Sludge Alone
Pyrolysis is a process that, once started, is virtually
selfdriving. However, in order to obtain the yields given
in the previous data, the input sludge must not have a
moisture content greater than ten percent of the total
feed. When secondary sludges are involved, conven-
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142 PYROLYSIS OF SLUDGES
•
Figure 3: Tar Removal and Gas Cleaning Train (U.S. Department of Interior—Bureau of Mines).
tional vacuum filtration technology will yield a final cake
solids content of 15 to 20 percent8. A cake in the mid-
point of this range contains about 9,100 pounds of water
foreach ton of dry sludge solids. Assuming away an odor
problem in a sludge drying process, this cake can be
dried in a rotary dryer at roughly 300°F and 80 percent
efficiency. Such an operation would require approxi-
mately 1460 BTU for each pound of water or 13 million
BTU's for every ton of dry sludge feed9.
The gas produced in the pyrolysis process would make
an excellent fuel for the dryer. However, from Table 2,
the gas fraction at 900°C contains only 5.4 million
BTU's. In fact, the total energy conversion in the form of
all three fractions does not total the required heat energy
for the drying process.
Co-P\rolysis of Sludge and Refuse
The pyrolysis of dried sludge alone, having been
proved successful, represents a substantial improve-
ment over conventional incineration with respect to fuel
consumption and air pollutant emissions. However, the
high moisture content of sewage sludge is an obstacle to
pyrolysis in the same manner that it is a hindrance to in-
cineration. It has been shown that, even without deodor-
ization, the sludge drying process will consume about as
much energy as is converted in the pyrolysis process.
Experience with sludge drying at the Bureau of Mines
indicates that a need for deodorization might exist. Con-
ventional deodorization technology requires that the
odorous gases be heated to temperatures in the range of
1200 to 1500°F. Such an operation would require sub-
stantially more heat input than the 300°F drying proce-
dure described earlier.
One approach to solution of the moisture problem
would be to simply feed a higher moisture cake into the
reactor. However, this method requires that the en-
trained water be brought up to pyrolysis temperatures of
1650°F (900°C) instead of evaporated at a maximum
temperature of 300°F. This is hardly a conservation of
energy. Also the presence of large amounts of water in
the feed substantially and detrimentally alters the com-
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PYROLYSIS OF SLUDGES
143
TABLE 1
Pyrolysis of Dried Materials
Energy in Pyrolysis
Energy Available Conversion Products Million Percent
in Raw Material BTU/Ton of Raw Material of Energy
Material Kyrolyzed Million BTU/Ton Gas Char Tar S Oil
Raw, Primary Sludge
SOO°C
900°C
Raw, Waste Activated
Sewage
500°C
900°C
15.00
15.34
12.44
12.36
1.2 5.5
6.3 4.2
1.9 5.1
5.4 4.6
8.0*
3.0
4.0
2.6
Total Recovered
14.7
13.5
11.0
12.6
98.0
88.3
88.9
96.5
Classified Municipal
Refuse - 900 C
•Preliminary
TABLE2
Summary of Yields from Pyrolysis
of Dried Activated Sludge
PYROLYSIS TEMPERATURE °C 500
Yields, Weight Percent of Feed
Char 57.7
Gas 5.8
Tar, Oils, Aqueous 25.3
Yields, Per Ton of Feed
Char, Ib. 1154
Gas, cu ft 2637
Tar, Oils, Aqueous, gal 57.7
Ammonium Sulfate, Ib 103.3
Energy, Million BTU/Ton of Feed
Char 5.1
Gas 1.9
Tar, Oils, Aqueous 4.0
900
54.1
29.3
13.9
1082
13415
29.6
73.4
4.6
5.4
2.6
900
TABLES
Analysis of Gas from Pyrolysis of
Dried Activated Sewage Sludge
PYROLYSIS TEMPERATURE, °C 500
Analysis, Volume Percent:
Hydrogen
Carbon Monoxide
Methane
Ethylene
Carbon Dioxide
Oxygen
Nitrogen
Butane
BTU/cubic foot 735 405
position and quality of the pyrolytic conversion
products 5
A more positive approach to the problem lies in com-
bining the sludge cake with a dry organic material that is
readily amenable to pyrolysis. The combination of the
wet sludge cake with sufficient quantities of the dry ma-
terial will result in a feed material with a moisture con-
44.6
8.2
25.0
6.2
4.3
3.0
5.1
1.8
46.6
22.2
12.8
0.4
4.2
1.6
10.3
< .1
TABLE4
Analyses of Residue (Char) from Pyrolysis of
Dried Activated Sewage Sludge
500
PYROLYSIS TEMPERATURE, C
Ultimate Analysis Percent:
Hydrogen
Carbon
Nitrogen
Oxygen
Sulfer
Ash
BTU/lb.
TABLES
Analysis of Liquid Fraction from Pyrolysis
of Dried Activated Sewage Sludge
900
1.3
27.0
3.0
1.1
0.6
67.0
4370
0.3
27.8
0.8
_..
0.7
70.4
4300
PYROLYSIS TEMPERATURE, C
Yields, Weight Percent
Tar (heavy oil)
Light oil
Free ammonia
Aqueous liquor
BTU/gal.
500
900
38.3 62.6
5.9 4.3
0.8 3.6
54.9 29.5
69,300 87,800
tent much lower than that of the sludge alone. This ad-
mixture would require much less of the converted en-
ergy for evaporation of entrained moisture. In fact, ex-
cess fuel for other in-plant uses or, even, for export could
be made available through the pyrolytic conversion
process.
The admix material could be almost any organic ma-
terial including coal, rubber, or wood. Substantial envi-
ronmental benefit can be achieved by the combining of
sewage sludge and solid waste. Such mixtures have
been pyrolyzed at the Bureau of Mines pilot plant as part
of the EPA-sponsored work on sludge pyrolysis. The re-
fuse used was shredded, classified material obtained
from the Altoona, Pennsylvania, composting plant.
Product yields, for various combinations of activated
sludge and the shredded solid waste are presented in
Table 6. For dried materials, the refuse to sludge ratio
of 20:1 is roughly equivalent to the proportions of gener-
ation of the two materials. As evidenced by the data, the
higher the ratio of solid waste volatiles to sewage sludge
solids the greater the volume of gas generated per ton of
feed.
A 20:1 mixture of solid waste (30 percent moisture)
and sewage sludge cake (80 percent moisture) would re-
sult in a combined feed with a moisture content of
roughly 32 percent. To dry this mixture under conditions
identical to those for the sludge alone case would require
-------
144 PYROLYSIS OF SLUDGES
TABLE6
Yields - Pyrolysis of Blends of Sewage Sludge
and Municipal Refuse - 750-900°C.
Pyrolysis feed
material
Feed*
million
Btu
per
ton
Gas*
Char residue4
Btu Cubic Million Million
per feet Btu per Btu Pounds Btu per
Percent cubic per ton Percent per per ton
weight foot ton pyrolyzed weight pound ton pyrolyzed
Municipal refuse 11.4 25.4 552 11,607 6.410 42.7 6,220 854
and activated
sludge 1-1 ratio
Municipal refuse 14.9 31.4 552 13,694 7.559 32.5 8,360 650
and activated
sludge 8-1 ratio
Municipal refuse 13.7 34.3 586 14,078 8.249 27.1 9,200 542
and activated
sludge 20-1 ratio
* All heat values and weights are on a water-free basis
5.311
5.434
4.997
approximately 1.1 million BTU per ton of solids py-
rolyzed. Since the mixture generated over eight million
BTU in the form of gas, a significant amount of con-
verted energy is available for external application or
sale. Forthe 20:1 feed situation, this amounts to roughly
12,000 cubic feet or seven million BTU in the form of gas
available for external use per each ton of dried reactor
feed.
Therefore, while pyrolysis of sludge alone compares
favorably with sludge incineration, co-pyrolysis of
sludge with solid waste is a more likely implementation
of pyrolytic activity with respect to sewage sludge. A
logical development would be the addition of sewage
sludge to the solid waste feed to one of the functioning
demonstration scale facilities described in Reference 7.
In fact, EPA has recently awarded a grant to the City of
South Charleston, West Virginia, to test the addition of
dewatered sludge cake to the refuse feed at the 200 tons
per day oxygen refuse conversion facility located in that
city (see Figure 4).
L»-
\ (TONS]
, Y
FURNACE
1
1.01
TONS
GAS
1 -
GAS
CLEANING
TRAIN
1
0.7 TONS
"FUEL GAS
1
WASTEWATER
0.28 TONS
0.22 TONS 0.03 TONS RECYCLE
GLASS AND METAL
Figure 4: Inputs and Products of Purox System.
Environmental Aspects of Pyrolysis
Since little plant scale pyrolysis work has been per-
formed, there is very little known about emissions from a
pyrolysis facility. Theoretically, at least, pyrolysis emits
no air pollution. The fact that pyrolysis operates without
excess air and produces a smaller volume of gas for
cleaning than does incineration would indicate that the
airborne emissions problem from pyrolysis is at least as
manageable, and probably, much less of a problem than
from incineration.
Heavy metal emissions should not be a major problem
in pyrolysis since temperatures are generally lower than
in incineration. Heavy metals, in general, tend to be con-
centrated in the pyrolysis char. Pyrolysis is being in-
vesitgated in Japan as a solution to the problem of the
leaching of hexavalent chromium from sludge incinera-
tor ash. In pyrolysis char, the chromium appears in the
much more stable Cr ' 3 configuration 10. Mercury can
be expected to volatilize in pyrolysis as well as in in-
cineration and if not removed in the scrubbing process
may exit with the spent exhaust from combustion of the
product gas.
Another area of concern is disposal of the aqueous li-
quor removed from the tar and oil fraction. This material
can represent as much as 13 weight percent of the feed.
While this material is 94 to 100 percent water it can con-
tain sizeable portions of organic compounds identified as
acids, ketones, and aldehydes. One possibility for treat-
ment of this aqueous fraction would be to utilize the char
fraction to absorb the organic compounds present in the
liquor3.
At this point, the only definitive statement that can be
made about the environmental aspects of pyrolysis is
that much further research is needed and planned for
this area.
Economics
Capital costs for solid waste pyrolysis facilities, in-
cluding product processing provisions, currently are in
the range of $14,000 to $20,000 per ton per day of gross
handling capacity 7"1J. This installation cost range is
-------
PYROLYSIS OF SLUDGES
145
roughly equivalent to that for pollution-free sewage
sludge incineration12. Assuming that labor require-
ments for both incineration and pyrolysis are identical,
the critical factor in cost comparison becomes fuel con-
sumption.
It has been shown previously that pyrolysis of sludge
alone is not quite fuel self-sufficient for the case of the 18
percent solids sludge cake. An energy balance reveals
that combustion of the same sludge cake in a multiple
hearth furnace without exhaust gas deodorization or
heat recovery requires the input of 8.5 million BTU of ad-
ditional energy in the form of auxiliary fuel for each dry
ton of sludge feed 13. This auxiliary fuel requirement is
equivalent to 59 gallons of No. 2 fuel oil, the most com-
mon fuel for sludge incineration.
Additional capital economies as well as operational
cost savings can be appreciated by combining disposal of
solid waste and sludge into a single facility. In this latter
case, the fuel products from co-pyrolysis would be avail-
able for external use or sale.
The carbon char remains an economic question mark.
This material constitutes over 50 percent of the material
feed. It is usually assumed, for the sake of discussion,
that this material can be sold as an adsorption char or, at
the least, given away for its fuel value. However, any
complications with this material, such as the leaching of
heavy metals, might detract from its value as an adsorp-
tion agent, or even, as a fuel. At any rate, combustion of
this material, which is about 70 percent ash, will still
leave a sizeable land disposal requirement.
If the char cannot be sold or given away, the pyrolysis
process becomes less efficient as a volume reduction
technique than is incineration. Disposal of the char can
become a substantial economic deficit. In a similar vein,
costs of processing and separating the tar, oil, and aque-
ous fractions prior to any constructive use must be taken
into account.
As with the environmental aspects, the economics of
sludge pyrolysis is an area requiring further investi-
gation.
Potential for Sludge Pyrolysis
Aside from the pure aesthetics and economics of the
process, the future growth in application of pyrolysis to
sludge disposal is dependent of a number of variables,
some of which will be discussed here:
First, what people decide to do with their solid waste is
important. If solid waste authorities choose direct com-
bustion-generation as in St. Louis, then the availability
of the solid waste admix for co-pyrolysis is restricted.
Secondly, pyrolysis techniques must be developed
that take advantage of existing equipment. Fuel may be-
come extremely costly, but a municipality will neverthe-
less hesitate to abandon a recently constructed $20 mil-
lion incineration plant because the hardware is incom-
patible with pyrolysis.
Thirdly, the development of mechanical dewatering
devices that can economically produce an autogenous
sludge cake might work against the implementation of
sludge pyrolysis. While a drier cake requires less en-
ergy for pyrolysis as well as incineration, the production
of an autogenous cake alleviates the fuel cost pressure at
existing incineration plants and makes conventional in-
cineration more feasible.
While the future for waste pyrolysis appears strong,
enthusiasm for the process must be tempered by the fact
that much development work lies ahead.
REFERENCES
1. Farrell, J.B., "Overview of Sludge Handling and
Disposal", in Proceedings of the National Conference on
Principal Sludge Management, June 11, 1974.
2. Kinnicutt, L.P., Winslow, C.E.A., and Pratt, R.W.,
Sewage Disposal, Second Edition Rewritten, John Wiley
and Sons, New York, 1919, pp. 438-441.
3. Sanner, W.S., Orluglio, C., Walters, J.G., and
Wolfson, D.E., Conversion of Municipal and Industrial
Refuse into Useful Materials by Pyrolysis, report of in-
vestigations 7428, U.S. Department of the Interior,
Bureau of Mines, 1970.
4. Sanner, W.S. and Wolfson, D.E., "Pyrolysis of
Municipal and Industrial Wastes", in Proceedings:
Symposium on Technology for the Future to Control In-
dustrial and Urban Wastes, University of Missouri,
Rolla Continuing Education Series, Feb. 8, 1971, p. 39.
5. Schlesinger, M.D., Sanner, W.S., and Wolfson,
D.E., "Pyrolysis of Waste Materials from Urban and
Rural Sources", in Proceedings: Third Mineral Waste
Utilization Symposium, March 14, 1972, p. 423.
6. Schlesinger, M.D., Sanner, W.S., and Wolfson,
D.E., "Energy from the Pyrolysis of Agricultural
Wastes", in Symposium: Processing Agricultural and
Municipal Wastes, Edited by George E. Inglett, The
A.V.I. Publishing Company, 1973, p. 93.
7. Levy, S.J., "Pyrolysis of Municipal Solid Waste",
Waste Age, October 1974, pp. 14-20.
8. Process Design Manual for Sludge Treatment and
Disposal, U.S. E.P.A. Technology Transfer, October
1974, pp. 7-21.
9. Keenan, J.H., and Keyes, F.G., Thermodynamic
Properties of Steam, Wiley and Sons, Inc., N.Y.
10. Annaka, Tokuji, Personal Communication to Dr.
J.B. Farrell, May 29, 1975.
11. Sussman, D.B., Baltimore Demonstrates Gas Py-
rolysis, First Interim Report (SW-75d.i.) on E.P.A.
Demonstration Grant N. S-801533, 1975.
12. "Sludge Handling and Disposal", Phase I, State
of the Art, Stanley Consultants, November 1972.
13. Hathaway, S.W., land Olexsey, R.A., "Improving
the Fuel Value of Sewage Sludge", News of Environ-
mental Research in Cincinnati (Prepublication).
-------
SLUDGE PYROLYSIS FOR ENERGY
RECOVERY AND POLLUTION CONTROL
F. MichaelLewis
Stanford Research Institute
MenloPark, California
INTRODUCTION
The advantages of sludge pyrolysis over conventional
incineration processes can be stated in terms of fuel
economy, energy recovery (steam generation), and con-
trol of heavy metals. To make technical comparisons be-
tween incineration and pyrolysis processes, we have
conducted fundamental engineering analyses using a
heat and material balance.
To make the analyses consistent, we have made some
assumptions regarding the thermodynamic properties
and the chemical composition of the solid portion of the
sludge. The following represents a typical municipal
sewage sludge with a light industrial loading:
Analysis of Volatile Solids
Carbon 52
Hydrogen 7
Oxygen 41
Volatile solids = 70% of total solids.
Heating value = 9500 Btu/lb volatile solids.
The sludge has been assumed free of nitrogen, lime,
ferric chloride, and other constituents usually present in
small amounts, to simplify the calculation. The above
analysis is for the solid portion of the sludge only. Dif-
ferent solids contents are assumed for specific examples
to illustrate certain points.
Fundamentals of Pyrolysis
By definition, pyrolysis is an irreversible chemical
change brought about by the action of heat in an atmos-
phere devoid of oxygen. Synonymous terms are thermal
decomposition, destructive distillation, and carboniza-
tion.
The pyrolysis of organic compounds yields the fol-
lowing:
• Char
• Organic liquids (pyroligneous acids)
• Fuel gas
• Water (present in either liquid or gaseous state de-
pending on final pyrolysis conditions).
The char contains any mineral ash or other noncom-
bustible material present in the sludge plus what is
termed the "fixed carbon," which represents the car-
bonaceous fraction of the original material that did not
volatilize on heating. The char also usually contains
sm all qu antities of hydrogen and oxygen, and nitrogen is
sometimes present.
The organic liquids are a complex mixture of chemi-
cals and are often called pyroligneous acids, because
they are acidic and were first produced by the destruc-
tive distillation of wood. The fuel gas consists of a num-
ber of combustible gases, such as carbon monoxide,
methane, hydrogen, ethylene, and other higher hydro-
carbons in minor quantities. The fuel gas also contains
an appreciable quantity of carbon dioxide and may con-
tain water vapor if it has not been previously condensed
out of the stream.
The ultimate yield and final composition of the solid,
liquid, and gaseous pyrolysis products are determined
by a number of variables, such as the chemical composi-
tion of the raw material, the heating rate, and the ulti-
mate material temperature. Several investigations '"4,
of these and other process parameters suggest a com-
plexity that makes final product characteristics from py-
rolysis impossible to predict.
A pyrolysis process may be endothermic (require
heat) or exothermic (give up heat), depending on the ul-
timate temperature achieved. In most materials, the
process is endothermic at lower temperatures and exo-
thermic at higher temperatures. In all cases, the heating
value of the pyrolysis products is the sum of the heating
value of the original material and the net energy added
during pyrolysis. In many cellulosic materials, the en-
ergy absorbed or liberated by the pyrolysis reaction is
very small compared with the heating value of the ori-
ginal material. Unfortunately, in most pyrolysis studies
to date, the emphasis has been identification of the many
complex chemicals generated by pyrolysis rather than
146
-------
PYROLYSIS FOR RECOVERY AND CONTROL
147
on heat and material balances for pyrolysis processes,
for which very few data are available.
However, since the heating value of the pyrolysis
products is always equal to the heating value of the ori-
ginal material plus any heat added, we can perform a
heat and material balance based on review of the avail-
able data. Details for performing heat and material bal-
ances for combustion and pyrolysis processes have been
previously described5'6 and will not be covered here.
Pyrolysis and Incineration Systems—
Comparative Thermodynamic Analyses
The first step in any thermodynamic analysis is to
draw a Thermodynamic System Boundary around the
system to be analyzed. Figure 1 shows a typical thermal
processing system for municipal sewage sludge, which
can be either a pyrolysis system or an incineration sys-
tem. The thermodynamic system boundary is indicated
for all systems being analyzed (Figures 2-5). In our
analyses, we will not consider the heat and mass transfer
operations taking place in the scrubbers usually asso-
ciated with sludge thermal processing systems. For the
systems to be analyzed, we will assume zero heat loss.
The zero heat loss assumption is very valid for compara-
tive analyses of alternative processes, except in the case
of a process with an unusually high heat loss. (Assuming
a heat loss of, say, five percent of the sludge heat input
would not have served any particular purpose.)
In the systems selected, the only correction to our as-
sumption was made in the analysis of the multiple hearth
Flue Gas
r
THERMODYNAMIC
SYSTEM BOUNDARY
Sludge-
Combustion Air-
Auxiliary Fuel-
TYPICAL THERMAL
PROCESSING SYSTEM
PYROLYSIS
OR
INCINERATION
incinerator, which, in addition to sustaining heat loss
through the walls, also exhibits heat loss in the form of
heated shaft cooling air discharged to the atmosphere.
The values taken for this loss are those reported in the
literature7.
The comparative analyses will be based on a balance
of the material and heat inputs and outputs (Heat and
Material Balance):
Material in = Material out
Heat in = Heat out.
These balances are a valuable tool that should always be
used in the comparative evaluation of sludge "thermal
processing systems.
In a thermodynamic analysis, material and heat are
accounted for only when they cross the thermodynamic
system boundary. Internal recycle loops, if they are
present, do not affect the overall heat and material
balance.
Sludge Thermal Processing Systems
The four systems selected for analysis are representa-
tive of the sludge thermal processing methods currently
available or under development:
• Multiple hearth incinerator
• Fluid bed incinerator
• Proprietary pyrolysis reactor
• Multiple hearth pyrolysis reactor
The following selected parameters provide a uniform
basis of comparison:
• Minimum afterburner temperature; 1400°F
• Minimum excess air in flue gas; 20 percent
Material Entering
Thermodynamic
System Boundary
Heat Entering
Thermodynamic
System Boundary
Material Leaving
Thermodynamic
System Boundary
Heat Leaving
Thermodynamic
System Boundary
Ash
Figure 1: Typical Thermal Processing System.
-------
148 PYROLYSIS FOR RECOVERY AND CONTROL
SLUDGE
25% Total Solids (TS)
70% Volatile Solids (VS)
9500 Btu/lb VS
INPUT POUNDS
Water 6000
Volatile Solids 1400
Ash 600
8000 Ib
13,300,000 Btu
AFTERBURNERS
ZERO HEARTH
Natural Draft Air ^ '^
MATERIAL INPUT POUNDS
Sludge 8,000
Natural Draft Air 5,231
Shaft Cooling Air 15,760
Burner Air 6,030
Natural Gas 349
Total 35,370
MATERIAL OUTPUT
Flue Gas 30,045
Shaft Cooling Air 4,725
Ash 600
Total 35,370
SY
^
>
Shaft Cooling Air
4725 Ib
272,630 Btu
HERMODYNAMIC
STEM BOUNDARY r
70% Recycle n 1
11,03
^
^
Y//'////
5 Ib '
•^ ~~\
S
Coo
15,
3
^y~
\-
haf
ing
76(
' Flue Gas
30,045 Ib
21,250,120 Btu
00°F V
100° F
^r
£i
=h-
£^
^r
\
—
— 1
COMBUSTION F
75% Sludge C
Excess A
15% Burner E
6030 Ib
349 Ib
8,333,750 Btu
HEAT INPUT
Sludge
Natural Gas
Total
HEAT OUTPUT
LJ^^^ Flue Gas
800°F| SWMW Shaft Cooling Air
1 1 Ash
t Ash Total
Air 600 Ib
3 Ib 111,000 Btu
Btu
13,300,000
8,333,750
21,633,750
21,250,120
272,630
111,000
21,633,750
TB-361522-9
Figure 2: Multiple Hearth Incinerator.
SLUDGE
25% Total Solids (TS)
70% Volatile Solids (VS)
9500 Btu/lb VS
INPUT POUNDS
Water
Volati
Ash
Sludge
Flue Gas
27,564 Ib
19,882,475 Btu
1400°F
6000
Solids 1400
8000 Ib
13,300,000 Btu
284 Ib
' "" 6,783,475 Btu
19,880 Ib
L INPUT POUNDS
8,000
tion Air 19,880
Gas 284
Tntal 9R 1R4
L-
SYSTEM E
THERMODYNAMIC~~I
Sludge
MATERIAL OUTPUT
Flue Gas
Ash
Total
27,564
600
28,164
1400°F
Ash
600 Ib
201,000 Btu
COMBUSTION PARAMETERS
40% Excess Air (Sludge and Gas)
HEAT INPUT
Sludge
Natural Gas
HEAT OUTPUT
Flue Gas
Ash
Total
Btu
13,300,000
6,783,475
Total 20,083,475
19,882,475
201,000
20,083,475
TB-361522-10
Figure 3: Fluid Bed Incinerator.
-------
PYROLYSIS FOR RECOVERY AND CONTROL 149
• Sludge solids content; 25 percent total solids
• Wall heat loss; none.
When excess air rates higher than the minimum value
stated above are necessary for proper operation of a
specific reactor, the higher rate has been used.
The four selected processes, briefly described, follow:
Multiple Hearth Incinerator. The multiple hearth in-
cinerator, shown in Figure2, represents thelatest design,
and the top (Zero) hearth has been used as an after-
burner. In sales literature for this unit, the portion of the
heated shaft cooling air recycled back to the bottom
hearth for combusion is presented as a heat credit, but
when a heat and material balances is performed, the
overall effect, as shown in the figure, is actually a heat
loss.
Fluid Bed Incinerator. The fluid bed incinerator,
shown in Figure 3, is conventional except for its excess
air rate, which is 40 percent. Sales and advertising litera-
ture claim excess air rates of the order of 20 percent,
which would represent an oxygen level of approximately
3.5 percent (dry gas-volume percent) in the flue gas,
whereas 40 percent excess air represents an oxygen
level of approximately six percent. Our experience indi-
cates that most fluid bed incinerators operate near the
six percent oxygen level.
Proprietary Pyrolysis Reactor. The proprietary py-
rolysis reactor, shown in Figure 4, represents an indi-
rectly heated rotary kiln incorporating specific, patented
design features. The application of this reactor for the
pyrolysis of sludge is under current development and
evaluation. This system has the following unique fea-
ture: After burning at temperatures above 1400°F for
complete combustion and deodorization, the flue gases
are used to evaporate the sludge moisture and pyrolyze
the sludge without ever coming in contact with the solid
material.
This type of indirectly heated pyrolysis process pro-
duces a char consisting of mineral ash and carbonaceous
material. Although this char may be used, for example,
as activated carbon for water treatment, it is our opinion
that the production of char can be used to its best pos-
sible advantage in the concentration and retention of
heavy metals contained in the sludge (see "Sludge Py-
rolysis for Pollution Control").
Multiple Hearth Pyrolysis Reactor. Figure 5 shows a
system for pyrolyzing sludge in a multiple hearth fur-
nace. The air and fuel supplied to each hearth have been
selected so as to maintain substoichiometric conditions
throughout all hearths except the afterburner which is
operated at 20 percent excess air. With the 25 percent
total solids sludge used in our comparisons, the avail-
able heat is not sufficient to recycle a portion back to the
furnace to sustain the process. Attempting to use the in-
ternal recycle loop, i.e., recycling the 1400°F exhaust
gas back to the bottom hearth, would be like trying to lift
yourself up by the bootstraps, and would not serve to
sustain the process; as mentioned above, heat is gained
or lost only as it crosses the thermodynamic system
boundary. With a sufficiently high sludge solids content,
the process could be made self-sustaining.
SLUDGE
25% Total Solids (TS)
70% Volatile Solids (VS)
9500 Btu/lb VS
INPUT POUNDS
Water 6000
Volatile Solids 1400
Ash 600
Flue Gas
14,940 Ib
9,453,200 Btu
Sludge-
8000 Ib
13,300,000 Btu
MATERIAL INPUT
Sludge
Combustion Air
Total
MATERIAL OUTPUT
Flue Gas
Char
Total
POUNDS
8,000
7,820 L .
15,820
14,940
880
THERMODYNAMIC
SYSTEM BOUNDARY
COMBUSTION PARAMETERS
20% Excess Air
'"I
7820 Ib
-Combustion Air
HEAT INPUT
Sludge
HEAT OUTPUT
Flue Gas
Char
Total
Btu
13,300,000
9,453,200
3,846,800
13,300,000
CHAR POUNDS
Carbonaceous 280
Ash 600
Total 880
HEAT Btu
Sensible Heat 206,800
Chemical Heat 3,640,000
Total 3,846,800
15,820
TB-361522-11
Figure 4: Proprietary Pyrolysis Reactor.
-------
150 PYROLYSIS FOR RECOVERY AND CONTROL
SLUDGE
25% Total Solids (TS)
70% Volatile Solids (VS)
9500 Btu/lb VS 1
INPUT POUNDS
Water 6000
Volatile Solids 1400
Ash 600
8000 Ib
13,300,000 Btu
MATERIAL INPUT POUNDS
Sludge 8,000
Shaft Cooling Air 15,760
Burner Air 8,645
Natural Gas 417
Total 32,822
MATERIAL OUTPUT
Char 880
Shaft Cooling Air 7,940
Flue Gas 24,002
Total 32,822
HEAT
Sensible Heat
Chemical Hea
Tota
Shaft Cooling Air
7940 Ib
458,230 Btu
THERMODYNAMIC
SYSTEM BOUNDARY.
50% Recycle n '
78
—+•
»
—+•
*
3
^—
20 Ib ' 1
AFTEF
4
Btu
c
162,800 ,, ,
t 3,640,000 C°°!.
I 3,802,800
1BI
haf
ng
'60
00° F
JRNER
Flue Gas
24,002 Ib
18,992,355 Btu
1400°F
I
800° F
t
Air
Ib
I
T±-|
:5^-
^r
CHAR
Carbonaceous
Ash
Total
COMPOSITION PARAMETERS
20% Excess Air (Sludge and Gas)
417 lb fJituml Go
9,953,385 Btu Njtural C°-
8645 1b Durncr Air
HEAT INPUT Btu
Sludge 13,300,000
Natural Gas 9,953,385
Total 23,253,385
HEAT OUTPUT
Char 3,802,800
Shaft Cooling Air 458,230
Flue Gas 18,992,355
Total 23,253,385
1
POUNDS
280
600
880 TB-361522-12
Figure 5: Multiple Hearth Pyrolysis Reactor.
As illustrated by this example, one cannot categorical-
ly state that all pyrolysis processes use less fuel and can
produce energy. Each process must be carefully evalu-
ated for each thermodynamic condition.
Comparison of Auxiliary Fuel Usage
The auxiliary fuel usage, expressed in pounds and
Btu's, for each of the four thermal processes are shown
in Table 1, below.
Comparing the fuel usage of the four processes, we
find that the fluid bed incinerator uses less fuel than
does the multiple hearth incinerator. If the multiple
hearth incinerator could operate without an afterburner,
so that the incinerator could exit at 800°F, the multiple
hearth incinerator could also operate without any aux-
TABLE1
Auxiliary Fuel Usage
Process
Multiple hearth incinerator
Fluid bed incinerator
Proprietary pyrolysis reactor
Multiple hearth pyrolysis
reactor
Natural Gas
Ib/ton of
Total Solids
349
284
0
417
Btu/ton
of
Total Solids
8,333,750
6,783,475
0
9,953,385
iliary fuel. However, afterburners operating at 1400UF
are now required in New York, California, and several
other states, and this requirement is anticipated to be
extended to other regions of the country in a govern-
mental effort to prevent the escape of odors and un-
burned hydrocarbons and to ensure complete destruc-
tion of pesticides and polychlorinated biphenyls (PCB).
The multiple hearth pyrolysis reactor shows extreme-
ly high auxiliary fuel usage, indicating improper process
design and indiscriminate use of pyrolysis.
Sludge Pyrolysis for PoUution Control
When comparing the particulate emissions from a py-
rolysis process which uses a high pressure drop venturi
scrubber (30 in. w.c.)with those from an incinerator us-
ing a low pressure drop (four in. w.c.) spray chamber,
obviously, the comparison should be made before the
flue gases pass through the scrubber. Unfortunately,
very few "hard" data are available on the emissions
from pyrolysis process, and information must therefore
be extrapolated based on first principles and similar
processes.
Sludge pyrolysis systems, in which the combustion
process is physically separated from the region where
-------
PYROLYSIS FOR RECOVERY AND CONTROL 151
the solid portion of the sludge is present, offer the poten-
tial for a significant reduction in the emission of pollu-
tants. Because of the absence of the combustion air from
the region of the solids, entrainment of ash by the flue
products is minimized. In fuel gas-producing pyrolysis
processes, the combustion can be achieved at a much
lower excess air rate, which, in addition to achieving
greater thermal efficiency, significantly reduces the
volume of flue gases, and therefore, makes possible a
greater level of control for the same energy input to the
scrubber *l
Where the combustion is separate from the solid ash-
containing portion of the combustion unit, operation at
higher, more efficient temperatures is possible because
the danger of slagging and clinkering is eliminated.
The presence of heavy metals, primarily lead, zinc,
cadmium, and nickel, in sludge and what becomes of
them during sludge disposal, is of major concern in cur-
rent sludge disposal programs. Scientific evidence now
supports the hypothesis that low-temperature, char-pro-
ducing pyrolysis processes may lead to the accomplish-
ment of significant heavy-metal retention in the char.
Analysis of coke indicates that heavy metals appear in
higher concentrations after pyrolysis of coal than in the
original coal sample. Studies of char produced by the py-
rolysis of scrap tires 9provide evidence that many poten-
tial pollutants remain chemically bound to the fixed car-
bon in the char. Unpublished experiments indicate that
zinc can be chemically bound to the char when hydro-
carbon is pyrolyzed.
In all studies indicating the possibility of heavy metal
retention in the carbonaceous portion of char, the ma-
terial has been indirectly heated in an atmosphere com-
pletely devoid of oxygen and at relatively low tempera-
tures, below 1700°F. High-temperature processes or
processes where air or oxygen, or both, are introduced,
may not offer this advantage.
A program is being developed in which the ability of
an indirectly heated sludge pyrolysis system to retain
heavy metals in the pyrolysis char will be investigated.
Sludge Pyrolysis for Energy Recovery
(Steam Generation)
The fourthermodynamic analyses developed here in-
dicate that the combustion of a 25 percent total solids
sludge cake offers very little incentive to attempt heat
recovery. A measure of heat recovery could be
accomplished with those processes exhausting at
1400°F, but a far better alternative would be to change
the process to minimize the usage of auxiliary fuel. In
any process where heat recovery is contemplated, such
recovery must not be accomplished at the expense of
auxiliary fuel usage further upstream in the process.
It is quite easy to play a "numbers game" with heat
recovery. It can be shown that a sludge incineration
process with a 1400°F exhaust temperature can produce
more energy (steam) (500°F boiler exit temperature)
when a wet sludge and high excess air is used; that is,
considering the total amount of steam produced. By ex-
amining the ratios, pounds of steam per pound of natural
gas, or pounds of steam produced per million Btu of aux-
iliary fuel input, we arrive at a better appreciation of the
process and the proper conclusion: the desirability of
high solids content in the sludge cake to be processed
and low excess air rate in the process system used.
Techniques are available today, such as heat treat-
ment followed by vacuum filtration or high pressure fil-
tration, which can produce a sludge cake in excess of 40
percent total solids.
To illustrate the principle of energy recovery, we per-
formed a heat and material balance on a 40 percent total
solids sludge cake. The proprietary pyrolysis reactor was
selected because of the previous comparison, which
showed this system to achieve the highest thermal effi-
ciency and to produce a char for the retention of heavy
metals. The combustion chamber is separated from the
solids region so that the gases can be burned at low ex-
cess air and high temperatures without the danger of
fusion of the ash. This system is shown in Figure 6.
As shown in the figure, only a portion of the hot flue
gases is necessary to sustain the pyrolysis reaction. This
analysis does not require accurate prediction of the
quantity of heat that must be recycled to the reactor to
sustain pyrolysis, because this recycling takes place in
an internal (inside the Thermodynamic System Boun-
dary) recycle loop and does not affect the overall heat
and material balance. If an actual system were to be put
into operation, then this recycle quantity would have to
be known accurately.
At a wastewater treatment plant, the steam generated
could be used for generation of electricity or for opera-
tion of the aerators and pumps, which are large con-
sumers of energy.
SUMMARY AND CONCLUSIONS
In any pyrolysis process, the heating value of the py-
rolysis products is equal to the heat of the original ma-
terial plus any heat added. In our comparative thermo-
dynamic analyses, using the thermodynamic system
boundary and a heat and material balance, we have
found that not all pyrolysis processes result in a reduc-
tion in auxiliary fuel consumption. Our analyses amplify
the need to perform a heat and material balance on any
proposed sludge thermal processing system before at-
tempting to determine thermal efficiency and auxiliary
fuel usage. Our analyses also indicate that, of the four
systems evaluated, a proprietary pyrolysis reactor that is
indirectly heated by the afterburner flue products re-
quires the least amount of auxiliary fuel.
Indirectly heated, oxygen-free low temperature, char-
producing pyrolysis processes have been found to also
have the potential for preventing heavy metal emissions
into air and water by chemically binding the metal in the
-------
152 PYROLYSIS FOR RECOVERY AND CONTROL
SLUDGE
40% Total Solids (TS)
70% Volatile Solids (VS)
9500 Btu/lb VS
INPUT POUNDS
Water 3000
Volatile Solids 1400
Ash 600
Boiler Feedwater
Flue Gas
11,938 Ib
5,699,610 Btu
Steam
3,753,590 Btu
3128 Ib
r
Sludge
MATERIAL INPUT
Sludge
Combustion Air
Boiler Feedwater
Total
MATERIAL OUTPUT
Flue Gas
Char
Steam
Total
POUNDS
5,000
7,818
3,128
15,946
11,938
880
3,128
15,946
THERMODYNAMIC
SYSTEM BOUNDARY
COMBUSTION PARAMETERS
20% Excess Air
AFTERBURNER
CHAR POUNDS
Carbonaceous 280
Ash 600
Total 880
7820 Ib
-Combustion Air
HEAT INPUT
Sludge
Btu
13,300,000
HEAT OUTPUT
Flue Gas 5,699,610
Steam
Char
Total
3,753,590
3,846,800
13,300,000
_J
HEAT Btu
Sensible Heat 206,800
Chemical Heat 3,640,000
Total 3,846,800
TB-361522-13
Figure 6: Proprietary Pyrolysis Reactor with Steam Generation.
carbonaceous fraction of the char. A program to study
the ability of an indirectly heated sludge pyrolysis re-
actor to retain heavy metals in the pyrolysis char is under
development.
Energy recovery from sludge combustion has been
determined to be feasible, but initial efforts should be
directed toward eliminating the use of auxiliary fuel dur-
ing normal operation.
REFERENCES
1. E.R. Kaiser and S.B. Friedman, "The Pyrolysis of
Refuse Components," presented at the 60th Annual
Meeting, American Institute of Chemical Engineers,
November 26-30, 1967.
2. D.A. Hoffman, "Pyrolysis of Solid Municipal
Wastes," NTIS PB-222 015, U.S. Dept. of Commerce,
July, 1973.
3. J.A. Knight, et. al., "Pyrolytic Conversion of Agri-
cultural Wastes to Fuels," Paper no. 74-5017, American
Society of Agricultural Engineers, June, 1974.
4. W. Garner and I.C. Smith, "The Disposal of Cattle
Feedlot Wastes by Pyrolysis," Research Report
EPA-R2-73-096, Project 13040 EGH, EPA Contract
14-12-850, EPA, Washington, D.C., January, 1973.
5. P.M. Lewis, "Heat and Material Balances for
Nonautogenous Wastes," to be published in Incinerator
and Solid Waste Technology 1962-1975, ASME, New
York, N.Y., pp. 103-111.
6. P.M. Lewis, "Fundamentals of Pyrolysis Processes
for Resource Recovery and Pollution Control,"
Presented at Air Poll. Contr. Assoc. 68th Ann. Mtg.,
15-20 June, 1975, Paper No. 78-38.4.
7. W. Unterberg, R.J. Sherwood, andG.R. Schneider,
"Computerized Design and Cost Estimation for
Multiple-Hearth Sludge Incinerators," Water Pollution
Control Research Series, 17070 EBP 07/71, Contract
14-12-547, EPA, Office of Research and Monitoring,
Wash., D.C. (July, 1971).
8. K.T. Semrau, "Dust Scrubber Design—A Critique
ontheState-of-the-Art," J. APCA, Vol. 13, No. 12, pp.
587-594 (December, 1963).
9. D.E. Wolfson, et. al., "Destructive Distillation of
Scrap Tires," RI7302, Bureau of Mines, U.S. Dept. of
the Interior (September, 1969).
-------
A SLUDGE POLICY FOR THE 70'S
L. Russell Freeman
United States Environmental Protection Agency
Region IX
San Francisco, California
I welcome the opportunity to present the views of
EPA, Region IX on municipal sludge disposal. Let me
begin by discussing EPA and the responsibilities im-
posed on us by Congress. Then I will mention the key
features of environmental law, and add a few observa-
tions on the tenor of the times. Against this background,
1 will present my analysis of implications for municipal
sludge management and disposal.
EPA is an independent agency in the executive branch
of the Federal government. It is headed by our Adminis-
trator, Russell E. Train. He is supported by five Assist-
ant Administrators: Assistant Administrator for Re-
search and Development; Assistant Administrator for
Enforcement; Assistant Administrator for Water and
Hazardous Materials; Assistant Administrator for Air
and Solid Wastes; and Assistant Administrator for Man-
agement.
The agency has about 10,000 people, equally divided
between headquarters; field laboratories and regional
offices. The regional offices, ten in number are responsi-
ble for implementing all phases of the agency's pro-
grams, except for research, which is handled by the
laboratories. Thus, by quick arithmetic, you can con-
clude that the average regional office has a compliment
of about 330 people.
When we were formed by Executive Order, EPA
brought together programs from a number of operating
agencies:
• Regulation of Pesticides from USDA.
• Water Pollution Control from Interior.
• Air Pollution Control from HEW.
• Solid Waste Management from HEW.
• Regulation of Ambient Radiation Levelsfrom HEW.
Since 1970, we have had two new major programs
added to our portfolio by the Congress: Noise Regulation
and most recently, Control of Drinking Water Quality.
Thus, under FIFRA, we must classify every pesticide
as to degree of hazard; ban those which are too danger-
ous to the environment; and see that anyone who uses
the more hazardous ones are properly trained and regu-
lated. Users of hazardous pesticides, of course, include
just about everyone in Agriculture. Under FWPCA, we
must license (or permit) every significant discharge to
surface waters, and under provisions of the new Safe
Drinking Water Act, we will have to regulate discharges
to groundwater as well. This, of course, is in addition to
insuring that virtually every purveyor of drinking water
meets Federal standards. Under the Clean Air Act, we
regulate every significant cause of air pollution. Let me
skip over noise and radiation, even though they can be-
come extremely important and time consuming concerns
under some circumstances. But before going on, I
should add, that we manage the largest capital construc-
tion programs in the Federal government. In California
alone, our office had available on July 1, about 1.2 billion
dollars for sewage treatment plant construction grants.
I mention these things to give you some idea of what
the 330 people in San Francisco do. It should be clear
that we have enough going on to keep busy. It should be
even clearer that we are not in the game alone. More
about this latter point in a moment.
Let me turn now to a discussion of the general nature
of environmental law. Almost all environmental laws
have the same general framework. They provide for: the
setting of standards; a plan to achieve the standards;
research anddevelopment; assistance; andenforcement.
The laws also have unique aspects, involving "state
primacy" and citizen participation. Let's look at all of the
foregoing elements briefly, beginning with standards.
Up until the Clean Air Act of 1970, and the FWPCA
Amendment of 1972, the law generally relied upon am-
bient standards. These are maximum levels of pollution
allowed in the ambient air, the open ocean or the flowing
streams.
In 1970, Congress turned to emmission and perform-
ance standards. Thus under the 1972 amendments to
FWPCA, every municipality must meet secondary treat-
ment requirements by 1977. Indeed, such performance
requirements have become the foundation of the law,
and they reflect a new philosophy which is woven into it.
Until 1970, the environment was looked upon as a proper
waste disposal sink; provided adequate dilution of the
153
-------
154
A POLICY FOR THE 70'S
wastes was achieved. The new philosophy is that each
discharger has a responsibility to keep his wastes out of
the environment to the maximum extent possible.
Let's examine the next feature of environmental law.
While the law generally provides for EPA to establish
environmental standards, it provides for state govern-
ments to insure that the standards are implemented.
This is the principle of primacy mentioned earlier. The
state develops basin plans under Title III, and adminis-
ters the NPDES permit program under Title IV of
FWPCA. These are the guiding policy and procedural
documents which govern implementation of the law. The
law also explicitly provides that Federal effluent limits
not diminish any state or local regulation or requirement.
As a corollary to primacy, EPA implements those as-
pects of the programs which a given state fails to under-
take. Our experience has been that the states assumes
those responsibilities which they judge to be reasonable
and politically viable. Thus, whenever you see EPA out
in front on a program, you should expect to find that the
program is controversial or politically untenable in that
State. The only exceptions to this situation are cases
where the State is lacking in resources or authority.
These exceptional cases generally do not come to the at-
tention of the public. The result of this corollary is that
EPA is widely regarded as a controversial and politically
naive agency. Given the situation under which we oper-
ate, one should expect that we would make a few mis-
takes. We do make them, and I won't deny it. However,
it is important to understand that primacy aspect of the
law works to force EPA into the forefront wherever there
is controversy or political pressure. These are the situa-
tions which everyone hears about because they are news.
Let me skip lightly over the research and assistance
provisions of the laws which I am sure you are familiar
with. The basic thrusts of research are to provide the
data base for environmental standards, and to develop
and demonstrate pollution control technology. The as-
sistance programs encompass grants to States to sup-
port their environmental programs, as well as the waste-
water treatment grant program mentioned earlier.
Let's also review another unique aspect of environ-
mental law. Beginning with the 1972 amendments to
FWPCA, local government was given an authorative
role in implementation. The section, popularly known as
208, provides for the development of Regional entities to
plan and manage pollution abatement. The scope of
planning and management required under the law is
quite broad. Unlike traditional planning, the institu-
tional, financing, regulatory and enforcement provisions
must be detailed. It is clear that Congress intended that
208 plans would be implemented.
Citizen participation is another key element of en-
vironmental law. As an aside, let me outline what citizen
participation means to me. We begin with the general
foundation; the citizen's right to know what government
is doing. This right to know applies to all activities of the
Federal government, and it is underwritten by the Free-
dom of Information Act. Then there is the citizen's right
to participate in the process of formulating action plans
and programs. This right is provided for legally by the
Administrative Procedures Act, as well as NEPA. Be-
ginning with the 1970 Clean Air Act, Congress added a
new dimension to citizen involvement; the right of a citi-
zen to hold government accountable for it's actions. EPA
can be sued for failure to take any action which is not dis-
cretionary under post 1970 environmental law. This citi-
zen standing aspect of the law has been tested and the
result is a new appreciation of the fact that we must act to
carry out the law.
Indeed, we must act even if we feel that all available
options are controversial. The new drinking water legis-
lation, passed in late December of last year, has taken
citizen involvement a step further. Under its provisions,
there is citizen standing to sue EPA, the State, or the
water utility to ensure delivery of water meeting Federal
primacy drinking water standards. Moreover, the water
utility is required to monitor the quality of it's water, and
to publicize any incident in which (1) a required measure-
ment is not made; or (2) a standard is exceeded. Thus,
the law establishes a mechanism for direct citizen en-
forcement.
If history is any teacher, a role for local government
and stronger citizen involvement will be embodied of all
future environmental legislation.
So much for the law, let's look at the "tenor of the
times." For the most part, experience in Region IX, and
I believe nationally as well, is that basic sewer systems
are in place. The task we face is generally to provide
treatment, or to upgrade the level of treatment with
some provision for expansion of the system. Secondary
treatment is the minimum; but in some cases, water
quality standards or other conditions will require AWT
techniques. Many of the needed system improvements
are now under construction, and within the next year or
so we expect that almost all of them will be in the design
or construction phases. Within another year or so, they
will be going into operation. What I am saying, is that
the rapid increase in sludge volume discussed in the
technical sessions will be here soon. Within the next
year or so, all the studies must be done in order to allow
time for implementation and for start up of operations of
sludge management systems.
That means we don't have time for prolonged re-
search. Results produced two or more years into the fu-
ture will have to await the next generation of sewage
plant construction to be implemented. What we need
now are studies leading to immediate implementation. It
should be emphasized that Step I grant funds are being
used, to fund sludge studies in Region IX, precisely be-
cause we expect the studies to be followed by design,
construction and operation of the sludge handling sys-
tems which the studies recommend. We view sludge
management as an integral part of the overall sewerage
-------
155
system. Where separate design of sludge facilities is un-
dertaken, as a matter of convenience for the parties in-
volved, it is treated as a separate phase-of-construction
rather than as a separate project.
The thought that we will actually build what we are
now planning leads me to another point that must be em-
phasized. 1 fully agree with Congressman Brown that we
cannot be satisfied with narrow technical solutions. To
be implementable, any sludge study should cover all the
aspects mentioned for a 208 study. The division of re-
sponsibility between various public and private agencies
must be spelled out, revenue and financing must be pro-
vided for, institutional arrangements must be provided,
and the regulatory and enforcement aspects of the prob-
lem should be addressed. These may be more or less im-
portant in any given situation. My point, however, is that
if we get well down the road toward land disposal at a site
in "Outlying County," only to find that the County Com-
missioners of "Outlying County" (or the local planning
and zoning board or whomever) oppose the site, then we
have failed just as surely as if we had imporperly de-
signed the sludge thickener.
This brings me to my final observation on the tenor of
the times. The social sciences literature, beginning with
Vance Packard in the late 1950's and maturing with Ken-
neth Boulding's monograph on the "Spaceship Earth"
has held that the social and economic system must
change. The reality that their thesis was true was
brought home to most of us by the energy crisis. It
should be noted, however, that energy is not the only
thing in short supply (besides money). We have in the
recent past seen shortages of lumber, cement, steel al-
loys, food products, and numerous other commodities.
The philosophy put forward by Boulding is that society
should shift from the concept of GNP (or rate of con-
sumption) as the measure of our well-being to the idea
that we are better off when we conserve our resources
and use them carefully. This principle is gradually be-
coming generally accepted in society, and the change in
philosophy in environmental law is only one aspect of
this general trend. My observation is that environmental
law is in the fore-front of this trend, however, and this
puts us in a position similar to the first year hydraulics
student who is about to experience water hammer. We
are experiencing as a society, the difficulties associated
with trying to change the system by closing the valve at
the outlet end. As professionals we know, if my analogy
is a good one, the valve must be closed slowly and that
the pressure waves back up through the system must be
monitored carefully. We also know fundamentally that
the right way to deal with the system is from the other
end.
What does all this mean from the practical point of
view? First, referring back to my comments on the law
and its requirements, we cannot use what I have just said
as the basis for delay. The arguments that we should
continue unregulated dumping sludge in the ocean, the
nearest large river, or a nearby gravel quarry have been
heard. The decision has been made by Congress. The
answer is no. Lingering arguments on behalf of this idea,
if there are any, particularly remind me of arguments
made a decade ago in favor of continuing raw sewage
discharges. Such arguments are not consistent with the
emerging philosophy of the 1970's.
Having said that, however, what principles do my ob-
servations suggest? Let me state a few of them, although
I am sure that the list is not inclusive.
An obvious first step towards the conservation ethic is
to reclaim or recycle our waste products. Thus, a pre-
ferred option for management of sludge is to utilize it for
some beneficial purpose.
Another obvious step is to attempt to reduce the
amount of material put into the sewer system, where
other more appropriate alternatives are available. Sys-
tems analysis of industrial process, where I have seen
them done indicate that there is a potential to reduce
wastes from this source. Where this is the case, industry
should be encouraged to reduce waste volume to the
sewers. Such encouragement should automatically re-
sult from the implementation of pre-treatment and in-
dustrial cost recovery requirements of the law, since
those industries which are subject to the highest charges
have the greatest incentive to reduce their flows. This
aspect of the institutional process should be reinforced
(or at least not circumvented) by the sludge manage-
ment program.
A third point, made previously, is that emphasis
should be on implementing existing technology to deal
with existing or impending problems.
A fourth point, especially pertinent here in California,
is that disposal of sludge to the ocean is not acceptable
for the simple reason that it is expedient. In accordance
with the principles of Federal law, and the requirements
of State/Federal policy, if there are feasible alternatives
to ocean disposal (and we believe that there are) these
must be pursued.
A last point is that we operate with unique citizen par-
ticipation requirements. While it is obvious that "you
can't please all of the people all of the time," as Con-
gressman Brown quoted yesterday, it is also true that
those who dissent have an authoritative way for doing so.
The only way to proceed without running into real
trouble in this situation is by adhering carefully to the
procedural requirements. Our experience has been
clear! Good decisions reached in accordance with proper
procedures will stand up. Where procedures have not
been followed, we encounter delays that have proven to
be more costly than any other type of error one can make.
Thus, today's manager must understand and carefully
follow proper administrative procedures.
While, as I said, it may not be an inclusive list of do's
and don'ts, I hope it provides some "food for thought."
-------
ECOLOGICAL IMPACT OF THE DISPOSAL
OF MUNICIPAL SLUDGE ONTO THE LAND
James Schmid, Dennis Pennington and JackMcCormick
JackMcCormick& Associates, Inc.
Devon, Pennsylvania
LEGISLATIVE BACKGROUND
The objective of the Federal Water Pollution Control
Act Amendments of 1972 (Public Law 92-500, as
amended) is "to restore and maintain the chemical,
physical, and biological integrity of the Nation's wa-
ters." To achieve this objective, the Congress estab-
lished two goals. The interim goal for 1983 is to assure
"fishable and swimmable" water, where attainable.
The ultimate goal for 1985 and beyond is to eliminate the
discharge of pollutants.
To expedite the achievement of these goals, Congress
instituted a two-step process by which publicly owned
treatment works are expected to meet the national goals:
• by 1977, they are to produce effluents at least equal
to national standards for secondary treatment; and
• not later than 1983, they will provide for the appli-
cation of the best practicable waste treatment tech-
nology (BPT).
During the formulation of the Act, Congress devoted
little attention to the matter of the generation and dis-
posal of sludge. In the House-Senate Conference, how-
ever, Senator Caleb Boggs noted that larger volumes of
by-products would be generated by the advanced treat-
ment processes required by the Act, and that the dis-
posal of sludge could produce serious problems. The
Conferees considered that the existing techniques for
sludge disposal were unsatisfactory. To provide a regu-
latory mechanism, they inserted into the Act, Section
405, which is entitled, "Disposal of Sewage Sludge."
Section 405 is designed to prohibit the disposal of sew-
age sludge in any manner that might affect the inland or
coastal navigable waters of the United States. This com-
prehends the dumping of sludge on land in such a fash-
ion as to run off into the waters. Land disposal sites will
be required to obtain a permit subject to "each criterion,
factor, procedure, and requirement" applicable to a per-
mit issued under Section 402—the National Pollutant
Discharge Elimination System.
The possibility that some "mid-course correction"
might be necessary in the requirements also was con-
sidered during the House-Senate Conference. The Con-
ferees amended Section 315 of the Act to provide for an
independent evaluation of the regulatory aspects of the
legislation. This evaluation is to be made by a
15-member National Study Commission that now is de-
signated as the National Commission on Water Quality.
The principal attention of the Committee is addressed
to the technological aspects of achieving the effluent
limitations and goals set for 1983, but it also is evaluat-
ing the impact of the 1985 goal of pollution-free water.
The Committee must examine the total economic, social,
and environmental impacts associated with the achieve-
ment of those goals. The findings of the Commission are
intended to serve as the principal data upon which the
need for "mid-course corrections" in scheduling or re-
quirements will be based. The report of the Commission,
with its recommendations, is to be submitted to Con-
gress not later than 18 October 1975.
PURPOSE AND SCOPE
The National Commission on Water Quality recog-
nized that facilities for the disposal of sludges on land
doubtless will be important components of wastewater
treatment systems designed to satisfy the 1983 regula-
tions and the 1985 goal set by Congress. Particularly be-
cause the environmental consequences of such an inter-
media transfer of potential pollutants were considered
only peripherally during the formulation of the Act, the
potential environmental impacts of land disposal were
questioned seriously.
This paper originated when a team formed by Envi-
ronmental Quality Systems, Inc. (EQSI), Geraghty and
Miller, Inc., and Jack McCormick & Associates, Inc.
(JM A), was selected by the Commission and contracted
to evaluate certain intermedia impacts of residuals dis-
posal. JMA was assigned responsibility for the assess-
ment of the impacts on wildlife and natural vegetation of
incineration, ocean dumping, and land disposal of re-
siduals, including both sludge and liquid effluent. The
present paper is a summary of our findings on the poten-
tial impact of the disposal of municipal sludge onto the
land.
156
-------
ECOLOGICAL IMPACT OF DISPOSAL ONTO LAND 157
Biological Effects of Constituents
The overall investigation was addressed to the vol-
umes and varying composition of sludges to be
generated by a wide range of industrial categories, as
well as to sludge from municipal treatment works. Be-
cause the team members had to work in parallel, rather
than in sequence, the JMA ecological assessment
needed some standard basis for comparison between
this great range of sludges.
One of the first major decisions in the program was to
examine the potential biological effects of individual
constituents of sludge. Constituents are those compo-
nents of any type of sludge that potentially are pollu-
tants. They include nutrients, microorganisms, and
toxic substances.
In collaboration with EQSI, a considerable amount of
information was collected on the composition of sludges.
These data were summarized to describe the range of
concentrations of various constituents in municipal
sludges. Because the ranges are so wide, and because
extremely high concentrations of virtually every consti-
tuent were reported in sludge from one or more plants, it
became apparent that municipal sludges are highly vari-
able, and that they overlap all or most industrial
categories.
A substantial proportion of the JMA work effort was
devoted to locating information on the biological effects
of sludge constituents. A basic resource was the Blue
Book], which was compiled by the Committee on Water
Quality Criteria for the US-EPA in 1972. We supple-
mented the Blue Book data and reassembled the infor-
mation into a format useful to this study.
Biological Magnification of Pollutants
In the assessment of the potential biological effects of
sludge constituents, an important consideration is the
tendency of organisms to accumulate metals, certain
pesticides, polychlorinated biphenyls (PCB's), and ra-
dioisotopes. Through a complex of processes that collec-
tively are known as biological magnification, the concen-
trations of these substances in the tissues of organisms
may come to be substantially greater than in the environ-
ment. The ratio of the concentration of a pollutant in an
organism to that in the environment is termed the con-
centration factor.
An experience at Clear Lake, California, demon-
strates biological magnification2. The lake was treated
with the pesticide DDD to control nuisance hatches of
flying insects. After treatment, the concentration of
DDD in the water was 0.02 ppm. In the lake plankton,
however, the concentration of DDD was five ppm. The
fat offish that fed on the plankton contained more than
2,000 ppm DDD. Grebes ate the fish and died. The tis-
sues of the birds contained 1,600 ppm DDD.
This case illustrates that the concentration of a per-
sistent contaminent generally is greater at successively
higher trophic levels. The concentration in the plankton,
the minute green plants in the lake, was 250 times as
great as the concentration in the water. The concentra-
tion in the tissues of the fish that fed on those plants was
100,000 times as great as that in the water.
The grebes, which preyed on the fish, had a concen-
tration that was 80,000 times as great as that in the wa-
ter, but the concentration was lower than that in the fish.
This does not contradict the general rule of "higher con-
centrations at higher trophic levels." Instead, it demon-
strates a second fact, organisms vary in their ability to
tolerate the toxic effects of a particular substance. The
fish still were alive, even though the concentration of
DDD in their fat was 2,000 ppm. In contrast, the birds
died when the concentration of DDD in their tissues
neared 1,600 ppm.
Through this process of biological magnification, a
substance that is sparse in the environment may be con-
centrated many thousandfold by organisms. This may
result in injury or death to sensitive organisms. It also
may render fish, shellfish, game, livestock, and crops
unfit for human consumption. The only technique that
can be used to protect the biota and man is to minimize or
prevent the entry of cummulative pollutants into
environment.
With a knowledge of potential biological magnifica-
tion , our consideration of the information assembled on
the biological effects of constituents led us to conclude
that the criteria previously recommended to protect wa-
ter quality for various types of uses are reasonable. Be-
cause the data base is sparse, however, more intensive
investigations may indicate that some criteria are more
conservative than is necessary, or they may be too liberal
to protect certain uses in some places. At this time, how-
ever, no such conclusions are warranted.
A basic assumption of this assessment is that all facili-
ties for the disposal of sludge onto the land will meet all
requirements of Section 405. They will satisfy all appli-
cable environmental standards, including standards for
surface water quality.
The Existing Conditions of the Nation
To assess the potential environmental impact of a pro-
posed action, one must understand the existing condi-
tions of the site on which the action is to occur. For this
investigation, the proposed action is the disposal of
sludge onto the land. The site is the entire nation.
The staff of the Commision and the members of the
team recognized early during this investigation that
some scale of assessment must be established. Very de-
tailed information is available for some areas, but the
analyses of other areas can be characterized as "coarse
grained." To assure comparability and uniformity, the
information in the National Atlas3 was selected as the
standard source and scale for the original ecological in-
ventory and assessment.
The basic input data, thus, are at a scale of one inch
equals 118.4 miles, or one square inch equals about nine
-------
158 ECOLOGICAL IMPACT OF DISPOSAL ONTO LAND
million acres. At the scale of the final report, one inch on
the map is equal to about 150 miles on the ground, so one
square inch includes about 14.4 million acres.
To visualize better, imagine that this assessment was
made from a space platform. It is an overview of the Na-
tion, and is addressed to major environmental features.
It should not be considered to be applicable even at the
scale of a single state, and certainly will be too coarse in
grain for application to any smaller political subdivision.
Natural Vegetation of the United States
In the background report prepared for this ecological
assessment, a detailed description of the vegetation
types of the United States is presented. Primarily on the
basis of vegetation characteristics, the conterminous
United States was separated into three major geographic
divisions: the western; the midcontinental; and the
eastern United States (Figure 1). Three subdivisions
were recognized in the West: The Pacific; the Basin; and
the Rocky Mountain Regions. Similarly, a northern re-
gion , a central region, and a southern region were recog-
nized in the East.
Endangered and Threatened Species
The inventory of existing conditions included an
analysis of the prominant species of wildlife in each of
the vegetation regions and in each major vegetation
type. As the investigation proceeded, however, it be-
came apparent that the impact of land disposal on wild-
life probably will be less significant than the impact of
wildlife laws on the availability of sites for land disposal!
The history of wildlife protection is long, and extends
back at least to ancient Egypt. Until recently, however,
the concern of man largely has been toward those spe-
cies that he hunts or which are important in various re-
ligions or ceremonial rites.
During the twentieth century, attention has been de-
voted more and more toward vanishing species. Piece-
meal approaches that have been implemented in the
past, however, have not checked the technological as-
sault on critical habitats or the surges of population
growth and sprawl that threaten to sweep many of our
co-habitants of the earth to extinction.
A series of international treaties and meetings ulti-
mately led, only a decade ago, to the passage of the first
Figure 1: Vegetation Areas.
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ECOLOGICAL IMPACT OF DISPOSAL ONTO LAND 159
law in a series of very important Federal wildlife laws.
This was the Endangered Species Protection Act of 1966.
The 1966 law was amended by the Endangered Spe-
cies Conservation Act of 1969. Initially, these laws
seemed to have little relevance to land use decisions.
The Secretary of the Interior issued lists of endangered
species, but few non-biologists seemed to be concerned
with them.
As the National Environmental Policy Act of 1969
stimulated a greater attention to environmental con-
cerns, however, the potential impact on endangered
species became an important topic in Federal decision-
making.
Because the 1969 Act regarded as endangered only
those species threatened with extinction throughout the
United States, very few project sites conflicted with
habitats that support endangered species.
The 1966 and the 1969 Acts were supplanted by the
more comprehensive Endangered Species Act of 1973
(Public Law 93-205). A more appropriate name for this
1973 law might be the "Wildlife Habitat Conservation
Act." The first purpose listed by Congress in the Act is:
• to provide a means whereby the ecosystems upon
which endangered species and threatened species
depend may be conserved . . .
The definition of wildlife was broadened to include "any
member of the animal kingdom", from elephants to pro-
tozoans, and two categories of endangerment were
established.
• An endangered species is one that now is in danger
of extinction, and
• A threatened species is one that is likely to become
an endangered species within the forseeable future
if present trends continue.
An equally significant aspect of the Act is that the desig-
nation of a species for Federal listing no longer is tied to
its nation wide status. Rather, it is to be based on "all or a
significant proportion of its range." Section 4(b)(2) of
the Act indicates that designations are to consider "any
political subdivision of any nation . . ." A recent
proposed action to reclassify the American alligator, and
to delist the species in three Louisiana parishes, sug-
gests that Federal designations in the future may differ-
entiate categories of endangerment to the county level.
As of 8 July 1975, the Federal list of endangered spe-
cies included 117 American species. Of these 51 are
birds, 31 are fish, 24 are mammals, seven are reptiles,
and four are amphibians. Seventy-five occur in the con-
terminous states, 26 are in Hawaii, four are in Puerto
Rico, and one is in the Virgin Islands. Eleven others are
oceanic.
The States also have enacted legislation to protect en-
dangered species. To date, 42 states have replied to a
JMA qustionnaire. Of these, 38 have endangered spe-
cies legislation or other laws that enable administrators
to promulgate regulations to protect endangered spe-
cies . Two other states indicated that endangered species
bills have been submitted and are expected to be acted
upon favorably. Two states reported that no legislation
exists and that none is contemplated.
State lists of endangered or threatened species cur-
rently include numerous taxa that are not on the Federal
list. It appears, however, that within a few years the
Federal power may be placed behind each state list by
virtue of the 1973 Act. It also is likely that state lists,
which now are based largely on statewide status, may be
diversified to recognize county-to-county variability.
Major Land Uses and Characteristics
Developed Lands and Undeveloped Lands. To provide
a basis for an assessment of the availability of areas suit-
able for the land disposal of sludges, the United States
was subdivided into two general categories of land use—
developed or urbanized lands and undeveloped lands
(Figure 2).
The largest proportion of the total volume of wastewa-
tcr treatment residuals will be generated in the urban
areas of the United States. Vacant tracts that are large
enough to be economical for land disposal are scarce
throughout the urban areas. Where they do exist, alter-
native potential uses, for industry, for commercial de-
velopment or for residences, will exert strong market
pressures, and may bid the price of the land to a point
that land disposal would be infeasible. Citizen opposi-
tion to disposal sites in densely populated areas also is
expected to be strong.
It virtually is certain that the bulk of the sites for the
disposal of residuals on land must be sought in the areas
characterized as non-urban, or undeveloped. Some of
these lands will not be suitable owing to adverse soil con-
ditions, high water tables, inappropriate climatic condi-
tions or other physical characteristics.
Lands that do satisfy the guidelines for the physical
quality of the site may be disqualified on other bases.
The Endangered Species Act of 1973 and state laws and
regulations that are coordinated with the Federal act, in
combination with other environmental legislation, soon
may exert a strong control over land uses in the United
States. Through the environmental assessment process,
these recent laws may restrict new development to the
existing urban areas and their immediate fringes. Such
controls, if they are applied to implement appropriate
regional plans, could increase the energy-efficiency of
the Nation. They also will increase the competition for
sites that are approved for use in the regional plans.
This enumeration, therefore, is addressed to the iden-
tification of areas with major natural or institutional
limitations on the use of undeveloped land for the dis-
posal of residues.
Critical Areas for Land Disposal of Sludges. Areas
that are critical for the disposal of sludges on land exhibit
environmental hazards and/or impose other limitations.
These lands and the biological communities they sup-
port may be affected adversely by the disposal of
-------
160 ECOLOGICAL IMPACT OF DISPOSAL ONTO LAND
Figure 2: Urban Areas (Adapted from U.S. Dept. of Interior Geological Survey, 1970}.
sludges. The potential for the contamination of the envi-
ronment in most critical areas is intensified by the sensi-
tivity of certain natural processes. Areas of steep slopes,
porous or unstable bedrock, or high water table, for ex-
ample, may be particularly susceptible to degradation.
Critical habitats of endangered or threatened animals or
plants could be altered to the degree that they no longer
function to support viable populations of the imperiled
species. Critical areas forthe disposal of residues by stor-
age or land application techniques are listed in Table 1.
National Park System 4'5
Most of the large National Parks are situated in the
western United States. A large proportion of the Na-
tional Historic Sites, National Historical Parks, National
Monuments, and National Seashores are in northeast-
ern states. Few properties administered by the National
Park Service are located in the midwestern states.
National Forests and National Wildlife Refuges
Most of the National Forest lands are located in the
western states, and the largest proportion of the acre-
TABLE1
Critical Areas for Land Disposal of Sludges
Disposal of
Residues by Storage
Land Spreading of Sludge
National Parks
National Seashores
National Lakeshores
National Historical Parks
National Memorial Parks
National Recreation Areas
National Battlefield sites
National Monuments
National Wildlife Refuges
National Forests
State parks
State wildlife areas
State forests
State recreational areas
Designated or potential natural areas
Flocdplains
Inland and coastal wetlands
Wet soils
Karst topography
Land with slopes greater than 8»
Densely populated areas
Critical areas for imperiled species
National Parks
National Seashores
National Lakeshores
National Historical Parks
National Manorial Parks
National Recreation Areas
National Battlefield Sites
National Monuments
National Wildlife Refuges
State parks
State wilcliie areas
State, recreational areas
Designated or potential natural areas
Karst topography
Wet soils
Land with slopes greater than 8%
Densely populated areas
Critical areas for imperiled species
-------
ECOLOGICAL IMPACT OF DISPOSAL ONTO LAND 161
Figure 3: Natural Areas (Adapted from American Institute of Biological Sciences, 1974).
age is in the Rocky Mountains and the mountains of the
Pacific states. National Wildlife Refuges are most
prominent in the western United States and in Florida.
State Parks
State parks and recreation areas are concentrated in
the eastern United States, the Midwest, and California.
Some parks, such as the Anza Borrego Desert Park (Cali-
fornia) and Baxter State Park (Maine), contain more
than 100,000 acres. Most state parks, however, contain
fewer than 500 acres.
Natural Areas
Natural areas are lands that are preserved, or which
have been recommended for preservation, to protect
representative natural ecosystems or populations of en-
dangered plants or animals (Figure 3). Most natural
areas have been disturbed only to a very limited degree
by human activities, but areas that are recovering from
disturbance also may be included.
An inventory of the natural areas of the United States
that was conducted by the American Institute of Biologi-
cal Sciences6 was the primary source of data. The com-
prehension of the inventory, however, varies from state
to state and no data were obtained from California,
Florida, and several other states.
The AIBS investigation identified areas that total
9,636 square miles. A survey conducted by the Nature
Conservancy 7 recorded 5,057 square miles of natural
areas that currently are administered by state govern-
ments in the conterminous United States and 6.9 square
miles administered by the government of the State of
Hawaii.
Floodplains
The most extensive areas of floodplain land in the
United States are located along the Mississippi River.
The floodplains shown in Figure 4 are based on the
northern and southern floodplain forest types mapped
by Kuchler8. Other extensive floodplains are situated
along the East Coast of the United States and along the
tributaries of the Mississippi River.
Steep Slopes
The slope of the land surface is critical to the use of a
site for the disposal of sludge. Owing in part to the char-
-------
162 ECOLOGICAL IMPACT OF DISPOSAL ONTO LAND
FLOOOPUMN
STEEP SLOPE
J-L_
Figure 4: Floodplains and Steep Slopes (Adapted from Kuchler, 1970, Hammond, 1970}.
acteristics of the equipment required, slopes of more
than eight percent generally are not suitable.
Operations on steep slopes, includingthe disposal site,
areas utilized to store cover materials, access roads, and
areas used for supporting services, generally will induce
accelerated runoff, will expose soils, will create artifi-
cially steep grades, and, consequently, will intensify
erosion and sedimentation.
Sections of the nation in which slopes steeper than
eight percent occupy at least 80 percent of the surface
are identified in Figure 4.
Wetlands
The wetlands of the nation consist of marshes,
swamps, open shallow waters, and seasonally flooded
lands. Wet soils are prominent in the plains of Minne-
sota, the Mississippi Valley, Florida, and other parts of
the Atlantic and Gulf Coastal Plain (Figure 5). These wet
soils are saturated with water either seasonally or per-
manently. Most wetlands feature organic soils (peat or
muck) or recently deposited alluvial soils. The aquatic
environment of the wetlands is an essential habitat for
waterfowl, many species of fur animals, and some spe-
cies of farm game, forest game, and warm-water fish 9.
Karst Lands
Karst lands primarily are developed in Texas, Florida,
and several Appalachian states (Figure 6). The rocks in
these areas predominantly are limestone, dolomite,
and/or gypsum. Solution channels and cavities in the
rocks act as conduits through which surface water rapid-
ly enters the groundwater system.
SUMMARY OF CRITICAL AREAS
Various kinds of lands that are expected to present
major restrictions for the disposal of sludges are listed in
Table 2. The gross area of each land type, in square
miles, was estimated from the best data available.
No nationwide measurements of the areas of state
forests, floodplains, steep slopes, or karst lands were
found. The total area of those types of critical sites for
which geographically separable, quantitative data were
available is 628,954 square miles.
The total of the quantified critical areas in the conter-
minous states in 547,799 square miles. This is approxi-
mately 18 percent of the total land surface of the conter-
minous states. Of the remaining 2,417,009 square
miles, 69 percent (1,660,244 square miles) is categorized
-------
ECOLOGICAL IMPACT OF DISPOSAL ONTO LAND 163
Figure 5: Major Wetlands (Adapted from Soil Conservation Service, 1970, U.S. Dept. of Interior Geological Survey, 1970).
as in farms (Table 2). Unquantified critical areas doubt-
less account for a substantial proportion of the other 21
percent of the land.
The equivalent figures for the critical areas of Hawaii
and Alaska, respectively, are 522 square miles, or eight
percent and 80,563 square miles, or 14 percent. Farms
occupy about four percent of Alaska and 50 percent of
Hawaii.
Approximately 46 square miles, or one percent of the
surface area of Puerto Rico is included in National Wild-
life Refuges or National Forest Land.
In addition, to the types listed, we obtained bulk
measurements for two other Federal agencies. These
were not accompanied by geographic breakdowns.
The Energy Research and Development Administra-
tion (ERDA), regulates 3,125 square miles of land. This
land is contained in twelve major sites. Two sites, which
cumulate to 1,206 square miles, have been designated as
national environmental research parks. The other areas
are being considered for designation.
The largest amount of Federal land, 709,375 square
miles, is administered by the Bureau of Land Manage-
ment (BLM). It is not certain, but can be presumed, that
substantial areas that are controlled by BLM will be
available for the full range of techniques for disposal of
sludge onto the land.
Synthesis and Application to
Minimum Geographical Regions
The National Commission on Water Quality seg-
mented the conterminous United States into 13 divi-
sions, or "minimum geographical regions" (Figure 7).
The boundaries of these regions are based on various
combinations of physical, biological, and water quality
features. As a contract requirement, the summary of our
study was addressed to these regions.
JMA composited the available maps of individually
restricted lands to produce two synthesis maps. The first
of these illustrates those lands on which 'sites for the
storage of sludge in landfills, trenches, or lagoons are
likely to be prohibited or severely limited (Figure 8).
These methods alter the characteristics of the site, and
generally are not suited to concurrent multiple uses.
They also may restrict the variety of choice for sequen-
tial, or future uses. This figure suggests that major diffi-
culties will be experienced in the Appalachian Region,
-------
164 ECOLOGICAL IMPACT OF DISPOSAL ONTO LAND
/ i
'7 r - - -
.^ ~ -----
< \' \ •':. -*
• > 6
<5-
0 > • ,-• ^ .??--• ^ ^.
!.. JM>'
"~r-
/
Figure 6: Karst Lands (Adapted from U.S. Dept. of Interior Geological Survey, 1970).
along the Atlantic and Gulf Coastal Plain, in the Miss-
issippi River embayment, in the central and northern
Rocky Mountains, and in the Cascades-Sierra-Coastal
Ranges section along the Pacific Coast.
The second synthesis map is composed of those lands
that are institutionally restricted or physically limited for
the application of granular or liquified sludges (Figure
9). The restrictions on the availability of sites for the ap-
plication of liquid sludge are not expected to be as strin-
gent as those on the availability of sites for the storage of
sludge. When properly treated sludges are applied at
appropriate rates and with suitable equipment, the land
and the biological communities it supports need not be
altered significantly. Multiple concurrent use is feasible,
and the range of choices for future, sequential uses
should not be affected. In point of fact, the use of a site
for the land application of residuals is a mechanism by
which decisions on the commitment of land can be re-
served for future generations.
This figure differs from the preceding figure in that
National forest lands, major wetlands, and the flood-
plains of the Mississippi River and of the rivers in the
Midcontinental Division have been subtracted. The
limitation on uses of steep slopes also may be relaxed
somewhat for granualr and liquified sludges, but the
permissable rates of application probably will be rela-
tively low, so that the size of the disposal sites will have
to be larger than on unrestricted lands.
Environmental agencies in the United States general-
ly have not yet recognized the suitability of natural wet-
lands or man made wetlands for the application of efflu-
ents or sludges from wastewater treatment processes.
Recent studies, however, have indicated that natural
wetlands are effective in nutrient removal l0'11 The
biological community near the point of application may
be simplified somewhat, but the area that is affected
measurably is proportionately small.
Effluents and sludges have been sprayed or flooded
on at least 26 sites in National forests and 14 sites in state
forests 12. Numerous tests have determined that forest
communities function effectively to assimilate effluents
and sludges if the rate of application is appropriate. The
growth of trees on inventoried disposal sites was from 27
to 118 percent greater than before residuals were ap-
plied u. Although short-term results appear to be bene-
ficial, no information is available to evaluate the long-
term effects of the application of effluents and sludges to
forest lands.
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ECOLOGICAL IMPACT OF DISPOSAL ONTO LAND 165
TABLE2
Geographically Separable Critical Areas
for the Disposal of Sludge
A. AREAS WITH SEVERE RESTRICTIONS
B. San RESTRICTION EXPECTED
Alabama
Alaska
Arizona
Arkansas
California
Colorado
Connecticut
Delaware
D. C.
Florida
Georgia
Hawaii
Idaho
Illinois
Indiana
Iowa
Kansas
Kentucky
Louisiana
Maine
Maryland
Massachusetts
Michigan
Minnesota
Mississippi
Missouri
Montana
Nebraska
Nevada
New Hanpahire
New Jersey
New Mexico
New York
North Carolina
North Dakota
Ohio
Oklahdna
Oregon
Pennsylvania
Puerto Rico
Rhode Island
South Carolina
South Dakota
Tennessee
Texas
Utah
Vernont
Virginia
Virgin Islands
Washington
Nest Virginia
Wisconsin
Wyoming
LAND
AREA
50,708
566,432
113,417
51,945
156.361
103,766
4,862
1,982
61
54,090
5B.073
6,425
82,677
55,748
36,097
55,941
81,787
39,650
44,930
30,920
9,891
7,826
56,817
79,289
47,296
68,995
145,587
76,483
109,889
9,027
7,521
121,412
47,831
48,798
69,273
40,975
68,782
96,184
44,966
3,435
1,049
30,225
75,955
41,328
262,134
82,906
9,267
39,780
133
66,570
24,070
54,464
97,203
STATE
PARKS
22
1,563
43
1,130
43
0
269
64
50
324
120
55
23
196
27
388
92
384
339
316
25
121
31
163
118
61
164
344
100
5
216
139
126
185
13
91
134
203
100
44
67
126
103
72
234
NATIONAL
WILDLIFE
REFUGE
72
34,843
2,468
192
301
76
<1
34
0
683
689
5
103
137
12
104
80
3
372
38
29
18
164
289
91
67
1,634
220
3,432
1
47
585
33
172
431
12
213
712
13
2
<1
253
66
127
310
147
7
115
<1
243
0
233
89
NATIONAL
PARK SYSTEM
10
11,777
4,371
163
7,037
957
0
0
(14)
3,335
97
402
136
<1
13
3
1
101
<1
58
97
71
1,061
355
72
128
1,996
10
1,222
<1
27
387
73
597
112
46
10
274
81
<1
<1
8
428
401
1,739
3,206
0
471
24
3,000
1
165
3,770
NATURAL
AREAS'"
69
89
32
33
54
16
236
266
608
254
298
75
65
27
109
167
513
3,578
189
256
228
220
377
38
436
89
123
363
646
160
30
URBAN
AREAS
714
493
266
3,933
429
956
55
61
1,507
729
115
29
1,698
1,084
436
331
303
362
124
527
1,368
1,511
847
214
734
49
120
159
81
1,567
114
2,189
468
14
2,109
605
332
1,590
211
344
27
595
3,073
260
0
949
647
122
734
0
STAT!
FORES- s
6(
(i
C>
30
lit
111
204
10
0
479
38,811
1,445
27
33
73
13
33
186
0
5,878
4,663
3
320
334
0
0
0
261
1,458
4,146
0
2'il
0
1,2!7
2,955
13
113
0
213
10
0
1>9
16
2,8)0
1>0
6 '9
0
NATIONAL
FORESTS
992
32,380
17,848
3,840
31,360
22,440
<1
0
0
1,690
1,330
0
31,800
387
263
1
169
964
930
78
0
0
4,199
4,370
1,776
2,252
26,100
548
7,982
1,068
0
14,370
22
1,774
1,727
241
454
24,188
775
44
0
935
3,103
959
1,213
12,567
380
2,404
<1
14,168
1,485
2,329
14,448
WETLANDS
2,498
44
5,915
874
632
37
205
26,852
9,249
1,063
668
443
216
319
427
15,074
596
453
362
5,027
7,883
4,046
589
293
1,015
301
21
422
76
333
6,335
2,380
153
437
738
83
40
5,590
1,175
1.-294
5,845
1,835
60
845
364
6
4,360
47
3,541,233 8,433 49,967
9,644 35,185 67,5'iO 292,352 117,520
8 235 square miles of NFS land is excluded; this includes the Appalachian Trail and «ter areas in the Gulf Islands.
b Environmental tesearch Parks designated by the Atonic Energy Coimission in Idaho (Idaho National Engineering Laboratory,
571,800 acres) art South Carolina (Savannah River Plant, 200,000 acres ) are inchxted in this oolum.
TOTAL
A t B
818
48,183
7,332
664
12,401
1,462
1,068
178
61
5,794
1,611
522
318
2,192
1,283
614
671
603
761
874
1,353
2,095
3,373
1,882
402
1,115
3,737
459
4,976
367
2,215
1,250
6,217
1,526
818
2,611
1,187
1,444
2,246
2
262
1,132
744
1,449
5,122
3,713
414
2,248
24
4,016
386
1,234
4,093
4,374
80,563
25,224
10,449
44,745
24,645
1,309
393
61
34,815
51,001
522
34,626
3,274
1,989
864
1,159
2,067
16,778
1,581
1,992
2,457
18,477
18,798
6,227
4,276
30,464
2,022
13,259
1,456
2,898
17,154
10,718
9,635
4,925
3,266
2,078
27,597
6,089
46
335
7,850
5,022
3,945
12,190
18,115
1,013
5,573
24
21,428
1,997
8,601
18,588
2
9
6
1
a
i
22
10
100
11
3
8
<1
4
4
1
1
2
2
3
14
27
6
2
1
2
3
1
5
4
29
1
13
3
1
6
2
2
5
<1
25
4
1
4
2
4
4
6
18
6
2
5
4
151,522 628,954
LAND IN
FARMS
21,335
2,507
59,692
24,523
55,816
57,339
846
1,053
0
21,925
24,597
3,216
22,526
46,739
27,458
52,453
77,172
24,950
15,295
2,750
4,380
1,095
18,594
45,071
25,062
50,657
102,813
71,616
16.732
957
1,619
73,113
15,857
19,896
67,372
26,737
56,262
28,153
13,907
107
10,925
71,225
23,525
222,761
17,677
2,993
16,640
6,782
28,281
55,432
FARMS AS
X OF AREA
53
47
36
55
17
53
43
50
27
84
76
94
94
63
34
9
14
33
57
53
73
71
94
15
11
22
60
33
41
97
94
57
85
21
32
42
28
52
57
The Potential Impact on Natural Vegetation and
Wildlife of the Disposal of Sludge onto the Land
There are two general categories of potential impact
insofar aslocational aspects are concerned. Site impacts
are those that are expected to occur immediately or in
the future on the tract that is dedicated to disposal activi-
ties. Offsite impacts are those that are expected to occur
at any place outside of the boundaries of the disposal site
and directly or indirectly as a result of the disposal
activities.
Land that is to be utilized in the future for the disposal
of sludges that are generated from wastewater treat-
ment facilities will have to satisfy certain guidelines.
These guidelines will be based on physical, biological,
and sociological criteria. Thus, land that may be suitable
from one point of view, may be unsuitable from another
point of view. The stringency of these guidelines and the
degree to which they are enforced will determine the
supply of land that is available for land disposal.
If the disposal facilities are designed, constructed,
and operated in a manner that will allow them to satisfy
all Federal laws and regulations, off site impacts will be
negligible. "Design," as used here, includes the selec-
tion of sites that will meet stringent guidelines.
In large part, the ecological impact of land disposal
will be measured by the total amount of land that is pre-
empted for disposal sites. The requirement for land is
related, in part, to the volumes of sludges and effluents
to be generated and to their qualities. It also is related to
the characteristics of the available disposal sites. Each
soil, for example, has a specific capacity to adsorb var-
ious constituents present in residuals.
-------
166 ECOLOGICAL IMPACT OF DISPOSAL ONTO LAND
Figure 7: Minimum Geographic Regions (Adapted from National Commission on Water Quality, 1975).
Figure 8: Areas Unsuitable for the Storage of Sludge.
No date that can be applied throughout the nation
were available to estimate the region-to-region vari-
ability in the expected life of disposal sites. It probably is
realistic to assume that the average life expectancy is 20
years. Thus, there will be a regular turn-over in disposal
sites. Plans should be drawn not to assure the avail-
ability of suitable sites for future use. similarly, the
planning should address the future uses of spent sites.
The intensity of site impacts will vary and will be a
function of the characteristics of the techniques utilized
for disposal and the characteristics of the disposal site.
The intensity of impacts generally will be progressively
-------
ECOLOGICAL IMPACT OF DISPOSAL ONTO LAND
167
^V- • '"* • "*:£ .- , --
v>-^4- -"••I*
- <;**V .' t-'A
'V>W
n AREAS GENERALLY SUITABLE FOR
THE DISPOSAL OF WASTEWATER EFFLUENT
AREAS GENERALLY UNSUITABLE FOR
THE DISPOSAL OF WASTEWATER EFFLUENT
Figure 9: Areas Unsuitable for the Disposal of Wastewater Effluents.
greater on sites that range from highly disturbed to pris-
tine. Sludge storage facilities generally will alter sites
totally. Some techniques for the disposal of liquified
sludges may produce only minor changes, whereas other
techniques will require drastic alteration of some sites.
The preparation of a site for the storage of sludge will
require the removal of all existing vegetation and the
termination of any existing activity, such as farming.
The removal of vegetation will destroy the value of the
site for wildlife. If the recommended guidelines are fol-
lowed, no endangered or threatened species will be af-
fected. Nevertheless, local populations of breeding wild-
life species will be reduced.
The area of impact of landfills will be extended by the
need to stockpile excavated material for use later as a
cover. Stockpile sites will be cleared of any woody vege-
tation, land herbaceous plants will be buried. Because a
ratio of one volume of sludge to one volume of soil is
recommended in sludge landfills, most of the material
that is excavated probably will have to be stockpiled.
Most of the common methods that are used to apply
liquid or dewatered sludge are practicable only on unob-
structed sites. Thus, agricultural land, grazing land, or
low-quality land (strip-mined areas, dredged spoils) are
suitable, but areas covered by trees or shrubs would
have to be cleared. Except for systems which employ
partable agricultural irrigation devices that can be
placed manually, techniques for spraying also will re-
quire unobstructed sites.
If it is necessary to clear natural vegetation from the
site that is to be used for the application of sludges to the
land, the intensity of impact will vary with the quality of
the vegetation and its utility to wildlife. Recent prelimi-
nary investigations by the New Jersey Division of Fish,
Game, and Shellfisheries 14"16, however, suggest that
the productivity and nutritional value of wildlife food
plants can be enhanced by the application of sludge.
When food patches in a public hunting reserve were
treated with sludge, deer grazed most intensively on
plots that received the heaviest applications. If disposal
sites can be dispersed, therefore, it may be possible to
enhance wildlife values even in forested areas.
SUMMARY
This investigation led us to the conclusion that land
disposal can be environmentally acceptable. Sludge ap-
plication, as contrasted to landfilling, is most
appropriate.
The supply of suitable sites will be restricted by
various natural and institutional limitations. Although
sites probably could be found on so-called vacant or
natural lands, the most attractive sites seem to be those
that already are utilized for crop and livestock produc-
tion. Multiple use of these lands should be considered to
be a national priority. The potential reuse ofwastewater
by-products to improve soil conditions and add fertility
could offset the anticipated substantial rises in the costs
of petroleum-derived fertilizers.
-------
168 ECOLOGICAL IMPACT OF DISPOSAL ONTO LAND
LITERATURE CITED
1. Committee on Water Quality Criteria, Water Qual-
ity Criteria 1972, National Academy of Sciences-Na-
tional Academy of Engineering, Environmental Studies
Board. U.S. Environmental Protection Agency, Wash-
ington, D.C., 594 pp., 1972.
2. United States Department of the Interior, Fish,
Wildlife and Pesticides, Fish and Wildlife Service,
Washington, D.C. (1966), 12.
3. United States Department of the Interior. National
Atlas of the United States, United States Department of
the Interior, Washington, D.C., 417 pp, 1970.
4. United States Department of the Interior, Park for
America—A Survey of Park and Related Resources in
the 50States; A Preliminary Plan, United States Depart-
ment of the Interior, Washington, D.C., 485 pp, 1964.
5. United States Department of the Interior, National
Park Service Computer Listing of Acreages, by Region,
United States Department of the Interior, Washington,
D.C., 9pp, 1975.
6. American Institute of Biological Sciences, Natural
Areas and Their Role in Land and Water Resource
Preservation. American Institute of Biological Sciences,
Arlington, Virginia, 286 pp, 1974.
7. The Nature Conservancy, "The Preservation of
Natural Diversity: A Survey and Recommendations,"
Final Report. Prepared for the U.S. Department of the
Interior, Contract No. CX0001-5-0110. Washington
D.C., variously pages, 310 pp, 1975.
8. Kuchler, A.W., "Potential Natural Vegetation,"
The National Atlas of the United States, United States
Department of the Interior, Washington, D.C., 1970,
89-91.
9. Shaw, S.P., and C.G. Fredine. Wetlands of the
United States, Their Extent and Their Value to Water-
jowl and Other Wildlife, United States Department of
the Interior, Fish andWildlife Service Circular 39 (re-
printed 1971), 67 pp, 1956.
10. McCormick, J., R.R. Grant, Jr., and Ruth Patrick.
"Two Studies of Tinicum Marsh,Delaware and Philadel-
phia Counties, Pennsylvania. The Conservation Founda-
tion, Washington, D.C., 123 pp, 1970.
11. Hartland-Rowe, R.C.B., and P.B. Wright.
"Swamplands for Sewage Effluents," Final Reports.
Environmental-Social Committee, Northern Pipelines,
Task Force on Northern Oil Development Report 74-4,
137 pp, 1974.
12. Olson, O.C., and E.A. Johnson, "Forest Service
Policy Related to the Use of National Forestlands for Dis-
posal of Wastewater and Sludge," W.E. Sopper and
L.T. Kardos eds. Recycling Treated Municipal Waste-
water and Sludge Through Forest and Cropland, The
Pennsylvania State University Press, University Park,
Pennsylvania, 1973, 435-439.
13. Sopper, W.E., "Effects of Trees and Forests in
Neutralizing Waste." Trees and Forests in an Urbaniz-
ing Environment, University of Massachusetts, Cooper-
ative Extension Service. Pennsylvania State University,
Institute for Research on Land and Water Resources Re-
print Series 23, 16 pp, 1971.
14. Tourine, Frank, and Joe Penkala. Upland Wildlife
and Habitat Investigations Job IV-C (Determine the In-
fluence of Sewage Sludge Application on Scrub Oak
Acorn Production), New Jersey Department of Environ-
mental Protection, Division of Fish, Game, and Shell-
fisheries, Job Progress Report, Project W-52-R-2, 8 pp,
1974.
15. Tourine, Frank, and Joe Pankala, Upland Wildlife
and Habitat Investigation. Job IV-B (Determine the
Fertilizer Value of Digested Sewage Sludge Applied to
Woodmansie Sand), New Jersey Department of Envi-
ronmental Protection, Division of Fish, Game, and Shell-
fisheries, Job Progress Report, Project W-52-R-2, 13 pp,
1974.
16. Tourine, Frank and Joe Penkala, Upland Wildlife
and Habitat Investigation, Job IV-E (Determine the In-
fluence of Sewage Sludge on Yields of Established Per-
manent Pasture). New Jersey Department of Environ-
mental Protection, Division of Fish, Game, and Shell-
fisheries, Job Progress Report, Project W-52-R-2, 12 pp,
1974.
-------
PLANT UPTAKE OF HEAVY METALS FROM
SEWAGE SLUDGE APPLIED TO LAND
Rufus L. Chancy
United States Department of Agriculture
Beltsville, Maryland
and Michael C. White, and Paul W. Simon
Maty land Environmental Service
Annapolis, Maryland
INTRODUCTION
Ultimate disposal of sewage sludges by utilization on
land is considered by many as the best solution available
to the municipal sludge problem. Ocean dumping of
sludge will not likely be allowed in the future. Incinera-
tion and pyrolysis require expensive fuels and may
pollute urban air pollution. Landfills may pollute the
groundwater and are difficult to initiate because of pub-
lic resistance. Although land disposal of sludge presents
special problems, many contend that this ultimate dis-
posal route would benefit society.
Sewage sludge appears to be very valuable in revege-
tation and reclamation of land disturbed by urban de-
velopment, coal and gravel surface mines, and road con-
struction. If properly used, sludge can transform these
disturbed lands into an environment suitable for plant
growth.
Many agronomists are concerned that disposal of
some sludges on agricultural land may impair crop
growth because of their heavy metal contents, or may
endanger the food chain through excessive accumula-
tion of these metals in the crop's edible portion. These
aspects have been reviewed in depth by Chancy''2,
Chancy and Giordano3, Webber4, and Page5. Many re-
searchers have shown that soil properties such as soil or-
ganic matter, cation exchange capacity, Fe and Mn
oxides, and clay content, as well as crop species can
strongly influence the potential for heavy metal prob-
lems when sludges are used on land.
It is likely that some sludges which contain high con-
centrations of certain heavy metals will present prob-
lems if used on agricultural lands. To avoid such prob-
lems municipalities will have to enforce pretreatment of
industrial wastes if land disposal of sewage sludge is to
result in long-term benefits to society.
This paper reports preliminary results of field experi-
ments with sludge and composted sludge. One section
describes a greenhouse pot experiment showing the ef-
fects of soil pH on Zn phytotoxicity and on plant uptake
of Zn and Cd. Another describes studies on the disposal
and the analyses of sludges currently applied to agricul-
tural land in the Northeast. These studies demonstrate
the complexity of heavy metal interactions in the soil-
sludge-plant system.
Experimental Results and Discussion
Chard Plots, 1974
Chard was grown on small plots of Woodstown silt
loam soil (CEC = 5.9 meq/lOOg) treated with different
sludges for use in feeding trials by our cooperators;
chard is noted for its metal accumulation.The sludges
used were: (1) anaerobically digested sludge cake from
the Blue Plains Water Pollution Control Plant in Wash-
ington, D.C. (B.P. sludge); (2) B.P. sludge composted at
Beltsville by the windrow method6 (B.P. compost); (3)
B.P. mixed raw sludge heat dried in a torroidal flash
drier (B.P. R-HD); (4) an anaerobically digested sludge
cake high in Zn and Cu (high metal); and (5) aheat-dried,
raw, secondary sludge with a somewhat high Cd/Zn rate
(High Cd/Zn).
Table 1 shows sludge metal analyses, Zn (equivalent),
the recommended maximum total applications [Zn
equivalent addition at ten percent of the C.E.C.], and the
actual application rates. The B.P R-HD sludge had
higher than expected Cd levels, and subsequently we
learned that the High Cd/Zn sludge was used in the start
up operations of the torroidal flash drier and comprised
over half of the sample. The plots remained fallow for
four weeks to avoid initial toxicity, and to leach salts
from the seedbed. Dolomitic limestone was added to ad-
TABLE1
Composition and Application Rates of Sludges
Applied in 1974 to Plots of Woodstown Silt Loam
Planted to Swiss Chard
169
-------
170
PLANT UPTAKE OF HEAVY METALS
just the soil to pH six. Soil pH increased when B.P. com-
post was added, but declined sharply with the B.P.
R-HD and high Cd/Zn sludges (Table 2). While normally
0.5 to Imt/ha/yr of these raw heat-dried sludges are ap-
plied as a N fertilizer, we applied 56 t/ha to provide suit-
ably high metal levels to meet our experimental objec-
tives. This high rate proved to be excessive and caused a
rapid pH decrease, initial toxicity, and severe growth
inhibition.
TABLE2
Soil pH and DTPA-TEA Extractable Metals in Plots of
Woodstown Silt Loam Amended with Sludges in 1974
Soil Treatment
Soil pH*
4/75 8/75
Zn
ppm
Cd
ppm
Cu
ppm
Ni
ppm
Control
B.P. Sludge
B.P. Compost
E.P. R-HD
High Metal
High Cd/Zn
6.2 6.6
6.0 5.7
6.7 6.7
5 :** 5.2
5.8 5.0
4.9** 5.5
1.6
64.8
29.4
13.2
60.6
14.4
0.02
0.32
0.23
0.59
0.12
0.93
0.8
14.6
11.6
4.5
26.4
5.2
0.4
1.1
1.7
1 .4
3.4
1 .6
* pH adjested to 5.0 in 6/74.
** line added in 4/75.
Table 3 shows metal analyses of the chard leaves.
Chard plants grown on the B.P. R-HD and High Cd/Zn
plots were inadvertantly mixed together and are labeled
"High Cd's" (Table 3). Sludge applications produced
chard higher in Zn, Cd, Cu, and Ni. The most striking in-
crease was that of Cd in chard grown on the "High Cd"
plots. Here, the high Cd/Zn ratio in the sludged soil re-
sulted in high chard Cd levels before Zn and other metals
began to limit plant growth. The "High Metal" treat-
ment chard, because of the low Cd/Zn ratio of the
sludge, resulted in a low chard Cd level when Zn or other
metals should have begun to limit growth. Plants readily
absorbed Cd in the absence of Zn phytotoxicity, especial-
ly at the low pH produced by addition of the R-HD
sludges. Chard samples were washed, wilted, freeze-
dried, and ground for mixing into a balanced diet for
guinea pigs. The feeding trials have been completed and
the animal tissues are being analyzed.
Sludge Vs. Sludge Compost Plots, 1973
In June, 1973 plots were amended with Blue Plains
anaerobically digested sludge cake, and B.P. sludge
composted by the windrow method at Beltsville6. These
sludge materials were applied at 0, 40, 80, 160, and 240
TABLE3
Metals Content of Swiss Chard Grown on Woodstown
Silt Loam Amended with Sludges in 1974
Soil
Treatment
Control
B.P. Sludge
B.P. Compost
High Metal
High Cd's*
Zn
70
580
257
950
796
Cd Cu Ni
u g/g dry leaves
0.73 11 1.4
4.0 22 3.5
1.7 18 1.7
2.0 23 22.3
24.0 23 6.9
Fe
94
89
94
77
93
Mn
290
1900
780
780
2390
Mt/ha. Dolomitic limestone was applied to half the plots
to establish pH ranges of 5.5 to 6 and 6.5 to 7. Field corn,
and many vegetable species and field crops have been
grown on these plots. Table 4 shows metal analyses for
corn ear leaves, and Table 5 for Swiss chard7.
TABLE4
Heavy Metal Content of Corn Ear Leaves Grown on
Woodstown Silt Loam Amended with Sludge and
Sludge Compost in 1973
Soil Treatment
Material Rate
Contro
Sludge
Mt/ha
40
80
160
240
80
160
240
Compost 40
80
160
240
80
160
240
* V.'ithin column,
pH
Zn
Cd Mn
Fe
LJ g/g dry leaves
5.47
5.25
5.65
6.48
6.36
6.35
6.29
6.90
5.48
5.99
6.51
6.81
6.85
6.90
f.96
values followed
35 f*
180 ab
224 a
168 b
143 be
117 cd
113 cd
148 be
0.41 e 92
.11 be 348
.74 299
.89 331
.69 219
.48- b 166
.82 292
.87 376
8" def 0.58 de 89
64 def
84 def
104 cde
3.62 de 57
3.81 ce 89
.10 be 99
56 ef 0.41 e 43
86 def
3.60 de 74
73 def 0.93 cd 90
de
b
1C
-d
b
de
de
de
de
e
de
de
112
109
123
108
113
111
145
81
107
105
113
116
112
117
112
by the same letter are not significantly
* Mixture of chard from B.P. R-HD and High Cd/Zn treatments.
different at the 5°' level according to the Duncan's Multiole Ranqe Test.
The following general effects of sludge and soil pH on
crop uptake of metals were observed: Zn, Cd, and Ni in-
creased, but Cu, Fe, and Pb were only slightly influ-
enced by sludge application. At the higher soil pH, plant
Zn, Cd, and Mn contents decreased. The plants grown
on compost plots had significantly lower Zn and Cd con-
tents than those grown on sludge plots. For the crops we
have grown, the increase in Cd content was generally not
significant from compost, while it was significant from
sludge, especially at the lower soil pH.
Several aspects of composting at Beltsville may have
influenced our results (Tables 4 and 5): (1) composting
generally produces a material which initially raises the
soil pH and does not cause as much subsequent slow
lowering of soil pH as digested sludge does; (2) compost-
ing stabilizes the sludge organic matter, and adds or-
ganic matter from composted woodchips; and (3) ser-
pentine rock chips from the composting pad add con-
siderable Mg silicate to the compost and the silicate may
reduce metal availability to plants, especially at the
higher soil pH. Experiments are now in progress to es-
tablish the basis for this apparent reduction in sludge
metal availability to plants by composting. Composting
of sewage sludge appears to be desirable not only from
the standpoint of pathogen reduction, odor control, dry-
ing and case of handling, and lower nitrate levels, but al-
so because of the reduced potential for metal uptake by
plants.
Urban Fill-Soil Revegetation Plots, 1971
Our oldest sludge amended plots at Beltsville were
established in October, 1971 on an acid, infertile, silt
loam fill soil area8. The plots were limed to a pH's of
-------
PLANT UPTAKE OF HEAVY METALS
171
TABLES
Heavy Metal Content of Swiss ChardLeaves Grown on Woodstown Silt Loam Amended
with Sludge and Sludge Compost in 1973
Treatment
Material
Control
Sludge
Compost
Rate
Mt/ha
40
80
160
240
80
160
240
40
80
160
240
80
160
240
PH
5.47
5.25
5.65
6.48
6.36
6.35
6.29
6.90
5.84
5.99
6.51
6.81
6.85
6.90
6.96
Zn
133 cd"
651 a
467 b
276 bed
293 bed
139 cd
205 cd
194 cd
308 be
247 cd
157 cd
129 cd
123 cd
98 d
91 d
Cd
u 9/9
2.05 de
5.88 ab
6.28 a
3.84 cd
4.30 be
2.90 cde
3.48 cde
3.54 cde
2.93 cde
2.09 de
2.28 de
2.27 de
1.51 e
1.60 e
1.62 e
Cu
dry leaves
7.4 f
27.7 ab
29.7 a
25.2 be
24.6 bed
23.4 bed
22.8 cd
23.1 cd
17.8 e
25.0 be
23.8 bed
23.8 bed
22.3 cd
21.2 cde
20.2 de
Ni
2. 19
1.34
3.13
1.16
1.71
0.90
1.10
0.81
10.7
3.67
2.97
2.42
1 .56
2.11
1.39
Pb
0.81 d
3.52 a-d
4.30 abc
4.22 abc
4.91 ab
2.10 cd
3.90 a-d
4.23 a-c
0.81 d
3.93 a-d
4.25 abc
5.34 a
2.41 bed
2.42 a-d
4.38 abc
Mn
772 b-d
1683 a
1414 ab
1417 ab
1153 abc
416 d
1249 ab
1442 ab
793 bed
380 d
451 d
511 cd
292 d
340 d
532 cd
Fe
175
173
165
190
192
171
185
164
209
168
161
180
146
135
140
Within column, values followed by the same letter are not significantly different at the 5% level according
to the Duncan's Multiple Range Test.
about 5.5 and 7.0, representing poor and good manage-
ment, respectively. We rototilled B.P. digested sludge
into either the surface 15 or 60 cm of the filled area.
In 1972, we grew corn, fescue, and chard, while only
fescue was grown in subsequent years. All plots were
fertilized with P and K as needed, while the control was
also fertilized with N. Table 6 shows the application rates
and mixing depths for each treatment.The higher sludge
rates provided adequate N for the fescue even during the
fourth year (1975). Table 6 shows the Zn, Cd, and Cu
contents of fescue forage sampled 3.5 years after the
plots were established (May, 1975). The Zn and Cd con-
tent increased as application rate increased at both
pH's, while Cu content increased little after the lowest
sludge rate. The Zn, Cd, and Cu uptake decreased at the
higher soil pH; however, Zn uptake decreased more than
for either Cd or Cu.
TABLE6
Heavy Metal Content of Tall Fescue Sampled in
May, 1975Growingon an Urban Fill Soil Amended with
Sludge to 15 and 60 cm Depths in October, 1971
Sludge
Rate Depth
Mt/ha cm
0 60
90 60
180 60
270 60
360 60
0 15
135 15
I*
13
25
32
42
49
15
50
Zn
NL **
u g/g
27
64
75
144
138
16
97
Cd_
L NL
dry forage
0.24 0.91
0.83 1.23
1.15 1.48
1.04 1.58
0.91 1.68
0.20 0.45
1.56 1.27
Cu_
L NL
3.7 7.3
7.2 9.8
7.4 10.3
8.2 13.0
8.5 12.0
3.4 4.1
7.5 10.3
** ML not limed, at about 5.5 pH.
Major differences in crop uptake of these metals were
found in 1972. For example, at alow pH a plot which had
received 360 Mt/ha of sludge to a 60 cm depth, produced
chard with 1800 ppm Zn, corn 400 ppm Zn, and fescue
only 100 ppm Zn. This study does not indicate rapid re-
version of metals to forms unavailable to plants. The fes-
cue Cd levels considerably increased (three to four fold
at the low pH), although values were within the observed
ranges for normal forage materials.
Com and Soybean Plots, 1972
In May, 1972, Blue Plains anaerobically digested
sludge cake was applied at 0, 56, 112, and 224 dry Mt/ha
to plots of Sassafras silt loam in a cooperative study with
the University of Maryland Department of Agronomy.
Plots were split to compare sludge with sludge plus
recommended P and K fertilizer applications. The con-
trol-fertilized corn plot also received recommended N
fertilizer rates. Both corn (Pioneer 3369A) and soybean
(Kent) were grown each year.
Tables 7 and 8 show the heavy metal contents of corn
ear leaves and soybean leaves grown in 1974 on Sassa-
fras silt loam amended with sludge in 1972. The Zn and
Cd contents of crops grown on sludge amended soil in-
creased as application rates increased. Although Zn and
Cu contents did not reach phytotoxic levels, they were
considerably higher than the controls (Zn in corn ear
leaves increased ten-fold). Sludge amended soils in
humid areas may soon decrease to levels at which metals
are more available to plants (Tables 5 and 6).
Our corn and soybean results differed greatly from
those of Hinesly, Jones, et. al. q-n, and Bingham, et.
-------
172 PLANT UPTAKE OF HEAVY METALS
TABLE?
Heavy Metal Content of Corn Ear Leaves Grown in 1974 on Sassafras Silt Loam Amended with Sludge in 1972
Soil Treatment
Sludge
Mt/ha
0
0
56
56
112
112
224
224
Pert. Soil
pH
5.54
** 5.15
5.33
+ 5.35
5.28
+ 5.29
5.25
+ 5.26
Zn
a* 20
b 36
ab 79
ab 70
b 165
b 135
b 247
b 210
f
ef
d
de
c
c
a
b
Cd
0.
0.
1.
1.
3.
2.
3.
3.
g/g
34e
68e
93 d
82 d
19 be
73 c
83 a
62 ab
Cu
dry
4.4
8.1
8.0
7.9
8.1
7.5
8.6
8.5
leaves
c
ab
ab
ab
ab
b
a
ab
Ni
0.48
0.40
0.35
0.40
0.42
0.65
0.56
0.34
abc
be
c
be
be
a
ab
c
Pb
5.7 b
6.8 a
6.4 ab
6.2 ab
4.6 c
4.6 c
4.1 c
4.0 c
Mn
26 d
67 ab
41 cd
43 c
63 ab
61 b
76 ab
79 a
V Within-column, values followed by the same letter are not significantly
different at the 5% level as according'to the Duncan's Multiple Range Test.
* Plots received N-Pe05 - K20 treatment of 180 - 90 - 90 kg/ha
+ Plots received H-?z^5 - K20 treatment of 0 - 90 - 90 kg/ha
TABLES
Heavy Metal Content of Soybean Leaves Grown in 1974 on Sassafras Silt Loam Amended with Sludge in 1972
Soil Treatment
sludge Pert.
Mt/ha
0
0
56
56
112
112
224
224
5
** 5
5
** 5
5
** 5
5
** 5
Soil
PH
.86 a*
.74 a
.43 b
.43 b
.42 b
.42 b
.38 b
.41 b
Zn
22 c
32 c
95 b
98 b
114 b
114 b
151 a
142 a
Cd
0.13 c
0.29 b
0.35 ab
0.31 b
0.42 ab
0.37 ab
0.51 a
0.43 ab
Cu
u g/g
6.4
8.2
10.1
10.1
11.0
10.9
11.6
11.3
Ni Pb
dry leaves
d
c
b
b
ab
ab
a
a
1.6 b
2.1 b
3.3 a
3.1 b
3.4 a
3.7 a
3.5 a
3.9 a
3.5
3.3
3.4
3.1
3.8
3.3
3.4
3.0
Mn
b 52
ab 57
ab 47
b 46
a 47
ab 43
ab 54
b 58
be
ab
be
be
be
c
be
a
Fe
92 ab
97 a
92 ab
89 abc
94 ab
84 c
86 abc
79 c
*_/Within-column, values followed by the same letter are not
significantly different at the 5% level according to the D
Duncan's Multiple Range Test.
** Plots received N - P205 - K20 treatment of 0 - 90 - 90 kg/ha
-------
PLANT UPTAKE OF HEAVY METALS
173
al. l2 We found lower Cd levels in soybean than corn,
while they found higher Cd levels in soybean than in
corn. Perhaps these differences resulted from Cd/Zn ra-
tios in the soil, and its effect on plant Cd uptake. Further,
plant foliar Cd/Zn could have affected the transport of
Cd into grains, and the varieties grown could have dif-
fered in Cd uptake.
Crops have shown considerable yield increases due to
sludge application, although for the first year yield in-
creases were not as great at the higher sludge rates be-
cause of "initial toxicity" from salts, ammonia, etc.
In these recently established field plot studies, we
have observed that agricultural use of sludge, even from
cities without industrial sources of heavy metal, in-
creased crop Cd levels compared with those grown at the
same pH on the same soil without sludge. Although
others generally confirm these results 13, regional dif-
ferences may exist, because of different Cd sources in
individual sludges, and differences in soil chemical
properties, especially soil pH (L.M. Walsh, personal
communications).
Old-Sludge Application Site Studies
Another method to assess the effects of land applica-
tion of sludge on increases in crop metal contents is to
test fields which have received large sludge applications
over the years. Both crops and soils in these treated
areas can be sampled, analyzed, compared with data
from adjacent untreated fields to estimate any changes
from the long-term use of sludge. The alternative is to
study newly established plots for many years.
The long-term sludge plots at Woburn, England, were
lost by intermixing because they were small and plowed
with a moldboard plow; their earlier results were not
readily interpretable and Cd levels were not
measured 14. The 15-year-old, low-rate (seven Mt/ha
sludge every second year) plots of Andersson and Nils-
son 1S showed significantly higher Zn, Cu, and Ni, but
only slightly higher or unchanged Cd, Pb, Hg, Se, Co,
Cr, or Mo in rape fodder. Johnson, et. al.16 reported that
the Werribee sewage farm of Melbourne, Australia, had
higher Zn levels but not Cd levels in perennial grasses.
Pasture grasses were analyzed by Chancy, et. al.17
from a 24-year-old sludge-utilization farm at Hagers-
town, Maryland (Table 9). Pasture grasses were
sampled from control, recently sludged, and previously
sludged plots of Hagerstown silt loam. Sludge increased
foliar Zn levels, but not Cd levels; Cu and Pb levels in-
creased because of foliar contamination by appplied
sludge. The sludge applied at Hagerstown was relatively
low in metals, well within the domestic 15 sludge cate-
gory. (Domestic sludge as defined by Chaney 2, contains
less than 2000 mgZn, lOOOmgCu, 200 mg Ni, ISmgCd,
1000 mg Pb, 10 mg Hg, and 1000 mg Cr/kg dry sludge,
with Cd less than or equal to one percent of the Zn con-
tent.) Since soil pH had decreased to below 5.5 in several
areas, proper pH management would probably have in-
TABLE9
Heavy Metal Content of Pasture Grasses in Unsludged,
Recently Sludged, and Previously Sludged Fields of
Hagerstown Silt Loam
Metal
Mean
Range
-"g/g-
Tilled Field Area ( previously sludged)
Zn 33.6 16.9 61.0
Cu 8.9 6.9 - 21.0
Cd 0.24 0.10 0.41
Pb 1.4 0.4 - 3.3
Until led Field Area (recently sludged)
Zn 74.0 18.0 -134.0
Cu 17.0 7.0 33.0
Cd 0.35 0.1 0.7
Pb 1.9 0.4 7.5
Control Field Areas (unsludged)
Zn 24.0 14.0 32.0
Cu 8.3 3.5 - 10.2
Cd 0.32 0.14 0.4
Pb 1.3 0.4 3.1
creased pasture yields and decreased the metal contents
of the grasses. Some pasture samples contained suffi-
cient Cu ( >30 ppm) to possibly injure ruminant animals.
Again, this probably resulted from surface contamina-
tion of the standing grasses from liquid sludge
applications. Studies are in progress to measure the ex-
tent of foliar contamination by applying liquid sludge to
recently clipped and standing grasses, and to see
whether sludge adhering to forages is washed off by
rain.
Based on our Hagerstown results, we decided to
locate old sludged sites representing a range of soil
types and/or sludge metal additions (particularly Cd),
and to crop them with chard, soybean, and orchard-
grass. We sampled and analyzed over 25 locations.
Table 10 shows the metal contents of sludges from some
of these locations where sludge is now being applied to
agricultural land in the Northeast. Neither Federal nor
state governments yet regulate land disposal of these
sludges. The Cd level varied from 0.6 ppm in a sludge in-
fluenced by food processing wastes to over 1000 ppm in a
sludge influenced by a metal-plating industry. Many
sludges had lessthan 15 ppm Cd and Cd/Zn less than or
equal to one percent, but most were high in either one or
several metals. Very few of these sludges had ever been
analyzed for metals or nutrients. Most fields that had
sludge applied for many years ranged from pH 5.3 to 5.8,
levels conducive to plant uptake of sludge applied
metals.
TABLE 10
Heavy Metal Contents of Digested Sewage
Sludges Used on Agricultural Land in the Northeast
City
20
18
19
12
15
9
13
22
Zn
230
870
1390
870
2380
5180
5800
1520
Cd
mg/kq dry sludge
0.6
7.0
6.1
5.9
11.1
168.0
716.0
1230.0
Cu
2600
690
570
800
680
1450
1560
1160
Ni
41
37
22
36
35
1140
590
100
Cd/Zn
%
0.26
0.80
0.44
0.68
0.47
3.30
12.30
81 .00
-------
174 PLANT UPTAKE OF HEAVY METALS
Basic Research on Cd Uptake by Plants
Cd enrichment of crops from ultimate disposal of
sludge on agricultural land is one of the primary con-
cerns governing sludge use. (See Braude, et. al. 18 in
these proceedings.) Haghiri19 reported that, at the
same soil pH, that as soil cation exchange capacity in-
creased, Cd uptake by oats decreased. He also found
that low Zn additions increased soybean Cd uptake,
while higher Zn additions reduced Cd uptake (Figure 1).
Higher soil temperature increased plant uptake of Cd. In
a greenhouse study, Cunningham, Ryan, and
Keeney 20, found that as soil Cu levels increased at con-
stant Zn and Cd levels, Cd uptake by corn and rye in-
creased. Bingham, et. al.12 showed that crops differed
markedly in their accumulation of Cd and that graphs of
increasing plant Cd vs. added soil Cd could have increas-
ing or decreasing slopes, or be even sigmoidal.
10.0
t.o
4.0
5
~ J.O
0.0
IQppm Cd iddcd In «ich lr«itm«nl
1000
0 10 100
ZINC ADDIO TO SOIL - LOG SCALE
Figure 1 : The Effects of Zn Addition and Soil Temperature on Cd Con-
tent of Soybean Tops Grown on Soil (pH 6.5) Amended with Ten PPM
Cd19.
We grew "Beeson" soybeans in a pot study to
examine the influence of soil pH on Zn phytoxicity and
Zn, Cd, Mn, and Fe uptake. Sassafras sandy loam soil
was amended with Zn (plus Cd at three percent of the
added Zn) at 0,65, 131, 262, 393, and 524 ppm Zn. Each
pot contained two kg of soil. N, P, K, Mg, Zn, Cu, B, and
Mo fertilizers were added at 200, 400, 226, 100, 1.31,
0.64, 0.5, and 0.094 nig/kg, respectively, which are high
fertility levels appropriate for pot experiments with
heavy metals. The soil pH was adjusted from 5.5 to 7.0
using CaCC>3; at higher Zn levels the low pH values were
omitted because of almost certain phytotoxicity. Three
plants per pot were grown for four weeks in a growth
chamber. At harvest the plants were separated into
roots, stems plus petioles, primary leaves, and trifoliate
leaves. Yield, and Zn, Cd, Mn, and Fe content of these
tissues were determined. The DTPA-TEA and 0.01 M
CaCl2 extractable Zn, Cd, and Mn and soil pH were
measured at the start and end of the four week growth
period.
No pronounced yield reduction or visual symptom was
observed at up to 131 ppm Zn. At lower pH levels and
262 ppm Zn, a severe interveinal chlorosis was observed
(Figure 2). When the soil pH was above 6.0 the symptom
and yield reduction disappeared. At high soil Zn concen-
trations, progressively higher pH levels were required to
reach normal yields, until, at 524 ppm Zn, increasing the
soil pH no longer alleviated Zn phytotoxicity. While the
Zn-induced chlorosis symptom resembles interveinal
chlorosis caused by Fe deficiency, the Fe in the trifoliate
leaves did not fall below 40 ppm. We have observed Zn
induced chlorosis in other studies and we think it is a
general symptom of Zn toxicity below 6.2 pH.
Boawn 21'22 from his studies at pH 6.5-7.5, has
suggested that Zn does not cause chlorosis but it is clear
from Figure 2 that Zn can causechlorosisatlowersoilpH.
|isr '*%
,
»
?- &h ;?
Figure 2: The Effect of Soil pH on Soybean Growth in a Sassafras Sandy
Loam Containing 0, 262, or 524 mgZn/kg. (Soil pH is Indicated on the
Pots.)
Figure 3 shows the influence of soil pH on the extract-
ability of soil Zn by DTPA-TEA and 0.01 M CaCl2 at the
end of the growth trial. Each plot was generated by 12 to
24 pH levels. Cd extractability was similarly affected by
soil pH. The extractable Zn decreased smoothly as the
pH increased, with no abrupt decrease in extractable Zn
at the critical pH range at which yield reduction or
chlorosis were alleviated.
Figure 4 shows the effect of soil pH on trifoliate leaf
yield of soybean, and their Zn and Cd content when
plants were grown at 262 mg Zn/kg soil (photograph in
Figure 2). The leaf content of Zn and Cd decreased as
soil Ph increased. Again, there was no abrupt change at
the pH at which yield reduction and chlorosis were
alleviated.
Figures 5 and 6 show linear regression plots and coef-
ficients of determination (r2)forthe Zn and Cd contents,
respectively, or trifoliate leaves. At lower soil Zn addi-
tions, where phytotoxicity is not severe, Zn in leaves is
correlated highly with soil pH, whereas at higher soil Zn
levels the leaf Zn correlations were not as high (Figure
5). Perhaps the Zn phytotoxicity becomes so severe that.
-------
PLANT UPTAKE OF HEAVY METALS 175
250
m «00
J
5 150
< 100
50
oi—
J 80
60
40
X
vr'z.i*
3*3
6.2
6.6
7.0
pH
Figure 3: The Effect of Soil pH on DTPA-TEA and 0.01 M CaCl2 Ex-
tractable Zn in Sassafras Sandy Loam Amended with 131 and 393 mg
Zn/kg.
above a certain foliar Zn content, Zn is no longer ab-
sorbed or translocated in proportion to available soil Zn.
Because Cd phytotoxicity was not the limiting factor in
plant growth, Cdtranslocation continued in proportion to
available soil Cd (Figure 6). This led to the Cd/Zn rates
shown in Figure 7: where no phytotoxicity was observed,
foliar Cd and Zn were similarly influenced by increased
soil pH; however, when Zn phytotoxicity was experi-
enced, foliar Zn was limited by the soybean plants'
natural mechanisms which limit translocation of Zn
to no more than 400 to 700 mg/kg trifoliate leaves.
Hence, Cd/Zn ratios increased when the applied Zn
(plus three percent Cd of Zn) increased to phytotoxic
levels (Figure 7).
Plant Cd uptake is extremely complex. It has been
shown that at the same soil Cd level soil pH, C.E.C., Zn,
Cu, etc., and temperature, and plant species, variety,
age, and part (grain vs. leaves) all affect the Cd content
of edible plant parts. We believe that by restricting
sludge use on cropland to only those sludges with Cd
less than or equal to one percent of their Zn content, the
food chain will be adequately protected from sludge-
borne Cd.
700
400
500
1 400
a.
v
5 30°
4
m 100
o
- 100
*6!ni|/K( SOIL ZINC
-,,30
o
h- '•
5.1 6.1
7.0
1.*
1.1
1.0
O.I
0.4
0.1
0.0
Figure 4: The Effect of Soil pH on Trifoliate Leaf Yield and Zn and Cd
Contents of Soybean Grown in a Sassafras Sandy Loam Containing 262
mg Added Zn/kg.
This, plus a maximum Zn (equivalent) application
equal to ten percent of the soil C.E.C. and mandatory
initial adjustment of soil pH to 6.5 or higher, will control
the increase in crop Cd resulting from sludge use on
land. Certainly, no one has yet established an acceptable
basis for applying high Cd and high Cd/Zn ratio sludges
on agricultural land.
Abatement of Metals at Source to Ensure Safe Sludges
The Environmental Protection Agency advises cities
to enforce abatement of metal release to the sewer to
protect surface waters and to obtain sludges low in
metals to protect: (1) ocean organisms, during ocean dis-
posal of sludge, (2) groundwater, during sanitary landfill
disposal of sludge, and (3) air, during incineration of
sludge, and groundwater, during disposal of incinerator
ash in sanitary landfills. When sludges are applied to
land, the metals remain in the topsoil. In order to main-
tain soil fertility, sludge metals should be minimized,
and the maximum amounts of metals which may be ap-
plied should be limited tonon-phytotoxiclevels. Chaney2
and Stewart and Chaney23 have discussed the need to
make the benefits to the farmer and society from sludge
use on land worth the risk. Most will agree that if crops
are to be grown, a soil should not be amended with more
than some maximum Zn, Cu, and Ni levels, based on
that soil's properties, e.g., Zn (equivalent) less than or
equal to ten percent of C.E.C. or some other maximum.
-------
176 PLANT UPTAKE OF HEAVY METALS
700
600
5OO
1 400
i
- 300
^
<
^
m 200
^
«
= 100
S-..II
• . i . i . i . i . i
5.8 6.2 6.6 7.0
Figure 5: The Effect of Soil pH on Soybean Trifoliate Leaf Zn Content at
Several Zn Levels. Zn Added (mg/kg) Is Indicated on Figure.
10
o 10
•Ml
$.*
S.O
4.1
4.4
7.0
Figure 6: The Effect of Soil pH on Soybean Trifoliate Leaf Cd at Several
Zn and Cd Levels. Zn Added (mg/kg) Is Indicated on Figure. Soil Cd
Levels Were 2,0, 3.9, and 11.8 mg/kg.
Thus, farmers will not accept high metal sludges which
would supply much less N and P than domestic sludges
at the same maximum metal application.
To protect the food chain from excessive Cd uptake by
plants, Chancy2 has recommended that only sludges
with Cd less than or equal to one percent of Zn should be
.060
.050
.040
.030
.020
.010
oL-ll-
7.O
Figure 7: The Effect of Soil pH on Soybean Trifoliate Leaf Cd/Zn Ratios
at Several Levels of Added Zn and Cd. Zn Added (mg/kg) Is Indicated
on Figure.
allowed on agricultural land. Although high soil pH
could be used to limit Cd uptake, there is no guarantee
that sludged fields will always be limed. Yield reduction
from metal toxicity can be recognized and lime applied
the following crop year. However, even this crop should
have Cd levels safe for the food chain, or an unaccept-
able, invisible, risk is being taken. Because Cd less than
or equal to one percent of Zn characterizes sludges not
impacted by abateable Cd, and this recommendation
would lead to a maximum of abut five ppm Cd in plant
leaves when phytotoxicity is caused by Zn and the other
sludge metals (worst case). Chancy2 has argued that
sludges with Cd less than or equal to one percent of Zn
are acceptable for use on land. Under the best manage-
ment (pH>6.5) the Cd contents of crop leaves would be
considerably lower than 5 ppm at maximum sludge
application [Zn (eq.) = ten percent of C.E.C.].
Abatement technology is already available. Lime pre-
cipitation 24'25 . ion exchange, reverse osmosis 26,
liquid-liquid extraction, evaporation, and adsorption on
activated carbon, shredded tires27, peat28, shredded
bark, lignite, starch xanthate 29, and many other ma-
terials can lower wastewater Cd to very low levels. In
some instances, waste metal recovery has resulted in net
savings! The abatement of Cd can be made more by fol-
lowing lime precipitation with filtration through a bed of
common peat, Cd abatement can be more nearly fail-
safe. Cd Values below drinking water standards can be
reached with minimum effort and expense.
Cd is a common contaminant of Zn wherever Zn occurs
or is used. Most of the Cd is recovered from the Zn dur-
ing ore processing, and nearly all Zn sold in the United
States contains<0.015 percent Cd of Zn 30. Thus, indus-
trial use of Zn is not the source of the Cd which becomes
-------
PLANT UPTAKE OF HEAVY METALS
177
a problem if it reaches sludges. Nor is the problem Cd
with the Zn in tires in street runoff. Rather, it is the spe-
cific use of Cd. Cd pollution can be identified and its
abatement enforced. We have analyzed many domestic
sludges withCd/Zn ratios at or below 0.80 percent (e.g.,
Table 10).
Our findings that many cities have sludges with Cd
less than or equal to one pecent of Zn without known Cd
sources and the report of Klein, et. al.-51 on sewage-
borne metals in New York City conflict which points out
the need for objective studies of the Cd sources in urban
areas.
Although sludge can be a valuable resource for agri-
culture, and its land disposal can save cities much money
and fuel, each of these benefits is contingent on ade-
quate control of metal release to the sewer and reliable
sludge-monitoring programs.
ACKNOWLEDGEMENT
We gratefully acknowledge the cooperation of person-
nel of the Biological Waste Management and Soil Nitro-
gen Laboratory, the University of Maryland, the Mary-.
land Environmental Service, and the District of Colum-
bia Department of Environmental Services: E. Epstein,
J.M. Walker, J.D. Menzies, J.F Parr, A.M. Decker,
D.S. Fanning, E. Levesque, J.C. Baxter, M.C. Morella,
D.C. Mullen, and T. Lathan.
REFERENCES
1. Chaney, R.L., "Crop and Food Chain Effects of
Toxic Elements in Sludges and Effluents," Recycling
Municipal Sludges and Effluents on Land, Nat. Assoc.
St. Univ. and Land-Grant Coll., Washington, D.C., pp.
129-141, 1973.
2. Chaney, R.L., "Recommendations for Manage-
ment of Potentially Toxic Elements in Agricultural and
Municipal Wastes," Factors Involved in Land Applica-
tion of Agricultural and Municipal Wastes, USDA Na-
tional Program Staff, Soil, Water, and Air Sciences,
Beltsville, Md., pp. 97-120, 1974.
3. Chaney, R.L. and P.M. Giordano, "Microelements
as Related to Plant Deficiencies and Toxicities," Soils
/or Management and Utilization of Organic Wastes and
Wastes and. Wastewaters, L.F. Elliott and F.J. Steven-
son (eds.), Soil Sci. Soc. Amer., Inc., Madison, Wise. In
press.
4. Webber, J., "Effects of Toxic Metals in Sewage on
Crops," Water Poll. Contr. Fed. 71(1972), 404-413.
5. Page, A.L., "Fate and Effects of Trace Elements in
Sewa°e Sludge When Applied to Agricultural Lands," A
literature review study, U.S. Environ. Prot. Agency
Rcpt. No. EPA-670/2-74-005 1974.
6. Epstein, E. and G.B. Willson, "Composting Sew-
age Sludge," Proc. National Conf. on Municipal Sludge
Management, Information Transfer Inc., Rockville,
Md., 1974, 133-138.
7. Simon, P.W., R.L. Chaney, and E. Epstein,
"Heavy Metal Contents of Selected Vegetable Crops
Grown on Sewage Sludge and Composted Sewage
Sludge Amended Soil at Two pH's," Agron. Abstr.
1974, 39.
8. J.M. Walker, "Sludge Disposal Studies at Belts-
ville," Proc. Conf. Land Disposal of Municipal Effluents
and Sludges. EPA-902/9-73-001. pp. 101-116, 1973.
9. Hinesly, T.D., O.C. Braids, R.I. Dick, R.L. Jones,
and J-A.E. Molina. "Agricultural Benefits and Environ-
mental Changes Resulting From the Use of Digested
Sludge on Field Crops," Report to EPA on Grant No.
D01-UI-00080. 1972.
10. Hinesly, T.D., R.L. Jones, and E.L. Ziegler, "Ef-
fects on Corn by Applications of Heater Anaerobically
Digested Sludge," Compost Sci., 13 (1972), 26-30.
11. Jones, R.L., T.D. Hinesly, and E.L. Ziegler,
"Cadmium Content of Soybeans Grown in Sewage
Sludge Amended Soil," J. Environ. Qual., 2 (1973),
351-353.
12. Bingham, F.T., A.L. Page, R.J. Mahler, and T.J.
Ganje, "Growth and Cadmium Accumulation of Plants
Grown on a Soil Treated with a Cadmium-Enriched Sew-
age Sludge," J. Environ. Qual. 4 (1975), 207-211.
13. Dowdy, R.H. and W.E. Larson, "The Availability
of Sludge-Borne Metals to Various Vegetable Crops," J.
Environ. Qual. 4 (1975), 278-282.
14. LeRiche, H.H., "Metal Contamination of Soil
in the Woburn Market-Garden Experiment Resulting
from the Application of Sewage Sludge," J. Agr. Sci., 71
(1968), 205-208.
15. Andersson, A. and K.O. Nilsson, "Enrichment of
Trace Elements from Sewage Sludge Fertilizer in Soils
and Plants," Ambio., 1 (1972), 176-179.
16. Johnson, R.D., R.L. Jones, T.D. Hinesly, and D.J.
David, Selected Chemical Characteristics of Soils, For-
ages, and Drainage Water from the Sewage Farm Serv-
ing Melbourne, Australia. Department of the Army,
Corps of Engineers, 1974.
17. Chaney, R.L., J.C. Baxter, D.S. Fanning, and
P.W. Simon, "Heavy Metal Relationships on a Sewage
Sludge Utilization Farm at Hagerstown, Maryland,"
Agron. Abstr. 1974: 24-25.
18. Braude, G.L., C.F. Jelinek, and P Corneliussen,
FDA 's Oven'iew of the Potential Health Hazards Asso-
ciated with the Land Application oj'Municipal Wastewa-
ter Sludges, 1975.
19. Haghiri, F., "Plant Uptake of Cadmium as Influ-
enced by Cation Exchange Capacity, Organic Matter,
Zinc, and Soil Temperature, ' J. Environ. Qual., 3
(1974), 180-183.
20. Cunningham, J.D., 1974. The Phytotoxic Effects
of Heavy Metals in Sewage Sludge. M.S. Thesis, Uni-
versity of Wisconsin, 1974.
21. Boawn, L.G., Zinc Accumulation Characteristics
of Some Leafy Vegetables. Commun. Soil Sci. Plant
Anal. 2 (1971), 31-36.
-------
178 PLANT UPTAKE OF HEAVY METALS
22. Boawn, L.C. and P.E. Rasmussen, "Crop Re-
sponse to Excessive Zinc Fertilization of Alkaline Soil,"
Agron. J. 63 (1971), 874-76.
23. Stewart, B.A. and R.L. Chaney, "Wastes: Use or
Discard, Proc. Soil Conscrv. Soc. Amer., In press.
24. Anonymous, "Reclaiming Zinc from an Industrial
Waste Stream," Environ. Sci. Techno/., 6 (1972),
880-881.
25. Rock, D.M., "Hydroxide Precipitation and Re-
covery of Certain Metallic Ions from Wastewaters,"
Chem. Eng. Prog. Symp. Ser. 67, 107, 442-444.
26. Golomb, A., "Application of Reverse Osmosis to
Electroplating Waste Treatment," Part HI—Pilot Plant
Stuclv and Economic Evaluation of Nickel Recovery, 60
(1973), 482-486.
27. Netzer, A., P. Wilkinson, and S. Beszedits, "Re-
moval of Trace Metals from Wastewater by Treatment
with Lime and Discarded Automotive Tires," Water
Res.. 8 (1974) 813-817.
28. Leslie, M.E., "Peat: New Medium for Treating
Dye House Effluent," Amer. Dyestujf Reporter, 63 (8)
(1974), 15-18.
29. Wing, R.E., C.L. Swanson, W.M. Doan, and C.R.
Russell, "Heavy Metal Removal with Starch Xanthate-
Cationic Polymer Complex," J. Water Pollut. Contr.
Fed. 46 (1974), 2043-2047.
30. Fulkcrson, W. and H.E. Goeller (eds), Cadmium,
The Dissipated Element, ORNL Rept. No. ORNL-NSF-
EP-21. Oak Ridge National Laboratory, Oak Ridge,
Tcnn., 1973.
31. Klein, L.A., M. Lang, N. Nash, and S.L. Kirsch-
ncr, "Sources of Metals in New York City Wastewater,"
,/. Water Pollut. Contr. Fed., 46(1974), 2653-2662.
-------
EFFECTS OF SEWAGE SLUDGE OR EFFLUENT
APPLICATION TO SOIL ON THE MOVEMENT OF
NITROGEN, PHOSPHORUS, SOLUBLE SALTS AND
TRACE ELEMENTS TO GROUND WATERS
A.L. Page and P.P. Pratt
Department of Soil Science and Agricultural Engineering
University of California
Riverside, California
INTRODUCTION
The downward movement of constituents or decompo-
sition products of organic materials and of reclaimed
wastewaters applied to land surfaces is an important fac-
tor in groundwater quality. The effect on groundwater
quality depends on many parameters including: (1) the
nature of the material, (2) its rate of application, (3) man-
agement of the land surface, (4) the properties of the soil
and the underlying sediments or geological materials,
(5) the depth to the saturated zone, (6) the amount of
water in the aquifer or aquifers and the recharge rate,
and (7) degrees of mixing in the saturated zone. The
movement of constituents to the groundwater is of con-
cern in all waste utilization and disposal projects, but is
most critical where groundwaters are the major or only
source of water for municipal supplies.
When considering the movement of nitrogen, pri-
marily as nitrate, soluble salts, phosphorus and trace
elements through soils, one must distinguish between
low rates consistent with utilization for crop production
and high rates that might be used for disposal of sludges
and effluents or for groundwater recharge using re-
claimed waters. At low rates of three to five tons dry
solids per acre per year to supply the phosphorus needs
of crops or 10 to 25 dry tons per acre per year to supply
their nitrogen needs most soils, excluding inert sands,
have sufficiently large capacities to retain phosphorus
and most trace elements that downward movement of
these constituents is nil or very slow. At rates of three to
five surface feet of effluent waters per year to supply
water needs for irrigated lands or at lower rates for sup-
plemental irrigation in humid regions, phosphorus and
trace elements added will not move downward to any
great extent in most soils. Of course, soluble salts and
nitrate will move with drainage waters. At high rates of
sludges or effluents adsorptive capacities of soils and
sediments can be saturated so that general statements
pertaining to low rate systems can not be applied.
In addition to rate of application the nature of the soil
is an extremely important factor in downward movement
of constituents. Inert sands and gravels of low organic
matter contents have low adsorptive capacities and allow
rapid transmission of water whereas the greater the
amount of colloidal materials (clays and organic matter)
the greater the adsorptive capacity for phosphorus and
trace elements. Also, generally, the higher the clay con-
tent the slower the water will move. Reactions of consti-
tuents with the soil increase with increase in adsorptive
capacity and with decrease in rate of movement.
This paper discusses the movement of nitrogen, solu-
ble salts , phosphorus and trace elements through soils in
terms of the chemistry of these individual constituents
and in relation to low and high rate applications of
sludges and effluents and soil properties.
Nitrogen
Nitrogen occurs in muinicipal sewage treatment plant
sludges and effluents in organic and inorganic forms.
The concentration of nitrogen (N) in effluents normally
does not exceed 50 mg N/l, of which approximately 85 to
90 percent is in the form of ammonium, 10 to 15 percent
is combined with organic matter, and a small percentage
occurs as nitrate1. The concentrations of N in liquid
sludge varies and depends largely upon percent solids
and the type of treatment plant. On a dry weight basis,
sludge commonly contains from one to seven percent
nitrogen2. Liquid sewage sludges containing about five
percent solids commonly contain from 1500-2500 mg
N/l3
The fraction of total N applied in sludges or effluents
which may move to underground water supplies de-
pends upon amounts removed by plants and lost through
denitrification or ammonia volatilization. The fate of N
once it is applied to soil regardless of the source is gov-
erned largely by the following reactions (somewhat
simplified):
Plant Uptake Plant Uptake
Organic
\
leachir
Volatilization "2
179
-------
180 MOVEMENT OF ELEMENTS TO GROUND WATER
The oxidation of NH 4 is a microbial process which pro-
ceeds in soil except at extremes in pH «PH4.5 and>pH
9), dissolved02 «0.2 mg/1) and temperature (<5 C and
>40 C). The mineralization of organic N to form NH 4
proceeds over a wider range of pH and temperature than
does the transformation of NH 4 to NO"^".Hence, min-
eralization of organic N is not rate limiting in the overall
process.
Below pH 4.5, high percentages of inorganic N occur
in soils as NH 4 . The NH 4 ion is adsorbed in part by
negatively charged surfaces of soil colloids and, as such,
its movement is restricted. In soils leaching of NH4—N
and organic N from the root zone is commonly ignored
since amounts leached are usually small compared to
amounts of NO-}—N leached. At soil pH's greater than
nine, sufficient NH-} forms to inhibit its oxidation to
N0~j" and nitrogen can be lost from the system as NH-}
gas. In the pH range four to nine, under conditions
where the dissolved C^ exceeds 0.2 mg/1, the NH 4
formed by the mineralization of organic N is oxidized to
N0~^~. Nitrate is quite mobile in soil and that which es-
capes the rooting zone of plants will move with water to
lower depths in the soil profile. In soil where regions of
low dissolved 02 may occur at depths within or below the
rooting zone, NO~J in the water may be denitrified if the
water contains sufficient organic C or reduced forms of
S. About one milligram of organic carbon is required for
each milligram of nitrate nitrogen to be denitrified
(Bower and Chaney).
Once NO-j—N escapes zones in soil where it is re-
moved by plants or denitrified, its movement in soil
parallels quite closely the movement of water. Ground-
water recharge systems using secondary treated efflu-
ent have been designed to minimize the amount of
NO-}—N which escapes the zone in soil where it is either
removed by plants or denitrified 4- 5 . The systems in-
volve cyclic flooding and drying (anaerobic and aerobic)
periods. The aerobic cycle isrequiredtoconvert NH4—N
to NO-}—N and the anaerobic cycle for the denitrification
of NO^—N. During flooding NH4—N is adsorbed on the
surfaces of soil particles. When the soil is permitted to
dry, oxygen enters the soil profile and the NH4—N is ox-
idized to N0~}~. During the next flooding period, anaero-
bic conditions develop and the NO-}—N is denitrified to
N2 gas. The Flushing Meadows project6 reported in a
ten day flooding period followed by a 10-20 day drying
period approximately 30 percent of the N was removed,
presumably by denitrification. Somewhat similar results
were obtained in the Whittier Narrows project7 when ten
day flooding periods followed by two week dry periods
were used.
Effluents or liquid sludges are placed in ponds or la-
goons for storage or dewatering by percolation into the
soil or evaporation. The purpose of these operations is
not necessarily groundwater recharge. There is no plant
cover and N loss is exclusively by either denitrification or
ammonia volatilization. Lund, et. al.8 have evaluated ni-
trogen leaching in soil profiles beneath effluent and
sludge lagoons at two locations in California. The soil
profiles at both locations were open and coarse textured
and conditions were quite conducive to rapid nitrifica-
tion and subsequent movement to lower depths. Con-
centrations of NO-}—N in the soil solution at a depth of
12m beneath sludge ponds which had been used for five
or more years were approximately 400 jug NO-}—N/ml.
This compared to a concentration of about 30 jig
NO-}—N/ml at an offsite location which had not re-
ceived sludge. The offsite control was an agriculture site
and the source of N0~^~ at the lower depths in this profile
was nitrogen fertilizers.
Soluble Salts
Concentrations of soluble salts in sewage treatment
plant effluents are usually 100-300 mg/1 greater than
those of the domestic water supply of the region in ques-
tion9. The percentage increase of soluble salts resulting
from wastewater treatment, therefore, depends largely
upon the quality of the domestic water supply.
When waters are applied to soils the changes in con-
centration of soluble salts which occur in the drainage
water depend upon the fraction of the water applied
which is consumed in evapotranspiration, the extent to
which the chemical constituents in the water applied
may precipitate in the soil or the extent of dissolution of
soluble materials in soil.
In groundwater recharge or wastewater disposal sys-
tems where volumes of water applied are large com-
pared to amounts consumed by plants via evapotranspi-
ration, the changes which occur in the composition will
be determined almost exclusively by the weathering of
soil minerals to produce soluble salts. This weathering
process may be enhanced by chemical transformation of
constituents in the water which produce acidity, since
the solubility of soil minerals increases as the pH of the
system decreases. With secondary sewage treatment
plant effluents, the main source of acidity arising from
biochemical reactions is the oxidations of NH 4 to NO"^".
In the process, two equivalents of hydrogen ion are pro-
duced for each equivalent of NH 4 oxidized. The extent
to which the protons generated react with soil minerals
to produce increases in soluble salt is variable. It de-
pends upon other reactions which consume protons but
do not increase soluble salts. In systems containing suf-
ficient concentrations of HCO~}~, for example, the pro-
tons produced may react to form carbonic acid or C©2
and water and the HCO~^~ ion is replaced by NO"^" ion
with no increase in dissolved salt. If, however, the pro-
tons generated react with CaQJ}, soluble calcium bicar-
bonate is produced and an increase in soluble salts re-
sults.
Field and laboratory studies have demonstrated that
effluents applied to soil which contain NH 4 produced
greater increases in soluble salts than did effluents
which contained comparable amounts of NO~T but no
NH 4 . Broadbent10 observed that input water contain-
-------
MOVEMENT OF ELEMENTS TO GROUNDWATER 181
ingNH jj" produced 64 to 128mg/l more soluble salts in
the drainage waters than did input waters containing an
equivalent concentration of NO~J. In a groundwater re-
charge project, McMichael and McKee, using the resi-
due at 100 C as a measure of total dissolved solids (TDS),
observed increases of 380 and 160 mg/1 TDS at eight
foot depths in two test basins. Bouwer, et. al. passed
large volumes (about 100 m) of effluent waters contain-
ing 20-40 meq NH 4/I through soil and sediment and
observed an increase in TDS of well waters of about two
percent.
When waters containing no NH 4 and low in dissolved
solids are percolated through soils weathering of soil
minerals occurs to produce soluble salts. In recent soils
(slightly weathered) of arid regions the weathering pro-
cess is sufficiently rapid to produce concentrations of
about 250 mg/1 TDS in the drainage waters''. Because
of the increment in TDS added in any one cycle of muni-
cipal use, most waters from secondary treatment plants
contain more than 250 mg/1 TDS even if the TDS of the
municipal supply is extremely low. Thus, in ground-
water recharge operations involving low NH 4 effluent,
unless soil materials and sediments have salts which are
residual from irrigated agriculture or geological pro-
cesses, the probability of substantial increases in TDS of
percolation water is slight.
In agricultural systems where effluent water is used as
a source of irrigation water, concentrations of dissolved
salts in the percolation water increase due to the con-
centrating effect of evapotranspiration. To maintain a
proper salt balance for the growth of plants, water in ex-
cess of that required by the plants must leach through
the root zone. The extent to which dissolved solids in-
crease by plant action depends upon irrigation manage-
ment. Rhoades, et. al12 has presented data which show
that minimizing the quantity of drainage water results in
the smallest possible return of applied salts in the return
flow. This occurs because by irrigating with the lowest
possible leaching fraction, maximum precipitation of
salts in the applied waters occurs, and the weathering of
soil minerals to produce salts is minimized.
Data from numerous sources show that NO~^j~, if not
lost by biological or chemical processes, will move with
water and is a source of N0~^~ contamination of ground-
water. The extent of groundwater contamination, how-
ever, cannot be assessed from concentrations which oc-
cur in soil solution. To evaluate total load of N per unit
time, the volume and rate of water movement through
the soil above the groundwater table needs to be known.
Transit Time
Free Drainage
The leaching of soluble salts, which consist mainly of
the anions NO-^, 504, Cl and HCOj and of the cations
Na, Ca, Mg, through soils is largely dependent on the
movement of water through the soil. That is, water
movement is so dominant that such factors as ion diffu-
sion, anion exclusion because of the negative charge on
clays or organic colloids and temporary trapping or by-
passing of salts in micropores or microsites can be ig-
nored for practical purposes.
In the situation where drainage water from the root
zone of croplands flows downward through a deep un-
saturated zone (where tile lines are not necessary to
maintain an aerated root zone), transit time for water
and salt to move to a given depth is directly proportional
to the water content of the soil material through which
the water is moving and inversely proportional to drain-
age volume. The simple relationship
T = se
7T
where T is the transit time in years, S is the soil depth in
cm, 9 is the volumetric water content and D is the drain-
age volume in surface cm, has been found useful in
studies of the leaching of NO~^ through the unsaturated
zone in coastal and inland areas of California13- 14' 15> 16.
The time for water and salts to move 30 m in these irri-
gated areas is usually 10 to 50 years. In the San Bernadi-
no-Redlands area, for example, fertilization of citrus
started about 1900 A.D., whereas NO~^~ started appear-
ing in wells about 1945 and the number of wells that con-
tained water with greater than 10 mg NO-j—N/l in-
creased as a function of time from 1945 through 1970. Ni-
trate in these well waters probably comes from various
sources but there is sufficient evidence that one of the
sources is fertilization of citrus. The time lag is of the
correct order of magnitude to be related to transit times
for water and salts to be moved through a deep unsatu-
rated zone.
When the drainage water from irrigated fields reaches
the saturated zone, it tends to mix very slowly with the
water already present and to stay in a surface layer that
moves in response to hydraulic pressures. The process
of mixing takes place mainly by changes in elevation of
the saturated zone in response to recharge or withdrawal
of water. For example, the drawn-down cone created
around a well that is being pumped promotes mixing of
the various layers of water.
In contrast to irrigated fields, the transit of water and
salts during groundwater recharge by surface spreading
on sandy or gravelly riverbed materials is very rapid. In
these cases, the volumes are in the order of magnitude of
100 to 200 surface feet of water per year in comparison to
one to two surface feet per year of drainage water from
irrigated lands.
The volume of drainage water from croplands cannot
be measured directly when this water moves through the
unsaturated zone and becomes groundwater. The tech-
nology of measuring water flux through the root zone is
not yet ready for application in a practical way to field
monitoring. Thus, for field studies, estimates of drain-
age water volume can only be obtained from the dif-
-------
182 MOVEMENT OF ELEMENTS TO GROUND WATER
ference between water inputs (infiltration) and evapo-
transpiration (ET). The problem with this approach is
that accurate measurements of ET are difficult to obtain
and, for a given field, runoff during rainfall events must
be measured directly.
In irrigation agriculture, the chloride balance has
been used to estimate drainage volumes from the equa-
tion:
Volume of drainage water_ Cl cone, in irrigation water
Volume of irrigation water Cl cone, in drainage water
In cases where significant amounts of chloride are added
in fertilizers or soil amendments such as organic materi-
als, or where harvested crops remove chloride, the con-
centration of chloride in the water can be adjusted for
these quantities.
Increasing irrigation efficiency in irrigated areas or in-
creasing the ET in humid areas will increase the transit
time for salts to move through the unsaturated zone. In
the case of irrigated agriculture, the mass emission of
salts in the drainage water can be decreased by decreas-
ing the drainage volume as a result of increases in on-
farm irrigation efficiency. Precipitation of carbonates
and silicates are increased by decreases in the drainage
volume. However, irrigation agriculture, for the most
part, cannot continue without some leaching. Thus, the
best that can be done to reduce movement to the ground-
water is to reduce mass emissions and increase the
transit time.
Tile Drainage
The transit time for water and soluble constituents to
move from the land surface into tile lines requires a two-
dimensional model whereas in a free-drainage situation
a one-dimensional model is sufficient. To get to the tile
line the water must move down, and, except in the small
area of land over the tile line, it must also move laterally.
The transit time is thus a variable depending on the dis-
tance from the tile line. Over the line the travel time
might be a few weeks or months depending on other fac-
tors. At the midpoint between two tile lines the time
might be many years.
Recent work by Jury17- '8 has developed a relatively
simple mathematical model dealing with transit times in
tile drainage systems. The variables are drain spacing,
depth of tile, depth of soil to an impermeable zone, soil
porosity and the volume of drainage water. The model
has been applied to a number of drainage systems with
considerable success. Actually the model predicts the
time for a certain fraction of the salt or nitrate from appli-
cations of irrigation water or nitrogen fertilizer to be re-
moved in the tile flow. For example, the time required
for a 50 percent removal can vary from one or two years
to 20 years or more depending on the soil, tile installa-
tion parameters and the volume of drainage water.
The model provides mathematical verification and
quantifies the concepts that response times to manage-
ment changes are long. The model also verifies that be-
cause of variable transit time, depending on distance
from the time line, the total response to changes in man-
agement of the land surface will occur over a period of
years. The systems are well-buffered because of the
amounts of materials in a continuum of transit times
from the tile line to the midpoint between tile lines. Be-
cause of this slow response there is a potential for
misinterpretation of the relationships between surface
management and outputs in tile effluents.
Phosphorus
Phosphorus concentrations of sewage treatment plant
effluents vary and commonly range from a few to 20 mg
P/liter19. On a dry weight basis, sewage sludges usually
contain from one to six percent phosphorus20. Large
quantities of phosphorus (P) are precipitated from sew-
age by lime, aluminum, or iron treatments and generally
effluents from sewage treatment plants which employ
these processes are lower than other conventional treat-
ment processes. Sludges, from treatment plants em-
ploying chemical precipitants (lime, aluminum or iron)
on the other hand commonly contain higher concentra-
tions of P than sludges from plants utilizing other types
of treatment processes.
In effluents dissolved P occurs as orthophosphates,
polyphosphates, and organic phosphates. Orthophos-
phate is adsorbed or precipitated in acid soils by crystal-
line and/or amorphous iron and aluminum oxides. In
neutral and calcareous soils, orthophosphate reacts with
calcium to form, depending upon the ionic composition,
a number of slightly soluble or insoluble calcium phos-
phates.
A number of minerals containing phosphorus occur
naturally in soil or have been identified as products of re-
actions between soil or soil minerals and phosphate
salts. Fluorapatite, Ca^PO^F^ is the main phos-
phate mineral in rocks, and probably occurs in most
slightly or moderately weathered soils. Other calcium
phosphates are hydroxyapatite, Ca^PO^^OR^; car-
bonapatite, Ca^PO^Q^; octacalcium phosphate,
Ca4H(P04)3-3H2O; and dicalcium phosphate, CaHPO4
•2H20. Dicalcium phosphate is the first product of phos-
phorus fertilizer reaction with soils, octacalcium phos-
phate, hydroxyapatite, and carbonapatite are thought to
form slowly from dicalcium phosphate in slightly acid to
alkaline soils. A number of iron and aluminum phos-
phate minerals have been identified as products of the
reaction between concentrated phosphate solutions and
clay minerals, and oxides and hydroxides of iron and
aluminum; and by inference are thought to occur in soils.
Minerals identified include variscite, A1(OH)2H2PO4;
strengite, Fe(OH)2H2PO4; barrancite (FE.A1) (OH)2
H2P04; andtaranakite, H6(NH4,K)3A15(PO4)8-18H20.
Concentrations of phosphorus in soil solutions of mod-
erately weathered temperate-region soils are between
-------
MOVEMENT OF ELEMENTS TO GROUNDWATER 183
0.1 and l.Ojig/ml. In many highly weathered soils of
tropical regions as well as andosols (soils high in oxides
of iron and aluminum) and in high pH arid areas (soils
high in calcium) phosphorus concentrations are less than
0.1 jag/ml. These solubilities are more or less in keeping
with those deduced from solubility product considera-
tions of the mineral forms mentioned.
Phosphate ions are adsorbed on the surface of many
substances found in soil. These include the clay minerals
or oxide coatings on clay minerals and the same sub-
stances which react with phosphorus to form slightly
soluble or insoluble compounds. In most cases, it is diffi-
cult to distinguish between the formation of new miner-
als and adsorption on the materials presumed to form to
the new minerals. Regardless of the mechanism by
which phosphorus is lost from solution (adsorption or
precipitation or both) reactions of phosphorus have been
reasonably well-described by the Langmuir adsorption
isotherm21' 22. In the linear form the Langmuir equation
has the following form:
c — 1 , c
_x_ kb b
m
where c= the equilibrium concentration of P in
mmoles/1, x/m = mmoles P adsorbed per unit weight,
b = the adsorption capacity in mmoles/g, and k is a con-
stant related to the bonding energy. A phosphorus
adsorption capacity (b factor) can be obtained from a plot
of P adsorption data according to the Langmuir equa-
tion. Ellis has used this approach and estimated the ad-
sorption capacity of several soils to range from about 80
to 900 IbsP per acre foot. Adsorption capacities as deter-
mined using the Langmuir constants, however, are not
permanent and part of the capacity of a soil to sorb phos-
phorus is restored with time (Ellis). The use of this ap-
proach, therefore, underestimates the potential capacity
of a soil to attenuate phosphorus in wastewaters or
sludges (Bouwer and Chaney). It should serve, however,
as a reasonable first approximation.
A number of long-term fertility trials have demon-
strated phosphorus mobility, except in all but the most
sandy soils, is quite restricted. Pratt, et. al.23 for ex-
ample, reported results for phosphorus concentrations
in soil treated with treble superphosphate at a rate of 57
Ibs P/acre/year for 28 years. More than 80 percent of the
P remained in the surface twelve inches and no move-
ment of phosphorus was observed at depths lower than
36 inches. The soil to which the phosphorus was applied
had a pH of 7.6, a trace of excess CaCO^, and an ex-
change capacity of approximately 10 meq/100 g. In
Florida, Fiskill and Ballard24 reported all of the phos-
phorus from an application of 3200 Ibs P per acre applied
over a six year period remained in the surface four feet of
a Lakeland fine sand.
A number of studies involving land applications of
sewage sludges or effluents have demonstrated that
phosphorus movement to lower depths in soil profiles is
quite restricted. Hook, et. al.25 observed movement of
phosphorus to a depth of approximately 120 cm after six
years of irrigation with sewage effluents at rates of five
cm per week. The concentrations of phosphorus at the
depths sampled were greater for a sandy loam soil than a
clay loam soil. Bray extractable phosphorus (O.025N
HC1-0.03N_NH4F) increased to a depth of 90 cm in the
sandy loam profile, but only to 30 cm in the clay loam
profile. In the sewage farm serving Melbourne, Aus-
tralia (Werribee Farm), Johnson, et. a.26 reported total
concentrations of phosphorus at depths between 25 to 45
cm in soils irrigated with primary effluent for a period of
48 to 73 years which were twice those of the non-effluent
treated soils. Most of the phosphorus applied, however,
accumulated in the surface 25 cm of soil. Mean concen-
trations of phosphorus draining from the irrigation pad-
docks were 2.9.ug P/ml compared to 32.1 jag P/ml for
the raw sewage, indicating a soil attenuation of about 90
percent. The soil at the Werribee Farm is acid in the sur-
face and has a CEC which, depending upon the plot,
ranged from 15 to 30 meq/100 g.
In systems where sewage effluents or liquid sludges
are applied to soils at high rates to recharge
groundwaters or dispose of wastewater, phosphorus
movement to considerable depths has been observed.
Bouwer, Lance and Riggs reported removal of approxi-
mately 50 percent of the phosphorus in an effluent con-
taining 10 mg P/l after passing through 30 feet of soil
and sediment (three feet of a fine, loamy sand underlain
by coarse sand and gravel layer to a depth of 30 feet).
Lund, Page and Nelson (1975) followed the movement of
phosphorus in soil beneath lagoons used as percolation
or storage ponds for effluents and liquid sludges. In their
study phosphorus movement to a depth of at least three
meters was observed. The type of soils or sediments in-
volved in the studies of Bouwer, Lance and Riggs and
Lund, Page and Nelson (1975) were sands and loamy
sands and those most conducive to the rapid movement
of phosphorus.
It seems reasonable to conclude the capacity of soils to
retain phosphorus is related to their content of reactive
colloidal surfaces of clays, clays coated with carbonates
and oxides of iron and aluminum, and alkaline earth
carbonates. Except for sandy soils, large amounts of
phosphorus applied to soil in the form of sludges or efflu-
ents will be retained in the surface horizons and conse-
quently restrict their movement to lower depths in the
soil profile. The period of time a particular soil can be
used as a filter to remove phosphorus will depend on
loading rate, rate and volume of water which moves
through the soil profile and the capacity of the soil to re-
tain phosphorus. Although methods are available to de-
termine short-term capacities for soils to retain phos-
phorus, more information is needed on long term effects
in relation to loading rate.
-------
184 MOVEMENT OF ELEMENTS TO GROUND WATER
Trace Elements
The trace element concentrations of sewage treatment
plant sludges and effluents vary widely and depend
upon the kinds and percentages of industrial input and
the nature of the treatment process. Usually trace ele-
ment concentrations of sludges increase and effluents
decrease in relation to the extent to which sewage waters
are treated. Chen, et. al.27 presents data which show
that secondary treatment reduced concentrations of Cd,
Cr, Cu, Hg, Pb and Zn in primary effluent by factors
which ranged depending on the element from 63 to 80
percent. Suspended particulates were 94 percent less in
the secondary effluent than the primary effluent,
demonstrating that high concentrations of trace ele-
ments in the primary effluent are largely associated with
suspended particles.
Page28 reviewed reported values for concentrations of
trace elements in sewage sludges and observed the fol-
lowing ranges to occur (in jug/g dry weight basis): B,
6-1000; Co, 2-260; Cu, 150-11700; Mo, 2-1000; Pb,
10-26,000; Zn, 100-49,000; Cd, 1-1500; Cr, 20-40,000;
Hg, 0.1-50; Ni, 10-5300; Se, <0.1-81; and As, 0.5-1800.
Concentrations in primary effluent are highly variable
and depend upon the percent suspended solids. Secon-
dary effluents almost without exception show lesser con-
centrations of trace elements than do primary effluents.
Ranges for trace element concentrations in secondary
effluents reported by Blakeslee29 for 23 treatment
plants in Michigan follow (in mg/1): As, < 0.005-0.23;
Cd, < 0.01-0.15; Cu, 0.01-1.3; Cr, < 0.01-1.2; Pb,
-------
MOVEMENT OF ELEMENTS TO GROUNDWATER 185
beneath a sewage lagoon which had been used to pond
secondary sewage sludges for a period of 20 years. With
the exception of B, the previously cited references point
out that trace element movement (As, Cd, Cr, Cu, Hg,
Mo, Ni, Pb, Se, and Zn) in all but very sandy soils and
long-term, high-rate volume operations to depths below
one meter in the profile is quite restricted.
In natural soils, concentrations of As in soil solutions
are usually less than 0.01 mg/1. Levels, as high as a few
mg/1 have been reported in solutions from surface soils
where arsenical agricultural chemicals have been ap-
plied to control disease or weeds. Where arsenicals have
been used for a number of years in orchards to control
diseases, movement of As to a depth of two meters in soil
profiles has been observed 35. In acid soils dissolved As
probably reacts to form iron or aluminum arsenates
which are quite insoluble. In calcareous soils, the forma-
tion of calcium arsenate is thought to limit the solubility
of As.
The concentrations of cadmium in uncontaminated
soil solutions are normally less than 0.005 mg/1. How-
ever, concentrations in soil solutions from soils treated
with sewage sludges as high as a few mg/1 have been re-
ported36'37. There are not sufficient published data
available to critically evaluate Cd movement in soil.
Some data are available for high rate and volume sys-
tems. Lund, Page and Nelson (1974) observed move-
ment of Cd to a depth of three meters in soil beneath a
sludge lagoon. Bouwer, Lance, and Riggs showed that
water containing 0.007 mg Cd/1 passed through soil to
underground wells with no change in the concentration
ofCd. Factors which control the solubility of Cd in natu-
ral systems are not well-understood and presently it is
not possible to evaluate movement in soils in relation to
their chemical properties. Most available information
suggests that Cd solubility in soils is controlled by ad-
sorption reactions involving colloidal clays, organic mat-
ter, and amorphorus oxides of iron and aluminum.
Concentrations of Zn and Cu in soil solutions are nor-
mally in the range of 0.01 to 0.1 mg/1. When sewage
treatment plant sludges or effluents containing Zn and
Cu are applied to agricultural soils (except for sands) the
concentrations of Cu and Zn in the soil solution from the
surface horizon may show some increase, but, unless
unusually high loading rates are employed movement to
depths below one meter are rarely observed. Boswell
observed some movement of Cu and Zn to a depth of 30
cm in a soil which was amended'with sewage sludge.
Lund, Page and Nelson (1974) observed movement to a
depth of three meters in soil beneath a sludge lagoon
which had received high loading rates for more than 20
years.
Molybdenum and selenium occur in soil solutions as
anions. Only limited data are available on concentrations
of these elements which may occur in effluents or
sludges. Both elements, when dissolved, are thought to
react in acid soils with iron and aluminum to form rather
insoluble compounds. In neutral and calcareous soils,
both elements react with calcium to form rather insolu-
ble compounds.For these reasons movement of either
Mo or Se is not expected to occur in agricultural soils re-
ceiving either effluent or sludge.
Chromium added to soil in dissolved form is thought to
react to form quite insoluble oxides. Unless high loading
rates of materials high in Cr are applied to soil, move-
ment of Cr to depths much below the point of application
are not anticipated.
The solubility of inorganic Pb in natural systems is
probably limited by the formation of sparingly soluble or
insoluble compounds such as lead oxide, sulfate, car-
bonate, and phosphate. Concentrations of Pb in the soil
solutions are normally less than 0.01 mg/1; however,
higher values have been reported for soil solutions near
or derived from parent materials high in lead. Very few
data are available for Pb concentrations of soil solutions
from soils which have received application of either sew-
age sludge or effluent. In the groundwater recharge pro-
ject at Flushing Meadows, Bouwer, Lance and Riggs re-
ported only 20 percent attenuation of Pb in effluent
which contained 0.08 mg P/l after the effluent had
passed through three feet of a loamy sand underlain by
27 feet of a sand-gravel mixture.
Concentrations of Hg reported to occur in natural
waters and soil solutions are usually less than 0.001
jag/ml 38. It may occur in solution as a cation, anion, or
uncharged molecule. Under reducing conditions Hg may
precipitate as HgS which would limit its concentration to
<0.002 jug/1. Mercury exhibits high affinity for humic
substances and hydrous oxides of iron and aluminum.
Because of its high affinity for humic substances and
other inorganic constituents in soil, movement of Hg in
soil is not expected.
Boron, except in highly alkaline soils (pH <8.5) occurs
in soil solutions as undissociated boric acid [B(OH)-j]. It
is sorbed by active oxides of iron and aluminum in soil,
but its affinity for these solid surfaces is low compared to
affinities of other trace elements for these surfaces. For
these reasons, B is quite mobile in soils. In sandy soils
low in organic matter and active iron and aluminum
oxides, B in water passes through soils essentially un-
charged. Organic matter and active iron and aluminum
oxides tend to limit the mobility of B in soils, but gen-
erally the equilibrium involved is such that substantial
percentages of dissolved B remain in solution and move
with percolating water.
SUMMARY
Soils, except for sands, have a high capacity to retain
As, Cd, Cr, Cu, Hg, Mo, Ni, Pb, Se, and Zn. In situations
where sludges of effluents are added to agricultural soils
to supplement plant nutrients or as a source of irrigation
water, essentially all of the above trace elements applied
should remain within the surface meter of soil. In
groundwater recharge or disposal operations where
-------
186 MOVEMENT OF ELEMENTS TO GROUND WATER
high application rates are involved, movement of trace
elements may occur and the extent of movement will de-
pend upon the amount and composition of the waters
applied, and the nature of the soil or sediment through
which the waters flow.
LITERATURE CITED
1. Focht, D.D. and A.C. Chang, "Nitrification and
Denitrification Processes Related to Wastewater Treat-
ment," Advan. Applied Microbiology, (Academic
Press, 1975).
2. Walker, J.M., "Sewage Sludges—Management
Aspects for Land Application," Compost Science, 16
(1975), 12-21.
3. Bouwer, H. and R.L. Chancy, "Land Treatment of
Wastewater," Advan. Agron., 26 (1974) 133-176.
4. D'ltri, P.M., T.P. Smith, H. Bouwer, and E.A. My-
ers, "An Overview of Four Selected Facilities That
Apply Municipal Wastewater to the Land," United
States Environmental Protection Agency, Technology
Transfer Program (1974).
5. McMichael, F.C. and J.E. McKee, "Research on
Wastewater Reclamation at Whittier Narrows,"
Environ. Health Eng., (California Institute of Tech-
nology, Pasadena, 1965).
6. Bouwer, H., J.C. Lance and M.S. Riggs, "High-
Rate Land Treatment: II. Water Quality and Economic
Aspect of the Flushing Meadows Report," Journal
Water Pollution Control Federation, 46:5 (1974)844-859.
7. Annual Report on Results of Water Quality Moni-
toring—Water Year 1972-1973 (Report to the Central
and West Basin Replenishment District, Downey, Cali-
fornia) (Bookman-Edmonston Engineering, Inc., 1974).
8. Lund, L.J., A.L. Page and C.O. Nelson, "Nitrogen
and Phosphorus Levels in Deep Soil Cores Beneath Sew-
age Disposal Ponds," Journal of Environmental Quality,
1975.
9. "Feasibility of Reclamation of Water from Wastes
in the Los Angeles Metropolitan Area" (Sacramento:
California Department of Water Resources, 1961), Bul-
letin No. 80.
10. Broadbent, F., University of California, Davis,
Personal Communication, 1975.
11. Rhoades, J.D., "Quality of Water for Irrigation,"
Soil Science, 113 (1972), 277-284.
12. Rhoades, J.D., J.D. Oster, R.D. Ingvalson, J.M.
Tucker and M. Clark, "Minimizing Salt Burdens of Irri-
gation Drainage Waters," Journal of Environmental
Quality, 3 (1974), 311-316.
13. Adriano, D.C., P.F. Pratt and F.H. Takatori, "Ni-
trate in Unsaturated Zone of an Alluvial Soil in Relation
to Fertilizer Nitrogen Rate and Irrigation Level," Jour-
nal of Environmental Quality, 1 (1972), 418-422.
14. Adriano, D.C., F.H. Takatori, P.F. Pratt and O.A.
Lorenz, "Soil Nitrogen Balance in Selected Row-Crop
Sites in Southern California," Journal of Environmental
Quality, 1 (1972), 279-283.
15. Ayers, R.S. and R.L. Branson (eds.), "Nitrates in
the Upper Santa Ana River Basin in Relation to Ground-
water Pollution," California Agricultural Experiment
Station, Bulletin No. 861, (1973).
16. Pratt, P.F. and D.C. Adriano, "Nitrate Concentra-
tions in the Unsaturated Zone Beneath Irrigated Fields
in Southern California," Soil Science Soc. Amer. Proc.,
37 (1973), 321-322.
17. Jury, W.A., "Solute Travel-Time Estimates for
Tile-Drained Fields (I. Theory)," Soil Science Soc.
Amer. Proc., 39 (1975).
18. Jury, W.A., "Solute Travel-Time Estimates for
Tile-Drained Fields (II. Application to Experimental
Studies)," Soil Science Soc. Amer. Proc., 39 (1975).
19. Pound, C.E. and R.W. Crites, "Characteristics of
Municipal Effluents," Recycling Municipal Sludges and
Effluents on Land (Washington: National Association of
State University and Land-Grant Colleges, 1973), pp.
49-59.
20. Page, A.L. and A.C. Chang, "Trace Element and
Plant Nutrient Constraints of Recycling Sewage Sludges
on Agricultural Land," Proceedings of the Second Na-
tional Conference on Water Reuse: Water's Interface
with Energy, Air, and Solids (American Institute of
Chemical Engineers, Environmental Protection Agency
and Technology Transfer, 1975). In Press.
21. Ellis, E.G., "The Soil as a Biological Filter," Re-
cycling Treated Municipal Wastewater and Sludge
Through Forest and Cropland (University Park: Pennsyl-
vania State University Press, 1973), pp. 46-70.
22. Lindsay, W.L., "Inorganic Reactions of Sewage
Wastes with Soils," Recycling Municipal Sludges and
Effluents on Land (Washington, D.C.: National Associa-
tion of State University and Land-Grant Colleges, 1973),
pp. 91-96.
23. Pratt, P.P., W.W. Jones and H.D. Chapman,
"Changes in Phosphorus in an Irrigated Soil During 28
Years of Differential Fertilization," Soil Science, 82
(1956), 295-306.
24. Fiskell, J.C. and R. Ballard, Prediction of Phos-
phate Retention and Mobility in Florida Soils (Gaines-
ville: Proceedings Workshop, University of Florida,
1973).
25. Hook, J.E., L.T. Kardos and W.E. Sopper, "Ef-
fect of Land Disposal of Wastewaters on Soil Phosphorus
Relations," Recycling Treated Municipal Wastewater
and Sludge through Forest and Cropland (University
Park: Pennsylvania State University Press, 1973), pp.
200-219.
26. Johnson, R.D., R.L. Jones, T. Hinesly and D.J.
David, Selected Chemical Characteristics of Soils, For-
ages, and Drainage Water from the Sewage Farm Serv-
ing Melbourne, Australia (Dept. of Army, Corps of
Engineers, 1974).
27. Chen, K.Y., C.S. Young, T.K. Jan and N. Rohatgi,
"Trace Metals in Wastewater Effluents," Journal Water
Pollution Control Federation, 46 (1974), 2663-2675.
-------
MOVEMENT OF ELEMENTS TO GROUNDWATER 187
28. Page, A.L., "Fate andEffectsof Trace Elements in
Sewage Sludge When Applied to Agricultural Lands,"
Environmental Protection Technology Series, EPA-670/
2-74-005 (Cincinnati: United States Environmental Pro-
tection Agency, 1974).
29. Blakeslee, P.A., "Monitoring Considerations for
Municipal Wastewater Effluent and Sludge Application
to Land," Recycling Municipal Sludges and Effluents on
Land (Washington, B.C.: National Association State
University and Land-Grant Colleges, 1973), pp. 183-198.
30. Boswell, F.C., "Municipal Sewage Sludge and Se-
lected Application to Soil: Effect on Soil and Fescue,"
Journal Environmental Quality, 4 (1975), 267-272.
31. Hinesly, T.D., R.L. Jones and E.L. Ziegler, "Ef-
fects on Corn by Application of Heated Anaerobically Di-
gested Sludge," Compost Science, 13 (1972), 26-30.
32. Andersson, A. and K.O. Nelsson, "Enrichment of
Trace Elements from Sewage Sludge Fertilizer in Soils
and Plants," AMBIO, 1 (5) (1972), 176-179.
33. Kirkham, M.B., "Trace Elements in Corn Grown
on Long-Term Sludge Disposal Site," Environ. Sci.
Technology, 9 (1975), 765-768.
34. Lund, L.J., A.L. Page and C.O. Nelson, "Move-
ment of Heavy Metals and Nitrogen Beneath Sewage
Sludge and Effluent Disposal Lagoon," Agron. Ab-
stracts (Madison, American Society of Agronomy, 1974).
35. Woolson, F.A., J.H. Axley and P.C. Kearney,
"The Chemistry and Phytotoxicityof Arsenic in Soils. I.
Contaminated Field Soils," Soil Science Soc. Amer.
Proc., 35 (1971), 938-943.
36. Bingham, F.T., A.L. Page, R.J. Mahler and T.J.
Ganje, "Growth and Cadmium Accumulation of Plants
Grown on a Soil Treated with a Cadmium Enriched Sew-
age Sludge," Journal Environmental Quality, 4 (1975),
207-211.
37. Bradford, G.R., A.L. Page, L. J. Lund and W. Olm-
sted, "Trace Element Concentrations of Sewage Treat-
ment Plant Effluents and Sludges, Their Interactions
with Soils and Uptake by Plants," Journal Environ-
mental Qualilty, 4(1) (1975), 123-127.
38. Lagerwerff, J.V., "Lead, Mercury, and Cadmium
as Contaminants," Micronutrients in Agriculture
(Madison: Soil Sci. Soc. Amer. Inc., 1972), pp. 593-628.
-------
ENVIRONMENTAL EFFECTS OF SLUDGE
DISPOSAL IN SANITARY LANDFILLS
Bruce R. Weddle
United States Environmental Protection Agency
Washington, D. C.
INTRODUCTION
The land disposition of sewage sludge is an area of
growing controversy. Those who advocate landspread-
ing of sludge on agricultural lands are facing increased
opposition from those who point out that insufficient in-
formation exists on the health implications to man from
the long-term low-level injection of crops grown on
sludge amended soil (or animals fed crops grown on
sludge amended soil). Further, citizen groups are using
our lack of information on pathogen survival and move-
ment in soils and groundwater to ' 'kill'' proposed sludge
utilization and disposal projects. The problem surround-
ing the ultimate disposition of sludge is one of the rea-
sons for holding this conference. This paper will address
only the small portion of that problem that deals with the
environmental effects of the subsurface disposal of
municipal wastewater sludges.
Oceanside Demonstration
In particular, this report will discuss two EPA pro-
jects, one of which is completed, while the other is on-
going. The first project was an investigation of the envi-
ronmental and economic effects of disposing liquid
sludge and septic tank pumpings into a sanitary landfill.
The work on this project was conducted by Ralph Stone,
Inc., a consultant located in Los Angeles, through a
demonstration grant to the City of Oceanside, Cali-
fornia. The objectives of the study were to determine:
• The capacity of solid waste to assimilate the mosi-
ture in liquid sludge and septic tank pumpings and
the significant factors affecting that capacity.
• The optimum means for nuisance-free admixture of
liquid sludge with solid waste in a landfill.
• The effects of combined liquid sludge-solid waste
disposal on the environment, landfill operating ef-
ficiencies, and personnel performance.
• The effects of liquid sludge on landfill compaction.
• The most economically feasible methods for trans-
porting and disposing of liquid sludge.
Rather than discussing the findings of this project in de-
tail, this report will touch upon the principal conclusions.
(Copies of the final report can be obtained by writing to:
Solid Waste Information Materials Control Section, U.S.
Environmental Protection Agency, Cincinnati, Ohio.)
Significant Findings
A laboratory analysis, based upon the moisture-ab-
sorbing capability of the particular components normally
found in solid waste, concluded that each pound of solid
waste (dry weight) can be expected to absorb 0.6 to 1.8
pounds of water. Table 1 provides a detailed breakdown
of the predicted range of absorptive capacity of muni-
cipal refuse. The moisture content of Oceanside's solid
waste was approximately 25 percent. Therefore, the cor-
rected absorption rate is 0.5 to 1.35 pounds of water per
pound of solid waste as received at the landfill. Addi-
tional testing, using Oceanside's waste, confirmed that
the City's waste fell into the upper half of the expected
absorption range.
' 'The City of Oceanside produces approximately 0.6 Ib
of sludge (average wet weight from three treatment
plants) for every 1.0 Ib dry weight of municipal refuse.
Theoretically, therefore, the solid waste generated by
the city should have adequate capacity to absorb all the
water in the liquid sludge. This was verified in a number
of field tests at the Oceanside landfill in which sewage
sludge was applied to solid waste at a rate of 0.35 to 0.6
Ib of sludge per 1.0 Ib of solid waste wet weight. A total
of 35 applications were made (one day per week for 35
weeks over a ten-month period). No leachate was ob-
served during this period. In cases where minor sludge
runoff occurred, it was the result of an inappropriate
spreading technique and the runoff was absorbed into
the fill cover."
The moisture content of solid waste varies widely de-
pending on seasonal waste characteristics, the weather
on the day the waste is collected, etc. If we use an aver-
age moisture content of 30 percent, the moisture absorp-
tion range changes to 0.42 to 1.25 pounds of water per
pound of solid waste.
188
-------
DISPOSAL IN SANITARY LANDFILLS
189
TABLE 1
Predicted Range of Absorptive Capacity of Municipal
Refuse as Received at Oceanside Landfill
Available field absorption
Component
capacity of
waste components*
Maximum
Minimum
Average
compositiorri-
(percent)
Field absorptive
capacity
Maximum
**
Minimum
Newsprint
Cardboard
Miscellaneous paper
Leaves and grass
Prunings
Garbage (food waste)
Textiles
Non-absorbents++
Total
262
146
397
312
207
229
284
0
97
92
0
0
84
0
7.2
8.3
23.6
3.8
6.3
9.2
2.3
39.3
100.0
19
12
94
12
13
21
7
0
178
23
4
0
0
2
0
60
*The absorptive capacities determined in laboratory tests reduced by the measured moisture
contents from Oceanside waste samples, percent dry wt basis.
+Average of year's (four quarters) composition of collected refuse arriving at Oceanside
municipal landfill site.
**Pounds water per 100 pounds of average mixed refuse as received at the landfill; derived
from product of available absorptive capacity and average composition for each component.
-H-Includes wood (absorption very slow), foam plastic (insignificant quantity), and dirt,
sand, and ashes (which entrain but do not absorb).
Source: Stone, R. Disposal of Sewage Sludge Into a Sanitary Landfill. Environmental
Protection Agency Publication SW-71d, Washington, D.C.
TABLE2
Predicted Average Liquid Sludge and Solid Waste
Generation Rates for 1973 and 1985
Average sludge
generation rate
(Ib/cap/day-dry wt)*
Average sludge Average liquid
generation after sludge generated
digestion after digestion
(Ib/cap/day-dry wt)+ (lb/cap/day-5% solids)
Average solid Ratio of
waste generation liquid sludge
rate to solid waste
(lb/cap/day)**
1975
0.18
0.12
2.34
3.6
.65
1985
0.21
0.14
2.73
3.9
.7
*Based on OSWMP internal calculations.
+Assuming a 50 percent reduction in volatile solids after digestion (the volatile solids
content of the sludge is assumed to be 70 percent), the net result is a 35 percent reduction
in the total solids digested.
**Based on OSWMP internal calculations for solid waste disposal quantities after resource
recovery.
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190 DISPOSAL IN SANITARY LANDFILLS
Table 2 shows that any given city, on the average, pro-
duced .65 pounds of liquid digested sludge (five percent
solids) to each pound of solid waste (wet weight) it gen-
erates. It therefore could be concluded that the solid
wastes generated by any given city should have
adequate capacity to absorb all the water in its liquid di-
gested sludge. However, since the amount of sludge
produced will vary greatly, and the population equiva-
lent served by a treatment plant may be greater than that
served by the disposal site, it is recommended that site
specific calculations be conducted before the disposal of
liquid sludge is initiated. Ultimately it is the sludge/
solid waste ratio achieved at the working face that deter-
mines acceptability.
Since the addition of liquid sludge, if properly man-
aged .should not bring a disposal site to its field capacity
(the theoretical point at which leachate will begin to mi-
grate from the disposal site since the waste has reached
its moisture retention capacity), the next question the
project addressed surrounds the quality of the leachate
formed. A comparison of leachate from the Oceanside
pilot test drums and field test cells to leachate collected
from control drums, control cells at the site, and from
other sites in Southern California, showed that addition
of sludge to solid waste produced a more acidic leachate
(pH 4.65.9 compared to 5.67.8). In addition, the 6005
averaged 19,600 mg/1 for the sludge/solid waste leach-
ate as compared to an average of 10,900 mg/1 for the
solid waste leachate. No other major differences in
leachate quality were reported.
The addition of sludge also resulted in changes in the
operational characteristics of the site. "The application
of liquid digested sewage sludge by spreading onto the
compacted landfill working face proved to be a better
methodology than admixing solid waste into a pool of
liquid sludge. The landfill dozers experienced no slip-
page in working the liquid sludge when it was spread
and allowed to dry and infiltrate for a few minutes over
and into the surface of a working face of less than 30 per-
cent slope. A greater working face slopes and in pooled
or fresh liquid sludge, the dozers experienced some
slippage."
A double splashplate assembly was used for gravity
spreading of the sludge. This configuration distributed
the sludge over an estimated area twelve feet wide and
six feet deep. In order to avoid channeling and the re-
sultant runoff, the truck (a 3500 gallon tank truck) had to
be moved at least three times during unloading. More
frequent moves were required in wet weather.
"Qualitatively, addition of liquid sewage sludge to
solid waste in the Oceanside landfill was observed to re-
duce dust and blowing litter due to the increased mois-
ture content of the disposed materials. Further, qualita-
tive observations of odors resulting from admixing
normal "well-digested" liquid sludge and solid waste
indicated a similarity in strength to typical solid waste
landfill odors. The pilot test drums, field test cells, and
the demonstration landfill tests indicated that admixture
with well-digested primary and secondary sludges pro-
duced a mild, earthy, non-noxious odor until the ab-
sorbed sludge dried, after which normal landfill odor
types prevailed. Undigested raw sewage sludges and
septic tank pumpings in the pilot test drums, however,
produced moderate to strong noxious septic odors. Such
noxious odors can be expected whenever raw sewage is
disposed to landfills in cases of digester upsets, treat-
ment plant strikes, natural catastrophes, etc. The septic
odors can be controlled by immediate cover with six in-
ches of soil or normal landfill dry solid waste. Even
though the Oceanside landfill was located in immediate
proximity to an urbanized area including apartments
and two schools, very few complaints concerning odors
were received."
From a site engineering viewpoint, the addition of
sewage sludge resulted in better solid waste fill compac-
tion and density. In a controlled field test, compaction
was approximately four percent better following sludge
application. (Density averaged 1,120 pounds per cubic
yard, which is well into the upper range of "solid waste
only" landfills.)
Environmental Effects
The Oceanside project added to our knowledge about
sludge disposal, however, it has several weaknesses.
Due to the climate in Southern California, it was neces-
sary to spray large quantities of water onto the test cells
to produce leachate. Further, while drum tests are valu-
able, there is a need to determine what happens in a
landfill under real-world conditions. Therefore, we
awarded a contract to SCS Engineers, in Long Beach,
California, to evaluate the environmental impact of
mixed sludge/solid waste and "sludge only" disposal
sites. These evaluations are being performed at full
scale disposal sites rather than in the laboratory or under
stringently controlled field test conditions. While we will
not be able to explain why groundwater contamination
did or did not occur with the same accuracy as we could
from a controlled demonstration, we will learn much
more about the "real world" impact of nine sludge
disposal sites.
Site Selection Criteria
In selecting the nine sites to be investigated, the fol-
lowing criteria were used:
• Subsurface placement of sludge should have been
practiced at the site for at least one year.
• The site should not have been closed for more than
three years.
• A mixture of sludge only and sludge/solid waste
sites must be selected.
• A range of operational practices, geographical, and
climatological conditions should be represented.
• Good operational and historical records are pre-
ferred .
-------
DISPOSAL IN SANITARY LANDFILLS
191
ANALYSIS
Sites have been selected in New York, New Jersey,
Virginia, Illinois, Arkansas, and Nebraska. After each of
the sites were selected either two or three wells were
drilled. Figure 1 illustrates the procedure used to cap-
ture leachate at the bottom of each fill and to measure
gas composition (C(>>, CH4, and air). Each well was
drilled down through the buried waste until the subsoil
was reached. Core samples of the soil between the bot-
tom of the fill and groundwater were taken every four
feet (up to a maximum of four samples). After reaching
groundwater, the hole was filled with gravel and cement
from the groundwater to a point approximately one foot
below the bottom of the fill. As shown in Figure 1, the re-
mainder of the hole was fitted with one leachate and two
gas monitoring conduits. A total of three leachate
samples will be taken; the first, one month after drilling,
and the remaining two will be taken on a monthly basis.
Two gas samples will be taken during the four month
analysis phase of the project.
GAS SAMPLE
CLAY OR CEMENT PLUG
GRAVEL
SOIL
BACKFILL
Depending on the depth to groundwater and the avail-
ability of onsite monitoring wells, either one or two
groundwater monitoring wells were drilled. The wells,
one in shallow groundwater, while the other was much
deeper, were located to capture any contamination mov-
ing from the site. Background water quality samples
were taken from neighboring wells located upflow from
the site. The groundwater from eachofthese wells, com-
posite samples of sludge collected at the treatment
plant, and the soil samples were tested for the consti-
tuents listed in Table 3. A similar, but more extensive
analysis is being conducted at municipal solid waste
sites. The purpose of that analysis is to determine the
quantity of leachate produced, the constituents of that
leachate, the effectiveness of the soil between the bot-
tom of the fill and groundwaterto attenuate the leachate,
and to monitor for contaminant movement in ground-
water. Of the sixteen sites being examined, some are
sanitary landfills, some converted dumps, and some
open dumps.
LEACHATE
SAMPLE
SURFACE OF LANDFILL
Y77/
BOTTOM OF LANDFILL
CLAY OR CEMENT PLUG
GROUND WATER
Figure 1: Typical Sampling Well Details.
-------
192 DISPOSAL IN SANITARY LANDFILLS
TABLE3
Sludge, Leachate, and Groundwater Sample Analysis
N03
TKN
COD
TOC
SO,
CL
Cu
Fe
pH
Ca
Cd
Cr
Hg
Pb
Total Coliform
Fecal Strep
A comparison of the constituents and strengths of
leachate produced at sites accepting sludge to those pro-
duced at "solid waste only" sites will enable us to better
understand the effects of adding sludge to solid waste
and their impact on leachate treatment technology. A
comparison between contaminant movement will begin
to provide the information needed to evaluate the envi-
ronmental effects of subsurface sludge disposal. We
recognize that soil types will vary from site to site, as will
leachate quality. This will complicate these compari-
sons, yet it is our opinion that there will be enough
similarity to enable valid comparisons.
Expected Results
Unfortunately, we are only now beginning to receive
the data from the first round of sampling. It was hoped to
be able to present some preliminary findings, but the
data is too sketchy. However, we do expect to find leach-
ate contamination and migration in the groundwater be-
low improperly located and operated sites accepting
sludge. This presumption is based on several factors:
1. Approximately 70 percent of the disposal sites in
the contiguous United States are located in areas
receiving greater than 30 inches of precipitation
annually.
2. Most of the 14,000 to 18,500 disposal sites in the
United States are dumps rather than sanitary land-
fills.
Information gathered from state solid waste programs
and in-house investigations shows that dumps located in
areas receiving 30 inches of annual precipitation will
produce leachate, and in many cases, that leachate will
contaminate groundwater beyond drinking water stand-
ards. In five groundwater contamination studies recent-
ly completed by our office, economic damage averaging
over $300,000 per site was incurred. In two of these com-
munities the cost is expected to rise further. In all of
these cases, only a small percentage of the groundwater
was being utilized, thus minimizing the current
economic damage.
The effects of the addition of sludge, whether liquid or
dewatered, on the quality of the leachate produced, as
well as the effects on the soil's ability to attenuate that
leachate and the ability of that leachate to migrate from
the site remain to be determined. If the projects proceed
as scheduled, we plan to release preliminary findings
within the next nine months.
REFERENCES
1. Stone, R., "Disposal of Sewage Sludge Into a Sani-
tary Landfill," Environmental Protection Agency Publi-
cation SW-71d., Washington, D.C.
-------
IMPACT OF LAND DISPOSAL OF
SLUDGES ON GROUNDWATER
George R. Wilson
Geraghty and Miller
Port Washington, New York
INTRODUCTION
This paper deals with the many problems involved in
evaluating the impact of land disposal of sludges on
groundwater quality, with particular emphasis on the
hydrologic aspects. It solves no problems and gives no
definitive answers. The purpose, rather, is to direct at-
tention to the complexity of the subject, and to suggest
some practical considerations that may be applied in
evaluating potential disposal sites.
From the following discussions it is evident that it is
possible to draw up guidelines for land disposal of both
sludge and effluent, and this of course has been done
(particularly for effluent disposal) by numerous agen-
cies (e.g., U.S. EPA1). It cannot be emphasized too
strongly, however, that these cannot be definitive. Each
proposed disposal site must be studied and evaluated
according to its own particular characteristics.
The extreme complexity of evaluating the potential
impact of land spreading on groundwater resources can
be illustrated by the implications of Table 1, which
shows 20 principal variables involved. We now assign
only three categories to each of these variables (high,
medium, low, or good, average, poor), which formany of
them is an oversimplification. The number of possible
variable combinations that can be encountered is then
3-20, or about 3.5 billion. Even if only two categories
(good-bad) are assigned, the variable combinations still
exceed one million. Obviously, the real-life evaluations
are not as appallingly difficult as these figures would in-
dicate. They do demonstrate, however, that there can be
no cut-and-dried answers to questions such as "if muni-
cipal sludge is applied by spreading, with an application
rate of 25 tons per acre per year, what will be the effect
on groundwater quality?"
Chemistry
While there is a very large body of data and informa-
tion on the behavior and fate of contaminants within the
/.one of biological activity in the soil, there is very little
indeed on what occurs within aquifers. Hence the latter
TABLE 1
Principal Variables in Land Disposal
Element
Sludge
Application
Soil
Climate
Variables
1 . Composition
2. Type of treatment
1 . Method
2. Loading rate
1. Texture a'
2. pH
3. Organic matter content
4. Cation exchange capacity
5. Percent base saturation
6. Depth
7. Slope
1. Temperature regime
2. Precipitation regime
Crop 1. Uptake
2. Management
Ground Water 1. Depth to zone of saturation
2. Nature of zone of aeration
3. Natural quality of ground water
4. Physical nature of aquifer
5. Chemical nature of aquifer
a~)This includes infiltration rate, permeability, and available moisture
capacity, each of which could well be considered as a separate variable.
must be evaluated almost entirely on theoretical con-
siderations, relating to the mineral composition of the
aquifers and the composition of the percolate. This ap-
plies to all contaminants, regardless of source.
The percolate concentrations for many sludge consti-
tuents vary by two orders of magnitude and the others by
one order, depending upon the composition of the
sludge and degree of retention in the soil. The consti-
tuents whose concentrations may exceed EPA limits for
drinking water include: iron, manganese, nitrate, cad-
mium, lead, silver, and possibly others (based upon per-
colate data in Table 2 2'7. All of the analyses are for per-
colate at the bottom of the zone of biological activity.
Further reduction in contaminants may take place in
passage to the water table, depending upon the depth of
the latter and the mineral composition of intervening
material. However, in the absence of evidence to the
contrary, it should be assumed that percolate will not
meet drinking water standards. The heavy metals, how-
ever, may be removed by ion exchange during passage
through the aquifer.
193
-------
194 IMPACT ON GROUNDWATER
TABLE2
Constituents of Sludge Percolate3
Percolate
concentration
Constituent
ng/l
Iron
Manganese
Calcium
Magnesium
Sodium
Potassium
Sulfate
Chloride
Ammonium
Nitrate
Total Nitrogen
Phosphate
Organic Carbon
Boron
Cadmium
Chromium
Cobalt
Copper
Lead
Mercury
Molybdenum
Nickel
Silver
Vanadium
Zinc
Total Heavy Metals
0.04
0.05
8
3
0.90
0.70
2.4
0.35
0.40
8
8
0
7
0.40
0.04
0.01
0.02
0
0.05
0.001
0.01
0.006
0.01
0.03
0.006
- 5.40
- 0.68
- 107
- 152
- 47
- 11
- 156
- 59
1.28
- 15
- 25
- 1.2
- 12
- 2.0
- 1.20
- 0.04
- 0.04
- 0.25
- 0.22
- 0.0014
- 0.05
- 2.00
- 0.30
- 0.04
- 0.27
-
^Values reported in References 2-6.
Walker8 has dealt with the problem of monitoring tox-
ic wastes at land disposal sites. He concludes that prac-
tically all such sites are equipped with generally ineffec-
tual monitoring systems, and outlines the measures that
would be required for evaluation of the fate of toxic
wastes.
The current tendency in predictive chemistry is to
combine it with flow and dispersion characteristics of the
aquifer, and solve the differential equations involved by
use of digital models, as will be discussed later. Of
course there is always the problem of just what should be
plugged into the equation. Hem 9 points out that the clas-
sical adsorption isotherms of Freundlich and Langmuir,
while useful for evaluating adsorptive capacities for
single ions, have little value in studies of ion-exchange,
which is the usual mechanism within aquifers. Back and
Langmuir 10 state that the two chemical unknowns that
most inhibit the statisfactory formulation of models are
the lack of information on chemical reaction rates and
the effect of organic ions on the behavior or inorganic
ions.
Hydrology
An understanding of the flow pattern of contaminants
is of great importance to the understanding of the entire
groundwater contamination picture. Figure 1 illustrates
an idealized flow pattern. From this it is seen that the
sludge-contacted water moves to its discharge area by a
definite route, and is not (as is often imagined) subject to
dilution by the entire body of groundwater lying between
the disposal area and the area of discharge. There is,
however, dilution caused by mechanical dispersion,
which results from the complexity (on a microscopic
level) of the paths followed by the fluid, and (on a macro-
scopic level) inhomogeneities within the aquifer. Be-
GROUND-WATER
DIVIDE
SLUDGE-DISPOSAL
AREA
IMPERMEABLE ROCK
FLOW LINES
EQUIPOTENTIAL LINES
NOTE : DRAWING NOT TO SCALE
CONSIDERABLE VERTICAL
EXAGGERATION
CONTAMINATED GROUND WATER
Figure 1: Flow in a Water-Hole Aquifer (Humid Region).
-------
IMPACT ON GROUNDWATER
195
cause of this, the contaminated fluid invades the natural
groundwatcrto some extent and is concurrently invaded
by the latter. Molecular diffusion also takes place, but
this is relatively unimportant except when the flow rate
of groundwater is very low, or the concentration of the
contaminant is very high. The latter is associated with
high density percolates, which will also distort the
idealized pattern by tending to sink to the bottom of the
aquifer.
The rate of groundwater movement within an aquifer
is obviously of great importance. It is governed by the
hydraulic gradient and aquifer permeability, the latter of
which varies far more widely than any other physical
property encountered in contamination studies. The
U.S. Geological Survey11 has determined permeabili-
ties for a gravel through which, under a gradient often
feet per mile, water would move at the rate of 60 feet per
day, and for a clay through which, under the same
gradient, the rate of movement would be one foot in
about 30,000 years. The factor is 450 million. Flow rates
in most aquifers, however, range from a few feet per day
to a few feet per year.
Theoretical solutions, some of them quite elaborate,
are available for the expression of all of these
phenomena. Unfortunately, these solutions are restrict-
ed to relatively uncomplicated systems quite unlike
those encountered in actual aquifers. Mechanical dis-
persion, which is usually predominant in determining
the shape of the plume of contamination, is so profound-
ly affected by heterogeneity that any attempt at detailed
prediction is futile. Skibitzke 12comments that ". . . the
nature of the heterogeneous region can hardly be des-
cribed through reference to the individual geometric dis-
continuities. Such a description would require an end-
less compendium of individual descriptions, a device so
obviously impractical that it renders the region not
amenable to description by measurement of any of the
characteristics visible or accessible from the surface of
the region."
One of the most informative studies on the spread of
groundwater contamination, and the modeling thereof,
is the one carried out at the National Reactor Testing
Station (NRTS) in Idaho and reported by Robertson and
Barraclough 1-3, with additional background material in a
report by Robertson, Schoen, and Barraclough 14. Their
findings show the state-of-the-art of digital modeling for
such purposes, and demonstrate clearly both the powers
and the limitations of the method. The following discus-
sion is directed to these ends, and technical details are
limited to those necessary for a proper understanding.
The NRTS site is on the Snake River Plain in southeast
Idaho, overlying an aquifer consisting of thin basaltic
flows and interbedded sediments, with a water table
about 450 feet below land surface. Industrial and low-
level radioactive wastes have been discharged to the
aquifer through seepage ponds since 1952, and since
1964 cooling-tower blowdown has been injected directly
into the aquifer through an injection well. The U.S. Geo-
logical Survey has monitored the facilities since their in-
ception, and has analyzed the fate of the wastes, using
data from about 45 observation wells. The complexity of
the subsurface regime, however, is such that no ex-
planation could be given for past behavior, and no pre-
dictions could be made about the future. To resolve
these questions a digital model, simulating the aquifer,
was developed. The modeling included a hydrology
phase to solve the equation for groundwater flow, and a
solute-transport phase to solve the equation for solute
movement, both of which were verified on the basis of
historical behavior. The verification procedure is used to
adiust the values of various parameters, and Robertson
and Barraclough note that the most speculative of these
are the dispersivitiesand dispersion coefficient, remark-
ing that "No effective way of measuring coefficients in
the field is presently practical because of the large-scale
aquifer inhomogeneities. It is therefore invalid to extend
ordinary laboratory measurements to field conditions."
Simulations were made for chloride, a conservative
ion; tritium, which is subject to radioactive decay; and
strontium-90, which was strongly adsorbed. It was con-
cluded that the model is a valid tool for estimating waste
distribution in the aquifer. Even so, the authors warn
that this is highly dependent upon future hydrologic con-
ditions, which can only be assumed.
The transverse despersivity value (450 feet) required
to give the best fit of the theoretical plume to the ob-
served plume is much larger than had been expected
from either classic theory or laboratory models. The ac-
tual chloride plume after 16 years, extended about five
miles downgradient and had a maximum width of almost
six miles. In contrast, Pinder 15 found a transverse dif-
fusivity value of only 14 feet in a case of chromium con-
tamination in a glacial aquifer on Long Island. In this
particular case, the shape of the plume of contamination
could have been predicted with moderate accuracy from
the time that contamination commenced, since the aqui-
fer is fairly homogeneous in two dimensions. Drawing a
three-degree cone (as suggested by Danel 16) along the
flow lines, using the mound formed under the disposal
ponds as an apex, gives nearly as good a fit as does the
digital model. This approach does not, of course, involve
the element of time. For practical purposes, however, it
could be applied to similar aquifers to provide an initial
idea of what the area of contamination would be. This by
no means eliminates the need for monitoring and
periodic analysis of collected data.
Thus far we have been considering natural groundwa-
ter flow, disturbed only by mounding effects at the dis-
posal site, which are small for sludge disposal. In prac-
tical application, however, there may be existing or po-
tential well fields, relatively nearby, that would utilize
the disposal aquifer. The inter-relationship in such cases
should be considered, since there is no reason why dis-
posal should preclude utilization, provided that both ac-
-------
196
IMPACT ON GROUNDWATER
I 10
20
[-«—Radius = I8,i
= 18,000 feet-
Transmissibihty = 10,000 gpd/ft
s = 2 2 feet
- Radius =40,000feet -
* 10
20
s = 2 5 feet-
Transmissibihty = 100,000 gpd/ft
Figure 2: Effect of Differing Coefficients of Transmissibility Upon the Shape, Depth and Extent of the Cone of Depression. Pumping Rate and Other
Factors Being the Same in Both Cases.
activities are planned on the basis of an understanding of
the hydrologic system.
Pumping from an aquifer alters the natural flow pat-
tern of groundwater, the degree of alteration depending
upon the hydraulic characteristics of the aquifer, the rate
of pumping, the duration of pumping, and recharge
characteristics. This alteration consists of a cone of de-
pression with the well at the center, towards which water
flows radially from all directions. Drawdown within the
well is required to create a sufficient gradient to move
water towards the well at a rate equal to the rate of
pumping. Neglecting recharge, the volume of the cone
at any given time, multiplied by the storage coefficient,
represents the total volume of water extracted from the
aquifer since pumping began. The effect of trans-
missivity on this radius is shown in Figure 2. Since the
drawdowns required to move water to the well are less in
the more transmissive aquifer, but the volume of water
pumped is the same, it is necessary for the radius of in-
fluence to be greater. As a corollary, wells in highly
transmissive aquifers will capture contaminants at
greater distances than those in aquifers of low transmis-
sivity. Because water-table aquifers have higher storage
coefficients than do artesian aquifers, the radius of in-
fluence and the volume of the cone are smaller in the
former, all other conditions being equal.
One effect of this cone of influence on wells pumping
in the vicinity of a plume, or of a source, of contamination
is shown in Figure 3, which illustrates that undesirable
effects cannot be eliminated, necessarily, by locating a
well or well field either out of the line of the natural
plume or upgradient from the source. On the other hand,
Figure 4 illustrates that even in a direct line downgradi-
ent from the source, only a portion of the water flowing to
the well will consist of contaminated water, and that this
portion decreases with increasing distance from the
source. Again, however, these are simple cases of per-
fect radial flow, and the pattern would be distorted by in-
homogeneities in the aquifer; by streams, lakes, or im-
permeable rock barriers within the radius of influence;
or by other pumping wells nearby.
Pumping from one aquifer in a series of two or more
alters the head relationships among them, and can re-
verse the naturally occurring interaquifer transfer of
water. (This is also true if two or more of the aquifers are
pumped, but only the simplest case is considered here
since the others differ only in detail, not in principle.)
It is commonly (but not universally) the case that the
natural head in an artesian aquifer is higher than that in
the overlying water table one. In this case, leakage will
occur upwards from the artesian aquifer into the water-
table aquifer, the amount per unit area depending upon
-------
IMPACT ON GROUNDWATER 197
DIRECTION OF GROUND WATER FLOW
'SLUDGE \ CONTAMINATED
DISPOSAL ] GROUND WATER PLUME
AREA
PRODUCTION WELL
( Not pumping )
DIRECTION OF GROUND WATER FLOW
SLUDGE\ CONTAMINATED
DISPOSAL) GROUNDWATER PLUME
AREA
PRODUCTION WELL
(Pumping)
CONE OF DEPRESSION
Figure 3: Illustration of Interception of a Contaminated Ground water Plume by a Pumping Well.
CONTAMINATED GROUND WATER
APPROXIMATELY 8% OF TOTAL
Figure 4: Effect of Distance of Contaminated Source from Pumping
Well on Percentage of Contaminated Water Pumped.
the thickness and vertical permeability of the confining
bed, and the difference in head between the two aqui-
fers. If the artesian aquifer is pumped, its head within
the cone of depression is reduced, as is (consequently)
the upward leakage. If the pumping rate is great
enough, the artesian head will fall below the water-table
head for some distance around the well, and in this area
the flow will be reversed and downward leakage will take
place (Figure 5).
From the above discussion it is apparent that even a
confined aquifer is not necessarily protected from con-
tamination. If the water-table aquifer in the example
given is contaminated, some of the contaminants will
eventually reach the confined aquifer and thence the
pump. The amount of such contaminant transfer will de-
pend upon the same factors that govern leakage, plus
the exchange and adsorptive capacities of the confining
bed. In some cases, it would be negligible; in others, sig-
nificant. There is also evidence that clay layers may act
as semipermeable membranes, with osmotic effects that
may create anomalies in both pressure heads and con-
centrations of dissolved ions9.
Obviously, all of these considerations are applicable to
cases where natural head in the water-table aquifer is
higher than in the artesian one. In this case, the natural
leakage would be downwards, and pumping from the
artesian aquifer would simply increase the rate of con-
-------
198 IMPACT ON GROUNDWATER
PRODUCTION WELL
( Not pumping ) \
ARTESIAN NON-PUMPING HEAD
WATER TABLED
UNCONFINED
I J S
/ 1 <
CONFINING *
1 ' uj
_i
ARTESIAN
.
1
LAND SURFACE
AQUIFER
LAYER
AQUIFER
CONFINING LAYER
DISCHARGE
PRODUCTION WELL
( Pumping) ^S>
><[-, LAND SURFACE
WATER TABLEx
UNCONFINED
ARTESIAN PUMPING HEAD' \
UJ 1 .
-------
IMPACT ON GROUNDWATER
199
ences in the United States, Memoires de ['Association
Internationale des Hvdrogeologues, Tome X-l, 1974,
31-37.
11. Wenzel, L.K., Methods for Determining Per-
meability of Water-Bearing Materials, U.S. Geological
Survey Water Supply Paper 887, 1942, 11.
12. Skibitzke, H.E., Extending Darcy's Concept of
Groundwater Motion, U.S. Geological Survey Profes-
sional Paper 411-F, 1964.
13. Robertson, J.B. and J.T. Barraclough, Radioac-
tive and Chemical Waste Transport in Groundwater at
National Reactor Testing Station, Idaho: 20-Year Case
History and Digital Model, In Underground Waste Man-
agement and Artificial Recharge, Vol. 1, AAPG, USGS,
and Int. Assoc. of Hydrological Sciences, 1973, 291-322.
14. Robertson, J.B., Robert Schoen, and J.T. Barra-
clough, The Influence of Liquid Waste Disposal on the
Geochemistrv of Water at the National Reactor Testing
Station, Idaho: 1952-1970, U.S. Geological Survey
Open-File Report, 1973.
15. Pinder, G.F., A Galerkin-Finite Element Simula-
tion of Groundwater Contamination on Long Island,
Water Resources Research, 9, 1973, 1657-1669.
16. Danel, P., The Measurement of Groundwater
Flow, Proceedings of Ankara Symposium on Arid Zone
Hydrology, UNESCO, Paris, 1953, 99-107.
-------
ENGINEERING STUDY AND FIELD
DEMONSTRATION TRIALS FOR SAND
DUNE STABILIZATION
George D. Ward
George D. Ward and Associates
Portland, Oregon
INTRODUCTION
The U.S. Navy Weapons System Training Facility is
located in the Boardman area of northeast Oregon that is
rated by the Columbia-Blue Mountain Resource Conser-
vation & Development Project as a severe wind erosion
area. The entire site is within an ancient lake bed making
the soil a collection of silt, sand and gravel layers. In ad-
dition to moving sand accumulations, concern with dust
in the mid-Columbia region has resulted in a request for
action by county authorities.
The eastern boundary of the Navy Range is bordered
by the Heppener highway. At times during 1971 and
1972 and mid-1974, blowsand has created traffic hazards
and a road maintenance problem. In addition, two sand-
blows along the east boundary have caused some crop
damage on adjoining farms.
Along the northern boundary of the Navy Range, sand
motion has caused concern since it has crossed the
boundary and is moving onto privately owned land.
Agricultural land development throughout this windy
region of Oregon has caused a high sensitivity to wind-
blown soil erosion.
As a result of numerous requests from county authori-
ties and adjoining neighbors, the U.S. Navy activated
two research contracts with the consulting engineering
firm of George D. Ward & Associates designed to pro-
vide soil stabilization in the critical areas.
The first Navy contract was a soil building program
using fiberous wastes. The first trials utilized a variety of
solid wastes in varying concentrations which were incor-
porated into a sandblow (test plot) on the Navy Range.
The treated sand was then planted to dryland grasses in
November 1972 and evaluated during 1973.
The intent of the second engineering study was to ap-
ply on a much larger scale sand control procedures found
to be effective during the initial contract. Seeding and
physical stabilization procedures were undertaken on
the second contract during the fall planting season of
1973 and the early spring planting season of 1974.
The program planned is similar to soil stabilization
programs being conducted in Israel, the Isle of Jersey in
the English Channel and at the Lowry Bombing Range in
Colorado. In Israel, shredded municipal waste is covered
with a layerof sand before reseeding with desert vegeta-
tion. In Jersey, shredded and composted municipal
waste is blended with blowsand for developing turf (and
disposing of the solid wastes). At the Lowry Bombing
Range the entire production of sewage sludge from Den-
ver is used in a soil building program. The mechanically
thickened sludge is deposited in a layer, plowed, disced
and seeded. The product is a healthy stand of range
grass that is both productive and highly resistant to wind
erosion.
RESULTS AND RECOMMENDATIONS
In order to establish adequate vegetative ground
cover on the many and widely disbursed areas needing
assistance, the careful selection of locally available,
lightweight and easily transportable farm equipment
plus organic soil additives is quite important. Experi-
ence gained in the initial field study clearly demon-
strated the high cost of transporting and distributing
large quantities of bulky organic materials to remote
areas of the range. Consequently, in order to achieve
maximum effectiveness at the least possible in-place
cost, it is essential that only fast moving, highly mobile
equipment plus easily transportable organic and inor-
ganic nutrients be considered. Additionally, the selec-
tion of equipment and procedures requiring the smallest
number of personnel is important due to high labor costs
and seasonal limitations on the availability of local field
personnel.
It was found that in order for the project to be eco-
nomically practical, it must be managed on a highly flex-
ible, seasonal basis. While it is known that planting can
occur either in the spring or fall, sudden and unexpected
seasonal variations require almost a day to day decision
making capability. This flexibility is also necessary in
order to assure maximum utilization of available mois-
ture, ground temperature and short wind-free intervals.
Therefore, it remains of prime importance that equip-
200
-------
SAND DUNE STABILIZATION 201
ment and operating personnel capable of being mobi-
lized quickly should be considered.
When considering the spring and fall planting seasons
during which commercial crops are customarily planted,
it must be remembered that the farmers basic objective
is to allow sufficient growing time to produce a crop of
maximum commercial value. This requirement there-
fore, appreciably shortens the time interval available for
commercial planting as compared to that which is avail-
able when the objective is to produce any degree of plant
growth so long as it is capable of retarding wind velocity
along the soil surface. Consequently, maximum advan-
tage should be taken of virtually all opportunities to
plant seed when conditions appear suitable to achieve
even partial germination and perhaps even stunted plant
growth unable to produce seed due to the lateness of
planting.
There is obviously an advantage if a seed crop can be
produced, since it may make it unnecessary to plant a
given area more than once. However, if for any reason no
seed stock is produced, even partial growth is advan-
tageous if it slows or stops sand action even in a portion
of a problem area. When new plant growth results are
marginal, it is recommended that a continuous reseed-
ing program be implemented in an attempt to gain full
control of the specific sand area involved before control
attempts are withdrawn.
Contrary to conventional farming practices, an area to
be seeded should not be plowed and cultivated in the
usual fashion which is customarily done to achieve maxi-
mum crop uniformity. In the case of soil erosion control,
any existing plant growth, whether still living or dead,
should be disturbed as little as possible in all reseeding
procedures. Where large areas are involved justifying
the use of tractor drawn drill seeders, both should be
operated in the standing stubble with the seed being
planted directly into the existing straw and root clumps.
The same is true of hand seeding where wheeled equip-
ment is either not recommended or incapable of
operating.
So long as existing plant residues are not disturbed
and remain essentially in an upright or leaning position,
protection is maximized. Any action, whether it be till-
age, grazing, flattening by the wind, or natural decom-
position, which either depletes or flattens the residue,
reduces its effectiveness to retard wind erosion. The ini-
tial increment of residue is normally the most effective
with each additional amount increasing the protection in
relation to the quantity originally developed.
The physical characteristics of plant residues are also
important, and their effect on wind velocity and turbu-
lance at ground level should be considered when select-
ing plant species. In general, the small finer textured
cereal grains and grasses afford greater protection than
equal quantities on a total weight basis of coarse stalked
plants such as sorghum and maize. Long, small grain
stubble, and that in a leaning position, is more effective
than if flattened.
Studies conducted by the Food and Agriculture Or-
ganization of the United Nations suggest that loamy
sands require 1,750 pounds of plant growth per acre to
control wind erosion providing the plant stalks remain in
an upright or leaning position. If laying flat, the same
degree of control would require 3,500 pounds of the
same type plant residue.
It is also quite obvious that wherever possible, me-
chanically planted seed rows should be oriented perpen-
dicular to the wind. Portable wind tunnel tests con-
ducted elsewhere on rows of nine inch high sorghum
stubble spaced at 40 inches between rows, showed soil
losses three times greater with rows parallel to the wind
than with the wind perpendicular to the rows. In the case
of Boardman sand, raw spacing over approximately
eight inches is not recommended.
Where wide, tractor drawn drill seeders are advan-
tageous in planting long and narrow belts of sand run-
ning parallel to the wind, a zig-zag pattern should be fol-
lowed to prevent an opportunity for wind to line up and
run unobstructed down the rows. Such areas should be
planted with two passes of the drill seeder. Each should
be done in opposing, zig-zag patterns resulting in a
"waffle" or "quilted" pattern as the rows cross each
other. This same technique is also recommended for
cross wind seeding as it affords greater protection than
parallel rows of plants. It also compensates for bald
spots caused by the occassional failure of planting equip-
ment resulting from clogging of seed chutes that carry
the seed from the drill hopper to the individual planting
discs.
Another important consideration is the type of seed
stock selected. Factors such as cost of seed and the
length of time it takes a given species to develop suffi-
ciently are quite important.
Generally speaking, the cereal grains are recom-
mended for the first erosion control seeding attempts
due to their ability to establish a maximum amount of
vegatative grown in a minimum amount of time. They
are annual however, meaning that new growth during
the following season is dependent on seed production
and survival through the winter. Seed losses due to
birds, rodents and drifting sand can, in some cases, de-
stroy nearly the entire crop, and where appreciable loss
is suspected, reseeding should be considered.
Slower growing perennials are more desirable over a
long period of time. In addition to not requiring reseed-
ing if a seed crop fails, they form very dense and tough
root formations having excellent resistance to wind
erosion.
Trials were made using individual plantings of Cougar
Rye and Nordan Crested Wheatgrass and also plantings
utilizing a blend of six parts rye to one part Crested
Wheatgrass on a weight basis. Results suggest that
Crested Wheatgrass is too costly and too slow to develop
-------
202 SAND DUNE STABILIZATION
to warrant its use on the first attempts at controlling
moving sand. The mix worked reasonably well, but due
to the large difference in seed size and the different
recommended planting depths, mixed seeding is not
considered overly successful.
Small seed such as Crested Wheatgrass should be
planted about one fourth inch deep while the larger seed
has an optimum planting depth of approximately one
inch. When planting in soft sand, these are very difficult
dimensions to adhere to, and it is therefore recom-
mended that the larger annual cereal grains be used first
to establish some degree of control before the more de-
manding perennial species are attempted. Costs for
these two species in the fall of 1973 were:
Seeds/
Cost Seeds Pounds Sq. Ft.
Perlb. Perlb. Per Acre lib/Acre
Couger Winter
Rye $.10 —- 60
Nordan Crested
Wheatgrass $.60 175,000 40 4
The seeding rate in pounds per acre was appreciably
greater than the normal recommended rate to compen-
sate for the mortality expected as a result of shifting
sand. On subsequent reseeding attempts, it is antici-
pated that the application rate could be dropped to ap-
proximately ten pounds to the acre which is still slightly
higher than the four to six pound seeding rate for normal
soils.
Broadcast seeding was attempted where surface con-
ditions were too irregular to permit the use of conven-
tional farm equipment. Although broadcast seeding is
not considered to be nearly as effective as drill seeding,
surprisingly good results were achieved in one site.
However, it was not until the second season that most of
the germination took place. In this instance, hand
cranked manually operated seeders were used.
Broadcast seeding utilizing a truck mounted, elec-
trically powered seeder was used in large and open but
nearly inaccessible areas during the late spring of 1974.
Results as of June, 1974 appeared to be limited. How-
ever, as in the previous successful example, it may re-
quire two or more seasons before the full results become
known.
Areas of natural reseeding should be watched careful-
ly as often the only plant capable of initially establishing
itself without help is a very durable and sturdy weed
commonly referred to as Russian Thistle. The sudden
appearance of this annual weed over large areas in as lit-
tle time as one season can be quite deceiving. While it
may appear that the presence of a dense mat of closely
spaced Russian Thistle plant starts has stabilized the
rapidly moving sand, it must be remembered that freez-
ing kills this species and once the tough, wood like plant
stems lose their original strength, sudden winds can tear
away entire patches of thistle in the form of tumbleweed.
The result is that large areas of unstable sand can be
stripped in a matter of hours of all tumbleweed type wind
protection, and movement over a wide area can re-occur
in a short period of time. Furthermore, during the windy
winter months, while plant growth as well as seed germi-
nation is dormant, no protective regrowth is possible.
Therefore, when zones of "natural healing" are found,
they should be hand or broadcast seeded with a mixture
of grasses and cereal grains in a manner that does not
disturb the frail but protective, naturally occuring,
groundcover.
In small areas, hand broadcast seed should be raked to
a depth of about one or two inches. The surface of all
bare sand should then be covered with loose straw or
mulch to prevent loss or gain of sand depth over the seed
until germination and regrowth of a new vegetative
cover. Nitrogen fertilizer should also be equivalent to a
rate of 40 pounds per acre.
It is of fundamental importance that each problem
area be evaluated throughout its surface area before ma-
jor control efforts are started. Control procedures should
obviously be started on the upwind side of problem areas
wherever possible. Failure to do so exposes unprotected
downwind efforts to serious damage or loss resulting
from incoming sand. It is therefore far better to start
from an area of obvious soil and vegetative stability and
move in a series of downwind steps until the full length
of each sand formation is secured than it is to attempt to
work "into" the prevailing wind and oncoming sand.
In situations where time is critical and it may be neces-
sary to also stop the advancement of sand on the down-
wind end of a sand formation, it maybe necessary to re-
sort to the placement of snow fencing in the path of ad-
vancing shallow sand blow type formation.
Snow fencing, although temporarily effective, is not
considered a permanent means of erosion control.
Nevertheless, its ability to trap sand to nearly the full
height of the fence section on the leeward side of the bar-
rier makes it a worthwhile device for retarding move-
ment of sand masses where vegetative cover is not im-
mediately available. This ability is of value in temporari-
ly holding the downwind portions of shallow depth sand
blows only. The use of snow fencing on the downwind
slopes of high dunes would be totally ineffective and is
not recommended.
Where high dunes are to be controlled, it is essential
that control procedures be started at ground level on the
upwind slope. Work can proceed step by step over sev-
eral seasons as long as it is done on continuously adja-
cent horizontal zones. By progressing in this manner up
the exposed face of a dune, it is possible to stop the lower
portion of a dune and hold it in a fixed position while al-
lowing the wind to continue moving the top downwind. If
desired, this process can be used to reduce the height of
a dune and to spread its mass out to a more or less prede-
termined depth and shape.
In general, the most difficult logistical aspect of the
project involves the distribution of various forms of or-
-------
SAND DUNE STABILIZATION
203
ganic nutrients in a thin layer across the sand areas. This
must be done concurrent with a carefully selected seed-
ing program utilizing drought resistant cereal grains and
grasses. Where moving sand is involved, it is first neces-
sary to physically stabilize the surface of the sand long
enough for germination and new plant growth to occur.
Otherwise, the higher cost of the initial physical control
process could be lost should the entire mass continue to
move.
The organic nutrients selected require a variety of
techniques for their uniform placement as determined
by their quantity, density and other physical characteris-
tics. They may occur in either liquid or bulk form each of
which require entirely different types of equipment for
their delivery and uniform distribution.
Waste organics, when used, were selected on the
basis of their availability, ease of handling, organic
value, physical ability to stabilize and their moisture re-
tention characteristics. Waste elements presently able
to meet these requirements are:
1. Liquid sewage sludge
2. Baled straw-purchased locally
3. Papermill sludge
4. Shredded bark and woodwastes
5. Feedlot bedding
6. Shredded paper
In remote areas lacking suitable access roads and
where planting may be effective without the opportunity
to first physically stabilize the sand, the use of chemical
fertilizers should be investigated. Both cost and avail-
ability of chemical fertilizer must be considered and than
balanced against the risk of plant growth failure that
might result due to the lack of physical stabilization.
However, even though more initial expense may be in-
curred through purchase of chemical fertilizer, their
greater nutritional value and reduced bulk warrant
their consideration on remote problem areas where ac-
cess and delivery costs are proportionately high.
Consideration must also be given to the carbon-nitro-
gen balance of each combination of either fiberous or nu-
tritionally rich waste organics. Papermill sludge, for ex-
ample, is high in fiber content, but virtually void of
measurable nutrients. Additionally, it has a high nitro-
gen demand as the natural decay process proceeds and
unless a nitrogen source is provided, it may rob suffi-
cient available nitrogen from the soil to either prevent or
greatly reduce germination and a healthy growth
response.
To off-set this effect, an available nitrogen source
must be provided. This can be in the form of inorganic
fertilizer (ammonium sulfate), sewage sludge of feedlot
waste. Feedlot bedding normally has enough available
nitrogen to be used in combination with either papermill
sludge or shredded bark. If used singly, both papermill
sludge and shredded bark need about ten pounds of ni-
trogen per ton of cellulose. Materials of this type are
typically applied in dry form.
For situations where liquid application is desired, a
blend of papermill "fiber" and nutritionally rich liquid
sewage sludge provides an excellent carbon-nitrogen re-
lationship. Additionally, this combination offers a blend
in which the fiberous material will concentrate on the
surface of the sand where wind resistance is needed,
while the nutritionally rich liquid phase soaks into the
soil where it is readily available for plant root uptake.
An examination of six month old root growth at the top
of a sludge soaked dune revealed an unusually healthy
interlocking network of hair-like roots in what had been
almost pure sand. In addition to assuring healthier plant
growth, the intricate system of roots offers significant
resistance to wind erosion of the subsurface zone. This
can be quite important where the surface layer of wind
protection might be lost due to fire, excessive grazing or
wind action.
For areas requiring considerable quantitiesof fiberous
wind stabilization materials, it is essential that the ma-
terials be stockpiled in advance. Once the seeding and
wind control procedure has been decided upon, ready
access to all materials, farm equipment and personnel
should be assured before the project is started.
Many of the tools and farm implements necessary to
complete a given dune assault can be obtained through
rental agreements with the local farming community.
Qualified operating personnel can sometimes also be ob-
tained in this same manner. However, it must be re-
membered that the farmers optimum planting season
nearly always coincides with dune seeding schedules
and farm hands can be hard to find during these busy
seasons.
Besides the farm implements to be used, there may al-
so be the need to assemble portable, engine driven
pumps, movable irrigation lines and large bore sludge
guns for use in unloading tank trucks and in the aerial
application of liquid mixes. Rental charges and the de-
gree of portability for large pumps must be carefully
considered.
Other tools needed will be analytical equipment for
determining soil moisture and temperature and for
charting plant growth and sand movement. Fencing may
also be essential, if uncontrolled grazing is permitted in
the general vicinity of the control project. Experience
has shown that cattle will destroy fences in some in-
stances in order to get at the dense green growth result-
ing from the use of highly nutritional organic fertilizers.
Deep dunes are especially vulnerable due to hoof dam-
age in soft sand.
Fences that are constructed for the protection of con-
trolled or otherwise fragile areas should be equipped
with a gate for future access and then left in position if at
all possible. It should be remembered that problem
areas were generally quite frail to begin with, and when
possible, they should be fenced off from grazing and
other intrusions for as long as possible in order to permit
a full recovery of native range grasses and shrubs.
-------
POTENTIAL HEALTH IMPACTS OF
SLUDGE DISPOSAL ON THE LAND
Gory J.Love, Edythalena Tompkins and WarrenA. Galke
United States Environmental Protection Agency
Research Triangle Park, North Carolina
The potential for adverse human health effects asso-
ciated with wastewater treatment and disposal systems
is related to many pollutants with multiple pathways to
man. The pollutants include pathogenic organisms,
trace metals, other inorganic materials such as nitrates,
and organic toxicants. The pathways include aerosols,
surface and groundwaters, direct contact, food chain,
and insect and small animal disease vectors.
Although the value of waste treatment, water treat-
ment, sanitation of the environment, and personal hy-
giene in disease prevention is well established in the
United States, insufficient effort has been made to estab-
lish the significance of waste treatment systems or re-
ceiving sites of the effluent as potential transmitters of
pathogenic organisms.
Few studies have addressed this issue in a reasonable
manner and yet the devastation in terms of human
health that can result from an epidemic of severe enteric
illness is well known. Levels of enteric disease and para-
sitic infections in the human population are generally
low, and because the number of carriers in the popula-
tion is small, it has been suggested that the potential for
the spread of infectious agents as a result of the applica-
tion of fecal wastes to the land is limited1. But levels of
enteric disease in the United States today are low pri-
marily because we have controlled the spread of enteric
pathogens by means of sanitary engineering activities
and the practice of good sanitation and personal hy-
giene. In more recent years the carrier rate has been fur-
ther limited through immunization and antibiotic thera-
py, but the major progress in the control of these dis-
eases had been accomplished through environmental
sanitation prior to the introduction of measures for re-
ducing susceptibility to disease and prior to the develop-
ment of the means for controlling clinical disease. Con-
sequently the number of illnesses that presently might
be attributable to treatment plants and their discharges
is unknown.
Often the lack of epidemiologic observations of
disease outbreaks associated with wastewater discharge
systems has been cited as evidence that the threat to hu-
man health is minimal. It should be recognized however
that the reporting of cases of enteric disease is notorious-
ly poor 2'3, and such disease related to the discharge of
wastes to waterways or to the land application of wastes
very well might not be recognized without intensive
surveillance.
That populations in the United States are highly sus-
ceptible to enteric disease has been demonstrated re-
peatedly by the association of human salmonellosis with
contaminated food, especially poultry, the association of
an estimated 280,000 cases of salmonellosis annually
among children with pet turtles raised in contaminated
ponds4"7 , and the association of shigellosis and hepatitis
in children attending day-care centers8-9. Weissman,
et. al.8 have suggested that the community as a whole is
at risk from outbreaks of shigellosis at day-care centers
and that the increasing incidence of Shigella sonnet in-
fections evident in several large cities may reflect the
impact of day-care associated shigellosis on urban
communities.
The application of wastes to the land could possibly
complete other cycles of infection not presently existing,
or functioning at low levels. This could lead to the estab-
lishment of significant new reservoirs of infection or to
increases in the levels of contamination in those already
existing, if the practice of applying wastes to land was to
be greatly expanded.
The major potential hazard exists where a break oc-
curs in efficiency of the waste treatment process 10'n .
This would be particularly important if epidemic strains
of the more serious enteric pathogens were to be im-
ported into the country. Again it is probably due only to
the effectiveness of sanitation in the United States that
such epidemic strains have not become established.
That epidemic cases might arise under relaxed vigilance
is suggested by the outbreak of cholera El Tor in Jerusa-
lem in 1970 which was attributed to the use of sewage for
irrigation of vegetables sold in the city12 .
Pathogens in Wastes
There is a wide variety of pathogenic bacteria, viruses
and parasites that occur in sewage (Table 1). However,
204
-------
POTENTIAL HEALTH IMPACTS 205
TABLE 1
Human Enteric Pathogens Occurring in Wastewater
and Sludge and the Diseases Associated With
the Pathogens
BACTERIA
VIRUSES
Vibrio cholerae
Salmonella typhi
ShigeTla species
Proteus species
Coliform species
Clostridium species
Pseudomonas species
Infectious hepatitis virus
Echoviruses
Coxsackie virus
Poliovirus
Diseases
Cholera
Typhoid and other enteric fevers
Bacterial dysentery
Diarrhea
Diarrhea
Botulism
Local infection
Hepatitis
Enteric and other diseases
Enteric and other diseases
Poliomyletis
Epidemic gastroenteritis virus Gastroenteritis
PARASITES
Entamoeba histolytica
Balantidium coli
lospora hominis & others
Giardia lamblia
Pinworms (eggs)
Tapeworms
Liver 8 Intestinal flukes
Amoebic dysentery
Balantidlal dysentery
Coccidiosis
Diarrhea
Ascariasis
Tapeworm infestation
Liver or intestinal infestation
the types of pathogens present as well as the concentra-
tion may vary considerably from community to com-
munity. Bacterial pathogens which may be present in
wastewater include Salmonella typhi^'^ , paratyphoid
and other Salmonella serotypes15'17"23 , Pseudomonas
aeruginosa^, mycobacteria25"31 and Clostridium per-
fringens 32'34 . Numerous viruses are excreted by
man35,36 including poliovirus (three types), coxsackie-
virus (25 types), echovirus (25 types), reovisus (three
types), and adenovirus (33 types). The only viral disease
definitely known to be water-borne and hence possibly
associated with wastewater is hepatitis A (infectious
hepatitis). Various parasites reported from wastewater
include Entamoeba histolytica^7, Entamoeba coli 38~40 >
schistosomes41, Naegleria42, various nematodes 43~47
and fungi48.
Counts of microbial pathogens in sewage vary con-
siderably, depending upon rates of disease in the con-
tributing population. Organisms, such as Entamoeba
histolytica, might be expected only in low numbers, if at
all 38. Many parasites and even the cholera vibrio how-
ever might be present in the sewage of a community
temporarily after a traveler carrying the organisms en-
ters the community. Some bacterial pathogens, includ-
ing Pseudomonas aeruginosa, are consistently present
in sewage. Fecal carriage of this organism occurs in ap-
proximately 11 percent of healthy adults, and concentra-
tions in excess of 10^ bacteria per 100 ml are common in
raw sewage. Concentrations in excess of 10" bacteria per
100 ml have been reported in sewage in Germany and in
hospital wastes in South Africa and the United States 49.
Concentrations of other bacterial pathogens, such as sal-
monellae, fluctuate with rates of disease in the com-
munity 17. Concentrations of non-typhoid salmonellae in
raw sewage have been shown to vary from about 110 to
11,000 per 100 ml50. Highest numbers occurred during
August and September when the reported isolations
from human sources normally are greatest51. Since the
number of isolations of shigellae also varies seasonally,
the numbers of shigellae in sewage undoubtedly fluc-
tuate in a similar manner. The numbers of salmonellae
or shigellae in sewage are several orders of magnitude
less than fecal coliforms and while there is some vari-
ability in the ratio of salmonellae to coliforms in the raw
sewage of different communities the ratio appears to be
quite consistent in a single community. Kehr and But-
terfield52 estimated that about six typhoid organisms
were present in sewage for every million coliforms.
Enteric viruses have been demonstrated in raw sew-
age in various countries in concentrations of one to ten
virus particles per ml53. The concentrations of virus
particles discharged in domestic wastes at any time is
determined by the number of cases of viral disease plus
the number of carriers in the community54. Investiga-
tors have reported 4000 virus particles per liter of do-
mestic wastewater during the warmer months of the
year and 200 particles per liter during the colder
months55 In Israel, five cities showed an average of
1050 virus particles per liter, although individual deter-
minations varied from 5 to 11,000 virus units per liter56.
This latter study demonstrated a ratio of one virus parti-
cle per 10^ to 10' coliform organisms. In contrast, how-
ever, other studies have demonstrated one virus particle
per 65,000 coliforms 57 and a ratio of one virus particle
per 50,000 to 100,000 coliforms may not be uncommon in
the United States58.
Because sewage contains pathogenic microorganisms
and viruses, it stands to reason that settled sludge
should contain large numbers of these pathogens. Pri-
mary settled sludges have been shown to contain large
populations of microbial pathogens 59.60. One study61
demonstrated that concentrations of tubercle bacilli in
settled sludge were 13 times greater than in the super-
natant liquor. That salmonellae may be present in
sludge has been shown also 62. A mean of 1000 salmo-
nellae have been demonstrated per 100 ml of raw sludge,
and 100 per 100 ml of digested sludge. Although less is
known about the viruses 63, sludge produced by floccula-
tion of sewage solids 64 and activated sludge may contain
large numbers of virus particles. Thus, significant num-
bers of pathogens can be demonstrated in both primary
and secondary sludges.
Effects of Treatment on Pathogens in
Effluents and Sludges
Many stuides indicate that bacteria are not removed
effectively from wastewater effluent during primary
treatment 27'60-61 . On the other hand, primary settling
produces sludges which contain significant numbers of
pathogenic microorganisms59. Apparently, few viruses
-------
206
POTENTIAL HEALTH IMPACTS
are removed from the effluent during primary
treatment 65-66.
Alternative means of killing pathogenic organisms in
sewage and sludge include ozonation, pasteurization,
gamma radiation, and chlorination. Ozone may be a very
effective agent against viruses. Shuval67 and Berg68
have stressed the potential usefulness of ozone based
upon limited reports of research, but each indicates the
need for more work on this disinfectant. Hess and Lott69
and Hess, et. al.62 reported that populations of Entero-
bacteriaceae in sludge were reduced by 93 to 99 percent
when heated to 70°C for 30 minutes. Limited studies of
pasteurization undertaken by the Environmental Protec-
tion Agency indicate that heating of digested sludge to
75°C for one hour kills pathogens, and Berg 70 sug-
gested that pasteurization was the only practical method
for the control of pathogens where large amounts of
solids must be penetrated as is the case with sludges.
However, the use of gamma radiation has been con-
sidered, and may be useful if radioactive wastes are
available as radiation sources. For example, Hess and
Lott69 employing a Cobalt 60 source, achieved 10 to
100,000 fold reductions in numbers of Enterobacteri-
aceae at 100 krad and up to 100,000,000 fold reductions
at 400 to 500 krad in raw and digested sludge. Whatever
methods are employed, destruction of nucleic acids of
viruses probably is desirable. Melnick 71 has pointed out
that viruses presumably inactivated by heat may contain
infectious nucleic acids and such virus particles may be
activated within macrophages, a phenomenon analogous
to the recovery of injured bacteria.
Persistence and Movement of Pathogens
in the Environment
Because pathogenic organisms present in sewage and
sludges may be transmitted from contaminated environ-
ments to man, the persistence of these pathogens in wa-
ter, soil, sludge, feces and aerosols is of fundamental in-
terest and concern. An understanding of the movement
and persistence of pathogens is needed to evaluate po-
tential risks associated with different pathways of trans-
mission.
Aerosols may be produced where sewage or sludge is
aerated or sprayed on the land. Randall and Ledbetter 72
found 1170 bacteria per cubic foot (42,000 bacteria per
m^) in samples of air obtained downwind of an activated
sludge plant, in contrast to eight organisms per cubic
foot (285 organisms per m^) in samples obtained upwind
of the facility. They concluded, furthermore, that in spite
of an initial "die-off," the bacteria persisted for a con-
siderable time and distance downwind of the plant. Con-
centrations in the air were observed to increase with in-
creasing wind velocity. Recently Goff, et. al. 73 pub-
lished data indicating that survival of bacteria in
aerosols were greater at night than during the day.
This would suggest that solar radiation causes death
either by direct action on aerosolized bacteria or by
action on the aerosol particles themselves. Greater
aerosol emission occurred at moderate wind speeds than
at high or low wind speeds. Poon 74 and Goff, et. al. 73
observed that death rates in aerosols increased with in-
creasing temperature and at relative humidities less
than 35 percent. Survival may be reduced also at high
relative humidity, which may be attributable to break-
down of RNA 75. Injury to the cell wall also may occur
during aerosolization 76.
Few investigations have been undertaken to explore
the dissemination of microorganisms from land applica-
tion sites. Merz 77 reported that bacterial travel in aero-
sols was limited to 1,000 to 1,300 feet (300 to 400 meters)
in eleven mph (18 km per hr) wind and that most of the
mist and bacteria settled within half that distance.
Adams and Spendlove 78 were able to recover coliform
organisms in the immediate vicinity of a trickling filter
plant and as far as 0.8 miles (1.3 km) downwind. Of bac-
teria isolated 125 feet (38 m) from aeration tanks by Ken-
line and Scarpino 79, 39 percent were Enterobacteri-
aceae; of which Klebsiella, Enterobacter, and Escheri-
chia accounted for 78 percent. Of the remaining isolates,
16 percent consisted of Citrobacter and unidentified
genera, and six percent consisted of Shigella,Arizona,
Hafnia, andSerratia. No Salmonella or Proteus were iso-
lated. Few studies have been undertaken to determine
the survival of viruses in aerosols. However, Walker 80
reported that poliovirus could survive for as long as 23
hours in aerosols when the relative humidity was high.
The persistence of pathogens in soil or on vegetation
has been examined more extensively. Most bacteria ap-
pear to be trapped after brief passage through soil 81-90.
Some pathogens can travel for miles through limestone
areas, but may be removed near the surface by heavy
textured clay soils as a result of adsorption and filtra-
tion 91. Thus the size of an organism and the type of soil
affects the distance an organism travels through soil.
Although several feet of soil appear necessary for com-
plete removal of bacteria, 92 to 97 percent may be re-
moved in the top 1cm 92. Mathur, et. al. 93 showed that
99.9 percent of bacteria were removed during passage of
sewage through a depth of 17 inches (43 cm) and a hori-
zontal distance of 15 inches (38 cm).
The movement of viruses through soil has not been in-
vestigated thoroughly. Results of limited percolation
studies 94 suggest that complete virus removal can be
achieved by careful application of sewage to land. Jop-
kiewicz, et. al.9S reported that concentrations of polio-
virus were reduced substantially during passage
through irrigation fields. Other viruses were removed
less effectively. Removal of viruses in soils is a function
of the characteristics of the soil. There is some indication
that viruses are removed as effectively as bacteria, prin-
cipally by adsorption 83,85,86 According to Drewry and
Eliassen 85 virus retention by soils is an adsorptive pro-
cess that is highly efficient at pH values below 7 to 7.5,
but which decreases at higher pH values. Drewry and
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POTENTIAL HEALTH IMPACTS
207
Eliassen demonstrated increased adsorption of viruses
by increasing clay and silt content, ion exchange capa-
city, and glycerol retention capacity of soil. Merrell, et.
al. 9" reported that viruses injected into percolating wa-
ter were removed completely in 200 feet (61 m) of hori-
zontal and vertical travel. Robeck, et. al.97 observed re-
tention of virus particles on sand beds two feet (61 cm)
deep when the flow rate was no more than four linear
feet (122 cm) per day. They concluded that pre-treat-
ment with alum followed by sand filtration at two to six
gpm per square foot (81 to 244 liters per min per m^) re-
tained 98 percent to 99 percent of virus particles.
Pathogenic organisms may survive in soil and on crops
for periods varying from a few hours to several months,
depending upon the type of organism, soil moisture, pH,
and predation and antagonism from the resident micro-
bial flora 98-102 Magnusson 103 reported that coliforms
remained viable on grass for 15 days in dry weather and
for seven days in wet weather. On the other hand, Hess,
et. al. 62 reported the survival of salmonellae on grass
contaminated with sludge for 40 to 58 weeks in a dry at-
mosphere. McCarty and King 104 found that enteric
pathogens could survive and remain virulent for up to
two months. But it has been reported also that coliforms
survive longer than S. typhiovM. tuberculosis 99,105,106
Kenner, et. al. 107 demonstrated that£". coli survived for
at least 21 weeks after a single application of sludge to
Pennsylvania fields during the spring. Furthermore, E.
coli persisted longer than did P. aeruginosa (17 weeks)
and salmonellae (eight weeks), and both pathogens and
indicators survived longest in winter. That indicator or-
ganisms survive longer in soil during winter than during
summerwasdemonstratedalsobyVanDonsel.et. al. 108.
Routes of Infection
In view of the obvious opportunities for contamination
of soil, groundwater, surface water, and air with patho-
genic microorganisms and viruses in the vicinity of land
application sites, there exists a clear need to identify
possible routes of infection and to determine their signi-
ficance.
The contamination of surface waters at land applica-
tion sites ordinarily would be expected to be less than
that expected as a result of the discharge of sewage di-
rectly to the surface water. The contamination of ground-
waters at land application sites, however, may be a mat-
ter of considerable concern in certain areas. While path-
ogenic microorganisms and viruses may be removed
rapidly in many soils, in limestone regions, viruses may
reach water supplies. The potential risks associated with
contamination of ground waters are not well defined, and
outbreaks of disease related to their contamination are
not well documented. Monitoring and epidemiologic
surveillance in high risk areas needs to be undertaken to
establish, not only travel of pathogens through the
ground, but rates of disease in exposed populations.
The significance of aerosols produced at land applica-
tion sites is not known. Although enteric organisms are
transmitted most commonly by contact it has been docu-
mented that chimpanzees can become infected with
aerosolized typhoid organisms 109. On the other hand,
there is little evidence of higher incidence of disease
among workers at sewage treatment plants 110 than
among other similar workers but extensive epidemiolo-
gic studies have not been undertaken, and there exists
little basis upon which to judge the true risk to workers
having sporadic exposure to aerosols.
Direct contact with contaminated environments may
present a risk to workers and to animals. At some heavily
contaminated application sites, workers may be exposed
to demonstrable risks. Hookworm and other enteric in-
fections apparently do occur more frequently among
farm workers on sewage farms in India than among the
farming population in general HI. Furthermore, Sebas-
tian 112 noted an increased incidence of schistosomiasis
in some areas of China where night soil was spread on
the land. Obviously these examples represent extreme
cases but even where contamination of the environment
is not as severe organisms may spread to man and
animals.
Animal infections also have been traced to sewage
pollution. Schaal 113 demonstrated that the source of an
outbreak of salmonellosis in a dairy herd was contami-
nated stream water. More recently, Bicknell 114 traced
an outbreak of S. aberdeen in a dairy herd to pasture
contaminated with overflows of sewage from a manhole.
Salmonellosis in cattle associated with spreading of ef-
fluent on pastures was reported by Jack and Hepper 11S.
Findlay 116 demonstrated salmonellae in fresh and di-
gested sewage sludges and has suggested that risks to
animals may result from use of sewage sludge as fertili-
zer. Harvey and Price '17 observed that persistence of a
Salmonella serotype in the sewers of an abattoir provid-
ing meat to a community was often followed by human
infection.
Risks of infection among animals exposed to sewage
are not limited to salmonellae. Pseudomonas aeruginosa
which may be waterborne 118-I23 can be a major cause
of mastitis in dairy cows !20-127 and pneumonia in
calves. Consequently the application of wastes contain-
ing P. aeruginosa to pasture, or to streams passing
through dairy farms may present a risk to the health of
dairy cows and calves.
Grunnett and Brest Neilson 12S suggested that wild
animals, especially sea gulls and rats which forage in
sewer outfalls and dumps, may transmit salmonellae
from sewage to domestic animals. Muller I26 demon-
strated a relationship between the proximity to sewage
outfalls and the frequency of carriers among gulls in
Hamburg, Germany. That salmonellae might be spread
similarly from land irrigated with sewage or fertilized
with sludge is apparent.
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208
POTENTIAL HEALTH IMPACTS
Crops used for human and animal consumption may
become contaminated with pathogenic bacteria and
viruses present in effluents and sludges applied to the
land. In spite of considerable reductions in the numbers
of pathogens in the field and on crops as a result of ex-
posure to ultraviolet irradiation, dessication, and com-
petition, sufficient numbers may survive to constitute a
health risk. Geldreich and Bordner 127 reviewed sources
of contamination of fruits and vegetables and provided
support for establishing a limit of 1000 fecal coliforms
per 100 ml in irrigation waters.
There have been reported in the literature records of a
number of outbreaks of disease attributable to the irriga-
tion of edible crops with wastewater. Gaub 128 reported
the isolation of Shigella flexneri from cabbage grown in
fields irrigated with sewage-contaminated water. Shi-
gella flexneri also was the cause of an outbreak of dysen-
tery traced to the irrigation of pasture land with waste-
water22. Cohen, et. al.12 reported an outbreak of
cholera El Tor in Jerusalem affecting about 250 persons.
They demonstrated that vegetables grown on land irri-
gated with sewage were responsible for the secondary
spread of the disease after the introduction of cases and
carriers from outside the country. The organisms were
recovered from sewage, soil irrigated with sewage, and
crops from contaminated fields which were for sale in the
market. Shuval67 cited a similar outbreak of cholera in
the City of Gaza. Thus, there may be a substantial risk
associated with the consumption of raw vegetables
grown on soil irrigated with sewage. Even crops which
are eaten only after cooking may represent a risk since
they may contaminate working surfaces and utensils in
the kitchen, which in turn can lead to contamination of
foods in which bacteria multiply. There would appear to
be no risk associated with surface irrigation of fruit
trees, but if sewage is sprayed, there may be risk both to
consumers and to workers.
Bovine tuberculosis can be transmitted on fodder
crops irrigated with raw or partially treated wastewa-
ter 129. However, the risk is thought to be minimal if ap-
plication of wastewater is stopped 14 to 20 days prior to
pasturing although there is some controversy on this
point. Some workers have reported that the bovine tu-
berculosis organism can remain viable for three months
in wastewater and for six months in soil. Jepsen and
Roth 13° found in Denmark that Corynebacterium bovis
infections in cattle can result from the irrigation of pas-
ture lands with sewage. So the possibility of disease
transmission to and through cattle that graze on such
pasture lands should be considered.
In general, bacteria appear not to enter healthy and
unbroken vegetables. They may, however, penetrate
broken, bruised, and unhealthy plants and vegeta-
bles^9. Once vegetables become contaminated, espe-
cially if bruised, they cannot easily be decontaminated
by rinsing with water or disinfectant. Therefore, germi-
cidal rinses with chlorine are unreliable but pasteuriza-
tion at 60°C for five minutes is effective 131.
In hot, humid climates where rainfall occurs during
the growing season, splashing may cause contamination
of plant parts growing above ground and growth of the
pathogens might occur during transit. If wastewaters
and sludges applied to the soil carry pathogens, the op-
portunity for contamination of the crops could thus be
enhanced.
Viruses also may contaminate vegetables. Christovao,
et. al. 132 recovered poliovirus Types I and III from five
of eleven samples of irrigation water taken from a vege-
table garden in the city of Sao Paulo, Brazil and reported
detection of enterovirus in soil, vegetables, andinwaste-
water used to irrigate the soil in which the vegetables
were grown. Viruses were commonly detected on vege-
tables that grew close to the ground, but not on those
that did not grow in contact with soil or wastewater dur-
ing the growing season. Moreover, viruses may be de-
tected more often in summer and autumn than in other
seasons 133. In extensive experiments, Mazur and
Paciorkiewicz 134 detected virus on the green parts of 13
species of plants grown in soil seeded with poliovirus.
The virus was isolated from 40.7 percent of ground parts
examined and 87.9 percent of samples from the upper
exposed parts of roots extending into water containing
virus. They also found that ten percent of soil samples
contained virus and suggested that virus may have
passed from water to soil by external capillaries along
the roots.
Infective Doses
Some idea of infective doses is necessary to the estab-
lishment of the potential for disease from environmental
transmission of infectious agents. Infective doses of
most enteric bacterial pathogens are relatively high. For
instance, approximately 10° enteropathogenic Escheri-
chia coli or V. cholerae cells must be consumed by
healthy male volunteers to produce disease in a "signifi-
cant" proportion of subjects. Approximately lO^Sa/-
monella cells (including S. typhi) are required to cause
disease, but only 10 to 100 Shigella cells are necessary to
cause dysentery 13S. Children, sick people, and old
people are more susceptible, however, and fewer cells
are needed to produce disease. Thus, only 15,000 Sal-
monella cubana cells caused disease in hospitalized pa-
tients 136. But it must be recognized that cross-contami-
nation by smaller numbers of cells entering the home on
food, followed by growth in an appropriate medium may
lead to the production of large numbers of cells which
can, and frequently do, cause disease.
The infectivity of virus appears to be high, particularly
if the small numbers capable of infecting cells in culture
can produce infections in man 70. Such low infective
doses, have lead to concern over the significance of low
numbers of viruses in drinking water and in contami-
nated environments.
-------
POTENTIAL HEALTH IMPACTS
209
Other Pollutants in Wastewater
The use of sophisticated analytical techniques has es-
tablished that virtually all public and private drinking
water supplies contain uncharacterized organic com-
pounds. These substances are derived from municipal
sewage, industrial waste, agricultural and natural run-
off, and from natural sources. There is little information
available on the concentrations or toxicities of organic
compounds in drinking water and even less is known
about organic compounds in sewage. Heavy metals and
inorganic compounds are also common constituents of
wastewaters. Although serious disease and even death
is known to have occurred subsequent to infection of
relatively large quantities of some organic and inorganic
compounds and heavy metals, little is known about the
health effects which might result from chronic ingestion
of small quantities of these substances. Exposure to en-
vironmental agents has been suspected of producing
cancer, birth defects, cardiovascular disease, and other
anomolies. However, little evidence exists to causally
link a compound or combinations of substances to any
specific illness.
CONCLUSION
It is obvious that a potential for producing adverse hu-
man health effects is associated with the practice of ap-
plying wastewaters or sludge to agricultural lands, and
that the risks relates both to toxic chemicals and to
pathogenic organisms. The extent of the risk relates to
the types of land on which materials are applied, to the
treatment the wastes have received and perhaps most
importantly to the dedication of individuals involved
with the land application or treatment processes, since
the greatest hazard probably would develop as a result of
disruption of good sanitary or treatment practices at any
point in the operation.
The fact that the utilization of wastewaters and
sludges to irrigate and fertilize crops is practiced in
many parts of the world suggests, in spite of the asso-
ciated outbreaks of illness recorded, that the practice
can function in a safe manner. The fixed nature of quan-
tities of water and essential chemicals available to pro-
duce the food vital to the worlds population makes it es-
sential that the means be found to safely use wastewater
and sludge in food production. But the uncertainties as-
sociated with this practice make it imperative that a con-
tinuing research program be vigorously pursued to find
the means to minimize the potential hazards associated
with the use of wastewater and to demonstrate this fact
as quickly as possible and thus help improve the quality
of life for all the world's population.
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-------
212 POTENTIAL HEALTH IMPACTS
85. Drewry, W.A., and Eliassen, R., "Virus Move-
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88. Wesner, G.M., and Baier, B.C., "Injection of Re-
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89. Stevens, R.M., GreenLand: Clean Streams. A Re-
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91. Sorber, C.A., "Protection of the Public Health,"
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92. Marculesseu, I., and Drucan, A., "Investigations
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93. Mathur, R.P., Chandra, S., and Bhardwaj, K.A.,
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96. Merrell, J.C., Jopling, W.F., Bott, R.F., Katko,
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97. Robeck, G.G., Clark, H.R., andDostal, K.A., "Ef-
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98. Falk, L.L., "Bacterial Contamination of Tomatoes
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100. Rudolfs, W., Falk, L.L., and Ragotzkie, R.A.,
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253.
101. Dunlop, S.G., "The Irrigation of Truck Crops
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103. Magnusson, F., "Spray Irrigation of Dairy Efflu-
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104. McCarty, P.L., and King, P.H., "The Movement
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105. Mallmann, W.L., and Litsky, W., "Survival of
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109. Crozier, D., and Woodward, T.E., "Activities of
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112. Sebastian, P.P., "Modern Technology Battles
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113. Schaal, E., "Uber eine durch Bachwasser ver-
ursachte Salmonella-Enzootie in einem Rinderbe-
stand," Deutsche Tierarztliche Wochenschrift, 70
(1963), 267.
114. Bicknell, S.R., "Salmonella aberdeen infection in
Cattle Associated with Human Sewage," Jour. Hyg., 70
(1972), 121.
115. Jack, E.J., and Hepper, P.T., "An Outbreak of
Salmonella typhimurium Infection in Cattle Associated
with Spreading of Slurry," Vet. Rec., 84 (1969), 196.
-------
POTENTIAL HEALTH IMPACTS 213
116. Findlay, C.R., "Salmonellae in Sewage Sludge:
Part I, Occurrence," Vet. Rec., 93 (1973), 100.
117. Harvey, R.W.S., and Price, T.H., "Sewer and
Drain Swabbing as a Means of Investigating Salmonel-
losis," Jour. Hyg., 68 (1970), 611.
118. Prasad, B.M., Srivastava, C.P., Narayan, K.G.,
and Prasad, A.K., "Source of Pseudomonas Infection in
Calves," Indian Jour. Anim. Health, 1 (1968), 51.
119, Pickens, E.M., Welsh, M.F., and Poelma, L.J.,
"Pyocyaneus Bacillosis and Mastitis due to Ps. aerugi-
nosa," Cornell Vet., 16 (1926), 186.
120. Cherrington, V.A., and Gildow, E.M., "Bovine
Mastitis Caused by Psuedomonas aeruginosa," Jour.
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121. Hoadley, A.W., andMcCoy, E., "SomeObserva-
tions on the Ecology of Pseudomonas aeruginosa and its
Occurrence in the Intestinal Tracts of Animals," Cornell
Vet., 58(1968), 354.
122. Curtis, P.E., "Pseudomonas aeruginosa Con-
tamination of Warm Water System Used for Pre-Milking
Udder Washing," Vet. Rec., 84 (1969), 476.
123. Malmo, J., "An Outbreak Due to Pseudomonas
aeruginosa in a Dairy Herd," Amer. Vet. Jour., 48
(1972), 137.
124. Szazados, I., and Kadas, I., "Role of. Pseudomo-
nas aeruginosa in Actinomyocosis-like Bovine
Mastitis," Acta Vet. Acad. Scient. Hungar., 22 (1972),
241.
125. Grunnet, K., and Brest Nielsen, B., "Salmonella
Types Isolated from the Gulf of Aarhus Compared with
Types from Infected Human Beings, Animals, and Feed
Products in Denmark," Appl. Microbiol, 18(1969), 985.
126. Muller, G., "Salmonella in Bird Faeces," Na-
ture, 207 (1965), 1315.
127. Geldreich, E.E., andBordner, R.H., "Fecal Con-
tamination of Fruits and Vegetables During Cultivation
and Processing for Market - A Review,'' Jour. Milk Food
Technol, 34 (1971), 184.
128. Gaub, W.H., "Environmental Sanitation A
Colorado Major Health Problem: A Review of the Prob-
lem," Rocky Mountain Med. Jour., 43 (1946), 99.
129. Krishnaswami, S.K., "Health Aspects of Land
Disposal of Municipal Wastewater Effluent," Can.
Jour. Pub. Health. 62 (1971), 36.
130. Jepsen, A., and Roth, H., "Epizootiology of
Cysticercus bovis: Resistance of the Eggs of Tacnia sag-
inata," In Report of the 14th Internal. Vet. Congress, 2
(1952), 43.
131. Rudolfs, W., Falk, L.L., and Ragotzkie, R.A.,
"Contamination of Vegetables Grown in Polluted Soil.
IV. Bacterial Decontamination," Sewage Ind. Wastes,
23 (1951), 739.
132. Christovao, D.d.A., Candeias, J.A.N., and laria,
S.T., "Sanitary Conditions of the Irrigation Water from
Vegetable Gardens of the City of Sao Paulo. II. Isolation
of Enteroviruses," Rev. Saude Publica., 1 (1967), 12,
Water Poll. Abstr., 42 (1969), 681.
133. Antykov, M.S., "Impact of Viruses in Wastewa-
ter on Agricultural Irrigation Fields," Gig. Sanit.,
(USSR), 38 (1973), 110.
134. Mazur, B., and Paciorkiewicz, W., "Dissemina-
tion of Enteroviruses in the Human Environment. I. The
Presence of Polio Virus in Various Parts of Vegetable
Plants Grown in Infected Soil," Microbiol. (Pol.), 25
(1973), 93.
135. DuPont, H.L., and Hornick, R.B., "Clinical Ap-
proach to Infectious Diarrheas," Med., 52 (1973), 265.
136. Lang, D.J., Kunz, L.S., Martin, A.R., Schroeder,
S.A., and Thompson, A., "Carmine as a Source of
Nosocomial Salmonellosis," New England Jour. Med.,
276 (1967), 829.
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FDA'S OVERVIEW OF THE POTENTIAL HEALTH
HAZARDS ASSOCIATED WITH THE LAND
APPLICATION OF MUNICIPAL
WASTEWATER SLUDGES
G.L. Braude, C.F. Jelinek andP. Corneliussen
Food and Drug Administration
Washington, D. C.
The responsibilities of the Food and Drug Administra-
tion include the protection of the human and animal food
chains from contamination by chemicals and pathogenic
microorganisms. Such contamination may occur, when
polluted sludges from industrial cities are used, or when
sludges are improperly processed or applied in an im-
proper fashion on the wrong corps. Such improper prac-
tices would clearly be of concern to this Agency, while
proper use of good sludge on land and crops would not
normally be expected to present a problem.
Several mechanisms can be visualized for the direct or
indirect contamination of food and/or domestic animals
by sewage sludge. One is direct physical contact, such as
by spraying sludge onto growing crops, or by contact be-
tween low growing crops (tomatoes, lettuce, etc.) and
sludge on or in soil. In such cases food contamination
may be microbiological or chemical. Direct absorption of
pesticides or persistent organics through plant tissues
may also occur. It is less likely for metals. Some heavy
metals and organics are taken up from sludge and soil by
roots and translocated within the plant. Of most concern
is cadmium, as discussed by others at this conference.
Livestock and domestic animals are exposed to these
contaminants when grazing on pastures or eating forage.
According to one estimate* grazing animals are known
to ingest soil (and probably sludge) in amounts ranging
from 2 to 14 percent of their total diet. This direct inges-
tion of sludge contaminants, which are present at higher
levels than in crops, could result in increased uptake of
heavy metals, such as cadmium, lead and mercury, and
of persistent organics (such as PCBs and chlorinated
pesticides). The latter may be retained and gradually
biomagnified in the fat tissues of the animals. From pre-
liminary data available, cadmium is found predominate-
ly in the liver and kidney, and lead in liver, blood and
bones. Other tissues and organs may also be contami-
nated. Research initiated under a joint FDA/EPA agree-
ment with Denver should help clarify this issue.
*W.H. Allaway, private communication.
Complete and precise definitions of safe or unsafe
practices are not available at this time due to insufficient
data on the transfer of many of these contaminants
through the food chain and on the toxicological effects to
be expected. Table 1 summarizes information now avail-
able on the heavy metals of most concern, some of which
has been developed only recently. Tolerable lead levels
are for adults and limits have not been suggested for
children.
The Total Diet Surveys, also called the Market Basket,
have been conducted annually by the Food and Drug Ad-
ministration since 1965. They are based on food con-
sumption information developed about a decade ago by
the U.S. Department of Agriculture and correspond to
the diet of a 15 to 20 year old male. A total of 117 foods
are included in each total diet sample. The foods are
cooked or prepared as normally eaten, and divided into
twelve different food class composites which are then
analyzed for the various contaminants. The total intake,
including water, is about 3,000 grams a day. The aver-
age concentration values of Table 1 are calculated on
that basis. As these are quite low, they could be greatly
affected by a major contaminated food.
Because of the limits of sensitivity of the current
analytical methods, "non-detected" and "trace" re-
sults are frequently obtained for food composites. The
contribution of the total intakes (not included in the data
shown in Table 1) has been estimated to be large for
lead, possibly tripling or quadrupling the value shown,
and for cadmium, increasing the cadmium intake by
about 50 percent. The effect on the other elements is
small. Comparing these higher cadmium and lead
values with the provisional tolerances of the World
Health Organization shows that we may have reached
the safe upper limits for cadmium intake and may be
close for lead also.
Table 2 shows the relative proportion of the diet repre-
sented by each of the twelve food classes. The contribu-
tion that lead and cadmium containing foods make to the
total intake of these metals and the average concentra-
tions in good groups are also presented. Some of the lead
214
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FDA'S OVERVIEW OF POTENTIAL HEALTH HAZARDS 215
TABLE 1
Heavy Metals in Foods
WHO/FAO, (1972),
Provisional Tolerances, (Adult)
Converted to yg/Person/3ay
Total Diet Findings, U.S.
Adult yg/Person/Day (1973)
CADMIUM
57-71
51.2
LEAD
A29
60.4
MERCURY
43
2.9
SELENIUM ARSENIC
Not. Establ. Not Establ.
150
10 (As AS203)
Average Concentration in
Entire Diet, Including
Drinking Water, PPM
0.018
0.021
0.001
0.05
0.003
Most Prevalent In:
(Grains &
(Cereals
I Leafy
(Vegetables
Fruits
Beverages
Legumes
Fruits
Meats,
Fish &
Poultry
(Grains &
(Cereals
! Meats,
Fish &
Poultry
Meats,
Fish &
Poultry
in several groups comes partly from cans (solder), which
adds to the level present in the original produce.
In assessing the safety of the sludge use practice, the
fact must be considered that not more than about one
percent of the total agricultural land in the United States
would be treated with sludge if all sludge available were
used on land at moderate levels. The resulting impact on
selected food commodities and the diet of the overall
population can not be clearly estimated at this time. In
addition, effects may be much greater on other than the
"average person", such as people in localized areas. We
should also consider the old, the sick and the very young
in these assessments.
More research is obviously needed to assess the
magnitude of the problem and to answer questions about
background values, toxicological effects, non-dietary
routes exposure, and permissible levels. Such informa-
tion is necessary to determine whether tolerances or
guidelines need to be developed for the more important
foods or crops we consume.
As discussed by other speakers, the uptake of heavy
metals from sludge-treated soil by plants and crops is
subject to many complex variables. However, many
metals, including cadmium, will be found at higher
levels in crops grown on sludged soil than in the controls
in the same area. The picture is not so clear for lead, and
there is little or no information available on mercury,
arsenic and selenium.
An example of the uncertainty regarding sludge use
involves mercury. It has been known for some time that
mushrooms accumulate metals, and some data were re-
ported to us in 1973 about high levels of mercury and
lead in mushrooms grown in sludge/refuse compost. A
recent paper from Switzerland* reports data showing
that mercury is biomagnified in some mushrooms 2 to 58
times from levels in the soil used. Part of the mercury is
methyl mercury.
We analyzed samples of commercial fresh U.S. mush-
rooms in 1973 and found low levels of mercury (0.03-0.1
ppm) and lead (0.01-0.03 ppm). Mushrooms are, of
course, only a small part of the total diet for the average
person. However, use of sludge-compost as mushroom
soil, as advocated by some, may lead to problems. We
expect to be doing a limited amount of work to help re-
solve this issue.
Sewage sludge is known to contain persistent organic
contaminants such as polychlorinated biphenyls and
chlorinated pesticides. Uptake studies have shown that
edible parts of plants contain these organics, but at
levels 5 to 20 percent of the levels in the soils used.
Table 3 lists a number of halogenated chemicals which
are likely sludge contaminants. Many municipal sewage
systems receive substantial inflow from industrial efflu-
ent sources. These may be pretreated, but limitations
used are based on COD, BOD, TOC, etc., usually with-
out identification of the specific organic contaminants.
In fact, some plant effluents contain a highly diverse
range of compounds. These may be the products from
manufacturing plants, some auxiliary chemicals, or par-
tial breakdown or reaction products from the effluent
treatment. Compositions are often highly complex, as
shown by EPA's studies (Athens, Ga.) of the effluents
from paper/pulp mills. The widely publicized range of
contaminants in drinking water is another indication of
the potential for sludge contamination.
As stated, available data are inadequate for a precise
hazard assessment of food contamination by organic
*T. Stijve, R. Roschnik, Trav. Chim. Aliment. Hyg. 65(1974), 209-220
(English).
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216 FDA'S OVERVIEW OF POTENTIAL HEALTH HAZARDS
TABLE2
Lead and Cadmium Intake in Total Diet
FOOD GROUP
LEAD
Intake % of
Total Diet
I. Dairy Products 25.9
II. Meat, Fish & Poultry* 9.9
III. Grain & Cereal Products 12.6
IV. Potatoes 7.0
V. Leafy Vegetables* 2.0
VI. Legume Vegetables* 2.5
VII. Root Vegetables* 1.2
VIII. Garden Fruits* 3.0
IX Fruits* 7.4
X. Oils, Fats & Shortenings 1.8
XI. Sugar & Adjuncts 2.8
XII. Beverages (including 23.9
water)*
% Of
Total Pb
Intake
0.0
6.6
6.9
1.2
5.0
31.1
6.4
18.8
15.7
1.1
0.9
6.3
Average
PPM
*Includes Canned Foods - Some Metal May Be From Can (Pb)
CADMIUM
% Of
Total Cd
Intake
0.0
0.013
0.010
0.0033
0.050
0.26
0.11
0.12
0.043
0.013
0.0067
0.0033
7.7
4.9
22.8
17.8
6.2
0.8
1.5
3.4
18.3
2.7
1.3
12.7
Average
PPM
0.005
0.0093
0.028
0.046
0.051
0.006
0.021
0.019
0.042
0.027
0.0083
0.0057
chemicals in sludge. It is expected that the most likely
contamination of foods would be (1) in animals ingesting
sludge (grazing, etc.); and (2) following failures of the
sewage plant operation with resulting incomplete break-
down of organic chemical contaminants.
The microbiological hazard from use of sewage on
land and crops is another problem of great complexity.
Microbiologists are concerned about the possibility that
increased use of pathogen containing sewage on land
and crops may adversely affect public health. For ex-
ample one concept is the development of a cycle with
ascaris eggs (intestinal worms) by: (1) increased intake
of these pathogens by, say, a small community ingesting
food grown on sludge amended soil in the area, followed
by (2) increased pathogen discharge into the sewage
system, and (3) increased numbers of pathogens surviv-
ing sewage treatment and returning into the food chain,
etc. Salmonella, tuberculosis and other bacteria are also
of concern in sewage treated crops, and there is the com-
plex question of pathogenic viruses still to be resolved.
For this reason, FDA microbiologists feel that crops
which are eaten raw should not be planted within three
years after the last sludge application. Crops such as
sweet corn, potatoes, etc., which may contaminate other
foods in the kitchen, should not be grown unless the
sludge used gives a negative test for pathogens. From
the microbiological standpoint only industrially heat
processed crops would be safe to grow in soil treated
with ordinary digested sludge.
To properly define chemical and microbiological haz-
ards requires reliable and extensive scientific data. FDA
is conducting programs of its own and collaborative
studies with EPA and USDA. FDA activities include: (1)
surveys for heavy metals and pesticides in selected raw
agricultural commodities grown in different parts of the
country; (2) development and improvement of analytical
methodology for heavy metals and pesticides; (3) inves-
tigations (in our Cincinnati laboratories) on the survival
of pathogens on vegetables grown in sludge treated soil,
and (4) toxicological studies to determine the effects of
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FDA'S OVERVIEW OF POTENTIAL HEALTH HAZARDS 217
TABLE 3 heavy metals and interaction between elements. These
Potential Organic Contaminants in Sludge (Persistent) studies should help provide the information needed to
establish guidelines and/or tolerances.
POLYCHLORINATED BIPHENYL AND TERPHENYL As stressed ear,ier we have no indication at this time
CHLORINATED PESTICIDES that sludge use on land needs to be limited to crops
HALOGENATED CYCLODIENE FLAME RETARDANTS which are not in the human food chain' or' conversely,
that all sludges are suitable for land application. Sludge
CHLOROBENZENES application should be selective and properly conducted
CHLOROPHENOLS to make it safe. This will eliminate some types of sludges
PHT nRTNATvn PARAFFINS from consideration- while in other cases' land applica-
CHLORINATED PARAFFINS tion system& may not be sufficiently cost effective to
MISCELLANEOUS HALOGENATED FLAME RETARDANTS compete with alternative disposal or use schemes.
-------
A SUMMARY OF OBSERVATIONS
ON THERMOPHILIC DIGESTER OPERATIONS
George T. Ohara and James E. Colbaugh
City of Los Angeles' Hyperion Treatment Plant
PlayadelRay, California
INTRODUCTION
A summary report is presented on observations made
while investigating two applications of thermophilic
sludge digestion.
The first concerns the enhancement of the sludge de-
\\atering process under certain conditions when thermo-
philically digested sludge is used instead of mesophili-
cally digested sludge. The second part concerns the en-
hancement of methane gas production during thermo-
philic digestion in comparison to mesophilic digestion.
All of the subject investigations were conducted at the
City of Los Angeles' Hyperion Treatment Plant. The in-
vestigations on sludge dewatering described herein
were initiated in 1972 and continued thru 1973. The in-
vestigations on thermophilic operations described here-
in were also initiated in 1972 and are continuing to date.
These investigations were necessitated by the imple-
mentation of state and Federal regulations which essen-
tially prohibited wastewater solids from being dis-
charged into the Pacific Ocean. Consequently, the City
of Los Angeles was obligated to seek alternative means
of wastewater solids disposal which hopefully would also
result in minimum environmental and economic impact.
Present investigations indicate that the alternatives to
ocean disposal of wastewater solids in the Los Angeles
area are limited to land disposal, basically due to the air
pollution situation. Unfortunately, chemical condition-
ing, mechanical dewatering, vehicular transport and
disposal of wastewater solids into sanitary landfills will
result in an adverse environmental and economic impact
in comparison to the present ocean disposal system at
the Hyperion Treatment Plant1. The thermophilic
sludge digestion process was one of the areas
investigated in an attempt to reduce chemical condition-
ing cost and enhance the dewatering process.
The Hyperion Treatment Plant
The Hyperion Treatment Plant, where these studies
were conducted is operated by the City of Los Angeles
Bureau of Sanitation. The plant serves over three million
people in the City of Los Angeles and neighboring com-
munities. The sewage flow comes from as far as 65 miles
away.
The plant is located on a 144 acre site in Playa del Key
next to Los Angeles International Airport, on the Santa
Monica Bay coast line.
During the 1974-75 fiscal year Hyperion treated
126,916.37 million gallons of wastewater, which aver-
ages out to 347.72 million gallons per day (mgd). All of
the flow receives preliminary and primary treatment,
100 mgd of the flow receives secondary treatment by the
conventional activated sludge process. Primary and
secondary effluents are blended and discharged into the
ocean five miles off shore at a depth of 220 feet.
Wastewater solids removed in the treatment process
are stabilized and reduced in 18 primary anaerobic
sludge digesters. Each digester has a capacity of 2.5 mil-
lion gallons. Presently three of the digesters are being
operated at thermophilic temperatures (120°F), the re-
maining digesters are being operated in the mesophilic
range (95°F).
Approximately 4.5 million cubic feet of digester gas is
recovered daily from the sludge digestion process. This
gas is used as the plants' energy source and presently
supplies the air for the activated sludge process and all
of the electric power except that used for three large ef-
fluent pumps. Excess digester gas is sold to an adjoining
thermo-electric power plant which generates electricity.
The residual solids from the digestion process are
screened to remove floatables, diluted and pumped to
the head of a submarine canyon, seven miles offshore at
a depth of 330 feet where the solids are dispersed into
deeper waters.
An abridged summary of plant process data pertinent
to sludge digestion and handling is shown in Table 1.
An abridged summary of digestion performance para-
meters is shown in Table 2.
Test Program
The sludge dewatering studies conducted at Hyperion
were organized into three progressive phases. The first
218
-------
THERMOPHILIC DIGESTER OPERATIONS 219
TABLE 1
Process Parameters
(1974-75 Averages)
TABLE2
Digestion Performance
(1974-75 Averages)
1. Plant flow
Sus Solids in=
BOD in =
2. Raw Sludge
Total Solids =
Vol. Solids =
3. Digested Sludge^
Total Solids =
Vol. Solids =
347.72 mgd
272 mg/1
255 mg/1
547,600 #/d
6.09%
77.5%
220,800 #/d
2.43%
61.7%
phase was laboratory testing to select the most promis-
ing physical and chemical conditioning processes for
anaerobically digested raw sludge. Next, numerous
tests were performed on a pilot scale level to verify pre-
vious laboratory results. Finally, full scale tests were
performed, whenever possible, based on the results of
the pilot scale tests. Approximately 18 months of effort
was devoted to the dewatering studies. These studies
started in 1972 and were concluded in late 1973.
The following parameters were used as criteria in
evaluating the sludge dewatering system.
1. Maximum capture of solids, i.e., minimum solids
remaining in the liquid fraction.
2. Maximum percent solids in the sludge cake, i.e.,
minimum moisture in the cake.
3. Maximum operational flexibility and reliability.
4. Minimum pre-conditioning requirements, i.e.,
minimum polymer or chemical dosage.
5. The most overall cost effective system, i.e., first
costs plus operations and maintenance costs.
In addition to the technical considerations above ma-
jor consideration was given to the environmental impact,
energy requirements, resource requirement, and ability
to meet legal requirements in the evaluation process.
As an initial goal, the test program established the fol-
lowing specific technical limits:
1. Solids capture (T.S.) 90%
2. Solids in cake (T.S.) 25%
3. Centrate or filtrate quality (S.S.) 1000 mg/1
Limitations
The following observations and discussions are
limited to chemically conditioned mesophilic anaero-
bically digested raw sludge containing approximately
five percent waste activated sludge, by weight.
Although other tests were performed without condi-
tioning the sludge or with other conditioning methods, in
general, the results were poorer and are not included in
this discussion. Only general economic inferences are
included due to the fluctuating economic conditions.
Gas Production = 3.63 X10 ft /d ,
per Volatile Solids Destroyed 12.82 ft /#
CH4 quality = 65%
Volatile Solids Reduction = 67.8%
Charging Rate
Detention time
0.11 Ib. V.S./ftJ
27.6 days
The basic theories underlying centrifugation and
vacuum filtration have been omitted, and only the re-
sults obtained from specific equipment are presented.
The percent solids capture (% recovery) is reported in
terms of total solids (T.S.). This method was used to fa-
cilitate laboratory analyses. Consequently, the actual
suspended solids (S.S.) capture is greater than numeri-
cal values indicated.
Solid Bowl Centrifuge
In this test series a Kruger Model KDF-500 solid bowl
centrifuge was used.
Table 3 indicates the test conditions which were used
to obtain the optimum performance from the Kruger
centrifuge. The "G" force for these tests was 920
"G's", at a bowl speed of 1860 RPM. The best results
were obtained by maintaining maximum pool depth.
Figure 1 illustrates the optimum performance ob-
tained from thermophilic and mesophilic sludges.
Capture of both mesophilic and thermophilic sludges
were very good at 88 percent and 92 percent (T.S.)
respectively.
Mesophilic sludge resulted in submarginal cake solids
content of 18 percent. Thermophilic sludge resulted in
an acceptable cake solids content of 30 percent, which
was 40 percent drier than mesophilic cake.
The suspended solids content in the mesophilic cen-
trate averaged 1550 mg/1 which was considered over the
desirable maximum. The suspended solids content in
the thermophilic centrate averaged 1100 mg/1 which
was slightly over the desired level, but considered ac-
ceptable.
TABLE3
Optimum Test Parameters.
Solid Bowl Centrifuge
Kruger KDF-500
1. Sludge Feed Rate
a) Mesophilic = 14.
b) Thermophilic = 25
2. Sludge Feed Concentration
aj Mesophilic =
b) Thermophilic
GPM
GPM
T.S.
T.S.
3. Polymer Dosage Rate
a) Mesophilic
b) Thermophilic =
11.0 Ibs.
8.0 Ibs.
per ton
per ton
-------
220
THERMOPHILIC DIGESTER OPERATIONS
CAPTURE - TOTAL SOLIDS - AVG. %
0 10 20 30 40 50 60 70 80 90 100 %
i i i
MESQ.
J
THERMO.
J
CAKE- TOTAL SOLIDS - AVG. %
0 10 20 30 40
J
THERMO.
J
CENTRATE- SUSPENDED SOLIDS-AVG.mg/1
0 500 1000 1500 2000
_l
THERMO.
J
SLUDGE FEED RATE-GPM.
0 10 20 30
MESQ, I
THERMO.
Figure 1: Test Data—Solid Bowl Centrifuge—Kruger KDF-500.
The optimum sludge feed rate for mesophilic sludge
was 14 GPM. The optimum sludge feed rate forthermo-
philic sludge was 25 GPM or 44 percent better than with
mesophilic sludge.
Basket Bowl Centrifuge
In this test a full sized 48 inch DeLaval Basket Centri-
fuge was used. Table 4 indicates the test conditions that
provided the optimum performance from the basket
centrifuge. The bowl speed was 1400 RPM which re-
sulted in a "G" force of 1330 "G's". The total cycle
period averaged 30 minutes.
Figure 2 illustrates the performance between thermo-
philic and mesophilic sludges in the 48 inch basket
centrifuge.
Capture of total solids was very good for mesophilic
sludge averaging 90 percent (T.S.). The thermophilic
TABLE4
Optimum Test Parameters
Basket Bowl Centrifuge
48" DeLaval
i.
2.
3.
Sludge Peed Rate
Mesophilic & Thermophilic = 40 GPM
Sludge Peed Concentration
a) Mesophilic
>)
b) Theimophlllc
Polymer Dosage Rate
Mesophilic & Themiophlllc
T.S.
T.S.
6.0 Ibs. per ton
capture was only 38 percent (T.S.) which was considered
unacceptable.
With respect to cake solids both mesophilic and
thermophilic sludges produced an acceptable 28 percent
and 31 percent respectively. Centrate concentration
from the mesophilic sludge produced a submarginal
1400 mg/1. The thermophilic sludge centrate was a
totally unacceptable 13,800 mg/1.
Vacuum Filter
In this test series an Eimco pilot belt vacuum filter was
used. The drum diameter was three feet and the belt
width one foot.
Table 5 indicates the test conditions under which opti-
mum results were obtained from mesophilic and ther-
mophilic sludges, and Figure 3, the optimum test re-
sults.
Mesophilic sludge resulted in an average capture of 91
percent (T.S.) and a thermophilic sludge resulted in a
capture of only 56 percent (T.S.). These values represent
overall capture percentages including elutriation. The
thermophilic sludge lost most of its fine solids in the
elutriation process. In the elutriation washwater, ther-
mophilic sludge had a suspended solids concentration of
1,380 mg/1 compared to mesophilic sludge which aver-
aged only 110 mg/1 suspended solids.
The cake solids content in both mesophilic and ther-
mophilic sludges were an acceptable 29 percent and 31
percent respectively.
The filtrate from the mesophilic sludge produced an
unacceptable 2500 mg/1 of suspended solids. The ther-
mophilic sludge produced an acceptable 990 mg/1 of
c
(
(
CAPTURE- TOTAL SOLIDS - AVG. %
) 10 20 30 40 50 60 70 80 90 100 %
i * i > i i , i . i
MESO. |
THERMO. ~l
CAKE - TOTAL SOLIDS - AVG. %
) 10 20 30 40
i i i i
MESO. 1
THERMO. |
CENTRATE - SUSPENDED SOLIDS- AVG. mg/l
) 5000 10000 15000
THERMO. |
Figure 2: Test Data—Basket Bowl Centrifuge—48" DeLaval.
-------
THERMOPHILIC DIGESTER OPERATIONS 221
1.
2.
3.
4.
5.
TABLES
Optimum Test Parameters
Vacuum Filter Eimcol'X3'
Elutriation Rate 1 Sludge and 3 water
Elutriation Polymer Dosage Rate
a) Mesophilic = 0.25%
b) Thermophilic = 0.50&
Elutriate Washwater
a) Mesophilic =
b) Thermophilic =
110 mg/1
1,380 mg/1
Chemical Conditioning-Elutriated Sludge
a) Mesophilic = 5% FeCl3 + 10% CaO
b) Thermophilic - 2.5% FeCl3
Feed Sludge Concentration
a) Mesophilic = 2.90% T.S.
b) Thermophilic - 2.78% T.S.
suspended solids, however, it already had eliminated
most of its fines in the elutriation process.
The yield rate for mesophilic sludge was a low 1.8 Ibs.
per square foot per hour (Ibs./ft.^/hr). Thermophilic
sludge averaged a yield of 4.1 Ibs./ft.^/hr.
DISCUSSION
Figure 4, summarizes the test data from the systems
evaluated. Based solely on the initial technical test goals
of "Capture", "Cake Solids" and suspended solids in
the "Filtrate-Centrate", the only system qualifying
would be the solid bowl centrifuge and thermophilically
digested raw sludge.
CAPTURE- TOTAL SOLIDS - AVG. %
0 10 20 30 40 50 60 70 80 90 100 %
MESQ
THERMQ.
J
CAKE- TOTAL SOLIDS - AVG. %
0 10 20 30 40%
MESO
THERMO
FILTRATE - SUSPENDED SOLIDS-AVG. mg/1.
0 500 1000 1500 2000 2500
MESQT
J
THERMQ.
YIELD RATE -AVG. Ibs./sq.tt./hr.
012345 6
i i i i i
M. I
.2/hr.
THERMQ.
J
EQUIPMENJ^
s^ TYPE
SOLID BOWL
CENTRIFUGE
meso.
thermo.
BASKET BOWL
CENTRIFUGE
meso.
thermo.
VACUUM FILTER
meso.
thermo.
FEED
RATE
GPM
14
25
40
40
YIELD
»/SF/HR
1.8
4.1
CHEMICAL
DOSAGE
«*/TON
II
8
6
l 6
5%F«CI3+
10% CaO
25%FeCI3
CAPTURE
%
88
92
90
38
91
56
CAKE
%
18
30
28
31
29
31
CENTRATf
S.S.
mg/1
1550
1100
1400
13,800
2500
1000
Figure 3: Test Data—Vacuum Filter— Eitnco (!' X 3').
Figure 4: Summary of Test Data.
However, Table 6 lists some of the other pertinent
factors influencing the selection of a dewatering system.
Assuming a system attains or nearly meets the test
goals, the next major consideration for ocean dis-
chargers in California would be how to effectively treat
the centrate or liquid fraction from the dewatering pro-
cess, to meet the state of California's Ocean Discharge
Plan. Table 7 indicated the proportionate amounts of
total chrome and arsenic found in mesophilic and ther-
mophilic sludges. From this preliminary data it could be
inferred that thermophilic digestion may solubilize some
heavy metals into solution, consequently before any firm
evaluation can be made additional analyses must be per-
formed in this area.
In all of the acceptable dewatering processes
examined, some forms of sludge conditioning was re-
quired. Since this is a continuous expense, careful eval-
uation and cost comparisons must be made on the unit
cost of conditioning chemicals as well as the quantity re-
quired. For Hyperion the conditioning by thermophilic
TABLE6
Evaluation Factors
1. Test Goals
2. Centrate Treatment
Expense
3. Sludge Conditioning Expense
4. Cake Transport & Disposal
Expense.
5. Operational Reliability
Flexability
6. Operations & Maintenance
Expense
7. First Costs
-------
222 THERMOPHILIC DIGESTER OPERATIONS
TABLE?
Heavy Metal Concentrations
TABLES
Heat Vs. Chemical Costs
Total"Cr" "AS"
mg/1 rag/1
1.
Prim. Sludge
dissolved 0.09
suspended 45.18
2.
Mesophilic
dissolved
suspended
0.06
50.26
3.
Thermophilic
dissolved 0.15
suspended 52.52
0.01
1.00
0.01
0.08
0.04
0.87
sludge and polymers. Table 8, shows that it was less ex-
pensive to operate at the thermophilic temperature
range and purchase less polymers, than to depend upon
a larger polymer dosage and conventional mesophilic di-
gestion. However, the additional capital expense that
may be required for thermophilic operation may modify
this conclusion.
The percent solids in the sludge cake dictates the
transport and disposal costs. To illustrate this, 100
Tons/day (dry solids) of sludge at 75 percent moisture
(25 percent T.S.) will weigh 400 wet tons, whereas, the
1.8
1.6
(0
4J
W
° 1 .4
u
nj
U) 10
o J--*
O,
03 ViJ
•H O
0 -i 1.0
«4I X
*^ *""* r\ Q
t . »** 1 1 _ C»
\
\
\
\
\
\
»
\
•
B
C 10 20 30 40
C-
tn
C
g Calce % T.S.
Me so.
Additional
Heat cost
$/Ton Avg.
Chemical
costs
per ton.
Total
conditioning
costs
$/ton
?15.00
Thermo.
$1.66
$11.00
$15.00
$12.66
Figure 5: Cake Solids Vs. Disposal Costs (100 T/d at S9.00/T).
same amount of sludge at 70 percent moisture (30
percent T.S.) will weigh 333.33 wet tons. Therefore a
five percent increase in cake solids will save 67 tons of
sludge to be transported and disposed.
Transport and disposal cost estimates have ranged
between $6.00 and $12.00 per ton of sludge. Using an
average cost of $9.00 per ton, for transport and disposal
25 percent cake will cost $3600/day and 30 percent cake
will cost $3000/day, annually this difference amounts to
$219,000. Figure 5, illustrates the relationship between
cake solids and transport-disposal costs, based on 100
ton per day of solids (dry wt.) and $9.00 per ton trans-
port-disposal costs.
Another of the prime evaluation factors is operational
and maintenance requirements of each system. It is dif-
ficult to accurately predict the long term situation based
on the relatively short term tests performed at Hyperion.
Consequently about the only comment that can be made
with respect to equipment is that the solid bowl centri-
fuge was a continuous process, the vacuum filter was
semi-continuous, due to the required elutriation process
and the basket bowl was a batch process.
Estimates on additional personnel required to operate
the complete dewatering operations and sludge
transport system indicate 36 personnel. An additional 18
personnel will be required to service and repair the fa-
cilities. And an additional five persons will be required
for technical and administration support. Therefore,
based on an annual average salary of $12,000 per year,
salary expenses are estimated to increase by $708,000.
The capital expense associated with each of the
systems appears largely related to the sludge feed capa-
cities of the individual dewatering machines, since the
conditioning and cake handling systems will be largely
similar. Manufacturers are continuously improving their
equipment and claim higher capacities for their ma-
chines. However, without well established scale up
-------
THERMOPHILIC DIGESTER OPERATIONS 223
factors, the capabilities of untried equipment remains
uncertain.
The City of Los Angeles is obligated to purchase the
low bid on equipment. Consequently, it is difficult to de-
termine what brand or system will be finally installed.
CONCLUSIONS
The following preliminary conclusions were derived
from the Hyperion dewatering studies. That thermo-
philically digested sludge and a solid bowl centrifuge
produced a drier sludge cake, contained less suspended
material in the centrate, required less chemical condi-
tioning than mesophilic sludge, and permitted a higher
sludge feed rate. The thermophilic sludge, solid bowl
centrifuge was the only combination to essentially meet
all of the dewatering requirements, e.g., solids capture
^ 90 percent (actual 92 percent), centrate suspended
solids 25 percent T.S. (actual 30 per-
cent). The above system also had a higher continuous
sludge feed rate when compared to mesophilic sludge,
i.e., 14 GPM for mesophilic vs. 25 GPM for thermo-
philic. Figure 4, summarizes the data.
However, before any final conclusions can be deter-
mined the other associated effects of thermophilic diges-
tion must be considered. One of the negative aspects of
thermophilic digestion is the large amount of additional
heat required, approximately 69 percent more BTU's
than mesophilic operations for Hyperions digesters
(95°F Meso., 120°F Thermo). This additional heat re-
quirement dictates that additional heating facilities
must be constructed for full thermophilic operations.
There is also some evidence that the centrate from
thermophilic sludges contains a greater amount of cer-
tain dissolved heavy metals, e.g., total chrome. Also,
centrate-filtrate from thermophilic sludges were ob-
served to contain higher C.O.D. levels (approximately
30 pecent higher than mesophilic centrate). Since the
major reason for limiting the centrate suspended solids
concentration to as low a value as possible was to mini-
mize the amount of additional treatment that would be
required for the centrate before it could be discharged,
any increase in heavy metals or C.O.D. must be con-
sidered counterproductive. One major unresolved prob-
lem is how to remove relatively small amounts of heavy
metals from relatively large flows in a practical manner,
so that discharge limits can be reliably met.
Thermophilic digestion also requires more careful
operations. Thermophilic bacteria appear more
sensitive to loading and temperature changes than the
mesophilic bacteria group. This signifies that better
process control feed and temperature controls systems
be developed (used), to optimize operations and in-
crease reliability.
For Hyperion the long term picture is complicated by
the eventual necessity to handle an estimated 4-6 mgd of
waste activated sludge (W.A.S.) when full secondary
treatment is achieved. The dewatering characteristics of
anaerobically digested raw and W.A.S. still remains to
be determined. In any case thermophilically digesting
the W.A.S. will require substantial amounts of addi-
tional heat.
Some preliminary pilot studies have been initiated to
determine the compatibility of raw and W.A.S. being
combined and anaerobically digested.
The question arises as to why did the thermophically
digested sludge dewater better? Several hypotheses
have been proposed.
First, sieve analyses (Figure 6) between mesophilic
and thermophilic sludges indicate that thermophilic
sludge contains a higher percentage of coarser particles
which tend to dewater easier. Second, it was observed
during laboratory scale dewatering tests (filter leaf
tests) that heated sludges tended to dewater easier, re-
duced liquid viscosity being considered the main factor.
Third, the filtrate from thermophilic sludges contained
greater quantities of ether solubles, C.O.D. and dis-
solved solids, consequently, the thermophilic digestion
process may have selectively solubilized those
compounds or particles which tend to hinder dewatering
i.e., grease and oils. However, before any final con-
clusions can be made, additional investigations must be
performed.
The final conclusion concerning dewatering opera-
tions at Hyperion is that regardless of whether
thermophilic or mesophilic sludge is used or what condi-
tioning agents are applied or what type of equipment is
used it will be outrageously expensive.
Thermophilic Digestion
This section of the report will summarize the
observations made, while operating three of Hyperion's
digesters in the thermophilic temperature range. The
first part will discuss the conventional operating para-
meters of thermophilic digestion. The second part will
discuss the apparent enhancement of methane gas pro-
90
g 70
50
30
10
30
RAW-
50
100
200 270
SIEVE
NUMBER
0.59 0 297 0149
SIEVE SIZE , mm
0074 0053
Figure 6: Sludge Particle—Size Distribution.
-------
224 THERMOPHILIC DIGESTER OPERATIONS
duction established by a comparison to a mesophilic di-
gester operating under identical conditions.
Full scale thermophilic operation was practiced at Hy-
perion during the 1953-57 period. The results of this
operation were documented by W.F. Garber (1954)2.
The following are some of the conclusions reached at
that time on thermophilic operations:
1. Thermophilic sludge was easier to dewater than
mesophilic sludge.
2. Thermophilic sludges had coarser particle sizes.
3. Volatile acids content in thermophilic digesters
was higher.
4. The percent volatile solids reduction was greater
for thermophilic temperature than for mesophilic
temperature at equal detention times.
5. Methane gas production at thermophilic tempera-
tures was lower than that for mesophilic tempera-
tures.
6. Methane gas quality was greater in thermophilic
digesters than in mesophilic digesters.
Based on conclusions 1 and 2 above, it was decided to
test the dewaterability of thermophilically digested
sludge as part of the Hyperion sludge dewatering
studies. Consequently, in April of 1972 one of
Hyperion's digesters was converted from mesophilic to
thermophilic operations. Digester tank 2-A was chosen
since it was equipped with a 600 CFM free lift gas mixing
system and digester tank profiles indicated excellent
uniformity of temperature, alkalinity and volatile acids.
The performance history of digester 2-A is depicted by
Figures 7, 8 and 9.
As expected the temperature increase from 95 °F to a
targeted thermophilic temperature of 125°F resulted in
much higher levels of volatile acids (V.A.), loss in both
methane gas production and quality, a drop in alkalinity,
loss in solids reduction, and a drop in pH. The digester
was not productive for approximately six months.
During this period the volatile solids (V.S.) loading was
reduced and the temperature lowered to a new target of
120°F. The digester began to show signs of recovery im-
mediately. From this, it was concluded, that for
Hyperion, a thermophilic digestion temperature of
about 120°F was desireable.
By late 1972 all processes parameters appeared to be
stable, i.e., volatile acids were dropping to 1000 mg/1,
alkalinity increased to 5000 mg/1, gas production was
near 14 cubic foot per pound of volatile solids added
(ft3/lb. V.S.) and gas quality was near 64 percent
methane (CH^.
With the thermophilic process now reasonably stabil-
ized, a program was initiated to determine the maximum
practical loading rate for Hyperion's thermophilic di-
gester. A loading rate of 0.3 pounds of volatile solids per
cubic foot of digester capacity was attained by October
1974. All process parameters appeared stable, except
for the methane gas production rate (ft-Vlb V.S.). The
gas production rate was down to 10 ft-Vlb. V.S.,
although total gas production was up to 1 X 10" ft.3 per
7/72 1/73 7/73 1/74 7/74
1/75
; 10
j "*
0
>
8
i 7
6
Q; 130
| ."• 120
u, HO
H
3 >
-------
THERMOPHILIC DIGESTER OPERATIONS
225
7/72 1/73 7/73 1/74 7/74
1/75
Figure 9: Thermophilic Tank 2-A Data.
day. The loss in gas production rate was later deter-
mined as being caused by physical gas leaks in the di-
gester dome. Apparently, the high volume of gas being
produced and thermophilic temperatures promoted in-
creased gas leakage in the previously cracked fixed roof
concrete domes.
Unfortunately, about this time mechanical difficulties
resulted in insufficient heat being available and the
digester temperature dropped down near 113°F. This
caused an immediate rise in volatile acids and forced a
drastic reduction in the loading rate, which in turn re-
sulted in a sharp drop in gas production.
As soon as heat was available, digester 2-A was
brought up to 120°F. at a temperature increase of 1°F.
per day. The process parameters indicated rapid
recovery (ro_30 days), from the temperature upset. Un-
fortunately, the recovery period was during the holiday
season and personnel shortages prevented a thorough
monitoring of all experimental parameters. Increased
regulatory monitoring demands forced further reduc-
tions in the comprehensive testing of digester 2-A. The
blank portions in Figures 7, 8, and 9 indicate periods
when samples were not taken and/or analysed.
At this point in time some of the previous conclusions
regarding thermophilic operations at Hyperion were
verified and others left in question. The following
previous conclusions were verified:
1. In some situations thermophilic sludges are easier
to dewater.
2. Thermophilic particles sizes are coarser than meso-
philic particles (Figure 5)
3. Volatile acid levels are higher in thermophilic di-
gesters, 400-500 mg/1 vs. 100 to 200 mg/1 for
mesophilic digestion.
Contrary to previous conclusions, there is some evi-
dence that methane gas production is higher and gas
quality is lower for thermophilic digestion, when com-
pared to mesophilic digestion. The remaining portion of
this report will be directed toward these observations.
DISCUSSION
Thermophilic Compared To
Mesophilic Digestion
Early in 1975 it was decided to make a direct compari-
son between mesophilic operations and thermophilic
operations. Two secondary digesters which had been
cleaned, and modified (gas mixing and heating added)
for primary operations were selected for this test. Both
digesters are in the same battery adjacent to each other
and connected to the same raw sludge feed line. Each di-
gester was(is) gas mixed at a rate of 3000 cfm. The meso-
philic temperature was targeted at 95°F and the thermo-
philic temperature targeted at 120°F. After start up,
stabilization occured in the spring of 1975 when both
digesters were loaded at 0.16 Ib. VS/ft^. Figure 10 and
Table 9 illustrate the results of this test. Digester 3-C
i nc.nmwrnii_iv^ IMIVFV *rv/
MESOPHILIC TANK 3C
1/75 4/75
130
«." nn
CL \\\J
2
£ 100
i» °-3
^ o
(K -o n 9
^ U.Z
? § O.I
<^
3* °
zio 600
0 g
| o 200
g 0
£ 30
OT J? 20
< ^~°
0 * * ,Q
§'
---•>J
.V
'
^
\
A,.
/
f
'*'
/
/I
\^*v.
r-/"
7
\
X
1 \
V
,c/^
"-*'*'
N'N.
X
•Vi,'
-*-/
/
/
<-.<-
— —
1 I
( -)
7/75 10/75
^
HHl
MF-
^
'M
^ .
.RM(
FFR
f
V
i—'C^
^
FRf
/
w
?OR
Figure 10: Gas Production.
-------
226
THERMOPHILIC DIGESTER OPERATIONS
TABLE9
Summary of Thermo. Vs. Meso. Tests
Parameter
Temperature, F
Loading Rate , #VS/CF/day
Gas Product ion, CF/day
Gas Production, CF/#VS. added
Gas Quality,* CH4
Volatile Acids, mg/1
A Ika 1 in ity , mg /I
Volatile Ac id /Alkalinity Ratic
pH
Total Solids, %
Volatile Solids, %
Hydraulic Detention Time, days
Raw
Sludge
77
1600
5tl
6.1
78
Meso.
Sludge
96
0.16
580,000
10.9
64
300
3900
0.08
7.4
2.5
60
10.2
Thermo.
Sludge
120
0.16
680,000
12.7
63
600
4100
0.15
7.6
2.1
65
18.2
which was operated at the conventional mesophilic mode
typifies Hyperion's sludge digestion operations. Diges-
ter 4-C was operated at thermophilic temperatures.
Based on the data from June 1975 to August 1975 the
following preliminary conclusions have been reached:
1. Thermophilic digester 4-C is producing more gas
(100,000 ft3/d) than mesophilic digester 3-C under
the same loading and detention times.
2. The gas quality of thermophilic digester 4-C is ap-
proximately one percent lower than for mesophilic
digester 3-C, 63 percent CH4 vs. 64 percent CH4
respectively. However, since Hyperion's com-
posite gas quality normally averages close to 65
percent CH4, the slightly lower values obtained
may not be significant.
3. As expected the volatile acid levels (600 mg/1) in
thermophilic digester 4-C are twice that of digester
3-C (300 mg/1).
4. The volatile acids alkalinity ratio of thermophilic
digester 4-C is 0.15, which indicates less buffering
capacity than digester 3-C at 0.08. This would tend
to support observations that thermophilic diges-
ters are more sensitive and require closer process
controls, e.g., increases in loading or changes in
temperature.
5. The total solids and volatile solids percentages
shown for mesophilic sludge were Hyperion plant
composite averages. Consequently, valid compari-
sons between digester 4-C and 3-C are not avail-
able.
6. Records at Hyperion (1973) indicate that it takes an
average of 20,000,000 Btu/day per mesophilic di-
gester for heating3. Calculations indicate that ap-
proximately 69 percent more heat energy is re-
quired to operate at thermophilic temperatures, in
this case 0.69 X 20,000,000 Btu/d/digesters =
13,800,000 Btu/day/digester. However assuming
that 100,000 ft3 of methane gas with a heat value of
600 Btu/ft3 can be obtained from each thermo-
philic digester (600 Btu/ft3 X 100,000 ft3/d =
60,000,000 Btu/d). Then an extra 46,200,000
Btu/d/digester (60,000,000 13,800,000 Btu/d/
digester) could be available from thermophilic
operations.
ACKNOWLEDGMENTS
The authors express their appreciation and acknow-
ledge the assistance provided by W.F. Garber, S. Raksit,
G. Wong, A. Liu, J. Nagano, and others of the Hyperion
technical staff who contributed to this paper.
REFERENCES
1. Garber, W.F., et. al. 1975. "Energy-Wastewater
Treatment and Solids Disposal." ASCE Journal of the
Environmental Engineering Division, 3, 319.
2. Garber, W.F. 1954. "Plant-Scale Studies of Ther-
mophilic Digestion at Los Angeles." Journal of the
Water Pollution Control Federation, 26, 1202.
3. Garber, W.F. 1975. "Thermophilic Digestion at the
Hyperion Treatment Plant." Journal of the Water Pol-
lution Control Federation, 5, 950.
4. Ohara, G.T., Raksit, S., Olson, D. April, 1974.
"Sludge Dewatering Studies at the Hyperion Treatment
Plant." Paper presented at the 46th California Water
Pollution Control Association Conference. San Jose,
California.
-------
UTILIZATION OF METHANE FROM
SLUDGE DIGESTION
SurinderK. Kapoor and Donald Newton
Greeley andHansen, Engineers
Chicago, Illinois
INTRODUCTION
Utilization of methane from sludge digestion, usually
called sludge gas, for in-plant uses has had its ups and
downs during the last fifty years. Commercial use of
sludge gas had been only occasional and rather experi-
mental in nature. In-plant utilization of sludge gas be-
came fairly well established in the 1930's and 1940's.
During the next two decades, the use of sludge gas ex-
panded moderately, inhibited largely by the availability
of cheap electrical energy and the effect of union rules in
the large plants on engine operating labor costs, but also
by the operating and maintenance problems with anaero-
bic digestion as compared to nonbiological methods.
During the last several years, substantial changes in
availability and costs of energy have sparked renewed
interest in the possibility of in-plant self-sufficiency in
energy needs or production of chemicals from sludge'
gas. The rising costs for power and chemicals and gen-
eral concern with energy conservation are rapidly chang-
ing the economics of inclusion in the waste treatment fa-
cilities of methane using processes which were hitherto
cost effective only at commercial scales. It is the purpose
of this paper to restate numerous conventional uses of
sludge gas and to discuss the feasibility of sludge gas
utilization for production of chemicals which may be
used in the plant or which could be marketed.
Historical Uses of Sludge Gas
Although the use of sludge gas was first demonstrated
in 1890's for street lighting in England, widespread use
of sludge gas for inplant uses was not established until
about 30 years later. While the earlier uses included
heating of plant buildings, laboratory uses and incinera-
tion of screenings, skimmings, sludge and grit, the utili-
zation of sludge gas got its biggest impetus with the suc-
cessful use of the gas as a fuel for internal combustion
engines in the 1930's. Large municipalities using sludge
gas engines currently include New York City, Los Ange-
les, Cincinnati and Boston. A total of 193,000 installed
engine horsepower was reported operating in waste
treatment plants in the U.S. A. in 1965'. More than half
of this installed power was used to run generators which
provide a more flexible form of power to meet almost all
plant needs. Engines have also been used as direct
drives for pumps, air blowers and other equipment. As a
secondary advantage, waste heat from engine cooling
water can be used for purposes normally requiring hot
water or steam boilers. These uses include digester and
space heating, air conditioning and other hot water uses.
Some generalized modes of sludge gas utilization for
various inplant uses are shown on Figure 1.
Historically there has been little or no commercial
utilization of sludge gas. In Europe, it was used to a
limited extent as a vehicle fuel. In this country, even dur-
ing the second world war and afterwards, when there
was a real shortage of gas for domestic and industrial
uses, the matter of sludge gas supply into local distribu-
tion networks never received widespread attention.
Among various reasons accounting for this are the lower
heat value compared to natural gas, variable sludge gas
characteristics, purification required to remove carbon
dioxide and hydrogen sulfide and additional gas com-
pression to meet the line pressures. In short, so far it has
not generally been cost effective to use the sludge gas for
commercial purposes compared to the price and avail-
ability of natural gas. This situation may change with the
rising prices and diminishing supplies of natural gas and
the possibilities of sale of sludge gas should be recog-
nized. For example, a study about a year ago for Sacra-
mento indicated a near break-even situation in purifying
and selling excess gas to the local utility. At least two
large plants do now sell excess gas: Los Angeles County
Sanitary District No. 2 delivers about two MCFD to a re-
finery and the Hyperion Plant of the City of Los Angeles
supplies a similar quantity to the City's municipal power
system. Gunson2 reported an average daily sale of
700,000 cubic feet of sludge gas to American Smelting
and Refining Company with additional provision that
their peak demands would be met on a standby basis.
Recent Developments
During the last 20 years or so, there has been a notice-
able decline in the use of anaerobic digestion as amethod
227
-------
228
UTILIZATION OF METHANE
SLUDGE GAS
PURIFICATION
COMPRESSION
BOILERS
USES INVOLVING
DIRECT SLUDGE
GAS BURNING
(INCINERATION, FUEL)
INTERNAL COMBUSTION
ENGINES
ENGINE COOLING
WATER
I
ELECTRIC POKER
GENERATION
ALL HOT WATER/
STEAM USES
SUPPLEMENTAL PLANT
ELECTRICAL NEEDS
Figure 1: Historical Modes of Sludge Gas Utilization.
for stabilization of sludges. Essentially, this has been
because of the low cost and availability of electricity,
natural gas or fuel oils for alternative sludge treatment
methods. Greater control required for the operation of
anaerobic digesters and development of other sludge
stabilization processes have also contributed to a shift
away from anaerobic digestion. The alternate sludge
stabilization and treatment methods, such as aerobic di-
gestion, heat treatment, centrifuging and sludge in-
cineration, have substantially added to the energy
requirements at treatment plants, in comparison with
the anaerobic digestion which provides net energy for
the plant needs.
Another major development which affects the waste
treatment energy needs is the adoption of secondary
treatment as minimum at all plants and tertiary treat-
ment, to varying degrees, at numerous locations in this
country. The Environmental Protection Agency3 esti-
mates the following energy requirements for different
types of treatment plants based on the 1968 inventory of
municipal facilities:
Primary - 0.029 Kwh/day/capita
Secondary - 0.113 Kwh/day/capita
Tertiary - 0.226 Kwh/day/capita
These figures or increased needs underscore the con-
cern of plant operators, faced with rising power rates,
over the increased operating costs. Because of increased
fuel needs and costs, and possible lack of dependability
of imported fuels on a national level, the need for re-
evaluation of plant energy requirements and sources has
never been greater.
Potential Sludge Gas Energy
Sludge gas is obtained as a byproduct during the anae-
robic digestion of the sewage treatment plant sludges.
Anaerobic digestion is a biological process employed for
the stabilization of sludges and essentially consists of 15
to 25 days detention of sludges at elevated temperature
and under anaerobic conditions. Optimum operating
temperatures vary from 90° to 95° F for mesophilic to
120° to 140° F for thermophilic conditions.
Sludge gas composition varies slightly from one treat-
ment plant to another but is largely a mixture of methane
(65 to 70 percent by volume) and carbon dioxide (30 to 35
percent by volume) with smaller quantities of nitrogen,
hydrogen, hydrogen sulfide and oxygen. Occasionally,
traces of carbon monoxide or other gases may be
present.
The average yield of gas in the United States is gene-
rally between 10 to 20 cubic feet per pound of volatile
solids destroyed with an average of about 17 cubic feet.
Existing anaerobic digestion practice commonly
-------
UTILIZATION OF METHANE
229
destroys about 50 percent of the volatile solids present in
the feed sludge. The solids destruction and gas yield are
somewhat influenced by the nature of the volatile ma-
terial and its susceptibility to biological degradation.
Techniques of increasing volatile solids destruction need
further investigations.
Recently ICI America (a subsidiary of Imperial Chemi-
cal Industries) has claimed that the destruction of vola-
tile matter and the gas yield can be substantially in-
creased (up to two times) by the addition of powdered
activated carbon at a dosage of approximately five per-
cent of the sludge solids4. A number of treatment plants
have been pilot testing during the last year or so to deter-
mine the feasibility and the cost effectiveness of this
claim, among them being, Cranston, R.I. (seven to eight
mgd) and Norristown, Pennsylvania (seven to eight
mgd).
The heat value of sludge gas averages about 640 Btu
per cubic foot compared to 1,000 Btu per cubic foot for
natural gas. These heat values essentially correspond to
the percentage of methane in each gas. Theoretically,
the electrical equivalent of one cubic foot of sludge gas is
187.52 X 10"3 Kwh. Assuming an average sludge gas
yield of 0.8 cubic feet per capita per day for a primary
treatment plant and 1.2 cubic feet per capita per day for a
secondary plant, the theoretical electric energy yields
are 0.150 and 0.225 kwh per capita per day, respectively.
Actual electrical power available would be 0.050 and
0.075 kwh per capita per day for primary and secondary
plants, respectively when an overall engine-generator
efficiency of 33 percent is used. These compare to elec-
trical needs of 0.029 and 0.113 kwh per day per capita for
primary and secondary treatment plants respectively 3-
These figures do not include secondary utilization of en-
gine cooling water for digesters, space heating and other
hot water requirements of a primary plant and to a sub-
stantial degree at a secondary plant can be supplied in-
plant from sludge gas utilization. If the sludge gas pro-
duction can be increased by the use of activated carbon
as claimed by ICI America, or by other techniques, it
may be possible to meet the total energy requirements of
a secondary treatment plant.
At present, power production at sewage treatment
plants in this country is usually through the use of gas,
dual-fueled, engine-generator systems. It has been sug-
gested by Murphy5 that the use of fuel cells can substan-
tially increase the energy conversion efficiency from
sludge gas to electricity. Fuel cells are relatively simple
in construction, create no air pollution, are modular in
nature and have no minimum system size. On the other
hand, the fuel cell production technology is still in a de-
velopmental stage and it will be some time before they
can be economically employed for in-plant uses.
New Considerations
There have been numerous happenings in the imme-
diate past as a result of which new alternatives for sludge
gas utilization have developed. A number of sewage
treatment plant operators all overthe country, especially
those of large cities or sanitary districts, have chosen to
consider these alternatives. A discussion of these alter-
natives is in order.
Due to recent increases in the cost of petroleum based
chemicals, the cost of fertilizers has gone up substantial-
ly. More and more farmers and city dwellers are using
stabilized dried sludge for fertilizing their lands and
lawns. These sludges are deficient in nitrogen, phos-
phorus and potash and need to be fortified to provide
balanced fertilization. Nitrogen required for this pur-
pose could be produced from sludge gas as an alternate
to commercially available nitrogen.
Another chemical likely to be in substantial demand at
some plants is methanol. Methanol has, so far, been
found to be the most cost effective purchased chemical
carbon source for the biological denitrification process
employed at a number of plants for removal of nitrate-
nitrogen. Commercially, methanol like ammonia, is
largely made from natural gas. It is believed that
methanol production from sludge gas is also a real
possibility.
Ammonia Production Technology
It has been reported 6 that approximately 60 to 65 per-
cent of world ammonia production is derived from
natural gas. Natural gas reforming and partial combus-
tion are two processes most widely used in the ammonia
synthesis. Out of these two, natural gas reforming with
steam accounts for 75 to 80 percent of total ammonia pro-
duction. Application of this process for production of
ammonia from sludge gas would employ the same steps
as in commercial ammonia production from natural gas.
The presence of 30 to 35 percent of carbon dioxide in the
sludge gas compared to very little or none in natural gas,
should not call for any major process modification as car-
bon dioxide production and its removal are essential
steps in the following process flow scheme.
Steam Reforming Process
A line diagram of this process is shown on Figure 2.
Essential steps leading to the production of ammonia
from methane in sludge gas are described as follows:
Gas Purification
This consists essentially of desulfurization of the gas
to as low sulfur levels as possible. In some sewage treat-
ment plants, using sludge gas as engine fuel, desulfuri-
zation is currently practiced using dry gas scrubbers
(ferric oxide mixed with hardwood shavings) or wet type
bubbling scrubbers. In commercial ammonia plants,
natural gas is usually desulfurized by passing over spe-
cially prepared activated carbon at ambient temperature
and high pressures. Regeneration of the carbon is done
with high temperature steam at low pressure.
-------
230
UTILIZATION OF METHANE
r
1
SLUDGE GAS
CH4+C02*S+TRACES
1
1
1
¥ ENERGY r
IN
DESULFURIZATION
& PURIFICATION
1
CrU+C02+TRACES
REFORMING
I
C02*H2+CO*N2*TRACES
CARBON MONOXIDE
SHIFT CONVERSION
2tH2+Np+
CARBON DIOXIDE
SCRUBBING
H2+N2+TRACES
FINAL
PURIFICATION
H2*N2
AMMONIA
SYNTHESIS
I
AMMONIA
NH3
Figure 2: Ammonia Production from Sludge Gas (Simplified Flow
Diagram).
Steam Reforming
Steam reforming or synthesis gas production is best
described by the following equation:
CH4 + H70 catalyst 3H7 + CO
(synthesis gas)
This reaction is endothermic and is carried out at a tem-
perature in the range of 800° C and pressure ranging
from atmospheric to 500 psig. A nickel based catalyst is
usually employed to assist the completion of this
reaction.
The gas reforming is carried out in two stages. In the
primary reformer the large endothermic heat is supplied
by burning natural gas with air in a furnace. About 40
percent of the methane gas supplied is used to furnish
this heat and about 60 percent is converted into synthe-
sis gas.
In the secondary reformer, the primary reformer
gases are mixed with air to introduce the nitrogen re-
quired for the reaction with hydrogen which results in
the production of ammonia. Methane concentration in
the synthesis gases at the end of this reaction is reduced
to about 0.3 percent.
Heat recovery from the gas combustion for this step
provides steam for turbines driving compressors needed
later in the production processes and makes the balance
of the production steps self-sufficient in energy
requirements.
Carbon Monoxide Shift
This step consists of conversion of carbon monoxide to
carbon dioxide and hydrogen using steam as per this
reaction:
CO + H20 catalystco2 + H2
This reaction is usually carried out in two steps, one at
high temperature 350° to 450° C; and second at low
temperature 200° to 300° C. Catalysts are required in
both steps. At the end of this reaction, the unreacted car-
bon monoxide is about 0.3 to 0.5 percent.
Carbon Dioxide Removal
In this step, the bulk of the carbon dioxide is removed
by one of the numerous methods available. Among those
commonly used are water scrubbing and hot potassium
carbonate absorption.
Final Purification or Methanation
This step consists of removal of the remaining carbon
monoxide and carbon dioxide since they poison the am-
monia catalyst as well as tend to form solid compounds
which can damage machinery.
This is essentially the reverse of the methane reform-
ing process and carbon monoxide shift steps, as follows:
CO + 3H2 catalyst CH4 + H2O
CO2 + 4H2 catalyst CH4 + 2H20
To achieve these reactions, the gases are preheated to
about 600° F and then passed over a nickel catalyst.
Ammonia Synthesis
Ammonia synthesis is carried out at pressures
ranging from 2,000 to 10,000 psi. Heat recovered from
The synthesis gas after this final purification is essen-
tially hydrogen, about 75 percent, and nitrogen, about
25 percent. The methane formed in the final purification
step is only about 0.3 to 0.5 percent, with less than ten
ppm of oxides of carbon. Synthesis gas together with all
remaining trace gases and inert impurities then pass on
to the synthesis step.
the gas reforming step is generally used to produce
-------
UTILIZATION OF METHANE
231
steam for turbine driving the compressors. The basic
ammonia reaction is given by this chemical equation:
N7 + 3H->catalyst2NHi
This reaction is exothermic in nature and is sensitive to
operating pressures and temperature, ratio of hydrogen
to nitrogen and concentration of inert gases. The reac-
tion is usually carried out in the presence of iron oxide
which acts as a catalyst.
Methanol Production
Methanol or methyl alcohol synthesis is very similar to
that of ammonia. Many ammonia plants are designed so
that methanol could also be produced. Like ammonia,
most of the commercial methanol production comes from
natural gas. A simplified process flow diagram for
methanol production from sludge gas is shown on Figure
3. Major differences in methanol production from sludge
gas in contrast to that of ammonia are described below:
r
SLUDGE GAS
CH4*C02*S+TRACES
DESULFURIZATION AND
PURIFICATION
I
CH4*C02*TRACES
ENERGY
IN
i
REFORMING
I
C02»H2+CO+TRACES
CARBON MONOXIDE
SHIFT CONVERSION
C02+H2+TRACES
METHANOL
SYNTHESIS
T
CH3OH+TRACES
I
METHANOL
PURIFICATION
METHANOL
CH3OH
*
Figure 3: Methanol Production from Sludge Gas (Simplified Flow
Diagram).
Stoichiometric Relationship
The basic chemical equation representing overall
methanol synthesis is:
3CH4 + C02 + 2H20 -
Actual sequence of conversion from sludge gas to meth-
anol is essentially the same as described under ammonia
synthesis. This includes conversion of methane to syn-
thesis gas (CO2 + H), carbon monoxide shift conversion
to carbon dioxide and methanol synthesis. However,
there is no CO2 scrubbing operation.
Carbon Dioxide Requirements
The Stoichiometric equation indicates a net addition of
one mol ecule of carbon dioxide for every three molecules
of methane. In commercial production of methanol from
natural gas, it is a practice to add make-up carbon diox-
ide from an external source. This addition may not be re-
quired in methanol production from sludge gas, since
the latter has approximately the same composition as in-
dicated in the Stoichiometric equation.
As seen on Figure 2, for ammonia synthesis, carbon
dioxide produced in the process is scrubbed prior to final
synthesis. This carbon dioxide scrubbing is not required
in methanol production since carbon dioxide is a part of
synthesis gases.
Purification
In ammonia production, the synthesis gases are puri-
fied of oxides of carbon, prior to ammonia synthesis be-
cause the impurities are poisonous to the catalyst em-
ployed. In methanol production, the required product
purity is obtained by condensation of converted gases
and conventional distillation methods after the synthesis
has taken place.
Cost Effectiveness of Ammonia and
Methanol Production
Recently a preliminary study was undertaken by
Greeley and Hansen of the cost of producing ammonia
from sludge gas. Production costs were based on pro-
duction capacities of 50 tons per day and 12.5 tons per
day. A summary of the capital and operating costs for
these plants are given in Table 1. These costs are based
on data by Buividas6, adjusted to current price levels.
It is estimated that about 80,000 cubic feet of sludge
gas will be required to produce one ton of ammonia. As-
suming one cubic foot of sludge gas per capita per day
and 100 gallons of sewage per capita per day, it will take
the entire sludge gas production of a 400 mgd and 100
mgd plant to produce 50 tons and 12.5 tons of ammonia
per day, respectively. In other words other energy
sources will be required to meet all other in-plant energy
requirements. This effect, on the overall plant
economics, can be approximated by assuming the pur-
chase of natural gas for chemical production. Assuming
-------
232
UTILIZATION OF METHANE
TABLE 1
Ammonia Manufacture from Sludge Gas
50 Ton Plant
First
Item Cost
Amor-
tized (a)
Cost
?/Ton
of
Ammonia
12.5 Ton Plant
First
Cost
Amor-
tized (a)
Cost
$/Ton
of
Ammonia
Capital Cost $5,000,000 $435,500
Operation
Cost (b)
Water
Catalyst &
Chems.
Labor
Power (c)
Total Production Cost
$24.00 $2,200,000 $192,000
1.05
0.60
1.25
7.65
Say
$34.55
$35.00
$42.00
1.05
0.60
5.00
7.65
$56.30
$57.00
(a) At 6% for 20 years - 8.7% annually.
(b) Sludge gas assumed free of cost.
(c) At 4C/kwhr. In this case, this power cost is based on feeding liquid
nitrogen instead of air in the secondary reforming step. It is fur-
ther assumed that liquid nitrogen is produced cryogenically.
a natural gas requirement of 50,000 cubic feet per ton of
ammonia compared to 80,000 cubic feet for sludge gas, it
will mean an additional cost of about $30 per ton of am-
monia (assuming natural gas costing $.60 per 1,000
cubic feet). In summary,
50 Ton PI ant 12.5 Ton Plant
Ammonia production cost
without cost of gas $35.00/Ton $57.00
Cost of natural gas $30.00 $30.00
Total cost of ammonia
production
$65.00
$87.00
Ammonia is commercially available at about $200 to
$250 per ton, depending upon the location.
Stoichiometrically, ammonia and methanol produc-
tion per unit volume of sludge gas are close. Dean7 esti-
mates that, theoretically, 25,000 cubic feet of sludge gas
would be required per ton of methanol produced. His
preliminary calculation for Washington, D.C. indicated
that sludge gas requirement per ton of methanol pro-
duced maybe as much as 75,000 cubic feet. This is close
to sludge gas requirement of 80,000 cubic feet per ton of
ammonia used in the estimated production costs. It is,
however, believed that both these numbers represent
fairly liberal requirements.
The cost of methanol production from sludge gas
would be about the same as for ammonia, since amor-
tized cost forms a major portion of the total costs, and the
manufacturing facilities for the two chemicals are essen-
tially the same.
CONCLUSIONS AND RECOMMENDATIONS
Utilization of sludge gas for in-plant uses is receiving
renewed interest lately because of rising costs of power
and chemicals and general concern for energy conserva-
tion. Apparently, both sludge gas utilization and produc-
tion should be maximized. Recently, it has been claimed
that use of activated carbon in the anaerobic sludge di-
gestion process substantially increases production of
sludge gas. A number of pilot plants are now being oper-
ated at different locations in the United States to test the
feasibility of this claim. Studies are continuing at the Hy-
perion Plant in the City of Los Angeles to see the effects
of thermophilic digestion on gas production and sludge
dewaterability. Interim results indicate increased
sludge gas production but do not outweigh the added
costs of energy due to higher operating temperatures.
Nevertheless, efforts should be continued to investigate
the methods of improving sludge gas production.
It appears that energy requirements at treatment
plants are increasing substantially due to proposed
secondary treatment at all plants and tertiary treatment
expected at many plants. This calls for more intensive
-------
UTILIZATION OF METHANE 233
use of sludge gas for plant purposes. It is believed that
historical modes of sludge gas utilization are still the
most economical methods. Generally speaking, the fol-
lowing order of conventional uses may be considered:
1. Generation of electricity. Engine cooling water
should be considered for digester heating.
2. Direct operation of pumps and blowers.
3. Hot water/steam production for space heating, air-
conditioning and digester heating.
4. Other uses.
In-plant storage will further help in increasing utiliza-
tion but only in equalizing short term—essentially
diurnal-fluctuation in supply and demand. More con-
sideration needs to be given to equalizing seasonal de-
mands such as winter heating and summer air-condi-
tioning loads, both served by gas using systems.
In some places, the utilization of sludge gas for con-
ventional uses may not be feasible. Use of sludge gas for
productions of ammonia and/or methanol for in-plant
purposes should be investigated. If applicable, ammonia
can be used for sludge fortification for using it as soil '
conditioner or fertilizer. Similarly, methanol can be pro-
duced from sludge gas at those plants which employ
biological denitrification for nitrate-nitrogen removal.
Commercial utilization of sludge gas has not been a
very attractive proposition so far. In exceptional cases,
like some plants in the Los Angeles area, sludge gas has
been effectively sold to a gas-using industry or utility.
Cost effectiveness of sludge gas use for commercial use
is likely to improve as natural gas and other energy
sources diminish in supply and become more expensive.
REFERENCES
1. O' Leary, W. A., " How to Cut Operating Costs with
Sludge Gas Engines," Public Works Vol. 96, (January,
1965), 95.
2.Gunson,C.P., "Half of Sludge Gas Soldto Smelting
Company." Wastes Engineering Vol. 32, (November,
1961), 641.
3. Smith, R., "Electrical Power Consumption for
Municipal Wastewater Treatment" Environmental Pro-
tection Technology Service, EPA-R2-73-281, (July,
1973).
4. Adams, A.D., "Improved Anaerobic Digestion with
Powdered Activated Carbon," presented at Annual
Conference Central States Water Pollution Control As-
sociation, Madison, Wisconsin (May, 1975).
5. Murphy, C.B., Jr., "Digester Off-Gas, An Un-
tapped Energy Source," presented at 47th Annual Con-
ference Water Pollution Control Federation, (October,
1974).
6. Buividas, L.J., et. al.,"Alternate Ammonia Feed-
stocks" Chemical Engineering Progress,Vol. 70, (Octo-
ber, 1974), 21.
7. Dean, R.B., "Municipal Wastewater: Source or
Sink for Methanol," presented at Engineering Founda-
tion Conference on Methanol Fuel, New England Col-
lege, Henniker (N.H.) (July, 1974).
BIBLIOGRAPHY
1. Adams, A.D., "Improved Anaerobic Digestion
with Powdered Carbon," Presented at Annual Con-
ference Central States Water Pollution Control Associa-
tion (May, 1975).
2. Anonymous, "From Sludge Gas to Power and
Heat," Wastes Engineering, Vol. 30, (November, 1959),
676.
3. Anonymous, "Sludge Gas Engines Handle Peak
and Standby Loads, "Public Works, (January, 1971), 53.
4. Brown, Wade G., "Sludge Gas Utilization," Public
Works, Vol. 90, (October, 1959), 110.
5. Buividas, L.J., et. al., "Alternate Ammonia Feed-
stocks," Chemical Engineering Progress., Vol. 70,
(October, 1974), 21.
6. Dean, Robert B., "Municipal Wastewater: Source
or Sink for Methanol," Presented at Engineering Foun-
dation Conference on Methanol Fuel, New England Col-
lege, Henniker, (N.H.) (July, 1974).
7. "Environmental Wastes Control Manual," Public
Works, (1974), 99.
8. Everett, A.D., "Digester Gas: Valuable Plant
Fuel," Water and Sewage Works, (May, 1975), 60.
9. Fischer, A.J., "Fuel and Fertilizer from Sewage
Aim of German Treatment Plants," Civil Engineering,
Vol. 16, (October, 1946), 448.
10. Fuhrman, Ralph E., "Sludge Gas Utilization,"
Sewage Works Journal, Vol. 12, (November, 1940),
1087.
11. Goeppner, Joe, andHasselmann, Detlev E., "Di-
gestion By-product May Give Answer to Energy Prob-
lem," Water and Wastes Engineering, Vol. 11, (April,
1974), 30.
12. Gould, Richard H., "Present Status of Sludge Gas
Utilization," Sewage Works Journal, Vol. 19, (March,
1947), 170.
13.Gunson, C.P., "Half of Sludge Gas Sold to Smelt-
ing Company, Wastes Engineering, Vol. 32, (Novem-
ber, 1961), 641.
14. Imhoff, Karl, "Digester Gas for Automobiles,"
Sewage Works Journal, Vol. 18, (January, 1946), 17.
15. Joseph, James, "Sludge Gas Becomes a Turbine
Fuel," Water and Sewage Works, (November, 1965),
419.
16. Martin, George, "Utilization of Sludge Gas in
Moderate Sized Treatment Plants," Sewage Works
Journal, Vol. 14, (March, 1942), 265.
17. Mignone, Nicholas A., "Anaerobic Digester De-
sign for Energy Generation," Public Works, (October,
1974), 71.
18. Murphy, Cornelius B., Jr., "Digester Off-Gas, An
Untapped Energy Source," Presented at 47th Annual
Conference Water Pollution Control Federation (Octo-
ber, 1974).
-------
234
UTILIZATION OF METHANE
19. O'Leary, W. A., "Howto Cut Operating Costs with
Sludge Gas Engines," Public Works, Vol. 96, (January
1965), 95.
20. Parker, W., "The Propulsion of Vehicles by Com-
pressed Methane Gas, West Middlesex Main Drainage
Works," Institute of Sewage Purification (November,
1945).
21. "Process Design Manual for Sludge Treatment
and Disposal," U.S. EPA, Technology Transfer, Wash-
ington, D.C. (January, 1975), 5-17.
22. Van Kleeck, L.W., "Operation of Sludge Drying
and Sludge Gas Utilization Units," Sewage Works
Journal, (November, 1945), 1250.
23. Van Kleeck, Leroy W., "Sewage Sludge Gas Its
Collection and Use," Wastes Engineering, Vol. 29,
(February, 1958), 77.
24. Ward, P.S., "Digester Gas Helps Meet Energy
Needs," Journal Water Pollution Control Federation,
Vol. 46, (April, 1974), 620.
25. Wilson, Harold, "Production of Formalin From
Digester Gas," The Surveyor, Vol. 105, (January, 1946).
26. Winkler, William W., and Welch, Fred M.,
"Energy Conservation Dictates Innovative Treatment
Plant Design," Public Works, (March, 1974), 86.
27. Wirts, John J., "Commercial Utilization of Waste
Digester Gas," Sewage Works Journal, Vol. 20, (Sep-
tember, 1948), 923.
-------
PROCESSING, ECONOMICS AND SALE OF
HEAT DRIED SLUDGE
Gerald Stern
United States Environmental Protection Agency
Cincinnati, Ohio
INTRODUCTION
The heat drying of municipal wastewater sludge for
treatment and disposal is an old approach. Between 1916
and 1921, about the same time the activated sludge pro-
cess was developed, Baltimore, Maryland, entered into
a contract with a private contractor to heat dry and dis-
pose of treatment plant sludge'. In the 1920's, Houston,
Texas, used filter presses to dewater the sludge followed
by rotary dryers2. In 1950, the sludge treatment system
was changed to vacuum drum filters and flash dryers
(C-E Raymond Division of Combustion Engineering,
Inc.). This system is still in use; in fact, it is being up-
dated and new dryers are being installed to increase the
heat dried sludge capacity.
The flash dryer was used even earlier, in 1932 at the
Chicago, Illinois, Sanitary District West-Southwest
Sewage Treatment Works^. These dryers are still being
used 43 years later. By 1951 numerous wastewater treat-
ment plants throughout the United States has installed
flash dryers4. Starting in 1935, units were installed that
permitted either incineration or drying or combinations
of the two, thus providing flexibility to combat fluctua-
tion in demand for sludge or reduce fuel needs. This
flexibility was useful only when a market for heat dried
sludge existed. By 1959, approximately 125 municipal
sewage treatment plants adopted the heat drying and/or
incineration approach for sludge treatment and
disposal5 With the strong surge of commercial fertili-
zers, however, the market for heat dried sludge did not
develop as hoped. Consequently, both heat drying alone
and heat drying and/or incineration options became less
popular. Many plants abandoned the heat drying option.
Thus, by the early 1970's, there were about 50 heat dry-
ing and/or incineration installations in the United States
and even these numbers are declining6.
Milwaukee, Wisconsin is an exception to the general
decline in the popularity of heat drying municipal
sludge. Its Milorganite production began in the early
1920's and this product is well known and is in strong de-
mand7. There have been several new entries into the
sludge drying arena. Winston-Salem, North Carolina,
dedicated a new heat drying sludge facility in 19748. The
heat dried product is produced by a private firm,
Orgonics, Inc., Slatersville, R.I., under the trade name
of Organiform SS. At the District of Columbia Blue
Plains Wastewater Treatment Plant another approach to
heat drying wastewater sludges for use as fertilizers is
currently being evaluated 3i9. At Baltimore, a small pilot
facility is also evaluating heat drying of sludge 10
Despite the exceptions cited previously, current liter-
ature on the subject of heat drying municipal wastewater
sludge emphasizes:
1. Heat drying is about the most expensive process
for sludge treatment.
2. The market potential hoped for to utilize heat dried
sludge as fertilizer, or soil conditioner, and there-
by recover at least part of the treatment cost has
not developed.
3. Improper heat drying operations and maintenance
could cause problems with heat drying of sludge.
Dust and fine sludge particles may be produced,
and in the presence of oxygen in the gases, fires or
explosions could result. However, it is important
to note that proper operations and maintenance
will greatly minimize these problems, and safety
features on heat drying units virtually eliminate
danger to personnel and equipment.
4. Many municipalities that have tried heat drying
have abandoned this process, when they can, for
other sludge treatment and disposal alternatives.
However, there are notable exceptions—Milwau-
kee, Chicago, Houston, Winston-Salem.
5. Consultants and design engineers today rarely
consider heat drying for sludge treatment.
Times are changing in the wastewater treatment field,
particularly for sludge treatment and disposal, under the
impact of recently enacted wastewater pollution laws
and concern for resource conservation. To meet the
"Now and Tomorrow" needs, a reassessment of the
heat drying approach may be useful, which is the
purpose of this presentation.
235
-------
236
HEAT DRIED SLUDGE
Overview of Heat Drying of Municipal
Wastewater Sludges
Heat Drying of Sludges
Heat Drying is the dehydration of wastewater sludge,
that is, most of the water is separated from the sludge as
a vapor without combustion of the solid material. In the
process air is heated to increase its vapor holding capa-
city and to provide the latent heat for water evaporation.
It is well known that water and sludge are difficult to
separate, and it takes a lot of heat energy (1,000 Btu/lb
of water at one atm.), to change water from a liquid to a
vapor. By the limits of the laws of thermodynamics for ir-
reversible processes, not all of the heat energy can be
converted to useful work. The theoretical amount of
heat energy needed to evaporate the water divided by
the total amount of heat energy input is a measure of the
thermal efficiency of the heat drying system. Improving
the thermal efficiency is sought because it reduces the
heat energy needed to accomplish the same objective.
To lower fuel consumption, as much water as feasible
is separated from the wastewater sludge prior to heat
drying. Thus, the wastewater sludge may be mechan-
ically filtered, or centrifuges, or pressed out, or
squeezed out, or air dried (provided that the sludge is
first digested) or any other dewatering method worth
trying. These dewatering processes cost money, from
about $5 to $35 per dry ton of sludge solids ".
When wastewater sludge is heat dried to a high solids
content, odorous chemicals are volatilized. In the in-
terest of preserving the air quality or maintaining a good
neighbor policy, the odorous chemicals must be re-
moved before the gases are released from the heat dry-
ing system. Most heat drying systems simply burn (deo-
dorize) these volatiles, which also unfortunately lowers
the thermal efficiency of heat drying.
In Table 1 are shown the Btu's required to dry sludges
in a flash dryer for various moisture to solid ratios 12 The
dried sludge contains about ten percent moisture. In this
table, approximately 2260 Btu* is needed to vaporize
one lb** of water. Of course, less fuel and lower costs
would result when the thermal efficiency is increased.
Several approaches are: (1) reduce the temperature of
the stack gases by greater heat recovery; (2) use chemi-
cal scrubbers; or (3) add chemicals prior to heat drying.
(Reference 5 can be referred to for information on ma-
terial and energy balances for heat drying sludge treat-
ment.)
Excessive drying may produce a sludge that is dusty
or contains many fine particles, which is less acceptable
for marketing. A pelletizing or granulation step may be
necessary which adds another cost. To meet air quality
standards dust or fine particles must be removed, usual-
*To convert Btu to kilocalories, multiply by 0.252
**To convert pounds to kilograms, multiply by 0.454
ly by wet scrubbers,before the gases are released from
the stacks. The scrubbing water is usually recycled to the
treatment plant. As in many other wastewater treatment
operations, standby heat drying equipment is desirable
for continuous operations. About 25 percent excess
capacity seems to be the right amount.
When one takes into account rising fuel costs, capital,
maintenance, and labor costs, possible costs for pelletiz-
ing or granulating, it is understandable that heat drying
of municipal wastewater sludge is about the most expen-
sive of all conventional sludge processing techniques 13.
In Table 2 are shown cost estimates for sludge
disposal "i14 based on 1973 dollars. These cost esti-
mates will vary at different locations. The estimates in-
clude preparation costs such as digestion and dewater-
ing, except for composting. Recent composting studies
show promise for processing unstabilized sludge. Land
costs are not included because they can vary widely.
Operating and maintenance cost may account for about
two-thirds of the total cost of heat drying 13- Also, these
cost figures do not include any credit for sale of products
or by-products.
Marketing Heat Dried Sludge
The gold that glitters at the end of the rainbow, left out
of the heat drying costs shown in Table 2, is credit for
sale of heat dried sludge used as organic soil condi-
tioner, or fertilizer, or for formulation in specialty pro-
ducts. Sale revenues rarely equal the cost for producing
the heat dried sludge. However, marketing the product
does reduce costs. Sludge contains concentrations of
major plant nutrients: nitrogen, phosphorus and potas-
sium that approximate one fifth of those found in chemi-
cal fertilizers 15. Sludge also contains organic matter
(humus) that improves the physical properties of the
soil. Heat dried sludge for agriculture and horticulture is
used mostly for its organic slow release nitrogen and
other organic matter. Waste activated sludge is pre-
ferred for heat drying because it contains higher concen-
trations of these nutrients as compared to primary or di-
gested sludges.
Heat drying destroys most of the bacteria in the
sludge. However, undigested heat dried sludge is sus-
ceptible to putrification if it is allowed to get wet in thick
layers on the ground. Heat drying separates most of the
water from the sludge solids, but one would not antici-
pate any significant decrease in the concentration of
heavy metals of concern with land application on agricul-
tural soils. Experimental studies, however, are needed
to determine whether there is a change in the availability
to crops of heavy metals.
In Table 3 are shown the mineral nutrient percents of
dried sludge. Chemical fertilizers generally contain
much higher nutrient concentrations. It takes about five
times as much heat dried sludge as chemical fertilizers
to obtain similar responses to nutrients. Therefore,
-------
HEAT DRIED SLUDGE 237
TABLE 1
Energy Required for Heat Drying Wastewater Sludge
Sludge
Moisture/Solids
Ratio
Lbs. Water
per
Ton Dry Solids
Approximate Btu x 10°
Required for
Heat Drying / ton Dry Solids
95/5
90/10
85/15
80/20
75/25
70/30
65/35
60/40
38,000
18,000
11,333
8,000
6,000
4,667
3,714
3,000
85.3
40.1
25.1
17.6
13.0
10.0
7.9
6.3
(1) After Olexsey, Reference 12.
(2) Thermal efficiency,
(3) Stack temperature,
(4) To
(5) To
(6) To
(7) 10
convert from Btu
62 percent.
800 F ( 427 C).
's to kJ (kilo joules), multiply by 1.054.
convert from gallons to liters, multiply by 3.785.
convert Btu/ton
percent moisture
(English) to kilocalories/ton (metric) multiply
in the heat dried sludge.
by 0.278.
about five times as much sludge as chemical fertilizers
must be shipped, stored, and spread. This difference
gives a decided cost advantage to commercial fertilizers
TABLE2
Approximate Total Costs for Sludge Disposal
Method
Total Costs
($ / Dry Ton)
Disposal as liquid soil conditioner
[or fertilizer)
Dewatered sludge as soil conditioner
(or fertilizer)
Lagooning
Landfilling dewatered sludge
Barging to sea
Pipeline to sea
Incineration
Composting
Heat drying
32
IS
32
15
14
32
30
64
for farming. Consequently, farm use of heat dried
sludge has simply not developed to the potential hoped
for. Also, selling fertilizer is essentially a seasonal ac-
tivity with highest sales in the fall and spring months.
Storage of about 20 to 25 percent of the heat dried sludge
may be needed for off-season demand. This storage
adds another cost factor.
Houston, Chicago, Milwaukee, and Winston-Salem
are notable exceptions to the adverse marketing trend.
Treatment plants in Houston, Chicago, and Milwaukee
use waste activated sludge dewatered by vaccuum filtra-
tion prior to heat drying. Digested, air-dried sludge is
used in the Winston-Salem heat drying facility, and ni-
trogen compounds are added prior to heat drying.
TABLE3
Mineral Nutrients Percent of Heat
Dried Waste Activated Sludge
(1) After Olexsey, Reference 11, Page 139 and 140, except see (3).
(2) Based on 1973 dollars, reference 12, except see (3).
(3) Composting cost from reference 14. Cost does not include di-
gestion and dewatering of the sludge.
f4) Cost figures do not include any credit for sale of products
or by-products.
(5) Land costs not included.
NUTRIENT
Total N
Organic N
P
P2°5
K
2
PERCENT
3
2
0
1
0
0.
CONCENTRATION
.5
.0
.8
.8
.2
24
6.
4,
3.
8
0.
0.
.4
.5
.9
.7
.7
.84
(1) After Dean e^ al, Reference 15.
-------
238
HEAT DRIED SLUDGE
Houston's dried activated sludge is sold in bulk, via a
five year competitive bidding contract, through a broker
under the copyrighted trade market name of Hou-Acti-
nite 16- The total heat drying capacity is utilized, and all
of the dried sludge produced is sold. Revenue received is
about $21/ton* of sludge solids (1972—FOB-Houston).
The cost for heat drying sludge at Houston was not avail-
able. However, when the $21 revenue is subtracted from
the $64 cost for heat drying (Table 2), the net cost ap-
proaches some of the sludge disposal methods shown in
Table 2.
The City of Milwaukee sells heat dried sludge through
a franchise and also directly to the public in 50 pound
bags, under the copyrighted trade market name of Mil-
organite (Milwaukee-organic-nitrogen)7- The total heat
drying capacity is utilized. There is no difficulty in sell-
ing Milorganite forturfgrass, lawns, golf courses, and to
industrial and farm users. Despite a higher unit price for
its nitrogen content, Milorganite sells well even at pre-
mium prices. Present cost for producing Milorganite is
about $90/dry ton and revenue is about $54/dry ton 17.
The net cost is $36 which is less than other sludge
disposal alternatives for Milwaukee and also approaches
some of the sludge disposal costs shown in Table 2.
The City of Chicago sells heat dried sludge through a
broker via competitive bidding. Published figures 18 in
1968 indicate a revenue of $15/ton of sludge solids
(FOB-Chicago) and a cost of $60 to produce the heat
dried sludge with a net cost of $45/ton. The current reve-
nue from sales of the heat dried sludge is about $17/ton
of sludge solids 19 which is only slightly higher than the
$15/ton of sludge solids received in 1968. Current cost
for producing the heat dried sludge is about $106/ton 20.
Clearly, the net cost has increased. The current output
from the Chicago heat drying units is about 165 dry tons/
day at 96 percent solids 19. This amount may be about
one half of the rated heat dried sludge production capa-
city.
The Organiform SS heat dried sludge produced at
Winston-Salem differs in that methylolurea and di-
methylolurea groups, previously formed by the chemical
reaction of urea and formaldehyde, are mixed with di-
gested air-dried sludge from the treatment plant. The
nitrogen content of the Organiform SS ranges between
15 and 20 percent by weight. This nitrogen content is
three to four times greater than that produced from
waste activated sludge only. No difficulty is expected in
sellingthe 10,000 ton/year production capacity. The Or-
ganiform SS, because of its higher nitrogen content, may
find good entry into the lucrative consumer/retail
market.
Thus far, the general tone on heat drying sludge has
been somewhat negative. It is time for a look at the
"Now and Tomorrow" for the heat drying approach to
sludge disposal.
Ton multiplied by 0.908 = metric ton.
Advantages to Heat Drying Municipal Sludge
The advantages to heat drying municipal sludge are:
1. Undigested sludge can be processed to produce a
useful product for agriculture and horticulture.
This utilization represents conservation of a natu-
ral resource by returning organics and nutrients
to the land.
2. Using heat dried sludge for agriculture and horti-
culture represents a way for ultimate sludge dis-
posal.
3. Processing undigested sludge eliminates diges-
ters which can be troublesome to operate and
costly.
4. Heat drying destroys most of the bacteria without
lowering the quality or diluting the sludge. The
heat dried sludge is readily acceptable from a hy-
gienic viewpoint for land application.
5. The treatment can handle sludges with different
moisture contents. However, in the interest of
conserving fuel prior dewatering is desirable.
6. The heat drying treatment is positive and consis-
tent, unlike biological sludge digestion which can
give below par performance for an extended time.
7. Heat drying units can be operated over a consi-
derable range of fluctuating loadings.
8. Waste heat (e.g., from an incinerator or gas tur-
bines, methane gas from digesters, etc.) can be
utilized in the heat drying operation thus reduc-
ing, or eliminating, need for auxiliary fuel.
9. The process can be operated on an intermittent
basis subject to plant requirements, and standby
fuel is not required.
10. Reducing the water content of sludge by heat dry-
ing facilitates its transportation and utilization. A
wide range of shipping possibilities exists, from
barge or rail for bulk amounts down to 5 to 50
pound bags.
11. Heat drying greatly reduces the volume of sludge,
permitting a wide range of disposal possibilities
(see No. 10 above).
12. Heat drying of sludge reduces odor levels thus
permitting storage.
There are other advantages but the twelve cited above
are sufficient for our purposes. The heat drying process
permits sludge utilization with a wide range of flexibil-
ity. What this treatment approach needs most is to sell
these advantages to the buying public that is ever be-
coming more aware of the need to conserve resources.
Processes for Heat Drying Sludges
Theoretically any type of heat drying process is appli-
cable for sludge. In the United States the following types
of heat drying units are used, have been used, or are be-
ing developed:
• flash dryer
• rotary dryer
• toroidal dryer
-------
HEAT DRIED SLUDGE 239
• multiple hearth dryer
• atomizing spray dryer
These dryers belong to a class designated as direct
heat dryers. Heat transfer is by direct contact of the
sludge with preheated gases, and control is achieved by
measuring and adjusting the temperature of the heated
gases 2. Costs for direct heat dryers are usually less than
for most other types. Organic fouling and inorganic scal-
ing from sludge preclude the use of indirect drying sys-
tems. Direct heat dryers can be more easily protected
from corrosion.
There are some disadvantages to direct heat dryers.
They tend to be thermally inefficient due to the sensible
heat loss in the stack gases. Heat losses can be mini-
mized by heat reuse, or keeping the material longer in
the dryer, thereby reducing stack temperature. Dust
can be cut down by reducing the air velocity or by pre-
drying or pre-forming the sludge into less dust-forming
particles.
Figure 1 is a schematic of a flash dryer/incinerator
system ". Figure 2 is a pictorial flow diagram of the
C.E. Raymond Flash Drying System used at Houston3.
Chicago uses a somewhat similar heat drying system 2I.
Both cities feed vacuum filtered, waste activated sludge
to the heat dryer.
Flash drying is the instantaneous vaporization of
moisture from solids by introducing them into a hot gas
stream. The flash dryer system is based on several dis-
tinct cycles which can be adjusted for different drying ar-
rangements. The first stage is blending wet filter cake
with some previously dried sludge in a mixer to improve
pneumatic conveyance. The blended sludge and hot
gases from the furnace at about 1200°F to 1400°F (650 to
760°C) are mixed ahead of the cage mill, and flashing of
the water vapor begins. The cage mill mechanically agi-
INCINERATOR
FUEL-
T
tates the mixture of sludge and gas, thereby providing
maximum sludge surfaces for exposure to the hot gases.
The residence time in the cage mill is a matter of
seconds. Drying is virtually completed by the time the
sludge leaves the cage mill. The dry sludge (eight to ten
percent moisture) is separated from the spent drying
gases in a cyclone. Part of the dried sludge is recycled
with incoming wet sludge cake, another part of the dried
sludge is screened and sent to fertilizer storage, and
what is left can be incinerated in the furnace. From the
cyclone, the heat dried sludge solids temperature is
around 160°F (71 °C) and the exhaust gases temperature
is about 220°F to 300°F (104° to 149°C).
The exhaust gases from the cyclone have to be deodo-
rized before release to the atmosphere. The gases are re-
cycled to a deodorizer preheater followed by burning in a
furnace or afterburner at temperatures between 1200°to
1400°F (650° to 760°C). The hot deodorized gases are
vented at between 600° and 800°F (315° to 427°C) de-
pending on the extent of heat recovery. The lower the
stack gas temperature the greater is the thermal effi-
ciency; but a trade-off is made on the capital cost of heat
recovery equipment. Unfortunately, the heat remaining
in the stack gases is too low for use in a gas turbine, but
the hot gases could have other plant uses such as heating
buildings. Dust particles in the gases are removed by
wet scrubbing or in a dry centrifuge before release to the
atmosphere.
Primary combustion air is preheated with the latent
heat from spent deodorized gases and introduced a high
velocity to promote complete combustion in the incinera-
tor (furnace). In the furnace the fuel used may be gas,
oil, coal, previously dried wastewater sludge or waste
heat from a solid waste incinerator, gasturbine, etc. Ash
is periodically removed from the bottom of the furnace.
FAN
CYCLONE
DRY SLUDGE
HOT FLUE GAS
ASH
O
SLUDGE CAKE
Figure 1: Flash-Dryer-Incinerator (After Olexsey, Reference 11).
-------
240
HEAT DRIED SLUDGE
K//X/.J COMBUSTION
DEODOHIZEO
I •/ '/-A
Figure 2: Flash Dryer System (Reference 3).
Milwaukee and Winston-Salem use rotary dryers. A
rotary dryer consists of a nearly horizontal cylinder
through which hot gases flow. The cylinder revolves
about five to eight rpm and is usually slightly inclined
from the horizontal so that the sludge can be made to
flow by gravity 13,22 _ jo break up the sludge, the inside
of the heat dryer cylinder usually is equipped with flights
or baffles throughout its length. The direct gas rotary
drier may be operated with gas flow parallel to or coun-
tercurrent to the sludge flow. Wet filter cake is mixed
with previously heat dried sludge in a pug mill for easier
conveyance into the dryer. The system may include cy-
clones for sludge and gas separation, dust collection
scrubbers, and a gas incinerating step. The finished pro-
duct is screened and sent to fertilizer storage. The over-
size particles may be crushed and passed through the
screen again or recycled to the dryer. Undersize sludge
may be pelletized or recycled to the dryer.
The sludge residence time in a rotary dryer is usually
longer (e.g., 45 minutes at Milwaukee) than in a flash
dryer. Consequently, larger capital equipment is
needed. This can be offset because the longer residence
time provides an opportunity for deodorization in the
dryer, and a separate deodorizing step may not be
needed. At Milwaukee, exhaust gases at 900°F (480°C)
from gas turbines are supplemented with additional heat
from natural gas to raise the temperature to about 1200°
to 1250°F (630° to 675°C)17. The hot gases enter along
the length of the dryer in counter-current flow to the
sludge flow. A wet scrubber is used to remove fines from
the spent gases.
A block diagram of the Organiform SS process at
Winston-Salem is shown in Figure 38. Urea and
formaldehyde, in a 1.5 to 1 mole ratio, are heated to be-
tween 86° and 140°F (30° and 60°C) in the reactor.
Methylolureas and dimethyl urea groups are produced.
The reactor contents are sprayed into the sludge in a
paddle mixer. Bacteria cell walls are lysed and steriliza-
tion and deodorization occur. The paddle mix is dehy-
drated in a rotary dryer using co-current, air-sludge
flow. The supplemental heat needed is about 950 Btu/lb
of water evaporated 23. Part of the heat was originally
furnished by the urea-formaldehyde reaction and reac-
tions with the sludge in the paddle mixer. The Organi-
form SS is odorless, has a granular consistency, and a ni-
trogen content between 15 and 20 percent by weight.
Figure 4 is a schematic of the Toroidal Process 3i9
being evaluated at the Washington, D.C., Blue Plains
plant. The capacity is about 40 to 54 tons dry sludge dai-
ly. The Toroidal dryer uses the jet mill principle, has no
moving parts, and dries and classifies solids simultane-
ously. The dryer may be likened to a 42 inch (1.07 me-
ters) pipe bent into a 16 foot (4.88 meters) diameter
doughnut with provisions for inlet of hot air and outlet of
moist air plus dried product 24-25. Dewatered mixed
sludge is metered and pumped into a mixer where it is
blended with previously dried sludge. The blended ma-
terial is fed to the doughnut shaped dryer where it comes
into contact with heated air at a temperature of 800°F to
1100°F (about 430° to 600°C). At the outlet, those parti-
cles which are dry and finely divided follow the air
stream out of the unit. The wetter larger particles are
retained for additional circuits around the doughnut un-
til drying is complete and they have broken up into fine
particles by impacting on one another. About 1180 Btu is
used to vaporize one pound of water. The outlet air
stream temperature, containing the dry sludge, is about
SEWAGE
SLUDGE
FORMALDEHYDE
UREA
ORGANIFORM
Figure 3: Block Diagram of the Organiform Process (After Yamamoto,
et. at., Reference 8).
-------
HEAT DRIED SLUDGE 241
WET SLUDGE
FROM WASTEWATER
PLANT
AIR & WATER
VAPOR
AIR INLET
POLLUTION
CONTROL
PRODUCT
IN BAGS
PRODUCT
TOROIDAL FERTILIZER
DRYER
FINISHING
Figure 4: Sludge Drying System Using the Jet Mill Principle - Toroidal Dryer.
200° to 220°F (82°C to 105°C). Cyclone separators re-
move most of the dried powdered sludge. In a revised
system the air stream will pass through a wet scrubber to
remove fines. If needed, chemical scrubbers can be uti-
lized for odor removal before the gases are discharged.
The dried powdered sludge, after additional nitrogen
and phosphorus are added, is formed into briquettes.
These briquettes are crushed and screened to produce
either bulk or bagged OrganaGroTM (trade market
name).
The multiple hearth furnace can be adapted for heat
drying I3 Modifications include fuel burners at the top
and bottom hearths plus down draft of the gases. The de-
watered sludge cake is mixed in a pug mill with pre-
viously dried sludges before entering the dryer. The
solids become drier and the gases become cooler as both
move downward through the furnace. At the point of exit
from the furnace, the solids temperature is about 100°F
(38°C) and the gas temperature is about 325°F (160°C).
Atomized drying is spraying liquid sludge in a vertical
tower through which hot gases pass downward. Dust
carried with hot gases is removed by a wet scrubber or
dry dust collector. Another spray dryer system 26 utilizes
a high-speed centrifugal bowl. The centrifugal forces
atomize the liquid sludge into fine particles and sprays
them into the top of the drying chamber where moisture
is transferred to hot gases. Nozzles can be used instead
of the centrifuge bowl if clogging can be avoided.
Comparison of Fuel Consumption
Commercial Fertilizer Versus Heat Dried Sludge
In these days of energy crisis, the amount of fuel re-
quired to run a process or produce a product is an im-
portant consideration. It is informative to compare the
consumption of fuel to produce commercial fertilizer
with the fuel needed to produce heat dried sludge. One
basis is to compare the two types of material at equiva-
lent nitrogen (N) content.
Two reports 21-28 suggest that about 45 X 106/Btu
(from natural gas) is needed to produce one ton of N for
commercial fertilizers. Another reference 29 indicates
that 915 gallons of crude oil are required to produce one
ton of N. Because one gallon of crude oil has the equiva-
lent of approximately 146,000 Btu's30, 915 gallons is
about 134 X 106 Btu/ton of N. Obviously there is about a
2.7-fold difference, but for comparison with the heat en-
ergy required to dry sludge, both energy values will be
used.
The N content in waste activated sludge is about 5.7
percent13, or 114 pounds in one ton of heat dried sludge.
About 17.6 tons of heat dried sludge are needed for one
ton of N. Referring to Table 1, note the 60/40 moisture/
solids ratio which is achievable with a filter press. This
sludge cake requires 6.3 X 10° Btu/ton of sludge times
17.6 which is 111 X 106 Btu/ton N from heat dried
sludge. If the 80/20 ratio sludge cake is used, as pro-
duced from vacuum filtration or centrifugation, the
Btu's needed are about 310 X 106 Btu/ton N. The above
comparison from Table 1 data implies that 2260 Btu is
needed for one pound of water vaporized. However, re-
cent advances in heat drying technology for wastewater
sludges suggest that only about'1200 Btu is needed. Us-
ing the 1200 Btu figure suggests that for the 60/40 mois-
ture to solid ratio, about 61 X 10^ Btu is needed for each
ton of N produced from heat drying of sludge.
The comparison of the energy requirements for nitro-
gen from fertilizer or sludge, which is summarized in
Table 4, show that the heat energy for equivalent
amounts of N from the heat dried sludge at the 60/40
-------
242
HEAT DRIED SLUDGE
moisture to solids ratio is comparable to the energy re-
quirements for producing N in commercial fertilizers.
More heat is needed for the N produced from the 80/20
ratio. If high efficiency is achieved in the sludge dryers
and the source of the ammonia in the inorganic fertilizer
is crude oil, the commercial inorganic fertilizers and
dried sludge are essentially equivalent in fuel consump-
tion per ton of nitrogen.
Production of Heat Dried Sludge for Sale
The approximate yearly production of heat dried
sludge sold by wastewater treatment plants is shown in
TableS. Small amounts may be produced by other plants
but their contribution appears to be negligible.
In Table 6 are shown the trends in production of muni-
cipal wastewater sludge •". In 1972, approximately 4.8 X
10" dry tons/year sludge was produced. Heat dried
sludge represents about 3.3 percent of the total sludge
produced.
In Table 7 are shown the trends in disposal of munici-
pal wastewater sludge31. Of interest is that about 20
percent (1 x 106 dry tons/year) of the sludge is utilized
on land. Thus heat dried sludge represents about 16 per-
cent of the total amount of sludge utilized, either directly
or in fertilizer mixes on land.
An interesting comparison is the amount of nutrients,
specifically nitrogen, available in sludge versus the
amount of nitrogen utilized in commercial fertilizers. In
1971, about 10 X 106 tons of nitrogen was utilized for fer-
tilizers 32. In Table 6, sludge production per year (ex-
cluding chemical sludge) totals 4.7 X 10° tons. Assum-
ing five percent nitrogen content, the total nitrogen is
235,000 tons or about 2.4 percent of the nitrogen used for
fertilizers. If all of the sludge generated were used for
agricultural purposes, it would make up only a minor
portion of the nitrogen used.
SUMMARY "NOW AND TOMORROW"
This presentation has discussed current aspects of
heat drying: advantages and disadvantages, processes
for producing heat dried sludge, energy relationships,
TABLE4
Comparison of Energy Needed for Nitrogen
Production for Fertilizer
Fertilizer Source
Millions of Btu's/Ton Nitrogen
Commercial fertilizer
Heat dried sludge (60/40 moisture/solids ratio)
Heat dried sludge (60/40 moisture/solids ratio)
Heat dried sludge (80/20 moisture/solids ratio)
Heat dried sludge (80/20 moisture/solids ratio)
50 and 134
(1)
61
310
172
(3)
(2)
(3)
(1) From three different references
(2) 2260 Btu/lb of water evaporated
(3) 1200 Btu/lb of water evaporated
TABLES
Production of Heat Dried Sludge for Sales
Location
Approximate average
daily production (ton/day)
Approximate quantity sold
ton / year
Chicago
Houston
Milwaukee
Winston-Salem
165
60
185
27
(1)
61,000
22,000
67,000
10,000
(1)
Total
437
160,000
(1) Houston's facility is undergoing upgrading of heat drying equipment. Additional heat
dryers are also being added. In 1976, production is expected to increase to about 140
tons/day, 50,000 tons/year.
-------
HEAT DRIED SLUDGE 243
TABLE6
Trends in Production of Municipal Wastewater Sludge*
Sludge Type
1972 1985
Population Dry tons^ Population Dry tons
per year served per year
(millions) X 106
served
(millions) X 10°
Primary (0.12 Ib/cap-da) ***
Secondary (0.08 Ib/cap-da)
Chemical (0.05 Ib/cap-da)
145 3.2
101 1.5
10 0.1
170
170
50
3.7
2.5
0.5
Data taken from a report by Farrell Ref. 31
ton X 0.908 = metric ton
*** Ib X 0.454 kg
TABLE?
Trends in Disposal of Municipal Wastewater Sludge*
Disposal Methods
1972
Percent
1985
Percent
Landfill
Utilized on Land
Incineration
Ocean (dumping and outfalls)
40
20
25
15
40
25
35
0
Data taken from a report by Farrell Ref. 31
production for sales and an overview of the process.
While heat drying of sludge is expensive, it can be a use-
ful and relatively cheaper alternative to sludge disposal
for many municipalities if the final product can be suc-
cessfully marketed. When one reviews the trends in pro-
duction of municipal wastewater sludge shown in Table
6, it is noted that over one-third of the sludge to be pro-
duced in 1985 will be waste activated sludge. This is pre-
cisely the sludge that has been successfully marketed.
Inorganic commercial fertilizers are preferred by
farmers because of their higher nutrient content, lower
bulk and lower costs. Heat dried sludge sales are di-
rected toward four other major markets: (1) industrial
fertilizers compounders; (2) citrus growers; (3)
nursery/ horticulture/turf grass markets; and (4) the
lucrative consumer/retail market. Thus, rather than
competition, it might be better to consider the heat dried
sludge as a complement to commercial fertilizers. Heat
dried sludge offers the slow-release organic nitrogen,
other organics that improve the physical structure of
soils, and the availability of trace elements such as zinc
(known to be deficient when solely using commercial
synthetic fertilizers).
Wastewater treatment authorities are faced with the
primary task of treating and disposing of sludge in the
most economical manner that least affects the environ-
ment Marketing imposes on municipalities a set of tasks
they may find difficult to accomplish because of prob-
lems of personnel training, of laws and regulations, and
even political restrictions. Therefore, marketing heat
dried sludge may best be done by a commercial firm with
the skills to handle the marketing and servicing aspects.
The key to heat drying of sludge is the market place,
and more information is needed on the acceptability of
the product to a public that is becoming increasingly
aware of the need to conserve resources. An added in-
centive to using heat dried sludge is the rapid increase in
commercial fertilizer cost. In 1973, the average cost was
about $75/ton and by the fall of 1974 it had risen to
$140/ton28. In today's market the cost of nitrogen per
pound from anhydrous ammonia is 11.3 cents, from urea
19.6 cents, and from ammonia nitrate 19.8 cents 33.As-
suming 114 pounds of N from one ton (5.7 percent nitro-
gen) heat dried sludge, the value of the N is from $13 to
$22.50. When value for phosphorus, organics, and mi-
nor nutrients also are included, the potential market
value for heat dried sludge is even more substantial. Be-
cause heat dried sludge is used on turfgrass, citrus
crops, tobacco, home gardens and lawns, there is a sub-
stantial potential demand. Heat dried sludge may be
much too valuable to either burn or bury.
A most lucrative potential market is at the consumer/
retail level. Consideration has to be given to selling
small units, e.g., 40 to 50 pound bags. These small units
require warehousing, and distribution at the retail point
of sale. Distribution, packaging, label definition, brand
names, registration, product uniformity, shelf life sta-
bility and safety are a few of the considerations a pro-
ducer must develop for the sludge commodity to reach
this premium market. In the Eastern United States, a 40
to 50 pound bag of organic plant nutrients is retailing at
$6.50 to $7.00 per bag, or about $260 per ton34
The consumer market is a full time effort requiring
daily participation. Price fluctuations in the consumer
market can vary widely and steeply (Milorganite is an ex-
ample of franchise and direct marketing). Other muni-
cipalities may find it more suitable to establish an out-
side mechanism to develop and maintain this market po-
tential. It will be most interesting to follow the marketing
trends of such products as OrganaGro^M and Organi-
form SS which are produced from heat dried sludge by
commercial firms.
ACKNOWLEDGEMENTS
The author gratefully acknowledges the assistance of
the following people: R.D. NickersonandG.C. Simons at
the C.E. Raymond/Bartlett-Snow Company; D. Wun-
derlich, R.R. Rimkus, A. Michuda and D. Zenn at the
Metropolitan Sanitary District of Greater Chicago; T.
Wolf at the Metropolitan Sewage Commission of the
County of Milwaukee; M.T. Garrett at the City of Hous-
ton; J.M. O'Donnell at Orgonics, Inc., Slatersville,
Rhode Island; W.B. Tarpley at the Organics Recycling
Inc., Westchester, Pennsylvania; D.A. Mays, TVA,
Muscle Shoals, Alabama; and R.J. Burns, Black, Crow
and Eidsness, Inc., Gainesville, Florida.
-------
244
HEAT DRIED SLUDGE
LITERATURE CITED
1. Keefer, C.E., "Sludge Granulating Plant Expected
to Increase Revenue," Public Works, February 1965,
pp. 114-116.
2. Bryan, A.C., and Garrett, M.T., Jr., "What To Do
with Sludge? Houston Has an Answer," Public Works,
December 1972.
3. "Processing Design Manual for Sludge Treatment
and Disposal," U.S. Environmental Protection Agency,
Technology Transfer Manual, EPA 625/1-74-006,
October 1974.
4. Flood, F.L., "Sewage Treatment Plant Equip-
ment—Flash Drying and Incineration,'' Water and Sew-
age Works, September 1951, pp. 394-398.
5. Leet, C.A., Jr., Gordon, C.W., Tucker, R.G., Ther-
mal Principles of Drying and/or Incineration of Sewage
Sludge, Presented at the Annual Meeting of the Federa-
tion of Sewage and Industrial Waste Associations, Dal-
las, Texas, October 1959, 21 pages.
6. Sludge Handling and Disposal, Phase 1, State-of-
the-Art, Stanley Consultants, November 1972.
7. Wilson, C.G., "Merchandizing Heat Dried
Sludge," Published in the Proceedings on the Confer-
ence on Land Disposal of Municipal Effluents and
Sludges, March 12 and 13, 1973, EPA-902/9-73-001,
U.S. Environmental Protection Agency, Region II, pp.
117-123.
8. Yamamoto, J.H., Schnelle, J.F., Jr., O'Donnell,
J.M.. "High Nitrogen Synthetic Fertilizer Produced
from Organics Wastes," Public Works Magazine, Janu-
ary 1975.
9. Tarpley, W.B., Jr., Organics Recycling Inc., West
Chester, Penn., Private Communication.
10. Farrell, J.B., Private Communication.
11. Olexsey, R.A., "Thermal Degradiation of
Sludges," Published in Pretreatment and Ultimate Dis-
posal of Wastewater Solids Research Symposium, May
21 and 22,1974, EPA-902/9-74-002, U.S. Environmental
Protection Agency, Region II, pp. 127-180.
12. Olexsey, R.A., Private Communication.
13. Burd, R.S., "A Study of Sludge Handling and Dis-
posal," Publication WP-20-4, FWPCA Grant No. PH-
86-66-32, May 1968.
14. Epstein, E., and Willson, G.B., "Composting
Sewage Sludge," Proc. of the National Conference on
Municiapl Sludge Management, Pittsburgh, Pa., June
11-13, 1974, pp. 93-95. Available from Information
Transfer, Inc., 6110 Executive Blvd., Suite 750, Rock-
ville, Md. 20852.
15. Dean, R.B., and Smith, J.E., Jr., "The Properties
of Sludges," Proc. of the Joint Conference on Recycling
Municipal Sludges and Effluents on Land, July 9-13,
1973, Champaign, Illinois, sponsored by the U.S. Envi-
ronmental Protection Agency, U.S. Department of Agri-
culture and the National Association of State Universi-
ties and Land Grant Colleges, pp. 39-47.
16. Garrett, M.T., Jr., "Drying of Sludge for Market-
ing as Fertilizer," Proc. of the National Conference on
Municipal Sludge Management, Pittsburgh, Pa., June
11-13, 1974, pp. 93-95. Available from Information
Transfer, Inc., 6110 Executive Blvd., Suite 750, Rock-
ville, Md. 20852.
17. Wolf, T., Private Communication.
18. Dalton, F.E., Stein, J.E., Lynam, B.T., "Land
Reclamation—A Complete Solution of the Sludge and
Solids Disposal Problem," Journal of the Water Pollu-
tion Control Federation, Vol 40, No. 5, Part I, May 1968,
pp. 789-800.
19. Rimkus, R.R., Private Communication.
20. Alter, J.H., "NU-EARTH-Chicago Merchandis-
ing Program," Compost Science, Vol. 16, No. 3, May-
June 1975, pp. 22-24.
21. Lue-Hing, C., and Brooman, D.L., "Evaluation of
Effects of Afterburner Operating Temperature on Stack
Gases," Metropolitan District of Greater Chicago Dept.
of Research and Development Report 75-1, October
1974, pp. 3-6.
22. Sloan, C.E., "Drying Systems and Equipment,"
Chemical Engineering, June 19, 1967, pp. 169-205.
23. O'Donnell, J.M., Private Communication.
24. Organics Recycling Inc., Westchester, Pennsyl-
vania.
25. Tarpley, W.B., Jr., Private Communication.
26. Metcalf and Eddy, Inc., Wastewater Engineering,
McGraw-Hill Book Company, New York, 1972.
27. Davis, C.H., Energy Requirement for Alternate
Methods for Processing Phosphate Fertilizers, Pre-
sented at the Technical Conference of International
Superphosphate and Compound Manufacturers Asso-
ciation Limited, Prague, Czechoslavakia, September
23-27, 1974.
28. Prior, L.A., "Interim Report on Land Availability
Crop Production and Fertilizer Requirements in the
United States," Systems Management Division, Office
of Solids Waste Management Programs, U.S. Environ-
mental Protection Agency, March 1975.
29. Lynam, B.T., Lue-Hing, C., Rimkus, R.R., The
Utilization of Municipal Sludge in Agriculture, Pre-
sented at United States/Soviet Seminar on "Handling,
Treatment and Disposal of Sludges, "Moscow, U.S.S.R.,
May 12-28, 1975.
30. Nelson, W.L., Petroleum Refining Engineering,
McGraw-Hill Book Company, Inc., New York, 1936.
31. Farrell, J.B., "Overview of Sludge Handling and
Disposal," Proc. of the National Conference on Munici-
pal Sludge Management, Pittsburgh, Pa., June 11-13,
1974, pp. 5-10. Available from Information Transfer,
Inc., 6110 Executive Blvd., Suite 750, Rockville, Md.
20852.
32. Farm Chemicals Handbook, Meister Publishing
Company, Willoughby, Ohio, 44094, pp. 13-47.
33. Mays, D.A., Private Communication.
34. Burns, R.J., Private Communication.
-------
COMPOSTING RAW SLUDGE
E. Epstein and G. B. Willson
Agricultural Re search Service, USD A
Beltsville, Maryland
INTRODUCTION
Disposal of sewage sludge is a major problem in waste-
water treatment. Incineration, ocean dumping, and sev-
eral land application systems also can present environ-
mental, sociological, and economic difficulties. The en-
vironmental problems are primarily associated with air,
land and water pollution by inorganic elements and
pathogens. Sociological concerns are generally about
aesthetics and odors. Transportation of sludge to disposal
sites and cost of fossil fuels have resulted in large in-
creases in sludge disposal costs.
In 1972, the Agricultural Research Service, U.S. De-
partment of Agriculture, began investigating the com-
posting of sewage sludge as an alternative to other dis-
posal methods.
Composting is a biological process by which organic
matter is decomposed into a relatively stable material.
Composted sewage sludge has no objectionable odors.
Temperatures generated during composting will greatly
reduce or eliminate pathogenic organisms. If composting
is done at the wastewater treatment plant, sludge trans-
portation costs are greatly reduced. The final product is
aesthetic, dry and easy to handle for use in urban areas or
on agricultural land. Although the product contains de-
sirable plant nutrients, it can also contain toxic ele-
ments J'7. Compost is an excellent soil amendment that
enhances the rooting media for plant growth by reducing
potential compaction, increasing soil water retention and
availability to plants, and providing for better soil water
movement and aeration 2-5>6.
The initial studies by the U.S. Department of Agricul-
ture at Beltsville, Maryland, were directed to composting
digested sewage sludge in windrows 3'8. The sludge was
obtained from the Blue Plains Wastewater Treatment
Plant in the District of Columbia. At present, ten dry
metric tons of digested sludge (50 tons, 23 percent filter
cake) are being composted daily.
In the fall of 1973, studies were begun on composting
raw (primary and secondary activated) dewatered (23
percent filter cake) sludge in the windrows. This proce-
dure was unsatisfactory because obnoxious odors were
produced. Several odor-masking or odor-reducing chem-
icals such as hydrogen peroxide, chlorine dioxide, and
gypsum, were triedbyeithermixingthem with the sludge
at the treatment plant or applying them during compost-
ing. Although odors sometimes were reduced initially,
they became strong enough later in the composting pro-
cess to negate this approach. One of the most effective
methods of reducing odors from raw sludge in the win-
drow was by mixing digested with raw sludge. Even with
mixtures of 75 percent raw and 25 percent digested
sludge, theodorlevel was reduced markedly. Since win-
drow composting of raw sludge proved unsatisfactory, a
forced aeration method was developed.
Description of Method
Design of System
The forced aeration system 4 consists of building a pile
of raw sludge mixed with woodchips or shredded bark to
provide bulk, and using a vacuum to draw air through the
pile. Finely screened compost from previous operations is
used to cover the pile to prevent odoriferous gases from
escaping into the atmosphere (Figure 1). The gases re-
moved from the pile are scrubbed by passing them
through another pile of screened compost.
AERATION PILE
SCREENED
FAN COMPOST
SCREENED COMPOST
WOODCHIPS AND SLUDGE
UNSCREENED COMPOST
PERFORATED PIPE*
Figure 1: Forced Aeration System.
245
-------
246
COMPOSTING RAW SLUDGE
Procedure
1. A flexible ten cm perforated drainage pipe is laid
in a "U" shape on the ground.
2. The pipe is covered by 30 cm of unscreened compost
or woodchips. This layer absorbs liquids seeping from the
pile and prevents clogging of the pipe.
3. Filter cake raw sludge (23 percent solids) is mixed
with woodchips at a ratio of 1:3 on a volume basis. This
mixture is placed over the unscreened compost or wood-
chips covering the pipe. The sludge-woodchips mixture is
built up to form a pile approximately six meters wide by
2.5tothreemetershigh.Thelengthofpiledependsonthe
rate of sludge production and the suction equipment
used.
4. The entire pile is covered with a 30 cm layer of
screened, cured compost that has passed a 1.0 cm screen.
Until screened compost becomes available, woodchips or
shredded bark can be used.
5. The perforated pipe is attached by a piece of solid
pipe and connectors to a blower. Suction is applied for ten
to 14 days; then the blower is reversed and air is con-
ducted into the pile for seven to ten days. By reversing the
air flow, temperatures are increased in the cold regions of
the pile. Moreover, after the initial period of negative
aeration, the concentration of odorous gases discharged
from the pile is negligible and presents no problem.
6. The gases removed from the pile during suction are
piped into an adjacent small pile of screened «1.0 cm)
compost that effectively absorbs the odors.
7. The gases removed during suction are warm and wa-
ter will condense in the pipe outside the pile. The conden-
sate can be drained and recycled into the sewage system,
or a sand filter bed or other disposal system can be used.
8. After 21 days, the compost is moved to a stockpile for
curing for about four weeks.
9. The cured compost is screened and the woodchips re-
covered for reuse.
Before screening, it may be necessary to dry the com-
post by spreading and periodically turning it with a spike-
tooth harrow. Blowing airthrough the curing pile hastens
curing and also produces a drier product.
Monitoring Requirements
Temperature. Temperatures below 45°C indicate im-
proper composting and may be caused by either too low or
too high aeration rates.
Oxygen. Oxygen values of gases exhausted and in the
pile should range from fiveto ISpercent. Lowervalues in-
dicate inadequate aeration and higher values indicate ex-
cessive aeration. Proper aeration can be maintained by
using a timer to cycle the blower as needed.
Equipment
The following equipment is needed to process a pile
containing ten dry metric tons (50 tons 23 percent filter
cake):
1.27 meters (90ft) often cm perforated plastic drainage
pipe—cost $24.00.
2. 12 m (40 ft) often cm solid plastic pipe—cost $11.00.
3. One0.33hp, 5.3 to 6.6 amp motor with blower - simi-
lar to Dayton Model 7C504C*—cost $73.37.
4. Two one cm plastic straight connectors—cost $0.70.
5. One ten cm plastic "T" connector—cost $2.65.
6. Timer similar to Dayton four hour cycle timer switch
Model No. 2E 131—cost $16.87.
The following monitoring equipment is useful:
1. Temperature probe.
2. Oxygen probe.
A front-end loader is necessary for the construction of
the pile. The front-end also can be used to mix the wood-
chips and sludge; however, better mixing is achieved by
spreading the sludge over a bed of woodchips and using a
rototiller.
Land Needs
Composting Area. A ten dry metric ton pile (50 ton 23
percent filter cake) is approximately six m wide, 12m long
and 2.5m high. The composting area would occupy a 72 m
square area (approximately 800 sq. ft.). This pile will
handle one week's sludge production from a city of ap-
proximately 35,000 to 50,000 persons. Additional area is
needed for maneuvering equipment and constructing
other piles during the three week composting period.
CuringArea. Sufficient space is needed to stockpilethe
composted material for four weeks after composting.
Several piles can be consolidated to save space.
Screening, Drying and Storage Area. An area must be
provided to store the final product until distribution.
Storage must also be provided for a supply of woodchips.
Administrative Area. Space is needed for an office and
for equipment storage.
Miscellaneous. Some land is needed for roadways and
parking. Also, a bufferstrip and runoff collection pond are
needed if the compost site is not located at a wastewater
treatment plant.
The estimated total land area required for composting
ten dry metric tons of sludge per week at a wastewater
treatment plant is 1.0 hectare (two acres).
Discussion of Method
Figure 2 shows the temperatures reached during com-
posting raw sludge. Measurements were taken at ten lo-
cations throughout the pile. These data represent mean
temperatures recorded in the centerof the pile. Tempera-
tures were lower at the pile edges. During the 26 days of
composting, temperatures throughout the pile exceeded
50°Cfor 15 days. In the coldest locations, temperatures
*Mention of trade name, proprietry product or specific equipment
does not constitute a guarantee or warranty by the U. S. Department of
Agriculture and does not imply its approval to the exclusion of other
products that may be suitable.
-------
COMPOSTING RAW SLUDGE 247
4 8
Figure 2: Temperatures Reached During Composting Raw Sludge.
12 16 20 24 28
DAYS
exceeded 60°C for nine days. These temperatures can
significantly reduce the pathogen population. Table 1
shows the survival of salmonellae and coliform after com-
posting raw sludge. The number of salmonellae or-
ganisms after composting was negligible. Fecal coliform
were reduced from 2.7x10'to an undetectable level. Fur-
ther research is being conducted on the survival of these
and other pathogens when different composting tech-
niques are used.
Table 2 shows the major components and nutrients of
the raw sludge and the compost. Nitrogen, phosphorus,
and potassium are three major elements essential for
plant growth. Total nitrogen of the composted material
was 1.6 percent; phosphorus, 1.0 percent; and potas-
sium , 0.16 percent. Only a small part of the nitrogen is im-
mediately available for plant growth since it is mostly in
TABLE 1
Salmonellae and Coliform Populations Before
and After Composting Raw Sludge
Sludge Compost
_cells/g_
Salmonellae
Fecal Coliform
Total Coliform
87
2.7xl07
4.4xl08
<5
<8
<8
the organic form. Thus, up to 30 dry metric tons can be ap-
plied without overfertilizing plants or releasing nitrate to
the groundwater. The organic nitrogen is slowly
mineralized so that it is continuously available to plants
over several years.
Calcium and magnesium also are essential elements
for plant growth. Heavy metals such as zinc, copper,
nickel, cadmium, and lead can be toxicto plants and to hu-
mans consuming these plants if present in excessive
amounts. The compost produced from sludge of the Blue
Plains Wastewater Treatment Plant does not contain high
levels of toxic elements. Studies at Beltsville, Maryland,
showed that the use of this material at recommended
rates did not increase the level of undesirable heavy
metals in food crops. Considerably more research is being
conducted on the use of this product and its effect on soil
properties and plant composition.
TABLE2
Composition of Raw Sludge and Compost
Component
Raw Sludge
Compost
Organic Carbon, %
Water, %
Potassium, %
Phosphorus, %
Calcium, %
Magnesium, %
Total Nitrogen, %
Ammonia, ppm
Nitrate-Nitrite, ppm
Z1nc, ppm
Copper, ppm
Nickel, ppm
Cadmium, ppm
Lead, ppm
31
78
.19
1.46
1.39
0.41
3.8
1540
1
980
420
87
10
420
23
35-58
.16
1.0
1.42
2.36*
1.6
235
3
770
300
300*
7.6
290
I/ Data provided by Dr. W. D. Burge, USDA,
Beltsville, Md. 20705.
* Increase In magnesium and nickel due to the serpentine rock
used 1n the compost pad.
CONCLUSIONS
The aerated pile method of composting shows promise
for controlling the odors associated with windrow com-
posting of raw sewage sludge. The blanket of screened
compost ensures that all of the raw sludge reaches tem-
peratures above the thermal death point of most patho-
gens. The process can be simply monitored by measuring
temperature and oxygen. The method can be adapted
readily by either small or large sewage treatment plants
and requires only a modest investment in equipment.
-------
248
COMPOSTING RAW SLUDGE
LITERATURE CITED
1. Chancy, R.L., "Crop and Food-Chain Effects of
Toxic Elements in Sludges and Effluents," Proc. Joint
Conf. Recycling Municipal Sludges and Effluents in
Land, Natl. Assoc. State, Univ. and Land Grant College,
Washington, D.C. 1974, pp. 129-141.
2. Epstein, E., J.M. Taylor and L.E. Gross, "Sewage
Sludge and Sludge Compost Applied to Soil: Effect on
Some Soil Physical and Chemical Properties," Agron.
Abst., Amer. Soc. Agron., Madison, Wise., 1974.
3. Epstein, E. and G.B. Willson, "Composting Sew-
age Sludge," Municipal Sludge Management, Proc.
Natl. Conf. Municipal Sludge Mgmt., Info. Trans. Inc.,
Rockville, Md., 1974, pp. 123-128.
4. Epstein, E., G.B. Willson, W.D. Surge, D.C. Mul-
len and N.K. Enkiri, "A Forced Aeration System for
Composting Sewage Sludge," Submitted for publication
in Journal Water Pollution Control Federation.
5. Hernstein, C.C. and D.F. Rothwell, "Pelletized
Municipal Refuse Compost as a Soil Amendment and
Nutrient Source for Sorghum," J. Environ. Qual, 2,
1973, 343-345.
6. Mays, D.A., G.L. Terman and J.C. Duggan,
"Municiapl Compost: Effects on Crop Yields and Soil
Properties," J. Environ. Quality 2, 1973, 89-92.
7. Page, A.L., "Fate and Effects of Trace Element in
Sewage Sludge When Applied to Agricultural Lands,"
EPA Technology Series, EPA-670/2-74-005, 1974.
8. Willson, G.B. and J.M. Walker, "Composting Sew-
age Sludge: How?" Compost Sci., 14(5) 1973, 30-32.
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POTPOURRI
INTRODUCTION
In hopes of establishing more feedback and participa-
tion by Conference attendees, the agenda was designed
with 1 '/2 hours of reserved time set aside on the final day
for spontaneous submissions from attendees, who, for
any reason whatsoever, wished to contribute an oral
mini-paper. An announcement was made at the
beginning of the conference for submittal of 8 minute
papers which would subsequently be presented andthen
published in the proceedings. The response was
exuberant.
This session illustrated the need for public participa-
tion as witnessed by the number of attendees and the vi-
brant discussions which followed each paper. Had there
been more time, this session could easily have continued
throughout the day.
Ten papers were presented. The following six papers
represent those which were submitted for publication.
These compose the session entitled "Potpourri" which
terminated the Conference, but opened "lines of
communication''.
SLUDGE MANAGEMENT AS VIEWED
BY AN AGRICULTURAL ECONOMIST
Lee A. Christensen
United States Department of Agriculture
Broomall, Pennsylvania
I'm an agricultural economist with the Economic Re-
search Service, USDA. By way of introduction, ERS is
the largest group of agricultural economists in the world.
Our tasks are varied, but in general it is to provide eco-
nomic information to aid USDA in policy formulation and
program implementation. You're more familiar with the
research of ARS, a companion USDA agency that con-
centrates on the physical, biological, and engineering
aspects of agriculture.
I've attended a number of conferences that have ad-
dressed primarily engineers and physical and biological
scientists. I've often felt in the minority in terms of back-
ground, training, and approach to questions related to
sludge management issues. Economists and other social
scientists view some of the issues from a different per-
spective. I would like to share some personal observa-
tions with you this morning.
1. We need each other. The solution to wastewater
management problems requires a multidisciplinary ap-
proach involving engineers, agricultural economists,
agronomists, soil scientists, lawyers, and others. Good
economic analysis requires valid data on physical and
technical relationships and responses. Conversely, the
implementation of engineering designs requires the ex-
pertise of economists, lawyers, and other social
scientists.
2. This leads to a second observation. There are too lit-
tle data from the multitude of operational systems for
sludge management that lends itself to good compari-
sons. Communities have limited information available to
compare costs of land application with incineration and
other approaches, especially data generated from a com-
parable data base. Cost components need better identi-
fication so that component costs such as labor, capital,
and energy can be readily identified. It seems to be that
the sludge treatment cost model discussed in Mr.
Smith's presentation is a step in this direction. I hope so,
because communities are making major decisions in the
allocation of their funds for sludge treatment and need
good cost data.
3.1 see a need for greater distinctions between waste
management alternatives and community size. Land ap-
plication may have greater potential for small and medi-
um sized communities, which often have the most homo-
geneous waste product available, open space, and fewer
resources to devote to community services. Discussions
of treatment alternatives should be more specific in rela-
tion to community size.
4. Greater attention needs to be paid to the numerous
options that exist for (1) the acquisition of rights to land
and (2) the management of farming or treatment opera-
tions. Certain functions can best be carried out on lands
owned by the wastewater authority, but present land-
owners can and have cooperated with public manage-
249
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250
POTPOURRI
ment systems. Greater attention should be given to de-
veloping information systems that will provide farmers
incentives to participate in a system, and which will also
assure cities adequate management controls.
5. Planning for waste management need not be a
single purpose activity. Waste management plans can
be incorporated with plans to channel urban growth, to
keep lands in open space, and coordinated with other
community goals.
6. Related to a total community planning approach is a
need to analyze possibilities for reducing the supply of
materials entering the waste processing stream. Indus-
try is moving in this direction with increased resource re-
cover and water reuse. However, municipal wastewater
management needs to investigate ways to reduce the
volume of material entering the treatment system con-
currently with treating what comes out of the end of the
pipe.
7. Many of you are involved directly in determining
the best way s of meeting the wastewater treatment goals
specified in the laws. I would raise with you, however,
the need to have more discussion of what a clean stream
is worth, and in particular, the application of the stand-
ards identified in PL 92-500 to all streams. Wastewater
treatment is only one of the many demands placed upon
the resources of our nation and communities. Estimates
prepared in conjunction with the work of the National
Water Quality Commission indicate $100 to $300 billion
dollars of expenditures over the next ten years. Some
communities are faced with making wastewater treat-
ment investments that exceed their entire tax base. Ex-
penditures of this magnitude divert resources from other
uses that may be of as great or greater priority, but
which don't receive as much attention in public policy
debate.
8. Keep in mind that relative prices can play a major
role in resource allocation to meet waste management
requirements. A price increase in an input, such as elec-
tricity, increases interest in processes using lower priced
inputs. While it is important to be interested in saving
energy in the sludge process, it is more important to pro-
vide a specified level of treatment at the lowest total cost
to the community. Fuel savings are important only as
they translate to total dollar savings and not in terms of
savings of calories or BTU's. The higher price of natural
gas has increased interest in sludge gas generation, just
as higher fertilizer prices has increased interest in the
value of sludge and effluent as fertilizers.
9. Finally, there is a need to be aware of and consider
the impact of land treatment of sludges or wastewater on
the agricultural economy, both directly and indirectly.
Parties impacted include not only the farmers whose
land is used, but also the suppliers of seed, fertilizer,
and machinery and the channels for marketing the
crops. Possible changes in ownership patterns and land
values need evaluation, along with changes in farm and
regional production.
COMBINED REFUSE/SLUDGE PYROLYSIS
IN THE OAKLAND AREA
N. W. Snyder and B.I. Loran
The Ralph M. Parsons Company,
Pasadena, California
In California, incineration of refuse and sewage
sludge is prohibited due to air pollution considerations.
Pyrolysis provides a viable alternative because, as
stated by Robert Olexsey, of EPA, this process is essen-
tially pollution free.
The Pacific Gas & Electric Company, located in San
Francisco, the East Bay Municipal Utility District
(EBMUD), Oakland, and the Oakland Scavenger Com-
pany commissioned The Ralph M. Parsons Company in
July, 1974 to verify the technical and economic feasi-
bility of the Union Carbide "Purox" pyrolysis process
and to prepare a preliminary engineering report.
The only data available at the time had been obtained
from a Union Carbide pilot plant which could pyrolyze
five tons per day of refuse or mixed refuse/municipal
sludge. The Parsons Company had developed in the past
commercial size plants based on pilot plant data. Addi-
tional data for the pyrolysis process became available
when the S. Charleston, W. Va. 200 tons per day demon-
stration plant became operational.
The facility designed would be located in Oakland or
San Leandro, California. Its capacity ranges from 1400 to
2100 tons of combined feed, comprising an average of
200 tons per day of digested sludge at 25 percent solids.
This is the entire output of the EBMUD District 1 Water
Pollution Control Plant; the dewatering is carried out by
vacuum filtration. The plant will also receive 125 tons
per day of shredded automobile wastes from the
Oakland Scavenger Company. This material has a
higher heat content, and will help offsetting the negative
heat value of the digested sludge at 25 percent solids.
Digested sludge is used because anaerobic digesters are
already in operation at EMBUD; undigested primary or
activated sludge would be otherwise preferable because
of the higher energy content.
Figure 1 depicts schematically several aspects of the
project. As shown, the main features of the study were
(1) receiving, storage, and handling of the shredded
municipal refuse, sewage sludge, and other waste; (2)
conversion of the waste to a 300 Btu synthetic gas
(syngas) using the Purox process; (3) utilization of the
syngas in four of the most promising methods including
methanation to 1000 Btu synthetic natural gas (SNG),
methanol synthesis, distribution of syngas to inter-
ruptible customers, and direct production of power with
a gas or steam turbine system.
The mixture of municipal refuse,.sewage sludge, and
shredded auto waste produces a feed which was esti-
mated to have a HHV of 4850 Btu/lb to 5200 Btu/Ib. The
solid waste is furnished shredded from a separate refuse
processing plant where materials such as iron are re-
moved. The shredded refuse is delivered by conveyor or
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POTPOURRI 251
COMMON
SUBSYSTEMS
SYNGAS GENERATION AND UTILIZATION
I
MATERIAL
HANDLING
SYNGAS
GENERATION
MUNICIPAL
SOLID WASTE
SEWAGE SLUDGE
SHREDDED
AUTO WASTE
III I METHANOL
Figure 1: Block Diagram.
transfer truck depending on the location of the fuel con-
version plant.
Two of the major problems encountered in pyrolytic
processes are the disposition of the char generated in the
process and of the large amount of ash. These problems
have been overcome in the Purox process by burning the
char completely with oxygen, producing the heat re-
quired for the pyrolysis process, and by carrying out the
pyrolysis at bottom temperatures of 3000°F, sufficient to
melt the ash into a low volume glassy frit which can be
used for road building and other applications.
The partial oxidation pyrolysis process produces a gas
comprised mainly of carbon monoxide and hydrogen
with some carbon dioxide and methane. The reactor is a
vertical shaft furnace with refuse entering the top and
oxygen blown in at the bottom to burn the char. Molten
slag leaves at the bottom and the syngas generated
passes out at the top.
The waste materials enter at the top as a moist feed
and slowly descend. A counterflow of hot gases, starting
in the combustion zone at the bottom, dries the wastes
which then decompose into synthetic gas, char, and or-
ganic liquids in the high temperature pyrolysis zone.
Melting of inorganics and combustion of the char occurs
in the hearth zone of the reactor producing an ascending
eas mixture of CO and CO2- Oil and tar droplets carried
upward by the hot gases are mostly scrubbed out by the
descending refuse and thus recycled for cracking to
gases and char. Relatively pure Q^ 's passed into the
hearth to burn all the char.
The heat of combustion is sufficient to maintain a
temperature of 3000°Fin the hearth, to melt oxides and
glasses as well as metals, and to provide the heat for py-
rolysis reactions, heat-of-vaporization of water in the en-
tering refuse, and heat losses from the vessel. The syn-
gas produced is cooled to approximately 200°F in drying
the refuse.
The product gas is passed through a wet electrostatic
precipitatorto remove fly ash, oil, and tar mist. Each ton
of combined wastes produces approximately 24,000 scf
of 300 Btu syngas.
An artist's rendition of the plant is shown in Figure 2.
It is seen that a fairly complex facility is required. Plant
capital costs for a 1750 tons per day facility are estimated
at $38 million for low-Btu syngas production, $42 million
if upgrading to 1000 Btu SNG is included, $44 million for
production of methanol, and $50 million for generation
of electric power (1974 $). Amortization costs range at
three to four million dollars per year, with operating
costs expected to reach a similar amount. The SNG op-
tion would produce ten million scf per day of pipeline-
quality gas; at present prices of $1/1000 scf, the product
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252 POTPOURRI
- SCRUBBING TOWERS
- MATERIAL STORAGE 81N
-REACTOR FEED CONVEYOR
• SLAG CONVEYOR
-QUENCH TANK
- REFUSE REACTOR
-FLARING COMBUSTOR
-PRECIPITATOR
GAS COLLECTION MAIN
REVERSING
HEAT EXCHANGER
COLUMN
AIR SURGE TANK
VALVE SKID ENCLOSURE
I BLOWDOWN SILENCER
I— AIR SUCTION FILTER
- AIR COMPRESSOR
COOLING TOWER
INSULATION SILO
LIQUID OXYGEN DRAIN TANK
OXYGEN VAPORIZER
NITROG£N TANK
LIQUID OXYGEN STORAGE TANK
Figure 2: Plant Perspective.
value would offset 50 percent of the costs; with decon-
trolled natural gas and prices stabilized around new-
source levels, both capital and operating costs would be
recovered.
ONE COMPANY'S EXPERIENCE
John P. Vircks
AAA Septic Tank Cleaning Co., Inc.
Milwaukee, Wisconsin
The company has been in existence since the early
1940's in the Milwaukee Metropolitan area.
We started with septic tank cleaning along with main-
tenance and repair of septic tanks, i.e., replacing col-
lapsed tops, repairing outlet baffels, and broken tiles,
and attempting to flush sludge out of clogged drain
fields when the owners have let the tank go without
cleaning far too long. We call it neglect.
Population growth—expansion intensified problems
with septic tanks, especially in areas where percolation
rates in the soils are low; and, we found a new market
developing when holding tanks came into more wide-
spread use.
Before holding tanks were used, the tank size of a sep-
tic tank service truck might have been in the area of 1000
to 1600 gallons.
Some surburban schools, country clubs, truck stops,
etc., created pressure for more economical equipment,
so 3000 gallon and 5000 gallon tank trucks came into use.
Where a residential septic tank might be cleaned on a
so called regular basis—once a year with five people
without a garbage disposal if the septic tank is 1000 gal-
lons; twice a year with a garbage disposal, a holding tank
might need to be emptied any where form once a month
to several 5000 gallon loads per day.
We discharge the septage to M.I.S. in the Metro area.
Many of our confederates must use land disposal.
Cities in Wisconsin needing to make repairs to heating
coils or mixing equipment in their digesters, or where an
accumulation of scum created problems, or when the
sludge draw off pipe became blocked, or where incinera-
tion could not keep up with sludge production, or new
construction dictated, complete emptying of the digester
became necessary.
The people involved found they needed someone with
enough equipment to do the work without stretching the
project out all summer.
Along with the need for repairs, etc., phosphorous
removal created additional volumes of sludge, and we
found people looking for new areas to put sludge. The
parks and airports and other places around town did not
have enough area for the whole volume.
In some cases, a hole was dug out at the city landfill
area. We loaded our trucks at the plant, drove out to the
landfill and unloaded into the pit. What happened after
that was the city's problem, and, reading between the
lines, we assume that these were not really acceptable
methods because they are being used less and less.
It is our observation that cities sometimes wait for one
reason or another till their back is against the wall before
asking for help. And when help is needed you have to do
something right away!
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POTPOURRI
253
We found one situation like this (there have been
others). We found a farmer with an acceptable field site
(100) acres of alfalfa sod, two thirds of which could be
used even though we would stay back 1000 feet from the
dwelling.
It rained and snowed and the ground was so wet that
farm tractors got stuck just pulling an unloaded farm
wagon across the field.
We had to go, so, we purchased 3000 feet of five inch
pipe, a rainbird Big Gun with 1.3 nozzle, the wrong kind
of pump, and proceeded.
After changing the big gun and the pump and pur-
chasing an additional 4800feet of pipe with 25 additional
gun stands, we have a system, that from an engineering
standpoint, works very well but, it turns people off.
The pressure drop at the nozzle, 1 believe, releases
gases into the air, mixes them well with the air, and they
drift downwind across the countryside. Also you have
this black or brown spray instead of a nice white spray as
when regular water irrigation is used. We have been
asked to not deliver sludge into that township anymore.
One gentleman accused us of almost killing a neighbor of
his who had a problem with asthma.
We now use the soil injection method when the ground
isn't frozen.
We have surface spread from tank trucks directly to
land, then followed immediately with a three bottom
moldboard plow.
We still surface spread directly from tank trucks to
land in cold weather, or in areas where the local people
indicate they can put up with odors, or where the dura-
tion of the job is only several days. We have a Big
Wheels unit like you see in the hall.
Right now we don't have enough sludge in those
areas.
Comments
City's should immediately, even though they don't
have a pressing need, should immediately set up a
demonstration plot. It takes several crop years some-
times to change farmers ideas—seeing is believing!
When the farmer can look across the fence and see for
himself that the crops have not all died and in fact look
pretty good, seeing is believing. And you can still drink
the water and that the project doesn't have to smell bad,
they may come around to your side.
A valid analysis of sludge for nitrogen, phosphorous,
and potash trace elements, including heavy metals,
should be run immediately. A problem we have is tre-
mendous variability between laboratories and their re-
sults. Work with your local County Agricultural Agent.
A heavy metal elimination or reduction program
should be initiated so we don't spoil the sludge recy-
clability.
I sometimes say we have a product that you cannot
spoil. It can be spoiled and sometimes is spoiled. Let's
not waste our wastes.
VEHICLE CRITERIA FOR LAND APPLICATION
AND UTILIZATION OF SLUDGE
Kenneth Decker
Big Wheels. Inc.
Paxton, Illinois
I have run the gamut of feelings while attending, lis-
tening and participating at this conference. I have been
interested, enlightened, amazed, shocked, frightened
and confused. I'm confused because in speaking about
agronomic utilization of sewage sludge we have been
told how valuable it is. But at the same time we are told
that it can't be given away. One person said that he pays
a farmer $5.00 a load to put it on his farm. That's in addi-
tion to $40.00 per load paid to the hauling contractor.
I don't think the problem is with the material in ques-
tion as much as it is with the people we're dealing with
and the manner in which we're promoting the use of
sludge.
Let me ask you a question. What would you think if
someone stopped you outside the motel and tried to give
you a $100.00 bill? You'd probably think he was some
kind of kookor there would be some strings attached. At
least I know I'd be skeptical. That's what we seem to be
doing with sludge though. We're up to our chin in it,
telling people how great it is. And then we say, "Why
don't you let me move some of this on you so you can
have as much fun as we are?"
If this stuff is really that good, why aren't we market-
ing it as any salable item should be?
What's the fastest way to promote sales of materials
and goods today? We get someone to predict a shortage
and the run on sales begins. I think George Ward has the
right idea when he entreats you not to waste your sludge
because it will one day be in short supply.
We believe that the answer to land application and
utilization is moderation. Someone said that if a little is
good than a lot must be great. But it's not true. Just as
eating, drinking, vacationing and other activities are en-
joyable in moderation, too much can cause negative re-
actions. So it is with utilization of sludge.
It would appear that if moderation is the key to utiliza-
tion of sludge the following items are necessary for
proper land application:
1. We must analyze the sludge material so we know
what's in it.
2. We must know the soil type, consistency and nu-
trient requirements for plant utilization.
3. We must spread the material in quantities dictated
by #1 and #2.
4. And finally, the material must be spread uniformly
on all areas of the acreages designated for utiliza-
tion.
Senator Muskie, chairman of the Senate subcommit-
tee on Environmental Pollution, said at a recent Interna-
tional Conference of Biological Improvement Alterna-
tives that current methods of treating wastes have been
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254 POTPOURRI
around for 60 years, without noticable improvement.
"As a result," he said, "millions of tons of nutrients
such as phosphorus, nitrogen, and potassium are viewed
as sludge disposal problems while the costs of fertilizers
skyrocket."
If fertilizer is the issue, why don't we handle it like
fertilizer. The pictures we saw yesterday of vehicles
used for quote "Land Application" brought laughter
from conference attendees. Don't you think those ve-
hicles affect farmers on whose land you expect to apply
your material, in the same way? The inaccuracy, unac-
countability and secrecy of those operations can only
elicit skepticism and suspicion from proposed recipients,
in my opinion.
The company I work with is planning its future on the
sincerity and honesty of the American people and more
importantly on the intelligence, integrity and abilities of
you who design, manufacture, control or operate pollu-
tion control systems, wastewater handling programs or
sewage treatment plants. Those plans also depend on
the foresight and substantial influence of regulatory
agencies at the local, state, and national levels. They
need to provide guidelines now.
People who have been closely associated with this
business, have researched and experimented and
actually used this process of land application, have come
to us with the determination that any "vehicle" used to
accomplish a practical recycling of sewage sludge, lime
slurries and sludges, manure slurries and other residual
materials on agricultural land must have the following
abilities:
1. The vehicle must have flotation abilities so that
when the material must be handled, it can be, and
farmland will not be adversely affected by travel
on it.
2. The vehicle must have a suspension system able to
withstand the rigors of travel through fields under
the severest of conditions.
3. The vehicle must be able to spread the materials in
thin layers over a wide area so that it can dry quick-
ly to prevent runoff and the buildup of odors.
4. The vehicle must be able to spread the material
uniformly so that all areas receive equal coverage
just as with commercial fertilizer.
5. The vehicle must be able to control the amount of
material applied per acre. If this material has valu-
able fertilizer and soil conditioning characteristics,
as Senator Muskie says, than it must be handled in
the same manner as any other valuable material.
Many systems are selling sludge for agronomic
purposes and this obviously limits the application
per acre to area and gets a return for any invest-
ment. We should stop looking for places to dump
sludge and get on with the business of using it
properly as a natural resource.
6. The vehicle must be able to spread either dry or de-
watered material, material in liquid solution or
suspension, or it must be able to incorporate the
material below the surface of the ground.
7. The vehicle must have mobility. It must be able to
not only work in the fields and do those things sug-
gested, but it must also be able to travel on roads
leading to those fields quickly.
8. The vehicle must have a guarantee that is backed
by one manufacturer. If good money purchases the
equipment, one should not have to go to a variety
of places for repairs in the event of a breakdown.
9. And finally, it must have a good looking appear-
ance to lend dignity and good taste to any project.
These are the conditions cited by those who have had
the experience and know what is needed. It's not neces-
sary to look any further. Vehicles with all of these abili-
ties and more, are being built by Big Wheels High Flota-
tion Systems of Paxton, Illinois. But the company can
only build the machine. You have to put them to work in
your program to get the job done. Each of us must do our
part. Together we can transform the problem of waste
material into a valuable recycling of natural resources.
As Big Wheels says in advertising for its new subsur-
face applicator, "It's and 'open and shut' case for land
application."
COMPOSTING SEWAGE SLUDGE IN THE
PUGET SOUND AREA
Bruce B. Rennie
Western Minerals, Inc.
Seattle, Washington
Two sludge composting facilities are now operating in
the Puget Sound area, one in South Tacoma and the
other in Bremerton. The original Pilot Plant was con-
structed in South Tacoma early in 1974 by the inventor of
the process, Mr. Willis R. Lebo. At this plant more than
three million gallons of septic tank sludge have been
aerated and composted to produce a plant food or soil
conditioner. The Bremerton facility was constructed in
1975 at the municipal wastewater treatment plant by Mr.
Robert Johnson who is in the septic tank pumping busi-
ness. This plant has been used to aerate and compost not
only septic tank waste but also both raw and digested
sludge.
The disposal of septic tank waste has been a
particularly troublesome problem. The most widely ac-
cepted method of disposal has been to discharge it into
the municipal sewer system or sewage treatment plant.
However, the inflow of this material into the sewage
treatment plant is not welcomed by plant operators be-
cause of its high level of contamination, and incompati-
bility with the raw sewage which the treatment plant was
designed to handle. Therefore, the septic tank pumpers
are generally charged a fee for the privilege of dumping
their sludge into the sewer system. By taking advantage
of this fact, Mr. Lebo was able to make his Pilot Plant in
South Tacoma economically successful by charging a fee
-------
POTPOURRI 255
to the septic tank pumpers and then producing a com-
post which can be marketed in bulk or bagged for sale as
a plant food and soil conditioner. In Bremerton, Mr.
Robert Johnson obtained the city's permission to con-
struct a Lebo facility rent-free on city-owned land at the
Municipal Wastewater Treatment Plant in return for
which he has solved the city's problem of sludge disposal
by composting their sludge along with his septic tank
waste.
DESCRIPTION
The Lebo Process provides a practical method for de-
odorizing and disinfecting sewage sludge. The material
is first deodorized by aeration in the Lebo Aerator. The
aerated sludge is discharged onto a compost pile and
then covered with a thin layer of sawdust (or compost),
and the pile is built up in this manner for composting.
Composting temperatures of approximately 150°F de-
velop in the pile, destroying pathogenic bacteria, fly
larvae, weed seeds, etc. and making the material safe to
use as a plant food and soil conditioner.
DISCUSSION
The technical feasibility and practicality of compost-
ing as an effective method of treating sewage sludge has
been demonstrated by the U.S. Dept. of Agriculture's
sludge composting program at Beltsville, Maryland. At
last year's Municipal Sludge Management Conference,
Dr. Eliot Epstein presented a paper describing the
USDA's method of composting dewatered digested
sludge at Beltsville where they use wood chips and
spread out the sludge in windrows with frequent turn-
ing. Dr. Epstein presented another paper at this year's
conference (included herein) describing an experimen-
tal program at Beltsville for composting raw dewatered
sludge. Since the Beltsville program has been widely
recognized and is well documented, it may be used as a
basis for comparing the methods used with the Lebo Pro-
cess for composting sewage sludge in the Puget Sound
area. The primary differences are as follows:
1. Lebo Process treats wet sludge (i.e., approx. six
percent moisture content) in lieu of dewatered
sludge.
2. Lebo Process uses sawdust (or ground bark) in lieu
of wood chips, and there is no screening; i.e., all of
the material goes into the end product.
3. The Lebo Process aerates the wet sludge in the
unique "Lebo Aerator" so as to deodorize it prior
to ejecting onto the compost pile.
4. The Lebo Process composts the material in large
piles (rather than windrows) and without periodic
turning. In this respect it is more like the method
used at Beltsville for composting raw sludge
(described elsewhere in these proceedings) than
the production method used at Beltsville with di-
gested sludge.
CONCLUSION
The Lebo Process is a proprietary method of compost-
ing and is in a "patent pending" status. However, the
rights to the process (for a specific area) and the Con-
sulting Engineering services of Western Minerals, Inc.
are available to implement the Lebo Process for com-
posting septic tank waste and/or municipal sewage
sludge to meet particular requirements.
SAFE DISPOSAL AND UTILIZATION OF
SLUDGE ON FOREST LANDS
James 0. Evans
United States Department of Agriculture
Washington, D.C.
Disposal of sludge economically and by environmen-
tally acceptable methods is a major problem confronting
most of the technically advanced countries of the world,
where urban development and living standards are high.
This, coupled with intensive development and use of
basic resources, high industrial productivity (and there-
fore waste products), and general non-use of waste by-
products, intensifies and magnifies the overall problem.
Because of this, providing suitable disposal for sludge
may be very costly.
In the United States, about 10,000 metric tons or more
of dry sludge solids are produced each day1. Sludge cur-
rently is disposed of by several methods. Much of it is
buried in landfills. A relatively small amount is dried,
composted, packaged, and sold as a soil conditioner-
fertilizer. About 15 percent is discharged to the oceans,
and 25 percent is incinerated2. Incineration is an ex-
pensive process, however, and without proper treatment
can cause serious air pollution. Increasingly, sewage
sludge is being spread on land surfaces or incorporated
into surface soils for disposal.
Man has disposed of sewage wastes by land applica-
tion throughout history. So the practice is not new. Be-
cause of the increasing waste disposal and pollution
problems of today, however, he is now taking a new look
at the soil as a treatment and disposal medium. Current-
ly, forest soils are of particular interest.
Land disposal of sewage effluent and sludge has both
advantages and disadvantages. Sewage wastes contain
valuable nutrient elements useful to plant life. They also
help build or restore soil organic matter, and the liquid
portions are sources of irrigation water. On the other
hand, sewage wastes may include toxic elements or
pathogenic organisms which in sufficient amounts po-
tentially can pollute surface or groundwaters or accumu-
late in soils and produce toxicity and environmental
damage along the plant-animal food chain.
Objectives of Waste Disposal Research
Criteria for environmentally safe land disposal of sew-
age wastes are needed. These criteria must provide pro-
tection for:
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256 POTPOURRI
1. Surface and groundwater supplies. Surface waters
may be harmed by enrichment from organics with
resultant high biological oxygen demand (BOD)
and depletion of dissolved oxygen. Eutrophication
of impoundments may result from nitrogen and
phosphorus enrichment. Nitrate pollution of
groundwater may occur, and pathogens may pol-
lute both surface and groundwater supplies.
2. Soils against excessive nitrogen enrichment,
build-up of trace elements or heavy metals, and
contamination with pathogens.
3. Vegetation from direct pollution of surface areas
and build-up of trace elements or heavy metals into
harmful accumulations in plant tissue.
4. Animals feeding in treated land areas. People also
should be protected from direct contact with sew-
age wastes during disposal operations, although
documentation of ill effects from contact with di-
gested sludge or chlorinated effluent is scant or
unavailable.
Waste Disposal Research
Considerable research is now underway in the U.S. on
the effects of applying treated sewage sludges in various
amounts and methods, on agricultural lands for the pro-
duction of agronomic crops.
Research is also underway on the effects of applying
sewage sludges to forest lands. Sludge and associated
effluent studies are currently underway at six Forest
Service (FS) Experiment Stations plus FS-supported co-
operative studies at several Universities. The most in-
tensive FS research is at the Michigan-based project.
Studies originating here involve:
• Effects of secondary treated sewage effluent on
groundwater quality in northern Michigan forests.
• Renovation of sewage lagoon effluents by aerial ir-
rigation on forested land.
• Effects of sewage effluent on growth, product qual-
ity, and nutrient recycling capability of several vari-
eties of hybrid poplars and Christmas trees.
• Effects of sewage sludge on the physical and chemi-
cal properties of coal-mine spoil and spoil lechates.
• Renovation of strip-mined lands by treatment with
sewage sludge.
• Bacteriological and chemical changes in soil and
groundwater following incorporation of sealed-
vault (untreated) sewage into forest soils.
Other Forest Service sewage and sludge disposal and
utilization research include:
• Effects of recycling sewage effluent and sludge on
forest soil invertebrate populations (in Pennsyl-
vania).
• Effects of municipal wastewater disposal on the for-
est ecosystem (at Pennsylvania State University).
• Effects of liquid sludge applications to forested
sites (in New Hampshire).
• The influence of ectomycorrhizae and sewage
sludge on growth and survival of loblolly pines on
kaolin spoils (in Georgia).
• Problems of applying sewage effluent to a forest
site in the winter (in Wisconsin).
• Agronomic and economic feasibility of combining
wood-processing residues with sewage sludge to
produce an acceptable soil amendment (in Colora-
do).
• Use of sewage effluent on semi-arid chaparral land
to provide geeenbelts and fuel breaks and safely
dispose sewage wastewater (in sourthern Cali-
fornia).
Forests as Disposal Sites
Certain factors and characteristics of forests may limit
the use of forests as sewage sludge disposal sites, for
example:
• Public acceptance and aesthetics.
• Distribution constraints (steep slopes, physical ob-
struction of trees).
• Loading and application rate restraints.
• Wildlife implications
• Remoteness (transport distance).
Other characteristics of forests favor their use:
• Abundance and distribution.
• Long cropping periods.
• Relatively low soil fertility status.
• Non-consumptive products for people.
• Remoteness from concentrated human use.
• Opportunity for year-round application in cold
climates.
Perhaps an expansion on some of the reasons favoring
the use of forests for sewage sludge disposal is in order:
Some commercial forest lands are more suitable than
croplands for disposal and utilization of large amounts of
heavy metals, trace elements, organic toxicants, and
pathogens. With forests, food chain considerations
should be of relatively little concern, and prevention of
damage to tree crops is the only major concern.
Prolonged overland flow is rare on forested water-
shed, and soils supporting thickly-forested sites are
much better protected from freezing than are open-
space croplands of the same general area. Healthy,
maturing forests also remove more water from soils
through evapo-transpiration than does other vegetation.
Consequently, forests may offer greater opportunities
than most agronomic crops for safe disposal of certain
potentially hazardous sewage sludges and other sewage
wastes, and for disposal of large quantities of certain
organic and inorganic wastes. Perhaps-a key to success-
ful use of forests for the disposal of sludges, or of similar-
ly constituted wastes, is the deliberate and careful selec-
tion of tree species (growing on suitable soil types) which
are (1) water tolerant, (2) capable of rapid uptake and
utilization of nutrients (with concomitant growth), and
(3) amenable to harvest operations such as clear cutting
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POTPOURRI
257
or clean harvesting for maximum use and removal of
nutrients.
Significant Findings in Sludge
Disposal on Forest Lands
1 • Liquid sewage sludge was used to ameliorate ex-
tremely acid strip mine spoil in southern Illinois. Appli-
cation rates of up to 672 metric tons of dry sludge per
hectare were more effective in reducing the concentra-
tion of A 1,S, and H ions in drainage water than agricul-
tural lime at rates up to 44.8 metric tons per hectare.
Sludge was far superior to lime in improving the physical
properties of the spoil materials.
2. Field tests in the Hiawatha National Forest
(northern Michigan) on a Kalkaska sand soil indicate soil
incorporation of untreated sewage vault wastes may not
pose an environmental hazard in areas protected from
public access. The wastes (roughly the consistency of
five to ten percent sludge) were mechanically injected
under the soil surface. Bacteriological contamination of
ground water occurred only at 1.83- to 2.44-meter depths
under the treated area when the area was flushed with
over 15 cm of water immediately after treatment.
3. First year loblolly pine (Pinus taeda) seedlings were
planted in kaolin spoil material (representative of
Georgia and South Carolina kaolin mine spoils) in micro-
plots amended with sewage sludge and grown for six
months. Concentrations of sludge were 1, 4, 9, 18, and
36 percent volume to volume. The best growth accurred
in four percent sludge which stimulated the seedlings to
grow 49 percent more in height, 79 percent more in stem
diameter and 126 percent more in fresh weight than the
controls. Developments of the ectomycorrhical fungus
(Pisolithus tinctorius) was better at four percent and
nine percent sludge than at zero percent, 18 percent, or
36 percent.
In a concurrent greenhouse pot study, both shortleaf
(P. enchinata) and loblolly pine seedlings grew better in
kaolin spoil with five percent volume to volume sludge
than at zero percent or 25 percent, but the improvement
of the five percent over the 25 percent was not statis-
tically significant. The five percent sludge level treat-
ment increased foliar-stem fresh weight 148 percent for
loblolly pine and 190 percent for shortleaf pine over the
controls.
REFERENCES
1. Evans, J.O. and W.E. Sopper, "Forest Areas for
Disposal of Municipal, Agricultural, and Industrial
Wastes," Paper presented at the Seventh World Fores-
try Congress, Buenos Aires, Argentina, October, 4-18,
1972.
2. Evans, J.O., "Research Needs—Land Disposal of
Municipal Sewage Wastes," Proceedings, Recycling
Treated Municipal Wastewater and Sludge Through
Forest and Cropland, The Pennsylvania State University
Press, University Park and London, 1973, 479.
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