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EPA/600/9-36/015C
July 1986
PROCEEDINGS
TENTH UNITED STATES/JAPAN CONFERENCE
ON SEWAGE TREATMENT TECHNOLOGY
OCTOBER 17-18, 1985
AND
NORTH ATLANTIC TREATY ORGANIZATION/COMMITTEE ON THE
CHALLENGES OF MODERN SOCIETY (NATO/CCMS) CONFERENCE
ON SEWAGE TREATMENT TECHNOLOGY
OCTOBER 15-16, 1985
CINCINNATI, OHIO
VOLUME II.
NORTH ATLANTIC TREATY ORGANIZATION/COMMITTEE ON THE
CHALLENGES OF MODERN SOCIETY (NATO/CCMS) PAPERS
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
CINCINNATI, OHIO 45268
n S Environmental Protection Agency
Region 5, Library (PL-12J)
77 West Jackson Boulevarjd, 12th Floor
Chicago, tl 60604-3590
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NOTICE
This document has been reviewed in accordance with
U.S. Environmental Protection Agency policy and
approved for publication. Mention of trade names
or commercial products does not constitute endorse-
ment or recommendation for use.
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FOREWORD
The maintenance of clean water supplies and the
management of municipal and industrial wastes are vital
elements in the protection of the environment.
The participants in the Japan-United States-North
Atlantic Treaty Organization/Committee on the Challenges
of Modern Society (NATO/CCMS) Conferences on Sewage Treat-
ment Technology completed their conferences in Cincinnati,
Ohio, in October 1985. Scientists and engineers of the
participating countries were given the opportunity to study
and compare the latest practices and developments in Canada,
Italy, Japan, The Netherlands, Norway, the United Kingdom and
the United States. The proceedings of the conferences comprise
a useful body of knowledge on sewage treatment which will be
available not only to Japan and the NATO/CCMS countries but
also to all nations of the world who desire it.
Lee M. Thomas
Administrator
Washington, D.C.
fii
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CONTENTS
Foreword iii
Japanese Delegation vi
United States Delegation vii
North Atlantic Treatment Organization/Committee on the
Challenges of Modern Society (NATO/CCMS) Delegation viii
Volume I.
Part A. Japanese Papers 3
Volume I.
Part B. United States Papers 367
Volume II.
North Atlantic Treaty Organization/Committee on the
Challenges of Modern Society (NATO/CCMS) Papers 633
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JAPANESE DELEGATION
DR. TAKESHI KUBO
Head of Japanese Delegation,
Counselor, Japan Sewage Works Agency
TOKUJI ANNAKA
Chief, Water Quality Section
Water Quality Control Division
Public Works Research Institute
Ministry of Construction
DR. KEN MURAKAMI
Deputy Director, Research and
Technology Development Division
Japan Sewage Works Agency
DR. KAZUHIRO TANAKA
Chief Researcher, Research and
Technology Development Division
Japan Sewage Works Agency
KENICHI OSAKO
Chief, Eastern Management Office
Sewage Works Bureau
Tokyo Metropolitan Government
SAKUJI YOSHIDA
Chief, Facility Section
Construction Division
Sewage Works Bureau
City of Yokohama
YUKIO HIRAYAMA
Director, Planning Division
Sewage Works Bureau
City of Fukuoka
MASAHIRO TAKAHASHI
Extraordinary Participant,
Researcher, Sewerage Section
Water Quality Control Division
Public Works Research Institute
Ministry of Construction
TAKASHI KIMATA
Extraordinary Participant,
Researcher, Research and Technology
Section, Research and Technology Division
Japan Sewage Works Agency
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UNITED STATES DELEGATION
JOHN J. CONVERY
General Chairman of Conference and
Head of Cincinnati U.S. Delegation
Director, Wastewater Research Division
Water Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnai, OH 45268
DOLLOFF F. BISHOP
Co-Chairman of Conference
Chief, Technology Assessment Branch
Wastewater Research Division
Water Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
FRANCIS T. MAYO
Director,
Water Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
LOUIS W. LEFKE
Deputy Director,
Water Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
DR. JAMES A. HEIDMAN
Environmental Engineer
Innovative & Alternative Technology Staff
Systems & Engineering Evaluation Br., WRD
Water Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
HENRY H. TABAK
Research Chemist,
Toxic Research & Analytical Support Staff
Technology Assessment Branch, WRD
Water Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
DR. ALBERT D. VENOSA
Microbiologist, Ultimate Disposal Staff
Systems & Engineering Evaluation Br., WRD
Water Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
ARTHUR H. BENEDICT, Ph.D.
Brown & Caldwell Consulting Engrs
P.O. Box 8045
Walnut Creek, CA 94546-1220
DR. WILLIAM C. BOYLE
Dept. of Civil Engineering
& Environmental Engineering
University of Wisconsin
3230 Engineering Building
Madison, Wisconsin 55706
DR. MICHAEL CARSIOTIS
Dept. of Microbiology
& Molecular Genetics
University of Cincinnati
College of Medicine
231 Bethesda Avenue
Cincinnati, OH 45267
DR. CLEMENT FURLONG
Dept. of Medical Genetics, SK50
University of Washington
Seattle, WA 98195
GILBERT B. MORRILL, P.E.
McCall, Elingson, Morrill,
Consulting Engineers
1721 High Street
Denver, CO 80218
Inc.
DR. GEORGE PIERCE
Battelle-Columbus Laboratories
505 King Avenue
Columbus, OH 43201
DR. JOHN N. REEVE
The Ohio State University
Dept. of Microbiology
484 West 12th Avenue
Columbus, OH 43210-1292
DR. H. DAVID STENSEL
Dept. of Civil Engrg, FX-10
University of Washington
Seattle, WA 98195
vn
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NORTH ATLANTIC TREATY ORGANIZATION/COMMITTEE ON THE CHALLENGES
OF MODERN SOCIETY (NATO/CCMS) DELEGATION
DR. J. DUANE SALLOUM
Chairman of NATO/CCMS Committee
Director, Technical Services Branch
Environmental Protection Service
Ottawa, Canada K1A 1C8
DR. B. E. JANK
A/Director,
Wastewater Technology Centre
Canada Centre for Inland Waters
P.O. Box 5050,
Burlington, Ontario L7R 4A6
Canada
DR. ROLF C. CLAYTON
Director,
Process Engineering
Water Research Laboratory
Elder Way, Stevenage, Herts, SGI 1HT,
England
DR. IR. WILHELMUS H. RULKENS
Department of Environmental Technology
Division of Technology for Society
MT/TNO
P.O. Box 342, 7300 AH Apeldoorn
The Netherlands
DR.ING. BJ0RN RUSTEN
Aquateam, Norwegian Water Technology Centre A/S
P.O. Box 6593
Rodelrfkka, N-0501 Oslo 5,
Norway
DR. MARIO SANTORI
Institute di Ricerca sulle Acque
Consiglio Nazionale delle Ricerche
Rome, Italy 00198
vm
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DELEGATES TO THE NATO/CCMS CONFERENCE AND THE TENTH UNITED STATES/
JAPAN CONFERENCE ON SEWAGE TREATMENT TECHNOLOGY
ANDREW W. BREIDENRACH ENVIRONMENTAL RESEARCH CENTER, CINCINNATI, OHIO
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DR. JOHN H. SKINNER, DIRECTOR, OFFICE OF ENVIRONMENTAL ENGINEERING
AND TECHNOLOGY, MR. FRANCIS T. MAYO, DIRECTOR, WATER ENGINEERING
RESEARCH LABORATORY, U.S. EPA AND DR. TAKESHI KUBO, HEAD OF
JAPANESE DELEGATION AND COUNSELOR, JAPAN SEWAGE WORKS AGENCY
MR. DOLLOFF F. BISHOP, U.S. DELEGATE AND DR. ROLF C. CLAYTON,
NATO/CCMS DELEGATE FROM THE UNITED KINGDOM
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VIEW OF CAPTOR WASTEWATER TREATMENT PROCESS
TEST AND EVALUATION FACILITY, CINCINNATI, OHIO
VISIT TO THE MULTIPLE DIGESTION PROJECT,
TEST AND EVALUATION FACILITY, CINCINNATI, OHIO
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NORTH ATLANTIC TREATY ORGANIZATION/COMMITTEE ON THE
CHALLENGES OF MODERN SOCIETY (NATO/CCMS) PAPERS
CANADIAN ADVANCES IN SLUDGE MANAGEMENT TECHNOLOGY 635
H.W. Campbell, T.R. Bridle, P.O. Crescuolo, and B.E. Jank,
Environment Canada, Environmental Protection Service,
Wastewater Technology Centre, Burlington, Ontario, Canada
ITALIAN ADVANCES IN WASTEWATER TECHNOLOGY 661
Mario Santori, Institute di Recerca sulle Acque, Consiglio
Nazionale delle Ricerche, Rome, Italy
JAPANESE ADVANCES IN WASTEWATER TREATMENT 719
Takeshi Kubo, Dr. Eng., Counselor, Japan Sewage Works
Agency
DEVELOPMENTS IN THE FIELD OF WASTE WATER TECHNOLOGY IN THE
NETHERLANDS 793
A.B. van Luin and W. van Starkenburg, Governmental Institute for
Sewage and Waste Water Treatment, Inland Waters Department,
Lelystad, The Netherlands; and W.H. Rulkens and F. van Voorneburg,
Netherlands Organization for Applied Scientific Research, Division
of Technology for Society, Apeldoorn, The Netherlands
NORWEGIAN ADVANCES IN WASTEWATER TREATMENT 827
Dr. ing. Bjtfrn Rusten, Aquateam, Norwegian Water Technology
Centre A/S, Oslo, Norway
RESEARCH AND DEVELOPMENT IN DOMESTIC WASTEWATER TREATMENT IN THE UK. . 851
Staff of WRC Processes, Water Research Centre, Elder Way,
Stevenage Herts, United Kingdom
ADVANCES IN WASTEWATER TREATMENT AND SLUDGE MANAGEMENT PRACTICES
RELATED TO PATHOGEN AND TOXICITY CONTROL 879
J.J. Convery, D.F. Bishop, and A.D. Venosa, Wastewater
Research Division, Water Engineering Research Laboratory,
U.S. Environmental Protection Agency, Cincinnati, Ohio, USA
633
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NORTH ATLANTIC TREATY ORGANIZATION/
COMMITTEE ON THE CHALLENGES OF MODERN SOCIETY
CONFERENCE ON SEWAGE TREATMENT TECHNOLOGY
CINCINNATI, OHIO
OCTOBER 15-16, 1985
A Committee on Advanced Wastewater Treatment of the North
Atlantic Treaty Organization/Committee on the Challenges of Modern
Society (NATO/CCMS) held a conference on sewage treatment technology
in Cincinnati, Ohio, on October 15-16, 1985. The NATO/CCMS Committee
on Advanced Wastewater Treatment, chaired by Dr. J. Duane Salloum of
Canada, included delegates from six NATO countries: Canada, Italy,
the Netherlands, Norway, the United Kingdom and the United States.
The conference on sewage treatment technology featured National
papers on advances in wastewater treatment and sludge management technology
in the participating NATO countries. Highlights of the conference included:
A Canadian report on improved control of sludge dewater-
ing and on conversion of sludge to oil;
Italian advances on control of toxic metals and innovative
anaerobic treatment of wastewaters;
Dutch studies on toxics removal and disposal of sludges;
Norwegian advances in sludge management, nutrient control
and septage handling;
British advances in sludge digestion and improved manage-
ment of wastewater treatment plants; and
American advances in wastewater treatment and sludge
management related to control of pathogens and toxics.
634
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CANADIAN ADVANCES IN SLUDGE MANAGEMENT TECHNOLOGY
by
W. Campbell, T. R. Bridle, P. J. Crescuolo
and B. E. Jank
Environment Canada
Environmental Protection Service
Wastewater Technology Centre
P. 0. Box 5050
Burlington, Ontario, L7R 4A6
Canada
The work described in this paper was
not funded by the U.S. Environmental
Protection Agency. The contents do
not necessarily reflect the views of
the Agency and no official endorsement
should be inferred.
North Atlantic Treaty Organization/Committee on the
Challenges of Modern Society (NATO/CCMS) Conference
on Sewage Treatment Technology
•j»
October 15-16, 1985
Cincinnati, Ohio
635
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CANADIAN ADVANCES IN SLUDGE MANAGEMENT TECHNOLOGY
by: H.W. Campbell, T.R. Bridle, P. J. Crescuolo
and B.E. Jank
Environment Canada
Environmental Protection Service
Wastewater Technology Centre
P.O. Box 5050
Burlington, Ontario, L7R 4A6
Canada
ABSTRACT
Two new approaches to sludge management in the sewage treatment industry
have been developed over the past few years. A new concept in automated
control of the conditioning and dewatering of sludge using rheology as the
control approach optimized the dewaterability of sludge while minimizing the
cost of polymer addition. The control strategy used a computer algorithm
which correlates the Theological properties of the sludge measured by a
viscometer with polymer demand. The viscometer and polymer feed pump,
interfaced to the computer, were successfully used by the control algorithm
to automatically adjust the polymer flow rate. In a second approach, the
conversion to sludge to oil has been developed at batch and continuous pilot
scale as an attractive alternative to the sludge disposal options currently
in operation. The conversion process, at 300 to 500°C heating dried sludge
in a nitrogen atmosphere, successfully produced oil and char from sludge.
The process was stable with typical oil yields of 25.4 percent, char yields
of 61.1 percent and non-condensable gas of 11.1 percent. The oil viscosity
under optimum operating conditions was 33.7 centistokes.
636
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INTRODUCTION
Sewage sludge is an unavoidable by-product of wastewater treatment and
roughly one tonne of sludge is generated per 4>540 nr (1.0 million gallons)
of wastewater treated (1). Disposal of sewage sludge is an expensive process
and normally constitutes up to 50% of the total annual costs for wastewater
treatment. It is estimated that over 500,000 tonnes of dry sewage sludge
are produced annually in Canada and disposed of at a total cost of about $104
million (2). Major sludge disposal options used in Canada include
agricultural utilization, landfilling and incineration, with estimated
disposal costs ranging from about $126/tonne for agricultural utilization to
over $300/tonne for incineration (3).
The problems of sludge disposal are expected to intensify in the future
due to a number of factors. The total cost of sludge disposal will increase
as the quantity of sludge to be disposed of, increases. The fraction of sludge
disposed of by agricultural utilization will probably decrease due to the
problem of finding suitable land within a reasonable distance of large
population centres. Potential restrictions on the loading rates for sludges
with high levels of heavy metals may also contribute to a decline in this
practice. The feasibility of landfilling will decrease as public opposition
to the licensing of new disposal sites continues to grow.
It would appear that the immediate future in sludge disposal technology
will feature a trend towards more complex systems, which also implies higher
costs. This will be especially true for the large urban areas where the impact
of the above factors will be most keenly felt. In order to control costs,
alternative resource recovery oriented solutions based on either the upgrading
of current technology or the implementation of new technology, are needed.
TECHNOLOGY REVIEW
Upgrading current technology has been primarily concerned with
improvements in dewatering and incineration. The trend has been towards
considering sludge treatment from an overall systems design approach. The
incentive for upgrading has been provided by the large increases in energy
costs over the last ten years, and the realization of how energy inefficient
most incinerator installations were. In 1973 when natural gas cost 3.6
cents/m , it was economically justifiable to incinerate sludge cakes of only
15 to 18% total solids. Today, natural gas costs are in the order of 18
cents/m3, and more cost-effective methods of accomplishing moisture removal
must be implemented.
637
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Modifications which have been designed to either increase cake solids or
improve the amount of energy recovered from an incinerator system include the
following:
1.Upgrading from vacuum filters to belt or membrane presses.
2.The use of incinerator off-gases to dry a portion of the sludge
stream.
3.Modification of incinerator burners to use digester gas as fuel.
4.Modifications to multiple-hearth incinerators to allow very dry
cakes to be introduced on an intermediate hearth.
5.Waste heat recovery to generate steam, which can in turn be used to
drive other processes such as thermal conditioning.
In Canada, the improvements described above are either still in the design and
construction phase or have only been in operation for a relatively short
period of time. Consequently, reliable information is not yet available with
respect to the cost of the modifications or their effect on the energy balance
of the system.
Another approach to offset costs is the introduction of process control
to make treatment systems more efficient. This is being investigated for the
treatment of the liquid train in areas such as dissolved oxygen control in
aeration basins, control of sludge inventories and the control of pumps in
lift stations, and shows promise of realizing substantial savings. With the
large expenditures being committed to sludge processing it seems reasonable to
assume that comparable savings could be achieved by the implementation of
process control. One of the major drawbacks to this has been the lack of
sensors capable of measuring sludge characteristics and consequently most
attempts have had to rely on indirect measurements. Knudsen and Mathes (4)
evaluated a strategy to control chemical conditioning, vacuum filtration and
multiple-hearth incineration. Indirect measurements had to be used because
sensors for the on-line measurement of sludge dewaterability, cake moisture
and sludge calorific value were not available. Under these circumstances,
they were still able to show a saving of approximately 26% in chemical
conditioning costs.
Alternative technologies also offer the potential for improved energy
recovery and decreased cost.One of the most advanced is the Hyperion Energy
Recovery System currently being installed in Los Angeles (5). This system
comprises digestion, dewatering, Carver-Greenfield dehydration and starved air
fluid bed incineration of the sludge derived fuel. It is estimated that
processing 366 tonnes of raw sludge per day will generate a total of 25 MW of
electricity, with 10 MW available for sale back to the local utility. The
complete plant is expected to be in operation by late 1985.
Sludge liquefaction has been reported as a viable method for energy
production from sewage sludge, but the technology is still in its infancy.
Researchers from Battelle Northwest Laboratories have reported on a
sophisticated process consisting of sludge alkaline pretreatment and
subsequent autoclaving at 320°C for one hour at 10,000 kPa under an Argon
atmosphere (6). This process produces oil, asphalt and char, with oil yields
ranging up to 15% (on a total sludge solids basis). The technology is
currently being evaluated at pilot scale.
638
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The basic concept of low temperature pyrolysis of sewage sludge to produce
fuel products has been known for many years (7). Recently, German researchers
have made significant advances in understanding the mechanisms by which sludge
is converted to oil (8). They heated dried sludge to 300-350°C in an oxygen
free environment for about 30 minutes. The researchers postulated that
catalysed vapour phase reactions converted the organics to straight chain
hydrocarbons, much like those present in crude oil. Analysis of the product
confirmed that aliphatic hydrocarbons were produced, in contrast to all other
processes which produce aromatic and cyclic compounds, whether utilizing
sludge, cellulose or refuse as the substrate. The German researchers have
demonstrated oil yields ranging from 18-27% and char yields from 50-60%. The
oil had a heating value of approximately 39 MJ/kg and the char about 15 MJ/kg.
Environment Canada's Wastewater Technology Centre is currently developing
two processes which involve both approaches to upgrading sludge management
practices. The first process which will be discussed is an example of
upgrading existing technology and consists of developing a method for the
automatic control of polymer addition for sludge conditioning. This work is
based on the concept that measured rheological properties can be used to
predict the dewaterability of a sludge. The second process is the conversion
of sludge to solid and liquid fuels, and is an example of alternative new
technology. The conversion process under evaluation is carried out at low
temperature and atmospheric pressure.
AUTOMATIC POLYMER CONTROL
BACKGROUND
Rheology can be defined as the study of the properties and behaviour of
matter in the fluid state. Most single-phase fluids exhibit Newtonian
behaviour in that the rate of viscous flow is proportional to the shear
stress. The addition of solid particles to the fluid interferes with the free
flow of the dispersion medium to a degree that is dependent on the rate of
shear. Dispersed systems such as these can exhibit a variety of rheological
behaviours including plastic, pseudoplastic and altered Newtonian. Most
sewage sludges have been interpreted as exhibiting either plastic or
pseudoplastic flow (9). They may or may not possess an initial characteristic
yield stress depending on the shape of the flow curve and the definition of
yield stress.
The rheology of sewage sludge is further complicated by the fact that
most sludges are also thixotropic, meaning they possess an internal structure
which breaks down as a function of time and shear rate. A flow curve or
639
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rheogram (Figure 1) of a typical sludge, showing the curves produced by a
rotating viscometer during the increasing and decreasing rate of shear cycles,
indicates that the rheology of the sludge has been altered during the initial
(increasing) phase of the test. The displacement of the two curves is
referred to as a hysteresis loop and is a measure of the degree of thixotropy
exhibited by the sludge.
250
200-
LLJ
CC.
55
QC
CO
100 200 300 400 500
SHEAR RATE (s~1)
600
700
Figure 1. Typical rheogram illustrating thixotropy.
The concept of using rheology as a control measure arose out of a sludge
characterization study conducted at the Wastewater Technology Centre (WTC)
(10). The general relationship between sludge rheology and polymer addition
shown in Figure 2 was consistent for all sludges tested and resulted in two
important observations. Firstly, the initial shear stress or yield stress was
observed to increase as the polymer dosage increased. Secondly, the polymer
dosage (6 kg/t) which resulted in an initial peak or point of inflection in
the rheogram compared favourably with that dosage which produced efficient
performance during concurrent pilot-scale dewatering trials. The fundamental
assumption which prompted evaluation of rheology as a means of control was
that optimum conditioning of the sludge would be achieved when a peak became
evident in the rheogram.
The use of rheology as a basic parameter required that a standardized
laboratory methodology be developed (11). This included both the method of
adding the polymer and the method of operating the viscometer. The method
selected for adding chemicals (polymers) to the sludge, consisted of adding
the required volume of polymer over a 10-second period, while mixing the
sludge at 1000 rpm by a standard stirrer developed by the Water Research
640
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Centre (12). A Haake Rotovisco RV3 rotational viscometer with a MVTI sensor
system (gap width = 2.5 mm) was used for all rheological measurements. The
acceleration rate was standardized at 75 rpm/min and the damping option was
not utilized.
300
POLYMER DOSE
(kg/tonne)
100 200 300 400 500 600 700
SHEAR RATE (s"1)
800
Figure 2. Rheograms of polymer conditioned sludge.
The second phase of the study (13) demonstrated the sensitivity of
rheograms to changes in sludge dewaterability and solids concentration.
During this phase the viscometer equipment was upgraded to a Haake RV-100 and
was interfaced to a real-time computer. Experiments were conducted using
sludge conditioned in batch samples and analyzed in the batch mode on the
viscometer. The results indicated that rheological measurements were
sufficiently sensitive to quantitatively identify differences between sludges,
the effect of polymer addition, the effect of changes in sludge solids
concentration and the effects of changes in dewaterability induced by
detergent addition.
PILOT-SCALE CONDITIONING SYSTEM
The most recent stage of the program involved the development of a
continuous-flow, pilot-scale sludge conditioning system, the modification of
the viscometer to function on-line and the development of a preliminary
control strategy.
A schematic drawing of the pilot-scale conditioning set-up is shown in
Figure 3. The sludge storage tank was capable of holding approximately 1200 L
641
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of sludge and was equipped with a variable speed mixer to prevent
sedimentation. The sludge pump was a variable speed positive displacement
Moyno pump with a range of 0.05 to 0.37 L/s. Solids concentration was varied
by the addition of dilution water to the suction side of the sludge pump.
Cationic polymer was injected into the sludge line just prior to the in-line
mixer. The in-line mixer was housed in a clear PVC pipe section (47 mm
internal diameter, 470 mm long) and consisted of a series of six stainless
steel, helical elements welded together. Each element was approximately 75 mm
long and rotated the flow through 180°, with adjacent elements being offset
by 90°. The sludge flowed into the flocculator through the bottom of the
tank and drained through an overflow. Although a mixer was provided to ensure
good mixing of the conditioned sludge, the final methodology involved shutting
off the mixer during the viscometer run in order to reduce turbulence. The
viscometer sensor system was attached to a bracket such that it could be
lowered into the conditioned sludge in the flocculator. Experiments were
conducted at a sludge flow rate of 0.08 L/s with a nominal retention time in
the in-line mixer of 9 seconds. The concentration of the polymer solution was
adjusted such that the polymer dosing rate never exceeded 10% of the sludge
flow rate.
VISCOMETER SENSOR
SYSTEM
FLOCCULATOR
Figure 3. Pilot-scale, continuous-flow, sludge conditioning system.
The viscometer sensor system had to be modified to allow measurements to
be taken in an open vessel. The sensor system selected was comparable to that
used in the batch experiments, in that it was an integral cup and rotor
system. The differences were that the gap was marginally wider (2.6 mm as
compared to 2.5 mm), the geometry was slightly different (length and
diameter), and the cup had four slots in the wall and several holes in the
bottom. The batch sensor was operated by putting the sample in the cup and
then inserting the rotor. In the pilot-scale sensor system the cup and rotor
642
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were assembled as a unit attached to the motor drive. The cup/rotor portion
was immersed in an open container of sludge where the sludge flowed through
the slots and holes in the cup, and filled the annular space between the cup
and the rotor. Additional modifications included enlarging the holes in the
bottom of the sensor cup and placing an inverted plastic container over the
cup/rotor assembly such that the bottom was completely open and there was an
annular ring around the sensor approximately 30 mm wide. These changes
facilitated the flow of sludge into the area between the cup and the rotor,
particularly when the sludge was highly flocculated.
The rheograms shown in figures 4, 5 and 6 were generated with the
pilot-scale sludge conditioning system and represent typical curves. The
general relationships were valid for all sludges tested. Although some
noise was apparent in the curves these rheograms have been drawn as smooth
curves to facilitate interpretation when there are several curves on one
figure. Capillary suction time (CST) was also used to measure the
dewaterability of the conditioned sludge and is shown in the figures.
Figure 4 shows the effect of polymer dosage on rheology when the sludge
is conditioned on a continuous basis. Since all of the experiments were
conducted with the intent of eventually applying the results to the operation
of a belt filter press, it was accepted that the sludge would have to be
highly flocculated. This condition is normally satisfied with a CST < 20
seconds. Reference to Figure 4 shows that the shear stress at low shear rates
«10s ) increases as the polymer dosage increases. The limiting condition
of CST = 20 seconds is achieved at a polymer dosage of 3.5 kg/t and a
0>
a
c
1/5
en
ac.
i—
en
a:
LU
i
CO
200
160 -
120
30 40 50 60
SHEAR RATE (s'1 )
Figure 4. Effect of polymer dosage on rheology.
643
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significant peak is evident in the rheogram. The trends shown are similar to
those observed with the batch system but the curves have a slightly different
shape. The continuous-scale curves rise very rapidly to a peak and then
decay, resulting in curves which are more definitely skewed to the right than
those generated on the batch system. This effect is attributed to the
differences between the geometries of the batch and continuous systems.
Another difference is also evident. With the batch system it was assumed
that a peak in the rheogram, i.e., a point of inflection with zero slope, was
sufficient to ensure optimum conditioning. This is no longer completely true
with the continuous system. Curve C in Figure 4 very definitely has an area
of zero slope at approximately 10 s~1 but the corresponding CST of 118
seconds indicates that the sludge is not optimally conditioned. The situation
is such that while the existence of a peak in the rheogram is still a
necessary condition for optimal conditioning, it does not represent adequate
flocculation as measured by the CST test.
Figure 5 shows the effect of varying the solids concentration when the
polymer flow rate is not adjusted accordingly. In this test the solids
concentration was altered by adding dilution water but the total sludge flow
rate (including dilution water) and the polymer volumetric flow rate were kept
constant. Under these conditions, as the solids concentration decreases, the
polymer dosage on a unit basis (kg/t) increases. At the highest solids
concentration (4.4%) the effective polymer dosage is 3.2 kg/t and results in a
CST of 37 seconds. At this CST the sludge would not be considered to be super
flocculated, and while a peak is present in the rheogram, it is not
substantial. As the solids concentration decreases to 3.1% the effective
140 -
10 20 30 40 50 60 70 80
SHEAR RATE (s'1 )
90
Figure 5. Interaction between solids concentration and polymer dosage with
respect to rheology.
644
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polymer dosage increases to 4.4 kg/t, the CST decreases to 17 seconds, and the
rheogram peak becomes quite pronounced. The situation has changed from one
where the polymer dosage is less than optimum to one where polymer overdosing
may be occurring.
The results in Figure 6 show the effect of detergent addition on sludge
conditioning and the resulting rheograms. Detergent, a deflocculant, was used
to artifically alter the dewatering characteristics and polymer demand of a
sludge without changing the solids concentration. Curve A, with a significant
peak and a CST of 16 seconds represents a well conditioned sludge. Curve B,
at the same polymer dosage but with the addition of 0.2% by volume of
detergent has the appearance of an unconditioned sludge in terms of both
rheogram peak and CST. As polymer addition increases, under a constant
detergent addition, the polymer (Curves C through E) overcomes the effect of
the detergent until at Curve E, the situation is very similar to that of Curve
A. The notable exception is that 4.4 kg/t of polymer is required for Curve E
as compared to 3.8 kg/t for Curve A. This is analagous to what happens in
actual operation. As the dewaterability of a sludge changes, usually for
unknown reasons, the polymer dosage must vary accordingly in order to maintain
the same level of performance.
30 40 50 60
SHEAR RATE
-------
3. respond to changes in sludge properties by altering polymer
dosage.
The control strategy developed at the Wastewater Technology Centre utilized a
HP87/HP1000 computer combination and the pilot-scale conditioning system shown
in Figure 3. A preliminary algorithm was developed which correlated the
rheological properties measured by the viscometer, with polymer demand. The
viscometer and polymer feed pump were interfaced to the computer, such that
data from the viscometer run was used by the control algorithm to
automatically adjust the polymer flow rate. A tentative optimum polymer
dosage was identified on the basis of CST (i.e., <20 seconds) and the
particular rheogram corresponding to that polymer dosage selected as a
reference rheogram. Specific characteristics of the reference rheogram were
stored in the computer memory and used as the control setpoints.
Figure 7 shows one of the preliminary attempts to automatically control
polymer dosage. It had been determined that the optimum polymer dosage for
the sludge was approximately 4 kg/t. The test run was initiated at a dosage
of 0.5 kg/t and the control system allowed to determine the optimum.
Viscometer tests were conducted at 8 minute intervals. Based on this input to
the control algorithm, polymer dosage was increased from the initial 0.5 kg/t
to 4.0 kg/t over a period of 70 minutes. Although the control is somewhat
crude due to the necessity of manual sampling, it is obvious that the basic
concept is valid.
N
CD
JC
a
a
a
o_
10
20
30
40
50
60
70
80
90
100
TIME (minutes)
Figure 7. Effect of automatic control on polymer dosage.
DEMONSTRATION
The final stage of the study, which is currently underway, involves
demonstration of the control package at full-scale. The general layout is
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shown schematically in Figure 8 and utilizes a 0.5 m Komline-Sanderson belt
filter press. Both the dilution water/detergent and polymer pumps are
interfaced with the computer. Temporal variations in feed sludge
characteristics are generated by programming the operation of the dilution
water/detergent pumps. Samples of the conditioned sludge are withdrawn to the
sample vessel at discrete intervals. Viscometer tests are initiated
automatically by the computer and data input to the control algorithm. The
computer will then initiate the appropriate control action with respect to the
polymer pump.
Sludge
Cake
Dilution Water
or
Detergent
Figure 8. Control strategy for full-scale sludge conditioning/dewatering.
The results in Figure 9 illustrate the response of the control system to
changes in the concentration of the feed sludge. During the initial 60
minutes the dewatering system was coming to equilibrium. During the
steady-state period (as defined by consistent belt press performance) from 60
to 200 minutes, the average polymer flow rate was 4.54 L/min. The break in
the data from 200 to 270 minutes resulted from some pluggage in the feed
lines, but when this had been rectified and the solids concentration of the
sludge decreased from 4.6 to 4.2 %, the resulting average polymer dosage had
also decreased. The decrease in polymer flow rate from 4.54 to 3.69 L/min
represents a polymer saving of approximately 20 % whereas the decrease in
solids was only about 10%.
In Figure 10 the effect of altering the dewaterability of a sludge by the
addition of detergent is shown. The polymer dose during the first
steady-state period was 4.45 L/min. At approximately 105 minutes a small
percentage (0.15% by volume) of detergent was added to the incoming sludge.
The control system sensed that the polymer requirement had changed and
proceeded to adjust the polymer pump accordingly. The average flow rate
required during the period of detergent addition was 5.51 L/min, or an
increase of approximately 24%. When the addition of detergent was
terminated, the polymer flow rate returned to the same general level as before
the addition.
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0 30 60 90 120 150 180 210 240 270 300 330 360 390 420
TIME (mm)
Figure 9. Response of control strategy to fluctuations in sludge solids
concentration.
o
Q-
0 30 60 90 120 150 180 210 240 270 300 330 360 390
TIME (mm)
Figure 10. Response of control strategy to fluctuations in sludge
dewaterability.
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The preliminary results from the demonstration phase have shown that the
control system is sensitive to gross changes in sludge dewaterability, whether
these are the result of changing solids concentration or the presence of
materials which act as deflocculants. The net impact on cost will depend upon
what degree of fluctuation in sludge dewaterability is observed when the
system is field tested. The projected benefits of an automatic control system
include reduced polymer cost, decreased product variability and reduced
process costs downstream.
CONVERSION OF SLUDGE TO LIQUID AND SOLID FUELS
The Wastewater Technology Centre's evaluation of low temperature
conversion of sewage sludge to fuel, an example of an alternative new
technology, was designed as a three phase program. The first phase involved
testing a number of sludges using a batch apparatus. The second phase
consisted of designing, constructing and testing a 1 kg/h continuous-flow
reactor. The primary purpose of the second phase was to generate process
design information and cost data, in order to assess the potential of the
technology at full scale. The final phase of the program will be
demonstration of the technology at full scale.
BENCH-SCALE STUDIES
Methodology
Raw sludges containing a mixture of primary and waste activated sludge
(WAS) from three different sewage treatment plants in Ontario were evaluated
during this study. All sludges were oven dried (70°C) to about 90-95%
solids. Analyses of these sludges indicated they were similar in composition
with volatile solids of 55-64%, calorific values of 15-18 MJ/kg and carbon
contents of 24-36%.
The bench-scale studies were carried out using a batch reactor and a
continuous flow system. The batch reactor, a pyrex tube 70mm in diameter and
720 mm in length, was heated in a three-zone Lindberg furnace under a nitrogen
atmosphere (Figure 11). Off-gases were condensed in a trapping system using
ice as the coolant. Non-condensable gases (NCG) were vented from the system.
A run was conducted by charging 550 g of dried sludge into the reactor and
deaerating with nitrogen. Once operating temperature had been reached, the
nitrogen purge rate was reduced. When all visible signs of reaction (i.e.,
gas/oil flow) ceased, the heat was switched off and the nitrogen purge rate
was increased for approximately 30 minutes. The system was dismantled and the
char, oil and reaction water collected and stored for analysis. Oil/water
separation was achieved using a separatory funnel.
A photograph of the continuous reactor system is shown in Figure 12. it
comprises a stainless steel shell, 50 mm internal diameter by 1000 mm long,
fitted with a sludge/char conveying system and is heated using the same
furnace as for the batch reactor system. The reactor is subdivided by a
helical gas seal, into a volatilization zone and a char/gas contact zone. The
649
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NZLINE
1. GAS CYLINDER
2. ROTAMETER
3. FURNACE
FURNACE CONTROLLER
REACTOR TUBE
TRAP
MULTIPLE THERMOCOUPLE SWITCH & DIGITAL READOUT
FURNACE THERMOCOUPLES
SLUDGE THERMOCOUPLES
POWDER DRY SLUDGE
GLASS WOOL PLUG
FUME
HOOD
ICE BATH"
Figure 11. Batch experimental equipment.
Figure 12. Continuous reactor system.
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reactor system is designed for dry sludge feed rates of up to 1 kg/h. Solids
retention time in the reactor is controlled by varying both the sludge feed
rate and reactor inventory. Sludge is fed to the reactor by a calibrated
screw conveyor and travels through the reactor by means of the reactor
conveyor. Volatilized material is withdrawn in the first zone and can be
contacted with the char in both co-current and counter-cur rent modes in the
second stage. Product vapours are condensed externally as per the batch
reactor system. Inert gas is used to purge the system of oxygen and the
operating pressure is generally less than 2 000 pascals. Prior to collection
of experimental data the system was allowed to reach thermal and chemical
equilibrium by operating for at least three solid retention times (SRT).
Results
The results achieved with both the batch and continuous reactor systems
are presented in detail in other publications (14,15). A summary of typical
results are presented in Table 1. All the data is expressed on a dry solids
basis (corrected for the normal 4-7% moisture present in the sludge) and the
calorific values are expressed on a total solids basis (not corrected for
volatiles).
TABLE 1. TYPICAL OPERATING CONDITIONS AND RESULTS
Batch Continuous
Feed Rate (g/h) NA 750
Temperature (°C) 450 450
OIL
Yield (%) 22.3 25.4
Viscosity (cstks) >214 33.7
Calorific Value (MJ/kg) 38.9 36.7
CHAR
Yield (%) 54.6 61.1
Calorific Value (MJ/kg) 9.4 6.2
NCG
Yield (%) 12.1 11.1
Calorific Value (MJ/kg) NM 5.8
REACTION WATER
Yield (%) 11.0 5.0
NA=Not Applicable
NM=Not Measured
In general, the results from the batch and continuous systems are quite
comparable. The oil and char yields are slightly higher from the continous
unit but it is difficult to say whether the difference is statistically
significant. The lower calorific value of the char from the continuous
reactor is the result of the lower carbon content. The most obvious
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difference between the products from the two systems is the oil viscosity. The
oil from the batch runs was solid at room temperature O214 centistokes),
while the oil from the continuous runs was fluid at room temperature (33.7
centistokes). The batch system generated approximately twice the amount of
reaction water as did the continuous one.
Although most observations are valid for either batch or continuous
results, the following discussion will be limited to only the continuous
system due to the fact that the experimental data base is much larger.
The yield of individual products and the split between products is a
function of operating temperature. At low temperatures, the product split
tends towards the formation of char. As the temperature increases to the
optimum, the oil yield increases (8 to 25%) while the char yield decreases (75
to 61%). Above the optimum temperature the oil yield begins to decrease as
conditions favour the formation of increasing quantities of non-condensable
gas. Oil yield appears to be related to solids residence time but since it is
impossible to completely separate the effects of SRT and char inventory, the
trends are not clear. The yield of reaction water does not appear to be
directly related to the operating parameters of the system. The yields of
both oil and char are very much a function of the specific sludge used as the
feed material.
The calorific value of the oil appears to be related to both SRT and
temperature but their effects are relatively small. A range of SRT's from 10
to 24 minutes resulted in calorific values from 36 to 37 MJ/kg, while
temperature variations from 300 to 500°C resulted in a range of only 36 to
39 MJ/kg. The calorific value of the char tends to decrease with increasing
temperature but is relatively insensitive to changes in SRT. The magnitude
of change in the energy of the char (i.e., from 10.4 to 5.5 MJ/kg), is
substantially greater than that of the oil. The calorific value of the
non-condensable gas increases in direct proportion to the temperature. This
is due to the increase in the percentages of hydrogen, methane and ethane
produced at higher temperatures.
The viscosity of the oil is a function of both SRT and temperature.
Viscosity decreases as either SRT or temperature increases. The viscosity of
the oil produced under a given set of operating conditions will be dependent
on the source sludge used. For example, under optimum operating conditions,
two different sludges produced oils with viscosities of 33.7 and 52.3
centistokes.
The elemental characteristics (C,H,N,0,S) of the oil appear to be quite
stable with respect to processing conditions. Some fluctuations in the carbon
content are evident, but the magnitude of change is relatively small. In
general, 40 to 50% of the carbon from the sludge is recovered in the oil.
Oxygen is difficult to measure because an unrealistically high oxygen result
will be obtained if water is present in the oil sample. Although oxygen is
generally in the range of 6-9%, levels as low as 2.7% have been obtained. The
elemental characteristics of the char tend to be affected more by processing
conditions than do those of the oil. As the temperature increases, the
carbon, hydrogen and nitrogen in the char tend to decrease.
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The reaction water has a total Kjeldahl nitrogen content (TKN) of 4-6% and
a total organic carbon content (TOC) of 10-18%. Based on the data currently
available, there does not appear to be any relationship between TKN/TOC and
operating parameters.
In general, the process has proven to be very stable, at least at bench
scale. As the process variables change, the split between products also
changes gradually. Similarly, the quality of the products is affected by
process modifications but the magnitude of the change is small. The result of
this is that over the practical range of operating conditions, the performance
of the system can be described as a relatively flat plateau as opposed to a
peak. In practical terms this means that if the temperature unexpectedly
changes by 50°c in full-scale operation, one can expect to see this
reflected in relative yields, but the process will not fail. It is also
unlikely that the product qualities will change sufficiently in short periods
of time to affect end uses or specifications.
IMPACT OF SLUDGE TREATMENT PRACTICES
The selection of the most appropriate sludge management scheme must
consider many factors including capital cost, operation and maintenance cost,
cost stability in the future, energy recovery/usage, environmental
acceptability and the difference between new construction versus upgrading
existing facilities. Other less tangibles include the desirability of capital
versus 0 and M expenditures, the public perception of acceptable technology
and the flexibility to respond to changing needs in the future. The impact of
sludge handling and disposal practices can be illustrated by examining the
four sludge management alternatives shown in Figure 13. They range from a
relatively low level of technology with many years of documented experience,
to a very sophisticated system which, to date, has only been proven at
bench-scale. In Table 2 the four alternatives are compared on the basis of
their energy recovery potential. The analysis uses a raw sludge input, for all
alternatives, of 25 dry tonnes of sludge solids per day. It is assumed that
sludge, char, NCG and reaction water are combusted at 75% efficiency. In
order to be consistent, the methane from digestion is only allocated 75% of
its gross energy, since it still has to be burned in a furnace of some nature
before the energy becomes usable.
Alternative A, the application of digested sludge on agricultural
land, has traditionally been the preferred method of sludge management for
many municipalities. For smaller communities which have a sludge with
acceptable levels of heavy metals, this is still the most cost effective
method of disposal. As communities become larger, drawbacks to this system
become evident. It is difficult for large municipalities to find sufficient
land within a reasonable distance of the plant on which to apply the sludge.
Even if the required land is available, the number of trucks needed to
transport liquid sludge may create a local traffic problem which can adversely
affect public relations. As municipalities become more industrialized, the
potential that the sludge may not satisfy heavy metal guidelines for land
application also increases. In terms of energy recovery the system is quite
efficient showing a net energy of 4.06 MJ/kg of raw sludge. The reason for
653
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TABLE 2. ENERGY BALANCE FOR SLUDGE DISPOSAL ALTERNATIVES
ALTERNATIVE (See Figure 13) A B C
Total Energy Available
in Raw Sludge (MJ/h) 17072 17072 17072 17072
ENERGY OF PRODUCTS
Methane (MJ/h) 4230 4230 4230 0
Oil (MJ/h) 000 8327
Char+NCG+H20 (MJ/h) 0 0 0 5111
Digested Sludge (MJ/h) 0 5414 5414 0
ENERGY REQUIREMENTS
Reactor/Dryer
Incinerator/Combustor (MJ/h) 0 12797 7580 1739
NET ENERGY
(MJ/h) 4230 -3063 2064 11699
(MJ/kg raw sludge) 4.06 -2.94 1.98 11.23
ENERGY RECOVERY
(%) 24.8 0 12.1 68.5
NOTE * Net Energy = Total Energy of Products - Total Energy Requirements
* Energy Recovery = (Net Energy / Raw Sludge Energy)x(100)
this level of efficiency is that there are no large energy requirements for
this alternative, although the energy required to transport the sludge to the
farmland has not been accounted for. One of the major problems with methane
as an energy source is that because it is difficult to store and transport, it
must be utilized on-site continuously. Many sewage treatment plants find that
this is not possible in summer, and consequently, flare a significant fraction
of their gas. Thus, while a digester may be generating potential energy at the
rate of 4230 MJ/h, the rate of utilization over the entire year may be
considerably less.
Alternative B has been a common practice for many installations. The
sludge is digested, dewatered to 20 to 22% and incinerated in a
multiple-hearth or fluidized bed incinerator. This alternative is
significantly more expensive than Alternative A and is much less energy
efficient. Reference to Table 2 shows that there is a net energy deficit of
2.94 MJ/kg of raw sludge, assuming that the incinerator has been modified to
burn methane as auxiliary fuel. This inefficiency is primarily due to the
energy requirements to evaporate the water (78%) in the incinerator. If the
energy deficit were satisfied by natural gas, this would translate to an
auxiliary fuel cost of approximately $150 000 per year. The positive
features are that there is a minimum quantity of material (ash) for ultimate
disposal, and the majority of heavy metals will be immobilized in the ash.
Due to the high energy requirements, this system is generally being phased
out.
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A. RAW
METHANE
*
DIGESTION
4% I
LAND DISPOSAL
1
METHANE
B. RAW
22%
HEAT RECOVERY
METHANE
C. RAW
STACK
30%
DEWATERING
30%
DRY I NG
90%
45%
INCINERATION
ASH
STACK
HEAT RECOVERY
D. RAW
40%
DRYING
95%
CONVERSION
*
OIL
COMBUSTION
ASH
NOTE: (%) numbers refer to sludge solids concentrations at various points in
the process.
Figure 13. Sludge disposal alternatives.
Alternative C is one approach to maintaining the same basic system as
outlined above, but upgrading it in order to improve energy efficiency and
subsequently reduce operation and maintenance costs. The sludge dewatering
equipment is upgraded in order to achieve 27 to 30% solids in the cake on a
consistent basis. A portion of the cake is then dried to 85 to 90% solids
using waste heat from the incinerator. This portion is backmixed with the
rest of the dewatered cake (30% solids) such that the combined sludge feed to
the incinerator is in the order of 40 to 50% solids. Depending on the
volatile fraction of the sludge, the cake may or may not be autogenous. The
655
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capital cost will be higher than for Alternative B due to the addition of the
dryer but the energy balance is much more positive. In this case, a net
energy surplus of 1.98 MJ/kg of raw sludge is produced but it should be
stressed that any net energy not utilized in the process is only available as
either methane gas or hot flue gas. Both of these represent a difficult
problem in terms of either storage or transportation. Another problem with
either Alternative B or C is that, in many cases, the public views sludge
incineration as an undesirable practice.
Either system could also be used without digestion. This would probably
increase the level of cake solids acheivable in dewatering and would
significantly increase the available energy in the sludge going to the
incinerator. The potential of using methane as auxiliary fuel would be lost
and the elimination of digestion would mean that a backup method for sludge
disposal during incinerator down-time would also be lost. When all factors
are considered, it is not clear whether it is more economical to incinerate
raw or digested sludge.
Alternative D has currently only been evaluated at bench-scale, but
appears to have a number of novel aspects which could make it a publicly
acceptable and economical method of sludge disposal. As mentioned above, the
fact that raw sludge is being dewatered indicates that cake solids in the
order of 40% can be achieved using technology such as a diaphragm filter
press. The energy balance in Table 2 shows the impact on recovered energy.
The net energy (11.23 MJ/kg of raw sludge) is 2.75 times higher than
Alternative A, and almost six times higher than Alternative C. All process
energy requirements for Alternative D could be supplied by 34% of the energy
in the char, NCG and reaction water. This would leave 3372 MJ/h of energy
available for other uses in the form of recovered heat, and 100% of the oil
(8327 MJ/h) would be available for sale. The primary reason for the
differences in the energy balances between Alternatives C and D is in the
manner of energy conversion. In C the conversion is either by biological
means (i.e., digestion), or by heat recovery. Neither of these methods are as
efficient as the process in D which consists of catalysed vapour phase
reactions converting the lipids and proteins in the sludge to straight chain
hydrocarbons.
The fact that a large percentage of the energy in Alternative D is
available as oil has a significant impact on the entire sludge management
philosophy. Instead of having to use recovered energy in-house, which is
usually the case with methane, steam, hot flue gas, and even electricity, the
energy is now in a storable, transportable and potentially saleable form.
Currently, the least valuable end-use for the oil appears to be as a
substitute for No. 6 fuel oil. If the oil can be sold for $30/barrel, then
the net revenue from a 25 tonne of dry sludge per day plant would be
approximately $365 000 per year. However, the potential exists to increase
end-use value, and upgrading to a transportation fuel is a possibility.
The use of a char combustor as opposed to a sludge incinerator may also
have a distinct advantage with respect to public acceptance. The combustion
of char may be seen to be more analagous to burning coal, rather than
incinerating sewage sludge with all of the perceived associated environmental
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concerns. The char combustor will be similar to an incinerator in that they
will produce the same amount of material for ultimate disposal and the heavy
metals will, to a large extent, be immobilized in the resulting ash. A char
combustor should also be considerably smaller than an incinerator to burn
sludge from an equivalent sized plant because the capacity to evaporate the
large amounts of water which are normally present in sludge, is not required.
Sludge management by conversion to oil will be most advantageous when
considering the construction of new plants. Since the major source of the raw
material for oil is the biomass from the biological treatment plant, the ideal
feed stock for the process is raw sludge. This eliminates the need for the
construction of digesters and can be translated into savings in capital
investment for new plant construction. The process is also compatible with
high-rate biological processes. One of the drawbacks of high-rate processes
has always been the additional quantities of sludge generated and the
corresponding increases in sludge disposal costs. By converting the excess
sludge to oil, any additional cost resulting from the increased quantity
requiring treatment, should be offset by the increased volume of oil produced.
CURRENT STATUS
The approach to sludge management in the sewage treatment industry has
changed over the past few years and will continue to change in the foreseeable
future. Considerations of energy, cost and availability have shown that many
sludge handling options, which were considered state-of-the-art only a few
years ago, are no longer economically justifiable. Sludge management schemes
must be designed with an overall systems approach to both the solids flow and
energy efficiency.
The automatic control of polymer in the conditioning/dewatering phase of
sludge treatment represents an opportunity to save money and improve process
performance. The basic concepts of the control logic developed at the
Wastewater Technology Centre have been shown to be valid. A Canadian company
is currently working on a government sponsored contract to develop a
commercial prototype of the control system which should be commercially
available in 1987.
The conversion of sludge to oil offers an attractive alternative to
sludge options currently in operation. The conversion technology is estimated
to be at least comparable to incineration in terms of capital cost and minimal
negative impact on the environment. The most important advantage is that the
recovered energy is in the form of oil which is storable, transportable and
potentially saleable.
It is estimated that in 1985, 350 000 tonnes of sewage sludge will be
incinerated in Canada. Thermal conversion of this sludge could produce 700
000 barrels of oil, with a market value of at least $21 million.
Environment Canada's long term plans are to demonstrate this technology by
construction of a 25 tonne per day facility. The first component of this
demonstration study has been completed,under contract, with the development of
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the pre-engineering data, identification of suitable sites and a thorough
assessment of the process economics. Current activities are centred around
the selection of a company to act as the licencee for the technology. The
25 tonne per day demonstration facility is scheduled to be operational in
1986.
REFERENCES
1. Black, S.A. and Schmidtke, N.W. Practises and Trends in Sewage Sludge
Utilization and Disposal, presented at 1st Workshop on Canadian-German
Cooperation, Burlington, Ontario 1979.
2. Bridle, T.R. Sludge Derived Oil: Wastewater Treatment Implications
Env. Tech. Letters vol. 3, pp 151-156, 1982.
3. Simcoe Engineering, Sludge Management Study for the Regional
Municipality of Halton, Pickering, Ontario, 1980.
4. Knudsen, D.I., and Mathes, G.A. Automatic Control of Sludge
Conditioning and Vacuum Filtration. Wat. Sci. & Tech., 13, Munich,
611-617, 1981.
5. Haug, R.T. and Sizemore, H.M. Energy Recovery and Optimization: The
Hyperion Energy Recovery System, presented at the International
Conference on Thermal Conversion of Municipal Sludge, Hartford, Conn.
1983.
6. Molton, P.M. Batelle-Northwest Sewage to Fuel Oil Conversion,
presented at the International Conference on Thermal Conversion of
Municipal Sludge, Hartford, Conn, 1983.
7. Shibata, S., Precede de Fabrication d'une Huille Combustible a Partir
de Boue Digeree. French Patent 838,063, 1939.
8. Bayer, E. and Kutubbudin, M. Low Temperature Conversion of Sludge and
Waste to Oil. Proceedings of the International Recycling Congress,
Berlin, West Germany, 1982.
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9. Dick, R.I. Physical Properties of Activated Sludge. Presented at
the NATO Advanced Study Institute, Sludge Characteristics and
Behaviour, University of Delaware, 1979.
10. Campbell, H.W., Rush, R.J. and Tew, R. Sludge Dewatering Design
Manual. Canada-Ontario Agreement Research Report No. 72, 1978.
11. Campbell, H.W., and Crescuolo, P.J. The Use of Rheology for Sludge
Characterization. Wat. Sci. & Tech., 14, Capetown, 475-489, 1982.
12. Cost-Project 68. Sewage Sludge Processing, Commission of the European
Communities Report No. EUCO/SP/48/75, 1975.
13. Campbell, H.W., and Crescuolo, P.J. Assessment of Sludge
Conditionability Using Rheological Properties. Proceedings of an EEC
Workshop on Methods of Characterization of Sewage Sludge, Dublin,
Ireland, 1983.
14. Bridle, T.R. and Campbell, H.W. Liquid Fuel Production from Sewage
Sludge, presented at the ENFOR Third Canadian Biomass Liquefaction
Experts Meeting, Sherbrooke, Quebec, 1983.
15. Bridle, T.R. and Campbell, H.W. Conversion of Sewage Sludge to Liquid
Fuel, presented at the 7th Annual AQTE Conference, Montreal, Quebec,
1984.
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ITALIAN ADVANCES IN WASTEWATER TECHNOLOGY
by
Mario Santori
Institute di Ricerca sulle Acque
Consiglio Nazionale delle Ricerche
Rome, Italy 00198
The work described in this paper was
not funded by the U.S. Environmental
Protection Agency. The contents do
not necessarily reflect the views of
the Agency and no official endorsement
should be inferred.
North Atlantic Treaty Organization/Committee on tke
Challenges of Modern Society (NATO/CCMS) Conference
on Sewage Treatment Technology
October 15-16, 1985
Cincinnati, Ohio
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ITALIAN ADVANCES IN WASTEWATER TREATMENT
by: Mario SANTORI
Institute di Ricerca sulle Acque
Consiglio Nazionale delle Ricerche
Rome, Italy 00198
ABSTRACT
Italian legislation on wastewaters control establishes fixed quality
limits not dependent on the characteristics of receiving water bodies. In
order to protect low receiving capacity water bodies, the limits are very
restrictive, especially with regard to heavy metals and nutrients. Further-
more, typical products of the Mediterranean area, and particularly of Italy,
such as olive oil, originate seasonal discharges with high BOD concentration
(up to 100,000 ppm) which are poor in nutrients. These discharges are not
easily treatable by means of traditional aerobic biological processes, as
they require a long start-up time and very high degrees of dilution, in order
to eliminate toxicity phenomena.
This situation created the necessity for the research reported herein:
- heavy metals removal by advanced precipitation processes; - nutrients
removal with a single sludge system without addition of external reactives;
- anaerobic treatment of highly concentrated soluble wastes either in UASB
reactors or mixed with domestic sludges in traditional 3ludge digesters.
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TOXIC METAL REMOVAL AND RECOVERY FROM WASTEWATERS
Two main research projects have been devoted by the Institute di Ricerca
sulle Acque (I.R.S.A.) to this problem:
- metal precipitation using the water soluble starch xanthate, a derivative of
an inexpensive natural product;
- synthesis and characterization of new Ionic Exchange (IE) materials high
with high affinity for metal ions
METAL PRECIPITATION WITH STARCH XANTHATE
Starch xanthate (SX) is a water soluble polymeric reagent which is
easily synthetizable starting from starch, CS2 and NaOH aqueous solution. It
shows high metal removal efficiency for Cd (II), Cr (III), Cu (II), Pb (II),
Hg (II), Ag(I) and Ni(ll), either separately or in combination, over a large
pH range. The parameter xanthate/metal ratio is most significant both for
metal removal efficiency and for solid/liquid separation efficiency, and can
be controlled by a potentiometric system.
Figure 1 report the residue concentration of Ag(l), Hg(II), Cu(ll),
Zn(ll) as a function of the SX/metal molar ratio, after 0.4S/™ filtration
at constant pH = 5 (7-5 for Ag) and ionic strength 0.1 M NaNO^, obtained
during batch tests.
The data indicate that very low concentrations are reached for Ag, Hg
and Cu (0.01; 0.005 and 0.09 mg Metal/1, respectively). On the contrary, the
removal of Zn is not complete, and the final concentration is in order of
20 mg/1.
As far as the stoichiometry and thermodynamics of uetal-xanthate systems
are concerned, literature data are available only for the metal-ethylxanthate
reaction. Preliminary numerical simulation with these data showed that neither
stoichiometric nor equilibrium parameters of metal-ethylxanthate systems could
be used to successfully model the behaviour of metal-starch xanthate systems,
as shown in Figure 1. According to the stoichiometry of the reaction between
metals and ethylxanthates, the theoretical SX/M molar ratios in the precipi-
tated compounds should be 1 : 1 for mono-valent metals and 2 : 1 for divalent
ones. For example the following reaction can be assumed for a divalent metal:
/ s
+ 2 R-O-C/' *• R-0-C7/ ,C-0-R
C— ^Q M Q
663
-------
io-3
0.5
SX/M
15
Figure 1. Effect of SX/M molar ratio on the residual metal ion concen-
tration in solution after 0.45 #m filtration
pH = 5-0 1 0.5 Stat ( 7-5 i 0.5 for Ag)
Ionic strength = 0.1 M NaNOo.
As Figure 1 indicates *he best experimental SX/M ratios for a complete
removal of metals are not consistent with the theoretical ones, for Ag(l)
and Hg(ll). In these cases the quantitative removal of the metals from the
solution ( > 99.9%) is reached when the SX/M ratios are 0.5 and 0.8, respec-
tively.
Experimental work was carried out in order to determine metal binding
capacities of the starch xanthate and conditional formation constants of the
metal-starch xanthate insoluble complexes.
Figure 2 shows an example of the the Scatchard pilot extrapolation method
applied to the results of the potentiometric filtration of starch xanthate
solutions with metal ions. The Scatchard extrapolation method evidenced two
metal binding mechanisms, the first related to chemical precipitation of the
metal ions with xanthate groups and, the second, to the adsorption of metal
ions on the precipitate.
The determined stability constants and complexing capacities of starch
xanthates with heavy metals were then incorporated in a computer program, in
664
-------
1.25-
1.00
T, 0.75
0.50
0.25
-«-*-*»«
05
1.5
Figure 2. Scatchard plot for the binding of Cd(ll) by ethylxanthate
at pH 7-5 and 0.1 M NaNO .
O
order to simulate the fate of a metallic ion in wastewater after treatment
with SX.
As an example, Figure 3 compares theoretical and experimental trends of
the residual silver concentration after treatment of uncomplexed Ag ions
(from AgNO^ salts) of initial concentration 10~4 M, corresponding to 10.7
mg/1 as Ag. The curve represents the theoretical behaviour, assuming K =10 j
n =2; K =6.9xlo3; n =2.5. The experimental points, determined either by po-
tentiometric ISE measurements or by AA analysis after 0.45 /um filtration,
are in good agreement with the predicted behaviour.
Further experiments are being run in order to compare the results of the
theoretical simulation of the process with the experimental ones, particular-
ly in the case of the presence of metal complexing agents in wastewaters.
665
-------
0.01
4 6
I05(mol/l)
Figure 3. Silver (from AgNO salt) removal with starch xanthate.
Starting solution: AgNO 1.0_x 1CT4 M5 0.1 M NaN03;
pH = 7.5; / SX_/ = 1.18 x 10~3M.
• from potentiometric data
A AA determinations
The continuous line represents the calculated curve.
The behaviour of the system is completely different when complexed
metal ions are to be precipitated. For the sake of example, Figures 4 and 5
report the distribution diagram ot the hydrolysis products and chlorocom-
plex species of Hg(II) in ionic strength 0.1 M NaNO and 0.1 M NaCl, respec-
tively. Working at pH = 5, the prevailing species in solution is Hg(OH)2 in
the first case, while the sum of HgCl" and HgCl^~ accounts for about 60% of
the total Hg in the second case.Figure 6 shows ttte difference in the kinetics
of precipitation of the mercury at pH = 5 starting from the hydroxocomplexes
(curve a) and from the chloro-complex (curve b). The removal of 99-9% of Hg
is obtained after 5 minutes and 35 h, respectively. The slow kinetics is
probably to be ascribed to the repulsive electrostatic forces between the
negative xanthic groups and the anionic chlorocomplex species of mercury.
666
-------
100
80-
:? so
"i
o
"CT
20
0
\H9 /'
\ /
\ ,'
\ 1
\ /
i i
\'l
I
1\
// V. H9(OH)3
2 i 6 8 10 12
s
«n
Q
Figure 4. Theoretical distribution of hydrolysis products of
Hg(ll) in NaNO^ 0.1 M test solutions.
100
80
60-
(J
=? 40
Ol
20
/Hg(OH)j
YV\
________ _ ' A \
'
Hg(OH)CI
I I
2
r <
6 8
pH
10
12
Figure 5- Theoretical distribution of hydrolysis products and
chlorocomplexes of Hg(ll) in 0.1 M NaCl test solutions
667
-------
101
Figure 6. Kinetics of precipitation of Hg(ll) at pH = 5 Stat.
a) hydroxide-complex in 0.1 M
b) chloro-complex in 0.1 M NaCl
It is interesting to note that, while metal speciation greatly affects
the kinetics of precipitation, it does not influence the solubility of the
mercury xanthate: the quantitative precipitation of the metal from 0.1 M
NaNO-i or 0.1 M NaCl solutions is obtained at
the same ratio SX/Hg =0.8.
Table 1 summarizes the experimental results obtained in batch tests
when the viscous SX(0.7 mmol S/g) was added to 1 dn>3 of solutions containing
dissolved metals In, Cu, Cd, Hg, and Ag (one at time) at pH stat = 5- The
final concentrations of the metals are still found to be below the limits of
current Italian Legislation. Also the optimum polycation dosage is report-
ed in Table 1 at the ionic strength indicated. The operative removal capa-
city in batch tests for Zn, Cu, Cd, Hg and Ag was found to be 19-1; 22.2$
39; 143; 154 g of metal/kg of SX (viscose), respectively.
The small amounts of sludge obtained after precipitation with SX are
668
-------
TABLE 1. EXPERIMENTAL RESULTS OBTAINED IN BATCH TESTS WITR METAL ION
SOLUTIONS (SEPARATE EXPERIMENTS) AT pH = 5 STAT. (INITIAL
STARTING VOLUME = 1 dm3. SX VISCOSE = 0.7 tnmol/g AS SULFUR
TOTAL REACTIVE).
Feed cone, (mg/1)
SX/M ratio (mol/mol)
Residual cone, after filtration
(0.45/un) (mg/1)
Optimum polyelectrolyte dosage
(mg/dm3 PC-7)
Operative removal capacity
(g/Kg SX Viscose)
Zn
500
2.4
10
100-;;-
19.1
Cu
50
2.0
0.01
10-"---
22.2
Cd
53
2.0
0.02
7+
39
Hg
100
1.0
0.001
30++
143
Ag
11
0.5
0.01
12+
154
*: Ionic strength = 0.3 M NaCl; **: 0.04 M NaN03$ +: 0.1 M NaN03?
++: 0.005 M NaN03.
easily dewaterable by traditional techniques (filtration, mechanical dehydra-
tion) . Preliminary tests carried out with acid solutions to recover metals
in solution gave unsatisfactory results. An oxidant treatment with NaCIO
solution and iodine to lower the pH below 3 gave quantitative recovery, as
reported on Figure 7, in the case of mercury sludge. In this case, the
reaction proceeded the formation of insoluble starch xanthide, a non-toxic
residue disposable without difficulty.
The SX process is now being tested in a pilot plant (1.5 m3/h), Figure
8,on a real chlor-alkali wastewater in order to verify its applicability
from the technical and economic point of view.
NEW I.E. MATERIALS FOR METAL ION UPTAKE
Two main types of materials are being investigated: the water insoluble
cellulose xanthate and the copolymer Poly /(N-Dithiocarboxylato)-iminoethen-
hydrogenoiminoethene_/(PIED). The water insoluble cellulose xanthate (ICX)
can be used as a chelating ion-exchange resin, characterized by relatively
low costs of synthesis. The ICX can be synthetized slightly modifying the
viscose synthesis procedure in the rayon process.
The research was initially aimed at finding the best operating condi-
tions for the synthesis in order to obtain an insoluble material with high
669
-------
100-
80- •
60
t-l
0)
o
0)
6 8 10
eq Ox/eq Hg
Figure 7. Recovery of mercury from sludge by chemical oxidation at
pH = 3-5.
a) NaCIO; b) I-
Figure 8. Lay-out of the plant.
VA = Storage tank; SI = Precipitation reactor? S2 = Settling
tank5 a) = Acid; b) = Base; c) = Starch xanthate; d) = Poly-
electrolyte.
670
-------
ion-exchange capacity. Under optimal conditions the final compound had a metal
extraction capacity in the range of 1 to 2.5 meq/q. The ICX was obtained
both in Ma and in Mg-form. The Mg-ICX (dried, in powder form) proved to be
stable for 1 year at ambient temperature.
Table 2 reports the results obtained with column operations with a bed
TABLE 2. EXPERIMENTAL RESULTS OBTAINED WITH CELLULOSE XANTHATE PROCESS
IN COLUMNS
ICX-Mg (Total capacity =1.2 mmol/g).
Flow velocity = 10 BV/h; Separate experiments for each metal.
Feed concentration (mg/1)
Initial pH
ICX-Mg used (g)
Volume of ICX-Mg (cm )
Concentration limits in Italy
(mg/D
Water treated (V/BV )-»-"-
Operative removal capacity
(mg of metal/g ICX-Mg)
(mmol metal/g ICX-Mg)
-"-: USA Regulation (1982)
Cu
30
6.5
8.4
40
0.1
65
9.28
0.15
Ag
30
6.6
7.6
30
0 . 2-"-
168
19-9
0.18
Cd
30
7.0
7.0
30
0.02
130
16.7
0.15
Hg
30
7.2
7.3
30
0.005
45
5.55
0.028
-;H;": to obtain a leakage corresponding to the maximum metal concentration
permitted by law.
of Mg-ICX as chelating resin. Working with feed solutions of 30 mg/1 of each
metal and at a flow rate of 10 BV/h, a leakage corresponding to the units
imposed by law for Cu, Ag, Cd and Hg was reached UD to 65? 168; 130 and 45
V/VR, respectively.
The corresponding operative removal capacities
5-5 mg of metal/g of ICX.
are 9.285 19.95 16.7 and
It is interesting to note that columns of CX can be used to "polish"
very low concentrations of metals in solution. By way of example, Figure 9
671
-------
0.05
50
Figure 9- Removal of trace concentrations of Cadmium by treatment with
ICX-Mg in column operation.
Initial Cd = 0.054 mg/dm3; Flow rate = 10 BV/h5 1: Limit by
law.
reports the effluent concentration of Cadmium, fed at a velocity of 10 BV/h
and at initial concentration of 0.054 mg/1, as a function of the treated bed
volumes.
The data show that the Cd concentration in the product water is below
the 0.02 mg/1 limit set by Italian Legislation. Furthermore, the removal
efficiency of the ICX-Mg is unchanged after a 69-day interruption of the run.
This is a confirmation of the good stability of this material with time, as
reported previously.
The exhausted ICX materials were then treated for metal recovery, with
either chemical or thermal treatment.
Table 3 shows the metal yields obtained by treating different ICX sludge
exhausted with Cu, Ag and Cd: 70-90% metal recovery was achieved.
Finally, the synthetic copolymer PIED was investigated, in cooperation
with the Chemical Department of Reading University (U.K.), for selective
metal extraction from wastewaters.
672
-------
TABLE 3. RECOVERY OF METALS FROM SLUDGE IN THE CX-Mg TREATMENT BY
BURNING AND CHEMICAL OXIDATION
Metal in sludge (mg)
Amount of sludge (g)
Metal recovery (mg)
a) by burning (mg)
(%}
b) by oxidation with NaCIO (mg)
(%}
Cu
121.5
8.4
108
89
87
72
Ag
246
7.6
219
89
—
—
Cd
152.5
7-0
118
77
136
89
The studied material is a copolymer which is prepared from poly(imino-
ethene) and carbon disulphide. An idealised formulation of the repeating unit
of PIED is given below:
The N-dithiocarboxy]ate groups are thought to be mainly on the primary
amine groups. In addition to the -NHCS" groups, there are the remaining pri-
mary amine groups and the other nitrogen-containing groups which can bonded
to the metal ion.
Figure 10 show that PIED rapidly extracts cadmium from aqueous solutions.
The addition of PIED (•*•*, Ig) to a solution (100 ml) containing cadmium (10.2
mg/1) reduce the concentration to 0.001 mg/1 in ten minutes. Moreover in accor-
dance with the fact that N-dithiocarboxylates had a greater affinity for cad-
mium than zinc, it was found that PIED can perform a useful separation of the
two metal ions. The results in Figure 11 refer to the extraction from solu-
tions containing cadmium (11.2 mg/1) and zinc (13-Omg/l) at pH 2 (H SO ) as
commonly experienced in waste waters containing both metal ions. The salt Zn-
PIED was used with different loadings of cadmium. The lower the loading of
cadmium the faster the kinetics, but the presence of zinc does not influence
the kinetics of cadmium uptake on PIED.
673
-------
1.0
25 30
t(min)
Figure 10. Uptake of Cd(ll) by PIED at pH 5-5 as a function of time,
Ionic medium 0.1 M NaNO-,
a) 0.09 mmol Cd added/g PIED
b) 0.392 " " " "
c) 0.72 " " " "
674
-------
0.01
Figure 11. Residual cadmium concentration in solution after treatment
with Zn-PIED (0.100 g) as a function of time.
Ionic medium 0.1 M NaN03 5 pH = 2 (H SO )
•: Initial (Cd) = 11.2 mg/dm3
H: Initial (Cd) = 11.2 mg/dm3 and (Zn) = 13-0 mg/dm3
a) Cd Loaded =0.10 mmol Cd/g Zn-PIED
b) Cd Loaded =0.50 mmol Cd/g Zn-PIED
675
-------
INNOVATIVE AND ALTERNATIVE ENGINEERING
ANAEROBIC PROCESS DEVELOPMENT
In recent years considerable interest has been focused on anaerobic
treatment of a wide range of waste waters, ranging from high strength ef-
fluents to very diluted ones, as an interesting alternative to high energy
consuming aerobic processes.
The main advantages of anaerobic digestion are well known: low high-grade
energy requirements for process operation and in many cases, a net overall
energy balance*, low production of well stabilized excess sludge; low capital
cost.
The main draw-backs consist of start-up and process control problems,
mainly due to the slow growth rates of some anaerobic bacteria and to the
still inadequate understanding of the complex interactions between biological
and the physicochemical factors.
Several Italian Research Institutes are developing innovative anaerobic
research processes.
Istituto di Ricerca sulle Acque
Most of the experimental activity carrieu out or currently in progress
at this Institute on anaerobic digestion is related to the treatment of olive
oil mill waste waters, which considerably increase the polluting load dur-
ing the milling season in the Mediterranean area and in the Apulia region,
where the Bari IRSA laboratories are located.
With reference to the anaerobic treatment of olive oil mill wastewaters,
IRSA has developed high rate UASB (Upflow Anaerobic Sludge Bed) reactors for
digesting these concentrated effluents (COD in the range 50-200 kg/m^).
UASB reactors are expanded bottom-fed sludge vessels? there is no mechan-
ical stirring in the system and this fact, as well as the relatively high
upflow velocity, promotes the formation of well settling sludges.
Treatment of olive oil mill waste waters in UASB digesters was made
possible by dilution with well water. For full scale applications, dilution
by sewage will be used as it also eliminates nitrogen deficiency in the waste.
Experiments have been performed both on laboratory and pilot-scale
reactors (volume 15 1 and 5 m-*, respectively) maintained under mesophilic
conditions (35°C).
676
-------
Most start-up problems have been solved by starting with a very diluted
waste (about 5 kg COD/m3) and then increasing the concentration by steps of
2, 5 kg COD/m^ to a final concentration of about 15 kg COD/m^, while also
adding suitable amounts of nitrogen (available nitrogen in the waste is
deficient) and alkalinity (sodium bicarbonate, soda and calcium hydroxide)
to the feed.
The hydraulic residence time (HRT) was kept constant at 1 d during the
tests. The volumetric loading rate was increased from 5 kgCOD/(m3.d) to 16
and 21 kgCOD/(m3.d) for the pilot and the laboratory reactor, respectively.
Removal efficiencies in the range of 70 - 75% on the COD were obtained,
as well as specific gas production rates of the order of 4 to 6 m^/m^r'd.
These results can be justified by the high concentration of active bio-
mass which built up in the reactor and by the beneficial effect which the
added chemicals seem to have on the net microbial growth rates.
Sludge granulation as achieved in Dutch UASB digesters, fed on carbohy-
drate wastes, was not obtained but, even so, the settleability of the sludge
proved very good.
Experimental results related to a start-up of a 5 m3 pilot reactor are
reported in Figure 1, where loading rates are given as kg TOC/(m3'd). Load-
ing rates as COD can be obtained by multiplying TOC values by 2.5 - 3. From
the diagram it can be seen that after about 30 days the system has been
overloaded with a consequent increase of volatile organic acids (TVA).
Present research is aimed at defining a start-up procedure to minimize
chemical consumption and energy (heating) requirements during the transient
operation until full load conditions are reached.
The experiments are currently being carried in laboratory and pilot
scale plants at the IRSA laboratory, and will be subsequently replicated on
a test bed plant (two 750 m-* digesters) the construction of which will be
funded by the Apulia Regional Authorities within 1986 in the municipality of
Pallo del Colle.
The design of this demonstration plant has been made by IRSA and by re-
gional technical engineers (as far as the sizing of the reactors and the
concrete structures, respectively, are concerned).
677
-------
g*j
0
ft —
TVA
/kgHAcN
\ m3 ,'
0
80-
(%) 40-
20
Figure 12.
•-YV'
20
40
60
80
100
(d)
Pgas = Specific Biological gas production) L = Specific
load; TVA = Volatile organic acids$ TOC = Removal efficiency,
Experiments are also being performed on the direct anaerobic treatment
at ambient temperature of raw sewage in sludge blanket reactors. The most
interesting feature of this process is a much lower production of sludge than
aerobic systems ( e.g.: activated sludge and trickling filters). Direct an-
aerobic treatment of raw sewage is being investigated on laboratory UASB
reactors and in the near future the tests will be extended to a 5 m^ pilot
plant.
Results obtained on the laboratory reactor are promising, as 50-60% of
the polluting load can be removed by this process.
Agip Giza S.p.A..
This Company, in cooperation with the ENI Research Laboratories
(ENI RICERCHE), has developed fixed film anaerobic digesters (anaerobic
filters) for wastewaters with a prevalently soluble pollution load.
The main advantantages of fixed film reactors are related to the high
sludge retention times, the high sludge concentrations that can be attained
678
-------
and maintained to their capacity to withstand very high temporary
hydraulic and organic overloadings. Two full scale plants have been built.
The first one, made of two 1500 m3 anaerobic filters using quartz rock as
filling media, has been successfully operating on a sugar factory for
several years. The second one, treating vegetable canning industry
effluents, is a 300 m3 anaerobic filter and was started up in Spring 1985.
The anaerobic filters in the sugar factory treat the regeneration
streams from ion exchange resin columns that purify the sugar juice from non
crystallizable organic (mainly proteinaceous) compounds.
The operating conditions are as follows: loading rate 9 kg
hydraulic retention time: 2 days, specific gas production 2.3
with 70% methane, removal efficiency 60% on the COD. All these data refer
to the full volume of the filters , which have a void fraction of approxi -
mately 50%.
ENI Ricerche
Eni ricerche has carried out the R. & D. for the above mentioned anaero-
bic filters on sugar wastewaters up to the pilot plant scale . A trucked pi-
lot plant has been designed and built for the purpose of carrying out treat-
ability experiments in the factories producing the effluents to be tested.
Eni ricerche is presently developing anaerobic fluidized beds using
sand particles as supporting media.
Very interesting results have been obtained using laboratory scale reac-
tors. At loading rates of the order of 150 kg COD/(m3-d) and retention
time of 0.11 days, specific gas production rates of 26.5 m3/(m3.d) and COD
efficiencies of the order of 45% have been achieved.
679
-------
PROCESS UPGRADING AND PLANT MANAGEMENT
BIOLOGICAL NITROGEN REMOVAL FROM INDUSTRIAL WASTEWATERS
Within the framework of biological nitrogen removal, the aim of this
work was to verify the applicability of single sludge systems (see Figure 13)
for treatment of high strength ammonia industrial wastewaters.
in
c/1
Figure 13. Flow-sheet of single sludge anoxic-aerobic process.
i: influent; e: effluent; a: nitrified mixed liquor
recycle? b: sludge recycle? W: waste sludge; Rj: an
oxic reactor; R2-. aerobic reactor; S: settling tank.
Effective application of such a system is dependent on the value assumed
by denitrification kinetics when internal carbon is used as electron donor sub-
stance; this means that the rate of this process must be high enough to be of
industrial interest.
Furthermore, in the case of industrial wastewater in which inhibitors
for nitrifying bacteria are present, the nitrification stage is the critical
phase of the whole process and ammonia oxidation is possible only if the
wastewaters are diluted. As inhibition problems are independent of the
chosen process scheme, the single sludge system is in any case preferable
to separate systems, and affords considerable saving of primary and
secondary energy.
The wastewaters examined (see Table 4 for typical composition) are rep-
resentative of two quite distinct categories: slaughter-house discharge is
characterized by high biodegradability and the absence of inhibitory com-
pounds; coke oven liquid wastes contain typical lowly biodegradable substances
680
-------
TABLE 4. TYPICAL COMPOSITION OF WASTEWATERS
Slaughter-house
Parameter
(mg/1)
COD
~Q(~\T\
D\JiJ C
TOC
TKN
NH4-N
SS
Non filtered
sample
3,070
2,050
-
260
-
610
Filtered sample
2,080
1,350
670
240
225
-
1
//
1
1
!
^
!
'i
''I
Coke plant
Parameter
(mg/1)
TOC
Phenols (Total)
NH4-N
ci-
SS
Non filtered
sample
3,300
2,500
3,800
3,000
0
and inhibitory compounds. The findings can therefore be extrapolated to
wastewater that have intermediate characteristics with respect to the two
effluents studied, thereby extending the applicability of the results
obtained.
Results
The experimental work, which takes in various sets of tests run in both
bench and pilot scale, is summarized in the data reported in Tables 5 and 6.
These data clearly show the applicability of single sludge anoxic-aerobic
systems for the biological treatment of both wastewaters studied.
As can be seen, satisfactory results have been also obtained with
coke-oven liquor. After suitable dilution, good removal efficiencies for
carbonaceous substances (phenols and thiocyanates) have been achieved, as
well as for nitrification. As far as denitrification efficiency is con-
cerned, the results show that the N03~N removal is the maximum that can be
obtained with a wastewater with such a phenol/nitrogen ratio*.
The process parameters obtained from the continuous tests of Tables 5
and 6 and, when necessary, confirmed by supplementary batch tests^, allowed
*This ratio (~ 0.7) is considerably lower than the specific phenol consump-
tion ratio found in anoxic reactor (1.7).
^Since in completely mixed biological reactors, the substrate concentration
in the effluent is practically the same as in the reactor, the rate of the
process could be kinetically limited by one or more substrates.
681
-------
TABLE 5. MEAN WORKING CONDITIONS AND RESULTS WITH SLAUGHTER-HOUSE WASTEWATER
Anoxic reactor
Analytical
data
Working
conditions
Process
parameter
Process
performance
Parameter
COD
BOD-
TOC
TKN
NH4-N
N03-N
Volume
Hydraulic retention time
Sludge age
Biomass concentration
PH
Temperature
Dissolved oxygen
Biomass nitrogen content
vss/ss
Nitrif. mixed liquor rec. rat.
Sludge recycle ratio
Denitrification rate
Net growth yield coefficient
COD removal efficiency
Nitrification efficiency
Nitrogen removal efficiency
Feed
A.
mg/1 2,080
mg/1 1,350
mg/1 670
mg/1 240
mg/1 225
mg/1 0
1
h
d
mg MLSS/1
°C
mg/1
% ss
kg N03-N/kg VSS-d
kg VSS/kg COD solub
% 88
% 100
% 74
or
reactor outlet
510
-
163
87
66
0
670
4-5
1.1
4,920
8.1
20
0.2
6.9
0.79
0.19
. 0.34
Aerobic reactor
or
A. reactor outlet
256
19
76
15
0
58
2,670
17.8
4.6
4,870
7-6
20
3-0
7-3
0.69
1.2
1
CD
00
-------
TABLE 6. MEAN WORKING CONDITIONS AND RESULTS WITH SLAUGHTER-HOUSE WASTEWATER
Analytical
data
Working
conditions
Process
parameters
Process
performance
Parameter
Phenols (total)
CNS-
NH4-N
N02-N
N03-N
Volume
Hydraulic retention time
Sludge age
Biomass concentration
pH
Temperature
Dissolved oxygen
Biomass nitrogen content
vss/ss
Sludge recycle ratio
Denitrification rate
Nitrification rate
Specific phenol consuption ratio
Net growth yield coefficient
Phenol removal efficiency
Nitrification efficiency
Nitrogen removal efficiency
Anoxi
Feed
A. rea
mg/1 400
mg/1 40
mg/1 600
mg/1 0
mg/1 0
1
h
d
mg MLSS/1 2
°C
mg/1
% ss
kg NO^-N/kg VSS-
kg NH4-N.kg VSS-
kg C6H5OH/kg N03
kg VSS/kg C6H5OH
% 95-0
% 98.3
% 35-8
c reactor
or
ctor outlet
28
1
300
3
78
5
20
40
,720
7.5
25
0
8.5
0.86
d 0.11
d 0.25
-N 1.7
0.13
Aerobic reactor
or
A. reactor outlet
20
0.5
10
3
374
7
28
47
2,310
7.5
25
2.5
8.5
0.86
1
Ol
oo
CO
-------
the plants to be designed and the costs estimated once the flowrate and the
concentration of pollutants were known.
Biological reactor design
Table 7 shows the flow-rates and concentration figures assumed for the
dimensioning of full-scale plant for both the wastewaters studied.
TABLE 7. DESIGN DATA
Wastewater
Parameter
Slaughter-house
Coke plant
Flow rate (m3/d)
Ammonia concentration (mg NH^-N/1)
Ammonia load (kg NH^-N/d)
4,000
300
1,200
250
3,800
950
More specifically, for the slaughter-house wastewaters, the economic
analysis refers to plants catering for 10^ equivalent inhabitants (referred
to nitrogen). Assuming 12 g N/d•inhabitant, the total nitrogen that must be
removed is : 12-10 '10^ = 1,200 kg N/d and the related flow rate : 1,200
kg N/d : 0.3 kg N/m3 = 4,000 m3/d.
As far as the coke oven wastewater is concerned, reference is made to a
discharge treatment plant that produces 1,000 t of coke a day. The discharge
produced is assumed to be 0.25 m3 of discharge for every t of coke and so
the flow rate will be : 1,000-0.25 = 250 m3/d.
Hydraulic residence times, sludge ages and recycle ratios can then be
calculated (see Table 8) using the model reported by Ramadori (1).
684
-------
TABLE 8. DIMENSIONING OF BIOLOGICAL REACTORS
Wastewater
Parameter
Hydraulic retention time in the anoxic reactor
Hydraulic retention time in the aerobic reactor
Sludge age (total)
Nitrified mixed liquor recycle ratio
Sludge recycle ratio
Slaughter-
house
6.7 h
14-4 h
5.9 d
13-3
1.0
Coke plant
38 h
21 h
87 d
0
2.0
Technical and economic evaluations of a full-scale plant
With regard to the schemes in Figure 14, which also include the sludge
treatment section, Table 9 and 10 summarizing the values of the design pa-
rameters for the various units considered. These values result from the
experimental work summarized in 3.1 and from the literature (2), (3).
Plant costs
Plant costs for each operating unit have been obtained from the func-
tions reported in Table 11. Plant costs are expressed as a functions of
parameters chosen as variables. For the sake of example, the costs of civil
works for biological reactors (both anoxic and aerobic) are expressed as a
vn
g
in
Figure 14. Process flow-sheet of full scale plant, a: influent; b: dilution
water (coke plant wastewater only); e: effluent; W: waste sludge;
r: sludge recycle; r': nitrified mixed liquor sludge (slaughter-
house wastewater only); 1: anoxic reactor; 2: aerobic reactor;
3: settling tank; 4: pre-thickner; 5: anaerobic digester
(slaughter-house wastewater) or aerobic digester (coke plant
wastewater); 6: post-thickner.
685
-------
TABLE 9. DIMENSIONING PARAMETERS FOR COMPONENT UNITS RELATED TO
SLAUGHTER-HOUSE WASTEWATER TREATMENT
Unit
Anoxic
reactor
Aerobic
reactor
Settling
tank
Pumping
station
Pre-
thick-
ner
Anaer .
dig.
Post-
thick-
ner
Belt-
press
Parameter
Biomass concentration^
Denitrification rate
Specific BOD consumption ratio
NOo-N in the effluent
Specifing stirring power installed
Net growth yield coefficient
Biomass concentration
Minimum sludge age
Dissolved oxygen
Oxygen required for nitrification
Mechanical efficiency:
oxygenation
BODr removal
TKN in the effluent
COD in the effluent
Hydraulic retention time
3verflow rate
Sludge recycle ratio
Recycle ratio
Pump pressure head
Pump efficiency
Residence time
Solids load
Concentration of sludge before thickening
Concentration of sludge after thickening
Residence time
Volatile solids reduction
Residence time
Solid load
Concentration of sludge before thickening
Concentration of sludge after thickening
Operating time
4,000 mg MLSS/1
0.2 kg N-N03/kg VSS-d
2.5 kg BOD5/kg N-N03
0 mg/1
15 W/m3
0.4 kg VSS/kg COD soluble
4,000 mg MLVSS/1
4 d
2 mg/1
4.6 kg 02/kg N-NH4
1.55 kg 02/kWinst-h
1.26 kg BOD5/kWinst-h
15 mg/1
256 mg/1
4 h
0.4 m/h
1
13-3
0.2 bar
0.70
38 h (1.58 d)
30 kg SS/m2-d
1% (' ' 10 kg SS/m3)
3% (~30 kg SS/m3)
480 h (20 d)
50$
38 h (1.58 d)
63.6 kg SS/m2-d
1.8% ("V18 kg SS/m3)
4% (AX 40 kg SS/m3)
8 h/d
£ Biomass characteristics: VSS/SS = 0.80; Nitrogen ponderal fraction = 0.075
686
-------
TABLE 10. DIMENSIONING PARAMETERS FOR ALL COMPONENT UNITS RELATED TO COKE
PLANT WASTEWATER TREATMENT
Unit '
Equalization
tank
Pumping
station
Anoxic reactor
Aerobic reactor
Settling tank
Pumping station
Pre-thickner
Aerobic-
digester
Drying bed
Parameter
Hydraulic retention time
Specific stirred power installed
Pump pressure head
Pump efficiency
Biomass concentration
Denitrification rate
Specific phenol consumption ratio
Specific stirring power installed
Net growth yield
Biomass concentration^
Nitrification rate
Oxygen required for nitrification
Efficiency of oxygenation
Overflow rate
Hydraulic retention time
Recycling ratio
Pump pressure head
Pump efficiency
Residence time
Solid load
Concentration of thickned sludges
4 h
15 W/m3
0.6 bar
0.7
3,000 mg SS/1
0.05 kg N03-N/kg VSS-d
1 . 7 kg phenols/kg NO^-N
15 W/m3
0.2 kg VSS/kg phenols
3,000 mg SS/1
0.25 kg NH4-N/kg VSS-d
4.6 kg 02/kg NH4-N
1.6 kg 02/kW'h
0.5 m/h
7 h
2
0.3 bar
0.70
20 h
30 kg SS/m2-d
20 kg SS/m3
Residence time 12 d
Specific oxygen consumption ratio 2.3 kg 02/kg VSS
Mechanical efficiency of oxygenation 1.6 kg 02/kW'h
Volatile solids reduction 50%
Specific area
Equivalent inhabitants
¥ Biomass characteristics: VSS/SS = 0.85; Nitrogen
200 m2/l,000 inhab.
0.08 kg SS/inhab.
ponderal fraction = 0.085
687
-------
TABLE 11. COST FUNCTIONS FOR CIVIL WORKS AND ELECTROMECHANICAL EQUIPMENT
Operating units
Equalization tank
Pumping station
Anoxic reactor
Aerobic reactor
Settling tank
Recycling pumping station
Thickner
Aerobic digester
Anaerobic digester
Drying bed
Beltpress
Electr. equip, and hydr. network
Accessory works
Cost functions
Civil works Eleotromech .
C
C
C
C
C
C
C
C
C
C
= 0
= 0
= 0
= 0
= 1
= 0
= 0
n
= 2
n
.308 v°
.308 v°
.308 v°
.882 V°
.162 v°
.37 V°
.204 V°
.165 s°
• 97 Q +
.11 Cg
.86
.86
.86
.74
• 71
.84
.916
.85
64.8
C
C
C
C
C
C
C
C
C
C
C
= 3-
o
= 3.
= 3-
= 2.
o
= 3.
= 2.
= 0.
= 13
o
332
566
332
332
702
566
668
5
370
.47
23
equipment
W°
Q°
wo
W°
A°
QU
Au
W°
VU
Q
Ct
.82
.82
.82
.88
.62
.86
.88
.853
+ 114-5
A: transversal area; C: cost (10^ Italian liras); Cg: total plant cost (10"
Italian liras); Ct: total cost plant without the accessory works (10" Italian
liras); Q: flow rate (m3-h~M; S: drying surface (m2). V: volume (m3);
W: power installed (CV).
function of the relative volumes while for electromechanical equipment, the
costs are expressed as a function of installed power. The functions in
Table 11 have been obtained from correlations with a statistical processing
of cost data from 35 treatment plants throughout Italy and from design esti-
mates (3).
Costs are referred to October, 1982.
Table 12, which summarizes total plant costs, shows the figures of
3,434-lo6 and 1,638-106 Italian liras for slaughter-house and coke-oven
wastewaters, respectively.
688
-------
TABLE 12. CAPITAL COSTS (106 ITALIAN LIRAS)
Operating units
Equalization tank
Pumping station
Anoxic reactor
Aerobic reactor
Settling tank
Recycling pumping station
Pre-thickner
Aerobic digester
Anaerobic digester
Post-thickners
Beltpress
Drying beds
Electr. equip, and hydr. network
Accessory works
Total plant cost
Slaughter-house
wastewater
Civil
works
-
-
129
249
108
-
92
-
216
42
82
-
918
-
378§
1,296
Electron).
equipment
-
-
43
620
65
67
128
-
242
80
190
-
1,435
703-
-
2,138
3,434 ( 1.7-106 $)
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
1 ,
1
I
1
I
I
1
Coke plant
wastewater
Civil
works
40
-
280
168
89
-
10
13
-
-
-
20
620
-
180"
800
Electrom .
equipment
H
8
91
254
82
13
31
10
-
-
-
-
503
335+
—
838
1,638 ( 0.8-106 $)
* 0.23(918+1,435+703) = 703? + 0.23-(620+503+335) = 335? 0.11-(9l8+l,435+
+703+378) = 378; " O.ll-(620+503+335+180) = 180.
Running costs
Running costs have been broken up as follows: staffing, electric power,
operation and maintenance and chemicals (Table 13). In further detail:
- Electric power has been calculated consistently with the value chosen for
the dimensioning parameters for each component units, considering also the
data reported in specialized literature (4), (5). The specific cost of
electric power has been assumed equal to 80 Italian liras/kWh.
- Operation and maintenance costs have been assumed equal to 3% of the
electromechanical equipment.
689
-------
The alkali consumption to neutralize the acidity released during nitrifica
tion, and the phosphorus need for bacteria metabolism resulted equal to 5
NaOH /m3 of wastewater and 63 g P 2 /m3 of wastewater, respectively. The
polyelectrolyte consumption for chemical conditioning of sludge has been
taken equal to 3 kg /t of SS.
TABLE 13. RUNNING COSTS (106 TTATJA.N LTRA/YR)
Item
Staffing
Power
Operation and Maintenance
Chemicals
Total
Slaughter-house
wastewater
258
280
64
14
615
(~0.3-106 $/yr)
/
/
/
'/
',
i
Coke plant
wastewater
168
113
25
134
440
("0.2 $/yr)
Overall Costs
The overall costs for treatment plants as outlined above (including
amortization and running costs) are reported in Table 14.
Amortization costs were determined on the basis of 15 years for the
electromechanical equipment and 30 years for the civil works and on an annual
interest on capital of 10%.
o
The specific costs, per mj of wastewater and per kg of incoming pollutant
are reported in Table 15.
250 Italian liras/kg
23,400 Italian liras/kg, as H-
37,000 Italian liras/kg
690
-------
TABLE 14. OVERALL COSTS (106 ITALIAN LIRAS/YR)
Item
Amortization costs:
civil works
electromechanical equipment
total
, Running
Overall costs
Slaughter-house
wastewater
137
281
418
615
1, 033(^0. 5 'I06$^r
Coke plant
wastewater
85
100
195
440
635(^0. 3 -lo6$/yr)
TABLE 15. SPECIFIC COSTS
Slaughter- house
Coke plant
Flow rate
Equivalent inhabitants
with respect to COD
with respect to NH^-N
Total cost (10^ Italian liras/yr)
Specific costs
Italian liras/m^
Italian liras/kg COD
Italian liras/kg
4,000
120,000
100,000
1,033
$/yr)
708 ( 0.3'$)
240 ( 0.1-$)
2,360 ( 1.2-$)
250
14,000
80,000
635
(• 0.3-106 $/yr)
6,960 ( 3-5-$)
1,200 ( 0.6-$)
1,831* ( 0.9-$)
-«- With reference to nitrogen removal equal to 36%
691
-------
In the case of slaughter-house wastewaters, Table 15 shows how these
costs are comparable to the costs related to urban sewage of the same strength
and with both BOD and nitrogen removal.
The specific cost referred to coke-oven wastewater is apparently very
high but it must be pointed out that conservative figures have been assumed
for design calculation, and consequently costs are also over-estimated.
Furthermore, treatment costs may be reduced by ammonia stripping before bio-
logical treatment; this would be facilitated by high temperature (~25°C),
high pH (~9.5) and by favourable free ammonia/combined ammonia ratio ( 40%)
of the raw discharge.
Lastly, it is worth observing that the specific cost of about 7,000
Italian liras per m^ for wastewater drops to less than 2,000 Italian liras
per t of coke produced. Furthermore, if we consider that in steel proces-
sing the most highly polluting stage is coke production, the cost is seen to
be greatly reduced if it is referred to each unit of steel produced,
UPGRADING CONVENTIONAL DIGESTERS BY FEEDING COMBINED SLUDGE AND CONCENTRATED
SOLUBLE WASTEWATERS
In most European countries many conventional digesters for sludge stabili-
zation operate under underloaded conditions. One of the probable reasons for
this situation is the overestimation of polluting load for the water works
or/and overestimation of sludge production at the design stage.
On the other hand many of the (agro) industrial wastes to be treated are
concentrated in organics, poor in nutrients and hence unfit for direct biolog-
ical treatment.
Mathematical modeling and experiments have shown that the addition of con
centrated wastewaters to underloaded once-through concentrational sludge diges-
ters is beneficial because existing works are upgraded by a "free of charge"
treatment of the concentrated wastes which could otherwise be treated and/or
disposed of in new wastewater plants.
Using mathematical models, I.R.S.A. researchers have investigated the
operation of anaerobic digesters as a function of the wastewater composition,
namely the ratio between suspended solids and soluble COD.
Although well known in practice, it has been further verified, that the
loading rate of a digester fed on suspended solids is relatively low because
of limitations on: a) the cell residence times (at low feed suspended solids
concentrations) which lead to wash-out of the microorganisms or b) maximum
692
-------
sludge concentration in the reactor. On the other hand, loading rates for di-
gesters fed on prevalently soluble wastewaters can be increased to much
higher values
One unforeseen aspect of the modeling study was that it is possible to
increase the loading rates of digesters fed on suspended solids if the extra
loading is provided as soluble substrate, because the increase of biomass con-
centration due to the latter substrate does not appreciably alter the total
sludge concentration in the reactor.
This functional relationship can easily be seen in figure 15, where the
sludge concentrtion in the reactor is plotted vs the sludge residence time
for a given voltatile suspended solids loading rate Lsa and for different
values of the soluble COD loading rate Lsb.
50
m
\
en
00
00
Lsa = 1 Kg VSS/m3d
20
40 60
SRT(d)
80
Figure 15. Relationship between solids concentration and solids
retention time of fixed loading rates.
693
-------
Taking into account these considerations and the fact that in Southern
Italy there are several oversized sludge digesters, as well as the urgent
need to treat or dispose of olive oil mill wastewaters, an experimental re-
search on the combined digestion of sewage sludge and of these highly pol-
luting agroindustrial effluents has been started by I.R.S.A.
Two 25 liter digesters are being tested. The first one is fed on sewage
sludge only while the second one is fed on both sewage sludge and olive oil
wastewaters. A mixture of primary and secondary sludges from the Bari water-
works is used as suspended solids substrate.
Preliminary results are reported in Table 16.
It is worth noting that specific gas production in reactor II fed on
sludge and olive oil effluents increased by about 75% with respect to
reactor I without any appreciable negative influence on the anaerobic
decomposition of the sludge.
The experiments will be continued on different loading conditions for the
two substrates on order to optimize the overall treatment process that will
then be tested on real scale plants to verify its application potential.
SLUDGE MANAGEMENT
SLUDGE MECHANICAL DEWATERING
Introduction
In municipal wastewater treatment processes residual sludges amount to
approximately \% by volume of the treated sewage, but in big plants their
treatment and handling account for up to 50% of the total operating costs. It
is then evident the importance of analysing the different technological alter-
natives appropriate for transforming a liquid matter (2-3% in concentration)
into a material to be disposed of without causing any damage to the receiving
body and eventually reused.
Among the sludge treatment processes, mechanical dewatering is considered
to be the most delicate and expensive one and is utilized in the majority of
the cases. The mechanical dewatering process can take place by filtration or
centrifugation; the various technologies available have well marked features
that render them capable to meet different requirements and suitable for dif-
ferent utilizations.
Characteristics and problems of sludge mechanical dewatering processes
are reviewed in this paper.
694
-------
C31
to
in
TABLE 16. ANAEROBIC DIGESTION OF SEWAGE SLUDGE AND OLIVE OIL WASTEWATERS.
CHARACTERISTICS OF THE FEED REACTOR I (SEWAGE SLUDGE ONLY):
COD = 56 kg/m3; COD FILT. =3.6 kg/m3; SS = 32.5 kg/m3;
VSS = 25.3 kg/m3.
REACTOR II (SLUDGE + OLIVE OIL WW): COD = 66.9 kg/m3;
COD FILT. = 27.6 kg/m3; SS = 33.5 kg/m3; VSS = 26 kg/m3.
Reactor I
Reactorll
Mean working
conditions of
reactors
kgCOD
2,6
4,2
kgVSS
1,2
1,2
i c
d
21
16
Gas
production
J^TTd
0,51
0,89
CH4$
62
58
Reactor outlet
pH
7,6
7,3
COD
inifil.
kg 02
23
30
COD
filt.
kg 02
0,6
6,5
SS
kg
21,5
22,8
VSS
kg
14,5
15,6
TVA
kg AC
m3
0,2
1,45
alkali
nity-
kg
m3
i\
2,95
3,5
Efficiency
COD
unfil
tered
%
59
55
-
34
32
-<
43
40
-------
Characterization and conditioning
One of the essential conditions to tackle the problem is the knowing of
the sludge characteristics.
Many laboratory tests are available for sludge technological characteri-
zation; the most often utilized parameters are the solid content (total, sus-
pended, volatile), the density of the dry solids (1.3-2.1 g/cm3), the pH,
the alkalinity (up to 6,000 g/m3), the SVI (Sludge Volume Index), the speci-
fic resistance to filtration (values of 1.1012 m/kg at 4-9 N/cm2 are general-
ly required for good filtration), the compressibility coefficient and the CST
(Capillary Suction Time; values of about 10s with 10 reservoir generally
mean good dewaterability).
These parameters, easy to determine, are indirect measurements of funda-
mental properties (e.g. particle size distribution, Zeta potential, rheologi-
cal properties) which would be necessary to measure in order to promote a
real technical innovation. The influence of these properties on the condi-
tioning and dewatering operation was studied by Campbell et al. (6) and Karr
and Keinath (7).
Dewatering is generally preceded by chemical or physical conditioning in
order to improve the sludge dewaterability.
In chemical conditioning a destabilization as well as a flocculation can
be distinguished. Reagents can be either organic or inorganic, the latter in-
cluding iron and aluminum salts, lime and a combination of these. Lime, in
particular, may be used either as a pre-conditioner (to reduce the alkalinity
and thus the reagent consumption), or as a filter aid with an important mass-
effect in those cases where cake of a certain thickness are required (as in
the case of vacuum-filters). According to Christensen ind Style (8) iron
salts give better results when used as ferric chloride combined with lime;
this treatment, moreover, is suitable (pH>12) for sludges to dispose on land-
fill. Aluminium chlorohydrate, instead, does not require the use of lime
since it does not interact with the alkalinity.
Organic reagents consist of polymeric macromolecular compounds which are
characterized by monomer type, molecular weight, ionic charge and hydrolysis
degree.
696
-------
The conditioner type and dosage can be assessed in laboratory by general
tests (jar-test, specific resistance to filtration, CST, etc.) and specific
tests for each type of dewatering technology (filter-leaf, drainability, floe-
strength, ecc.) which are in many cases useful to predict full-scale equip-
ment performances. In the following the main specific tests are briefly out-
lined .
Filter-leaf allows to simulate in laboratory the phases of a vacuum-
filter cycle. Methods for predicting beltpress performance have been
proposed by Baskerville et al. (9) and Heide et al. (10); the first one
consist in a series of drainage tests and one pressure test with a piston
press, the second, uses a Modified Filtration Test (MFT) to give an impres-
sion of the final dry solid content and of the rate of dewatering. CST
measurements at 1,000 rpm stirring with standardized stirrer may be
employed to obtain information about the optimal conditioner dosage for
centrifugation (Mininni et al. (11); measures of the Theological properties
utilizing a modified rheometer (12, 13) give indications similar to that
obtainable from the above mentioned tests, while measures of sludge con-
sistency (penetrability) and centrate concentration (14) have not provided
satisfactory results with activated sludges. When sludge flocculation is
necessary, it is suggested (15) stirring at about 100 rpm for 10-15 minutes
followed by stirring at 30 rpm only to avoid sedimentation.
Physical methods include thermal conditioning, freezing and the use of
inorganic admixture.
Thermal conditioning involves heating of sludges at a temperature of
180-220 °C for 30-90 minutes. With a mixed sludge it is possible to obtain a
high reduction of the specific resistance to filtration operating at 210 °C
for 30 minutes (16). After such a process the supernatants or filtrates
recycled back to the plant cause a supplementary load of 15-20%; odour
problems could also arise. This process has been applied in Europe in big
plants equipped with filter-presses or vacuum-filters where it is possible to
reach cake concentration up to 50 and 40% respectively.
Conditioning by freezing generally results in a sludge that dewaters ex-
tremely well by gravity on subsequent thawing, in this case also the effluent
would exert a considerable supplementary load if recycled back to the treat-
ment plant. Energy requirements seem to iustify this process only if accom-
plished by natural means. The use of inorganic substances (ash, diatomaceous
earth, etc.) allows to obtain a mixture with improved filtering character-
istics and usually less compressible than the sludge alone, but the calorific
value is reduced. Ratios of admixtures to sludge solids typically range
from 0.5:1.0 to 2:1.
697
-------
Machine operation
A survey concerning conditioning and dewatering practice in EEC Coun-
tries (17) showed that centrifuge (as of now indicated with CF) and filter-
presses (FP) are the machines mostly used; belt-presses (BP) are utilized on
the average of 20%, while scarse interest is shown for vacuum-filters (VF),
except for France.
For the future everything seems to indicate a growing interest towards
BP and FP, while the percentage of CF can be expected to keep constant. Si-
milar trends are to be found in N. America where, at present, VF are widely
utilized (about 30$).
As far as conditioning is concerned, polyelectrolytes and iron salts,
with or without lime, are widely used, while an increasing preference is
shown toward the first ones.
Filter-press
2
Filtration under pressure (50-140 N/cm ) is the dewatering operation
which allows to obtain the highest final solid concentrations. The schematic
section of a traditional fixed-plate filter is shown in Figure 16.
The operating variables affecting the process are: pressure, filtration
time, thickness of chambers and type of cloth. Ferric chloride, with or with-
out lime, and aluminium chlorohydrate are used for conditioning; the use of
organic polyelectrolytes has been considered (18) also in view of the savings
brought about by the elimination of the flocculation tank, but care must be
taken since an overdose would cause cloth blinding. Typical results of
filter-pressing are reported in Table 17.
Plate FP operation requires a great deal of labour for filter opening
and cleaning; moreover the filter yield is low compared to BP and VF. Experi-
mental tests (15) showed an average yield of 1.5 kg/m^.h at 147 N/cm^ and 1.0
at 69 N/crn^ with an average pressing time of 2-3 h, beyond which filtrate
flow rate gets down to very low values (~ 4 1/m^h).
Different systems have been introduced in order to overcome these incon-
veniences; the automation of plate movement and cloth washing have made pos-
sible a reduction of the costs due to labour, while it has been possible to
increase filter yield by the membrane FP (see Figure 16). Parallel tests con-
ducted on chemical sludge conditioned with lime ( 23 ) indicated that
membrane FP dewater satisfactorily at lower lime dosage and with a greater
yield (2.0-3-5 kg/m2h). Other tests (15) indicated that mixed
sludges conditioned at 19.6% of lime and 6.5% of ferric chloride reach
698
-------
Figure 16. Schematic view of a fixed-plate filter-press (oi) and a membrane
press (ft): I filtration phase, II compression phase.
A: feed sludge; B: filtrate; C: pressurized air or water;
1: cloth; 2: soft rubber membrane; 3= cake under compression;
4: moulded rubber body.
699
-------
TABLE 18. FILTER-PRESS OPERATING DATA
Input
Sludge type (sludge cone.
volume
T)
X
•H
fe
volume
H
Variat
Raw Primary. U.S. EPA (19)
Digested Prim. Parkhurst
et al. (20)
Raw Prim. + Activ. U.S.
EPA (20)
Raw Prim. + Activ. White
and Baskerville (21)
Dig. Prim. + Activ. U.S.
EPA (19)
Dig. Activ. Spinosa and
Mininni (22)
Raw. Prim. + Activ. U.S.
EPA (19)
Dig. Prim. + Activ. (U.S.
EPA (19)
5-0-10.0
3.8- 4-0
1.0- 6.0
4.6- 7.6
3.5- 5.0
4-4- 5.6
4.0
2.5-6.4
Cake
cone .
45
23-37
45
27-41
42
37-42
40
36-50
Time of
filtration
(min. )
90-120
60-180
150
290-390
-
240-360
Yield
(kg/m2h)
4-4
3.0-9.8
Conditioner dosags
FeCl3
40-60
40-60
50-60
-
27
—
50
40-90
CaO
100-140
200
100-120
-
170
—
150
110-290
Alum ,-Chlor
(kgA!203/t)
o
o
-------
a final cake concentration of 38.7%? a yield of 2.4 kg/m h with 17 minutes
of pumping at 69 N/cm2 and 18 minutes of pressing at 147 N/cm2 was obtained.
The most accepted method of generating design information is to operate a pi-
lot scale plant; being this not always possible, it should be useful to have
methods to predict the industrial FP performance. The prediction of pressing
time on the basis of the well known equation developed by Jones provides
values equal to about 40% of the actual ones. Tests carried out with pilot
scale FP have made it possible to develop a new model which allows to corre-
late the coefficients a and b of the equation expressing the filtrate flux
vs time (4 = a . t^) with pressure, specific resistance and input sludge
concentration. Once a, b, the chamber volume, the filtration surface and the
dry solids density are known, it is possible to estimate the values of the
yield and cake concentration.
A new theory of filter pressing has been developed by Hoyland et al.
(24).- A small micro-processor programmed with the theory, which is an exten-
sion of the classical one of parabolic filtration, can monitor the progress
of any filter pressing and, in its later stages, predict the residual press-
ing time required to produce a cake of a given quality.
Belt-press
BP have been recently introduced into the specific field of sludge dewa-
tering.Dewatering takes place through drainage and compression; moreover, in
the final zone, sludge undergoes also a shearing action due to the relative
movement of the two belts. A schematic section is reported in Figure 17.
//t»v
Figure 17. Schematic view of a belt-press.
A: feed sludge; B: dewatered sludge? C: filtrate.
701
-------
The operating variables affecting the machine performance are: belt
speed, the pressure exercised on the belts in the compression zone and the
specific sludge flow rate (m^/h-m); this last variable is limited due to the
need of avoiding lateral leakage of the sludge. High speed of belts allows to
operate at higher capacity values, but a lower final concentration is
obtained. In practice, the belts operate at speed ranging between 50 and 100
m/h with a sludge flow rate of 2-5 m^/h'm. For good machine operation, it is
advisable to feed the sludge at a concentration not lower than 3-4%. Special
care must be taken in belt washing: rinsing water flow rates of 50-200% of
that of the sludge at a pressure of 40-60 N/cm^ are reported by Eckenfeder
and Santhaman (25) but higher values (up to 10 nrVh'm) are not uncommon.
Conditioning is carried out by polyelectrolytes with mixing immediately
before the drainage zone. Typical results are reported in Table 18 .
TABLE 18. BELTPRESS OPERATING DATA, U.S. EPA (19); IMHOFF, (26)
Sludge type
Raw Primary
Raw Activated
Raw Primary + Activated
Aerobic Digested
Anaerobically Digested
Thermal Conditioned
Input Sludge
concentr .
(0?\
\/o)
3 -10
0.5 - 4
3 - 6
1 - 8
3-9
4 - 8
Cake concentr .
(%}
25 - 44
12 - 32
20 - 35
12 - 30
18 - 34
38 - 50
Polyelectrol.
dosage
(kg/t)
0.5 - 4.5
1.0 - 6.0
0.6 - 5.0
0.8 - 5.0
1.5 - 4-5
—
Tests carried out (27) with pilot machine (belt width
0.5 m) on sludges from slaughter house wastewater enabled to correlate dewa
tered sludge concentration C^ (%) with belt speed (m/h), input sludge flow
rate Q (m^/h) and initial concentration CQ (kg/m^) with the equation:
Ck = 76.54 -
having a correlation coefficient of 0.92. The input specific flow rate ranged
from 1.2 to 3.4 m^/hm.
702
-------
Centrifuge
The type of machine mostly utilized for sludge centrifugation consist of
a cylindrical-conical bowl shell with an internal Archimedean screw (the
scroll) which revolves at a slightly lower speed. The solid liquid separa-
tion takes place like sedimentation, but at g values up to 3000. A centrifuge
schematic section and some typical results are reported in Figure 18 and
Table 19, respectively.
A •
Figure 18. Schematic view of a bowl centrifuge.
A - feed sludge; B - dewatered sludge;
C - centrate
The operating variables which the performance of the machine depends on
are: bowl speed, liquid ring height, bowl/conveyor differential speed and in-
put sludge flow rate. Widely accepted indications on the effects of such va-
riables are not found in literature and it is commonly known that for some of
them opposite results may also ensue due to values of other variables. For ex.
an increase of the differential speed generally causes an increase in solid
recovery, but under certain conditions (low liquid ring volume, sludge with
a low floe strength) the results might be the opposite due to the high turbu-
lence induced by the scroll which determines the breaking off of the floes
and their resuspension.
703
-------
TABLE 19. CENTRIFUGE OPERATING DATA, U.S. EPA (19) AND EXPERIMENTAL
STATISTICAL CORRELATIONS, MININNI ET AL. (27)
Sludge type
Raw Primary
Raw Activated
Raw Primary + Activated
Digested Primary +
Activated
Thermal Cond. Prim. +
Activated
Feed
cone .
(%)
5- 8
0.5- 3
4- 5
2- 4
4- 7
9-14
13-15
Cake
cone.
(%}
25-36
28-36
8-12
18-25
15-18
17-21
35-40
29-35
Cond.
dosage
(kg/t)
0.5-2.5
0
5-0-7.5
1-5-3-5
3-5-5.0
2.0-4.0
0
0.5-2.0
Solid
rec.
(50
90-95
70-90
85-90
90-95
90-95
90-95
75-85
90-95
bl b2
Type equations: Y = axj X2
bn
y
W)
"d
^watered sli
concent.
n
T* b
•O O
CO O
^«
Slude
type
1
2
3
4
5
6
4
5
6
Coeff .
a
73.75
81.79
61.25
1.22
11.97
0.0122
93-95
397.30
96.78
Exponents of x^ = ....
xi = tb
(s)
0.215
0.203
0.244
0.123
0.092
0.230
hlr
(mm)
0.273
0.093
0.263
-0.056
- 0.272
0.399
GSU
—
0.717
0.084
1.745
—
—
—
CO
(rpm)
—
0.313
0.399
0.311
0s
(kg/In)
-0.946
- 1 . 594
-0.493
t^: sludge resid. time on the beach; h^r: liquid ring height; Csu: cone, after
2 h settling in 11 cylinder; CO : differential speed; 0S: solids input flow
rate/liquid ring volume (solids flux); 1: 4>8% Aerob. Dig. Activated; 2: 3-2%
Aerob. Dig. Activated with dephospation by A^SO^K; 3: 4-5% Aerob. Dig.
Activated with dephospatation by FeSO^ 4: 0.7% Aerob. Dig. Activated using
pure 02; 5: 1.5% Aerob. Dig. Activated using pure Q£; 6: 2.1% Aerob. Dig.
Activated using air.
704
-------
To clear up the aspects linked to the solid/liquid separation mechanisms
in a centrifuge, pilot scale tests have been carried out with different kinds
of sludges(19). From the statistical correlation of the results obtained it was
evidenced that the most significant variables influencing the dewatered
sludge concentration are the sludge residence time on the beach (which is
correlated to the differential speed through the beach length and the scroll
pitch) and the liquid ring height. As far as solid recovery is concerned,
similar relationships have been looked for, but only with liquid ring heights
higher than 11 mm (bowl diameter 151 mm) good correlations were obtained; the
differential speed and the flux of solids (referred to liquid ring volume)
fed in the centrifuge resulted the most significant variables. Coefficients
and exponents experimentally obtained are reported in Table 19. Lower bowl
speed values corresponding to 500-800 g bring about advantages in lowering
power consumptions, noise, maintenance needs, floes mechanical stress and,
then, conditioner consumption.
It must be kept in mind that, in order to guarantee a good performance
and a long life of the machine, coarse or abrasive materials should be
avoided, while skilled labour must be employed for maintenance. The advan-
tage of this technology consists above all in the fact that the solid/liquid
separation occurs in a place completely isolated from the outside and that
the equipment size is limited.
Selection criteria
In treatment plants great care has to be taken in the proper selection
of the dewatering machine from which depends the good performance of the sub-
sequent treatments (incineration, composting, etc.) and the easyness and
cheapness of disposal.
The most important items to be considered in selecting the dewatering
machine are the following:
concentration of the dewatered sludge;
volume of sludge to dewater;
characteristics of the sludge;
investment costs;
operational costs;
treatment of liquids separated during the dewatering operation.
As far as the first point is concerned, the field of application of dif-
ferent technologies is well known: CF allows to obtain a final solid concen-
tration of less than 20% with activated sludges, BP up to 30% and FP of 40%
705
-------
and even greater if sludge is thermal conditioned. The advantage of a higher
solid concentration is easily quantified either if the sludge is subsequently
carried to landfill or agricultural soil (volume to be disposed of is reduced)
or if it is incinerated (saving of auxiliary fuel). The input sludge flow
rate does not prove, in general, to be discriminating toward the various tech-
nologies since the potentiality of the dewatering machines available on the
market is very wide; in case, the plant has to be equipped with an adequate
number of units in parallel with, at least, a spare unit.
Sludge characteristics, either biological or technological, are instead
an important factor in the choice of the most suitable equipment. Parameters
and tests which is possible to utilize for characterizing sludges and asses-
sing the optimal conditioner dosage have been already mentioned; the evalua-
tion and application of the technological characterization parameters was
discussed by Spinosa et al. (29). If the sludge is not well stabilized (vola-
tile solids concentration > 70% and 0 up-take>10 mg/gSSVh) technologies apt
to keep the sludge separated from the ambient are to be preferred thus avoid-
ing any trouble to the operators; CF has this requirement.
Another aspect to be taken into account is the area occupied by the de-
watering equipment because dimensions are very important in the costs of
i
civil works. In Figure 19, the area required for different machines as a
function of the feed sludge flow rate is shown; the advantage of a more
compact machine is then made up by a lower final concentration.
Operational costs are heavily affected by labour ones; as already men-
tioned, FP operation, carried out with traditional machines, requires
considerable personnel being the working cycle intermittent, while CF as well
implies high personnel costs due to the fact that skilled one is required
for maintenance. From this point of view, it is then evident the advantage
of BP.
Another important feature of dewatering machines is the efficiency of
the solid-liquid separation which is good for FP (> 95%), intermediate for BP
(around 95%) while with CF lower values (<95%) are generally obtained. Since
the liquid separated after dewatering is recycled back to the treatment plant,
the additional load brought about by this, either in terms of solids or orga-
nic matter, is not negligible and could causing the bad operation of the
sewage treatment work; from this viewpoint FP has to be preferred.
Design criteria
The designing of dewatering equipment is generally based on empirical
criteria derived from experience, rather theoretical developments of general
applicability since modelling of filtration and centrifugation processes is
706
-------
1000 Q(m3/d)
Figure 19. Area occupied by dewatering machines vs wet sludge flow rate
(a) centrifuge, (b) belt-press, (c) filter-press
Design data:
m3/d 20 50 100 500 1000
h oper./d 88 8 12 24
n of units 1 1 2 (n + 1 spare)
very complex and it is not possible to reach functional relationship, solved
in finite terms, between the dependent variables (cake concentration, solid
removal efficiency) and independent ones (input sludge characterization
parameters, operating variables of machines).
For FP designing it is necessary to determine the chamber volume V for
treating a daily amount Q of sludge having a concentration C :
V =
Q Cf
707
-------
where:
n = number of daily
filtration cycles;
C = concentration required for the cake, weight fraction;
n = cake density.
To calculate this volume it is essential to know the concentration C,
K
obtainable after a certain time of filtration; it has therefore to carry out
tests on pilot scale. As already mentioned, it is possible to estimate theo-
retically Ck as a function of time and pressure (20); estimated cake concen-
trations and actual ones for several cases are compared in Figure 20.
50
o
u
30
20-
to
10
20
30
50
Figure 20. Comparison of calculated cake concentrations and observed
ones
a) IRSA-CNR (l) tests; b) IRSA-CNR (I) tests; c) WRC (UK)
tests; d) TNO (NL) tests.
As far as BP is concerned one often refers to values taken from expe-
rience and that, in particular, are referred to the wet sludge flow rate
which can be treated per unit of belt width. Data available in literature
708
-------
-J2-
E
•£•10-
cr
8-
6-
4-
2-
A A
a
a
o 1
D 2
* 3
v 4
A 5
• 6
• 7
0 2 4 6 8 10 12
C0(%)
Figure 21. Sludge specific flow rate in belt-pressing vs initial
concentration.
1) Imhoff (26); 2) Baskerville et al. (31); 3) Sibamat
belt-press tests; 4) Zeper and Pepping (37); 5) Hansen
and Budgaard-Hansen (33); 6) Sernagiotto (34); 7)
Ecomacchine (35).
(Figure 21) are very discordant thus making difficult to draw general conclu-
sions; it appears however to be appropriate to consider values not higher
than 4 m^/h-m, but a value between 2 and 3 seems to be on the safe side in a
stage project. Due to the wide variation in reported results it would stress
the need to conduct pilot-scale tests before specifying the size of BP.
Designing of a CF is generally made by utilizing the theory of 2 (14)
being:
Q, Qa
2, 2,
where Q is the flow rate and 2 a peculiar characteristic of the equipment
representing the area which a gravity sedimentator should have in order to
obtain the same solid recovery; subscript 1 is referred to a pilot machine
and subscript 2 to an industrial one.
709
-------
Tests are carried out to determine sludge flow rate Q , which can be
treated by the pilot CF having a known.2, characteristic with a solid liquid
separation efficiency not lower than 80%; the above equation gives then the
characteristic 2^ of the industrial CF for treating a flow rate Q2 . This
procedure, however, only accounts for liquid loading while the movement of
solids out of the machine is not considered; the 2 concept (14) allows to
estimate the solids handling capacity. The lowest rate (liquid or solid) is
then to be considered the limiting factor and must be used for scale-up.
Consumptions and costs
It has been dealt with the different aspects characterizing the various
dewatering technologies and which have to be taken into consideration in or
order to select the proper dewatering equipment.
In the absence of specific requirements the choice should fall upon the
cheapest alternative.
Cost item to consider are the following:
Cost of installation
electromechanical equipments
civil works
Cost of operation
amortization
electric power
labour
maintenance
chemicals
Costs due to the outputs
dewatered sludge disposal
biological treatment of the liquid (filtrate or centrate)
separated during dewatering.
Just an example, Table 20 shows the costs for dewatering a 4% digested
mixed sludge produced in a sewage treatment plant for 100,000 inhabitants;
figures considered in the cost analysis are summarized in Table 21. As for
calculation of plant costs,up-dated relationships by Beccari et al. (36)
have been taken into consideration.
710
-------
TABLE 20. COST COMPARISON OF DEWATERING SYSTEMS FOR A 100,000
INHAB. PLANT
Cost item
-* Civil work amortization
";H;" Electrom . eq. amort.
-:;-;:-;;- Maintenance
+ Electric power
++ Operation personnel
+++ Chemicals
§ Cake disposal
§§ Biol. treat, of filtrates
Total
(Lit/cap, y)
Filterpress.
(MLit/y)
15.04
86.89 101.93
14.80
5.08
18.25
35-37 73-50
93.98
10.95 104.93
208.36
2.800
Beltpressing
(MLit/y)
9-36
117.14 126.50
21.59
7.05
13-69
44.71 87.04
101.51
27.37 128.88
342.42
3-400
Centrifuging
(MLit/y)
13.18
69.34 82.52
18.50
7.20
18.25
51.10 95-05
H4.36
54-75 199-11
376.68
3.800
*: Interest rate 10%, 25 years; *#: Interest rate 10% 12 y for FP, 10 y for
BP, 8 y for CF; **: 2.5% of electromech. eq. cost/y for FP, 3% for BP, 5%
for CF; +: 80 Lit/kWh; ++: 12.500Lit/h; +++: FeCl3 340 Lit/kg, CaO 60 Lit/kg,
Polyelectr. 7-000 Lit/kg; §: 17-500 Lit/t wet sludge transported? §§: 600
Lit/kg BOD treated
-"- 1 $ = 1.400 Lit.
The prevailing energy consumption for FP is due to sludge pumping; con-
sumptions for filter opening and cloth cleaning may be considered equal to
10$ of pumping ones. With a pressure of 98 N/cm2 and a 2$% efficiency the
energy required is given by:
E = 437-6 Q(kWh/y)
being Q the wet conditioned sludge flow rate (t/d).
The following equation has been taken into consideration for BP:
E = 23600 F°'74 (kWh/y)
o
where F is the flow rate (m /h) and taking into account a specific flow rate
of 3 m3/hm.
o
CF consumptions are generally between 1 and 2 kWh/m of treated sludge,
being the lower values referred to units at low speed. In calculations a
value of 1.7 has been considered as it represents an average value for
machines by Pennwalt operating at 3000-4000 rpm.
711
-------
TABLE 21. ANALYSIS OF DEWATERING EQUIPMENT OPERATION
(PLANT FOR 100,000 INHAB.)
Input dry solids* (kg/d)
Input sludge flow rate (m^/d)
Conditioners*"" (kg/d)
Conditioner solution (m /d)
Cake concentration (%)
Solid/liquid separation effic. (%)
Cake density (kg/m^)
Sludge to dispose (kg/d)
Filtrate to treat (kg.BOD^/d)
Machine design***
FP
5000
125
985
17-7
40
98
1129
14712
50
1 unit
BP
5000
125
17-5
17-5
30
95
1094
15892
125
3 units
CF
5000
125
20
20
20
90
1061
22600
250
1 unit
*: 50 g/cap.d; **: FP: 27 kgFeCl3/t$S + 170 kgCaO/tSS, BP: 3,5 kgPolyel./
/tSS, CF: 4,0 kgPoluel./tSS; ***: 8 h/d, 2 cycles/d for FP, FP chambers
volume: 6,51 m3, BP belt width: 2 m, CF: 18,1 m^/h.
To calculate costs for operation and maintenance the following values
were considered (37):
0.5 h/operational h/machine for FP and CF
0.125 " " " BP
From Table 20 it appears that filter pressing is the most convenient
system if the additional costs due to outputs are considered. Otherwise the
three machines seem to be equivalent; the total cost of only dewatering is
equal to 95-115 lit/kgSS. Dewatered sludge disposal and filtrate biological
treatment involve additional costs of 60% for FP and BP and 112$ for CF.
Technological progress
The operating problems the various dewatering equipments present forced
manufacturers to search for any kind of technical and economical solutions
apt to overcome them.
Manufacturers have shown a great interest toward FP and have introduced
innovations to extenuate the inconveniences due to non-continuous operation
and low yield.
712
-------
Improvements for BP concern the route of the cloths (with presence of
many rollers of different diameter), the drainage phase and the belt washing.
Low speed CF allow, above all, a reduction in power and conditioner con-
sumption. In Equicurrent CF the settled solids are not disturbed by the oppo-
site movement of the liquid and solids are collected throughout the drum
length thus bettering compaction and reducing conditioner demand.
Conclusions
What previously discussed can be so summarized:
Filter-press, belt-press and centrifuge are the machines most widely used in
sludge mechanical dewatering.
With filter-press the highest cake concentrations are obtained,but opera-
ration is discontinuous and yield low. Belt-press allows to.couple advantages
of good cake concentration and continuous operation,but problems can arise
in belt washing.
Centrifuge has a lower performance, but the operation is simple and,
above all, the liquid-solid separation takes place completely isolated from
the out-side.
Filter-pressing is the most convenient system if costs for cake disposal
and filtrate or centrate treatment are considered; otherwise the three machi
nes seem to be equivalent.
The main general features of filter-presses, belt-presses and centrifu-
ges are reported In Table (22).
From a general point of view efforts in the future have to be addressed
in assessing simple and reliable laboratory methods for selecting conditioner
agent type and optimal dosage. Moreover, it seems necessary to go deep into
the knowing of a few sludge fundamental properties and of the theoretical
modelling of filtration and centrifugation processes if a real technical
innovation has to be achieved.
713
-------
TABLE 22. DEWATERING EQUIPMENT FEATURES
Filter-press
Belt-press
Centrifuge
Flow rate
range per
unit
(m3/h)
0.1 - 35
1.0 - 25
0.5 - 80
Cake
concentrat .
(af\
\/o}
30
20 - 30
20
Solid/liquid
sep.effic .
(%)
95
about 95
95
Area
requirement
high
med - high
low
Energy
demand
low
medium
med - high
Typical
advantage
high solid/liquid
separ. efficiency
low personnel
requxrem.
dewatering oper.
separated from
ambient
-------
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715
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29. Spinosa, L., Aveni, A., Lamarca, V. Valutazione ed applicazione dei
parametri di caratterizzazione tecnologica dei fanghi. Seminario sul
tema Disidratazione meccanica del fanghi. I.R.S.A. - C.N.R., Bari,
November, 1982.
30. Mininni, G., Spinosa, L., Un nuovo modello per la valutazione delle
prestazioni della filtropress. Seminario sul tema Disidratazione mec-
canica dei fanghi. I.R.S.A. - C.N.R., Bari, November, 1982.
31. Baskerville, R.C., Komorek, J.A., Gale, R.S., Effect of operating vari-
ables on filter-press performance. Journal of the Institute of Water
Pollution Control, 4, 1971.
32. Zeper, J., Pepping, R., Handling of aerobic mineralized sludges by
centrifuges and belt-press filters. Water Research, 6, (4/5), 507.
1972.
33. Hansen, T., Bundgaard-Hansen, E., Comparison of centrifuge and filter-
belt press in wastewater sludge dewatering. Progress in Water Technol-
ogy, 8, (6), 361. 1977.
34. Sernagiotto S.p.A. Prove di disidratazione su fanghi residui da im-
pianti di depurazione acque di caseificio e allevamento suinicolo.
Private communication. 1978.
35. Ecomacchine s.r.l. Dati di prove su impianti di depurazione. Private
communication. 1981.
36. Beccari, M., Di Pinto, A.C., Mauri, A., Passino, R., Santori, M.,
Spaziani, P.M., Costi degli impianti di depurazione delle acque di
scarico urbane. I.R.S.A. - C.N.R., Quaderno 46. 1981.
37. U.S. EPA. Sludge handling and conditioning. Report 430/9-78-002.
1978.
717
-------
JAPANESE ADVANCES
IN
WASTEWATER TREATMENT
Takeshi Kubo,
Dr. Eng., Counselor
Japan Sewage Works Agency
The work described in this paper was
not funded by the U.S. Environmental
Protection Agency. The contents do
not necessarily reflect the views of
the Agency and no official endorsement
should be inferred.
North Atlantic Treaty Organization/Committee on the
Challenges of Modern Society (NATO/CCMS) Conference
on Sewage Treatment Technology
October 15-16, 1985
Cincinnati, Ohio
719
-------
TABLE OF CONTENTS
Page
1. INTRODUCTION 721
2. MICROPOLLUTANT (TOXICS) CONTROL IN JAPAN 729
2.1 Outline of Toxics Control System in Japan 729
2.2 Toxics Control by Effluent Standards 729
2.3 Other problems of pollution Related to Toxic Substances 735
2.4 Measures Relating to Safety of Chemicals 740
3. CURRENT STATUS OF SLUDGE TREATMENT AND DISPOSAL IN JAPAN 743
3.1 Introduction 743
3.2 Improvement in the Incinerating Process for
Energy Conservation 745
3.4 Development of a Technology Producing Construction Materials
from Sewage Sludge 751
3.5 Regional plan for Treatment and Disposal of Sewage Sludge 755
4. RECENT TECHNOLOGICAL DEVELOPMENT IN WASTEWATER TREATMENT 765
4.1 Overview 765
4.2 Some Typical Examples of the Recent Technological Development . 770
5. UPGRADING OF EXISTING WASTEWATER TREATMENT PLANTS 784
5.1 Background 784
5.2 Necessity for Upgrading of Existing Wastewater
Treatment Plants 784
5.3 Tentative Guideline for Upgrading of Existing
Treatment Plants 786
5.4 Examples of Upgrading of Existing Plants 787
720
-------
1. INTRODUCTION
The sewage works in Japan started in 1880 when a sewer of about
2.5 km was constructed in the Kanda area in Tokyo after experiencing
epidemics of infectious diseases/ such as cholera, several times. Later
in 1900, the government enacted the Sewerage Law (old) to provide
sewerage systems systematically throughout the country. However, the
investment for the sewage works was not big. As of 1940, forty years
after the enactment of the law, the sewered area was merely 26,393 ha,
and the population served was 5.06 million or about 8 percent of the
total population at that time. Main purposes for the sewage works at
that time, were to prevent from flooding in urban areas and to maintain
the cleanliness in cities. Due to the increase in population in cities,
the amount of wastewater discharged increased, and therefore, it became
necessary to construct wastewater treatment plants in big cities from a
viewpoint of public health. In this connection, the secondary treatment
of sewage in major cities started rather early. The first wastewater
treatment plant with tricklig filters was constructed in Tokyo City in
1922. In succession, two plants using the activated sludge process were
constructed in Nagoya City in 1930. In 1940, 12 plants with secondary
treatment were in service.
The economic growth, particularly the growth of heavy industries,
and the concentration of population in big cities in 1950's were quite
marked posing the serious problem of river and coastal water pollution
especially around big cities. Water pollution became more serious
during late 1950's and 1960's, which was typically represented by two
tragic events, namely "Minamata" disease (an organomercury poisoning)
and "Itai-Itai" disease (a cadmium poisoning). To cope with these
situations, the relevant laws for the water pollution control were
enacted late in 1960's. The Basic Law for Environmental Pollution
Control was established in 1967; through this enactment the
environmental water quality standards relating to human health and
living environment were set up as shown in Tables 1.1 and 1.2,
respectively. In addition, such concrete steps as the preparation of. a
public hazard prevention plan were established one after another. Also,
in 1970, the water pollution control law was revised to strengthen the
effluent regulation. Through this amendment, uniform effluent standards
were established by the national government as a minimum requirement,
and also, it was guaranteed that the prefectural governments could
establish more stringent standards by their ordinances depending on the
conditions of each water body. The national uniform standards are given
in Table 1.3. At present, all of the prefectural governments have
established their own ordinances which enforce standards more stringent
than the national uniform ones. As a typical example of the overlay
standard, the effluent standards of Chiba prefecture are also shown in
Table 1.3. The prefectural governments are also authorized to set
effluent standards relating to pollutants which are not regulated by the
national uniform standards. The effluent standards for phosphorus and
nitrogen were established by the Shiga Prefecture for the Lake Biwa
basin in 1979, which is shown in Table 1.4 is an example of the
standards of this kind.
721
-------
Regarding to the pretreatment standards which are applied to the
industries discharging their wastewater into a public sewerage system, a
sewerage authority under the Sewerage Law can establish the same
standards as those applied to the industries discharging their
wastewater directly into the public bodies of water under the Water
pollution Control Law as far as the toxic substances are concerned.
Table 1.1 Environmental water quality standards relating to
human health (Dec. 28, 1971)
Item
Cadmium
Cyanide 2
Organic phosphorus
Lead
Chromium (sexivalent)
Arsenic
Total mercury
AlkyZ mercury
FCB
Standard values
0.01 ppm or less
Not detectable
Not detectable
0.1 ppm or less
0.05 ppm or less
0.05 ppm or less
0.0005 ppm or less
Not detectable
Not detectable
Notes: 1. Maximum values. But with regard to total mercury, standard
value is based on the yearly average value.
2. Organic phosphorus includes parathion, methyl parathion, methyl
demeton and E.P.N.
The sewage works actually restarted from the enactment of the new
Sewerage Law in 1958. Since the role of sewage works in the field of
water pollution control had been widely recognized, the clause, "to
contribute to the preservation of water quality in public water bodies",
was added to the purpose of the sewage works defined by the law through
its amendment in 1970. The construction of sewerage facilities has
further been promoted by the amendment. Figure 1.1 shows trends in the
investment in the sewage works in the past. Prom this figure, it is
seen that the investment in sewage works increased at a far higher rate
when compared with that of the GNP or the government fixed capital
formation. Although the investment after fiscal year 1982 declined a
little reflecting the financial condition of the Japanese government,
the investment in fiscal year 1983 remained 1.6 billion yen, which
accounted for 0.57% of the GNP. As the result this rush investment in
sewerage construction, population served has recently increased fairly
rapidly in big cities for instances, 80% in Tokyo, 99% in Osaka, 87% in
Nagoya, 72% in Kyoto, 56% in Yokohama and 46% in Hiroshima in 1984,
although its nationwide ratio still remains rather low at 33%.
Therefore, the situation of water pollution has improved considerably.
The ratio of compliance to environmental water quality standards has
become steadily better as shown in Fig. 1.2. The problem relating to
toxic substances is discussed in Chapter 2.
There still remains, however, a lot of problems in the field of
sewage works, such as sludge treatment and disposal, advanced wastewater
treatment, energy conservation and proper wastewater treatment process
for smaller scale facilities. For preventing eutrophication of lakes,
environmental water quality standards for phosphorous and nitrogen were
set up in 1982 as shown in Table 1.5. At present, the standards are
722
-------
being individually set for lakes throughout the country. Some
wastewater treatment plants which discharge effluent to this kind of
lakes have already started treatment to remove phosphorous and nitrogen
from their effluent. In this paper the recent progress in wastewater
treatment technology in Japan will be summarized.
Table 1.2 Water quality standards relating to the living
environment (rivers, lakes, coastal waters)
Coastal waters
Cate-
gory
A
B
C
0s e
Fishery class le;
bathing; conservation
of natural environment,
and uses listed in B-C
Fishery class 2,
industrial water , and
uses listed in C
Conservation of
environment
Standard values
EH
7.8-8.3
7.8-8.3
7.0-8.3
Chemical
oxygen
demand
(COD"")
2 mg/£
or less
3 mg/i
or less
8 rag/4
or less
Dissolv-
ed oxgen
(DO)
7.5 mg/£
or more
5 mg/*
or more
2 mg/£
or more
Number of
coliform
groups'*
1000 MPN/100
mi or less
-
-
N-hexane
extracts
Not
detectable
Not
detectable
-
a The standard values are based on the daily average values. (The same
applies to standard values for lakes and coastal waters.)
b At the inlet of agricultural water, pH shall be between 6.0 and 7.5
and dissolved oxygen shall not be less than 5 rag/jt. (The same applies
to standard values for lakes.)
c With regard to fisheries, classes 1, 2, and 3, the standard values for
suspended solids shall not be applicable for the time being.
d With regard to the quality of fisheries, class 1 for planting oysters,
the number of coliform groups shall be less than 70 MPN/100 ml.
e Fishery class 1: Aquatic life such as red sea-bream, yellow tail,
seaweed.
f Fishery class 2: Aquatic life such as gray mullet, laver, etc.
Notes: Conservation of natural environment: of scenic spots and other
natural resources.
Water supply class 1:
Water that requires simple cleaning treatment such as filtration.
Water supply class 2:
Water that requires normal cleaning treatment such as
sedimentation and filtration.
Water supply class 3:
Water that requires highly sophisticated cleaning treatment
including pretreatment.
Fishery class 1:
For fish such as trout and bull trout in oligosaprobic waters, and
those of fisheries class 2 and class 3.
Fishery class 2:
For fish such as fish of the salmon family and sweetfish in
oligosaprobic waters and those of fisheries class 3.
Fishery class 3:
For fish such as carp and silver carp in S-mesosaprobic water.
Industrial water class 1:
Water should be given normal cleaning treatment such as
sedimentation.
Industrial water class 2:
Water should be given sophisticated treatment by chemicals.
Industrial water class 3:
Water should be given special cleaning treatment.
Conservation of environment:
Up to the limits at which no nuisance is caused to people in daily
life (including walking by the riverside, shore, and so on).
723
-------
Table 1.2 Water quality standards relating to the living
environment (rivers, lakes, coastal waters) (Cont'd)
Lakes (Natural lakes, reservoirs, marshes, and artificial lakes or
more than 1 x 16* n3 water)
Cate-
gory
AA
A
B
C
Use
Water supply class 1|
fishery class li
conservation of natural
environment, and uses
listed In A-C
Water supply classes 2
and 3t fishery class 2>
bathing, and UBBS
listed In B-C
Fishery class 3;
Industrial water
class 1; agricultural
water, and uses
listed In C
Industrial water
class 2; conservation
of environment
Standard values9
P"
6.5-0.5
6.5-8.5
6.5-8.5
6.0-8.5
Chemical
oxygen
demand
(COD"")
I mg/i
or less
3 rag/*
or less
5 ag/i
or less
8 mg/i
or less
Sus-
pended
solids
(SS)
1 mg/i
or less
5 mg/i
or less
15 mg/i
or less
Floating
matter
such as
garbage
should
not be
visible
Dissolved
oxygen
(DO)
7.5 mg/i
or more
7.5 mg/£
or more
5 mg/i
or more
2 mg/i
or more
Number of
collform
groups
500 MPN/100 i
or less
1000 MPN/100
mt or less
-
-
Rivers
Cate-
gory
AA
A
B
C
D
E
Use
Water supply class 1;
conservation of natural
environment, and uses
listed in A-E
Water supply class 2)
fishery, clasa 1;
bathing and uses listed
in B-E
Water supply class 3;
fishery class 2, and
uses listed In C-E
Fishery class 3|
industrial water
class 1, and uses
listed in D-E
Industrial water
class 2s agricultural
water, and uses '
listed in E
/
Industrial water
class 3; conservation
of environment
pH
6.5-8.5
6.5-8.5
6.5-8.5
6.5-0.5
6.0-8.5
6.0-8.5
Bio-
chemical
oxygen
demand
1 mg/£
or less
2 mg/i
or less
3 mg/£
or less
5 mg/i
or lees
8 mg/i
or less
10 mg/i
or less
Standard
Sus-
pended
solids
(SS)
25 mg/i
or less
25 mg/£
or less
25 mg/i
or less
50 ag/i
or less
100 mg/i
or less
Floating
matter
such as
garbage
should
not be
visible.
values
Dissolved
oxygen
(DO)
7.5 mg/i
or more
7.5 mg/i
or more
5 mg/i
or more
5 mg/i
or more
2 mg/£
or more
2 mg/£
or more
Number of
coll form
groups
50 MPN/100 I
or less
1000 MPN/100
ml or less
5000 MPN/100
ml or less
-
_
-
724
-------
Table 1.3 Effluent standards
Substances related to human health
(Dnit mg/l)
Toxic substances
Cadmium and its compounds
Cyanide compounds
Organic phosphorus compounds
(parathion, methyl parathion, methyl
demeton and EPN only)
Lead and its compounds
Chromium (Vl) compounds
Arsenic and its compounds
Total mercury
Alkyl mercury compounds
PCS
National uniform
standards
0.1
1
1
1
0.5
0.5
0.005
Not detectable a
0.003
Overlay standards of
Chiba Pref.
0.01
Not detectable a
Not detectable a
0.1
0.05
0.05
0.0005
Not detectable a
Not detectable a
Items related to living environment
Item
PH
BOD, (DDM"
SS
N-hexane extracts
phenols
Copper
Zinc
Dissolved iron
Dissolved manganese
Chromium
Fluorine
No. of coliform groups
(per cc)
National uniform
standards
5.8-8.6 for effluent
discharged into public
water areas other than
coastal waters, and
5.0-9.0 for effluent
discharged into coastal
waters
160 mg/Jt (daily average
120 rag/*)
200 mg/£ (daily average
150 rag/i)
5 mg/£ (mineral oil)
30 mq/Z (animal and
vegetable fats)
5 mq/S.
3 mgj.
5 mg/je
10 mg/i
10 mg/£
2 rag/jj
15 mg/Jj
3000 (daily average)
Overlay standards of
Chiba Pref.
5.8-8.6 for effluent
discharged into public
water areas other than
coastal waters, and
5.0-9.0 for effluent
discharged into coastal
waters
25 mg/je
50 rag/*
3 mg/£ (mineral oil)
10 mg/£ (animal and
vegi table fats)
0.5 mq/i
1 mq/i
3 mq/i
5 mq/i
5 mq/i
1 mg/i
10 mq/i
3000 (daily average)
a By the term "not detectable" is meant that substance is below the
level detectable by the method designated by the Law or the ordinance.
Note: The effluent standards in this table are applicable to effluents
from industrial plants or other business places whose volume of
effluents per day is 50 m^ or more. The effluent standards for
BOD are applied to public waters other than coastal waters and
lakes, whereas the standards for COD*1" are applied only to
effluents discharged into coastal waters and lakes.
Overlay standards shown in this Table as examples are those
provided for by the ordinance of Chiba Prefecture and are applied
for food industry with a discharge of 500 m3/day or more.
725
-------
Table 1.4 Effluent standards relating to phosphorus and nitrogen
provided for by the ordinance of Shiga Prefecture for
controlling eutrophication of Lake Biwa
(Units mg/i)
parameter
Total
nitrogen
Total
phosphorus
New or
existing
facility
Existing
New
Existing
New
Discharge
m3/day
30 - 50
50 - 1,000
more than 1,001)
30 - 50
50 - 1,000
more than 1,000
m /day
30 - 50
50 - 1,000
more than 1,000
30 - 50
50 - 1,000
more than 1,000
Food
industry
25
20
15
20
12
10
4
3
2
2
1.5
1
Textile
industry
15
12
10
12
8
8
2
1.5
1
1.2
0.8
0.5
Chlmical
industry
(excluding
gelatin
industry)
12
10
8
10
8
8
2
1.5
1
1.2
0.8
0.5
Gelatin
manufacturing
industry
20
15
12
15
10
10
Z
1.5
1
1.2
0.8
0.5
Other
manufacturing
industries
15
12
8
12
8
8
1.5
1.2
0.8
1
0.6
0.5
Sewage
treatment
plant
Average
20
20
20
Provisional
20
20
20
Average
1
1
1
0.5
0.5
0.5
Collective
night soil
treatment
Average
20
20
20
10
10
10
Average
2
2
2
1
1
1
night soil
treatment
plant
Average
(20)
(20)
(20)
(20)
(20)
(20)
Average
(5)
(5)
(5)
(5)
(5)
(5)
Other
businesses
30
25
20
25
20
20
5
5
3
4
3
2
Remarkat 1. Values for sewage treatment plants, collective night soil treatment plants and night soil treatment facilities are daily average.
Others are maximum.
2. Standards for night soil treatment facilities shall not be enforced for the time being.
3. Nitrogen standard for sewage treatment plants shall be a provisional one.
-------
ABC
(Bill. (%) (%)
Yen)
2.0 1.0 10
1.6 0.8 8
1.2 0.6 6
0.8 0.4 4
0.4 0.2 2
Investment in Sewage Waters USW) (A) billion yen
ISW/GNP (B) %
ISW/Gov. Inv. Fixed Capital (c) %
1960
1965 1970
1975
1980
Fig. 1.1 Investment in sewage works in the past
ul
•O
a
•o
§
4J
tfl
0
a)
u
c
H
e1
0
o
o
o
H
4J
a
100
90
80
70
60
50
40
30
20
10
0
-
-
Coastal Waters (COD\,
x^ ^« •"' '"
«-—•""" Rivers (BOD)
0 ^°"~-^ o
0. o/
o
Lakes (COD)
A^ . ^^' A A &
^A--
, , i
1974 75 76 77 78 79 RO 81 82
Remarks: 1. .,.,.,
Number of water bodies where
,. environmental standards are met
Rate of compliance = Numbec of watec bodles whe[e " "0 (*)
environmental standards are set
2. For the environmental water quality standards, 6 categories
are set for rivers, 4 categories for lakes, and 3 categories
for coastal waters according to the water uses.
Pig. 1.2 Ratio of compliance to environmental water quality standards
727
-------
Table 1.5 Environmental water quality standards for
lakes relating to phosphorous and nitrogen
\ Item
Category \
I
II
III
IV
V
Applicability to
water use
Conservation of natural
environment and for water
uses listed in Categories
II - V
Water supply classes 1, 2,
and 3 (excluding special
ones). Fishery class 1,
Bathing and water uses
listed in Categories
III - V
Water supply class 3
(special ones) and water
uses listed in Categories
IV and V
Fishery class 2 and water
uses listed in category
Fishery class 3,
Industrial water,
Agricultural water, and
Conservation of
environment
Standards
Total nitrogen
Less than 0.1 mg/i
Less than 0.2 rag/£
Less than 0.4 mg/2
Less than 0.6 mg/2
Less than 1 mg/jj
Total phosphorous
Less than 0.005 mg/2
Less than 0.01 mg/£
Less than 0.03 mg/je
Less than 0.05 mg/£
Less than 0.1 rag/S.
Remarks: 1. standards are based on the annual average values.
2. The standard of total phosphorous is not applied to agricultural
water.
Notes: 1. Conservation of natural environment: of scenic spots and other
natural resources.
2. Water supply class 1:
Water that requires purifying operation such as filtration.
Water supply class 2:
Water that requires normal purifying operation such as
sedimentation and filtration.
Water supply class 3:
Water that requires highly sophisticated purifying operation
including pretreatment.
3. Fishery class 1:
Water for fish, such as salmon and sweetfish, etc., and those
of fishery classes 2 and 3.
Fishery class 2:
Water for fish, such as pond smelt, etc., and those of fishery
class 3.
Fishery class 3:
Water for fish, such as carp and crucian.
4. Conservation of environmental conditions:
Up to the limits at which no nuisance is caused to people in
daily life (including walking by the shore and so on).
728
-------
2. MICROPOLLUTANT (TOXICS) CONTROL IN JAPAN
2.1 Outline of Toxics Control System in Japan
The fundamental law for environmental pollution control in Japan is
the Basic Law for Environmental Pollution Control which was established
in 1970. The legal system for water quality management based on this
law is shown in Fig. 2.1.
In order to maintain better environmental quality, particularly
relating to toxic substances, a comprehensive policy should be adopted
taking local conditions into consideration. The major countermeasures
against toxic substances pollution would be classified as follows:
(1) effluent discharge regulation
(2) construction of wastewater treatment facility
(3) regulation on production and use of particular substances
(4) stream flow augmentation and removal of contaminated sediments, and
(5) others such as monitoring, development of treatment technology, tax
or financial system, compensation for damage and so forth
The effluent discharge regulation is done based on the water
Pollution Control Law. It is difficult, however, in most cases to
control pollutant discharge from small scale industries or household
individually. Therefore, the construction of sewerage systems is quite
important for protecting public water bodies. It sometimes is effective
to introduce dilution water or to dredge contaminated sediments,
particularly for polluted rivers in urban areas.
Some of chemical compounds might have properties affecting
seriously on human health or on the environment. In order to prevent
potential hazards of this kind, new and existing chemical substances are
being examined by the system provided by the Chemical Substances
Screening and Control Law.
2.2 Toxics Control by Effluent Standards
2.2.1 Compliance of toxic substance with environmental water quality
standards
As described in Chapter 1, environmental water guality standards
relating to toxic substances are set for nine items: cadmium, cyanide,
organic phosphorous, lead, chromium (hexavalent), arsenic, total
mercury, alkyl mercury, and PCBs. (Refer to Table 1.1) Most of these
values are identical to those for drinking water supply. For mercury
and PCB, however, their standard values were determined taking into
consideration damage caused by their accumulation/concentration in fish
and shellfish.
According to measurement results for public water bodies throughout
Japan in 1983 for these substances, of the total number of samples
179,000 taken at 5,239 stations throughout the country, the percentage
of samples exceeding the environmental standards was only 0.04% as shown
in Table 2.1. Mercury, organic phosphorous, and PCB were not detected
at any sampling stations. No sampling stations recorded average annual
729
-------
concentrations of total mercury in excess of the environmental quality
standard.
Table 2.1 Ratio of toxic substances exceeding environmental standards
Item
Cadmium
Cyanide
Organic
phosphorus
Lead
Hexavalent
chromium
Arsenic
Total
mercury
Year
1971
1983
1971
1983
1971
1983
1971
1983
1971
1983
1971
1983
1971
\
1983
""\^
Alkyl
mercury
PCBs
Total
1971
1983
1975
1983
1971
1983
Number of samples
(A)
15,944
27,881
12,453
23,500
5,116
8,529
14,515
27,962
11,532
24,167
11,530
25,488
12,364
Number of samples
29,978
Number of samples
(A)
5,624
7,850
3,130
4,086
89,074
149,463
Number of samples
exceeding environmental
standards (B)
114
28
142
8
11
0
202
7
15
3
48
12
32
Number of samples
exceeding 0.0005 mg/£
13
Number of samples
exceeding environmental
standards (B)
0
0
12
0
504
58
Ratio (%)
(B)/(A)
0.72
0.10
0.14
0.03
0.22
0
1.39
0.03
0.13
0.01
0.42
0.05
0.26
Number of points
exceeding
environmental
standard value
0
Ratio (%)
(B)/(A)
0
0
0.38
0
0.57
0.04
Fig. 2.2 shows trends in the ratio of non-compliance with the
environmental standard for each toxic substance. As shown in this
figure, the water quality in public water bodies has been remarkably
improved over these 15 years as the result of the efforts in water
pollution control.
730
-------
Basic Law for Environmental
Pollution Control
Environmental Pollution Control
Programs:
Established by the prefectural
governments
Water Quality Standards: set by national government
For the protection of
human health: applied
equally to all public
water areas in the
country
For the conversation of the living
environment
Application of the categories
of standards to each water area
Inter-prefectural water areas:
by national government
Other water areasi by prefec-
tural governors
L
Source Control Laws
Water Pollution Control Law: effluent control
Marine Pollution Prevention Lawi oil and
wastes dumping and discharge control
Sewerage Law: comprehensive programing for
river-basin sewarage
Mine Safety Law
Coal Washing Law
River Law
Port Regulation Law
Natural Parks Law
Fishery Resource Protection Law I
—| Waste Disposal and Public Cleaning Law I
Poisonous and Deleterious Substances
Control Law
Agricultural Chemicals Regulation Law
Chemical Substances Screening and Control
Law
Fig. 2.1 Legal system for water quality management
-------
u
9
'Total Mercury
, Organic Phosphorus
, PCBs
FY1971 72 73 74 75 76 77 78 V9 80 81
Remarks: 1. Standards for alkyl mercury, organic phosphorus, and PCBs were
set at N.D. from 1971, 1972 and 1975, respectively.
2 For total mercury, annual average at each point was determined as
' the base for evaluation since September, 1974. No locations was
found to exceed the standard value since then.
3. The total was obtained for 8 substances excluding mercury.
Fig. 2.2 Changes in the rate of non-compliance with water quality standards
(ratio of samples exceeding the standards)
2.2.2 Sources of water pollution
In the Water Pollution Control Law, facilities which discharge toxic
substances or facilities of more than certain scale, which.discharge
non-toxic pollutants, are defined as specified facilities, and the
factories which have these specified facilities are made a subject for
control.
As shown in Table 2.2, the total number of specified factories as of
31 March 1985 was 278,861 in Japan. Out of them, the number of factories
where toxic substances were discharged was 13,161, constituting 4.7
percent of the total number.
732
-------
Table 2.2 Number of specified factories
^^^
(A) Fiscal Year
1984
(B) Fiscal Year
1983
Rate of increase
(A)/(B)
Discharge more than
50 m3/day
30,006 (3,820)
29,913 (3,782)
1.01 (1. 01)
Discharge less than
50 n>3/day
248,855 (9,341)
247,227 (8,652)
1.01 (1.08)
278,861 (13,161)
277,140 (12,434)
1.03 (1.06)
Note: Numbers in parenthesis are factories which discharge toxic
substances.
The major types of factories which discharge toxic substances are
given in Table 2.3.
Table 2.3 Types of facilities discharging majot toxic substances
(1983)
\
1
2
3
4
5
6
7
8
9
10
Kind of business or name of
facilities
Natural science institute
and laboratory
Electroplating facilities
Acid and alkali treatment
facilities of metal surface
Cement manufacturing
Ready mixed concrete
manuf actur i ng
Glass manufacturing
Metallic goods manufacturing
and machinery industry
Wastes treatment plant
photo developing
Automatical washing
facilities of car
Number of
facilities
2,832
2,226
1,554
776
672
633
600
508
459
328
Major toxic substances being
discharged
CN, Alkyl mercury, organic
phosphorus, Cd, Pb, Cr6+, As, Hg
CN, Cd, Pb, Cr6+
Cd, Pb, Cr6+, As
CN, C8, Pb, As
CN, Cd, Pb, Cr6+, As, Hg
CN, 03, Pb, Hg
Hg
2.2.3 Control of factories
The responsible person for controlling and monitoring factories is
the governor of each prefecture. When a factory installs a specified
facility or changes the structure of his specified facility, he must
notify it to the prefectural governor. When the governor judges that the
effluent from the specified facility is unlikely to be compliant with the
standards, he can order an alternation for the plan in installment or
structure within 60 days from acceptance of the notice. In 1983, the
number of notice reporting an installment of a specified facility was
9,493 (cases) (including those discharging non-toxic pollutants). While,
the number of notice reporting an alternation in the structure was 5,146
(cases). In neither of these cases was change in plan asked by the
governor.
When a prefectural governor judges that effluent from an existing
specified facility does not comply with the effluent standards, he can
order an improvement in the structure or operation of the specified
733
-------
facility, or the wastewater treatment method within a specified period;
or he can order to temporarily discontinue the use of the specified
facility or the discharge of effluent. The number or factories ordered
to improve their structure or operation of the specified facilities, or
the wastewater treatment method totalled 304 (cases) in 1983. While, the
number of specified facilities ordered to temporarily discontinue use of
those specified facilities or the effluent discharge totalled 14 (cases)
in the same year. In addition, those subjected to the administrative
guidance for improvement, although not ordered to improve, totalled
17,000 (cases).
The law provides that if dischargers violate the standards, they are
sentenced to a prison term not exceeding 6 months, or punished with a
fine not exceeding 300 thousands yen. The number of cases violating the
effluent standards totalled 201 in 1983. Two cases resulted from regular
inspection, 19 cases resulted from reports by local inhabitants, and 180
cases resulted from police or Maritime Safely Agency action. The
parameters that were violated are shown in Table 2.4, and the types of
industries which violated the standards are shown in Table 2.5. Of those
who were arrested until 1982 and sentenced within 1982, nobody was given
a prison term, however, 114 persons were fined.
The prefectural governor can send his personnel to enter a specified
factory for inspection of the structure, the wastewater treatment
facilities, and relevant documents of the factory. Inspections made in
1983 were 88,155 cases during the day and 2,335 cases at night, totalling
90,470 cases.
2.2.4 Measures taken at sources
To prevent pollution from public water bodies, it is necessary for
the relevant authorities to take proper measures to enforce the standards
and to monitor the discharge from working places where use any toxic
substances. However, it is essential as well that each polluter makes
his effort to curb the discharge of pollutants as far as possible. It is
the first step for a discharger in reducing effluent toxicity to change
the manufacturing process if there is a better process or to reduce or
change chemicals and materials used, or to recover wastes. To treat the
effuent is the second step to comply with the effluent standards.
The treatment method varies according to the toxic substance to be
treated. Table 2.6 shows typical treatment methods for toxic substances
used in Japan.
734
-------
Table 2.4 Violation of effluent standards
(1983)
\
1
2
3
4
5
6
7
8
9
10
parameters violated
Suspended solid
BOD
pH
COD
Hexavalent chromium
Cyanide
Number of coliform
groups
Normalhexame
extracts
Copper
Zinc
Number of violations
102
80
70
32
23
10
8
7
6
5
Table 2.5 Types of facilities violating toxic substance discharge standards
(1983)
Item
Hexavalent chromium
Cyanide
Lead
Cadmium
Kind of violating facilities
1 Electroplating facility
2 Cement manufacturing
3 Acid and alkali treatment
facilities of metal surface
4 Metallic goods manufacturing and
machinery industry
5 Textile industry
1 Electroplating facility
2 Acid and alkali treatment
facilities of metal surface
3 Metallic goods manufacturing and
machinery industry
1 Electroplating facility
2 Raw pottery materials
manufacturing
3 Glass manufacturing
1 Industrial waste treatment plant
Number of violations
14
4
3
1
1
8
5
1
2
2
1
1
Table 2.6 Typical treatment methods for toxic substances
Item
Cyanide
Heavy metals ^
(Cd, Pb, Cu, Zn, Pe, Mn, Cr )
Hexavalent chromium
Mercury
Arsenic
PCB
Organic phosphorus
Treatment method
Alkaline chlorination
Electrolytic oxidation
Complex ion method
Chemical precipitation
ion exchange
Reduction and neutralization
Ion exchange
Sulfide precipitation
Carbon absorption
Chelate resin adsorption
Hydroxide co-precipitation
precipitation carbon absorption
Carbon absorption
735
-------
2.3 Other Problems of Pollution Related to Toxic Substances
2.3.1 Bottom sediment contamination by mercury and PCB
Toxic substances accumulated in bottom sediments affect the human
health through fish and shellfish. Now in Japan, provisional removal
standards for bottom sediments have been set for mercury and PCB.
Contaminated sediments are removed on the basis of these standards. The
standards for removing sediments are 25 mg/kg DS for mercury (this value
varies according to conditions for sediments in the sea) and 10 mg/kg DS
for PCB.
For mercury contaminated sediments, 42 water areas in Japan have
been specified as areas where sediments must be removed according to
surveys conducted since 1973. Of these, contaminated sediments have
already been removed from 38 areas and sediments from the remaining water
areas are now being removed.
For sediments contaminated by PCB, 79 water areas have been
specified as areas for sediment removal according to surveys conducted
since 1972. Of these, contaminated sediments have already been removed
from 70 water areas and sediments in other two areas are now being
removed.
The most typical one of these sediment removal projects is the
mercury contaminated sediments removal project in the Minamata Bay, shown
in Fig. 2.3.
Uroeda Portj' (Chisso Corp.)
,X£
Shiranui Sea
Noncon tarn mated
public waters
1 jDredging area
Master monitoring stations
O Auxiliary monitoring stations
A Underground water monitoring
s-caticns
Stationary fishing net
G- purse for catching fish
Pisciculture grounds
Fig. 2.3 Dredged sediments disposal plan for Minamata Bay
736
-------
The Minamata Plant of Chisso Corporation had used mercury as a
catalyzer in the manufacturing process of acetaldehyde for about 40 years
since 1932. The amount of mercury discharged from the plant and
accumulated in the bay is estimated to have been approximately 70 to 250
tons or more. The thickness of the bottom deposit containing mercury
reached 4 meters in some places in the bay. The project in this bay is
to partly reclaim or dredge about 1.5 million m3 of bottom sediments
containing mercury of 25 mg/kg DS or more in concentration. In carrying
out this project, to maximize safety, a strict monitoring of water
quality as well as fish and shellfish has been done to prevent secondary
contamination by the diffusion of bottom sediments.
In the disposal of removed bottom sediments, banks are constructed
to divide the dump site and public water area, thus preventing toxic
substances from flowing outside or exuding from "the reclaimed area. The
surface layer is covered with good quality soil, and groundwater
conditions in the surrounding area are strictly monitored.
2.3.2 Groundwater contamination by chemical substances
(1) Present state of groundwater contamination
Groundwater use in Japan is about 14 billion m3 a year. This
accounts for 16 percent of the total amount water used. When
restricted to water for domestic use only, groundwater accounts for
24%.
Main environmental problems for groundwater have so far been
ground subsidence and salinity intrusion caused by excessive pumping
of groundwater. For groundwater contamination problems, accidents
caused by hexavalent chromium and cyanide have been reported in a
quite few cases.
Recently, as a result of water supply surveys in some cities,
there arose a suspicion of local groundwater contamination by
chlorinated organic compounds. In this connection, a nationwide
survey of groundwater contamination was done in 15 representative
cities shown in Pig. 2.4 in 1982. The number and percentage of
samples in which each pollutant was detected, and the ranges of
detected concentration from this survey are shown in Table 2.7.
Pollutants which were in high percentage of detection were
@ nitrate and nitrite (approx. 87%), (2) trichloroethylene (28%),
(3) tetrachloroethylene (27%), (?) chloroform (22%), (5) 1. 1.
1-trichloroethane (14%), and (6) carbon tetrachloride (10%).
According to the result of the survey in nearby rivers carried out
for reference, those six pollutants were also detected highly in the
river water.
No water quality standards are set for groundwater in Japan at
present. However, since groundwater is used for the drinking
purpose in the majority of areas throughout Japan, it is necessary
to maintain the quality of the groundwater suitable for drinking
water. Table 2.8 shows a comparison between the results of the
above survey and the water quality standards provided by the Water
Works Law in Japan, or specified in the tentative guideline for
737
-------
drinking water by the World Health Organization (WHO). Of the water
quality parameters compared, nitrates and nitrites in 9% of the
samples exceeded the water quality standard of the Water Works Law.
Of the other pollutants, tetrachloroethylene and trichloroethylene
exceeded the tentative guideline of WHO in 4% and 3% of samples,
respectively.
Fig. 2.4 Map of surveyed area
Table 2.7 Detection of chemical substances in ghoundwater
Classification
Number of samples
~~~^-^samples, etc.
Name of sub8tance~~~-^^^
Nitrate and Nitrite
Methyl chloride
Dichloro methane
Chloroform
Carbon tetrachloride
1.1-dichl or oe thane
1.2-dichloroe thane
1.1. 1-trichloroethane
1.1-dichloroethylene
Cia-l.2-dlchl.oro-
ethylene
Trans-1. 2-dichloro-
ethylene
Trichloroethylene
Tetrachloroethylene
Benzene
Toluene
Xylene
Di-n-butyl ph thai ate
Di-ethylhexyl phthalate
Shallow well
1,083
Number and
percentage
oE detected
samples (%)
980 (90)
2 ( 0)
5 ( 0)
240 (22)
84 ( 8)
20 ( 2)
14 ( 1)
142 (13)
10 ( 1)
68 ( 8)
15 ( 1)
269 (27)
289 (27)
3 ( 0)
12 ( 1)
5 ( 0)
27 ( 2)
40 ( 4)
Detected
range
20 - 12,000
-
6
0.5 - 31
0.05 - 1.7
1-30
3-13
0.2 - 70
1-5
1 - 338
2-10
0.5 - 210
0.2 - 190
-
3-15
-
8
5-10
Total
1,360
Number and
percentage
oE detected
samples (%)
1,162 (87)
2 ( 0)
6 ( 0)
305 (22)
131 (10)
29 | 2)
16 ( 1)
186 (14)
13 ( 1)
119 ( 9)
20 ( 1)
379 (28)
372 (27)
3 ( 0)
20 ( 1)
5 ( 0)
26 ( 2)
45 ( 3)
Detected
range
(M9/O
20 - 80,000
2
2-6
0.5 - 31
0.05 - 2,200
1 - 175
1-33
0.2 - 1,600
1-7
1 - 537
1-15
0.5 - 4,800
0.2 - 23,000
4-11
2-42
3-17
2-46
4-16
River (Reference)
139
Number and
percentage
of detected
samples (1)
127 (91)
0 I 0)
9 ( 6)
40 (291
8 ( 6)
0 ( 0)
1 ( 1)
33 (24)
0 ( 0)
2 ( 1)
0 ( 0)
5< (39)
50 (36)
0 0)
2 1)
1 1)
1 1)
< 3)
Detected
range
lug/*)
20 - 25,000
-
1-5
0.5 - 13
0.05 - 0.20
-
7
0.2 - 93
-
1
-
0.5 - 16
0.2 - 3.0
-
14
3
9
5-21
It was found by this survey that the contamination of
groundwater was noticeable in a fairly wide area unexpectedly.
738
-------
Therefore, a follow-up survey was made in 1983 on the same wells in
13 cities and their adjacent wells for trichloroethylene and
tetrachloroethylene which were detected in high concentration in
many samples in 1982.
Prom the results of the follow-up survey, the groundwater
contamination by trichloroethylene and tetrachloroethylene was
confirmed to have been noticeable in most parts of those wells and
in even a wider area in many cases. Although some factories were
checked to find the sources, no particular sources could not be
identified.
Table 2.8 Comparision of detect concentration with water quality in
Water Works Law or WHO'S guideline
^*. Classification
\.
\^
\v
\.
Name of substanceX^
Nitrate and Nitrite
Chloroform
Carbon tetra-
chloride
1.2-dichloroe thane
1. 1-dichloroethylene
Trichloroethylene
Tetrachloroethylene
Benzene
Number of samples exceeding water quality standard or WHO'S
guideline
Shallow well
Number of
surveyed wells:
1,083
116 (11%)
0(0)
2(0)
3(0)
10 ( 1 )
26 ( 2 )
41 ( 4 )
1(0)
deep well
Number of
surveyed wells:
277
3 ( 1%)
1(0)
0(0)
1(0)
3(1)
14 ( 5 )
12 ( 4 )
0(0)
Total
Number of
surveyed wells:
1,360
119 ( 9%)
1(0)
2(0)
4(0)
13 ( 1 )
40 ( 3 )
53 ( 4 )
1(0)
River (Reference)
Number of
surveyed rivers:
139
4 ( 3»)
0(0)
0(0)
0(0)
0(0)
0(0)
0(0)
0(0)
Water quality
standard valuer
or WHO ' s
guideline
10 mq/Z
30 g/i
3 1/i
10 g/i
0.3 g/i
30 g/i
10 g/i.
10 g/i
Remarks
Water quality
standard in Water
Works Law
WHO'S guideline
WHO'S guideline
WHO'S guideline
WHO'S guideline
WHO'S guideline
WHO'S guideline
WHO'S guideline
(2) Measures taken for contamination control
As a result of the nationwide surveys made in 1982-1983, the
groundwater contamination was feared to be in progress in urbanized
areas over a fairly wide area. Since wide area contamination of
groundwater had not been revealed in the past in Japan, no primary
legal control has been set for the groundwater quality.
In view of the fact that such chemicals as trichloroethylene,
which contaminate groundwater, are widely used in various forms in
dry cleaning industry, metal processing industry, semiconductor
manufacturing industry, and many other industries, and that it is
very difficult to recover groundwater once contaminated; it has been
considered necessary to put some regulation toward proper use and
management of these chemicals in the factories using them.
As an urgent measure, for the time being, to prevent the
contamination from these chemicals, "Provisional Guideline for
Discharge of Trichloroethylene and other Compounds "was set in
August 1984. In this guideline, control targets are set for water
quality when discharging the wastewater into goundwater or surface
water. The control targets were set for trichloroethylene,
tetrachloroethylene, and 1.1.1 trichloroethane; the letter's use
has recently increased since it is an alternate chemical for other
two. The same guideline is being applied to the discharge of
739
-------
wastewater to the public sewerage system.
these chemicals are shown in Table 2.9.
The cbntrol targets for
Table 2.9 Control targets for selected chlorinated hydrocarbons
^^—^^^
Tr i chl or oe thyl en e
Tetrachloroethylene
1.1.1-trichloroe thane
Control targets to prevent
from penetration
Less than 0.03 mg/£
Less than 0.01 mg/S.
Less than 0.3 mg/Jl
Control targets for discharge
into public water bodies
Less than 0.3 mg/£
Less than 0.1 mg/£
Less than 3 mg/£
2.4 Measures Relating to Safety of Chemicals
Chemical substances are varied in their use and types. Their number
is said to reach several tens of thousands even when confined to those
used in industry. Some of them are discharged into the environment
during their manufacture or during various processes in their use, thus
contaminating the enviroment.
To cope with this problem, the Chemical Substances Screening and
Control Law was established in Japan in 1973. According to this law, new
chemicals are examined, before manufacture or importation, for their
three properties, namely, degradability, accumulativity and effect on
human health by continuous ingestion. Any chemicals having properties of
low degradability, high accumulativity and toxic effect on human health
are designated as "specified chemical substances", and its manufacture,
importation and use are regulated. The control system under this law is
shown in Fig. 2.5.
Among new chemical substances, 2,482 were reported by industries to
the government as of 31 December 1984. Of them, 1,985 chemicals were
publicized by the government as not classified as the specified chemical
substances and approved to be manufactured and imported.
As to existing chemical substances, investigation and checking is
also under way for their biological degradability, accumulation in fish,
toxicity and distribution in the environment. So far, 7 chemicals; PCB,
HCB, PCN, aldrin, dieldrin, endrin, and DOT have been designated as
specified chemical substances. To check the safety of existing chemical
substances efficiently, a test for decomposition and accumulation is
being done mainly on alternative substances those similar in structure to
specified chemical substances, as well as on chemicals with large
production and large imports. At the end of 1984, 511 chemicals were
determined to be high in decomposition and low in accumulation.
To expedite checking of existing chemical substances earlier and
more effectively, efforts are being made to develop a decomposition
testing method using anaerobic bacteria, an evaluation method using
physical and chemical properties of the substances, and a data reference
system for information on the sefety of ofeemical substances.
A special investigation on the distribution and the level of
chemical substances in the environment has been under way since 1974.
This investigation was strengthened in 1979 and named as "comprehensive
740
-------
checking of chemicals in the environment" to make it more effective for
systematic assessment of existing chemicals.
In this assessment system, the checking is made in three steps as
shown in Fig. 2.6. In the 1st step, a screening is made for chemical
substances presumed to readily remain in the environment (about 50
chemical substances/year). In the 2nd step, residual chemicals are
selected (about 5 chemicals/year) by the water quality and bottom
sediment surveys some ten areas throught the country, and a further
detailed environmental survery on these residual chemicals is made for
the water quality, bottom sediments, and in fish and shellfish in 40
areas throughout Japan. In the 3rd step, certain chemicals which reguire
particular attention are screened from residual chemicals (1 or 2
chemicals in 2 years). A special test to examine their effects on the
eco-system is performed with respect to these substances, and a long-term
biological monitoring survey using fish, shellfish, and birds is carried
out in 14 areas throughout the country.
In 1983, general environmental surveys were made on 45 chemicals.
In this test, no chemical was detected from water samples, but 10
chemicals were detected from sediment samples as shown in Table 2.10. It
was determined that a more detailed environmental survey would be made on
6 of those chemicals picked up by their residual results in 1984.
, Free manufacture and use,-.
etc. are permitted until
designated or recommended
as specified chemical >
ssubstances
Application to manufacture or
importation of chemicals
_L
Reference to list of existing chemicals
substances declared "White" and
specified chemical substances
Existing
chemicals
'Manufacture or impor-
tation prohibited
until results of
screening available
See if they are produced or imported below a
Certain volume and if they are likely to pol-
lute environment and to affect human health
judging from the knowledge already available.
_L
Application for recog-
nition as small-volume
chemical product
_L
Prior notification
Examination of
documents
/"Enforcement of\
V regulations /
/Free manufacture,
\importation and use
Pig. 2.5 System of controls under the Chemical Substances Control Law
741
-------
Chemicals
(tens of thousands)
Im
de
an
me
Identification
chemical residu
in the environm
tl
alytical
thod
t__
__
of Priority list j *>for»tion °"
(about 2,000 ltOX!;C che»^als
. i in Japan and
ent substances) *
(overseas
5-20 substances! (200 substances)
ng tests
(50 substances)
Development 1
of analyses — '
method — ,
General environmental
~" " surveys (of air, water",
bottom sediments)
([Detailed environmental
"Hpurveys (of-aJ.r, water,
(bottom sediments .'~ documented information
I ] Laborat<
.ory surveys
(I JField
surveys
Fig. 2.6 Scheme of total checks of chemicals
Table 2.10 Result of general environmental survey (1983)
Name of substances
Tributyl tin compounds
Dibutyl tin compounds
Acenaph thyl enc
Acenaphthene
Fluorene
Diphenyl methane
2-Naph thyl ami ne
Benzothiazole
Dibenzothiophene
P-Bromophenol
Water
Incidence of
detection/
Number of
samples
0/75
0/75
0/33
0/33
0/33
0/33
0/48
0/30
0/45
0/33
Detected
range
nd
nd
nd
nd
nd
nd
nd
nd
nd
nd
Bottom sediments
Incidence of
detection/
Number of
samples
9/75
3/75
13/33
13/33
27/33
3/33
5/48
4/30
6/45
5/33
Detected range
(wg/g-dry)
0.05 - 0.70
0.02 - 0.03
0.008 - 0.053
0.008 - 0.13
0.003 - 0.091
0.059 - 0.16
0.0017 - 0.0079
0.0016 - 0.0033
0.001 - 0.005
0.02 - 0.03
Remark: "nd" indicates that the concentration is less than detectable
limits.
742
-------
3. CURRENT STATUS OP SLUDGE TREATMENT AND DISPOSAL IN JAPAN
3.1 Introduction
As of the end of March 1985, municipalities operating public sewer
systems totaled 496, and the number of cities started to implement
sewage treatment operations has increased significantly within past
several years. Table 3.1 shows the increase in the number of
municipalities that have started operation of sewage treatment.
Table 3.1 The number of municipalities that have started sewage
treatment operations (cumulative total)
^~-\^^ Fiscal year
Size of^~\^^
municipal i ty"^^.^
Population in
thousands persons
More than 1000
300 to 1000
100 to 300
Less than 100
Total
'71
6
15
63
64
148
'75
10
37
87
93
227
'76
10
37
95
109
251
'77
10
37
97
127
271
'78
10
37
101
143
291
'79
10
38
104
174
326
'80
10
38
107
198
353
'81
10
44
116
212
382
'82
10
44
120
236
410
'83
10
44
120
281
455
'84
10
45
123
318
496
The total amount of sewage sludge produced in these treatment
plants from April 1983 to March 1984 was about 2,200,000 m3/year. As
shown in Table 3.2, 67% of the sludge was disposed of by landfill, 9% by
coastal reclamation 10% by ocean disposal, and 14% was utilized as
resources such as agricultural use.
Table 3.2 Status of sewage sludge disposal
(From April 1, 1987 to March 31, 1984)
(in 1,000 mj)
\^ Method of
^\disposal
State of\^
sludge ^^^
Dewatered cake
Ash
Dried sludge
Digested,
thickened sludge
Total
j (%)
Landfill
1,241
229
10
2
1,482
(67)
Coastal
reclamation
127
75
0
0
202
(9)
Utilization as
resources
246
30
30
4
310
(14)
Others
44
0
0
168
212
(10)
Total r(%)
1,658 (75)
334 (15)
40 (2)
174 (8)
2,206
(100)1
743
-------
Thus, the greater part of sewage sludge is disposed by landfill.
As cities continue to expand, finding sites for landfill has become
increasingly difficult. In large cities and their peripherals it has
become especially difficult for an individual municipality to
independently secure a potential disposal site. To cope with these
problems, there has been an increasing need for sewerage authorities to
take an regional approach to prepare for proper disposal site or to seek
the possibility of using more sludge as resources.
To achieve a stable and ever-lasting disposal of sludge, efforts
should be made to facilitate its reuse by recognizing sewage sludge as a
useful resource. The status of sludge reuse were as shown in Table 3.3
according to the survey made in 1984. The total amount of reuse
achieved was about 310,000 m3, almost all of it was for agricultural
use. The greater part of agricultural use was done in a state of
dewatered cake.
Table 3.3 Status of utilization of sludge as resources
(From April 1, 1983 to March 31, 1984)
\ State of sludge
Classification \
Agri-
cul-
tural
use
Executed by
local
municipalities
Delivered to
fertilizer
companies
Subtotal
Construction
materials
Total
Dewatered
cake
193
53
246
0
246
Ash
3
6
9
21
30
Dired sludge
5
0
5
0
5
Compost
18
7
25
0
25
Digested
sludge
4
0
4
0
4
Total
223
66
289
21
310
As of the end of March 1985, public organizations that are
utilizing sludge as resources are 6 prefectures and 92 local
municipalities, including Tokyo. The number of sewage treatment plants
is 118. The greater part of farmland in Japan consists of paddy fields
for growing rice, where the use of sewage sludge is difficult and
therefore, sludge is used for farmland and green spaces other than paddy
fields.
Even though the greater part of the reuse of sludge is in the form
of dewatered cake, a certain amount of sludge is used after being
composted for farmland application. The advantages of composting are
easiness in handling and minimum odor. These properties are quite
desirable because of the agricultural situation in Japan, wherein the
lifestyle of farmers has become urbanized, the farmers are getting old,
and the houses have come to be nearer the farmland. Besides these
points, when the reuse of sludge in farmland or in green spaces is
attempted, care should be taken in regard to the quality of sludge
products to keep the soil free from pollution by heavy metals. Efforts
should be made to help people understand the usefulness of sludge
products by distributing information on its proper use.
744
-------
The use of sewage sludge as a construction material could be a
promising way because of sludge's good potentiality for this kind of
use. Research and investigations on this matter have been continued by
the government, by municipalities, and by private companies. . The
Ministry of Construction has been continuing research on the use of
sewage sludge as construction materials in the comprehensive technical
development project.
As a result, it has been shown that sewage sludge has bright
prospects of being used as molten sludge, light weight aggregate, and
ceramic materials. Because feasibility studies have proved that these
objects can be achieved technically and economically, the on-site use
and the establishment of a distribution system will be the next subjects.
3.2 Improvement in the Incinerating Process for Energy Conservation
3.2.1 General
As the sewer systems are expanded, the quantity of sewage sludge
produced is continuously increasing. There has been a necessity,
therefore, to reduce the quantity of sludge to be disposed of and to
stabilize its quality because of the difficulty in securing sites for
disposal and the environmental problems. This has resulted in an
increase in the quantity of sludge incinerated. Table 3.4 shows the
change in the total capacity of sewage incinerators during post several
years.
Table 3.4 Change in Total Capacities of Sewage Sludge
Incinerators in Japan
Tons of Wet Cake/day
1978
7,917
1979
8,469
1980
9,091
1981
10,042
1982
10,557
Inasmuch as a great deal of auxiliary fuel was required to
incinerate the dewatered cake, with energy crises on two occasions in
1973 and 1975 being the turning points, technologies for achieving
energy-saving, resource-saving, and incinerating systems with less air
pollution have considerably progressed.
Generally speaking, to maintain a stable autogeneous combustion in
an incinerator, a conventional multiple-hearth furnace requires a cake
with a lower heating value of about 600 Kcal/kg-cake, and a conventional
fluidized bed reactor requires about 800 Kcal/kg-cake. From a view
point of heat balance, measures to save energy in incineration can be
classified into the following three categories:
(a) increase in the heating value of the cake, (b) decrease in the
amount of exhaust gas and lowering its temperature, and (c) effective
use of the exhaust heat.
745
-------
3.2.2 Example of improvement in an existing multiple-hearth furnace
Takaoka City improved their seven-hearth incinerators at the
Yotsuya Sewage Treatment Plant, and has been operating them without any
auxiliary fuel for the past several years. The major improvements being
made were as follows: (Fig. 3.1):
Hopper
To exhaust gas
ventilator
' Cake mixer
Cake cutter
Maximum tempera-
ture controlling
unit
Heavy oil
Burner
Air for
burners
Secondary combus
tion air port
Primary combustioi
air port
Other ventilated
air with offensive
odor
To funnel through exhaust
gas treatment facilities
Air from
blower
Blower for shaft
cooling
Fig. 3.1 Schematic diagram of the multiple-hearth incinerator of
the Yotsuya STP, Takaoka City Improved for energy saving
(a) The primary combustion air was taken by means of natural
ventilation from the bottom (7th) furnace, and the secondary air
was supplied at normal temperature at the 5th hearth.
(b) Cake mixers were installed at the 1st and the 3rd hearths in
addition to the normal teeth to assure complete mixing.
(c) Special teeth were used at the 4th and the 5th hearths to reduce
short circuit.
(d) A controlling system was introduced, which could maintain the
optimum temperature in the incinerator at a constant level by
746
-------
manipulating the secondary combustion air supply. This control was
effective to reduce the air supply.
(e) Heating value of the cake was improved by changing the dewatering
method. High pressure belt presses were used with a polymer and
ferric chloride addition. Water content of the cake is normally
about 70%.
The limit of the lower heating value for autogeneous combustion
with this improved multiple-hearth furnace is 350 to 370 Kcal/kg-cake.
The range of loading with which autogeneous combustion is possible is
from 32% to 135% of the design loading when the low heat value of the
cake is more than 400 Kcal/kg-cake.
Heat losses due to unburned sludge and radiation account for only
3% of the total heat input to the incinerator.
The combustion air supply system of this furnace, that is, to
supply the primary air by natural ventilation from the bottom hearth and
to control the secondary air supply so as to maintain the temperature at
the combustion hearths at 800 to 900°C, was found very effective against
variation of sludge cake loading and fluctuation of heating value of the
cake.
3.2.3 Example of improvement in a fluidized bed furnace
The Arakawa Basin-wide Sewage Treatment Plant of Saitama Prefecture
employed a fluidized bed furnace with a preliminary sludge drier using
exhaust heat to decrease the auxiliary fuel requirement.
The schematic diagram of the furnace is shown in Fig. 3.2.
In this system, the heat of the exhaust gas is recovered at the
heat exchanger, and the recovered heat is supplied to a sludge drier in
the form of heated oil at temperature about 250eC. The drier is an
hollow screw type of indirect heating. The evaporated vapour is
returned to wastewater treatment process after condensation, and the
exhaust gas with some offensive odor is supplied to the freeboard of the
furnace for deodorization.
The percentage of moisture evaporated at the drier is about 25% of
the original water content. The lower heating value becomes twice as
much as that of the sludge cake before drying. The reduction of the
auxiliary fuel consumption is 60 to 100% as shown in Fig. 3.3
3.3 Development in Technology to Produce Compost from Sewage Sludge
3.3.1 General
To facilitate the use of sewage sludge for farmland and green
spaces, it is desirable to improve the characteristics of the dewatered
cake for its safety, stability, and easiness in handling. To counter
these problems, technology has rapidly developed to produce sewage
sludge compost capable of maintaining a stable quality through an
aerobic fermenting process.
747
-------
Fig. 3.2 Schematic diagram of the fluidized Bed Furnace of
the Arakawa Basin-wid SCP Improved for Energy Saving
100 r Direct incineration
(without drying)
80
rH X
o)
-------
(4) To meet the standards relating to heavy metals as a special
fertilizer regulated by the Fertilizer Management Law, which is
shown in Table 3.5.
As to application of sewage sludge to farmland, a management
guideline was stipulated using Zinc as an index as shown in Table 3.6.
Table 3.5 Standards concerning heavy metal contents in special fertilizers
(Regulations by the Fertilizer Management Law)
Item
Arsenic
Cadmium
Mercury
Standard
Less than 50 rag/kg DS
Less than 5 mg/kg DS
Less than 2 mg/kg DS
Table 3.6 Management guideline to prevent the accumulation of
heavy metals in the soil of farmland
(Notification of Water Quality Protection Bureau of
the Environment Agency)
1. The Index for controlling accumulation of heavy metals In the soil of
farmland shall be the zinc content.
2. The management guideline relating to controlling accumulation of heavy
metals In the soil of farmland shall be 120 mg of zinc per 1 kg of dry
soil.
3. The analytical method to measure the zinc content In the surface soil
shall be the atomic absorption spectrophotometry following the
digestion by mineral acids.
3.3.2 Methods of composting
The methods for producing compost using sewage sludge can be
classified depending on the types of fermentation tank. Each type of
method could be further classified depending on with or without addition
of bulking agent and with or without preliminary drying of the dewatered
cake prior to composting.
r- Vertical
type
Type of
compostors
—Horizontal-
type
-Pile type
Multi-stage —
system
Single-stage •
system
-Flap-door type, Paddle type,
Moving-floor type and Arm type
- Silo type
• Scoop type, Paddle type, Auger
type, Circular auger type,
Shovel type
749
-------
3.3.3 Design data for composting facilities
The first sewage sludge composting facility in Japan started
operation in 1976 and composting does not have a long history.
Therefore, concrete design criteria have not been established yet.
Table 3.7 summarizes the range of design data of the composting
facilities based on experiments and actual facilities.
Table 3.7 Composting facility design data
Pre-con-
ditioning
Primary
Fermenta-
tion and
Secondary
Fermenta-
tion
I ten
Water content of
feed mixture (%)
Feed mixture pH (-)
Bulking agent M
(% - WB)
Return ratio Re
(* - WB)
Apparent specific
gravity (t/m3)
Fermentation period
Pile height (m)
Frequency of mixing
(days)
Air supply
Data values
840 - 55
60 - 70
About 8 to 10
(2) 15-40
§100 - 300
30 - 100
Remarks
The feed mixture means input
materials to the ferment tank
that is a mixture of raw
materials (cake and bulking
agent) and the return compost.
When pH of the dewatered cake ia
excessively high, an adjustment
is necessary.
Bulking agent's wet weight
„ , (kg/day)
oewatered cake's wet weight
(kg/day)
Return compost's wet weight
nc _ (kg/day)
Dewatered cake's wet weight
(kg/day)
(Feed mixture) (Primary compost,
secondary compost)
§0.65 - 0.75 0.60 - 0.80
0.50 - 0.65 0.65 - 0.75
Primary fermentation 10 to 14 days
Secondary fermentation (Forced ventilation)
7 to 14 days)
(Natural ventilation)
1 to 2 months
Primary fermentation
® { Silo type 3.0 - 5.0
(Other than silo type 0.6 - 1.4
® j Shovel type 2.5 - 3.0
1 Other than shovel type 1.0 - 1.5
®! (Natural ventilation) 1.0 - 2.0
1 (Forced ventilation) about 2.5
The pile height for secondary fermentation is
about 1-1.3 times as high as that for primary
fermentation.
Primary Secondary
fermenta- fermenta-
tion tion
(3) 0.5 - 4 7 - 14
ft. I Shovel type 4-7 7-14
^ i Other than shovel type 1-3 7-14
ff. 1 (Natural ventilation) 0.3 - 0.5 7-14
'*' 1 (Forced ventilation) - 2-10
100 - 200 4/min-m3
Note: @ Composting without bulking agent
(2) Composting with bulking agent
Vertical type
Horizontal type
Pile type
750
-------
3.3.4 Composting facilities under operation
As shown in Table 3.8, composing of sewage sludge is being done at
15 cities as of the end of October 1984. The capacities of the
facilities are from 3 tons of wet cake a day to 206 tons of wet cake a
day. For promoting the agricultural use of sewage sludge compost, an
efficient and stable distribution system needs to be structured with a
consideration for competition with conventional fertilizers both
chemical and organic and through the cooperation with farmers
associations and private businesses, depending on the actual situation
of the districts.
3.4 Development of a Technology Producing Construction Materials from Sewage
Sludge
3.4.1 possibility of sludge utilization
Composting is a technology to utilize organic subtances contained
in sludge, whereas production of construction materials from sludge is a
technology to utilize mineral contents of sludge such as Si02,
and CaO.
(1) Dewatered cake
Direct use of dewatered cake for banking or filling materials
is not practical because of problems such as insufficient strength,
subsidence due to compaction and leachate. However, after mixing
with incinerated ash or cement, it has been used for that purpose
to some extent.
(2) Incinerated ash
When the ash is compacted under conditions near an optimum
water content, the finished product has the sufficient
ground-resistant force required for the construction machine
operation, and exhibits a consistency near that of sandy soil.
Therefore, it is suitable for use in a wide range of construction
materials, such as road foundation, banking, and landfill.
The possibility of its indirect use has been explored
extensively for various purposes including production of light
weight aggregates, clay pipes, bricks, earthenwares concrete
products such as Hume pipe, or additives for cement. Some of them,
such as production of light weight aggregates, which is explained
more in detail below, are very promising. For producing clay
pipes, it was found that ash can be added up to about 25% without
problems.
751
-------
Table 3.8 Sewage sludge composting facilities under operation
Installation site
Name of city
Tendo city
Yamagata city
Akita city
Hitachi city
Tokyo
Kasugai city
Okayama city
Koriyama city
Ibaragi pref.
Tokorozawa
city
Kayano city
Nozawa
hotspring
village
Sapporo city
Kagoshima
city
Kofu city
Mobara city
Fukuoka city
Name of plant
(Date of completion)
Tendo sewage
treatment plant
(April 1979)
MaeaJcashi cake
treatment plant
(April 1980)
Akita city compost
center (April 1982)
Namekawa sewage
treatment plant
(Oct. 1982)
Hinamitama sewage
treatment plant
(Hay 1980)
Kozoji sewage
treatment center
(April 1984)
Takashima sewage
treatment center
(April 1981)
Koriyama city sewage
treatment center
(April 1983)
Kasumigaura sewage
treatment center
(April 1984)
Tokorozawa sewage
treatment center
(Sept. 1983)
Lake Shirakaba
sewage treatment
center (Sept. 1983)
Nozawa hotspring
village sewage
treatment center
(April 1983)
Atsubetsu sludge
compost plant
(April 1984)
Kagoshima city
sewage sludge
compost plant
(april 1981)
Otsu sewage
treatment plant
(April 1984)
Kawanakajima sewage
treatment plant
(Aug. 1984)
Fukuoka sewage
sludge control
center (Jan. 1982)
Composting facilities
Addition of
bulking agents
With addition
Without
addition
With addition
Ditto
Without
addition
Ditto
With addition
Without
addition
Ditto
Ditto
Ditto
Ditto
Ditto
Ditto
With addition
Ditto
Without
addition
Primary fermentation
Type
Vertical
silo type
Horizontal
shovel type
vertical
multi-stage
paddle type
Vertical
multi-stage
flap- door
type
Horizontal
scoop type
Horizontal
scoop type
Vertical
two-stage
paddle type
Horizontal
scoop type
Horizontal
scoop type
Vertical
multi-stage
paddle type
Horizontal
scoop type
Vertical
multi-stage
type
Horizontal
paddle type
Vertical
silo type
Vertical
silo type
Vertical
multi-stage
flap- door
type
Horizontal
shovel type
Capacity and
number of units
ton/day x number
5 x 1
15 x 1
(8- tanks)
30 x 1
IS x 1
(2- tanks)
7x1
(4- tanks)
13 x 1
0.72 x 1
12.2 x 1
(3- tanks)
3x1
10 x 1
3x1
(2- tanks)
4x1
(2- tanks)
50 x 1
(4- tanks)
53.6 x 1
(8- tanks)
17.5 x 1
8.8 x 1
206 x 1
(13- tanks)
Fermenting
period
days
14
12
12
35
10
14
14
14
16
10
10
10
12 - 13
8
14
21
30
Secondary fermentation
Method
Indoor
piling
Included in
primary
fermentation
Indoor
piling
Included in
primary
fermentation
"
—
Open-air
piling
Included in
primary
fermentation
Ditto
"*
"
Indoor
piling
(Forced
ventilation)
Horizontal
shovel type
Indoor
piling
(Forced
ventilation)
Horizontal
shovel type
(Forced
ventilation)
(Entrusted
with private
businesses)
Fermenting
period
days
40 - 60
15
"
"
About 60
14
14
"
30
60
30
752
-------
(3) Smelted slug
The smelted slug satisfies almost all of the conditions
required for the materials sustitute for sands or gravels. In
addition, it has an advantage of no resolubilization of heavy
metals. The only problem is the cost, and efforts are being made
to reduce the production cost, as well as to find the other uses
which justify the higher cost.
3.4.2 production of light weight aggregate from incinerated ash
This technology was developed by paying attention to the similarity
of the constituents of incinerated ash to shale, which is the light
weight aggregate raw material. The Metropolitan Tokyo Government
constructed a multi-stage jet-flow furnace with a capacity of 3 tons a
day, which is shown in Fig. 3.4, and has been producing light weight
aggregates as a routine practice.
Aggregates are produced in such a way that a bonding agent (waste
alcohol liquor) is added to ash to give it viscosity, and the mixture is
subsequently granulated and dried. It is then burned in an air current
heated to a temperature of from 1,100°C to 1,150°C and cooled. During
burning, a portion of the constituent is gasified, causing the granules
to inflate. While cooling, the granules maintain their inflated volume,
and the finished products have cavities inside and a hard shell
outside. The specific gravity of the product is 1.3 to 1.65, which is
only half that of gravel or sand. It is easy to produce completely
spherical aggregates with a diameter of from 0.3 mm to 3.5 mm. The
strength of the aggregates is considerably high. The destruction
strength is about several kilograms per granule. It lends itself to
many uses. Direct uses are for backfill materials for shield
tunnelling, aggregates for permeable pavement, block wall material, and
precast outer wall material. Indirect uses include backfill material
for sewer construction, tennis court floor materials, and supporting
materials for potted growth of plants.
The Metropolitan Tokyo Government has entrusted with certain
experienced private companies the distribution of the lightweight
aggregates on an experimental basis to investigate the types of suitable
and potential markets, the estimated future demand, the required
quality, and the appropriate prices. The percentages of the product
classified by use in fiscal 1983 are shown in Table 3.9.
Although selling prices differ depending on the types of packing,
the amount of sale, and the types of shipping work, the product is being
marketed at a price of from about 9,500 yen/ton to 20,000 yen/ton.
Problems still to be solved include restructuring of shipping facilities
and warehouses, arranging bagging facilities, integrating production and
shipments, and optimizing the amounts of production and sales.
753
-------
Green pellet
Exhaust
Heating by
a burner
Heating gas
Sedimentation
layer
Dense flowing
layer
Thin flowing
layer
Finished
product
Fig. 3.4 Schematic diagram of a multi-stage jet flow furnace
Table 3.9 Ose of light-weight aggregate made from sewage sludge
(FY 1983, Metropolitan Tokyo)
Use
Filling materials
for underground
storage of liquid
combustibles
Aggregate for GRC
products
Aggregate for
resin concrete
and other resin
Cement concrete,
and other
construction
materials
Gardening, filter
media, and others
Total
Reason of use
Absolute dryness
Light-weight
Absolute dryness.
Light-weight
Light-weight,
Absolute dryness.
Fire-resistant,
Sound proof
High void ratio,
water absorption
characteristics,
light-weight
-
Amount of use
Quantity
163 t
41 t
25 t
3 t
4 t
242 t
Percentage
67%
10%
10%
1.5%
2.5%
100%
754
-------
3.5 Regional Plan for Treatment and Disposal of Sewage Sludge
3.5.1 Current status of sludge treatment and disposal in the Tokyo Bay and
Osaka Bay basins
Both Tokyo Bay and Osaka Bay are symbolic water bodies from the
viewpoint of maintaining proper water quality of Japan's coastal sea.
The statistics in 1983 show that the Tokyo Bay basin (Metropolitan
Tokyo, Chiba prefecture, and Kanagawa Prefecture) has a total areas of
8,591 km2, a population of 25.1 million and total of 169 local
municipalities including cities, towns, and villages. The Osaka Bay
basin has a total area of 7,441 km2, a population of 16.1 million, and
total of 123 local municipalities. Both are densily populated developed
areas (Table 3.10)
Table 3.10 Outline of the Tokyo Bay and Osaka Bay basins
(1983)
Basin
Area (km2)
Prefecture
Number of
municipalities
Population
(person)
Tokyo Bay
8,591
Metropolitan Tokyo, Chiba,
Saitaraa and Kanagawa
Prefectures
169
(23 wards, 97 cities,
44 towns, and 15 villages)
25,093,236
Osaka Bay
7.441
Osaka, Kyoto, Byogo,
prefectures
123
(66 cities, 53 towns,
4 villages)
and Nara
and
16,137,972
Japan's total area is 377,765 km2, and total population is
119 million, of which the Tokyo Bay basin accounts for 2.5% in area and
21% in population. The Osaka Bay basin accounts for 2.0% in area and
14% in population. Both districts also have prominent industrial areas,
with a great number of sources of pollution.
In order to comply with the environmental standards set for Tokyo
Bay and Osaka Bay it was considered that the enforcement of the effluent
quality regulation was not sufficient in strength. This has resulted in
an implementation of the loading regulation system for Tokyo Bay in 1979
and for Osaka Bay in 1980. The water quality parameter regulated by
this system is COD^ at present, but a guide line was also issued to
control the total loading of phosphorus. To comply with the regulation
and to improve the water quality of the bays, the construction of
sewerage systems is one of the most effective measures. The current
status of sewerage systems in Tokyo Bay and Osaka Bay Basins in 1983 is
shown in Table 3.11.
755
-------
Table 3.11 Current status of sewerage systems in
the Tokyo Bay and Osaka Bay basins
Basin
Population
Population served
Percentage
Tokyo Bay
25,093,236
11,726,506
46.7
Osaka Bay
16,137,972
7,760,513
48.1
The total volume of sewage sludge produced during one year in 1980
was 1,120,000 m3 in Tokyo Bay and 830,000 m3 in Osaka Bay,
respectively, expressed in terms of dewatered cake. As shown in
Fig. 3.5, the greater part of dewatered cake produced was disposed of by
landfill; a very small amount was applied to form land and green spaces.
Tokyo Bay basin
Others *
9,000 ton/year
1.5%
(Expressed in term*, of
disposed sludge weight)
(Expressed in terms of
, dewatered cake weight)
22,500 ton/year
2.0%
Landfill
240,900 ton/year
21.6%
* "Others" means sludge utilized for farmland and green spaces.
Fig. 3.5 The amount of sludge classified by disposal methods in 1980
756
-------
Osaka Bay basin
(Expressed in terms of
disposed sludyu weight)
(Expressed in terms of
dewatered cake weight)
"Others
6,775 ton/year
1.6%
* Others
37,942 ton/year
* "Others" means sludge handed to fertilizer
Fig. 3.5 The amount of sludge classified by disposal
methods in 1980 (Cont'd)
Because of the difficulty in obtaining proper site for sludge
disposal due to an increased density of population in these areas, local
municipalities are anxious to secure potential sites for the disposal of
sludge. Most of the minicipalities have disposal sites of capacities
only less than five years. Some local municipalities have been seeking
sites to dispose of sludge, where are more than 100 km apart from their
home teritories, because no proper site in their districts are available
(Table 3.12).
Table 3.12 Distance from the sewage treatment plant to
the landfill site (1980)
^\, Classifi-
^\. cation
District ^^^^
Tokyo metropolitan
district
Kinki district
Total
Transportation distance and the number of
sewage treatment plants
Less than
10 km
8
17
25
10 - 20 km
13
14
27
20 - 50 km
5
4
9
50 - 100 km
2
0
2
More than
100 km
9
6
15
Note: In the Tokyo metropolitan district, sewage treatment plants
operating in Tokyo, Chiba, Saitama, and Kanagawa prefectures are
taken for investigation, in the Kinki district, those in Osaka,
Kyoto, Hyogo, and Nara prefectures are taken for investigation.
757
-------
3.5.2 The necessity for a regional sludge treatment and disposal plan
Because of progress and expansion in sewerage systems and the
necessity to advance the level of treatment, it will become more and
more difficult to depend on only landfill to dispose of sludge.
Therefore, the possibilities of converting sludge into resources, such
as construction materials and fertilizers for cultivation of farmland
and green spaces must be explored as a method for sewage sludge disposal.
There are, however, social, economical and technical problems to be
solved before the majority of sludge can be effectively used as
resources. Therefore, the most practical way will be to continue the
disposal by means of landfills while simultaneously expanding the
effective uses of sludge as resources.
In 1981, the government asked the opinions of municipalities within
the area of the Tokyo Bay and Osaka Bay basins, about the measures to
reduce the volume of sludge to be disposed of, the problems associated
with, and the planned disposal methods. As a result, it was made clear
that every municipality considers that it will be more difficult in the
future to dispose of sludge in its own jurisdiction independently.
Figure 3.6 shows the estimated amount of sludge disposed classified by
disposal methods in 1995.
Tokyo Bay basin
(Expressed in terms of
disposed sludge weight)
(Expressed in terms of
dewatered cake weight)
Landfill
15,300 ton/year
0.8%
Others
30,400 ton/year
1.6%
Disposal depending on
the regional treatment
and disposal plan
1,880,000 ton/year
97.6%
Landfill
24,500 ton/year
0.4%
Others
128,600 ton/year
2.2%
Fig. 3.6 The estimated amount of sludge classified by
sludge disposal methods in 1995
758
-------
Osaka Bay basin
(Expressed in terms of
disposed sludge weight)
Landfill
52,500 ton/year
4.3%
Others
6,000 ton/year
0.5%
Landfill
276,000 ton/year
8.4%
(Expressed in terms of
dewatered cake weight)
Others
32,300 ton/year
1.0%
Disposal depending on the
regional treatment and
disposal plan 2,988,000
ton/year
90.6%
Fig. 3.6 The estimated amount of sludge classified by
sludge disposal methods in 1995 (Cont'd)
The ratio of the sludge disposed of by means of landfill is
expected to be just 0.8% in the Tokyo Bay basin and 4.3% in the Osaka
Bay basin, respectively. The ratio of the sludge utilized for farmlands
or other resources is estimated to be only 1.6% in the Tokyo Bay basin
and 0.5% in the Osaka Bay basin, respectively. The amount of sludge
that are expected to be disposed of by means of the regional plan
accounts for 98% in the Tokyo Bay basin and 95% in the Osaka Bay basin,
respectively.
To carry out regional treatment and disposal of sludge, it is
necessary to collect sludges by some means. As the result of a study on
the sludge collection system from both technical and economical
viewpoints, it was found that collecting raw sludge to a central sludge
treatment plant by a pipeline followed by dewatering and incineration is
more advantageous than the dewatering and incineration at each treatment
plant when the transportation distance is within 20 to 30 km (Fig. 3.7).
759
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500
;o 400
tn
mB
>2 300
200
100
0.8
.. u
X
10
20
40
50
60
70
80
90
Distance from the
disposal site
Notes: 1. The numerals in the diagram are
The case of raw sludge transportation
The case of incinerated ash transportation
representing the ratios of costs to each other. The diagram
indicates that the raw sludge transportation is possible at
less than 1.0.
2. The cost for raw sludge transportation includes the
construction expenses of transportation facilities, joint
sludge disposal facilities (thickening * dewatering *
incineration), and their maintenance expenses. The cost for
the incineration ash transportation includes the construction
and maintenance expenses of the sludge disposal facility
(thickening •» dewatering •* incineration) in the individual
treatment plant and also the expense for transporting the
incinerated ash to the disposal site.
Fig. 3.7 Review on the characteristics of sludge collected
and the total cost of sludge disposal
In consideration of the current status of sludge disposal in both
Tokyo Bay and Osaka Bay basins and of the opinions of local
municipalities, a regional sludge treatment and disposal plan including
the effective use of sludge, needs to be materialized.
3.5.3 A conception of a regional sewage sludge treatment and disposal plan
On the basic assumption that landfill will be continued for the
time being but that there will be a gradual shift to other effective
ways such as utilization as resources, the following business concept is
under review.
(1) A centralized sludge treatment plant including incineration is
constructed on the landfill site, and sludge within an area of 20
to 30 km range from this centralized plant is collected by means of
a pipeline. In the future, the disposal of the greater part of
the sludge will be shifted from landfill to such effective uses as
construction materials.
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(2) As to treatment plants outside 20 to 30 km range from the
centralized plant, such effective uses as the agricultural use of
composted sludge should be considered as a first choice.
(3) When the agricultural use is not possible, and when reduction of
the sludge volume is needed, a joint incineration will be taken.
(4) As for the site for landfill of incinerated ash or dewatered cake
the coastal reclamation site for regional is to be jointly used,
and simultaneously landfill sites in the inland area are to be
seeked for.
3.5.4 A detailed plan in the Osaka Bay basin
Of the two districts of Tokyo Bay and Osaka Bay basins, the
necessity for the regional treatment and disposal plan is much higher
for the Osaka Bay basin being highly desirable and advantageous from an
economical viewpoint.
(1) Disposal districts
The project area needs to be divided into disposal districts
for actual planning, paying attention that the collection,
transportation, and treatment of sludge will be performed in an
efficient and economical manner from a long term view point, even
when an effective use of sludge becomes possible in the future.
In the Osaka Bay basin, three disposal districts were
formulated as shown in Fig. 3.8 considering the following
conditions:
(a) The time when each sewage treatment plant wants to join the
regional sludge treatment and disposal plan
(b) The economy of sludge collection, including the basic
assumption of pipeline collection within 20 km range from the
central sludge treatment plant.
(c) Long rivers, such as Yodo River, as a boundary.
(2) Planning the pipeline transportation of liquid sludge
The liquid sludge (with a water content of 90%) within 20 km
range is to be pumped from the sludge storage tank at each sewage
treatment plant to the central sludge treatment plant through a
pipeline. All pipeline system will be constructed as a dual-line
structure for easiness in repair and in coping with increase in the
amount of sludge as time goes. A relay pumping station will be
installed where the length of the pipe becomes about 10 km or more.
761
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Prefectural boundary
Sewage treatment plant to be
included in the sludge disposal district
.
'• * I Osaka nort
Osaka City / block
• - X I
Fig. 3.8 Map of the Regional Sludge Treatment and Disposal Plan
(3) The central sludge treatment plant
The basic policy on sludge treatment and disposal is to reduce
the volume of sludge as much as possible for conserving the
disposal site for the time being, and to shift gradually from
landfill to utilization and of sludge other effective purposes. To
meet these requirements, thickning -> dewatering -»• incineration
(melting) system will be employed. Returning wastewater treatment
facility, a control building and an electrical room will also be
installed at the site.
The block diagram of sludge collection, treatment and disposal
system is shown in Fig. 3.9, and an example of the layout of a
central sludge treatment plant is shown in Fig. 3.10.
762
-------
(Facility for effective
uses in the future)
Fig. 3.9 Block diagram of sludge collection, treatment and disposal system
(4) Economical analysis
The regional sludge treatment and disposal plan was formulated
as a long-term plan extending about 24 years, from 1986 to 2010.
The construction of this facility was planned on the assumption
that national grant would be provided, as in the case of the public
sewerage system. The results of trial computation on the revenue
and expenditure of the projects relating to each disposal district
shows that in order to make the cumulative account positive 10 and
20 years after the project starts, the treatment and disposal cost
per unit volume of liquid sludge should be 575 - 730 yen/ra^ and
570 - 695 yen/m-3, respectively. These costs are cheaper than
those when sludge is treated and disposed at each existing
treatment plant, which is 680 - 2,770 yen/m^.
The construction case of the facilities at each disposal
district is estimated to be from 63.3 billion yen to 81.4 billion
yen.
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320.0
Designed sludge disposal amount = 35,500 mVday
Fig. 3.10 An example of the layout of a central sludge treatment plant
764
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4. RECENT TECHNOLOGICAL DEVELOFMENT IN WASTEWATER TREATMENT
4.1 Overview
In the recent technical advances of wastewater treatment in Japan,
large cities, the Ministry of Construction, and the Japan Sewage Works
Agency have had leading roles. Technical development has especially
been made in such large cities as Tokyo, Osaka, and Yokohama, where the
sewage works have been carried out since the 1920s, progress in
technology has been particularly notable in such fields as the
development of equipments, the vertical utilization of wastewater
treatment plant sites, the improvement of dewatering machines and
incinerators to reduce the volume of sludge, and the development of
automation and instrumentation. All these technologies were essential
to the construction of wastewater treatement plants in Japanese large
cities where the population density is extremely high.
The Ministry of Construction is responsible for the administration
of the sewage works in Japan. It has been planning and funding the
research and development programs relating to common and urgent problems
in conducting sewage works. Most of the actual research works are
carried out by three institutions, namely, the Water Quality Control
Division of the Public Works Research institute of the Ministry of
Construction, the Research and Technical Development Division of the
Japan Sewage Works Agency, and the Japan Sewage Works Association.
The research projects, including those performed by the Ministry of
Construction itself, in fiscal 1984 were as follows. The greater part
of them are being continued for FY 1985.
(1) Researches on rational design methods for wastewater treatment
facilities
• Comprehensive planning for offensive odor control
• Evaluation of the effect of the nutrient load reduction on lake
eutrophication control
• Treatment methods for storm sewage
• Investigations on the fate of micropollutants within the
wastewater treatment processes
(2) Researches on treatment and disposal of sludge
• Guidelines on the use of sludge for green spaces and agricultural
land
• Testing methods for converting sludge into construction materials
• Investigations on ocean disposal and land reclamation of sludge.
• Investigations on improving the management techniques of sludge
dewatering processes
(3) Researches on advanced wastewater treatment processes and the reuse
of the effluent
• Research on the reuse of treated effluent
• Research on removal of nutrients in wastewater
765
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• Research on removal of dissolved organics in wastewater
« Soil treatment of secondary effluent for nutrient removal
(4) Research on development of automatic water quality monitoring
devices for controlling industrial discharge
(5) Research on resource and energy conservation in sewerage facilities
« Guidelines for coincineration of sewage sludge and municipal refuse
• Research on the recovery of energy through sludge digestion
(6) Research on the small wastewater treatment system
• Research on the treatment characteristics of small wastewater
treatment plants
• Research on development of facilities suitable for a small
wastewater treatment plant
Private industries have also played preeminent roles in developing
new technologies in Japan. Many of their research and development have
attained highly advanced technical levels. Therefore, it is necessary
to promote technical cooperation with these private industries for
carrying out sewage works effectively and properly.
There has been, however, a tendency for a sewerage authority to
take a cautious attitude toward employing new technology developed by a
particular private company for sewerage construction projects, which are
inherently public-oriented projects.
This has been attributable to the followings:
(1) The source of funds for construction are completely the public
expenses, such as those originating from taxes.
(2) The economical benefit induced by the use of new technology may not
be evaluated readily, and
(3) Any failure resulting from the use of a new technology cannot be
tolerated easily.
Therefore, to utilize the fruitful results of new technologies
developed by private industries, there was a necessity to formulate a
proper system for evaluating these new technologies.
The Ministry of Construction has established a new technology
assessment system in 1978. This system is intended to evaluate properly
the functions and performances of new technologies developed by private
industries and to promote actual use of these new technologies
extensively by disclosing publicly the results of the evaluation. The
Minister of Construction announces the particular technology to be
assessed in an official publication and invites private industries to
submit applications for assessment. An assessment certificate is issued
to each applicant after the assessment is completed.
Table 4.1 summarizes the subjects on which the assessment has been
made.
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Table 4.1 Themes of technology assessment by Ministry of Construction
Fiscal year
of invitation
1978
1979
1980
Subjects
Development of microwave
furnace for sewage
sludge to melt
Development of large-
diameter egg-shaped hard
vinyl chloride pipe with
high rigidity
Development of ultra-
deep aeration system for
sewage treatment
Objects of development
To develop microwave
melting furnace capable
using microwaves to melt
and solidify sewage
sludge , turning it into
chemically stable glassy
material without however
generating harmful
exhaust gas but
permitting, the melted
and solidified
substances to be used as
construction materials.
To develop hard vinyl
chloride pipe having an
egg-shaped section with
excellent hydraulic
properties, large
diameter, sufficient
strength and endurance.
To develop activated
sludge process using
ultra-deep aeration tank
requiring only a small
area.
Goals of development
) Maximum treating
capacity of furnace of
about 5 tons/day.
) Exhaust gas generated
from the process, being
capable of meeting the
requirements set forth
in Air Pollution
prevention Law
(Law No. 97 in 1968) .
) Melted and solidified
glassy materials being
capable of meeting the
Order of Prime
Minister's Office (Order
Ho. 5 in 1973)
determining the criteria
for industrial wastes.
4) Melted and solidified
glassy substances being
capable of providing the
strength required for
aggregates.
5) Comparatively low costs
of manufacturing.
operating and
maintaining the melting
furnace.
1) strength determined by
the flat test (in
accordance with test
method established by
Standard K-l of Japan
Sewage Works
Association) being
capable of meeting the
strength of class 1
centrifugal reinforced
concrete pipe (external
pressure strength
against cracking load of
JIS A 5303).
2) Nominal diameter of
about 500 mm.
3) Endurance almost equal
to or higher than that
of class 1 centrifugal
reinforced concrete
pipe.
1) Required processing
capacity greater than
1,000 m3/day.
2) process providing values
of biochemical oxygen
demand (BOD) and
suspended solids (SS) of
final effluent capable
of meeting the technical
requirements set forth
in para. 1 of Article 6
of the Enforcement
Ordinance of Sewarage
Law (Cabinet Order
No. 147 in 1959) .
3) simple operation.
4) Low maintenance and
management costs.
5) Simple environmental
measures.
ssuance date of the
evaluation certificate
September 1979
July 1980
July 1981
767
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Table 4.1 Themes of technology assessment by Ministry of
Construction (Cont'd)
Fiscal year
of invitation
1981
1982
1983
1984
Subjects
Development of energy-
saving type aerator by
diffused air.
Development of
mechanical aerator for
oxidation ditch process
Development of sewage
solid-liquid separation
method by screen process
Development of highly
efficient belt-press
for sewage sludge
dewatering
Objects of development
To develop energy-saving
type aerator to be used
for diffused air type
activated sludge process
at the sewage treatment
plant.
To develop efficient
mechanical aerator using
oxidation ditch process
as one of sewage
treatment methods.
TO develop solid-liquid
separation process using
screens for economically
separation of sewage
solids from liquids,
conventionally performed
with settling basin.
To develop a belt-preas
capable of efficiently
dewatering sludge to
obtain a cake with low
moisture content.
Goals of development
1) power consumption is to
be reduced by more than
20% compared to
conventional air
diffusing equipment.
2) For ordinary sewage, the
aerator is to be able to
provide the values of
biochemical exygen
demand (BOD) and
suspended solids (S3) of
final effluent meeting
the technical
requirements set forth
in Para. 1 of Article 6
of the Enforcement
Ordinance of Sewerage
Law.
3) Connection to existing
aeration tank is to be
easily made.
4) Simple operation.
1) Required current speed
is to be obtained.
2) Oxygen is to be
efficiently supplied.
3) Sufficient mixing and
agitating ability.
4) Easy equipment
maintenance and
operation.
5) Simple environmental
measures.
1) Quality of treated water
almost equal to that of
settling basin is to be
obtained.
2) Eeasiness in operation
and maintenance.
3) Sufficient durability.
4) Economical operation and
maintenance.
1} The system must have a
highly efficient
dewatering capability.
2) Easiness in operation
and maintenance.
3) Sufficient durability.
4) Economical operation and
maintenance.
Issuance date of the
evaluation certificate
July 1982
July 1983
July 1984
Expected to be
July 1985
As seen in the Table 4.1, four subjects are related to wastewater
treatment, two are related to sludge handling, and one is related to
sewers.
The period required for assessment under this system is about one
year from the time of inviting applications until completion of
assessment, thus making a quick evaluation possible. This is a very
convenient system for assessing equipments or machinery within short
period of time, but is not suitable system for evaluating treatment
processes which requires usually a relatively long time to evaluate.
The Japan Sewage Works Agency has a technology evaluation committee
which was established in 1974, to evaluate new technologies, particularly
treatment processes. This committee consists of representatives from the
768
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Ministry of Construction and Local municipalities as well as from the
academic circle.
The president of the Japan Sewage Works Agency asks the committee to
evaluate a particular technology, and the committee discusses the
features and the functions of the technology, the scope of its
applicability and the design parameters based on the data obtained from
actual plants employing the technology. The committee prepares a
evaluation report which is incorporated into the design criteria of the
Japan Sewage Works Agency to be reflected in the Agency's daily
operations. The official report is published openly, and those published
so far have contributed greately not only to the Japan Sewage Works
Agency but also to the Ministry of Construction, local municipalities and
private industries for proper utilization of the new technologies.
Table 4.2 shows the technologies that have been evaluated by the
committee so far.
Table 4.2 Technologies evaluated by the JSWA evaluation committee
Items submitted for deliberation
@ Automatic control of sewage
treatment plant
(|) Oxygen-activated sludge
process
@ Existing sludge incinerating
facilities
(?) Single hearth cyclonic furnace
(?) Evaporation-dewatering-
incinerating process
(C-G process)
(D RBC for small flow wastewater
treatment plant
(7) Sewage sludge composting
facilities for agricultural
use of sludge
(8) Oxidation-ditch process
Date of
inquiry
July 1974
July 1974
July 1975
Aug. 1977
Aug. 1977
Aug. 1977
June 1981
Dec. 1982
1st report
Oct. 1975
Oct. 1975
June 1980
Oct. 1980
Aug. 1979
Nov. 1978
"
Dec. 1983
2nd report
June 1980
Nov. 1978
-
-
"
Dec. 1982
"
-
3rd report
Aug. 1983
June 1981
-
-
"
-
™
-
Technologies evaluated by the Japan Sewage Works Agency's system are
in principle those being developed competitively by several companies,
and those being already used at some actual treatment plants. The field
data for evaluation are collected by the personnel of the Agency over a
necessary period of time, and are submitted to the evaluation committee
after analysis.
Design and 0 & M manuals for the new technology are usually prepared
after the report of the evaluation committee is published.
The Public Works Research institute of the Ministry of Construction
is reviewing the existing rules so that joint research with private
companies can be positively under-taken. The joint research projects on
development and utilization of biotechnology in wastewater treatment will
be the first case of joint research with private companies. The Japan
Sewage Works Agency has a provision on the joint research with private
companies since 1984. The projects being carried out now include the
769
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sequencing batch activated sludge process, a simplified sludge collector
for a small flow sewage treatment facility, and a technique to reduce
phosphorus returned from the sludge treatment process dealing with excess
sludge from biological phosphorus removal process.
To carry out this joint research project, the expenses generally are
shared evenly between the Agency and the private company, and the fruits
of the project such as patents are also shared equally.
In the following, some typical instances of the recent technological
development in Japan are outlined.
4.2 Some Typical Examples of the Recent Technological Development
4.2.1 Multiple deck sedimentation tank and deep aeration tank
In Japan, the area of a wastewater treatment plant site is generally
determined to be roughly 4.5 times as large as the area required for the
major treatment facilities and service passages. In such large cities as
Tokyo, Osaka, and Kyoto, however, it is often difficult to obtain a land
enough as prescribed in the guidelines mentioned above, for reasons of
cost and availability of land. Also, room must sometimes be left for the
future expansion or for constructing advanced wastewater treatment
facilities.
In addition, special considerations often become necessary in
heavily urbanized area to take coordination between wastewater treatment
plant and its surrounding environment or residents by means of
multipurpose use of the site. Under these circumstances, the concept of
the high degree and vertical uses of a treatment plant site was
introduced around 1960, and the design method for a multiple deck
sedimentation tank and a deep aeration tank have been established. In
most cases, these facilities are designed to have covers, and the top of
the cover are utilized as a park, tennis courts or similar facilities.
In Fig. 4.1, the comparison of site areas for wastewater treatment
plants with multiple deck sedimentation tanks and/or deep aeration tanks
and for those with conventional design is shown. The average site area
of a wastewater treatment plant per unit capacity of the plant is about
0.5 m^/WVday in Japan. The site area in Metropolitan Tokyo,
however, is just 0.3 nr/m /day on the average.
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40
30
a 20
a
a>
\4
•s
d>
3 10
e
e
go-
••o°'e°0
o
o
• o
..o
o o o
o.s
1.5
Capacity of STP (million m /day)
o STP with multiple deck settler and/or deep aeration tank
• STP with conventional design
e STP that part of its facility is multiple deck structure
Fig. 4.1 Comparison of site areas for sewage treatment plants with
multiple deck settlers and/or deep aeration tanks and
for those with conventional design
Gear box
Section
Overflow weir
Fig. 4.2 Double deck secondary sedimentation tank
(1) Sedimentation tank
The concept of surface loading proposed by T.R. Camp indicates
that the removal by sedimentation can be determined only by the
surface loading to the sedimentation tank. Experience suggests that
the suitable ranges of surface loadings for primary and secondary
sedimentation tanks are 20 to 50 m?/m*/3ay and 20 to
30 mVm2/day, respectively. However, when the sedimentation
tank is structured into two stories or more by placing one on the
771
-------
top of another, it is possible to acquire the treatment capacity
multiplied by the number of stories with the same site area. The
first double deck sedimentation tank (Fig. 4.2) was constructed in
1964 at the Ochiai Sewage Treatment Plant in Tokyo. Later in Osaka,
a three deck sedimentation tank was constructed for more effective
use of the site. As the experience of construction and maintenance
of these facilities is accumulated, the important points in the
design have become clear, which are as follows:
(a) The flows in the upper and lower decks should be made equal as
much as possible by the proper installation of valves and
overflow weirs.
(b) The sedimentation tank should also be structured so that no
scum accumulates on the bottom of the partitioning slab between
the upper and lower decks; this can be accomplished through the
utilization of a lower deck rake as a scum collector.
(c) Smooth collection and withdrawal of sludge should be guaranteed
by proper equipments and maintenance, which include the use of
a durable link belt, careful consideration about the shape and
capacity of the sludge hopper, and a device to prevent the
sludge withdrawal pipe from clogging.
(2) Deep aeration tank
In 1970, the Metropolitan Tokyo Government decided to employ
aeration tanks with a depth of 10 meters for constructing the
Shingashi and Morigasaki Higashi sewage treatment plants in order to
utilize the site effectively. The cross section of the tank is
shown in Fig. 4.3. This plan was beyond the experience of the
conventional design with 5 m depth. The problems which might
associate with such a deep aeration tank were thought to be the
adaptability of microorganisms to high hydraulic pressure and the
energy efficiency. The tests made before design had proved the
following facts:
(a) The microorganism activities did not decline even when the
cyclic hydraulic pressure of 0 to 20 m was repeatedly applied.
(b) As shown in Fig. 4.4 the theoretical energy required to supply
unit volume of air increased as the depth of the diffuser
increased. When this relationship was expressed by an
exponential function of the depth H as anB, the exponent 3 was
roughly 0.7. On the other hand, the oxgen transfer capacity
was also found to increase proportionally to the 0.7th power to
the depth H as shown in Fig. 4.5. Therefore, it was found that
the energy efficiency was not dependent on the depth of the
tank.
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Cross section
Air supply pipe
Diffuser
Baffle wall -_ j
Fig. 4.3 Deep aeration tank
,*
X
0)
o
3
o<
OS
M
0)
H
m
• H
4J
OJ
0
OJ
H
2
1
1
1
1
1
0
o
0
0
.0
.8
.6
.4
.2
.0
.8
.6
.4
.2
0
X
X
/
/'
/
/
*
/
/
/
/
•/
I
2 4 6 8 10 12 14 16 18
Depth of Diffuser(m)
Fig. 4.4 Relationship between
Theoretical Energy
Requirement and the Depth
of Diffuser
2,000
1,000
500
, 200
100
50
0
4 6 8 10 20
M (M)
Fig. 4.5 Relationship between Overall
Oxygen Transfer Rate Kj^'V
and the Depth of Diffuser H
(c) When the depth of the diffuser was more than 5 meters, it
became difficult to continue stable treatment because of poor
settlability of sludge due to gassification of the
supper-saturated air.
From these experiences, it was concluded that the following
consideration should be taken for the design of the facility:
(a) TO prevent activated sludge from floating, the diffuser is
placed at about a depth of 5 meters, not near the bottom of
the tank.
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(b) To assure good mixing even with an increased cross sectional
area, it is necessary to use the baffle walls effectively.
The design concept noted above has been employed in the
"Design Criteria for Sewerage Facilities" issued by the Japan
Sewage Works Association.
In fact, 7 wastewater treatment plants out of 10 plants in
service in Tokyo, or 55% of the total capacity of
5,880,000 mV<3ay, are those employing multiple deck sedimentation
tanks and/or deep aeration tanks. In Osaka City, among 12
wastewater treatment plants, 8 plants employ multiple deck primary
sedimentation tanks, 4 plants have deep aeration tanks, and 10
plants have multiple deck secondary sedimentation tanks. Another
fomous example is the kisshoin wastewater treatment plant in
Kyoto. This treatment plant employs the oxygen activated sludge
process, and the aeration tank is installed above the final
sedimentation tank. (Fig. 4.6.) Coupled with the effective use of
space created on the top of the cover of the treatment facilities,
the greater part of the facilities to be constructed in big cities
in the future will employ this kind of technique.
Effuent
Mixers
Aeration tank
Final sedimentation tank
Return sludge pump
Electricity room
Oxygen generators
Compressors
Ventilators
Fig. 4.6
Perspective view of secondary treatment facilities of
the Kisshoin STP in Kyoto
4.2.2 Phosphorous and nitrogen removal technology
In 1972, the public Works Research Institute of the Ministry of
Construction established a pilot plant with a treatment capacity of
250 m3/<3ay at the Shimomachi Sewage Treatment Plant in Yokosuka City,
and started the research on removal of phosphorous from secondary
effluent by means of chemical coagulation. This was the start of the
research on advanced wastewater treatment technology in Japan. Since
then, research and development for advanced treatment technology has
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come to be carried out extensively by major research institutions
including Research Division of the Japan Sewage Works Agency Tokyo and
other large cities.
Research at the beginning focused on physical-chemical treatment.
However, after the energy crisis in autumn in 1973, the saving or
conserving of resources and energy has become a demand of society, and
therefore, the emphasis on research and development for advanced
treatment technology shifted to the biological removal of phosphorous
and nitrogen.
During these periods, phosphorous removal by addition of a
coagulant to the aeration tank has been put to practical use. This
method has been employed by the wastewater treatment plants at Lake
Kasumigaura and Lake Biwa. In addition to minimize the amount of sludge
being generated, the crystalization method has been developed. This
method is to crystallize orthophosphate ions on the surface of the
contact media as calcium hydroxyapatite. In 1983, a full-scale plant
with a capacity of 12,000 m^/day was built by Metropolitan Tokyo.
As for the biological nitrogen removal process the single stage
nitrification and denitrification process with nitrified liquor recycle
has been put to practice as a means of removing nitrogen. The Konan
Chubu Sewage Treatment Center in the Lake Biwa area began to operate in
April 1982 as a full scale facility employing this method.
At a small sewage treatment plant in Hamamatsu City, biological
denitrification by the Wuhrmann process, which utilizes endogeneous
respiration, has been successfully carried out using the facility which
originally designed as an extended aeration process. An anaerobic
section is installed in the latter half of the aeration tank.
The first full-scale evaluation project of the biological
phosphorus removal process in Japan was performed by the Japan Sewage
Works Agency at the Arakawa Sewage Treatment Center in 1982. Since
then, researches for practical application have started at many
treatment plants in various cities such as Hamamatsu, Kawasaki, Kyoto,
Tokyo, Fukuoka and so forth.
One of the major targets of research on biological phosphorus
removal in Japan is to find the method to stabilize the treatment even
during the rainy season and the typhoon season in the summer time;
another target might be to pursue measures to reduce the return load of
phosphorous from the sludge treatment processes.
Another research field of interest is to reduce the capacity of a
nitrification tank by increasing the efficiency of nitrification. The
effect of installing rotating disks or other media in the aeration tank
has been studied at various institutions by pilot scale experiments.
Application of biotechnology for improving the efficiency of
nitrification has also been persued at many research institutions.
Also, as an advanced wastewater treatment process for a small flow
treatment plant, nitrogen and phosphorous removal by sequencing batch
activated sludge process has been studied.
Table 4.3 shows a list of wastewater treatment plants that have
been performing phosphorous and nitrogen removal as a routine practice.
Besides these plants, many demonstration projects for biological
phosphorus and nitrogen removal have been carried out at many places,
including Tokyo, Kyoto, and Osaka cities.
775
-------
Table 4.3 List of wastewater treatment plants employing
advanced wastewater treatment technology for
phosphorous and nitrogen removal
Receiving water
body
Lake Kasumigaura
Lake Hamana
Lake Biwa
Name of
wastewater
treatment plant
Kasumigaura
Wastewater
Treatment Center
Itako Wastewater
Treatment Center
Hitomigaoka
Hastewater
Treatment Center
Koto Wastewater
Treatment Center
Konan Chubu
Wastewater
Treatment Center
Okinoshima
Wastewater
Treatment Center
Kosei Wastewater
Treatment Center
Design
capacity
(m /day)
55,400
4,200
1,620
1,980
14,000
210
5,000
Treatment method
Nitrified Liquor recycle method
with coagulant addition to the
aeration tank
The same as above, and the
modified Phoredox process
Biological phosphorus removal,
and biological nitrification and
denitrif ication by the Wuhrmann
process
Same as above
Nitrified Liquor recycle method
with coagulant addition to the
aeration tank, and the modified
Phoredox process
Batch operated oxidation ditch
with coagulant addition
Bardenpho process with coagulant
addition
4.2.3 Instrumentation
One of the most advanced instrumentation technologies applied to
wastewater treatment systems in Japan is the centralized supervision and
distributed control system. In this system, process computers,
microcontrollers (CTR), and sequence controllers (SQC) are rationally
arranged so that the surveillance, data processing and supervision are
executed at the control center, and the actual control is executed
locally at the site.
This system has been realized as the result of advances in digital
control technology applied to instrumentation, including quantitative and
qualitative measuring devices, various control units, data transmission
units, and data processing units. The use of this system has resulted in
stable automated control, and efficient and labor-saving wastewater
treatment.
Taking an example of the Kanagawa Wastewater Treatment Plant of
Yokohama City, which employs this system, detailed explanation of the
system will be made. The Kanagawa Treatment Plant is a relatively new
treatment plant with a design capacity of 540, 000 m3/day. The plan of
the treatment plant is shown in Fig. 4.7.
(1) Configuration of the supervision and control system
The control center of this system consists of central computers
installed at the control room, and microcomputers and sequence
controllers distributed to each electric room.
776
-------
Pig. 4.7 Plan of Kanagawa Sewage Treatment Plant
The complicated controls for automation are performed by the
microcontrollers and sequence controllers at the local stations
according to the instructions given by the central computer. The
contents and results of these controls are transmitted to the
central computer from remote stations for CRT display in characters
and diagrams by means of the high-speed data transmission system
using optical-fiber cables.
This centralized supervision and distributed control system can
process an enormous amount of informations required for automated
process control.
Because the supervision function and the control function are
separated and work independently of each other, continuous control
is possible for stable wastewater treatment operations even while
the central computer is down.
Fig. 4.8 shows the system configuration.
(2) Function of the central computer system
To ensure reliability and maintainability, the central computer
system employs a dual system; one is for operation and the other is
a standby.
These two computers are operated by means of the load-sharing
and duplex system.
The standby computer is used for off-line processing, such as
preparation for the equipment management ledger and other off-line
batch processing.
777
-------
CTR: Mlcorcontroller
dH^)
1 Disk 1
System
rypewn ter
snt roller
jller
computer
l
Data way
controller
System
Console
|d>
1 I Disk)
1 l^-^l
^ **^ Data link
Graphical monitoring
panel controller
x 3
t
Peripheral equipment
Standby
computer
i
Data way
o-
7
CTR
1
J
SfiC
Data way (optical fiber
transmission)
Same as
left
1 1
Same as
left
1
Same as
left
I
Same as
left
1
1
^
1
1
1
' Same as
1 left
I
1
1
(
L
Same as
left
L_
1
Trans-
mission
control-
ler
MODEM
1 1
1 1
1 1
Trans-
mission
control-
ler
MODEM
1
-^
. -. - J
Receiving and
power station
block
Main pump and Blower
grit chamber facility
block block
Primary Secondary Disinfection Sludge
sedimentation sedimentation and filtration treatment
tank block tank block block block
Transmission Pumping stations
to and from (remote supervision
other treat- and control)
ment plants
Fig. 4.8 Schematic diagram of the centralized supervision
distributed control system
The major functions of the central computer system are as
follows:
(a) Supervision and operation
The system processes such information as the status of the
equipments, control modes, and measured values transmitted from
each local station to be displayed at a CRT and/or a graphical
monitoring panel for man-machine interface.
Operators can operate the equipments, and alter the
automatic control modes or predetermined values by looking at
the CRT.
778
-------
(b) Slips and books generating function
This system can store various process values into the
files sequentially and, using these data/ it can produce
automatically an output on the typewriter to generate various
slips and books.
(3) Functions of local stations
A local station consists of a microcontroller, a sequence
controller, and a high-speed data transmission system.
Normally, these controllers perform various complex automatic
controls and arithmetic controls.
The system is provided with a backup unit capable of
performing the minimum required controls to ensure trouble-free
operations of the wastewater treatment system even when these
original controllers have failed.
Table 4.4 shows the principal control parameters. Note that
those in the table to which the * mark are attached are the
controls that are not regularly executed.
(4) Measuring instruments
Besides such data as water levels, flow, pressure, and air
supply which are necessary to control operations, a need for
collecting water quality data has increased. In this treatment
plant, a PH meter is installed in the grit chamber; a
sludge-density meter in the primary sedimentation tank; DO, MLSS,
PH, and temperature meters in the aeration tank; and sludge
density, turbidity, PH, and UV absorption meters in the secondary
sedimentation tank. The readings of these meters are used as
inputs for automatic control, and are stored in the computer as
well as being displayed on the central CRT.
(5) Effect of the automatic controls
As mentioned, the Kanagawa wastewater treatment plant in
Yokohama is a relatively large treatment plant with a design
capacity of 540,000 m3/day. By employing an automatic control
system it has been possible to reduce the number of plant operators
significantly. This has been especially noticeable in the number
of operators in service at night and on holidays; only two
operators are required to operate the whole plant including two
relay pumping stations during these times.
In addition, DO control of the aeration tank makes some
contribution to the reduction in operation cost. It has been found
that air supply, particularly during storm period when the strength
of sewage is weak, can be reduced from 20 to 30% compared with that
with the flow proportional air supply strategy.
779
-------
Table 4.4 List of control modes
Local station
Extra-high
tension receiving
and transforming
power block
power station block
Grit chamber and
Main pump block
Blower facility
block
Primary
sedimentation tank
block
Aeration tank and
secondary
sedimentation tank
block
Disinfection and
filtration block
Control device
1. Power-receiving
equipments
2. Power-distributing
equipment
3. Generating station
4. Main pump and
blower
1. Main pump
1 . Blower
1. Primary sludge
pump
1. Aeration
2. Return sludge
pump
3. Excess sludge pump
1. Disinfection
2. Filtration
Control mode
1. Power failure control
2. Recovery control
3. Automatic receiving line switching
control
1. Manual pattern shifting control
2. Power factor control
1. Peak load cut control
2. Automatic starting control
3. Automatic synchronized control
4. Number of units control
5. Load transition control
6. Automatic frequency control
7. Automatic voltage control
B. Load sharing of active and
reactive power control
9. Dummy load control
1. Load limit control
2. Load lock control
1. Constant water level control*
2. Constant flow control*
3. Level and flow control
4. Revolutions control
1. Constant pressure control*
2. Constant air flow control*
1. Constant sludge density control*
2. Intermittent withdrawal control*
3. Continuous withdrawal control
(preset control)
1. Constant DO control
2. Constant air flow control*
1. Constant MLSS control*
2. Constant flow control
3. Constant return rate control
1. SRT control*
2. Intermittent withdrawal control*
3. Continuous with drawal control
(preset control)
1. Constant injection volume control*
2. Constant injection rate control
1. Inflow control
2. Number of units control
Note: Those with * mark are the control systems available as an option.
4.2.4 Control of offensive odor from wastewater treatment plants
The offensive odor prevention law was enacted in 1966. As shown in
Table 4.5, eight substances generating offensive odors are presently
regulated. The governers of prefectures shall determine the actual
standards within the ranges of concentration listed in the Table 4.5
considering the actual situations of the local districts. These
standards are applied to the concentration at a site boundary.
780
-------
Table 4.5 Regulated substances under the offensive odor prevention law
Restricted
materials
Ammonia
Methyl mercaptane
Hydrogen sulfide
Methyl sulfide
Tr line thyl ami ne
Methyl disulfide
Ace tal deny de
Styrene
Range of
standard (ppm)
1 - S
0.002 - 0.1
0.02 - 0.2
0.01 - 0.2
0.005 - 0.07
0.009 - 0.1
0.05 - 0.5
0.03 - 20
Note: Standards are applied to the concentrations
at the boundary of the site.
Wastewater treatment plants in Japan must often be built adjacent
to residential areas; therefore, attention has to be paid usually to
prevent offensive odors. For this reason, measures to control offensive
odors have attained significant advances. The operating wastewater
treatment plant have never failed to meet the legal standards, and only
a few complaints about odors have been made to wastewater treatment
plants.
As shown in Table 4.6, most of the wastewater treatment plants
install a cover on their main source of offensive odors, such as
thickners, and the percentage of treatment plants without such a cover
is only about 30%.
As shown in Table 4.7, 43% of treatment plants have odor control
facilities for sludge thickners, and 57% of treatment plants have
control facilities for sludge dewatering machines. Even 41% of the
total treatment plants have control facilities for grit chambers which
are known to generate little offensive odor. The deodorizing method
most widely used is chemical scrubbing with sodium hydroxide and sodium
hypochlorate, and it accounts for about half the total deodorizing
facilities in use. The absorption method using activated carbon or ion
exchange resin and the ozone oxidization method each accounts for only
12% of the total deodorizing facilities. The rest of the facilities
almost employ highly advanced means of deodorization by combining these
methods.
A representative method of this category is activated carbon
absorption following acid and alkali scrubbing, or a method that
combines ozone oxidation and activated carbon absorption. In some
treatment plants, soil deodorizing method is used, which passes
offensive odor through a soil layer. A method that induces the air with
offensive odor into the aeration tank is also being applied. This
method is less-costly in both construction and maintenance costs.
781
-------
CXI
Table 4.6 status of covers for wastewater treatment facilities
Secondary
sedimentation tank
Sludge thickening tank
Dewatering machine
Indoor
(T) Covered
67
38
198
(2) uncovered
128
46
150
Outdoor
(5) Covered
26
168
-
(T) Uncovered
78
97
-
percentage of
uncovered facility
0/®+
-------
About 12% percent of the total wastewater treatment plants in Japan
have spaces which are open to the public within their premises as a
park, an athletic field, or a district public meeting facility, all of
which has contributed to better relations with residents living near
wastewater treatment plants. Progress in odor control technology has
contributed significantly to this kind of practice. In addition, when
the construction of a wastewater treatment plant is undertaken, it is
sometimes difficult to obtain the consent of residents near the
prospective construction site. Complete control of odor, in some cases,
is a key factor to get consent from nearby residents. In this sense,
odor control technology has become one of the indispensable technologies
relating to wastewater treatment in Japan.
783
-------
5. UPGRADING OP EXISTING WASTEWATER TREATMENT PLANTS
5.1 Background
During the 100 year history of Japan's sewage works, there have
been considerable changes in the socioeconomic situation that have
brought more variety in the concept of planning and designing the
sewarage systems. In the past, sewerage systems were only constructed
at large cities where the population desity was high, and most of the
wastewater treatment plants had large capacities. At present, however,
the demand for wastewater treatment has increased in small and medium
sized cities, and many small and medium-sized plants are being built.
As to the collection system in the past, the combined sewer system was
employed for the construction of sewers in large cities, but now, new
sewer systems are being constructed by the separate system.
The changes in socioeconomic situation, such as people's lifestyle,
concentration of population in cities, and development of industries,
were very fast and large. In some cases, they were more than expected
at the time of planning of the facilities. These changes have directly
affected treatment plant operation, often resulting in deterioration of
effluent quality.
5.2 Necessity for Upgrading of Existing Wastewater Treatment Plants
There has been a variety of causes which made upgrading of existing
treatment plants necessary. Typical ones are as follows:
(T) Upgrading the effluent standards
Legal system concerning environmental protection was
restructured and subsequently enacted around 1970, and the
environmental standards on the major water bodies in Japan were
then established. The importance of sewage works in controlling
pollution of public water bodies was legally defined by the
amendment of the Sewerage Law at that time. For almost all of the
river basins, the effluent standards requiring secondary theatment
were established. In some areas, more stringent standards which
require better treatment than the conventional secondary treatment
have been enforced based on local necessity.
(g) Rapid concentration of population and industrial development
Some treatment plants became overloaded because of the
unexpectedly rapid concentration of population and industrial
development. Especially industrial wastewater discharge often
affects greatly on the operation of a treatment plant. Large
variation of flow and load, and discharge of non-biodegradable
organics are another problems associated with industrial
wastewater. At present almost all of the municipalities have
pretreatment standards, and can order industries to improve their
pretreatment facilities according to its necessity. They also have
surveillance systems to enforce the pretreatment standards.
784
-------
Increase in load
The improvement of the standard of living and the change in
food consumption have caused a considerable increase in pollutant
load per person. Per capita BOD load used to be 35 - 40 g/cap/day
in 1950's. However, it increased rapidly since then and is now
about 50 - 60 g/cap/day in large cities as shown in Fig. 5-1.
1973
1975
1977
1979
1981
: Hei}0 STP
: Arino STP
: Tamon STP
O: Nishiyama STP
A: Sayama STP
Fig. 5.1 Change in per capita BOD Load
Recent increase in organic content in sludge, which is mainly
due to increase in fats and oil in sewage, has created difficult
problems in sludge handling. Poor thickenability and
dewaterability often required upgrading the sludge treatment
facilities.
Revision of design criteria
The conventional design criteria were determined in reference
to data obtained from large sewage treatment plants connected with
combined sewer system. At a medium or small sized treatment plant
of the separate sewer system based on these criteria troubles
sometimes occurred even under normal loading conditions. For
example, at a small treatment plant treating sewage from a housing
complex, due to extremely large flow variation, sludge washout
ocurrs at the time of peak flow, or sludge bulking may easily occur
due to high organic loading.
The conversion of a collection system from combined to
separate sewer adversely affects the sludge's settlability,
compressibility, and dewaterbility, and some treatment plants have
troubles in sludge handling. The treatment plant employing a
separate sewer system can easily be upset by inflow and
infiltration of storm water and ground water. Thus, a measure to
reduce inflow and infiltration needs to be taken throughout the
collection system.
785
-------
(5J Direct discharge of collected night soil into the wastewater
treatment plant
There have been cases in which night soil collected from
non-sewered area was directly discharged into the wastewater
treatment plants at large amount, or partially treated effluent or
sludge produced from the night soil treatment plants was disposed
into the sewer systems. These activities often caused treatment
plants to malfunction because of overloading and excessive nitrogen.
(&) improper operation and maintenance
A wastewater treatment plant cannot produce good quality
effluent unless it is properly operated and maintained. It is
desirable that plant-operators are well-trained, employing such an
operator, however, may sometimes be difficult. In a medium or
small-sized treatment plant, personnel expenses may tend to account
for the greater part of its total operating cost, resulting in
reduced personnel expenses. A treatment plant without well-trained
operators often fails to discover the early symptom of malfunction
and cannot take any remedial measures to prevent deterioration of
effluent quality.
(?) Others
To attain a reduction of operational costs and efficient
energy conservation the improvement of existing facilities and
adequate operation and management are required.
5.3 Tentative Guideline for Upgrading of Existing Treatment Plants
The existing sewerage facilities in the greater part of sewer
districts in Japan are under continuous construction and expansion.
Therefore, the wastewater flows at treatment plants are continuously
increasing. Consequently, almost all of treatment plants in Japan have
experienced the both conditions that their treatment capabilities were
temporarily too small or too large, and the personnels of these
treatment plants have experienced troubles caused by these conditions.
These experiences have become valuable references to the future
operation & maintenance, and they have been reflected in the design of a
facility in the case of expansion projects.
Although some common problems to be solved have been made clear,
and the case studies and experiences for upgrading in these matters have
been utilized for operations or design of other treatment facilities,
seldom are the cases in which the detail of the experience and process
of upgrading from identification of the cause of malfunction to the
improvements achieved have often been disclosed to the public.
The Japan Sewage Works Agency collected information on cases
concerning the causes of malfunction and improvements applied throughout
the country during a six-year period from 1975 to 1981. In some cases,
on-sight identifications of the causes were made and corrective steps
were taken in close cooperation between the Agency and the persons in
786
-------
charge of the plants. The Agency also investigated to verify the
effectiveness of some measures to counter the problems by using pilot
and full-scale plants. A report was subsequently made by summarizing
these results.
The Japan Sewage Works Association organized a committee consisting
of competent engineers with an expert knowledge on the plant's
management to prepare a guideline based on this report. The results
were disclosed to the public as "Tentative Guideline for Upgrading of
Existing Treatment Plants".
The guideline describes the causes and symptoms of troubles
encountered in operation and maintenance of the activated sludge
process, and explains the precautions to be taken and the methods to be
employed being classified by causes.
5.4 Examples of Upgrading of Existing Plants
Among many cases in which existing treatment plants were upgraded,
some representative cases are introduced in the followings.
5.4.1 Improvement in effluent quality by means of separate treatment of
supernatant from the sludge treatment processes
There have been many cases in which treatment plants are suffering
from loading by supernatant from the sludge treatment facilities.
The examples described below are the Toyohiragawa Treatment Plant
in Sapporo City and the Senboku Sewage Treatment Plant in Sakai City,
each of which has a heat treatment process for sludge treatment. Both
treatment plants experienced deterioration in performance caused by high
supernatant loading from sludge heat treatment process, and have been
successfully improved by separate treatment of supernatant.
(1) Conditions before improvement
The strength of the supernatant generated by the heat
treatment process is very high, and the following troubles occurred
in the wastewater treatment facilities.
The aeration tank became overloaded.
The loading to the aeration tank varied largely depending on
the on-off operation of the heat treatment facility.
The secondary effluent was colored, and an offensive odor was
generated.
Besides the common problems mentioned above, the following
troubles were added to the Senboku Sewage Treatment Plant.
(T) The treated water could not easily conform with the effluent
standard (Relating to COD^).
(2) The function of sludge thickening was extremely deteriorated,
and solids twice as much as those in raw sewage were
recirculating from sludge treatment processes.
787
-------
Because of these troubles, both plants were unable to obtain
the stable effluent quality.
(2) Corrective measures
As the results of detailed investigations, separate treatment
process on the supernatant from sludge treatment process was taken
to be the basic policy for both treatment plants.
(a) Improvement applied to the Toyohiragawa Treatment Plant
The supernatant is diluted with an equal amount of the
secondary effluent, and is treated by means of the extended
aeration process. The effluent from this separate treatment
process is returned to the primary sedimentation tank.
In order to prevent wash-out of sludge at the secondary
sedimentation tank, the weir loading was reduced and the
arrangement of the weir was redesigned.
(b) Improvement applied to the Senboku Sewage Treatment Plant
The facility for treating supernatant separately has been
constructed. The process was the aerobic/anaerobic biological
process including biological denitrification, and the effluent
is returned to the primary sedimentation tank.
(3) Plant performance after improvement
BOD, COD, and SS removals have been considerably improved
after improvements at both plants, and effluent quality has come to
conform with the effluent standards. Offensive odor was completely
removed from the effluent.
The effect of upgrading by means of separate treatment process
is summarized in Fig. 5.2.
Table 5.1 shows a comparison of the effluent qualities of the
Senboku Sewage Treatment before and after the improvement.
Fig. 5.3 shows a comparison of stability of the effluent qualities;
and Fig. 5.4 shows a comparison of solid mass balances before and
after the improvement.
Table 5.1 Comparison of effluent qualities of the Senboku Sewage
Treatment Plant
788
-------
L i
Stabill zed settling
efficiency in primary
sedimentation tank
Refreshing of sludge
(eliminated putre-
faction)
Secured optimum
solids concentration
to gravity thickener
(primary sedimenta-
tion tank) and to
centrifugal thickener
Improved and stabilized
effluent qualtiy
Improved removal rate
Promoted nitrogen removal
in wastewater treatment
Simplified operation
control
Improved and stabilized
gravity thickening and
centrifugal thickening
functions
Early removal of sludge
generated in wastewater
treatment system
Simplified operation
control
Allowance in facility
capacity particularly in
sludge treatment system
Fig. 5.2 Effects by introduction of supernatant separate treatment
- 100
dP
o1 80
c
(U
g- 60
>H
n 40
.u
J3 20
«
0
Jan. to Sept. 1982
(n=273)
.
. r
_.
— i
~ 100
dP
requency
en CD
a, 40
•H
«
0
Oct. to Jan. 1982
(n=124)
• , r
i, ,
10 20 30 40 50
COD (mg/JU
Before improvement
Fig. 5.3 Comparison of the effluent
improvement
10 20 30 40 SO
COD (mg/Ji.)
After improvement
histograms before and after
789
-------
Raw sewage
394 kg/day
(290 kg/day)
Upper figure: Before improvement
(Lower figure: After improvement)
4,028 kg/day
(4,098 kg/day)
8,533 kg/day
(1,460 kg/day)
Fig. 5.4 Comparison of Solid Mass Balances before and after
the Improvement in the Senboku STP
5.4.2 Improvement in Treatment Capabilities by Chemical Dosing to Primary
Sedimentation Tank and by Injecting Pure Oxygen to Return Sludge at the
Tobu Sewage Treatment Plant in Mitaka City
(1) Condition before improvement
This plant is of combined flow type with a design capacity of
21,000 mV<3ay« Due to the increase of population in the drainage
area, the volume of influent increased annually to 40% in excess of
the design capacity about 30,000 mV^ay as of 1975. As a
solution to this overloading condition, expansion of the treatment
facility was the first consideration, however, it was practically
impossible due to restrictions from location and site space. As
such being the situation, this plant was taking great pains in
finding effective measures for oxygen supply to the aeration tank.
(2) Corrective measures
Additional installation or rebuilding of blowers could not be
chosen due to the limited budget. After studying a method to
supply dissolved oxygen to the aeration tank, injection of pure
oxygen into the return sludge was decided and applied after the
repeated experiments on pure oxygen injection on site started in
January, 1975.
The newly installed equipment for pure oxygen injection
consisted of an oxygen supply unit and an oxygen dissolving unit.
In the oxygen supply unit, liquid oxygen was gasified and regulated
to 1.5 to 2.5 kg/cnr by the final pressure control valve, and
then supplied to the line mixer, which was installed just after the
return sludge pump.
As the second corrective measure to mitigate the load of the
aeration tank, a coagulant was dosed into the sewage at the primary
sedimentation tank, and thus upgraded the efficiency of primary
sedimentation tank.
790
-------
For this purpose, a coagulant dissolving tank and a dosing
tank were provided, and a diffuser pipe was installed in the
conduit to the primary sedimentation tank for mixing. Because the
raw sludge production increased as a result of coagulant addition,
beltpress filters were installed instead of vacum filters for
sludge dewatering.
(3) Plant performance after improvement
The injection of pure oxygen has been made at a rate of
40 £/min. for the amount of 5.3 m3/min. of the return sludge. As
a result, even the sewage to be treated increased from
24,000 m3/<3ay to 30,000 m3/<3ay, the effluent quality after
improvement was equivalent or better than that before the
improvement. Because dissolved oxygen in the aeration tank was
maintained at a desirable level by increasing the oxygen supply, a
stabilized effluent quality could be obtained. These results are
shown in Table 5.2.
Table 5.2 Comparison effluent qualities before and after improvement,
Tobu Sewage Treatment Plant, Mitaka City
Item
Before
improvement
1975/1 - 2
After
improvement
1975/3 - 4
Flow
23,703 m3/day
29,563 m3/day
DO of aeration
tank effluent
1.65 mg/je
2.31 rng/H
Effluent
Trans-
parency
43 cm
68 cm
COD
9.8 mg/i
11 mq/H
BOD
-
17 mg/i
SS
-
25 mg/Z
5.4.3 Other Proposed Methods for Upgrading
The followings are the list of other methods recommended in the
tentative guideline for upgrading.
(1) Corrective measures for overloading
(T) improving the efficiency of the primary sedimentation tank by
addition of a coagulant
(g) Reducing the supernatant loading by improving the performance
of sludge treatment processes
(5) Increase in oxygen supply by employing the improved aerator
(4) Conversion from the conventional activated sludge process to
the step-aeration process
(§) Employment of the pure oxygen-activated sludge process
(2) Corrective measures for large flow variation
(T) To install more capacity of the equalization tank
791
-------
© Utilization of the capacity of trunk sewers
(T) Conversion of the primary sedimentation tank to an
equalization tank
(3) Corrective measures for bulking
Modification of the operating condition of the aeration tank
Addition of inorganic SS to the aeration tank
Addition of chemical coagulant to the aeration tank
Employment of the anaerobic/aerobic activated sludge process
Employment of the pure oxygen-activated sludge process
(4) Improvement of the aeration tank operation
(1) Use of efficient aeration devices
§ Automatic DO control
Effective use of baffle boards to prevent from short-circuit
of flow
(4) Reaeration of return sludge
(5) Improvement in secondary sedimentation tank to prevent wash-out of
sludge
792
-------
DEVELOPMENTS IN THE FIELD OF WASTE WATER TECHNOLOGY
IN THE NETHERLANDS
by
A. B. van Luin and W. van Starkenburg
Governmental Institute for Sewage and
Waste Water Treatment
Inland Waters Department
DBW/RIZA
P.O. Box 17
8200 AA Lelystad
The Netherlands
W. H. Rulkens and F. van Voorneburg
Netherlands Organization for Applied
Scientific Research
Division of Technology for Society
MT/TNO
P.O. Box 342
7300 AH Apeldoorn
The Netherlands
The work described in this paper was
not funded by the U.S. Environmental
Protection Agency. The contents do
not necessarily reflect the views of
the Agency and no official endorsement
should be inferred.
North Atlantic Treaty Organization/Committee on the
Challenges of Modern Society (NATO/CCMS) Conference
on Sewage Treatment Technology
October 15-16, 1985
Cincinnati, Ohio
793
-------
DEVELOPMENTS IN THE FIELD OF WASTE WATER TREATMENT
IN THE NETHERLANDS
by: A. B. van Luin and W. van Starkenburg
Governmental Institute for Sewage and
Waste Water Treatment
Inland Waters Department
DBW/RIZA
P.O. Box 17
8200 AA Lelystad
The Netherlands
W. H. Rulkens and F. van Voorneburg
Netherlands Organization for Applied
Scientific Research
Division of Technology for Society
MT/TNO
P.O. Box 342
7300 AH Apeldoorn
The Netherlands
ABSTRACT
Recent advances in waste water treatment in the Netherlands are summa-
rized in this paper for three major research areas of micro-pollutants,
sewage sludge and innovation and upgrading of waste water purification
systems.
In micro-pollutant research, the sources and amounts of organic and
inorganic micro-pollutants in domestic waste water, municipal waste water
with industrial contributions and direct industrial waste waters are
characterized. A surprisingly large dispersion of dichloromethane was
observed in the domestic wastewaters. In addition to trace metals,
municipal waste waters with industrial contributions usually contain
volatile chlorinated hydrocarbons, chlorophenols, hexachlorocyclohexane,
polychlorinated biphenyls, and polycyclic aromatic hydrocarbons, generally
at low concentration levels. Industrial wastewaters invariably contain
volatile chlorinated hydrocarbons such as tetrachloromethane and chloro-
phenols, especially pentachlorophenol. Removals for the various
micro-pollutants are presented.
In research on sewage sludge, substantive studies on autothermal
combustion, sludge thickening and dewatering, pathogenic content and disin-
fection, and disposal of sludge as agricultural soil conditioners and as a
794
-------
substrate for trees have been completed. Raw sludge with an ash content of
about 20% and dry matter content of about 25% may be burnt autothermically.
Thickening can be improved by use of polyelectrolytes. Laboratory studies
on sludge conditioning have characterized sludges such that practical (full-
scale) improvements in dewatering are likely. The hygienic problems from the
use of sewage sludge in agriculture are highly dependent on regional factors
and a "safe" procedure for disposal on agricultural applications cannot be
provided in general terms, each case must be assess separately.
Research on innovation and upgrading of waste water purification
systems has produced novel elements, especially in anaerobic treatment. The
research should stimulate potential applications of anaerobic treatment of
municipal waste water using either the anaerobic sludge bed (USAB) reactors
or fluidized bed technology. Industrial uses of anaerobic treatment are
extensive and successful in a variety of Dutch industries. A novel approach
to removing nitrite from ground water features ion exchange removal of the
nitrate with biological denitrification to eliminate the nitrate and provide
regenerant for the ion exchangers.
INTRODUCTION
In this report a review is given of water pollution control research
currently in progress and the application of waste water treatment processes in
the Netherlands. The accent is placed on advanced waste water treatment pro-
cesses. Additional attention is also given to the possibilities of reducing
waste water discharges by internal measures and the application of "clean
technology". The research described here is mainly related to work which is
still in progress or has just finished at universities, research institutes,
engineering firms and industries, the results of which are publicly available.
Much of the work is carried out for central or local government in the form of
contract research. The work is partly paid by industry and partly by the
research institutes themselves.
This report comprises three major sections:
The first section describes the problems of pollution by micro-pollutants. A
great deal of research on monitoring micro-pollutants as well as research in the
field of curbing this pollution has been done.
Sewage-sludge is the main-subject of the second section. There are great
problems with the quality and the application of sewage sludge. In the past,
most of the sludge was applied in agriculture. Over the past few years alter-
native applications and treatment methods have been investigated.
The third section describes the innovation and upgrading of waste water
purification systems. This section reviews the developments concerning the
treatment of municipal, industrial and agricultural waste waters, and contami-
nated ground water.
795
-------
Primary sources on which this paper is based are:
The (Dutch) journal "HO", mainly the volumes for the years 1982, 1983,
1984 and 1985.
Research reports from the Dutch Ministery of Housing, Physical Planning and
Environment.
Research reports from the Governmental Institute for Sewage and Waste Water
Treatment (RIZA) and several research institutes and industries.
It has to be noticed that the information in this report does not fully
reflect the state of the art of water pollution control research in the Nether-
lands, but a serious attempt has been made to show principal developments.
MICRO-POLLUTANTS
INTRODUCTION
The legal framework for the fight against water pollution in the Nether-
lands has been laid down in the Pollution of the Surface Water Act which was
passed on 1 December 1970. It prohibits the unlicensed discharge of polluting or
harmful substances into surface water. Although considerable progress has been
made in recent years, surface water pollution continues to be a serious cause
for concern, and its curbing remains the chief objective of governmental policy.
In the years after the Pollution of the Surface Water Act had become law,
emphasis was placed on oxygen consuming substances. More recently, however,
attention has primarily focused on non-oxygen consuming substances.
To this category of substances belong:
Nutrients (phosphate and nitrate);
Inorganic micro-pollutants (e.g. heavy metals);
Organic micro-pollutants (e.g. persistent pesticides and PCB's).
The name micro-pollutants is used because the concentrations at which these
substances may cause harmful effects are at the level of micrograms and even
nanograms per liter. In cases of oxygen consuming substances the concentration
levels amount to tens of milligrams per liter.
In this chapter the results are given of a number of research projects in the
field of inorganic and organic micro-pollutants.
SOURCES OF ORGANIC MICRO-POLLUTANTS
Organic micro-pollutants in domestic waste water
In 1984 the Governmental Institute for Sewage and Waste Water Treatment
carried out an initial study on the presence of a number of organic micro-
pollutants in domestic waste water. Waste water of five residential areas was
sampled and analysed. The waste water streams contained neither rain-water nor
industrial waste water. The results of the study are given in Table 1.
The enormous dispersion in the figures for dichloromethane is especially
striking and its causes are still unclear. The study will be continued.
796
-------
TABLE 1. ORGANIC MICROPOLLUTANTS IN DOMESTIC WASTE WATER7
(in mg/inhabitant/year)
Compound
d ichloromethane
tr ichloromethane
tetrachloromethane
trichloroethene
1 ,2-dichloropropene
tetrachloroethene
1,2 dichloroethane
1,1, 1-trichloroethane
monochlorobenzene
1 , 2-dichlorobenzene
1 ,4-d ichlorobenzene
hexachlorobenzene
°\-hexachlorocyclohexane
y-hexachlorocyclohexane
2 , 4 , 5- tr ichlorophenol
2,4 , 6- tr ichlorophenol
2,3,4, 5-t«trachlorophenol
2,3,4 ,6-tetrachlorophenol
pen tach lorophenol
polychlorinated biphenyls
polycyclic aromatic
hydrocarbons^)
') number of samples: 10
2) number of samples: 5
3) average over 35 samples
4) sum of PCB 8,52,101,138
Amsterdam! )
min. max. mean
157 80000 9000
84
Q6)
0
0
212
0
0,8
5.5
2.1
4.4
10,2
0
13
204
296
394
299
1680
0,8
2*1
77
4.4
11
36
3.4
27
150
88
40
0
0
29
0
647
0,15
0.31
21
0
6,2
0
6,9
23
0,73
21
Steenwijk2) Enschede(I) 1 ) Enschede ( II ) 1 ) Maarssen2)
min. max. mean min. max. mean min. max. mean min. max. mean
400 390103 124103 0 110
146
146
84
0
0
6,2
3.7
3,7
12
0
6,9
285
402
281
0,8
0.4
26
4.7
4.7
33
2,2
1.6
,153 and 180
5) sum of fluoranthene, benzo(6) fluoranthene,
(benzo(k) fluoranthene,
perylene and indeno(1,2
benzol a) pyrene
, benzo(g ,h,i) ,
,3-c,d)pyrene
6) zero means concentration below
detection limit
190 48 139
157
0 0 139
0 0 2835
0
0
0 0 139
197 869 1830
0,32
0,07 0 0,91
15 1.4 3,5
0 0 28
4,0 2.3 14
0
4.0 8,4 32
20 18 51
0.9
11 18 68
40 0 92000
102 58
0 0
51
686 0
0 0
0
28 0
1190 0
0 0
0.4 0
2.0 1.0
8.4
6.2 2,7
0 0
14 0
35 12
0
20 6.2
7 ) 1 , 3-dichloropropane
1 , 1 ,2-trichloroethane
1 ,2,3-trichloropropane
1 ,2,3-trichlorobenzene
1 , 2 , 4- tr ichlorobenzene
1 ,3,5-trichlorobenzene
(\ -hexachlorocyclohexane
)
325
270
172
157
270
2770
0,51
1.1
4.0
16
7.7
27
439
18
in
15000 73 383
200 820 1570
80 0 606
0
29
15
0
120
836 1350 4590
0,04 Oi91 1,5
0.58 1,3 3.5
2,7 3,6 7,7
0
7.3 4,4 9.5
0.7
5,8 28 139
77
0
13 2,3 16
all samples below
256
1130
223
0
0
0
0
0
2960
1.1
2.1
5,5
0
7t7
0
53
0
0
1 1
MEAN3)
24600
303
102
1R
106
4.0
0,4
40
1040
0,26
0,91
12.8
1.1
6.6
0,2
14
36
0,32
16
detection limits
-------
Organic micro-pollutants in municipal waste water treatment plants
In 1983 the Governmental Institute for Sewage and Waste Water Treatment
(RIZA) studied the presence of organic micro-pollutants in influent, effluent
and sewage sludge of six municipal waste water treatment plants.
The results of the study were published and presented at the IAWPRC-
congress of Amsterdam in September 1984. The conclusions of the study are:
The conclusions of the study are:
Volatile chlorinated hydrocarbons in sewage appear to originate mostly from
industrial emissions. The amount of the emissions may fluctuate considera-
bly, especially in the case of dichloromethane and 1,2-dichloroethane.
Chlorophenols, hexachlorocyclohexane, polychlorinated biphenyls (PCB) and
polycyclic aromatic hydrocarbons are - on a low basic level - invariably
present in municipal waste water and in many industrial waste water
streams.
In addition to point sources there are also diffuse sources such as
deposit from the air and road traffic, which are responsible for the extra
sewage pollution. In the study this is demonstrated especially in the case
of polycyclic aromatic hydrocarbons.
PCB and fluoranthene are invariably detected in sewage sludge. Occasionally
hexachlorobenzene, 2,4,5-trichlorophenol, 2,3,4,6-tetrachlorophenol, penta-
chlorophenol and benzo(b)fluoranthane were also present.
In the study it has not been possible to give a full assessment of the fate
of these substances in a treatment plant. More intensive research will be
initiated for that purpose.
The overall removal in the municipal treatment plants amounts to:
volatile chlorinated hydrocarbons 50-90%
hexachlorobenzene 95%
hexachlorocyclohexanes 40-65%
chlorophenols 20-40%
PCB about 90%
polycyclic aromatic hydrocarbons 85-95%
Organic micro-pollutants in industrial waste water
Since 1980 RIZA has been researching the presence of organic micro-
pollutants in industrial waste water (1). In 1983 waste water of 37 industries
was examined for the presence of:
Heavy metals
Drins (e.g. aldrin)
Polychlorinated biphenyls
Chlorophenols
Benzene and chlorinated benzenes
Tri- and tetrachloromethane.
The overriding conclusion was that components such as pentachlorophenols
are present in most waste waters. Even in brewery waste water. In this
particular case the waste water became "polluted" because of the glue on the
beer-bottle labels.
798
-------
Table 2 shows that a large number of components are present in the various
waste water streams. It has not yet become clear why these components are
present in most cases. Consequently, research is continuing.
TABLE 2. SURVEY OF THE PRESENCE OF HAZARDOUS SUBSTANCES IN
INDUSTRIAL WASTE WATER FROM DIFFERENT INDUSTRIES
substance
branch of industry
(number of plants measured)
slaughtery (2)
dairy products (3)
fruit and vegetables (1)
margarine and fats (2)
sugar (1)
soft drinks and
carbonated waters (1)
brewery (1)
textile (2)
leather (2)
paper, pulp and
paperboard (2)
wood-impregnation (2)
printing (1)
painting (2)
soap and cleaning (detergent)
preparations (1)
rubber (2)
dye (3)
electroplating (4)
photographic laboratory (1)
laundry (1)
motor-overhaul (1)
hospital (1)
incineration of refuse (1)
v
d
18
41
O
u
•1-1
0
0
0
0
0
0
0
0
0
o
d
«
4-1
O
U
o
I—I
.d
u
4-1
0)
4-)
O
u
JS
a
o
u
o
JO
u
•H
VI
4-1
0
0
0
0
0
0
0
0
0
o
v
JS
a
o
d
OJ
a,
d
v
N
d
v
.a
o
J3
U
18
X
.
xi d
U (U
>> -C
ft 04
O -H
a, f>
0
0
0
0
+ = present in waste water
= undetected in waste water
0 = research has not finished, no positive results thus far
*) = (probably) one or more of the isomers: PCB 28, 52, 101, 138, 153 and 180
799
-------
REDUCTION IN THE EMISSION OP ORGANIC MICRO-POLLUTANTS
Polycyclic aromatic hydrocarbons
In 1984 Hoogovens IJmuiden installed two precoat-vacuumfliters - each with
a filter surface of 36 m2 - for the removal of polycyclic aromatic hydrocarbons
(PAH). The amount of waste water to be processed is 120 m3/hr. PAH-emission has
been reduced from 15 to less than 1 kg/day. The costs of investment of the
filters were 1.7 million Dutch guilders. Total investments, constructional and
electrotechnical supply included, amounted to 3.1 million Dutch guilders.
PAH are among other components caused by pyrolysis of organic material such
as occurs in the coke oven process. A coking-plant produces coke by heating
coal, air-free, to a temperature of about 1300 °C. The volatile substances
released in the process are called coke oven gas and are used in the production
plant.
Before use the gas has to be cooled and purified. In this process waste
water containing PAH and other substances is produced.
Analyses show that PAH is generally present in - or on the surface of -
suspended solids in the waste water (Table 3).
TABLE 3. PAH IN WASTE WATER (IN pG/L)
liquid
total
54
suspended solids
naphthalene
acenaphthene
dibenzfurane
f luorene
fenanthrene + anthracene
f luoranthene
pyrene
1,2-benzanthracene + chrysene
benz(b+j+k)f luoranthene
( 1 , 2+3 , 4)benzpyrene
1,12 benzperylene
coronene
n.d.
n.d.
n.d.
2
30
15
6
1
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
5
5
185
405
205
280
120
155
60
35
1470
n.d. = non-detectable (< 1
For the removal of PAH a particular filtration method has been chosen. Pre-
coat filtration gives the best environmental and economical results (Table 4).
800
-------
TABLE 4. RESULTS PILOT-PRECOAT FILTER. (PAH IN
infl. effl.
infl. effl.
infl. effl.
naphthalene
acenaphthene
dibenzfurane
f luorene
fenanthrene + anthracene
fluoranthene
pyrene
1,2-dibenzanthracene + chrysene
benz (b+j +k) fluoranthene
1,2-3,4 benzpyrene
1 , 12-benzperylene
n.d.
n.d.
n.d.
n.d.
65
487
448
873
755
965
160
n.d.
n.d.
n.d.
n.d.
5
4
n.d.
15
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
7
225
1435
1093
2660
1315
1180
240
n.d.
n.d.
n.d.
n.d.
10
8
n.d.
4
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
10
370
356
1190
440
520
70
n.d.
n.d.
n.d.
n.d.
15
20
7
4
n.d.
n.d.
n.d.
total
3753
24
8155
22
2956
46
dissolved 13 24
adsorbed 3740 n.d.
removal percentage (%) 99,4
38 22
8117 n.d.
99,7
41 46
2915 n.d.
98,4
n.d. = non-detectable (< 1 pg/1)
It should be noticed that a biological treatment process has been in-
plemented - following filtration -to remove other components. The biological
treatment process will effect a further reduction in the concentration of
PAH (2).
Volatile chlorinated hydrocarbons and dioxines
In the beginning of 1985 the pesticides factory Duphar (Amsterdam) realized
the second phase of its scheme for waste water purification.
The first phase uses filtration and a steam-stripper for the removal of
suspended solids and volatile chlorinated hydrocarbons such as tetrachloro-
methane, trichloromethane and monochlorobenzene. This phase has been in
operation since the spring of 1984. The application of a filtration step also
reduces the emission of dioxines and dibenzofuranes considerably to values below
the detection limit (25 ng/1). This emission amounted to 40 g a year.
Filtration consists of four steps: coarse filter, gravel filter and two
close grained anthracite filters. Steam-stripping reduces the concentration of
volatile solvents from 210 to less than 10 mg/1; a removal efficiency of more
than 95%. The emission of these substances amounted to 33,000 kg a year.
The second phase, activated carbon adsorption, is meant to remove non-
volatile, adsorbable chlorinated hydrocarbons. Two columns in series are used.
The activated carbon is regenerated by a thermal method. The content of ad-
sorbable compounds in the waste water is reduced from 160 to less than 10 mg/1.
The emission amounted to 25,000 kg/year. Total costs of investment are in excess
of ten millions of Dutch guilders. The annual exploitation involves several
millions of Dutch guilders.
801
-------
Duphar is also taking part in research on the disintegration of organic
chlorinated compounds through thermolysis with hydrogen. This "hydrodechlorina-
tion process" is a discovery of the University of Leiden, which University is
developing the process in co-operation with Kinetics Technology International
(KTI) of Zoetermeer.
Thermal hydrodechlorination may be an effective method in eliminating
dioxines. Duphar's initial research is scheduled to finish early in 1986 (3,4).
Volatile chlorinated hydrocarbons and hexachlorinated compounds
AKZO Zout Chemie (Delfzijl) is investing several millions of Dutch guilders
in the construction of a treatment plant for the removal of volatile chlorinated
hydrocarbons such as tetrachloroethylene and tetrachloromethane and hexa-
chlorinated compounds.
The volatile compounds are removed from waste water by the use of a
stripper. The current emission comes to at least 16,500 kg/year. The removal of
hexachlorinated compounds occurs through sedimentation, its costs of investment
will amount to two million Dutch guilders.
Hexachlorobenzene, -butadiene and -ethane are byproducts of solvents. Most
of the compounds (99,9%) are separated, collected in drums and sent to salt
mines in W-Germany. The discharge of about 60 kg of hexachlorinated compounds a
year and the pollution of the sediment through this emission will soon belong to
the past (5).
Phenoxy acetic acids and chlorinated cresols
AKZO Zout Chemie (Rotterdam) intends to construct a waste water treatment
plant to process waste water from the pesticides plant and the vinylchloride
plant. The new treatment process consists of an activated sludge plant with
activated carbon dosing (PACT-process). The treatment plant is due to come into
operation in January 1987 and will cost 15.5 million Dutch guilders.
The pesticides plant produces phenoxy acetic acids (MCPA and MCPP). The
plant's waste water contains these acids as well as chlorinated cresols. The
annual emission of these substances comes to 6600 kg.
Using the foregoingly mentioned treatment process the governmental demand
for a concentration of less than 1 mg/1 of the cited substances in the waste
water may be met. This is comparable with a maximum emission of 1650 kg/year.
In cases of peak loads of chlorinated aromates, the waste water is pre-
treated with hydrogen peroxide. Additional process-integrated measures have also
been taken.
Instead of the use of activated carbon, resin-adsorption with Amberlite
XAD-4 was taken into consideration as a pretreatment. Its execution would prove
to be successful. Higher costs of investment have resulted in the selection of
the PACT-process. The waste water of the vinylchloride-plant is pretreated by
steamstripping, precipitation and sodiumsulphite dosing. Ethylenedichloride,
copper and chlorine concentrations are reduced below 1 ing/1.
The treatment plant must have a capacity of 70 m3 of waste water per hour.
The volume of the aeration tank amounts to 3800 m3 (6).
802
-------
INORGANIC MICRO-POLLUTANTS
Sources of inorganic micro-pollutants
In 1984 the presence of arsenic and heavy metals in domestic waste water
was studied. Domestic waste water - unmixed with rainwater or industrial waste
water - of seven residential areas was sampled and analysed four times. The
results are given in Tables 5 and 6. The annual sum of the average quantity of
arsenic and heavy metals is 16.5 grams per inhabitant.
A study of this nature has never previously been executed in the Nether-
lands. Calculations on the basis of literature data have been used thus far (7).
TABLE 5. ARSENIC AND HEAVY METALS IN DOMESTIC WASTE WATER
(CONCENTRATIONS IN |JG/L)
Location
Zn
Cu
Pb
Ni
Cr
As
Cd
TABLE 6. ARSENIC AND HEAVY METALS IN DOMESTIC WASTE WATER
(G/INHABITANT/YEAR)
Location
Zn
Cu
Pb
Ni
Cr
As
Cd
Hg
Amsterdam
- Meijehof
- Nieuwlandhof
Enschede
- Stokhorst
- Stro'inkslanden
Maarssen
Steenwijk
Vught
168
143
172
155
212
195
146
166
244
139
127
149
33
96
15
13
22
18
18
28
15
11
13
9
10
6
13
9
5
4
5
4
4
4
4
4
3
4
4
4
3
4
1.5
1.3
1.0
1.0
1.8
1.3
0.6
0.7
0.6
0.6
0.3
0.2
0.3
0.3
Hg
Amsterdam
- Meijehof
- Nieuwlandhof
Enschede
- Stokhorst
- Stro'inkslanden
Maarssen
Steenwijk
Vught
Median
Mean
7.2
6.5
7.6
8.9
10.1
8.7
7.5
7.5
8.1
7.1
11.1
6.2
7.3
7.1
1.5
4.9
7.1
6.5
0.6
0.6
1.0
1.0
0.9
1.2
0.8
0.9
0.9
0.5
0.6
0.4
0.6
0.3
0.6
0.5
0.5
0.5
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.1
0.2
0.2
0.2
0.1
0.2
0.2
0.2
0.05
0.06
0.04
0.05
0.09
0.06
0.03
0.05
0.05
0.03
0.03
0.03
0.02
0.01
0.01
0.02
0.02
0.02
The environmental problems of heavy metals focus especially on the
pollution of subaquatic soils, the consequences for organisms in water and
sediments and the pollution of sewage sludge. Heavy metals in surface water are
for a considerable part (75% as an average) attached to suspended solids.
803
-------
Reduction in the emission of inorganic pollutants
The solution to the heavy metal problem has to be found in the fight
with the pollution source, aimed at reducing the pollution. In principle,
two ways are open: process alteration and waste water purification.
To prevent polluting substances from originating by applying less polluting
production processes is of main interest where the fight against water pollution
by heavy metals is concerned. Two, so-called clean technology processes are: the
use of a new, blue passivating-bath and the substitution of cadmium by galvano-
aluminium.
The first process - developed by TNO - consists of a blue passivating
technique without nitric acid or nitrate-ions, with substitution of chromic-acid
by the less agressive potassium chromium sulfate. When this process is applied,
savings are especially made in the field of reducing costs of waste water treat-
ment. The process control at varying product supplies remains a restriction,
rendering it as yet only suitable for the treatment of one constant product.
The second clean-technology-process, the substitution of cadmium by
aluminium, has been developed by the electroplating industry of Hegin Galvano
Aluminium in co-operation with the German Siemens Company. The process consists
of the electrolytic precipitation of aluminium at a temperature of about 100 °C
in an organic electrolyte, excluding water and air, and it precludes pollution
of water or air. The process has been successfully tested in a so-called "rack"
machine (parts placed on racks), which is already on the market.
When choosing a purification plant, a distinction may be made between
systems for the treatment of the total waste water flow and systems for partial
treatment. Systems belonging to the first category are precipitation, de-
toxification, neutralization, de-watering (ONO) and ion exchange. These systems
are extensively applied in the electroplating industry. By applying process
integrated techniques or provisions for treatment of reaches of streams which
contain heavy metals, the metals in question may be re-used in principle. A
couple of process integrated systems which are being developed appear to offer
fair prospects. They concern the removal and the recuperation of heavy metals
from waste water with the aid of membrane filtration and the electrolytic
recuperation of heavy metals from diluted solutions. Hyperfiltration (reverse
osmosis) can be applied on separate rinsing water streams as well as on the
total waste water flow. With regard to a number of types of rinsing water,
especially those originating from nickel baths, the treatment by means of
hyperfiltration offers economic advantages.
An investigation into the applicability of electrolysis for the removal and
recuperation of nickel and zinc from rinsing tanks in the plating industry
is carried out by TAUW, TNO and Magneto Chemie. Thus far, application of
electrolysis mostly takes place when precious metals have to be removed.
Finally, in the field of heavy metal removal, a number of recent develop-
ments may be mentioned, namely the recuperation of metal by means of fluidized
bed crystallization and the removal of metal (Cd) with the aid of bacterial
processes.
Further activities in the field of metal removal will give priority to
process integrated provisions. The further development of the membrane tech-
nology and the electrolysis are also expected to gain more attention (8).
804
-------
SEWAGE SLUDGE
When municipal sewage water (a combination of domestic and industrial waste
water) is treated, sludge containing heavy metals developes. The level of heavy
metals in sewage sludge has decreased considerably during the past few years due
to reorganizations in industry. The decrease for nickel, cadmium and mercury
amounted to 50% or more in the period 1976-1980. The copper and lead content
decreased by 30%, while the chromium content decreased by 20%. At present the
heavy metal contents are on average below the limits set for direct agricultural
use. However, it does not mean that every quantity of sludge necessarily
satisfies the limit. From the sludge that was deposited in agriculture in 1981
only 42% satisfied the limit.
Notwithstanding the observed opposition against combustion, an increasing
interest in sludge combustion as a sludge processing method may be noticed in
the Netherlands. The opposition against combustion is especially based upon the
supposed environmental objections and the heavy costs. The increasing interest
in combustion is expressed by an intensification in combustion research.
However, the interest has not yet produced an expansion of the number of
combustion plants. The preference for the fluidized bed combustion system
is remarkable in this context.
Within the scope of study and research much attention has been given to the
problem of energy, because this item is of major interest with regard to
capacity and costs of combustion. It is important that the sludge may be burnt
autothermically (energetic equilibrium). Important factors in this respect are
the dry matter content of the sludge and the ash content of the dry matter.
Based upon energetic equilibrium, the mutual relation between these factors has
been worked out in Figure 1.
From the above it appears that - roughly speaking - raw sludge with an ash
content of 20% and a dry matter content of 25% (heat of combustion equals
23 MJ/kg of organic material) may be burnt autothermically. This type of rela-
tion, based upon the thermal balance, may be a useful expedient when application
of sludge combustion is considered. It is possible to check the degree of
de-watering necessary for autothermal combustion and/or to check whether the
required degree of de-watering is feasible in technical terras. Combustion of
sludge becomes expensive when additional fuel has to be added. In these cases
the capacity of the combustion plant decreases, while extra energy has to be
added. It can be stated in general that new developments in the field of
de-watering, resulting in higher dry matter contents and improvement of
energy-efficiency of the combustion process may take combustion closer within
the range of sludge processing methods (9,10).
Within the scope of an investigation into sludge combustion, carried out in
a fluidized bed incinerator (inner diameter 0.5 m, total height 5 m), attention
has been given to the energy balance as well as to the environmental aspects of
the combustion process. In this investigation long-term experiments (52 hours)
were carried out with de-watered sewage sludge (14% dry matter) under the
following conditions: sludge output 100 kg/hr, temperature of the bed 825 °C,
805
-------
5C
kg V3/ton cat
JS X »36 10
Degree of dewatering % TS
Figure 1. Autothermal combustion. Thermal
efficiency of incinerator 70%.
excess air 20% and static height of the bed 0.55 m. The composition of the
flue-gases was as follows: 0 3.5% by volume, C02 11.4%, CO 78 mg/Nm3, N0x 348
mg/Nm3, C H 14 mg/Nm3 and SO- 923 mg/Nm3. By applying a cyclone and a cloth
filter^heavy'metals remained (about 98%)in the solid residue. In other words,
about 2% of the heavy metals disappears into the atmosphere. Fluidized bed
combustion may be an attractive treatment method for sewage sludge. Test runs
are required to realize a well-made design for a full scale combustion plant
plant (11,12).
Within the scope of sludge thickening and de-watering the following
developments can be mentioned.
806
-------
From research it has appeared that the thickening of digested sludge may be
improved upon the addition of a polyelectrolyte. The mixing of polyelectrolyte
and sludge appears to be of vital importance in this process. A relatively low
amount of polyelectrolyte is applied to improve the thickening. The poly-
electrolyte present in the water phase must be dispersed uniformly over the the
sludge particles. However, excessive mixing must not occur, to avoid destroying
the formed sludge flocks. By means of experiments at a sewage treatment plant a
correct mixing between polyelectrolyte and sludge has been obtained. Using a
polyelectrolyte dosing (Praestol 423 K) of 2.5 g/kg of dry matter, the dry
matter content - after thickening - was increased from 3% to almost 6%. This
signifies a reduction in the sludge volume that has to be disposed of(13).
An investigation has been carried out into optimization of the conditioning
of sewage sludge with inorganic chemicals in relation to sludge handling with
filter presses. In 1982 twelve municipal sewage treatment plants in the Nether-
lands were equipped with filter presses, with a total processing capacity of
4.2 million population equivalents (p.e.). The sludge of about 3.3 million
p.e.'s is conditioned with inorganic chemicals. This involves an amount of money
for chemicals of about 3.5 million Dutch guilders. Even a minor reduction in
chemical consumption will result in considerable savings on running costs.
An investigation has been carried out into simple tests for conditioning
on a laboratory scale, a method which can also be used to characterize the
sludge. A standard mixer in an experimental set-up of 1 liter appears to
work well. After adding Fed , 15 seconds of mixing at a speed of 1000 rpm is
required; after adding Ca(OH} , 60 seconds at 500 rpm is required. With this
set-up and method of conditioning, characterization of sludge becomes possible.
For that purpose, conditioning tests at 2.5, 5, 7.5 and 10% Fed by weight and
10, 20, 40 and 60% Ca(OH) by weight, based on dry matter are carried out,
whereupon pH-value, suction Time and MFTx-dry matter are determined. After these
tests combinations of FeCl3 and Ca(OH) are selected, which simultaneously
satisfy the following conditions: pH > 12, suction time ^ 100 seconds and
MFT-dry matter ^ 21% of dry matter. Close agreement appears to exist between the
results of the laboratory experiments and the practical (full-scale) results.
The developed test method is also suitable for checking whether other condi-
tioning chemicals e.g. A1C13 instead of Fed , or waste lime are suitable for
the chemical conditioning of a specific type ol sludge (14).
An other aspect of sewage sludge permanently drawing attention is the
further processing and disposal of the sludge. For the benefit of the applica-
tion of sludge in agriculture, attention has been given to the hygienic aspects
of this particular application. Pathogenic bacteria such as Salmonella,
Clostridium botulinum, Taenia saginata, Ascaris Itonbricoides, Escherichia coli,
Campylobacter jejuni, Toxoplasraa gondi'i, Sarcocystis spp and viruses have the
potential to spread by sewage sludge. With regard to pathogenic bacteria three
ways of restriction may be recognized:
Restriction of the application of sewage sludge (in the production of crops
for human consumption);
Restriction of the use of land following application of sewage sludge (to
institute waiting times);
Disinfection of sewage sludge.
1MFT = Modified Filtration Test.
807
-------
Disinfection processes may be divided into a group which has disinfection as its
primary target (pasteurization, irradiation) and a group in which stabilization
is the primary aim, but in which proper dimensioning can also realize adequate
disinfection (aerobic thermophilic stabilization, composting and stabilization
with lime). The hygienic problems of the application of sewage sludge in agri-
culture are complex and highly dependent on regional factors. This leads to the
conclusion that a "safe" procedure cannot be indicated in general terms, and
each case has to be assessed separately (15) .
It has been verified to which extend the forests, which take up eight
percent of Dutch soil area, can contribute to the disposal of sewage sludge.
Some aspects have been investigated, such as sewage sludge in existing forests,
sewage sludge as soil conditioner and sewage sludge as a substrate for trees.
Research has led to the conclusions that sewage sludge is a material of widely
varying composition and qualities, which may alter considerably in the course of
time (flushing of lime, degradation of organic substances) and that therefore
planting advice for dumping sites for sewage sludge can only be given con-
ditionally. The necessity for planting research on sewage sludge of various
origins remains. Dutch forests offer hardly any potential at all for the
disposal of sewage sludge (16).
INNOVATION AND UPGRADING OF WASTE WATER PURIFICATION SYSTEMS
MUNICIPAL WASTE WATER
In the past few years the technology for the purification of municipal
waste water is strongly developing in the Netherlands. Novel techniques are in-
creasingly being used.
Biological dephosphating constitutes an important development in this
field. Its has been proven that biological dephosphating is also a suitable
method for removing phosphate at moderate temperatures. An important fact - when
using this technique -is that it makes the removal of the phosphate possible in
such a way that the removed phosphate is regained in a very pure form.
In the past five years a great deal of research has been done on the
potential use of Nitrilotriaceticacid (NTA) in detergents. The biodegradability
of NTA and also the influence of NTA on the binding of heavy metals to the
sewage sludge have been researched.
The research has been done on laboratory-scale (batch) and on pilot-plant
scale (continuous-system). The content of NTA in the waste water amounted to
20-40 g/m3 (as free acid H-NTA). This content is expected whenever NTA is used
on a large scale.
It has been proven that NTA has no adverse effects on the metal "household"
of the activated sludge system when it has become completely degraded. When this
is not the case, the introduction of NTA is thought to give a higher effluent
load, especially of the metals nickel, zinc and lead in the activated sludge
process (17).
Two cases have been investigated: an activated sludge plant with low sludge
load and an activated sludge plant with high sludge load.
808
-------
The investigation of the plant with the low sludge load (0.13 kg BOD/kg.
dry mater per day) resulted in the following conclusions:
- The adaptation to 10 g of NTA/m3 takes three days. From literature it
appeared that many researchers experienced adaptation times of two weeks.
- After adaptation NTA degradates very well. Even a strong changing influent
flow does not have adverse effects on the degradation of NTA.
The degradation of NTA decreases greatly when the temperature falls. Below
7 °C the degradation becomes very poor, a fact confirmed by literature
references.
The bio-degradation of NTA is especially sensitive to interruptions in the
degradation process of the total amount of organic materials. A disturbance
of the process, for instance a decrease in the COD-degradation from 95% to
80%, will result in a decrease in degradation of the NTA of up to 60%. When
the COD-degradation drops to 60%, the degradation of NTA stops completely.
Recovery of the COD-degradation is much faster than recovery of the
NTA-degradation (18).
The investigation of the plant with the high sludge loading (0.4-0.8 kg
BOD/kg dry matter per day) resulted in the following conclusions:
- The degradation of NTA takes more time when the sludge load is higher and
the sludge age is lower.
The degradation of NTA is poor when the plant is overloaded or when there
is a disturbance in the COD-degradation.
At temperatures below 7 °C, the NTA-degradation decreases greatly.
NTA is degrading very well during periods of non-disturbance (at sludge
loadings of 0.13-0.41 kg BOD/kg dry matter per day). This is even the case
when the NTA-content of the waste water is varying widely.
When the NTA content remains constant adequate degradation occurs, also at
sludge loads of 0.83 kg BOD/kg dry solids per day. There are problems with
the NTA-degradation when the NTA-content varies.
The overall conclusion must be that adequate degradation will occur in an
activated sludge system when:
The sludge load is beyond 0.4 kg BOD/kg dry solids per day;
There is no strong change in NTA-contents;
There are no disturbances during the purification proces;
The temperature is not lower than 7°C (19).
Similar research has been done on three types of purification plants. They
were an oxidation ditch, an activated sludge system and a trickling filter. The
research concludes that a content of 20 mg of NTA/1 degrades completely in
an oxidation ditch and in an activated sludge system. In cases of trickling
filters the degradation will not be above 75%. None of the plants produced
increased transportation of heavy metals. When the NTA content is 40 mg/1,great
differences in degradation will occur because of the type of plant and the time
of year. When the degradation of NTA is poor, chances of increased metal-
transport activities are higher and sensitivity to peak loads is higher. The
presence of NTA in the influent does not interfere with the biological activity
of above mentioned plants (20).
809
-------
Novel elements in the field of waste water treatment in the Netherlands
mainly deal with anaerobic treatment. Scientists have succeeded in getting a
high sludge content inside the reactor. This high sludge content in the Upflow
Anaerobic Sludge Blanket (UASB) reactor is caused by the development of granular
sludge in the reactor. This particular sludge has a high settling velocity. In
filter- and fluidized bed reactors the sludge is fixed to supporting media.
In the past few years a great deal of research has been done to stimulate
the application of anaerobic treatment of municipal waste water. A full-scale
plant is expected to be built in 1986. In this plant municipal waste water will
be treated before it is sent to an aerobic plant.
Haskoning, a Dutch engineering consultancy has done research - together
with the Agricultural University of Wageningen - on the treatment of municipal
waste water in Colombia. Thus far results have been outstanding. The opinion is
that the success of this research will stimulate the application of anaerobic
treatment in moderate temperature regions too (21).
At the Technological University of Delft a process-model of a methane-
reactor has been constructed. This model will improve the control of the system
(22)-
Another perspective constitutes the use of the fluidized-bed technology.
This type of anaerobic treatment is already operating on full-scale for the
treatment of industrial waste water (23).
The major problem of the future will constitute the application of sewage
sludge. This problem has both quantitative and qualitative aspects. Currently
the greater part of the sludge is put to agricultural use. Because an excess of
fertilizer is already available, this application becomes more and more of a
problem and the quality requirements become increasingly demanding. The major
demands are in the field of the heavy metal content of the sludge. It has to be
expected that in the future demands will also be introduced with regard to the
content of organic pollutants. To reduce its quantity, research is in progress
on thermophilic digestion.
It is expected that within 15-30 years a great deal of waste water treat-
ment plants will have to be partially or totally renewed. On that moment invest-
ments will have to be made to fulfil future environmental demands. Noise, odour,
effluent quality come to mind. The financial aspects are naturally very
important (exploitation, costs of investment).
At TNO and the engineering consultancy of Witteveen en Bos, a feasibility-
study is in progress aimed at coming up with an answer to the question of
renovation. The study is required to give the correct answer to the above-
mentioned question, and will be completed in 1985 (24).
INDUSTRIAL WASTE WATER
Abattoirs and slaughter-houses
The Dutch engineering consultancy Technisch Adviesbureau voor de Unie van
Waterschappen (TAUW) has developed a complete waste water purification system
for the waste water from slaughter-houses.
810
-------
The system (Figure 2) consists of an anaerobic treatment step (UASB-reactor)
followed by an aerobic treatment step (biorotor). Thus far many problems have
occurred. The major problem was the passage of sludge - from the biorotors
used -by suspended materials. Owing to the presence of suspended materials no
granular sludge developed. The COD-load remains limited to about 4 kg of
COD/m3.day (27).
Sugarwork factories
The engineering consultancy Grontmij has developed an anaerobic treatment
plant to treat the waste water from sugarwork factories. The waste water has a
high content of starch and invert-sugars. The plant has already been started up.
The load by volume is 9 kg of COD/m3.day and the conversion is 90% (based on
COD) (28).
TREATMENT PLANT
BUILDTNG CONTAINING
PUMPS. HEATING EQUIFHEKT
AND SLUOGK OEWATERING
EQUIPMENT
Figure 2. Waste water purification of slaughter-house waste water.
811
-------
Dairy industry
The production of dairy products results in large amounts of waste water.
Normally the waste water is treated aerobically. In 1984 the Dutch consultancy
Grontmij applied the so-called AB-process for the purification of dairy waste
water. The AB-process consists of a high-loaded aerobic first step (A) with
sludge recycling and a sedimentation tank. The second step (B) is a low-loaded
aerobic one with sedimentation and separate sludge recycling.
There has been an investigation on a pilot-plant scale with a flow of
240 1/h. The waste water (dairy/cheese factory) had the following features:
COD 3000 mg/1
Kjeldahl-N 110 mg/1
pH 5.0-13.0
Temperature 24 °C
COD/BOD 1.6
The following results have been obtained:
A step COD-load 35 kg/m3.day
BOD-reduction 45%
B step COD-load 1.7 kg/m3.day
BOD-reduction 97%
Sludge load 0.3 kg BOD/kg volatile suspended solids per day
The removal percentage of BOD for the whole plant were better than 99%. The
waste water did not have to be neutralized. The settling characteristics and
the digestion of the sludge proved to be excellent. At this moment the con-
struction of a full-scale plant is being taken into consideration (29) .
Maize starch industry
The engineering consultancy Heidemij has developed an anaerobic waste water
treatment plant for the purification of waste water from a maize starch
industry. It concerns a reactor of the UASB-type with a volume of 800 m3. Before
the water enters the methane reactor, it is held in a buffer basin of
1000 m^. The basin is necessary to smooth the hydraulic peaks in the flow.
Some acidification also takes place in this basin. Because of the peaks in
the flow, the load varies from 5-30 kg (COD/m^.day. The conversion of the
organic materials remains nevertheless highly constant. The removal,
on the basis of BOD, varies between 91-94%. The presence of granular
sludge in the plant is taken to be responsible for this positive result
(26,30,32,32).
812
-------
Potato starch industry
The potato starch industry is a very important branch of industry in the
Netherlands. The winning of starch from potatoes results in large amounts of
waste water. For the purification of this water an anaerobic reactor of 5500 m3
was built in De Krim. After 4 years the following results have been obtained:
Sludge-activity 0.65 kg COD/kg volatile suspended solids.day
biogas production 1000-1200 m3/h
COD conversion 16.5 kg COD/m3.day
COD reduction 80%. (31,33)-
Yeast- and alcohol industry
Gist-Brocades of Delft is a yeast- and alcohol producing factory. With
governmental financial support Gist-Brocades has developed an anaerobic
fluidized bed plant.
In the beginning of 1984 the full scale reactors were started up. It
concerns a two-phase process. The acidification-reactor has a volume of 80 m3.
The methane-reactor has a volume of 300 m3.
The following results have been obtained:
Acidification
COD-load 60 kg/m3.day
COD-conversion 13 kg/m3.day
Sludge activity 0.8 kg COD/kg. volatile suspended solids day
COD-reduction about 20%
Methanization
COD-load 47 kg/m3.day
COD-conversion 30-35 kg/m3.day
Sludge-activity 2-2.5 kg COD/kg volatile suspended solids day
COD-reduction about 70%
The third step of the plant consists of a nitrogen removal reactor. In this
reactor nitrification and sulfide-oxidation take place. The micro-organisms are
also fixed to inert materials in this reactor. The laboratory- and pilot-plant
experiments have already been completed. In the reactor a nitrogen-conversion of
1.5-2.0 kg Nitrate-N/m3.day at a retention time of 1.5 hours is obtained. On
account of the positive results a full-scale reactor with a volume of 300 m3
will be built in 1986 (26,32,34).
Gist-Brocades has also put a full-scale plant into operation to regain
ammonia from waste water. In this case it concerns waste water with a large
amount of solvents. The purification method is based on cold extractive
distillation (35).
Breweries
In 1984 the construction firm Paques BV carried out a pilot-plant investi-
gation on anaerobic treatment of brewery-waste water. The waste water had a
very low COD (1000-1500 mg/1) content and a low temperature (20-24 °C). Never-
theless, results were positive enough to merit the construction of a full-scale
plant.
813
-------
A r® dosingpwiip
9»I
imam,
REAKTOR
_o
J
GASHOLDER
GASFLARE
MMMO'Mm
aOWOIAGRAM
influwt SETU1NG TANK
AlUIROaiC Ct>.
BBtWWY
^"W
MK&i
<»*fcij^
°*^7t
Figure 3. Anaerobic treatment of brewery waste water.
The full-scale plant (see Figure 3) , was put into operation in November
1984 and is charactarized by the following features:
Flow 6000 m3/day
COD-influent 1000-1500 mg/1
Temperature 20-24 °C
Volume buffer 1500 m3
Volume UASB-reactor 1400 m3
Because the plant was started up with sludge of another waste water
treatment plant it reached design capacity within two weeks.
The results of the full scale plant are very similar to those of the
pilot-plant:
COD-load 4.5-7 kg COD/m3.day
COD-reduction 80%
Biogas-production 0.25 m3/kg COD (removed).
Because of the construction of the anaerobic plant the quality of the
sludge of the aerobic plant (second step) of the waste water purification
improved. The effluent quality is less than 5 mg BOD/1 (36,37,38) .
Paper industry
The waste water of paper factories contains among other things cellulose.
Waste and waste water containing cellulose are very hard to treat, because
cellulose is difficult to degrade.
814
-------
The department of microbiology of the University of Nijmegen studies the
destruction of high concentrations of cellulose containing wastes such as verge
grass, and primary and secondary sewage sludge from waste water treatment plants
applied in the paper- and cardboard-industry. The experiments are carried out by
way of a two-phase-system consisting of a mixed reactor on laboratory scale
(30 1) connected in series with a UASB-reactor.
In the first phase cellulose fibers are partly converted by micro-organisms
by hydrolysis into fatty acids, carbonic acid and hydrogen. Methane is formed
out of hydrogen and carbon dioxide. The aqueous phase with the dissolved fatty
acids is pumped into the UASB-reactor where the acids are converted into
methane.
On laboratory scale positive results have been obtained. Some results are
presented in Table 7.
TABLE 7. RESULTS LABORATORY STUDY
Waste Load Retention-time COD-reduction
(kg COD/m3.day) (days) (%)
Paperpulp
Grass
Potato-waste
30-40
30-30
20
2
2
2
60-70
70-80
60-70
Potential sources for application may be waste- and waste water streams
from the paper industry, waste- and waste water streams from the canning
industry, the processing of verge grass, wastes from parks, the processing of
waste from vegetable markets etc.
The system will be further developed through the testing of a reactor on a
pilot-plant scale at an industrial firm. This phase will be started in 1985
(39)-
Large amounts of water are used in paper making. The waste water contains
high concentrations of dissolved organic substances and must be treated via a
biological process. In 1981 Biihrmann-Tetterode, a Dutch paper industry group,
started a study on the application of anaerobic waste water treatment.
After a short testing period on laboratory scale a pilot-plant was put into
operation. The results were satisfactory enough that at this moment three full-
scale plants (Figure 4) for paper industries have been realized in co-operation
with Paques BV (Balk) and a fourth plant is currently under construction
(Industrie-water Eerbeek).
By using anaerobic (pre)treatment, short pay-back times may be realized
(about 1.5 years). Moreover, the present overloaded aerobic treatment plants
will come down in costs after they have been expanded with an anaerobic pre-
treatment system.
Table 8 gives a survey of the anaerobic treatment plants in the paper
industry.
815
-------
A (before upgrading)
(after upgrading)
darifier
Recycled
sludge
//////
f '
1
Aeration
basin
1.400 m'
1
i
I
\
— r°
i
Aeration
basin
1.400 m'
//////
Aeration
basin
1.400m"
-
1
r
I
i
f
\
r°
1
Aeration /
basin/
n.OOOm*
•»
"„ r IT
&-
Buffer
basin
^ -
400m"
Ik
L - >• -
J
Nutrients ^
UASB
reactor
(14.5 m)
Gasholder
Steam-
boiler
capacity
2.5 tons/hr
Steam (10 bar)
to paper mill
Wastewater
from paper mid
Wastewater
from paper mtU
Figure 4. Schematic diagram of the waste water treatment plant
at Papierfabriek Roermond.
816
-------
TABLE 8. ANAEROBIC WASTE WATER TREATMENT PLANTS IN THE PAPER INDUSTRY (40)
(SEPTEMBER 1985)
Factory Product Date of Reactor Temp. Load Inf1. COD-
operation volume (°C) (kg COD/ COD reduction
(m3) m3.day) (g/m3) %
Ceres
Cardboard
April
1983
70
35
5000 70
Papier-
fabriek
Roermond
Celtona
Others
Testliner
cora-
medium
Schrenz
Hygienic
paper
Testliner
cora-
medium
cardboard
envelopes
October 1000 30-40
1983
November 700 20-25
1984
September 2200 25
1985
10 3500 75
5 1200 60
* ca.1300 *
Fertilizer-industry
The production of phosphoric acid, a raw material for phosphate fertiliz-
ers, results in the formation of about two million tons of waste gypsum a year.
Until now this gypsum has been discharged into surface water. Since gypsum from
phosphoric acid production is contaminated with heavy metals, among which are
cadmium and mercury, governmental policy has been directed at stopping these
gypsum discharges. However, it has so far proved impossible to find suitable
processing- or marketing potentials for phosphate-gypsum. Government, industry
and research institutes, cooperating in the "Phosphate-gypsum working group",
are making enquiries into the potential of phosphate-gypsum, by supporting
research projects among other things.
The Dutch firms UKF, DSM and the Technological University of Delft are
carrying out research on the development of a new phosphoric-acid process. This
process distinguishes itself from the conventional hemihydrate processes by
dividing the disclosure of the phosphate ore and the crystallization of the
hemihydrate -which normally occur simultaneously - into two separate stages. In
the first stage, the so-called predisclosure stage, the ore is totally converted
into a monocalcium phosphate (MCP) solution by a recycle stream of phosphoric
acid, whereupon hemihydrate is precipitated (Figures). Impurities such as
heavy metals - present in the ore - are removed during, or directly after the
predisclosure. This process makes it possible to produce a relatively clean
gypsum and phosphoric acid. The study is still in a laboratory phase. At the end
of 1986 the technical, economical and environmental consequences of this
promising process will have become more clear (41) •
817
-------
phosphate ore
Figure 5. Process scheme of new phosphoric acid process.
Oil-containing waste water streams
The treatment of oil-containing waste water streams from garages, bunker-
stations and waste-oil refiners can be improved using membrane filtration,
flocculation/flotation or flocculation/filtration. The use of conventional oil-
separators results into an oil concentration in the effluent of about 200 mg
oil/1 or more. By using the above mentioned techniques, concentrations of less
than some scores of mg of oil/1 may be reached. However, the average costs will
increase by a factor 2 to 5.
These are the results of a study done by Tebodin Engineering Consultancy by
order of the Governmental Institute for Waste Water Treatment.
Electrochemical detoxification of aqueous waste solutions
TNO has studied a method which uses cathodic dehalogenation of penta-
chlorophenol (PCP) in aqueous solution as a model reaction. PCP has been
chosen because it is a representative pollutant of the type of waste waters in
question, and because it has strong carbon-chlorine bonds and a relatively
high solubility in (alkaline) aqueous solutions.
After 30 minutes of electrolysis the PCP concentration (Figure 6) had
fallen below the detection limit of 0.5 ppm. Simultaneously, the chloride con-
tent of the solution showed that five chlorine atoms per molecule of PCP were
removed. The current efficiency for complete dehalogenation is 1%. The adding
of small quantities of certain surface active agents, improves the efficiency.
During electrolysis the toxicity of the solution fell from an initial
EC 50 = 2% to a final 40%, indicating almost complete detoxification.
818
-------
IPfPI/ppm
nunotr ef Cl'ioni
ptr PCP mottcult
S
JO 45
hmt of Htctratysii limn I
Figure 6. Decay of PCP and yield of Cl ions per PCP molecule during
electrolysis of 1 litre of solution containing 50 ppm PCP.
An experiment with two litres of the test solution was conducted for the
purpose of determining the intermediates and product(s) formed. Figure 7 shows
the formation and decay of tetra-, tri-, di- and monochlorophenols, finally
resulting in the formation of phenol and, possibly, monochlorophenols. The
experiment shows that the total molar concentration of the phenols remains
constant in time.
Experiments with other organohalogens and industrial waste waters are in
progress.
fraction
IV.)
60 90 W ISO
' hat of tltctrolysis (mini
Figure 7. Mole fraction of the phenols during electrolysis of
2 liters of solution containing 50 ppm PCP.
1. PCP
3. Trichlorophenols
5. monochlorophenols
2. tetrachlorophenols
4. dichlorophenols
6. phenols
819
-------
The advantage of electrolysis over alternative methods of chemical
treatment is that additional chemicals are not generally required. Electrolysis
with electrodes of a large specific area, such as those composed of very thin
fibres, may reduce the concentration of toxic compounds to a very low level.
Agricultural industry
Seed-potatoes are treated with a mercury containing disinfectant for
protection against diseases. The disinfection takes place in plunging tanks. In
the Netherlands it is obligatory to treat the used mercury containing plunging
liquids at specified central places.
In the past the treating was done decentralized, with activated carbon. The
use of activated carbon filters rendered unsatisfactory results, because the
saturated filters were not replaced in time. This resulted in soil- and surface
water pollution.
In 1984 a central treatment plant was put into operation in Dronten. The
treatment plant consists of the following process steps:
- Pre-sedimentation
- Coagulation/flocculation
- Sedimentation
- Filtration
- Activated carbon adsorption
The effluent figures are mostly below 10 (Jg/1 mercury.
AGRICULTURAL WASTE WATER (MANURE PROCESSING)
Owing to the great increase and the concentration of the so-called bio-
industry during the last decades in the Netherlands, a large surplus of manure
(mainly pig- and cattle manure) has formed. Roughly estimated, this surplus
amounts to about 17 million tons a year. This surplus constitutes a menace to
the fertility of the soil (too much phosphate) and the environment. The emission
of ammonia, the formation of nitrate in ground water, eutrophication of surface
water and pollution of surface water by salts present in the manure may be
mentioned. The problem of manure surplusses is mainly a problem of minerals.
In principle the problem of the manure surplusses may be solved. A
possibility is the large-scale processing of manure surplusses in central
processing plants where the manure is converted into products, which no longer
constitute a menace to the fertility of the soil and the environment. Central
processing of manure may take place in various ways. Each way consists of a
series of a number of known processes or unit operations. The more important
processes are: anaerobic digestion, separation, dewatering, NH -stripping,
desalination, concentration, drying, combustion and aerobic biological treat-
ment. In Figure 8 one of the potential ways of processing is outlined. Most of
these unit-operations are frequently applied in the processing industry. The
various ways of processing are distinguished by differences in endproducts and
running costs. Dependent on the market for endproducts, a selection may be made
for the best possible way of processing.
820
-------
The costs for central manure processing are estimated at 30 to 60 Dutch
guilders per m3 of manure to be treated, for a plant capacity of some hundreds
of thousands of m^ a year, not including the costs for transportation of the
manure to the central processing plant. The profit of potential products,
which can be obtained at the central manure processing plant, are not taken
into account. This expected profit, however, will not cover the total costs
of manure processing.
On short-term, central manure processing might solve the problem of the
manure surplusses. Perhaps long-term solutions are also possible by way of the
cattle feed. The paramount thought is of a pre-treatment of the feed, aimed
at the improvement of the nitrogen digestibility and the increase in the
availability of phosphorus, or, of an alteration of the composition of the feed,
aimed at a reduction in the nitrogen and phosphorus content and any other
minerals such as, e.g. potassium.
Animal Slurry
Main Route
Centralised
Processing
Effluent
Cake
NH
Oven
Ash
solution
A Brine
Dried
Cake
Dried
Brine
Figure 8. Manure processing.
821
-------
GROUNDWATER
Owing to the production of manure surplusses and connected over-manuring,
at some locations the nitrate content in groundwater has greatly increased
during the last years. A high concentration of nitrogen in ground water creates
a problem for the preparation of drinking water. The problem has become even
more pressing since on 1 July 1984 the standard for nitrate in drinking water
was brought down from 100 mg/1 to 50 mg/1.
Recently the Landbouwhogeschool Wageningen (Agricultural University)
developed a method to remove nitrate from groundwater. The method consists
of a combination of two techniques, namely, ion exchange and microbiological
denitrification. Nitrate ions are adsorbed in the ion-exchanger. After satura-
tion regeneration takes place, releasing the nitrate. The regenerate, high on
nitrate content is then biologically denitrified, by which process nitrate is
converted by micro organisms into elementary nitrogen under the addition of
methanol. The regenerate, from which the nitrate has been removed, contains
hydrogen carbonate, a product of the microbiological conversion. Hydrogen
carbonate may be used to regenerate the ion-exchanger, so that the regeneration
liquor may be used again. By using two ion-exchange columns and one denitrifica-
tion column, one exchanger may adsorb nitrate from groundwater, while at the
same time the other exchanger -which is saturated with nitrate - may be
regenerated again.
The process is shown in Figure 9.
L
denitrification
reactor M
NOj — N2
org
H
NaCl
HCl
~" E^-3 ^on exchanger for
// "regeneration
^ cr+ NO;— -CT+NO;
\
NOj 1
1
. C-source
Figure 9. Biological regeneration of an ion exchanger
by means of a denitrification column.
822
-------
The major benefits of this process are:
The groundwater that is to be treated does not come into contact with the
denitrifying organisms and the carbon source (e.g. methanol);
The regeneration of the ion-exchangers takes place in a closed loop. A
bulky waste brine, such as is the case in the usual way of regenerating, is
therefore avoided. Regeneration of the ion-exchanger may of course also be
carried out with chloride, e.g. as NaCl or HC1.
The chloride content in the recirculation loop must be maintained at
a constant level, so that salt consumption for the regeneration will also
decrease. Aspects, which will come forward in the investigation are:
The adaptation of denitrifiers to a high chloride content;
The prevention of a pollution of the ion-exchanger in the regeneration loop
with organic material;
The effect of an increasing sulphur content on the regeneration. Sulphur
will accumulate in the regeneration loop, because it is fixed during the
removal of nitrate and is released again during regeneration. However,
contrary to nitrate, sulphate is not converted (42,43,44).
REFERENCES
1. Van Luin, A.B., Van Starkenburg, W. Hazardous substances in waste water,
Wat. Sci. Tech. Vol 17, 843-853, 1984.
2. Welraadt C. Van afvalstoffen naar grondstoffen in de staalindustrie.
H20 (16) 1983, no. 16, 364-368, 375.
3. Anonymus, Chemisch Weekblad 26 juli 1984, pag. 238.
4. Anonymus, Chemisch Weekblad 2 mei 1985, pag. 169.
5. Anonymus, Nederlandse Chemische Industrie (NCI), 31 oktober 1985. pag. 25.
6. Anonymus, AZC Interlocaal, 29 maart 1985, also communication.
7. STORA-rapport maart 1985. Het inwonerequivalent getoetst.
8. Allessie, M.M.J., van Luin, A.B. en Visscher, K. Bestrijding water-
verontreiniging door zware metalen. H?0 (17), 1984, nr. 24, 569-574.
823
-------
9. Eggink, H.J. Verbrandingswaarde van zuiveringsslib en de vereiste
ovencapaciteit. H2
-------
24. Communication RIZA. Problematiek huishoudelijk afvalwater Lelystad.
20 juni 1985.
25. Lettinga, G., Heijnen, J.J. en Houwink, E.H. Verslag European Anaerobic
Waste Water Symposium. Nederland koploper in de anaerobe technologie.
PT/Procestechniek 39. 1984, nr. 3, 59-61.
26. Rulkens, W.H., Van Voorneburg, F., Van Luin, A.B. en Van Starkenburg, W.
Ontwikkeling op het gebied van de afvalwaterzuivering in Nederland.
NATO/CCMS, Bari, 1982.
27. Communication TAUW-Infra Consult, Deventer, 22 mei 1985. Zuivering van
slachthuisafvalwater.
28. Communication Grontmij, Zeist, 23 november 1984. Anaerobe behandeling van
het afvalwater van een dropfabriek.
29. Communication Grontmij, Zeist, 23 november 1984. Behandeling van zuivel-
afvalwater met de AB-technologie.
30. Van Luin, A.B., Van Starkenburg, W., Rulkens, W.H. en Van Voorneburg, F.
Ontwikkeling op het gebied van de afvalwaterzuivering in Nederland.
NATO/CCMS. Apeldoorn, 1983.
31. Maaskant, W. Operational aspects of anaerobic waste water treatment plants,
especially for starch industries. Heidemij Arnhem, mei 1985.
32. Euroconsult. Energy saving by anaerobic waste water treatment.
3rd Mediterranean Congress on Chemical Engineering, Barcelona.
November 1985.
33. Communication AVEBE, Veendam, 20 juni 1985. Afvalwaterbehandeling aard-
appelzetmeelindustrie.
34. Communication Gist-Brocades, Delft, 15 mei 1985. Volledige zuivering van
het afvalwater van de gist- en alcoholfabricage.
35. Communication Gist-Brocades, Delft, 15 mei 1985. Ammoniak terugwinning uit
afvalwater door koude extractieve destillatie.
36. Paques B.V., Balk, 1984. Anaerobe zuivering van het afvalwater van Bavaria
met een U.A.S.B.-pilot plant.
37. Hack, P.J.F.M. (Paques B.V.). Application of the U.A.S.B.-reactor for
anaerobic treatment of brewery effluent. Poster at I.A.W.P.R.C.-symposium
1984. Amsterdam, September 1984.
38 Swinkels, K.Th.M, Vereijken, T.L.F.M., Hack en P.J.F.M. Anaerobic treatment
of waste-water from a combined brewery, malting and soft-drink-plant.
20th Congress of the European Brewery Convention, Helsinki, 1985.
825
-------
39. Communication Haskoning, Nijmegen, 20 december 1984. De anaerobe verwerking
van cellulosehoudend afval of afvalwater.
41. Habets, L.H.A. en Knelissen, J.H. Application of the U.A.S.B.-reactor for
anaerobic treatment of paper and board mill effluent. Water Science and
Technology, 1985. vol 17, no. 1.
41. Weterings, K. en Van Rosmalen Cr. Een schoon fosforzuurproces. Chemisch
magazine, September 1984, 473-474, 493.
42. Anonymus. L.H. Wageningen ontwikkelt methode om nitraat uit grondwater te
verwijderen. H20 (18), nr. 2, 1985, N7.
43. Van der Hoek, J.P. en Klapwijk, A. Nitraatverwijdering uit grondwater.
H20 (18), nr. 3, 1985, 57-62.
44. Van der Hoek, J.P. en Klapwijk, A. Biologisch/fysisch-chemische methoden
Nitraatverwijdering grondwater. PT/Procestechniek 40 (1985) nr. 5, 22-25.
826
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NORWEGIAN ADVANCES IN WASTEWATER TREATMENT
by
Dr.ing. Bjeirn Rusten
Aquateam, Norwegian Water Technology Centre A/S
P.O. Box 6593 Rodeldkka
N-0501 Oslo 5
Norway
The work described in this paper was
not funded by the U.S. Environmental
Protection Agency. The contents do
not necessarily reflect the views of
the Agency and no official endorsement
should be inferred.
North Atlantic Treaty Organization/Committee on the
Challenges of Modern Society (NATO/CCMS) Conference
on Sewage Treatment Technology
October 15-16, 1985
Cincinnati, Ohio
827
-------
NORWEGIAN ADVANCES IN WASTEWATER TREATMENT
by: Dr.ing. Bj0rn Rusten
Aquateam, Norwegian Water Technology Centre A/S
P.O.Box 6593 Rodelokka
N-0501 OSLO 5
Norway
ABSTRACT
This paper gives a short summary of some recent advances in wastewater
treatment and sludge handling in Norway.
Projects briefly summarized are:
Aerobic, thermophilic digestion of pre-thickened sludge using air.
Septage handling.
Phosphorus removal from wastewater by the use of granular activa-
ted alumina.
Treatment plants for single houses.
Wastewater treatment with aerated submerged biological filters.
Separate treatment of septage liquor.
828
-------
INTRODUCTION
In Norway today research concerning industrial and municipal wastewater
treatment and sludge treatment is mainly carried out by Aquateam, Norwegian
Water Technology Centre A/S and by The Water Treatment Group, Norwegian
Hydrotechnical Laboratory, The University of Trondheim.
This paper will give a short summary of some of the recent projects
relevant to advanced wastewater treatment and sludge handling.
SLUDGE MANAGEMENT
AEROBIC THERMOPHILIC DIGESTION OF PRE-THICKENED SLUDGE USING AIR
Several methods for hygienization of sewage sludge have been evaluated
in Norway: lime treatment, composting, long-term storage and aerobic,
thermophilic digestion using pure oxygen. In 1983 the Danish company JANCA
introduced on the Norwegian market a new version of the aerobic, thermophi-
lic digestion process using a special device (vibrating sieve) for thicken-
ing the raw sludge up to 8-10% DS before digestion. With this concentrated
sludge, a closed and insulated reactor and oxygen supply from a surface
aerator, it was claimed that the sludge would be hygienized with a retention
time of about 1 day (batch operation).
Aquateam has performed a pilot plant study of the JANCA-process at the
HIAS sewage treatment plant (1). A flow diagram of the OANCA pilot plant is
shown in Figure 1.
Polymer
Aerobic digester
Sludge from
plant thickener
r? ={g) >• Hygienized sludge
Sludge liquor
Figure 1. Flow diagram of the JANCA pilot plant.
The digester was operated on a draw and fill basis (batch operation).
Mixed primary-activated-chemical (Al) sludge was pumped from one of the
treatment plant thickeners to the vibrating sieve.
829
-------
The hygienic quality of the sludge was monitored by microbiological
examinations of faecal coliforms, faecal streptococci, spores of Clostridium
perfringens, Salmonella bacteria and bacteriophages (coliphage MS 2). The
bacteriophages were added to the feed sludge.
Due to variations in solids concentration of the pre-thickened sludge
and operational problems with the thickening device, both organic and
volumetric loadings on the digester varied considerable during the study.
Table 1 gives data on retention time and organic loading for the test
periods.
TABLE 1. LOADING DATA FOR THE DIGESTER
Phase
Retention time >
(days)
Organic loading
(kg VS/m3 . d)
Start-up
Test period 1
Test period 2
Range
2.1-3.6
1.5-2.2
2.4-4.0
Mean
2.8
1.9
3.1
Mean
16
27
11
*) Retention time is calculated as the sludge volume in digester after
feeding (m^) divided by the sludge feed rate (m-Vd).
During test period 1 and 2 the digester temperature normally followed
the curves shown in Figure 2.
12 18 24 30 36
Time after start of feeding sludge to the reactor (hours)
42
48
Figure 2. Typical temperature curves in digester after start of feeding
sludge.
830
-------
Based on the results from the pilot plant study the following con-
clusions were drawn:
The JANCA-process with sludge draw and fill every morning (average
retention time 1.9 days) could raise the sludge temperature to
above 60°C and maintain this level for 8-12 hours. This caused a
limited improvement in the sludge hygienic quality.
With sludge draw and fill every second morning (average retention
time 3.1 days) temperatures above 60°C could be maintained for 27-
34 hours, and the sludge was satisfactorily hygienized.
The data on organic matter reduction during the process is
uncertain, but figures of 20-25% is indicated. This means the
treated sludge is not stable and can create odor problems during
subsequent handling and disposal.
The original pre-thickening unit (vibrating sieve) did not
function properly with the mixed primary-activated-chemical
sludge. Mean dry solids concentrations after sieving was 7.1% and
5,5%, respectively,for test period 1 and 2. Another device
(dewatering container) seemed to be capable of concentrating the
sludge up to about 10% dry solids.
Total power consumption for the pilot plant was 30 and 42 kWh per
m3 sludge from plant thickener with sludge feeding every day and
every second day, respectively. These figures are higher than
expected for a full scale plant with automatic process control.
Capital cost for a 2100 tonnes DS/year plant is about NOK 2
million (1984). The operating costs (energy and polymer) will be
about NOK 150/tonne DS.
SEPTAGE HANDLING
Treatment and handling of septage is a major problem in Norway. A
project concerning separate treatment of septage liquor will be presented
later in this paper. Here, a short summary of two other projects will be
given,
Septage Discharge to Sewer System
The VEAS treatment plant outside Oslo is a primary precipitation plant
designed to handle wastewater from 565,000 population equivalents. Septage
from the Oslo area can be discharged to the sewer system.
During a test period Aquateam evaluated the effects of septage dis-
charge on the operation and performance of the treatment plant and the
sewer system (2). The sludge quantities used were the same as those expected
to be discharged from the Oslo area in the future. The septage was added to
the sewer about 25 km upstream from the treatment plant.
831
-------
The results from the one month test period led to the following
conclusions:
It is possible to maintain the previous treatment efficiency
at the treatment plant, even after addition of about 200 m-Vd
of septage to the sewer system. This does, however, require a
10-15% increase in the consumption of chemicals (ferric chloride),
in order to keep phosphorus concentration in plant effluent below
0.5 mg P/l. The sludge production will increase approximately 10%.
The composition of the septage during the test period was such
that installation of bar screens and a grit removal unit at the
discharge facility was found unnecessary.
Only a slight increase in odor level can be expected at the
treatment plant. At some ventilation points along the sewer
quite high odor levels were found. At these points the use of
simple odor reduction methods should be considered.
Mobile Septage Dewatering
As an alternative to septage treatment at a wastewater treatment plant.
mobile dewatering units have recently been introduced in Scandinavia. Mobile
dewatering has several potential advantages:
Reduced overall septage volume for treatment and ultimate dispo-
sal.
Lower costs for transportation.
Higher capacity. On-the-road dewatering increases the number of
septic tanks that can be visited before disposal.
Filtrate is returned to the septic tanks. This reduces the
problems caused by adding untreated septage liquor directly
to the treatment plant influent.
A Swedish system, called "Hamstern" was evaluated by NIVA (Norwegian
Institute for Water Research) in 1980. This system is based on lime condi-
tioning and dewatering in a special type of vacuum filter.
Recently Aquateam tested a Danish mobile dewatering system, called MOOS
KSA (3). Figure 3 shows the sequential steps in septage collection and
on-the-road dewatering using the MOOS KSA-system.
First the septage is sucked into a tank. Then filtrate from the
previous dewatering is returned from the filtrate collection tank to the
empty septic tank. Polymer is added when the septage is pumped from the
vacuum tank to the dewatering tank. The sludge settles while the filtrate
drains through a filter cloth to the filtrate collection tank. The dewater-
832
-------
ing sequence goes on all the time, while the truck goes from septic tank to
septic tank. After a day of work the sludge is left in the dewatering tank
overnight, in order to achieve higher dry solids concentrations.
Suction of septage
into the vacuum tank
Septic tank
Filtrate from the previous
dewatering operation is
returned to the empty
septic tank
Septage from vacuum tank
pumped into dewatering
tank with simultaneous
addition of polymer
All day through there is
continuous dewatering
of the sludge cake.
Filtrate goes to the
filtrate collection tank
Figure 3. Sequential steps in septage collection and on-the-road dewatering
using the MOOS KSA-system.
The following conclusions were drawn from the tests of this mobile
dewatering unit:
Actual capacity will depend on the distance between septic
tanks, type and size of septic tanks, septage composition,
standard of roads, maximum allowable weight etc. Until we get
833
-------
performance in relation to the adsorption capacity and kinetics. Such an
understanding is required in order to optimize the process design and
operation. The scope of this work has been to contribute to such an under-
standing, in interpreting the results from isotherm and column experiments
with the help of a mathematical model based on generally accepted mass
transfer theory.
The Homogeneous Surface Diffusion Model (HSDM) was used to describe the
process. More information about this model can be found in (4) and (5). The
input data for the model was found in equilibrium experiments on alumina
powder, and in lab-scale tests of fixed-bed adsorption of a synthetic
secondary wastewater using granular alumina. The lab-scale column system is
shown in Figure 4.
1.50m
1.15m
0.85m
0.55m
0.20m
0.00m
head-columns -
columns
/ \
T "7
]
I/
0
\.
/
rs
\
L M HC1 1 H NaOH
CFG Prominent
Dulcometer
Underdrain
Influent
water
tank
Figure 4. Lab-scale column system for phosphorus adsorption on granular
activated alumina.
The adsorption capacity is very pH-dependent, as shown by the adsorp-
tion isotherms in Figure 5. The capacity is at its maximum at pH = 4.5.
834
-------
3.0
O
81
2.0
1.0
-4.0
-3.0
pH
pH
PH
pH
5
6
7
8
K
K
K
K
F
F
F
T*
a
%
3
as
7
7
5
3
36
1
3
1
4
1
7
.2
.5
.7
. 1
n
n
n
n
at
_
3,
3
0
0
0
0
.12
.20
.20
.25
7
7
8
3
Q(mmoleP/kg
C(mmoleP/l)
Figure 5. Adsorption isotherms for Compalox AN/V at different pH values,
T = 20°C, t = 7 days.
The HSDM model was found to give a fairly good description of the
process. The process is well suited for designing a beds-in-series system.
Figure 6 shows the recommended design criteria for a semi-continuous
countercurrent system of three bed units with a total bed length of 6.0 m.
The design criteria was calculated by the model for a pH of 6.0 and a
required effluent quality of 0.5 mg P/l.
Figure 6 demonstrates that the influent phosphorus concentration and
the alumina particle size are important factors regarding the design liquid
flow velocity. A sensitivity analysis of the model stated that the three
most important parameters determining the column performance were the pH,
the alumina particle size, and the column length. The rate of adsorption is
limited by intraparticle diffusion. Therefore the use of a coarse-grained
type alumina will necessitate a low hydraulic loading and a long contact
time within the bed.
Treatment of Real Wastewater
One possible application of this adsorption process is selective
removal of phosphorus from small scale/on-site treatment plant effluents.
The effluent from a small RBC package plant was treated in two pilot-
835
-------
scale columns for a period of about 10 months (6). Coarse-grained type
alumina (1.9 mm diameter) was used in order to reduce the potential for
clogging of the beds. The influent concentration was close to 10 mg PCty-P/l
and the pH was close to 7.0 throughout the experiment. Both columns had
variable flowrates that simulated the daily fluctuations in a real treatment
plant. However, the mean liquid flow velocity was low (0.2 m/h) in order to
provide sufficient contact time for intraparticle diffusion of phosphate.
The bed-heights were 1.0 m and the column diameters were 0.2 m.
10.0
o
g
UJ
O
Q
O
5.0
0
0.050
0.075 0.100
PARTICLE RADIUS R(cm)
Figure 6. Recommended design criteria for a 6.0 m long in-series system of 3
bed units, for phosphorus adsorption on activated alumina (Compa-
lox AN/V). Valid for pH = 6.0 and an effluent concentration of 0.5
mg P/l.
The breakthrough curves at different column lengths are shown in Figure
7. The dashed lines show the expected breakthrough curves for a simple
phosphate adsorption process, as predicted by the mathematical model
mentioned earlier.
From these results it is evident that a significant amount of phospho-
rus has been removed by mechanisms other than simple adsorption. Such
mechanisms could be complexation, chemical precipitation by Ca^+ and Mg2+
present in the wastewater, and biological consumption of phosphate. Conse-
quently, use of the mathematical model presented earlier on, will give
conservative design criteria. It is, of course, an advantage that these
mechanisms increase the column's capacity for phosphorus removal.
Phosphorus removal from wastewater using granular activated alumina
seems to be an efficient and reliable treatment process, with a minimum of
operation and maintenance requirements. However, important questions are
still to be answered. The most urgent ones are pretreatment requirements and
836
-------
the influence of organic matter and more condensed type phosphates when
treating a real wastewater, and in particular how regeneration of spent
alumina should be optimized.
0
Figure 7. Breakthrough of PC^-P at different column heights, treating real
secondary wastewater. Columns filled with activated alumina
(1.9 mm diameter Compalox AN/V). Solid lines show actual break-
through curves, based on the mean value from the two columns.
Dashed lines show expected breakthrough curves, predicted by a
mathematical model.
TREATMENT PLANTS FOR SINGLE HOUSES
In a lot of countries there is a big demand for simple and reliable
plants that can treat wastewater from a single house. These plants have to
meet the regulatory effluent criteria under highly variable loads and over a
long period of time.
Biovac A/S of Norway has developed and produces a unit for year-round
treatment of wastewater from single houses. Over the last couple of years
10-15 such units has been monitored. Three units for removal of organic
matter were closely monitored and evaluated over a 6-month period (7). Later
two more units designed for removal of both organic matter and phosphorus
were thoroughly tested by Aquateam from July 1984 to January 1985 (8).
Flow diagram of a BIOVAC treatment plant with co-precipitation of
phosphorus is shown in Figure 8. In the two process tanks the wastewater is
biologically treated in an aerated suspended growth system. A vacuum fan
sucks air into the process tanks, keeps the sludge in suspension and
recycles the sludge from the clarifier. The sludge return is intermittent
837
-------
and Is controlled by a timer. Once a week, at night, the clarifier is
stirred for a few seconds, in order to prevent accumulation of floating
sludge.
Sodium aluminate
Air in
Influent-
Effluent
Air out
o
Vacuum fan
I »
Sludge drier
Sludge return
Filtrate to
process tank 1
Figure 8. Flow diagram of a BIOVAC treatment plant.
The process tanks have a total effective volume of 1.08
clarifier has an effective area of 0.35 m^.
while the
Liquid sodium aluminate (Na^l^) is used as precipitant. It is added
to process tank 2 intermittently, either once every hour or once a day.
Excess sludge is pumped to the sludge drier by an airlift pump once a
day. The sludge liquor is returned to process tank 1. The biological-
chemical sludge dewaters quite well, and excess heat from the vacuum fan is
used to dry the sludge further.
The plants are supposed to be routinely serviced every 4 months. The
service people then dispose of the accumulated sludge and fill the sodium
aluminate tank.
So far the BIOVAC treatment plants have been very reliable and have
performed very wel 1 .
Oxygen concentrations between 2.5 and 6.3 mg/1 have been observed in
process tank 1, while the concentrations in process tank 2 have been
slightly higher, 4.5 to 6.8 mg/1.
838
-------
The organic loading has been low, with F/M-ratios from 0.02 to 0.07 kg
BOD7/kg MLSS . d. Hence, BOD-removal has been excellent, with effluent
concentrations «c10 mg BODy/l.
Co-precipitation with sodium aluminate has given residual total phospho-
rus concentrations of 0.1-0.6 mg P/l. An addition of chemicals equivalent to
2.0 mol Al/mol P is recommended. For a home with 4 people this will be
equivalent to 11.7 1 of sodium aluminate solution over a 4-month period.
Daily fluctuations in wastewater flow has no negative influence on the
performance, provided that the total daily flow is less than 700 I/day.
WASTEWATER TREATMENT WITH AERATED SUBMERGED BIOLOGICAL FILTERS
Almost all the wastewater treatment plants in Norway are inside
buildings. This is because of the strict rules governing working conditions
and the cold winter climate. To reduce the plant construction costs, it is
essential to use a compact treatment process. Many biodisc plants have been
built in Norway during the last few years. They have, however, had some
mechanical problems. An aerated submerged biofilter has no moving parts, and
with a high density filter medium it should be possible to get a high
organic removal rate per unit volume.
Figure 9 shows the principle for a two-stage aerated submerged bio-
filter.
Influent
*x
• 1
\
Aeration
system
t
Effluent
Filter
medium
Figure 9. Principle lay-out of a two-stage aerated submerged biofilter.
In 1982 the Water Treatment Group at The University of Trondheim
started pilot-scale research on aerated submerged biofilters. Filter media
with specific surfaces of 140 m2/m3 and 230 m2/m^, respectively, were used
to treat municipal wastewater (9). The removal rates were the same in both
filters, as organic matter removed per unit surface area. Thus, the filter
839
-------
2 3
with the 230 m /m medium gave the highest volumetric removal rate. The
air bubbles stripped off excess biofilm and the strong turbulence also
ensured that the substrate was evenly distributed to all parts of the
filter. Tracer response curves showed both filters to behave as complete
mix reactors.
Figure 10 shows removal rate versus organic load when the filters were
run as single-stage reactors. Figure 11 shows the same with the filters
operating as a two-stage reactor.
D
O
80 -
60 -
$
a
n 40
o
I
20 -
tilter A (MO m /m ) : O
Total COD influent.
Soluble COD effluent.
>^x
>'0
X
-n . VCOD .
'A, COD -" Bft|COD * 360
20
40
60
80
100
120
Organic load, g COD/m -d
Figure 10. Total organic removal rate versus total organic load. Filter
A and Filter B operated as single-stage reactors, treating
municipal wastewater. r^coo = organic removal rate, B^CQD
= organic load.
Two-stage process
Total COD influent
Soluble COD effluent
r - ,„. BA,COD
A, COD BA>COD+ 120
10 15 20 25 302 35
Organic load, g COD/m -d
Figure 11. Total organic removal rate versus total organic load. Filter
A and Filter B operated as a two-stage reactor without
intermediate clarification, treating municipal wastewater.
r/\ coo = organic removal rate, B^CQD = organic load.
Volumetric removal rates in excess of 10 kg COD/m^ . d were observed in
both filters, treating municipal wastewater with low COD-concentration.
840
-------
With the filters operating as single-stage reactors, specific sludge
production was between 0.35 and 0.55 g TS/g COD removed. With the two-stage
process the sludge production increased from virtually zero at an organic
removal rate of 3 g COD/m? . d, up to 0.40 g TS/g COD removed at a rate of
25 g COD/m2 . d.
Oxygen transfer was good in both filters. In a full-scale plant, with a
depth of aeration of 3 m, an air supply of about 10 to 15 m^ per kg COD
applied should be sufficient with the tested filter media.
A different study compared high-rate treatment of food-industry
effluents in an activated sludge unit and in a submerged aerated biological
filter (10). The filter had a medium with a specific surface area of 230
m2/m3.
Removal rate versus organic load is shown in Figure 12, for the
submerged biofilter. The maximum volumetric removal rate was in excess of 15
kg COD/m^ . d. This was about four times higher than the maximum achievable
rate in the activated sludge unit.
§
o
00
4)
•P
a
j-i
va
D
K
80-|
60-
QAir= 25.0 m3/m3«h : o
Q.. = 12.5 m3/m3.h : •
Air
Organic load, g COD/m «d
Figure 12. Total organic load versus total organic removal rate in the
aerated submerged biological filter treating food-industry
wastewater. Air supplies of 12.5 and 25.0 m^ per m^ filter
volume and hour have been used, r^ QQQ = organic removal rate,
fy\ COD = organic load.
On an average basis, an effluent concentration of 1000 mg COD/1
corresponds to a removal efficiency of about 70% using the wastewater in
this study. The activated sludge unit and the biofilter could be loaded at
2.8 kg COD/m3 . d and 12.7 kg COD/m^ . d, respectively, in order to obtain
841
-------
an effluent concentration of 1000 mg/1. This shows that the aerated sub-
merged biological filter was superior to the activated sludge process in
terms of required tank volumes.
It can be seen from Figure 13 that the aerated submerged biological
filter can be operated at a lower specific air supply than the activated
sludge unit. With the same specific air supplies, the biological filter
always showed the highest dissolved oxygen concentrations. The filter medium
increases the contact time between the air and the liquid. Thus more oxygen
can be transferred.
\
e
«• c
jxygen
a. c
i
w t
0)
M „
o ^
en
w
•H
Q
^
1
•
/
O
0
t
/
•
/
0 '
2
•.
*
0
S
^
,
o
3
^
•
0X
0 <
^" \
^
0 6
*^
\
^
0
—
1
o- —
00 1!
Biological Filter:
Activated Sludge:
Specific air supply, ra /kg COD
Figure 13. Specific air supply versus dissolved oxygen concentration for
the two pilot-plants, treating food-industry wastewater.
Data recalculated to a submerged depth of 3 m.
The first full-scale aerated submerged biological filter in Norway was
put into operation in 1984. Two more plants were started in the spring of
1985 and several plants are on the planning stage.
Two of the plants in operation treat municipal wastewater. The third
plant treats mainly dairy wastes, and some municipal wastewater.
As of yet there are no performance data available from these full-scale
installations. However, aerated submerged biological filters seem to be a
good alternative to other biological treatment processes. The microorganisms
grow on the media, eliminating sludge recycle and any disturbance resulting
from sludge bulking. Trickling filters need a certain minimum hydraulic load
to work efficiently. In aerated submerged biological filters the air bubbles
are believed to erode the biofilm and prevent clogging of the filter media.
The strong turbulence also ensures good contact between substrate and
microorganisms. An aerated submerged biological filter with a high surface
area filter media should be a simple and compact treatment process.
842
-------
PROCESS UPGRADING AND IMPROVED MANAGEMENT OF WASTEWATER TREATMENT SYSTEMS
SEPARATE TREATMENT OF SEPTAGE LIQUOR
Treatment of septage is a major problem in many European countries. In
Scandinavia septage is quite often discharged directly to the sludge
treatment units at a municipal sewage treatment plant. Small primary or
secondary chemical precipitation plants are very common in Norway. The
operational problems due to septage discharge have been severe at these
plants. In addition, the return of untreated septage liquor to the treatment
plant influent frequently leads to unacceptable effluent qualities.
One way to reduce the problems caused by septage discharge is to treat
the septage liquor separately in a biological unit. No data about separate
treatment of septage liquor have been found in the literature, except for a
brief experiment made by the Norwegian Institute for Water Research.
In order to gain more knowledge, pilot-scale research using both the
RBC-process and the activated sludge process was initiated in 1983. This led
to a full scale demonstration project in 1984 and 1985. These projects were
carried out by research engineers presently employed by Aquateam.
Pilot-Scale Research
This work had two main objectives: to study biological treatment of
septage liquor, and to study chemical precipitation of treated and untreated
septage liquor when mixed with primary treated municipal wastewater.
Treatment in RBCs (ID-
Biological treatment of septage filtrate was studied in two pilot-scale
RBCs, one operating at 5.4°C and the other at 14.5°C. In addition, chemical
precipitation of untreated and RBC-treated septage liquor, mixed with
municipal sewage, was studied in order to find the effects of return flows
of septage liquor on alum treatment of wastewater. The septage filtrate used
in this study was less concentrated than typical septage liquor.
Figure 14 shows total organic removal rates versus total organic loads
for the two RBCs. Most of the reduction of organic matter in the RBC systems
took place in the first stage. Removal rates as high as 80-90 g CODj/m^ . d
were observed at 14.5°C. A maximum removal efficiency of about 85% total COD
was found at a temperature of 14.5°C and an organic load of about 80 g
CODT/m2d.
Based on the removal rates of total COD at 5.4 °C and 14.5 °C respec-
tively, a temperature coefficient (9) of 1.10-1.11 was found.
The results indicated simultaneous nitrification and denitrification in
the RBC unit operated at 14.5°C. The low temperature RBC unit showed no sign
of nitrification.
843
-------
T
20
~t
40
1 I \ 1 1 T
60 80 100 120 140 160 180
Total organic load, g COD /m d
RBC A ( 5.4 °C) :
Stage 1 : o
Stage 1+2 : *•
Stage 1+2+3 : T
Stage 1+2+3+4: •
RBC B (14.5 °C):
Stage 1 : O
Stage 1+2 : a
Stage 1+2+3 : v
Stage 1+2+3+4: o
Figure 14. Separate treatment of septage filtrate in pilot-scale
RBCs. Shows total organic removal rates versus total organic
loads, based on data from all 4 stages. r/\tcOD = organic
removal rate, B/\ QQQ = organic load.
to
Jar-tests showed that nitrification of the septage liquor was required
reduce the consumption of chemicals for phosphorus removal.
Low effluent phosphorus and SS concentrations could be obtained in the
jar-tests with both treated and untreated septage liquor. With respect to
COD, previous RBC treatment was essential, as shown in Figure 15. High rate
treatment in a RBC unit (<30% removal of CODy) was sufficient to have a very
positive effect on the residual concentrations of total and filtrable COD
after blending with municipal sewage and precipitation with alum.
844
-------
100-
80-
8 60-
i
40-
20-
TnfL
cone., mg/l
10% untr.
40 % untr.
10%AI
40%AI
10%BI
271 a o 40%BI
100
120-
100-
80-
o
O
o
O)
60-
40-
20-
200 300
Alum addition, mg/l
400
Infl.
cone., mg/l
126 •—-• 10% untr.
343 o—o 40 % untr.
98 T v 10%AI
169 w „ 40%AI
81 •—• 10%BI
171 a o40%BI
'V — '
100
200 300
Alum addition, mg/l
400
Figure 15. Total and filtrable COD concentrations after alum precipitation
in jar-tests, for different fractions of RBC treated and un-
treated septic sludge filtrate in primary treated municipal
wastewater.
845
-------
Treatment With the Activated Sludge Process (12)—
The septage liquor used in this experiment was more concentrated
than the filtrate used in the RBC-experiments. Figure 16 shows removal
efficiency versus F/M-ratio. The pilot-plant operated at 8°C and a F/M-ratio
of 0.41 kg BOD7/kg MLVSS . d was obviously overloaded. Otherwise the pilot-
plants performed excellent at the temperature levels indicated in Figure 16.
f-
Q
O
03
90
80-
o 70n
| 60H
tt>
01 50H
10°C
8°C
0.1 0.2 0.3 0.4 0.5
F/M-ratio (kg BOD7/kg MLVSS • d)
0.6
Figure 16. Separate treatment of septage liquor in pilot-scale
activated sludge units. Shows removal rates versus F/M-ratios.
Chemical precipitation of treated and untreated septage liquor, mixed
with municipal wastewater, was studied in jar-tests. The alkalinity of the
septage liquor determined the required alum addition. Thus nitrification of
the septage liquor is necessary in order to reduce the consumption of
chemicals.
An alum addition equivalent to 2-3 mol Al/mol P is required for
satisfactory removal of phosphorus. Consequently the phosphorus concentra-
tion will determine the necessary alum addition for nitrified septage
liquor.
Similar to RBC-treatment, pretreatment of septage liquor with the
activated sludge process significantly reduced the residual concentrations
of organic matter after blending with municipal wastewater and precipitation
with alum.
846
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Full-Scale Demonstration Project (13)
Sorumsand sewage treatment plant was chosen for the full-scale demon-
stration project. This is a secondary precipitation plant designed for
6 000 p.e., but with an actual load of about 1 500 p.e. Alum is used as
precipitant.
Septic sludge is discharged to the sewer a few yards upstream the
treatment plant. The volume of septage discharged at this plant is equiva-
lent to 5-10% of the total flow to the plant.
The sludge going from the plant thickener to the dewatering centrifuge
is a mixture of septic-primary-chemical sludge. This is a common situation
at many Norwegian treatment plants.
The full-scale test was carried out over a period of 6 months. The
sludge liquor from the centrifuge was treated in an activated sludge unit,
operated as a batch system.
Figure 17 shows the flow diagram for this process. Sludge liquor from
the centrifuge flowed to a tank. From there it could either be returned to
the treatment plant influent, or be pumped to the activated sludge unit. The
activated sludge unit had a total volume of 30 m^r Every morning a maximum
of 17.5 m^ of treated sludge liquor was pumped out of the tank, and replaced
with an equivalent volume of untreated septage liquor. Air was supplied
through coarse bubble aerators at the bottom of the tank.
Centrifuge
Untreated
Floating pump
Treated
sludge liquor
r
«
i
r
»
_J
Max.
Return to
treatment
plant influent
Min.
Batch-operated
activated sludge unit
Excess sludge
Figure 17. Flow diagram of a full-scale, batch-operated, activated sludge
system for separate treatment of sludge liquor.
847
-------
Dewatering units at Norwegian treatment plants are normally in opera-
tion only during regular working hours, from Monday to Friday. Thus, we had
an ideal situation for batch operation of the activated sludge unit. A
regular cycle was like this:
Aeration was stopped early in the morning, and the sludge was
allowed to settle for 1-1.5 hours.
Treated sludge liquor was pumped to the treatment plant influent.
Aeration was resumed and the tank was filled with untreated sludge
liquor.
Aeration was continued until the following morning.
On Saturdays and Sundays the activated sludge unit was aerated all day.
The process cycle was controlled by two simple timers.
Results from a one month period with intensive monitoring are shown in
Table 2. During this period the aeration tank had a pH of 6.8-7.2 and a
temperature of 12-13 °C. The organic loading (F/M-ratio) was between 0.049
and 0.137 kg BODy/kg MLSS . d, with a mean value of 0.094 kg BODy/kg MLSS.d.
A COD/BODy-ratio of 1.8 was found for untreated sludge liquor. Treated
sludge liquor was not analysed for BOD.
TABLE 2. SEPARATE TREATMENT OF SLUDGE LIQUOR IN A FULL-SCALE PLANT.
RESULTS FROM PERIOD WITH INTENSIVE MONITORING
Parameter Influent Effluent Rem. Eff. %
Range Mean Range Mean Range Mean
COD, mg/1
SS, mg/1
Tot-N, mg/1
Tot-P, mg/1
P04-P, mg/1
Alkal inity,
meq/1
990-3050
688-1403
68-237
6.0-22.9
1.1-2.4
2.8-17.2
1539
1047
no
16.5
1.8
4.7
62-760
110-640
20-111
0.1-10.9
0.1-1.0
1.0-8.0
244
319
60
3.4
0.4
3.1
63-96
46-88
1-73
17-99
29-95
~~
86
70
45
76
78
33
In general the removal of organic matter was very good. A fairly good
reduction of suspended solids was also obtained. At the low F/M-ratios used
in this study nitrification took place. The data are not consistent, but it
is assumed that some of the nitrogen was used for cell synthesis, and that
some was removed by nitrification/denitrification due to the batch operation
of the activated sludge process.
848
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The previous pilot-scale experiments have shown that the alkalinity and
the phosphorus concentration determines the required chemical addition for
phosphorus removal. Table 2 shows that the alkalinity was reduced, but only
with 33% on an average basis. However, the removal of phosphorus was
excellent. The removal of particulate phosphorus can be attributed to the
reduction in suspended solids. The extremely low concentration of soluble
phosphorus may have been caused by precipitation, due to the fraction of
chemical sludge in the sludge mixture.
ACKNOWLEDGEMENT
The author wants to thank Mr. B. Paulsrud, Mr. R. Storhaug,
Dr. A.S. Eikum and Dr. H. Brattebo for their contributions, by permitting
the author to use their material in the preparation of this paper.
REFERENCES
1. Paulsrud, B. and Langeland, G. Aerobic, thermophilic digestion of pre-
thickened sludge using air. Paper presented at COST 68-seminar, New
Developments in Processing of Sludges and Slurries, RIVM, Bilthoven,
April 21, 1985.
2. Paulsrud, B. et al. Tilf0rsel av septikslam til VEAS-tunnelen. Project
3684, Aquateam, Norwegian Water Technology Centre A/S, 1984. 48 pp.
3. Paulsrud, B. Mobilt avvanningsutstyr for septikslam — Utpreving av
MOOS-KSA-system. Project 4284, Aquateam, Norwegian Water Technology
Centre A/S, 1985. 28 pp. 9*
4. Bratteb0, H. Phosphorus removal from wastewater by fixed-bed adsorp-
tion on granular activated alumina. Ph.D.-thesis, The University of
Trondheim, 1983.
5. Brattebo, H. Phosphorus removal from wastewater by the use of granular
activated alumina. Paper presented at Int. Conf. on Management Strate-
gies for Phosphorus in the Environment, Lisbon, July 1-4.
6. Brattebo, H. et al. Rensing av av!0psvann ved spredt bebyggelse.
Fosforfjerning ved adsorpsjon pa aktivert alumina. Report no. STF 21
A84080, SINTEF, Trondheim, 1984. 43 pp.
7. Paulsrud, B. Driftsoppf01ging av BIOVAC renseanlegg for helarsboliger.
VA-report 16/84, Norwegian Institute for Water Research, 1984.
849
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8. Eikum, A. S. et al. BIOVAC husanlegg — Fjerning av fosfor og organisk
stoff i avlep fra enkelthus. Project 1084, Aquateam, Norwegian Water
Technology Centre A/S, 1985. 36 pp.
9. Rusten, B. Wastewater treatment with aerated submerged biological
filters. J. Water Pollut. Control Fed. 56: 424, 1984.
10. Rusten, B. and Thorvaldsen, G. Treatment of food-industry effluents —
Activated sludge versus aerated submerged biological filters. Env.
Techn. Letters, 4: 441, 1983.
11. Rusten, B. Treatment of septic sludge filtrate in rotating biological
contactors. In: Proceedings of the Second Intern. Conf. on Fixed-Film
Biological Processes, Arlington, Virginia, July 10-12, 1984.
12. Storhaug, R. Separat behandling av slamvann fra avvanning av septik-
slam — Biologisk rensing med aktivslam. Prosjektraport 14/84, NTNF
Program for VAR-teknikk, 1984. 54 pp.
13. Paulsrud, B. Full-scale demonstration of separate treatment of sludge
liquor. In preparation.
850
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RESEARCH AND DEVELOPMENT IN DOMESTIC WASTE WATER TREATMENT
IN THE UK, 1985
by
Staff of WRC Processes
Water Research Centre
Elder Way
Stevenage, Herts
United Kingdom
The work described in this paper was
not funded by the U.S. Environmental
Protection Agency. The contents do
not necessarily reflect the views of
the Agency and no official endorsement
should be inferred.
North Atlantic Treaty Organization/Committee on the
Challenges of Modern Society (NATO/CCMS) Conference
on Sewage Treatment Technology
October 15-16, 1985
Cincinnati, Ohio
851
-------
LOPMEM1 JN DOMESTIC WASTE WAI
IN THE UK. 1985
by: Staff of WRc Processes
Water Research Centre
Elder Way
Stevenage, Herts
SGI 1TH
United Kingdom
ABSTRACT
Research in the UK Water Research Centre in wastewater treatment
include studies on sewage treatment, biological sludge treatment and
handling, operational aids and management aids. Research in sewage
treatment features studies on optimising aeration efficiency, both
fine-bubble and mechanical surface aeration, energy saving in sewage
pumping, the CAPTOR process, nitrification in a biological fluidised bed,
anaerobic treatment of sewage, a modified rotating biological contactor
system, and biological filtration of finely screened sewage. Highlights of
the research in biological sludge treatment and handling include studies of
aerobic digestion of sludge, submerged combustion of digester gas for
prepasteurization of sludge, digester gas utilisation, consolidation
thickening filter pressing control, oil from sludge and instrumental
analyses of biogas. In operational aids, the research includes studies on
desludging of sedimentation tanks, management of small dispersed unmanned
plants and maintenance simulation studies. The research in management aids
include studies on per capita sewage load assessment, cost performance
indices and field evaluation of instruments.
852
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1. INTRODUCriON
This paper provides a summary of the current state of R & D Projects
being undertaken at the UK's Water Research Centre Processes Laboratory in
Stevenage together with an overview of relevant research in British
Universities.
1. Brief introduction
2. Sewage treatment
3. Biological sludge treatment and handling
4. Operational aids
5. Management aids
6. Research in British Universities (Appendix)
2. SEWAGE TREATMENT
2.1 OPTIMISATION OF FINE-BUBBLE AERATION
Since the last NATO/CCMS meeting this project has been completed. The
object of the project was to improve the efficiency of oxygen utilisation in
conventional fine-bubble diffused aeration sewage treatment plant (STP) and
to achieve nitrification of the treated waste. The project was funded by
the Water Research Centre, the UK Department of Energy, the US EPA and the
Canadian Department of the Environment with assistance from the Thames Water
Authority. The work was carried out on the Thames Water Authority's
full-scale STP at Rye Meads.
Aeration tanks have been modified by the installation of an optimised
diffuser layout and DO control system to achieve and maintain a 50%
improvement in aeration efficiency compared to similar unmodified tanks.
Results have indicated that the production of a high quality, fully
nitrified effluent may be no more expensive than the production of
non-nitrified effluents if the costs of surplus sludge disposal are taken
into account. The optimisation of the aeration tank layout and the
installation of a DO control system also allows a greater flow rate of
sewage per unit tank volume to be treated, thereby reducing the capital cost
of new plants.
A general procedure for the design of efficient activated sludge plants
has been established and published as a replication guide. Optimisation
projects are currently in progress at about fifteen large activated sludge
plants in the UK.
A cost-benefit study has been carried out by the Thames Water Authority
on the "Net Present Value" of the energy which can be saved by introducing
this system into all fine-bubble sewage treatment plants of >10,000
population: the NPV (using a discount rate of 5% and plant life of 20 years)
was £16 million (about $22.5 million) (and roughly £35 million or $50
million for the UK).
853
-------
The success of this project has led to the establishment of another
project, the Optimisation of Mechanical Aeration (see below).
2.2 OPTIMISATION OF MECHANICAL SURFACE AERATION
A survey of the aeration efficiencies achieved at large activated
sludge plants in the UK have revealed that diffused-air systems are
potentially more efficient than surface aeration systems when installed in
processes designed to produce fully nitrified effluents. However, it has
been found that mechanical surface aeration systems may be more efficient in
non-nitrifying processes.
The same general principles of optimisation of aeration efficiency
should apply to surface aeration systems as well as diffused-air systems and
there is potential for considerable energy savings to be made at large
installations.
Accordingly a full-scale project has recently been initiated at the
Blackburn Meadows STP of the Yorkshire Water Authority to develop
improvements in surface aeration efficiency. One of the primary objectives
of the project is to assess the performance of several different dissolved
oxygen control mechanisms which may be used separately or in combination to
vary the oxygenation capacity of surface aerators. These mechanisms include
on-off switching of individual aerators, controlling aerator speed and
adjusting the depth of immersion of aerators in the aeration tank (1).
Equipment for this project is being ordered this month and the project
itself will be commencing in early 1986.
2.3 ENERGY SAVING IN SEWAGE PUMPING
This project was reported in the UK paper at the NATO/CCMS Conference
in 1983. Since then the work has been completed with the satisfactory
demonstration that savings can be made by modifications in the design and
operation of sewage pumping stations. The project examined two different
installations, one small and one medium sized.
The first, at a small rural pumping station, showed that 80% of the
flow could be delivered at pipe velocities of 0.4 metres/second, provided
the remainder is delivered in excess of 0.9 m/s, without problems of
deposition or slime growth in the pipeline. The recommended minimum pimping
velocity for a single rate pumping system is 0.76 m/s. Savings due to
reduced friction head exceeded 25% on a bill of £1,600 ($2,200) annually.
At a larger urban pumping station, a microprocessor was used to control
the pumps according to a flow-balancing algorithm, this saved energy equal
to £3,200 pa ($4,500) and increased the use of night-time, off-peak energy
to make a total saving of £5,000 pa ($7,000) on a bill of £35,000 pa
($50,000 or about 14%). The experimental system is now being replaced by a
permanent system by the Wessex Water Authority. The Water Research Centre
is negotiating to license the FLOBAL control software for inclusion in a
commercial computerized pump controller. Work is under way to extend the
854
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algorithm to optimise pimping against a tidally varying head (2).
As an additional aid to design engineers a computer program has been
developed to help to optimise the selection of pumps for sewage pumping
stations. The program will perform all the necessary calculations to size
the pumps for a specified duty, and it then selects the pump with the
optimum efficiency from a pump data-base. The program uses inter-active
graphics and produces hard copy of pump curves and the selected design data
for inclusion in procurement specifications.
2.4. THE "CAPTOR" PROCESS
The project was reported in detail in the 1983 NATO/CCMS paper, and
details of the process have been given elsewhere (3, 4). It is a joint
project with funding from the Water Research Centre, the Severn-Trent Water
Authority (STWA), Simon-Hartley Limited, the UK Department of Trade &
Industry and the US EPA.
The current objective of the project is to evaluate a CAPTOR
installation at the Severn-Trent Water Authority's full-scale STP at
Freehold. The CAPTOR installation (Figure 1) is being used as a
pre-treatment stage to reduce a substantial proportion of the BOD load so
that the subsequent activated sludge stage can be operated with a greater
sludge age and thus achieve nitrification.
So far about 50% removal of dissolved BOD has been achieved in the
initial CAPTOR stage but it has been found that a significant proportion of
the biomass in the CAPTOR sponge-particles disengages and passes forwards
into the activated sludge stage thus reducing sludge age and the
concentration of nitrifiers.
The CAPTOR process enables us to double the activated sludge
concentration in the aeration stage but laboratory evidence suggests that
the activity is only about 50% of non-captured sludge. The nett effect is
therefore relatively little different from conventional AS systems.
Pilot-scale work has been started since the last report with the
objectives of examining
(i) the use of CAPTOR sponge particles to enhance biomass concentration in
the secondary process; and
(ii) the use of CAPTOR sponge particles as a tertiary stage for
nitrification which currently looks premising.
855
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EFFLUENT
NITRIFICATION
EFFLUENT
I
RETURN SLUDGE
Figure 1. Diagram of the arrangements made at
Freehold WRW to uprate the activated
sludge plant using CAPTOR and allow
its evaluation.
2.5 NITRIFICATION OF A SECONDARY SEWAGE EFFLUENT IN A BIOLOGICAL
FLUIDISED BED (BFB)
The intention to establish a plant at the Horley Works of the Thames
Water Authority was reported in the 1983 NATO/CCMS paper following
small-scale tests by the Authority at its Beckton STP. This work indicated
that it was possible to remove about 30 mg NH3-N/1 in a reactor with a
retention time of 35 minutes.
The process has recently been tested on a much larger scale in a joint
development project with the Water Research Centre, Thames Water Authority
and Dorr-Oliver Ltd at the Horley Sewage Treatment Works (South of London)
of the Thames Water Authority. The pilot plant (1.83 m x 1.22 m x 5.4 m
high) had previously been used in carbonaceous oxidation and nitrification
tests at the Water Research Centre's former Coleshill Experimental Site.
The pilot plant layout is shown in Figure 2.
The plant has been operated at three different ammonia loading rates
for extended periods to determine the optimum performance. During the
latter part of 1985 the plant will be operated over a diurnal flow pattern.
The results of the plant performance at the design flow rate is shown
in Table 1. It has not been found necessary to sand clean when operating
under nitrifying conditions.
856
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NITRIFIED EFFLUENT
4f
I
EFFLUENT
FEED-f-RECYCLE
>-
FEED
co
NITRIFYING
BFB
////////////^^^
^ BELOW GROUND
OXYGENATOR
Figure 2. Flow sheet for the nitrifying BFB at Horley STW.
-------
TABLE 1. PERFORMANCE OF NITRIFYING BFB AT HORLEY SOW
(AVERAGE VALUES FOR THE PERIOD)
Operational conditions
Feed flow 370 m3/d (1700 pe)
Bed volume 9.8 m3
Superficial HRT 38 rain
Biomass concentration 8.1 g BTS/1
Temperature 17.9QC
Run length 69 d
Performance
Effluent
BOD5 mg/l 18 12
NH3.N mg/l 27 3
SS mg/l 30 23
pH value mg/l 6.8 6.1
Loading and removal rates
BOD loading rate 0.084 kg BODAg BTS.d
NH3-N removal rate 0.112 kg NH3~NAg BTS.d
NH3-N removal rate 0.91 kg NHs-N/m3.d
The work has shown the process is feasible on a larger scale. Cost
evaluations done during the project have shown that the BFB has a much lower
(60% less) capital cost than a comparable activated sludge extension but the
operating cost is higher because of the cost of oxygen. The BFB is about
10% lower in total cost using DCF analysis, but is sensitive to the cost of
oxygen (5).
2.6. ANAEROBIC TREATMENT OF SEWAGE
Fermentation using anaerobic (methane-forming) bacteria to convert
oxygen demand to methane has proved successful for the treatment of food
processing and agricultural wastes.
Following pioneering studies in Holland (6) using enrichment cultures
of methane bacteria at 12-20°C and laboratory trials at the Water Research
Centre (7) using digested sewage sludges at 20OC, pilot-scale trials were
initiated to determine the performance of the process at UK ambient
temperatures.
A 30 m3 capacity UASB reactor was constructed at the Stevenage
Laboratory by converting an existing sewage storage tank; it was
commissioned in Spring 1984 and fed continuously with settled domestic
sewage.
858
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We had operational problems with the design of the gas
collection/sludge settlement system (which does not allow free passage of
settled solids back to the fermentation zone) and with the low methanogenic
activities of the digested sewage sludges used for inoculation, but
otherwise the mechanical and hydraulic performance of the plant proved
satisfactory and entirely trouble-free.
The level of BOD reduction was disappointing and appeared to be
severely limited by the relatively low temperatures of the incoming sewage.
During the summer and autumn of 1984 purification efficiencies were 27-46%
at hydraulic retention times of 12-48 hours and sewage temperatures of
15-20OC. During the winter of 1984/85, sewage temperatures fell to lOoc,
fermentation ceased and purification efficiencies fell to zero.
The reactor was reinoculated with digested sludge in the simmer and
trials will continue until December 1985.
2.7 MDDIFIED ROTATING BIOLOGICAL CONTACTOR (RBC) SYSTEM
Problems have been encountered in RBC plants - especially on small
flows - as a result of uneven growth of biomass on the discs. The Water
Research Centre developed a technique for overcoming this problem which is
currently the subject of a patent application.
A joint project has been established between the Water Research Centre,
the Wessex Water Authority and Dewplan (ET) Ltd to develop, construct and
evaluate a prototype WRc RBC on a Wessex Water Authority site. The
operation of the prototype commenced during the first quarter of 1985.
There were initial mechanical problems to be overcome and although soluble
BOD is satisfactorily removed the unit's mode of operation tends to cause a
higher level of solids to appear in the treated effluent. These problems
are being currently addressed.
2.8 BIOLOGICAL FILTRATION OF FINELY-SCREENED SEWAGE
(THE "LOSLUJ" ® PROCESS)
The cost of sludge treatment and disposal in the UK is typically about
45% of the total cost of running a sewage treatment works. One approach
towards reducing this cost is to thicken sludge prior to treatment and
disposal. An alternative approach is to modify sewage treatment in order to
produce less sludge. About two thirds of the total sludge production is
derived from primary sedimentation, and if this stage could be eliminated
total sludge production could be reduced provided the settleable solids were
biologically oxidised in the secondary treatment stage. This approach is
not economically attractive in activated sludge plants because of the
increased energy consumption required to oxidise the additional solids load.
However, in biological filtration plants the oxygen consumed in destroying
the solids is provided by natural convection at no cost.
The operating costs of this biological filtration treatment show a
reduction of approximately 45% compared with traditional biological
859
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filtration. In this method sewage is finely screened (about 1.5 ram aperture
size) to remove large particles before being treated in a filter containing
a specially developed high voidage plastic medium. The screened sewage is
discharged to the filter via a self-cleaning distributor (also developed by
WRc). Final clarification takes place in a conventional humus tank.
This method has been successfully demonstrated on a large pilot scale
installation which showed that total sludge production was reduced by 45%.
Estimates of costs for a typical works of 5,000 population indicate savings
of about 30% for capital and 20% for operating costs.
A full-scale installation is under construction for the Welsh Water
Authority and two further plants are being designed.
2.9 THE SEWAGE TREATMENT OPTIMISATION MODEL (STOM)
The UK water authorities spend around £150M pa to construct and extend
sewage treatment works, and about £300M pa on operating the works. STOM
provides these water authorities with a means to:
a) assess the performance of existing works, to allow any remedial
measures to be targetted more effectively on those works and processes
which are in need of improvement,
b) check the effectiveness and costs of proposed extensions or complete
new works, so that satisfactory performance is achieved without
over-design,
c) predict the effects of long-term trends in operating conditions so that
a view can be taken of the plant's future capability and any plant
changes can be planned well in advance.
The Sewage Treatment Optimisation Model (STOM) is a complex computer
program developed by the Water Research Centre following an initiative by
the British Construction Industry Research & Information Association, and is
now in routine use by the UK water undertakings, consultants and
universities. It offers a flexible means of modelling performance and costs
for groups of processes at sewage works. The model contains modules for
individual treatment processes such as activated sludge, biological
filtration, anaerobic digestion, and auxiliary processes such as flow mixing
and division. Each module relates performance and costs to design and
operation; most of the common processes are included. The user links the
corresponding modules together to represent a complete works.
The model is under continuous development involving both the addition
of modules for further processes and enhancement of existing modules.
Models for some processes have yet to be included (e.g. rotating biological
contactors and tertiary treatment). Currently a module for the performance
of tertiary rapid sand filtration, prepared in co-operation with Imperial
College, London, is being evaluated for eventual inclusion in the model.
860
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The standard capital and operating costs in STOM are updated from their
1976 base by government cost indices, although the user can substitute his
own costs. The cost indices do not take into account changes in operating
and maintenance practices since 1976 (e.g. the replacement of resident staff
by mobile gangs). A detailed manual containing all the formulae and
parameters used in the model has also been prepared.
3. BIOLOGICAL SLUDGE TREATMENT AND HANDLING
3.1 AEROBIC DIGESTION OF SLUDGE
When aerobic conditions are maintained in sewage sludge, exothermic
reactions take place and the temperature of the sludge can rise to 55OC or
higher in a well lagged tank. This increase in temperature offers an
opportunity to reduce the retention times required to achieve stabilisation
and/or to achieve a disinfection.
Successful aerobic digestion using pure oxygen and subsequently using
air was reported in the 1983 NATO/CCMS paper. Costs when using oxygen were
unacceptably high, but further work showed that the process was viable and
economically attractive when air was used to maintain aerobic conditions.
It has been established that the layer of foam which builds up on top of the
sludge is critical in achieving very high oxygen utilisation efficiencies
from air and recent work has concentrated upon more detailed evaluation of
foam management techniques. Economic comparisons show that the process
could be competitive with alternative methods of pre-treatment prior to
anaerobic digestion for producing a disinfected sludge should this prove to
be necessary.
The next stage of this project will consist of a joint evaluation of a
technique developed in Switzerland in which aerobic digestion is followed by
anaerobic digestion. This technique appears to produce a sludge in which
all pathogens have been killed or deactivated and which readily consolidates
to thicknesses of 8-10%.
3.2 SUBMERGED COMBUSTION OF DIGESTER GAS FOR PRE-PASTEURISATION
OF SLUDGE
An alternative method to aerobic digestion of achieving a disinfected
and stable sludge is to pre-heat the sludge to about 65°C by burning
digester gas in a submerged combustion device. The hot sludge is then
cooled and anaerobically digested at about 35°C.
The joint project reported in the 1983 NATO/CCMS paper encountered
problems with the submerged combustion equipment and this resulted in
delays. These were eventually overcome and sufficient data were obtained
for the design of a full-scale system. The full-scale (20,000 pop)
demonstration plant comprising automatic primary tank desludging,
consolidation thickening, submerged combustion pre-pasteurisation, and
mesophilic anaerobic digestion has now been designed and is currently being
installed in the north of England.
361
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Commissioning will be completed in the first quarter of 1986 when a 12
month intensive monitoring programme of the plant performance and
microbiological quality of the sludge will commence.
3.3 DIGESTER GAS UTILISATION
A survey of digester gas utilisation in the UK has recently been
completed which shows that of the 1.4 million tonnes dry solids of sewage
sludge produced each year in the UK, about 50% is anaerobically digested and
produces about 250 x 106 m3 of gas with an energy value of about IQlO
Joules. This is less than 0.1% of all UK energy needs, but is about 30% of
the energy consumption of the UK water industry.
About 30% of digester gas is used for digester heating and 50% is used
to generate electrical power for use in sewage works, mainly in dual-fuel
engines on large works. Waste heat from the engines is used to heat the
digesters.
Minor uses for digester gas include use as a road vehicle fuel «1%)
but this is not an economic proposition. Before use the gas must be
scrubbed to remove corrosive sulphides and then compressed.
About 40 x 106 m3 of digester gas is unused each year, mostly on sewage
works in the size range 10,000 - 100,000 population, and there has been
significant interest recently in installing small packaged spark-ignition
engines for combined heat and power generation in these works. Case studies
at a small works (10,000 pop) and large works (100,000 pop) is currently
being carried out. Results to date show that the economics are very
doubtful on works of 10,000 pop or lower, but that at larger sizes of works
considerable savings can be made.
3.4 CONSOLIDATION THICKENING
Consolidation under gravity can be a very cheap and cost-effective
method of thickening sludges in order to reduce the cost of treatment,
transport and disposal. A study undertaken by the Water Research Centre has
indicated that savings in operating costs of £15-20M pa ($20-$30 million)
could be achieved in the UK by the planned use of consolidation thickening
of sewage sludges.
Consolidation thickening of sludges is an apparently simple process.
The sludge is held in a tank and consolidation takes place under the
influence of gravity as the sludge is compressed under its own weight
forcing the interstitial water within the sludge into the supernatant liquid
above. The performance of the process depends upon a number of factors
including the sludge blanket height, sludge retention time, the method of
operation (i.e. batch or continuous), and the design and operation of
mechanical aids including picket fences. The sludge height and retention
time, in particular, are critically dependent upon the properties and
characteristics of the particular sludge but until now there has been no
reliable method of relating tank dimensions and sludge characteristics to
862
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plant performance. Consequently, many thickening tanks perform poorly, and
it is not uncommon to see sludge solids floating rather than consolidating.
Theoretical and full-scale plant studies have led to an improved
understanding of the fundamental mechanisms involved in consolidation
thickening. Consolidation can be predicted from three easily measured
sludge parameters, the Compression Coefficient, Compression Index and the
Resistance to Consolidation which can be measured in the laboratory using
specially developed procedures.
A mathematical model programmed into a computer handles the data to
produce performance curves showing how sludge blanket height and sludge
retention time affect the solids concentration in the output sludge. A
family of curves is produced depending on the mode of operation of the
thickener, i.e. batch or continuous. These performance curves enable the
engineer to select with confidence an appropriate combination of the sludge
blanket height, tank diameter and method of operation to give the required
performance.
Picket fences and effective process control are essential for optimum
performance and further experimental work has shown how these components
should be designed and operated.
This design procedure has already been used to produce process designs
and plant specifications for a wide range of sludges, and in most cases the
size and shape of thickener has been suitable for prefabricated construction
methods using steel tanks. Several full-scale demonstration plants are
being installed and the first to come on-line was commissioned early in 1985
and produces a thickened sludge of about 12% solids from a primary sludge
feed of about 4% solids.
3.5 FILTER PRESSING CONTROL
The 1983 NATO/CCMS paper described a co-operative project between the:
Severn-Trent Water Authority and the Water Research Centre which had as its
objective the automation and optimisation of sludge filter-pressing. This;
project is now nearing completion and a study has shown that potential
savings in the UK are in the region of £5M.
About 30% of UK sludge is chemically conditioned and dewatered, mostly
in filter plate presses. The operating cost is about £25M pa and the
process is expensive, the major elements of cost being chemicals and labour,
which each account for nearly 50% of total operating costs.
The microprocessor-based process control system which has been
developed has achieved a reduction in the costs of both labour and chemicals
of about 50% on the full-scale installation at the Severn-Trent Water
Authority's Mansfield STP.
863
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The essential features of this system are:
- Accurate and efficient chemical dosing over the wide variation in
sludge flow rate that occurs during the pressing cycle.
- Control of press feed pumps to achieve and maintain optimum
conditions throughout the press cycle.
- Continuous monitoring of cake quality and termination of the
pressing cycle when adequate product quality has been achieved.
Chemical conditioning and filter pressing are thereby made very competitive
with other sludge treatment and disposal routes. The process management
system is now commercially available and it is being installed at several
other sites.
3.6 OIL FROM SLUDGE
The UK water industry currently operates a well managed system of
sludge treatment and disposal that takes due account of envirormental
protection. However, looking to the long-term future it is essential to
consider alternative sludge treatment and disposal routes that could either
be cheaper than current methods or could meet new targets for environmental
constraints in the most cost effective manner.
Against this background the Water Research Centre is evaluating a
number of Long Term Options for alternative sewage sludge treatment and
disposal routes. Any radical alternative approach is likely to be economic
only if some of the resource-value of sludge can be offset against
processing costs. Any financial value a raw sludge may have is associated
mostly with its fat and protein content and there are many strategies
available for tapping this resource. A preliminary desk study showed that
thermochemical processing of sludges to produce fuels was potentially
attractive, and that slow pyrolysis was amongst the processes that warranted
further investigation.
Professor Bayer in Germany has already shown that it is technically
possible to convert by pyrolysis much of the organic matter in sewage sludge
to oil and char with both products having potential value as a fuel.
Comprehensive process design and economic studies have recently been
completed of a pyrolysis route for both raw and digested sludges using UK
cost data.
The process flow sheet is potentially complex (see Figure 3) and a
process model has been developed to study the interaction between the
various process stages, and to evaluate the numerous options for heat
recovery within the process route.
These studies indicate that the process could be very competitive with
incineration (see Figure 4) but it is important to note that the capital and
operating costs of the pyrolysis stage are only a small fraction (less than
10%) of the total route costs, and therefore the economical viability of the
864
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SEDIMENTATION TANKS
oo
CTv
cn
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CONDFNSATE TO PRIMARY
SEOIHENfAION TANKS
MAIER-tFFLUENI
SURPLUS PYROLYIIC
CHAR FOR STORAGE
DISTRieuriON/OlSPOSAL
SUPPLfnENIARY
NATURAL GAS/IP6
Figure 3
Draft process flow diagram for the pyrolytic processing of
anaerobically digested sewage sludge.
-------
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process lies in optimising the total route and not simply concentrating
effort upon the reactor design. Route costs are critically dependent upon
the following:
(i) Process route energy demand.
Critical areas are the energy required for drying and the measures
taken for heat recovery between the various process stages. The
energy for drying depends upon the performance of the pre-thickening,
dewatering and drying stages.
(ii) Anaerobic digestion.
Whilst the quantity of oil produced from raw sludge is substantially
greater than that produced from digested sludge a desk study has shown
that this advantage is more than offset by the greater on-site costs
of processing raw sludge. This is due, in part, to the reduction in
quantity of sludge solids passing forward for processing, and hence a
reduction in capital cost of downstream plant. There are also savings
in fuel costs due to the reduced load on the drying stage.
Furthermore, the inclusion of anaerobic digestion considerably
increases the scope for cost-effective recovery of low grade heat,
which further reduces the need to burn primary fuel.
(iii) The value of the pyrolytic oil produced.
The studies being carried out by the Water Research Centre are
complementary to the work being undertaken at the Wastewater Technology
Centre in Burlington Ontario with whom there has been regular contact. It
is hoped that these contacts will be strengthened into more formal
arrangements for collaboration.
3.7 INSTRUMENTAL ANALYSIS OF BIOGAS
Studies are being undertaken to develop new and improved strategies for
the monitoring and control of the anaerobic digestion process, based on
detailed analysis of the composition of the biogas produced.
Theoretical (mathematical modelling) studies of the microbial ecology
of the fermentation (8) identified hydrogen (H2) as a key intermediate in
the conversion of organic matter to methane and trials are now in progress
to determine whether on-line monitoring of H2 in biogas can be used to
detect small fluctuations in the performance of the anaerobic digestion
process.
Typical concentrations of hydrogen in the biogas from sewage sludge
digesters are 36-220 vpm (parts per million by volume (average 73 vrjn).
At one particular works, a comparison was made between the start-up of
two identical new digesters. Late modifications and last-minute
"teething-troubles" during the commission of one digester caused the
867
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concentration of hydrogen in the biogas to rise to 240 vpm before settling
down to a baseline value of 60 vpm. In the other digester, the
modifications were completed before commissioning and the concentration of
hydrogen in the biogas remained at 40 - 80 vpm throughout.
The extreme sensitivity of the analysis can be seen from Figure 5 which
shows the changes in hydrogen content of the biogas from one of these
digesters during its hourly feeding cycle (9).
4. OPERATIONAL AIDS
4.1 DESLUDGING OF SEDIMENTATION TANKS
In order to reduce significantly the frequency of visits by mobile
gangs to unmanned sewage treatment works, automatic control of sedimentation
tank desludging is essential. Following extensive field trials carried out
in association with the Thames and Anglian Water Authorities it has been
established that simple timer-only control is rarely satisfactory since it
results in blockages or in the production of very thin sludges.
Using existing equipment a microprocessor based control system has been
developed which has been used satisfactorily over many months. Control is
achieved by a combination of timing and monitoring of sludge blanket level
in the tanks.
As a result of this work, a commercial unit has been developed and is
undergoing field trials. This unit offers a choice of desludging pumps and
a range of sensing devices to deal with most situations likely to be met on
small to medium sized works (less than 10,000 population equivalent).
4.2 MANAGEMENT OF SMALL DISPERSED UNMANNED STP
Following a joint study undertaken by the Water Research Centre with
the Anglian Water Authority to develop an ICA based operating strategy for
some 150 sewage pumping stations and 50 treatment works, it was decided to
implement the proposed scheme on a pilot scale before proceeding with the
full scheme.
The pilot scheme has now been completed and encompasses a biological
treatment works, an oxidation ditch treatment works and a pumping station
each equipped with micro-processor based outstations and appropriate
Instrumentation, Control & Automation (ICA) equipment and connected via a
telemetry network (representative of that proposed for the full scheme) to a
master-station at the Central Operations Room. The master station is based
upon a DEC LSIll/23 computer but nevertheless has software which provides
full management information facilities. Data and operating experience
collected from the pilot system is now being used for the final designs for
the full-scale scheme.
The results obtained will be used in a Guideline for the development of
a process management system for dispersed works.
868
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c»
o-i
ID
mixing
feed
mixing
feed
100 105
Hme (hours)
110
115
Figure 5. Variations in the concentration of hydrogen in the headspace
gas during the feed cycle of an anaerobic sludge digester.
-------
4.3 MAINTENANCE SIMULATION STUDIES
The study described in section 4.2 and the resulting pilot evaluation
have provided valuable experience in the selection of operating strategies
for groups of dispersed works. However, the selection of an appropriate
maintenance strategy is nearly always left to chance. Following some
success using a simulation technique (originally developed for study of
production line queueing problems in the motor industry) in the study of the
consequences of alternative operating strategies carried out with the
Anglian Water Authority, the Water Research Centre is now applying the
technique to the study and optimisation of maintenance strategies.
5. MANAGEMENT AIDS
5.1 PER CAPITA SEWAGE LOAD ASSESSMENT
There is concern in the UK water industry about the accuracy of
available data on the strength of domestic sewage and the volume of sewage
produced per person since these data are used in the calculation of trade
effluent charges.
In agreement with the Confederation of British Industry (CBI) the
Mogden formula is used as the basis for charging, viz.
C = R + V + S. .Svi + B. Q£
Ss Os
Where
C = total charge per cubic metre of trade effluent
R = reception and conveyance charge per cubic metre
V = volumetric and primary treatment cost per cubic metre
S = treatment and disposal costs of primary sludges per cubic metre of
sewage
Sw = suspended solids content of trade effluent
Ss = suspended solids content of crude sewage
B = biological oxidation cost per cubic metre of settled sewage
Ow = COD of trade effluent after settlement
Os = COD of settled sewage
870
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In response to this concern, the Water Research Centre is undertaking a
project to assess the contribution per head of population to the flow and
strength of domestic sewage. The project will provide the necessary
up-to-date information to enable the water authorities to set firmly based
and readily defensible trade effluent charges.
The data generated by the project will also be useful to the water
authorities in connection with performance measurement.
The project, which is due to start in the third quarter of 1985,
consists of a scheduled programme of sampling and analysis, over a 12 month
period, of sewage frcm a residential catchment which is entirely domestic
except for a small number of retail shops. The sewer frcm the catchment
passes under the Water Research Centre's Stevenage site. Flow measuring
facilities have been installed to permit flow related analysis. The study
will cover diurnal, hebdomadal and seasonal variations in flow and strength.
The sewerage system is a separate one and will permit the study of the
effects of storm flows and of infiltration. The catchment is well defined
and accurate population figures are available. Demographic data are
available frcm census returns and these will be used for data analysis.
The variables being determined include BOD, COD, suspended matter,
settleable matter, total organic carbon, ammonia, Kjeldahl nitrogen,
nitrite, nitrate, orthophosphate and chloride.
A similar study was carried out on the same sewer in 1956-57 and thus
it will be possible to see what changes have occurred during the 29-year
intervening period.
5.2 COST PERFORMANCE INDICES STUDY
A useful management tool is the setting of performance targets. In
wastewater treatment this can take the form of setting targets for the
quality of the treated effluent and for the total running costs of the
treatment plant. The former is set by reference to envirormental quality
objectives, or - in some countries - by legislation or directive. Quality
targets are relatively easy to set and monitor since they can be defined
numerically in terms of well established variables (e.g. concentrations of
BOD, NH3 etc).
However, operating-cost targets are more difficult to set. There is
relatively little data available to guide managers in assessing whether or
not a sewage treatment plant is operating as efficiently as it might. There
are many factors which affect the operating cost, and similar plants
treating similar sewage may justifiably have very different operating costs.
The problem becomes more difficult if the manager has a number of different
types of treatment plant under his control (e.g. activated sludge,
biological filters, RBC etc) and cannot therefore compare the costs of
similar processes.
871
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In an attempt to improve efficiency water authorities in the UK have
asked for guidance on target costs for the operation of treatment plant. A
co-operative project has therefore been established by the Water Research
Centre, involving all ten UK water authorities, in which operating cost data
are being collected for the majority of sewage treatment plants in England
and Wales. These data are then collated and analysed making it possible to
produce median costs for plants of similar types and size. These data then
allow managers to identify plants whose operating costs lie outside the
norm and then to evaluate the reasons for the performance. Since the data
are held in a large database with facilities for data manipulation it is
possible to make individual comparisons between specified plants, groups of
plants, different regions, different processes etc. This will enable
managers to set more realistic cost-performance targets.
A further objective of the project is to enable the Water Research
Centre to identify areas of greatest cost and thus to develop R & D projects
with the best potential for savings. It will also help to identify the most
efficient plants which can then be evaluated to provide guidelines for the
operators of other treatment plant.
5.3 FIELD EVALUATION OF INSTRUMENTS
The 1983 NATO/CCMS paper reported on the development of this project
which is designed to obtain "the cost of ownership" of instruments used in
the water industry and thus to enable management to ensure that the best
instruments are bought for any specified application. An important
criterion is that the test fluids and test environment should be those for
which the instruments will normally be bought rather than in a laboratory
environment with clean water as the test fluid.
Two full-scale test facilities have now been established in the UK with
partial funding from the Department of Trade & Industry. The first
Evaluation and Development Facility (EOF) was opened early in 1985 at the
Witney STP of the Thames Water Authority. The second EOF was opened in
early June at the Eccup Drinking Water Treatment Plant of the Yorkshire
Water Authority. The former EOF provides evaluation facilities for
instruments for sewage treatment plant, whilst the latter EOF will take
instruments intended for use in Drinking Water Plant.
A careful testing and evaluation protocol has been developed which has
been discussed with a number of organisations including the IAWPRC so that
reports on instruments tested at one of the UK EDF's may have validity
internationally. Already instruments from a number of countries, including
the UK, have been submitted to the Water Research Centre for evaluation and
are currently being evaluated under field conditions at the EOF for a 12
month period, relevant data being logged automatically via the on-site
computer system for later off-line analysis on the Water Research Centre's
own computer facilities.
872
-------
A concise report is produced for each instrument detailing the results
and findings of the evaluation and providing an indication of the total cost
of ownership, taking into account:-
accuracy
reliability
response times
maintenance needs
calibration
cleaning
construction
ease of use.
These reports are made available to potential users in the Water
Industry to assist them in equipment selection. Benefits to manufacturers
include reference to reports in publicity material and the feedback of
valuable field test data to the design and marketability of the instruments.
In the first year of tests, up to ten instruments are being evaluated
in each of the following categories:
activated sludge flow measurement
crude sewage flow measurement
open channel flow measurement
ammonia measurement.
Evaluation of DO measuring instruments will commence shortly with
further test programmes being introduced at regular intervals over the next
few years.
873
-------
T,;./'•' v"' ''•-'" '' :;;'"-: ' " REFERENCES, .,.
1. Thomas, V.K. Optimisation of Aeration Efficiency - internal WRc
Report. Proposals for Automatic Control of the Simplex Plants,
Blackburn Meadows S1W, Southern Division, Yorkshire Water Authority.
April 1985.
2. Hobson, J.A. "Energy Saving: Pumping of Sewage". Dec, 1982. WRc
Report No 189-S.
3. Atkinson, B., Black, G.M. and Pinches, A. "The characteristics of
solid supports and bicmass support particles when used in fluidised
beds". From "Biological Fluidised Bed Treatment of Water &
', Wastewater", ed. Cooper & Atkinson, pub. Ellis Horwood Ltd,, 1981, p.75.
!4. Walker, I. and Austin, E. "The use of plastic, porous bicmass supports
>:in a pseudo-fluidised bed for effluent treatment", ibid, p.272.
5. Williams, S.C., Harrington, D.W., Quinn, J.J. and Cooper, P.F.
High-rate nitrification in a biological fluidised bed at Horley STW.
Paper presented to the Metropolitan and Southern Branch of the
Institute of Water Pollution Control, High Wycombe, Bucks., 21 May,
1985.
6. Grin, P.C., Roersma, R.E. and Lettinga, G. "Anaerobic Treatment of Raw
Sewage at Lower Temperatures". Proc. of European Symp. on Anaerobic
Waste Water Treatment (AWWT), Noordwijkerbout, 1983.
7. Fernandes, X.A., Cantwell, A.D.C. and Mosey, F.E. "Anaerobic
Biological Treatment of Sewage". Wat. Pollut. Control, 1985, 84, (1),
pp 99-110.
8. Mosey, F.E. "Mathematical modelling of the anaerobic digestion
process: regulatory mechanisms for the formation of short-chain
volatile acids from glucose". Water Science and Technology, 1983, 15,
pp 209-232.
9. Collins, L.J., Fernandes, X.A. and Paskins, A.R. "Hydrogen in the
headspace gas during start-up of anaerobic digesters at Cotton Valley
Sewage Treatment Works, Milton Keynes, 21/11/84 - 3/4/85". WRc Report
355-S. April 1985.
874
-------
6. APPENDIX
A SELECTION OF UNIVERSITY DEPARTMENT RESEARCH PROJECTS RELEVANT TO
WASTEWATER TREATMENT
institution
University of
London Imperial
College of Science
and Technology
University of Leeds
University of
Birmingham
Pro-iect description
Risk analysis in planning
and design of wastewater
treatment processes in both
the developed and developing
countries. Modelling, fore-
casting and real-time control
of wastewater treatment
processes.
Dynamic modelling and design
of waste stabilisation ponds.
Analysis and removal of
herbicides and related
materials in wastewater treat-
ment processes. Behaviour
of nitrilo triacetic acid in
sewage and sludge treatment
systems.
Design and performance of
rotating biological contactors.
Anaerobic treatment of
high-strength waste water in
a fixed film system.
Use of immobilised whole
cells in the treatment of
domestic and industrial waste-
waters.
Role of extra cellular
poly-saccharides in sludge
flocculation and sludge bulking.
Use of aerated lagoons for
industrial wastewater
treatment.
Stable foams in activated
sludge process.
Flocculation and attachment
in anaerobic systems.
Principal
Researcher
Jowitt, P W
Lumbers, J P
Perry, R
Lumbers, J P
Stentiford, E I
Horan, N J
Tebbutt, THY
Forster, C F
875
-------
Trent Polytechnic
Paisley College
of Technology
University of
Newcastle upon Tyne
University of
Manchester Institute
of Science and
Technology
Loughborough
University of
Technology
University of Surrey
University of York
Degradation of stored
treated and untreated waste-
water prior to its use in
the flushing of household
toilets.
Sludge activity measure-
ments in biological
oxidation of wastewaters.
Mathematical modelling of
the scale-up of aerobic
reactors for wastewater
treatment.
Attachment of bacteria to
solid surfaces in anaerobic
wastewater filters.
Evaluation of performance
and mathematical modelling
of anaerobic rotating
biological contactors for
wastewater treatment.
Fluidised bed fermentation;
applications in aseptic
fermentation and wastewater
treatment.
Supported biomass in reactors;
hold-ups, substrate uptake,
product formation.
Design formula for aerated
lagoon wastewater treatment.
Inhibiting conditions in
biological removal of
nitrogenous pollutants
from wastewater.
Development of attached
microbial film process
variants for wastewater
treatment; relationship
between biochemical
activity and population
structure in activated
sludge systems.
Ferris, S A
Clark, J H
Shaaban, M G B
Sanderson, J A
Echaroj, S
Black, G M
Ellis, K V
Winkler, M A
Davies, M
876
-------
University of Oxford Characterisation of Beckett, P H T
insoluble compounds of
toxic elements in sewage
sludge and sludge treated
soil.
Decomposition of sewage
sludge and character of
decomposition products.
Study on recovery from
sewage of phosphorus
usable as fertiliser.
University of Control of nuisance flies Dancer, B N
Wales Institute in sewage filter beds by
of Science & Bacillus thuringiensis.
Technology
University of Stability of bubble induced Davidson, J F
Cambridge circulation of liquid in a
deep shaft u-tube sewage
treatment plant.
University of Design of electro-separators Wakeman, R J
Exeter for the filtration and
thickening of slurries.
877
-------
ADVANCES IN WASTEWATER TREATMENT AND SLUDGE MANAGEMENT PRACTICES
RELATED TO PATHOGEN AND TOXICITY CONTROL
by
J. Convery, D. F. Bishop and A. D. Venosa
Wastewater Research Division
Water Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
This paper has been reviewed in ac-
cordance with the U.S. Environmental
Protection Agency's peer and adminis-
trative review policies and approved
for presentation and publication.
North Atlantic Treaty Organization/Committee on the
Challenges of Modern Society (NATO/CCMS) Conference
on Sewage Treatment Technology
October 15-16, 1985
Cincinnati, Ohio
879
-------
ADVANCES IN WASTEWATER TREATMENT AND SLUDGE MANAGEMENT PRACTICES
RELATED TO PATHOGEN AND TOXICITY CONTROL
by: J. J. Convery, D. F. Bishop and A. D. Venosa
Wastewater Research Division
Water Engineering Research Laboratory
U.S. Environmental Protection Agency
26 West St. Clair Street
Cincinnati, Ohio 45268
ABSTRACT
Research to support municipal sludge regulations includes the deter-
mination of the kinds and concentrations of pathogens in sewage sludge from
various wastewater treatment systems and the characterization of the pathogen
reduction capabilities of alternative solids handling processes. The extend-
ed aeration process produces greater reductions in bacterial densities of
waste sludge than conventional aeration and achieves in the waste sludge
a one-log reduction in Salmonella. Sludge handling processes, producing
significant reduction in pathogens but not disinfecting the sludge, include
conventional aerobic digestion, anaerobic digestion, conventional composting
and lime stabilization. Processes, producing further reduction in pathogens
and disinfecting the sludge, include composting for 3 days at 55°C for with-
in vessel and static pile systems and 15 days at 55°C for windrow systems,
heat drying, heat treatment and thermophilic digestion. Autothermal
thermophilic aerobic digestion produces especially effective inactivation
of Salmonella and total plaque forming units (viruses) in the sludges.
Ultraviolet light (UV) processes for disinfection of wastewater have
evolved from the development and demonstration stage to full-scale application
with 60 facilities now in operation. UV processes are competitive, if not
less expensive, than chlorination. Suitable design approaches and disinfec-
tion models have been developed. Operation and maintenance experiences are
summarized.
Toxics treatability and control research includes the characteri-
zation of removals and effluent concentrations of specific toxics in a range
of treatment systems, the determination of the fate of these toxics by the
three principal removal mechanisms of sorption, volatilization and biodegra—
dation, and the evaluation of the toxicity reduction capability of treatment
systems for the removal of overall toxicity. The toxics removal data indicate
that conventional primary-activated sludge treatment provides best overall
control of specific toxics. The limited kinetic studies on the specific re-
moval mechanisms suggests that biodegradation in activated sludge systems is
880
-------
the principal removal mechanism for the organics studied but that volatili-
zation of the moderately volatile compounds also is important. Further
work is needed to appropriately characterize the three removal mechanisms
especially for highly volatile and sorbable toxics. Conventional primary-
activated sludge treatment provides good toxicity reduction capabilities
for complex mixtures of toxics. The use of biomonitoring methods for
toxicity appears to provide a practical method for managing complex
mixtures of toxics, especially in municipal wastewaters.
INTRODUCTION
This paper presents recent information and control approaches for
pathogens and toxicity in municipal wastewater and sludge process streams.
The rationale behind the pathogen control technology standards for munici-
pal sludge application to the land are described together with relevant
performance and cost capabilities of the Autothermal Thermophilic Aerobic
Digestion Process.
A rational procedure for designing Ultraviolet Radiation facilities
for disinfecting wastewaters is described. Observed performance of a full
scale operating facility is compared to the performance predicted by the
model.
Two approaches, described in this paper, are being used to evaluate
and control toxics in wastewater treatment. The first approach using repre-
sentative specific toxics evaluates overall removals in pilot scale treatment
systems and specific removal mechanisms in laboratory studies. The second
approach uses bioassay tools for characterizing toxicity control for complex
mixtures of unknown toxics.
MUNICIPAL SLUDGE DISPOSAL REGULATIONS
The interim final regulations specifying the criteria for sludge use
on land pertaining to disease prevention and pathogen control as required by
The Resource Conservation and Recovery Act (RCRA) were published in September
1979 - Code of Federal Regulations (CFR, Title 40, "Criteria for Classifica-
tion of Solid Waste Disposal Facilities and Practices", Para. 257.3-6, Disease,
Interim Final Regulations, Effective October 15, 1979). Farrell (1) described
the rationale behind these regulations as being either:
0 eliminate the possibility of contact by eliminating the
pathogens
881
-------
0 require a series of formalized barriers (including processing
to reduce pathogen densities) that insure that the probability
of human contact is low. Figure 1 illustrates the management
options provided by the regulations for use of sludge on the
land.
Two technology-based standards for control are included in the
regulations:
0 processes to significantly reduce pathogens (PSRP)
0 processes to further reduce pathogens (PFRP).
Processes to significantly reduce pathogens are described in
Table 1 (1). These technologies provide a one-log reduction of bacterial
and viral pathogens. While a two-log reduction in indicator organisms,
such as fecal coliform and total coliform densities, is attainable with
anaerobic digestion under these operating conditions, the relative reduc-
tions in pathogens and indicator organisms varies with each technology.
TABLE 1. PROCESSES TO SIGNIFICANTLY REDUCE PATHOGENS
Technology Conditions
Aerobic Digestion 60 days @15°C
or 40 days @20°C &
38 % volatile solids (V.S.) reduction
Anaerobic Digestion 60 days @20°C to
15 days @35°C - 55°C &
38% V.S. reduction
Composting 5 days @40°C &
4 hours @>55°C
Lime Stabilization pH 12 & 2 hours contact
Other Equivalent reduction
of pathogens and
volatile solids
882
-------
Raw Sludge
From POTW
NoPSRP |
i
1
Receives
PSRP
1
1
1
1
1
Receives
PFRP
NP
No Use On Land i
Public Access To Site
Is Restricted
For 12 Months
After Use Of Sludge
Grazing
No Restrictions
On Use
Grow Crops
Animal
Products
Not
Consumed
By Humans
Animal
Products
Consumed
By Humans
No Crop
No Grazing
Crops Not
For Direct
Human
Consumption
Crops For
Direct Human
Consumption
1 Month Waiting
Period Before
Grazing
T
Crops That
Do Not
Touch The
Sludge
T
Crops That
Touch The
Sludge
P • Permitted
NP • Not Permitted
Crops Not Grown
Until 18 Months
After Sludge Use
T
Figure 1. RCRA criteria for use of sludge on land (1).
883
-------
The inability of anaerobic digestion and most of the other PSRP
processes to reduce the density of helminth eggs is offset by the restric-
ted access and proper siting considerations identified in the regulations.
In addition to pathogen reduction, PSRP's must eliminate the poten-
tial of. the sludge to cause a vector problem by either drying the sludge,
raising the pH or reducing the odor and organic content.
Processes to further reduce pathogens (PFRP) which disinfect the
sludge (i.e., reduce pathogens to below their detectable limits, viruses
- 1 PFU/100 ml, Salmonella-3 CFU/100 ml and Ascaris - 1 viable EGG/100
ml) are described in TABLE 2 (1).
TABLE 2. PROCESSES WHICH FURTHER REDUCE PATHOGENS
Technology
Conditions
Composting
Heat Drying
Heat Treatment
Thermophilic Aerobic
Digestion
Other
3 days @55°C for
within vessel & static pile
15 days @55°C & 5 turns
for windrow
Cake moisture <10% & 80°C
wet bulb temperature of gas
stream in contact with sludge
or sludge particles reach 80° C
30 minutes @180°C
10 days @55°C & 38% V.S.S.
reduction
Equivalent pathogen & volatile
solids reduction
PSRP PROCESSES PLUS
Beta Ray Irradiation
Gamma Ray Irradiation
Pasteurization
Other
1.0 Megarad @20°C
1.0 Megarad @20°C
30 minutes @70°C
Equivalent pathogen reduction
884
-------
The U.S. EPA plans to issue revised municipal sludge disposal
regulations in 1986 for use of sludge on the land, as well as land-
filling, distribution and marketing, incineration and ocean disposal.
This regulation development activity has stimulated a high level of
interest and effort in characterizing and improving the pathogen reduc-
tion capabilities of sludge stabilization processes and practices as
well as identifying more cost-effective designs.
Figure 2 from Farrell (2) shows the log of the bacterial densities
(no/gram) in the influent wastewater solids from five treatment plants.
The bacterial densities are surprisingly consistent. This study was
conducted to determine the bacterial content of the waste activated
sludge from extended aeration-type facilities. Figure 3 shows that this
type of facility is capable of achieving greater reductions in bacterial
densities than conventional treatment facilities and a one-log reduction
in Salmonella. The current sludge regulations, however, require a separate
sludge processing step which achieves an additional one-log reduction in
pathogens. ta ^
Salmonella
Fecal
Streptococcus 7
10
Fecal
Collform
10
Total
Coliform
City
Williamsburg
Sardina
Frankfort
Jackson Center 0.25
Little Miami 38
8 9
Process
Extended Aeration
Extended Aeration
Brush Aerator
Brush Aerator
Conventional
Confidence Interval
(95%)
Figure 2. Log of bacterial densities (No./gram)
in influent wastewater solids (2).
885
-------
A recent summary of the available literature and research had identi-
fied the kinds and concentrations of pathogenic bacteria, viruses, helminths,
protozoans and fungi found in sewage sludges, as well as their fate and trans-
port in the environment and their infectivity to man (3). Table 3 summarizes
the survival times for major pathogens of interest. The long survival times
(>1 year) for helminths are usually for organisms underground where human
exposure and risk are very low. While the Agency has affirmatively evaluated
the feasibility of conducting a pathogen risk assessment there are important
data gaps to be filled. Among these are control technology issues such as the
performance of aerobic digesters. Many of the 3,400 aerobic digesters in the
U.S.A. are incapable of meeting the PSRP requirements; particularly during the
winter months in the northern States. A research study is currently being con-
ducted at Cornell University on how to upgrade, at minimum cost, the PSRP per-
formance of aerobic digesters through the use of submerged aeration, covers,
and insulation.
A feed solids concentration of 2% will be used. A primary research
objective is to establish the minimum time requirements (5 to 20 days) to
reliably achieve a one-log reduction of pathogens while maintaining an
operating temperature of about 30°C. This work is a followup on activity
to our earlier research at Cornell on autothermal thermophilic aerobic
digestion (ATAD).
Salmonella
Fecal
Streptococcus 6"
Fecal
Coliform
Total
Coliform
City
Williamsburg
Sardina
Frankfort
Jackson Center
Little Miami
K
Extended Aeration
Extended Aeration
Brush Aerator
Brush Aerator
Conventional (Mixed SI)
(Return SI)
-^1 Confidence Interval
Figure 3. Reductions in log of bacterial densities
(No./gram) caused by treatment (2).
886
-------
TABLE 3. SURVIVAL TIMES OF PATHOGENS ON SOIL AND PLANTS (3)
PATHOGEN
BACTERIA
VIRUSES
PROTOZOA
HELMINTHS
SOIL PLANTS
Absolute Common Absolute Common
Maximum Maximum Maximum Maximum
1 year 2 months 6 months 1 month
6 months 3 months 2 months 1 month
10 days 2 days 5 days 2 days
7 years 2 years 5 months 1 month
AUTOTHERMAL THERMOPHILIC AEROBIC DIGESTION
The most extensive study of ATAD in the U.S. was conducted by Jewell
(4). This full-scale study, using a 28.4 nH (1,000 cu. ft.) reactor, demon-
strated that a single-stage digester utilizing self-aspirating aerators
with ambient air, treating a continuous feed of primary and waste activated
sludge (3%-6% total solids), resulted in autoheated reactor temperatures
normally in the range of 50°C to 60°C. Complete inactivation, that is
below the limits of detection, of Salmonella and total plaque forming
units (viruses) was observed except for one test date. Parasites (viable
ova) were reduced significantly, but not completely. Maximum temperature
development (55° C to 60° C) and a maximum organic removal rate of 6.5 kg
BCOD/m-'-day (.4 Ib/day/cu. ft.) occurred when the organic loading rate was
12 to 15 kg TS/m3-reactor-day (.75 to .94 Ib/day/cu. ft.) and the dissolved
oxygen concentrations were <1 ppm. Where BCOD is the biodegradable chemi-
cal oxygen demand and TS is total solids. Oxygen transfer efficiencies of
20% or more were reported with recommended power input levels of 150 to 200
W/m^ of reactor. Both a DeLaval Centri-rator aerator and a Midland-Frings
aerator were evaluated. Hydraulic retention time varied from 3 to 11 days
with 5 days being the most typical value. The dewaterability of the
digested sludge deteriorated significantly at all HRT's evaluated.
Even though Jewell's full-scale reactor was not completely mixed
as evidenced by stratification of the dissolved oxygen concentration, he
described the process performance as being approximately a first-order,
887
-------
completely-mixed steady state system where K, the reaction rate coefficient
can be determined by the expression:
SE = 1 (1)
SI 1 + K (HRT)
where SE = biodegradable organics out [TVS, gm/1]
SI = biodegradable organics in [TVS, gm/1]
HRT = hydraulic retention time, day
K = reaction rate coefficient,
gm biodegradable TVS removed per gm
of biodegradable TVS in the reactor per
day, day~l
The biodegradable fraction (%) of the sludge constituents was found by
Jewell (4) to be as follows:
COMPONENT BIODEGRADABLE FRACTION (3Q
Chemical Oxygen Demand 47.4 - 76.5
Total Solids 22.9 - 62.0
Total Volatile Solids 42.2 - 71.7
Total Kjeldahl Nitrogen 57.0 - 85.0
The reaction rate coefficient K (using COD as a measure of bio-
degradable organics) is shown in Figure 4 (5). The temperature relationship
shown below, which was developed by Jewell (4), is in basic agreement with
that of other researchers in the temperature range of 45° to 55°C.
K = (0.022) 1.076TR-20 (2)
where
TR = temperature of the reactor, °C
888
-------
RetcttM Rite CotMclent Versus AeraMc
Ngtsltr Liquid Ttmptratynt
I
«
A
Airimn ind KimMw 1970)
) — ,
Tinwefibn Of LH«« In *«itk DlfMtif, *C
Figure 4. Reaction rate coefficient versus aerobic
digester liquid temperatures (5).
Figure 5 illustrates the sources and losses of heat for the aerobic digester.
There are three types of heat loss:
0 loss through the discharge of exhaust gas
loss with the digested sludge
loss to the surroundings.
The first two are the major losses (6). They can be controlled by provid-
ing efficient aerators (e.g., 15% efficiency or better) to reduce the flow
through the reactor and thickening the sludge fed to the reactor in order
to reduce the total quantity of material to be processed. Thickening of sludge
to 3% solids or greater has been recommended (5). Convection losses from the
reactor can be controlled by covering of the digester and adding insulation.
889
-------
Heat With
Sludge Input
Heat With
Gas Input
Mixing Heat
-------
oo
C
i
600,000 —
500,000—
400,000 —
300,000—
200,000—
100,000 —
Comparative Digestion Capital Costs
ATAD
I
250
I
500
I
750
1000
I
1250
I
1500
1
1750
I
2000
2250
I
2500
I
2750
Kg/Day of TS Throughput
Figure 6. Comparative digestion capital costs (7).
-------
per day was required to operate and maintain the system. Performance was
very acceptable including: 40% reduction of volatile solids, thermophilic
(>43°C) temperature operation in the second stage reactor, apparent pathogen
reduction to the FRG limitation of 100 enterobacteria/ml and infrequent
incidence of odors. The ATAD process has been shown by Strauch and Bohm
to be capable of destroying salmonella, parasite eggs and viruses provided
a temperature of 50°C is maintained for 57 hours of aeration time (6).
A summary of the design parameters for all three of the ATAD
manufacturers in FRG is shown in Table 4. The Fuchs and Thieme systems
employ two insulated and covered reactors in series operation with batch
feeding cycles. The Thieme system uses a rotary screen to prethicken the
sludge feed concentration to 10 to 12 percent solids which results in a
70% reduction in reactor volume requirements. Fuchs also prethickens the
sludge to 3 to 5 percent solids. Dissolved air flotation thickening of
primary and waste activated sludge is practiced. The batch feeding cycle
is used to prevent contamination of the pasteurized sludge with incoming
raw sludge. Mechanical components in a typical Fuchs reactor consists
of two rotary blade type foam cutters, two side mounted aspirator type
aerators and one center floating aerator depending upon reactor sizing.
Design oxygen transfer efficiency is 2.1 kg 02/kWh (3.5 Ib 02/hp-hr).
A 20-day storage period is recommended for the digested sludge to cool
(20°C) to improve post thickening or dewatering.
Figure 7 shows the schematics for all three systems. The Babcock
ATAD system utilizes a single reactor with semi- or fully-continuous
sludge feeding. A submerged turbine is used for aeration in this system.
Actual operating conditions for five Fuchs systems is shown in
Table 5 (7).
The ATAD batch operating strategy maximizes pathogen destruction
potential and minimizes the possibility of product contamination from
incoming sludge. A specific volume is removed daily from the second stage
reactor. A comparable volume is then transferred daily from the first
stage to the second stage which provides a minimum detention time of 24
hours at thermophilic temperatures. Some researchers have been concerned
about possible temperature depression in the first stage with a batch
feeding operation . Deeny et al, (7) observed that the first and second
stage temperatures were depressed by approximately 5 to 6°C and 3 to 4°C,
respectively. Both reactors recovered at a rate of 1° per hour. Volatile
solids destruction were reported as being >40 percent at detention times
in excess of 4 days.
There are only limited data on sludge dewatering performance.
Experience at the Vilsbiburg ATAD facility using a belt press and decanter
centrifuges indicate acceptable performance with sludge cake total solids
of 30 to 35 percent with a feed solids content of 2.5 percent (7). Polymer
dose was approximately 5 g/kg of sludge. Feed temperature range was 48
to 63°C.
892
-------
TABLE 4. SUMMARY OF ATAD DESIGN PARAMETERS (7).
DESIGN PARAMETER
Sludge Feed Concentration, percent (%)
Hydraulic Detention Time, Days
Number of Reactors
Sludge Storage Capacity, Days
Operating Strategy
Aeration Requirement,
KWH/M3 of sludge throughput
Mixing Requirements,
W/M3 reactor volume
FUCHS
3-5
5-6
2
20
Batch
12-14
86
MANUFACTURERS
THIEME
10-12
6-7
2
70
Batch
.
200-300
8ABCOCK
3-6
3-6
1
-
Semi-Continuous
12-17
-
TABLE 5. SUMMARY OF ATAD ACTUAL OPERATING CONDITIONS
Parameter
No. of Reactors
Dimension, 0xH, M
Volume (Occupied by
Sludge) Total, m3
Sludge Influent Flow,
m3/day
Sludge Concentration,
TSS/TVSS, percent
Sludge Mass Loading,
TVSS, kg/day
Sludge Volumetric
Loading, kg/day/m3
Reactor(s) Detention
Time, days
Aeration Installed
Power, kw
Aeration Power
Consumption , kwh
Aeration Power/
Sludge Volume,
kwh/m3/day
Aeration Power/
Reactor Volume,
w/m3
Aeration Power/
Sludge Mass,
TVSS, kwh/kg/day
Facility
2
5x3
120
9
4/3.1
280
2.3
13
(6.6)
8.8
211
23.4
(12.0)
73
0.75
2
7.0x
3.5
120
20
4/3.4
680
5.7
12
(6)
9.5
228
22.8
(12.6)
79
0.74
893
2
7.5x4
360
70
5.5/
3.6
2,520
7.0
5.1
38
912
13.0
106
0.36
2
3.5x
2.5
48
8
5/3.0
240
5.0
6.0
4.4
106
13.3
92
0.44
2
6.5x
2.25
150
15
3.5/
2.8
420
2.8
10
11.8
284
18.9
79
0.68
-------
Sludge
Thickener
V
Ti
To Land Application
ATAD Reactors
Sump Sludge Storage
Sludge
co
UD
Sludge
n.,,
Mazorator
Holding Tank
Thickener
Fuchs ATAD System
*L1
JUj^J
Rotating Screen
Conditioning Tank
Thieme ATAD System
5
ATAD Reactor
ATAD Reactors
Foam Breaker Scrubber
Q
Heat Exchanger Sludge Storage
Babock ATAD System
Figure 7. Alternative flow schemes of ATAD systems.
L_L.
Sludge Storage
Land Application
To Land Application
-------
APPLICATION OF ULTRAVIOLET LIGHT FOR DISINFECTING WASTEWATER
The use of Ultraviolet Radiation (UV) for the disinfection of treated
domestic wastewaters has evolved relatively quickly from the development and
demonstration stages to full scale application. This has been spurred in
large part by the U.S. Environmental Protection Agency's (EPA) direct re-
search funding efforts and its encouragement to build UV plants through its
Construction Grants Innovative and Alternative (I/A) Program. Over the last
10 years the technology has received considerable attention, with an increas-
ing number of full-scale plants coming on line, particularly over the last
three to five years. UV disinfection is being considered at approximately
120 municipal wastewater facilities in the U.S.A. Currently some 60 are in
operation with the remainder under design or construction. Most of these
facilities are quite small. The largest facility at, Madison, Wisconsin,
will have design flow of 2.4 m-Vs (55 MGD). The process application is
viable, technically feasible, and cost-effective for most wastewater situ-
ations.
A comparison of costs had been performed in 1979 as part of an evalua-
tion of UV disinfection at Northwest Bergen County, New Jersey. This study
had assembled unit costs for a number of disinfection processes and compared
them to the estimated unit cost for UV disinfection. These same unit costs
are presented on Figure 8, updated to 1984 (USEPA Index = 460). Unit costs
developed from a recent study (8) of existing full-scale UV disinfection
facilities have also been included in Figure 8. In certain cases, a wide
range in cost estimates was found for a specific process. The values used
on Figure 8 represent an approximate average of the various estimates
to achieve an effluent quality objective of 200 FC/100 ml. Additionally,
the costs presented in various sources may differ in their assumptions for
labor, power, etc. Caution is, therefore, warranted in any direct cost
comparisons.
The analysis presented on Figure 8 suggests that UV is considerably
less expensive than ozonation and is competitive, if not less expensive,
than the chlorination or chlorination/dechlorination processes. It was
found that the costs estimated for UV in our recent study (8) were less
than the estimates from the 1979 report. The reasons for this are primarily
the reduction in real costs for equipment and the more rational manner in
which UV systems can now be designed. A noted shortcoming in the applica-
tion of UV, however, has been the lack of a generic, technically acceptable
design approach. Most in-field designs, with a few notable exceptions, have
relied on equipment manufacturers for system sizing and hardware designs.
These have been based on limited experience with wastewater applications and
have often followed generalized rules of thumb. The design assumptions and
the hardware configurations themselves often do not adequately account for
the basic variables that are key to effective UV design and performance.
The most common configurations are the "submerged" quartz covered
lamp designs of Pure Water Systems, Inc. and Ultraviolet Purification
Systems, Inc. and the teflon tube flow-through design of ENERCO.
895
-------
1.0 *-
0.4 0.5
1.0
Figure 8.
Design Annual Average Daily Flow (m'/min)
Comparison of unit costs for a1,'-"T"laflve
disinfection processes (9;.
A systems analysis procedure has been developed as part of a recently
completed EPA study at the Port Richmond Water Pollution Control Plant in
New York City, and reported by Scheible, et al. (9). The procedure incorpor-
ates the use of mathematical modeling techniques, which generically describe
the hydraulic, kinetic, and water quality elements important to UV disin-
fection. The utility of the modeling approach, when properly applied, is
the efficient evaluation and optimization of an existing system, and the
optimization of a design for a new system.
The following discussion presents the application of this procedure
to a full-scale system. The tasks associated with this study involved col-
lecting the appropriate data to calibrate the disinfection model, and then
using the model to evaluate the system design, particularly under anticipated
design loading conditions. The objectives were to assess the utility of the
procedure and to determine what modifications and/or refinements would be
appropriate to strengthen it. A brief discussion of the model is first
presented; this is followed by a discussion of the key elements of the
model and how these were determined for the study site. The use of the
calibrated model is then presented, with a discussion of observations and
conclusions derived from the study.
896
-------
UV DISINFECTION MODEL
The reader is referred to the Port Richmond study report (9) for a
detailed development of the disinfection model. It incorporates an estimate
of the residence time distribution in the reactor, describes the inactiva-
tion rate as a function of the intensity, and empirically accounts for the
effect of particulates on UV performance efficiency. The expression is
written:
N = Nn exp rux {!-(!+ 4EK)1/2}] + N (3)
2E U2
where:
N = the bacterial density remaining after exposure to UV
(organisms/100 ml)
N0 = the initial density, measured immediately before entry
into the UV reactor (organisms/100 ml)
x = the distance traveled by an element of water while
under direct exposure to UV light (cm). This is gener-
ally taken as the reactor dimension in the direction of
flow.
u = the velocity of the wastewater as it travels through
the UV reactor (cm/sec). This is calculated as:
u = x/Vv/Q)
where Q is the flow rate in liters/second and Vv is the
reactor liquid volume in liters.
E = the reactor dispersion coefficient in cm^/sec.
K = the inactivation rate coefficient (second"^-).
Np = the bacterial density associated with the particulates in
the wastewater. These coliforms are affected minimally by
the UV radiation, effectively becoming the base residual
density determining the performance of a given system.
Thus, the information required by the model includes the dimensions of
the reactor (x,Vv), and the system loading conditions (Q and No); E describes
the hydraulic characteristics of the unit. The sensitivity of the coliforms
is described by the inactivation rate, K; this, in turn, is estimated as a
function of the calculated intensity. The wastewater characteristics are
described by the K rate, the particulate coliform density, Np, and by the
UV absorbance coefficient.
897
-------
DETERMINING THE MODEL PARAMETERS FOR EXISTING FULL-SCALE SYSTEMS
The following discussion briefly describes the approach and data re-
quirements for properly calibrating the model. From the above presentation,
this can be addressed by evaluating three basic elements:
1. hydraulic characteristics,
2. intensity of UV in the UV reactor, and
3. water quality conditions for the wastewater.
Hydraulic Characteristics
The data requirement for determining the appropriate hydraulic char-
acteristic of the UV reactor lies principally in determining its residence
time distribution (RTD). Hydraulically, the design objectives are to have
a reactor that behaves in a plug flow manner with minimal dispersion; that
the flow be turbulent radially from the direction of flow; and that the
reactor liquid volume be used effectively.
Figure 9 from (10) presents a "typical" RTD curve, which can be devel-
oped by injecting a conservative tracer into the influent of a reactor and
measuring its concentration, c, as it exits the reactor with time. Several
indices can be estimated from the RTD curve that are useful in describing
the hydraulic behavior of the reactor. Referring to Figure 9, these are
defined as follows:
tgo/tio = the ratio of the time for 90% of the tracer to pass to the
time for 10 percent of the tracer to pass. This is common-
ly known as the Morrill Dispersion Index; it would be
equal to 1.0 for ideal plug flow conditions, and 21.9 for
complete mix. Generally, it is best to have this index
less than 2.
tm/T = the ratio of the actual mean residence time (first moment
of the RTD curve) to the theoretical residence time. T is
computed as the Liquid volume, Vv, divided by the flow
rate, Q.
tp/T = the ratio of the time at which the peak concentration occurs
to the theoretical residence time.
tf/T = the ratio of the time when tracer first appears to the
theoretical residence time.
= tne ratio of the time for 50% of the tracer to pass to the
mean residence time. The deviation from a value of one is
a measure of skew from a normal distribution. As an
example, a value significantly less than one would char-
acterize an RTD with a long tailing effect, indicative of
stagnant areas within the reactor.
898
-------
o
S
s
g
CJ
u
Figure 9. Typical residence time distribution curve (10).
A very useful parameter, particularly in reactor design, is the dis-
persion number:
Dispersion Number = E/ux
where E is the dispersion coefficient (cm^/second), u is the fluid velocity,
and x is the reactor dimension in the direction of the flow. The dispersive
properties of a reactor are indicated by the relative spread of the RTD
curve. The value of E will approach infinity in completely mixed systems,
while in ideal plug flow systems it will approach zero. Levenspiel (11)
suggests values of the dispersion number for a plug flow reactor with
increasing degrees of dispersion:
E/ux = 0; plug flow, no dispersion
= < 0.01; low dispersion
= 0.01 to 0.1, moderate dispersion
= > 0.1 high dispersion
In cases where the RTD is a normal (Gaussian) distribution, the dispersion
number can be estimated from the variance of the distribution:
~ 2(E_)
ux
(4)
899
-------
where the variance, 002, normalized to the mean residence time, is dimension-
less.
Intensity
Intensity is the rate at which energy is being delivered. The unit
generally used for UV disinfection is microwatts/cm^; the energy is speci-
fically at the wavelength of 253.7 nm. This is the maximum spectral line
for low pressure mercury arc lamps, which are almost universally used in
wastewater disinfection systems. A serious shortcoming in the design of
UV systems has been the inability to estimate accurately the light intensity
in complex multi-lamp reactors. Detectors are generally planar and will
account for only a portion of the light energy available within a system.
Several approaches have been proposed to estimate light intensity, includ-
ing chemical actinometry, biological assays (12), and calculation. It is
suggested that the calculation approach offers the most versatile and
efficient means to determine the intensity within a reactor, and is the
method used in this study.
The point source summation method is generally the technique used
to calculate intensity. It was first applied to UV disinfection systems
by Johnson and Quails (12) and then applied by Scheible, et al (9). It
presumes that the lamp is a finite series of point sources, each of which
radiates its energy radially. The energy attenuates by two mechanisms:
the first is by dissipation and is proportional to the inverse of the
radius squared; the second is by absorption by the medium through which
the energy is passing.
A single receptor in the reactor will be exposed to all point sources
that have an unobstructed straight line path to the receptor. The inten-
sity, therefore is the sum of the intensities from all point sources
affecting the receptor. This calculation is then performed for a number
of receptors located in a defined cross-sectional grid pattern, allowing
one to eventually compute the average intensity in the reactor. The
final product is generally a plot of the average nominal intensity as
a function of the wastewater UV absorbance coefficient.
The reader should refer to the cited references for a more detailed
discussion of the calculation technique. The information required to
compute the intensity for a given system may be summarized as follows:
- reactor dimensions and the configuration of the lamps and lamp
enclosures
the output rating of the lamp. The nominal rating for low pressure
mercury arc lamps is approximately 18.2 Watts/meter of arc (at
253.7 nm). This will degrade with use; thus it is also important
to understand the lamp output with time.
the absorbance of the liquid to be treated. This is the absorbance
coefficient at 253.7 nm (base e), with the units cm"1.
900
-------
the transmissibility of the enclosures; submerged lamp systems have
quartz sheaths about each lamp. Other systems utilize Teflon tubes
to carry the liquid, with the lamps surrounding the tubes. In
either case, the energy must pass through the enclosure before it
reaches the liquid. Thus, it is important to account for the loss
of energy through these enclosures.
In the example that is to be provided, the intensity calculation is
made assuming that all the lamps are at their nominal output rating and
that the enclosures will transmit 100 percent of the energy. This allows
general use of the calculation output; the resulting intensity need only be
adjusted (by direct ratio to nominal) for actual and/or projected conditions.
Wastewater Quality
The four wastewater parameters that most affect the design or per-
formance of a UV system are the flow, initial bacterial density, suspend-
ed solids (or some measure of the particulates in the wastewater), and
the UV absorbance of the wastewater. The flow rate is set by the design
of the main plant and projected hydraulic loads from the facility collec-
tion system. The initial density is a parameter that is not generally
monitored at a facility; in the case of disinfection by UV, however, it
is a critical parameter.
The occlusion of bacteria in particulates will have a significant
effect on the design of a system. For model calibration and system
evaluations it is best to use the suspended solids analysis as the
primary indicator of particulates. The level of suspended solids in
the effluent of a wastewater treatment plant is, in effect, set by the
design of the plant, limiting the range of suspended solids concentrations
to be considered in the design of the UV process.
The one parameter that is solely in the venue of UV disinfection is
the UV "demand" of the wastewater, in which components in the water will
absorb energy at the 253.7 nm wavelength. The spectrophotometric UV ab-
sorbance coefficient is a measure of the UV "demand" of the water and is
used in the context of the model expression (and intensity calculations),
with the units cm~l.
The single beam spectrophotometric method for measuring absorbance
is the simplest procedure. This "direct" method, however, does not
account for light which is scattered and still available; the detector
does not receive this light and thus considers it to be absorbed. Inte-
grating sphere accessories are available to correct the absorbance reading
for this effect and give a more representative measure of the true absorb-
ance. If such an instrument is not available, a direct measurement of
the sample filtrate would give a reasonable approximation of the true
absorbance.
901
-------
Calibrating the Model
Referring to Equation 3, for a fixed, existing system, we are given
the variables of flow, the dimension x, the velocity u; from the water
quality data we can estimate the initial density, No. The task of
calibrating the model, for an existing system, then involves determining
the dispersion coefficient E, the inactivation rate K, and the density
associated with the particulates, Np.
Dispersion Coefficients. As discussed above, the dispersion coef-
ficient can be estimated from the RTD curve developed from direct tracer
analyses of the reactor. If the distribution is approximately normal,
E can be estimated from Equation 4. Alternatively, the E can be estimat-
ed from a series of trial and error solutions to the following equation:
dc = W exp r-(x - ut)2-i (5)
dt 2A(irEt)1/z 4Et
where:
dc = observed change in concentration of tracer with time (gm/l/sec)
dt
W = rate of mass input (gm/sec)
A = cross-sectional area of the tracer stream at x (cm2)
x = distance from injection to the observation point (cm)
u = velocity (cm/sec)
t = time (sec)
E = dispersion coefficient (cm2/sec)
Estimate of the Coliform Density Associated with Particulates
The data required to estimate these densities are collected from the
UV system at very high apparent dose levels. This can be done by operating
the full system at low flow rates. The premise is that the remaining den-
sities measured after such high doses are those that are associated with
the particulates and would not have been affected by the UV radiation.
These data are then correlated with the suspended solids of the sample
(or some other measure of particulates, such as turbidity).
A linear regression analysis can be performed of the log effluent fecal
coliforms as a function of the log effluent suspended solids. When trans-
formed this will yield an expression in the form,
Np = cSSd (6)
where Np is the density associated with the suspended solids (organisms/
100 ml) and SS is the suspended solids concentration (mg/1). The co-
efficients c and d are the intercept and slope of the regression line,
respectively. The coefficients c and d at Port Richmond were 0.25 and
2.0, respectively.
902
-------
Estimate of the Fecal Coliform Inactivation Rate. The required data
are those in which the operating conditions would allow a still significant
coliform density in the effluent. This permits one to use the influent
and effluent coliform densities to estimate the rate of inactivation.
These data are generally collected under high hydraulic loading conditions.
Once the data are collected, the rate can be estimated for each
sampling by manipulation of the model expression (Equation 3) to solve
for K. The estimate of Np is first made (as discussed earlier) and sub-
tracted from the measured effluent density:
N' = N - Np (7)
Manipulation of Equation 3 yields:
K = [U2(p2 - 1)]/4E (8)
where:
P = 1 - [2E In (N'/Nn)l (9)
ux
The log K can be regressed against the log intensity for the corre-
sponding sampling. This would yield the expression (when transformed) in
the form:
K = a Iavgb
where K is the inactivation rate in seconds"1, and Iavg is the average in-
tensity (uWatts/cm2). The coefficients a and b are the intercept and the
slope of the regression line, respectively.
In summary, the final calibrated model will take on the form:
1/2
N = N0 exp {ux [1 - (1 + 4E al b) ]} + cSSd (10)
2E U2
SITE EVALUATION AT SUFFERN, NEW YORK
A full-scale, operating UV system was evaluated as part of this special
study project. Recall that the intent was to collect the appropriate infor-
mation about the system's hydraulics, performance, and the wastewater char-
acteristics. These would be used to calibrate the disinfection model, which
in turn would be used to evaluate the system design. Secondarily, an ob-
jective was to evaluate the model analysis procedure itself, and to deter-
mine refinements and/or modifications necessary to enhance its utility.
903
-------
Methods
Analytical methods for fecal coliforms, chemical oxygen demand (COD),
suspended solids (SS), and turbidity followed Standard Methods (13) and
USEPA (14) procedures. The UV absorbance coefficient was measured at
253.7 nm with a Perkin-Elmer 552A-UV Visible Scanning Spectrophotometer.
The correction for scattering in the UV absorbance measurement (spherical
absorbance coefficient) was accomplished with a necessary Integrating Sphere
(Model No. B010-3751). The materials and methods for measuring the resi-
dence time distribution of the UV reactors, and the output and transmit-
tance of the UV radiation were described elsewhere (8,9).
Process Description. The UV process at Suffern consists of two parallel
units, designated as Units 1 and 2, both designed for 10,600 1pm (4.0 mgd)
maximum flow. The average design flow is 5,000 1pm (1.9 mgd). The units
are submerged quartz systems with the flow directed perpendicular to the
lamps. Upon entering the influent chamber the water must pass through an
inlet stilling plate prior to contact with the UV light. A similar plate
exists at the exit from the lamp pattern. These were installed to ensure
uniform flow distribution through the unit. Each unit has 260 lamps
arranged in a staggered pattern with the length having a total of 35 lamps
and the height alternating between 7 and 8 lamps. The units can be operat-
ed with one to four banks of lamps on.
Systems Hydraulics. Several tracer measurements were made at Suffern
to determine the hydraulic characteristics of the units.
From an analysis of the mean and variance of the distribution, the
dispersion number is estimated to be 0.037. This suggested a low to
moderately dispersive plug flow reactor. The hydraulic indices can also
be calculated, and are summarized on Table 6. These suggest that there
is a degree of axial mixing occurring in the reactor. This is supported
by the low value of tf/T, and the dispersion numbers. The lower value of
tp/T suggests that the total void volume is not being used effectively.
These data and those from the other tracer runs indicated that an
effective volume of 70 percent actual should be used in subsequent
analyses.
TABLE 6. SUMMARY OF HYDRAULICS ANALYSIS, SUFFERN. N.Y
Parameter
Dispersion Coefficient, E, cm^/s
Dispersion Number, d
tf/T
tp/T
t90/t!0
tm/T
t- •-^ /t-
Measured Value
150
0.037
0.35
0.83
2.2
0.88
1.04
__ Lm
Estimated Effective Volume
(% of Actual) 70
904
-------
Intensity Calculation. The cross-sectional dimensions of the lamps
and quartz sleeves are given on Figure 10, which also presents an example
of the intensity field calculated for an absorbance coefficient of 0.2 cm""*-.
The average intensity is reduced from this type of intensity field analysis.
The final product of these calculations is presented on Figure 11. As
already discussed, these estimates must then be adjusted for the actual lamp
output and the estimated quartz transmissibility at the time of sampling.
Direct measurements were made at Suffern. The lamp outputs were found to
average 95 percent of their nominal rating (the plant was in startup); the
quartz transmittance was determined to range from an average of 60 to 40
percent (relative to a clean quartz sleeve) during the term of the study.
These were applied to the intensity estimates for each sampling. The data
are summarized on Table 7.
Estimation of the coefficients c and d. Insufficient data were gen-
erated at Suffern to give an accurate estimate of the coefficients c and d.
It was presumed, therefore, that the values derived for the coefficients in
the Port Richmond project would give a reasonable approximation of the fecal
coliform density associated with the effluent suspended solids.
QUARTZ SLEEVE
EQUAL AREA GRIDS
LAMP
CALCULATED INTENSITY
AT AN<*-0.2cm-1
WATTS/cm2 x103)
D HO
A
21.1
18.9
22.1
'—^
s
D At
/21.0
17.9
16.7
18.3
y 21.7
16.7
16.4
16.7
16.7
16.9
16.1
16.2
16.7
16.6
16.1
17.0
20.5
19.7
19.7
22. ( BULB 55
20.0
17.0
^
19.8
tfti
19.8
\
17.0
23.4
] 23.
20.0
16.9
16.1
16.9
16.7
16.6
16.1
1v3.7
16.4
15.7
16.6
16.9
21.0
17.3
16.6
18.3
21.8/
k
21.0
18.8
22.1
_^,
Rill I
'— -x
y t
Figure 10. Cross sectional dimensions of lamps/quartz
in Suffern unit, with an example of a
calculated intensity profile in one area (9),
905
-------
20.000
ASSUME NOMINAL LAMP OUTPUT
AND
100% QUARTZ TRANSMITTANCE
0.00
0.20
0.40
0.60
0.80
1.00
1.20
~1
ABSORBANCE COEFFICIENT (cm )
Fi'gure 11. Calculated average intensity vs. UV absorbance coefficient
TABLE 7. SUMMARY OF FIELD DATA FROM SUFFERN, N.Y.
Parameter Measured Value
No. of Samplings
Flow Range, 1/s
N0, fecal colif orms/100 mL
(Geometric Mean)
(Range)
UV absorbance coefficient, cm"-'- (base e)
(avg)
(range)
Nominal Intensity,
Adjusted Intensity,
(95% lamp output, 40-60% transmittance)
64
52 - 138
95,500
20,000 - 274,000
0.282
0.235 - 0.350
13,880
6,600
Estimation of the Inactivation Rate Coefficients. The samplings
selected at Suffern to estimate the inactivation rate were those ir> which
there was a single bank operating at a high flow. A shortcoming in the
analysis of the data at Suffern is that the range of intensities over which
the rate data were collected was very narrow. The system configuration at
Suffern did not allow for artificial adjustments to the unit intensity
906
-------
(such as reducing the line voltage, etc.); the variation would only be
induced by the changes naturally occurring in the UV absorbance of the
wastewater.
The estimates of K were regressed as a function of the estimated
average intensity. The effective volume that was used to estimate the
velocity in Equation 10 was assumed to be 70 percent of the actual liquid
volume; this was based on the hydraulics analysis discussed earlier. The
transformed regression line from the log-log plot of the Suffern data is
written:
K = 0.00059 I
0.922
avg
Model Calibration. The calibration of the Suffern wastewater to the
model (Equation 10) uses the following coefficient values:
a = 0.00059
b = 0.922
c = 0.25
d = 2.0
The dispersion coefficient E was assumed to be 150 cm^/second.
Figure 12 presents a comparison of the observed data to the predicted data
for effluent fecal coliforms. As can be seen, the model was very effective
in predicting the performance of the system and responding correctly to the
e.oo
5.25
4.50
3 3.75
O
O
u! 3.00
in
O
O
2.25
1.50
0.75
0.00
FECAL COLIFORM
LOG Nobs= 0.944 LOG N ca,c + 0.1 91
(r=0.91.)
REGRESSION
LINE
IDEAL LINE
0.00 1.00 2.00 3.00 4.00 5.00
LOG NCalc
-------
parameters that defined the process operations. Ideally, the slope of the
regression line for the correlation of the observed and predicted data
should equal 1.0, with an intercept of zero. Analysis indicated that in
either instance the regression line was not significantly different
(0.05 level) from the ideal line.
Analysis of the Suffern UV System
Figure 13 presents solutions to the calibrated model expression in
situations where there are 1, 2, 3, and 4 banks of lamps in operation.
The Suffern plant is designed to handle an average flow of 5,000 1pm
(1.9 mgd) and a peak daily flow of 10,600 1pm (4.0 mgd). The treatment
requirements at the plant call for seasonable nitrification and disinfec-
tion (April through October). The two units at Suffern are each designed
to handle the total plant flow, even during peak conditions.
Let us first consider the system under average loading conditions:
Average UV absorbance Coefficient = 0.3 cm"-'-
Average Suspended Solids = 15 mg/1
Average daily flow = 5,000 1pm (1.9 mgd)
Average Initial Fecal Coliform Density = 120,000/100 ml
Assume that the average output of the lamps is approximately 80
percent nominal and that the quartz transmittance is maintained at a
level no less than 60 percent. Referring to Figure 11, the calculated
intensity is 13,500 yWatts/cm^ at an absorbance coefficient of 0.3 cm"-'-.
This is then adjusted:
Average Intensity = 13,500 x 0.8 x 0.6 = 6480 yWatts/cm^
The density associated with the suspended solids i.s estimated:
Np = 0.25(15)2 = 56 FC/100 mL
Assuming a mean effluent density of 200 FC/100 mL is required, the N'
is equal to 200 - 56 = 144 FC/100 mL. This yields,
Log N'/N0 = Log (144/120000) = -2.92
From Figure 13, the following Log N/N0 is predicted at average flow and
at an average intensity of approximately 6500 uWatts/cm^:
1 Bank, Log N/NO = -1.75
2 Banks, Log N/NO = -3.40
3 Banks, Log N/NO = -5.00
4 Banks, Log N/NO = -6.80
908
-------
0
-1
-2
-3
-6
-7
-8
t BANK
2000
AVG 0 (1.9 MOD)
PEAK 0 (4
0 MOD)
4 6 8 10 12
FLOW (
-------
This analysis suggests that under average conditions, the system will
meet its performance requirements with 2 banks in operation. This presumes
maintenance of the quartz transmissibility and lamp output at or above the
levels used in these calculations. As an example, a similar simulation at a
quartz transmittance of 40 percent (the lower level determined during the
study period) indicates that three banks would be required to meet the re-
quired performance goal. This points to the economic benefits (in addition
to the obvious performance benefit) derived from keeping a system clean.
OPERATION AND MAINTENANCE EXPERIENCE
As part of its I/A technology assessment program, EPA funded a study
in 1984 to evaluate the performance of six UV disinfection systems currently
in operation in the U.S. The following discussion briefly summarizes the
results of certain aspects of that field study as well as the performance
of the Port Richmond facility (9).
The survey results indicate highly variable performance depending on
the water quality of the influent and the reactor design. Some facilities
such as those at Togus, Maine, Suffern, New York and Pella, Iowa were capa-
ble of consistently producing effluent fecal coliform levels of <200/100 ml.
Start-up problems including overheating and failure of electrical components
such as lamps, ballasts and circuits were experienced at some facilities
necessitating redesign. Operational availability of 75% were recorded for
experimental units at Port Richmond (9). Twenty-five percent of the down-
time was process influent related (foaming) and seventy-five percent of the
downtime was related to equipment failure.
Two major considerations in the proper and effective operation of a UV
system are: 1) the hydraulics of the unit, and 2) the cleaning methods
required for each of the different types of units. The importance of plug
flow hydraulics has already been discussed earlier. Suffice it to say
that every unit studied in the field suffered in some very fundamental way
from axial dispersion resulting in short-circuiting and non-ideal flow.
This, in turn, caused a certain degree of non-compliance with coliform
limitations. The rest of this report will focus on the cleaning methods in
use and the general maintenance requirements of UV systems.
Cleaning of UV Units
An overriding concern in the proper maintenance of a UV reactor is to
keep all surfaces through which the UV radiation must pass as clean as pos-
sible. The effects of surface fouling on energy utilization efficiency can
be quite significant. Maintaining clean UV radiation transmission surfaces
is a very important operation and maintenance parameter and fouled or dirty
Teflon or quartz tubes can very often be pointed to as the primary reason
for the poor disinfection performance of a particular system.
910
-------
Typically, fused quartz sleeves are rated at a UV transmittance of 90
to 95 percent when new. The transmittance of Teflon tubes will vary with
the thickness of tube wall and, under typical designs, one should expect
a transmittance between 70 and 85 percent for a virgin Teflon. Current
Teflon units are utilizing thinner wall tubes and the virgin UV trans-
mittance is close to 85%. Fouling can occur on both the wetside and the
dryside surfaces of both quartz and Teflon tubes. For quartz tubes, water-
side fouling on the outside of the tube typically causes the highest per-
centage of UV intensity loss. Depending on the water quality of the
wastewater to be disinfected, fouling of the outside quartz surfaces can
be caused by relatively high oil and grease content or by a hardness
scaling phenomenon that occurs due to the higher temperature (from the
UV lamp) at the outside surface of the quartz tube. The scale on the
quartz surfaces, and to a lesser extent on the Teflon surfaces, has been
found to be inorganic magnesium and calcium hydroxides and carbonates.
Organic fouling is usually caused by a high oil and grease content, but
biofilms can also grow on quartz or Teflon surfaces that are not fully
irradiated or irradiated non-continuously.
The inner (dry) side of a quartz tube can become fouled due to the
passage of air and dirt particles in between the UV lamp and the quartz.
Reductions of 15 to 25 percent in the quartz UV transmittance have been
noted due to this inside fouling. The outside surfaces of Teflon tubes
have been observed to become heavily coated with dust, thereby reducing
UV penetration. This is thought to be caused by the highly charged
atmosphere between the UV lamp and the Teflon tube, creating an ideal
environment for electrostatic precipitation of dust onto the Teflon
tubes.
There are basically two approaches to cleaning the quartz and Teflon
tube units, chemical and physical. Most of the quartz units recently
constructed have been equipped with accessory equipment that attempts to
maintain clean outside surfaces on the quartz tubes. The two most common
types of accessory equipment for the quartz units are mechanical wipers
and ultrasonics. These devices are used on a frequent basis and are con-
sidered part of the normal operation of the unit. Chemical cleaning is a
task that will typically be required for quartz units on a routine basis.
For example, the quartz tube units at Pella, Iowa were mechanically
wiped once every three hours and chemically cleaned once every two weeks.
The chemical cleaning required one hour per unit.
Cleaning of UV units will be required in all cases to improve the UV
transmittance properties of the Teflon or quartz. Teflon has been market-
ed as a non-fouling material, however, observations and measurements made
during this study and prior studies have demonstrated that it is capable
of being fouled by secondary wastewater, in some cases quite severely.
Frequent visual monitoring of the Teflon tubes in a unit is recommended
in order to determine the need for physically and chemically cleaning
the tubes. A high pressure nozzle cleaning device is available for
scouring fouled surfaces. Swabbing of the tubes, where possible, is
also recommended.
911
-------
The need for cleaning quartz tube UV units has been anticipated
since their first usage. Quartz will foul biologically and/or chemically,
with the rate of fouling dependent on water quality and whether the UV
lamps are on or not. Accessory cleaning equipment, usually ultrasonics
or mechanical wipers, are provided with most quartz units. Wipers appear
to have a greater potential for keeping the quartz surfaces clean than
do ultrasonics, however, neither device will preclude the necessity for
chemical cleaning. Designs incorporating quartz UV units should provide
for some form of chemical cleaning, preferably a recirculation system.
A solution of the cleaning agent is prepared in the tank with
warm water, then recirculated for a period of time, usually overnight,
typically with the lamps on. Food-grade citric acid and sodium hydro-
sulfite are the typical cleaning agents used. Both of these chemicals
have been tested for their ability to clean fouled surfaces of quartz,
including biologically-fouled and inorganic chemically fouled.
Sodium hydrosulfite is a highly reactive chemical and a strong
oxidant. This material appears to be most effective in sealed systems
where the cleaning relies solely on contacting the surface under agitated
conditions. It must be handled with great care, however, and special
requirements will be required to properly store and handle this material
and also to dispose of the spent recirculation waste. At Suffern, after
an overnight cleaning period, the sodium hydrosulfite, at a concentration
of 0.15%, returned the UV transmissibilities of the quartz tubes to like-
new conditions, roughly 92% UV transmittance for all of the tubes measured.
Even though this chemical is relatively hazardous to handle, it should be
considered as one of the chemicals to be used in cleaning a quartz unit.
Citric acid is also a commonly used agent to clean quartz surfaces.
A similar testing procedure was followed at Suffern as with sodium hydro-
sulfite, only using citric acid at a concentration of 0.15% as the recircu-
lation chemical cleaning agent. Although the results of the citric acid
cleaning were not as impressive as with the sodium hydrosulfite, neverthe-
less, citric acid appeared to do an adequate job of cleaning the fouled
surfaces of quartz tubes.
Other types of cleaning agents can be considered for use with quartz
systems. Diluted mineral acids such as sulfuric or hydrochloric could be
used to dissolve inorganic scales and to remove biological films from quartz
surfaces. In a couple of locations, it was noted that a chlorine solution
was being used in an attempt to clean the surface of the quartz. Chlorine,
which is a disinfectant, will not provide the dissolving ability necessary
to remove the inorganic scales, although it can remove some types of bio-
logical films from the surface of the quartz.
An effective technique for cleaning the teflon tubes was to spray
a detergent solution through a high pressure (2,800 kgf/cm^ - 400 psi)
circular spray nozzle on the end of a flexible hose which was snaked through
each tube. The technique took an hour for each set of eight, three meter
tubes.
912
-------
TOXICS TREATABILITY AND CONTROL
The U.S. Environmental Protection Agency (EPA) has established a
National "Policy for the Development of Water-Quality-Based Permit Limita-
tions for Toxic Pollutants." The EPA national policy was developed
because of data indicating that, even with efficient removal of conven-
tional pollutants, toxic substances in amounts significant to water quality
are being discharged through the Nation's wastewater treatment systems. An
overall water-quality based toxics control process (15) is available to
support the policy of water quality-based permit limitations on toxic
pollutants entering treatment plants. The toxics control process includes
procedures for evaluating toxics problems in receiving waters, for identi-
fying bioaccumulative potential of the toxics for locating and identifying
the responsible point source discharges and for controlling the toxic dis-
charge to eliminate the water quality problem.
Research on toxics in wastewaters by the EPA has revealed that water
quality problems associated with point source discharges of toxics exhibit
extensive site-specific factors including the amounts, types and sources of
toxics, the control effectiveness of existing treatment plants and the char-
acteristics and dilution capacity of the receiving water. Unfortunately,
solutions to such water quality problems have complex site-specific aspects.
In the past, the study of toxic discharges into receiving waters by
treatment plants had focused chiefly on specific chemicals (16,17). The
complexity of many wastewaters, especially municipal wastewaters involving
multiple industrial components, however, has also forced the use of bio-
logical measurements for assessing (18,19) ecosystem toxicity (overall
ecosystem toxic effects) and potential health effects of these wastewaters.
Thus an integrated monitoring and control approach using both specific
chemical and bioassay techniques is evolving for evaluating toxics water
quality problems. The monitoring, especially by bioassays on plant
effluent, provides sensitive screening for identifying potential toxic
impacts from plant discharges.
RESEARCH APPROACHES
As part of the overall toxics control process, two parallel approaches
are being employed to solve the toxics control problems in wastewater
treatment. The first approach uses representative specific toxic compounds;
the second uses bioassay tools for characterizing toxic impacts of complex
mixtures of unknown toxics.
In the first approach, the characterization of removals and effluent
concentrations of spiked representative toxics for a range of treatment and
management practices involves three levels of research:
Characterization of specific toxics removals for representative
treatment systems and management practices.
913
-------
0 Deterministic assessments of the fate of specific toxics and the
inter-relationships (treatability research) of various removal
mechanisms in the treatment and management practices.
0 Development of predictive correlations from the treatability
research and the specific removal studies.
A study of specific chemical removals of representative toxics has
recently been completed on conventional secondary treatment and on alter-
native treatments (20) for marine discharge. Significant treatability
assessments(21,22,23) with a number of representative specific compounds have
also been completed. One assessment includes predictive methods for fate and
removals of toxics in the activated sludge process using experimentally
determined kinetic rates for the principal removal mechanisms. Additional
treatability assessments with representative chemicals are also underway. A
treatability protocol is being developed to permit municipalities and indus-
tries to evaluate, at bench scale, the fate and treatability of both specific
chemicals and unknown toxic mixtures during wastewater treatment. Finally,
in the first research approach, a structure for modeling is beginning to
evolve for predicting, from molecular and structural properties of the
toxics, the removal and fate of toxics during treatment.
In the second approach, characterization of the toxicity removal cap-
abilities of representative treatment and management practices involves
biological assessments (bioassay for ecosystem and health effects) and, to
reduce costs of water quality management, assessments with near real-time
chemical, bacteriological or enzymatic indicators potentially useful as
surrogate bioassays. Studies are ongoing to relate the biological
assessment/monitoring, especially of complex toxic mixtures, to treatment
operations and management practices including treatment alternatives for
marine discharge.
An important step in the overall toxics control process is called a
Toxicity Reduction Evaluation (TRE) at individual municipal or industrial
wastewater treatment plants. Initiated after confirmation of a toxics water
quality problem, the TRE, using an integrated monitoring approach at the
treatment plant, determines the toxics sources, the toxics fate during and
impact on treatment, the variability of pass-through of the overall toxicity
in the effluent wastewater and finally the probable solutions for controlling
the toxicity discharge. Case histories of toxicity reduction evaluations are
being initiated at the Patapsco Treatment Plant in Baltimore and at other
sites for the purpose of developing TRE protocols for use by the wastewater
treatment industry.
TOXICS REMOVAL STUDIES
The EPA's Office of Marine and Estuarine Protection is concerned about
toxics pass-through in alternative treatment systems for marine discharge
cases where removal of conventional pollutants by full secondary treatment
is not necessary to meet conventional water quality objectives. Primary
interest has been focused on a list of 129 organic and inorganic priority
914
-------
pollutants developed from a Consent Decree between the National Resources
Defense Council and the Administrator of the U.S. Environmental Protection
Agency (24). A specific toxics removal study (20) using a spiking mixture
of 21 volatile and semi-volatile organic priority pollutants and the
indigenous trace metals in the Cincinnati wastewater was completed for five
alternative systems with the conventional primary-activated sludge treatment
system used as a control. The pilot-scale alternative treatment systems
included primary treatment plus commercial pulsed-bed filtration, chemical
clarification with alum, primary-high rate trickling'filter treatment, and
single stage aerated and facultative lagoon treatments.
Removal efficiencies for total suspended solids (TSS), chemical
oxygen demand (COD), total Kjeldahl nitrogen (TKN), and total phosphorus
(TP) for each alternative system during the study averaged:
TSS % COD % TKN % TP %
0 Primary plus filtration - 86 40 15 44
Chemical clarification - 89 49 12 75
0 High rate trickling
filtration - 76 47 14 39
0 Aerated lagoon - 85 60 2 19
Facultative lagoon 84 65 11 31
o
Activated sludge - 93 82 80 58
The removals of the volatile, semivolatile and the trace metal priority
pollutants for the alternative treatment systems and for primary and primary-
activated sludge treatment are shown for the three pollutant classes in
Tables 8, 9 and 10, respectively. Paralleling the removals of conventional
pollutants, the primary-activated sludge control system produced the best
overall removals of organics, typically 80-90% removal of volatiles, 85-95%
removal of semivolatiles and 24 to 82 percent removal of the metals. The
facultative lagoon with 26-day hydraulic retention was the best overall
alternative treatment system followed by the aerated lagoon (6-day hydraulic
retention) for overall control of toxics. Metals removals, however, were
not established for chemical treatment and primary plus filtration. Chemi-
cal treatment (25) is known to remove most metals very efficiently.
While none of the alternative processes provided overall toxics removal
capabilities equal to the activated sludge system, the facultative lagoon
provided similar removals of volatile organics and the best observed
removal of lindane. The chemical treatment system produced good removals
of those organics which partition strongly to the solids in the treatment
system. The study revealed that alternative treatment systems, especially
those without biological treatment components, would permit significantly
increased toxics pass-through.
915
-------
TABLE 8. VOLATILE ORGANICS REMOVALS BY DIFFERENT PROCESSES (20)
Primary Primary Plus
Compound Inf Treatment Filtration
>ig/L jig/L ZRem jug/L ZRem
Carbon Tetra- 69 63 19 56 22
chlorJ.de
1,1, Dichloro-
ethane 144 144 - 98 32
1,1, Dichloro-
ethylene 212 188 5 138 22
Chloroform 135 143 -7 113 18
1,2 Dichloro-
ethane 153 135 7 96 34
Bromoform 90 83 18 119 2
Ethylbenzene 111 102 9 70 35
Average Removal
of Volatiles 7 24
Chemical
Clarifi- Trickling Aerated Facultative Activated
cation Filter Lagoon Lagoon Sludge
jug/L ZRem .ug/L %Rem jug/L ZRem jug/L ZRem *ig/L ZRem
101 -13 26 59 15 70 11 77 13 74
111 21 94 34 45 68 19 87 8 94
150 25 85 58 83 60 35 85 14 92
106 20 102 25 53 61 31 80 18 86
109 22 93 33 45 70 15 90 22 84
114 -6 41 57 15 80 22 84 29 65
73 31 31 71 27 70 12 96 6 93
14 48 68 86 84
-------
TABLE 9. REMOVAL OF SEMIVOLATILE ORGANICS BY DIFFERENT PROCESSES (20)
vo
Compound
Bis(2 ethylhexyl)-
phthalate
Dibutylphthalate
Naphthalene
Phenanthrene
Pyrene
Fluoranthene
Isophorone
Bis(2-chloroethyl)-
ether
p-Dichlorobenzene
Phenol
2,4 Dichlorophenol
Pentachlorophenol
Lindane
Heptachlor
Inf
pg/L
168
73
108
95
104
104
89
143
93
126
228
84
39
39
Primary
Treatment
Pg/L
90
68
92
76
84
80
77
122
75
112
133
78
40
26
ZRem
37
2
13
21
18
22
4
6
19
23
45
16
-4
32
Primary Plus
Filtration
Mg/L
47
56
86
48
39
39
74
120
66
131
300
90
-
-
ZRem
75
22
20
49
61 .
61
8
20
29
4
-
19
-
-
Chemical
Clarifi-
cation
«/L
15
47
79
24
12
13
80
114
66
99
92
50
32
14
ZRem
89
31
23
74
88
87
5
17
28
21
60
50
17
64
Trickling
Filter
/ig/L
39
52
74
51
48
49
72
132
58
64
200
82
34
18
ZRem
75
26
28
45
54
53
17
-
36
50
31
4
13
53
Aerated
Lagoon
>ug/L
34
44
36
40
36
36
68
102
31
84
155
57
22
13
ZRem
77
40
64
55
63
64
22
23
65
30
48
37
42
66
Facultative
Lagoon
«AL
30
14
13
16
25
23
62
78
12
18
65
20
7
13
ZRem
80
78
87
82
75
77
25
43
87
86
73
74
80
62
Activated
Sludge
«/L
18
7
4
4
5
5
2
30
5
14
1
3
31
13
ZRem
87
88
97
95
95
95
98
80
94
86
99
96
18
65
-------
TABLE 10. METALS REMOVALS BY DIFFERENT PROCESSES (20)
Metal Inf
yg/L
vo Cr 221
CO
Cu 345
Ni 141
Pb 165
Cd 25
Primary
Treatment
yg/L
206
279
136
115
22
%Rem
7
19
4
30
12
Trickling
Filter
yg/L
107
137
98
86
18
%Rem
52
60
30
48
28
Aerated
Lagoon
Ug/L
65
89
91
70
_
%Rem
71
74
35
50
_
Facultative
Lagoon
Ug/L
46
71
81
82
17
%Rem
79
79
43
50
32
Activated
Sludge
Pg/L
40
61
81
58
19
%Rem
82
82
43
65
24
-------
TREATABILITY RESEARCH
The completed studies (21,22,23) on treatability have evaluated the
relative removals of selected toxics by the three principal removal mecha-
nisms—volatilization, biodegradation and sorption—in the activated sludge
process. Two of the studies (21,22) also evaluated the impact of the selected
toxics on anaerobic digestion. One study (23) assessed the effect of powdered
carbon adsorption on toxic removals in the activated sludge system. These
studies have generated experimental kinetic data on the competitive removal
rates of the principal removal mechanisms and have provided insight into
effects of operating design factors such as sludge retention time (SRT) on
the toxic control capabilities.
Data from the Purdue studies (21,22) on 8 representative priority
organics in Table 11 reveal that efficient (often more than 99%) removal
of the organics was achieved after treatment using acclimated biomass, even
for highly chlorinated organics such as pentachlorophenol (PGP). The data
further reveal that biodegradation was the principal removal mechanism.
The sorption mechanism contributed approximately 20% of the removal of
bis(2-ethylhexyl) phthalate (BEHP) for all operating SRT except 3 days. At
the low 3-day SRT, sorption was responsible for 55% of the removal. The
volatilization mechanism contributed from 20 to 80% of the removals of
toluene (TOL) and naphthalene (NAPTH) with the high volatilization
contributions occurring at the high SRTs of 7 and 11 days. The modest
removal contributions of the sorption mechanism in the activated sludge
process indicates that biodegradation by acclimated biomass will degrade
even those organics with high octanol water partition coefficients such as
bis(2-ethylhexyl) phthalate. The study found that the rates of volatiliza-
tion for moderately volatile organics such as toluene and naphthalene were
competitive with the rates of biodegradation.
Data on acclimated anaerobic digestion of the same 8 organics revealed
that parachlorometacresol (PCMC) was partially refractory to the anaerobic
process with 30 to 40% remaining after digestion. Four organics, penta-
chlorophenol, dimethyl phthalate (DMP), dinitro-orthocresol (DNOC) and
bis(2-ethylhexyl) phthalate were reduced in concentration by more than 99%;
chlorobenzene (MCB) and naphthalene were reduced by more than 95% and
toluene, by 91%. In the anaerobic process, variable amounts of these
organics were removed by the sorption and volatilization mechanisms.
Data from the University of Michigan studies (23) on 8 priority organics
in Tables 12 and 13 confirm the importance of the biodegradation mechanism
in removing organics of moderate volatility. For the organics studied,
sorption contributed little to the removal process. The relative importance
of the biodegradation and volatilization mechanism shown in Table 12 revealed
that volatile but non-biodegradable organics such as 1,2,4-trichlorobenzene
are removed effectively from the water by the volatilization mechanism.
Non-biodegradable and poorly sorbable organics such as lindane pass through
the treatment process. The relative importance of the volatilization and
biodegradation mechanisms in the removal of the organics depended upon the
919
-------
TABLE 11. FATE OF ORGANICS IN ACCLIMATED ACTIVATED SLUDGE (22)
PO
o
Compound
PCP
MCB
DMP
BEHP
TOL
NAPTH
PCMC
DNOC
SRT
Days
3
5
7
11
3
5
7
11
3
5
7
11
3
5
7
11
3
5
7
11
3
5
7
11
3
5
7
11
3
5
7
11
Compound
in
Feed
mg/L
20
20
20
20
16.3
16.3
16.3
16.3
20
20
20
20
2.64
2.64
2.64
2.64
26.1
26.1
26.1
26.1
4.24
4.24
4.24
4.24
20
20
20
20
20
20
20
20
Compound
Remaining
in Eff .
Ug/L
214
105
68
64
<5
<5
<5
<5
<5
<5
<5
<5
138
75
66
68
<5
<5
<5
<5
<5
<5
<5
<5
7.9
4.8
4.0
5.0
666
760
301
85
Affected
Other
COD
Removal?
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
Fate of Compound: Percentage
Stable
Compound
Removal ?
No
No
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
No
Yes
Yes
In
Effluent
1.07
0.53
0.34
0.32
<0.03
<0.03
<0.03
<0.03
<0.03
<0.03
<0.03
<0.03
5.2
2.8
2.5
2.6
<0.02
<0.02
<0.02
<0.02
<0.12
<0.12
<0.12
<0.12
0.08
0.05
0.04
0.05
6.7
7.6
3.0
0.85
Sorbed
on Solids
0.31
0.15
0.10
0.08
2" x 10~4
2 x 10~4
2 x 10~4
2 x 10~4
<10~2
<10~2
<10~2
<10~2
55.4
15.5
13.3
18.7
<10~2
<10~2
<10~2
<10~2
0.23
0.19
0.19
0.20
3.04
0.95
0.83
1.26
0.11
0.17
0.02
<10~2
Vola-
tilized
0.03
0.03
0.03
0.04
<7
<11
<16
<21
<10~2
<10~1
<10~1
<10~1
<10"2
<10~2
<10~2
<10"2
<21
<32
<48
<60
<29
<32
<68
<84
<10"2
93
>89
>84
>79
>99.9
>99.9
>99.9
>99.9
39.4
81.7
84.2
78.7
>79
>68
>52
>40
>71
>68
>32
>16
96.9
99.0
99.1
98.7
92.7
91.7
96.7
99.0
-------
TABLE 12. FATE OF TOXIC ORGANICS IN ACCLIMATED
ACTIVATED SLUDGE BIOREACTORS (23)
Percent of Influent
Compound Effluent Off-Gas Biosorbed Biodegraded
Benzene
Toluene
Ethylbenzene
o-Xylene
Chlorobenzene
1 , 2-Dichlorobenzene
1,2, 4-Trichlorobenzene
Nitrobenzene
Lindane
-------
relative kinetic rates of the two removal mechanisms (Table 13). Dichloro-
benzene, a relatively slowly degradable organic, exhibited the highest
volatilization removal contributions. Acclimation periods for the organics
ranged from 7 to 14 days.
The addition of powdered activated carbon (PAC) provided enhanced
removals of 1,2-dichlorobenzene, 1,2,4-trichlorobenzene, and lindane.
Powdered carbon addition effected reductions in both the effluent and off-
gas concentrations of volatile, non-biodegradable compounds. PAC doses as
small as 25 to 50 mg/L produced significant improvements in non-biodegrad-
able toxics removal compared with control activated sludge systems. Greater
than 90% removals occurred at influent carbon doses of 100 mg/L. The
addition of PAC at influent doses less than 100 mg/L did not enhance the
removal of the biodegradable toxic organics.
PAC bioreactor studies in the University of Michigan study, conducted
at solids retention times (SRT's) of 0.25 to 12 days and a 50-mg/L carbon
dose, showed that the removal of non-biodegradable toxics was the same over
the range of SRT's studied. The most important operating parameter with
respect to removals of toxics was the influent PAC concentration.
A major EPA inhouse research effort has recently been initiated to
expand the data on specific removal contributions of the principal removal
mechanisms in the activated sludge process. Studies on biodegradation
using bench scale completely mixed reactors and electrolytic respirometry
techniques (Figure 13) are underway on selected organics to ultimately
permit prediction of the biodegradability from molecular properties and
structures. The electrolytic respirometry techniques readily provide
acclimation data, toxics inhibition data, and biodegradation kinetics.
Parallel kinetic studies with appropriate organics on raw solids, accli-
mated and unacclimated biomass and digester solids are also being conducted
to provide the needed removal contributions from the sorption and volatili-
zation mechanisms.
The inhouse research effort is also evaluating the fate and removal of
metals in the conventional primary-activated sludge process. The sorption
of metals on raw solids, biomass and digestion solids is being evaluated in
equilibrium and kinetic studies. Typical empirical adsorption isotherms
for metals on activated sludge biomass are shown in Figure 14. The desorp-
tion of metals and organics from sludges, both in seawater and freshwater
is also being evaluated.
922
-------
Oxygen Consumption (mg/L)
500
10
ro
CO
400
00
6
-------
100
10
r
1.0
0.1
F
j'
TTT
Cu
Cr
0.001
0.01 0.1
Residual Cone. (C,), mg/l
1.0
10
Figure 14. Adsorption isotherms for metals on aerobic biomass.
THE TOXICITY REDUCTION EVALUATION (TRE)
The biomonitoring screening of point source discharges and the follow-
on studies to evaluate the impact of the toxic discharge on the receiving
water establish the control requirements for the TRE at the treatment
plant. The control requirements usually are presented as integrated
toxicity levels that must be achieved by the point source discharge to
eliminate the toxic water quality impact. Such levels will ultimately be
established using a statistical approach that will be based upon desired
water quality and the historical variability of the receiving water flow or
dilution capacity.
With the desired toxicity levels established for the discharge, the
overall elements of a typical TRE at the treatment plant are presented in
Table 14. The first step is the evaluation of the toxicity reduction occur-
ring across the treatment plant and the determination of the probable cause
of the excessive toxicity in the discharge. A key determination is whether
operational deficiencies at the plant significantly contribute to the
toxicity pass-through or whether the presence of toxicity refractory to the
plant's treatment processes principally produces the excessive toxicity.
924
-------
The next step in the TRE involves two elements, occurring in parallel,
in which the toxicity is traced to its sources and the important toxicity
components, if possible, are identified and the ecosystem and the health
effect biomonitoring assays, in-plant toxicity monitoring assays, and
specific chemical analytical techniques are all employed to achieve the
goals of this step.
Finally, an evaluation of the control alternatives to eliminate the
excessive pass-through is conducted. The evaluation includes assessing
possible industrial process modifications to minimize release of the toxics,
the use of pretreatment approaches to control the toxics before discharge
to the central plant, and improvement of the central plant's operations to
control the toxicity.
The research approach to developing appropriate protocols on TRE for
use in municipal wastewater treatment involves:
0 Toxicity reduction studies on pilot and full-scale treatment
systems to determine representative toxicity reduction capabili-
ties of municipal wastewater treatment processes.
0 Case histories of research TRE at selected full-scale treatment
plants to assess the capabilities of the monitoring tools and the
treatability and pretreatment approaches likely to be incorporated
in the municipal protocols for TRE.
0 Research on techniques to enhance the toxicity reduction capabili-
ties of the central treatment plant.
TABLE 14. ELEMENTS OF A TOXICITY REDUCTION EVALUATION
Treatment Plant Evaluation of Causes of Toxicity Pass-through.
A. Plant Operations Deficiency.
B. Presences of Refractory Toxicity.
Tracing of Toxicity to Sources.
A. Bioassay Monitoring.
B. Alternative Monitoring Techniques.
Identification of Toxicity Components.
A. Specific Chemical Identification.
B. Bioaccumulative Potential.
Evaluation of Control Alternatives.
A. Industrial Process Modifications.
B. Pretreatment Alternatives.
C. Central Treatment Plant Control of Toxicity.
925
-------
Parallel research is also ongoing on TRE protocols and case histories for
industrial wastewater treatment. The parallel research will include the
assessment of approaches for industrial process modification to minimize
toxicity release. These industrial techniques will be appropriately
referenced in the protocols on the municipal TRE.
TOXICITY REDUCTION CAPABILITIES
Pilot-scale research using wastewater spiked with representative toxic
mixtures has revealed a good capability of the central treatment plant to
reduce toxicity, but toxicity penetration into the plant effluent does
occur. As an example of the treatment plant capabilities, acute toxicity
reductions (18) of 100 percent based upon Fathead Minnow bioassays (26) were
achieved in a pilot-scale primary-activated sludge treatment plant for the
indigenous (metals and organics) toxicity in an industrialized raw Cincin-
nati wastewater. The spiking at 50 yg/L levels of each compound in a
mixture of 22 of the Agency's priority organic pollutants into the same
wastewater, however, produced an increase in the toxicity of the raw waste-
water and substantial pass-through, even with acclimation, of residual
toxicity (Table 15). Selected compounds, most importantly lindane in the
spike, were refractory to the treatment processes. High conventional pollu-
tant removals (17) were always achieved during this study, independently of
the spiked toxics.
Pilot and full-scale studies (19), using Ames (27) and mammalian
cell (28) assays have revealed the presence and pass-through of mutagenic
materials in municipal wastewaters. The mutagenic materials were extracted
from several Cincinnati wastewaters with methylene chloride, first at pH 2,
then at pH 11. The concentrated extracts were combined and solvent trans-
ferred into dimethyl sulfoxide (DMSO) to eliminate the effect of methylene
chloride on the subsequent mutagenicity assays. The results of the Ames
assays (Table 16) revealed substantive but variable amounts of mutagenicity
in the influent wastewaters, ranging to approximately 20,000 revertants per
liter.
The mutagenicity removals in these tests with efficient conventional
treatment, varied from substantive removal to essentially no removal of the
mutagenicity. This study and others also revealed that wastewaters of
domestic origin have extractable mutagenicity levels, usually around 500
revertants per liter of effluent.
The high number of not detectable (N.D.) responses in these studies on
the raw wastewaters or primary effluents are usually caused by cytotoxic
effects from the large amounts of extracted organics in the extract. Unlike
the secondary effluent tests, the cytotoxic effects prevented testing of the
extracted organics from the raw or primary wastewater over an appropriate
concentration range to properly evaluate the mutagenicity. Additional tests
with mammalian cell assays (28) using Syrian hamster cells reveal qualita-
tively similar responses between the two assays. The results from the
mammalian cell assays suggest higher removals of mutagenicity measured by
the mammalian cell compared with the results from the Ames test.
926
-------
Currently, the assay results from the Ames test or other health effects
screening assays have not been related to health effects risk. Research,
currently ongoing, is attempting to establish a link between health risks
and the screening assay results.
TABLE 15. ACUTE TOXICITY* IN WASTEWATER TREATMENT
Control System
Spiked System**
LC-50 percent % Toxicity
Inf. Eff. Reduction***
30
11
9.3
30
10.2
18.5
10.1
20.6
> 100
> 100
> 100
> 100
> 100
> 100
> 100
> 100
100
100
100
100
100
100
100
100
LC-50 Percent I
Inf. Eff.
4.6
2.7
9.5
4.5
4.3
5.8
6.5
1.9
13.1
16.1
35.5
6.6
9.4
30
30
8.0
I Toxicity
Reduction***
65
83
73
32
55
81
78
76
*Fathead Minnow acute toxicity. (Data developed by the Environmental
Monitoring and Support Laboratory-Newtown Facility, Cincinnati, Ohio.)
**Spiked with 22 priority organics.
[(l/LC-50) inf - (l/LC-50) eff]
***% Toxicity Reduction
x 100
(l/LC-50) inf
At an LC-50 in the effluent of > 100; equation does not apply and
the acute toxicity reduction is considered as 100%.
927
-------
TABLE 16. MUTAGENICITY IN THE AMES TEST OF MUNICIPAL WASTEWATER SAMPLES AT VARIOUS TREATMENT STAGES
ro
00
TA98 Mutagenicity
Treatment Wastewater
Plant Type
Mill Creek Industrial/
T&E Facility Domestic
Mill Creek Industrial/
Plant Domestic
Muddy Creek Domestic
Plant
Sample
Designation
(Date)
Series Aj
09/02/81
Series A2
09/09/81
Series Bi
08/31/82
Series 82
06/20/83
Series C,
01/11/83
Total
Treatment Liters
Stage Extracted
Raw Wastewater
Primary Effluent
Secondary Effluent
Secondary + Cl2
Raw Wastewater
Primary Effluent
Secondary Effluent
Secondary + Cl2
Raw Wastewater
Secondary Effluent
Primary Effluent
Secondary Effluent
Raw Wastewater
Secondary Effluent
2
2
6
6
2
2
6
6
8C
50C
23
86
24C
92C
Conc.a
(mg/L)
48.8
41.8
4.9
4.6
66.5
46.0
4.6
4.0
91.0
7.7
70.4
8.7
36.8
2.2
net
revertants/
mg
-S9
173
1,057
169
196
N.D.
77
5,645
6.370
N.D.
417
N.D.
693
N.D.
161
+S9
381
524
1,376
1,768
182
392
4,074
4,318
89
353
129
761
N.D.
175
netb
rever-
tants/
liter
18,593
21,903
6,674
8,133
12,103
18,032
18,944
17,272
8,099
2,718
9,082
6,621
385
TA100 Mutagenicity
net
revertants/
mg
-S9
N.D.
N.D.
N.D.
N.D.
N.D.
N.D.
1,836
2,246
N.D.
N.D.
N.D.
928
N.D.
208
+S9
N.D.
N.D.
258
409
N.D.
N.D.
1,035
2,146
N.D.
244
N.D.
1,540
N.D.
284
ne^
rever-
tants/
liter
;
1,251
1,881
™
4,813
8,584
1,879
13,398
625
N.D. - not detectable (i.e. response at any sample dose level was less than 2-fold above concurrent solvent control).
aRefers to the concentration of extractable organlcs based on the residue weights of the extract*.
bBased on the mutageniclty values from the assays with S9 activation.
Extraction at pH 11.0 was omitted.
-------
TOXICITY REDUCTION SURVEY
A toxicity reduction survey is now being completed at six municipal
wastewater treatment plants in the State of Ohio. The plants were selected
for the survey to represent wastewaters of chiefly domestic origin, waste-
waters with modest industrial contributions, and wastewaters with substantial
industrial contributions. The toxicity entering and leaving the treatment
plants were measured using static renewal seven-day acute-chronic Fathead
Minnow (29) and Geriodaphnia (30) assays for assessing ecosystem effects, the
Ames test and mammalian cell assays cells for mutagenicity screening, and the
Sister Chromatid Exchange assay (31) using Chinese hamster ovary cells for
genotoxicity. Analyses for conventional pollutants and for specific toxic
trace metals and individual organics were also provided. The State of
Ohio's Environmental Protection Agency also conducted fish diversity studies
using electroshock techniques on the receiving waters associated with some of
the treatment plants.
Examples of representative toxicity reductions are shown in Tables 17
and 18 for the wastewater treatment plant at Akron, Ohio and the Little
Miami Plant in Cincinnati. The Akron Plant, with substantive industrial
contributions to the wastewater, exhibited the highest influent toxicity of
all the surveyed plants with no effect concentrations (NOEC) ranging from
0.3 to 1 percent of the influent wastewater. The Akron plant, which was
achieving nitrification and meeting its conventional pollutant removal
requirements during the survey, also achieved efficient toxicity removal
with the NOEC ranging from 10 percent of the effluent for acute (survival)
effects on Fathead Minnows to 100 percent effluent for acute (survival)
effects on both the Fathead Minnow and the Ceriodaphnia assays. The NOEC
of 10 and 30 percent in the Akron effluent suggests only a modest toxicity
in the discharge to the receiving water ecosystem.
The Little Miami Plant, with modest industrial contributions to its
wastewater, exhibited less toxicity in the influent wastewater but also
achieved little toxicity reduction across the treatment plant. The Little
Miami effluent with NOEC of 1 to 10 percent effluent for the Ceriodaphnia
assay was the most toxic of the effluents evaluated in the survey, even
though the plant was meeting its conventional pollutant removal require-
ments. Finally, the data presently available on plants in the survey with
wastewaters of chiefly domestic origin revealed modest toxicity in the
influent and essentially no aquatic toxicity in the effluent.
To assess the probable effect of the effluent on the receiving stream,
however, the stream dilution capacity must be considered. For the Akron
Plant, the effluent contributes more than 50 percent of the stream flow
during summer low flow conditions. In contrast, the Little Miami effluent
provides less than 1 percent of the flow to the Ohio River, even at summer
low flow conditions. With substantive dilution, the Little Miami toxicity
discharge is unlikely to affect the Ohio ecosystem. The effluent-dominated
Cuyahoga River at Akron, however, could be affected by the modest toxicity
discharges from the Akron Plant.
929
-------
TABLE 17. TOXICITY REDUCTION AT AKRON, AS NO OBSERVED EFFECT
CONCENTRATIONS* (NOEC), IN PERCENT EFFLUENT
Fathead Minnows Ceriodaphnia
Sample Survival Growth Survival Reproduction
8/84 5/85 8/84 5/85 8/84 5/85 8/84 5/85
Influent <0.3 1.0 0.3 1.0 0.3 1.0 0.3 1.0
Secondary
Effluent 30 10 10a 30 >30 30 30 30
Chlorinated
Secondary 10 10 M00b MOO 30 MOO 30 30
Dechlorinated
Secondary MOO 10 M00b 30 30 MOO 30 30
a - CLo may have been present in sample.
- Low control value, NOEC may be lower.
*A11 NOEC data are subject to final statistical review. (Data developed
by the Environmental Monitoring and Support Laboratory-Newtown Facility,
Cincinnati, Ohio.)
TABLE 18. TOXICITY REDUCTION AT LITTLE MIAMI, AS NO OBSERVED EFFECT
CONCENTRATIONS* (NOEC), PERCENT EFFLUENT
Sample
Influent
Secondary
Effluent
Fathead Minnows Ceriodaphnia
Survival Growth Survival Reproduction
12/84 5/85 12/84 5/85 12/84 5/85 12/84 5/85
10 10 10 10 3 10 0.3 3
MOO MOO 30 30 1 10 1 3
Chlorinated 30 30 30 30 1 10
Plant Effluent
Dechlorinated 30 30 30 30 1 10
Plant Effluent
*A11 NOEC data are subject to final statistical review. (Data developed
by the Environmental Monitoring and Support Laboratory-Newtown Facility,
Cincinnati, Ohio.)
930
-------
The fish diversity studies (Figure 15) on the Cuyahoga River, indeed,
indicated a major toxic impact on the fish population beginning at the point
of discharge of the Akron Plant. Upstream of the discharge, the fish popula-
tion was found to be good. The fish populations in the River's tributaries
also, usually ranged from fair to good. The fish diversity study, conducted
three times during the Summer of 1984 and spanning the time of the toxicity
survey, revealed a persistent loss of fish in the Cuyahoga for about 10 miles
down stream of the Akron discharge and a second toxics impact when the River
entered the Cleveland Ship Channel at Lake Erie. No other significant waste-
water discharges enter the Cuyahoga immediately below Akron, as the River
passes through the Cuyahoga National Park Recreational Area. In addition,
appropriate measurement of stream dissolved oxygen (D.O.) and ammonia concen-
trations revealed no D.O. or ammonia toxic impacts on the River immediately
below Akron. Overall, the stream fish diversity indicated major toxicity
impacts on the River, perhaps the most significant impacts in the State of
Ohio.
o
x
O
UJ
o.
t-
o
DC
X
HI
Q
CO
cc
Ul
X
CO
10-
8.
6-
Ul
UJ
CC
O
UJ
z
Q
Z
<
a.
m
in
UJ
cc
o
CO
cc
UJ
J_
0.
H
Ul _l X
Ul CC UJrf
CC UJ Wo
°|Egl
2 co mo
—U U_B
LU
Z
z
X
o
I CLEVELAND HARBOR
co
O - TRIBUTARY MEASUREMENT
EXCEPTIONAL
GOOD
POOR
45 40 35 30 25 20 15 10
CUYAHOQA RIVER, miles
-5 -10 -15
Figure 15. Toxicity impact on the Cuyahoga River.
(Data developed by the Ohio EPA.)
931
-------
Other data obtained during the survey revealed low metals concentra-
tions (Table 19) and very modest concentrations of specific extractable
organic residuals in the Akron plant's effluent (Table 20). In addition, the
relatively complex GC chromatograms on the highly toxic plant influent, and
the relatively "clean" GC chromatograms of the effluent (Figures 16 and 17)
supported the observed efficient toxlcity reduction achieved by the treat-
ment plant. Further, the Ames test screening for mutagenicity (Table 21)
also revealed only modest mutagenicity in the effluent, indeed not signifi-
cantly different from effluents from plants treating chiefly domestic
wastewater. Unfortunately, because the plant's Influent is highly toxic
its mutagenicity could not be determined.
TABLE 19. AKRON METALS REMOVAL*
Concentration (mg/L)
Metal
Inf.
As BDL**
Ca 90.3
Cd 0.0012
Cr .088
Cu 0.19
Fe 0.28
Mg 22.7
Mn 0.204
Ni 0.34
Pb 0.057
Zn 0.447
1984
Eff.
0.0077
75.8
BDL
.016
.026
0.17
14.5
0.102
BDL
BDL
0.038
Inf.
BDL
95.6
0.028
BDL
.029
2.14
24.2
0.417
0.022
0.046
1.333
Eff.
BDL
72.1
0.0094
BDL
.011
0.913
16.5
0.313
0.013
BDL
BDL
1985
Up
Stream
BDL
65.1
0.0041
BDL
BDL
0.583
15.7
0.200
0.0062
BDL
BDL
Down
Stream
BDL
67.6
0.0097
BDL
BDL
0.633
16.5
0.165
0.010
BDL
BDL
*Data developed by the Water Engineering Research Laboratory-Cincinnati,
Ohio.
**BDL - Below detection limit.
932
-------
cX
TABLE 20. EXTRACTABLE ORGANIC ANALYSIS OF AKRON CHLORINATED SECONDARY*
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
Compound
d( 10) anthracene
n,n-dimethylf ormamide
tetrachloroethene
1 , 6-hexanediol
1 -cyclohexen- l-ol
2-cy clohexen- 1-one
benz aldehyde
unknown
unknown
hydrocarbon
hexane
unknown
5-hexen-2-ol
benzothiazole
unknown
unknown
unknown
unknown
unknown
hexanedioic acid, bis(2-ethylhexyl)
bis(ethylhexyl)phthalate
unknown
Pg/L
Internal. Std.
8
65
10
7
4
6
5
4
3
2
2
7
4
2
24
2
2
5
ester 50
7
2
*Data developed by the Water Engineering Research Laboratory-Cincinnati,
Ohio.
933
-------
Detector Response
O
o
o
o
O
i-i
5T O
fD ft
u>
rt H-
tt> O
Pi O
eg g"
(* o
0) rt
Ol
O
O
O
o
o
b
TO
g. Q-
fu r^ Cr ^^
r( ftj (0 O
s-*-H
c-1
pi CO
o1 rf
o n>
rt
o
O ^^
H- O
3 IB
O rt
H. pj
3 O.
in m
rt <
O
o-o
-
2
2
2.
*
IN)
O.
o
o
IN}
en.
o
o
CO
o
o-
o
O
Z
c
m
z
H
-------
AKRON CHLORINATED EFFLUENT
16.7-x
UD
OO
tn
01
p
000
500
1 I '
1000
1500
2000
1 I '
2500
1 I '
3000
3500
scan number, seconds
Figure 17. Total ion chromatogram on plant effluent. (Data developed by
the Water Engineering Research Laboratory, Cincinnati, Ohio.)
-------
'/I
TABLE 21. AKRON MUTAGENICITY STUDY*
Concentration of
Sample Extractable Organics AMES Mutagenicity
(1984) mg/L REV**/mg Rev*/L
Raw Wastewater 45.09 N.D.***
Secondary Effluent 3.66 140 512
Chlorinated Secondary 3.02 130 393
*Data developed by the Health Effects Research Laboratory-Cincinnati, Ohio.
**REV = revertants.
***N.D.** = Not detectable (i.e., response at any sample dose level was less
than 2-fold above solvent control).
The toxicity in the Akron effluent with the relatively "clean" waste-
water, as measured by residual metals and specific extractable organics,
raised questions about the sources of the toxics causing the observed and
persistent loss of fish in the Cuyahoga River at Akron. Thus, studies to
measure variability of the effluent toxicity, to reconfirm the lack of fish
in the River, and to identify responsible specific toxics in the effluent
are being conducted this summer.
Finally, a preliminary review of the plant's operating records has
also revealed intermittent bypassing of combined sewer flows at the treat-
ment plant. Indeed, the bypassing of the highly toxic plant influent could
represent the most important contribution to Cuyahoga's toxicity problem at
Akron. A full-scale TRE, as a research case history, is now under consid-
eration for Akron. The decision to use Akron as a detailed case history
will follow the review of the ongoing confirmatory studies on the toxicity
impact.
TRE CASE HISTORIES
Two case history studies on TRE's are about to begin. The first case
history, to begin this fall, is at the Patapsco Wastewater Treatment Plant
in Baltimore, Maryland. The second case history will likely be at Akron,
if the ongoing confirmatory studies confirm the need.
The Patapsco Wastewater Treatment Plant, completed in 1982, is a 70 mgd
pure oxygen activated sludge plant, currently treating 35 mgd at design
conditions using one-half the plant's treatment capacity. The industrial
contribution to the Patapsco municipal wastewater, chiefly from the organic
chemicals industries in Baltimore, currently totals about 30 percent of the
936
-------
plant influent. The case history TRE for Baltimore was selected not only
because of substantive influent toxicity at the treatment plant and a
history of intermittent pass-through of that toxicity (Tables 22 and 23)
but also because of a historical and ongoing in-plant toxicity monitoring
and control program.
Two sources of wastewater, a chiefly industrial flow (IPI) and a flow
(SWD) from domestic-commercial sources are combined to form the plant
influent. The in-plant monitoring MICROTOX procedure (32) on daily composite
samples at the plant uses a maximum of 45.5 percent wastewater in the test.
For low toxicity levels that require more than 45.5 percent wastewater to
produce a measurable EC5Q, the £€50 of the sample was recorded as > 45.5
percent. Thus, the low toxicity effluents and the domestic-commercial
influent flows (SWD) do not always have a defined £€50- To provide the
monthly average perspective given in Table 22, EC^Q values of > 45.5 percent
were included in the monthly averaging procedure as 45.5 and the monthly
average EC5Q in the table was presented as a greater than (» value. The
number of days in the month that an EC5Q lower than > 45.5 occurred is also
included in Table 22. The averaged monthly ^€59 values for the effluent
are all less than > 45.5 and indicate a toxicity pass-through during each
month. The number of days that measurable toxicity pass-through occurs
ranged from 7 days per month to 26 days per month.
TABLE 22. MICROTOX TOXICITY AT PATAPSCO*
1985
Jan.
Feb.
Mar.
Apr.
May
Jun.
IPIa
Avg.
3.
2.
3.
3.
5.
8.
INF.
EC5QC
o . '
7 :
6 :
2 :
8 :
2 :
SWDb
Avg.
> 18.
> 34.
> 33.
> 33.
> 16.
> 13.
2
5
9
9
4
4
INF.
EC5Q
(27)**
(12)**
(18)**
(20)**
(27)**
(29)**
COMBINED INF.
Avg. EC50
16.
26.
18.
12.
9.
9.
5
6
2
8
4
4
EFFLUENT
Avg. EC50
> 41
> 35.3
> 25.8
> 34.7
> 36.0
> 40.7
(7)**
(17)**
(26)**
(18)**
(16)**
(12)**
aIPI, plant influent chiefly from industrial sources.
plant influent from chiefly domestic-commercial sources.
"EC
50
for a 5-minute exposure time is given as percent effluent.
*Data developed by the Patapsco Wastewater Treatment Plant, Baltimore,
Maryland.
**Number of days, the EC50 was less than > 45.5 during each month.
937
-------
The limited ecosystem bioassay toxicity developed by the EPA on
Patapsco plant effluents (Table 23) qualitatively confirmed the variability
and pass-through of toxicity indicated by the routine MICROTOX measurements.
The results suggest that a desirable statistical link between the pragmatic
in-plant monitoring and the expensive Agency ecosystem bioassay may be
developed.
Effective toxics control at treatment plants require monitoring tools
that can preferably respond in real-time and be used in monitoring approaches
to provide warnings of potential toxic impacts or pass-through before the
toxics reaches the treatment plant. The specific chemical, (33,34) bioassay
toxicity (26,35) and health effects (15) screening tools, many available to
the Environmental Protection Agency for the water-quality-based toxics
control process, require relatively long measurement times with multi-step
procedures. The practical functions of these tools in a TRE are as
monitors of the plant's discharge requirements and as linkage to probable
receiving water effects and to waste load allocation procedures.
Although limited by their costs, these bioassays could also be used in
the development of monitoring approaches for warning of potential toxic
plant impacts or pass-throughs and for tracing toxics to their source.
However, less expensive and simpler monitoring tools, are more desirable for
routine in-plant and in-sewer toxics monitoring.
TABLE 23. EPA BIOASSAY EVALUATION OF THE EFFLUENT AT THE PATAPSCO PLANT
Fathead Minnow* Ceriodaphnia**
Test Date
3/8 - 15/84***
Survival
100% Mortality
in 100%
Effluent
Growth
NOEC at 30%
Effluent
Survival
100% Mortality
in 3% Effluent
Repro-
duction
NOEC at
0.37%
Effluent
6/23/84***
45% Mortality
in 100%
Effluent
100% Mortality
in 10% Effluent
7/13-20/84***
No Mortality
at 100%
None up to
6% effluent
100% Mortality None up
at 30% effluent to 6%
effluent
*Seven-day Early Life Stage Growth Test using Fathead Minnow.
**Ceriodaphnia Seven-day Life Cycle Toxicity Test.
***Data developed by the Duluth Environmental Research Laboratory, Duluth,
Minnesota.
****Data developed by the Environmental Monitoring and Support Laboratory-
Newtown Facility, Cincinnati, Ohio.
938
-------
In November 1980, the City of Baltimore in anticipation of potential
industrial toxics impacts during the start-up and operation of its new
activated sludge treatment process at the Patapsco Plant began monitoring
its wastewaters for toxicity using the 5-minute MICROTOX (32) analyses.
The City ultimately will expand its evaluation to three candidate in-plant
monitoring approaches for the TRE study at its Patapsco Wastewater Treat-
ment. These in-plant monitoring tools for indicating the presence of
toxicity are the Beckman MICROTOX analyzer with a fluorescent bacterium,
respirometry (oxygen uptake) measurements (36,37) on the plant's biomass,
and Adenosine Triphosphate (ATP) measurements. These inexpensive moni-
toring tools have near real-time responses ranging from actual real-time
for the TOXIGARD respirometry alternative to about a 1-hour response time
for the ATP measurement.
The overall objectives of the planned case history TRE at the Patapsco
Plant are given in Table 24. These objectives emphasize use of the prag-
matic in-plant monitoring methods and the development of a link between the
near real-time measures and the Agency's ecosystem bioassays used in the
toxics regulatory process.
TABLE 24. PATAPSCO TOXICITY REDUCTION EVALUATION
Research Objectives:
0 Evaluate toxicity reduction across plant using MICROTOX,
Respirometry and ATP
0 Summarize specific chemical inventory across plant
(organics and metals)
0 Assess techniques to identify and trace toxicity
to sources
0 Evaluate link between in-plant monitoring and ecosystem
bioassays
0 Assess treatability of wastewater for toxics control
as related to plant design
0 Develop techniques to minimize toxicity pass-through
939
-------
SUMMARY
The progress on the toxicity reduction research suggests that the TRE
concept, with protocols, has potential to support the wastewater treatment
industry's efforts to solve the site specific problems of toxicity dis-
charges by treatment plants. Indeed, the TRE concept with the pragmatic
in-plant monitoring tools may be the only affordable approach for managing
complex mixtures of toxics, especially in municipal wastewaters.
Key procedures for efficient tracing of the toxicity to its source,
identifying the principal components of the toxicity, and demonstrating
practical control responses to eliminate excessive toxicity discharges,
however, have not yet been sufficiently tested at full-scale treatment
plants to confirm the ultimate utility of the concept. Research on
approaches to improve the operation of municipal plants for toxics control
also has not yet been initiated. The EPA will diligently pursue these
remaining research needs to confirm the TRE concept and, thereby, improve
the Nation's ability to control toxicity water quality problems from point
source discharges.
ACKNOWLEDGEMENTS
The use of data in this paper from the ongoing research effort in
Cincinnati, Ohio, is appreciated and acknowledged (38,39).
The authors would like to acknowledge and thank their coworkers,
Dr. Farrell, Dr. Heidman, Dr. Smith, Mr. Neiheisel, Dr. Dobbs, Dr. Austern,
Mr. Reed, Mr. Tabak and Dr. Hannah, for generously sharing their research
information for this paper.
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