EPA-670/2-74-068
AUGUST 1974
Environmental Protection Technology Series
AN ASSESSMENT OF
WET SYSTEMS
FOR RESIDENTIAL REFUSE COLLECTION:
Summary Report
National Environmental Research Center
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
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EPA-670/2-74-068
August 1974
AN ASSESSMENT OF WET SYSTEMS
FOR RESIDENTIAL REFUSE COLLECTION:
Summary Report
By
P. M. MEIER
J. KUHNER
R. E. BOLTON
Curran Associates, Inc.
Northampton, Massachusetts 01060
Contract No. 68-03-0183
Program Element No. 1DB064
Project Officers
Donald Oberacker
Solid and Hazardous Waste Research Laboratory
and
Harry Bostian
Advanced Waste Treatment Research Laboratory
National Environmental Research Center
Cincinnati, Ohio 45268
NATIONAL ENVIRONMENTAL RESEARCH CENTER
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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REVIEW NOTICE
The National Environmental Research Center—
Cincinnati has reviewed this report and approved its
publication. Approval does not signify that the
contents necessarily reflect the views and policies
of the U.S. Environmental Protection Agency, nor
does mention of trade names or commercial products
constitute endorsement or recommendation for use.
ii
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FOREWORD
Man and his environment must be protected from the
adverse effects of pesticides, radiation, noise and other
forms of pollution, and the unwise management of solid
waste. Efforts to protect the environment require a focus
that recognizes the interplay between the components of our
physical environment—air, water, and land. The National
Environmental Research Centers provide this multidisciplinary
focus through programs engaged in
• studies on the effects of environmental contaminants
on man and the biosphere, and
• a search for ways to prevent contamination and to
recycle valuable resources.
This report presents a summary of research directed toward
development of utilizing existing sanitary sewer systems to
transport ground solid waste. Individual subcomponents were
designed, tested, and the overall economic feasibility of this
approach was determined.
A. W. Breidenbach, Ph.D.
Director
National Environmental
Research Center, Cincinnati
iii
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ABSTRACT
This summary is a synopsis of a series of four technical reports evalu-
ating the technical and economic feasibility of wet systems for residen-
tial refuse collection prepared by Curran Associates, Inc., under Contract
68-03-0183 to the EPA Solid Waste Research Laboratory, Cincinnati, Ohio.
The most promising wet system alternative is identified as a system using
individual household grinders in low density areas, vacuum collection and
neighborhood grinders in high density areas, dilute slurry transport of
ground refuse in the existing sanitary sewer system, and joint treatment
of refuse and sewage at an expanded treatment facility that includes
anaerobic digestion for methane generation. However, the economic
feasibility of even the most promising alternative is doubtful because of
the high cost of grinding, and hydraulic transport of ground refuse in
existing sewer systems may be feasible only if both metals and glass are
excluded. A conventional collection of the nongrindable and bulky consti-
tuents of residential refuse will still be needed, albeit of a diminished
frequency. The total 1973 cost of such a wet system is estimated at
$113-196 per household per year, of which $80-$105 is for grinding. This
compares to a total cost for refuse and sewage collection and disposal
under existing concepts of up to $115 per household per year. Projections
for 1988 indicate that the wet system cost might rise to $130-$228,
against a range of $61-$143 under conventional concepts. However, if the
cost of the grinder is excluded (on the basis that individuals would
purchase grinders for their convenience benefits), the 1973 wet system
costs (to the public sector) would be only $33-$91, thus possibly less
than existing public sector costs of about $43-$115 per household per year.
iv
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CONTENTS
Page
Abstract iv
List of Figures vi
List o£ Tables vii
Acknowledgments viii
Sections
I Conclusions *
II Recommendations ^
III Introduction ^
IV Grinding 9
V Collection and Disposal of Nongrindables 18
VI Hydraulic Transport 23
VII Treatment 30
VIII Sludge Handling 46
IX Environmental and Socioeconomic Impacts 63
X Total System Cost Analysis 79
XI Recommendations for Further Research 82
XII References 86
XIII Publications 92
v
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FIGURES
No._
1 Preliminary Design for a Household Grinder 1°
2 Basement Installation of a Household Grinder H
3 Limiting Refuse Concentrations for Hydraulic 26
Transport in Sewers
4 Grinding Water Requirement 27
5 Existing Process Configuration at the Springfield 33
Wastewater Treatment Plant
6 Planned Process Configuration at the Springfield 35
Treatment Plant
7 Computer Model Representation of the Recommended 40
Treatment Process Configuration for Ground Refuse
8 Dry Sludge Solids as a Function of Population Size 48
and Refuse Generation
9 Flow Diagram of Sewage Treatment Plant Handling 49
100 gal/cap/day
10 Flow Diagram of Sewage Treatment Plant Handling 50
100 gal/cap/day plus 2.25 Ib/cap/day
11 Sludge Handling, Alternative 1 54
12 Sludge Handling, Alternative 2 55
13 Sludge Handling, Alternative 3 56
14 Total Cost of Sludge Handling (Alternative 1, 2 and 3 58
as a Function of Population; for Average Refuse Generation
Rate of 2.25 Ib/cap/day
vi
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TABLES
No. Page
1 Cost Estimates for Installations of Refuse Grinding 13
System
2 Cost Comparisons Between the Foster-Miller and 14
Meier-Nebiker Concepts
3 Estimated Rates of Flow and Strengths of Wastewater 34
from All Contributors
4 Present and Projected Waste Concentrations 37
5 Seasonal Variations Due to Ground Refuse Addition 41
6 Treatment Costs for Sewage Alone; Planned Bondi 43
Island Treatment Plant
7 Treatment Costs for Sewage Containing Ground Domestic 44
Refuse
8 Total Cost of Sludge Handling (Alternative 1) in $/ton 59
Dry Solids for Various Populations and Various Raw
Refuse Generation Rates
9 Total Cost of Sludge Handling (Alternative 2) in $/ton 60
Dry Solids for Various Populations and Various Raw
Refuse Generation Rates
10 Total Cost of Sludge Handling (Alternative 3) in $/ton 61
Dry Solids for Various Populations and Various Raw
Refuse Generation Rates
11 Total Annual System Cost per Household Comparisons for 80
Springfield
vii
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ACKNOWLEDGMENTS
This study was conducted by Curran Associates, Inc., Engineers and Plan-
ners, Northampton, Massachusetts, under the direction of Dr. Peter M.
Meier. Dr. Roger Bolton and Mr. Jochen Kuhner played major roles in the
conduct of the study and other contributions are due to Messrs. James
Martel, Don Cooper, George Fisette and Michael Joyce.
The contribution to the study of a Review Panel was substantial, both in
review of the early drafts of this report and in the opening of many in-
teresting perspectives during the five discussion meetings held at peri-
odic intervals in the course of this study. The panel members consisted
of Mr. Donald Oberacker and Dr. Harry Bostian of the EPA National Envi-
ronmental Research Center, Cincinnati, Ohio; Professor Bernard B. Berger,
Director of the Massachusetts Water Resources Research Center; Dr. Roger
Bolton, Professor of Economics at Williams College; Mr. Thomas G. Sanders,
independent consultant and one of the initiators of research interest
into Wet Systems for Refuse Collection; Dr. Donald D. Adrian, Professor
of Civil Engineering, University of Massachusetts; Mr. Herbert B. Wyndham,
Jr., Vice President, Malcolm Pirnie, Inc., New York; Mr. Adi Guzdar,
Manager, Engineering Studies Division, Foster-Miller Associates, Waltham,
Massachusetts; Dr. Iraj Zandi, Professor of Civil and Mechanical Engi-
neering, University of Pennsylvania; and Mr. Wylie C. Hubbard, Superin-
tendent of the Department of Public Works, City of Springfield, Massa-
chusetts. Dr. Boyd Riley and Dr. Rudi Schmut, independent consultants,
Mr. Al Fisk of Foster-Miller Associates, and Mr. Oscar Albrecht of the
EPA National Environmental Research Center in Cincinnati also attended
some of the panel meetings or gave substantial assistance.
The writers especially acknowledge the assistance of Mr. Wylie C. Hubbard,
Superintendent of the Department of Public Works, City of Springfield,
Massachusetts, and his staff, without whose cooperation the case study
could not have been satisfactorily conducted. In particular, we acknowl-
edge the contribution of Mr. Lawrence J. Dowd, Deputy Superintendent of
the Division of Solid Wastes, who provided major assistance in the collec-
tion of data and information. Others whose assistance we acknowledge in-
clude Mr. Paul Sullivan, Chief Foreman, and Mr. Donald Ferris, Foreman,
both of the Division of Solid Waste, Springfield; in the Springfield Sewer
Division, Mr. James Moyland, Deputy Superintendent, Mr. John Risinski,
Chief Sewage Treatment Plant Operator, and Mr. Fred Mascole, Working
Foreman; in the Engineering Division, Mr. Joseph Cote, Office Engineer,
and Mr. Tony Masuch, Engineer; Mr. George E. Sweeney, Manager of the
Springfield Water Department; Mr. John Godfrey, Civil Engineer in the
Springfield Department of Public Works; Mr. Edward Beaudry in the person-
nel office of the City of Springfield; Mr. James Fitchet, Chief Accountant
of the Department of Public Works, Springfield. Finally, Mr. David
Goodman of Harry Goodman, Inc., Springfield, Massachusetts, provided
valuable information on recycling.
viii
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The authors benefited greatly from the comments and suggestions of
the EPA Project Officers, Mr. Donald'Oberacker and Dr. Harry Bostian,
and the assistance of Mr. Robert Smith and Mr. Richard Eilers, also
of the EPA National Environmental Research Center in Cincinnati, was
invaluable in the development of the treatment plant computer model.
These many contributions notwithstanding, the responsibility for the
accuracy and opinions expressed in this report is solely that of the
writers.
ix
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SECTION I
CONCLUSIONS
The major conclusions of this case study can be summarized as follows:
1. Implementation of a wet system for residential refuse col-^
lection in the case study area of Springfield, Massachusetts,
or any other urban area, is at least a decade distant.
2. The ability of existing gravity sewer systems to successfully
transport the glass and ceramics fraction of refuse remains
questionable. Maximum flow velocities encountered in many
sewer systems are below the necessary scour velocities to
prevent excessive deposition of ground refuse. Metals must
definitely be excluded. The frequency of collection of non-
grindables is likely to be higher than might be expected
because of seasonal variations and the substantial quanti-
ties of bulky wastes not amenable to grinding. The adequacy
of available grinding water without substantial additions of
fresh water is also questionable.
3. To the extent that realistic cost estimates can be made in
the face of the technical uncertainties that still exist
in the Springfield, Massachusetts case study area would rise
from $39 per year to $110-$140 per year under a wet systems
implementation. However, if the cost of the grinder is ex-
cluded, costs tp the public sector under the wet system
might decrease to as low as $35-$40 per year,
A consideration of national conditions is more favorable
to the wet system, showing a total cost of $113-$196 per
household per year, of which $80-$105 is for grinding.
This compares to a total cost for refuse and sewage collec-
tion and disposal under existing concepts of up to $115 per
household per year. Projections for 1988 indicate that the
wet system cost might rise to $130-$228, against a range of
$61-$143 under conventional concepts.
4. Given the premise of technical feasibility, any implemen-
tation that does occur is likely to be gradual, not unlike
the spread of garbage grinders and trash compactors, and
will depend on the development of a domestic grinder pur-
chased by individual households at a cost consistent with
consumer acceptance and its perceived domestic convenience
benefits. Existing grinding concepts are not regarded as
practically feasible.
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5. Analysis of the socioeconomic impacts of a wet system
implementation shows the resultant reduction of the refuse
collection labor force in Springfield to be a minor prob-
lem, due to other employment opportunities within the
public works sector and because of the gradual nature of ,
system implementation.
6. The most important impacts of ground refuse additions on
wastewater treatment facilities will be on preliminary,
primary and sludge handling facilities. Conventional
secondary and advanced waste treatment processes do not
appear significantly affected. The major uncertainty re-
lates to the possibility of introduction of toxic, nonbio-
degradable compounds (mercury, chlorinated hydrocarbons,
etc.).
7. The presence of numerous combined sewers in many urban
areas, including the Springfield, Massachusetts case study
area, is a serious barrier to the wet systems concept.
This problem apart, our investigations show that an appro-
priately modified treatment facility can produce effluents
of comparable quality to conventional effluents at plants
treating only sewage.
8. The cost of dewatering and disposal of the sludge
generated at a sewage treatment facility handling ground
refuse is in the range of $15 to $25 per ton of dry solids,
and substantially below that of a treatment facility
handling only sewage solids. The major determinants of
total per ton cost are per capita refuse generation rates
and the number of persons served by the facility. Economies
of scale and the predominance of a more readily dewaterable
primary sludge are the major reasons for the relatively low
unit costs. The sludge handling facilities of a plant
handling an average residential refuse generation rate cor-
respond to the size of the facilities handling only sewage
sludge generated by 9 to 12 times the number of inhabitants.
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SECTION II
RECOMMENDATIONS
The presently available factual evidence is still insufficient to make
definitive judgments on the technical feasibility of the wet systems
concept. This study has therefore identified and recommended a se-
quence of bench-scale investigations designed to resolve these uncer-
tainties. Successful completion of the following studies, presented
in order of priority, are regarded as prerequisites to further invest-
ments at a demonstration scale:
1. Study of hydraulic transport of ground refuse under unsteady
flow and load conditions representative of sewer laterals
in residential areas.
2. A field survey of refuse generation, water consumption and
sewage generation to establish the daily correlation of
refuse and sewage generation for individual households,
a necessary prerequisite for the development of realistic
grinder design specifications.
3. Evaluation of the wet systems concept from an energy
consumption viewpoint.
4. Evaluation of potentially hazardous and non-treatable
components in ground refuse - sewage mixtures, using
advanced instrumentation methods on simulated treat-
ment plant streams.
5. Development of alternative grinding concepts, including
a laboratory study of mixing characteristics of refuse
slurries and domestic sewage and actual construction
and testing of a prototype grinder. The inability to
develop a grinder within the cost limits established
in the present study and the specifications developed
under task 2 would be sufficient to abandon the concept
as economically or technically unrealistic.
6. Re-evaluation of the economic and overall technical
feasibility of the concept using the new information
available from the above studies.
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SECTION III
INTRODUCTION
The Concept of Wet Systems
for Residential Refuse Collection
The wet system for residential refuse collection of prime interest to
this research involves the use of the existing sewer system to transport
domestic refuse from the .individual home to the point of treatment and
disposal, thereby eliminating conventional house-to-house collection by
trucks. This idea depends on three technical prerequisites: the fea-
sibility of reducing refuse in the home to a size suitable for hydraulic
transport, the feasibility of transport of ground refuse in an existing
sewer system without deleterious effects, and the feasibility of joint
treatment of refuse and sewage at an existing or modified treatment plant,
Implementation of the idea requires also economic feasibility, which de-
mands that a rigorous cost-benefit analysis shows the proposed system to
be economically favorable over other existing and proposed systems. Each
of these prerequisites will be examined at some length in the sections
that follow.
From the viewpoint of solid waste management, the major incentive for
analyzing such a concept is the high cost of collection. The increasing
costs are due primarily to an increase in per capita waste generation
and an increase in labor wage rates. As noted by Clark, the latter has
been far in excess of inflationary trends as the increasing tendency for
collective bargaining has had a substantial effect on the wage rates for
individuals employed in local solid waste management functions. Al-
though productivity of collection in the last decade has increased sub-
stantially, there are limits to further increases under the constraints
of existing solid waste management concepts; substitutions of capital
for labor can be accomplished only to the point of having a one-man crew
on a truck so large it can no longer efficiently navigate the streets
and, consequently, only basic changes to existing practice offer any hope
to reduce the cost of solid waste collection.
Previous Research
The concept of wet systems for residential refuse collection has been
previously studied by several university investigators and government
funded research contractors. There is also a considerable body of re-
search on pipeline systems for refuse transport that have as their prime
focus not the collection of refuse, but the transportation of refuse from
a few centrally located collection centers to the site of disposal. Much
of this is directly applicable to the goals of this study.
Research on Wet Systems for Residential Refuse Collection. The first to
investigate the feasibility of using sewers for refuse transport and
joint refuse-sewage treatment was the Los Angeles County Sanitation
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District, which conducted experiments with ground refuse in large inter-
ceptors in July 1963,2 It was concluded that the idea was probably
feasible, but not pursued further because of anticipated problems at the
treatment plant, the most important of which being a projected 25-fold
increase in sludge volume.
The next to study the idea \vas the ASCE Combined Sewer Separation Project.
In a report published in February of 1968, the idea of including ground
refuse in pressurized sewers was examined, but no experiments were con-
ducted. ^ Independently in 1968, Nebiker and Meier^ analyzed the idea
from a social and environmental viewpoint, and they concluded on the
basis of some preliminary cost/benefit estimates that the idea should be
further pursued.
In 1970, Etzel suggested the use of hydropulpers, widely used by the
pulp and paper industry, as a means of refuse size reduction prior to
discharge into the sewers. Etzel also suggested some radical changes at
the sewage treatment plant, including the use of advanced waste treatment
processes such as reverse osmosis to treat the high solids loadings that
would result.
The first detailed research study was conducted by Foster-Miller under
contract to EPA.^ The objectives of this study were to evaluate the
feasibility of hydraulic transport of ground refuse in existing sewer
lines by experimentation in a section of straight sewer pipe, and to
evaluate the feasibility of treating a sewage-refuse mixture at a conven-
tional sewage treatment plant by laboratory analyses of sample refuse-
sewage slurries. However, because the hydraulic experiments used water
rather than sewage, and because limited treatment experiments were con-
ducted, technical feasibility was not unequivocably demonstrated. In a
second phase, Foster-Miller developed a preliminary design for a household
refuse grinder.^ Experiments during this second phase showed that refuse
was amenable to size reduction in small, low-powered slurry grinders and
that the few components that were not easily ground constituted a rela-
tively small weight and volume fraction of the total domestic refuse.
g
McKinney and Mahloch examined the costs of the concept in late 1971 and
concluded that at the present time, conventional collection was more
economical. They stressed, however, that increased labor costs for ref-
use collection, improved wastewater treatment methods, and the successful
development of grinders* would very likely make grinding and discharge
to the sewers the preferred method.
In 1971, the Brookhaven National Laboratory planned a three-year,
$800,000 study for the Atomic Energy Commission to demonstrate the fea-
sibility of the concept, followed by a $2.2 million study to investigate
resource recovery at the treatment plant. The Brookhaven concept en-
visaged the use of neighborhood pulpers and transportation in sewers to
a treatment plant which would recover paper fiber, glass, and metals and
use pyrolytic treatment for the remaining constituents. The goal was an
effluent of sufficient quality for aquifer-recharge. This planned pro-
ject, however, was never funded.12
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A second contract was let by EPA to Foster-Miller to study the feasibility
of hydraulic transport of refuse in sewer appurtenances and other poten-
tial problem areas in sewer systems (siphons, manholes, T-junctions, bends,
etc.).13 Again, water rather than sewage was used as the transport medium.
However, the results of this research did indicate some potential problems,
and will be discussed further in later sections of this report.
Finally, in late 1972, Courtney and Sexton compared the sewer transport
concept against pneumatic and pressurized alternatives. They concluded
that sewer transport appeared particularly suitable for existing urban
areas.1^
Other Pertinent Research. The area of research that is most directly re-
lated to the wet system for refuse collection is that of pipeline trans-
port of refuse. However, the emphasis has previously been on hydraulic
transport from centrally located collection points to the ultimate dis-
posal site, as an alternative to truck or rail haul, rather than elimina-
ting house-to-house collection.
Of all the alternative pipeline systems considered to date, slurry
transport has received most attention. This calls for refuse to be ground
and mixed with sewage or water and conveyed under pressure as a slurry of
between 6 and 12 percent solids content. However, several other pipeline
concepts have been considered, including hydraulic transport of briquettes
and slugs.
The slurry pipeline idea has been pursued by Zandi and co-workers at the
University of Pennsylvania for many years, and extended to include a
vacuum system to bring refuse from the individual home to the neighborhood
stations where the refuse is ground and injected into a slurry pipeline
network.16 This combination is therefore a direct competitor to the pro-
posed system, in that it completely replaces conventional collection.
Pipeline transportation of shredded solid waste was also investigated by
researchers at the Western Company, who proposed the use of friction-
reducing polymer additions to increase pipeline capacity.17
In the area of grinding, we must turn to recent developments in the pulp
and paper industry, for the latest generation of hydropulpers appears to
be eminently suited to the size reduction of paper-rich solid waste.
The experience of the paper industry is also very important to an assess-
ment of treatability. For many years it has worked in treating cellulose
and fiber-rich wastes by technologies similar to sewage treatment, and
with special emphasis on recovery. ° In particular, screening is a
technology well developed in the paper industry that is suitable as a
modification to existing treatment plants for solids removal in prelimi-
nary treatment.
The feasibility of treating refuse slurries by technology adapted from
the paper industry is currently under study at a demonstration project
at Franklin, Ohio.19 Designed by the Black Clawson Company for 150 tons
of municipal refuse per day, the objective of the treatment plant is to
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recover metals, glass and paper. The first step in the treatment process
is to pulp the incoming refuse in a hydropulper, using recycled process
water and secondary effluents. Although a sewage-refuse slurry would re-
quire some substantial modifications in the treatment process configura-
tion, the proposed system of wet collection of residential refuse appears
to be entirely compatible with these latest efforts toward resource re-
covery from municipal solid wastes.
Detailed Technical Reports
The details of the technical, environmental and economic studies conducted
under this contract have been published in four separate technical "reports
which are available from the National Technical Information Service,
Springfield, Virginia 22151. The first report undertook a preliminary
assessment of the economic and technical feasibility of the concept with
a view to establishing the order of magnitude of costs involved and iden-
tifying the major areas of technical uncertainty,20 A second report ana-
lyzed the economics of processing and disposal of refuse sludges, pub-
lished separately in view of its possible interest to an audience not
necessarily also interested in the wet systems concept.2^ The third re-
port describes a detailed evaluation of the wet systems concept in the
Springfield, Massachusetts Case study area to develop specific conclusions
and cost estimates for the conditions encountered in an area typical of
the Nation's urbanized regions.22 And finally the fourth report documents
the computer program developed for the assessment of treatment costs.2^
Again the motivation for a separate publication is the possible interest
of the subject matter to an audience not necessarily interested in wet
systems for residential refuse collection.
The Case Study Area
The choice of the Springfield Standard Metropolitan Statistical Area
(SMSA) in Massachusetts as the case study area, and the city of Spring-
field as its major focus, is not dictated solely by its proximity to the
contractor's home office and its representative size. Located in the
picturesque Connecticut River Valley in western New England, considerable
environmental awareness exists among its inhabitants, evidenced for exam-
ple by its relatively advanced refuse recycling efforts. The SMSA has
recently completed a planning program for both solid waste disposal and
wastewater treatment and its wastewater treatment plant is in the process
of being upgraded from primary to secondary treatment. Thus the case
study addresses an area that is in a very active stage of environmental
improvement, and thus displays an interest in the evaluation of innovative
concepts. Indeed, the willingness of the city officials to assist the
contractor in his investigations, especially the superintendent of the
city's Department of Public Works and his deputies in charge of the ref-
use and sewer divisions, has been of valuable assistance. Moreover,
Springfield exhibits many of the problems that must be addressed in a
realistic evaluation of the concept, including the presence of a signifi-
cant proportion of combined sewers and significant seasonal variations.
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In retrospect, perhaps the major apparent disadvantage of the choice of
Springfield as a case study area is the fact that the wet system imple-
mentation has had to be compared to an existing collection system of
high cost-efficiency. But we have thereby avoided the pitfall of over-
estimating the benefits of a wet system implementation by comparison to
an existing system that could easily be improved by other means. We
recognize, of course, that there are undoubtedly areas of the country
where many of the problems of a wet system encountered in Springfield do
not exist or are of a much lesser magnitude. On the other hand, the
most important consideration has been to ensure that all the important
questions have been addressed, so that the research priorities that this
study seeks to define have in fact been based on an evaluation of the
the widest possible range of conditions.
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SECTION IV
GRINDING*
Introduction
Although the original concept called for a refuse grinder in every resi-
dence, the existence of substantial economies of scale made a considera-
tion of alternative grinding concepts potentially attractive. Grinders
installed on a one-per-structure and one-per-block or neighborhood were
examined, but rejected; the former because of serious questions as to
ownership and maintenance responsibilities, the latter because of the
very high cost of the vacuum collection system required to convey the
refuse from the individual home to the central grinding station. Indeed,
very high residential densities would be required to justify the block
or neighborhood approach, densities found only in the older, central
parts of urban areas where the practicability of installing vacuum sys-
tems in old housing was open to serious question (apart from also being
those areas showing high incidence of combined sewers).
The investigations therefore returned to the one-per-residence approach,
for which Foster-Miller had prepared a preliminary conceptual design.24
An artist's impression of this design is shown on Figure 1. However,
several questions arose as to the actual feasibility of the approach
suggested by Foster-Miller, which centered on re-use of all domestic
wastewater except that from water closets. This wastewater re-use would
be attained by a plumbing separation feeding all non-fecal wastewater
into a storage tank, the installation concept being shown on Figure 2.
First, because of power limitations, the grinding of ferrous metals at
this scale was considered unrealistic. However, the exclusion of steel
and heavy gauge aluminum was not judged a serious restriction, because
it would be necessary anyway because of difficulties in hydraulic trans-
port in-gravity sewer systems. Because the design results in nongrindable
materials staying within the grinder, and cleaned during the freshwater
flushing cycle following a grinding, the metal nongrindables would be
free of putrescible matter, and of relatively small volume; laboratory
tests indicated that even tin cans would be considerably compressed.
Storage until infrequent conventional collection would thus be feasible.
Finally, the nongrindable metals would be clean (paper labels and paint
would be removed during grinding, for example), and thus represent a
much better raw material for metal recovery than raw refuse from which
nonmetals must first be separated.
For more detailed discussions, see Meier, Kuhner and Martel,
(Ref. 20), Chapter II and Meier, Kuhner and Bolton (Ref. 22), Chapter II.
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-Water Gauge
-Locking Handle
-Lifting Handle
Water Nozzle
40"
Lid
Shredder Ring
Breaker Bar
Motor
Figure 1: Preliminary Design for a Household Grinder (Source: Fisk $ Guzdar, op. cit., p.* 83).
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To
Sewer
&.
r
IXI
X
/— •
V
** * * *^
t'
Fecal Waste from
Upper Floors
Fecal Waste from
First Floor
Clean-Out
Connecting all
Non Fecal - Containing
Wastes from All I
Floors 1
Vent
Grinder
Overflow
to
Drain
/ / Pump
Anti-Siphon
" Valve
Tank
//A -
>
> > -
Figure 2: Basement Installation of a. Household Grinder (Source: Fisk § Guzdar, op. cit., p. 32).
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Second, the sufficiency of the quantity of reuseable wastewater necessary
for grinding at a solids concentration at which no deleterious effects
would occur during subsequent sewer transport (See below, Section VI),
was found to be open to question. The subject is a complex one that did
not lend itself to definitive resolution because of lack of data. How-
ever, the need to use some amount of fresh water, for either grinding or
flushing (at the end of the grinding cycle) or both, was clear.
The most serious deficiency related to cost. Apart from the cost of the
grinding unit itself, the cost of replumbing an existing residence to
provide the grinding unit with its source of reused wastewater is pro-
hibitive, as shown on Table 1. These costs were estimated by a plumbing
contractor in the Springfield Case Study Area as bid price estimates,
and are generally comparable, although about $200 higher, to the Foster-
Miller estimates conducted two years previously. An alternative con-
cept was also examined, whereby the grinding would occur at high con-
sistency (say 5-10 percent refuse by weight), pumped to the sewer in a
pressurized building connection, and relying on the flow already present
in the sewer for dilution to the 0.5 to 1.0 precent concentration re-
quired for hydraulic transport. Grinding at high consistency would re-
quire less water for a given weight of refuse. However, the cost of the
pressurized building connection, even though lower than under the waste-
water reuse concept, was still found to be prohibitive. Table 2 shows
an analysis of the cost of these two alternatives, which, at over $100 per
household per year, completely outweigh all other costs of a wet system
imp1ementat ion.
For the purposes of further investigation, it was therefore concluded that
some grinding concept would need to be developed that required neither a
plumbing separation nor a pressurized building connection. But this still
left open the question of the cost of the grinding unit itself, and the
cost at which such an appliance might be considered a reasonable propo-
sition.
The Refuse Grinder as a Domestic Appliance
The first approach in analysing a refuse grinder in terms of a domestic
appliance is to study cost trends of similar household appliances; sim-
ilar to a refuse grinder in either use, such as the garbage grinder;
in consumer appeal, such as the refuse compactor; or in similarity to
electromechanical sophistication and probable industrial production tech-
nique such as the automatic dishwasher. Unlike the washing machine, all
three appliances still have connotations of convenience rather than ne-
cessity, and, also unlike washing machines, are many years from market
saturation.
An analysis of the trends in price of these appliances over the last
twenty years shows dramatic decreases; not only decreases in terms of
inflation adjusted dollars but even in terms of actual selling prices.
12
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Table 1: Cost Estimates for Installations of Refuse Grinding System
Construction Type Estimated Total Cost
New Construction 2 Story Slab $ 500.00 - 550.00
New Construction 2 Story Basement S50.00 - 600.00
New Construction 1 Story Slab 400.00 - 450.00
New Construction 1 Story Basement ' 450.00 - 500.00
Old Construction 2 Story Slab 1300.00 -1400.00
Included in above:
Excavating concrete floor and patching 150.00
Excavating pit and concrete fill 300.00
Cut and patch and paint walls 175.00
Remove and relay carpets 75.00
Old Construction 2 Story Basement 925.00 -1025.00
Included in above:
Excavating concrete floor and patching 75.00
Cut and patch and paint walls .175.00
Old Construction 1 Story Slab 1100.00 -1200.00
Included in above:
Excavating concrete floor and patching 150.00
Excavating pit and concrete fill 300.00
Cut, patch and paint walls 100.00
Remove and relay carpets 75.00
Old Construction 1 Story Basement 725.00 - 825.00
Included in above:
Excavating concrete floor and patch 75.00
Cut, patch and paint walls $ 100.00
-------
Table 2: Cost Comparisons Between the Foster-Miller
and Meier-Nebiker Concepts
Foster-Miller Meier-Nebiker
(Grinding at 1% Solids (Grinding at 7% Solids
with Wastewater Reuse) Discharge via Pres-
surized Building Con-
Assumed
Item Life Cost
Grinder 15 $180
Installation 15 75
Distr. and Sales
Costs 15 191
Storage Tank 30 116
Installation 30 75
Distr. and Sales
Costs 30 143
Building Con-
nection 30 0
Plumbing
Modification 30 520-1,050
Total Initial Costs 1,300-1,830
Water
Power
Repairs
Total Annual Cost
nection)
Annual Cost
at i = 6% Cost
$18.50 $200
7.70 75
19.65 19.1
8.40 0
v 5.40 0
10.40 0
0 450-500
37.75-
76.20 0
108-146 916-966
1.50
2.50
16.00
128-166
Annual Cost
at i = 6%
$20.60
7.70
19.65
0
0
0
32.60-
36.30
0
80-84
3.00
2.50
16.00
101-105
14
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For example, in 1952, the automatic dishwasher rated best by Consumer
Reports cost $354; in 1969, the cost had decreased to $280, a decrease
of $74.Z5 If one adjusts for inflation, say by use of the consumer price
index, the decrease in real cost was $210. Similar decreases were estab-
lished for the other appliances mentioned above.
The conclusion from such a comparison is that the initial selling price
of a newly introduced appliance will fall (if not in current dollars,
certainly in inflation adjusted dollars), and that whatever the initial
cost that might be hypothesized, this would fall as manufacturing refine-
ments, competition and economies of scale becpme operative with increas-
ing production levels.
The Appliance Industry Viewpoint. In view of the aforementioned simi-
larities between the refuse grinder, the trash compactor, and other simi-
lar appliances, a discussion of the appliance industry viewpoint on
compactor sales is clearly pertinent to an assessment of the prospects
of a refuse grinder. The appliance industry sees trash compactors as
an item having strong growth potential in the upcoming years. The trash
compactor is the first new major domestic appliance in years, having
been introduced only in 1970, and is therefore felt to have "novelty
value." In reply to critics of the trash compactors' comparatively low
sales volume, it is often pointed out that it took dishwashers many years,
literally decades, to become the strong selling item they presently are.
The existing price level of around $200 is felt to be a strong selling
point. This is considered low, and the prospects for even lower prices,
as previously documented, are good. It is also noted that despite hin-
dered consumer appeal of dishwashers at the time, some 15 years ago, that
their price was in excess of $300, sales did ultimately accelerate as
price decreases became possible. Indeed, one can identify a psychologi-
cal barrier at a retail sales price of around $300, and any major appli-
ance selling for less is considered likely to gain broad consumer appeal.
In view of the presently identifiable market for trash compactors, namely
residents of relatively high-income, suburban single-family home areas,
speciality advertising that has maximum impact on sales is regarded as
very effective. Retailers are pressing the manufacturers for additional
advertising in this direction. And yet another perceived advantage is
the feeling that because ecology and the environment will become of in-
creasing concern to the householder, advertising can make the compactor
appear to have a strong.positive affect on the environment - thus ap-
pealing to the "environmentally conscious" consumer.
Implications for the Refuse Grinder. Whatever the shortcomings of the
industry viewpoint toward trash compactors, and especially with regard to
its exaggerated environmental benefits, it must nevertheless be concluded
that some degree of, consumer acceptance already exists, and that this is
likely to grow.
15
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Unquestionably, a refuse grinder would offer much greater convenience
benefits than the compactor. Since refuse would be ground daily, there
would not be the odor problem that characterises compactors. The spe-
cial bags that are required for the compactors would no longer need to
be purchased, nor would the compacted refuse need to be carried to the
point of pickup, a task, incidentally, that because of the high density
of the compacted product, would certainly be beyond the many persons un-
able to carry heavy loads.
There would of course be some relative disadvantages over the compactor,
including that of higher noise levels and the need to periodically remove
nongrindables. Nevertheless, it does not appear unreasonable to suggest
that consumer acceptance of an appliance offering unquestionably greater
convenience benefits would be almost assured at an initial price of some-
what less than $300, falling gradually as sales increase to perhaps a
level of around $200.
One aspect that must be stressed, however, is the need for operational
reliability if consumer acceptance is to be gained. As an appliance that
might require housecalls by either plumbers or electricians in the event
of malfunction, the potentially high cost of repairs might prove to be a
substantial deterrent, even to the relatively affluent suburban resident.
Conclusions
If the similarities of the refuse grinder to the garbage grinder, auto-
matic dishwasher, and trash compactor are indeed valid, several conclu-
sions can be drawn from the analysis of recent cost trends.
1. A refuse grinder selling at less than $300.00 would gain
consumer acceptance.
2. The cost of the grinder should decrease in the first few
years of production because of design improvements, econo-
mies of scale and competition.
3. The real cost (inflation adjusted) of the refuse grinder
should at worst remain stable, but probably decrease with
time.
The conclusions with respect to the feasibility of the wastewater reuse
concept appear quite unfavorable. The cost of replumbing existing
housing units is clearly prohibitive, and it is even questionable wheth-
er the additional plumbing costs in new housing would be acceptable.
Although such costs might well be included in the total purchase price,
and hence buried in the mortgage payments, the high interest costs there-
by incurred have considerable bearing on the real social cost of the wet
systems concept.
16
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The presently ascertainable costs of grinding have some very interesting
consequences for judging the most likely initial wet systems implementa-
tion. Because of their high cost, grinders would inevitably find their
first purchasers in the relatively affluent suburbs for installation in
single-family homes of low residential density. Moreover, such areas are
very often characterised by very high conventional collection costs be-
cause the low costs of an efficient municipal house-to-house service are
not available at such low densities. Many suburban residents spend $1
to $2 a week for a private refuse pick-up, and consequently there may be
a real economic benefit in addition to the convenience benefits. This
motivation exists far less in the central urban areas where municipal
collection, as for example in the Springfield Case Study Area, may cost
as little as $12.00 per household per year. It could of course be
argued that scale economies of grinding could be exploited in central
urban areas by virtue of the -possibility of a one-per-structure or a
one-per-neighborhood installation of grinders, as noted previously.
However, again by reference to the case study area, almost 70 percent of
the housing units in Springfield are single-family or duplex residences,
for which only one-per-living unit installation is feasible; and in those
areas where the housing density is sufficient for, say, neighborhood
grinders, the presence of combined sewers makes the concept inoperable.
All the preceding assumes that a grinding concept can be developed that
does not require replumbing or a. pressurized building connection, yet it
is clear that the details of such a concept have yet to be researched.
In the absence of such concepts, we may conclude that installation of
existing grinding concepts in single-family or duplex housing is economi-
cally infeasible. The necessity for further research in this area is
obvious, and is again addressed in the concluding section.
One alternative that might lessen the impact on the home owner is that of
public or quasi-public rather than private ownership. In a manner simi-
lar to the leasing of hot water heaters from electric utilities (common
in New England), so might refuse grinders be leased from a municipal
refuse utility. This utility would also be responsible for maintenance,
and could readily arrange for emergency conventional collection during
grinder breakdowns. Indeed, in areas of multi-family housing where
ownership and maintenance responsibilities are defined only with diffi-
culty, such an arrangement appears mandatory. However, as so eloquently
argued by Foster-Miller in their preliminary grinder design report, it
is unlikely that anything less than private ownership would engender
sufficient respect for the appliance, which in contrast to hotwater
heaters, will require continuous care and attention if frequent break-
downs are to be avoided. But again, even definition of the utility con-
cept depends first on the development of a grinding concept of reasonable
total cost.
17
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SECTION V
COLLECTION AND DISPOSAL OF NONGRINDABLES*
Introduction
Although the intent of the wet systems for residential refuse collection
is to eliminate conventional collection methods, it is readily apparent
that some residual conventional collection will still be necessary, al-
beit of a drastically reduced scope. Even if grinders were to be capable
of handling metals, large bulky items would still need removal. Moreover,
many other small constituents in residential refuse are not amenable to
grinding in the small grinders of single homes, especially resiliant plas-
tics, rubber, leather and some synthetic textiles.
But the conventional collection and subsequent disposal of only the non-
grindable constituents will bring some major changes to existing solid
waste management practice. Volume will be markedly reduced, and density
markedly increased as the light, bulky constituents (paper, food pack-
aging, garbage) are easily ground. The frequency of collection may be
very low, but acceptable, because all putrescible materials will be
ground. The increased density and weight of standard containers would
require trucks to be fitted with hydraulic lifts for the much heavier
full containers, and may demand that all containers be picked up from a
rear-house rather than curbside location. Calculations developed else-
where suggest that the density of nongrindables may be up to 50 percent
higher than the density of uncompacted raw refuse.26 Changes in truck
design to allow for the more difficult compaction of the collected mate-
rial and the increased axle load would also be necessary; indeed, the
compactor trucks widely used today may be quite inappropriate under the
proposed system. A major impact of a wet systems implementation would
of course be a dramatic decrease of the collection labor force. The
socioeconomic consequences of such a decrease are considered in detail
in Section IX, below; but were found to be much less serious than might
at first appear, especially with respect to layoffs.
Quantity of Nongrindables in the Case Study Area:
The 1972 city-wide average domestic refuse generation rate for Spring-
field was established as 2.56 lb/cap/day,27 broken down as follows:
Bulky refuse, collected by appointment 0.07 Ib/cap/day
Separately collected garbage 0.11
Garbage now ground to sewer 0.11
See Meier, Kuhner and Bolton, Ref. 22) , Chapter III for details
relative to the case study area, and Meier, Kuhner and Martel, (Ref.20)
Chapter VI for a general discussion of the relationships involved.
18
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Separately collected newspaper
All other components (regular collection)
2.56 Ib/cap/day
However, these averages were shown to hide considerable quantity varia-
tion, both by season and by route, and also considerable variation in
composition. But no data other than an occasional sampling or our
brief survey were available. Moreover, the figures also include an un-
determined amount of commercial refuse from a downtown collection on
Friday evenings. Exact calculations to derive the quantity and components
of refuse ground, and not ground, were therefore very difficult because
of lack of appropriate data. The calculations developed to measure the
impact on wastewater treatment facilities were therefore based on the
assumption that of the 2.56 Ib/cap/day, 10 percent or 0.256 Ib/cap/day
was nongrindable (based on doubling the amount of bulky refuse, as noted
below, plus continued separate collection of newspaper, plus about 4
percent of nonbulky heavy metals, hence: 0.07 + 0.07 + 0.01 + 0.106 =
0.256). To the extent that glass, ceramics and light metals would not
be ground, the weight percentage of nongrindables would be substantially
higher.
It should perhaps also be noted that the 2.56 Ib/cap/day residential
refuse generation fate for Springfield is consistent with a national
average of 2.25 Ib/cap/day, as established on the basis of the latest
data from the EPA Data Aquisition and Analysis System for Solid Waste
Collection.28
Seasonal Peaks. Substantial seasonal peaks, and especially the fall peak
of garden wastes in areas such as New England as typified by the case
study area, will have an important impact on the final design of a wet
systems implementation. If one assumes that the peaks are composed of
largely grindable material, as would be the case for the fall peak, then
the treatment plant would need to be able to handle load fluctuation^
much higher than otherwise necessary. Moreover, substantial quantities
of fresh water would be necessary to augment the normally available
grinding water supply, which in turn might impose significant demands on
the water system. On the other hand, if the peaks are composed of largely
nongrindable materials, as would be the case in spring, at which time
relatively bulky attic wastes appear to be the major component, a regular
schedule of nongrindable collection (based on a more or less constant
generation rate of nongrindable residuals) would be substantially dis-
rupted by strong peaks. Indeed, aperiodicity in nongrindable collection
might follow unless additional storage space is available. Perhaps com-
pactors might continue to play an important role here, as the operational
complexities of aperiodic collection schedules are formidable.
Bulky Wastes. The problem of bulky wastes was also found to be much
greater than originally anticipated, because one must expect that a
significant fraction of the bulky wastes now collected by the regular
collection could not be ground by virtue of its bulk (rather than by vir-
tue of its composition). The majority of the bulky waste appears to be
19
-------
of such a size that it can be included in a normal container, or is picked
up by the collection crews as a matter of habit (if not as a matter of
regulation); and thus the existing bulky item collection is reserved pri-
marily only for the exceptionally heavy or bulky material. But small
furniture, large plastic toys, small appliances, and the like, would not
be readily grindable, and thus the demand for bulky item collection would
undoubtably increase under a wet systems implementation. At the very
minimum, a doubling of the bulky item collection might be expected.
Unfortunately, we have only our qualitative observations taken during the
route surveys in the case study area to support this contention, and
quantitative data is needed before a more exact judgment can be made. We
shall return to this point in our recommendations for further research.
Commercial Establishments. With regard to the case study area, the city
of Springfield seems to feel very strongly about providing solid waste
collection service to commercial establishments, as evidenced by the
city's willingness to pickup commercial refuse on residential routes
without charge. It seems reasonable to assume, therefore, that the city
would also be willing to let such commercial establishments install,
grinders, to the extent that the nature of their refuse would be com-
patible with sewer transport. Because the collection of nongrindables
would be infrequent, inclusion of commercial establishments in the latter
collection would not replace the need for regular weekly collection of
commercial refuse were grinding not allowed.
If commercial establishments were allowed to use refuse grinders, rigorous
enforcement of ordinances specifying prohibited materials would be neces-
sary. A permit granted only after analysis of a commercial establish-
ment's refuse, with the permit fee applied to the cost of sampling and
analysis of the refuse, might be one way of regulation. Because the new
water quality legislation requires those who add industrial wastes to the
sewerage system to pay an equitable portion of treatment costs, it is
probable that commercial establishments would likewise need to pay some
form of user charge. Grinders at most commercial establishments would
obviously depend entirely on fresh water for grinding water, and hence
metering of the freshwater inflow to the grinder could be used for an
equitable user charge since the quantity of water used will be propor-
tional to the weight of refuse ground and introduced to the sewer.
Emergency Collection. An important consideration in assessing the accept-
ability of the wet systems concept is that of its flexibility to accomo-
date failures. The capital intensity of the wet system would appear at
first glance to compare poorly with the existing system whose labor-inten-
sity and the possibility of incentive and overtime schemes makes it
relatively easy to handle unforeseen refuse peaks or equipment failures;
witness for example, the existing arrangements in Springfield where crews
who have finished early are assigned to other routes in cases of breakdown
or exceptional peaks.
20
-------
There are two sources of potential failure of the wet system. The first
is that of grinder breakdown, and clearly an emergency collection, avail-
able on demand, would need to be available for such situations-. However,
some form of incentive would be necessary to expedite repair of the
grinding equipment, and a nominal pick-up fee imposed after one or two
weeks of emergency collection might be appropriate.
The second, and potentially more serious problem, would follow a sewer
blockage. If a sewer blockage did occur, some mechanism would be neces-
sary to inform upstream residents to cease use of their grinders until
repairs were complete, as the continued load of refuse solids to a situa-
tion of reduced flow velocities would clearly aggravate the problem.
These problems, coupled with the possibly aperiodic collection of non-
grindables and the by appointment bulky item collection, would necessitate
both an intensive public information campaign as well as a unified opera-
tions center for refuse collection and sewer maintenance.
Frequency and Cost of Collection. Using relationships for the frequency
and cost of collection of nongrindables as developed in the Phase I re-
port, 29 it was estimated that between three and four regular collections
would be needed in the Springfield case study area per year (in addition
to increased frequency of the by appointment bulky waste collection), and
that a typical annual per household collection cost would fall from $17.50
to $2.50.30 Because of the present lack of detailed data, a more precise
definition of the collection frequency is not yet possible.
Because of the drastically reduced collection frequency for nongrindables,
and especially in view of the possible aperiodicity resulting from sea-
sonal peaks, it may be necessary to send some form of media reminder to
householders a few days in advance of the nongrindables collection.
Clearly, it would be unreasonable for a householder to remember the days
of collection if spaced at such long intervals. Such notice might entail
considerable administrative effort, and would probably presuppose a cen-
tralized and computerized system run in conjunction with the operational
control of the collection vehicles.
Disposal
Disposal methods would also be affected significantly. Because most of
the nongrindable materials are incombustible, incineration of nongrind-
ables is not a feasible proposition. On the other hand, recovery of
metals from the ungrindables will doubtless be aided in the absence of all
light, putrescible matter. But landfill disposal is the most likely op-
tion, until such time as resource recovery and recycling of metals becomes
more widespread. Unfortunately, the economies of scale in conventional
disposal methods will have a negative impact on the disposal of nongrind-
ables under a wet systems implementation; a 90 percent reduction in volume
will bring less than a 90 percent cost reduction, and the per ton cost of
disposal will increase.
21
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It has been argued that the cost of existing solid waste collection could
oe substantially reduced if the volume of domestic refuse were reduced by
tne^elimination of relatively bulky glass containers resulting from a ban
on no-deposit no-return" bottles. But this would also benefit the wet
system, as ground glass is one of the major refuse categories that can be
expected to cause problems in sewer transport (see below, Section V).
22
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SECTION VI
HYDRAULIC TRANSPORT*
Introduction
The key to the feasibility of the wet systems concept is the ability of
an existing sewer system to transport ground refuse without adverse ef-
fects. Unfortunately, the literature and experience dealing specifically
with the ability of sewers to transport solid waste is extremely limited,
and only three studies were considered of any consequence to our analysis.
One mentioned earlier was a result of depositing very coarsely ground ref-
use in large sanitary sewers performed in 1963 by the County Sanitation
Districts of Los Angeles County.2 The other two were studies conducted
by Foster-Miller Associates for the Environmental Protection Agency.31'32
A detailed review of this literature shows that two conditions must be
present for hydraulic transport in an existing system to be judged feas-
ible;33 a scour velocity of about 2.5 ft/sec is necessary to prevent accu-
mulation in the sewer of the heavier components such as glass and metals,
and the concentration of refuse must be below the so-called "limiting con-
centration" for the sewage-ground refuse mixture to have hydraulic proper-
ties similar to sewage alone. This limiting concentration is also a func-
tion of flow velocity, increasing with increasing velocity and depth of
flow, and lies between about 0.5 and 1.5 percent refuse solids by weight.
Although the Foster-Miller experiments covered steady-state conditions in
both straight sewer pipes and in a variety of appurtenances (including
manholes and siphons), their conclusions of feasibility must be put in the
light of actual rather than designed conditions in a sewer system. Some
preliminary analysis showed that although both conditions are generally
met in interceptors, there might be substantial difficulty in meeting them
in lateral street sewers. Consequently, the focus of the case study in-
vestigation with respect to hydraulic transport was to establish the mag-
nitude of maximum velocities in typical street sewers, and to establish
the relationship between the quantity of freshwater needed for grinding
and the limiting refuse concentration in the sewer. Obviously, by adding
sufficient freshwater to the grinding, the limiting refuse concentration
can always be met; the problem, however, is that such freshwater additions
may be undesirable both from the viewpoint of increasing total freshwater
consumption as from the viewpoint of increasing flows at the treatment plant,
Scour Velocity Investigations
The laboratory studies conducted by Foster-Miller Associates have deter-
mined that for the particle size distribution emanating from their pre-
liminary grinder design, a minimum velocity of 2.5 ft/sec (0.76 m/sec) is
needed to maintain self-cleansing conditions in sewers. Since steel cans
*For more detailed discussions, see Meier, Kuhner and Martel,
(Ref. 20), Chapter III and Meier, Kuhner and Bolton, (Ref. 22), Chapter IV.
23
-------
have already been eliminated due to excessive power requirements for
grinding, high grinding costs and problems in appurtenances, especially
siphons, this velocity is required to transport the glass, ceramic, and
aluminum components only. No determination was made as to how often or
how long this scouring velocity should be present. However, in order to
avoid excessive accumulation of debris, it would not be unreasonable to ^
require daily scouring of settled materials. Otherwise, deposited materi-
als may combine with grease or other cohesive materials to form a cake re-
sulting in a further loss in hydraulic properties.
Assuming unobstructed flow conditions, there are two occasions where
sewers are incapable of providing the required 2.5 ft/sec (0.76 m/sec)
scour velocity. The first occasion is where sewers are designed according
to the minimum requirements of most health departments which specify a
"minimum full-conduit velocity of 2 fps."34 Since maximum flow velocities
are achieved at full or near full flows, these sewers cannot be expected
to flow faster than 2.0 ft/sec (0.61 m/sec). The second occasion is where
sewers are not flowing full enough to attain a 2.5 ft/sec (0.76 m/sec)
velocity.
Investigation of the Springfield sewerage system revealed that sewers
laid at minimum slope (to produce a full pipe velocity of only 2.0 ft/sec)
are not uncommon. It also revealed, through a sewer survey, that even in
sewers where the design slope is great enough to produce velocities in
excess of 2.5 ft/sec (0.76 m/sec), the quantity or depth of flow is insuf-
ficient. The highest maximum velocity reached during a 7 day survey of 7
lateral sewers in August 1973 was 1.62 ft/sec (0.5 m/sec), and the lowest
maximum velocity occuring in a 24 hour period was 0.74 ft/sec (0.225
m/sec). The conclusion that glass and other high specific gravity materi-
al would accumulate in such sewers is inescapable.
One obvious alternative to resolve this problem would be the elimination
of glass, ceramic and aluminum material from the list of grindables, along
with steel cans, heavy gauge plastic and heavy gauge aluminum. However,
this would increase the collection cost of nongrindables and would seri-
ously reduce the convenience to the user. On the other hand, instead of
prohibiting the grinding of glass and other high specific gravity materi-
als , it may be feasible to simply flush accumulated materials from the
affected sewer lines at regular intervals. The frequency of flushing
would depend on the rate of accumulation and the effect of the accumulated
deposits on the hydraulic properties of the pipe. Without actual experi-
ence or field test results, one can only assume a likely frequency. But
based on some calculations which indicate an accumulation of about 2.2
inches of glass in a typical 8-inch lateral sewer per year, an intensive
flushing program would probably be required. Discussions with municipal
officials with great experience in sewer maintenance indicated the impos-
sibility of accurate prediction in this area in the absence of actual
data.
Another alternative to eliminating glass as a grindable item is to rede-
sign the sewer system to achieve the minimum scour velocity of 2.5 ft/sec
24
-------
(0.76 m/sec) at the shallower depths common in sewer flows. This would
mean steeper sloped sewers and a more frequent use of lift stations. This
might be considered feasible for newly developing and urban renewal"areas
that could readily implement new design standards. However, some sample
designs and cost analyses quickly showed that a tripling of construction
and operating cost was involved and this alternative, too, was rejected
as a feasible proposition.
Grinding Water Investigations
The sewer survey showed that street sewers rarely, if ever, flow greater
than half full. This is important because the limiting refuse concentra-
tion is strongly influenced by the flow depth. Foster-Miller defined
limiting refuse concentration as that concentration at which the friction
resistance is the same as that for water and beyond which the friction
resistance increases rapidly.35 Consequently, if refuse mixtures above
the limiting concentration are introduced into the sewerage system, re-
duced flow characteristics would result. Figure 3 shows the relationship
between limiting refuse concentration and flow depth. For the depths of
flow normally experienced in street sewers (between .1 and .3 d/D or d =
2 inches) it appears that the limiting concentration should be in the
vicinity of 0.5 percent, instead of 1.0 percent as originally thought
(the latter figure being used by Foster-Miller as a basis for the grinder
design). However, in the larger interceptors where greater depths of
flow can be expected, the limiting refuse concentration may be as high as
1.5 percent if flowing full or near full.
Since the ground refuse must flow through the street sewers of residential
areas before discharging into an interceptor, the lower limiting refuse
concentration of 0.5 percent should govern the dilution water requirements
at each grinder installation. This is unfortunate because the lower lim-
iting refuse concentration (0.5 percent) is made to apply in an area where
the least amount of dilution water is available. In street sewers, only
residential flows and some infiltration can be expected whereas in the
larger interceptors, dilution water is available from industrial and com-
mercial sources as well.
The relationship between the amount of grinding water required and the
percent solids content for various refuse generation rates is shown in
Figure 4. This graph was developed from the equation:
_ L(l-fl-X)
q " 8.34X
where q is the gallons of grinding water required per capita per day, L
is the pounds of refuse per capita per day, fi is the moisture content of
the refuse (assumed to be 20 percent) and X is the grinding consistency
(0
-------
5-1-
4--
in
JC.
O
3
u_
u_
O
I
a.
Id
o
3--
2--
I --
6LASS
TRANSITE
(ASBESTOS CEMENT)
6 INCH DIAMETER PIPES
0.5 1.0
LIMITING REFUSE CONCENTRATION,
1.5
percent
Figure 3: Limiting Refuse Concentrations for Hydraulic Transport in Sewers
(Source: Guzdar § Rhee, op. cit., p. 98)
-------
POUNDS OF REFUSE PER CAPITA PER DAY
(INCLUDING MOISTURE)
234
PERCENT SOLIDS CONTENT
Figure 4: Grinding Water Requirement
27
-------
is 2.56 Ibs/cap/day (1.14 Kg/cap/day), the amount of grinding water re-
quired is approximately 48 gals/cap/day (182 £/cap/day).
Because of this high grinding water requirement, Foster-Miller suggested
that household nonfecal wastewater be stored and reused for grinding. For
the purpose of this analysis, nonfecal wastewater includes discharges from
all plumbing fixtures except the toilet. Therefore, the total household
water consumption required to allow refuse grinding using only nonfecal
wastewater is the sum of the household grinding water requirement and the
household fecal wastewater component. The household grinding water re-
quirement can be determined by multiplying the number of persons per
household times the per capita grinding water requirement determined from
Figure 4. The household fecal wastewater component can be calculated
based on an average toilet use of 4 uses/cap/day at 5 gals/use (19 £/use).
For an average household with 3 persons per household, the household water
consumption rate needed to grind refuse is approximately 204 gals/HH/day
(3 persons per household x (48 + 20) gals/cap/day), which is substantially
above actual consumption rates.
The water consumption records were examined for homes in two neighborhoods
in Springfield, one of 36 single-family homes, the other of 50 duplexes.
Analysis showed that the single family home area would require an 8.5
percent increase in water consumption in the winter and a 39 percent in-
crease in the fall. The duplex area would require a 3.7 percent increase
in the winter and a 12 percent increase in the fall. The seasonal depen-
dance is dictated by the seasonal fluctuations in refuse generation, as
noted in Section IV, above. Considering that over 65 percent of the
housing units in the city of Springfield are either single-family homes
or duplexes, this would represent a large increase in total water demand.
Moreover, while increased flows could probably be accommodated in the -
lateral sewers without difficulty (because, as shown by our survey, they •>
rarely flow at more than half depths), there may be problems in intercep-
tors that are more likely to reach flows nearer their design value, and
of course, the total inflow at the sewage treatment plant would also in-
crease. A conclusion from this analysis is that much of the garden wastes
collected in the fall, which is largely responsible for the higher refuse
quantities in that season, cannot be ground for reasons of unacceptable
freshwater demands, and would therefore need a special conventional coir
lection.
Hydraulic Transport at Higher Than Critical Concentrations
The large quantity of dilution water required to maintain hydraulic flow
characteristics similar to water raises the question as to the impact of
depositing refuse in sewers at concentrations higher than the limiting
refuse concentration (0.5 percent). If higher refuse concentrations of 1
percent and more were hydraulicly transportable, substantially less dilu-
tion water would be required. From Figure 4 it can be seen that at 1 and
2 percent refuse concentrations, dilution water requirements can be re-
duced substantially. This in turn -would mean that a much larger percen-
tage of homes would possess the necessary dilution water and very little
28
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additional fresh water would be needed. Also, the laboratory experiments
of Foster-Miller have shown that flows at higher refuse concentrations (2
percent and above) have the ability to maintain heavier particles in sus-
pension. This would eliminate the need to attain a specific scour veloci-
ty to remove settled materials. However, these heavier particles would
likely settle out as the mixture is diluted further downstream.
But, Foster-Miller also noted that head losses increase dramatically at
refuse concentrations above the limiting refuse concentration. Con-
sequently, mixture velocities would be less than for sewage alone, or for
refuse mixtures below the limiting refuse concentration. Depending on the
condition of the sewer, this could cause more frequent blockages. Also,
the detention of sewer flows may encourage septic conditions which would
be more objectionable in residential areas. Although sewers can be ex-
pected to flow fuller as a result of the decrease in velocity, this is not
expected to be a problem since most street sewers are overdesigned with
respect to hydraulic capacity as evidenced in .the sewer survey, and rarely
flow above half-full.
Thus although there appear to be some benefits to be derived from grinding
and transporting refuse mixtures at higher than critical concentrations,
it is difficult to make judgments of its technical feasibility until fur-
ther experiments have been conducted.
Alternatives to Hydraulic Transport in Gravity Sewers
A number of alternative modes of hydraulic transport were examined in the
early stages of the study, but rejected from further consideration either
for reasons of lack of data or for obvious technical reasons at the scale
of application here under investigation. Briquette and slug flow systems,
investigated by the Stanford Research Institute for point-to-point pipe-
line transport of refuse^ were rejected for both technical reasons and
because of the obvious impossibility of providing briquette and slug
forming equipment at a scale smaller than neighborhood. Similarly,
pressure systems were rejected on the basis of both cost (since a new
pressure conduit would need to be built in existing areas) and operational
difficulties.37
29
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SECTION VII
TREATMENT*
Introduction
There is a critical lack of information on the physical-chemical charac-
terization and treatability of ground refuse in sewage, and therefore ac-
curate predictions of the impact of ground refuse to an existing treatment
facility, or detailed design specifications for new facilities, are not
easy. Indeed, the only comprehensive study is that undertaken by Metcalf
£ Eddy38 as part of the initial Foster-Miller contract, although some
limited information is also available from the experiments conducted in
the early sixties in Los Angeles.2
A detailed review of this literature and other sources considered relevant
is contained in Chapter IV of the Preliminary Assessment,20 and we shall
here summarize only the most important conclusions:
- Existing grit chambers would probably be adequate to handle
increased load; major problem would be increased entrapment
of organics and paper fibers.
- Suspended solids (SS) concentrations into primary settling
units would increase about 10-fold over existing levels.
Existing primary settlers would probably be adequate, but need
much strengthened skimming and sludge scraping devices. BOD
and SS concentrations in the effluent would be of the same
order of magnitude as those encountered at existing treatment
plants.
- Screens were found by Metcalf § Eddy to be effective as a
primary treatment device, especially the Bauer "hydrosieve."
- The need for equalization of either load or flow is largely
unknown, because the hour-to-hour patterns of refuse grinder
operation are still conjectural.
- Secondary treatment appears to be little affected by the ad-
dition of ground refuse. Long-term BOD exhertion studies showed
no inhibitory effects and identical rate constants. Phosphorous
and nitrogen were determined to be adequate, with little change
over the case of sewage alone. Heavy metal concentrations were
also largely unchanged, with no evidence of toxicity.
See Meier, Kuhner and Bolton, (Ref. 22), Chapter V and Meier, Kuhner
and Martel, (Ref. 20).Chapter IV for detailed discussions. The problems
of sludge handling and disposal are discussed also in Section VIII of
this report, below.
30
-------
- Theoretical analyses of the maximum mercury concentration that
might be introduced by residential refuse showed the pos-
sibility of mercury concentrations in sewage substantially
higher than those encountered today. Metcalf § Eddy's measure-
ments, however, showed no increase.
- The impact of ground refuse addition on advanced waste treatment
was concluded to be marginal. Tertiary polishing devices (e.g.,
microstrainers) were the only type of AWT that might need to be
specified for reasons of ground refuse additions because of the
difficulty in aerobic degradation of cellulose fibers. The im-
pact on phosphorus, nitrogen or dissolved organics removal pro-
cesses was considered immeasurable in the absence of data.
Because of the difficulties encountered in making generalizations, con-
siderable effort went into an examination of treatment in the case study
area, using mathematical simulation techniques as the major tool. The
mathematical model utilized for this purpose is described in detail in
a separate report.23 The most immediate shortcoming of using a mathe-
matical model based primarily on design relationships valid for conven-
tional sewage is that the addition of ground refuse may dramatically
change the physical-chemical relationships involved. Whenever possible,
such changes were incorporated, but the basis for the changes were the
very limited studies discussed above and hence may well be subject to
question. Nevertheless, in the judgment of the writers and the review
panel, the results generated by the model were consistent with the goals
of the study, and, whatever their shortcomings, certainly an improvement
over mere qualitative and subjective opinions as to the consequences of
ground refuse additions.
Existing Treatment Facilities in the Case Study Area
At the present time, Springfield utilizes two wastewater treatment facili-
ties, each providing primary treatment for domestic sewage and most of the
industrial wastes in the city. The smaller facility, Indian Orchard
Treatment Plant, is located in the northeast section of the city on the
Chicopee River. At present the plant handles only domestic sewage from
the Indian Orchard section of Springfield, and wastes from the Monsanto
industrial complex are dumped directly into the river. The nominal capac-
ity of the plant is estimated at 3.0 mgd (11,355 m3/day). The treatment
process consists of screening, grit removal, and sedimentation prior to
discharge of the unchlorinated final effluent. Settled sludge is digested,
dried on glass-covered drying beds, and used as fill.
The major portion of Springfield's waste load is treated at the main
treatment plant located on the Connecticut River at Bondi Island in Agawam.
In addition to Springfield, the plant presently treats wastes from West
Springfield, Agawam, and parts of East Longmeadow. The treatment facility
is quite old, having been completed in 1940 as a Works Progress Administra-
tion (WPA) project. It provides units for coarse screening, grit removal,
31
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comminution of solids, and primary settling. Sludge handling facilities
include heated digestion tanks, elutriation tanks, a vacuum filter, and
land disposal site. There is no chlorination before discharge. Figure 5
provides a schematic of the present operation.
Although the design capacity of this existing plant is rated at 30 mgd,
flows in excess of this figure are regularly recorded, with a resulting
decrease in removal efficiency. Flows beyond 45 mgd (170,325 m /day) are
automatically bypassed directly to the Connecticut River.
The primary factor limiting the treatment capacity of the existing plant
is the sludge disposal system. The digestion process is impeded when
large volumes of sludge are fed to the digesters. Also, one unit must be
dewatered each year for grit removal. As a result of the digesters in-
ability to handle the present sludge volumes, approximately half of the
settled sludge is now bypassed directly to the elutriation tanks. There
the two sludge streams, digested and raw, are mixed prior to vacuum fil-
tration.
The computer model representation of the existing system further stressed
the inadequacy of the present removals.39 On the basis of the model, it
was estimated that only 48 percent of the BOD is removed by the existing
facility. The theoretical addition of 2.56 pounds of refuse per capita
per day (1.15 Kg/cap/day) would obviously aggravate the present plant
limitations even further.
32
-------
BAR SCREEN
/? , GRIT «r78!™
// CHAMBER W
SCREENINGS
GRlf
BY-
PASS
PRIMARY CONNECTICUT
CLARIFIER
1
i
i
(
i
SLUDGE PUMPS
JFIRST STAGE DIGESTER
JSECdND STAGE DIGESTER
i
. ELUTRIATION
VACl
FILT
i
JUM
ER
TRUCK HAUL
. ^
RIVER
LANDFILL
f\
Figure 5: Existing Process Configuration at the Springfield Wastewater Treatment Plant
-------
Proposed Sewage Treatment Plant
In light of the inadequacy of the present plant, the city of Springfield
has contracted for development of a new treatment facility. The plan
calls for abandonment of the Indian Orchard facility, and construction of
a new plant at the Bondi Island site. This new plant would provide sec-
ondary treatment for all the present participant towns and, in addition,
would include the.town of Ludlow and the industrial flow from the Monsanto
Chemical Company. The rates of flow and strengths of wastewater projected
for each contributor for the design year (1990) are listed in Table 3.
The plant as designed will consist of bar screens, grit separation units
(cyclones), primary settling tanks, aeration tanks, flocculation tanks,
final settling and chlorination facilities. Pumping units will be pro-
vided to discharge the plant effluent into the Connecticut River during
flood seasons. The sludge handling facilities will include gravity
thickeners for primary sludge, flotation thickeners for waste activated
sludge, holding tanks for both primary and waste activated sludge, and
wet oxidation facilities to sterilize arid reduce sludge volumes and thus
the size of the vacuum filters. A process schematic of the proposed
64.1 mgd (264,618 m3/day) waste treatment plant is shown in Figure 6.
Table 3: Estimated Rates of Flow and Strengths of
Wastewater From All Contributors
City
Ludlow
Monsanto
Indian Orchard
East Longmeadow
Springfield
West Springfield
Agawam
Flow,
Average
2.7
8.8
• 3.5
2.3
31.7
9.0
6.1
,a
mgd
Peak
8.2
19.1
15.7
7.4
91.7
16.9
15.4
BOD .
lbs/day°
4,500
48,500
7,300
3,400
45,700
11,300
11,800
s.s. 1
Ibs/day
3,380
23,500
5,850
4,400
44,500
16,200
14,500
TOTAL 64.1 174.1 132,500 112,330
Smgd x 3,785 = m3/day
blbs/day x .454 = Kg/day
34
-------
BAR SCREEN
en
SKIMMINGS
_C
PRIMARY
CLARIFIER
POLYMERS OR ALUM
SLUDGE
PUMPS
AERATORS
CYCLONE
CLARIFIERS
SLUDGE RETURN
AIR
FLOAT-
ATION
GRAVITY THICKENER
a HOLDING TANKS
COMMINUTER
^SLUDGE PUMPS
CHLORINE CONTACT CHAMBER
TO
CONNECTICUT
HOLDING TANKS
COMMINUTER
SLUDGE PUMPS
BY-PASS
RIVER
TRUCK HAUL LANDFILL
I
Figure 6: Planned Process Configuration at the Springfield Treatment Plant.
-------
Generation of Input Parameters
In order to estimate what effect the inclusion of ground refuse would have
on the proposed plant's performance, it is necessary first to model the
plant as it is presently envisioned*2 and then to adjust the input quality
parameters to reflect the additional load occasioned by 1.79 pounds of
ground refuse per capita per day (0.81 Kg/cap/day).
As noted previously, there is a critical lack of information on the char-
acter of ground refuse in sewage. For this reason, figures dealing with
the physical and chemical characteristics of ground refuse in sewage must
necessarily be best estimates based on the limited information which does
presently exist. Because of the large amounts of solids and floatables
present in sewage containing ground refuse, and the subsequent problems
these solids cause in laboratory analyses, all past tests have been per-
formed on primary effluents. In the Metcalf and Eddy study,43 ground
refuse was added to Boston sewage in varying concentrations ranging from
0.25 percent to 1.0 percent based on a per capita daily wastewater genera-
tion of 100 gpcd (378.5 Jl/cap/day). In Springfield, records show that
about 140 gallons (530 litres) of sewage are generated per person per day.
Thus, at a refuse generation rate of 1.79 Ib/cap/day (0.81 Kg/cap/day)
the loading on the treatment plant will average only about .2 percent by
weight.
In order to estimate the quality parameters associated with a refuse-
sewage stream of this strength, it is necessary to estimate the nature of
the primary effluent and then to work back, using a solids balance to
obtain reasonable values for the influent flow. Following this procedure,
estimated concentrations associated with a 1.79 Ib/cap/day (0.81 Kg/cap/
day) loading in the Springfield sewerage system were developed. These
concentrations, along with those of the sewage flow, are listed in Table
4. The 1.79 Ib/cap/day is based on the assumption that of the total 2.56
Ib/cap/day generation rate, 10 percent by weight is nongrindable and 20
percent by weight is moisture. In the following analysis, therefore, the
Ib/cap/day figures used are on a dry weight basis.
Effects of Refuse on the Proposed Bondi Island Plant
The imposition of ground domestic refuse on the proposed Bondi Island
Treatment Plant would affect some processes to a greater degree than
others. It was our intent, through the computer model, to highlight
those plant functions which would be most severely limited. Once these
problem areas have been designated, it is then possible, again with the
help of computer simulations, to try various alternative schemes in order
to obtain the best quality effluent at the least possible cost.
As might be expected, the increased concentrations of solids and BOD will
greatly influence the sizing of many plant components, especially sludge
handling processes. It is estimated that a loading of 1.79 pounds of
36
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Table 4: Present and Projected Waste Concentrations
mg/l,
Present With
Parameter Sewage .2% Refuse
Solid Organic Carbon
Solid Nonbiodegradable Carbon
Solid Organic Nitrogen
Solid Organic Phosphorus
Solid Fixed Matter
Solid BOD CSBOD)
Volatile Suspended Solids
Total Suspended Solids (TSS)
Gross Suspended Solids (GSS)
Normal Suspended Solids (NSS)
Heat, BTU/gallon
Grit CGRIT)
Dissolved Organic Carbon
Dissolved Nonbiodegradable Carbon
Dissolved Nitrogen
Dissolved Phosphorus
Dissolved Fixed Matter
Alkalinity, mg/5, as CaCQ^
Dissolved BOD
Dissolved Organic Matter
105.0
30.0
10.0
2.0
73.0
93.0
91.0
164.0
0.0
154.0
616.0
10.0
43.0
19.0
11.0
5.5
259.0
92.0
40.0
160.0
181.0
60.0
12.0
4.0
473.0
113.0
1,041.0
1,514.0
525.0
699.0
5,692.14
290.0
73.0
20.0
20.0
8.25
500.0
250.0
115.0
320.0
ground refuse per capita per day (0.81 Kg/cap/day) will result in an
average total solids concentration of 1,514 mg/H entering the plant. This
figure is roughly ten times the present loading. A great portion of these
added solids will be in the form of grit from ground glass (290.0 mg/£),
and gross solids from packaging and the like (525.0 mg/fc). The quantities
of these two constituents place particular constraints on the design and
operation of the grit handling facility. The proposed plant will feed all
the primary sludge, including the grit, to a cyclone separator. Although
this scheme should provide adequate removal for all projected grit quanti-
ties resulting from sewage alone, the greatly increased concentrations ex-
pected as the result of ground refuse addition could cause numerous prob-
lems with clogging and inefficient grit separation. Rather than increase
the capacity of the cyclone separators, a cheaper and more efficient solu-
tion was found to incorporate a conventional aerated grit chamber and grit
washer prior to primary settling. Such a modification will have the ef-
fect of removing grit prior to primary sludge pumping, and should provide
a more effective operation under the changed conditions anticipated with
ground refuse additions.
37
-------
As presently envisioned, the proposed plant will utilize two separate
sludge thickeners. Primary sludge will flow from the cyclone separator
directly to a series of gravity thickeners. Waste activated sludge, on
the other hand, will be thickened to about 4 percent solids by use of
six air flotation units. There are holding tanks for each stream of
thickened sludge prior to mixing and injection into the wet air oxidation
unit. The ratio by weight of dry solids of primary to waste activated
sludge in a conventional wastewater treatment plant handling the sewage
alone is about 1.2:1, or even 0.5:1. By comparison, the ratio which
could be expected by adding 1.79 lb/cap/day (0.81 Kg/cap/day) ground ref-
use soars to about 12:1, primary sludge to secondary. At such high ra-
tios, the cost-effectiveness of two separate thickening processes would
appear questionable. Because the waste activated sludge portion is so
small, it can be mixed with the primary sludge and then thickened together
with little loss of efficiency, but at great cost savings.45 Therefore,
should a wet system of refuse disposal be initiated, it would be more
economic to thicken both sludge streams together in a gravity thickener.
This is confirmed by the cost analyses presented below.
The wet-air oxidation process operates under the principle that organic
substances may be oxidized under high pressures at elevated temperatures
with the sludge in a liquid state by feeding compressed air into the
pressure vessel. The process was developed in Norway for pulp-mill
Wastes, but has been revised for the oxidation of raw sewage sludge,
pumped directly from the primary settling tank or thickener. Combustion
is not complete. For the Springfield plant, a low pressure oxidation
unit has been specified. Performance characteristics of such a unit in-
clude a 15 percent reduction of Chemical Oxygen Demand (COD) and a 30
percent destruction of the insoluble volatile matter. The end product
of the process is a sterile dewaterable and oxidized liquid mass. As a
result of the rather low degree of oxidation and the destruction of the
volatile solids, a good portion of the solid COD is converted to dis-
solved COD and returned with the supernatant from the vacuum filter to the
head of the plant. For normal sewage this additional COD loading is not
significant, but when ground refuse has been added to the sludge stream,
the COD of the supernatant can be expected to be of such large magnitude
as to severely affect the aeration processes to which the vacuum filter
supernatant is returned.
This would not be as serious a problem if anaerobic digesters were used
since the digesters convert organic acids to methane gas and carbon dir
oxide, and thus remove a great deal of the COD from the return stream.
As noted by Kos et al.,4" there is sufficient evidence to show that
ground refuse can be satisfactorily digested with sewage sludge. More-
over, contingent on a favorable local market, this technique can provide
a valuable commodity through methane gas production. For these reasons,
we would recommend that should ground refuse be added to the sewage stream
at Bondi Island, anaerobic digesters would provide a better solution than
wet-air oxidation. However, if the methane gas would yield less than
$0.80/1000 cu ft, our detailed studies on sludge handling show that the
digester should be omitted, with the thickener underflow fed directly to
holding tanks and vacuum filters. '
38
-------
In addition to those processes already mentioned, many other plant func-
tions would need to be enlarged to handle the additional load; foremost
among these are the sludge holding tanks, sludge pumps, thickeners and
the aeration basins.
The computer analyses indicate that as a result of ground refuse additions
dissolved BOD loadings into the aerator will increase threefold and solid
BOD would increase by a factor of 1.2. Total solids to the aerator would
increase by a factor of about 4.5. In order to achieve the same degree
of BOD removal as the proposed plant with just sewage, the aeration basin
would need to be substantially enlarged. This seems in sharp contrast to
the primary settler, which would not need to be enlarged. The reasons
for this apparent discrepancy is that using existing settling curves, the
great majority of solids added by the ground refuse would either float to
the surface or settle easily within the alotted detention period. This
fact is further detailed by comparing solids concentrations in primary and
secondary sludge stream. With ground refuse added, the total solids in
the primary sludge stream increases elevenfold over that expected from
just sewage. On the other hand, the solids in the waste activated sludge
stream remain virtually the same for both cases.
This increase in primary sludge solids will affect the sizing of all sub-
sequent sludge handling processes. Accordingly, there will be increased
capacity and cost associated with the sludge pumps, sludge holding tanks,
thickeners, digesters and vacuum filters. Specifics regarding these pro-
cesses, including landfill requirements, are discussed in detail in the
separate report on sludge handling and disposal.48
Figure 7 shows the computer model representation of the recommended plant;
the notation and abbreviations are detailed in Meier and Fisette.24 We
have indicated that a microscreen would be used just prior to chlorination.
The effect of the screen would be to compensate for seasonal variations
and to polish the effluent by removing many of the trace solids (cellulose)
which might remain. The result is that the plant as a whole will remove
92 percent of the BOD from the refuse-sewage mixture and will provide an
effluent which is at least as good as that forecast for the proposed plant
with sewage alone.
In addition to these quality parameters outlined in Table 4, there remain
a number of variables associated with ground refuse in sewage about which
we have little or no knowledge. These include possible effects connected
with grease and oil, toxic materials and heavy metals. It is important
that a complete investigation into the nature of ground domestic refuse
in sewage be conducted in order that effects on the various treatment
processes associated with these additional parameters might be fully ad-
dressed in the preliminary phase of our investigations.
Seasonal Variations. As detailed in Section III of this report, one can
expect substantial seasonal variations in both the character and quanti-
ties of refuse generated. Just as these variations affect present
39
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BSCRNI GRIT
COMM
PRSET SKIM
AEMFS SPLIT
21
MICRO CHLOft
15
27
34
29
33
MI)T 33
ABBREVIATIONS ARE
EXPLAINED IN Mcitr a Flscttt, op. cit.
MIX SHAUL LANDF
Figure 7: Computer Model Representation of the Recommended Treatment Process Configuration
for Ground Refuse
-------
disposal techniques, they would also affect treatment plant operation
should these peaks be ground into the sewers.
Table 5 shows the expected seasonal variations in influent quality para-
meters, given that the fractions of each refuse category ground remain
constant throughout the year.50 Clearly, the peak seasonal load would
be expected in the fall.
Table 5r Seasonal Variations Due to Ground Refuse Addition
*
Parameter
SBOD, ppm
VSS, ppm
TSS, ppm
DBOD, ppm
GRIT, ppm
GSS, ppm
NSS, ppm
Summer
112.25
1002.80
1450.00
112.12
267.50
518.17
665.85
Fall
118.92
1354.00
1850.00
133.00
277.45
628.84
944.69
Winter
108.32
794.97
1213.50
100.26
260.36
464.94
491.73
Spring
112.95
1012.05
1542.30
114.58
354.76
488.65
692 .-73
Annual
Average
113
1041
1514
115
290
525
699
*See Table 4 for abbreviations.
In order to evaluate the effect such a seasonal peak would have on the
treatment plant operation, the computer model was run first with input
parameters representative of fall alone, and then with the average values
for summer, winter and spring. The results of this analysis indicate
that some additional capacity would be needed to handle the increased
sludge volumes, but that the major impact would be on secondary treatment
facilities. It is estimated that the fall seasonal loading would result
in a 44 percent increase in total solids and 20 percent increase in BOD
entering the aeration basin. These increased concentrations would there-
fore require either increased aerator capacity or subsequent microscreen-
ing to provide equivalent removal efficiency. Microscreening affords the
cheaper of the two alternatives ($2,000,000 as against $3,000,000 to in-
crease the size of the aerator) and thus is included in our recommended
treatment scheme.
Cost Analysis
As mentioned previously, the intent of this analysis is to provide a
treatment scheme which could handle the higher concentrations of pollu-
tants occasioned by ground domestic refuse, and yet not jeopardize the C
classification of the Connecticut River at Bondi Island. The costs
associated with such a proposal are necessarily a prime consideration in
determining the feasibility of the wet systems concept.
41
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According to the construction specifications of Springfield's consult-
ants,51 the Bondi Island plant will require a capital investment of
$36,865,000. Our computer analysis provides a somewhat lower figure of
$34,460,912. One reason for this discrepancy is that the computer pro-
gram relies on national construction cost averaged to predict individual
plant costs, yet at the present time Naw England costs exceed the na-
tional average. Also, in the case of particular plant operations, the
two cost figures may not describe identical processes. For example, the
consultant's specification of sludge conditioning and filtration costs
may include more than just wet air oxidation and vacuum filtration, which
the computer uses to establish its cost figure. Moreover, it would be
unreasonable to expect a program that is focussed on preliminary design
to yield identical results with those of the final construction specifi-
cations. Table 6 provides a breakdown of the capital expenditure required
for analysis. Using an interest rate of 6 percent and a 25 year amortiza-
tion period, the capital cost would range between 11.50^/1000 gallons
(3^/1000 fc) and 12.25^/1000 gallons (3.25*/1000 £). Operation and main-
tenance costs are projected to be 5.8^/1000 gallons (1.5^/1000 &), such
that the total cost of treatment would be 17.3 to 18.05^/1000 gallons
(4.6 to 4.7^/1000 A) of sewage treated.
If the individual plant processes were to be kept as presently planned,
but enlarged to handle ground refuse, the total treatment cost of these
same facilities is estimated at 30.64{/1000 gallons (8.04^/1000 £), or
slightly less than twice the projected present cost for sewage alone.
But, as mentioned previously, the introduction of ground domestic refuse
would require modification of a number of plant processes, particularly
those dealing with sludge handling, in order to avoid problems of clog-
ging and inefficient operation. Therefore, it is more instructive to
compare existing costs for sewage alone with those associated with the
recommended wet systems treatment scheme.
The initial capital cost of this modified treatment facility (Figure 70
is estimated at $49.4 million. Operation and maintenance would run in
the neighborhood of 7^/1000 gallons (1.85f'/1000 &), such that the total
treatment cost would be only 23^/1000 gallons (6^/1000 £) or just more
than 1.3 times the projected cost for sewage alone. The major cost
savings would result from the replacement of the wet air oxidation unit
with a conventional anaerobic digestion system. There was no provision
in the cost analysis for income derived from methane gas production.
Additionally, the computer model of the recommended treatment stream was
run to simulate equivalent removal efficiency for a .4 percent by weight
mixture of ground refuse in sewage, corresponding to a doubling in refuse
generation rate to 3.58 Ibs/cap/day (1.62 Kg/cap/day). Despite this in-
crease, economies of scale results in an estimated cost increase of only
30 percent, up to 29.9^/1000 gallons (8.0^/1000 A), -A summary of the
cost data for treatment of ground refuse in sewage is provided in Table 7.
42
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Table 6: Treatment Costs for Sewage Alone;
Planned Bondi Island Treatment Plant
Item
Consultant's
Estimated
Project Cost
Computer
Estimated
Project Cost
Grit and screenings
Primary settling tanks
Secondary treatment
facilities
Sludge pumping
Sludge conditioning and
filtration
Sludge thickening
Chlorination
•
Electrical and
Instrumentation
Yard piping
Site preparation
Land acquisition and fees
TOTAL CAPITAL COST
$ 520,000
4,160,000
12,630,000
650,000
5,980,000
840,000
1,250,000
3,250,000
2,600,000
4,290,000
695,000
$36,865,000
$ 127,270
4,076,472
11,177,441
352,833
4,823,516
2,175,906
890,763
3,250,000*
2,600,000*
4,290,000*
696,711
$34,460,912
$/1000 gallons
TOTAL AMORTIZATION COST
TOTAL 0 § M COST
TOTAL TREATMENT COST
12.25
5.8
18.05
11.50
5.8
17.3
Reproduced consultant's figures.
43
-------
Table 7: Treatment Costs for Sewage Containing
Ground Domestic Refuse
Item
Grit 5 screenings
Primary settling
tanks
Secondary treatment
facilities
Sludge pumping
Sludge conditioning
$ filtration
Sludge thickening
Chlorination
Microscreen
Electrical and
Instrumentation
Yard piping
Site preparation
Land acquisition
and fees
TOTAL CAPITAL COST
Proposed
Plant
.2% Refuse
$ 128,225
4,140,375
16,906.792
551,872
13,542,624
4,190,909
889,166
4,991,556
3,993,245
6,588,854
695,989
$56,619,607
Recommended
Plant
.2% Refuse
$ 72,951
3,972,556
15,764,124
885,936
7,876,073
1,356,862
828,845
2,388,640
4,991,556
3,993,245
6,588,854
696,221
$49,415,863
Recommended
Plant
.4% Refuse
$ 84,026
3,953,085
20,940,392
1,159,230
13,951,909
2,216,045
812,324
2,017-, 394
5,557.500
4,446,000
7,335,900
693,835
$63,167,640
i/lOOQ gallons
TOTAL AMORTIZATION
COST
TOTAL 0 5 M COST
TOTAL TREATMENT COST
18.84
11.80
30.64
16.0
6.60
23.0
21.10
8.80
29.90
44
-------
Conclusions
Our results for the cost of treatment of ground refuse-sewage mixtures
are at first glance at considerable variance to those of Metcalf § Eddy.52
If one excludes land acquisition and site preparation, our calculations
show an increase in capital cost from $31.91 million to $42.63 million,
or by a factor of 1.33; whereas Metcalf § Eddy anticipated an increase
from $1.6 million to $4.1 million, or by a factor of 2.5
There are several explanations for this discrepancy.. First, the Metcalf
§ Eddy estimates are for a facility of 1 mgd (3,785 m3/day) whereas our
estimates are for a 64 mgd (242,240 m3/day) facility. Second, the Metcalf
§ Eddy estimate was based on a refuse concentration of 0.5 percent by
weight. Indeed, our calculation for an 0.4 percent by weight addition of
refuse, corresponding to a 4.5 Ib/cap/day (2.04 Kg/cap/day) generation
rate, shows an increase of 1.72, which approaches the Metcalf § Eddy
figure.
The approach taken in our analyses might perhaps be questioned on the
basis that the use of design relationships based on sewage inputs are
not necessarily valid for ground refuse additions. Whilst conceding that
this may well be so, we have at least used a rational quantitative basis
for our inferences and cost estimates, which, surely, must be preferable
to intuitive qualitative judgments.
45
-------
SECTION VIII
SLUDGE HANDLING*
Introduction
Although the treatment plant simulations described in the previous sec-
tion were judged adequate to determine overall treatment costs, a more
detailed investigation into sludge handling was deemed necessary, because
the unit operation routines in the treatment plant simulation model were
operating at solids concentrations in excess of their original design.
Perhaps the most important specific goal of the detailed study was to
establish the unit cost of sludge processing and disposal. The cost of
collection and disposal of residential refuse under existing management
concepts lies in the range of $20 to $60 per ton; consequently, if the
cost of just the sludge handling in a wet system is also $20 to $60 per
ton (of dry solids), as would be expected on the basis of existing prac-
tice at sewage treatment plants, then the economic feasibility of the wet
systems concept is questionable, even given that the transformation of
solid waste to sludge solids is not 1 to 1.
It should be noted, however, that our efforts should be interpreted as
only a preliminary effort to analyze a very complex problem, arid will
need to be extended considerably before even a pilot scale demonstration
facility is contemplated. The major constraint limiting both the scope
of the analysis and its accuracy was the exceptionally limited experi-
mental evidence available to us. However, we are conficent that our pre-
dictions of total costs are entirely adequate for the primary- purpose of
the contract which is to establish the order of magnitude of cost for
the wet systems concept as a whole, even if we have not been able to
address the myriad of operational complexities in sufficient detail to
make definitive judgments on process selection and operation.
Sludge Quantities
The major factor affecting the quantity of sludge produced at a treatment
facility handling ground refuse is. the per capita refuse generation rate.
Other factors to be considered include sedimentation efficiency, the con-
version of dissolved organic matter to settleable biomass and the per
capita generation of sewage spiffs. In the case of an average raw refuse
generation rate of 2.25 Ib/cap/day (1.02 Kg/cap/day), the addition of
ground refuse to the sewage will result in about a fifteenfold increase
in the quantity of primary sludge. On the other hand, because of a very
small increase in the BOD in the primary settler effluent due to the
ground-refuse, the volume and dry solids content of the waste activated
o
Sludge Processing and Disposal is the subject of a separate report
by Kos, Joyce and Meier, (Ref. 21).
46
-------
sludge will change much less. Under the same condition (2 25 Ib/cap/day
of raw refuse) there will be only a 45 percent increase of the quantity
of waste-activated sludge, which is still in the range of variation ex-
hibited by existing sewage treatment plants. The quantity and the con-
centration of the mixture of primary and waste-activated sludge is there-
fore affected primarily by variations in the primary sludge. The amount
of dry solids of the sludge mixture of primary and waste-activated sludge
in tons per year, as a function of population and refuse generation rate,
is shown on Figure 8. The report by Kos et al.21, should be consulted for
the derivation of these assertions.
In order to dramatize the impact of the ground refuse upon the sludge
handling, quantity-concentration flow diagrams of a conventional sewage
treatment plant and a^sewage treatment plant handling ground refuse in
addition to sewage were constructed. Assuming a sewage generation rate
of 100 gal/cap/day (378.5 J$cap/day), Figure 9 shows the consequent flows
(in the percentages of the incoming sewage) and their solids concentrations,
Similarly, Figure 10 shows the flow diagram of a treatment plant handling
100 gal/cap/day of sewage plus 2.25 Ib/cap/day of ground refuse.
Comparison of these diagrams reveals the magnitude of the impact of ground
refuse additions. For example, the volumetric flow rate of vacuum filter
cake shows an increase from 0.04 to 0.34 percent of the influent volume.
This implies that at a 10 mgd (37,850 cu m/day) facility, the filter cake
would increase from 4,000 to 34,000 gal/day (15,140 to 128,690 Vday).
For the total raw refuse generation rates of 1.0, 2.25, or 4.5 Ib/cap/day
(0.454, 1.02, or 2.04 Kg/cap/day), a 2.5, 4.3 and 7.8-fold increase of
sludge quantities must be expected. Using a dry solids basis (which is
unaffected by concentration variations of the sludge) rather than a
volumetric measure, the introduction of ground refuse into the sewage
under the same conditions as above will result in the 4.7, 9.3 and 17.5-
fold increase of dry sludge solids, respectively. Note that the dif-
ference between the volumetric and dry solids increases are due to the
increase in concentration of the primary-secondary mixture. In summary,
the sludge handling facilities of a sewage treatment plant handling an
average 2.25 Ib/cap/day (1..02 Kg/cap/day) of ground refuse will correspond
to a conventional treatment plant handling a population that is approxi-
mately nine times larger.
Sludge Quality
Information on the quality parameters of ground refuse sludges is very
limited, consisting of studies conducted by Metcalf & Eddy as part of
the original Foster-Miller work, and isolated information from a few
"studies whose focus was energy production from solid waste. In particuT-
lar, there appear to be no measurements of quantitative sludge parameters
such as coefficient of compressibility or specific resistance, both of
obvious importance to assessments of dewatering characteristics. This is
an area that is in urgent need of more detailed investigation if the wet
systems concept is to be further pursued.
47
-------
7 -r
6 • •
5 • •
4 • •
CO
u.
o
§
o
2 •
500,000
POPULATION
1,000,000
Figure 8: Dry Sludge Solids as a Function of Population Size and Refuse
Generation
48
-------
PRIMARY
CLARIFIER
AERATION TANK
SECONDARY
CLARIFIER
o
H
CM
M
Q«I0049%
C*
0" -89%
C»
0*140%
C*30OOppm
0>
c«
0« 40%
C* 10,000 99m
THICKENER
DIOESTER
VACUUM FILTER
TRUCK HAUL
LANDFILL
DISPOSAL
Figure 9: Flow Diagram'of Sewage Treatment Plant Handling 100 gal/cap/day
-------
PRIMARY
CLARIFIER
AERATION TANK
SECONDARY
CLARIFER
in
o
0=100%
C= I860 ppm
Q»40%
C= lO,OOOppm
0 = 99.66%
C=40ppm
Q=.34%
C=25.%
THICKENER
DIGESTER
VACUUM
FILTER
TRUCK HAUL
t=l
LANDFILL
DISPOSAL
Figure 10: Flow Diagram of Sewage Treatment Plant Handling 100 gal/cap/day plus 2.25 Ib/cap/day
-------
Raw Sludge. Metcalf § Eddy53 found that 1-hour settling of ground refuse
in sewage produced a sludge of about 5 percent solids content Much of
the suspended solids, consisting mainly of paper products, did not settle
or only very slowly. However, the dewatering characeristics of this pri-'
mary sludge (including the floatables) appeared to be good. Metcalf §
Eddy tested three devices for dewatering the primary sludge produced by
adding ground refuse to sewage, although tap water rather than sewage
was used in these laboratory tests: a Smith and Loveless sludge concen-
trator, a Komline-Sanderson vacuum filter, and a Bird centrifuge. All
three devices worked well, and neither the vacuum filter nor the centri-
fuge required addition of chemicals. For all three methods tested, they
obtained a sludge cake of at least 25 percent solids content. The yield
of a vacuum filter was at least 8 pounds per square foot per hour (39.06
Kgs/sq.m/hr), and Metcalf § Eddy judged that it could serve as the only
dewatering unit.
The specific resistance and coefficient of compressibility of sludge are
quantitative measures of its dewatering characteristics, but unfortunately
Metcalf § Eddy did not evaluate them, and these are as yet unknown for
the sludges obtained when ground refuse is added to sewage. The vacuum
filtration yield reported by Metcalf and Eddy is in the range of expected
yields of chemically conditioned primary sludge, and therefore the de-
Watering characteristics of primary sludge of a sewage treatment plant
handling ground refuse will be considered to be the same as those of
chemically conditioned primary sludges. This assumption is not unrea-
sonable in the light of some recent experiments at the University of
Texas by Garden and Malina on the efficacy of pulped newsprint as a
sludge conditioner. Pulp additions of about 100 to 125 percent of the
weight of sludge solids were found to reduce the specific resistance of
activated sludge to levels comparable to the optimal levels attained with
ferric chloride or cationic polymers. It was noted that the conditioning
effect of the newspaper pulp increased as the solids content of the,
activated sludge increased, and it was concluded that the chemical condi-
tioners could be replaced by the paper pulp with essentially similar re-
sults. This means that we might expect paper fiber in the primary sludge
to act as a conditioner for the activated sludge fraction.
There is no information on the thickening of the sludge that would be
generated in a sewage treatment plant handling refuse, On the basis of
the apparent similarity between filtration characteristics of the primary
sludge at sewage treatment plants handling ground refuse and between
ordinary chemically conditioned primary sludge, the thickening of these
two kinds of sludges may also be assumed to be similar.
The remaining problem is the effect of adding a small portion of secondary
treatment sludge upon the character of primary sludge. It is usually re-
ported that the specific resistance or vacuum filter yield is less than
for the mixture of primary and activated sludges than for primary sludge
alone. On thecbasis of the laboratory thickening experiments, Konicek
Kos and Pardus55 found, however, that the addition of activated sludge to
51
-------
primary sludge in the ratio occurring in a conventional secondary treat-
ment plant had little significant effect on the thickening of primary
sludge.
In light of these facts and because of the very high ratio of primary to
waste-activated sludge at the treatment plant handling refuse, the addi-
tion of waste-activated sludge to the primary sludge will most likely .have
little or no effect upon the thickening and filtration characteristics of
the primary sludge. Consequently, the characteristics observed for pri-
mary sludge by Metcalf § Eddy may be assumed to hold also for the primary-
secondary mixture.
Digested Sludge. Pfeffer, who used the filter-leaf technique, found that
the residue from digestion of refuse-sewage sludge dewatered very easily,
without addition of conditioners.56 This is in contradiction to the
findings of Wise,57 who found that the digester residue dewatered only
with difficulty. However, the reactor solids concentrations used by Wise
were below 2 percent, whereas Pfeffer's were generally above 6 percent.
In the absence of a comprehensive study of the residue after digestion
of refuse-sewage sludges, we must assume that the quality of the digested
refuse-sewage sludges will be the same as that of the ordinary digested
sludge. Although it is recognized that this assumption is subject to
question, it is unavoidable in the absence of any actual data. But inso-
far as this asssumtion does imply a need for chemical conditioner addi-
tions prior to dewatering, it is probably conservative.
Analysis
As in the case of treatment, mathematical modelling and simulation was
chosen as the method by which the answers to some of the questions re-
lating to cost would be examined. In order to keep the simulation efforts
within reasonable time and cost limits, four likely process configurations
were selected in advance, all purposely involving only traditional tech-
nologies. This was justified on the basis that cost functions for many
of the newer processes such as wet oxidation or pyrolysis are not pre-
sently available in the absence of a sufficiently widespread practical
experience. But more importantly, perhaps, is the inability to make pre-
dictions of process performance. Whilst it is relatively easy to predict
the consequences of ground refuse addition to, say, thickening or vacuum
filtration, in the absence of even laboratory data, similar predictions
for the more sophisticated technologies would be quite speculative. In-
deed, we are already at the limit of reasonable prediction by including
digestion as one of the alternatives.
This is in no way to imply that these technologies are inferior or even
more expensive than the traditional ones to which we have addressed our
detailed analysis. Rather, our goal is to establish a reasonably accurate
picture of the costs involved in the handling and disposal of ground ref-
use sludges, in order that the economics of the entire wet systems concept
can be established.
52
-------
Considerations in the Selection of Alternative Process Configurating
Because of the dramatic increase in the ratio of primary to secondary'
sludge at a facility accepting ground refuse, it was earlier concluded
that the addition of secondary sludge to the very much larger quantity of
primary sludge would not alter the latter's physical-chemical characteris-
tics. Consequently, separate treatment of these sludges does not appear
reasonable. Many new treatment plants provide different treatment pro-
cesses for primary and secondary sludge streams; as noted in an earlier
chapter, the planned additions to the treatment facilities in the Springfield
area will use air floatation thickening for the waste-activated sludge
and gravity thickening for the primary. It is questionable whether such
a configuration would be beneficial for handling ground refuse sludges,
especially from the viewpoint of scale economies. Therefore, the initial
operation for all process configurations is a mixing of the two sludge
streams.
Because activated sludge is currently the most widespread secondary treat-
ment method, we restricted our focus to that particular source of second-
ary sludge. The assumption of a 1 percent solids concentration of the
waste activated sludge may well be questioned, but in view of the wide
diversity of concentrations encountered in practice, and the fact that
the much higher primary to secondary sludge ratio tends to make subsequent
computations relatively insensitive to the assumed secondary concentration,
the 1 percent figure does not appear unreasonable.
The impact of the addition of advanced waste treatment processes to a
secondary treatment plant must doubtless be considered in the very near
future. And while the sludge production varies considerably with the
process selected, there is as yet insufficient information upon which to
base a rational choice of advanced waste treatment at a plant handling
ground refuse. Consequently, we may rationalize our omission of advanced
treatment sludges not only on the basis that the quantity involved would
be small in comparison to that from the ground refuse (that will settle
as primary sludge), but also that the uncertainties involved are still
too great for the selection of any one process to have real meaning.
Three of the process configurations chosen for study are illustrated on
Figures 11, 12, and 13. The fourth configuration, including both anaero-
bic digestion and incineration was also examined, but was found to be
quite uneconomic.
Model Representation and Cost Functions. Mathematical models for all of
the unit operations considered were constructed for inclusion into the
computer simulation model. Most of the cost functions built into the
individual unit operation models were from the study conducted for EPA
by Black § Veatch,58 whereas the design relationships were taken from a
variety of published sources or derived by the writers. Details of the
model representations for each of the unit operations considered can be
found in Chapter III of Kos
53
-------
ALTERNATIVE I
in
CO
K
i
FILTRATE
GRAVITY
THICKENER
SLUDGE
HOLDING
TANK
VACUUM
FILTER
TRUCK
HAUL
LANDFILL
DISPOSAL
Figure 11: Sludge Handling, Alternative 1
-------
ALTERNATIVE 2
tn
tn
GRAVITY
THICKENER
DIGESTER
SLUDGE
HOLDING
TANK
VACUUM
FILTER
TRUCK
HAUL
LANDFILL
DISPOSAL
Figure 12: Sludge Handling, Alternative 2
-------
tn
I
oc
a:
a.
ALTERNATIVE 3
bJ
(9
O
in
O
UJ
I
UJ
FILTRATE
GRAVITY
THICKENER
SLUDGE
HOLDING
TANK
VACUUM
FILTER
INCINERATOR
INCINERATOR
RESIDUE
DISPOSAL
Figure 13: Sludge Handling, Alternative 3
-------
The simulation model was then run for each process configuration under a
wide range of operating parameters, sludge solids concentrations size of
facility, input solids generation rates, and the details of the results
plotted and analyzed in detail in Chapter IV of Kos et al.21
Comparison of Alternative Process Configurations. The costs of the three
feasible process configurations are summarized on Figure 14. Alternative
1, involving thickening, vacuum filtration and land disposal, is the indi-
cated choice, with a cost of between $10 - $15 per ton ($11.02 - $16.53
per Kkg) of dry solids for facilities serving in excess of 100,000 popu-
lation. If a digester is added (Alternative 2), total costs will be about
$5/ton ($5.51/Kkg) dry solids higher, an increase that is almost offset
by the value of the digester gas produced. Under the assumed conditions
of a landfill at 10 miles (16 km) distance, incineration as a means of
disposal (Alternative 3) is shown to be another $4/ton ($4.41/Kkg) more
expensive. Digestion together with incineration was dismissed as an
economically infeasible alternative.
Tables 8, 9, and 10 summarize the costs of these three alternatives as a
function of population size and per capita refuse generation rate, with
an indication of the corresponding cost for a facility treating only
sewage sludge. It is quite evident that the unit cost of handling sludge
at a facility handling ground refuse is substantially lower than if only
sewage sludge were handled. This is due to the economies of scale re-
sulting from larger absolute quantities involved, and the very different
physical nature of the sludge to be dewatered and disposed.
Optimal Solids Concentrations. Our analyses show that in those cases
where the total cost is sensitive to solids concentration, such as those
process configurations involving digesters, an optimum appears to lie in
the vicinity of 14 percent solids. If this appears high, as it doubtless
does in comparison to solids concentrations encountered at existing
treatment plants, one should be reminded of the drastically different
nature of the sludge involved. A feed of such a high solids concentration
is essential whenever digesters are used, as the cost of digester capacity
would otherwise be prohibitive. Where digesters are not used, the decrease
of vacuum filtration cost resulting from higher solids concentration is
balanced by the increase in the cost required to thicken the sludge to
the higher concentration, and no optimum solids concentration can be
^identified.
Digestion. Our calculations show that the cost of anaerobic digestion is
somewhat higher than the resultant value of methane produced, and that the
cost of process configurations using landfill for ultimate disposal is
insensitive to whether or not digestion is included, given a methane
value of $0.80 per 1000 cu ft ($28.50/100 cu m). A lesser methane value
would make the use of digesters unlikely, whereas an increased value, or
consideration of the more intangible benefits of increasing energy sup-
plies given the current energy shortages, such as benefits to the balance
of payments, would tend to make digestion more attractive. All this, of
57
-------
70
9
$
oc
Q
O
W
8
60
50-
40
30
20
"VALUE OF DIGESTER GAS
10
500,000
POPULATION
1,000,000
Figure 14: Total Cost of Sludge Handling (Alternative 1, 2 and 3) as a
Function of Population; for Average Refuse Generation Rate of
2.25 Ib/cap/day
58
-------
tn
Table 8; Total Cost of Sludge Handling (Alternative 1) in $/ton Dry Solids for Various Populations
and Various Raw Refuse Generation Rates
Raw Refuse
Generation Rate
Ib/cap/day
0
(Sewage Siudge Only)
0.5
1.0
2.0
2.25
3.0
4.0
POPULATION
10,000
80.75
39.16
30.35
23.92
23.04
21.13
19.51
50,000
41.96
22.79
19.21
16.26
15.99
15.07
14.37
100,000
34.23
19.59
16.72
14.55
14.31
13.66
13.09
250,000
27.68
16.58
14.47
12.97
12.76
12.30
11.93
500,000
23.98
14,95
13.27
12.10
11.95
11.60
11.33
1,000,000
21.03
13.69
12.36
11.47
11.35
11.11
10.92
-------
Table 9: Total Cost of Sludge Handling (Alternative 2) in $/ton Dry Solids for Various Populations
and Various Raw Refuse Generation Rates
Raw Refuse
Generation Rate
lb/cap/day
0
(Sewage Sludge only)
0.5
1.0
2.0
2.25
3.0
4.0
POPULATION
10,000
134.58
56.30
42.71
33.46
32.25
29.64
27,47
50,000
53.94
30.95
26.31
22.93
22.47
21.58
20.70
100,000
43.25
26.52
23.20
20.87
20.54
19.86
19.27
250,000
34.72
22.93
20.68
19.07
18.84
18.36
17.94
500,000
30.57
21.09
19.34
18.07
17.89
17.48
17.09
1,000,000
27.32
19.74
18.31
17.20
17.03
16.61
16.20
-------
Table 10: Total Cost of Sludge Handling (Alternative 3) in $/ton Dry Solids for Various Populations
and Various Raw Refuse Generation Rates
Raw Refuse
Generation Rate
Ib/cap/day
0
(Sewage Sludge only)
0.5
1.0
2.0
2.25
3.0
4.0
POPULATION
10,000
265.74
107.61
77.88
56.89
54.08
48.01
42.92
50,000
87.67
44.47
38.29
31.27
30.30
28.17
26.37
100,000
64.15
37.14
30.99
26.35
25.72
24.37
23,29
250,000
46.28
28.94
25.24
22.75
22.44
22.56
21.80
500,000
37.96
25.30
22.94
21.89
21.64
21.45
21.20
1,000,000
32.36
24.04
22.05
21.26
21.04
20.77
20.64
-------
course, is contingent on the assumption that anaerobic digestion is in
fact feasible, an assumption that is yet to be convincingly demonstrated.
As noted in a recent paper on management aspects of methane production
from solid wastes,59 reliability of supply will play a crucial role in
successful marketing of the recovered energy. But skeptics who cite the
traditional unreliability of sewage treatment plant digesters as a key
argument against digesters might be reminded that sophisticated physical-
chemical sludge treatment methods, such as the wet oxidation processes
currently very much in favor, are surely at least as dependent on trained
and experienced operator personnel as are digesters.
The constraints of this study have not allowed as detailed an investiga-
tion of the trade-offs in digestion as will be necessary if digestion
were to be seriously considered in an actual implementation. In particu-
lar, the physical characteristics of the digesting sludge require identi-
fication if factors such as mixing cost are to be adequately analyzed.
Other areas not fully explored include the impact of climate (which has
a substantial impact on heating costs), the relationship between deten-
tion time and reliability, the impact of recycling the digester super-
natant to the secondary treatment stages, and nutrient addition. A
comprehensive study focussed on a. complete economic model of digesters
would thus be recommended as a segment of further investigations into
sludge handling.
Disposal Method. Of the two disposal methods examined by our studies,
incineration is shown to be preferable to direct landfill disposal only
if the distance to the landfill exceeds 45 miles (72.4 km). The magnitude
of this critical distance, of course, is dependent on many contributory
factors, and would tend to increase as the cost of air pollution control
equipment drives up the cost of incineration, and would tend to decrease
with increased land or unit transportation costs. But, given the politi-
cal realities as they presently exist, it is questionable whether a city
that cannot find a landfill site within its own city limits or with an
immediately adjacent community could ever use a more distant landfill,
regardless of cost. Thus, all that can usefully be concluded in general
terms is that both alternatives are technically feasible, and that their
"cost is of comparable magnitude. Indeed, it would appear that the wet
systems concept offers little significant advantage over conventional
practice with respect to the ultimate disposal problem. And although ad-
vanced technologies such as pyrolysis might offer a solution, such
technologies are not dependent on a wet collection method.
62
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SECTION IX
ENVIRONMENTAL AND SOCIOECONOMIC IMPACTS*
Environmental Impact
The conclusions with respect to environmental impact are necessarily
qualitative, rather than quantitative, and we have not attempted to at-
tach dollar values to the environmental costs and benefits identified
And although the conclusion of the analysis is that the net impact will
probably be beneficial, there are one or two potentially serious impacts
which cannot yet be assessed due to lack of data. Thus, even if accepted
methodologies were available for the dollar measurement of intangible
environmental impacts, inclusion of these dollar values into the engir
neering cost comparisons would be presently quite premature.
One of the difficulties in assessing the environmental impact of the wet
systems concept is the need to assess the totality of environmental quali-
ty. Thus, air quality might improve at the same time that water quality
might diminish, yet there is no accepted way to effect the trade-off in
even qualitative terms. Is one additional unit of BOD in a river worth
the decrease of one unit of particulate emissions? Clearly, such questions
can only be answered by reference to a specific situation and perspective,
and the goals and priorities that govern the evaluation.
Air Quality
Air Pollution from Conventional Practice. There are two major potential
sources of air pollution from conventional refuse collection and disposal
practice: the emissions from collection trucks, significant especially
in the central city, and emissions from incineration or illegal open
burning in dumps.
With respect to emissions from collection trucks, the conditions under
which they must operate make for very unfavorable emission conditions.
Internal combustion engines burn fuel most efficiently at relatively
constant speeds, and the amount of unburned fuel increases sharply when
a motor vehicle is accelerated or decelerated. Emissions of hydrocar-
bons, carbon monoxide and particulates may be 50 to 100 percent greater
for average speeds less than 10 miles per hour (mph) as compared to
30-35 mph, and especially idling, acceleration and deceleration are as-
sociated with high emission levels.
In-central urban areas where distance traveled by collection trucks is
slight compared to time spent, the contribution to urban air pollution
*See Meier, Kuhner, and Bolton, (Ref. 22) Chapters VI, VII and VIII
for detailed discussions.
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from the collection fleet may be in excess of what it would appear to be
if total miles traveled is used as a measure. For example, in the Spring-
field study area, the miles of travel by the 21 collection trucks may be
conservatively estimated at 500 miles by map measurement. For each truck,
the measured distance included length of the assigned route plus allowance
for two trips to the landfill site. Since vehicular travel in Springfield
amounts to over 1.1 million miles per day60 this 500 miles is negligible.
However, considering the substantial time spent idling and the fact that
emissions during idling and speed changes may be greater than cruising
emissions by factors of 2 to 6, the total contribution of the fleet to
automobile air pollution may be on the order of 0.5 percent of the total.
Although neither refuse incineration nor open burning occurs in the Spring
field area, the impact of such practices elsewhere is well recognized.
The costs of municipal refuse incineration are expected by many to
double as enforcement of emission standards becomes widespread,62 and the
impact of open burning was demonstrated all too tragically by the fatali-
ties of a recent multiple car crash on the New Jersey turnpike reportedly
caused by aggravation of fog conditions by smoke from a nearby dump.63
The Impact of Wet Systems on Air Pollution. Introduction of wet systems
disposal for residential refuse would greatly decrease the number of
refuse trucks on the streets. Collection by vehicle could be eliminated
for all but those crews necessary to handle the nongrindable fraction of
the refuse. Estimations discussed previously show that between three
and four pickups per year will be required to handle nongrindables, re-
quiring at most four collection trucks. Assuming identical unit emis-
sion levels would imply that air pollution from collection truck exhausts
would be decreased 75 percent from present levels. A corresponding de-
crease should be experienced in support vehicle travel, such as vehicles
operated by foremen and other supervisory personnel. .On the other hand,
it is expected that bulky item collections, currently involving two crews
a day in Springfield, will require more vehicles for operations in con-
junction with wet systems implementation, perhaps doubling in size.
Wet systems collection would virtually eliminate air pollution from on-
site burning. The availability and ease of disposal of rubbish into the
grinder should drastically decrease the incentive for on-site burning,
making the enforcement of existing ordinances a more feasible proposition.
But since it is primarily garden waste that continues to present incen-
tives for on-site incineration in residential areas, the practical
feasibility of having to carry such wastes into the house and to the
basement grinder location is somewhat questionable. Nevertheless, im-
mediate removal of such wastes by grinding may well offset this apparent
inconvenience.
Because the wet system would landfill refuse in the form of a sludge that
may have 70 percent moisture or more, opportunities for open burning are
clearly diminished relative to filling raw refuse. To the extent that
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the refuse sludge would be incinerated rather than landfilled, an addi-
tional source of pollutant emissions might be created; but there is no
reason to assume that control of emissions at incinerators burning sludge
is more difficult or costly than control at incinerators burning raw ref-
11«A . °
Noise Quality
Noise from Conventional Refuse Collection Practices. Collection vehicles
generate noise from the truck motor, the compaction mechanism and the
crew during the loading process. Solid waste collection trucks travel
their routes rarely at more than walking speed, and high sound levels are
associated with both stopping, due to the "sigh" of air brakes, and
starting, due to revving the motor as the clutch is released. The truck
motor must be revved during movement from stop to stop and during the
compaction cycle. This produces a loud, low frequency sound of varying
length in the first case, of approximately 30 seconds duration in the
latter, and sound levels of 90 dBA or higher depending on the type and
condition of the truck. When the motor is engaged for compaction, a
second source of.sound is added to the motor noise. This comes from the
compaction mechanism itself and sounds associated with the compression
of loose rubbish. Although specific references are not available, it
may be that higher estimates of noise production from collection opera-
tions found in the literature of 100-110 dBA may be associated with this
peak output level.
The noise resulting from the banging and clanging of the rubbish cans
while being emptied may also be quite severe. This occurs not only when
the collectors are carrying and emptying the containers, but also earlier
in the morning when residents are bringing their cans to the curbside.
Large steel drums tend to be more offensive since they are often too
heavy for the collectors to lift and so are dragged out to the truck
causing the high frequency rasping of metal against pavement. They are
then banged against the hopper lip to assist in emptying. Less noise is
produced if rubber, plastic or fiber containers are used instead of gal-
vanized metal. Plastic and paper bags can be carried or dragged and
loaded with little or no noise.
It should be pointed out, however, that the annoyance associated with a
particular noise level is closely related to its duration, and thus the
aforementioned impacts are not necessarily as great a nuisance as might
be supposed. Nevertheless, a substantial proportion of complaints under
newly introduced noise ordinances concern refuse collection,05 and efforts
are now underway for the promolgation and enforcement of federal noise
emission standards for collection vehicles.
Observations in the Study Area. In the Springfield, Massachusetts study
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was significantly different from all other models regarding noise level
production. The compaction mechanism in this truck is a cylinder in which
a corkscrew shaped blade turns continuously. Since compaction is con-
tinuous, the truck motor is constantly idling at a high rate. The blade
gradually forces the waste material deeper into the cylinder, compacting
the rubbish with new rubbish as it is loaded in. This continuous circu*
lar path of the rubbish against the corkscrew, cylinder walls, and breaker
blade in the truck causes a great deal of noise as the material is smashed
and splintered into smaller pieces. Glass and metal pieces are notably
noisy as they fall by force of gravity from the top of the cylinder.
**
Conversations with several Springfield residents living on routes ser-
viced by the screw compactor trucks showed the people were aware of the
increased noise from this type truck. One gentlemen remarked that he had
not complained because the truck was faster during loading than others
and so the noise was of a more temporary nature.66 This was a valid
point since the collectors do not have to halt loading operations for a
compaction cycle. This interview also verified the tendency of people
noted earlier to discount disturbing noise if it is temporary. The
majority of collection trucks in Springfield are rear loading hydraulic
compactors of American manufacture, which are relatively quiet while
idling. We observed that at every third stop a compaction cycle was
necessary, at which time the truck motor is speeded up and the compaction
mechanism is engaged; As noted above, the two loudest sources are thus
operative simultaneously.
Impact of Wet Systems on Noise from Conventional Collection Vehicles.
Since wet systems collection will require vehicular collection only of
nongrindables, collection frequency will decline. With collection of
refuse by vehicle decreased from once a week to an average of once every
16 weeks, the frequency of noise from collection vehicles would obviously
decrease. In neighborhoods which may be near collection or disposal
facilities, corresponding decreases in vehicle traffic could greatly
lower the ambient noise level. Perhaps the most significant effect
might be felt in dense urban areas where refuse collection contributes
significantly to both noise levels and traffic congestion.
Wet systems will not of course affect noise levels when the trucks do
collect in a neighborhood. In fact, because the frequency of collection
would be much reduced, the presence of collection trucks might be much
more noticeable.
Impact of the Wet System on Noise Levels in the Home. The major noise
impact of the wet systems concept is that of increased noise levels in
the home, and the household refuse grinder designed by Foster-Miller in-
corporates several noise reduction features.67 it is a wet process
grinder which reduces noise from the tumbling of loose and flyaway pieces
of refuse in the hopper. The grinder as designed is supported on an
elastomer vibration isolation pad. Additionally, the hopper and top of
the device are coated with a sound absorbing material to reduce grinding
noise. In fact, noise levels might be less than from garbage grinders,
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since the latter has no lid to mask the grinding noise, and, for conven-
ience of installation in sink, the motor and mountings may not be shrouded
or mounted on dampers. Foster-Miller estimates their appliance as de-
signed would be slightly more noisy in operation than a kitchen dish-
washer,0 with the noise levels estimated to lie in the range of 65-75
dBA.
Since it is recommended the grinder be placed in the basement or other
service area, the operator would be probably the only person receiving
direct effects of the noise. The operator's exposure to the noise would
most likely be infrequent and of brief duration. This moderates the
relatively high noise level which might be encountered. The direct ef-
fects during operation would include speech interference; operators
would probably avoid communication at this time, much the same as the
operator of a vacuum cleaner presently does. But, if the actual noise
level falls in the upper levels of the estimated range, hearing damage
risk cannot be dismissed. Although the average exposure to such levels
would be limited to fractions of hours per week, certain elements of the
population might be subject to prolonged exposure. For instance, apart-
ment maintenance men could be exposed to several hours of this noise
daily. Although this exposure would not constitute an imminent hazard
to hearing, it could nonetheless hasten eventual hearing damage in the
context of cummulative exposure from many sources. However, unlike
other noisy appliances, the operator for the grinder need not remain in
the same room when the machine is grinding. Sound insulation afforded
by moving to an adjacent room would reduce noise to acceptable levels.
Sleep interference would probably be minimal. In the household, opera-
tion times of the appliance could be arranged to avoid conflict with
times persons are usually asleep. Due to service area or basement
placement, noise levels from the grinder in bedrooms would probably be
negligible.
Annoyance is probably the most significant of any indirect consequences.
Operator annoyance is usually not as severe as annoyance to persons to
whom the noise is intrusive. In single family homes, this effect is
deemed slight since family members will have control over when the ap-
pliance is used. And as mentioned previously, frustration may not occur
when the ability to stop or reduce intrusive noises is possible. Neigh-
bors outside the single family home would not be exposed to significant
noise levels due to shielding effects of the structure.
Noise standards for appliances are currently only a function of market
place pressures. A survey of appliance manufacturers by the EPA showed
that with the exception of air conditioners, there is little customer
pressure for quieter appliances.69 Indeed, sales of machines such as
vacuum cleaners show strong demand for noisier machines; perhaps the
American public equates power with noise.
In spite of the weakness of market pressure, many man*********> ^e
research and development projects aimed at noise reduction. Most felt
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further reduction was possible with present technology, but that a 5 -
20 percent cost increase would be the penalty for quieter appliances.70
It thus seems reasonable to conclude that noise from the refuse grinder,
while noticeable, may not be serious. Provided they are of short dura-
tion, high noise levels are accepted by householders, and are not re-
garded as health hazards.
Public Health and Visual-Aesthetic Considerations
The impact of refuse collection practices on public health and on the
visual-aesthetic environment are closely related, being both largely de-
pendent on refuse storage methods preceding collection, and hence a si-
multaneous consideration of both elements is indicated. A wet systems
implementation would largely eliminate the problems of storage of refuse
awaiting collection, and a major beneficial impact on public health and
the visual-aesthetic quality of the environment can be expected.
Storage Facilities. One study indicates that at least among low-income
families, areas of multi-family dwellings may contribute less waste per
capita than families in less dense, single-family structures,7* and thus
storage space required for each household may be greater in single-family
neighborhoods. This will be offset to a large degree by the greater
availability of places to store refuse in these areas. The typical
occupant of a single-family detached home stores his refuse in trash
cans, barrels, or bags. These are commonly placed outside the dwelling
in a spot out of view such as the back or side of the structure. In row
houses and apartment buildings, a central deposit area or receptacle is
often provided. Location may vary from outside a parking lot to indoors
in the basement of the building.
For both single-family and multi-unit dwellings, storage locations can
influence visual-aesthetic and public health impact. Outside storage
relies on the refuse receptacle itself to hide the refuse, keep it from
pests, and prevent litter and odor. An inside location, whether inside
the dwelling, in the basement for example, or enclosed in an outside
location, could compensate for inadequate containers. It should be
noted, however, that insect and rodent vectors may not be impeded by any
but the most secure enclosure.
Observations in the Study Area. Although Springfield has adequate
legislation to ensure proper refuse disposal, the ordinance is rarely en-
forced. The vast majority of containers placed on the curbside were
inadequate in one or more of the four categories mentioned above. Pre-
dictably, these inadequacies were most notable in the poorer sections of
the city, but present to a lesser degree in all sections.
In all but the most well-to-do suburban sections of the city, the major-
ity of rubbish containers were not the standard 30-gallon galvanized
trash cans with lids. Prevalent in numbers were plastic trash bags
followed by galvanized 30-gallon cans without lids, then industrial metal
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drums of 50-55 gallon capacity, corrugated cardboard boxes, paper super-
market bags, pressed cardboard drums of 40-60 gallon capacity and ««»ii
standard 30 gallon cans with lids. No wet-strfngth papS bags made ll
especially for refuse were observed.
The most popular storage methods in low income and redeveloped areas of
the city observed are plastic bags, large metal and cardboard drums,
paper supermarket bags and corrugated cardboard boxes, in that order.
The plastic bag, often lauded for saving collectors' time, we found to
be frequently misused. The abuses include stuffing the bag so full it
tears, not tying the bag closed, and placing articles in the bag which
puncture and tear the bag. These abuses, when they occur, render the
bag useless in preventing litter, odor, pest breeding and feeding. The
plastic bag properly used should be stored in a rodent and dog-free area
since these creatures can easily make the food inside available by
tearing the plastic. The plastic bag may retard animals somewhat by re-
taining odors which let the animals know food is near. However, bags
stored habitually in the same place may not even be effective in this.
The large drums were found to have several disadvantages. They are not
manufactured for rubbish and so have no lids, making their contents
available to rodents, flies, and dogs. Litter is generated from these
cans in another way. The cans are so large and often so heavy that they
are tipped on their side and rolled by the collectors from curbside to
the packer. This tipping often results in refuse being spilled out of
the top of the drum since the drums are packed full to overflowing. The
collectors seem to resent these drums and may not bother to pickup this
spillage. As an alternate to tipping, the drums are often dragged to
the truck. The cardboard containers develop holes in their bottoms from
this, and are 'also susceptible to wetness from rain and wet garbage.
The other two containers common in the low income areas, paper supermar-
ket bags and cardboard boxes, are obviously deficient in all areas. Ad-
ditionally, when wet from rain or garbage, these bags and boxes often
rip when picked up, depositing their contents on the roadway or alley.
It is interesting that our survey teams noticed that the care taken in
packaging the refuse at curbside was reflected in the care taken by the
collectors in loading the refuse and in cleaning up spills and litter.
Consequently, in areas where inadequate containers cause spills, where
rubbish and garbage is dripped through wet paper sacks, torn bags, and
tipped drums, collection crews are likely to leave the mess right where
it falls. On spills which were their own fault, the collectors were
usually diligent in cleaning up their mistakes.
The above phenomena may have a correlation with individual pride. In
the single family neighborhood, more space is available for Placement of
refuse for pickup. A messy, untidy pile of rubbish is ^^^"f*
the home owner. In multi-dwelling units where less space is P«»sent. un
sightly communal storage areas do not reflect as directly on an Divid-
ual occupant, hence the individual's sense of responsibility is absent.
un-
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Cross Connections. Perhaps the most serious potential public health im-
pact, and the one that would certainly attract close attention from
public health authorities, is the possibility of a faulty cross connec-
tion in the grinder.73 This possibility exists because of the need to
provide fresh water for the flushing cycle that must follow grinding.74
Cross connections are a recognized public health hazard, and major epi-
demics of water borne diseases in the developed countries almost invari-
ably follow the incursion of wastewater into the water distribution
system via some form of cross connection.
However, it could be argued that the stringent laws and regulations con-
cerning cross connections were developed of necessity in a time when
water and wastewater systems were introduced to urban areas haphazardly,
and without adequate supervision. But if the grinder is designed in such
a way as to inherently avoid possible hazards, the anticipated fears of
the public health authorities might well be allayed. The engineering
principles of cross connection control are well understood,75 and no
insurmountable difficulties are anticipated in adhering to these in the
design of refuse grinders.
Impact on Rodent Control. As all putrescible components of refuse would
be quickly disposed of through the grinder, no burden is placed on the
householder to safeguard the refuse or garbage against vector infestation.
Refuse would, in the storage and collection phases, virtually be elimi-
nated as a source of food for rodents and insects, with the possible
exception of rodent populations in the sewers. It is conceivable that
the rodent problem in sewers might be increased if more food in the form
of ground garbage and food waste were delivered to the sewers. Evidence
has been offered to support the fact that a high density of garbage
grinders in a community may be associated with increased rodent popula-
tions. 76 This relationship is uncertain, however, because rodents com-
monly reside in sewers, even when'food sources are on the outside. In
the study area, serious rat problems occur in areas of combined storm
and sanitary sewers, rather than in the areas where garbage grinders
are prevalent. Indeed, there is evidence that domestic sewage without
ground refuse may be capable of supporting rat populations. The Building
Research Advisory Board of the National Academy of Sciences feels that
grinding garbage for disposal to sewers offers a net benefit to control
of a community's rat population.77 And since it is known that shredded
raw refuse in landfills is not suitable for rodent consumption, one can
only surmize that mixed refuse suspended in water would be even less
suitable.
The elimination of curbside refuse storage has some further unexpected
and beneficial consequences. For example, a recent study linked urban
stray dogs to the urban solid waste problem78 and established the free-
running urban dog as a part of the cycle of urban waste, litter, and
disease. It was found that the dogs may exist in a symbiotic relationship
with urban rats. The dogs often assist the rats unknowingly by tearing
bags and spilling trash cans in their own search for food, and were ob-
served feeding on refuse side by side with rats. To the extent that this
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food source would be eliminated, a wet systems implementation might play
a substantial role in the control of the stray dog population, a problem
that is becoming to be recognized as very serious.
Water Quality
The impact of a wet systems implementation on water quality in the Spring-
field area must be put in the context of existing shortcomings in water
quality management in the region. Three areas are currently of concern;
the landfill at Bondi Island, the discharge of stormwater overflows into
the Connecticut, and the inadequacies of the existing primary wastewater
treatment facility. Only in the last area are current plans sufficient,
and the new planned secondary treatment facility is about to enter con-
struction.
The refuse disposal site currently used in the study area is regarded by
many as a threat to surface and groundwater supplies. Located on Bondi
Island in the town of Agawam, Massachusetts, adjacent to the Westfield
and Connecticut Rivers, most of the site is a flood plain that includes
a post-glacial oxbow pond. But recommendations to close this facility
must be put in the light of the realities of the fragmented New England
governmental structure, and the exceptional difficulty of finding
politically acceptable sites.
In Springfield, combined sewers still serve the downtown and surrounding
older sections of the city while newer suburbs have separate systems.
The impact of stormwater overflows on the water quality of the Connecti-
cut River below Springfield is substantial. Presently, a two month fre-
quency storm of 30 minutes duration results in the carrying of 10 tons
of BOD into the river.79 Significant reduction of dissolved oxygen
levels in the river results, although the depletion is not sufficient to
violate the Massachusetts C water classification of the Connecticut.
Present plans to alleviate this situation were outlined in Section VII,
above.
Impact of Wet Systems on Water Quality. Although recognizing the limita-
tions of the computer model and its results as discussed in Section VII,
we would not anticipate any difficulty in meeting the same effluent
quality with ground refuse as will be the case for the new planned facili-
ty treating just wastewater, and the water quality of the Connecticut
River, as measured by conventional parameters, would not be compromised.
Indeed, to the extent that the Bondi Island landfill site, which might be
unsatisfactory from a water quality viewpoint, would be used for land-
filling of a stabilized digested sludge containing no free moisture rather
than for filling of raw refuse, the net impact on water quality would be
positive.
With regard to the combined sewer overflows, we have already noted that
the implementation of a wet system in Springfield would be contingent on
a prio? or simultaneous separation of combined sewers. But since we an-
ticipate that grinders would first be installed in the relatively affluent
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OQ
suburbs, all that would need replacement initially are any combined
interceptors that carry wastewater from outlying areas through the cen-
tral areas where combined sewers are prevalent. This would avoid any
additional stormwater loads on the Connecticut River resulting from
ground refuse additions.
Need for Revised Effluent Standards. In view of the rather limited in-
formation on the possible quality of effluents from wastewater treatment
facilities handling ground refuse, the need for revised effluent stand-
ards is difficult to ascertain. Metcalf § Eddy's experiments do show,
however, that the COD of a conventional secondary effluent would be sub-
stantially higher than present levels, due mainly to fine cellulose
fibers in suspension. A standard for COD would therefore be indicated
for such facilities, although establishment of the permissible levels
would need further bench and pilot scale studies. As indicated by our
computer model results, there appears to be little difficulty injecting
existing effluent quality limitations for BOD, suspended solids, dis-
solved nutrients or other parameters commonly in use for sewage treatment
effluents.
Socioeconomic Impacts
The prediction of socioeconomic impacts, and in particular predictions in
quantitative terms, is a difficult and complex task. Two chapters in the
case study report address these impacts at some length,* to which the
reader is referred for further detail, and we shall here summarize only
the more important points. A detailed econometric analysis of refuse
generation in the Springfield SMSA was also conducted as part of this
study with a view to identifying socioeconomic factors affecting spatial
and seasonal variations in generation rates. The results of this analysis
are reported separately in a technical paper. (See Section XIII0
Impact on Private Capital. A shift from conventional handling to wet
systems would reduce the scope of both private industry and municipal
activity in refuse collection and disposal, and increase municipal ac-
tivity in sewerage. If the shift were to be widespread, it would replace
some frequent private house-to-house collection in sewered areas, leaving
only occasional collection of nongrindables. Thus, some investment op-
portunities will be lost to private enterprise. But as any shift seems
bound to be very gradual, and as the total private capital is small rela-
tive to the national economy or to any particular metropolitan area, the
effect will hardly be noticeable in the aggregate in any one year. Our
conclusion here is more optimistic than in the case of labor (see later
discussion), because the owners of capital are undoubtedly more capable,
on the average, of adjusting to the decline. They can turn their talents
and money elsewhere. A very important factor in smoothing the adjustment
is the market for used equipment. There is national advertising of used
Meier, 'Runner and Bolton, (Ref. 22), Chapters VII and VIII.
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equipment, and it can be transferred to other geographical areas at a
cost which is small relative to its value (a ten-year old collection ve-
hicle might still sell for $3,000 to $4,000 in the second hand market).
Used equipment is bought and sold by private operators, municipalities,
new equipment dealers, and firms specializing in reconditioning and re-
fitting older vehicles.81 There will still be need for landfills, and
the general scarcity should prevent serious decline in value. Naturally,
there may be some difficult adjustments and permanently adverse conse-
quences on a few entrepreneurs, but neither the waste of capital, nor
the losses to individuals, should be serious enough to count for much in
the aggregate picture.
Unemployment. As the primary cost-reducing effect of wet systems is in
the elimination of labor in conventional collection, the unemployment
problem naturally comes to mind. Indeed, pressure from workers and
unions to avoid reductions in municipal forces, and public sympathy for
unemployed workers, will be an important barrier to adoption of wet
systems. It might be especially strong in a city like Springfield, which
is in a labor market area which has had unemployment well above the na-
tional average in many years. In April and May 1973, for example, the
unemployment rate in the. Springfield-Chicopee-Holyoke labor market area
was 6.8 percent (in June the flood of students looking for jobs raised
it to 8.2 percent, but that was a seasonal increase). The average
monthly rates were 8.5 percent in 1971 and 7.9 percent in 1972.8*
The concern with unemployment is entirely valid in principle. However,
we feel it is not a very important consideration in the present context.
Any adoption of wet systems should come gradually, and some of the workers
laid off in refuse operations will find jobs in the sewerage operation of
the same city, or in other public works departments. The small number of
workers laid off in any given year would easily be absorbed elsewhere as
normal attrition opened up new vacancies. It should be stressed that the
case will not be one of massive layoffs, as have occurred or been threat-
ened in cities where refuse collection has been drastically altered over-
night, such as by eliminating backyard collection, or by reducing the
frequency of collection, and resulted in drastic reduction in crews.
There are about 225,000 workers in the labor force in Springfield's
labor market area, and the few workers who would be released outright,
not having been transferred to other jobs in the city, would have an
almost negligible effect on the total picture. Even a fairly rapid
changeover to wet systems by Springfield would take 5 to 10 years, and
the number of workers released outright could be as low as 20 per year.
Furthermore, refuse work requires no special skill or experience, so the
workers will not suddenly find themselves with obsolete human capital
which they have built up at cost to themselves. Obviously, the city
would find it desirable to smooth the workers' transition to new jobs,
perhaps with special unemployment payments and certainly by careful
phasing in of new methods. The point is that such extra costs would be
very small and should not be a significant barrier to the new method.
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Impact on Municipal Finance. On the municipal side, the net financial
impact is to decrease expenditures out of current income and to increase
expenditures financed by borrowing. The net effect of this depends on
the monetary cost comparisons between the two alternative methods -
counting only the monetary cost to the local government. This depends on
the total monetary cost comparisons in the economy as a whole and on the
shares of the costs which local governments must pay, and also on whether
waste reclamation brings net profits to municipalities.
A very important factor will be state and federal policy on grants for
sewerage facilities construction, which, unfortunately is very difficult
to predict. The question is whether such grants will be as liberal when
facilities handle solid waste. On the one hand, there is a long tradi-
tion of sewerage grants, and the federal stance was reaffirmed in the
1972 legislation which mandated higher standards to be achieved. On the
other hand, this tradition has been essentially lacking in solid waste.
This is not an arbitrary distinction; the principle has been that sewerage
aid was needed to prevent pollution of environmental resources, which
benefitted numbers of people far greater than the population of a single
town or city. This principle is much less applicable to solid waste,
although not totally irrelevant there. Especially the federal government
would find it hard to justify aid for facilities to handle solid waste,
although it has a clear role in research, demonstration, regulation of
packaging, incentives for reclamation, etc.
Whatever the federal and state governments decide to do will be crucial
for whether wet systems are introduced extensively. For many areas, the
total costs of the two alternatives are bound to be closely matched, and
even a small change in the percentage of cost defrayed by grant will tip
the scales. This is not to deny that wet systems will sooner or later
make some headway in some areas even without any grants to cover the
added sewerage costs, or that even extensive grants will not be suffi-
cient in some other areas.
There is another aspect of grants policy which bears mention. All federal
sewerage grants are now being made conditional on the municipality levying
user charges, which distribute costs to users in proportion to their loads
on the system, and sufficient to cover all operation and maintenance (in-
cluding replacement of components) costs. Some municipalities will have
to increase user charges over what they would want to charge in the absence
of needing the grant, others will have to institute sewer charges for the
first time. This will accentuate the difference between conventional
handling and sewage treatment in the relative reliance on user charges,
to which we now turn.
It is not inevitable that conventional methods be financed more by taxes
than user charges. Nor would wet systems automatically result in more
reliance on user charges. The technical nature of handling does not dic-
tate financing; we note for example the great variation from city to city
in the use of charges in both solid waste and sewerage. However, it
seems appropriate to compare the two systems taking as given the present
differences in financing of government costs, as shown by the national
averages.
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The picture is clouded, however, by the heavy subsidy from state and
local governments in sewerage. Do we measure reliance on charges by
their proportion of private costs plus municipal costs, or their propor-
tion of total national costs? The second proportion is much lower. The
present subsidy is composed of two parts. The first is the federal tax
treatment of municipal interest, which applies to all local capital ex-
penditures financed by borrowing, sewerage among others. The second
is the construction grant, which is tied to sewerage p_ejr se_. The first
part might be justified on very general grounds--it is essentially a
form of revenue sharing. The second part might be justified by con-
sidering rivers and lakes as national resources, and assuming localities
deserve to be offered heavy subsidies for avoiding polluting those re-
sources. The subsidy does not now seem to be offered as an incentive
to avoid pollution, because recent legislation has moved toward pro-
hibiting that in any event.
The first part of the subsidy would continue to operate if sewage treat-
ment plants were enlarged to handle refuse—the extra capital cost would
be covered by borrowing at the same interest rates as on other municipal
borrowing. We shall assume here that the second part would not be ex-
tended to cover such extra capital costs, that is, we assume that locali-
ties will have to finance the extra costs of handling solid waste on their
own. This is a reasonable assumption given the histories of federal poli-
cies on sewerage and solid waste, and the already high grants projected
for sanitary sewerage alone. We also assume that grinding costs will not
be subsidized, certainly not by state and federal governments. All these
assumptions imply that there definitely will be more reliance on user
charges in wet systems than there is at present, resulting in an improve-
ment in efficiency.
One important characteristic of wet systems is that the transactions
costs of using the price system are much lower in wet systems than under
conventional methods, if the load on the sewerage system can continue to
be fairly well measured by water flow. Presently, water flow is commonly
assumed to be an equitable proxy for sanitary sewerage costs. It is
widely used to determine sewerage charges, and is expressly permitted in
the new federal regulations on acceptable charge schemes for facilities
aided by construction grants.83 If some households have grinders and
others do not, water flow-based charges can be used for all households,
but the level of rates would be higher for those with grinders (their
charges for conventional collection would be lower, of course).
Water use is already measured for many households and the additional
clerical and administrative costs (and complaints) would be very low. If
water is not already metered, the advantages of simultaneously measuring
water usage, liquid waste loads, and solid waste loads would justify the
expense of introducing metering, for the transactions costs would contrib-
ute to efficiency and equity for several public services and a much larger
block of scarce resources.
Water use is certainly not a perfect measure of waste loads under wet
systems. But a charge based on water use would be preferable to no
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charge at all or a charge completely unrelated to waste flows. The goal
in cost assessment cannot be perfection, for the transactions costs are
too high for that; it is merely to strike a balance which improves ef-
ficiency and equity without using too many resources in measuring and
billing. The scope for this seems considerably greater for the wet sys-
tem approach than for conventional management. (More research is needed
to determine the accuracy of water flow as a measure of sewerage costs
under wet systems. Some of the research suggested in Section XI would
also accomplish this result.)
A by-rproduct of wet systems and user charges would seem to be improvement
in efficiency of use for water in other purposes than grinding, for the
amount of money spent on water by a typical household would be more no-
ticeable than at present and make it worthwhile to economize on its use.
Income Distribution Effects. The change toward user charges identified
above will have an extremely small effect on income distribution. User
charges will replace taxes, and the net effect will depend on the rela-
tionship between income and collection costs on one hand, and between in-
come and tax burdens on the other. Neither relationship can be specified
precisely. Under the most plausible assumptions, the change would prob-
ably cause some extremely small change toward more inequality if all
families had grinders and user charges replaced taxes in financing munici-
pal costs. However, if adoption came about voluntarily, lower income
families would not necessarily be absolutely worse off. If only upper
income families adopted grinders, and paid higher user charges, the effect
would be less inequality, because the higher user charges would replace
some taxes paid by lower income groups. But whatever the effect may in
fact be, its magnitude is likely to be quite insignificant.
Collective Bargaining. Various aspects of collective bargaining offset
the choice between conventional systems and alternative systems. Labor
relations .are relatively very important in conventional collection, be-
cause the function is inherently labor intensive and is also important
enough for public health and general amenity that disruptions due to labor
disputes are very costly. Strikes in some functions have little more ef-
fect than to delay production of useful output for a time. The only cost
is from the change in time of availability of a product, and that cost
may be minor. In refuse collection, however, as in some other public
services, even relatively short delays can have serious consequences.
Disruptions in sewerage could also be costly, but the system is more
mechanized and depends much less on constant, massive labor inputs; this
would still be true even if sewerage were expanded to carry and treat
solid waste. A work stoppage in sewerage, although possibly costly if
treatment must be partially cut back, is less likely to cause a public
emergency than a refuse collection stoppage.
The nature of the occupation and the vulnerability of the city to work
stoppages contribute to union activity and use of strikes or threats of
strikes as means of winning higher wages in refuse collection. Refuse
collection is no different in this from many other activities in the
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economy. However, for a long time, legal prohibitions and public opinion
inhibited unionization and strikes among public employees. More recently,
some of the legal barriers have been falling.
In 1940, Ziskind could already note that strikes by refuse collectors
were especially common relative to other government employees: "The
removers of refuse, the pariahs of the municipal personnel, have mani-
fested a group consciousness and a maturity of strike techniques that have
surpassed by far the protective efforts of the higher paid municipal em-
ployees." While he listed refuse collection strikes in 26 cities, Ziskind
devoted most attention to their history in New York and Chicago. In 1907
and 1911 in New York, strikes of several days duration were broken by the
importation of strike breakers, which occasioned violence. In the 1920's
and 1930's, there were seven strikes in Chicago, some several days long,
over a variety of issues, such as the attempt of the depression-plagued
city to reduce forces or hours and its failure to pay full wages, dis-
putes over rights to jobs in return for political activity (for instance,
in 1933, "a spectacular struggle between politicians and trade-union
bosses," p. 89), and control of employment at private disposal sites where
the city dumped its refuse.
Ziskind also commented on strikes of sewerage workers, contrasting their
near-negligible effect on the public with the effect of refuse workers:
"The strikes have...never seriously interfered with the normal functioning
of existing sewer systems," although they may have retarded the extension
or improvement of a system (p. 95).
Over the 1960's, the number of strikes in refuse collection, and man-days
idle in strikes, increased greatly, along with other strikes by other
government employees. Refuse collection has continued to be one of the
government functions most plagued by strikes, although it comes nowhere
close to the schools in that respect.85 Both the costs of strikes and
the time, energy and resources expended in collective bargaining must be
considered costs of conventional methods of solid waste handling, and
costs which will grow as unionization increases employee awareness of
wage parity; employees in one function make demands with a view to what
others are demanding or have already won at the bargaining table.86 The
unionization of a function for the first time thus has a true marginal
effect greater than indicated by the resources devoted to bargaining in
that function alone. Another aspect is the predominance of black labor
in some municipal collection forces. Some labor disputes have been aggra-
vated by more general civil rights grievances. And it is not only wage
negotiations which absorb time and energy; negotiations over working con- gg
ditions are also costly, in time and possibly in inefficient practices. »
All of these factors may make alternative methods appear attractive to
many. But one must not forget that alternatives which reduce the scope
for labor disputes may have the inevitable consequences of altering the
balance of political power in a city, consequences which are impossible
to evaluate on economic criteria alone. The true significance of public
employee unionism may be as much political as economic. It offers some
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group (public employees or blacks) the chance to increase their political
power. One therefore cannot unequivocally say that an alternative like
wet systems would be superior.
Wellington and Winter note that the costs of collective bargaining are
less severe when public functions, including refuse collection, are per-
formed by private firms, even if the firms' employees are unionized.°9
There may be times when economic and political forces encourage near-
general strikes by all public employees, although such have been rare in
fact. Public refuse collection may be stopped even when the collective
bargaining issues are less relevant in refuse collection than in some
other functions. Also, private employers may resist union demands more
than public employers, because they are better organized and have more
experience in bargaining, and because the latter are more open to politi-
cal pressure to yield. Governments are organized in ways (division of
powers, checks.and balances) which make it difficult to present a united
front. Even if a city government is forced to intervene in a strike of
a private firm, the government is a neutral intervenor and not a direct
adversary of the union. The authors also argue that a private employer
can offer a more credible threat of unemployment as a result of higher
wages - he is better able to substitute capital for labor and is more
likely to raise prices to cover higher costs and thus permit a slower
growth in demand. And governments seem more able to pass on higher costs
to other levels of government, or to hide the increased cost in a complex
and little understood budget. For these reasons, a government is more
likely to meet a strike with a higher settlement, and thus to be struck
in the first place.90 The authors thus conclude that whether a particu-
lar function is appropriate for government now depends in part on the
growth of public employee unionism, and they note refuse collection is one
example where the choice between public performance and private firms de-
pends partly on unionization. Similarly, the relevance of unionization
for conventional handling depends somewhat on whether it is performed by
public agencies or not.
All this may be true, but it remains ambiguous how to value these factors.
While administrative costs and wages may be kept lower when private firms
perform the function, employees are deprived of an avenue of economic
power. This consideration may be important in assessing conventional
methods versus alternatives. The wet systems method certainly inherently
offers municipal workers somewhat less scope for exercising political and
economic power. We can say, however, that the total numbers of workers
affected by this would be small relative to the total of municipal em-
ployees, even if large scale changes were affected. Because any adoption
of wet systems is likely to be gradual, the quantitative significance of
loss of power will be even less.
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SECTION X
TOTAL SYSTEM COST COMPARISONS
Economic Feasibility
The estimated total system costs, on an annual per household basis, for
both the wet system and a continuation of existing conventional practice
are shown on Table 11. The 1988 costs, which are shown in terms of 1973
dollars, have been derived on the basis discussed in Chapter VIII, uti-
lizing a two percent annual increase in labor costs. A comparison of
the system totals is even more unfavorable to the wet system than the
generalized comparisons of Phase I (where the 1973 figures were esti-
mated at $125-$182 for the wet system as against $43-$101 for conventional
practice). Evidently, conventional waste management practices in Spring-
field are very efficient, with per household costs at the very bottom of
the national spectrum.
But it should be reiterated that the $80-$105 annual cost of grinding is
that for the Foster-Miller or Nebiker-Meier grinding concepts, both of
which were rejected on the basis of excessive cost. Moreover, this is
an annualized cost, which, again as noted previously, is not the basis
upon which individuals would base a decision on grinder purchase. Con-
sequently, the totals inclusive of grinding do not appear very useful.
If the cost of grinding is excluded, on the assumption that grinding costs
would be borne by the householder, then the remaining costs are those to
just the public sector, and these are considerably more favorable to the
wet sys.tem, possibly 10 to 15 percent lower than conventional by 1988.
Because this margin is rather small, the conclusion would be that imple-
mentation of the wet systems concept is still very distant. Yet on the
other hand, if our prediction of potential consumer acceptance is correct,
implying heavy involvement of the private sector appliance industry in
developing and marketing refuse grinders, then it behoves the public sec-
tor to examine the consequences on its waste management systems, as it
might otherwise be faced with the necessity of banning refuse grinders.
Other than the grinding cost component, most of the uncertainty in the
wet system cost is attributable to the cost of sewer maintenance. As
explained in Section VI, it is simply not yet possible to determine the
necessary flushing frequency; yet it is the flushing frequency that pri-
marily determines sewer maintenance costs. If flushing is necessary
four times rather than only once per year, then the $6-$9 range assumed
in Table 11 for 1973 would rise to $24-$36.
A problem perhaps inadequately addressed in the economic analysis is that
of transition costs, i.e., the costs during that period when both conven-
tional systems and wet systems coexist. The cost items for sewage treat-
ment, sewer maintenance and grinding might be assumed to rise linearly
with increasing number of installed grinders; however, it is unclear
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Table 11: Total Annual System Cost per Household Comparisons for Springfield
00
o
1973
Refuse Collection
Collection of Nongrindables
Bulky Refuse Collection
Disposal
Sewer Maintenance
Grinding
Treatment
Sludge Handling
Sludge Disposal
Total
Total to Public Sector
(Excluding Grinder)
Conventional
$17.50
•*
1.00
3.50
2.00
-
9.00
5.50
0.75
$39.25
$39.25
Wet
System
$2.50
2.00
1.00
6.00-9.00
80-105
12.50
8.50
2.00
$114.50-142.50
$ 34.50-37.50
1988
Conventional
$21.50
1.50
4.50
3.75
-
10.00
6.00
1.00
$48.25
$48.25
Wet
System
$4.00
3.00
1.50
7.50-11.00
80-105
14.00
10.00
2.50
$122.50-151.00
$ 42.50-46.00
-------
whether the cost items for collection and disposal would also decrease
linearly, and thus the possibility of a higher than expected transitional
cost cannot be discounted. It may therefore be only at the point of com-
plete implementation of the wet system that the expected wet system costs
are attained. But until such time as the necessary detailed data on
refuse characteristics becomes available, data that was unavailable to
us, any attempt at quantifying the transition would be excessively specu-
lative. This is not, however, to deny the importance of the problem.
Conclusion
Having shown the economics of the wet system to be somewhat unfavorable
over existing and alternative concepts, having raised serious questions
as to its technical feasibility, but also having shown some significant
(even if unquantifiable) environmental and socioeconomic benefits, what,
then, is our final judgment at the conclusion of our investigation?
Unfortunately, the complexity of the concept and its place within the
many interlinked efforts at rational environmental management make any
definitive pronouncement on the concept at the present time a very dan-
gerous undertaking. The major reason for our reluctance to express
absolute conclusions is the limited information on the technical aspects
of the concept that is to date available. Taken at face value, the re-
sults of the economic analysis presented in these pages is indeed un-
favorable to the wet systems concept, showing approximately a doubling
of total per household cost for all the elements of domestic waste manage-
ment. Yet at the same time, we have shown that if the cost of the grinder
is borne by the householder, there may be situations where the cost of the
wet systems concept to the public sector may be less than any conceivable
improvement of today's concepts. Thus, given the premise of technical
feasibility, we arrive at the conclusion that its economic feasibility,
by which we mean that cost is no greater than that of its competitive
alternatives, rests upon the willingness of householders to purchase a
grinder for benefits of convenience and aesthetic or environmental im-
provement of their homes. Such a premise is not to be dismissed lightly,
given the indications of continuing increases in disposable income. And
skeptics might be reminded of the realities of the current market for trash
compactors, an appliance that surely offers fewer convenience benefits
than refuse grinders.
Certainly we may conclude that demonstration scale research investments
are as yet unwarranted. At the same time, however, we believe that a
limited program of further studies directed specifically at the resolution
of a few key technological uncertainties would allow judgments that are
based on more substantial evidence than the largely circumstantial infer-
ences that are available to us at the present time. If these further
studies, as elaborated in the following section, have favorable results,
then we believe that the wet systems concept would gain consumer acceptance
to the point where implementation became feasible. This is contingent,
however, not only on a confirmation of technical feasibility, but on the
availability of a grinder whose cost is compatible with consumer acceptance.
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SECTION XI
RECOMMENDATIONS FOR FURTHER RESEARCH
Our investigation has pinpointed several areas of technical uncertainty,
and consequently definitive judgment on the technical feasibility of the
ideal are made only with great difficulty at this time. However, it has
been possible to analyse these uncertainties to the point where a program
of a few selected, but pertinent, investigations could resolve these un-
answered questions, and to this end we have set forth a program of re-
search tasks. The sequence of tasks is ordered in such a way that the
most critical questions be addressed first, and so that further invest-
ments may be terminated if the results of the most critical investiga-
tions are negative.
Because these unresolved technical questions are quite substantial, we
feel that investment of research monies as the next step, at the level
required for demonstration scale project would be premature, and a deci-
sion on such investments should be preceded by the program of laboratory
scale studies herein described. A detailed analysis of the quality para-
meters and conventional treatibility of ground refuse-sewage mixtures may
be regarded as a first priority, and ,is already under consideration as an
in-house study at the EPA National Environmental Research Center in
Cincinnati. The information yielded by this study will considerably ex-
tend the existing knowledge on the subject developed by the Metcalf and
Eddy investigations, and will allow much more reliable estimates to be
made for the likely cost of treatment. There remain to be addressed,
however, the following series of tasks, presented in the recommended
sequence. Note that Task 5 is probably the most costly, and should
therefore be undertaken after the other, relatively cheaper, tasks.
Task 1: Hydraulic Studies Under Unsteady Flow Conditions. The most im-
portant known limitation to the technical feasibility of the wet systems
concept concerns the ability of an existing gravity sewer system to trans-
port ground refuse. The results of the Springfield case study show very
clearly that in many sewer laterals, the scour velocities required to
prevent excessive deposition of the glass and ceramic component are
rarely present, if indeed at all. Moreover, it remains questionable
whether the generally optimistic conclusions of the Foster-Miller studies,
which would appear to show few problems to occur under steady-state con-
ditions, are at all valid for the unsteady flow conditions actually en-
countered in most parts of a gravity sewer system, and in particular, in
the laterals at the periphery of the system.
In order to resolve these problems, a study of hydraulic transport of
ground refuse in a simulated system of sewer laterals is proposed, with
the objective of extending the findings of the existing Foster-Miller
studies to unsteady flow and solids load conditions. The experiments
should be conducted in a test loop of eight^inch glass sewer several
hundred feet long, and with a representative selection of appurtenances.
82
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The injection of ground refuse should be through simulated building con-
nections spaced at appropriate intervals along the test loop, and dis-
charges timed to simulate as closely as possible real conditions. The ground
refuse injected should include the glass fraction, and the experiments run
over at least weekly cycles in order that quantitative judgments on accu-
mulation problems can be substantiated. Although it is recognized that
such a simulation program may involve substantial effort and considerable
sophistication in laboratory procedures, anything less would not yield
information that will provide conclusive evidence on the feasibility of
hydraulic transport in real systems.
Task 2: Field Survey of Refuse Generation and Water Consumption. The
case study was unable to fully answer the questions of the feasibility of
refuse grinding and sewer transport because of certain data inadequacies.
In particular, no data is available on' the refuse generation, water con-
sumption and sewage production of single households. The use of average
values for groups of households may be dangerous if the degree of cor-
relation between these three variables is unknown. If in fact households
with high refuse generation also generate high sewage quantities, the
problem of adequate grinding water will be less acute than is suggested
by use of average values. Unfortunately, knowledge of this correlation
is crucial to a judgment of feasibility, and, therefore a field investi-
gation to rectify this deficiency is proposed. This field survey would
involve the selection of a series of representative refuse collection
truck routes in the study area, and sample a series of households on this
route for water consumption and refuse generation. The program might
include:
Weekly readings of water meters on the day of refuse collection.
Water meters can generally be read without requiring access to
the interior of a dwelling unit, thus involving no inconvenience
to householders.
Curbside weighing of refuse containers on the day of collection
prior to pick-up by the collection crews. This sampling might
be conducted half an hour ahead of the collection, involving no
impediment to the collection crews. Portable scales mounted on
a suitable push-cart would be adequate for this purpose. By
sampling only a portion of the households on each route, the
sampling crew could operate at the same speed as the collection
crews, thus preserving a constant difference between the two
operations. A certain number of samples could be collected
in plastic bags for subsequent composition analysis and deter-
mination of which components could not be ground by virtue of
their bulk.
Determination of the maximum flow depth (and hence velocity) of
the sewage flow at manholes along the sample routes.
Continuous monitoring of sewage flows in a selection of resi-
dences.
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Statistical analysis and interpretation of all data collected.
Because of strong seasonal variations, this study should be conducted
over a 52 week period. It is, however, probably unnecessary to sample
all households every week; once every four weeks would be sufficient for
all but a few sample households.
Only data collected at this level of detail will allow meaningful con-
clusions on the feasibility of refuse grinding and the development of
adequate grinder specifications. Ideally, this task should run concur-
rently and be closely coordinated with Task 1, and be conducted in the
same Springfield case study area as used by this investigation.
Task 3: Energy Balance Studies. In the 18 months that have elapsed since
the start of this wet systems evaluation, national energy shortages have
reached major proportions. An evaluation of any radical innovation, such
as the wet systems concept, must therefore include examination of the im-
pact of its implementation on energy consumption, but unfortunately could
not be included as part of this study for reasons of time and resources.
A focus on energy consumption is especially important in view of the
energy market distortions resulting from government controls. Energy
costs, and total systems costs, may thus not necessarily be an adequate
indicator of the true social costs of the various alternatives.
(At first glance, the trade-off appears to be savings in fuel for collec-
tion vehicles as opposed to increased electricity use for grinding and
treatment plant operations. However, to the extent that anaerobic di-
gestion and its methane by-product could satisfy a substantial portion of
treatment facility power requirements, the net impact of a wet system on
energy consumption would probably be positive.)
Task 4: Evaluation of Potentially Hazardous Components in Refuse-Sewage
Mixtures. Phase I of this investigation established the possibility of
potential problems arising from the addition of potentially hazardous
materials to the treatment plant. But because there is no actual evi-
dence, only indirect estimates that are inconclusive, it is recommended
that a series of laboratory investigations provide some facts on this
question. Advanced instrumentation analyses of simulated treatment plant
inflows and secondary effluents should provide the necessary evidence of
higher (or lower) concentrations of specific materials (pesticides, herbi-
cides, toxic heavy metals) resulting from the addition of ground refuse.
Such evidence would further allow appropriate additional advanced waste
treatment processes (or changes needed to already existing processes) to
be identified with some degree of confidence and thus make estimates of
treatment cost in the presence of ground refuse more credible than those
that can presently be made.
Task 5: Development of Alternative Grinding Concepts. The results -of
our investigations show clearly that existing grinding concepts envisaged
for wet systems are unlikely to be implemented for economic reasons. Re-
plumbing of existing housing as would be necessary under the Foster-Miller
84
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concept is prohibitively expensive and must be regarded as infeasible.
On the other hand, grinding at high consistencies, as called for by the
Nebiker-Meier concept, requires a pressurized building connection, the
cost of which is also very high. Moreover, the question of how much
grinding water is available, and what minimum solids concentrations are
necessary to prevent deleterious effects in the sewer system under the
unsteady flow conditions encountered in practice are obviously crucial
to the development of grinder specifications. Consequently, additional
effort in this area rests on the results of Tasks 1 and 2. Since the
major cost of existing grinding concepts lies not in the grinder itself,
but in ancillary arrangements, a successful grinding concept that would
avoid these would have some chance of success in removing a major barrier
to a wet systems implementation. One such alternative concept might in-
volve grinding at high consistency, but discharging to the building con-
nections only at such times when the flow from other domestic appurte-
nances, such as following toilet flushing or washing machine discharge,
would provide adequate dilution water.
Task 5 should be divided into 3 phases. In Phase I, alternative con-
cepts should be evaluated with the help of laboratory simulations that
would examine the behavior of refuse slurries and their dilution and
mixing with other domestic wastewaters. Phase II would develop an
appropriate design which should be constructed and tested in a third
phase. Any demonstration project would obviously depend on the avail-
ability of an already constructed and tested grinder.
Task 6: Comprehensive Reevaluation of the Concept. Completion of the
previously specified Tasks 1 through 5, and the study shortly to be con-
ducted by the EPA National Environmental Research Center in Cincinnati
that will obtain further data on the quality parameters and conventional
treatability of ground refuse-sewage mixtures, should allow an evaluation
of the concept that is founded on much more concrete evidence than has
been available to this study. This proposed reevaluation would be in a
position to make a definitive judgment on the economic and technical
feasibility of the concept, and, if found to be feasible, would have as
a major goal the planning of a subsequent demonstration project. This
reevaluation is felt to be very necessary prior to commencement of a
demonstration program that would involve investments of a very much higher
order of magnitude than the studies previously conducted.
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SECTION XII
REFERENCES
1. Clark, R., "Urban Solid Wastes Management: An Economic Case Study,"
EPA Environmental Protection Series EPA-R2-73-012, August 1972.
2. Two unpublished memoranda report pn the results of these experi-
ments; one dated September 13, 1963, entitled, "Report on a Study
of the Feasibility of Disposing of Rubbish into a Sewage Disposal
System," the other dated May 26, 1965, by R. Whitley, is entitled,
"Evaluation of Settling Characteristics of Ground Refuse in Sewage,"
3. Waller, D. H., "An Examination of the Benefits and Disadvantages
With Respect to the Disposal of Solid Wastes," ASCE Combined Sewer
Separation Project, Technical Memorandum No. 10, February 1968,
4. Nebiker, J. and P. Meier, "Hydraulic Disposal of Solid Wastes,"
Proc. 1st Annual Northeastern Regional Anti-Pollution Conference,
University of Rhode Island, Kingston,, ,Rb,pde Island, July 1968,
5. Etzel, R., "One System Treats Sewage and Solid Waste," Chemical and
Engineering News, March 23, 1970, pp. 44-45.
6. Contract CPE-70-115, originally let by the Bureau of Solid Waste
Management, Environmental Control Administration, Department of
Health, Education and Welfare, in June 1970.
7. Guzdar, A, and S. Rhee, "Feasibility of Hydraulic Transport and
Treatment of Ground Household Refuse Through Sewers," report by
Foster-Miller Associates to EPA Solid Waste Research Laboratory,
Cincinnati, Ohio, January 1973.
8. Fisk, A. T. and A. R. Guzdar, "Preliminary Design of a Household
Refuse Grinder," report by Foster-Miller Associates to EPA
Solid Waste Research Laboratory, Cincinnati, Ohio, January 1973.
9. McKinney, R. and J. Mahlock, "An Economic Evaluation of Garbage
Grinding Versus Surface Collection and Disposal," Water and Sewage
Works, Reference Number, November 1971.
10. The authors were apparently unaware of the Foster-Miller research
and of recent developments in the pulp and paper industry.
11. McGraw-Hill's 1972 report on Business and the Environment, pp. 6-7.
12. Personal communication with Mr. Maxwell Small of Brookhaven National
Laboratory, November 1972.
86
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13. Monaghan, D. A. and A. Guzdar, "Feasibility of Hydraulic Transport
of Ground Refuse Through Sewer Appurtenances," report by Foster-
Miller Associates to EPA Solid Waste Research Laboratory, Cincinnati,
Ohio, March 1973.
14. Courtney, R. and D. Sexton, "Refuse Collection from Houses and Flats
by Pipeline," Proc., 2nd International Conf. on Hydraulic Transport
of Solids in Pipes, Coventry, England, 1972.
15. "Pipeline Transportation of Solid Waste," report by the Stanford
Research Institute to Bureau of Solid Waste Management, Environmental
Control Administration, Department of Health, Education, and Welfare,
(Contract PHS-1-DP-1-U1-00208-01) February 1971.
16. Zandi, I., and J. Hayden, "A Pneumo-Slurry System of Collecting and
Removing Solid Wastes," in I. Zandi, Editor, "Advances in Solid-
Liquid Flow in Pipes and its Applications," Pergamon Press, New
York, 1971.
17. See, "Pipeline Transport of Shredded Solid Waste," report by the
Western Company to the EPA Solid Waste Management Program, 1971,
open-file Report SW-36C, and Overfield, J. L., et al., "Increasing
Wastewater Flow Velocity Using Chemical Additives," J. WPCF, 41, 9,
pp. 1570-1585, September 1969.
18. See for example, Bishop, F. W. and A. E, Drew, "Disposal of Hydrous
Sludges from a Paper Mill," Journal of the Technical Association of
the Pulp and Paper Industry, Volume 54, No. 11, (November 1971), pp.
1830-1832.
19. See for example, Herbert, W., "Recycling Municipal Waste," Chemical
Engineering, January 10, 1972, pp. 66-67.
20. Meier, P., J. Kuhner and C. J. Martel, "A Preliminary Assessment of
Wet Systems for Residential Refuse Collection," report by Curran
Associates, Inc. to EPA Solid Waste Research Laboratory, Cincinnati,
Ohio, March 1974.
21. Kos, P., M. Joyce and P. Meier, "Economic Analysis of Refuse Sludge
Processing and Disposal," report by Curran Associates, Inc to EPA
Solid Waste Research Laboratory, Cincinnati, Ohio, March 1974.
22 Meier P J. Kuhner and R. E. Bolton, "Wet Systems for Residential
SE; Collection; A Case Study for Springfield, Mass." Report by
Curran Associates, Inc. to EPA Solid Waste Research Laboratory,
Cincinnati, Ohio, March 1974.
23 Meier P and G Fisette, "Modifications to the Executive Computer
23' £ ger,m^Steady-State Simulation of ^stewater Treatment Facili-
ties " report by Curran Associates, Inc., to EPA Solid Waste Re
search laboratory, Cincinnati, Ohio, March 1974.
87
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24. Fisk, A. T. and A. R. Guzdar, op. cit.
25. Buying Guide Issues, Consumer Reports 1953 + 1968, Consumers Union
of the United States, Inc., Mt. Vermon, New York.
26. Meier, Kuhner and Martel, op. cit., p. 112.
27. Meier, Kuhner and Bolton, op. cit., p. 42.
28. See e.g., "Data Acquisition and Analysis System, Quarterly Reports by
ACT Systems, Inc., Winter Park, Florida to the EPA Solid Waste Re-
search Laboratory, Cincinnati, Ohio, 1971, 1972 and 1973. See also
Meier, Kuhner and Martel, op. cit., pp. 27-29-
29. Meier, Kuhner and Martel, op. cit., pp. 110-118.
30. See Meier, Kuhner and Bolton, op. cit., p. 193.
31. Guzdar, A. and S. Rhee, op. cit.
32. Monaghan, D. A. and A. Guzdar, op. cit.
33. Meier, Kuhner and Martel, op. cit., Chapter III.
34. "Design and Construction of Sanitary and Storm Sewers," WPCF Manual
of Practice No. 9, Water Pollution Control Federation, 1969, p. 128.
35. Guzdar and Rhee, op. cit., p. 90.
36. Meier, Kuhner and Martel, op. cit., pp. 51-52.
37. Ibid., p. 52-53.
38. Metcalf § Eddy, Inc., "Feasibility of Treating Sewage with Household
Refuse," report to Foster-Miller Associates, Inc., 1971, included
as part of Guzdar and Rhee, op. cit., Chapter 5.
39. For further details of this model, see Meier and Fisette, op. cit.,
Chapter IV.
40. "City of Springfield, Massachusetts - Report on Sewage and Industrial
Waste Disposal," report by Camp, Dresser and McKee, Inc., 1971.
41. "Supplemental Study of the Connecticut River in Connection with the
Proposed Bondi Island STP," report by Camp, Dresser and McKee, Inc.,
1971.
42. This model of the planned treatment facility is also discussed in
detail in Meier and Fisette, op. cit.
88
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43. Metcalf § Eddy, op. cit.
44. Kos, et al., op. cit., p. 13.
45. Ibid., p. 14.
46. Ibid., p. 20.
47. Ibid., p. 69.
48. Ibid., Chapter IV.
49. Meier, Kuhner and Martel, op. cit.t Chapter IV.
50. The calculations assume the following average fractions of refuse
categories to be ground: Paper 1.0; Garbage 1.0; Glass and Ceramics
1.0;. Garden Waste 1.0; Wood 1.0; Plastics 0.9; Rubber, Leather and
Textiles 0.8; Metal 0.3, Other 0.1.
51. "Contract and Specifications for Bondi Island Treatment Plant Con-
struction," report by Camp, Dresser and McKee, Inc., 1972.
52. Metcalf & Eddy, op. cit.
53. Metcalf § Eddy, op. cit., p. 4-2.
54. "Sludge Conditioning - Can Waste Paper be Used?" Water and Wastes
Engineering, 10, 5, p. c-10, May 1973.
55. Konicek, Z., P. Kos and C. Pardus, "Gravity Thickening of Industrial
Sludges," Proceedings, Conf. of the Czechoslovak Civil Engineering
Society, Brno, 1970.
56. Pfeffer, J. T., "Reclamation of Energy from Organic Refuse," EPA
Solid Waste Program Grant EP 00364, Progress Report, September 1971,
p. 31.
57. Wise, D. L., "Fuel Gas Production from Solid Waste," Proc., NSF Bio-
conversion Energy Research Conference, University of Massachusetts,
Amherst, Massachusetts, June 1973.
58. Patterson, W. L., R. F. Banker, "Estimating Costs and Manpower
Requirements for Conventional Wastewater Treatment Facilities,"
Report by Black § Veatch to Office of Research and Monitoring, EPA,
Project #17090DAN, October 1971.
59. Meier, P., "Management Aspects of Refuse Bioconversion," Proc., NSF
Bioconversion Energy Research Conference, University of Massachusetts,
Amherst, Massachusetts, June 1973, pp. 79-87.
60. Based on 7.1 miles/capita-day and adjusted for 1970 population of
163,905; see Wilbur Smith and Associates, "Land Use and Transporta-
tion Inventories, Volume I," May 1969, p. 100.
89
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61. It is estimated that over 100 truck-hours each day may be spent
idling. Applying an emissions factor of 6 between idling and
cruising and an average speed of travel in a metropolitan area of
15 miles/hour, this idling time may produce emissions equivalent to
an additional 10,000 miles of travel.
62. See Meier, Kuhner and Martel, op. cit., Chapter VI for further dis-
cussion on this point.
63. New York Times, October 17, 1973.
64. U.S. EPA, "Noise Pollution," August 1972, p. 1.
65. See e.g., "Noise Facts Digest," report by Informatics, Inc. to
Office of Noise Abatement and Control, EPA, Washington, June 1972,
p. 3.
66. The conversations occurred in June-July 1973.
67. Fisk and Guzdar, pp. cit.
68. Ibid., p. 94.
69. The Administrator U.S. EPA, "Report to the President and Congress on
Noise," February 1972, pp. 3-55.
70. Ibid.
71. Davidson, George R., Jr., "Residential Solid Waste Generated in Low
Income Areas," U.S. EPA, 1972.
72. For further discussion on this point see, Nebiker, J. H. and P. M.
Meier, op. cit., pp. 133-138.
73. For an explanation of the hazards involved see, "Water Supply and
Plumbing Cross Connections," U,STPVH,S, Publication 957, 3rd printing,
1969.
74. See also Meier, Kuhner and Martel, op. cit., Chapter II.
75. See e.g., Salvato, J., "Environmental Engineering and Sanitation,"
Wiley Interscience, New York, N.Y., 2nd Edition, 1972.
76. U.S. Department of Health, Education and Welfare, Public Health
Service, "Control of Domestic Rats and Mice," 1970, p. 16.
77. Davis, P. L., "Solid Waste Management in Buildings," Building Re-
search Institute, November 15-16, 1972.
78. Beck, A. M., "The Ecology of Stray Dogs; A study of free-ranging
urban animals," York Press, Baltimore, 1973.
90
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79. Camp, Dresser and McKee, Inc., "Report on Overflows for the City of
Springfield, Mass,," October 1971.
80. See above, Section IV.
81. The monthly issues of Solid Waste Management, a national trade publi-
cation, are a good source of information on the used equipment market,
82. Monthly data are published in U.S. Department of Labor, Manpower
Administration, Area Trends in Employment and Unemployment, about
two months after the month to which the data apply.
83. Federal Register, Vol. 38, No. 161, August 21, 1973, p. 22527.
84. Ziskind, David, One Thousand Strikes of Government Employees,
Columbia U.P., 1940, pp. 94-95.
85. For extensive data on strikes in public employment, see Harry H.
Wellington and Ralph K. Winter, Jr., The Unions and the Cities,
Brookings, Washington, 1971, Appendix B; U.S. Bureau of Labor Statis-
tics, Work Stoppages in Government, 1958-68, Report 348, 1970; see
also the Bureau of Labor Statistics annual bulletin, Analysis of
Work Stoppages, the latest of which is for work stoppages in 1971
(Bulletin 1777, published in 1973). Work stoppages by sewerage
workers are not reported separately by the BLS, but are combined
with other occupations in a wider category.
86. Wellington and Winter, op. cit., p. 61; David T. Stanley, Managing
Local Government Under Union Pressure, Brookings, Washington, 1972,
pp. 68, 79. Stanley notes a case where an unusual increase for sani-
tation men resulted in a larger-than-planned increase for police and
firemen as well.
87. Stanley, op. cit., pp. 3, 68; also W. Donald Heisel, "Anatomy of a
Strike," Public Personnel Review, Vol. XXX, No. 4, October 1969, pp.
226-232, where details are given of a strike of public employees
(refuse collectors and others) in which racial feelings were a
factor.
88. Stanley, op; cit., cites many examples, including some in refuse col-
lection.
89. Wellington and Winter, op. cit., pp. 62-64.
90. Ibid., pp. 195-196.
91
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SECTION XIII
PUBLICATIONS
The following papers are in preparation for publication in technical
journals. Some further papers are in the planning stages. At least one
of these will be submitted to German and Swiss journals.
, Bolton, R., "An Econometric Analysis of Household Refuse Generation," in
preparation for submission to J. of Environmental Economics and
Management.
Meier, P. and J. Kuhner, "Simulation Analysis of Wet Systems for Residen-
tial Refuse Collection," to be submitted for publication in the
J. Environmental Engineering Division, ASCE.
Meier, P., p. Kos and J. M. Joyce, "The Treatment of Ground Refuse at
Modified Sewage Treatment Facilities," to be submitted for publica-
tion in the J. Water Pollution Control Federation.
The following papers were presented or will be presented at technical
conferences:
Meier, P., "Management Aspects of Refuse Bioconversion," presented to the
National Science Foundation Bioconversion Energy Research Conference,
University of Massachusetts, Amherst, Massachusetts, June 1973.
(Published in the conference proceedings, p. 79-87; available from
The Institute for Man and His Environment, University of Massachusetts,
Amherst, Massachusetts 01002.)
Meier, P., "Wet Systems for Handling Solid Waste," to be presented at the
annual meeting of A.I.Ch.E., Pittsburg, June 4, 1974.
The following technical reports were prepared in the course of the re-
search project and are available from the National Technical Information
Service, Springfield, Virginia 22151.
Meier, P., J. Kuhner and C. J. Martel, "A Preliminary Assessment of Wet
Systems for Residential Refuse Collection."
Kos, P., J. M. Joyce and P. Meier, "Economic Analysis of Refuse Sludge
Processing and Disposal."
Meier, P., and G. Fisette, "Modifications to the Executive Computer
Program for Steady-State Simulation of Wastewater Treatment
Facilities."
Meier, P., J. Kuhner and R. E. Bolton, "Wet Systems for Residential
Refuse Collection; A Case Study for Springfield, Mass."
92
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fflease read Instructions on the reverse before completing)
REPORT NO.
EPA-670/2-74-068
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
AN ASSESSMENT OF WET SYSTEMS FOR RESIDENTIAL
REFUSE COLLECTION: Summary Report
5. REPORT DATE
August 1974; Issuing Date
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO
P. M.' Meier, J. Kuhner, and R. E. Bolton
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Curran Associates, Inc.
182 Main Street
Northampton, Massachusetts 01060
10. PROGRAM ELEMENT NO.
lDB064/ROAP-09ADA/Task 04
11. CONTRACTXQfOMflXNO.
68-03-0183
12. SPONSORING AGENCY NAME AND ADDRESS
National Environmental Research Center
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES See also E P A - 6 7 0 / 2 - 7 4 - 0 3 7 (PB-234 498/AS) ; EPA-670/2-
74-038 CPB-234 499/AS); EPA-670/2-74-065 (PB-234 496/AS); and EPA-670/2-
74-066 CPB-254 497-/AS)
16. ABSTRACT
The most promising wet system alternative is identified as a system
using individual household grinders in low density areas, vacuum collec-
tion and neighborhood grinders in high density areas, dilute slurry
transport of ground refuse in the existing sanitary sewer system, and
joint treatment of refuse and sewage at an expanded treatment facility
that includes anaerobic digestion for methane generation. However, the
economic feasibility of even the most promising alternative is doubtful
because of the high cost of grinding, and hydraulic transport of ground
refuse in existing sewer systems may be feasible only'if both metals and
flass are excluded. A conventional collection of the nongrindable and
ulky constituents of residential refuse will still be needed, albeit of
a diminished frequency. The total 1973 cost of such a wet system is
estimated at $113-$196 per household per year, of which $80-$105 is for
grinding. This compares to a total cost for refuse and sewage collec-
tion and disposal under existing concepts of up to $115 per household
per year. Projections for 1988 indicate that the wet system cost might
rise to $130-$228, against a range of $61-$143 under conventional con-
cepts. However, if the cost of the grinder is excluded (on the basis
that individuals would purchase grinders for their convenience benefits),
the 1973 wet system costs (to the public sector) would be only $33-$91,
thus possibly less than existing public sector costs of about $43-$115
per household per year.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
*Refuse, Collection, Sanitary
sewers, Garbage disposal,
Economic analysis, *Pipeline
transportation, Mathematical
models, Sewage treatment,
*Grinders
*Solid waste collection,
Ground refuse transport,
*Home refuse grinders,
Economic feasibility study,
*Hydraulic transport,
*Combined refuse/sewage
treatment
13B
'18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report)
UNCLASSIFIED
21. NO. OF PAGES
103
20. SECURITY CLASS (This page)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
93
U.S. GOVERNMENT PRINTING OFFICE: I974-657-58II/5305 Region No. 5-11
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