EPA-600/2-77"053b
December 1977
HANDLING AND DISPOSAL OF SLUDGES
FROM COMBINED SEWER OVERFLOW TREATMENT
Phase [I - Impact Assessment
by
Kathryn R. Huibregtse, Gary R. Morris,
Anthony Geinopolos and Michael J. Clark
Envirex Inc., Environmental Sciences Division
Milwaukee, Wisconsin 5321^
Contract No. 68-03-02^2
Project Officer
Anthony N. Tafuri
Storm and Combined Sewer Section
Wastewater Research Division
Municipal Environmental Research Laboratory (Cincinnati)
Edison, New Jersey 08817
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
This report has been reviewed by the Municipal Environmental Research
Laboratory, U.S..Environmental Protection Agency, and approved for publi-
cation. 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
The Environmental Protection Agency was created because of Increasing public
and government concern about the dangers of pollution to the health and
welfare of the American people. Noxious air, foul water, and spoiled land
are tragic testimony to the deterioration of our natural environment. The
complexity of that environment and the Interplay between Its components re-
quire a concentrated and integrated attack on the problem.
Research and development Is that necessary first step In problem solution
and It Involves defining the problems, measuring its impact, and searching
for solutions. The Municipal Environmental Research Laboratory develops new
and improved technology and systems for the prevention, treatment, and
management of wastewater and solid and hazardous waste pollutant discharges
from municipal and community sources, for the preservation and treatment of
public drinking water supplies, and to minimize the adverse economic, social,
health, and aesthetic effects of pollution. This publication is one of the
products of that research; a most vital communications link between the
researcher and the user community.
This report documents the results of an assessment of the effort that the
United States will have to exert In the area of sludge handling and dis-
posal If, in fact, full-scale treatment of combined sewer overflows is to
become a rea11ty.
Francis T. Hayo
Director
Municipal Environmental
Research Laboratory
111
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ABSTRACT
This report documents the results of an assessment of the effort that the United
States will have to exert in the area of sludge handling and disposal if, in fact,
full-scale treatment of combined sewer overflows (CSO) Is to become a reality. The
results indicate that nationwide an average yearly sludge volume of 156 x 10° cu m
(41.5 x ID? gal.) could be expected from CSO if complete CSO treatment were achieved.
This compares to a raw primary sludge volume of 60.9 x 10° cu m (16.1 x 10-* gal.).
However, the average solids concentration in CSO sludge is about 11 compared to 2-71
in raw primary sludges. This is due to the high volume, low solids residuals gen-
erated by treatment processes employing screens. The sludge volume generated and
the reported characteristics of the sludge vary widely, depending on the type of
treatment process used. The most notable differences from raw primary sludge were
the high grit and low volatile solids content in CSO residuals plus their intermit-
tent generation.
Evaluation of the effect of bleed/pump-back of CSO sludge on the hydraulic, solids
and/or organic loadings to the dry-weather plant indicated that overloading would
occur in most Instances. Disregarding grit accumulation in sewers plus other
transport problems, it was established that solids loadings to the secondary clari-
fier were limiting and required 8-22 day bleed/pump-back periods. There may also
be a toxic danger to dry-weather treatment plant biological processes.
The most promising treatment trains were found to include possible grit removal,
lime stabilization, optional gravity thickening, optional dewatering and land appli-
cation or landfill. Land application systems can be considered as viable alterna-
. tives for CSO treatment and disposal. The cost of the collection-transportation
and/or equalization system may be the crucial factor in disallowing the alternative
of direct application of raw CSO. If CSO treatment is employed by a city, land
spreading of CSO sludges should be evaluated. Public health concerns dictate sludge
stabilization before disposal and pollutant loading limitations based on nitrogen
and heavy metal concentrations. An environmentally safe rate of application was
determined as 19-0 metric tons/ha/yr (8.5 tons/ac/yr).
Preliminary economic evaluation indicated that lime stabilization, storage, gravity
thickening, and land application was the most cost-effective treatment system.
Costs for overall CSO sludge handling depend on the type of CSO treatment process,
volume and characteristics of the sludge and the size of the CSO area, among other
considerations. Estimates indicate that first investment capital costs range from
$Mi7-10,173/ha ($!8l-*il29/ac) with annual costs of $139~l630/ha ($56-660/ac). It
is recommended that the use of grit removal, lime stabilization and gravity thick-
ening, plus dewatering, be further investigated to establish specific design
criteria related to CSO sludge.
This report was submitted in partial fulfillment of Contract No. 68-03-0242 under
the sponsorship of the Municipal Environmental Research Laboratory, Office of
Research and Development, U.S. Environmental Protection Agency. Work was
completed In February 1976.
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TABLE OF CONTENTS
Sections Pa9e
ABSTRACT iv
TABLE OF CONTENTS v
LIST OF TABLES vi
LIST OF FIGURES *
ACKNOWLEDGEHENTS xi(
I CONCLUSIONS 1
11 RECOMMENDATIONS 8
Ml INTRODUCTION 3
IV MAGNITUDES AND CHARACTERISTICS OF SLUDGES PRODUCED
BY NATIONWIDE TREATMENT OF COMBINED SEWER OVERFLOWS 12
V EFFECT OF HANDLING CSO TREATMENT RESIDUALS BY BLEED-
BACK TO THE MUNICIPAL DRY WEATHER PLANT 26
VI EFFECT OF HANDLING CSO TREATMENT RESIDUALS BY
SEPARATE ON-SITE TREATMENT Jk
VII CONSIDERATIONS FOR LAND APPLICATION OF CSO WASTES 92
VIII ECONOMIC IMPACT OF HANDLING CSO TREATMENT
RESIDUALS 135
IX REFERENCES 191
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LIST OF TABLES
Table
Number Page No.
1 TOTAL U.S. SLUDGE VOLUMES AND PERCENT SLUDGE SOLIDS
PRODUCED BY VARIOUS CSO TREATMENT PROCESSES 13
2 POPULATION EQUIVALENT COMPARISONS 16
3 CSO SLUDGE VOLUMES FOR VARYING TREATMENT EFFICIENCIES AND 1?
SLUDGE CONCENTRATIONS
4 CHARACTERISTICS OF CSO SLUDGES FROM PHYSICAL TREATMENT
PROCESSES 19
5 CHARACTERISTICS OF CSO SLUDGES FROM PHYSICAL/CHEMICAL
TREATMENT PROCESSES 20
6 CHARACTERISTICS OF CSO SLUDGES FROM BIOLOGICAL TREATMENT
PROCESSES 21
7 CHARACTERISTICS OF CSO AND PRIMARY SLUDGES 23
8 SUMMARY OF DESIGN AND OPERATIONAL PARAMETERS FOR VARIOUS
DRY WEATHER TREATMENT PROCESSES 30
9 GRAVITY THICKENER SURFACE LOADINGS AND OPERATIONAL
RESULTS 3k
10 TYPICAL DESIGN CRITERIA FOR STANDARD RATE AND HIGH RATE
DIGESTERS 3k
11 AEROBIC DIGESTION DESIGN PARAMETERS 35
12 VACUUM FILTRATION DESIGN PARAMETERS AND PERFORMANCE 36
13 CRITERIA FOR THE DESIGN OF SANDBEDS 36
1^1 CSO TREATMENT METHODS UNDER EVALUATION 38
15 SLUDGE PRODUCTION AND SOLIDS DISPOSAL METHODS FOR VARIOUS
CSO TREATMENT PROCESSES 39
VI
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LIST OF TABLES (continued)
Table
Number Pa_ge_No.
16 EFFECT OF BLEED-BACK OF CSO TREATMENT SLUDGES ON HY-
DRAULIC OVERLOAD OF DWF TREATMENT PLANT 1,2
17 EFFECT OF iLEED/PUMP-BACK OF CSO TREATMENT SLUDGES ON
SOLIDS OVERLOAD OF DWF TREATMENT PLANT Ml
18 VARIATION IN QUANTITIES 0F GRIT REMOVED DURING WET WEATHER
AND PERIODS OF AVERAGE FLOW 46
19 ORGANIC CHARACTERISTICS (BOD) OF CSO TREATMENT RESIDUAL
SLUDGES 47
20 CONCURRENT SOLIDS LOADING ON SECONDARY TREATMENT PLANT
UNDER THE OPERATING CONDITIONS DESCRIBED IN TABLE 13 51
21 METAL LOADING FROM ROAD SURFACE RUNOFF COMPARED TO NORMAL
SANITARY SEWAGE FLOW 52
22 EFFECTS OF HEAVY METALS ON BIOLOGICAL TREATMENT PROCESSES 52
23 COMPARISON OF HEAVY METAL CONCENTRATION IN SANITARY
SEWAGE AND VARIOUS CSO TREATMENT SLUDGES 54
2k EVALUATION OF THE POSSIBLE TOXIC EFFECT OF HEAVY METALS
ON DRY WEATHER TREATMENT DUE TO BLEED/PUMP-BACK OF CSO
TREATMENT SLUDGES 55
25 CONCENTRATION OF SELECTED PESTICIDES IN CSO TREATMENT
SLUDGES 58
26 EFFECT OF BLEED/PUMP-BACK OF CSO TREATMENT SLUDGES ON
DRY WEATHER PLANT INFLUENT PESTICIDE CONCENTRATIONS 58
27 LIMITING FACTORS IN DAYS FOR BLEED/PUMP-BACK 59
28 EFFECT OF BLEED/PUMP-BACK OF DILUTE EFFLUENTS FROM DE-
WATERING OF CSO SLUDGES ON DRY WEATHER TREATMENT PLANT
HYDRAULIC AND SOLIDS LOAD 63
29 VOLATILE SOLIDS CONTENT OF SLUDGES FROM VARIOUS CSO
TREATMENT PROCESSES 66
VI 1
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LIST OF TABLES (continued)
Table
Number Page No.
30 ESTIMATES OF DRY WEATHER PLANT SLUDGE VOLUMES PRODUCED
FROM THE TREATMENT OF DILUTE EFFLUENTS PUMPED BACK
AFTER DEWATERING CSO TREATMENT SLUDGES 6?
31 ESTIMATED SOLIDS TO THE DRY WEATHER SLUDGE HANDLING
FACILITIES FROM THE TREATMENT OF DILUTE EFFLUENTS
OBTAINED FROM CSO SLUDGE DEWATERING 72
32 COMPARATIVE CHARACTERISTICS OF IRRIGATION, INFILTRATION-
PERCOLATION, AND OVERLAND FLOW SYSTEMS 95
33 COMPARISON OF IRRIGATION, OVERLAND FLOW, AND INFILTRA-
TION-PERCOLATION SYSTEMS 97
3k SITE SELECTIQH FACTORS AND CRITERIA FOR EFFLUENT IRRI-
GATION 98
35 REPORTED REMOVAL EFFICIENCIES OF LAND DISPOSAL AFTER
BIOLOGICAL TREATMENT 100
36 NATIONAL PRIMARY DRINKING WATER STANDARDS 104
37 RECOMMENDED AND ESTIMATED MAXIMUM CONCENTRATION OF
SPECIFIC IONS IN IRRIGATION WATERS 114
38 IMPORTANT MONITORING SEGMENTS OF LAND APPLICATION
PROCESS 117
39 SUMMARY OF RECOMMENDED APPLICATION RATES FOR VARIOUS
RAW CSO POLLUTANTS AND THE RELATED LAND AREA REQUIRE-
MENT 124
40 SUMMARY OF RECOMMENDED DRY SLUDGE SOLIDS APPLICATION
,RATES FOR VARIOUS CSO SLUDGE POLLUTANTS AND THE
RELATED LAND AREA REQUIREMENT 132
41 COSTS FOR BLEED/PUMP-BACK-MILWAUKEE 158
42 COSTS OF TREATMENT AT PARALLEL DRY-WEATHER FACILITIES-
MILWAUKEE 159
43 COST ESTIMATES FOR CSO SLUDQE HANDLING BY SATELLITE
TREATMENT - MILWAUKEE 160
VIM
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UST OF TABLES (continued)
Table
Number PageNo.
44 COST ESTIMATES FOR CSO SLUDGE HANDLING BY SATELLITE
OPERATION - SAN FRANCISCO 167
45 COST ESTIMATES FOR CSO SLUDGE HANDLING BY SATELLITE
TREATMENT - KENOSHA 1J1
46 COST ESTIMATES FOR CSO SLUDGE HANDLING BY SATELLITE
TREATMENT-NEW PROVIDENCE 177
4? ASSUMPTIONS FOR COST CALCULATIONS 180
48 COST ESTIMATES FOR 500 ACRE CSO AREA 18!
49 COST ESTIMATES FOR 5,700 ACRE CSO AREA 183
50 COST ESTIMATE FOR 25,000 ACRE CSO AREA 18$
51 COST ESTIMATES FOR 60,000 ACRE CSO AREA 18?
52 ANNUAL COST FOR CSO SLUDGE HANDLING 189
53 CAPITAL COST INFORMATION FOR CSO SLUDGE HANDLING 190
IX
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LIST OF FIGURES
Figure
Number Page No,
1 Relative use of combined sewers by states Ik
2 United States median annual precipitation 15
3 Conventional activated sludge plant 23
k Schematic diagram of the various steps leading to
ultimate sludge disposal 32
5 Raw wastewater and BOD variation 37
6 Limiting percent of CSO area based available capacity 61
7 Sludge handling systems 78
8 Lime stabilization process conceptual flowsheet 81
9 Methods of land application 94
10 Generalized climatic zones for land application 107
II Storage days required as estimated from the use of the
computer program as described 110
12 Potential evapotranspiration vs. mean annual precipi-
tation (inches) 111
13 Capital cost estimate basis-primary sludge pumping 137
14 Capital cost estimate basis-gravity thickening 138
15 Capital cost estimate basis-lime stabilization 139
16 Capita) cost estimate basis-vacuum filter dewaterlng
17 Capital cost estimate basis-landfill
18 Manpower cost estimate basis-primary sludge pumping 142
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LIST OF FIGURES (continued)
Figure
.Number Page^ Mo.
!9 Manpower cost estimate basis-gravity thickening H3
20 Hanpower cost estimate basis-vacuum filter dewatering lM
21 Electrical energy cost estimate basis-primary sludge
pumping
22 Electrical energy cost estimate basis-gravity thickening
23 Electrical energy cost estimate basis - vacuum filter
dewatering
2k Capital arid 0/M costs for sanitary landfills
25 Truck transport total annual cost with loading 6 unloading
facilities 8 hour operation per day liquid sludge 1976
26 Truck transport total annual cost with loading & unloading
facilities 8 hour operation per day dewatered sludge 1976 t$G
27 Storage (0.05-10 million gallons) 152
28 Storage ,(10-5,000 millions gallons) 153
29 Field preparation - site clearing 154
30 Typical monthly distribution of precipitation in San
Francisco, California 163
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ACKNOWLEDGEMENTS
The authors gratefully acknowledge the assistance of other Environmental
Sciences' Division personnel who provided technical and clerical Input to
thfs report. Special thanks are extended to the technical Project Officeri
Mr. Anthony Tafurl, for providing needed technical information and
guidance throughout the course of the project.
XI I
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SECTION I
CONCLUSIONS
Nature of the Problem
a. It Is established that |3 percent of the sewered population or
approximately 36,2 x 10 people are served by combined sewers. This
service Is approximately 1.23 x 106 ha (3.03 x 10b acres) and is
mainly concentrated In the Northeast and Great Lakes regions of the
country.
b. Assuming an average annual rainfall of 91.4 cm (36 in.) and that 50
percent of the rainfall results in overflow, then the yearly combined
sewer overflow (CSO) is 5,6 x 10? cu ra (1.5 x 1012 gal.).
Similarly, the annual dry weather flow for the combined sewer popu-
lation served is 6,3 x 10° cu m (1.7 x 10** gal.), assuming *»73 *>
(125 gal.) per capita per day.
c. The volume of sludge generated from CSO treatment is dependent upon
many factors including area served, rainfall and type of CSO treat-
ment method used* The sludge volume generated will range from 0.6
to 6 percent of the CSO volume treated, depending on the CSO treat-
ment process utilized.
d. There have been six state-of-the-art processes proposed for treating
combined sewer overflows. If It is assumed that the total combined
sewer overflow volume is treated by each technique, the following
volumes and solids concentrations of CSO residuals may be estimated,
assuming 70 percent solids removal:
6 o
storage-sedimentation: 50.^ x 10 cu m (13.3 x 10 gal.), 1.7%
solids
microscreening: 336 x 106 cu m (88.8 x 1Q9 gal.), 0.7? solids
screening/dissolved air flotation: 268 x 10° cu m (71.1 x 10°
gal.), 0.84% solids , q
dissolved air flotation: 33.6 x 10 cu m (8.8 x 10y gal.),
2.751 solids 6 q
contact stabilization: 196.1 x 10 cu m (51.8 x 10 gal.), 1.0%
solids , -
trickling filtration: 39-2 x 10 cu m (10.3 x 10* gal.), 3.2|
solids
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e. The average yearly volume of CSO sludge Is estimated to be 156 x
10° cu m (M.5 x 1CP gal.) compared to an annual primary sludge
volume of 60.9 x 1Q*> cu m (16,2 x 10^ gal.). However, the average
percent solids In CSO sludge is 1.04 percent compared to a primary
sludge with 2-7 percent solfds. The low value for CSO sludge can be
attributed to the high volume-low solids residuals generated by
backwash of the screen frig processes used.
f. Comparison of per capita CSO sludge values with the per capita dry
weather values over a 365 days per year period Indicates that the
values are comparable. However, the magnitude of the CSO disposal
problem on a per unit time basis Is six times greater when it Is
recognized that overflows occur only 60 times per year.
g. The characteristics of CSO sludges vary widely depending upon the CSO
treatment method utilized. A comparison of quality with dry weather
primary sludges indicates that the volatile solids content of CSO
sludge Is significantly lower than that found In most primary sludge.
In other parameters, the ranges of reported values overlapped.
Generally, nutrient concentrations and fecal collform counts were
lower for CSO sludges than for raw primary sludges. Metal concen-
trations varied wldetyj however, In general, nickel concentrations
were higher and lead concentrations were lower In CSO sludges com-
pared to raw primary.
h. Differences in CSO sludge characteristics compared to dry-weather
sludge most pertinent to further handling are the high grit and low
volatile sludge concentration, the lower average percent solids,
the variable volume of sludges produced and their intermittent
generation.
2. Alternatives for Handling and Disposal of CSO Generated Residues
Alternatives for handling CSO treatment sludges Include (a) bleed/puwp-
back to the dry-weather facilities, (b) dewaterlng at parallel facilities
at the dry-weather plant or at central facilities separate from the dry-
weather plant and (c) dewaterlng at on-slte facilities.
a. Bleed/pump-back of CSO treatment sludges to the dry-weather
facilities.
(I) The more excess capacity available at the dry-weather plant,
due to built-in safety factors for expansion, the more feasible
bleed/pump-back of CSO sludges.
(2) This procedure would Involve the lowest costs due to reduced
transportation and use of existing dry-weather facilities for
handling. However, this alternative has inherent disadvantages
which make the procedure generally not applicable.
(3) Bleed/pump-back will not be possible unless sufficient scouring
velocity can exist in the individual sewer interceptors to
prevent accumulation of grit In the lines. Excessive grit
deposition In the sewer can cause odor, septicity, and blockage
problems and if flushed to the plant, adversely affect normal
operation.
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(4) The bleed/purop-back of CSO sludges or the residuals from on-
site dewaterfng will have an effect both on the dry-weather
treatment plant and the sludge handling facilities. These
Impacts can be considered separately.
(5) Impact of bleed/pump-back of CSO sludges on the dry-weather
treatment plant has been evaluated with respect to hydraulic,
solids (primary and secondary), organic and toxic materials
loadings to the various processes. Bleed/pump-faack of the
sludge over a Ik hour period although desirable from a stand-
point of limited storage and reduction In septlcity, is not
possible In most instances.
(6) The limiting factor to consider Is the solids loading to the
final clarlfler. Calculations Indicate that bleed/pump-back
periods of 8-22 days are necessary depending upon the CSO
treatment method Involved.
(7) Bleed/pump-back of CSO treatment sludges directly to the dry-
weather sludge handling facilities over a 2k hour period will
overwhelmingly overload these facilities hydraulIcally, solids
wise and organically. These gross overloads will be expected
to detrimentally affect the dewatering and stabilization per-
formance and treatment efficiency of the dry-weather sludge
handling facilities. The down-grading in treatment efficiency
would be manifested In poorly stabilized sludge for disposal
and grossly deteriorated thickener effluents, filtrates,
supernatants, etc. for recirculation back to the dry weather
treatment plant.
(8) Disadvantages of bleed/pump-back also Include the adverse
effect on the operation and efficiency of the dry-weather plant
caused by loading the plant at excessive levels constantly
and the difficulty In storing CSO residuals without stabiliza-
tion for any excessive length of time.
b. Oewaterlng CSO treatment sludges at parallel facilities at the dry-
weather plant or at central facilities separate from the dry-weather
plant.
(I) Transportation and potential space problems limit the applica-
bility of parallel facilities or central locations.
c. Dewatering at on-site Facilities.
Handling of CSO treatment sludges in the dry-weather plant or In
additional parallel facilities at the dry-weather plant or in
separate facilities at the dry-weather plant do not appear to be
generally feasible, therefore It is indicated that CSO sludges
will have to be treated separately at the on-slte facilities.
(I) Evaluation of sludge handling processes from the standpoint
of the high grit and low volatile content of CSO sludges along
with the variable and intermittent generation reduces the
number of processes applicable for CSO sludge handling.
(2) Preliminary screening on the basis of CSO sludge characteristics
and known information about the processes, Indicates that the
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following processes may be generally applicable:
conditioning: chemical treatment
thickening: gravity thickening
stabilization: lime stabilization
anaerobic digestion
dewaterfng: vacuum filtration
centrlfugatlon
disposal: land application
landfill
(3) Combinations of the above processes yields approximately ten
potential treatment schemes. Examination indicated that bleed/
pump-back of dilute residuals from on-site dewaterlng to the
dry-weather plant appears to be practical and warrants further
consideration where applicable*
Further evaluation of stabilization techniques Indicates that
anaerobic digestion Is more costly and difficult to operate
than lime stabilization and therefore this process was not
considered for further study.
(4) Four sludge handling alternatives were than developed for CSO
sludge hand!ing:
(a) Lime stabilization •> gravity thickening •* vacuum filtra-
tion •»• landfill
(b) Lime stabilization •> gravity thickening -*• vacuum filtra-
tion •»• land application
(c) Lime stabilization -*• gravity thickening •*• land application
(d) Lime stabilization •+ land application
i Preliminary indications are that the flow scheme utilizing lime
stabilization plus gravity thickening and then land applica-
tion Is the most cost effective for CSO sludge handling on a
generalized basis.
(5) The logistics of operating and maintaining multiple CSO solids
handling plants (5,10,100) at different locations throughout
a city are formidable but not Insurmountable. Similar, If not
greater logistics would be required for multiple CSO treat-
ment facilities from which the sludges to be handled are de-
rived.
3. Costs for Handling and Disposing of CSO Generated Sludges.
It Is emphasized that all costs presented are generalized and should not
be applied to Individual situations.
a. To establish generalized CSO sludge impact, the cities served by
combined sewers were evaluated. Of the total 259 cites, It was
found that about 12.5 percent had CSO areas of kOS ha (1000 ac) or
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less, 47.5 percent had areas from 405-4050 ha (1000-10000 ac), 35 percent had
CSO area from 4050-16,188 ha (10000-40 000 ac) and about 5 percent had larger
areas. From this Information, four generalized CSO areas were chosen for
further cost evaluation.
b. The generalized costs for CSO sludge satellite treatment assuming
50 percent of rainfall Is CSO and that either contact stabilization
or dlssolved-alr flotation was used for treatment, are presented
below:
CSQ area Annual 'Cosj]T$I '
ha acres
203
2,307
10,118
24,282
500
5,700
25,000
60,000
0.105
0.36
2,24
3.33
~ 0.330 x 10
- 1.96 x 106,
- 10.38 x 10
- 26.1 x 10b
210 -
64 -
77 -
56 -
660
345
415
435
For four example cities, cost estimates were prepared for handling
and disposing of their sludges if complete CSO treatment Js achieved
(for New Providence the cost Is for treatlnq Increased sanitary sewer
flows due to wet weather sewer infiltrations). The four treatment
schematics [see Conclusion 2.c.(4)] were evaluated and a cost range
is included.
City
Milwaukee, Wl
San Francisco
Kenosha, Wl
New Providence, NJ
CSO
ha
7,006
12,150
539
0
area
ac
17,300
30,000
1,331
0
Annual Cost (range)
$1.49 - 2.53 x 1o!
$1.19 - 2.U x 10?
$0,21 - 0.46 x 10?
$0.09 - 0.15 x 10
d. The economic impact of treating CSO sludges nationwide using one
of the treatment systems evaluated would range from $169 x 10 -
$1,720 x 109 annually with initial capital costs estimated to range
from $548 x 106 - $12.5 x 109.
4. Land Application for Disposal of CSO Raw Waste and of CSO Treatment
Sludges.
a. General
(1) Land application systems can be considered as viable alterna-
tives for waste treatment and disposal. The feasibility of
land application of CSO wastes may be evaluated under various
conditions. This development would provide a rational screen-
ing ruethod which should lead to; 1) the Identification of
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specific limiting factors, 2) an Indication of the public
health and legal constraints in using land application and
3) site locations that combine the required characteristics
for safe pollutant management.
(2) For most land application systems, vast numbers of design possi-
bilities are available to suit specific site characteristics,
treatment requirements and overall project objectives. The
scope of factors that are commonly considered in the design
process include: a) preapp]ication treatment requirements;
b) storage requirements; c) climatic factors; d) pollutions!
loading constraints: e) land area requirements; f) crop selec-
tion and management; g) system components; h) site monitoring
program; and I) cost-effectiveness.
b. Handling CSO Raw Waste
(1) An alternative to the treatment of CSO and the resultant
problems of sludge handlitig and disposal Is direct application
of the raw CSO to the land. Land area requirements necessary
for a safe rate of application, as controlled by liquid loading
limitations, are 3k,k x 106 £ of CSO/ha/yr (3.6 x 106 gal./ac/
yr).
(2) The cost of the collection - transport and/or equalization
system may be the crucial factor in disavowing land disposal
of raw CSO as an alternative to other CSO treatment methods.
It may be feasible to use land disposal in cities which have
relatively small CSO areas and have land available in close
proximity to the city, but cities with large CSO areas, even
if the land Is available, may find that the cost of the collec-
tion - transport system might be prohibitive.
(3) Considering the hydraulic loading limit and if the land re-
quired for actual disposal is 70 percent of the entire disposal
site, nationwide disposal of raw CSO would require a total land
area of 323,560 ha (587,300 acres), inclusive of that required
for buffer zones and storage and pre-treatment facilities.
c. Handling CSO Treatment Sludges
(1) if CSO treatment is employed by a city, one viable alternative
to the disposal of CSO sludges can be by landspreading applica-
tion. Three management options would be available: 1) land-
spreading a dilute sludge (1% solids); 2) landspreading a
thickened sludge {4-6% solids) and 3) landspreading a dewatared
sludge (>12| solids).
(2) if regulations require CSO sludges to be treated prior to land
application, lime stabilization appears to be a promising
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preappllcation treatment process because of its flexibility
and effectiveness. In terms of both cost and performance.
(3) In transporting CSO sludges, It appears that truck transporta-
tion of either liquid or dewatered sludge is the most desirable
alternative In CSO areas with significant volumes of sludge to
be handled. Truck transportation of dewatered sludges might
prove to be the more desirable alternative If transporting and
storing costs are greater than the additional thfckening-de-
watering costs.
(k) For field area requirements, the nitrogen content Is the limit-
Ing loading factor for application of CSO sludges. An environ-
mentally safe rate of application was assumed as 18.9 metric
tons/ha/yr (8»5 tons/ac/yr). This Is tower than the average
range of 22 to k5 metric tons/ha/yr (10-20 tons/acre/yr) re-
ported In the literature for disposal of municipal sludges.
This discrepancy Is a result of differences in waste charac-
teristics (i.e. nutrients and metals).
(5) For sludge application to non-agricultural lands (*•£• strip
mine reclamation), higher loading rates may be allowable but
the migration of pollutants through the soil must be closely
monitored.
(6) Considering the loading limit established for nitrogen and the
fact that, on the average, the land required for actual disposal
Is 70 percent of a disposal site; nationwide disposal of CSO
sludges would require 117,760 ha (290,760 acres) of land, In-
cluding that required for buffer zones and pre-treatment facili-
ties.
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SECTION It
RECOMMENDATIONS
1. A CSO sludge treatment system consisting of nonvolatile solids removal,
lime stabilization, gravity thickening, optional sludge dewaterlng and
land application appears promising. However, since several aspects
are experimental, It is recommended that the swirl concentrator and or
other suitably available equipment be assessed with respect to Its
applicability for grit removal from CSO sludges and further investiga-
tion and demonstration of lime stabilization for application to CSO
sludges and to establish basic design and operating criteria be pursued.
In addition, the applicabiHty of further thickening and dewaterlng be
investigated to establish feasibility and obtain basic design criteria.
2. It is recommended that further information on the effect of lime on
sludges which may be applied to land be established. Particular atten-
tion should be given to the effect on crop growth, physical characteris-
tics of the soil and uptake of toxic materials. This Information can
then be utilized to modify current design criteria for land application
of CSO sludges.
-------
SECTION III
INTRODUCTI ON
The discharge of untreated sanitary and stormwater overflows from combined
sewers to receiving waters during and after heavy rains Is an important
source of Impairment of water. These storm generated discharges constitute
a high degree of pollutlonal load to water courses as measured by the usual
standards of biochemical oxygen demand, solids, collform organisms, and
nutrients.
The pollutlonal contribution of storm generated discharges is of national
significance, and the magnitude of the problem is Illustrated by the fact
that more than 1300 U.S. communities serving 36.2 million people have com-
bined sewer systems which provide one collection system for both sanitary
sewage and stormwater runoff (1). Sufficient information has been accumu-
lated to confirm that the combined sewer overflow problem Is of major Im-
portance and Is growing worse with Increasing urbanization, economic expan-
sion, and water demands (1,2,9),
Various alternatives have been proposed for dealing with the problems of
storm generated discharges. There appear to be four possible methods of
eliminating or minimizing the problems. These are:
I. Construction of larger interception sewers and expansion of treat-
ment capacity.
2. Construction of separate sewers,
3. Construction of holding tanks with provisions to bleed/pump-back
flows into the sewer system after the storm.
k. Treatment of the storm generated discharges at various possible
locations.
Each of these techniques has advantages and disadvantages when utilized for
CSO abatement at Individual locations. Construction of larger interceptors
throughout the country appears to be a formidable undertaking. Normal de-
sign capacity for interceptors is between 1.5 and 5.0 times the dry weather
flow (3)(*0« During a storm, the flow In a combined sewer may Increase from
50 to 100 times the dry weather flow (3). It is apparent that enlarging the
Interceptors to handle the great increase in anticipated stormwater flow
will have to be accompanied by enlargement of present sewage treatment plants
which must treat the Interceptor flow. The cost of this construction under-
taking would be In the multlblllJon dollar range. In addition, there are
monetary losses which would have to be borne by communities, individuals,
businesses and Industrial establishments as a result of extensive physical
inconveniences occurlng during construction.
-------
It has been estimated that providing complete separation of storm and sani-
tary sewers throughout the country would cost 48 billion dollars
(1967 prices)(1). In addition, the monetary losses to communities, Indi-
viduals, etc. as a result of separation would be considerable. Separation
of the sewers may not completely solve the problem, for studies indicate
that there is the distinct probability that separated stormwater may require
treatment under some circumstances (9).
The holding tank concept Is being used as a method of handling storm gener-
ated discharges. This method has met with limited success because of the
cost of tank Installation, the economic and physical limitations of holding
capacity, and the need for returning the flow to the Interceptor system for
treatment after the storm subsides. In many locations, an overloaded con-
dition exists at the treatment plant for several days after a major runoff
event and any additional runoff fn excess of holding tank capacity is dis-
charged to the receiving waters.
The fourth alternative for dealing with storm generated discharges is the
treatment of the discharge itself. Promising physical, physical-chemical,
and biological methods have been proposed for treating storm generated dis-
charges. Many of these concepts have been demonstrated or are planned for
demonstration by the U.S. Environmental Protection Agency (5,6»7).
As with most wastewater treatment processes, treatment of combined sewer
overflow will result in residuals which contain, in concentrated form,
the objectionable contaminants present in the raw combined sewer overflow.
However, handling the disposal of the residual sludges from the combined
sewer overflow treatment systems have been generally neglected, thus far, in
favor of the problems associated with the treatment of the discharge itself.
Sludge handling and disposal should be considered an Integral part of the com-
bined sewer overflow treatment because it will significantly affect the
efficiency and cost of the total treatment system.
The objective of this report, then, is to attempt a rough quantification of
the effort the United States wlM have to exert fn the future, fn the area
of sludge handling and disposal, if full-scale treatment'of'combined sewer
overflow is to become a reality. The results of this report will con-
tribute to a better understanding of the problem and will afd In the develop-
ment of future planning and research needs. It may be found. In fact, that
the potential problem of handling the sludges from combined sewer overflow
treatment may be greater than the problem of treatment Itself. Also, the
disposal of these residual solids Is only going to compound the disposal
problem now caused by the solids from dry-weather treatment plants.
Therefore, alternative techniques for handling combined sewer overflow
sludges have been presented In this report. The first section defines the
magnitude of the problems associated with combined sewer overflow treatment
residuals and the unique characteristics of the sludge itself. After the
problem has been defined, several handling methods are identified and
evaluated. One method Involves bleed/pump-back of the CSO sludge to the
dry-weather treatment plant. This technique has the advantage of utilizing
10
-------
existing transportation systems, but has Inherent difficulties such as grit
deposition and potential solids overload at the treatment plant. If bleed/
pump-back is not feasible, then the sludge must be treated with separate
facilities. These facilities may be located at the dry-weather treatment
plant, at a separate central location or at satellite locations throughout
the area served by combined sewers. Evaluation of the existing sludge
handling processes indicate that traditional solids treatment trains may not
be generally applicable due to the different characteristics and Intermittent
nature of the CSO sludge. However, the use of lime for stabilization, plus
thickening and possibly dewatering, and then land application for disposal
appears to be a viable treatment system for CSO sludges. The economics of
various treatment schemes for both actual cities and specific CSO areas have
been calculated and are presented. In this way, the magnitude of the
problem can be defined and a preliminary assessment of the Impact can be
made.
11
-------
SECTION IV
MAGNITUDES AND CHARACTERISTICS OF SLUDGES PRODUCED
BY NATIONWIDE TREATMENT OF COMBINED SEWER OVERFLOWS
INTRODUCTION
The problems associated with treatment or handling of any type of sludge are
formidable. The recent Increased emphasis on sludge handling has created
more interest In this aspect of wastewater treatment. With regard to treat-
ment of combined sewer overflow sludges, however, the most feasible handling
techniques are just beginning to be developed. Before the problem can be
adequately addressed, it is beneficial to define, as much as possible, the
volumes of siudges to be produced and their associated characteristics. To
do this, it Is necessary to make general assumptions regarding many aspects
of CSO treatment systems. But It must be emphasized at this point that the
characteristics and flow volumes presented herein are generalteat tons and
do not reflect Individual CSO sludge systems. Def1nitIon of quaffties and
quantities of sludges resulting from Individual processes is dependent upon
the treatment system utilized, pretreatment and location of the CSO site,
among many other factors. Specific applications and design of sludge han-
dling techniques should be developed Individually for each site. However,
for the purpose of defining the magnitude and severity of the problems asso-
ciated with handling various CSO sludges, a basic overall approach is
necessary. The ranges of values for CSO sludges have also been compared to
generalized dry-weather sludge volumes and characteristics. The basis for
the generalizations and the result of the quantifications have been included
In this section of the report.
COMBINED SEWER OVERFLOW VOLUMES
In order to estimate the total volume of combined sewer overflow and its
associated sludges, it is necessary to establish many variables which affect
CSO before ft is possible to accurately assess the overall situation. Among
the pertinent considerations are: the area served by combined sewers; land
use; rainfall volumes; number of overflows; type of treatment utilized;
population of area; etc. It Is necessary to evaluate the effect of these,
and other pertinent variables, In order to prepare a generalized potential
volume of CSO and associated sludges.
The sewered population of the United States as projected from 1962 data is
125,770,000 (1). Of this total, 36,236,000 or 2? percent of the sewered
population Is served by combined sewers. The combined sewer service area
12
-------
totals 1,226,745 ha (3,029,000 acres) (1). Figure 1 shows the distribution
of combined sewers throughout the United States (10). It can be seen that
the most concentrated use of combined sewers is In the Northeast and Great
Lakes regions of the country.
Figure 2 shows the distribution of the median annual precipitation through-
out the United States (11). The annual median precipitation across the
Northeast and Great Lakes regions of the country where combined sewers are
used extensively ranges from 63.5 to 114.3 cm (25-45 in.). A selected
average value for the purpose of further calculations Is 91.*! on (36 In.).
Using 1,226,745 ha (3,029,000 acres), an average yearly rainfall of 91.4 cm
(36 in.) and assuming 50 percent of the rainfall results in overflow, the
yearly volume of combined sewer overflow In the United States would be
5.6 x 109 cu m (1.5 x 1Q12 gal.).
Table 1 gives the sludge volumes produced, the percent solids of the sludges
produced by various combined sewer overflow treatment processes that have
been investigated (12), and the calculated sludge volume if treated by the
selected CSO treatment processes based on a total yearly combined sewer over-
flow volume of 5.6x1fl9 cu m (I.SxlO12 gal.).
TABLE 1. TOTAL U.S. SLUDGE VOLUMES AND PERCENT SLUDGE
SOLIDS PRODUCED BY VARIOUS CSO TREATMENT PROCESSES (12)
Treatment process
Storage with settling
Microscreening
Volume of
sludge as
percent of
volume treated
0.3
6.0
S 1 udge
percent
sol ids
1.74
O.JO
Sludge
vo 1 umes
produced
cu m
50.4x10
336.2xi06
Screen i ng/d ? ssolved-aIr
flotation
Dissolved-alr flotation
Contact stabilization
Trickling fiIter
4.8
0.6
3.5
0.7
0.84
2.75
1.00
3.20
269.0x10
33.6x10
39.2xl0
13
-------
LEGEND
RATIO OF PROJECTED POPULATION
SERVED BY COMBINED SEWERS TO
TOTAL SEWERED POPULATION. 1962
| | 0-10%
HI II- 25%
26- 5O%
51-75%
OVER 75%
Figure 1. Relative use of combined sewers by states (10),
-------
Figure 2, United States median annual precipitation (11)
-------
Assuming an equal mix of the various treatment methods, an average yearly
sJudge volume resulting from,treatment of all combined sewer overflows na-
tionwide would be 156.8 x 10 cu m (41.45 * 109 gal.}, or 2.8 percent of
the volume treated. The average percent solids of the sludge would be 1.04,
This value compared to an estimated 125,000,000 cu m (33-0 x ^Qy gal.) of
primary and secondary sludges generated annually (13). The average solids
concentration of the dry-weather sludge is approximately 2-31. The average
value for CSO sludge solids concentration is lower because of the high volume
- low solids residuals that are generated by the screening processes, micro-
screening (6% of volume treated at 0.71 solids) and screenlng/dlssolved-alr
flotation (4.81 of the volume treated at 0.84% solids).
Another approach to comparison of dry-weather sludge and wet weather sludge
is to use population equivalent factors. Table 2 shows a comparison between
total flow, sludge volume and solids mass based on the population served.
TABLE 2. POPULATION EQUIVALENT COMPARISONS(14)
Parameter
Flow: raw
waste
Flow: sludge
only
Solids loading
Units
gal ./capita-day
gal ./capita-day
]b/capl ta-day
Dry -weather
population
equivalent
125
2.65
0.44
CSO
365 days/yr
111
3.10
0.27
CSO
60 days/yr
679
18.90
1.64
gal. x 3.785 - £
Ib x 0.454 - kg
As can be seen the population equivalents for CSO sludge are approxi-
mately equal to that for dry-weather treatment plant design when considered
on the basis of 365 days per year. However, the average number of combined
sewer overflows annually Is 60 so that the actual loading Is more than six
times greater than typical design data.
The preceding calculations were based on the sludge volume and solids data
reported for the various processes In the literature (12). On the average,
the processes achieved a suspended solids (SS) removal of 70 percent. Dif-
ferences In the removal efflcfences and/or the sludge concentrations produced
will result In corresponding changes In the final sludge volumes. Table 3
shows the different sludge volumes that will be generated at varying treat-
ment efflclences and sludge concentrations If the nationwide combined sewer
16
-------
TABLE 3. CSO SLUDGE VOLUMES FOR VARYING TREATMENT
EFFICIENCIES AND SLUDGE CONCENTRATIONS
Volume Treated - 5-6 x 109 cu m (1.5 x 10 2 gal./year)
Influent SS = 409 mg/1
Percent SS
reraova 1
ach 1 eved
50
55
60
65
70
75
80"
85
90
95
Sludge volume produced at:
0.5*
CU TO X 10
228.6
252.1
274.4
298.3
320.5
344.0
366.4
389.9
412.5
436.0
solids
6 MGxTO"3
( 60.4)
( 66.6)
( 72.5)
( 78.8)
( 84.7)
( 90.9)
( 96.8)
(103.0)
(109-0)
(115.2)
1.0$ sol
cu in x tO
114.3
126.0
137,4
149.1
160.1
171.8
183.2
195.0
205.9
218.0
fds
HGxfO~3
(30.2)
(33-3)
(36.3)
(39.4)
(42.3)
(45.4)
(48.4)
(51.5)
(54.4)
(57.6)
Z.Q% sol
cu m x !Q
57-2
63.2
68.5
74.6
79.9
85.9
91.6
97.7
102.9
109.0
Ids
MGxIO"3
(15.D
(16.7)
(18.1)
(19.7)
(21.1)
(22.7)
(24.2)
(25.8)
(27.2)
(28.8)
3.0% sol
cu m x 10
38.2
42.0
45.8
49.6
53.4
57.2
60.9
65.1
68.9
72.7
Ids
MGxTO"3
(10.1)
(11. 1)
(12.1)
(13-1)
(14.1)
(15.D
(16.1)
(17.2)
(18.2)
(19.2)
-------
overflow volume Js treated. The values are based on an average combined
sewer overflow SS concentration of kOS rag/1 (9); and It should also be noted
that the volumes are based on the SS removal. Biological treatment methods
such as contact stabilization and trickling filters will also produce solids
fay conversion of dissolved organic matter to biological cell mass; and any
chemical addition that Is employed In the selected treatment process will
also add solids. These additional solids can Increase the final sludge
vo}ume.
From Table 3» it can be seen that as the treatment efficiency Is Improved
the volume of sludge that must be handled will increase. However, whenever
a thicker sludge can be produced the residual sludge volume will be reduced.
CSO TREATMENT SLUDGE CHARACTERISTICS
There are significant differences In the chemical and physical characteris-
tics of sludges which are generated by various CSO treatment methods. Tables
k, 5 and 6 (12) indicate the reported sludge characteristics from biological,
physical and chemical treatment systems. Even within these more specific
categories, there are large differences in the qualities which result.
Biological treatment sludges show the highest volatile fraction, about 60
percent, while the physical and physical/chemical treatment processes produce
sludges with a 25 to 48 percent volatile fraction. The BOD, total organic
carbon, dissolved organic carbon, total phosphorus, and total Kjeldaht nitro-
gen concentrations vary widely as the solids concentrations vary. The solu-
ble nitrogen forms; ammonia, nitrites, and nitrates, are, for the most part,
low In concentration except for the trickling filter secondary sludge which
has a very high content. The sludge densities range from 1.005 to 1.07 with
an average value of 1.026. The pH of the sludges ranges from 5.2 to 7-9.
The low value of 5.2 was found for the dtssolved-air flotation process in
San Francisco where alum addition is used to facilitate the flotation process,
As would be expected with higher volatile solids, the biological sludges have
the greatest fuel values. The biological sludges have an average fuel value
of 3515 cal/gm (6333 BTU/lb) while the other sludges have an average vaiue of
2032 cal/gm (3661 BTU/lb). Among the PCB's and various pesticides, the PCB's
are generally of the highest concentration. Zinc is usually the heavy metal of
highest concentration in the sludges, with the concentration of lead also being
fairly high. 6
COMPARISON OF CSO SLUDGES TO DRY-WEATHER FLOW SLUDGES
in order to more fully understand both the magnitude and the uniqueness of
the problems associated with treatment and handling of CSO sludges, it Is
valuable to compare CSO sludges to dry-weather flow sludges. The most
direct comparison which can be drawn Is between undigested primary sludge and
CSO sludge. Although the solids concentration of waste activated sludge most
closely resemble CSO sludge solids concentrations, the actual biomass charac-
teristics are different since grit removal and primary sedimentation have
preceded the process and removed the more easily separated materials. These
18
-------
TABLE k. CHARACTERISTICS OF CSO SLUDGES FROH
PHYSICAL TREATMENT PROCESSES (12)
Parameter
Total solids
Suspended sol 1 ds
Total volatile solids
Volatile suspended solids
BOD
TOC
Dissolved organic carbon
Total phosphorus (as P)
Total kjeldahl nitrogen
(as H)
Ammonia (as N)
NO. (as N)
NO* (as N)
Specific gravity
pH
Total collforms
Fecal colfforms
Fue I va 1 ue
PCB's
pp'DDD
pp'DDT
Dieldrin
Zinc
Lead
Copper
Nickel
Chromium
Mercury
Units
mg/1
rog/1
mg/1
mg/1
mg/1
mg/l
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
—
__
1/100 ml
1/100 ml
ca 1 /gm
yg/kg dry
pg/kg dry
pg/kg dry
ug/kg dry
mg/kg dry
mg/kg dry
mg/kg dry
mg/kg dry
mg/kg dry
mg/kg dry
Storage
sedimentation
(Milwaukee, W!)
18,900
17,400
9,150
8,425
2,200
7,250
55
109.1
56
4.1
0.15
1.7
1.015
6,*
-
-
-
47
ND
ND
20
799
2,063
201
159
243
2.7
Storage
sedimentation
(Cambridge, MA)
126,900
110,000
57,500
41,400
12,000
16,200
946
293.4
28
3.2
0.4
0.5
1.06
5.7
210,000,000
2,800,000
2,721
6,570
ND
170
58
946
1,261
757
126
260
0.01
Mfcroscreenlng
(Philadelphia, PA)
8,660
7,000
2,520
1,755
-
1,032
.
11.5
46
-
-
-
1.05
7.4
-
-
1,791
ND
ND
ND
ND
1,189
2,448
200
289
52
2.1
ND = None Detected
-------
TABLE 5. CHARACTERISTICS OF CSO SLUDGES FROM PHYSICAL/
CHEMICAL TREATMENT PROCESSES (12)
Parameter
Total solids
Suspended sol ids
Total volatf/e solids
Volatile suspended solids
BOD
TOC
Dissolved organic carbon
Total phosphorus (as P)
Total kjeldahl nitrogen
(as N)
Ammonia (as N)
NO (as N)
N(T (as N)
Specific gravity
pH
Total coliforms
Fecal conforms
Fuel value
PCB's
pp'DDD
pp'DDT
Dieldrln
Zinc
Lead
Copper
Nickel
Chromium
Mercury
Units
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
rag/1
—
--
#/100 ml
#/100 ml
cal/gm
jjg/kg dry
yg/kg dry
pg/kg dry
wg/kg dry
mg/kg dry
mg/kg dry
mg/kg dry
mg/kg dry
mg/kg dry
mg/kg dry
Screening/
dissolved-air
flotation
(Racine, Wl)
9,769
8,433
3,596
3,340
1,100
260
60
39.2
112
6.3
<0,1
<0.1
1.01
6.g
40,000
Moo
1,961
603
ND
ND
2k
1,638
1,023
481
251
251
2.3
Dissolved-air
flotation
(Milwaukee, Wl)
42,700
41,900
11,350
10,570
3,200
6,050
340
149
517
12.5
<0.1
<0.1
1.07
7.2
6,400,000
220,000
1,359
775
225
TR
9
855
164
248
173
150
2.1
Dissolved-ai r
flotation
(San Francisco, CA)
24,000
22,500
9,400
8,850
1,000
1,600
67
166
375
7-5
0.02
O.I
1.014
5.2
6,300,000
17,000
1,950
113
29
96
192
708
1,583
367
<83
1,667
3.9
ND = None Detected
TR «* Trace (<0.2 yg/1 on wet basis)
-------
TABLE 6. CHARACTERISTICS OF CSO SLUDGES FROM
BIOLOGICAL TREATMENT PROCESSES (12)
Parameter
Total sol f ds
Suspended solids
Total volatile sol ids
Volatile suspended solids
BOD
TOC
Dissolved organic carbon
Total phosphorus (as P)
Total kjeldahl nitrogen
(as^N)
Ammonia (as N)
NO (as N)
NO^ (as N)
Specific gravity
PH
Total col i forms
Fecal coltforms
Fuel value
PCS' 5
pp'DDD
pp'DDT
Dieldrin
Zinc
Lead
Copper
Nickel
Chromium
Mercury
Units
mg/1
mg/l
mg/1
mg/1
mg/1
mg/l
mg/1
mg/1
mg/l
mg/1
mg/1
mg/I
--
—
#/IOO ml
1/100 ml
cal/gm
yg/kg dry
yg/kg dry
yg/kg dry
pg/kg dry
rug/kg dry
mg/kg dry
mg/kg dry
mg/kg dry
mg/kg dry
rag/ kg dry
Contact
stab! 1 ization
(Kenosha, WI )
8,527
8,300
5,003
5,225
1,700
3,400
29
194
492
42
0.055
0.065
-
7-9
1,200,000
79,000
3,446
767
93
TR
88
7,154
528
1,454
528
1,278
2.6
Trlckl
Ing f i Iter
(New Providence, NJ)
p_rtmary_
2,010
1,215
1,120
780
728
700
220
22
65
9
0.02
0.11
1.005
-
3,400,000
44,000,000
3,585
547
NO
NO
ND
697
<498
995
995
746
100.5
secondary
25,500
25,070
15,500
14,770
11,200
13,000
710
436
6
180
0.02
0.09
1.013
-
1,000,000
1,300,000,000
3,583
-
-
-
-
1,294
353
1,020
784
2,471
—
ND =» None Detected
TR » Trace {<0.2 yg/1 wet basis)
-------
solids are then not associated with waste activated sludge but are present in
CSO sludges. In addition, CSO sludges have not been stabilized and therefore
a comparison to undigested residues Is valid.
A summary of generalized sludge characteristics including CSO sludges, raw
primary and digested primary Is Included In Table 7- The data presented has
been drawn from several sources, as indicated. Wide ranges have been pre-
sented because of the extreme variation In values obtained from the different
references. However, it Is understood that the large differences are due
mainly to large variations in influent wastewater characteristics and treat-
ment plant efficiencies throughout the country. There is also a large var-
iation in values indicated for the CSO sludges due to the different treatment
techniques utilized and the many other variables previously mentioned. There-
fore, It is necessary to provide only broad comparisons between the dry-
weather primary sludge and the CSO sludges.
The table Indicates that the potential volume of CSO sludges exceeds the
estimated primary sludge volume. However, the pounds of dry solids of the
two residues Is much more comparable due to the higher solids concentration
In raw primary sludges. Tnis difference in solids concentration Is an Im-
portant aspect when considering CSO sludges and is mainly due to the very
dilute backwash residue produced from the screening processes which treat
raw CSO, Additional thickening is required to reduce the volume of CSO
sludge to be either further stabilized or transported. This is desirable
since an increase In solids of 1% can halve the total volume being handled.
In addition to having a low solids content, the percent volatile solids In
CSO sludges Is significantly lower than that found In most raw primary
sludges. The highest value obtained for CSO sludges was associated with the
biological type of treatment, as expected. Even with this Input, the volatile
percentage was significantly lower for CSO sludge than for raw primary. Fur-
thermore, the values were much more comparable to already digested primary
solids. Therefore, lower effective removals of volatile solids are expected
as the microblal mass Is diminished due to a smaller feed source.
Comparison of other parameters Indicate that there are some differences, but
that the ranges of concentrations overlap In most categories. General ob-
servations indicate that the total nutrient concentrations are generally lower
In CSO sludges than In raw and digested primary sludge. Fecal col I form num-
bers are also tower possibly due to dilution of Influent from the rainfall.
No comparable data regarding pesticide content was available for raw CSO
sludges and raw primary, however, concentrations In digested primary were
somewhat higher than those detected In raw CSO sludges. Metals concentra-
tions tn all of the sludge types showed extremely high variations. The
concentration of metals In CSO sludges ranged close to the values obtained
for raw primary residue. The concentration of nickel was somewhat higher for
CSO sludges, however, lead concentrations did not reach the high levels re-
ported for some raw primary sludges.
One significant difference between CSO sludges and raw primary which Is not
apparent from Table 7» ts the high grit content of most CSO sludges. This
22
-------
TABLE 7. CHARACTERISTICS OF CSO AND PRIMARY SLUDGES
Parameter
Volume
Dry solids
Sludge production
TS
Volatile solids
Phosphorus (as P)
TKN
Ammonia
Fecal coll form
PCB's
pp'DDT
Dleldrin
Zinc
Lead
Copper
Nickel
Chromium
Mercury
Units
cu m/year
metric ton
m3/Mm3
percent
I of TS
mg/kg
mg/kg
mg/kg
#/100 mis
pg/kg
P9/kg
wg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
CSO Sludges*
156 x 106
1,67 x 106
2,000 - 200,000
0-3 - 6(1.04)
26,6 - 48.4
2,875 - 7,450
1,100 - 13,000
80 - 750
1.4 x 103 - 2.8 x 106
ND - 6,570
ND - 170
ND - 192
697 - 7,154
164 - 2,448
200 - 2,454
83 - 995
52 - 2,471
0.01 - 100.5
Raw
primary sjudge
60.9 x 10
6(3}
2.88 x 10!
2,440 - 3,530
(4)
60 - 80l '
3,500 - 12,200^
15,000 - 40,000
II x ,06<3>
(1)
900 - 8,400^
150 - 26, 000
200 - 1,740^
44 - 740
66 - 3
1.2 -
Digested
pri mary s 1 tidge
30.3 x 10
2.88 x 106
,(2)
(D
500
6 - 12(10)
30 - 60{1)
4,700 - 13,900
6,700 - 54,000
3,000 - 13,000
(1)
(D
(2)
6(3)
0.4 x 10
ND - 10,500
(3)
ND - 1,000
(3)
100 - 2,000
72 - 12,800
(3)
(5)
9,000 - 22,000
290 - 1,3&Q
20 - 1,500^
44 - 7,200^
1.4-7.0(5)
(5)
* All CSO values referenced from Tables 3, 4 and 5.
Superscript Indicates reference number attached.
-------
REFERENCES FOR TABLE 7
1. Metcalf 6 Eddy Inc., Wastewater Engineering: Collection, Treatment,
Disposal, McGraw-Hill Book Company, 1972, p. 586, Table 13-2.
2. Reed, S., Wastewater Hanagement by Disposal on the Land, Cold Regions
Research and Engineering Laboratory, Hay 1972, Tables B-l - B-4.
3. Farrell, J. B.» Overview of Sludge Handling and Disposal Proceeding
Pretreatment and Ultimate Disposal of Wastewater Solids, Rutgers
University, May 21-22, I97^» p. J-22.
k, U.S. EPA Process Design Manual for Sludge Treatment and Disposal.,
EPA 625/1-74-006, p. 3-1-
5. ilakelee, P. A. , Monitoring Considerations for Municipal Wastavater
Effluent and Sludge Application to the Land, Proceedings of the Joint
Conference on Recycling Municipal Sludges and Effluents on Land,
Champaign, IL, p. 183-198.
-------
high concentration of heavy participate matter Is caused by the high velocity
scouring of materials which accumulate fn sanitary sewers and the lack of
preseparatton of grit before treatment. Primary sedimentation Is generally
preceded by grit remova! which usually separates materials that settle
faster than 5 fpni or have a specific gravity greater than 2.6$. Without grit
removal for CSO residues, the characteristics of the sludge are significant-
ly affected by the presence of this grit. Special handling methods are
necessary to stabilize and dewater these materials since most traditional
techniques are not designed to take the heavy loading. This Is especially
true when transporting the sludges In a liquid form. The heavy partlculates
will tend to settle to the bottom of sewers or tanks and enhance putrefaction.
This situation may be extremely difficult to remedy and should be considered
before determining handling methods.
Another aspect of CSO sludge which Is difficult to quantify Is the Inter-
mittent nature of sludge production. This factor Itself presents problems
when compared to primary sludges which are produced dally with approximately
the same volume and characteristics. The Intermittent nature of the sludge
production Indicates that holding and pumpback of the material is necessary
to equalize the flows, however, holding the sludge may cause significant
changes in its characteristics, and create odor and sept!city problems. If
equalization Is not possible, then the sludge handling method must be flexi-
ble enough to accept shock loadings from wet weather sludge or a separate
facility capable of Intermittent operation must be constructed and utilized.
ft is therefore evident that the problems associated with handling CSO
sludges are unique and difficult to solve. The potential volumes of sludges
and the accumulation of pollutants Including solids, organ Ics, heavy metals
etc. generated by the treatment of combined sewer overflows are formidable.
The relatively dilute nature and low volatile solids content of the sludges
along with their intermittent generation create a. situation significantly
different from that encountered when dealing with raw primary sludges.
These differences and proposed techniques for dealing with them will be
considered in the following sections of the report. The evaluations of
various alternatives for handling these residuals are developed to assist
In arriving at an assessment of the impact, effort required, and resources
needed, if full-scale treatment of CSO discharges on a national level is
to be implemented.
-------
SECTION V
EFFECT OF HANDLING CSO TREATMENT RESIDUALS BY
BLEED/PUMP-BACK TO THE MUNICIPAL DRY-WEATHER PLANT
One of the possible methods for handling CSO treatment residuals is bleed/
pump-back of these materials to the dry-weather treatment plant. These
sludges may be either the dilute residuals themselves or the supernatant
liquor which was generated by on-site dewaterlng. In addition, the return of
residuals can affect either the total dry-weather treatment plant or the
sludge handling facilities, or both, depending upon the nature of the return
system. Full evaluation of the effect of residual bleed/pump-back can then
be broken down Into several sections:
1. Effect of bleed/pump-back of dilute residuals on the treatment plant.
2. Effect of bleed/pump-back of residuals from on-site dewaterlng
on the treatment plant.
3. Effect of b1eed/pump-back of dilute residuals on the sludge handling
facilities.
4. Effect of bleed/pump-back of residuals from on-site dewatering on
the sludge handling facilities.
To accomplish the evaluation, It is necessary to consider the effect of bleed/
pump-back on the design characteristics of the dry-weather treatment plant.
The following aspects are to be studied:
a) Hydraulic overload
b) Sol ids overload
c) Organic and inert solids overload
d) Toxic!ty to treatment
e) Treatment efficiency
f) Effluent quality (treatment system only)
These Individual considerations have been studied with regard to the bleed/
pump-back of residuals to the various parts of the treatment plant. The
results of the evaluation are discussed individually in this section of the
report*
TRANSPORT CONSIDERATIONS
it Is apparent that bleed/pump-back of the sludges to the dry-weather treat-
ment plant offers the simplest solution to handling CSO siudges. This al-
ternative utilizes existing transport facilities, a centralized treatment
-------
location and trained dry-weather treatment plant staff to provide handling.
However, there are inherent problems involved in bleed/pump-back, due to both
the general design of combined sewers and the high grit content of CSO sludge.
This section briefly presents some of the problems involved in bleed/pump-
back. The sections which follow assume that the CSO sludge has been satis-
factorily bled/pumped-back to the plant and the calculations establishing the
effect of the CSO sludges continues from that point.
One of the main problems with bleed/pump-back is that combined sewers cannot
be designed to provide needed velocity for scouring heavy particles during
dry-weather conditions. The WPCF Manual of Practice No, 9 states that, "It
is rarely possible to design combined sewers with adequate self-cleaning
velocities at minimum dry-weather flow if the capacity of the sewer also must
be adequate for stonnwater runoff. Hence, combined sewers often are subject
to deposition during dry weather and are dependent on frequent rainfall for
flushing" (15).
Calculations of the possible velocity in an existing combined sewer verifies
that statement. Using Camp's formula for calculation of the velocities re-
quired to transport sediments, the velocity in a 0.97 m x 1,27 m (38" x 50")
Interceptor required to transport a grit particle 0.2 mm in diameter with
specific gravity of 2.65 was 0.87 m/s (2.87 fps). The interceptor was de-
signed at a slope of 0.06 m/100 m (0.06 ft/100 ft) and velocity flowing full
was calculated to be 0.7 m/s (2,31 fps) which would scour particles less than
0.13 mm. Typical grit chamber design can remove particles of 0.2 mm or more
at velocities of 0.305 m/s (1 fps). So these calculations indicate that
there would be significant accumulation of particulates greater than 0,13 mm
in this sewer under dry-weather flow conditions.
It must then be recalled that there are high concentrations of grit within
the CSO sludges. This is due in part to grit and associated stormwater
infiltration through leaky joints in the sanitary sewers which is flushed
to the CSO treatment site during storm flow. Replacing the gritty sludge
in the downstream line will cause this accumulation to recur in the sewers
under most conditions. The problem is augmented by the fact that it is
desirable to equalize the flow to the treatment plant. Therefore, sludge
bleed/pump-baek would ideally occur at low flow, low velocity time periods,
causing even greater solids deposition. Once the solid materials have
collected on the sewer bottom, flow capacity usurpation and septicity and
odor problems can occur. These nuisances can create premature flooding and
pollution causing overflows, public relations problems and dry-weather
treatment plant operations difficulties. The septic solids can exert a
significant oxygen demand on the raw sewage flow and cause excessive
oxygen requirements at the treatment plant.
In conclusion, problems of bleed/pump-back of the sludge are therefore diffi-
cult to overcome and should be considered prior to recommendation of this
alternative for handling CSO sludges. If sufficient carrying velocity is
not available, the excessive grit deposition can cause a myriad of secondary
problems. Careful examination of the individual sewer interceptors to be
used for bleed/pump-back and knowledge of the sieve analysis and density or
particle settling velocities of the CSO sludge will be necessary in order to
determine if bleed/pump-back will cause deposition of solids in the inter-
ceptors .
27
-------
TREATMENT CONSIDERATIONS
GeneraJ
In order to accurately assess the impact of bleed/pump-back of CSO residuals
on any portion of the treatment plant, it is necessary to calculate the ef-
fects for each Individual site. However, It is desirable to approximate the
effects of bleed/pump-back of CSO sludges on a generalized basis to establish
what aspect of bleed/pump-back is limiting and when this technique might be a
viable handling method for CSO sludges. Therefore, it Is necessary to make
a series of assumptions in the approach to establishing the effect of bleed/
pump-back of CSO sludges or their dilute residuals on the dry-weather treat-
ment plant and the existing sludge handling facilities. Among the factors
to be considered are the type and degree of treatment utilized, the effect
of diurnal flow variation and contaminant strength, the CSO sludge charac-
teristics, the percent of CSO area contributing sludge to treatment, etc.
Degree and Type of Treatment Used, and. Effluent Discharge Requirements
It is essential to know the type of treatment processes utilized at the dry-
weather treatment plant In order to establish the effect of the bleed/pump-
back of both sludges and residuals. It is also Important to determine the
type of sludge handling facilities used for dewatering and then consider the
effect of CSO sludge bleed/pump-back on this portion of treatment individually.
U.S. Public Law 92-500 (1972) requires that by July I, 1977, publicly owned
(municipal) treatment works provide a minimum of secondary treatment. More-
over, effluent discharge limitations for suspended solids and BOD have been
promulgated at 30 mg/1 (monthly average) and k$ mg/1 maximum (seven day
average). Therefore, for purposes of this discussion, it may be assumed that
the dry-weather treatment facilities to which CSO treatment residuals are to
be bled/pumped back will provide a minimum of secondary treatment. Further-
more, for purposes of evaluating the effect of the CSO treatment residuals
bleed/pump-back on dry-weather treatment efficiency, the effluent discharge
limitations promulgated will be used. A schematic diagram of a typical acti-
vated sludge secondary treatment plant is shown In Figure 3. The end products
of waste treatment, namely, treated effluent and residual sludge solids, must
be disposed of efficiently and economically. Therefore, the dry-weather
facility consists of two systems, the waste treatment system and the sludge
handling system. The elements comprising the waste treatment system are
shown In Figure 3.
Referring to Figure 3» the process elements making up the treatment portion of
a municipal pollution control facility are grit removal, primary sedimenta-
tion, biological oxidation and final clarification. Various dry weather de-
sign and operational parameters associated with these process elements are
summarized in Table 8 and were obtained from the literature (16, 17, 18, 19).
These criteria are among those that will be used In the evaluation of the
effect of the CSO treatment residuals bleed/pump-back to dry weather treatment
facilities with regard to hydraulic, solids and organic overload as well as
treatment efficiency.
28
-------
U)
**M ^ MIT ^ HUKAII¥ - AERATiO* ,, , , -J FIK
IAL 1 i
SEWAGE ^ CHAMiEft " ^ TAUK { ' TAMK ' \ TAMK j '
\
f RETURN .
SLUDGE
i
UAS1
SLUC
PMMAftY
SLUME
i
1
[
'E
KE
i
TO
SLUDGE
DISPOSAL
EFFLUENT
figure 3. Conventional activated sludge plant.
-------
TABLE 8. SUMMARY OF DESIGN AND OPERATIONAL PARAMETERS FOR VARIOUS DRY
WEATHER TREATMENT PROCESSES (16)(1?)(18)(19)
UJ
O
Treatment
process
Grit removal
(0.2 mm, SP,
Gr. 2.65)
Plain sedimen-
tation
Aeration
Final sedimen-
tation
Hydraul Ic
Overflow rate
1/mJn/sq m
(gpm/sq ft)
1258
(30.9)
16-65
(0.4-1.6)
-
10-31
(0.25-0.75}
Suspended
Solids loading
Tcg/dayfsq m
(Ib/day/sq ft)
2.4-9.8
(0.5-2.0)
-
98-146
(20-30)
Organic
loading
kg BCD/day
kg MLSS
-
-
0.35-0.50
-
Detention
time
30-60 sec
1,5.2-5 hr
6-8 hr
2-3 hr
%
Sludge produced
cu m/1000 cu m Sludge
(cu ft/MG) solids
0.01-0.09
(1-12)
2.43 5
(325)
_
18.7 0.5-1-5
EffJuent
SS
fflf/1
-
80-120
-
10-50
-------
The treatment scheme shown In Figure 3 Is the minimum required In the near
future, and is one which is in common use today. It should be recognized
that many existing treatment plants are not capable of meeting the more
stringent performance levels required today [See Table 7 and compare final
clarification effluent suspended solids content expected (10-50 rag/I) with
that presently required (30 rng/l)]. Moreover, meeting additional regulatory
agency stipulations, such as (1) more stringent disinfection requirements,
(2) phosphorus removal and (3) partial or complete oxidation of ammonia ni-
trogen or high nitrogen removal, will require significant expansion and/or
modification of existing facilities.
Sludge handling should be considered an Integral part of the total waste
treatment process. Although the volume of dry weather residual sludges ob-
tained Is relatively small, usually 2% to 31 of the wastewater volume treated,
sludge handling and disposal Is complex, troublesome, and represents up to
251 to 501 of the capital and operating costs of a waste treatment plant (20).
Moreover, the problem Is growing. With the expansion of the economy and the
population and with the greater degree of treatment required, it Is expected,
within the next 5 to 10 years, that the volume of sludge requiring handling
and disposal will Increase by 601 to 70% (20). By far, the major portion
of the increased sludge volume expected will be obtained from secondary
treatment sludges, which are less concentrated than primary sludges, and
which are most difficult and expensive to treat. For example, In 1080 It Is
anticipated that 530,000 cu m/day (IkO MGD) of secondary sludge (2% solids)
will be produced, whereas only about 37,850 cu m/day (10 MGD) of primary
sludge (6% solids) are expected In that year (21).
The various steps leading to the ultimate disposal of the residual sludges
are presented, schematically, In Figure 4. From Figure 4, sludge handling
for ultimate disposal consists of a series of dewaterlng steps in which
the volume of sludge Is progressively reduced by removal of the water
associated with the sludge solids.
Thickening Is usually the first step In sludge handling and Is responsible
for removing the major portion of the water associated with the solids.
Thickening may be carried out by gravity sedimentation or by dlssolved-alr
flotation. Flotation thickening Is more amenable than gravity thickening
for dewatering biological sludges because flotation thickening Is not ad-
versely affected by the decomposition gases produced by the activity of the
biological sludges.
As shown In Figure k, further treatment and sludge volume reduction may be
obtained by digestion. Digestion Is a biological treatment process and may
be carried out aeroblcally or anaeroblcally.
Further dewaterlng may also be performed using vacuum filtration or centrf-
fugatlon, either with or without chemicals, or using sand drying beds or
1agoons.
Ultimate disposal of sludges Includes disposal on land (landfill, drying for
soli conditioning, land application) discharge to sea, and use of incinera-
tion and related processes,
31
-------
DIGEST 1 OH
MUST!
SLUDGE
THICKENING
t
t
1
t
i
I
i
1
WET
DISPOSAL
FILTRATION
L-.UJ
MY
DISPOSAL
CENTRirUGATION
— *
INCINERATION
4. Schamatlc diagram of tha various staps leading to
ultimata siudga •*«-—*»
-------
For a particular location, the combination of the sludge handling and dis-
posal steps to be used should be Integrated in such a manner as to arrive at
an optimum economical solution.
Various dry-weather design and operational parameters associated with several
of the sludge handling and disposal methods were obtained from the litera-
ture (20)(22) and are summarized In Tables 9-13. Criteria for other sludge
handling methods include:
I. ^Fjota11on Thicken Ing
Solids loading of 49-59 kg/day/sq m (10-12 Ib/day/sq ft) without
chemicals to produce a thickened sludge concentration of k-$% when
thickening waste activated sludge.
2. Lagoons
Solids loading rates suggested for drying lagoons are 36 to 39 kg/year/
cu m (2.2 to 2.4 Ib/year/cu ft) of lagoon capacity.
3. Centrlfugatlon
Pilot tests used to evaluate applications. Scale up procedures are
considered proprietary and are generally not available.
These criteria, discussed above, are among those that will be used in the
evaluation of the effect of CSO treatment residuals bled/pumped-back to the
dry-weather sludge handling facilities.
Diurnal Dry Weather Flow and Contaminant Strengths
Another pertinent consideration to establishing the effect of bleed/pump-
back is the diurnal dry-weather flow variation and contaminant concentration
patterns. These patterns can have a significant effect upon the viable
bleed/pump-back of CSO sludges. A typical diurnal flow and BOO pattern Is
shown in Figure 5. It Is Important to note that the diurnal pattern will
vary from day to day, from week day to weekend and also from month to month.
It Is apparent that the diurnal patterns developed for a dry-weather facility
may be used to compare the actual loading parameters with those of the plant
design values, to determine the degree of diurnal overload during dry-weather
periods. It is also evident that bleed/pump-back of CSO treatment residuals
will superimpose or increase the flow and contaminant loadings on the dry-
weather diurnal patterns, and therefore, on the actual loadings to the dry-
weather treatment facilities.
CSO Treatment Sludges Flow and Contaminant Strengths for Pump~Back
The magnitude and quality of the CSO treatment sludges to be pumped back to
the dry-weather facilities is a function of the type and efficiency of CSO
treatment, used. The CSO treatment methods presently being evaluated (12)
may be broadly classified as physical, physical-chemical and biological.
In general, it should be recognized that as treatment complexity and sophis-
tication increase (say, from physical to biological treatment), treatment
efficiency and sludge residue production also Increase. The specific CSO
33
-------
TABLE 9. GRAVITY THICKENER SURFACE LOADINGS
AND OPERATIONAL RESULTS (22)
Solids-surface loadings
Thickened
sludge sol ids
Type of sludge
Separate sludges
Primary
Modified activated
Activated
Trickling filter
Combined sludges
Primary and modified
activated
Primary and activated
Primary and trickling
filter
kg/day/sq m
98-146
73-122
24-29
39-49
98-122
29-49
49-59
(1b/day/ftz)
(20-30)
(15-25)
(5-6)
(8-10)
(20-25)
(6-10)
(10-12)
concentration (%)
8-10
7-8.5
2.5-3
7-9
8-12
5-8
7-9
TABLE 10. TYPICAL DESIGN CRITERIA FOR STANDARD
RATE AMD HJGH RATE DIGESTERS (22)
Parameter
Solids retention time (SRT), days
Solids loading, kg VSS/cu m/day
(ib VSS/cu ft/day) -
Volume criteria cu m/caplta
(cu ft/cap.)
Primary sludge
Primary sludge + thickening
filter sludge
Primary sludge •*• waste
activated sludge
Combined primary •+• waste biological
Sludge feed concentration per-
cent solids (dry basis)
Digester underflow concentra-
tion, percent solids (dry basis)
Lowrate
30 to 60
0.64-I.60
(0.04 to 0.1)
.056-.084
(2 to 3)
.112-.140
(4 to 5)
.112-.168
(4 to 6)
2 to 4
4 to 6
High rate
10 to 20
2.40-6.40
(0.15 to 0.40)
.037-.056
(1-1/3 to 2)
.065-.093
(1-2/3 to 3-1/3)
.075-.112
(2-2/3 to 4)
4 to 6
4 to 6
-------
TABLE 11. AEROBIC DIGESTION DESIGN PARAMETERS
Parameter Value
Solids retention time, days ^"^b
Solids-retention time, days t5-2Q
Volume allowance, cu m/capfta .084-.112
cu ft/captta 3-4
VSS loading, kg/cu m/day .384-2.24
Ib/cu ft/day .024-0.14
a
Air requirements
Dfffuser system, cu m/mln/1000 cu ra 20-35
cu ft/min/1000 cu ft 20j-35
DJffuser system, cu m/mln/1000 cu m 60
cu ft/mln/1000 cu ft 60
Mechanical system, kw/1000 cu m 26.6-33.3
hp/1000 cu ft 1.0-1.25
VSS, redaction, percent 35-50
Minimum DO, mg/1 J.0-2.0
Temperature, °C (°F) >J5 (>59)
Power requirement Bkw/10,000 pop.
equlv. 6-7.5
BHP/10,000 pop.
equlv, 8-10
Excess activated sludge only.
Primary and excess activated sludge, or primary sludge
alone.
35
-------
TABLE 12. VACUUM FILTRATION DESIGN PARAMETERS
AND PERFORMANCE (20)
Type of sludge
1 , Raw primary
2. Digested primary
3. Elutriated Di-
gested primary
4. Raw primary +
filter humus
5. Raw primary +
activated sludge
6. Raw activated
sludge
7. Digested primary
+ f 1 1 ter humus
8. Digested primary
•*• activated sludge
3. Elutriated digested
primary + acti-
vated sludge:
(a) average
w/o lime
(b) average
w/1 I me
TABLE 13
Type of digested
s 1 udge sq
Primary
Primary and standard
trickling filter
Primary and activated
Chemically precipitated
Chemical dose
rate, (%)
ferric
chloride lime
2.1 8.8
3.8 12.1
3.* 0
2.6 11.0
2.6 10.1
7.5 0
5.3 15.0
5.6 18.6
8.4 0
2.5 6.2
. CRITERIA FOR THE
SANDBEDS {22}
Yteld
kg/sq m/hr
(Ibs/sq ft/hr)
33.7 (6.9}
35.1 (7.2}
36.6 (7-5}
34.6 (7.0
22.0 (4.5)
—
22.5 (4.6)
19.5 (4.0}
18.6 (3.8)
18.6 (3.8)
DESIGN OF
Cake
moisture
<*)
69.0
73-0
69.0
75.0
77-5
84.0
77.5
78.5
79-0
76.2
Area Sludge loading dry solids
m/ capita (sq ft/capita) kg/sq ra/yr (Ib/sq ft/yr)
0.09 (1.0)
0.15 {1.6}
0.28 (3.0}
0.19 (2.0}
134.4
107.4
73.2
107.4
(27.5)
(22.0)
(15.0)
(22.0)
36
-------
LEGEND
A BOD LOADING, Ib/hr
g FLOW RATE, MGD
C BOD CONCENTRATION, mg/1
8
7 -
6 -
5 -
k
3
2
1 H
0
12
MIDNIGHT
12
NOON
TIME OF DAT
\
'300
,.600
-200 § •
J?
• tOO g-200
Q
e
a
-L 0
12
MIDNIGHT
NOTE: MCO x 3785 - cu m/dty
Ib/hr x .454 - kf/hr
Figure 5. Raw w«stewat*r and BOD variation (19)
37
-------
treatment methods being considered are listed In Table 14. Estimated sludge
production solids concentrations and solids disposal methods for the various
CSO treatment processes are shown in Table 15. Note from Table 9, that the
CSO treatment sludge quantities are based upon the quantity and quality of
the raw CSO treated.
TABLE 14. CSO TREATMENT METHODS UNDER EVALUATION
1. Physical Treatment
a> storage alone
b. Storage-sedimentation
c. Dlssolved-air flotation
d. Screening/dlssolved-afr flotation
e. Screening
2. PhysIcaI-Chemlca1 Trea tment
aTScreeni fng/dissolved-a?r flotation
b. Dlssolved-air flotation
3._ BlologJca 1 Treatment
a. Contact stabilization activated sludge
b. Trickling filters
c. Rotating biological contactors
d. Treatment lagoons
Furthermore, from Table 15 the major sludge disposal method used was dis-
charge to the Interceptor with ultimate disposal along with dry-weather
treatment facility sludge.
The quality of the CSO treatment sludges was observed in a recently com-
pleted EPA study (12) and, In general, the conclusions drawn with regard to
raw sludge characteristics were as follows;
1. The sludge volumes produced from the treatment of combined sewer
overflows varied from less than \% to 3% of the raw flow volume
treated. (This Is generally In agreement with Table 15).
2. The solids concentration of the sludge residuals from CSO treatment
varied widely, ranging from 0.121 to 111 total suspended solids.
The wide range observed is attributed to the CSO treatment method
used and treatment plant operation. (This is also In general agree-
ment with Table 15).
3. The volatile content of the sludge solids varied between 251 and
631 for the sludges obtained from the treatment types Investigated.
Biological treatment sludges showed the highest volatile solids
fraction (about 60S), whereas that for sludges from physical/chemical
treatment showed only 25 to 401 volatile fraction.
38
-------
TABLE 15. SLUDGE PRODUCTION AND SOLIDS DISPOSAL METHODS FOR
VARIOUS CSO TREATHENT PROCESSES (9)
Sludge %
Process Solids
Sedimentation 2.5-5-0
OIssoJved-AIr Flotation 1.0-2.0
Bar Screens HA
Rotary Fine Screens -•*-
Ultraflne Screens and
Mtcrostrairwrs
Filtration 0.4-1.":
Contact Stabilization 0-5-1-5
Trickling Filters and
Rotating Biological f
Contactors 3. 0-1 0.0
Physical -Chemical 2.0-5.0
SS
Removal _[5!)
1*0-75
40-70
___
27-34
25-90
50-90
80-95
60-30
80-100
Wet Sludge Volume
cu m/IOOo"eu ra (cu ft/HG)
1.92-7. kQ
4.96-17.0
0.01-0.03
—
_-„
8.14-55.5
13. 3-W.6
1.48-7.40
3. 92- \ 2.6
(260-1000)
(670-2300)
(l-4)c
---
._-
(1100-7500)
(I800-6300)e
(200-1000)
(530-1700)^
Dry Sol Ids
cu ffl/1000 cu
0
0
0
0
0
0
0
0
.07-0.
.07-0.
—
,04-0.
.04-0.
.07-0.
,15-0.
.11-0,
.15-0.
IS
15
07
18
18
18
18
IB
Volume
m (cu ft/HG)
(10-20)
(10-20)
—
(5-10)
(5-25)
(10-25)
(20-25) 6
(15-25)
(20-25)q
Sludge
Disposal Method For
Demonstration Project
Return
Return
land Ft 1
Return
Return
Return
Raturn
Return
to
to
1
to
to
to
to
to
Interceptor
Interceptor
Interceptor
Interceptor
Interceptor
Interceptor
Interceptor
Inclnerat ion/Land Ft 1 1
a. Assuming 250 mq/1 SS In the CSO end dry solids sp. qr. - 1.30
b. NA » not avallable
c. Volumes shown for screenings only, not SS (
d. Low value for unsettled backwash water; hiqh value for settled backwash water
e. Does not Include waste bloloqical solids produced in aeration tanks
f. Assuming sludge recycle
g. Does not include added chemicals
-------
k. As might be expected, fuel value of the sludges was correlated with
volatile solids content, and the biological sludges were observed
to have the highest fuel values among the sludge types Investigated.
5. Pesticide and PCB concentrations in the residual sludges Investi-
gated were observed to be significant. Generally, the PCB concen-
treations were higher than those for pp'DOD, pp'DDT and Dieldrin.
The range of PCB and pesticide values for the various sites Investi-
gated were presented in Section IV.
6. Heavy metal (Zn, Pb, Cr» Cu, Hg and Nl) concentrations in the
residual sludges were also significant, and varied widely for the
sludges investigated. The range of heavy metal concentrations for
the various sites investigated were also presented in Section IV.
Using the above and previous information, an attempt can be made to deter-
mine the effect of pumping back CSO treatment residuals on the operation
and performance of the dry~weather plant from the standpoint of hydraulic,
organic and solids overloads, effluent quality, and treatment efficiency and
toxlcity to treatment.
Capacity Available at Dry-Weather Plant and Percent of CSO Area Contributing
Sludge
Other considerations must include both the treatment and sludge handling
capacity available at the dry-weather plant and the percent of the total CSO
area which has treatment of runoff and therefore contributes sludge for
bleed/pump-back. Basic design of a new sewage treatment facility includes a
"built In" safety factor (which varies with the type of process equipment)
from 1.5~3 times the average loading. If the total "safety capacity" Is
available for handling CSO sludge or residual bleed/pump-back, this will have
a significant effect on the ability of the dry-weather plant to function
properly when CSO sludges are bled/pumped-back, For the purpose of the
following calculations, it is assumed that the total excess capacity is
available for hydraulic, solids and organic loads to the dry-weather treat-
ment plant and sludge handling facilities.
Another variable Is the total amount of CSO area which is treated by one of
the state-of-the-art CSO treatment methods. If 1001 of the total CSO volume
Is treated, this Impact on the dry-weather plant Is significantly greater
when considering bleed/pump-back. Also, the type of CSO treatment Is
crucial. The sludge characteristics and volume range widely, depending upon
the CSO treatment method. It Is not feasible to generalize, so, for most
of the calculated effects, each process has been considered individually.
Basis for Bleed/Pump-Back Calcyjatlons
The sections which follow address the effects of CSO sludges and dilute
residuals on a composite dry-weather treatment plant and sludge handling
facilities. \t must be reemphaslzed that actual determination of the
feasibility of bleed/pump-back will require the complete analytical charae-
40
-------
terlzatlon of the CSO residuals and the dry-weather treatment plant influent
and sludges, a knowledge of dry-weather flow characterization and actual de-
sign constraints for each of the unit processes In the treatment plant.
However, for this generalized approach it has been assumed that a secondary
treatment plant followed by thickening and dewaterlng will be the basic dry-
weather plant which would be affected by bleed/pump-back. This plant Is a
composite of all dry-weather treatment plants which serve the population of
36,236,000 having combined sewer systems. Also, it is assumed that ali CSO
area and volume in the U.S. has been treated by one of the CSO treatment
methods and that these sludges will affect the composite dry-weather plant.
The specific aspects for each of the four general effects are discussed
Individually.
EFFECT OF CSO TREATMENT RESIDUALS BLEED/PUMP-BACK ON THE OPERATION AND
PERFORMANCE OF THE DRY-WEATHER TREATMENT PLANT
The bleed/pump-back of CSO sludges can have an effect on any of the design
aspects of the composite treatment plant. Hydraulic, solids loading, organic
loading and toxlcity limits are considered individually,
K__ Hydraul l.c loading Cons jderattons.
It was previously brought out (Section IV) that the sewered population
served by combined sewers is estimated at 36,236,000. At 473 £(125 gal.)
per capita per day, the dry-weather treatment plants serving that g
population would have a dry-weather average design flow of 1J.I x 10
cu m/day {4.53 x 10° gal,/day). Most water pollution control plants
are designed to function properly at flows up to some low multiple of
the average dry-weather flow. Typical multiples range from 1.5 to 3.0
(9). Using this criterion, our composite national dry-weather plant
might be expected to function properly up to 25.7 x 10° cu m/day to
51.4 x 106 cu m/day (6.8 to 13-6 x 10'2 gal./day). Therefore, the sum
of the dry-weather average design flow (17.1 x 10° cu m/day) (4.53 x lo"
gal./day) plus the estimated dally CSO residual flows to be pumped back
may be compared to the above two figures to determine the effect of
bleed/pump-back on hydraulic overload to the dry-weather plant.
Previous discussion has estimated the annual volume of combined sewer
overflow in the United States as 5.6 x \Qr cu m (1.5 x 10^2 gal.).
Assuming 60 storm days per year (based on a 20 year average of 63 storm
days per year in the Milwaukee area), the average daily combined sewer
overflow is 93.4 x 10 cu m/day (24.7 x 10^ MGDJ.
CSO treatment methods currently under evaluation have been listed in
Table 14 and the sludge volumes produced by various CSO treatment pro-
cesses have also been given previously (Table 1 and in Table 9). Shown
In Table 16 Is the effect of CSO treatment sludges bleed/pump-back on the
hydraulic overload of the composite dry-weather treatment plant for
the various CSO treatment processes. It should be pointed out that
the data In Table 16 were calculated on the basis that the entire CSO
was treated by each of the selected treatment processes alone. From
4?
-------
TABLE 16. EFFECT OF BLEID-BACK OF CSO TREATMENT SLUDGES
ON HYDRAULIC OVERLOAD OF DWF TREATMENT PLANT (12)
Sludge Vol
CSO Treatment
Process
•Storage Alone
Storage-Sedimentation
1
CSO
ume
of million
Treated cu m/day MGD
100
0
•
Dlssolved-Air Flotation 0.
Screen
!ng/OAF
Microscreenlng
Contact Stabilization
Trick!
Ing Filter
DWF = Dry Weather
4
6
3
0
Flow = 1
•
*
•
*
7
9
6
8
0
5
7
,146,
Hydraulic overload determi
volume plus average DWF wi
DWF plants are expected to
cu m/day (6.8 to 13.6xlo3
CSO Treated = 93-
5xl06 cu
m/day
93.
0.
0.
4,
5-
3-
0.
000 cu
5
83
57
50
60
26
6*1
24700
220
150
H90
1480
860
170
m/day (4530
Sludge Vol
Plus Ave.
ml 1 1 Ion
cu m/day
no
18
17
21
22
20
17
ume
DWF
MGD
.6 29230
.0
4750
.7 4680
.7
.7
.4
.8
5720
6010
5390
4700
Hydraul Ic
Overload
Yes
No
No
No
No
No
No
MGD) (average)
nations made bv comparing sludcje
th design range of flows that
function properly: 26 to 51x10
MGD)
{24.7x1
03
MGD) -"Entire ."low hied
6
/Dumped
back
-------
Table 16, It Is evident that hydraulic overload would be expected only
when storage alone was used to Impound the entire CSO flow for bleed/
pump-back. This becomes apparent when comparing the average dally CSO
190,840,000 cu m/day (24,000 MGD)] with the average dally DWF of
[17,144,000 cu m/day (4,530 MGD)]. For the other CSO treatment processes
Investigated in Table 16, hydraulic overload would not be expected.
However, the rate of residual sludge bleed/pump-back over a 24 hour
period would have to be carefully controlled, with due regard to the
diurnal dry-weather flow (DWF) fluctuations (See Figure 5).
The apparent hydraulic overload produced by pumping back Impounded CSO
from storage alone over a 24 hour period raay be alleviated by spreading
the bleed/pump-back period over three or more days. (Of course, any
additional storms during the bleed/pump-back period may adversely affect
bleed/pump-back operation). Again, the rate of bleed/pump-back would
have to be carefully controlled, with due regard to the diurnal DWF
flucutatIons.
2. So 11 ds Loa d Ingl. ^Cgnsjje raj^Iorre
Untreated municipal sewage generally contains an average suspended solids
content of 200 mg/I (9). For our hypothetical average DWF of 17.1 x 106
cu m/day (4,500 MGD), an average dally dry solids loading to the dry-
weather plant of 3.4 x 106 kg (7.6 x 106 Ibs) per day may be expected.
Assuming that the range multiple of desfgn solids that a dry-weather
plant can properly handle Is typically 1.5 to 3.0, the dry-weather plant
raay be expected to handle from 5.1 x 10b kg (11.3 x 106 Ibs) per day to
10.3 x 106 kg (22.7 x 106 Ibs) per day of dry solids. The above cri-
terion will be used as one measure in evaluating the effect of solids
overload resulting from pumping back CSO treatment residuals to the dry-
weather plant.
Shown in Table 17 Is the effect of bleed/pump-back of CSO treatment
sludges on the solids overload of the composite dry-weather treatment
plant for the various CSO treatment processes Investigated, Again, It
Should be pointed out that the data In Table 17 were calculated on the
basis that the entire CSO was treated by each of the selected treatment
processes alone. The solids removal efficiencies In Table 17 for the
CSO treatment processes Investigated are reasonably In the range of
those expected as Indicated In the literature (9),
From Table 17, It 5s evident that a marked solfrds overload may be ex-
pected by pumping back CSO treatment sludges to the DWF treatment plant
over a 24 hour period, fn fact, the minimum solids overload varies
from about 150* to about 400%. The magnitude of the solids overload
varies directly with the solids removal efficiency of the CSO treatment
processes In question. The appreciable solids overload exerted on the
DWF treatment plant by pumping back CSO treatment residuals may be
expected to additionally adversely affect organic loading, effluent
quality and treatment plant efficiency,
43
-------
TABLE 17. EFFECT OF BLEED/PUHP-BACK OF CSO TREATMENT SLUDGES ON SOLIDS OVERLOAD
OF DWF TREATMENT PLANT (12)
Sludge Pumped Back
CSO Treatment
Process
Storage Alone
Storage-Sedimentation
Dissolved-Alr Flotation
Screen i*ng/DAF
-e-
Mlcroscreenlng
Contact Stabilization
Trickling Filter
million
cu m/day
93-5
0.83
0.57
4,50
5-60
3.26
0.6ft
HGD
24700
220
150
1190
1 WO
860
170
Percent
Solids
0 041
1.74
2.75
0.8k
0,70
1 .00
3-20
Dry Sol ids Dry Sol Ids
kg/dayxlQ J_b/dayx10_~_
38.4 8k 5
14.5
15-6
37.9
39.2
32.6
20.6
31
34
83
86
71
45
.9
4
k
.4
.7
It
CSO + DWF Solids
ka/dayxio'6 tb/dayxio"6
41
17
19
41
42
36
24
.8
• 9
.1
-3
-7
.0
.1
92
39
42
91
9'i
79
53
.1
• 5
.0
.0
0
-3
.0
Solids
Overload
Yes
Yes
Yes
Yes
Yes
Yes
Yes
CSO Treated = 93.5 x 10 cu m/day (24,700 MGD)
Solids overload determination made by comparing sum of CSO + DWF Mil Ids with the
design ranqm of solids that DWF plants ares expected to function properly:
5.1 x 106 to 10.3 x I06 kg/day (11.3 x I06 to 22.? x !06 Ib/day)
Available Capacity - 5.2 million kg/day
*iiescret>ancles in dry solids, are due to inaccuracies in pilot plant experimental data
-------
That substantial amounts of solids are transported to the dry-weather
plants during wet weather conditions is substantiated by significant
data available from the literature. For example, presented In Table 18
are data showing the quantities of grit collected during dry and wet
weather periods for various United States installations. The data in
Table 18 show that the grit volume ratio of wet to dry weather was
appreciable, with the highest ratio at 1800 times the average dry-weather
grit production.
The literature (9) also Indicates that often the stonnwater solids con-
tribute a large Increase tn fine solids (silt) which Is too fine to
be removed In the grit chambers and results In overloading the primary
sedimentation basins. The magnitude of the solids overload on the pri-
mary tanks may be estimated. For example, In Table 8 are shown the
allowable range in hydraulic loading for primary tanks (16.3-65-1 A/mln/
sq m) (0.4-1,6 gal./min/sq ft) and the allowable solids loading range
for those basins (2.4-9.8 kg/day/sq m) (0.5-2.0 Ib/day/sq ft). Assuming
a dry weather influent solids concentration of 100 mg/1 at the higher
overflow rate (65.1 fc/raln/sq m) (1.6 gpra/sq ft), the addition of CSO
treatment residual solids may result In Increasing the primary tank In-
fluent solids concentration to an estimated 150 mg/1 to 400 mg/l. This
would be expected to result in grossly overloading (14.2 to 37.6 kg/day/
sq m) (2.9 to 7.7 Ib/day/sq ft) the primary basins and detrimentally
affecting primary effluent quality and treatment efficiency. Moreover,
the high primary overflow rate (65.1 Jt/m!n/sq m (1.6 gpm/sq ft) would
result In grossly hydraulically overloading the activated sludge final
tanks and to adversely affect final effluent quality and overall treat-
ment efficiency.
Again, It may be apparent that the solids overloads to the dry-weather
plant described above may be alleviated by storing the CSO treatment
sludges and spreading the bleed/pump-back period over two to four days
or more. Of course, any additional storms during the bleed/pump-back
period may adversely affect the bleed/pump-back operation. Additionally,
the rate of bleed/pump-back would have to be carefully controlled, with
due regard to the diurnal OWF fluctuations,
3. Organic LoadingConsiderations
Untreated municipal sewage contains about 200 mg/1 BOD (9) (19). Shown
in Table 19 are the BOD characteristics observed for various CSO treat-
ment residual sludges (12). The BOD concentrations of the sludges In-
vestigated varied widely, Increasing with Increasing sludge concentra-
tion. The BOD values shown in Table 19 were those associated with the
solids contents of the corresponding sludge presented tn Table 17.
One of the criteria to be used in evaluating organic overload Is
associated with the activated sludge portion of the treatment. Design
organic loading DWF parameters for the aeration tank are shown In Table
8, and the organic loading range indicated Is 0.35 to 0.5 kg (1b) BOD/
day per kg (Ib) MISS, In addition, removals of BOD from DWF primary
45
-------
TABLE 18. VARIATION IN QUANTITIES OF GRIT BEHOVED
DURING WET WEATHER AND PERIODS OF AVERAGE FLOW (17)
Hunfctpality
Baltimore, MD
Battle Creek, Ml
Beacon, NY
Birmingham, AL
Cleveland, Ohio
(East)
Fort Dodge, IA
Green Bay, Wl
Jeannette, PA
Kokoroo, IN
La Crosse, Wl
Muskegon, Ml
Rockford, IL
Springfield, OH
Virginia Beach, VA
GrI
cu m/106
average
day
to (5.4)
139 (18.8)
23 (3.1)
6 (0.8)
2 (0.3)
24 (3.2)
52 (7.0)
42 (5.7)
10 (1.3)
20 (2.7)
tO (1.3)
50 (6.8)
16 (2.2)
18 (2.4)
t removed
cu m (cu ft/MG)
maxlmum(wet)
day
109 (14.8)
1258 (t70.0)
138 (18.7)
6 (0.8)
3995 (540.0)
24 (3.2)
56 (7.6)
60 (8.1)
74 (10.0)
42 (5.7)
60 (8.1)
tt9 (16.0)
48 (6.5)
56 (7.5)
Ratio
between
maximum
and average
2.7
9.0
6.0
1.0
1,800.0
1.0
1.1
1.4
7.7
2.1
6.2
2.3
2.9
3.1
46
-------
TABLE 19. ORGANtc CHARACTERISTICS (BOD) OF cso TREATMENT
RESIDUAL SLUDGES (9) (12)
P-IprtTU BOD Rfimoved BV
Pumped Back „„„ D , „,_,. B_. T _ ..
CSO Treatment
Process
Storage Atone
Storage-
Sed [mentation
Oissol ved~Ai r
Flotation
Screen ing/DAF
Contact
Stab!) notion
Trickling
Filter
BOD
115
2200
1000
1100
1700
moo
Billion
cy _m/dgy
93 5
0.83
0.57
3.18
3-26
0 6^
HfiD kq/dayxl(f6 Ib/dayxlo"6 ka/dayxlO"6 Ib/dayxlO"6
2!i?OD 10 0 23.7 1 « 8.3
220 1 R 1).Q 06 1 'i
150 0~.fi IT 0.2 05
8*0 3.5 7.7 1,? 27
860 5 5 12.2 2,0 4.3
170 7.2 15 9 2 $ 5 (•
BOD To
Activated Sludge
ksj/dayxlQ~6 Ib/dayxlO"6
7.0
I.?
0 k
2 3
3 6
k 7
15 '(
2 6
O.1?
5.0
7-5
10,3
(lumber Of
Days Required
For Pu«p Back
11.9
2.0
0.6
3.8
6 1
7-9
Assumed 35% BOD removal by primary treatment at 'iQ.8 cu m/day/sa m (1000 qpd/sq ft]
Number of days are based on BW organic toadinq of 0-35 kg ROD/day/kq HLSS with
possibility of Increasing the organic loadlno to a maxioum of 0.5 kg BOD/clay/ko
HLSS or an Increase of 588,076 kg BOD/day (1,295,321 lb BOD/day)
-------
sedimentation Is about 351 at an overflow rates of 40.8 cu m/day sq m
(1000 gal./day/sq ft) (14) (15), Suspended sot ids and BOD removals drop
drastically at primary tank overflow rates greater than 40.8 cu m/day/
sq m (1000 gal./day/sq ft). For example, at an overflow rate of 19.8
cu m/day/sq m (2300 gal./day/sq ft), BOD removal decreases to about 201
(15) and suspended solids removal decreases to about 37% 04).
From previous discussion, !t has been Indicated that bleed/pump-back of
CSO treatment sludges to the dry-weather plant over a 2k hour period will
result in hydraulic and/or suspended solids overload. Furthermore, it
was Indicated that the overloads to the dry-weather plant may be allevi-
ated by spreading the bleed/pump-back period over several days or more.
Moreover, it is Indicated that the bleed/pump-back period would be fur-
ther extended because the primary tank operation Is critical with regard
to BOD and suspended solids removal and the resultant organic load to
the secondary treatment system. Optimum operation of the primary tanks
is an overflow rate of 40.8 cu m/day/sq m (1000 gal./day/sq ft) In order
to maximize BOD and suspended solids removal. This overflow rate is
appreciably less than the maximum normally allowed for DWF operation,
[93.&CU m/day/sq m (2300 gal./day/sq ft] (See Table 8).
Untreated municipal sewage generally contains an average BOD content of
200 mg/l and an average suspended solids content of 200 mg/1 (9). For
our hypothetical average DWF of 17.1 x 10^ cu m/day (4,500 MGD), an
average daijy BOD and suspended solids loading to the dry-weather plant
of 3.4 x 10 kg (7.6 x 10° Ibs) per day each may be expected. Operating
the primary treatment plant at a design overflow rate of 40.8 cu m/day/
sq m (1000 gal./day/sq ft)(l3)» BOD removals of 351 (1.2 x 10° kg/day)
(2.6 x 10 Ib/day) may be expected and suspended solids removals of 601
2.1 x 106 kg/day (4.5 x 10° Ib/day) would be anticipated. Therefore,
the organic (BOD) loading on the secondary activated sludge treatment
system during dry-weather flow would be 2.2 x 10" kg/day (4.9 x 10® Ib/
day), and the corresponding solids loading to the secondary treatment
plant would be 1.4 x 10^ kb/day (3.0 x 10° Ib/day) during dry-weather
periods. From Table 8, the allowable organic loading range on the acti-
vated sludge system Is 0.35-0.50 kg(lb) BOD/day/kg(lb) MLSS. Assuming
our activated sludge plant Is operating at the lowest end or" the organic
loading scale (0.35 kg(lb) BOD/day/kg(lb) MLSS) or 600,000 kg (1.3 x 10°)
Ib) BOD/day may be added In the form of bled/pumped-back CSO treatment
residuals. Of course, If the activated sludge plant Is operating con-
sistently at the upper end of the organic loading scale (0.5 kg(lb) BOD/
day/kg(lb) MLSS), then no additional CSO treatment residuals can be bled/
pumped-back to the DWF plant without organically overloading It. Also,
if the DWF secondary plant is operating at somewhere in between the
allowable organic range, then legg additional BOB load than was pre-
viously Indicated can be pumped back to the DWF plant.
Inasmuch as the rate of flow of CSO sludges bleed/pump-back Is limited
to the extent that the primary tank operation does not exceed an overflow
rate of 40.8 cu m/day/sq m (1000 gal./day/sq ft), It becomes apparent
from an examination of Figure 5 (DWF diurnal variations) that bleed/pump-
48
-------
back will be intermittent and restricted to low DWF periods during the
day.
The above described constraints all tend to restrict the rate of bleed/
pump-back flow downward to the extent that the total time period for
pumping back the total CSQ sludges volume fs extended, which Is an un-
favorable trend from the standpoint of handling the effects of a suc-
ceeding series of storms. Shown In Table 19 are the number of days re-
quired for bleed/pump-back of the CSO treatment sludges from one average
storm from an organic loading standpoint, when the DWF plant Is operating
at a low organic loading (0.35 kg(lb) BOD/day/kg(lb) MLSS). The number
of days required to bleed/pump-back the CSO treatment residuals Increases
proportionately from those In Table 19, as the DWF organic loading In-
creases from 0.35 to 0,5 kg(lfa) BQD/day/kg(lb) MLSS. Also, as mentioned
previously, DWF plants having organic loadings at the maximum of 0.5
kg(lb) BOD/day/kg(Ib) MLSS may not be able to accept CSQ treatment
residuals j.f they are consistently heavily loaded.
Frora Table 19. it may be seen that four of the six CSO treatment methods
investigated would require about four or more days for bleed/pump-back
of a single storm's treatment sludges to the DWF plant when the dry-
weather plant Is operating at a low organic loading level. The time re-
quired for bleed/pump-back would be expected to Increase as the dry"
weather organic loading level increased.
From Table 19, It may also be seen that two of the six CSO treatment
methods investigated would require two or less days for bleed/pump-back
of a single storm's treatment sludges to the DWF plant when the dry-
weather plant is operating at a low organic loading level. Again, the
time required for bleed/pump-back would be expected to increase as the
dry-weather organic loading level Increased. Furthermore, it should be
pointed out that the two CSO treatment methods Involved here, sedimenta-
tion and dlssolved-air flotation, were relatively low efficiency solids
removal processes (about 401 suspended solids removal, (See Table 17))-
Any increase in solids removal efficiency for these treatment processes
would result in an increase In the bleed/pump-back period. Moreover,
the CSO treatment processes in question are primary treatment methods
and the treated effluents produced may require further treatment which
would produce additional sludge for bleed/pump-back, thereby Increasing
the total bleed/pump-back time period.
Concurrent with the organic loading considerations, described above and
under the operating conditions listed In Table 19, Is the solids loading
Imposed on the secondary treatment plant and Its concurrent affection
that operation. For our hypothetical DWF plant treating 17.1 x 10 cu m/
day (4,530 MGD), ft was previously calculated that the suspended solids
loading to the dry-weather plant was 3.4 x 10° kg/day (7-6 * 'Ob Ib/day).
Operating the primary treatment plant at an overflow rate of 40.8 cu m/
day/sq m (1000 gal./day-sq ft), suspended solids removals of 601
2.1 x 106 kg/day (4.5 x 106 Ib/day) may be expected, and the suspended
solids loading to the secondary treatment plant would be 1.4 x 10 kg/day
49
-------
3.0 x 106 Ib/day) during dry-weather periods. From Table 7, the allowa-
ble solids loading on final clarlflers is 98 to 146 kg/day/sq m (20-30
Ib/day/sq ft). Assuming our final clariflers during dry-weather are
operating at the lowest end of the solids loading scale 98 kg/day/sq m
(20 Ib/day/sq ft), then an additional solids load (up to 146 kg/day/sq m)
(30 Ib/day/sq ft) of 0.7 x 106 kg/day (1.5 x 106 Ib/day) may be added fn
the form of pumped back CSO treatment residuals. Shown in Table 20 Is
the solids loading effect on the secondary treatment plant when pumping
back CSO residuals at a rate which will prevent organic overload (See
Table 13). From Table 20 It may be seen that under the operating con-
ditions previously described, a gross solids overload Is effected, and
this indicates that solids overload is the limiting factor affecting
the bleed/pump-back time period. It is indicated, therefore, that the
bleed/pump-back time periods shown In Table 19 should be appreciably in-
creased, which makes the concept of CSO residuals bleed/pump-back to
the dry-weather plant more impractical from the standpoint of success-
fully handling the effects of succeeding storms In series.
4. ToxicIty to Treatment
Some possible toxic substances In CSO treatment sludges for which data
is available Include heavy metals (zinc, lead, copper, nickel, chromium
and mercury), PCB and pesticides (pp'DDD, pp'DDT and dieldrln). Heavy
metal, PCB and pesticide concentrations in CSO treatment sludges were
found to be significant, and the ranges of concentrations observed have
been previously reported herein.
Heavy Metals - Domestic wastewater generally contains low concentrations
of metals. The high concentrations of metals in wastewater are normally
caused by the discharge of industrial wastes (such as metal finishing
shops, plating wastes, etc.). Therefore, the metals content for munici-
pal treatment plants may range from traces to 20 mg/1 or more (23).
During wet weather, street runoff may produce high concentrations of
certain metals in combined sewers, on the order of 10 to 100 times and
more than those normally present In domestic wastewater as shown in
Table 21 (23,24).
Pertinent to this discussion Is the determination of any toxic effect of
heavy metals to treatment In the dry-weather plant operation caused by
pumping back of CSO treatment sludges. The toxic effect, If any, would
manifest itself in the secondary treatment portion of the dry-weather
plant. Shown in Table 2E are criteria which are to be used In arriving
at such a determination. Moreover, the literature Indicates that mer-
cury dosages of 5 mg/l or higher definitely Inhibit aerobic biological
processes (25). The inhibitory effect of lead on biological treatment
was not uncovered In the literature, however, ft was observed that pri-
mary sewage treatment removes "most" of the lead In sewage (21).
Presented in Table 23 are the heavy metal concentrations found in sani-
tary sewage (from Table 21) (24) and In the sludges from various CSO
treatment processes (12). It may be recalled that previous discussion
50
-------
TABLE 20. CONCURRENT SQUDS LQAQWG ON SECONDARY TREATMENT PLANT
UNDER THE OPERATING CONDITIONS DESCRIBED IN TABLE 13
CSO Treatment
Process
Storage Alone
Storage-Sedimentation
Olssolved-AIr Flotation
Screen Ing/DAF
Contact Stabilization
Trickling Filter
SoHds Pumped Back
kg/dayxlQ~6
38.4
14.5
15-6
37-9
32.6
20.6
Ib/dayxlO~f
84.5
31.9
34.4
83.4
71-7
45.4
Solids
BY_ Pr Iroary
kg/dayx!0"
22.7
8.7
9.4
22.7
19.5
U.3
Removed
Treatment
lb/dayxlO~6
50.1
19-1
20.6
50.0
43-0
27.2
Bleed/
Pump-
Back
Period
(days)
11.9
2.0
0 6
3.8
6.1
7-9
Sol ids To
Activated Siudde
kq/dayxlQ
1 3
2.9
10 4
4.0
2.1
1.0
Ib/dayxlO"
2.9
6.4
23-0
8.8
4-7
2 3
Secondary
Sol ids
Overload
Yes
Yes
Yes
Yes
Yes
Yes
Bleed/Pump-Back solids were obtained from Table II.
Assumed &0% SS removal by primary treatment at 40.8 cu m/day/sq m (1000 gpd/sa ft)
Solids overload was established when the CSO solids to the activated sludge system
exceeded 686,088 kg/day (1,511,208 Ib/day)
-------
TABLE 21. METAL LOADING FROH ROAD SURFACE RUNOFF
COMPARED TO NORMAL SANITARY SEWAGE FLOW (2k)
Metal
Pb
Cd
N!
Cu
Zn
Fe
Mn
Cr
Road runoff
(rag/ I)
6.2
0.012
0.10
0.37
1.4
83
1.6
0.80
Sanitary
sewage
(mg/1)
0.03
0.00075
0.01
0.04
0.20
13
2.3
2.8
Runoff J
sewage
(ratio)
210
16
10
9
7
6
0.7
0.3
Note; From a 0.25 cm rain (0.1 in.)
TABLE 22. EFFECTS OF HEAVY METALS ON BIOLOGICAL
TREATMENT PROCESSES (26)
Metal
Cr
Cu
Ni
Zn
5-101
reduction
in aerobic
treatment
efficiency
tO mg/1
1
1-2.5
5-10
4-hr slug
dose, causing
reduction !n
COD removal
>500 mg/1
75
50-200
160
Highest al lowable
dose for
satisfactory
anaerobic
sludge digestion
>50 mg/1
5
>10
10
52
-------
has indicated that bleed/pump-back of CSO treatment sludges over a 2k
hour period would result in hydraulic, solids and organic overload of
the dry-weather treatment plant facility. Moreover, It was further In-
dicated that to prevent overload conditions, CSO treatment sludges would
have to be stored and pumped back to the dry-weather plant over extended
periods of time. For example, for efficient CSO treatment processes
(storage alone, contact stabilization, screen Ing/DAF» etc.) bleed/pump-
back periods appreciably greater than 4 to 12 days have been indicated.
However, for purposes of this discussion in determining the toxic effect
of CSO treatment sludges' heavy metals on dry-weather secondary treat-
ment, a bleed/pump-back period of 2k hours will be assumed. If the
combined heavy metal concentrations obtained under this condition are
found not to be toxic to secondary treatment during dry weather con-
ditions, then toxic conditions may not be expected over the more ex-
tended bleed-back periods.
Using our hypothetical average dry weather flow of 17.] x 10 cu m/day
(4,500 MGD), the dally CSO treatment sludge volumes expected (Table 5;
and the appropriate heavy metal concentrations fn the two flows (Table
23), the average heavy metal concentration of the blend of dry weather
and CSO residual flows at the dry weather plant influent may be deter-
mined. The results of these calculations are shown In Table 2k on the
basis that the entire CSO was treated by each of the selected CSO treat-
ment processes alone. Also presented In Table 2k are the heavy metal
concentrations contributing detrimentally to the efficiency of aerobic
biological treatment. Noted In Table 2k are those values which signifi-
cantly exceed the toxlcity causing concentrations listed at the bottom
of Table 2k. It Is indicated that copper and zinc in contact stabili-
zation, storage alone and trickling filter treatment residuals warrant
further discussion regarding toxlcity to treatment. The values shown
In Table 2k are the heavy metal concentrations at the Influent to the
dry weather plant. Assuming the heavy metals are predominantly of a
partlculate nature, a 601 reduction may be expected by primary treat-
ment. Therefore, the primary effluent to secondary treatment will con-
tain heavy metal concentrations of kQ% of the values presented In Table
2k. The primary effluent heavy metals contents so calculated will all
be below the critical concentrations detrimental to secondary treatment
efficiency. The general conclusion may be drawn from the above discus-
sion that pumping back of CSO treatment sludges to the dry-weather plant
will not result In heavy metal toxlclty to secondary treatment. However,
this Is a preliminary and elementary study and the subject requires further
attention, j n
PCS (12) (.271 - This chemical, which has been contaminating fish, has been
in common use since 1929. It is used in many products ranging from soaps
to electrical transformers. In 1972, Monsanto Industrial Chemical Co.,
the only. PCB manufacturer in the United States, stopped selling it except
for use in closed electrical items such as transformers and capacitors.
However, it still continues to get into waters from past usage and spills.
PCB is suspected of causing reproductive failure in fish, birds, and
53
-------
TABLE 23. COMPARISON OF HEAVY METAL CONCENTRATION IN SANITARY
SEWAGE AND VARIOUS CSO TREATMENT SLUDGES
Sanitary Sewage
CSO Treatment Process
Storage Alone
Storage-Sedimentation
Dissolved-AJr Flotation
Screen ing/DAF
Microscreenlng
Contact Stabilization
Trickling Filter
Zinc
nig/1
0.20
0.6
15.2
19.4
13-8
3.3
71-5
41.7
Lead
mq/1
0.03
0.7
29.0
43.3
8.6
17-1
5-3
11.4
Copper
mg/1
0.04
1.5
8.4
10.0
4.1
1.4
14.5
32.8
Mickel
mg/1
0.01
0.1
2.5
2.3
1.8
2.0
5-3
25-2
Chromium
mg/1
2.80
0.05
4.4
45-6
1.8
0.4
17-3
79.5
Mercury
O.OO'l
0.05
0.11
0.02
0.01
0.03
-------
TABLE 2k. EVALUATION OF THE POSSIBLE TOXIC EFFECT
OF HEAVY METALS ON DRY WEATHER TREATKENT DUE
TO BLEED/PUMP-BACK OF CSO TREATMENT SLUDGES
CSO Treatment
process
Storage
Storage-sedimentation
Dissolved-ai r
flotation
Screen Ing/DAF
Microscreenlng
Contact stabilization
Trlckl ing filter
Concentration (mg/1 after blending
sludge with dry weather flow)
Zinc Copper Nfckel Chromium
0.5 I.
0.9 0.
0,8 0.
3.0 0.
2.2 0.
11. 5* 2.
1.7 1.
Concentrations of heavy
reduction In aerobic
Zinc
Copper
Nickel
Chromium
3* 0.1 0.5
k 0.1 2.9
k O.I 4.2
9 0.4 2.6
k 0.5 2.2
3* 0.9 5-1
2* 0.9 5-6
metals causing a 5" 101
treatment efficiency:
5-10 mg/1
1 mg/1
1-2.5 mg/1
10 mg/1
CSO
.Mercury
.001
.002
.0001
.004
.002
.005
--
* Values that are within or above given concentrations for causing
a reduction In efficiency.
55
-------
mammals. In human beings, It is suspected of causing cancer, skin dis-
colorations and liver disorders. It is also suspected of affecting a
person's recovery from other illnesses.
The literature (27) indicates that PCB Is present In municipal sewage In
amounts varying from O.I? to 1^0 yg/1. Moreover, It Is further Indicated
that municipal treatment plants are capable of removing more than 701 of
the incoming PCB. However, over half the municipal treatment plants
studied (27) had effluent concentrations ranging from 0,1 to 0.5 ug/l
PCB, and about 201 of the plants studied had effluent concentrations
greater than J.O yg/1 PCB.
The mechanism of PCB removal in treatment plants appears to be adsorption
on the solids with subsequent sedimentation clarification of the solids.
This Is evident from data collected (2?) which show comparatively high
concentrations of PCB in primary settling sludges (50 mg/1) and digester
sludges (22 mg/l). In contrast, the CSO treatment sludges may be ex-
pected to contain PCB concentrations varying from 0.008 mg/l to 0.118
mg/l (27) which are several magnitudes lower than those concentrations
reported from municipal dry weather sludges.
From the above discussion, It appears that the PCB content of the CSO
treatment sludges will not cause toxlcity to dry weather treatment If
the CSO sludges are pumped back to the dry weather plant, all other
things being equal. However, bleed/pump-back of CSO treatment sludges
to the dry weather plant can increase the effluent PCB concentration and
mass PCB transport to receiving waters if the dry weather facility becomes
overtaxed»
Pes11cides (28)J23) - Pesticides may be described as natural and synthet-
ic materials used to control unwanted or noxious animals and plants.
They may be conveniently classified according to their usage, such as
fungicides, herbicides, insecticides, fumigants and rodenticides. The
widespread presence of pesticides in the environment has caused much
public and private concern because of their potential for upsetting eco-
logical balances. Their dispersal in drainage systems and possible
eventual accumulation In estuaries makes our coastal flsherl.es (for ex-
ample, oysters, shrimp, crab and menhaden) especially vulnerable to
their toxic effects. Laboratory tests show that these economically im-
portant animals are especially sensitive to the toxic effects of low
levels of pesticides. For example, oysters will exist In the presence
of DDT at levels as high as O.I mg/l In the environment, but at levels
1000 times less (0.1 ug/l), oyster growth or production would be only
201 of normal, shrimp populations would suffer a 201 mortality, and men-
haden would suffer a disastrous mortality. Some Insecticides are toxic
enough to kill SQ% or more of shrimp populations after kB hours exposure
to concentrations of only 30 to 50 nanograms per liter of the compounds.
Pesticides may be classified by their chemical affinities, their degree
of toxlclty and their degree of persistence. Pesticides which are
acutely toxic to shrimp at low concentration levels (yg/1) Include the
organochlorine and organophosphorous Insecticides. The organochlorlnes
56
-------
include the well-known DDT and aldrlntoxaphene group, and typically,
they are persistent compounds. The organophosphorous compounds include
parathlon, and typically, they hydrolyze or break down into less toxic
products much more readily than the organochlorlne compounds. Therefore,
the organophosphorous compounds are usually preferable as control agents
because of their relatively short life.
The pesticide content in municipal sewage was not uncovered In the
literature. However, the concentrations of selected pesticides found In
CSO treatment sludges are shown In Table 25- From Table 25, the pesti-
cide content observed varied from non-detectable to significant. Note
in Table 25, that the pesticides investigated were organochlorlne fn-
secticfdes.
Pumping back CSO treatment sludges to our hypothetical dry-weather plant
over a 2k hour period will result in Influent pesticide concentrations
of the combined flow as shown in Table 26. The values shown in Table 26
were calculated using an average dry-weather flow of 1/«' x 10° cu m/day
(4,5QQMGQ) (assuming no pesticide content), the daily CSO treatment
residual volumes expected (Table 17) and the pesticide concentrations in
the CSO treatment sludge volumes (Table 25). The results shown in Table
26 are on the basis that the entire CSO was treated by each of the
selected CSO treatment processes alone.
The kB hour TL (shrimp) for DDT and dleldrin are 0,6 ug/1 and 0.3
respectively (28). Comparing these values with those In Table 26 Indi-
cates that the corresponding values for the combined Influent before
treatment are well below the limit.
Also not covered in the literature was the extent of pesticide removal
In municipal sewage treatment plants. However, it was Indicated that
pesticides are subject to a number of degrading actions. Including
volatilization, decomposition by ultraviolet light and other radiation,
chemical degradation, ndLcrobial degradation and sorptlqn by solids*
Mleroblal degradation and sorptlon. on aollds appears to be the mechanism
by which pesticides would be removed in. a sewage treatment plant. The
pesticide levels shown in Table 26 would not appear to be toxic to
sewage treatment.
5_. ^^.tJJ^g^^4gjJ^y_^4..TrA^|<>gi1'X^ Efficiency
One of the most Important criterion In evaluating the alternative of the
bleed/pump-back of CSO treatment residuals to the dry weather plant Is
Its effect upon treatment efficiency and effluent quality. Previous
discussion has dwelled upon the effect of CSO residuals bleed/ pump- back
on the dry-weather treatment plant with regard to such criteria as
hydraulic overload, solids overload, organic overload and toxlclty to
treatment. The effects on these criteria were found to be Interrelated
and to affect treatment efficiency and effluent quality for each treat-
ment process element as well as for the overall treatment plant itself.
It was observed that Inasmuch as the treatment processes comprising the
57
-------
TABLE 25. CONCENTRATION OF SELECTED PESTICIDES
IN CSO TREATMENT SLUDGES (12)
CSO Treatment
process
Storage alone
Storage-sedimentation
DI ssolved-alr flotation
Screen I ng/DAF
Mlcroscreenlng
Contact stabilization
Trickling filter
pp'DDD
pg/l
ND
ND
0.79
1.90
ND
0.93
ND
pp'DDT
wg/l
0.03
3.00
2.63
ND
ND
ND
ND
Dlel^rln
MS/ 1
0.006
0.67
5-25
0.14
ND
0.88
ND
ND » non-detectable
TABLE 26. EFFECT OF BLEED/PUMP-BACK OF CSO TREATMENT SLUDGES
ON DRY WEATHER PLANT INFLUENT PESTICIDE CONCENTRATIONS
CSO Treatment
process
Storage alone
S torage-sed Imenta 1 1 on
Dlssolved-alr flotation
Screen I ng/DAF
MIcroscreenfng
Contact stabilization
Trickling filter
Concentration (iig/l after blending CSO
sludge with dry weather flow)
pp'DDD
ND
ND
0.03
0.4
m
0.15
ND
pp ' DDT
0.03
0.14
0.08
ND
ND
ND
ND
Dleldrln
0.005
0.04
0.17
0.03
NO
0.14
ND
ND « non-detectable
-------
dry-weather plant are In series, any significant effect on any upstream
treatment process will have significant effect on the performance of one
or more of the downstream treatment processes. The discussion below
summarizes the effect of CSO residuals bleed/pump-back on dry weather
treatment plant treatment efficiency and effluent quality.
The effect of bleed/pump-back on various aspects of treatment plant loading
have been discussed in detail, tt Is apparent that the rate of bleed/pump-
faack of CSO sludges to the dry-weather treatment plant Is critical and
appreciably affects the subsequent operation of the plant and the plant per-
formance achieved.
ideally, bleed/pump-back of the CSO treatment residuals over a 24 hour period
would be most favorable from the standpoint of permitting the handling of
subsequent CSO events in series. Previous discussion Indicated, however,
that discharge of the expected quantities of CSO treatment residuals to the
dry weather plant over a 24 hour period would grossly overload the dry~
weather treatment plant either hydraulfcally, solids-wise and/or organically,
resulting in appreciably decreasing the treatment efficiency and Intolerably
(above allowable limits, see Table 8 and EPA regulations) deteriorating the
plant effluent quality with regard to suspended solids, BOD, heavy metals,
PCB and/or pesticides.
Inasmuch as a CSO residuals bleed/pump-back rate over a 24 hour period is
impractical, the overload and unfavorable operating conditions caused there-
by may be alleviated by storing the CSO treatment residuals and extending
the bleed/pump-back period (reducing the bleed/pump-back rate) as required.
Table 27 Includes a summary of the limiting time periods for bleed/pump-
back which can occur without overloading the capacity of the dry-weather
treatment plant.
TABLE 27. LIMITING FACTORS IN DAYS FOR BLEED/PUMP-BACK
Treatment process
Storage
Sedimentation
Dissolved Air Flotation
Screen I ng/D 1 sso 1 ved
Air Flotation
MIcroscreening
Contact Stabilization
Trickling Filter
Days for bleed/pump-back
Solids
Hydraulic (Prim.)
2.1 7-4
<1 2.8
<1 3.0
<1 7.3
<» 7-5
-------
that the capability of handling succeeding CSO treatment residual events Is
reduced. In fact, the longer the extended bleed/pump-faack period, the more
unfavorable this alternative becomes. Another disadvantage of any bleed/
pump-back alternative Is the necessity for carefully controlling bleed/pump-
back (flow rate and constituent strength), with due regard for the diurnal
DWF fluctuations (flow rate and constituent strength) to Insure that peak
treatment plant design operating conditions are not exceeded.
The final disadvantage Is that the treatment efficiency and effluent quality
would be lower than when CSO sludges are not bled/pumped-back. In order to
minimize the bleed/pump-back period and the associated storage volumes re-
quired, it Is assumed that the bleed/pump-back rate will be established so
the dry-weather treatment plant will operate at the peak design operating
conditions. It is felt that under this severe loading, the effluent dis-
charge limitations (30 mg/1 suspended solids and 30 mg/l BOD) would be ex-
ceeded. If the suspended solids loading Is higher, then the effluent quality
would range In the upper portion of the performance expectation and may reach
concentrations of 50 mg/1 (Table 14).
Using the assumptions that a 5 day bleed/pump-back period Is feasible for
storage and bleed/pump-back, and that the loading rate to the final clarf-
fiers is the most limiting design parameter, the volume of CSO sludge
which can be handled at the treatment plant can be calculated. This volume
can then be related to the percent of CSO area and CSO volume which can be
treated using the existing dry-weather treatment plant for sludge handling.
A plot of this Information Is Included in Figure 6. It is apparent that as
the treatment plant tends to the higher design capacity, less CSO sludge can
be adequately handled (disregarding the negative Impact of constant maximum
loading conditions).
It is therefore apparent that the problems associated with bleed/pump-back
to the dry-weather treatment plant are complex. If the Initial transport
problems can be eliminated or overcome, the effect of the sludges on the
operation and efficiency of the dry-weather treatment plant must be care-
fully evaluated. The built-in safety factors for design can provide a cer-
tain amount of additional capacity, however, operating a peak flow due to
bleed/pump-back of CSO sludges at all times Is difficult and will adversely
affect effluent quality.
EFFECT OF BLEED/PUMP-BACK OF DILUTE RESIDUALS FROM THE ON-SITE DEWATERING
OF CSO TREATMENT SLUDGES ON THE DRY-WEATHER TREATMENT PLANT
Previous discussion has Indicated overwhelmingly that bleed/pump-back of raw
CSO treatment sludges Is not practicable In most situations. Another al-
ternative is to separately dewater (on-slte) the raw CSO treatment sludges,
ultimately dispose of the dewatered sludge and bleed/pump-back the dilute
effluents from the dewaterlng steps to the dry-weather plant,. The purpose
of this discussion Is to evaluate the effect of pumping back the dilute
effluents from the CSO sludge dewaterlng processes to the dry-weather treat-
ment plant.
60
-------
LOADINGS BASED ON
5 DAY BLEED/PUMP-BACK PERIOD
80
70
to
Ul
<
u-
-------
The only pertinent Information uncovered In the literature (12) was based
upon bench scale dewatering studies performed on raw CSO treatment sludges
obtained from various CSO treatment sites throughout the country. The con-
clusions drawn from the study Indicated that centrlfugatlon alone or In
combination with thickening and thickening followed by vacuum filtration
were found to be the optimum sludge dewatering processes based on such cri-
teria as performance, costs and space requirements.
Based upon our hypothetical dry-weather plant handling a design flow of
17.1 x 10° cu m/day (4,500 MOD) sewage and design solids load of 3.4 x 10°
kg/day (7.6 x 10° lb/day)( shown in Table 28 are the combined flows and
solids anticipated from the bleed/pump-back of the dilute effluent arising
from the dewatering of the CSO treatment sludges.
Assuming the range multiple of design flow and solids that a dry weather
plant can handle is 1.5 to 3»Q» examination of Table 28 shows that a hydrau-
lic or solids overload would not be expected when the dilute effluents from
dewatering CSO sludges are pumped back over a 24 hour period.
BOD, heavy metal, PCS and pesticide data on the dilute effluents from de-
watering CSO sludges were not discovered in the literature, and therefore,
no comment Is made at this time regarding organic overload and toxic!ty to
treatment due to heavy metals, PCB and pesticides caused by the bleed/pump-
back of dilute effluents from dewatering CSO sludge to the dry-weather plant.
EFFECT OF CSO TREATHENT RESIDUALS BLEED/PUMP-BACK ON THE OPERATION AND
PERFORMANCE OF THE DRY WEATHER SLUDGE HANDLING FACILITIES
Previous discussion has dealt with the effect of pumping back CSO residuals
on the operation and performance of the dry-weather treatment plant. One
of the by-products of the dry-weather treatment plant is the residual sludges
arising from treatment which have to be handled and disposed of. The dis-
cussion which follows Is concerned with the effect of pumping back CSO treat-
ment residuals on the operation and performance of the dry weather sludge
handling facilities.
Previous discussion regarding the bleed/pump-back of CSO treatment sludges to
the treatment portion of the dry weather plant has shown that bleed/pump-baek
over a 24 hour period results In a gross solids overload on the treatment
plant. Moreover, depending upon the existing dry weather operating organic
loading on the secondary treatment plant, bleed/pump-back of the CSO treat-
ment sludges may not be permissible or would have to be extended over periods
of one to two weeks or more, which does not appear practical from the stand-
point of having the capability of handling the sludge residuals from succes-
sive combined sewer overflows.
However, assuming the dry weather treatment plant could handle the pumped
back CSO treatment sludges, or assuming for the moment that the CSO treatment
sludges are bled/pumped-back directly to the dry-weather sludge handling fa-
cilities, what would be the effect on those sludge handling facilities?
62
-------
TABLE 28. EFFECT OF BLEED/PUMP-BACK OF DILUTE EFFLUENTS FROM DEWATERING OF CSO
SLUDGES ON DRY WEATHER TREATMENT PLANT HYDRAULIC AND SOLIDS LOAD
ON
Raw CSO Sludge
volume!
CSO Treatment
Process
Storage-Sedimentation
Dissolved -Air
Flotation
Screen i ng/BAF
Contact Stabilization
Trickling Filter
rat 1 1 ion
0.83
0.57
4 W
3. 26
0 64
HGD
220
ISO
i no
860
170
Dewaterinq
Method
Used
C
C
T-C
T-F
T-C
01 Wa
F.low__
million
cu m/day HflD
0 76 200
0 '13 HO
•> 3T MM
3-07 RIO
0 W 17-)
Effluents
Solids
mrj/1
3A7
".'l
n?i
3^1
170
Bteed/Puirjr-Baek Bleed/Ptop-Back + DWF
Solids -- -|-,— "•— Solids
-& -.6 i»M lion -7-
iq/tJayxifi Ib/HavxlO cu m/day HfiD kQ/da^nlO
r>.?<; 1 51 17 10 'i730 3 73
f\ f}li n rjfl 1 7 j'iJi i.^ rp 1 I|7
•: "o i? 7« 31 v vm •) 21
1 P? 2 2'i 2n 21 1340 Ji iij
nil o 2(1 1/71 ^710 "i.S'i
G.l'i
7 '.5
/O 1'i
q Pi
7 SO
r-*
MOTE C » centrlfuqation alone
T-C " combination of thlckeninq fotlowed by centrlFuqation of the thickened sludnc
T-F m cooiblnation of tbickemnq followed by vacuum filtration of the thjcfcencd slud
-------
Shown In Table 8 are typical sludge volumes produced In a dry-weather
plant. Primary sedimentation [2,440 cu m(gal.) sludge (5% sol Ids) per
million cu m (gal.) sewage treated] and waste activated [18,700 cu m (gal.)
sludge (II solids) per million cu m (gal.) sewage treated] sludges are perti-
nent to this discussion.
Sludge handling facilities are usually based upon the estimated sludge pro-
duced at average design flow (17). For our hypothetical dry-weather plant
treating an average dally flow of 17-1 x 106 cu m/day (4,500 MGD} a primary
sludge volume of 42,000 cu m/day (11.1 MGD} and a waste activated sludge
volume of 320,000 cu m/day (84.7 MGD) may be expected to be handled by the
dry-weather sludge handling facilities,
1. Hydrau 1 i c J-oadlng Cons Ideratjons
The daily design volume (primary plus activated) of sludge to be handled
by the dry-weather sludge handling facilities Is 363,000 cu m/day (96
MGD). Shown In Table 16 are the dally CSO treatment sludge volumes ex-
pected If the entire CSO were treated by each of the various CSO treat-
ment methods Investigated. Table 17 shows that the dally volume of CSO
treatment sludges from each of the CSO treatment methods Investigated Is
of a higher order of magnitude than the design dally dry-weather sludge
anticipated, varying from 5.8x10? cu m/day (150 MGD) to 5.6 x 106 cu m/
day (1480 MGD). The above information Indicates that the addition of
CSO treatment sludges to the dry-weather sludge handling facilities would
result In drastically reducing the detention time of the various process
elements in the sludge handling facilities.
Since detention time is one of the important factors In the performance
of sludge handling processes (thickening, digestion, vacuum filtration,
centrifugation, sand bed drying, etc.), It may be concluded that the CSO
treatment sludge volume would hydraulica!ly overload the dry-weather
facilities, thereby, appreciably adversely affecting their performance.
Additionally, the hydraulic overload may be expected to result In de-
teriorated by-products (such as thickener effluents, digester superna-
tants, filtrates, centrates, etc.) which are normally returned to the
head end of the treatment plant and will result In overloading the treat-
ment plant with fine solids, organlcs, nutrients, etc., thereby detri-
mentally affecting treatment plant performance.
2. Sol Ids LoadIng Considerations
For our hypothetical dry-weather plant, the design dry weather solld| to
be handled (primary plus activated) are 5.3 x 10& kg/day 01-69 x 10
Ib/day). Presented in Table 17 are the daily dry weight of CSO treatment
sludge solids expected If the entire CSO were treated by each of the
various CSO treatment methods investigated. Table 17 shows that the
daily dry weight of CSO treatment sludge solids from each of the CSO
treatment methods Investigated Is several times greater than that of the
design dally dry weather solids anticipated, varying from 14.5 x 10°
kg/day (31.9 x 106 Ib/day) to 39-^2 x 105 kg/day (86.4 x 106 Ib/day).
64
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The above Information Indicates that the addition of CSO treatment
sludges to the dry-weather sludge handling facilities will drastically
overload the various process elements comprising the sludge handling
facilities from a solids standpoint. For example, those process ele-
ments whose equipment capacities are based on solids loading (see Tables
9—13) (such as thickening, filtration, lagoonlng, sand drying beds,
centrlfugatlon, etc.) would require 3 to 8 times additional capacity to
handle the excess load. Digestion processes are more affected by organic
and Inert solids and the effect of CSO treatment sludges on digestion
will be covered separately below.
3. Organic and Inert Sol Ids Considerations
The organic content (as measured by volatile solids) of municipal sludges
(primary sludge and waste activated sludge) Is 65% on a dry solids basis
(30). For our hypothetical dry-weather plant, the design dry weather
total solids to be handled (primary plus waste activated) has been pre-
viously established at 5.3 x 106 kg/day (11.7 x 1G6 Ib/day). The cor-
responding volatile solids content is 3.5 x 10° kg/day (7-6 x 10° lb/
day). Presented In Table 29 are the daily dry weight of CSO treatment
sludge volatile solids expected If the entire CSO were treated by each
of the various CSO treatment methods Investigated. From Table 29 It may
be seen that the volatile solids content of the CSO sludges was signifi-
cantly to appreciably lower than that for dry-weather municipal sludges.
For the CSO treatment methods shown In Table 29, the higher volatile
solids contents are observed for the sludges derived from the biological
treatment methods. This was expected because the biological treatment
methods were preceded by treatment steps which removed the major portion
of the grit and Inert solids present In the raw CSO. The physical and
physical-chemical treatment methods shown in Table 29 treated raw CSO
with little or no preliminary treatment for Inert solids removal.
Examination of Table 23 and comparison with the hypothetical dry-weather
municipal volatile solids loading, shows that the dally volatile solids
rate from the CSO treatment methods varied from about 1.5,to 5.5 times
the design dry-weather rate of 3-5 x 106 kg/day (7-6 x 10b Ib/day) pre-
viously determined. It is apparent from this comparison that additional
digestion facilities (aerobic and anaerobic) will be required to handle
the CSO sludges by these treatment methods. These additional digestion
facilities (either on-slte or parallel to the DWF facilities) for
handling the CSO sludges should be preceded by a grit removal step to re-
duce the possibility of grit and other Inert solids from settling In the
digesters and occupying valuable space.
k. Tox i c I ty to T_re_a.tmen_t
Pertinent to this discussion Is the determination of any toxic effect of
heavy metals In the CSO sludges to treatment In the dry-weather sludge
handling facilities. The toxic effect, If any, would manifest Itself
in the biological treatment portions of the sludge handling systems,
such as In the aerobic or anaerobic sludge digestion processes.
65
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OS
TABLE 29, VOLATILE SOLIDS CONTENT OF SLUDGES FROM
VARIOUS CSO TREATMENT PROCESSES
Sludge Characteristics
CSO Treatment
Process
Storage- Sedimentation
Dlssolved-Alr Flotation
Screen Ing/DAF
Mlcroscreenlng
Contact Stabilization
Trlckl ing Fil ter
Total Sol
kg/dayxlQ~6
14.5
15-6
37-9
39-2
32.6
20.6
Ids
Ib/dayxlO
31-9
34,4
83.4
86, 4
71,7
45.4
Percent
Volatile
Solids
46.9
30.9
34.2
29.1
58.7
60.8
Volatile
kg/dayxIO"6
6.8
4.8
12.9
11.4
19.!
12.5
Sol Ids
Ib/dayxlO
15.0
10.6
28.5
25-1
42.1
27-6
Inert Sol
kg/dayxlO~6
7.7
10.8
24.9
27-8
13-4
8.1
ids
Ib/dayxlO
16.9
23.8
54.9
61.3
29.6
17.8
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Previous discussion has Indicated that It Is Impractical to direct the
CSO treatment sludges to the dry-weather sludge handling facilities be-
cause this would cause a gross hydraulic, organic and solids overload
of those facilities. However, for purposes of this discussion, for those
isolated cases where the dry-weather sludge handling facilities could
handle the CSO sludges, what would be the effect with regard to toxic Ity
of digestion sludge treatment?
Shown In Table 22 are the effects of various heavy metal concentrations
on aerobic and anaerobic Biological treatment processes. The data in
Table 22 Indicate, for example, that copper concentrations greater than
5 mg/I and zinc concentrations greater than 10 mg/1 will detrimentally
affect anaerobic sludge digestion. Another source (32) indicates that
soluble heavy metal concentrations greater than 1 mg/l are toxic to
anaerobic digestion. Still another source (31) Indicated that raw sludge
copper concentrations of 14.3, 27.7 and 60,6 mg/1 for three sewage treat-
ment plants in Ohio did not adversely affect anaerobic sludge digestion
or gas production. The Information presented above appears to be In
conflict. It is Indicated that the concentration at which a substance
starts to exert a toxic effect is difficult to define because it can be
modified by antagonism, synergfsm and acclimation. Moreover, In the
case of Intermittently treating CSO treatment sludges in dry weather
sludge handling facilities, the digesters act as equalization basins to
dilute any heavy metal concentration present In the CSO treatment sludges
and thereby ameliorate any potential heavy metal toxic effect.
Presented In Table 23 are the heavy metal concentrations found in the
sludges from various CSO treatment processes, ft was observed that the
heavy metal concentrations In the CSO treatment sludges were significant
and In some cases, such as for zinc and copper, were generally excessive
(based on the allowable values In Table 22). Moreover, the data showed
that the heavy metal concentrations of the CSO sludges from blotreatment
processes (contact stabilization and trickling flIteration) were appre-
ciably higher than those for the sludges from the physical and physical-
chemical CSO treatment processes.
That CSO treatment sludges may be handled Intermittently In dry-weather
digesters (where applicable and all other things being equal) In spite
of high heavy metal concentrations Is exemplified by the Kenosha, Wis-
consin sewage treatment plant which has a 75,700 cu m/day (20 MGD) dry-
weather plant and a 75»70Q cu m/day (20 MGD) wet weather contact stabi-
lization plant. The relatively high heavy metal concentrations In the
Kenosha CSO contact stabilization waste sludge are shown in Table 23
(zinc, 71-5 mg/1; copper \k.5 mg/1). The Intermittent handling of this
wet weather sludge by the Kenosha anaerobic digesters has been satis-
factory with no apparent adverse effect on digestion or gas production.
Handling of CSO treatment sludges In parallel digester facilities at
the dry-weather plant Is another story because essentially no dilution
or equalization Is obtained with dry-weather sludge. It Is questionable
whether digestion should be used In the CSO sludge handling scheme when
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CSO treatment sludges are to be treated on-site or In parallel digester
facilities at the dry-weather plant.
In any event, If toxtclty Is suspected for a given application, potential
solutions to toxiclty problems should be evaluated fn laboratory or pilot
digesters.
Alternatively, a promising method for the rapid stabilization of difff-
cult-to-handle sludges, such as CSO treatment sludges, is 1lme stabili-
zation, and ft Is recommended that further Investigation of this method
be conducted.
5. Treatment Efficiency
It Is readily evident from previous discussion that directing the CSO
treatment sludges to the dry-weather sludge handling facilities will
grossly overload those facilities from a hydraulic, organic and Inert
solids standpoint. These gross overloads will detrimentally affect the
dewatering and stabilization performance and treatment efficiency of
the dry-weather sludge handling facilities. The downgrading In treat-
ment efficiency would be manifested in poorly stabilized sludge for dis-
posal and grossly deteriorated thickener effluents, filtrates, superna-
tants, etc. for recirculation back to the dry-weather plant.
As previously recommended, alternative on-site treatment methods, such
as lime stabilization, should be investigated for handling CSO treatment
sludges.
EFFECT OF BLEED/PUMP-BACK OF THE DILUTE RESIDUALS FROM THE ON-SITE DEWATER-
ING OF CSO TREATMENT SLUDGES ON THE DRY-WEATHER SLUDGE HANDLING FACILITIES
From previous discussion, It appeared that from a hydraulic and solids aspect
the dry-weather treatment plant would be able to handle the bleed/pump-
back of dilute residuals from the on-site dewatering of CSO treatment sludges.
However, data was not available to evaluate the effect of dilute effluents
bleed/pump-back on organic overload or toxiclty to treatment in the dry-
weather plant. This section allows evaluation of the separate effect of
pump back of the dilute CSO sludge dewatering residuals on the dry-weather
treatment plant sludge handling facilities.
Shown in Table 30 are the flows and characteristics of the dilute effluents
from the dewatering of the CSO sludges pumped back to the hypothetical dry-
weather plant. It mav be noted In Table 28 that only solids data was availa-
ble from the dilute effluents pumped back. It may also be seen from Table 28
that the strength (solids) of the dilute effluents varied widely with the
CSO treatment process from which they were derived. Some of the dilute
effluents were stronger than domestic sewage and some were weaker. The sus-
pended solids content of sewage has previously been assumed at 200 mg/1 (9).
In order to estimate the quantity of sludge produced from the treatment of
the dilute effluents bled/pumped-back, the dilute effluent flows shown In
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TABLE 30, ESTIMATES OF DRY WEATHER PLANT SLUDGE VOLUMES PRODUCED FROM THE
TREATMENT OF DJLUTE EFFLUENTS PUMPED BACK AFTER DEWATERING CSO TREATMENT SLUDGES
vo
Dilute Effluents
Pumped Back
CSO Treatment
Process
Storage-Sedimentation
DIssolved-AIr
Flotation
Screen I rig/DAF
Contact Stabilization
Trickling Filter
cu in/day
757,000
'192,050
i*, 390, ooo
3,066,000
643,000
MGD
200
130
1160
810
170
Solids
tng/1
3*7
fM
1,321
331
170
Equivalent Sawaqe
cu ra/day
1J25.000
227,000
23,993,000
6,21(5,000
530,000
MOO
350
SO
7660
1650
Ho
Solids
imj/1
200
200
200
200
200
Sludqe Flew Produced
Primary
cu m/day
3,217
568
70,7^0
15, 254
1,287
MGD
0.85
0.15
18.7
4.03
0.3*1
Activated
cu m/day
2k,f>kQ
4,353
5!i2,012
116,956
9,8'.!
MGD
6.51
1. 15
1*3-2
30.9
2.60
Total
cu in/day
27,858
4,920
612,792
I32,09fc
1 1 , 1 23
HGO
7.36
1.30
161.9
31* 9
2.94
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Table 28 were converted to equivalent domestic sewage by adjusting their
suspended solids content to 200 mg/1. Then the sludges produced from treat-
Ing the dilute effluents pumped back are estimated by assuming a primary
sludge production of 22kQ cu m (gal.) (5% solids) per million cu m (MG) of
adjusted flow and 18,700 cu m (gal.) {1% solids) of waste activated per
million cu m (MG) of adjusted flow. These calculations are summarized In
Table 30.
}_._ Hydrau^l Ic Considerations
It may be seen from Table 30 that the estimated sludge volumes produced
varied widely with the CSO treatment sludges dewatered, and this varia-
tion is attributable to the quality of the dilute effluents bled/pumped-
back. That Is, the poorer the dilute effluent quality, the greater the
sludge volume produced by the dry-weather plant, which is to be expected.
For example, the data in Table 30 show that the quality of the dilute
effluent from screening-flotation is of appreciably poorer quality than
those of the other dilute effluents Investigated, and the sludge volumes
produced as a result of treating the dilute effluents from screening-
flotation are correspondingly appreciably greater than those from any of
the other CSO treatment methods.
It was previously established that the dally design volume of sludge
(primary plus activated) to be handled by the hypothetical dry-weather
sludge handling facilities Is 3.6 x 10^ cu m/day (96 MGD). Comparing this
value with the additional sludge volumes expected and shown In Table 30
Indicates that three of the five sludge volumes shown (from storage -
sedimentation, dissolved air flotation and trickling filtration) can be
Intermittently handled by the dry-weather sludge handling facilities,
assuming that the dry-weather sludge handling facilities are below de-
sign conditions (which Is a reasonable assumption).
On the other hand, It appears that two of the five sludge volumes In
Table 39 (screenIng/DAF and contact stabilization) would hydraulically
overload the dry-weather sludge handling facilities. Closer examination
of Table JO shows that the two sludge volumes In question were derived
from dilute effluents comparatively higher In quantity and poorer In
quality than the other dilute effluents. This lends emphasis to the
importance of performing the CSO treatment methods and the CSO treatment
sludge dewaterfng method as efficiently as possible so as to permit the
bleed/pump-back of dilute effluents to the dry-weather treatment plant.
For example, further Investigation (f2) Into the dewaterlng tests per-
formed on the sludges from screenlng/DAF of CSO yielding the dilute
effluent qualities shown in Tables 21 and 30 Indicate that the thicken-
ing-filtration dewaterlng was accomplished without the aid of chemicals.
The use of chemical conditioning would probably Improve the dilute
effluent quality permitting bleed/pump-back to the dry-weather plant with
an appreciable reduction In the amount of sludge produced for further
treatment by the dry-weather sludge handling facilities.
70
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2 . joUjs Load ing Cons iderat i
For our hypothetical dry-weather plant, the design dry-weather solids to
be handled (primary plus activated) has been established at 5-3 x 10°
kg/day (H.7 x 10" Ifa/day). The additional sludge solids produced by
pumping back the dilute dewaterfng effluents (whose estimated sludge
volumes are shown in Table 30) are estimated by assuming a primary
sludge concentration of 51 and a waste activated sludge concentration of
II. A summary of the additional sludge solids expected Is shown In Table
31.
The conclusions drawn from the solids information contained in Table 31
are similar to those derived from Table 30 with regard to the hydraulic
considerations evaluated, namely,
a. Comparison of the sludge handling facility design solids loading of
5.3 x 106 kg/day (11.7 x 1Q6 Ib/day) with the additional solids
loadings shown in Table 29 indicates that three of the five solids
loadings shown in Table 30 (from storage-sedimentation, dissolved-
air flotation and trickling filtration) can be intermittently handled
by the dry-weather sludge handling falcllities, assuming that the
dry-weather sludge handling facilities are below design conditions
(which is a reasonable assumption),
b. On the other hand, it appears that two of the five solids loadings
in Table 30 (screen ing/DAF and contact stabilization) would create
a solids overload problem for the dry-weather sludge handling fa-
cilities. However, as Indicated previously, it is felt that this
problem may be minimized by more efficient CSO treatment and CSO
treatment sludge dewatering performance, thereby permitting the
satisfactory bleed/pump- back of the dilute effluents to the dry-
weather plant.
BOD, heavy metals, PCB and pesticide data on the dilute effluents from de-
watering CSO sludges were not discovered In the literature, and therefore,
no comment Is made at this time regarding organic overload, toxicity to
treatment, and sludge handling efficiency due to these pollutants.
In summary, It may be concluded that bleed/pump- back of CSO treatment sludges
to the dry-weather plant does not appear to be a viable or practical solution
on a generalized basis. If ]QOl of the CSO volume was treated and generated
sludge, ft would result In gross overloading of the dry-weather treatment
plant and the dry-weather sludge handling facilities. The most limiting as-
pect of bleed/pump-back of sludge through the treatment plant and sludge
handling facilities Is the solids loading (to the ftnal clarfflers and the
digesters). On the other hand, bleed/pump-back of the dilute residuals from
cm-site dewatering of CSO treatment sludges to the dry-weather plant appears
to be practical and warrants further considerations where applicable. How-
ever, ft must be stressed that actual evaluation of the feasibility of bleed/
pump-back of CSO sludges must be completely evaluated for each individual
site. The potential problems associated with transport of a gritty sludge,
solids overload to the treatment and sludge handling processes and lower
71
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TABLE 31- EST1HATED SOLIDS TO THE DRY WEATHER SLUDGE HANDLING FACILITIES
FROM THE TREATMENT OF DILUTE EFFLUENTS OBTAINED FROM CSO SLUDGE DEWATERtNG
CSO Treatment
Process
Storage-Sedlmentat
Dtssolved-Atr
Flotation
Screen ing/DAF
Contact Stabilizat
Trick! ing Filter
Primary S
kg/dayxlO
ion 0,16
0.03
3.54
Ion 0.76
0.06
1 udge
Ib/dayxio"6
0.35
0.06
7-79
1.68
0.14
Activated
kg/dayxlO
0.25
0.05
5-42
1.17
0.10
Sludge
Ib/dayxio"6
0.54
0.10
11.94
2.57
0.22
kg/dayxH
0.40
0.07
8.96
1.93
0.16
Total
:f6 Ib/dayxio"6
0.89
0.16
19.73
4,25
0.36
NOTE: Sludge volumes used for the calculations were obtained from Table 29-
-------
treatment plant efficiency must be evaluated at each site and cost-effective-
ness of bleed/pump-back determined.
73
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SECTION VI
EFFECT OF HANDLING CSO TREATMENT
RESIDUALS BY SEPARATE SLUDGE HANDLING FACILITIES
INTRODUCTION
The most feasible method for handling specific CSO treatment residuals must
be evaluated on an Individual basis. As Indicated In the previous section,
bleed/pump-back Is not a viable solution In most situations due to problems
of transport In pipelines and potential solids overload In the various dry-
weather treatment processes. Once evaluation indicates that bleed/pump-back
Is not an acceptable alternative, then separate sludge handling facilities
must be provided. The processes must be capable of handling the specific
characteristics associated with CSO sludges. They also must be sufficiently
flexible for anticipated intermittent operation. Once applicable processes
for sludge handling are Identified, treatment trains can be established to
integrate all phases of sludge handling. It must be emphasized at this
point that the systems proposed In this section are generally suited for CSO
sludges, however design of a specific system must be considered on an indi-
vidual basis where much different schemes may be appropriate. The last
step In evaluation of separate sludge handling facilities Is location.
There are essentially three systems which can be considered: 1} transporta-
tion to parallel facilities at the dry-weather plant, 2) transportation to a
centrally located CSO sludge handling site and 3} satellite sludge treatment.
The advantages and disadvantages of each technique are presented.
This section has been divided to consider several aspects of sludge treatment
for CSO residuals individually. The limitations Imposed by the nature of
CSO sludges are presented first. Then a brief discussion of various sludge
handling processes Is included, followed by development and technical evalua-
tion of viable sludge handling alternatives. The final portion of the sec-
tion discusses alternative locations available for treating the sludge.
SPECIAL HANDLING REQUIREMENTS FOR CSO TREATMENT RESIDUALS
The characteristics of CSO treatment residuals directly affect the number of
processes which can be used for handling these sludges. Specific attention
must be given to the high grit content and low volatile solids concentration
of these materials. In addition, the wide variation in frequency and volume
of each occurrence requires that the sludge handling process be flexible
enough to handle intermittent operation.
-------
The Information Indicating the effects of high grit and low volatile solids
content has been presented previously throughout sections IV and V. The
following Is a summary of this Information for convenience:
a. That substantial amounts of solids are transported to the dry
weather plants under wet weather conditions Is substantiated by sig-
nificant data available from the literature (17). For example, pre-
sented in Table 18 were data showing the quantities of grit col-
lected during dry and wet weather periods for various United States
installations. The data in Table 18 showed that the grit volume
ratio of wet to dry weather was appreciable, with the highest ratio
at 1800 times the average dry weather grit production.
b. The literature (9) also indicates that often the stormwater solids
contribute a large increase In fine solids (silt) which is too fine
to be removed in the grit chambers and results in overloading the
primary sedimentation basin to the extent that chain and flight
collectors are sometimes burled and unable to function.
c. It was further shown that the volatile solids contents of the sludges
from the various CSO treatment methods were significantly to appre-
ciably lower than that for dry-weather municipal sludges. The higher
volatile solids contents were observed for the sludges derived from
the CSO biological treatment methods. This was expected because
the biological treatment methods used were'preceded fay treatment
steps which removed the major portion of the grit and Inert solids
present in the raw CSO, whereas the physical and physical-chemical
treatment methods used treated raw CSO with little or no preliminary
treatment for inert solids removal.
d. It was found that the net effect of the excess Inert solids in the
CSO sludges (when bled/pumped-back to the DWF plant) was to con-
tribute to the solids overload on the dry weather treatment^ and
5 JudgeJiang11 ing fac111ties. Moreover, it was Indicated that alterna-
tive CSO sludge" treatment, either on-slte or in additional parallel
facilities at the DWF plant, would require additional capacity to
handle the excess inert solids load.
It can then be proposed that the high grit and low volatile solids content
of the CSO treatment residuals will also have a direct bearing on the effec-
tiveness of various sludge handling processes. The large amount of inert
material will require compensation in the equipment designs which are based
on solids loading such as thickening, filtration, lagoon ing, sand drying
beds, centrlfugatlon, etc. Also, grit and other inert solids would detri-
mentally affect digestion (aerobic or anaerobic) facilities because the
possibility of settling of those solids In the digesters, thereby occupying
valuable space. The heavy solids loading could also cause mechanical com-
plications in some equipment.
The low volatile solids content will have the most effect on the processes
which utilize the organic substrate. Of special concern are digestion
75
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processes, since the lower organic loadings will reduce the efficiencies of
removal, and incineration, since many of the CSO residuals have significantly
lower heat values (12).
The Intermittent nature and wide variations fn flows of CSO sludges could
pose problems when many common sludge handling processes are considered.
Most sludge systems are designed for operation on a continuous flow-through
basis which is generally not possible when dealing with CSO sludges (unless
extensive holding basins are provided). The volumes of CSO sludge generated
will vary with the storm intensity and duration, time between storms,
process efficiency, etc. Therefore, either additional holding (storage)
capacity is needed or the unit processes must be designed to handle maximum
anticipated flows and still effectively process lesser amounts. Several
sludge handling processes, notably digestion, may be adversely affected by
the intermittent operation. It Is important to consider these factors
when the sludge handling processes are evaluated.
From the foregoing d}scussionf several evaluation criteria can be established
and they should be considered when choosing applicable sludge handling
methods for CSO residuals. The following considerations are important:
1. Is the process design established by solids loading criteria?
If so, the large volume of Inert solids may adversely affect the
system operation and additional capacity will be required.
1. Will the volume of inert solids affect the operation of the process?
If so, then again additional capacity may be needed which may be
detrimental to the process efficiency.
3. Is the process dependent on a specific amount of organic constituents
for proper or efficient operation?
If so, then the unusual ratio of volatile solids to inert material
may cause severe problems In the overall design of the system.
k. Will Intermittent use adversely affect the operation or efficiency
of the process?
If so, then the degree of lower efficiency must be established and
the process evaluated from this criterion.
5. Will overdeslgn of the system (to handle maximum flow rates) ad-
versely affect the process operation under lower loading rates?
If so, then use of large storage basins preceding the sludge
handling system or process are mandatory. If space for holding
Is not available, the given process may not be applicable.
Therefore the individual sludge handling processes must be reviewed with
these criteria In mind when considering their use for CSO treatment
residuals.
76
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SLUDGE HANDLING PROCESSES
General Sludge Hand! I r>g Systems
In general, sludge handling processes can be grouped according to the general
phases shown in Figure 7. Various combinations of these processes can be
utilized, to provide the overall sludge handling schematics. Basically the
potential flow schematics are as follows:
1. (Conditioning)- * Thickening •*• Stabilization •* (Dewaterfng) •*
Disposal
2. (Conditioning) -» (Thickening) -*• Oewatering •+ Reduction -»• Disposal
3. (Conditioning) -»• Stabilization -» Thickening -> (Dewaterlng) •*• Disposal
k. (Conditioning) •* Stabilization •> Disposal
* parentheses indicate optional process
Individual processes can now be evaluated and the appropriate systems de-
veloped for CSO treatment residual handling.
Cond_? 1 1 on I ng
Conditioning Is used to pretreat the sludge to allow more effective thicken-
ing or dewatering. The processes used can Include chemical addition of
polymer, lime, ferric chloride or alum, among others, or heat treatment.
Effective conditioning can increase the efficiency of the processes when
applied properly. However, choice of proper chemicals for this type of
conditioning is dependent upon Individual sludge characteristics. If there
are significant variations in sludge quality, as are common with CSO treat-
ment residuals, then the needed chemical dosages will change.
If provision cannot be made to correct the dosages utilized in the field,
which Is difficult with Intermittent CSO generation, then the effectiveness
of chemical conditioning can be severely reduced. Heat treatment can also
be utilized with temperatures from H9-260 °C (300-500 °F) and pressures
of 10.2-27.2 atm. (150-400 psfg)(22). The treatment breaks up cell masses
and Improves dewatering characteristics. However, the resulting supernatant
Is highly polluted with various organlcs and requires that additional capac-
ity be available at wastewater treatment facilities. In addition, the
process Is extremely energy intensive which may cause future problems.
Thickening removes the major portion of the liquid In sludge and Is often
the initial step in sludge dewatering. Thickening Is applicable to the
dewatering of CSO sludges, and In particular, gravity thickening equipment
Is usually employed for sludges derived from physical and physical -chemical
CSO treatment methods, whereas flotation thickening Is normally more
amenable to thickening sludges emanating from biological treatment methods.
Centrifugal thickening may also be applicable to some CSO sludges, however
prior grit removal is necessary to prevent excessive wear on the centrifuge
77
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GENERAL TREATMENT PROCESS
Conditioning Thicken I tig
Chemical
Heat
Gravity
Dissolved-alr
Flotation
Centrifuge
Stabilization
Anaerobic digestion
Aerobic digestion
Chlorine oxidation
Lime treatment
Heat treatment
Composting
Pewaterlng
Vacuum filtration
Centrifugation
Drying beds
Drying lagoons
FlIter press
Moving screen
Capillary belt
** DCG/MRP
Reduction
Incineration
Flash drying
Wet alr oxi-
dation
Pyrolysls
Cyclonic
furnace
Electric
furnace
0}sposaI
Sanitary
landfill
Ocean
Land applI-
catton
Land reclama-
tion
OS
GENERALTREATMENT TRAIMS
I. (Conditioning)* •*- Thickening •*• Stabilization •* (Dewaterlng) + Disposal
2. (Conditioning) •*• (Thickening) -+ Oewatering ->• Reduction -* Disposal
* Parentheses Indicate optional process.
** Rotating Gravity Concentrators
Figure 7. Sludge handling systems.
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mechanism.
Stafailizatlon
in most cases, stabilization of the sludges is required before ultimate dis-
posal in order to minimize organic solids mass, health hazards and nuisance
conditions. In fact, where final disposal is on land [50% of U.S. installa-
tions (22)], such as by sanitary landfill, cropland application and land re-
clamation,, it is essentail that sludges be stabilized prior to spreading on
land.
Stabilization, therefore, minimizes nuisance conditions by decomposing
organic solids to a more acceptable stable form and minimizes health hazards
by reducing or eliminating pathogenic organisms. Stabilization processes
and equipment available include anaerobic and aerobic digestion, heat treat-
ment, composting and chemical treatment (chlorine oxidation and lime treat-
ment). Some of these stabilization processes are established and some are
experimental- Further discussion regarding them and their applicability
for handling CSO sludges Is included.
AnaerQblc and[_ Aerobic Digestion ~ Both anaerobic and aerobic digestion are
established processes and because of the current energy shortage are in-
creasing in popularity; the former because of the potential benefits of
methane production and the latter because it can produce exothermic con-
ditions. These processes are applicable for handling CSO sludges derived
from biological treatment methods and the associated equipment required
should be located at the dry weather treatment plant along with the CSO
biological treatment equipment so as to be able to keep the "CSO digesters"
viable with dry-weather sludge between storms. It may be evident that
these processes are not applicable at remote on-slte CSO physical and
physical-chemical facilities where the means for keeping the processes viable
between storms is not existent.
Heaj:JYea^tmeivt - Heat treatment of sludges has seen rapid growth !n recent
years and includes the following: pasteurization, low pressure oxidation
(Sterling Drug) and the Porteous heat treatment process. At this time, the
heat treatment of sludges has many vigorous advocates and equally vigorous
opponents. Usual complaints Include failure of equipment, excessive cost
and high supernatant BOD and color. Because of the Impact of this process
on cost and the unknown effect of high supernatant BOD on organically over-
loading the dry-weather plant, this process will not be further considered
as a CSO sludge stabilization alternative.
Cojn^osjjnji - Composting of sludge has not been widely applied In North
America. Of the 18 composting plants constructed in the U.S. between 1951
and 1969, few are currently operated and many of these are operated intermit-
tently. The primary problem has been the lack of a market for the stable
product to offset the coat of the process and make it economical. Composting
will not be further considered for handling CSO sludges.
Chemical StabNIzation - Chemical stabilization processes Include chlorine
ox!dation and1! me stabi Hzat!on. The Purlfax process oxidizes sludge with
73
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heavy doses of chlorine (about 2000 mg/1) and produces a stable and sterile
sludge which fs low in pH (about 2). The treated sludge dewaters well on
sandbeds and is amenable to vacuum filtration after conditioning. Chlorine
cost only Is about $5-50/metric ton dry solids ($5/ton). Other operating
and capital costs would increase this figure. The primary concern with this
process is that the drainings from the treated sludge contain high concen-
trations of chlorinated compounds which may be toxic. Because of this con-
cern and the possibility of ultimate disposal on land, further consideration
of this process for handling CSO sludges will not be made.
The lime stabilization process is also a chemical stabilization process de-
signed to reduce many of the harmful properties of sludges. The process
Involves addition of slurrled calcium hydroxide to a pH greater than 11-12
and continued mixing of the solution for thirty minutes. This time period
allows the slower reacting lime to hydrolyze and provides contact for patho-
gen destruction. A schematic of the typical process Is shown In Figure 8.
Previous studies (32, 33) on the subject have Indicated that this procedure
effectively reduces the indicator organisms for bacterial pollution up to
99 percent and significantly reduces nuisance odors (34). In addition, the
dewatering characteristics of the sludge are markedly improved. Investiga-
tors (3k) concluded that lime stabilized sludge is as safe to handle as that
produced from conventional anaerobic digesters. However, there can be
problems with lime stabilized sludge If proper disposal methods are not
utilized. The high pH of the sfudge Is not permanent and as the pH decreases
during the degradation process, odor and bacteria problems may reoccur.
Excess lime dosages and proper disposal can retard or eliminate the problem.
Lime stabilization seems to be quite adaptable to CSO sludge treatment for
several reasons. First, the process is flexible. It can be used intermit-
tently with sludges of a wide variety of characteristics. The process con-
trol Is commonly performed utilizing pH measurements so that operator Inter-
vention is minimal. The anticipated total capital Investment is lower due
to simple operation and shorter detention times than other stabilization
techniques. If necessary, a portable treatment unit could be developed for
use. This type of system may be used to augment dry-weather sludge handling
facilities when not required for CSO sludge treatment. However, the lime
dosages required are high and this cost must be considered. Previous studies
(35) have Indicated that lime dosages range from 102-208 g Ca(OH). per kg
of dry solids and operating and maintenance costs are estimated to be §9~$19
per metric ton ($8-17 per ton) of dry solids. In addition, direct land applica-
tion, of lime stabilized sludges requires hauling large volumes of liquid
sludge which may not be practical in some situations. In these situations,
further dewatering using centrifugation or vacuum filtration is a necessary
Subject for further study, Rq^eyer, it is anticipated that with lime stabili-
zation, furEher chemical conditioning requirements woiiH Ee" minimal since the
lime addition significantly improves sludge dewatering capabilities. Another
advantage of using lime stabilization is the reduction of potential odor prior
to further handling. This aspect may be Important if storage for any length
of tine is required.
80
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NO. 2
Ca(OH).
SLURRY
FEED PUMP
NO. 1
Ca(OH),
SLURRY
FEED PUMP
RAW SLUDGE
SLURRY
STORAGE
PUMP
CONTROLLE
pH MONITOR
AND RECORDER
SLUDGE/
Ca(OH)
MIXING
VESSEL
SLUDGE/
Ca{OH)_
CONTRACTOR
pH MONITOR
AND RECORDER
STABILIZED SLUDGE
TO THICKENER,
STORAGE, OR
IMMEDIATE DISPOSAL
Figure 8. Lime stabilization process conceptual flowsheet (35).
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Dewatering
Dewatering !s used to remove additional moisture from the sludge (50-901) to
produce a damp cake (22, 36). The devices utilize several methods Including
natural evaporation and percolation plus mechanical techniques such as fil-
tration, squeezing, vacuum withdrawal, centrifugation and compaction.
Referral to Figure 7 indicates that there are many potential techniques
available for dewatering. When considering these processes with respect to
CSO sludges, some can be eliminated due to apparent operational problems.
Space restrictions will eliminate use of both drying beds and drying lagoons,
in most cases. Devices such as moving screens, capillary systems and ro-
tating gravity concentrators (DCG/MRP) are new systems which have not been
defined with respect to their applicability to the high grit content of CSO
sludges. The techniques may be appropriate, however, further investigation
would be needed prior to their use.
More conventional techniques Include filter press, vacuum filtration and
centrifugation. Use of a filter press Is desirable If Incineration or other
combustion technique Is being utilized, otherwise It may be too expensive for
CSO sludge dewatering. In addition, conditioning requirements and operator
control needs may be greater. It may be more desirable to use vacuum fil-
tration, which will provide a workable cake (approximately 201 solids) for
landfill or land application. Preliminary studies (12) have Indicated that
dewatering thickened sludges by vacuum filtration was amenable to CSO sludges
derived from contact stabilization. Centrifugation may also be an appro-
priate dewatering technique if the grit concentration will not cause ex-
tensive mechanical wear. It was indicated that the use of thickening and
centrifugation was applicable to the CSO sludges emanating from treatment by
screenlng/DAF and trickling filtration. In some instances It was Indicated
that some CSO sludges may be most effectively dewatered by centrifugation
alone (without pre-thicken Ing). These Included sludge from storage-sedi-
mentation and from dissolved-alr flotation alone (25) (see Table 28).
Reduction
In some cases reduction can be utilized as a stabilization and/or disposal
process. Several types of processes can be utilized as outlined In Figure
7 and these can be further divided into new or established types. Pyrolysis
and the use of cyclonic and electric furnaces are new techniques which have
been used mainly on a small scale basis. The effects of the high grit and
low volatile solids content Is not readily predictable. However, It Is
speculated that the same features which affect the use of incineration for
CSO sludge handling are applicable In these systems.
Incineration can be used to reduce the sludge to ash after thickening and
dewatering. Incineration although costly, Is receiving Increased attention
as an alternative with decreasing land availability and the possibility of
more stringent standards for land disposal. However, wastewater treatment
sludges have low heat values In comparison to common fuels to the extent
that combustion Is not self-sustaining unless extremely high solids contents
are reached in feed cakes. Often an auxiliary fuel Is required, if waste-
82
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water sludges are incinerated alone. The heat value for typical dry-weather
activated sludge solids is 3563 cal/gm (6413 BTU/lb) as compared to gasoline
with a value of 11,100 cal/gm (19,980 BTU/lb). Furthermore, it was observed
(12) that the heat value of most other CSO treatment sludges was even less.
The average heat value for CSO sludges from physical and physical-chemical
treatment was 2032 cal/gm (3657 BTU/lb), whereas that for similar dry-weather
sludges is estimated at 4581 cal/gm (8246 BTU/lb) (27). This difference in
heat value is attributed to the higher inert and low volatile solids content
of the CSO treatment sludges in question. On the other hand, the heat value
of the biological sludges from CSO biological treatment was comparable to
that for the dry-weather biological sludges, and that was expected because
of the similar solids characteristics.
Because the heat value for CSO sludges is relatively low, the cake solids in
the feed must be proportionately higher to avoid the use of auxflHary fuel.
The energy and capital costs of obtaining a sufficient solids concentration
In the feed cake may be prohibitive. If auxilliary fuel Is utilized, in
the light of the Increase in energy cost and the current energy shortage,
Incineration would not be a viable method for handling CSO sludges at this
time. However, Interest In using incineration may be revived if the com-
bined incineration of solid waste residues and wastewater sludges are in-
corporated with energy recovery as a prime feature.
Wet air oxidation is the final technique which may be used for sludge re-
duction. It fs used at higher temperatures and pressures than heat treatment
and theoretically oxidizes any materials capable of burning in water at
temperatures of 121-371 °C (250-700 °F). Preliminary thickening and dewater-
Ing are not necessary, however it is necessary to provide disposal for the
oxidized material. The main disadvantages associated with this technique
are the high energy cost and the associated problems due to intermittent
operation. High pressure and temperature operations should be run as con-
tinuously as possible to alleviate start-up problems and energy loss.
Disposal Techniques
Disposal techniques Involve either the land or oceans. However, recent regu-
lations have restricted ocean dumping, so that only land disposal remains-
Three techniques are applicable; land reclamation, land application and land-
fill. Land reclamation fs most restrictive since It requires that land
needing to be reclaimed (such as abandoned strip mines) be located near the
sludge generation site. This criterion will not generally be met with re-
gard to CSO sludges. Land application does pose a viable solution for dis-
posal and has been considered in depth In Section VIII. Further discussion
Is not Included here.
Landffiling of sludges and other residual by-products of municipal and In-
dustrial waste treatment Is a major ultimate disposal alternative. A
sanitary landfill accepting sludge must be designed In accordance with EPA
"Guidelines for Land Disposal of Solid Wastes" (37) even if sludges are dis-
posed of separately or along with municipal solid wastes. These guidelines
are a result of Increasing concerns for public health and environmental
quality (38). The guidelines state that prior to landfilllng, (a) sludges
83
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must be stabilized (le. digestion, lime, heat etc.) to prevent odor problems
and reduce health hazards and (b) sludges must be dewatered to eliminate
leachate migration.
A sanitary landfill must be managed so that wastes are systematically deposited
and covered with sol! to control environmental impacts within defined limits.
Proper management consists of four basic operations (39). I) wastes are
added in a controlled manner in a prepared portion of the site; 2) the wastes
are spread and compacted In thin layers; 3) the wastes are covered daily or
more frequently, if necessary with a layer of soil; and *f) the cover material
Is compacted daily.
Proper site selection is an important step toward establishing an acceptable
sanitary landfill operation. Some of the major factors which should be
considered in site selection are (^0): a) land requirements, b) waste haul
distances, c) cover material, d) geology, and e) climate.
Important public health and nuisance aspects which must be considered In
landfill operation are l) vector control, 2) water pollution, 3} odors, and
4) gas production
EPA guidelines require that a program must be developed and implemented to
provide for adequate monitoring of landfills accepting sludges (38) . This
plan would Include groundwater observation wells, and surface runoff collec
tion basins to measure pollutant migration from leachates or surface water.
DEVELOPMENT OF VIABLE TREATMENT SCHEMATICS
General
The first step in the development of viable treatment schematics is to
identify those processes which are applicable to possible use for CSO sludge
handling. Once this has been accomplished, then various treatment trains
can be identified and further evaluated from a space and preliminary economic
standpoint.
Generally, the process elements comprising a CSO sludge handling system might
Include grit and low volatile solids removal, sludge dewatering, stabiliza-
tion and ultimate disposal. The specific treatment train used will vary with
the CSO treatment method employed and location and the ultimate disposal
method used. For example, It has been shown that the grit and low volatile
solids contents of CSO sludges are greater than those for dry-weather munici-
pal sludges. Moreover, for the CSO treatment methods investigated, greater
concentrations of grit and low volatile solids contents were associated with
sludges from physical and physical -chemical treatment than from sludges de-
rived from biological treatment. This was expected because the biological
treatment methods (contact stabilization and trickling filtration) were
preceded by treatment steps which removed the major portion of the grit and
Inert solids present In the raw CSO, whereas the physical and physical -chemi-
cal treatment methods (storage-sedimentation, DAF, screenlng/DAF and micro-
-------
screening) treated raw CSO with little or no preliminary treatment for Inert
solids removal. Therefore, it would be expected that the sludges from
physical and physical-chemical treatment might require provision for grit
and low volatile solids removal whereas those sludges from bloJoqical treat-
ment might not. Suitable equipment for grit removal includes;
chain and flight grit removal devices, hydroclones, and the swirl concentra-
tor (41). Hydroclones are commercially available for grit removal from
sludges. The swirl degritter is a newly developed device (77) (78) (79).
Specific Processes for Use In CSO Sludge Handling
The previous discussion briefly identified various processes which could be
used for handling CSO treatment residuals. Due to the discussion presented
therein and evaluation of the question criteria outlined previously In this
section, the following processes are considered to be potentially applicable
to CSO sludge handling:
Conditioning: Chemical treatment
Thickening: Gravity thickening
Stabilization; Lime stabilization
Anaerobic digestion (in some cases)
Dewatering: Vacuum filtration
Centrlfugation
Reduction: None
Disposal: Land application (LA)
Landfill
Pp.tentT_a.1 Treatment Schemes^
As indicated, the individual treatment scheme chosen is determined by the
specific characteristics of the CSO sludge to be treated. However, for
generalization, the biological sludges can be grouped Into one type and the
physical or physical/chemical sludges Into another. Another important con-
sideration Is the location of the sludge handling system, especially when
biological treatment techniques are being considered. Usually, if biological
systems are applicable, the treatment system and sludge handling facilities
are located at or near the dry-weather treatment plant. When this Is the
case, a different flow schematic than that generally proposed may be desira-
ble.
Combination of the processes chosen which may be applicable to CSO sludge
handling yields the following ten alternatives;
I. Lime Stabilization -*• Gravity Thickening -*• Vacuum Filtration •*• Landfill
2. Lime Stabilization •* Gravity Thickening -»> Vacuum Filtration -»• Land
Application
85
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3. Ltroe Stabilization •*• Gravity Thickening -*• Land Application
k. Lime Stabilization -»• Land Application
5. Anaerobic Digestion -*• Gravity Thickening •*• Vacuum Filtration -»•
Landffll
6. Anaerobic Digestion ->• Gravity Thickening •* Centrlfugation -»• Landfill
7. Anaerobic Digestion •* Gravity Thickening •* Vacuum Filtration ->-
Land Application
8, Anaerobic Digestion •*• Gravity Thickening •*• Centrlfugation •* Land
Appl5 cat I on
9. Anaerobic Digestion •*• Gravity Thickening -*• Land Application
10. Anaerobic Digestion •*• Land Application
It is observed that Centrlfugation was not Included as a thickening method
when lime stabilization was utilized. This is mainly due to the fact that
the large doses of lime used for stabilization should allow vacuum filtra-
tion to proceed easily, with a minimum of additional chemicals. Also these
schematics do not presently Include provision for grit removal, so the
potential wear on a centrifuge might be a problem. Therefore, .centrifugal
dewatering was not considered at this time. However, both vacuum filtration
and centrifugation were considered if anaerobic digestion was utilized as
the stabilization technique, since prior grit removal Is generally included.
Chemical conditioning Is anticipated to be needed and the chemical type can
be tailored to meet the optimum dosage for the given dewatering method.
Both landfill and land application have been considered as viable disposal
techniques, although land application can accept much more dilute sludges,
if transportation costs are not prohibitive.
Pre11roIna ry Eva1 ua t i on of Schema t ics
Evaluation of the flow schematics given Involves an Initial comparison of
lime stabilization and anaerobic digestion. Considering operational vari-
ables plus cost and space requirements, the advisability of using lime
stabilization over digestion Is indicated even when biological treatment
of CSO Is utilized. For example, lime stabilization Is less complex in
operation, less subject to upsets, can be more easily automated and is more
adaptable to Intermittent operation (digestion process would have to be
kept viable between storms). Moreover, lime stabilization appears to require
less space. A lime sludge contact time of about 30 minutes Is needed for
lime stabilization (*»2), whereas 10-15 days solids retention time is re-
quired for digestion (See Tables 22 and 23). From the standpoint of costs,
it appears that the cost of digestion is appreciably greater than that for
lime stabilization. For example, for a 37,850 cu m/day (10 MGD) sewage
treatment plant which produces a total sludge flow of approximately 2$4
cu m/day (0.067 MGD), the capital cost of a lime stabilization process
is estimated at $28,000, and this cost Includes tankage, piping, chemical
feed system and automatic control instrumentation. On the other hand, the
construction cost for an anaerobic digestion system to handle the same
quantity of sludge is estimated at $800,000 and this cost Includes sludge
heating, circulating and control equipment and control building (43). The
operating costs for digestion are also appreciably greater than those for
lime stabilization. . For example, the total annual costs for anaerobic dlges-
86
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tfon (including amortization) are estimated at $31 per metric ton dry solids
($28/ton) whereas those for lime stabilization are about $10 per metric ton
dry solids ($9/ton) (kk). From the above discussion, it is evident that
lime stabilization is a promising method for handling the unique CSO treat-
ment sludges. It should be recognized that lime stabilization is not an
established sludge handling method and demonstration of Its application for
treating CSO treatment sludges should be pursued to obtain baste design
and operating criteria and further investigation is recommended.
Sludge dewaten'ng by thickening, where economically feasible, should be per-
formed after lime stabilization because it has been found that lime treat-
ment enhances the sludge settling characteristics (44). Further dewatering
may be achieved by vacuum filtration. Ultimate disposal of the sludge, de-
pending on land availability and other factors, would be by landfill or land
application. Therefore preliminary screening indicates that four treatment
systems may be applicable for handling CSO residuals. All Involve lime
stabilization but the degree of intermediate treatment, prior to disposal
cannot be estimated at this point. Individual transportation and storage
costs must be considered to establish which of these general alternatives
Is most cost-effective.
IMPACT OF HANDLING CSO SLUDGES AT VARIOUS SITES IN THE CITY
Genera^
When considering separate treatment of CSO sludges by any of the chosen
handling schemes, it Is necessary to establish the location at which the
sludge will be treated. There are three potential locales: treatment at
parallel facilities at the dry-weather treatment plant; treatment at a
central location and treatment at remote satellite locations.
A natural basis for selection of the location for CSO sludge treatment Is
the CSO treatment method used for treatment of the raw CSO. The physical,
physical-chemical, and biological processes used on storm flows each have
limitations as to where they can be used (9). Biological treatment facili-
ties should be located at sewage treatment plants to provide a continuous
active blomass. Physical and physical-chemical treatment facilities lend
themselves more easily to remote satellite locations. Inasmuch as the CSO
sludges from biological treatment will be treated both "on-site" and "at
parallel facilities at the DWF plant", the question arises as to which
alternative to use for treatment of the CSO sludges from physical and physi-
cal-chemical treatment.
Treatmentpj^ CSO Res I dual s at Parallel FacllI ties at the Pry-Weather Plant
Handling these CSO sludges in additional parallel facilities at the dry-
weather plant does not appear to be generally feasible because of the
problems Involved in transporting the sludges from the CSO treatment site
to the dry weather treatment plant. Alternative means for transporting the
sludges to the parallel facilities at the dry-weather plant Include bleed/
87
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pump-back to the combined sewers, transport by separate pipeline and hauling.
It Is apparent from previous discussion that sludge bleed/pump-back to exist-
ing combined sewers would not be feasible in most cases because it would re-
quire storage, the sludge would be admixed with the sewage contributing to
an overload on the dry-weather plant and grit fn the sludge may settle out
quickly In the interceptor causing blockage and premature overflow via
backwater effect.
Separate pipeline transportation of sludges, say from remote overflow treat-
ment points, would not appear to be feasible since ft would require separate
pipelines from many treatment points to the dry-weather plant which would
appear to be costly. Moreover, because the flows through these lines are
Intermittent, grit and other solids deposits ean accumulate between storms
increasing pluggage problems. It may be possible to partially alleviate
these accumulations by flushing the lines, however, this procedure may
cause hydraulic overload problems at the treatment plant due to large
volumes of water needed. In addition, the characteristics of the waste-
water is extremely different from typical influent, and may adversely affect
plant operation. However, where the CSO treatment facilities are centrally
located near the dry-weather plant, pipeline transportation of CSO treat-
ment sludges to parallel sludge treatment facilities at the dry-weather
plant may be a. viable alternative in spite of potential problems.
Similarly, hauling of CSO treatment sludges to parallel treatment facilities
at the dry-weather plant may be feasible in isolated instances, but would
not appear to be generally feasible because of the cost involved and the
logistics for a trucking operation from many remote overflow points.
Utilization of pipeline transportation and hauling for bringing CSO sludgesto
the dry-weather plant may be enhanced ff the major portion of the grit and
inorganic solids were removed on-site at the overflow treatment facility
and If subsequently the sludges were treated by digestion (aerobic or anaero-
bic) in parallel facilities which were kept viable between storms with dry
weather sludge. If transportation of CSO sludges by bleed/pump-back, pipe-
line or hauling to the parallel sludge handling facilities at the dry-
weather plant Is not feasible, as is indicated from previous discussion,
then the other alternatives must be considered.
Treatment of CSO Res I duaj_s at^ Centra 11 y Located S1 udge Hand H ng Fac 11111 es
This alternative Involves transportation of the CSO treatment residuals to
a central location for stabilization, storage and further dewatering. All
of the disadvantages associated with transport of the sludge to parallel
dry-weather facilities are applicable with the exception of bleed/pump-back,
which may not be possible. There may be some additional difficulty associated
with obtaining sufficient property for locating the treatment plant, since
in most areas of the country the combined sewers are located In the center
of the city. This may possibly be a prohibitive factor In utilizing the
88
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central location alternative. If property Is scarce and If transportation
using separate pipelines, or hauling is not feasible, as was indicated in the
previous section, then on-site treatment of CSO sludge Is the only remaining
alternative. This choice Is not without problems, such as the operation
and maintenance of several solids handling plants at different remote loca-
tions in a city, but does have the advantage in that it eliminates the
operational problems and cost associated with transporting the sludges from
the remote CSO treatment sites to the dry weather plant.
TreatmentL oj;__C_SOL ResJdualis at Satel lite Treatment Sites
The remaining alternative to consider Is therefore treatment of the CSO
residuals at separate sites throughout a city. It is necessary to evaluate
the effect of this handling with respect to performance, operation, mainte-
nance and cost (9). The disadvantage of maintaining and operating several
treatment systems is obvious with respect to both manpower and utilities
costs. In addition, capital equipment costs are anticipated to be greater
since the typical economics of scale can not be fully utilized. However,
overall evaluation is necessary before this alternative can be implemented
or disregarded.
The following discussion is pertinent to and limited to CSO treatment fa-
cilities at remote satellite locations. In this regard, and as previously
noted, physical, physical-chemical and biological treatment processes used
on storm flows each have limitations as to where they can be applied.
Biological treatment systems should be located at sewage treatment plants
which can supply a continuous active biomass. On the other hand, physical
and physical-chemical treatment processes lend themselves more easily to
remote locations at overflow points, and It is these locations which are
the subject of this discussion.
The question has been raised that if on-site treatment of residual sludges
is performed as recommended, what effects on operation, performance and
maintenance would occur due to the logistics of operating and maintaining
several sludge handling facilities at different locations, say 5 to 10 or
perhaps 100, by one municipality? It is evident that sludge handling and
disposal is an integral part of a CSO treatment system and the effectiveness
with which sludge handling Is carried out influences the efficiency of
treatment, operation and maintenance, and overall costs. Moreover, the
effective operation of a total CSO treatment system requires not only the
physical operation of the components (overflow treatment and sludge handling)
but also their operation in unison and on-call. Therefore, the aspects of
operation and maintenance for CSO treatment and residual sludge handling
should be equally emphasized. These aspects Include operating controls and
options, sustaining (dry-weather) maintenance, support facilities and supply,
and safety.
Storm events occur at random intervals, and for this reason it is essential
that multiple remote treatment sftes be capable of automatic startup and
shutdown. Furthermore, the instrument and equipment reliability require-
ments may be much more demanding than for dry-weather treatment facilities.
89
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The lime stabilization process, for example, lends itself well to automation
because two of the most important variables in the process are pH and contact
time. Contact time may be adequately controlled by system design, and pH
Is relatively simple to control and automate.
It fs indicated that a sustaining or preventative maintenance program is the
one key to a successful combined sewer overflow pollution abatement and
control system. The program begins with the careful planning and design of
the combined sewer overflow treatment and solids handling facilities. For
example, whenever several systems are needed, which is the primary thrust
of this discussion, it is usually economical to use the same type device,
equipment, and design to reduce operation and maintenance costs. Also, de-
signing in increased automation permits minimization of cleanup and mainte-
nance.
The performance of remote site facilities are greatly enhanced by strict
adherence to a well-planned sustaining maintenance program. Generally, the
sustaining maintenance required increases as the degree and complexity of
treatment sophistication increases. Effective control and operation of such
facilities are usually dependent upon varying degrees of instrumentation.
For example, to ensure reliable startup and shutdown, all instrumentation
roust be checked and calibrated on a regular basis.
Satisfactory operation of combined sewer overflow abatement and treatment
facilities depends, to a large extent, on adequate regular inspection and
maintenance. The purpose of this Is twofold: first, to locate and correct
any operational problems or failures and second, to prevent or reduce the
probability of such problems or failures.
Inspection should be as frequent as necessary to keep such facilities In
good operating condition. Generally, this means inspections both on a weekly
schedule and following each major storm. All equipment must be exercised
regularly to check and Insure readiness, and facility cleanup, lubrication
and dewatering must be done following each storm.
Complete records should be kept of all Inspection and maintenance. The time
and date of each inspection should be recorded, together with a description
of the condition of the equipment and the work performed. The number of
man-hours spent on each piece of equipment should be noted. These data
should be tabulated for each piece of equipment requiring excessive mainte-
nance or that is out of service with unusual frequency. These records can
provide the data needed to compare the cost and efficiency of different
types of equipment for guidance In the design and purchase of new equipment
or the remodeling of existing equipment. Such records also aid in the
scheduling of preventive maintenance. Required maintenance common to most
off-line facilities may include lubricating of equipment; Inspecting and
cleaning of chemical pumps, electrical and pneumatic sensing probes, flow
measuring and recording devices, and automatic samplers; checking and
calibrating instruments; checking emergency power generators and starting
batteries; and inspecting all pumps, valves, and piping.
90
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The Importance of maintenance support In the operation of treatment facilities
increases as the number and/or size of such facilities Increases. In view
of the wide variety of control and treatment processes, no attempt will be
made to cover the specific requirements of each Individual process; only the
common general requirements will be listed. The four major requTrements are
(1) access to equipment, (2) adequate tools and equipment, (3) a specialized
work area, and (k) spare parts stock.
Finally, storm flow management applications expose personnel to very real
and very dangerous environmental conditions. The hazards are a function of
the working environment, operating procedures and practice, and condition
and design of facilities. The chemicals used or stored present another
problem because of their toxicJty, eorrosiveness, etc. Plant features,
such as railings, kickboards, safety treads, multiple access/egress points,
ventilation, lighting, auxiliary power sources, and detection and observation
points, must be fully Incorporated into design and practice.
In summary, the logistics of operating and maintaining several solids han-
dling plants at different locations throughout a city is formidable but not
insurmountable.
91
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SECTION VIJ
CONSIDERATIONS FOR LAND
APPLICATION OF CSO WASTES
Land application of wastes, in general, entails the use of plants, the soil
surface, and the soil matrix for removal of certain pollutions! constituents.
Land application systems can be considered as viable alternatives for waste
treatment and disposal.
However, the consideration of land for the treatment and disposal of any
type of waste is a very complex matter that encompasses a wide range of de-
sign possibilities which are available to suit specific site characteristics,
treatment requirements and project objectives. To date, no generalized de-
sign procedure is in use or available which would assist in evaluating the
major variables that influence the design of a land application system.
Therefore, the information In this section is intended to summarize the pre-
sent state-of-the-art technology and, from this knowledge, provide informa-
tion and criteria for evaluating the feasibility of applying CSO constituents
to, the land. The storm generated discharge residuals that will be con-
sidered for study Include:
I. Raw CSO
2. CSO sludges, liquid and dewatered
The following discussions are primarily based on the following EPA Technical
Bulletins and Information Transfers: "Wastewater Treatment and Reuse by
Land Application" (**5); "Land Treatment of Municipal Wastewater Effluents"
(46); "Evaluation of Land Application Systems" (4j); "Costs of Wastewater
Treatment by Land Application" (W); and "Municipal Sludge Management:
Environmental Factors" (38).
LAND APPLICATION TECHNOLOGY
The Inclusion of this technology section is to establish a general procedure,
based on an understanding of the pollutant management capabilities of soils,
for evaluating the feasibility of land application of CSO wastes under
various conditions. This development will provide a rational screening
method which should lead to 1) the Identification of specific factors, 2) an
indication of the public health and legal constraints In using land applica-
tion, and 3) site locations that combine the required characteristics for
safe pollutant management. Essentially, the information presented in this
section Includes state-of-the-art discussions of the following areas: land
-------
application methods, public health considerations, Imposed government regu-
lations, site selection and factors, and design considerations.
Land App1|cat1on Methods
The three basic methods of land application are Irrigation, infiltration -
percolation, and overland flow. Each method, shown schematically in Figure
9, can produce renovated waters of different quality, can be adapted to
different site conditions, and can satisfy different overall objectives.
Tables 32 and 33 compare major design and operational characteristics em-
ployed for these application systems. Relevant characteristics, Including
factors Involved In selection and design of land application systems, will
be briefly reviewed In this text.
Irrigat Ion - Irrigation Is the most widely used method of land application
in practice today. The controlling factors In implementing this type of
land application system are site selection and design, methods of Irrigation,
loading constraints, management and cropping practices, and the expected
treatment or removal of pollutional constituents.
Important factors involved in site selection are: type, drainablllty and
depth of soil; the nature, variation of depth and type of underground forma-
tion; topography; and considerations of present and future land use trends.
Climate is equally as Important as the land in the design and operation of
irrigation systems. However, climate fs not a design variable since it is
specific to regions under consideration.
Table 3k lists major factors and generalized criteria for site selection.
Soil drainablllty is considered the primary factor because, coupled with
the type of crop or vegetation selected, it directly affects the hydraulic
loading rate. The ideal geological formation is a nwderately permeable soil
capable of Infiltrating approximately 5 cm per day (2 In/day) or more on an
intermittent basis. In general, soils ranging from clay loams to sandy
loams are suitable for Irrigation. Soil depth should be a minimum of 0.6
meters (2 ft) of homogenous material and preferably 1.5 to 1.8 n (5~6 ft)
throughout the site. This depth is necessary to promote extensive root
development of some plants, as well as for wastewater treatment.
The minimum depth to groundwater should be 1.5 m (5 ft) to ensure aerobic
conditions. Control procedures, such as underdrains or wells, may be re-
quired If the groundwater is within 3 to 6 meters (10-20 ft) of the surface
and site drainage is poor.
For crop Irrigation, slopes should be limited to about 10 percent or less,
depending upon the type of harvesting equipment to be used. Densely foli-
ated hillsides, up to 30 percent In slope, have been spray irrigated
successfully.
Spray, rtdge and furrow, and flood are three of the most common methods of
irrigating. Spray irrigation 5s accomplished using a variety of systems
from portable to solid-set sprinklers. Ridge and furrow irrigation consists
93
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SPRAY OR
SURFACE
APPLICATION
EVAPORATION
CROP
ROOT ZONE
SUBSOIL
•.SLOPE
"•VARIABLE
5- DEEP
.* PERCOLATION
a. IRRIGATION
EVAPORATION
" ;.".••" •-" :"-INFILTRATION ^
.'•ZONE OF AERATI.CW" " ••
;.'. AND. TREATMENT; • •'.
" " MOUND '
SPRAY OR SURFACE
APPLICATION
V-: PERCOLATION THROUGH,
^nnnnn in:nm i^ nrmnnnnnnnnr """""""I" ^^Vnnrmnnnn innnm jT'^'''^.-^^j. I *'" """"""Jl'-\""" JTSSET" =jj=^ji^ ^^ ::= ==~~~"^ , : ~ * *
. =jj=ji ::= ==^ , :
=. ^_^_ ^xr± ~Tr- — ^[7l - -x ^^L- •:::r-^Ii ^3- "' i
-^J^I^r-Zr- rJE^ftfrj"^
-------
TABLE 32. COMPARATIVE CHARACTERISTICS OF
IRRIGATION, INFILTRATION-PERCOLATION, AND
OVERLAND FLOW SYSTEMS (48)
Factor
Liquid loading rate,
In./wk
Annual application,
ft/yr
Land required for
Irrigation
Low- rate High-rate
0.5 to 1.5 1.5 to 4.0
2 to 4 4 to 18
280 to 560 62 to 280
Infiltration-percolation
4 to 120
18 to 500
2 to 62
Overland flow
2 to 9
8 to 40
28 to 140
l-mgd flowrate,
acres9
m Application tech-
niques
Vege ta 11on req uI red
Crop production
Soils
Spray or surface
Yes Yes
Excellent Good/fair
Moderately permeable
soils with good produc-
tivity when Irrigated
Climatic constraints Storage often needed
Wastewater lost to;
Evaporation and
percolation
Usually surface
No
Poor/none
Rapidly permeable soils,
such as sands, loamy
sands, and sandy loams
Reduce loadings In
freezing weather
Percolation
Usually spray
Yes
Fa i r/poor
Slowly permeable soils,
such as clay loams and
clays
Storage often needed
Surface runoff and
evaporation with some
percolation
(continued)
-------
TABLE 32. (continued)
factor
Wastewater lost to:
Needed depth to
groundwater
Probability of In-
fluencing ground-
water qua!Ity
J_r_r_l_g_a_t_tp_n_
Low-ra te High-rate
Evaporation and
percolation
About 5 ft
Moderate
In ft 11T at1 on-perco J at_1 on
Percolation
About 15 ft
Certain
Overland flow
Surface runoff and
evaporation with some
percolation
Undetermined
Slight
Dependent on crop uptake
Metric conversion: In. x 2.5^ *" cm
ft x 0.305 ° m
acre x 0,405 = ha
-------
TABLE' 33. COMPARISON OF IRRIGATION, OVERLAND FLOW,
AND INFILTRATION-PERCOLATION SYSTEMS
Type of approach
Objective
Use as a treatment process with
a recovery of renovated water
Expected Treatment Performance:
1 . For BOD,, and suspended
solids removal
2. For nitrogen removal
3. For phosphorus removal
Use to grow crops for sale
Use as direct recycle to the
land
Use to recharge groundwater
Use in cold climates
1 rrlgatlon
0-701
recovery
98+%
85+*b
80-99*
Excel lent
Complete
0-701
Fafrc
Ove r 1 and f 1 ow
50 to 80*
recovery
92+1
70-901
40-80*
Fair
Partial
Q-tOt
— d
Infiltration-
percolation
Up to 97*
recovery
85-99%
0-503;
60-951
Poor
Complete
Up to 971
Excel lent
Percentage of applied water recovered depends upon recovery technique and the climate,
Dependent upon crop uptake.
Conflicting data--woods Irrigation acceptable, cropland Irrigation marginal.
Insufficient data.
-------
TABLE 31*. SITE SELECTION FACTORS
AND CRITERIA FOR EFFLUENT IRRIGATION
Factor
Soil type
Soil draInability
Soil depth
Depth to groundwater
Groundwater control
Groundwater movement
Slopes
Underground formations
Isolation
Distance from source
of wastewater
CrUerlon
Loamy soils preferable but most
soils from sands to clays are
acceptable.
Well drained soil is preferable;
consult experienced agricultural
advisors.
Uniformly 5 to 6 ft or more
throughout sites Is preferred.
Minimum of 5 ft Is preferred.
Drainage to obtain this minimum
may be required.
May be necessary to ensure
renovation If water table Is less
than 10 ft from surface.
Velocity and direction must be
determined.
Up to 15 percent are acceptable
with or without terracing.
Should be mapped and analyzed
with respect to interference
with groundwater or percolating
water movement.
Moderate isolation from public
preferable, degree dependent on
wastewater characteristics,
method of application, and crop.
A matter of economics.
m « 0.305 x ft
98
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of grooming relatively flat land into alternating ridges and furrows and
applying water by gravity to these furrows. Flood irrigation is the
Inundation of land with several inches of wastewater.
The type of irrigation system to be used to maintain specified ground and
surface water criteria depends on soil drainabi1!ty» crop, topography, cli-
mate and economics. PreapplIcation treatment is provided for most irriga-
tion systems, and a wide range of treatment requirements are encountered.
The bacteriological quality of wastewater Is usually limiting where food
crops or landscape areas are to be irrigated, or where aerosol generation by
sprinkling is of concern. In other cases, reductions in BOO and suspended
solids may be necessary to prevent clogging of the distribution system, or
to eliminate odor problems.
The important loading rates are hydraulic loading in terms of cm(inches) per
week, and nitrogen loading in terms of kilograms per hectare per year (Ibs/
acre/yr), Organic loading rates are not considered important if an Inter-
mittent application schedule is followed. Hydraulic loadings should not
exceed the infiltration capacity of the soil and may range from 1.3 to 10.7
cm per week (0.5-4.2 in./wk) depending on soil, crop, climate and wastewater
characteristics. Typical hydraulic loadings are from 3.8 to 10.2 cm/wk
(1.5-^«0 in./wk). Although irrigation rates have ranged up to 20.3 cm/wk
(8 in./wk), a generalized division between irrigation and infiltration-
percolation systems is 10.2 cm/wk (k in./wk).
Nitrogen-load ing rates have been considered because of nitrate occurrences
in groundwaters and aquifers. To minimize such occurrences, application
rates should be such that the total amount of plant available nitrogen added
is no greater than twice the nitrogen requirement of the crop grown (38).
In most cases, the permissible nitrogen loading rate will be the controlling
factor.
Crop selection can be based on several factors: high water and nutrient
uptake, salt or boron tolerance, market value, or management requirements.
Popular crop choices are grasses with high year-round uptakes of water and
nitrogen and low maintenance requirements. A drying period ranging from
several hours each day to several weeks Is required to maintain aerobic
soil conditions. The length of time depends upon the crop, the wastewater
characteristics, the length of the application period, and the texture and
drainage characteristics of the soil. A ratio of drying time to wetting
or application time of about 3 or 4 to 1 should be considered as a minimum.
Treatment of the wastewater often occurs after passage through the first
0.6 to K2 m (2-k ft) of soil. Treatment efficiencies or removals are
found to be on the order of 85 to 99 percent for BOD, suspended solids and
bacteria (Table 35). Loamy soils with considerable organic matter have been
found to almost completely remove heavy metals, phosphorus and viruses by
adsorption and fixation. Nitrogen is taken up by plant growth, and If the
crop is harvested, removals can be in the order of 90 percent.
InfI Itrat ion-Percolation - In this method, wastewater Is applied to the soil
by flooding or spraying onto basins and Is treated as It percolates through
99
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TABLE 35- REPORTED REMOVAL EFFICIENCIES OF LAND
DISPOSAL AFTER BIOLOGICAL TREATMENT (47)
Removal efficiency, %
Const! tutent
BOD
COD
Suspended sol ids
Nitrogen (total as N)
Phosphorus (total as P)
Metals
Microorganisms
TDS
a. Depends on crop uptake
1 rr I gat ion
98+
80+
98+
85+a
90-99
95+
98+
+3Q-Qf
Inf i 1 tratlon-
percolation
85-99
50+
98+
o-sob
60-95
50-95d
98+
+I0-0f
Overland
flow
92+
80+
92+
70-90a'b
40-80°
50+
98+e
+30-Qf
b. Depends on denitrlf ication
c. May be 1 imlting
d. Ion exchange capacities
e. ChJorlnation of runoff
f. May increase
may be limited
may be needed
100
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the soil matrix. Infiltration-percolation has been used with moderate load-
Ing rates [10 to 30 cra/wk (4-12 in./wk)] as an alternative to discharging
effluent to surface waters. High-rate systems [1.53 to 2. Ml m/wk (5-8 ft/
wk) ] have been designed to recharge groundwater,
Sofl drainabillty on the order of 10 to 30 cm/day (4-12 in. /day) or more is
necessary for successful use of the Infiltration-percolation approach. Ac-
ceptable soil types Include sand, sandy loams, loamy .sand, and gravel. Very
coarse sand and gravel are less desirable because they allow wastewater to
pass too rapidly through the first few feet where the major biological and
chemical action takes place.
Important criteria for site selection include high percolation rates; depth,
movement, and quality of groundwater; topography; and underlying geologic
formations. To control the wastewater after it Infiltrates the surface and
percolates through the soil matrix, the hydrogeologlc characteristics must
be known. Recharge should not be attempted without specific knowledge of
the movement of the water In the soil system.
Preappl ication treatment Is generally provided to reduce the suspended solids
content and thereby allow the continuation of high application rates. Dis-
infection Is often provided prior to spreading or ponding to control bac-
teriological quality.
Depending on wastewater characteristics and water quality objectives, load-
Ings of nitrogen, phosphorus, organic, or trace elements may be critical.
Although hydraulic or nitrogen loading is most often limiting, loadings of
salts and heavy metals may be critical in some cases. Loading schedules
that Include alternating loading and resting periods are required to main-
tain the infiltration capability of the soil surface and to promote optimum
BOD and nitrogen removals by aerobic-anaerobic conditions.
In most cases, the filtering and straining action of the soil is extremely
effective, so suspended solids, bacteria, and BOD are almost completely re-
moved (Table 35) « Nitrogen removals are generally poor unless specific
operating procedures are established to maximize deni trl f Ication. Phospho-
rus removals range from 70 to 90 percent, depending on the percentage of
clay or organic matter In the soil matrix which will adsorb phosphate ions.
The useful life of an Infiltration-percolation system will be less than that
of Irrigation or overland flow. This is a result of unacceptably high load-
ings of Inorganic constituents, such as phosphorus and heavy metals which
are fixed In the soil matrix and not positively removed. Once the fixation
capacity for phosphorus and heavy metals have been exhausted, removal effi-
ciencies will deteriorate.
Management practices Important to infiltration-percolation systems include
maintenance "of hydraulic loading cycles, basin surface management, and
system monitoring. Intermittent application of wastewater is required to
maintain high infiltration rates, and the optimum cycle between Inundation
periods and resting periods must be determined for each individual case.
101
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Basin surfaces may be bare or covered with gravel or vegetation. Each type
of surface requires some maintenance and Inspection for satisfactory opera-
tion. Monitoring of groundwater levels and quality is essential to system
management.
Overland Flow - In this method, wastewater Is applied on the upper reaches
of sloped terraces of relatively Impermeable soils and allowed to flow
across the vegetated surface to runoff collection ditches. Renovation is
accomplished by physical, chemical and biological means as the wastewater
flows In a sheet through the vegetation. A high percentage of the applied
water Is collected as runoff at the bottom of the slope, with the remainder
being lost to evapotranspiration and percolation.
Important factors in overland flow are site selection, application rates and
design loadings, management practices, and expected removal efficiencies.
If the collected runoff Is to be discharged Into a navigable water, it will
have to meet the stream discharge criteria.
Criteria Important for site selection include: soil conditions, topography
and climate. Soil conditions is perhaps the most important. Soils with
minimal Infiltration capacity, such as clays, clay loams and soils underlain
by Impermeable lenses are best suited for this method. However, a mantel
of 15 to 20 cm (6-8 In.) of good topsofl is desirable. The land should have
a slope of between 2 and 6 percent, so that the wastewater will flow as a
sheet over the ground surface. Grass is planted to reduce soil erosion and
to provide a habitat for the mlcrobial flora which help purify the waste-
water.
Since groundwater will not likely be affected by overland flow, it Is of
minor concern In selection. However, the groundwater table should be deeper
than 0.6 m (2 ft) to Insure aerobic conditions for plant growth.
When overland flow Is used as a secondary treatment process, the minimum
preapplicatlon treatment is screening and possibly grit and grease removal
to avoid clogging of the distribution system. Disinfection prior to appli-
cation may avoid post-disinfection and allow spraying at higher pressures.
Overland flow systems are generally designed on the basis of hydraulic load-
ing rates, although an organic loading rate or detention time might be the
Hmftlng criteria. The treatment process Is essentially biological, requir-
ing a minimum contact time between soil microorganisms and applied waste-
water for adequate removals. Liquid application rates used in design have
ranged from 6 to 14 cm/wk (2.4-5.5 in./wk), with a typical loading being
10 cm/wk (4 in./wk).
Treatment of wastewater by overland flow is only slightly less efficient
than that by Irrigation (Table 35). Results from field demonstration proj-
ects have suggested BOD and suspended solids removals of 95 to 99 percent,
nitrogen removals of 70 to 90 percent, and phosphorus removals of 50 to 60
percent. Solids and organics are removed by biological oxidation of the
solids as they pass through the vegetative mat. Nutrients are removed
102
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mainly by crop uptake. Removal mechanisms for other waste constituents
Include biological uptake and transformations and adsorption and fixation in
the soil. Management practices Important in overland flow are; maintaining
the proper liquid application and resting cycles; maintaining an active
biota and a growing grass; and monitoring the performance of the system.
Hydraulic loading cycles have been found to range from 6 to 8 hours of spray-
ing followed by 6 to 18 hours of drying. Cropping practices are necessary
to stimulate growth and subsequent nutrient uptake. Monitoring of loading
cycles Is needed to achieve maximum removal efficiencies.
Public Health Considerations
The passing of the Federal Water Pollution Control Act Amendments of 1972
has focused attention on the public health aspects of land application of
wastes. Consequently, the Impact of land application on the environment,
including public health, social and legal aspects, will be regulated by
state and federal agencies.
Potential public health problems are attributed to (a) transmission of patho-
gens, (b) groundwater quality, (c) crop contamination, and {d) insect propa-
gation. Generally, state health regulations and guidelines serve to pro-
tect against many of these potential public health problems.
The concern for pathogen survival and transmission Involves aerosols, runoff
and leachates from waste application. The danger of spray aerosols lies
In their potential for transmitting pathogens which could conceivably be
inhaled or contaminate adjacent lands. Aerosol travel and pathogen survival
and transmission arc dependent on several factors, Including wind, tempera-
ture, humidity, and vegetative screens. In order to reduce pathogen trans-
mission from spray-irrlgated aerosols, some safeguards can be employed.
Among these are disinfection, sprinklers that spray horizontally or down-
ward with a low nozzle pressure, and adequate buffer or vegetative screening
zones.
Survival times of various organisms fn soil, water and vegetation have been
extensively reported in the literature (W). The survival of pathogenic
organisms In the soil can vary from days to months, depending on the soil
moisture, temperature, and type of organisms. In relation to survival of
collform organisms, some bacteria do survive for a longer time in soil.
The survival of viruses In soli is essentially unexplored.
Contamination of groundwater is another public health aspect that must be
considered. In most cases, a sufficient degree of renovation will be re-
quired to meet the best practicable treatment requirements for groundwater
protection. EPA regulations on National Primary Drinking Water Standards,
listed In Table 36, Impose groundwater quality guidelines upon land applica-
tion systems. Nitrates are the most common concern, but other constituents,
including stable organfcs, dissolved salts, trace elements, and pathogens
should be considered. Thus, proper management practices and extensive moni-
toring programs are necessary to comply with regulatory restrictions.
103
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TABLE 36. NATIONAL PRIMARY DRINKING WATER STANDARDS (49)
Con s111uent or characteri stic
Physical;
Turbidity, units
Chemical, rag/1;
Arsenic
Barium
Cadmium
Carbon chloroform extract
Chromium, hexavalent
Cyanide
Fluoride
Lead
Mercury
Nitrates as N
Selenium
Silver
Bacteriological:
Total collform, per 100 ml
Pesticides, rag/1:
Chlordane
Endrln
Heptachlor
Heptachlor Epoxlde
Llndane
Methoxychlor
Toxaphene
2,4-0
2,4,5-TP
Value
0.05
1.0
0.01
0.7
0.05
0,2 .
0.05
0.002
10
0.01
0.05
0.003
0,0002
0,0001
0.0001
0.004
O.I
0.005
0. J
0.01
Reason for standard
Aesthetic
Toxic
Toxic
Toxic
Toxic
Toxic
Toxic
Toxic
Toxic
Toxic
Toxic
Toxic
Cosmetic
Dl sease
Toxic
Toxic
Toxic
Toxic
Toxic
Toxic
Toxic
Toxic
Toxic
5 mg/1 may be substituted If It can be
does not Interfere with disinfection.
demonstrated that It
Dependent upon temperature, higher limits for lower temperatures
104
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Another public health consideration for the land disposal site Is maintain-
ing crop quality with regards to safety for consumption. Many states have
regulations dealing with the types of crops that may be irrigated with
wastewater, degrees of preappllcation treatment required for various crops,
and purposes for which the crops may be used.
Propagation of mosquitoes and flies, poses a health hazard as well as a
nuisance condition. Mosquitoes are known vectors of several diseases.
Mosquitoes may Increase in population because of the wetter environment and
the availability of standing puddles for breeding (50). For these reasons
a mosquito control program may be required as part of the land disposal site
operation.
Governmen t Reg u1 at I ons
On a nationwide basis, the Federal Water Pollution Control Act Amendments of
1972, PL92-SOO, has been responsible for the renewed Interest In land appli-
cation of wastes. PL92-500 places emphasis on waste management alternatives
which are cost-effective; utilize the best practicable treatment technology;
and consider reuse and recycling of water and nutrient resources. Land
application can comply with these recommendations. A preliminary bulletin
(38) released by the EPA, addressed several factors which are important to
the environmental assessment of a particular land application option, In-
cluding considerations and guidelines for design.
Other laws which are pertinent to the practice of land application are the
National Environmental Policy Act of 1969 (NEPA) and The Safe Drinking Water
Act. NEPA requires the preparation of an environmental Impact statement for
all projects Involving Federal funds. The Safe Drinking Water Act sets
forth National Primary Drinking Water Standards which apply primarily to
groundwater sources used for drinking water. Therefore, land application
systems discharging to groundwater will be forced to meet these standards.
In general, the national requirement for land application of sludges to
lands on which crops will or may be grown must be examined closely in terms
of protecting public health and future land productivity. Sludges must be
stabilized to reduce public health hazards and to prevent nuisance odor con-
ditions. For some wastes, It may be necessary to achieve Increased pathogen
reduction beyond that attained by stabilization. Additionally, groundwater
should be protected from pollution. Consideration should be given to the
duration of the project, the quality of the groundwater, and If the ground-
water Is typically used for drinking water supplies with little or no
additional treatment. Specific groundwater criteria for land application
application systems are contained in the EPA publication, "Alternative
Waste Management Techniques for Best Practicable Waste Treatment" (51).
State regulatory agencies have recognized the Increasing Interest in the
land application alternative and thus, are developing regulations and guide-
lines concerning land application for use within their own boundaries.
Twenty-six states have Issued regulations or guidelines for this practice
whereas five states are currently preparing guidelines. Of the remaining
105
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states, design plans are approved on a case by case basis. At present,
these regulations and guidelines vary according to local geography, cli-
matology and economy of the states (52). However, similar restrictions can
be observed for state land application guide!!nes because many of the states
have used similar reference materials: "Great Lakes-Upper Mississippi River
Board of State Sanitary Engineers - Recommended Standards for Sewage Wastes -
Addendum $2" (53) and EPA's "Evaluation of Land Application Systems" (47).
Site Se1ect1on a nd Eva1ua t i on
The wide range of potential site characteristics greatly complicates any
attempt to develop standardized evaluation criteria. Even so, initial
planning concerns have some degree of commonality which include considera-
tions for land use, climate, topography, groundwater, and soils and geology.
The selection of a site location should Include both the distance and eleva-
tion difference from the wastewater collection area. These factors will
affect the feasibility and economics of the transmission of the waste to
the site. Also, of significant importance fn site selection fs the com-
patibility of the Intended use with regional land-use plans. Knowledge
of current land-use in an area provides an Indication of the quantity of
land potentially available or suitable for waste application. A review of
land use maps can avoid consideration of areas with conflicting features.
Prevailing climatic conditions will affect a large number of design decisions
including; the method of land application, storage requirements, total land
requirements, and loading rates. Relationships between climate and land
application systems are shown in a generalized Climatic map (Figure 10).
The depicted zones are only useful In preliminary planning stages, since
detailed analysis of local climatic data is essential for design purposes.
Zone A has a seasonal pattern of precipitation of about 38 to 64 cm (15-25
In.) during the months from November to April. Temperatures are mild In
winter and hot in sunroer. Plant growth can continue through the year
assuming Irrigation is provided. Storage of effluent Is not required for
climatic reasons. Zone B covers the areas that are very hot and arid year
round. Winter storage is not a major concern. Zone C Includes the areas
where precipitation fs distributed throughout the year, w?th hot, humid
summers and fairly mild winters. Year round operation of land application
systems is possible in these areas. Zone D has moderately cold winters
and hot summers. Precipitation is distributed throughout the year. Winter
conditions are such that storage will often be required for periods up to
3 months. Zone E has precipitation occurring In all months of the year,
averaging from 50 to 100 cm (20-40 In.) annually. Winter operations are
severely limited due to low temperatures, Ice and snow, thus requiring
storage for periods up to six months.
The National Weather Service, local airports, and universities are potential
sources of clImatologlcal data. Climatic factors of concern Include pre-
cipitation, storm Intensity, duration and frequencies, temperature, evapo-
transpiration, and wind velocity and direction. The data base should con-
sider sufficient durations of time so that long-term averages and fre-
quencies of extreme conditions can be established,
106
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o
--J
CLIMATIC ZONES
* MEDITERRANEAN CUHATE -
ORf SUHHEft - MILD, WEf 1INTER
B ARID CLIMATE - HOT, DRV
C HUMID SUBTROPICAL - MILD WINTER - HOT, *ET SUMMER
(•ASHINQTON, ORE60M AREA MILD. HOIST SUMMER)
0 HUMID CONTINENTAL - SHORT VINTER. HOT SUMMER
E HUMID CONTINENTAL - LOH6 tINTIR, RARM SUHHER
Source: EPA publication 660/2-73J)Q6b (1973}
Figure 10. GeneraIf zed climatic zones for land application
-------
Topography affects both the water handling capability of a site and the ex-
tent of contact between waste constituents and soil particles. Examination
of local and surrounding topography Is useful In determining drainage pat-
terns and flow rates of surface and subsurface water. Topographic maps,
available from the USGS, are necessary for site selection and subsequent
system design. Topographic Information of concern Includes ground slope,
proximity of surface water, erosion and flood potential, and existing vege-
tative cover.
Sofl properties determine the suitable waste application or loading rate,
thereby affecting the amount of land required and the method of application.
Thus, soil properties are often considered the most important factors In
selecting both the site and the land application method. Properties that are
important fn describing and evaluating soils Include soil texture, structure
and profile, permeability, aval Iable water capacity, and chemical charac-
teristics such as pH, salinity, nutrient levels and adsorption and fixation
capabilities. Information on soil properties can be obtained from the
National Cooperative Soil Survey, the Agricultural Extension Service and some
state universities.
Groundwater characteristics are important considerations In selecting a
particular site. The effect of groundwater levels on renovation capabilities
and the effects of the applied waste on groundwater movement and quality
should be extensively evaluated. Additionally, the depth to groundwater
should be determined, along with an evaluation of the groundwater rate of
flow and direction and the permeability of the aquifer. Information on
these sources can be obtained from the U.S. Geological Survey or State Di-
visions of Water Resources.
Desj gn_. Cons i derat Ions
For most land application systems, vast numbers of design possibilities are
available to suit specific site characteristics, treatment requirements and
overall project objectives. The scope of factors that are commonly con-
sidered In the design process Include: a) preapplI cation treatment require-
ments; b) storage requirements; c) climatic factors; d) pollutlonal loading
constraints; e) land area requirements; f} crop selection and management;
g} system components; h) site monitoring program; and 1} cost-effectiveness.
It should be recognized that since land application system designs are site
specific, design criteria must be based on the actual conditions of the site
and therefore cannot be generalized.
PreappJ I cat ion Treatment RequIrements - Treatment of wastes prior to land
application may be necessary for a variety of reasons, Including: 1) public
health regulations, 2) loading constraints with respect to critical waste-
water characteristics, and 3) the desired effectiveness and dependability of
the system components. In areas where long-term winter storage is required,
some degree of treatment may be necessary to prevent nuisance conditions dur-
ing storage.
Public health considerations, pathogen transmission and groundwater quality
are usually the most important factors in determining the required degree of
108
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preappllcatlon treatment. Wastewater constituents that may tend to limit the
application rate or hinder the quality of renovated water may also necessi-
tate pretreatment. High concentrations of grit, suspended solids and grease
and oil can deteriorate the effectiveness and dependability of the pumping
and distribution systems, thus requiring some degree of pretreatment prior
to applIcation,
Storage RequJrements - In most land application systems, considerations !n
determining storage capacity include the local climate, the design period of
operation, flow equalization, and system back-up If breakdown occurs. Re-
quired storage capacities may range from one day's storage to several months'.
Storage requirements will most often be based on the period of operation and
the local climate. Three different conditions that may necessitate storage
Include: 1) winter weather requiring cessation of operation; 2) precipita-
tion requiring the temporary reduction or cessation of application; or
3} winter weather requiring reduction of winter application rates. When
cessation of operation is expected, storage requirements should be based on
the maximum expected period of nonoperatlon. The number of consecutive non-
application days due to climatic constraints (I.e. precipitation, tempera-
ture and snow) may be determined through the use of a computer program de-
veloped by the National Weather Service (5^). Figure 11 presents a nation-
wide estimation of storage days as calculated from this computer program.
C11ma11c Factors - Design assumptions must be evaluated with regard to cli-
matic factors. Climatic conditions most often considered are precipitation,
temperature and wind.
Precipitation, such as rainfall, snow and hail, will affect a number of de-
sign factors, such as: 1} hydraulic loading rates; 2) storage requirements,
and 3) system drainage requirements. Precipitation data that will be
necessary for design purposes Include: total annual precipitation; maximum
and minimum annual precipitation; monthly distribution of precipitation;
storm intensities; and snowfall characteristics.
Temperature, because of Its Influence on plant growth and freezing con-
ditions, will affect liquid loading rates and the period of operation.
Temperature data that may be incorporated Into system design include: month-
ly or seasonal averages and variations; length of growing season; and
periods of freezing conditions.
For spray application systems, wind conditions may require a reduction or
temporary cessation of waste application in order to prevent disease
transmission. Wind velocity and direction should be determined with respect
to frequencies and durations.
Another cllmatologfcaJ factor that should be considered Is the potential
amount of evapotransplration for the area. Figure 12 presents a nationwide
comparison of potential evapotransplration rates versus the mean annual pre-
cipitation. The effect of the evapotransplration, If the yearly evapotran-
splratlon. Is greater than the mean annual precipitation, Is that It will
reduce the liquid volume of waste to the applied on the land.
log
-------
Figure 11. Storage days required as estimated from the use of the computer
program as described
-------
+20
+38
tSO
•¥ipo t rintp I ritlai Mr* thin
••in tnoutl pricip I t«l l«n
• Nttillil itipetrant)I ratlin Itn thin
•••a innutt prtelpltiit»a
+50
+30
Figure 12, Potential evapotransp?ration vs, mean annual precipitation (Inches) (46).
-------
Pol Iutlona1 Loading Cons traInts - Loading rates for the liquid applied and
the pollutional constituents of the waste will form the basis In determining
design criteria for land requirements, application rates, and crop selection.
To determine what characteristics of the applied waste will be limiting,
balances should be conducted for water, nitrogen, phosphorus, organic matter,
and other constituents that appear high In concentration. On the basis of
these balances, a loading rate can be established for each parameter which
then can be used In calculating the required land area. The critical load-
Ing rate will be the one requiring the largest field area.
The hyd ra u11 c_ _[oa d_ Ing ra t e can be determined by conducting a water balance
on the effluent applied, precipitation, evapotransplratlon, percolation, and
runoff. In other words, the amount of effluent applied plus precipitation
should equal the evapotransplratlon plus a limited amount of percolation.
In all cases except overland flow, surface runoff from Irrigated fields
should not be permitted. The water balance can be expressed as:
Precipitation -f- ESS] - t " Evapotransplratfon + Percolation [+ Runoff]
Seasonal variations should be taken Into account when encountering these
values. This can be done by means of evaluating the water balance for each
month as well as the annua! balance.
N11rogen 1oadIngs must be balanced against acceptable nitrogen losses and
removals because nitrate Ions are mobile In the soil and can affect ground-
water quality. On an annual basts, the applied nitrogen must be accounted
for in crop uptake, denltrlfIcatlon, volatilization, leachate, or storage In
the soil. A nitrogen mass balance equation for a terrestrial system can be
developed as:
Hi6"* prei?Pt-- N R-oval + Leaching + Denltrl- + ^M-
waste tation 'n crops Loss flcatlon zatton
This balance equation can be used to calculate nitrogen loading rates for
waste applications.
For most land application systems, the phosphorus JloacUng will usually be
well below the capacity of the soil to fix and precipitate the phosphorus.
Typically, 95 percent of the phosphorus applied can be removed from the per-
colating wastewater. The removal mechanisms for phosphorus are crop uptake,
mlcroblal uptake, chemical precipitation, and fixation by the soil.
The average dally organic loading rat^e should be calculated from the hydrau-
lic loading rate and the BOD concentration of the applied waste. Thomas (55)
has estimated that organic loading rates between ll to 28 kg/ha/day (10 to 25
Ib/acre/day) are needed to maintain a static organic-matter content In the
soil. Additions of organic matter at these rates help to maintain the tilth
112
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of the soil, replenish the carbon oxidized by microorganisms, and would not
be expected to pose problems of soil clogging. Higher loadings rates of 56
to 112 kg/ha/day (50 to 100 Ib/acre/day) can be employed successfully, de-
pending upon the type of system and the resting period. Resting periods,
which are standard with most application systems, give soil bacteria time to
break down organic matter and allow the water to drain from the top few
Inches, thus restoring aerobic conditions.
Loading rates for suspended and dissolved solids are the two major types of
remaining constituents that are of Interest for land application systems.
The organic and inorganic fractions of the suspended solids are usually fil-
tered out and become incorporated Into the soil, which can reduce the Infil-
tration rate Into the soil. As a result, preappllcation treatment for sus-
pended solids reduction may be necessary.
Dissolved solids are affected differently In the soils depending on their
movement through the soil matrix. Chlorides, sulfates, nitrates, and bi-
carbonates move relatfveJy easy through most soils without being tied up in
the soil profile. These compounds can, therefore, be readily leached into
the groundwater. Other dissolved solids, such as sodium, potassium, calcium,
and magnesium, are exchangeable and react with the soil so that their con-
centrations will change with depth. Other constituents, such as heavy metals,
pesticides and other trace elements may or may not be removed by the soil
matrix, depending upon such factors as clay content, soil pH and soil
chemical balance. On the basis of the analyses of waste characteristics,
any constituent suspected of having a limiting loading rate should be calcu-
lated. Table 37 gives recommended concentration limits for specific ele-
ments based on common application rates for land application systems. If
the limiting criteria Is met, there should be little concern about toxic
effects on plants or excessive accumulation In soils.
Land Area Reo^u 1 rements - The total land area required includes provisions
for treatment; buffer zones; storage; sites for buildings, roads and ditches;
and land for emergencies or future expansion. If any on-sfte preapplIcatlon
treatment Is required, provisions must also be provided for land furnishing
these facilities-
The field area is that portion of the disposal site In which the waste Is
applied to the land. It Is determined by calculating acceptable loading
rates for each different loading parameter (liquid, nitrogen, phosphorus,
organic, or others) and then selecting the largest area. The loading
parameter that corresponds to the largest field area requirement would then
be the critical loading parameter.
Regulatory agency requirements may specify buffer zones around application
sites because of concern about the effects of aerosol-borne pathogens.
Buffer zones ranging from 15 to 61 meters (50 to 200 ft) wide have been re-
ported (45)-» although requirements for even larger buffer zones may exist
depending on a number of factors.
Land application systems will generally require land for off-season or
13
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TABLE 37. RECQMMEHDED AND ESTIMATED MAXIMU
IN IRRIGATION WATERS
CONCENTRATIONS OF SPECIFIC
mg/1
IONS
Element
Removal
Mechanism
(2)
For Waters Used
Continuously on All SoIJ
0.9 tn/yr Application
Recommended ^
For Waters Used Up to 20 Years on
Fine-Textured Soils of pH1 6.0 to 8.5
0.9 in/yr Application
Recommended Limit
2.'t m/yr Application
Estimated Limit
h ni/yr Appltcatlon
Estimated Limit
Aluminum
Arsenic
Beryl Hum
Boron
Cadmium
Chromium
Cobal t
Copper
Fluoride
Iron
Lead
L I th 1 urn
Manganese
Mercury
Molybdenum
Nickel
Selenium
Silver
Zfnc
PR,
AD,
PR
AD,
AD,
AD,
AD,
AD,
AD,
PR,
AD,
CE,
PR,
AD,
AD,
AD,
AE,
AD,
AD,
S
S
W
CE,
CE,
CE,
CE,
S
CE,
CE,
W
CE,
CE,
S
CE,
W
CE,
CE,
S
S
s
s
s
s
s
s
s
s
s
5-
0.
0.
0.
0.
0.
0.
0.
I.
5.
5.
2.
0.
__
0.
0.
0.
—
2.
0
10
10
75
010
10
050
20
0
0
Q. .
5
20
-
010
20
020
-
0
20
2
0
.0
,0
.50
2.0-10.0
0
1
5
5
15
20
10
2
JO
--
0
2
0
--
10
.050
.0
,0
.0
.0
.0
•QtL\
• 5
.0
/ ,
.050
.0
.020
-
.0
8
0
0
2
0
0
2
2
6
8
4
2
4
-
0
0
0
-
11
.0
.8
.2
.0
.02
.!»
.0
.0
.0
.0
.0
.5
.0
/£-\
.02 '
.8
.02
--
.0
0
0
0
2
0
0
0
0
0
0
0
2
0
"™
0
0
0
-
0
.8
.08
.02
.0
,002
.Qlt
.2
.2
.6
.8
.4
.5
.4
"" (5)
.002°''
.08
,02
— —
•*
(1) These levels will normally not adversely affect plants or soils. Mo data are available for mercury, silver, tin, titanium,
or tungsten*.
(2) AO • adsorption with Iron or aluminum hydroxide, pH dependent; AD •* anion exchange; CE • cation exchange; PR •" precipitate,
pH dependent—iron and manganese are also subject to changes by oxidation reduction reaction; S •* strong strength of removal-,
W » weak strength of removal
(3) EPA Mater duality Criteria, 1972.
(k) Recommended maximum concentration for Irrigating citrus Is 0.075 rog/1.
(5) For only acid fine-textured soils or acid soils with relatively high iron oxide contents.
-------
winter storage
also be necessary
, especially in the northern states. Storage capacities may
ary to equalize flow rates or to provide backup services.
Crop Selection and Management ~ Crops grown at the land appl (cation site can
have a significant effect on treatment efficiencies and loading rates, es-
pecially the removal of nutrients from the applied waste. Factors that
should be considered In crop selection Include: 1) relationship to critical
loading, 2) public health regulations, 3) ease of cultivation and harvesting,
and k) the length of the growing season. Also, If the crop is to be har-
vested, the local market for the crop must be considered. The four general
classes of crops that may be considered are perennials, annuals, landscape
vegetation, and forest vegetation.
Compatibility of the loading rates with the selected crop is important to
ensure both the survival of the crop and the efficiency of wastewater reno-
vation. Loading rates should have allowances with respect to the tolerances
and uptake capacities of the intended crops. Therefore, crop selection will
be dependent on a combination of loading parameters, including 1) water re-
quirement and tolerance, 2) nutrient requirement, tolerance, and removal
capability, and 3) sensitivity to various inorganic ions,
As of 1972, at least 17 states had public health regulations that exist with
regard toJ the types of crops that may be irrigated with wastewater; the de-
gree of preapplicatfon treatment required for certain types of crops; and
the methods of application that may be employed (56).
System Compgnen ts ~ Typically, land application systems are composed of a
number of different system components, such as: preappl feat ion treatment
facilities, transmission facilities, storage facilities, distribution system,
recovery system and monitoring system. The design of each component of a
land application system Is highly variable and is dependent on many factors
relating to site characteristics and project objectives.
The design of _p_re_app_U cat_io_n treatment f act 1 ft I es will be controlled by fac-
tors sych as the loading rate of various const! tuents, the method of appli-
cation employed, and the type of crop grown. In most cases, regulations con-
cerning required levels of preappllcatlon treatment have been set forth by
local agencies*
Design of the t ransm I ss I on fad lit i es to the site from the collection area
may become a very Important aspect to consider If land application fs to be
cost-effective. Selection of a conveyance method will usually depend on the
production rate, distance to application site, seasonabUfty of application,
and planned lifetime of the site. Three potential methods of wastewater con-
veyance Include gravity piping, open channels and force mains. For each
of these methods, standard design criteria should be used since these trans-
mission facilities will rarely differ from that designed for conventional
treatment systems. In conveying sludges, additional methods have included
tank trucking for liquid sludges and open bed trucking for dewatered sludges.
In almost all cases, some sort of storage facj IJ^ty wl ]\ be necessary. If
storage Is to be provided for wl nter flows ¥nd Storage requirements are high,
115
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winter storage, especially in the northern states. Storage capacities may
also be necessary to equalize flow rates or to provfde backup services.
Crop Select ior| grid Management - Crops grown at the land application site can
have a significant effect on treatment efficiencies and loading rates, es-
pecially the removal of nutrients from the applied waste. Factors that
should be considered In crop selection Include; I) relationship to critical
loading, 2} public health regulations, 3) ease of cultivation and harvesting,
and *l) the length of the growing season. Also, If the crop Is to be har-
vested, the local market for the crop must be considered. The four general
classes of crops that may be considered are perennials, annuals, landscape
vegetation, and forest vegetation.
Compatibility of the loading rates with the selected crop is important to
ensure both the survival of the crop and the efficiency of wastewater reno-
vation. Loading rates should have allowances with respect to the tolerances
and uptake capacities of the intended crops. Therefore, crop selection will
be dependent on a combination of loading parameters, Including 1) water re-
quirement and tolerance, 2) nutrient requirement, tolerance, and removal
capability, and 3) sensitivity to various Inorganic ions.
As of 1972, at least 17 states had public health regulations that exist with
regard to*, the types of crops that may be Irrigated with wastewater; the de-
gree of preapplfcatfon treatment required for certain types of crops; and
the methods of application that may be employed (56).
SyAt^nL^Comgpnents - Typically, land application systems are composed of a
number^of different system components, such as: preappl Ication treatment
facilities, transmission facilities, storage facilities, distribution system,
recovery system and monitoring system. The design of each component of a
land application system Is highly variable and Is dependent on many factors
relating to site characteristics and project objectives.
The design of p reappj I ca 1 1 on t rea tmen t f ac 1 II 1 1 es will be controlled by fac-
tors such as the load I ng rate "of var lous cdns~t I tuents , the method of appli-
cation employed, and the type of crop grown. In most cases, regulations con-
cerning required levels of preappl Ication treatment have been set forth by
local agencies.
Design of the t ransm 1 sst p_n_ f ac\J it leg to the site from the collection area
may become a very Important aspect to consider If land application Is to be
cost-effective. Selection of a conveyance method will usually depend on the
production rate, distance to application site, seasonabll Ity of application,
and planned lifetime of the site. Three potential methods of wastewater con-
veyance Include gravity piping, open channels and force mains. For each
of these methods, standard design criteria should be used since these trans-
ralsslon facilities will rarely differ from that designed for conventional
treatment systems. In conveying sludges, additional methods have Included
tank trucking for liquid sludges and open bed trucking for dewatered sludges,
In almost all cases, some sort of storage JacM Ity will be necessary. If
storage Is to be provided for winter flows and storage requirements are high,
115
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TABLE 38. IMPORTANT MONITORING SEGMENTS OF
LAND APPLICATION PROCESS (59)
I. Influent Quality (Treatment Quality)
a. Nutrient levels (N, P, K)
b. Sodium absorption ratio (SAR)
c. Heavy metal concentration, having potential toxiclty to
plant and animal life (2n» Cu, Ni, Cd, Pb, Hg)
d. Other physical and chemical determinations (pH, BOD, COD, TS, TOC)
e. Pathogens, viruses, salmonella and protozoa
II. Soil Condition and Quality (Preservation of Soil's Physical 5
Chemical Characteristics)
a. Nutrient profile - N, P, K distribution
fa. Cation exchange capacity
c. Hazardous heavy metal distribution
d. Organic content
e. Soil kind - physical
- Infiltration rate
- size distribution
- soil horizons
- redox profile, pH
III. Drained or Leachate Water Quality and Groundwater (Prevention of
Contamination of Surface and Groundwater)
1. Groundwater
a. Nutrients (NO,/NO , P)
b. Heavy metals
c. Pesticides, herbicides, etc.
d. Microbiological
- fecal col I form
- fecal strep
- salmonella
- viruses
e. Other physical, chemical determinations
- pH, specific conductivity, detergents
2. Receiving Surface Waters
a. Nutrients
b. Heavy metals
c. Microbiological
- fecal coll form
d. Other physical and chemical determinations
3. Crop Quality and Yield (Safe for Animal/Human Consumption)
a* Heavy metals content
b. Nutrient content
c. Pathogens
117
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gradient groundwater quality, as well as Influent to the system, should be
monitored for the parameters commonly measured to ensure environmental quali-
ty and any additional parameters that are of concern to the land application
system, such as heavy metals. In the case of overland flow application, the
effluent discharging from the site will have to be monitored for the parame-
ters required by state and federal discharge requirements.
In addition to quality, changes in groundwater levels should also be moni-
tored. The effect of Increased levels should be assessed with respect to
changes In the hydrogeologic conditions of the area. Changes In the ground-
water movement and the appearance of seeps and perched water tables should
be noted and system modifications, such as underdraining or reducing appli-
cation rates in the area should be undertaken (46).
When vegetation is grown as a part of the treatment system, monitoring may
be required for the purpose of optimizing growth and yield and preventing
buildup of toxic materials. Measurements should Include: heavy metal con-
tent; nutrient content; and pathogens.
Cost-EffectIveness - In selecting the best wastewater treatment alternative,
a cost-effectiveness analysis should be properly performed. To conduct such
an analysis, detailed cost estimates must be prepared and evaluated for
each alternative on an equivalent basis in terms of total present worth or
annual cost. Generally, cost estimates for an alternative would Include
costs for operation, maintenance and supervision and the amortized capital
cost. Capital and operating cost considerations of Importance for land
application systems have been documented in current reports entitled "Costs
of Wastewater Treatment by Land Application" (kB) and "Water Pollution
Abatement Technology: Capabilities and Cost" (43).
LAND APPLICATION OF RAW CSO
An alternative to the treatment of CSO and the resultant problems of sludge
handling and disposal is direct application of the raw CSO to the land.
This method would eliminate the need for extensive CSO treatment facilities
and the further problem of sludge handling and disposal facilities.
The waste management alternative of applying raw CSO to the land will be
discussed with respect to many of the design factors presented In the pre-
vious section.
Preappj I catIon Tr_ea tment
If the land Is used for treatment and disposal of raw CSO, It Is apparent
that some form of preappllcatlon treatment wfll be required. First, since
high densities of coilform have been reported for CSO (g), disinfection will
most likely be required as a preapplIcation treatment process. Second,
since CSO's are Intermittent events, storage will have to be provided to
equalize the flow to the land site and thus, some type of stabilization to
prevent nuisance conditions from developing will be required. If spray
118
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Irrigation is employed, grit, oil and grease removal combined with a re-
ductfon in suspended solids may be necessary to prevent potential clogging
of the distribution system. Since the raw flow w!!J be held in a storage
facility, grit and organic solids could be removed there and some provision
would have to be made for disinfection prior to land application.
Cg11 ectjon and TranSJK?rta11 on of Raw CS0
A very Important aspect to consider, if land disposal of raw CSO is to be
used, is how the CSO will be collected and transported to the land disposal
site. The cost of such a collection and transportation system could be more
than the land disposal facility itself. In most cities, a collection system
will be necessary to intercept all CSO discharge points and deliver the
flows to a transport system. The collection system must function year round
and must be sized to carry peak flows. The transport system would have to
convey the CSO out of the urban and suburban areas to a selected land
site. The transport system normally would be a pipeline but under some cir-
cumstances, could be an open channel.
Several problems will become apparent when implementing conceptural plans
for transmission facilities. First, combined sewers are usually located in
the older, central sections of metropolitan areas. Therefore, the collection
system may require sewer construction in densely populated commercial areas,
which couJd prove to be very costly. Second, in order to convey the CSO out
of the urban area to a selected treatment site, the transportation distance
could easily be 32 to 64 km (20 to 40 miles). These distances may prove to
be impractical because of the high costs for transportation systems. Third,
and probably most important, the transmission facilities must be capable of
handling peak storm flows. To Illustrate this better, a typical city In the
Great Lakes region with a combined sewer area of 972 ha (2400 acres), would
require transport pipelines in the order of 5-3 m (17-5 ft) in diameter to
provide for peak flow design rates based on one hour storm intensities at
one year return frequencies. If longer return periods or shorter time in-
tervals are used In order to achieve complete CSO abatement, the sizes of
the collection and transport systems would Increase significantly. To avoid
the design capacities needed for peak flow rates, It would be necessary to
provide for equalization basins and temporary storage basins to maintain a
constant transportation program. The cost for these facilities alone may be
prohibitive.
Storage
Design considerations for storage facilities are usually based upon incoming
flow rates and the number of consecutive unfavorable application days over
the year. The nonapplicatlon period is determined by the number of days
during which the following exist: temperature below freezing 0 C (32 F),
total dally rainfall greater than 1.3 cm (0.5 inches), and greater than 2.5
cm (I Inch) of snow cover (5^). For the Great Lakes and Northeastern regions
of the U.S., the average number of nonapplicatlon days for which storage
would normally be required is around 100 days (Figure 10). However, in de-
termining the storage requirement, It Is necessary to conduct a monthly
19
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water balance considering Intermittent CSO flow rates, precipitation, evapo-
ration and soil percolation rates.
Therefore, it appears that storage facilities will be required to handle
CSO flows for periods up to four months. In addition to providing storage
facilities, because of the large amounts of solids that can be expected fn
raw CSO, precautions will have to be taken to prevent nuisance problems
from occurring. These precautions could be stabilization and/or disinfection
of the CSO during storage and a mosquito control program. The storage
area could also support extensive algal growths which could become a signifi-
cant problem.
C11mato1ogIca1 Eff ec t s
The general climate of the area can have a significant effect on the opera-
tion of a CSO land disposal site. As seen from the previous discussion,
the winter season will greatly reduce the time that a land disposal operation
can be used. On the average, the operation of a site In the Great Lakes
region would have to be shut down for 3 1/2 months.
The yearly precipitation over the area will also affect the operation since
the Irrigation or overland flow methods of application can not be used during
periods of rainfall because the highly polluted CSO could be carried away
from the site with the surface runoff. Wet ground that results from the
rainfall events will also reduce the capacity of the soil to hydraulically
assimilate the added loadings of the raw CSO. These factors will increase
the amount of land required for the disposal site. The days of operation
were approximated as 205 days for an average year In the Great Lakes region
of the country. Thfs value was arrived at by subtracting TOO days for winter
conditions and 60 days for non-operative conditions due to periods of rain-
fall-runoff.
Another clImatologlcal factor that should be considered is the potential
amount of evapotransplration for the area. The effect of the evapotranspir-
ation rates can be shown by using the Great Lakes region of the country as
an example. From Figure 11, It Is estimated that the potential yearly evapo-
transpI ration Is less than the mean annual precipitation rate. The Impact
of evapotransplration Is that It must be considered as part of the hydraulic
loading. Therefore, It will not significantly reduce the added precipitation
that will necessitate disposal.
It can be seen that for the Great Lakes and the Northeastern regions of the
USA, the precipitation and evapotransplrat Ion rates can be significant fac-
tors affectlng-the liquid volume of the waste to be handled.
Pol 1 utant Load I ng Cons trjjjits
Since CSO represents large quantities of urban runoff, It can contain large
concentrations of heavy metals which may be In excess of those that can be
removed by the soil. The leaching of these metals Into the receiving water
could pose a serious health problem. This fact, and the fact that high
120
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concentrations of some pollutants in CSO may cause operational problems for
the land disposal site, may lead to constraints on the loading rates allowed
and thus, on the overall feasibility of land disposal of raw CSO. As the
first consideration in design, the factors which may limit land disposal of
wastes and the risks involved with this practice will be estimated. This
will be accomplished by identifying the parameter that limits loading rates.
For preliminary calculation purposes, the following CSO values, based on
average characteristics obtained from the literature, have been assigned for
use in this section. The raw CSO volume is an arbitrary value to serve as a
basis for design calculations.
Raw CSO volume: 1382 x 10 Vyr (3&5 x JO6 gal./yr)
Yearly CSO solids volume". 552 metric tons (609 tons-dry weight basis)
Pollutions! Characteristics:
SS 400 mg/1
BOD 120 rng/1
N 16 mg/1
P 5 mg/1
Zn 1000 mg/kg SS
Cu kOQ mg/kg SS
Ni 200 mg/kg SS
ToxicElements - The most common concern wfth land application of pollutants
fs the question of the effect of toxic elements on the soil-crop system. !n
order to protect the land from toxic elements accumulation from waste appli-
cations, Wisconsin (60) has adopted guidelines, based on an Interim guide
recommended by the EPA, which takes into account the combined effect of the
metals by using a measurement entitled the zinc equivalent (ZE). The ZE
can be determiend as follows:
It = (1 x [Zn]) + (2 x [Cu]) + (k x [N5])
where all concentration values are expressed in mg/kg dry weight. The total
dry solids loading is calculated from the formula (60):
Total Solids (BOUSES) . 32,500 x CEC
acre ZE
To determine area requirements, the following assumptions were made:
1) the cation exchange capacity (CEC) of the soil is 15 meq/100 g; and 2)
the life span for the soil is 20 years. As a result, the area requirements
for land application of CSO would be about 1.9 x 10~2 ha/10b £ CSO/yr
(17.8 x 10~2 ac/10b gal. CSO/yr).
Organ i c So H ds Appji cat ?on Rates - The organic assimilation capacity of
soils Is highly variable depending on detailed soil characteristics. In
general, organ Ics are continuously added to soils as plant residues, dead
animals, etc. and are continuously oxidized by soil organisms. As organic
additions increase, soil respiration also increases until a maximum rate of
121
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oxidation fs reached. Although few guides are available, regulations have
been proposed to limit BOD,, and SS application rates to around 672.6 kg/ha-
day (600 I fas/acre-day) . If this limitation-Is used, the safe application
areas for raw CSO wastes would be 0.4 x 10 ha/10 £ CSO/yr (3.7 x 10*^
ac/106 gal. CSO/yr) for BOD and 1.6 x 10~2 ha/106 t CSO/yr (15-0 x 10"*2 ac/
10^ gal. CSO/yr) for SS.
Nitrogen and Phosphorus Control - The nitrogen and phosphorus constituents
In CSO wastewater are likely to appear as major limiting factors for land
application designs. Current knowledge Indicates that phosphorus removal
to levels of 0.05 mg/1 can be achieved over site lifetimes of 20 years or
more at annual loading rates within the 168 to 336 kg P/ha-yr (150-300
Ib P/acre - yr) range (6). Using this assumption, the total land area re-
quired for safe application of phosphorus would be 1.9 x 10~2 ha/10" S, CSO/yr
(17.8 x 10" 2 ac/10° gal. CSO/yr).
Conversion of nitrogen forms to nitrates may result In contamination of the
groundwater. Thus, nitrogen must be considered as a nutrient which must
be applied at a controlled rate. To calculate nitrogen loading rates for
wastewater applications, the following equation can be used (6):
N*= - a(P~ET) - cP
"
y-a
whe re :
N = total nitrogen In applied waste ( Ib/ac-yr)
C = removal of N In crop (Ib/ac-yr)
P = precipitation (ac-in./ac-yr)
c = concentration of N in precipitation (mg/1)
a - allowable N In leachate (mg/1)
ET = potential evapotranspi ration (ac-in./ac-yr)
y = total nitrogen concentration In waste (mg/1)
* conversion factor = N x 1.122 = kg N/ha-yr
The following assumptions are made to determine nitrogen loading rates for an
area In the Great Lakes region: I) average annual precipitation is 89 ha-cm/
ha-yr (35 ac»in./ac-yr) ; 2) evapotranspi ration is 5' ha-cm/ha-yr (20 ac-In./
ac-yr); 3) allowable N concentration In leachate Is 10 mg/1; and 4) crop ni-
trogen removal rate Is 280 kg/ha-yr (250 Ib/ac-yr).
Using these assumptions, the wastewater application rate would be approxi-
mately 83^ kg N/ha-yr (7^3 Ib M/ac-yr), thus resulting In p land area re-
quirement of 1.9 x 10~2 ha/106 4 CSO/yr (17.8 x 1Q~2 ac/10 gal. CSO/yr).
Hyd rau 1 1 c Load i ng^ - The maximum hydraulic loading rate for the CSO must also
be taken into consideration. This rate will be dependent on the application
method employed and the type of soil characteristics given for the area.
First, ft will be assumed that a loam type soil Is characteristic of a possi-
ble land disposal site In the northern states. This soil type suggests the
122
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use of the Irrigation method of land application. Secondly, It Is assumed
that an allowable liquid loading rate for the selected application method
and the predominant soil type would be 12,7 cm per wk (5 in./wk). Finally,
if the operational period is assumed as 30 weeks a year, the annual applica-
tion rate becomes 3pl cm (150 in.}. This results/.In a land area requirement
of 2.6 x I0~2 ha/10 £ CSO/yr (24.7 x 10~2 ac/ 10b gal. CSO/yr).
Land Area RegjJi_reme_nts_
After a suitable land site has been selected, the next consideration for a
city using land disposal of raw CSO will be the amount of land required
for actual application. For field area requirements, a summary of the
application rates estimated to be acceptable and the resulting land require-
ments are shown in Table 39- ,11 is perhaps surprising to note that the
limiting factor is the hydraulic loading of the CSO. Hydraulics often Is
the limiting factor for application of wastewaters, usually in cases where
the application rate Is controlled by surface runoff and groundwater pro-
tection. Hence, If the liquid loading is assumed to determine the required
land area, it can.be seen that the application rates of the other pollutants
are one-third to two-thirds that which is considered to be an environmentally
safe rate of application. Therefore, recommendation of the use of a 2-9 x
10~2 ha/!0 £ CSO/yr (27.1 x 10" 2 ac/106 gal. CSO/yr) land area requirement
should Incorporate a safety factor large enough to account for unpredictable
events. The above land area requirement can also be expressed in terms of
a design application rate: 34.4 x 10 £/ha/yr (3.6 x 10° gal./ac/yr).
This "first cut" land estimate can increase significantly as more criteria
are considered because additional land may be required for storage and
possible pretreatment facilities, necessary non-application buffer zones,
runoff control structures, etc.
For example, the Inclusion of a 122m (400 ft) buffer zone around the site
increases the required area significantly; if 61 m (200 ft) is acceptable
with a line of trees and shrubs, the area requirement still is significant.
Other buffer areas may also be required within the site around roads,
streams, buildings, and storage areas. This, of course, would further In-
crease the area required for the total operation.
Employing an application rate of 34.4 x 10 H/ha/yr (3.6 x 10 gal./ac/yr)
and If the nationwide annual volume of CSO totals 5.60 x 10^ cu m (1.48 x
10' gal.), field area requirements for raw CSO disposal would approximate
166,500 ha (411,110 acres) of land. However, this Is land required for
actual disposal only. Assuming that, on the average, the land required fdr
actual disposal Is 70 percent of a disposal site, the nationwide disposal
of raw CSO would require a total land area of 237,857 ha (587,300 acres).
As discussed in the previous section, the crops grown at the land applica-
tion site can have a significant effect on treatment efficiencies and load-
ing rates, especially for the removal of nutrients from the CSO. Since.
123
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•ft-
TABLE 39. SUMMARY OF RECOMMENDED APPLICATION RATES
FOR VARIOUS RAW CSO POLLUTANTS
AND THE RELATED LAND AREA REQUIREMENT
Pollutant
Toxic metals
Nitrogen
Phosphorus
BOD
SS
Acceptable
application rate
kg/ha/yr
21.0
834
252
672
672
(Ibs/ac/yr)
(9.4)a
(744)
(225)
(600)b
(600) b
Land area
requirement
10~2 ha/ 10 A/yr
1.9
1,9
1.9
0.4
1.6
(10~2 ac/10 gal./yr)
(15.8)
(15.8)
(15.8)
(4.1)
(13.3)
expressed as metric tons/ha/yr (tons/ac/yr) - dry weight basis
expressed as kg/ha/day (Ib/ac/day)
-------
removal of nitrogen Is a primary objective, a perennial forage grass
appears to be the best selection because It can remove nitrogen to low
concentrations (62). Reed canary grass has been shown to be effective fn
removing nitrogen; however, other grasses may be just as good and may
respond better under some circumstances.
Horn toring
Contamination of groundwater is a public health aspect that must be con-
sidered. The proposed EPA regulations on National Primary Drinking Water
Standards (^9) must be maintained for the groundwater. The land disposal
of large volumes of CSO has the potential to significantly increase the
nitrate and total dissolved solids of the groundwater. Therefore, these
parameters should be monitored closely. Since CSO represents large quanti-
ties of surface runoff, it could contain high concentrations of heavy metals
and pesticides; concentrations in excess of what can be removed by the soil.
Any leaching of these pollutants could pose a serious health problem. Due
to the lack of information on the passage of the large concentrations of
pollutants expected in CSO through the soil, extensive monitoring programs
would have to be established to guard against contamination of groundwater
and nearby surface waters that may be used as water supplies.
Another public health consideration for the land disposal site is maintaining
crop quality. When vegetation Is grown as a part of the land disposal
system, a detailed vegetation monitoring program may be required in which
the uptake of certain elements must be analyzed. The analysis Is usually
required because of the potentially toxic constituents that may be present
in CSO In abnormally high concentrations.
Summary
Hence, it can be concluded that land application of CSO wastewaters to the
soil may be a viable treatment alternative. However, land application has
two major limitations in allowing the process to become cost-effective.
First, regulations require the CSO to be disinfected and fn some cases
stabilized before application. This might prove to be a very costly ex-
penditure. Secondly and most importantly, the cost of the collection-trans-
port and/or equalization system may be the crucial factor In disallowing
land disposal of CSO as an alternative to other CSO treatment methods. Jt
may be feasible to use land disposal of the raw CSO fn cities which have
relatively small CSO areas and have land available In close proximity to the
city, but cities with large CSO areas, even tf the land is available, may
find that the cost of the collection-transport system might be prohibitive.
LAND APPLICATION OF CSO SLUDGES
If CSO treatment is employed by a city, the residual sludges that are pro-
duced will require some method of treatment and. disposal. One alternative
that can be considered is land disposal. It could be land disposal of the
liquid sludge which can range from 0.7 to about 4.0 percent solids depending
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on the CSO treatment process employed; or It could be land disposal of the
sludge after It has undergone thickening and/or dewaterlng. The disposal
of liquid sludge on land Is popular because it can meet two basic objectives:
simplicity and cost-effeetfveness. The objectives of land disposing a de-
watered sludge are similar to those for a liquid sludge, although in the
latter case solids-liquid separation must be achieved prior to disposal. In
both cases, the sludge may be useful as a soil conditioner or as fertilizer
for crop growth.
The sludges that are produced by CSO treatment can vary greatly from the
sludges that are produced at conventional municipal wastewater treatment
plants. Therefore, any criteria developed for land disposal of municipal dry-
weather sludges way not be applicable for land disposal of CSO sludges.
As with the land disposal of the raw CSO, this section will attempt to pre-
sent the design considerations necessary for the land disposal of sludges,
either liquid or dewatered, and then relate these considerations to the
unique characteristics of CSO produced sludges and to the problems that may
be caused by these characteristics.
PreappJI cat Ion Treatment
Variable characteristics, presented earlier in Tables 4, 5 and 6 have
been observed for various CSO sludges around the country (12). The very
high values of BOD's, volatile solids and col I forms indicate that direct
disposal of raw sludges may present problems for public health (through
possible disease transmission) and development of odor problems. For these
reasons, it appears that CSO sludges must be stabilized before land applica-
tion.
The stabilization method most frequently used is anaerobic digestion. How-
ever, there are numerous other acceptable methods, such as aerobic digestion,
chemical treatment, heat stabilization or heat drying, and composting, which
may be used. A promising method of stabilization for CSO sludges Is lime
treatment. The use of this method would allow for the stabilization of the
CSO sludges either at the site of the CSO treatment facility or at the land
disposal site. If dewaterlng of the CSO sludge Is employed in order to
reduce transportation and handling costs, lime stabilization can be accom-
plished prior to dewaterlng.
A procedure for the lime stabilization of municipal sludges has been de-
veloped and operated successfully on a pilot scale (35)- Significant reduc-
tions in pathogenic bacteria and obnoxious odors resulted from lime treat-
ment. Growth studies indicated that disposal of lime stabilized sludge on
cropland produced no detrimental effects.
For high rate application either by entrenchment or sanitary landfill, It
has been reported that the sludges should first be limed and dewatered
(63). The pH of the sludge at the time of dewatering should exceed 11,5 to
reduce pathogen survival and potential nuisance conditions.
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Because of the success of stabilization of municipal sludges by 1 Icne treat-
ment and the ability to achieve the stabilization at the site of the CSO
treatment facility instead of transporting the sludge to a central stabili-
zation facility and also, the ability to treat intermittent flows; lime
stabilization should be considered as a feasible preapplication treatment
process for a land application system,
T r a n s po r ta 11 on of the S1udg e
The solids characteristics of the sludge will be a primary factor Influencing
the type of transportation selected. If the sludge has a solids content
less than 8S, it may be transported by pipelines, tank trucks or tank wagons.
When the sludge is dewatered to a solids content of 15$ or higher, it must
be transported by either dump trucks or manure spreaders. Selection of the
desired transportation mode will usually depend on production rate, distance
to application site, and planned lifetime of the s!te.
Many large cities may optimize sludge handling and disposal costs by pumping
their liquid sludges relatively long distances through pipelines. However,
pipelines are probably uneconomical for small communities due to economics
of scale. In addition, convenience and accessabi1ity of satellite CSO treat-
ment sites, may make pumping very difficult to Implement. As has been pre-
viously discussed, the combined sewer areas of most cities are centrally
located thus creating two problems." 1) construction in heavily built up
areas; and 2) vast pumping distances to avoid urban-suburban areas. These
considerations along with other factors such as Intermittent peak quantities
of sludge to be handled and settling of grit in pipelines would probably
make transportation of CSO sludges by pipeline impractical and uneconomical.
The land disposal of liquid CSO sludge can become very expensive If truck
hauling is employed over long distances. The costs will be extensively de-
pendent on the hauling distance (which can be great from the CSO treatment
sites to the disposal site), the size of the truck, and the quantity of
solids being hauled. However, tank trucks provide considerable flexibility
with regard to site selection and hauling schedule and have the additional
advantage that liquid sludge can be applied directly from the truck. These
considerations seem to indicate that tank truck transportation of CSO sludges
may be a viable approach.
Thickening and dewaterlng of the sludge could significantly reduce the
operating cost of transporting CSO sludges to a land disposal site. For
example, a sludge volume requiring disposal can be reduced fifteenfold if a
sludge of one percent solids is thickened and dewatered to 15 percent solids.
This In turn, would significantly reduce the city's annual sludge transpor-
tation costs.
From the discussion of the transportation aspects of land disposal of CSO
sludges, it appears that truck transportation of either liquid or dewatered
sludge Is the most desirable alternative In CSO areas with significant
volumes of sludge to be handled. Truck transportation of dewatered
sludges might prove to be the more desirable alternative because it repre-
127
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sents a significant reduction In operational costs from trucking the liquid
sludges. However, a detailed economic analysis should be required for each
individual case to determine If these savings would cover the added costs of
thlckenlng-dewatering facilities.
S^to rage Requ i rements_
Since CSO events are Intermittent and thus sludge volumes will not be a
continuous flow, storage facflfties will be required to maintain a constant
application program. Storage will also be required if land disposal Is pro-
hibited due to inclement weather, frozen soil and snow cover as well as the
possibility of equipment breakdown. As was previously discussed for land
application of raw CSO, the average number of nonapplicatlon days for which
storage would normally be required fn colder climates Is about 100 days. De-
watering the sludge would significantly reduce the volumes required for
storage even though the solid weights remain the same. For example, if
dewaterlng to 15% solids Is used, the volume to be stored is reduced to 1/15
of the original liquid volume. For a dewatered sludge, temporary storage
pits have been used into which the sludge is dumped and from which front-end
loaders obtained the sludge for application. The pits can then be closed
as they become impassable and/or too far from the application area (63).
Liquid sludges are usually stored in tanks or lagoons located at the disposal
site. If liquid sludge is stored, settling of the sludge solids will occur
In the basin. Therefore, provisions should be made for resuspending these
solids before the sludge Is applied to the land. The storage facility could
also become a source of odor problems and a breeding ground for mosquitoes
and other Insects, therefore precautions will have to be taken to prevent
these problems from occurring. These precautions could be stabilization
with lime before storage and a possible insect control program.
A dewatered sludge storage area would not be as troublesome as a storage
basin for liquid sludge. However, the dewatered sludge could become a
source of odor problems and then some remedial action would be required.
Cllmatologlcal Effects
The general climate of the area will have some effects on the operation of
the disposal site, although the effects will not be as pronounced as that for
raw CSO.
The main c]Imatologlcat concern will be the restrictions that Inclement
weather will impose on the application operation. For the disposal of
liquid CSO sludges, rainfall periods will prevent application to the land
and therefore, lagoons are usually designed for the site so that they can be
used for storage until the weather permits application. During winter
weather, the application of both liquid and dewatered sludge may be pro*-
hiblted because of frozen ground. Any CSO sludges generated during this
period must be stored until application Is allowed. On the average, the
operation of facilities in the Great Lakes region will have to be shut down
for about 3 1/2 months.
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If the liquid sludge is to be applied by a truck, all-weather roads that
would allow for discharge to either side of the road should be constructed
at the site. This would help to offset wet periods and compaction problems.
For inclement weather operation, flexibility could be established by use of
fixed piping or movable irrigation equipment (64). For a dewatered sludge
disposal operation, all-weather roads should be provided so that disposal
can be utilized during periods of rainfall and wet grounds.
Po I1utJ ona1 Load ing Cons t ra i n t s
In applying CSO sludges to the land, the control of loading rates will be
based mainly on concerns for the migration of pollutants to the groundwater
and the accumulation of heavy metals In the soil and vegetation. As was
illustrated using raw CSO, some of the pollutants that may lead to restric-
tions on the loading rates of sludges to the land will be investigated using
similar constraints as that presented earlier. The following CSO values,
based on average characteristics, have been assigned for use in this section.
Raw CSO Volume: 1382 x 106 &/yr (365 x 106 gal./yr)
Volume of Sludge as Percent of Volume Treated: 2.8%
Yearly CSO Sludge Volume: 38.6 x 106 £{10.2 x 106 gaj.}
CSO Sludge Concentration: 1 percent solids
Yearly CSQ Sludge Solids Volume: 186 metric tons (425 tons)-dry weight basis*
Pollutlonal Characteristics:
SS
BOD
N
P
Zn
Cu
NI 200 mg/kg
Yearly CSO Sludge Volume after Thickening to 4S Solids: 9.8 x 10 £(2.6
x 106 gal.) fi
Yearly CSO Sludge Volume after Dewatering to 151 Solids: 2.6 x 10 2.
(0.7 x 106 gal.)
ToxicElements - Restrictions have been placed on the practice of land dis-
posal In order to limit the maximum loading of the metals on the land (16).
Wisconsin has developed an approach which takes Into account the combined
effect of the metals by using a measurement entitled the zinc equivalent.
This was presented and discussed In the previous section. From this approach
it is possible for a standard to be developed which would maintain heavy
metal concentrations below toxic levels.
Since calculation of the ZE of the CSO sludge material requires knowledge
of zinc, nickel and copper concentrations, It was assumed that the concen-
trations (mg/kg} will be similar to raw CSO. Using the Wisconsin approach,
the acceptable total zinc equivalent loading would approximate 21 metric
tons/ha/yr (3.4 tons solids/ac/yr) for soils having cation exchange capaci-
ties of15meq/100 gm and 20 year designed life. Thus,thearea requirements
*A11 metric tons throughout this section are expressed on a dry weight basis
129
10,000
100
12.5
10
1000
kQQ
200
rag/1
mg/gm
mg/gm
mg/gm
mg/kg
nig/ kg
mg/kg
SS
SS
SS
-------
for safe control of toxic metals would be about 4,7 x 10"^ ha/metric ton/yr
(10.6 x 10~2 ac/ton/yr).
In addition to the metal equivalents' limitations, cadmium additions may be-
come a serious limiting parameter because of its toxicity effects to both
humans and plants. Cadmium loadings must be limited to a maximum of 2.2 kg/
ha/yr (2 Ib/ac/yr) and the total site lifetime maximum of 22 kg/ha (20 Ib/ac)
(65). To determine loading constraints, a cadmium value of 40 mg/kg was
assumed. The calculation of loading rates indicate that cadmium loadings
limit annual application to 56 metric tons/ha (25 tons/ac) and overall cad-
mium loading to 560 metric tons/ha (250 tons/ac), assuming a 20 year site
life. Therefore, the area requirements necessary for safe applications of
cadmium would be about 3.8 x 10~2 ha/metric ton/yr (4.0 x 10~* ac/ton/yr).
It Is apparent that from the differences In land area requirements the metal
equivalents are the limiting loading constraints In the application of toxic
materials to the land.
jjlt.rogen and Phosphorus Cont_rol_ - In determining the allowable loading of
nitrogen to the land, the objective shall be to match as closely as possible
the quantity of nitrogen removed from the soil by the harvesting of the
crop. The allowable loading rate will thus be determined by the nutrient
content of the sludge and the nutrient uptake capabilities of the particular
crop under consideration. The rate of application for CSO sludges can be
calculated using the same equation as that used for the application of raw
CSO. Additional assumptions that had to be made Included: 1) crop nitrogen
removal rate for corn Is 201 kgN/ba-yr (180 lb N/ac-yr) and 2) the nitrogen
concentration in CSO sludges Is 12.5 «ig TKN/gm SS or 125 mg/1.
Using these assumptions, the sludge application rate would be approximately
255.4 kg N/ha-yr (228 lb N/ac~yr) thus resulting in a land area reauiremen*
of 4.9 x 10"^ ha/metric toa sludge/yr (llTl x lQ~2ac/ton sludse/yr). If oracg
is grown Instead of corn, the land, area requirements could be reduced to 3.7 x
10"" ha/metric tori"sludge/yf (8.3 x 10~2 ae/ton sludge/yr).
Besides nitrogen, phosphorus has also been a nutrient of concern. Current
restrictions limit phosphorus annual loading rates within the 68 to 136 kg
P/ha-yr (150-300 lb P/ac-yr) range. On this basis, the total land area re-
quired for safe application of phosphorus should not exceed 4.0 x 1Q~2 ha/
metric ton sludge/yr (8.9 x 10~2 ac/ton sludge/yr) for CSO sludses contataltip
P concentrations of 10 mg I/gm SS.
Organ ic AppJfca11on Rates - Although the rate of organic carbon oxidation In
soils Is known to be high, limitations for waste additions are not adequately
established. A few regulations have been proposed to limit BOD,- application
rates to around 6J2.6 kg/ha-day (600 Ibs/ac-day). However, Jewell (66) re-
cently reported that a soil system could degrade organlcs at a rate exceeding
4480 kg/ha-day (4000 Ib/ac-day). If this latter limitation is used, the
safe application areas for CSO organics would be 2.3 x 10"' ha/metric ton
sludge/yr (5.2 x 10"2 ac/ton sludge/yr),
HydrauHe Loadfng - Since the permeability of much of the area in the northern
states exceeds 5 cm per hr (2 in./hr), It can be Inferred that the trans-
130
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mission of water from the sludge would be a minimal problem. However, the
application of the more dilute sludges (I.e. }% solids) may be restricted
to several application periods per year to prevent surface flooding and
runoff.
Land Area Requirements - The actual land area required for the disposal of
the CSO sludges, either liquid or dewatered, will be dependent on the allowa-
ble application rates which, In turn, will be dependent on the soil type, the
nutrient and heavy metals content of the particular sludge, and the nutrient
uptake characteristics of any vegetation crops on the site.
For field area requirements, a summary of the application rates estimated to
be acceptable and the resulting land requirements are shown In Table kO.
Similar to raw CSO, the limiting pollutant loading factor is the nitrogen
content of the sludges. Nitrogen is most often the limiting factor for
application of municipal sludges. If nitrogen limitations determine the re-
quired land area, it can be seen that the application rates of the other
pollutants are one-third to two-thirds that which is assumed to be an en-
vironmentally safe rate of application. Recommendation of the use of a
5.3 x 1Q~2 ha/metric ton sludge/yr (11.8 x 10*" 2 ac/toti sludge/yr) land area
requirement should provide a safety factor large enough to account for any
unpredictable events. This application is equivalent to adding a CSO sludge
(4% solids) once at a depth of 4.8 cm (1.9 in,); or an application rate
equal to 19.0 metric tons/ha/yr (8.5 tons/ac/yr).
These land requirements are for the actual application only and, as shown In
the discussion of land disposal of the raw CSO, additional land may be re-
quired for roads, buffer zones, possible storage and pretreatment facilities,
etc. In studies of land application of municipal wastewater plant effluents,
it has been found that only 70 percent of the total site area is available
for actual application (67).
Employing the above application rate of 19.0 metric tons/ha/yr (8.5 tons/ac/
yrL and if the nationwide .annual generation of CSO solids totals 1.57 x
10 metric tons (1.73 x 10 tons), field area requirements for CSO sludges,
either liquid or dewatered, would approximate 82 x 103 ha (203x103 acres) of
land. Assuming that, on the average, the land required for actual disposal
Is 70 percent of the entire disposal site, the nationwide disposal of CSO
sludges would require a total land area of 118x10* ha (290x103 acres).
App 11 ca 11 on T.echnJques
The application technique that Is employed at a specific land disposal site
will be dependent to a large extent on the characteristics of the site,
physical properties and quantity of sludge, and the objectives of the land
disposal program. The techniques presented here are those that have been
reported In the literature for municipal treatment plant sludges.
Systems are available for surface and subsurface application of liquid
sludges. Surface application of liquid sludge Is generally accomplished by
ridge and furrow Irrigation or by tank truck land spreading. The most common
131
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technique is direct application to the land by spraying from tank wagons.
Most communities employing this technique use city-owned tank trucks with
capacities ranging from 3.8 to 18.9 cu m (1,000 to 5,000 gal.) and equipped
with various spreading devices operated by gravity or pumping (64). The
tank truck has the advantage that It can also be used for sludge transport.
Liquid manure spreaders, pulled by farm tractors, have been found to be very
effective and accurate In the application of the sludge to the soil. It
may be desirable to incorporate the sludge into the soil as soon as possible
following application in order to prevent possible odor and runoff problems.
TABLE 40. SUMMARY OF RECOMMENDED DRY SLUDGE SOLIDS
APPLICATION RATES FOR ?ARIOUS CSO SLUDGE POLLUTANTS AND
THE RELATED LAND AREA REQUIREMENT
Acceptable Land area
application rate requirement
^ ' .-- - ^
Po Mutant kg/hr/yr (Jb/ac/yr) 10"z ha/me trie ton/yr (10 ac/ton/yr)
Toxfc 21. Oa (9.4)a 4.7 (10.6)
Nitrogen 255-6 (288) 4.9 (11,1)
Phosphorus 252 (225) 4.0 (8.9)
Organlcs 4,484b (4000)b 2.3 (5.2)
Expressed as metric tons/ha/yr (ton/ac/yr) - dry weight basis
Expressed as kg/ha/day (Ib/ac/day)
Flooding and ridge and furrow irrigation methods have also been used as
sludge application techniques. Ridge and furrow has the advantage that it
Is suitable for row crops during the growing season.
Soil Incorporation of liquid sludge can be accomplished In a number of ways.
The most common methods are plow-furrow cover and subsurface injection. The
plow-furrow-cover method involves the spreading of sludge In a narrow swath
from a wagon and immediately covering the waste using a plow. Subsurface
Injection involves the discharging of liquid sludge Into subsurface channels
caused by chisel-like plows.
132
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Another disposal technique has been used at non-agricultural land sites.
Disposal by small treatment plants may incorporate digging of shallow
trenches, filling them with liquid sludge and covering the sludge with soil
to prevent nuisance conditions (69), The literature shows that, with the
use of ridge and furrow irrigation, trench disposal, and flooding techniques
on non-agricultural land, It Is possible to use greatly increased loading
rates. However, groundwater and other public health consideration may place
significant constraints on these loading rates.
When dewatered sludge Is applied to the land, the usual method of applica-
tion is to spread the sludge on the land and then disc It into the soil
using earth moving equipment and farm machinery. The one disadvantage of
this method is that it may be difficult to break up the sludge cake In such
a manner that it can be easily spread.
Entrenchment Is another application method that has been employed. En-
trenchment has been found to be a feasible method for simultaneously dis-
posing of sewage sludges and improving marginal agricultural land, particu-
larly for dewatered (20% solids) raw, lime treated sludge (63).
In devising an application system for land disposal of CSO sludges, minimiz-
ing costs and maximizing the application season should be the major con-
siderations. The proceeding discussion shows that there is a very wide
range of application techniques that have been used with varying application
systems. It appears that many considerations may dictate the possible appli-
cation technique at the site, however, the most economical application
technique should be selected.
Growth Of Crops On The SIte
For the disposal of CSO sludges on agricultural land, the growth of crops or
vegetation on the disposal site can be a very important aspect of the site
operation. The basic reason for cultivating crops or a vegetative cover is
to achieve nitrogen uptake so that the nitrogen Is removed from the soil
and ultimately removed from the site when the crops or vegetation are har-
vested (64),
It is generally agreed that alfalfa Is a most desirable crop, particularly
if sufficient nitrogen Is available In the sludge to eliminate nodule forma-
tion on the root structure (64). This ensures that the maximum uptake of
nitrogen occurs and that the movement of nitrates into either ground or sur-
face water will be minimized. By cutting alfalfa three or four times during
the growing seasons Increased quantities of nutrients may be removed. In
addition, each cutting allows for additional sludge application. This would
be advantageous for the more dilute sludges requiring several application
periods.
Corn is perhaps the next best and most widely used cover crop, having the
advantages of high nitrogen uptake and good saleabillty. It has limited
flexibility for sludge application during the growing season unless the
ridge and furrow method of liquid sludge application can be used.
133
-------
The other general purpose group of crops Is the forage grasses. The greatest
advantage of these crops, In addition to nitrogen uptake, is their accessi-
bility in inclement weather, during early spring planting. In late fall be-
fore the soil cools down, and during the active growing season when other
crops restrict tank truck operation (64).
Monitoring Program
The application of sludge to land disposal sites must be managed to minimize
the risks of nitrogen and pathogen contamination of surface and groundwaters;
to minimize the risks of soil degradation by metal overloading and of toxic
metal uptake by crops; to minimize the risks of pathogen transmission by in-
sects and animals; and to minimize offensive odors. Thus, the monitoring
program employed at the disposal site will be extremely Important, A compre-
hensive monitoring program, as that suggested earlier, will be essential to
ensure that proper renovation of the CSO is proceeding without degradation
of environmental quality.
Application rates should be subject to good record keeping and monitoring be-
cause overloading of a particular soil can be a major reason for failure of
a land site. Caution should be used In dealing with acid soils because of
the possible release of heavy metals. Here the general rule Is to maintain
a pH above 6.5 to control heavy metal solubility (64).
Summary
In discussing the logistics of treatment and disposal of CSO sludges, it Is
apparent that land application In general may be extremely feasible, both
practically and economically. Therefore, the municipality or sanitary dis-
trict should regard land application as a viable alternative. However, Its
implementation should be based upon this alternative being the least-cost
acceptable means of sludge handling and disposal.
Three management options are available: 1) land spreading a dilute sludge
(II solids); 2) land spreading a thickened sludge (4-81 solids); and 3) land
spreading a dewatered sludge (>12| solids). It should be noted that land
area requirements are the same for all three options, however, the solids
handling and disposal costs will differ greatly. The high costs associated
with transporting, storage and Intermittent application of dilute sludges
will probably cause option one to be least cost-effective. In most cases,
options two and three will be economically feasible. The difference will
depend on transporting and storing costs versus additional dewaterlng costs.
Land application of CSO sludges has one major limitation which must be con-
sidered when evaluating the cost-effectiveness of this alternative to that
of another management technique. Before sludge can be disposed, it must
first be treated (stabilized) to reduce adverse Impact on receiving land.
From some stabilization processes, this can be a very costly expenditure.
The most promising and possibly the most cost-effective method of stabiliza-
tion of CSO sludges may be lime treatment.
134
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SECTION VII!
ECONOHIC IMPACT OF HANDLING CSO TREATMENT RESIDUALS
INTRODUCTION
The economic Impact of handling CSO residuals Is difficult to estimate on a
generalized basis, This section presents baste economic data to approximate
the costs associated with handling generated volumes of CSO sludges using
various CSO treatment systems. It Is emphasized at this point that the costs
presented herein are guidelines and are Included only as a first approximation
of the actual costs Involved, If a detailed economic evaluation is necessary
or desired, the individual site must be evaluated separately with respect to
locale, rainfall patterns, type and location of treatment system, etc. Then
the equipment costs should be established by estimates of manufacturers, not
by generalized cost curves. However, the Information presented will allow
an approximation of the ranges of costs for handling CSO treatment residuals
throughout the country and Is valuable when properly applied.
BASES OF COST ESTIMATES
In providing cost estimates, it was desirable to utilize similar bases for
all of the treatment trains evaluated. This was done, as much as possible, by
utilizing published cost curves or other data and then adjusting them to
reflect June, 1976 prices. Whenever a similar unit process was applied in
different schemes, the same cost estimating structure was used.
When satellite treatment systems were evaluated, the same four systems were
considered for each site. These included the following;
1. Lime Stabilization •* Storage •»• Gravity Thickening -*• Vacuum Filtra-
tion -*• Landfill
2. Lime Stabilization •* Storage -*• Gravity Thickening -»• Vacuum Filtra-
tion •*• Land Application
3. Lfme Stabilization •*• Storage -»• Gravity Thickening •*• Land Application
4. Lime Stabilization •*• Storage •* Land Application
An average of the annual CSO sludge volume was used to establish system de-
sign flow rates and the following assumptions were made to size equipment:
1. Storage - store 48 hours of CSO sludge.
2, Lime Stabilization - treat within 24 hours.
3. Gravity Thickening - treat within 48 hours.
4. Vacuum Filtration - treat within 48 hours.
135
-------
It was assumed for all cities, that half of the rainfall results In combined
sewer overflow and of this volume, a ffxed percentage Is CSO sludge, depend-
ing upon the CSO treatment system used. Also It was assumed that addition
of lime for stabilization Increased the solids to be handled by 15%. (35).
Figures 13 - 17 were used to estimate capital costs for pumping, gravity
thickening, lime stabilization, vacuum filtration and landfill (43). Storage
tank costs were estimated using unit costs per volume as listed below (69),
Tanks:
m Gallons S Installed
936 (250,000) 98,000
1872 (500,000) 150,000
3744 (1,000,000) 230,000
7488 (2,000,000) 355,000
Ti976 (4,000,000) 560,000
22464 (6,000,000) 760,000
Operation and maintenance costs were estimated from several sources. Figures
18 - 23 Included manpower and utilities costs for pumping, gravity thickening
and vacuum filtration. These costs were adjusted to dollars using a dally
rate of $32 per man-day and utilities cost of $O.OQ1/KWhr. Lime stablll?
zation operating and maintenance costs were estimated based on published data
regarding lime stabilization (35):
Sludges from physical treatment » $9-lO/metr!c ton ($8~9/ton)
Sludges from physical/chemical treatment « $l4-19/metrlc ton ($13"17/ton)
5luges from biological treatment *• $l3~!7/
-------
xxxo
--J
100
in
O
tj
PBIMARY SLUDGE PUMPING
CAPITAL COST
10
'.Ot M 01 6 10 50 100
metric tons - 0.907 x tons DRY SOLIDS, tons/day
m 100
soo 1,000
Figure 13. Capital cost estimate basis-primary sludge pumping (43).
-------
IOC XI
CO
100
o
•o
VI
o
o
g
-------
LIME STABILIZATION
CAPITAL COSTS
(ENR 1900)
0.0001
01 OS 0.1
metric tons « 0,907 x tons
j 10 so too
DRY SOLIDS, tons/day
boo i.ooo
Figure 15. Capital cost estimate basis-lime stabilization
-------
-£-
o
100
s
fl
8
01
0-01
NOTE; For items A, B, D, F and
G, see references 76» 77. 78,
79 and 80 respectively.
.0] 05 01
metric tons x 0.907 x tons
5 10 50 100
DRY SOLIDS, tems/diy
PROCESS ASSUMED NOT
APPLICABLE TO SLUDGE
QUANTITIES LESS THAN 0.5 TPD
VACUUM FILTER DEWATEBING
CAPITAL COST
(ENR 1900)
60 100
SOQ 1000
Figure 16, Capital cost estimate basts-vacuum filter dewaterlng
-------
100
to
M
L.
to
V)
V)
o
u
ot
O.01
PROCESS ASSUMED NOT
APPLICABLE TO SLUDGE
QUANTITIES LESS THAN
0.1 TPD.
LANDFILL
CAPITAL COSTS
(ENR 1900)
DOC I
UJ
01 OS 0.1
metric tons - 0,90? x tons
5 10 50 100
DRY SOLIDS, tons/day
100
500
1000
Figure 1?. Capital cost estimate basis-landfill
-------
ia,ooo
ro
1,000
I
3E 100
10
PRIMARY SLUDGE PUMPING
MANPOWER
01 05 01
metric tons » 0.907 x tons
5 10 60 100
DRY SOLIDS, tons/diy
50 100
SCO 1000
Figure 18.
cost estimate basis -primary sludge pumping (43),
-------
lo.ooo
1,000
100
10
MAINTENANCE
i I l
GRAVITY THICKENING
MANPOWER
.OB at
J 10
so too
50 100
500 1000
metric tons - 0.90? x tons DRY SOL I OS, tons/d«y
Figure 19, Manpower cost estimate basis-gravity thickening
-------
10,000
i.ooo
in
VACUUM FILTER DEWATER1NG
MANPOWER
01 05 D 1
metric tons » 0.90? x tons
S 1 0 5 0 WO
DRT SOLIDS, tons/day
SO 100
500 1,000
Plgure 20. Hanpower cost estimate basis-vacuum filter dewaterlng
-------
1000000
100 000
10000
-t-
Ul
1,000
PRIMARY SLUDGE PIMPING
ELECTRICAL ENERGY
01 05 01 .5 10
metric tons « 0.907 x tons BUY SOLIDS, tens/day
Figure 21. Electrical energy cost estimate basis-prfmary sludge pumping (43).
-------
1,000,003
100,000
10,000
1,000
100
GRAVITY THICKENING
ELECTRICAL ENERGY
i i mm
90 100
1U
01 JK 01
metric tons - 0.907 x tons
5 10 SO 100
DRY SOLIDS, tons/day
500 1.000
Figure 22, Electrical energy cost estimate basis-gravity thickening
-------
io.ooo.ooo
1,000,000
100,000
10,000
1.090
VACUUM FILTER DF.W VTERING
ELECTRICAL ENERGY
Ol 05 01
metric tons «• 0.907 x tons
s 10 so 100
DRY SOLIDS, cons/day
500 l.OQO
Figure 23. Electrical energy cost estimate basis - vacuum filter
dewatering
-------
0.01
1000
4 6 10.000
QUANTITY, w«t ton/day
NOTES;
1. Minnwpolit. Mar^ 1972. ENR Construction Con Indvc of 1827,
2. Amortization of 7% for 20 years.
3. Labor reta of $6.26 par hour.
4. Quantity assumes 6-day work week.
6. Wat sludge must be considered for cost par ton.
6. Source: U. S. P. H. S. and Stanley Consultants.
NOTE; $/ton * .907 " $/««trlc ton
ton/day X .907 • metric ton/day
i.
*
i
(A
§
fc
o
o
—
I
v»
Figure 24. Capital and 0/M costs for sanitary landfills (22).
-------
10,0009
o
o
o
1ft
o
i
1,000
100
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100 i
2
i 4
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) (
5 '
'(
J9
. 80
- 40
20
10
<^
1,000
u
I
ANNUAL SLUDGE VOLUME,
NOTES:
1. Most economical type truck from selection of standard frame or semi
trailer mounted bodies; tanks for liquid and dump or ram type for
dewatered, F
2. Eight hours of trucking operation per day.
3. Full cost at $.60 per gallon.
4. Operating and maintenance labor at $8.00 per hour including fringes.
5. Electric energy at $.02 per kwh.
6. Amortisation of truck capital cost over six years at seven percent.
I, C°St> excludi^ fuel and operator, $0.20 to $0.30 per mile
depending on type of truck.
8. Truck loading time 30 minutes and unloading time 15 minutes.
9 Truck average speed 25 nph for first 20 miles one way and 35 mph for rest.
10. General and administrative costs 25 percent of total O&M cost.
Figure 25. Truck transport total annual cost with loading s unloading
facilities 8 hour operation per day liquid sludge 1976 (71).
-------
1,000
e
§
w
s
100 1
7
&
5
4
10
X
3 456789
10
3 4 5 6 7 83
100
3456 769
80
40
20
10
5
in
t>
ui
a
1,000
ANNUAL SLUDGE VOLUME, 1000 ycT
cubic meters «* 0,765 x yd
km - 1.61 x miles
NOTES :
1. Most economical type truck from selection of standard frame or semi
trailer mounted bodies; tanks for liquid and dump or ram type for
dewatered.
2. Eight hours of trucking operation per day.
3. Full cost at $.060 per gallon.
4, Operating and maintenance labor at $8.00 per hour including fringes.
5. Electric energy at $.02 per kwh.
6. Amortization of truck capital cost over six years at seven percent.
7, Truck O&M cost, excluding fuel and operator, $0.20 to $0.30 per mile
depending on type of truck.
8, Truck loading time 30 minutes and unloading time 15 minutes.
9. Truck average speed 25 mph for first 20 miles one way and 35 mph for rest.
10. General and administrative costs 25 percent of total O&M cost.
Figure 26. Truck transport total annual cost with loading &
unloading facilities 8 hour operation per day dewatered
sludge 1976 (71).
150
-------
season and that laqoon storaae would be required for only 10S of the genera-
ted sludqe volume. Thickened or vacuum filtered sludge would be stored for
longer time periods and applied approximately two times per year, fn sprlnct
and fall. Storage of kO% of the volume was then required. The basis for
these costs are alven In Figures 27 and 28. Distribution costs were assumed
to be a percentage of the transportation costs associated with a site. For
haul distances of 32.2kfn {20ml} or less, distribution costs were estimated
to be 251 of the transportation costs and for haul distances of 33~64 km
(21-*fOmf) the distribution costs were estimated to be 12.51 of the transpor-
tation costs.
Land requirements were calculated based on 18.? metric ton/ha/yr (8.5 ton/
acre/year) as established In Section VII. These were adjusted to Include
borders, buffer zones, roads, etc. using $ multiplier of \.k for acreage less
than or equal to ^OSha (1000 acres) or 1.1 for larger land requirements. The
land costs were based on the assumption that the purchase value of the land
Is equivalent to Its salvage value and the anual cost was equal to the
annual interest on the' purchase price (5 7/81). The purchase price of land
was estimated to be $3706/ha (51500/acre) (^*0). The land preparation costs
included clearing, leveling and site preparation. These costs were estimated
from Flqure 29.
Once all capital and ooeratlng costs were estimated based on the various cost
curves etc., then these were amortized to establish a total annual cost
for the system. The amortization was based on 5 7/8% Interest and a 20 year
life for all systems.
IMPACT OF SLUDGES PRODUCED BY CSO TREATMENT ON FOUR EXAMPLE CITIES
The potential economic Impact of treatment and handling of CSO treatment
residuals Is considered In this subsection with respect to four example
cities. Four actual cities have been chosen to Illustrate different CSO
treatment sludqes and different size systems. The cities which have been
evaluated are Milwaukee, Wisconsin; San Francisco, California; Kenosha,
Wisconsin; and New Providence, New Jersey.
Extensive analysis Involving the various CSO sludge handling alternatives
has been performed for the Milwaukee site. The evaluation Includes poten-
tial costs for bleed/pump-back, treatment at parallel sludge handling faci-
lities, and satellite treatment using several different treatment trains.
It Is apparent from these analyses and previous discussion, that although
bleed/pump-back raay be most inexpensive. It Is likely to be most impractical,
Treatment at parallel facilities at the dry-weather plant Is expensive if
handled in 120 days and may be impossible due to space limitations. There-
fore further evaluation of the potential impact of CSO sludges In other
cities was limited to satellite treatment considerations.
The Individual evaluation was then divided Into several steps. The first
step Involved estimation of the extent of the CSO problem based on precipi-
tation data, area of the city served by combined sewers, the potential pro-
151
-------
in
TJ
c
ro
w
3
O
VI
O
CAPITAL COST
EIIANKIENT PROTECTION
RESEIVOIR CONSTRUCTION
STORAGE VOLUME, million gallons
l.i"
V*
o
o
...
II
•••I
cubic meters * 3.78^ *
10* million gallons
OPERATION 6 MAINTENANCE COST
MATERIALS
LABOR
9,1
10
STORAGE VOLUME, million gallons
Figure 27. Storage (0.05-10 million gallons)(48).
152
-------
*»•
i
u
g
i
RESERVOIR
CONSTRUCTION
EMBANRIINT PROTECTION
111
1.1(1
STORAGE VOLUME, million gallons
ti.in
t,
C9
v*
i
10
0.4
cubic meters - 3.78 x
1CK x million gallons
OPERATION & MAINTEHANOE COST
U10R
111
I,lit
11,911
STORAGE VOLUME, railUon gallons
Figure 28. Storage (10-5,000 millions gallons)(48).
153
-------
IM.III
II,IH
1,900
M
•O
II
M
I ft!
O
u
O.
l.t
IOODED:
-TOTAL
BRUSH AND TBEEt;
JRAJS ONU
II
III till
FIELD AREA, acres
11,111
hectares « O.'tOS x acres
Figure 29. Field preparation - site clearing (48).
-------
cess used for CSO treatment and the characteristics of the sludges produced
by the CSO treatment process.
The second step will be to present Information on each city's dry-weather
sludge handling facilities, Including capacities, amount of solids presently
being handled, and any excess handling capacity presently available.
Once the necessary Information has been developed, the final step wlH be
to assess the Impact of the CSO generated solids on the city's present
sludge handling and disposal system. The impact will be evaluated on both
a physical and economic basis. Rough estimates of what the capital costs
will be for constructing new sludge handling facilities at the site of CSO
treatment have been developed and are presented In the following discussion.
CSO SLUDGE HANDLING IN MILWAUKEE, WISCONSIN
Evaluation of the various methods of handling CSO sludges In Milwaukee, Wis-
consin was completed In depth to Illustrate the effect of bleed/pump-back of
CSO sludge and sludge handling at parallel sludge facilities and on-slte
satellite treatment. In Milwaukee, the dry-weather treatment plant Is pre-
sently at capacity with respect to Its sludge handling facilities. This Is
a common situation for plants serving combined sewer areas since often the
treatment plant has reached design capacity and sometimes exceeded ft, due
to age. Therefore the example provided by Milwaukee Is somewhat typical of
conditions at treatment plants serving combined sewered areas.
In Milwaukee, the entire drainage area Is 25,110 ha (62,000 acres). Of
this total, 7,006 ha (17,300 acres) or 28 percent are served by combined
sewers. The average annual precipitation for the city Is 74.7 cm (29.4 In).
If It Is assumed that 50 percent of this rainfall accounts for comBlned sewer
overflow, the annual volume of CSO for the city of Milwaukee is 26 million
cu m (6,910 MG).
Presently In Milwaukee there Is a CSO storage tank demonstration facility.
This storage tank Is equipped with mixers so that when the contents are
bled/pumped-back to the dry-weather treatment plant, ft is similar to the
raw CSO, However, when the storage tank has Its capacity exceeded, the
mixers are not operated and the tank functions similar to a sedimentation
basin. The Impact of CSO sludges on the city of Milwaukee wtU be based on
the assumption that complete CSO treatment is achieved by storing the 26
million cu m (6,910 MG) In storage tanks located In four parts of the city.
The supernatant from the tanks will be continuously bled/pumped-back to the
dry-weather treatment plant. After bteed/pump-back of the supernatant, a
residual settled sludge will remain to be handled and disposed of.
Based on bench scale settling tests (12), It has been found that the sedi-
mentation process will produce a sludge volume equal to 0.9 percent of the
CSO volume stored. The resultant sludge will have an average total solids
concentration of about 1.7 percent. The sludge characteristics were given
In Table 4.
155
-------
Based on the reported data, Milwaukee can expect an fnnual CSO volume of
26 million cu m (6,910 MG). Of this total 25.9 x 106 cu m (6,8x106 MG) would
be bled back to the dry-weather plant as supernatant and 2.3 x 10^ cu in
(62 MG) would remain as residual sludge at a concentration of 1.7 percent.
The average raw CSO concentration of suspended solids at the Milwaukee CSO
storage facility fs 192 mg/1. Storage of all the CSO would mean storage of
5.0 x 1()6 kg (11.0 x 10° Ibs) of CSO solids. The residual sludge volume of
2.3 x 105 cu m (62 MG) would represent 4.0 x 106 kg (8.8 x 106 Ibs) of the
solids. The remaining 1.0 x 10" kg (2.2 x 10° Ibs) of solids would be bled
back to the dry-weather treatment plant with the 25.9 x ID6 cu m (6,8 x 10°
MG) of supernatant. This means a supernatant suspended solids concentration
of kQ mg/1.
The metropolitan Milwaukee area is served by two sewage treatment plants, the
Jones Island Plant and the South Shore Plant. The Jones Island Plant is the
major plant and serves almost all of the city's combined sewer areas and,
therefore, will be the subject of analysis. The treatment consists of pri-
mary screening followed by the conventional activated sludge process, and
chlorination. Plant data indicates that the facility has an average dally
flow of 6.5 x 10' cu m/day (1.7 x 10 MGD) with an average suspended solids
concentration of 236 mg/1. This results in 1.5 x 10^ kg/day (3.4 * 105 lb/
day of sol Ids. ^
The primary sludge is incinerated. The waste activated sludge Is gravity
thickened, vacuum filtered, and then processed into a commercial fertilizer.
The sludge handling capacity at the plant fs 199 metric tons/day (220 tons/
day), and the facilities run near capacity at all times.
The use of storage/settling facilities for complete CSO abatement will have
two impacts on the dry-weather plant. First, there may be an Impact due to
bleed/pump-back of the supernatant and, second, there may be a much greater
Impact from the residual sludges If they are bled/pumped-back.
For complete CSO abatement, the supernatant represents 25-9 x 10 cu m
(6.8 x 10j MG) and 1.0 x 106 kg (2.2 x 106 Ibs) of wet weather solids. On an
annual basis, the supernatant volume represents a hydraulic loading increase
of 11 percent to the dry-weather plant. The additional solids loading to the
dry-weather plant represents an Increase of only 2 percent. The design capa-
city of the Jones island Plant Is 757,000 cu m/day (200 MGD) and It is pre-
sently operating at 6.5 x 105 cu m/day (1.7 x 10^ MGD) or 86 percent of
capacity. Therefore It should be able to handle the Increased flows due to
bleed/pump-back of the supernatants frora the storage facilities. This
assumes a constant yearly bleed/pump-back of 7,1 x 10* cu m/day (19 MGD)
from the facilities.
Although the solids handling facilities at the dry-weather plant are operat-
ing near capacity, the slight solids loading increase of 2 percent due to
the supernatants should be manageable without the need for expansion of the
facilities. Therefore, the impact of the supernatants on the dry-weather
treatment plant will probably be minimal.
156
-------
The bleed/pump-back of the settled sludge, on the other hand, does not appear
to be feasible. The 4,0 x 10° kq (8.8 K 10° Ibs) of sludge solids represent
a 7 percent Increase In solids loading to the dry-weather plant. Since
these solids would be fed along with the supernatant, the total solids load-
Inq will be Increased by 9 percent. Since the solids handling facilities are
now ooeratlng near capacity, a 9 percent solids Increase would probably re-
aufre construction of new facilities.
In addition to the 9 percent solids loading Increase, other const derations
seem to rule out bleed/pump-back as a means of handling the CSO generated
solids. One factor to be considered Is that Hllwaukee's waste activated
sludge Is converted to a commercial fertilizer. Thus, even If the solids
handling facilities are adequate for the Increased solids loading, the
effect of these solids on the fertilizer being produced may be a significant
problem. The volatile solids percentage of the CSO sludge Is 48,4 percent
which Is very low when compared to waste activated sludges. This casts
doubt on the quality of the CSO solids as a fertilizer material.
The second consideration also relates to the low volatile content of the
CSO sludge. As stated previously, the primary sludge at the Jones Island
Plant Is Incinerated. The Inclusion of the low volatile CSO solids In the
dry weather sludge could greatly reduce the efficiency of the Incineration
process and a significant amount of auxiliary heat may be required for com-
bustion due to the presence of CSO solids.
A final consideration Is the logistics of bleed/pump-back Itself which may
be difficult to effectively accomplish. The potential accumulation of grit
and organlcs In the sewers could be a problem without sufficient carrying
velocity from dry-weather flow.
However, If it Is assumed that the CSO sludge can be bled/pumped-back to the
treatment plant without problems and that the plant operation will not be
adversely affected by the sludge, then a preliminary cost estimate for this
approach can be made. There are two potential techniques to consider. One
involves holding the sludge and pumping It back over the entire year (3&5
days) and the other Involves approximately 48 hour storage or a 120 day bleed/
pump-back period, The difference has a significant effect upon the size of
the additional facilities required at the plant,
With the addition of the South Shore Treatment Plant In Hllwaukee, the hy-
draulic loading on the Jones Island faclljty has been decreased. However,
the sludge handling facilities are operating at maximum capacity. Therefore
bleed/pump-back of the sludge will require that the sludge handling system
Including thickeners, Incinerators, vacuum filters, sludge dryers and Mllor-
ganlte bagging be Increased In size to handle the excess loading. The opera-
ting costs at the plant will also be greater.
Assuming that the sludge is handled through the treatment plant, the solids
will increase from 3.6 to 11.4 metric tons/day (4 to 12.6 tons/day). This ad-
ditional loading will require a significant increase in sludge handling facili-
ties. According to cost estimates prepared from various sources (72, 73),
157
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the capital and 0 K M costs for bleed/pump-baek are Included In Table 41 for
either a 365 or 120 day bleed/pump-back perJod, As can be seen, costs will
range from approximately $1.26 mill lon-$1.56 million annually for CSO
sludge treatment using bleed/pump-back.
Tdble I*] COSTS FOR 8LEED/PUHP-BACK-MILWAUKEE
Pump-back Time 120 day 365 day
Capital Costs:
Storage Tanks $ 520,000 $1,692,000
Incinerator 117,000 30,000
Pumps 1,360,000 1,360,000
Sludge Handling Equip. 7,082,000 3,376,000
151 Contingency 1,362,000 968,000
Total Capital Cost 10,441,000 7,^27,000
Amortized Capital Cost 885,000 629,000
Annual Operation S
Maintenance Cost 677,000 635,000
Total Annual Cost 1,562,000 1,264,000
Another approach, given that bleed/pump-back Is not feasible due to the
difficulty In transport through pipelines, Is to haul the sludge to parallel
facilities at the dry-weather treatment plant Itself. This procedure would
Involve trucking of the dilute sludge to the treatment plant and placing It
directly Into the sludge handling facilities. It Is assumed, at this
plant, that the additional toad will not adversely affect the Htlorganlte
operation but tt will require additional solids handling equipment. Two
approaches are utilized as before. One Involves storage and hauling over
the complete 365 days and the second Involves hauling over a 120 day period.
The costs for these procedures are presented In Table 42. It Is apparent
that due to the transportation costs, that this option Is more costly for
both time periods than bleed/pump-back.
The third system which can be evaluated Involves handling the CSO sludges at
the sites of the CSO storage/settling facilities. The CSO facilities will
generate 234,670 cu m (62 MG) of sludge at 1.7 percent solids annually. The
first step In handling the sludge on site should be lime addition to raise
the pH above 12. This should destroy any pathogens present In the sludge and
prevent odor problems from developing at the sites. After this the sludge
can be gravity thickened and then possibly dewatered. Vacuum filtration
should be used because of the targe amounts of I tnte In the sludge. For a
number of CSO storage/settling facilities located throughout the city, It may
be more economically advantageous to have a mobile unit that could move from
158
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site to site rather than vacuum fHtratfon facilities located at each Indi-
vidual site. However, for this evaluation It has been assumed that the
sludge has been handled at four sites wfthln the city with each site process-
Ing an equal volume of sludge.
Table k2 COSTS OF TREATMENT
AT PARALLEL DRY-WEATHER FACILITIES-MILWAUKEE
Hauling Period 120 day 365 day
Capital Costs;
Storage $ 520,000 $1,692,000
Pumping 1,360,000 1,360,000
Sludqc Handling Equip. 7,082,000 3,376,000
15% Contingency 1,344,000 964,000
Total Capital Cost 10,306,000 7,392,000
Amortized Capital Cost 873,000 626,000
Annual Operation £
Maintenance Cost 977,000 935,000
Total Annual Cost $1,850,000 $1,561,000
Based on the Information available on CSO sludge generated In Milwaukee and
the four treatment schemes developed oreviously, cost estimates for satellite
treatment In Milwaukee were developed. The basis of costs and figures pre-
sented earlier In this chapter were utilized and the results are presented in
Table 43. It can be seen that hauling the stabilized only sludge to a land
application site (Alternate 4» Table 43} Is extremely expensive due to the
transportation costs. These costs Indicate that Alternative 3 or lime sta-
bilization followed by gravity thickening and land application may be the
most cost effective approach In Milwaukee. High costs of vacuum filtration
at several sites Indicate that use of this dewaterlng technique Is not cost
effective.
A comparison of the annual costs for all three approaches to handling CSO
sludge Is presented below:
Method 1 - Bleed/Pump-back
120 days - $1,561,000
36$ days - $1,264,000
Method 2 - Treatment at Parallel Dry-Weather Facilities
120 days - $1,850,000
365 days - $1,561,000
159
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TABLE 43. COST ESTIMATES FOR CSO SLUDGE HANDLING
BY SATELLITE TREATMENT - MILWAUKEE
Alternative
Number Element
1 Pumping
Storage
Lime StabM fzatlon
Gravity thickening
Vacuum filtration
Transportation
Landfill
Subtotal
\5% Contingency
TOTAL
2 Pump i ng
Storage
Lime Stabilization
Gravity Thickening
Vacuum Filtration
Transportation
Land Appl test Ion
Subtotal
15% Contingency
TOTAL
Capital Cost
$
1.3&XI06
0.426x106
1.1 93x1 O6
5. 11 2x1 O6
2.272x106
1.36xl06
0.426x106
1.193xl06
5.1 12x1 Q6
—
— -
Operation £
maintenance
cost
$ 55,000
223,000
24,000
185,000
60,000
•
$ 55,000
223,000
24,000
185,000
—
—
Annual cost
$ 170,000
120,000
259,000
125,000
617,000
130,000
252,000
$1,673,000
251,000
$1,924,000
1 170,000
120,000
259,000
125,000
617,000
130,000
86,000
$1,507,000
226,000
$1,733,000
-------
TABLE 43 (continued).
cr»
Alternative
Number
3
k
Element
Pumping
Storage
Lime Stabl 1 Izatlon
Gravity Thickening
Transportation
Land Application
Sub Total
15% Contingency
TOTAL
Pumping
Storage
Lime Stabilization
Transportation
Land Appl I cat ion
Sub Total
\S% Contingency
TOTAL
Operation fi
Capital Cost Maintenance
$ Cost Annual Cost
U3&XI06 $ 55,-DOO $ 170,000
1.42x10** -- 120,000
Q.426xl06 223,000 259,000
I.I93xl06 24,000 125,000
_ 490,000
137,000
$1,301,000
195,000
$1,496,000
I.36xlQ6 $ 55,000 $ 170,000
1.42x10^ -- 120,000
0.42x1 Q6 223,000 259,000
J, 400 ,000
249,000
$2,198,000
33Q,000_
$2,528,000
-------
Hethod 3 - Satellite Treatment (120 days)
Alternative 1 - 1,924,000
Alternative 2 - 1,733,000
Alternative 3 - 1,496,000
Alternative 4 - 2,528,000
It can be seen that the cost of bleed/pump-back Is less than other after-
natives when considered over 365 days, but It begins to exceed other
alternatives when, a shorter bleed/pump-^back period is established.
Treatment at parallel dry-weather facilities does not offer significant ad-
vantages over satellite treatment and when coupled with potential Interference
In plant operation and space limitations at Jones Island, this method becomes
Jess viable. Finally, the various alternatives chosen for satellite treatment
could be utilized without operating problems associated with bleed/pump-back
or parallel facilities. The costs are similar to other alternatives presented,
Therefore the most cost effective and least problematic approach at thfs time
seems to be satellite treatment using lime stabilization, storage, gravity
thickening and land application.
CSO SLUDGE HANDLING IN SAN FRANCISCO, CALIFORNIA
In San Francisco, the entire drainage area of 12,150 ha (30,000 aeres) Is
served by a combined sewer system. The average annual precipitation for the
area is 47.5 cm (18.7 In) and typically occurs on a monthly basis as shown
In Figure 30. It can be seen that very little precipitation occurs during
the summer months while the majority of the precipitation occurs from November
through April. If It Is assumed that 50 percent of this rainfall produces
combined sewer overflow, the annual volume of CSO for the city of San Fran-
cisco Is 28.8 million cu m (7,620 MG).
Presently, a dissolved air flotation CSO treatment demonstration unit Is lo-
cated in San Francisco. It has been reported that this unit will produce
a sludge volume equal to 0.6 percent of the CSO volume treated. The result-
ant sludge will have an average total solids content of approximately 2.2
percent. Other pertinent sludge characteristics are presented In Table 5.
Since this unit Is working In San Francisco and data Is available, it will
be assumed for this evaluation that all CSO Is treated using the dlssolved-
alr flotation process. The sludge data Indicates that San Francisco can
expect an annual,CSO sludge volume of l^xtO-3 cu m (46 MG) at 2.2 percent
solids or 3-9x106 kg (8.6x106 Ibs) of wet weather produced solids that
must be handled and disposed of. The metropolitan San Francisco area is
served by three separate primary sewage treatment plants with a total de-
sign capacity of 1,135,500 cu m/day (300 HGD). The three treatment sites
produce approximately 5.0x10* cu m/day (1.3 MGD) of sludge at 1.1 percent
solids, This results In 54,480 kg/day (120,000 Ibs/day) of solids to be
handled. The sludge Is gravity thickened, anaeroblcally digested, and vacuum
filtered to a solids concentration of about 28 percent before being disposed
of In a landfill or used as a soil conditioner. The present solids handling
facilities In San Francisco are operating at capacity (12).
J62
-------
i 3
«j
0*
O.
U.
O
(A
Ul
-l-p-T
JFMAMJJASONO
NONTH
MOTEJ In, x 2.5^ - on
Figure 30. Typical monthly distribution of precipitation
In San Francisco, California (7*))*
163
-------
ff complete CSO treatment Is achieved In the city, the yearly volume of CSO
sludge will represent a hydraulic Increase of 9.6 percent over the dry-
weather sludge volume presently being handled and an 18.8 percent Increase
on a dry solfds basis. The percentages calculated, however, are based on a
constant yearly flow of CSO sludge to the sludge handling facilities. Since
CSO events are Intermittent In nature and will occur with greater frequency
during certain times of the year, It would be Impossible to space the flow
of CSO sludge to the handling facilities over the entire year unless storage
facilities are employed. Therefore, the Impact of the CSO sludges has also
been calculated based on the following assumptions: no storage In the system,
a 72 hour period of CSO sludge bleed-back to the handling facilities, and
rainfalls of 1.3 and 0.5 cm (0.5 and 0.2 In) over the CSO area.
The 1.3 cm (0.5 In) rainfall over the CSO area will produce k.6x10-^ cu m
(1.2 x 106gal) of CSO sludge and 1.0x10$ kg (2.3 x IflS Ifas) of CSO solids.
Bleeding the residue Into the sludge handling facilities over three days re-
sults In additional flows of 1.5xto3 cu in/day (4.1x1Q2 MG) and S-SxIO1* kg/
day (7.6x10^ Ibs/day). These flows represent a 31 percent Increase In the hy-
draulic loading and a 6l percent Increase In the solids loading. Thus, the
Impact of the CSO sludges has Increased slanlfIcantly. The 0.5 cm (0.2 In}
rainfall over the CSO area will result In a 12 percent Increase In the hy-
draulic loading, and a 2k percent Increase In the solids loading over the
three day bleed-back period.
Based on the preceedlng calculations, It appears that the first considera-
tion In developing a method of handling the CSO sludge problem will be to
reduce the Impacts caused by the sporadic flows of the CSO Itself. This
could be achieved by storage of the CSO In conjunction with the CSO treat-
ment facility. Based on the yearly rainfall of 4?.5 cm (18.7 In), San Fran-
cisco can expect a yearly CSO volume of 28,840,000 cu m (7,620 MG), Year
round operation of a CSO treatment facility would require a treatment plant
capacity of 79,485 cu m/day (21 HGD).
The storage facility capacity based on the monthly ramfall variations
(Figure 30) is calculated on the next page. These calculations indicate a
maximum storage capacity of 11.4 x 10" cu m (3.0 x 10^ MG) required for the
system at the end of March. This value should then be Increased to protect
against the yearly fluctuations in rainfall amounts.
This volume, of course, would be for one storage facility serving the entire
city. Numerous storage facilities could be located throughout the city and
they could then feed a number of small CSO treatment facilities or one
79 x 103 cu m/day (21 MGD) central CSO treatment plant.
The treatment of 79x10 cu m/day (21 MGD) of CSO using the dlssolved-alr
flotation process would result In the generation of 4§Q cu m (126,000 gal)
per day of sludge at about 2,2 percent solids. Some of the data reported
from the San Francisco demonstration system has Indicated floated sludge con-
centrations of only 1000 to 2000 mg/1. The value of 2.2 percent solids for
the floated sludge being used Is based on samples taken at the demonstration
site and the reported values for floated sludge at other sites using the
dissolved-alr flotation process (12). Based on the 2.2 percent solids,
164
-------
10,600 kg/day (23,400 Ibs/day) of CSO solids will have to be handled and
disposed of from the CSO treatment site.
CSO Volumes Volume Treated Difference
10 cu m (HG) 10 cu m (MG) 10 cu m (MG)
Cumulative
Storage
10 cu m (HG)
November
December
January
February
March
April
Hay
June
July
Auqust
September
October
2.91 (770)
5.31 (1402)
5.95 (1573)
5.03 (1328)
4.23 (1117)
2.11 (558)
1.06 (281)
0.26 (69)
0.06 (16)
0.06 (16)
0.40 (106)
1.45 (383)
2.38 (630)
2.46 (651)
2.46 (651)
2,23 (588)
2.46 (651)
2.38 (630)
2.46 (651)
2.38 (630)
2.46 (651)
2.46 (651)
2.38 (630)
2.46 (651)
+0.53 (+140)
-2.84 (-1-751)
+3.49 (+922)
+2.80 (+740)
+1.76 (+466)
-0.27 (-72)
-1.40 (-370)
-2.12 (-561)
-2.40 (-635)
-2.40 (-635)
-1.98 (-524)
-1.0! (268)
0.53 (140)
3.37 (890
6.86 (1813)
9.66 (2553)
11.43 (3019)
11.15 (2947)
9.75 (2577)
7.63 (2016)
5.23 (1381)
2.82 (746)
0.84 (222)
0
The two available alternatives for handling the CSO sludge are handling at
the CSO treatment site or transporting It to the dry-weather plant and hand-
ling It with the exlstlnq or expanded dry-weather plant facilities. As
mentioned previously, the dry-weather sludqe handling facilities are opera-
ting at capacity and the addition of the CSO sludges would Increase the hy-
draulic loadings by 10 percent and the solids loadings by 19 percent.
The ftrst consideration would be to transport the sludge to the dry-weather
treatment plant by bleeding It back to the sewer system after the CSO event
Is over. However, due to the characteristics of the CSO sludge, the sludge
should not be handled with the processes used for the dry-weather plant. The
low volatile content of the sludge, 39.2 percent. Indicates that digestion
would be Ineffective. Therefore, If the solids are Introduced Into the
anaerobic digesters, they would Increase the solids and hydraulic loadings
and may not digest. This would result In reductions In volatile solids de-
struction and gas production. There Is also the possibility that the heavy
metals present In the CSO sludge could pose a toxic hazard to the biological
life In the digesters.
The dry-weather sludges are usually gravity thickened before they are pumped
to the digesters. The CSO sludge produced by the dlssolved-alr flotation
process can be expected to be over 2 percent solids, and, therefore, may not
require further thickening. If the CSO sludge Is bled back to the dry-weather
165
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plant, It will be diluted In the sewer system and, then, would have to be
re-thickened at the dry-weather plant. The sludge volumes would also fn-
crease the hydraulic loading on the gravity thickeners by 10 percent.
Based on the proceeding discussion, bleed-back of the sludge to the dry-
weather plant should not be attempted for the following reasons;
1. necessity to dilute and then re-thicken the solids,
2. Introduction of the low volatile solids Into the anaerobic
digesters will require valuable space and reduce digester
efficiency, and
3. the solids may pose toxic hazards to the anaerobic digesters.
By eliminating bleed-back of the CSO solids to the dry-weather plant, the CSO
sludge will have to be transported by tank truck If sludge handling Is to be
achieved at the dry-weather plant. This would require trucking 477 cu m
(126,000 gal) of sludge per day. Since the sludge Is already thickened It
could go directly to the vacuum filtration process. The vacuum filter fa-
cilities, of course, would have to be expanded to handle a solids loading
Increase of 19 percent. After vacuum filtration the CSO sludge cake could be
disposed of at the landfill along with the dry weather sludge. The dry-
weather plant now trucks approximately 203 cu m (7260 cu ft) of sludge cake
per day to the landfill. The CSO sludge, dewatered to 20 percent solids,
will Increase this amount by 26 percent to 256 cu m/day (9l*»3 eu ft/day).
Because the CSO sludge has not undergone anaerobic digestion, the sludge
should be limed to a pH of greater than 12 In order to stabilize It. This
could be accomplished just before vacuum filtration. The liming should In-
sure pathogen destruction before the sludge Is landfllled (35).
As the previous discussion Indicates, however, the applicability of bleed/
pump-back or treatment at additional facilities Is a questionable procedure,
at best. Considering the results of the total cost evaluation presented for
Milwaukee, It can be seen that only a small cost benefit can be achieved by
Implementing these two questionable processes. Therefore, detailed costs
have been prepared only for the alternatives with potential for handling CSO
sludge generated In San Francisco at six Individual sites throughout the
city. These costs are Included In Table M for the four sludge handling
schematics previously chosen applicable for CSO sludge treatment. It can be
seen from Table kk that the handling alternative Involving lime stabilization,
additional thickening and land application of the resultant sludge Is antici-
pated to be most cost effective of those Investigated. Further dewaterlng
does not appear to be feasible,
TREATMENT OF CSO SLUDGES IN KENOSHA, WISCONSIN
The entire drainage area for the city of Kenosha Is 3850 ha (9507 acres). Of
this total, 539 ha (1331 acres) or l4 percent are served by combined sewers.
The average annual precipitation for the area Is 77.5 cm (30,5 In). If It
166
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TABLE M. COST ESTJHATES FOR CSO SLUDGE
HANDLING BY SATELLITE OPERATION - SAN FRANCISCO
Alternative
Number Element
1 Pumping
Storage
Lime Stabil Izatfon
Gravity Thickening
Vacuum Filtration
Transportation
Landfill
" 1»ub Tota 1
IS& Contingency
TOTAL
2 Pumping
Storage
Lfme Stabilization
Gravity Thickening
Vacuum Filtration
Transportation
Land Appi i cat ton
Sub Tota!
15% Contingency
TOTAI
Capital Cost
$
I.53xl06
Q,50xlG6
7.67xl06
2.68xl06
0,588xI06
O.SOxlO6
7.67xl06
-»
_-
Operation £
Maintenance
Cost
$ 68,000
92,000
31,000
212,000
89,000
$ 68,000
92,000
31,000
212,000
— .
-.
Annual Cost
$ 197,000
50,000
13^,000
IS2*, 000
860,000
120,000
316,000
$1,831,000
275,000
$2,106,000
$ 197,000
50,000
13^,000
15MQQ
860,000
120,000
82,000
$1,596,000
239,000
$1,835,000
-------
TABLE M (continued).
00
Alternative
Number Element
3 Pumping
Storage
Lime Stabilization
Gravity Thickening
Transportation
Land AppI feat ion
Sub Total
15% Contingency
TOTAL
4 Pumping
Storage
Lime Stabilization
Transportation
Land Appl i cat Ion
Sub Total
151 Contingency
TOTAL
Operation 6
Capital Cost Maintenance
S Cost
I.53xl06 $ 68,000
0.588xlQ6
O.SOxlO6 92,000
1.45x10^ 31,000
—
__
l.53xlQ6 $ 68,000
0.58x10
O.SOxlO6 92,000
—
„.
Annual Cost
$ 197,000
50,000
134,000
15^,000
380,000
118,000
$1,033,000
155,000
$1,188,000
$ 197,000
50,000
134,000
1,000,000
194,000
$1,575,000
236,000
$1,811,000
-------
is assumed that 50 percent of this rainfall accounts for combined sewer over-
flow, the annual volume of CSO for Kenosha Is 2.1 x 10b cu m (550 MG).
In Kenosha, CSO treatment Is being achieved at a demonstration project by the
use of the contact stabilization process and data Is available concerning the
treatment of CSO using this process. For this reason, the Impact of CSO
sludges on the city of Kenosha will be based on complete CSO treatment using
contact stabilization.
The combined sewer overflow treatment system In Kenosha Is slqnlfIcantly
different from those discussed previously because it is located on the same
grounds as the existing conventional dry weather treatment plant. In fact,
since the system utilizes biological treatment It depends on the dry-weather
plant as a source of active blomass. Waste activated sludge from the dry-
weather treatment plant Is continuously fed through the CSO treatment system
stabilization tank, where It has a hydraulic retention time of approximately
five days before going on to flotation thickening. When the CSO treatment
system Is In operation, the contents of the stabilization tank are pumped to
a contact tank Instead of to thickening.
It has been reported (12) that the Kenosha contact stabilization process
will produce a sludge volume equal to 3.5 percent of the CSO volume treated.
The resultant sludge will have an average total solids concentration of 0.85
percent. Other characteristics of the sludge were previously presented In
Table 6. The sludge data indicates that Kenosha can expect an annual CSO
sludqe volume of 73-0x103 cu m (19 MG) at 0.85 percent solids or 6.2x105 kg
(1.4 x 10" Ibs) of wet weather produced solids that must be handled and dis-
posed of.
The conventional dry weather treatment plant at Kenosha Is a 8.7x10 cu m/day
(23 HGO) activated sludqe process. Waste'activated sludqe, approximately
300 cu m/day (83,000 gpd) at a solids concentration of 1.47 percent or 4.5x10
ka/day (10,000 Ibs/day) of solids, Is flotation thickened to about 5 percent
solids concentration before aoing on to anaerobic digestion. The digested
solids are then further dewatered by means of a filter press. The total
dally loading on the digesters, primary and waste activated sludge combined,
Is 190 cu m/day (50,000 gpd) resulting In a dry solids weight of 1.1x10^ kg/
day (2.4x10^ Ibs/day). The filter press is operated at less than capacity
and would be able to handle an additional solids load. The digesters, on
the other hand, are already at capacity and additional solids loadings would
require construction of additional digestion facilities.
The CSO treatment system presently located on the grounds of the Kenosha dry-
weather treatment plant has a capacity of 75*700 cu m/day (20 MGD). The
average flow rate during system operation has been found to be 6.1x10^ cu m
(16 HGO)(54). Assuming complete CSO treatment Is achieved, this means that
In an average year the treatment process will be operated 34 1/2 days. Of
course, some.form of storage will have to be provided In conjunction with
the CSO treatment system in order to detain flows in excess of the 75t700 cu
m/day (20 MGD) plant capacity.
In the Kenosha area, rainfall usually occurs from mld-Harch to mid-December,
169
-------
a total of nine months, with snow being the form of precipitation during the
other three months. During the period of rain there occurs about 50 CSO
events. Based on these assumptions, then, a CSO event can be expected to occur
every fifth day. On the average, each event will generate 42x1Q3 cu m {II MG)
of CSO and require 0.7 days of treatment process operation. This, then,
allows for 4,3 days of wet weather sludge bleed/pump-back to the dry-weather
plant solids handling facilities.
The 42xiQ3 cu m (11 KG) of CSO per storm event will generate 1^60 cu m
(385,000 qal) of sludge and 12x103 kg (27xt03 Ibs) of solids. Feeding this
sludge to the dry-weather plant flotation thickening unit over the next *».3
days results frt additional loadings of 340 cu m/day (fJQxIO3 gpd), an Increase
of 108 percent, and 2.8xlQ3 kg/day (6.3x1Q3 lb/day), an Increase of 63 percent,
Aoparently a very significant Impact can be expected.
The Increased solids due to the CSO sludge will also mean an Increased solids
loading to the anaerobic digesters of 26 percent and a hydraulic Increase of
30 percent. This could result In decreased digester efficiency.
Since the CSO treatment process Is located at the dry-weather plant, CSO
sludge handling can be accomplished on-slte. The two available alternatives
are to either handle the CSO sludge with separate parallel facilities or with
the existing and/or expanded dry-weather plant facilities.
The handling of the Kenosha CSO sludge will require a treatment scheme similar
to the dry-weather plant's process: thickening, stabilization, and dewaterlnp.
The primary consideration here Is that the dry-weather plant's anaerobic dl-
g'esters are presently operating at capacity, therefore, the use of anaerobic
digestion for the CSO sludge would require digester expansion to handle a 30
percent Increase in hydraulic loading and a 26 percent Increase In solids
loading. This construction would be very costly.
It Is possible that excess sludge produced by CSO treatment could be stabi-
lized by lime and this process Is therefore a viable alternative to anaero-
bic digestion. The use of lime stabilization also Indicates that gravity
thickening Is most appropriate, rather than flotation thickening, because
the lime treatment will greatly enhance the settling characteristics of the
s1udge.
It Is therefore Indicated that the CSO sludges should be handled by parallel
processes at the dry-weather plant dye to the present location of the CSO
treatment unit at this point. Final disposal of dry-weather sludge Is pre-
sently accomplished using land application, which may be most feasible. How-
ever, landfill will also be Investigated. The same four CSO sludge handling
alternatives have been evaluated for the biological sludge from Kenosha and
the results are presented In Table 45, The annual costs range from $205,000-
$462,000 for the various alternatives. As Indicated previously, the most
feasible approach appears to be lime stabilization and gravity thickening
followed by land application at an annual cost of approximately 5205,000.
However, when further consideration Is given to the specific circumstances at
170
-------
TABLE 45. COST ESTIMATES FOR CSO SLUDGE HANDLING
BY SATELLITE TREATMENT-KENOSHA
Alternative
Number Element
1 Pumping
Storage
Lime Stabilization
Gravity Thickening
Vacuum Filtration
Transportat ion
Landfill
Sub Total
151 Contingency
TOTAL
2 Pumping
Storage
Lime Stab! 1 ization
Gravity Thickening
Vacuum Fl Itration
Transportation
Land Appl ! cat I on
Sub Total
15% Contingency
TOTAL
Capital Cost
$
0.28xl06
O.I39xl06
0.085xl06
Q.25&XI06
l.28xI06
—
O.SOxlO6
0.284xl06
O.I39xl06
Q.QBSxtO6
0.256xi06
l.28xlQ6
—
_-
Operation S
Maintenance
Cost
$12,000
«•»
14,000
5,000
38,000
29,000
$12,000
—
14,000
5,000
38,000
—
-_
Annual Cost
$ 36,000
12,000
15,000
27,000
146,000
16,000
71,000
$323,000
48,000
$371,000
$ 36,000
12,000
15,000
27,000
146,000
16,000
16,000
$268,000
40,000
$308,000
-------
TABLE 45 (continued).
Alternative
Number Element
3 Pumping
Storage
Lime Stabilization
Gravity Thickening
Transportation
Land Appl J cat Son
Sub Total
15% Contingency
TOTAL
4 Pumping
Storage
Lime Stabilization
Transportation
Land Appl i cation
Sub Total
151 Contingency
TOTAL
Capital Cost
$
0,284x10
0.1 39x1 O6
0. 085x1 O6
0. 256x1 O6
—
__
Q.284x1Q6
0.1 39x1 O6
0. 085x1 O6
—
—
Operation £
Maintenance
Cost Annual Cost
$12,000 $ 36,000
12,000
14,000 15,000
5,000 27,000
60,000
28,000
$178,000
27,000
$205,000
$12,000 $ 36,000
12,000
14,000 15,000
260,000
79,000
$402,000
60,000
$462,000
-------
Kenosha, other variables must be discussed. One aspect Is that the land
application costs could be reduced since the cfty of Kenosha is presently
disposing of their dry-weather treatment olant sludge on private farms and
If this arrangement could be continued for the additional CSO sludge, there
would be no capital expense for land disposal fn alternatives 2-4. The
second factor fs that, as discussed previously, the dry-weather plant's
pressure ^Jlter has available, enough additional capacity to handle the CSO
sludge. cor the estimates In Table 45, a complete handling and disposal
system was set up to handle all the CSO sludge flows assuming no additional
capacities being available In the dry-weather plant. Vacuum filtration was
selected as the dewaterlnq method because It was felt that this method would
be most amenable for dewatering the heavily limed sludge resulting from the
lime stabilization process. For the specific case of Kenosha, Investigations
should be conducted to determine the ability to pressure filter the lime
sludge. If these tests show that pressure filtration will produce satisfac-
tory results, then, for Kenosha, the capital costs of vacuum filtration could
be eliminated from alternatives No. 1 and 2.
With these factors considered, the annual costs for alternatives 1 through 4
become:
01d New
Alt. 1 $371,000 $247,000
Alt. 2 308,000 171,000
Alt. 3 205,000 193,000
Alt. 4 462,000 456,900
Therefore, since additional dewatering capacity Is available, this process,
with land application using the existing dry-weather sludge disposal pro*-
cedure, seems to be very economically attractive for Kenosha.
WET WEATHER SLUDGE HANDLING FOR NEW PROVIDENCE, NEW JERSIY
In New Providence, the entire drainage area for the sewage system Is 985 ha
(2432 acres). There are no areas serviced by combined sewers but during
periods of wet weather, high flows are experienced because of Infiltration
Into the sanitary sewers. If these high flows are treated. New Providence
wlU experience increased solids production due to wet weather conditions
even though there are actually no combined sewer overflows.
The average annual precipitation for the area Is 109.0 cm (42.9 In). It
has been reported In the literature (9) that about 10 percent of this rain-
fall can be expected to appear as Increased flow In Infiltrated sanitary
sewers. Using these values, then, the annual volume of Increased flow due
to wet weather for the city of New Providence fs 1.1 x 10° cu m (280 MG).
There Is a demonstration treatment system employing the trickling filter
process In New Providence. The trickling filters are used to treat both
173
-------
the dry-weather flows and wet weather flows. The trickling filters are oper-
ated In series during dry weather and switched to parallel operation for high
flow rates generated by wet weather. The trickling filter removal efficiency
data Is available but the necessary sludge production data Is not. Therefore
the sludge production data required will be estimated based on the pollutant
removal efficiencies. The sludge estimates will then be used to assess the
Impact of wet weather sludges on the city of New Providence.
The following values have been reported (9) for the trickling filter process:
Dry Weather
Average Flow 2,044 —^ (0.5*1 MGD)
SS (Influent) IS'* mg/1
SS (primary effluent) 86 mg/l
SS (final effluent) 20 mg/1
BOD (primary effluent) 104 mg/1
BOD (final effluent) 23 mg/1
Wet Weather
Average Flow 14,989 —- (3.96 HGD)
SS (Influent) 109 mg/l
SS (primary effluent) 6k mg/I
SS (final effluent) 36 mg/l
BOD (primary effluent) 86 mg/l
BOD {final effluent) 39 mg/l
Based on the suspended solids removals achieved by primary sedimentation,
140 kg/day (300 Ibs/day) of sludge solids can be expected during dry weather
and 680 kg/day (1500 Ibs/day) during wet weather. Using a primary sludge
concentration of 5.5 percent solids, this results In a rate of (2.5 cu m/day)
(670 gal/day) during dry weather and 12 cu m/day (3000 gal/day) during
wet weather.
The production of secondary sludge Is based on suspended solids removal and
the production of 0,5 kg(lb) of solids per kg(lb) of BOO removed. During
dry weather, the sludge solids production by secondary treatment will be
220 kg/day (480 Ib/day) and 770 kg/day (1700 Ibs/day) during wet weather.
It has been reported that trickling filter sludges will vary from 5 to 10
percent solids depending on the time they are held In the filter (25). For
this reason, It Is estimated that the secondary sludge will be 7 percent
solids during dry weather (low flow) and 5 percent solids during wet weather
(high flow). These values result In the production of 3 cu m/day (800
gal/day) of secondary sludge during dry weather and 15 cu m/day (4000
qal/day) of secondary sludge during wet weather. Combining the primary and
secondary sludqes means the trickling filter will produce 6 cu m/day
174
-------
(1600 aal/day) of sludae at 6.3 percent solids during dry weather and 28
cu m/day (6200 qal/day) of sludqe at 5.2 percent sol Ids during wet weather.
The wet weather value represents 0.2 percent of the wet weather flow volume
treated. Some of the other sludqe characteristics based on samples taken
at the trickling filter site were qiven In Table 6 (12).
For the annual wet weather volume of 1 • I x ID*5 cu m (280 HG), New Providence
can expect an excess sludge volume of 2.1x1o3 cu m (5-6x105 gal.) at 5-2 per-
cent solids or l.lxlO^ kg" (2.5x105 lb) of wet weather produced solids that
must be disposed of.
As mentioned previously, the trickling filter operation also serves the city
of New Providence duclng dry weather. During drv weather the plant treats an
average flow of 2x1 (H cu m/day (0.5 HGD) and produces a 6.0 cu m/day (1600
gal/day) of sludge, primary and secondary, at 6.3 percent solids or 350 kg/
day (770 Ibs/day) of solids. There are no sludge handling facilities at the
trickling filter plant. The solids settling in the secondary clarifier are
pumped to the primary sedimentation tank where they settle out with the pri-
mary solids. This combined sludge Is then drained to a sewer which flows to
a larger sewage treatment plant downstream. Apparently the downstream treat-
ment plant has the capacity to remove and handle the solids produced at the
New Providence facility; and since the New Providence plant handles the entire
wet weather flow, no appreciable increase in flow will occur in. the future.
Therefore, the bleed/pump^back of both dry weather and wet weather sludges
from the New Providence facility to the downstream plant appears to be func-
tioning as planned and will continue to be used in the future. In this case,
then, there is no impact due to wet weather conditions in the sanitary sewers.
The Impact of the wet weather generated solids would be great, however, If
the plant were to construct sludge handling facilities. As presented pre-
viously, during dry weather the trickling filter plant can be expected to
generate 2,5 cu ni/day (550 gal./day) of primary sludge at 5-5 percent solids
and 3 cu m/day (660 gal./day) of secondary sludge at 7 percent solids.
Combining the two sludges gives 6 cu m/day (1600 gal./day) at 6.3 percent
solids or 350 kg/day (770 Ibs/day) of dry solids.
Any new sludge handling facilities must take into consideration the volumes
of sludge generated by wet weather. On an annual basis, wet weather flows
will generate a sludge volume of Z.lxlO^ cu m (5.6x1Q-> gal.) (primary plus
secondary) at approximately 5.2 percent solids or l.lxlQ^ kg (2.5xlo5 ibs)
of solids, if these sludge volumes can be bled/pumped-back to the sludge
handling facilities over an entire year, the additional loadings would be
6 cu m/day (1600 gal./day), a 100 percent Increase over the dry weather
flow, and 300 kg/day (660 Ib/day), an 86 percent Increase over dry weather.
If bleed/pump-back of the wet weather sludge fs not achieved over the entire
year, the impacts of the sludge will be much greater. The reported daily
dry weather flow is 2x10^ cu m/day (0.5 HGD) while during wet weather con-
ditions the average flow is 15x103 cu m/day (4 MGD). This wet weather flow
will generate a sludge flow of 28 cu m/day (7.3x10-* gal./day) and 1.4x10* kg/
day (3.1x10^ Ib/day). These flow rates are ^92 and *|Q6 percent, re-
I75
-------
speetfvely, above the daily dry weather flow rates.
Thus, even though the city of New Providence does not have a combined sewer
System, the Impact of wet weather generated solids in the sanitary sewer
,could be significant. If sludge handling facilities were to be constructed,
the wet weather flows would dictate capabilities 2 to 4 times greater than
those that would be required based on the dry weather flow rates.
Since there are no available sludge handling facilities at the New Providence
site, the same sludeje handling schemes were evaluated with respect to the
generated volume of wet weather sludge. The coits were developed as before
and based on a sludge volume of % cu m/day (9.4x10* gpd) at solids concentra-
tion of 5.2 percent. Therefore the only applicable alternatives involved
hauling the stabilized sludge directly to a land application site or de-
watering followed by landfill or land application. The cost estimates are
included in Table 46. It is indicated that stabilization followed by direct
land application of the sludge is the most cost effective approach for the
New Providence sludge handling. This alternative provides a srgnrfleant
cost advantage over the other methods, although it Is readily apparent that
any attempt at on-slte sludge handling is costly.
ECONOMIC IMPACT OF NATIONWIDE HANDLING AND DISPOSAL OF CSO TREATMENT SLUDGES
General
This evaluation Involved developing an approximation of the economic Impact
of handling CSO treatment residuals across the country. In order to accomp-
lish this task, the cities containing CSO areas were statistically evaluated.
Four specific areas were evaluated for two types of CSO treatment methods
(dissolved air flotation and contact stabilization). The same four sludge
handling schematics as previously Indicated were developed for both types
of sludges. All economic data was based on the same cost criteria as pre-
sented previously.
Basis of Eva1ua 11on
There were several aspects Involved In developing the necessary Information
for hypothetical cities across the United States. The first Involved choice
of CSO areas for evaluation. The next Involved establishing both the sludge
volume and characteristics so that the process equipment could be properly
sized,
To select the city size, the area served by combined sewerage systents In ur-
ban United States was obtained (75) and analyzed. The available data consis-
ted of combined sewerage areas serving the fifty states and Washington, D.C.
and more specifically included a tabulation of the combined sewerage areas
serving the urbanized areas (cities) of the country. A total of 248 urbanized
areas were covered with the combined sewerage areas ranging from none to
about 205,000 acres. Of the 248 urbanized areas for which data was available
128 of them were not served by combined sewerage systems. The remaining 120
urbanized areas had areas served by combined sewers ranging from 40.5 - 83,025
176
-------
TABLE 46. COST ESTIMATES FOR CSO SLUDGE HANDLING
BY SATELLITE TREATMENT-NEW PROVIDENCE
Alternative
Number Element
1 Pumping
Storage
Lime Stabilization
Gravity Thickening
Vacuum Filtration
Transportation
Landfill
Sub Total
I5t Contingency
TOTAL
2 Pumping
Storage
Lime Stabilization
Gravity Thickening
Vacuum Filtration
Transportation
Land App) (cation
Sub Total
15% Contingency
TOTAL
-— -
Capital Cost
$
O.I2xl06
O.OIOxlO6
O.Q28xl06
N/A
0.6l8xl06
—
O.I28xl06
O.I2xJ06
o.oigxio6
0.028xl06
N/A
O.filOxlO6
..
-.
Operation 6
Maintenance
Cost
$ Moo
__
2,000
N/A
12,000
—
11,000
$ 4,000
--
2,000
N/A
12,000
__
Annual Cost
$ H.OOO
2,000
Moo
M» •»
54,000
27,000
22,000
$133,000
20,000
$153,000
$ 14,000
2,000
4,000
-.
b4,000
27,000
9,000
$120,000
18,000
$138.000
-------
TABLE 46 (continued)
-j
00
Alternative
Number
3
N/A
4
Element
Pumping
Storage
Lime Stabilization
Gravity Thickening
Transportation
Land Appl i cat ion
Sub Total
15? Contingency
TOTAL
Pumping
Storage
Lime Stabi lization
Transportation
Land Appl i cat ion
Sub Total
I5l Contingency
TOTAL
Operation &
Capital Cost Maintenance
$ Cost Annual Cost
__
—
_,
--
„
--
N/A
O.J2xl06 $ 4,000 $14,000
Q.019xl06 — 2 000
Q.02BxIQ6 2,000 4,000
35,000
27.000
$82,000
12,000
$94,000
-------
ha (100-205,000 acres). Hie combined sewer area data for the 12U urbanized
areas noted above were examined and the following conclusions drawn:
I, The mean combined sewer acreage served was 2309 ha (5700 acres).
2. As mentioned previously, the areas served by combined sewers ranged
from 40.5 - 82,025 ha (100-205,000 acres). The following further
breakdowns were observed;
a. Fifteen cities (about 12,51) had combined sewer areas serving
less than 40.5 Na (1000 acres) each,
b. Fifty-seven cftles (about 47,51) had combined sewer areas
serving between 405-4050 ha (1000-10,000 acres) each.
c. Forty-two cities (about 35%) had combined sewer areas serving
between 4050 and 16,200 ha (10,000 and 40,000 acres) each.
d. Only six cftles (about 5t) had combined sewer areas greater than
20,250 ha (50,000 acres) each (San Francisco, CA; Cincinnati,
OH; New York, NY; St. Louis, HO; Detroit, Ml; and Chicago, IL),
From this Information It was established that four example areas could be
chosen and representative costs established. An area In each range was used
as follows;
a. 12.5% - 0-405 ha (0-1000 acres) CSO area choice: 203 ha (500
acres)
b. 47.51 - 405-4050 ha (1001-10,000 acres) CSO area choice; 2307 ha
(5700 acres)
c. 35% - 4050-16,200 ha (10,001-40,000 acres) CSO area choice:
10,118 ha (25,000 acres)
d, 5% - >16»200ha (>40,000 acres) CSO area choice: 24,300
(60,000 acres)
Once the size of the affected area was established, further assumptions were
made regarding the volume of CSO sludge generated. Two types of CSO treat-
ment sludges were considered to allow a range of costs due to varying residue
characteristics. One type was biological and contact stabilization sludge
was considered and the second type was physical/chemical so dissolved afr flo-
tation sludge was evaluated. The criteria listed In Table 4? were then ap-
plied to establish CSO sludge flow rates and characteristics.
Economic Results
Each of the CSO areas and resultant sludges were then evaluated with regard
to the costs for utilizing one of the four sludge handling alternatives:
Alternative I. Lime Stabilization •* Gravity Thickening •* Vacuum Filtra-
tion •* Landfill
2, Lime Stabilization •* Gravity Thickening -*• Vacuum Filtra-
tion •* Land Application
3. Lime Stabilization •* Gravity Thickening •*• Land Application
4. Lime Stabilization **• Land Application
179
-------
Table 47 ASSUMPTIONS FOR COST CALCULATIONS
CSO Volume
1. 50? of rainfall Is CSO
2. Average rainfall Is Q.9l4m/year (36'Vyear)
3. 60 storm events occur per year
CSO Sludge - Biological
1. 3.5% of CSO volume « sludge volume
2. Solids concentration Is 10,000 mg/l
CSO Sludge - Physical/Chemical
1. 0.61 of CSO volume - sludge volume
2. Solids concentration Is 27,500 mg/l
The results are presented In detail for each of the chosen CSO areas In
Tables 48-51. A comparison of the cost ranges for the city size Is summa-
rized In Tables 52 and 53. It can be seen that the cost for treatment of CSO
residuals can vary significantly depending upon the type of CSO treatment
used, the sludge handling schematic and the total volume of CSO to be treat-
ed. The overall annual cost ranges from $139/ha-$l*i03/ha ($56-$660/acre)
of CSO swerved area. When It is recalled that there are 1.2x10° ha
(3.0x10° acres) of area served by combined sewers throughout the country,
the economic Impact of treating CSO sludges nationwide could range from
$169,000,000 - $1,720,000,000 annually.
If Initial capital costs are evaluated, as Indicated In Table 53. this first
expense ranges from $4it7~$10»173/ha ($l8l-4l20/acre). These capital costs
assume an initial expenditure for the land which will be recovered when the
land Is sold. When considering the nationwide Impact with respect to Initial
capital costs, this could range from $5**8 x 106 - $12.5 x 10? to provide
sludge handling and disposal for all treatment residues.
180
-------
TABLE 48. COST ESTIMATES FOR 500 ACRE CSO AREA
Alternative
Number Element
1 Pumping
Storage
Lime StabI I Izatlon
Gravity Thickening
Vacuum Filtration
Transportation
Landfill
Sub Total
15S Contingency
TOTAL
2 Pumping
Storage
Lime Stabilization
Gravity Thickening
Vacuum Filtration
Transportation
Land Application
Sub Total
15? Contingency
TOTAL
Annual
Biological Treatment
$ 25,000
8,000
12,000
18,000
108,000
31,000
44,000
$246,000
37,000
$283,000
$ 25,000
8,000
12,000
18,000
108,000
31,000
19,000
$221 ,000
33,000
$254,000
cost
OIssolved-AIr
Flotation
Treatment
$ 19,000
13,000
6,000
13,000
74,000
25,000
27,000
$177,000
27,000
$204,000
$ 19,000
13,000
6,000
13,000
74,000
25,000
9,000
$159,000
24,000
$183,000
acres x 0.405 ** ha
181
-------
TABLE 48 (continued).
Alternative
Number Element
3 Pumping
Storage
Lime Stabilization
Gravity Thickening
Transportation
Land Appl i cat I on
Sub Total
151 Contingency
TOTAL
4 Pumping
Storage
Lime Stabilization
Transportation
Land Appl i cat ion
Sub Total
151 Contingency
TOTAL
Annual Cost
Biological Treatment
$ 25,000
8,000
12,000
18,000
42,000
182,000
$287,000
43,000
$330.000
$ 25,000
8,000
12,000
140,000
43,000
$231,000
35,000
$266,000
Dissolved-Afr
Flotation
Treatment
$ 19,000
13,000
6,000
13,000
30,000
11,000
$ 92,000
14.000
$106,000
$ 19,000
13,000
6,000
40,000
n.ooo
$ 91,000
i4,ooo
$105,000
acres x 0.405 a ha
182
-------
TABLE '{9. COST ESTIMATES FOR 5700 ACRE CSO AREA
A] ternat Ive
Number Element
1 Pumping
Storage
Lime Stabil fzatlon
Gravity Thickening
Vacuum Filtration
Transportation
Landfill
Sub Total
15* Contingency
TOTAL
2 Pump I rig
Storage
Lime Stabilization
Gravity Thickening
Vacuutn FI Itratfon
Transportation
Land AppJ Icatlon
Sub Total
15% Contingency
TOTAL
Annual cost
Biological Treatment
$ 104,000
51,000
108,000
102,000
375,000
90,000
247,000
$1,077,000
162,000
$1,239,000
$ 104,000
51,000
108,000
102,000
375,000
90,000
87,000
$ 9l7,ooo
138,000
$1,055,000
Qissolved-Ai r
Flotation
Treatment
$ 78,000
!7,ooo
58,000
54,000
229,000
38,000
100,000
$574,000
86,000
$660, OQO
$ 78,000
17,000
58,000
54,000
229,000
38,000
39,000
$513,000
77,000
$590,000
acres x 0.405 ° ha
133
-------
TABLE 49 (continued).
A| ternative
Number Element
3 Pumping
Storage
Lime Stab! I Ization
Gravity Thickening
Transportation
Land Application
Sub Total
15% Contingency
TOTAL
4 Pumping
Storage
Lime Stabilization
Transportation
Land Appl I cat I on
Sub Total
I5l Contingency
TOTAL
Annual cost
Biological Treatment
$ 104,000
51,000
108,000
102,000
375,000
140,000
$ 880,000
132,000
$1,012,000
$ 104,000
51 ,000
103,000
1,100,000
346,000
$1,709,000
256,000
$1,965,000
THsso7vecF-AJir
Flotation
Treatment
$ 78,000
17,000
58,000
54,000
60,000
46.000
$313,000
47,000
$360,000
$ 78,000
17,000
58,000
240,000
346,000
$739,000
110,000
$849,000
acres x 0.405 B ha
184
-------
TABLE 50. COST ESTIMATE FOR 25000 ACRE CSO AREA
Alternative
Number Element
1 Pumping
Storage
L i me Stabilization
Gravity Thickening
Vacuum Fl It rat Ion
Transportation
Landfill
Sub Total
151 Contingency
TOTAL
2 Pumping
Storage
Lime Stabilization
Gravity Thickening
Vacuum Filtration
Transportation
Land Application
Sub Total
15% Contingency
TOTAL
Annual cost
Biological Treatment
$ 322,000
141,000
451,000
354,000
1 ,025,000
450,000
432,000
$3,175,000
476,000
$3,651,000
$ 322,000
141,000
451,000
354,000
1,025,000
450,000
276,000
$3,019,000
453,000
$3,472,000
t>tssolved-Alr
Flotation
Treatment
$ 186,000
56,000
244,000
209,000
731 ,000
100,000
474,000
$2,000,000
300,000
$2,300,000
$ 186,000
56,000
244,000
209,000
731,000
100,000
141,000
$1,667,000
250,000
$1,917,000
acres x 0.405 a ha
185
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TABLE 50 (continued)
Alternative
Number Element
3 Pumping
Storage
lime Stabilization
Gravity Thickening
Transportation
Land Appl I cat ion
Sub Total
15% Contingency
TOTAL
4 Pumping
Storage
Lime Stabilization
Transportation
Land Appl 1 cat I on
Sub Total
151 Contingency
TOTAL
Annua 1
Biological Treatment
$ 322,000
141,000
1*51,000
354,000
1,800,000
456,000
$3,524,000
529,000
$4,053,000
$ 322,000
141,000
451,000
7,000,000
1,111,000
$ 9,025,000
1,354,000
$10,379,000
cost
DIssolved-Air
Flotation
Treatment
$ 186,000
56,000
244,000
209,000
1,000,000
258,000
$1,953,000
293,000
$2,246,000
$ 186,000
56,000
244,000
1,700,000
346,000
$2,532,000
380,000
$2,912,000
acres x 0.405 ° ha
186
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TABLE 51. COST ESTIMATES FOR 60,000 ACRE CSO AREA
Alternative
Number Element
1 Pumping
Storage
Lime Stabl ! Ization
Gravity Thickening
Vacuum Filtration
Transportation
Landfill
Sub Total
15? Contingency
TOTAL
2 Pumping
Storage
Lime Stabilization
Gravity Thickening
Vacuum Filtration
Transportation
Land Aoal Jc.it I on
Sub Total
15% Contingency
TOTAL
Annual cost
Biological Treatment
$ 287,000
328,000
1,056,000
630,000
2,199,000
900,000
1,572,000
$6,972,000
1,046,000
$8,018,000
$ 287,000
328,000
1,056,000
630,000
2,199,000
900,000
626,000
$6,026,000
904,000
$6,930,000
lllfssoJfved-Air
Flotation
Treatment
$ 600,000
126,000
209,000
832,000
941,000
190,000
1,015,000
$3,913,000
537,000
$4,500,000
$ 600,000
126,000
209,000
832,000
941,000
190,000
265,000
$3,163,000
474,000
$3,637,000
acres x 0.405 = ha
187
-------
TABLE 51 (continued)
Alternative
Number Element
3 Pump I ng
Storage
Lime Stabilization
Gravity Thickening
Transportation
Land Appl (cation
Sub Total
151 Contingency
TOTAL
4 Pumping
Storage
Lime Stab! 1 IzatJon
Transportation
Land Appl I cat I on
Sub Total
JSt Contingency
TOTAL
Annual
Biological Treatment
$ 287,000
328,000
1,056,000
630,000
4,000,000
1,043,000
$7,344,000
1,102,000
$8,446,000
$ 287,000
328,000
1,056,000
20,000,000
1,043,000
522,714,000
3,407,000
$26,121,000
cost
DIssolved-Air
Flotation
Treatment
$ 600,000
126,000
209,000
832,000
780,000
347,000
$2,894,000
434,000
$3,328,000
$ 600,000
126,000
209,000
3,400,000
677.000
$5,012,000
752,000
$5,764,000
acres x 0.405 *• ha
188
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TABLE 52. ANNUAL COST FOR CSO SLUDGE HANDLING
CO
Treatment ail tgrna_tl_y_e
Alternative 1:
Biological sludge
DAF sludge
Alternative 2:
Biological sludge
OAF sludge
Alternative J:
Biological sludge
DAF sludge
Alternative 4:
Biological sludge
OAF sludge
$/acre
500 acres
$283,000
204,000
254,000
183,000
330,000
106,000
266,000
105,000
$210-$660
S_jIze of CSQ area
n57bjO ¥cjresi 25,000 acnes 60,000 acnes
Cost in dollars
$1,239,000 $3,651,000 $8,018,000
660,000 2,300,000 4,500,000
1,055,000 3,472,000 $ 6,930,000
590,000 1,917,000 3,637,000
1,012,000 4,053,000 $8,446,000
360,000 2,246,000 3,328,000
1,965,000 10,379,000 26,121,000
849,000 2,912,000 5,764,000
$/ton of dry solids $347~$H40
$64-$345
$188-$483
$77-$4l5
$t93-$S8l
$162-$61Q
Acres x 0.405 * na
Tons x 0.907 " metric tons
-------
TABLE 53. CAPITAL COST INFORMATION* FOR CSO SLUDGE HANDLING
UJ
o
Size of CSO area
Treatment alternative
Alternative 1:
Biological sludge
DAF sludge
Alternative 2;
Biological sludge
DAF sludge
Alternative 3'
Biological sludge
OAF sludge
Alternative 4:
Biological sludge
OAF sludge
$/acre
$/ton of dry sol ids
500 acres
$2.06 x 10*
1 .49 x I0b
1.86 x lof
1.39 x IOB
0.74 x lof
0.53 x 10°
0.5* x 1o!
0.42 x 10°
$84Q-$412Q
$13*0- $8660
5700 acres
Cost
$8.43 x 10J?
5.37 x 10"
7.48 x lof
5.29 x 10
4.56 x lof
2.37 x 10°
2.36 x 10?
1,03 x 10°
$181-$1*.79
$S38-$2804
25,000 acres
In dollars
$22.54 x 10J?
16.94 x 10
20.86 x 10?
14.85 x 10d
H.48 x 1fl!
8.69 x 10&
10,68 x 10?
6.36 x 10&
$254- $902
$598- $20 18
fiOjOOO acres
$52.54 x 1o5
38.17 x 10°
46.76 x 10?
32,37 x 10°
34.07 x 10?
14.68 x 10b
26.36 x 10?
14. 49 x 10
$242- $876
$616-$1892
* All handling and distribution costs for land application were considered
operating only.
Acres x 0.405 * ha
Tons x 0.907 • metric tons
-------
SECTION IX
REFERENCES
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8. DELETE
9. Lager, J. A., and Smith, W. G., "Urban Stormwater Management and
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191
-------
12. Clark, H, J.» et al., "Handling and Disposal of Sludges from Combined
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18. "Recommended Standards for Sewage Works", Health Education Service,
Albany, New York, 1973.
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20. Burd, R. S., "A Study of Sludge Handling and Disposal", USEPA Report
No. EPA-17070- 05/68, BTIS-PB 179 514, May 1968.
21. McCarty, P. L., "Sludge Concentration-Needs, Accomplishments, and
Future Goals", Jour. Water Poll. Control Fed., 3|, 493 (1966).
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23. Maruyama, T., et a_1., "Metal Removal by Physical and Chemical Treat-
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24. "Toxic Materials Analysis of Street Surface Contaminants", Environ-
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NTIS-PB 224 677. August 1973.
25. Ghosh, M, M., and Zugger, P. D., "Toxic Effects of Hercury on the
Activated Sludge Process", Jour. Water PolJ^. Conjro^^JFejd^, 45_,
424 (1973).
192
-------
26. "Interaction of Heavy Hetals and Biological Sewage Treatment Pro-
cesses11, Environmental Health Series, Water Supply and Pollution
Control, US Public Health Service, May, 1975.
27. Dube, D. J., et a!.> "Polychlorlnated 8i-Phenyls in Treatment Plant
Effluents", Jour. Water Pot I. Control Fed. t 46., 966 (1974).
28. "Water Quality Criteria", Report of the National Technical Advisory
Committee to the Secretary of the Interior, FWPCA, Washington, D.C.,
April, 1968.
29. Sartor, J. D., and Boyd, G. B., "Water Pollution Aspects of Street
Surface Contaminants", USEPA Report No. EPA-R2-72-081, NTIS-P8 214 408,
November, 1972.
30. Babbitt, H. E., Sewage and Sewage Treatment, John Wiley and Sons,
Inc., New York, New York, 1953.
31. Tarvln, D., "Metal Plating Wastes and Sewage Treatment", Sewage
and Industrial Wastes, 28, 1371 (1956).
32. Morrison, S. M.' and Martin, K. L., Lime Disinfection of Sewerage
Bacteria at Low Temperature, paper presented at the International
Symposium on Research and Treatment of Wastewaters In Cold Climates,
Univ. of Sakatchewan, Saskatchewan, Canada, August, 1973.
33. Rlehl, M. L., Welser, H., Rheins, B. T., Effect of Lime-Treated Water
on Survival of Bacteria, Journa1 AmerIcan Water Works AssoclatIon,
44, 5» 466-470, May, 1952.
34. Farrell, J. B., Smith, J. E.» Jr., Hathaway, S. W., Deen, R, B.,
Lime Stabilization of Primary Sludges, Journa 1^jrfPCF;, 46, 1, 113-122,
January, 1974.
35. Counts, C. A., and Schuckrow, A. J., "Lime Stabilized Sludge: Its
Stability and Effect on Agricultural Land", EPA Report No. 670/2-75-012,
NTIS-1B 241 809, April 1975.
36. Metcalf and Eddy, "Water Pollution Abatement Technology, Capabilities
and Cost", National Commission on Water Quality, Report No. PB-250
690, March 1976.
37- USEPA, "Guidelines for the Land Disposal of Solid Wastes", Federal
Register; 40 CFR, 241.
38. USEPA, "Municipal Sludge Management Environmental Factors", Proposed
Technical Bulletin, MCD-28, June 1976.
39. Sanitary LandfMj Facts, US Department of Health, Education and
Welfare, 1970.
193
-------
40. Battelle Memorial Institute, "Municipal Sewage Treatment - A Comparison
of Alternatives", Report prepared for CEQ, Contract EQC 316, February,
1974.
41. Sullivan, R., etal.^ "The Swirl Concentrator as a Grit Separator
Device", USEPA Report No. EPA-670/2-74-026, NTIS-PB 233 964
June 1974.
42. Smith, J. E., and Roaenkranz, W. A., "Municipal Sludge Management
Research Program In the U.S.A.", Presented at US/USSR Seminar,
Moscow, USSR, May 1975.
43. Metcalf and Eddy, "Water Pollution Abatement Technology Capabilities
and Cost", National Commission on Water Quality PB-250 690
1976.
44. "Pretreatment and Ultimate Disposal of Wastewater Solids", Proceedings
of Research Symposium, Rutgers University, May 1974,
45. Pound, C. E. and Crltes, R. W., "Wastewater Treatment and Reuse by
Land Application", USEPA Report No. EPA-660/2-73-006, Volumes 1 and
II, August 1973.
46. EPA Technology Transfer, "Land Treatment of Municipal Wastewater
Effluents", USEPA Report No. EPA-625/1-77-008, October 1977.
4?. Metcalf and Eddy, Inc., "Evaluation of Land Application Systems",
USEPA Report No. EPA-43Q/9-75-001, March 1975.
48. Pounds, C. E,, Crltes R. W., and Grlffes, D. A,, "Costs of Wastewater
Treatment by Land Application", USEPA Report No. EPA-430/9~75~003,
June 1975.
49. US Environmental Protection Agency, "Manual for Evaluating Public
Drinking Water Supplies", p. 4-12, 1971; Updated with "Proposed
Primary Drinking Water Regulations", June 1975.
50. Dardos, L. L., et__a1., "Renovation of Secondary Effluent for Reuse
as a Water Resource", USEPA Report No. EPA-660/2-74-016, NTIS-PB-234
176, February 1974.
51. Environmental Protection Agency, "Alternative Waste Management
Techniques for Best Practicable Waste Treatment", Report No.
430/9-75-013, October 1975.
52. Morris, C. E., and Jewell, W. S., "Regulations and Guidelines for
Land Application of Wastes - A 50 State Overview", Paper presented at
the 8th Annual Cornell University Agricultural Waste Management
Conference, Rochester, New York, April 1976.
194
-------
53. Great Lakes - Upper Mississippi River Board of State Sanitary
Engineers, "Recommended Standards for Sewage Works", Addendum No.
2 - Ground Disposal of Wastewaters, April 1971.
51*. Whiting, D, M,, "Use of Climatic Data In Dosing of Soils Treatment
Systems, "USEPA Report No. EPA-660/2-75-018, July 1975-
55- Thomas, R. £., "Fate of Materials Applied", Paper Presented at
Conference on Land Disposal of Wastewaters, Michigan State
University, December 1972.
56. Stevens, R. M., "Green Land-Clean Streams: The Beneficial Use of Waste
Water Through Land Treatment", Center for the Study of Federalism,
Temple University, Philadelphia, PA, 1972.
57. Zimmerman, J. P., Irrigation, John Wiley and Sons, Inc., New York,
New York, 1966.
58. "Handbook", Rain Bird Sprinkler Hanufacter Corporation, Glendora, GA
1971.
59- Demi rj Ian, Y. A., "Design Seminar for Land Treatment of Municipal
Wastewater Effluents: Muskegon County Wastewater Management System",
USEPA Technology Transfer, April 1975.
60. Department of Natural Resources, "Guidelines for the Application of
Wastewater Sludge to Agricultural Land In Wisconsin", Technical
Bulletin No. 88, Madison, WI 1975.
61. Cornell University, "Land Application of Wastes - An Educational
Program", Workshop sponsored by EPA, May 1976.
62. Sopper, W. E., "Crop Selection and Management Alternatives -
Perennials11, Proceedings of Joint Conference on Recycling Municipal
Sludges and Effluents on Land, University of Illinois, July 1973-
63. Walker, J. M., "Trench Incorporation of Sewage Sludge", Municipal
Sludge Management, USEPA and ASCE, June
64. Hanson, R. L., and Merritt, C. A., "Land Application of Liquid
Municipal Wastewater Sludges", Jour . Water Pol 1 . Control Fed . , kj,
20, 1975.
65. Chaney, R. L., "Recommendations for Management of Potentially Toxic
Elements in Agriculture and Municipal Wastes", In National Program
Staff, Factors Involved In Land Application of Agricultural and
Municipal Wastes, Agriculture Research Serv tee. Soil, TJater' and Air
Services, USDA, Beltsvlile, Maryland, pp 97-120,
195
-------
66. Jewell, W. A., "Organic Assfmulation Capacities of Land Treatment
Systems Receiving Vegetable Processing Wastewater", 31st Industrial
Waste Conference, Purdue University, West Lafayette, IN 1976.
67. Gulp, G., "Design Seminar for Land Treatment of Municipal Wastewater
Effluents: Example Comparisons of Land Treatment and Advanced Waste
Treatment", USEPA Technology Transfer, April 1975.
68, Burd R. S., "A Study of Sludge Handling and Disposal", USEPA Report
No. EPA-17070—05/68, NT1S-PB 179 511*, Hay 1968.
69. Building Construction Cost Data, 1976, Robert Snow Means Company,
34th Annual Edition, p. 18*1.
70. US Environmental Protection Agency, Office of Water Program Operations,
Municipal Construction, Division, Sewage Treatment Plant and Sewage
Construction Cost Indexes, 1976.
71. Ehllch, W. F., "Economics of Transport Methods of Sludges", Presented
at the 3rd National Conference on Sludge Management, Disposal and
Utilization, Miami, FL, December 14-16, 1976.
72. Wolf, T. F,, "Sludge Handling Facilities-Sewerage Commission of the
City of Milwaukee", Inter-Department Memorandum, June 12, 1975-
73« Personal Communication, Mr. Frank Munsey, Process Supervisor Engineer -
Milwaukee Metropolitan Sewerage District to Mrs. Kathryn Hulbregtse,
Envfrex.
71*. Llnsley Jr., R. K., etrJalv Hydrology for_EngIneers, McGraw-Hill
Books Co., New York, Mew York, 1958.
75. Heaney, J. F,, et_aj_,» "Nationwide Evaluation of Combined Sewer Over-
flows and Urban Stormwater Discharges, Vol. II: Cost Assessment and
Impacts," USEPA Report No. EPA-600/2-77-064(b), NTIS-PB 266 005, March
1977.
76. SulHvan, R. H., et_aj_., "The Swirl Concentrator as a Grit Separator
Device," USEPA Report No. EPA-670/2-74-026, NTIS-PB 233 964, June 1974.
77' EPA Technology Transfer, "Swirl Device for Regulating and Treating
Combined Sewer Overflows," USEPA Report No. EPA-625/2-77-012, 1977-
78. Sullivan, R. H., e_t a 1., "Field Prototype Demonstration of the Swirl
Degritter," USEPA Report No. EPA-6QG/2~77-l85, NTIS-PB 272 668,
September 1977.
196
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing}
1 REPORT NO
EPA-6QO/2-77-053b
3 RECIPIENT'S ACCESSION«NO,
4 TITLE AND SUBTITLE
HANDLING AND DISPOSAL OF SLUDGES FROM
COMBINED SEWER OVERFLOW TREATMENT
Phase iI - impact Assessment
5 REPORT DATE
December 1977 (Issuing Date)
6 PERFORMING ORGANIZATION CODE
? AUTHOR(S)
Kathryn R. Huibregtse, Gary R. Morris, Anthony
Geinopolos and Michael J. Clark
8, PERFORMING ORGANIZATION REPORT NO
9 PERFORMING ORGANIZATION NAME AND ADDRESS
Envi'ronmental Sciences Division
Envfrex Inc. (A Rexnord Company)
5103 West Beloit Road
Milwaukee, Wisconsin 53214
10 PROGRAM ELEMENT NO.
1BC6H
NO.
68-03-0242
12, SPONSORING AGENCY NAME AND ADDRESS
Municipal Environmental Research Laboratory—C?n.,OH
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Final, 2/74-2/76
14 SPONSORING AGENCY CODE
EPA/600/14
IS SUPPLEMENTARY NOTES
See also Phase I, EPA-600/2-77-053a, NT IS PB-270 212
Project Officer; Anthony N. Tafuri, Phone: (201)321-6679, Ext. 6679
(8-3^0-6679)
16 ABSTRACT
This report documents the results of an assessment of the effort that the United
States will have to exert In the area of sludge handling and disposal if, in fact,
full-scale treatment of combined sewer overflows is to become a reality. The results
indicate that nationwide an average yearly sludge volume of 156 x 10^ cu m (41.5 x
gal.) could be expected from CSO if complete CSO treatment were achieved.
Evaluation of the effect of bleed/pump-back of CSO sludge on the hydraulic, solids
and/or organic loadings to the dry-weather plant indicated that overloading would
occur in most instances. The most promising treatment trams were found to include
possible grit removal, lime stabilization, optional gravity thickening, optional
dewatering and land application or landfill. Land application systems can be con-
sidered as viable alternatives for CSO treatment and disposal.
Costs for overall CSO sludge handling depend on the type of CSO treatment process,
volume and characteristics of the sludge and the size of the CSO area, among other
considerations. Estimates indicate that first investment capital costs range from
$447-10,173/ha ($!8l-4l29/ac) with annual costs of $!39-l630/ha ($56-660/ac).
17.
K.6V WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b IDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
Combined sewers
Sludge
Sludge disposal
Thickening
Dewatering
Lime stabi1ization
Land application
Bleed/pump/back
Sludge characterization
Sludge treatment
13B
19 SECURITY CLASS (This Report)
UNCLASSIFIED
18, DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
21. NO OF PAGES
209
20 SECURITY CLASS (Tilts page)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
197
»u,s«rauiyDffPHKnnc[>mei.!)7t— 7S7-
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