1977
DESIGN SEMINAR HANDOUT
Sludge Treatment and Disposal
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U.S. Environmental Protection Agency
Environmental Research Information Center
Technology Transfer
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LNViKCf'MENTAl PRQTECPOfl
*i J. 013317
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1977
US EPA
Headquarters and Chemical Libraries
EPA West Bldg Room 3340
Mailcode 3404T
1301 Constitution Ave NW
Washington DC 20004
202-566-0556
DESIGN SEMINAR HANDOUT
Sludge Treatment and Disposal
U.S. Environmental Protection Agency
Environmental Research Information Center
Technology^Transfer *'
.:,VL'iRi
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TABLE OF CONTENTS
Introduction by page
Donald Ehreth i
SESSION I
"SLUDGE PROCESSING"
"Stabilization and Disinfection of Wastewater Treatment
Plant Sludges" by Richard T. Noland and James D. Edwards xi
"Review of Conditioning, Thickening and Dewatering of
Sludge" by John R. Harrison 68
SESSION II
"CONVERSION AND PRODUCT RECOVERY SYSTEMS"
"Anaerobic Digester Gas, Solar Energy and Sludge Composting
in Municipal Wastewater Treatment" by G. M. Wesner 120
"Chemical Fixation of Wastes" by Robert E. Landreth and
Jerome L. Mahloch 178
SESSION III
"PRINCIPLES OF LAND APPLICATION OF SLUDGE"
"Introduction to the Principles of Land Application of
Sludge" by Bruce R. Weddle 195
"A Preliminary Assessment of the Effects of Subsurface
Sewage Sludge Disposal on Groundwater Quality" by
Dale C. Mosher 210
"Principles of Land Application of Sewage Sludge" by
L.E. Sommers 228
11
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INTRODUCTION
By Donald J. Ehreth, OALWU, Washington, D. C.
Of the utilization/disposal options available for sludge, each has
its own specific set of environmental problems. In order to implement
any policy, resolution to a number of problems that presently inhibit
sludge management must be developed. These problems can be summarized
and categorized into four general areas of research needs:
- Public Health Issues
Technological Factors
- Intermedia Issues
- Social/Economic/Institutional Factors
The Environmental Protection Agency's (EPA) sludge management
research and development program encompasses four major technical areas:
processing and treatment, utilization, disposal, and health and ecological
effects. The primary objective of the program is to develop new and
improved technology and management schemes which will enable communities
to solve problems associated with the residues or byproducts of wastewater
treatment in a cost effective and environmentally acceptable manner.
The present stateoftheart provides adequate (but expensive) capability
to dewater sludges. Incineration practice is well established with
exception of the potential impact of air emissions on health and ecology.
However, coincineration (e.g., sludge plus solid waste) and pyrolysis
technology is just emerging. Controversy continues both within and
outside the Agency with regard to the environmental acceptability of
applying municipal sludges to the land. This is especially true for
agricultural uses. Heavy metals (especially cadmium) complex organics
and microbiological contaminants are the constituents of primary concern.
Specific examples of technological gaps presently existing are:
- Cost of sludge processing and disposal is a major factor in
wastewater treatment.
- Methods of converting sludge to beneficial byproducts are
in the embryonic stages.
- Limited confidence exists in the efficacy of local industrial
pretreatment programs for metals removal and methods for monitoring
their effectiveness.
- Relative risks associated with land application need to be
established with greater precision.
Varying climatic and soil conditions as well as varying sludge
composition require evaluation for a variety of sludges with
optimum combinations of soil and vegetation.
- Methods for removing toxicants at the treatment plant are in the
development stage; application is impeded because of economics
of technology.
ill
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Processing and Treatment
Sludge must undergo some processing or treatment to prepare it for
ultimate disposition.
The goal of processing and treatment R&D is to produce technology
alternatives which can be used to prepare the sludge for application to
the land or for one of the conversion processes so that the total cost
of handling or disposal is minimized.
Implementation of the program is focused on the following objectives:
- Evaluate the efficacy of pretreatment as an option to minimize
toxicants in sludge.
- Characterize the nature of, and the dewatering properties of,
"new" sludges using existing, upgraded and new technology.
- Develop hardware capable of producing a substantially drier
sludge cake.
- Develop and define performance of existing and new processes
for stabilizing sludge (anaerobic digestion, autothermal
thermophilic aerobic digestion, composting, etc.).
- Investigate ways to minimize energy consumption while simultaneouly
maximizing fuel production (activated carbon enhancement, solar
heating, etc.).
- Determine cost and environmental impact of sludge processing
systems.
- Provide guidance on technology for disinfection (up through
sterilization) of sludge.
Conversion Processes
This part of our research program has been divided between efforts
devoted to upgrading conventional incineration and tasks oriented toward
development of new processes.
Current program objectives directed to meeting these needs include
several projects, ongoing and planned to:
- Develop techniques for substitution of more abundant, less
costly supplemental fuels such as coal and solid wastes
(incineration and co-incineration).
- Develop processes and hardware for pyrolysis, co-pyrolysis
and starved-air combustion.
- Characterize emissions to determine levels of potential
pollutants (gaseous, liquid, solid) contained in emissions
from sludge conversion facilities.
IV
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Establish the "least cost" approaches to sludge conversion
to the satisfaction of administrators, technologists and the
general public.
- Evaluation of cementation processes and other beneficial use
alternatives.
Land Application - Management
Our objective relating to landapplication management is to develop
methods and technology to control the transformation and/or movement of
pollutants through the soil, plants, groundwater, and human food chain.
The function of R&D associated with the health and ecological area is to
analyze, evaluate, and interpret the data for purposes of establishing
safe loading rates.
We anticipate that accomplishment of the primary objectives will
result in the establishment of management schemes for a variety of
sludges with optimum combinations of soil and vegetation. Practices can
then be defined for applying sludge to the land for purposes of reclaiming
marginal or sub-marginal land, agricultural uses for both food and
fiber, and landfill disposal.
Health Effects
The difficulty in resolving this issue is that data which will
permit a definitive evaluation and decision regarding the significance
of sludge in human food chain impact do not exist to the satisfaction of
the several scientific disciplines involved. EJPA is, therefore, working
cooperatively with other Federal agencies, particularly USDA, and FDA,
to develop the information required to resolve the issue. Information
developed by others, notably universities, State agencies and municipalities
is also being obtained.
Some of the current work directed to this issue includes:
Evaluation of current knowledge of potential health effects.
- Determine viral contamination of ground and surface water
of a land reclamation site.
- Developing methods for isolating viruses and-chemicals.
- Characterize type, quantity and biological persistance
of biologicals, trace metals, and other organic and inorganic
substances in the environs of a sludge disposal site.
- Determine the potential of biologicals, metals, and organic
substances entering the human food chain when digested sludge
is used as a fertilizer.
- Study of heavy metal uptake in beef animals grazed on sludge
amended pasture.
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Being planned for the ensuing years are studies related to health
effects of trace metals, persistent organics and pathogens when sludge
is applied to the land.
We also plan to evaluate potential environmental impacts from
incineration, composting and pyrolysis.
Other Activity
Additional activity is underway in our Technology Transfer Program.
At least four major seminars are planned for FY 77. In FY 78, we plan
to expand on these and complete state-of-the-art documents in sludge
treatment, processing and disposal.
We have initiated an effort to centralize the information on analytical
testing methods and in FY 78 to do the same for site monitoring practices.
Initially, both of these efforts will rely on published data and procedures;
ultimately our goal is to standardize the test procedures and develop
methods to fill the gaps.
Funding History
Figure I illustrates the sludge management R&D funding since 1969.
This does not include funds dedicated for health and ecological effects
research, nor does it include in-house research resources. The latter
however ranged between $500K per year to $600K per year, basically man-
power resources.
In fiscal years (FY) 1974 through 1977 the budget of Health and
Effects research area ranged from 0 dollars to about $620K.
The sludge technological research and development budget for FY
1977 is $2.325 million. Table I summarizes the funding actions since FY
75. Over the past 3 or 4 years, approximately 20-30% of the municipal
wastewater treatment technology R&D budget has been devoted to the
municipal sludge program. There has been a shift of emphasis from
dewatering studies to studying the options for ultimate disposal. In FY
78 we plan to emphasize pyrolysis and compost related studies to provide
planners and design engineers with the operating and economic data
necessary to implement these technologies.
Land application studies will be expanded to monitor the fate and
effects of the organics and pathogenic organisms in the soil/plant
system to compliment our data bank on heavy metals.
VI
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Table I. Major Projects Funded in Municipal Sludge
Technology & Health R&D Programs
Task Description
Funding Level
Processing & Treatment
a. Disinfection/Stabilization
(Includes irradiation
and composting)
b. Dewatering
c. Metals Extraction Processes
d. Heat Treatment
e. Engineering, economic,
sociological evaluations,
and planning documents
(EESE, GD)
Conversion Processing
a. Fuel substitution
b. Pyrolysis
c. Non-thermal Processes
d. EESE, GD
e. Environmental Effects
Utilization on Land
a. Agricultural Land
b. Renovation of Improverished
Land
c. Non-Food Crops
d. Disposal
e. EESE, GD
Other Projects
In-House
Sub Total
FY 75
$665K
265
-
138
—
380
205
450
8
—
231
100
78
50
—
_
510
$3,080K
FY 76
$300K
120
155
190
—
350
100
-
—
526
100
78
82
50
- 89
630
$2,770K
Proj ected
FY 77
$291K
-
100
50
285
-
61
-
200
416
100
-
50
75
132
565
$2,325K
Health
68K
558K
620K
Total
$3,148K
$3,328K
$2,945K
VI1
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In addition to our own program,'the construction grants program has
funded approximately $11.0 million dollars worth of Step I planning
grants associated with sludge processing treating, conversion and/or
land application. One of the most comprehensive of these is the project
undertaken by the Los Angeles - Orange County Metropolitan area (LA/OMA).
The purpose of that project is to develop a regional sludge management
plan for the metropolitan area. Nearly $2.0 million dollars have been
allocated for a myriad of studies.
Coordination Efforts
At the Federal level, EPA, in addition to FDA and USDA, is cooperating
with Energy Research and Development Agency (ERDA); Bureau of Mines
(ERDA); Corps of Engineers, National Science Foundation and the Council
on Environmental Quality. In most cases EPA is providing funding to
supplement the budgets of the other Federal organizations.
The interagency agreements with ERDA focus on pyrolysis and treatment
technology (use of reactor waste products to provide gamma radiation and
heat to disinfect the sludge). With EPA assistance, USDA is conducting
research on management practices of land application (trenching, composting,
spreading, etc.), and effects of various loading rates on plant life.
FDA projects are focusing on the impact of trace metals on the human
food chain through the production of crops and meats grown on land to
which sludge has been applied. Evaluation of the uptake of metals in
the crops and in animals grazed on land to which sludge has been applied
is part of this effort.
In addition to EPA, and the agencies participating directly with
EPA, several other agencies and organizations are studying sludge management
problems. These include the National Science Foundation (NSF); National
Academy of Sciences (NAS); through the National Research Council; General
Accounting Office (GAO); an interagency committee including EPA, USDA,
FDA, land grant colleges and universities.
The NSF program is closely coordinated with our own. They have at
least six projects on-going related to hardware development, virology
experiments and economic modeling. Their program mission is oriented to
funding higher risk projects than our own. Consequently, they plan to
evaluate the efficacy of disposing of raw sludge that has only been
subjected to disinfection before being injected into the soil. Both
concepts are based on projects funded earlier by NSF.
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FIGURE 1
MUNICIPAL SLUDGE
MANAGEMENT PROGRAM
EXTRAMURAL FUNDING
H-
X
oe-
69 70 71
$M 0.5 0,5 0.5
2.6* 2.1** 1.76
* Includes A $1.6 Million Dollar Congressional Supplement
** Includes A 3 Month Fiscal Year Transition Period Add on Of $350K
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"STRBILIZATICK £ND DISINFECTION
OF KASTEWKEER TREATMENT PLWflT SLUDGES"
U. S. Environmental Protection Agency
Technology Transfer
by
Richard F. Nolard, P.E.
Janes D. Edwards, P.E.
Burgess & Niple, Limited
Consulting Engineers
5085 Reed Road
Columbus, Chio 43220
This study was conducted in cooperation with the National Environmental
Research Center, U. S. Environmental Protection Agency, Cincinnati, Ohio 45268
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INTRODUCTION
Sludge constitutes the most significant by-product of wastewater treat-
ment; its treatment and disposal is perhaps the most complex problem which
faces both the designer and operator. Raw sludge contains large quantities
of microorganisms, mostly fecal in origin, many of which are pathogenic and
potentially hazardous to humans. Sludge processing is further complicated
by its variable properties and relatively low solids concentration. Solu-
tions have long been sought for better stabilization and disposal methods
which are reliable and economical and able to render sludge either inert or
stable.
The purpose of this report is to present a review of stabilization and
disinfection methods for municipal wastewater treatment plant sludges.
Particular emphasis is on lime stabilization. Other unit processes which
are discussed include anaerobic and aerobic digestion, chlorination, heat
treatment, flash drying, long-term lagooning, and irradiation.
A case history of lime stabilization is presented which includes
capital and annual operation and maintenance costs; chemical, bacterial, and
pathological properties; land application techniques; and design considera-
tions. A comparison of the performance, capital and annual operation and
maintenance costs for lime stabilization and anaerobic digestion have also
been included.
The report is intended to serve as a guide to designers and operators
during the evaluation of sludge treatment and disposal alternatives as a
result of the need to:
1. Provide alternate means of sludge treatment during the period when
existing sludge handling facilities, e.g., anaerobic or aerobic
digesters, are out of service for cleaning or repair.
2. Supplement existing sludge handling facilities, e.g., anaerobic or
aerobic digesters, incineration or heat treatment, due to the loss
of fuel supplies or because of excess sludge quantities above
design.
3. Upgrade existing facilities or construct new facilities to improve
odor, bacterial, and pathogenic organism control.
Trends for ultimate sludge treatment and disposal for the period 1970-
1985 have been summarized as shown in Table 1. By 1985, at least 75 percent
of all sludges produced will require stabilization by some method other than
incineration.
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Table 1
TRENDS IN DISPOSAL OF MUNICIPAL WASTEWATER SLUDGE AND
RELATIONSHIP BETWEEN SLUDGE DISPOSAL METMUD AMU PROibtJJJSKa SlEJb'b'1
Percent of Total
Disposal Method
Ocean
Landfill
Utilized on Land
Incineration
Lagoon
1972
15
35
20
25
5
1985
0
40
30
25
5
Stabilization
Needed
Yes
Yes
Yes
No
Yes
Dewatering
Needed
No
Yes
No
Yes
NO
Stabilization Method (1)
An.
F
F
F
O
F
Aer.
F
0
F
N
0
Heat
N
0
0
0
R
Chemical
N
0
R
N
R
K)
(1)
F = frequently vised; 0 = occasionally used; R = rarely used; N = not used.
*Portions from Farrell and Stern
(1)
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Farrell ard Stern ^ ' have reported the following attenuation effects
for various well conducted processes for stabilizing wastewater treatment
sludges.
Table 2
ATTENUATION EFFECT OF WELL CONDUCTED PROCESSES,,.
FOR STABILIZING WASTEWATER TREATMENT SLUDGES U;
Degree of Attenuation
Putrefaction
Process Pathogens Potential Odor
Lime treatment Good Fair Good
Anaerobic digestion Fair Good Good
Aerobic digestion Fair Good Good
Heavy chlorination Good Fair Good
Pasteurization (70° C) Excellent Poor Poor
Ionizing radiation Excellent Poor Fair
Heat treatment (195° C) Excellent Poor* Poor*
Composting (60° C) Good Good Good
Long-term lagooning of
digested sludge Good — —
Heat drying Excellent Good** Good**
*Good for filter cake
**Anaerobic conditions in the soil after sludge is applied could cause
odors.
Enteric pathogens which have been identified in sewage sludge and their
associated diseases have been surtniarized in Table 3.
Table 3
HUMMJ ENTERIC PATHOGENS OCCURRING IN
WASTEWATER AND SLUDGE AND THE DISEASES
ASSOCIATED WITH THE PATHOGENS (2)
Pathogens Diseases
Vibrio cholerae Cholera
Salmonella typhi Typhoid and other enteric fevers
Shigella species Bacterial dysentery
Coliform species Diarrhea
Pseudomonas species local infection
Infectious hepatitis virus Hepatitis
Poliovirus Poliomyletis
Entamoeba histolytica Amoebic dysentery
Pinworms (eggs) Ascariasis
Tapeworms Tapeworm infestation
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Typical concentrations of fecal colifonn, fecal streptococci, Salmonella,
and Pseudononas aeruginosa in sewage sludge have been reported as shewn in
Table 4.
(2\
According to Love et al, ' "the infective doses of most enteric bac-
terial pathogen are relatively high." "For instance, approximately 108
enteropathogenis Escherichia coli, or v. choleral cells must be consumed by
healthy male volunteers to produce disease in a significant proportion of
subjects. Approximately 1(P Salmonella cells (including S. typhi) are
required to cause disease, but only 10 to 100 Shigella cells are necessary
to cause dysentery. Children, old people and sick people are more suscep-
tible." Smaller number of cells introduced into an appropriate medium may
lead to production of large numbers and thus cause disease.
Most currently accepted sludge stabilization methods, e.g., line sta-
bilization, anaerobic, and aerobic digestion, have been shown to signifi-
cantly reduce pathogen concentrations. Sludge does not need to be completely
sterile prior to ultimate disposal but good sanitation practices are es-
sential during both processing and ultimate disposal operations.
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Table 4
BACTERIA DATA FOR SLUDGES
(3)*
Sludge Type
Raw Primary*
Raw Primary
Raw Waste Activated*
Raw Waste Activated-A
Raw Waste Activated
Thickened-B
Raw Waste Activated-C
Anaerobic Digested*
Anaerobic Digested
Primary
Anaerobic Digested
Waste Activated
Aerobic Digested
Waste Activated
Raw Septage*
Trickling Filter
Lime Stabilized
Primary
Line Stabilized
Waste Activated
Lime Stabilized
Septage
Salmonella
#/100 ml
62
460
6
74
9.3 x 10^
2.3 x 10
6
29
7.3
N/A
6.4
93
3
3
3
Ps
Aeruginosa
#/100 ml
195 ,
4.6 x 10-
5.5 x ID,
1.1 x 10
2.0 x 10,
2.4 x 10
42
34
o
1.0 x 10
0.66
754 ,
1.1 x 10D
3
13
3
Fecal
Coliform
MF
N/A c
11.4 x 10 _
2.65 x 10 '
2.8 x 106
2.0 x 10?.
2.0 x 10°
2.6 x 10°
c
3.9 x 10°
c
3.2 x 10°
N/A 7
1.5 x 10 '-
1.15 x 10 '
o
4.0 x 10
A
1.6 x 10*
265
Fecal
Coliform
MPN
8.3 x 108
N/A
N/A
N/A
N/A f.
1.45 x 10°
N/A
N/A
N/A
N/A
N/A
N/A
N/A
Total
Coliform
MF
N/A
N/A
8.33 x 10°
N/A
N/A
N/A -
2.42 x 10'
N/A
N/A
N/A p
2.89 x 10
N/A
.
2.76 x 10
c
2.12 x 10D
_
2.1 x 1.0
Total
Coliform
MPN
2.9 x 109
N/A
N/A
N/A
N/A _
2.78 x 10 '
N/A
N/A
N/A
N/A
N/A
N/A-
N/A
Fecal
Streptococci
3.41 x 107
N/A _
1.025 x 10
N/A
N/A
N/A
2.7 x 10°
N/A
N/A
N/A 5
6.7 x 10
N/A
4
2.3 x 10
4
6.1 x 10*
665
*Based on unpublished data by Burgess & Niple, Limited
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LIME STABILIZATION OF SLUDGE
A CASE HISTORY
Background
Results of previous lime stabilization work have been presented in the
literature. Farrell et al*4' reported that line stabilization of primary
sludges reduced bacterial hazard to a negligible value, improved vacuum
filter performance and provided a satisfactory means of stabilizing sludge
prior to ultimate dipsosal. Pilot scale lime stabilization studies by C. A.
Counts et al*5) showed significant reductions in pathogen populations and
obnoxious odors when the sludge pH was greater than 12. Counts conducted
growth studies on greenhouse and outdoor plots which indicated that the
disposal of lire stabilized sludge on cropland would have no detrimental
effect.
A research and demonstration contract was awarded to Burgess & Niple,
Limited in March, 1975 to complete the design, construction and operation of
full scale lime stabilization facilities for a 3,785 cu m/day (1 MGD) waste-
water treatment plant, including land application of treated sludges. The
contract also included funds for cleaning, rehabilitating and operating an
existing anaerobic sludge digester. Comparisons were made between the
pathogen concentration, odor, and agricultural benefits of lime stabilized
primary, waste activated, anaerobically digested, and septic tank sludges
and anaerobically digested sludge without lime stabilization.
Location
T.ime stabilization facilities were incorporated into the existing 3,785
cu m (1.0 MGD) single stage activated sludge wastewater treatment plant
located at Lebanon, Ohio. Lebanon has a population of about 8,000 and is
located in southwestern Ohio, 48.27 km (30 mi) northeast of Cincinnati. The
surrounding area is gently rolling farmland with a small number of light
industries, nurseries, orchards, and truck farms.
Process Schematic of Exiting
The Lebanon wastewater treatment plant has a capacity of 3,785 cu m/day
(1.0 MGD) . Average influent BODcj and suspended solids concentrations are
180 and 243 mg/1, respectively. The treatment plant flow schematic is shown
on Exhibit 1.
Waste activated sludge is returned to the primary clarif iers and is
resettled with the primary sludge. Combined primary/Vjaste activated sludge
is pumped to the anaerobic sludge digester. Digested sludge is dewatered on
sand drying beds followed by ultimate disposal either in a landfill or on
agricultural land.
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CREEK
Exhibit Nal
Treatment Plant Flow Schematic Pr ,-r
to Incorporating Lime Stabilizatio
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Revisions to the Existing Wastewater Treatment Plant
Lime Stabilization. The lime stabilization process was designed to
treat raw primary, waste activated, septic tank/ and anaerobically digested
sludges and was integrated with the existing treatment plant facilities.
Eydrated lime was stored in a bulk storage bin and was augered into a volu-
metric feeder. The feeder transferred lime at a constant rate into a 94.6
liter (25 gal) slurry tank which discharged an 8-10 percent lime slurry by
gravity into an existing 25 cu m (6,500 gal) tank. Ihe lime slurry and
sludge were mixed with diffused air. A flow schematic for the lime stabi-
lization facilities is shown on Exhibit 2. Design data are shown in Table 5.
Table 5
DESIGN DATA FOR LIKE STABILIZATION FACILITIES
Mixing Tank
Total volume
Working volume
Dimensions
Hoppered bottom
Type of dif fuser
Number of diffusers
Air supply
Bulk Lime Storage
Total volume
Diameter
Vibrators
Fill system
Discharge system
Material of construction
Type & manufacturer
Volumetric Feeder
Total volume
Diameter
Material of construction
Type & manufacturer
Feed range
Average feed rate
Lime Slurry Tank
Total volume
Diameter
30 cu m (8,000 gals)
25 cu m (6,500 gals)
3.05 m x 3.66 m x 2.38 m (101 x 12' x 7.81)
0.91 m (31) e 27° slope
Coarse bubble
4
14-34 cu m/min (500-1,200 cf/min)
28 cu m (1,000 cu ft)
2.74 m (91)
2 ea Syntron V-41
Pneumatic
15 cm (6") dia. auger
Steel
Columbian Model C-95
0.28 cu m (10 cu ft)
71 cm (28")
Steel
Vibrascrew LBB 28-10
45-227 kg/hr (100-500 Ib/hr)
78 kg/hr (173 Ib/hr)
94.6 1 (25 gal)
0.61m (21)
8
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-VOLUMETRIC FEEDER
-LIME SLURRY TANK
DIFFUSED AIR
FOR MIXING
TREATED SLUDGE
ANAEROBIC DIGESTED SLUDGE f
PRIMARY SLUDGE
WASTE ACTIVATED SLUDGE
SLUDGE
WELL a
PUMP
TREATED SLUDGE TI
TANK TRUCK FOR
DISPOSAL
00—00
Exhibit No. 2
Lime Stabilization Process
Flow Diagram
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Septic Tank Sludge Holding Tank (septage tank)
Total volume 18.4 cu m (650 cu ft)
Working volume 15 cu m (4,000 gals)
Dimensions 3.66 m x 1.92 m x 2.62 m
Mixing Coarse bubble
Number of dif fusers 1
Air supply 2.8-8.4 cu m/min (100-300 cf/tnin)
Transfer Pumps
Raw and treated sludge 1,136 I/tain (300 gpm)
Septage transfer pump 379 I/tain (100 gpm)
Anaerobic Digester. The exist ing single stage anaerobic sludge digester
was inoperative and was being used as a sludge holding tank. The digester
pH was approximately 5.5-6.0. Grit and sand accumulations in the digester
had reduced its effective volume to 40-50 percent of the total. The gas
safety equipment, hot water boiler, piping, and controls were inoperable.
The digester and auxiliary equipment were completely renovated and returned
to good operating condition. A new boiler was installed, the digester was
cleaned, and all necessary repairs were made to piping, valves, pumps, and
electrical equipment.
The anaerobic digester design data are shown in Table 6.
Table 6
ANAEROBIC DHZSTER FEHABILITATICN DESIOJ DATA
Tank dimensions 15 m (501) dia. x 6.1 m (201) SWD
Total volune 1,223 cu m (43,200 cu ft)
Actual volatile solids ^
loading 13.6 g VSS/.028 cu m (0.03 Ib VSS/ft )
Hydraulic detention time 36 days
Sludge recirculaticn
rate 757 Vmin (200 gpm)
Land Application. Treated sludges were applied to drying beds, to test
plots, and to three agricultural areas. land spreading operations began in
late February and continued through October. The sludge hauling vehicle was
a four wheel drive truck with a 2.3 cu m (600 gal) tank.
Cost for Facilities Modifications. The capital costs for modifications
and additions to the existing wastewater treatment plant were as follows:
10
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Litre stabilization process $29,507.45
Anaerobic sludge
digester cleaning,
temporary lagoon & rehabilitation 32,183.81
Septic tank sludge storage & transfer
facilities 6,174.70
Total Capital Cost $67,865.96
Results and Analysis
Operation and Sampling. Paw sludge, e.g., primary, waste activated,
septage or digested sludge, was pumped to the mixing tank where it was mixed
by diffused air. Samples were taken from the untreated, but thoroughly
mixed, sludge for chemical, pH, bacteria, and parasite analyses. After the
initial pH determination, the lime slurry addition was started. The sludge
pH was checked every 15 minutes as the lime slurry was added until the
sludge reached a pH of 12, at which time it was held for 30 minutes. During
the 30 minute period, lime slurry continued to be added. After 30 minutes,
samples were taken for chemical, bacteria, and parasite analyses. Air
mixing was then discontinued, allowing the limed sludge to concentrate. The
sludge then flowed by gravity to a sludge well from which it was pumped to
the land disposal truck.
Lime which was used for the stabilization of all sludges was industrial
grade hydrated lime with a CaO content of 46.9 percent. All lime require-
ments are expressed as Ca(GH)2 except as noted.
All chemical analyses were performed in accordance with procedures as
stated in "Methods for Chemical Analysis of Water and Wastes, USEPA,"'6' and
Standards Methods for the Examination of Water and Wastewater. (?)
Salmonella species and Pseudomonas aeruginosa were determined according
to a method developed by Kenner and Clark. (8) Fecal coliform, total coli-
form, and fecal streptococcus were determined according to methods specified
in Standard Methods for Examination of Water and Wastewater. Parasite
analyses were performed by the Tulane University School of Msdicine.
Results. Approximately 868,700 liters (229,500 gal) of primary, waste
activated, septage and anaerobically digested sludges were treated. The
lime dosage required to exceed pH 12 was found to be affected by the type of
sludge, its chemical makeup, and percent solids. A summary of the lime
dosage required is shown in Table 7. These values include five to ten
percent excess lime which was added during the 30 minute contact time after
the pH had reached 12. Exhibits 3 to 7 show lime dosage versus pH for
various sludges and total solids concentrations.
Lime requirements are in excellent agreement with those reported in the
literature.(9)
11
-------
Table 7
T.TMP. REQUIRED FOR STABILIZATION
TO pH 12 FOR 30 MIM7IES
Sludge Type
Primary sludge
Waste activated
sludge
Septage
Anaerobic
Percent
Solids
3-6
1-1.5
1-4.5
6-7
2
Average Lbs
Ca(CH)2/Lbs
Dry Solids
0.12
0.30
0.20
0.19
2
Range Lbs
Ca(CH)2Abs
Dry Solids
0.06-0.17
0.21-0.43
0.09-0.51
0.14-0.25
Total3
Volume
Treated
136,500
42,000
27,500
23,500
Average
Total
Solids,
mg/1
43,276
13,143
27,494
55,345
Average
Initial
PH
6.7
7.1
7.3
7.2
Average
Final
PH
12.7
12.6
12.7
12.4
^Tncludes some portion of waste activated sludge
2Nunerically equivalent to Kg Ca(OH)2 per Kg dry solids
3Multiply gallons x 3.785 to calculate liters
-------
13.0
12.0
11.0 - •
10.0- •
I
ex
9.0--
8.0-•
70--
6.0
6% Primary
7% Anaerobic
4% Primary
7% Anaerobic
1% SEPTAGE
1.5% W.A.&
4% PRIMARY
6% PRIMARY
7% ANAEROBIC DIGESTED
8,060 MG/L
I,OOO
2000 3,OOO
DOSAGE Ca (OH)2 MG/L
4,000
5,000
Exhibit No. 3
Average Lime Dosage vs. pH
For Various Sludges
-------
6% PRIMARY SLUDGE
/ ^4% PRIMARY SLUDGE
/ I
II
I *"-5% PRIMARY SLUDGE
4.5% PRIMARY SLUDGE
3.5%PRIMARY SLUDGE
3% PRIMARY SLUDGE
3% PRIMARY SLUDGE
3.5% PRIMARY SLUDGE
4% PRIMARY SLUDGE
4.5% PRIMARY SLUDGE
5% PRIMARY SLUDGE
6% PRIMARY SLUDGE
1,000
2POO 3JOOO
DOSAGE Co (OH)2 MG/L
4JOOO
5JOOO
Exhibit No. 4
Lime Dosage vs. pH
Primary Sludge
-------
13.0
12.0- •
11.0 - •
10.0- •
X
Q.
9.0--
8.0 •
7.0-•
- 6.5%
-- 7.0%
- 7.5%
6.0
2,000 4000 6,000 8,000
DOSAGE Co(OH)2 MG/L
10,000
Exhibit No. 5
Lime Dosage vs. pH
Anaerobic Digested Sludge
-------
13.0
x
Q.
1,000
2pOO 3,000
DOSAGE Co (OH)2 MG/L
4,000 5,000
Exhibit No. 6
Lime Dosage vs. pH
Waste Activated Sludge
-------
13.0
12.0-
n.o-
10.0-
9.0
8.0
7.0-
6.0
1%
1.5%
3%
4%
4.5%
-f-
1,000 2,000 3,000
DOSAGE Co (OH) 2 MG/L
4,000 5,000
Exhibit No. 7
Lime Dosage vs. pH
Septage
-------
The mixing times for each sludge type were as follows:
Primary sludge 2.4 hours
Waste activated sludge 1.7 hours
Septic tank sludge 1.5 hours
Anaerobic digested sludge 4.1 hours
Mixing time was a function of lime slurry feed rate and was not limited
by the agitating capacity of the diffused air system. Mixing time could
have been reduced by increasing the capacity of the lime slurry tank.
pH Versus Time. All treated sludges had less than 2.0 pH unit drop
after six hours. T.-iinprl primary sludge was the most stable with septic tank
sludge being least stable. Only limed primary sludge pH was measured over a
period greater than 24 hours. Exhibit 8 summarizes the results of the pH
versus time studies.
A series of laboratory tests were set up in a standard jar test appa-
ratus to establish the effect of excess lime on pH decay. The tests were
made on six one-liter portions of primary sludge with 2.7 percent total
solids. The pH of each of the samples was increased to 12 by the addition
of ten percent hydrated lime slurry. One sample was used as a control. The
retaining samples had 30 percent, 60 percent, 90 percent, 120 percent, and
150 percent by weight of excess lime applied. The samples were mixed con-
tinuously for six hours and then again ten minutes prior to each additional
pH measurement. There was negligible variance in pH decay when excess lime
was added. Therefore, with a 30 percent excess lime quantity added to
assure a pH of 12, no advantage is gained by adding additional lime. The
results of the jar tests are shown on Exhibit 9.
Odors. In all cases, when a batch of sludge was pumped to the lime
stabilization mixing tank, there was a noticeable odor which became more
intense when diffused air was first applied for mixing. As the sludge pH
increased, the sludge odor decreased. However, as the pH increased, the
odor of ammonia greatly increased with ammonia being air stripped from the
sludge. The ammonia odor was most noticeable with anaerobic digested sludge.
Wnen standing close to the mixing tank, the ammonia concentration was strong
enough to cause nasal irritation.
(then all sludges except septage were spread, they retained a slight
musty odor, which dissipated quickly. Septic tank sludge did not have a
significant odor reduction as a result of lime treatment and retained the
odor when spread.
During the land application of lime stabilized primary sludge, one
complaint was received from a resident whose house was approximately 76
meters (250 feet) southeast of the land spreading site. On the day the
complaint was received the wind direction was directly toward the house.
18
-------
13.0 . i i i i I ' » i i I i '•-+•
12.0-
activated sludge
•I I I | i H-t—*—|~t—»-(—»-+-+""* ' +~M-~
il.0-
UJ
o
g 10.0
^X
Q Q.
UJ
UJ
K
9.0
8.0
Primary sludge
\
^Septic tank sludge
7.0 I i I i I | i i i i I I
0
10
ANAEROBIC DIGESTED
SEPTIC TANK SLUDGE
PRIMARY
SLUDGE
15 20 25 30 35 40
TIME-HOURS
Exhibit No. 8
pH Decay Versus Time
For Treated Sludges
-------
H 1 1 h
H h
12.0
0% EXCESS LIME
H h
11.0
12.0
30% EXCESS LIME
11.0
pH 12.0
60% EXCESS LIME
11.0
12.0
90% EXCESS LIME
11.0
12.0 •-
150% EXCESS LIME
20 40 60 80 IOO 120
HOURS
Exhibit No. 9
pH vs. Time with Excess Lime Dosage
Laboratory Scale Tests
140 160 180 20
-------
The weather was very humid with warm daytime temperatures and relatively
cool nights. The location of the residence in relation to the land disposal
site is shown on Exhibit 10.
Following the receipt of the odor complaint, land spreading operations
were switched to the site as shown on Exhibit 11. This site was approxi-
mately 152 meters (500 feet) from the nearest residence with a woods sepa-
rating the site and the adjacent land in the direction of the prevailing
wind. No additional complaints were received.
Chemical Properties. The addition of lime and mixing by diffused air
altered the chemical characteristics of each sludge. In all sludges, lime
stabilization resulted in an increase in alkalinity and soluble COD and a
decrease in soluble phosphate. Total COD and total phosphate decreased for
all sludges except waste activated. Ammonia nitrogen and total Kjeldahl
nitrogen decreased for all sludges except waste activated. The results of
the chemical analyses are summarized in Table 8.
Lime stabilized sludges have lower total phosphate, ammonia nitrogen
and total Kjeldahl nitrogen concentrations than anaerobically digested
sludges as shown in Table 9.
Table 9
NITROGEN AND PHOSPHORUS O»CENTRATIONS
IN ANAEROBICALLY DIGESTED AND LIME
STABILIZED SLUDGE
Total
Total Kjeldahl Anmonia
Phosphate, Nitrogen, Nitrogen.,
Sludge Type mg/1 mg/1 mg/1
Lime Stab. Primary 283 1,374 145
Lime Stab. Waste Activated 263 1,034 53
Lime Stab. Septage 134 597 84
Anaerobic Digested 580 2,731 709
The volatile solids concentrations of raw and lime stabilized sludges
are shown in Table 10. The actual volatile solids concentrations following
lime stabilization are lower than those which would result only from the
addition of line. Hydrolysis reactions with the line probably result in the
lower volatile solids concentrations.
21
-------
Table 8
to
to
CHEMICAL F«JttiKI.'JLES
LIME STABILIZED
Sludge Type
Raw primary
Lime stab, primary
Waste activated
Line stab, waste act.
Septage
Line stab, septage
Anaerobic digested
Line stab, anaer. digest
Alkalinity,
rog/1
1,958
4,313
1,265
5,000
2,245
4,305
3,406
11,400
Total
COD,
mg/1
54,146
41,180
12,810
14,697
24,940
17,487
66,372
58,692
Soluble
COD,
mg/1
3,046
3,556
1,043
1,618
1,223
1,537
1,011
1,809
i OF RAW AND
SLUDGES
Total
Phosphate,
mg/1
350
283
218
263
172
134
580
381
Soluble
Phosphate,
mg/1
69
36
85
25
25
2
15
3
Total
Kjeldahl
Nitrogen,
mg/1
1,656
1,374
711
1,034
820
597
2,731
1,980
Ammonia
Nitrogen,
mg/1
223
145
38
53
92
84
709
494
Percent
Total
Solids
4.5
4.9
1.3
1.7
2.6
2.7
6.9
5.8
-------
WIND DIRECTION
WHEN ODOR COMPLAINT
WAS RECEIVED
LOCATION OF RESIDENT WHO
REGISTERED ODOR COMPLAINT
SCALE; 1"= 1,250'
Exhibit No. 10
Site Plan
Glosser Road Land Disposal Area
-------
li
SCALE: l"= 1,225'
Exhibit No.II
Site Plan
Utica Road Land Disposal Area
-------
Table 10
VOLATILE SOLIDS CONCENTRATION OF
RAW AND LIME STABILIZED SLUDGES
Raw Sludge Lime Stabilized Sludge
Volatile Solids Volatile Solids
Solids Concentration, Solids Concentration,
Sludge Type mg/1 mg/1
Primary 73.2 54.4
Waste activated 80.6 54.2
Septage 69.5 50.6
Anaerobically digested 49.6 37.5
Heavy Metals Concentration. An analysis of heavy metal concentration
was made for primary, waste activated, and anaerobically digested sludges.
The results, as shown in Table 11, reflect the lack of rrajor industrial
waste sources tributary to the wastewater treatment plant.
Table 11
HEAVY METAL (XNCENTRATION IN SLUDGES
Waste Anaerobic
Primary Activated Digested
Sludge, Sludge, Sludge,
Parameter mg/1 mg/1 mg/1
Cadmium 0.141 0.109 0.151
Chromium 0.23 0.08 0.38
Copper 1.57 0.170 2.94
Lead 1.05 0.81 1.88
Mercury 0.88 0.77 0.84
Nickel 0.714 0.525 0.79
Zinc 5.82 5.15 13.82
Kill, The pH of 12.0, or greater, significantly reduced the
number of pathogenic organisms. The indicator organisms used were the
Salmonella species, Pseudomonas aeruginosa, fecal coliforms, total coliforms,
and fecal streptococci, in all sludges, Salmonella and Pseudomonas aeruginosa
concentrations were reduced to near zero. Fecal and total coliform concen-
trations were reduced greater than 99.99 percent in the primary and septic
sludges. In waste activated sludge, the total and fecal coliform concentra-
tions decreased 99.97 percent and 99.94 percent, respectively. The fecal
25
-------
streptococci kills were as follows: primary sludge, 99.93 percent; waste
activated sludge, 99.41 percent; septic sludge, 99.90 percent; and anaerobic
digested, 96.81 percent. (Based on raw sludge data as shewn in Table 4 and
lime stabilized sludge values as shown in Table 12.)
A comparison of bacteria concentrations in anaerobically digested and
lime stabilized sludges is shown in Table 12.
Table 12
CCMPARISCN OF BftCTERIA W ANftERCBIC
DIGESTED VERSUS LIME STABILIZED SLUDGES
Fecal Fecal Total Ps.
Coliform Streptococci Coliform Salmonella Aeruginosa
3/100 ml tAOOml 3/100 ml ft/100 ml #/100 ml
Anaer. digested I,450xl03 270xl03 27,800xl03 6 42
Lime stabilized* , , ,
Primary 4x10, 23x10:; 27.6x10, 3** 3
Waste activated 16x10 61xlOJ 212x10 3 13
Septage 265 665 2,100 3 3
*To pH equal to or greater than 12.0
**Detecticn limit = 3
A pilot scale experiment was completed in the laboratory to determine
the viability and regrowth potential of bacteria in lime stabilized primary
sludge over an extended period of time. The test was intended to simulate
storing stabilized sludge in a holding tank or lagoon when weather conditions
prohibit spreading. The test has not been completed, but preliminary re-
sults have indicated that little or no regrowth has occurred with the ex-
ception of fecal streptococci.
In the laboratory test, 18.9 liters (5 gal) of seven percent raw sludge
from the Mill Creek sewage treatment plant in Cincinnati were lime stabilized
to pH 12.0. Lime was added until equivalent to 30 percent of the weight of
the dry solids which resulted in a final pH of 12.5. The sample was then
covered with foil and kept at room temperature 18.3 C. (65° F.) for the
remainder of the test. The contents were stirred before samples were taken
for bacterial analysis.
The preliminary results are shown on Exhibit 12, and indicate that a
holding period actually increases the bacteria kill. Salmonella in the raw
sludge totaling 44 per 100 ml were reduced to near zero by lime stabilization.
Pseudonanas aeruginosa totaling 11 per 100 ml in the raw sludge were reduced
to the detection limit by lime stabilization. The initial fecal coliform
count of 3.0 x 10? was reduced to 5 x 10^ after lime stabilization, and
26
-------
E
O
O
z
8
IT
UJ
O
DO
'FECAL STREP
I
^
FECAL COLIFORM
TOTAL COLIFORM
L/PS. AERUGINOSA
20 fl
lO-ll
o 1
/^SALMONELLA
1 1 1
1
10
20
30
40
50
TIME , DAYS
Exhibit No. 12
Bacteria Concentration vs. Time
Laboratory Regrowth Studies
-------
after 24 hours was reduced to less than 300. The raw sludge contained 3.8 x
108 total coliform but 24 hours after liire stabilization the total coliforro
were less than 300. The fecal strep count in the raw sludge was 1.8 x 108
which decreased to 9.6 x 10^ after lime stabilization. After 24 hours, the
count was down to 7.0 x 103 and after six days reduced to less than 300.
The count increased to 8 x 105 after 40 days.
Parasites. The high pH of the sludge seemed to have little or no
effect on the viability of the parasites in the limed sludges. Viable
parasites were found in both limed and unlirred samples with reduced numbers
in the limed samples. The unlimed septic sludge seemed to have a certain
toxicity for Toxacara and Ascaris eggs. All the sludges had similar para-
sites as shown in Table 13 with Toxacara, mites, and nematcdes common to
each of the sludges. Viable parasites were found in both anaerobic digested
and limed sludges.
Table 13
IDENTIFIED PARASITES IN SLUIX2S
Primary
Waste
Activated
Sludge
Septic
Toxacara cards eggs Toxacara
Trichuris vulpis
Mites, adult,
larva, eggs
Trichuris trichiura Nematcdes adults,
larva, eggs
Enterobius vermi-
cularis larva
Mites, adults and
eggs
Nematodes-adults,
larva and eggs
Rotifers
Toxacara
Ascaris
lurnbricoides
Trichuris
trichiura
Trichuris vulpis
Mites-adult,
larva, eggs
Nematodes-adults,
larva, egg
Anaerobic
Digested
Toxacara canis
Toxacara cati
Ascaris
Trichuris
vulpis
Mites-adult,
larva, eggs
Nematcdes-
adult, larva,
eggs
ultimate Sludge Disposal
Agricultural r^nd. Two areas were used for disposal of the sludges, as
previously shown on Exhibits 10 and 11. The Glosser Road site, as shown on
28
-------
Exhibit 10, was predominantly a light colored, moderately well drained silt
loam soil. Two test areas (area "A" and area "B", as shown on Exhibit 13}
with a combined area of 1.46 hectares (3.6 acres) were used. The entire
field, which conprises approximately 16.2 hectares (40 acres) had been
planted with winter wheat the previous fall. The field was fertilized when
planted and, except for the 1.46 hectares (3.6 acres) test area, had re-
ceived a nitrogen application approximately two weeks before land spreading
began. The wheat was about 2.54 centimeters (one inch) high when primary
sludge was first applied March 1, 1976, and, weather permitting, sludge was
spread twice weekly through April 191 1976. The narrow sludge application
swath, 0.61 meter (two feet), required numerous trips across the field
causing mechanical abuse to the wheat. The line stabilized sludge formed a
filamentous mat 0.32 to 0.64 centimeters (1/8-1/4 inch) thick that choked
out the wheat.
Table 14
APPIJCATICN PATES FOR NUTRIENTS IN SLUDGE
GDOSSER BDAD SHE
Area "A" Area "A" Area "B" Area "B"
Parameters Kg/hectare Ib/acre Kg/hectare Ib/acre
Line as Ca(OH)2 979 872 545 485
Total phosphorus as P205 110 98 52 46
Soluble phosphorus as P205 14.4 12.8 8.6 7.7
Total Kjeldahl nitrogen as N 238 212 135 120
Ammonia nitrogen as N 27 24 15.7 14
The sludge application rates were 8.19 metric tons per hectare (3.65 tons/acre)
and 4.53 metric tons per hectare (2.02 tons/acre) to areas "A" and "B",
respectively. (Values based on tons dry solids.)
Random wheat samples were taken as shown on Exhibit 13. Areas C-l, C-
2, C-3, and C-4 were used as controls. Areas A-l, A-2, A-3, and A-4 had
approximately twice the sludge application rate as Areas B-l, B-2, B-3, and
B-4, as previously summarized in Table 14. Yield data are shown in Table
15.
29
-------
POWER POLES
o
GLOSSER ROAD
Exhibit No, 13
Layout of Land Disposal Area
Glosser Road
DENOTES 4'x4' RANDOM SAMPLE AREA
-------
Table 15
GLOSSER ROAD WHEAT FIELD
YIELD ANALYSIS
Area
Control
01
02
03
04
Average
Area "B"
B-l
B-2
B-3
B-4
Average
Area "A"
A-l
A-2
A-3
A-4
Average
No.
Shafts
Per
1.47 sm
(4'x4')
Area
657
747
N/A
672
692
386
441
487
495
452
522
288
620
662
523
3,426
3,500
N/A
3,210
3,379
1,602
1,817
2,302
1,945
1,916
1,709
1,306
2,053
2,672
1,935
Chaff
Kg/ha
397
323
N/A
478
399
195
202
209
202
202
350
316
424
565
414
*QDWT = oven dried weight
Shaft
ODWT*
2,571
2,645
N/A
2,248
2,488
1,184
1,238
1,629
1,359
1,353
1,777
1,036
1,629
2,207
1,662
Bionass
Kg/ha
6,394
6,468
N/A
5,936
6,266
2,981
3,257
4,139
3,506
3,471
3,836
2,658
4,247
5,445
4,046
Yield,
gig/head
0.775
0.696
N/A
0.710
0.727
0.617
0.612
0.702
0.584
0.630
0.487
0.674
0.477
0.600
0.556
In all cases, the areas which had received sludge had lower yields
which resulted principally f ran mechanical abuse by the land spreading
vehicle. The area which had received the higher sludge application rate had
a higher nuitiber of shafts with a greater mass, but had higher chaff weight
and smaller heads than the lower sludge application rate.
A second land application area (Utica Road site), as shown on Exhibits
11 and 14, was a Fincastle silt loam, which is a light colored, somewhat
poorly drained soil. This land was tiled. Seven plots were used, as shown
on Exhibit 14. Plot Nos. 2 and 5 were 0.22 hectare (.55 acre) and Plot frtos.
3, 4, and 6 were 0.11 hectare (.275 acre). Plot Nos. 1 and 7 were used as
control. The limed primary sludge was applied after the field had been
plowed and roughly disked. The sludge formed a thick filamentous mat
31
-------
0 QQ
O
O O
—I
3*60
3+90
4+20
4+50
4+80
5+10
5+40
5+70
400'
200'
LIMIT OF WOODS
RESERVE AREA FOR NERC.
TEST PLOTS 1.38 ACRES
0 (
1 1
"o
o
8
1
"8
2 1 "°
rO| ro
OJL
v I
V
XAREA FOR LAND APPLICATION
o A
OF LIMED SLUDGES 3.86 ACRES ^~\ 1
O / T
o / V
PLOT 7 /
PLOT 6 /
1
PLOT 5 ^ «
PLOT 4
PLOT 3
• PLOT 2
0
S!
1
i
1
o
N-
IT)
PLOT
Exhibit No. 14
Layout of Land Disposal Area
Utica Road
-------
which was easily disked under before planting. All sites were planted with
soybeans; site 1 the first week in May, sites 2, 3, and 4 the first week of
June and sites 5, 6, and 7 the first week of July. The test areas had been
fertilized in previous years but did not receive fertilizer prior to sludge
spreading. Sludge and nutrient application rates are shown in Table 16.
Unlike at the Glosser Road site, tomato and watermelon plants prolif-
erated in the test areas at Utica Road. Seeds for these plants were con-
tained in the sludge and were not sterilized by the lime. Hie absence of
these plants at Glosser Eoad was attributed to frequent frost and no sludge
incorporation into the soil.
A random selection of three soybean plants which were designated A, B,
and C from individual plots showed the following pods per plant. This would
indicate plots 2 and 5 with a higher sludge application rate would have a
higher yield per acre than plots 1 or 4. Plant growth shows plots 2 and 5
yielded plants two inches taller than plots 1 and 4.
Table 17
PCDS AND HEIGHTS OF SOYBEANS FROM VARIOUS PLOTS
Pods per Plant Plant Height in Inches
A_ B_ C_ Average A B C_ Average
1 49 32 33 38 37 1/2 33 32 34 1/2
4 48 33 33 38 35 1/2 34 1/2 39 36 1/3
2 39 44 37 40 39 29 38 35 1/3
5 29 34 58 40 37 41 37 38 1/3
A random sample of soybeans was selected for heavy metal analysis. The
results are shown in Table 18. Kb consistent increase in metal concentration
as a result of increasing sludge application was observed. Only zinc con-
centration increased with increasing sludge application rate. The lack of
increases in other metals probably resulted from the relatively low concen-
trations of these elements in the sludge.
Sludge Dewatering Characteristics
Standard sand drying beds which were located at the wastewater treat-
ment plant were used for sludge dewatering comparisons. Each bed was 9.2 x
21.5 meters (301 x 70'). For the study, one bed was partitioned to form
two, each 4.6 x 21.5 meters (151 x 70'). Limed primary sludge was applied
to one bed with limed anaerobically digested sludge being applied to the
other side. A second full sized bed was used to dewater unlimed anaerobically
digested sludge. The results of the study are summarized on Exhibit 15.
33
-------
Table 16
APPLICATION RATES FOR NUTRIENTS IN SLUDGE
UTICA ROAD SITE
Plot 2 Plot 3 Plot 5 Plot 6
Parameter
Line as Ca(GH)2
Total Phosphorus as P205
Soluble Phosphorus as PJD,.
Total Kjeldahl Nitrogen as
Armenia Nitrogen as N
Sludge Application Pate*
Kg/ha
1,226
236
40.4
N 438
56
14 , 147
Lbs./Acre Kg/ha
1,092
211
36
391
50
12,600
849
120
20.2
220
28
6,961
Lbs./Acre Kg/ha
756
107
18
196
25
6,200
989
161
28
297
38
9,566
Lbs./Acre Kg/ha
881
1.44
25
265
34
8,520
520
102
18
188
24
5,951
Lbs./Aa
463
91
16
168
21
5,300
*Lbs. dry solids/acre
Note: Plots 1, 4 & 7 were used as control and received no sludge application.
-------
20
15--
CO
o
UJ
o
IT
LU
Q.
10--
5 —
I I I I I I I I I I I I I I I I I I I I I I I
0' i i i i | i i i i | i i i i | i l » I | i I l i [ i i I i I i I i I | l i i
0 5 10 15 20 25 30 35 40
TIME-DAYS
Exhibit No. 15
De water ing Characteristics of
Various Sludges on Sand Drying Beds
-------
Table 18
HEAVY METALS IN SOYBEANS
No Sludge Tons/Acre Tons/Acre
Plot 1 Plot 4 Plot 7 Plot 3 Plot 6 Plot 2 Plot 5
Metals ppm* ppm* pptn* ppm* ppm* ppm* pj-tii*
Cadium .00035 .0002 .0001 .0003 .0002 .00045 .0003
Copper .0063 .0062 .0136 .0069 .0110 .0086 .0126
Cobalt .0019 .0017 .0004 .0016 .0010 .0014 .0010
Lead .0005 .0005 .0003 .0005 .0005 .0003 .0005
Potassium as K 3.11 5.38 6.53 4.75 4.40 5.29 7.35
Potassium as K,0 3.75 6.48 7.86 5.72 5.30 6.37 8.86
Mercury ^ .0015 .0040 .0040 .0055 .0003 .0065 .0003
Nickel .0036 .0037 .0031 .0036 .0030 .0031 .0028
Zinc .0055 .0054 .0051 .0093 .0093 .0056 .0116
*Results are recorded as ppm dry weight
The anaerobically digested sludge cracked first and dried more rapidly
than either of the lime stabilized sludges. Initially, both of the lime
stabilized sludges matted, with the digested sludge cracking after approxi-
mately two weeks. The lime stabilized primary sludge did not crack which
hindered drying and resulted in the lower percent solids values.
Economic Analysis
Lime Stabilization Versus Anaerobic Digestion. The capital costs for
incorporating lime stabilization at the existing 3,785 cu m/day (1.0 MGD)
wastewater treatment plant, including septage storage, were as follows:
Lime stabilization $29,507.45
Septage holding & transfer frtciliHps 6,174.70
Total Capital Cost $35,682.15
These capital costs do not include a sludge holding lagoon, land ap-
plication truck, sludge pumps or mixing equipment.
The cost of cleaning and rehabilitating the existing anaerobic sludge
digester at the same site was $32,183.81. Individual costs were as follows:
Digester cleaning $ 6,327.07
Temporary sludge lagoon 2,315.20
Digester repair 23,541.54
Total Cost $32,183.81
36
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Capital and annual operation costs for lime stabilization and anaerobic
digestion facilities were estimated assuming new construction of a 3,785
(1.0 MGD) treatment plant. The costs have been summarized in Table 19.
Table 19
COST COMPARISON LIME STABILIZATION
VERSUS SINGLE STAGE ANAEROBIC
SLUDGE DIGESTION
Anaerobic
Stab. Digestion
$/ton $/ton
Dry Anaerobic Dry
Solids Digestion Solids
Item
Lime
Stab.
Capital cost of equipment & structures
Capital cost of farmland
Annual cost of capital
Operating labor
Maintenance labor and materials
Truck capital cost
Annual truck cost
Truck operations
Truck driver
Laboratory analyses
Lime
Fertilizer return
Land return
Digester gas credit
Total Annual Cost
$53,000*
42,000*
7,700
4,700
1,100
35,000*
5,000
8,000
6,000
1,000
6,000
(3,000)
(2,000)
$18.32
11.19
2.62
11.90
19.04
14.29
2.38
14.29
(7.14)
(5.00)
$420,000*
25,000*
36,000
2,400
1,800
35,000*
5,000
5,000
4,000
1,000
(1,800)
(1,300)
(1,800)
$ 85.82
5.71
4.29
11.90
11.90
9.52
2.38
(4.29)
(3.10)
(4.:.9)
$34,400 $81.89 $ 50,300 $119.84
*Capital cost was amortized and included in annual cost
The capital costs for lime stabilization facilities included a bulk
lime storage bin, auger, volumetric feeder, lime slurry tank, sludge mixing
tank with a mechanical mixer, interconnecting piping and pumps, and 30 day
detention sludge holding lagoon for sludge storage during inclement weather.
The total cost was estimated to be $53,000 which was amortized at seven
percent interest over a 30 year period (CRT = 0.081).
Lime stabilization operation assumed one man, two hours per day, 365
days per year, at $6.50 per hour, including overhead. Maintenance labor and
materials assumed 52 hours per year labor at $6.50 per hour and $800 for
maintenance materials. The total quantity of lime required was 138 tons per
year at $44.50 per ton.
37
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Capital cost for a single stage anaerobic sludge digester included
mixing equipment, floating cover, gas safety equipment, heat exchanger,
pumps, and interconnecting piping. The total cost was estimated to be
$420,000 and was amortized at seven percent interest over a 30 year period.
Digester operation assumed one man, one hour per day, 365 days per year
at $6.50 per hour, including overhead. Maintenance labor and material
assumed 52 hours per year at $6.50 per hour and $1,500 per year for mainte-
nance iraterials.
Both the lime stabilization and anaerobic digestion alternatives
assume land application of treated sludge as a liquid hauled by truck. One
truck cost was estimated to be $35,000, which was depreciated over a seven
year period. The assumed hauling distance was 6 to 10 miles round trip.
Hauling time assumed 10 minutes to fill, 15 minutes to empty, and 10 minutes
driving, or a total of 35 minutes per round trip. Truck volume was 5,680
liters (1,500 gal) per load which resulted in five loads of lime stabilized
and three loads of digested sludge per day. The cost of truck operations,
excluding the driver and depreciation, were assumed to be $8.50 per hour.
The truck driver labor rate was assumed to be $6.50 per hour.
Although it may be possible to obtain the use of farmland at no cost,
i.e., on a voluntary basis, the economic analysis assumed that land would be
purchased at a cost of $1,000 per acre. To offset the land cost, a ferti-
lizer credit of $3.65 per ton of dry sludge solids was assumed. This rate
is 50 percent of the value published in the Ohio Agricultural ifesearch and
Development Center Bulletin 598 based on medium fertilizer market value and
low fertilizer content. (10) The published value was reduced to reflect
resistance to accepting sludge as fertilizer. The land cost was further
offset by assuming a return of $50 per acre either as profit after farming
expenses, or as the rental value for the land.
The cost of anaerobic digester operation was offset by assuming a value
of $2.10 per minim BTU for all digester gas produced above the net digester
heat requirement.
In both cases, laboratory analysis costs were assumed to be $1,000 per
year.
Lime Stabilization Design Considerations
Overall Design Concept. T.-ima and sludge are two of the most difficult
materials to transfer, meter, and treat in any wastewater treatment plant.
For these reasons, design of stabilization facilities should emphasize
simplicity, straightforward piping layout, ample space for operation and
naintenance of equipment, and gravity flow wherever possible. Exhibit 16
schematically shows these considerations. As discussed in more detail in
the following sections, lime transport should be by auger with the slurry or
slaking operations occurring at the point of use. Lime slurry pumping
38
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LIME
STORAGE
WATER
-LIME SLURRY TANK
t ^MECHANICAL OR
DIFFUSED AIR MIXING
SLUDGE
SLUDGE GRINDER
TANK TRUCK
TEMPORARY
HOLDING
LAGOON
PUMP
ALTERNATE TRUCK
LOADING PUMP
Exhibit No. 16
Design Concepts For Lime Stabilization Facilities
-------
should be avoided with transport being by gravity in open channels. Sludge
flow to the tank truck and/or temporary holding lagoon should also be by
gravity if possible.
Lime Requirements. The quantity of lime which will be required to
rai.caa tJTp pH of Tnnnjr;ipal wastewater sludges to pH greater than 12 can be
estimated from the data presented in Table 7 and from Exhibits 3 to 7.
Generally, the lime requirements for primary and/or waste activated sludge
will be in the range of 0.1 to 0.3 Kg per Kg (Ib per lb) of dry sludge
solids. Laboratory jar testing can confirm the dosage required for existing
sludges.
Types of Lime Available. Lime in its various forms, as quicklime and
hydrated lime, is the principal, lowest cost alkali. Lime is a general term
but by strict definition it only embraces burned forms of lime - quicklime,
hydrated lime, and hydraulic lime. The two forms of particular interest to
"Hire stabilization however, are quicklime and hydrated lime. Not included
are carbonates (limestone or precipitated calcium carbonate) that are oc-
casionally but erroneously referred to as "lime."
Quicklime is the product resulting from the calcination of limestone
and to a lesser extent shell. It consists primarily of the oxides of calcium
and magnesium. On. the basis of their chemical analyses, quicklimes may be
divided into three classes:
1. High calcium quicklime - containing less than 5% magnesium oxide.
2. Magnesium quicklime - containing 5 to 35% magnesium oxide.
3. Dolomitic quicklime - containing 35 to 40% iragnesium oxide.
The magnesium quicklime is relatively rare in the United States and,
while available in a few local:!ties, is not generally obtainable.
Quicklime is available in a number of more or less standard sizes, as
follows:
1. Lump lime - the product with a maximum size of 20.3 cm (8") in
diameter down to 5.1 on (2") to 7.6 cm (3") produced in vertical
kilns.
2. Crushed or pebble lime - the most common form, which ranges in
size from about 5.1 to 0.6 on (2" to 1/4"), produced in most kiln
types.
3. Granular lime - the product obtained from Flue-Solids kilns that
has a particulate size range of 100% passing a #8 sieve and 100%
retained on a f 80 sieve (a dustless product).
4. Ground lime - the product resulting from grinding the larger sized
material and/or passing off the fine size. A typical size is
substantially all passing a #8 sieve and 40 to 60% passing a #100
sieve.
40
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5. Pulverized lime - the product resulting fron a more intense
grinding that is used to produce ground line. A typical size is
substantially all passing a #20 sieve and 85 to 95% passing a #100
sieve.
6. Pelletized lime - the product made by compressing quicklime fines
into about one inch size pellets or briquettes.
As defined by the American Society for Testing and Materials, hydrated
lime is: "A dry powder obtained by treating quicklime with water enough to
satisfy its chemical affinity for water under the conditions of its hydration."
The chemical composition of hydrated lime generally reflects the compo-
sition of the quicklime from which it is derived. A high calcium quicklime
will produce a high calcium hydrated lime obtaining 72 to 74 percent calcium
oxide and 23 to 24 percent water in chemical combination with the calcium
oxide. A dolomitic quicklime will produce a dolomitic hydrate. Under
normal hydrating conditions, the calcium oxide fraction of the dolomitic
quicklime completely hydrates, but generally only a small portion of the
magnesium oxide hydrates (about 5 to 20%). Ihe composition of a normal
dolomitic hydrate will be 46 to 28 percent calcium oxide, 33 to 34 percent
magnesium oxide, and 15 to 17 percent water in chemical combination with the
calcium oxide. (With some soft-burned dolomitic quicklimes, 20 to 50% of
the Mgo will hydrate.)
A "special" or pressure hydrated dolomitic lime is also available.
This lime has almost all (more than 92%) of the magnesium oxide hydrated;
hence, its water content is higher and its oxide content lower than the
normal dolomitic hydrate. (^
Hydrated lime is packed in paper bags weighing 23 Kg (50 pounds) net;
however, it is also shipped in bulk.
Quicklime is obtainable in either bulk carloads or tanker trucks or in
36.3 Kg (80 pound) multiwall paper bags. Lump, crushed, pebble, or pelle-
tized lime, because of the large particle sizes, are rarely handled in bags
and are almost universally shipped in bulk. The finer sizes of quicklime,
ground, granular, and pulverized, are readily handled in either bulk or
bags.
Lime Storage and Feeding. Depending on the type of lime, storage and
feeding can be either in bag or bulk. For small or intermittent applications,
bagged lime will probably be more economical. In new facilities, bulk
storage will probably be cost effective. Storage facilities should be
constructed such that dry lime is conveyed to the point of use and then
mixed or slaked. Generally, augers are best for transporting either hy-
drated or pebble lime. Auger runs should be horizontal or not exceeding an
incline of 30°.
The feeder facilities, i.e., dry feeder and slaking or slurry tank,
should be located adjacent to the stabilization mixing tank such that lime
41
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slurry can flow by gravity in open channel troughs to the point of mixing.
Pumping lime slurry should be avoided. Slurry transfer distances should be
kept to a ittinimum. Access to feeder, slaker and/or slurry equipment should
be adequate for easy disasserrbly and iraintenance.
Mixing* Lime/sludge mixtures can be nixed either with mechanical
mixers or with diffused air. Tfte level of agitation should be great enough
to keep sludge solids suspended and dispense the lime slurry evenly and
rapidly. The principal difference between the resultant lime stabilized
sludges in both cases is that ammonia will be stripped from the sludge with
diffused air mixing. Mechanical mixing has been used by previous researchers
for lime stabilization but only on the pilot scale.
With diffused air mixing, adequate ventilation should be provided to
dissipate odors generated during mixing and stabilization. Coarse bubble
diffusers should be used with air supplies in the range of 150-250 cu m/mn
per 1,000 cu m (150-250 cfm per 1,000 cu ft) of mixing tank volume. Dif-
fusers should be mounted such that a spiral roll is established in the
mixing tank away from the point of lime slurry application. Diffusers
should be accessible and piping should be kept against the tank wall to
minimize the collection of rags, etc. Adequate piping support should be
provided.
With the design of mechanical mixers, the bulk velocity (defined as the
turbine agitator pumping capacity divided by the cross sectional area of the
mixing vessel) should be in the range of 4.6 to 7.9 m/min (15 to 26 fpm).
Impeller Reynolds Numbers should exceed 1,000 in order to achieve a constant
power number. (!2) Ibe mixer should be specified according to the standard
motor horsepower and AQflA. gear ratios in order to be ccmmercially available.
For convenience, Table 20 was completed which shows a series of tank
and mixer combinations which should be adequate for mixing sludges up to ten
percent dry solids, a range of viscosity, and Reynolds number combinations
which were as follows:
Max. Reynolds number 10,000 @ 100 cp sludge viscosity
Min. Reynolds number 1,000 @ 1,000 cp sludge viscosity
Mdifion?! assumptions were that the bulk fluid velocity must exceed 7.9 m/min
(26 ft/aan), Jupeller Reynolds number must exceed 1,000 and that power
requirements range from 0.5 to 1.5 horsepower per 3,785 liters (0.5-1.5
HP/1,000 gals) is necessary. One mixing tank configuration assumed that the
liquid depth equals tank diameter and that baffles with a width of 1/12 the
tank diameter were placed at 90° spacing. Mixing theory and equations which
were used were after Badger t12), Hicks f13) and Fair (14).
42
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Table 20
MIXER SPEdFICATICNS FOR SLUDGE SLURRIES
Tank
Size,
gallons
5,000
15,000
30,000
75,000
100,000
Tank
Diameter,
feet
9.6
13.9
17.5
23.75
26.1
Prime Mover, HP/
Shaft Speed, HEM
7.5/125
5/84
3/56
20/100
15/68
10/45
7.5/37
40/84
30/68
25/56
20/37
100/100
75/68
60/56
50/45
125/84
100/68
75/45
Turbine
Diameter,
inches
32
38
43
45
53
63
67
57
61
66
81
62
74
79
87
72
78
94
Raw and Treated Sludge Piping, Pumps, and Grinder. Sludge piping
design should include allowances for increased friction losses due to the
non-Newtonian properties of sludge. Friction loss calculations should be
based on treated sludge solids concentrations and should allow for thickening
in the mixing tank after stabilization. Pipelines should not be less than
5.08 centimeters (2 inches) in diameter and should have tees in major runs
at each change in direction to permit redding, cleaning, and flushing the
lines. Adequate drains should be provided. If a source of high pressure
water is available (either nonpotable or noncross-connected potable), it can
be used to flush and clean lines.
Pumps should be spared and mounted such that they can be disassembled
easily. Pump impeller type and materials of construction should be adequate
for the sludge solids concentration and pH.
43
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Sludge grinding equipment should be used to make the raw sludge homo-
genous. Sticks, rags, plastic, etc., will be broken up prior to lime sta-
bilization to improve the sludge irixing and flow characteristics and to
eliminate unsightly conditions at the land disposal site.
44
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T.TMR STABILIZATION BY OTHERS
Historically, lime has been used to treat nuisance conditions resulting
fron open pit privies and from the graves of domestic animals. Prior to
1970, there was only a small amount of quantitative information available in
the literature on the reaction of lime with sludge to make a more stable
material. Since that time, the literature contains numerous references
concerning the effectiveness of lime in reducing microbiological hazards in
water and wastewater. d5) (16) (17) Information is also available on the
bactericidal value of adding lime to sludge. A report of operations at the
Allentown, Pennsylvania wastewater treatment plant states that conditioning
an anaerobically digested sludge with lime to pH 10.2 to 11, vacuum filtering
and storing the cake destroyed all odors and pathogenic enteric bacteria. (18>
Karopelmacher and Jansen^19) reported similar experiences. Evans(20) noted
that lime addition to sludge released amnonia and destroyed bacillus coli
and that the sludge cake was a good source of nitrogen and lime to the land.
Lime stabilization has been conducted in the laboratory and in full
scale plants. Farrell et al(4) reported, among other results, that Lute
stabilization of primary sludges reduced bacterial hazard to a negligible
value, improved vacuum filter performance, and provided a satisfactory means
of stabilizing sludge prior to ultimate disposal.
Work by C.A. Counts et al ^ ' on lime stabilization at pilot scale
showed significant reductions in pathogen populations and obnoxious odors
when the sludge pH was greater than 12. Counts conducted growth studies on
greenhouse and outdoor plots which indicated that the disposal of line
stabilized sludge on cropland would have no detrimental effects.
During the period 1975 through 1976, a full scale research and demon-
stration project was completed which utilized lime stabilization and land
disposal of primary, waste activated, septage, and anaerobically digested
sludges. (21) A case history of this work is presented herein, with the
final report to be completed in late 1977.
A considerable amount of lime stabilization work has occurred in
Connecticut. A number of incinerators have been shut down and replaced by
lime stabilization. In each case, the time required to process the sludge
produced was greatly reduced. The following tabulation and contents re-
flects and summarizes the situation in December, 1976.I22' This summary
shows that eight of nine communities had either wholly or partially aban-
doned incineration. While no chemical or bacterial data are available,
qualitative observations indicate that disposal is satisfactory. Most of
the ccmnunities have indicated that they will continue with lime stabiliza-
tion and disposal in landfills.
Plants in Connecticut which abandoned incineration in favor of lime
stabilization:
45
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Stratford ^L
Bridgeport
Stamford &). .
MLddletown J5\
WLllimatic* '
/ /"\
Glastcnburg1 '
Torringtonv7)
Naugatuck(8)
EnfieldO)
Plant
Size,
rogd
6
N/A*
N/A*
N/A
N/A
N/A
^J fP^
»"/ •*
5
N/A
Incinerator
Installed
Yes
Yes
Yes
Yes
N/A
Yes
Yes
Yes
Used
Yes
Yes
No
No
N/A
No
No
Yes
Hours
24
24
-
N/A
N/A
N/A
N/A
1/3 Of
year
Lime Stabilization
Used
Yes
Yes
N/A
Yes
Yes
Yes
Yes
Yes
Yes
Hours
8
8
N/A
16
N/A
N/A
N/A
2/3 of
year
Ult. Disp.
Landfill
Landfill
Landfill
Land &
Landfill
N/A
N/A
Landfill
Landfill
denotes data not available at the tine of writing
(1) Incinerator abandoned in favor of lime stabilization to pH 12.
TWo shifts of labor no longer required.
(2) Stabilized coke used as final cover at landfill. Labor problem when
incinerator shut down because labor force reduced.
(3) Oentrifuged with lime sludge
(4) Previously plagued with odors; now all sludge processed in
two shifts, five days per week with no odors.
(5) Began lime stabilization in 1973. Screened sludge and leaf material
on parks as fertilizer.
(6) Mix dewatered raw sludge and lime before disposing in landfill.
(7) Fluid bed reactor broke down; reluctant to go to lime stabilization.
(8) Incinerator too expensive to operate; lime stabilized sludge
used as final cover at landfill.
(9) Incineration is used in winter during inclement weather.
Several cities in Ohio have used lime stabilization to offset short-
term equipment outages and as a long-term sludge disposal method. One city
is utilizing bagged hydrated lime, mixed as a slurry and fed into a sludge
mixing tank which is agitated with diffused air. Ultimate sludge disposal
is onto farmland. No significant odor or runoff problems have been encountered.
In conclusion, lime stabilization has been shown to be an effective
method of sludge stabilization. Odors are effectively eliminated. Regrowth
46
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of pathogens following lime stabilization is minimal. Of the organisms
studied, only fecal streptococci have a potential for remaining viable.
Ihe success of lime stabilization lies essentially with the ability to
efficiently contact lime with the sludge solids. Lime stabilization facil-
ities should be designed following careful analysis of lime and sludge
storage, transport, and mixing guidelines.
Lime stabilization facilities can be constructed and operated at lower
capital and annual operation and maintenance costs than comparable anaerobic
digestion facilities, and present an attractive alternative either as a new
process or to upgrade existing sludge handling facilities.
47
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ANAEROBIC AND AEROBIC DIGESTION
Anaerobic and aerobic digestion have been used to accomplish sludge
stabilization for many years. Properly designed and operated anaerobic
digesters provide substantial reduction in bacteria, putrifaction potential,
and odor potential. Ihe theory and operation of the process is fairly well
understood by engineers and operators today. Problems which do occur can
usually be traced to poor design, poor operation and maintenance, overloading,
poor mixing or lack of mixing, and toxic substances in the influent sludge.
The survival of various bacterial populations is inhibited to varying
degrees by anaerobic digestion. The destruction of different bacteria is
shown in Table 21 and Table 22. Table 21 shows a high percentage of de-
struction at various digestion periods for four different bacteria.
Table 21
BACTERIAL SURVIVAL IN ANAEROBIC DIGESTION
(9)
Bacteria
Endamoeba
hystolytica
Salmonella
typhosa
Bacilli
Escherichia
coli
Digestion Period,
days
12
20
35
49
Removal,
percent
100
92
85
100
Remarks
Greatly reduced population at 68° F,
85% reduction in 6 days retention
Digestion cannot be relied upon for
destruction
Greatly reduced populations at 99° E
about the same reduction in 14 days
at 72° F.
Table 22 shows that greater bacterial reduction is obtained with in-
creased digester temperatures. The additional costs to maintain these
temperatures may not be cost effective.
48
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Table 22
PATHOGEN REDUCTION IN MESOPEELIC
THERWDPHIL3C ANAEROBIC DH3STION FOR 20 DAYS
HYPERION PIANT, LOS ANCELES
Digesting
Temperature Pseudomonas Fecal
Type of Digestion °C Salmonella aeruginosa Coliform
No digestion — 240 35 2 x 1010
Mesophilic fi
digestion 35 23 43 4 x 10
Thermophilic 5
digestion 47 None detected 4 2 x 10
The design of digesters has been examined extensively and guidelines
are presented in the literature. W Experience has shown that a digester,
sized adequately with good mixing and with normal operation and maintenance,
will provide reasonable sludge stabilization. Detention time, solids loading,
and mixing are three of the more critical requirements. The interrelation-
ship of these parameters needs further quantification.
Anaerobic digesters fell into disfavor with designers in the late
sixties and early seventies. The availability of cheap energy, comparative
ease of operation, and ability to eliminate odors lead to the design and
construction of many aerobic digesters.
However, at the present time, increasing costs of energy and the need
for energy conservation have caused the reexamination of anaerobic digesters.
The use of sludge as a resource for its heat value or fertilizer value is
being reconsidered. The fact that raw sludge may be used both as a source
of energy and fertilizer provides ample justification for evaluation of
anaerobic digestion as a viable alternative in many situations.
The design and operation of anaerobic digesters is much more complex
than lime stabilization. Design comparisons with other methods can be made
by consulting the U. S. Environmental Protection Agency Process Design
&)
Manual for Sludge Treatment and Disposal (Oct. 1974) ) and various texts
and literature sources. * ' ' ' * ' A summary of design data for anaerobic
and aerobic digestion processes is shown on Tables 24 and 26.
In making comparisons between alternative processes, care must be
exercised to assure that all associated factors, features, and costs are
included. Oftentimes when different processes are evaluated, all factors
and costs are not included. In particular, when making comparisons between
old and relatively new processes, erroneous comparisons are often made. The
long history of performance and cost of an established technology is compared
49
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with pilot plant data and scaled up costs of a new technology. In making a
comparison, the long history of plant scale and real world data are compared
with lab work and scaled up costs as though the technology and history were
of equal duration. This frequently leads to the erroneous conclusion that
the new technology is most practicable. When the facilities of the new
technology are constructed and operated on a plant scale, actual costs may
be roughly two to four times the original cost estimate.
One of the most important design considerations in the design of either
anaerobic or aerobic digestion is mixing capability. Too little attention
has been given to the mixing problems in digesters. As an example, the
process design manual reports design parameters for detention times, vola-
tile solids loadings, percent solids, etc. However, no specific design
guidelines are given on how to achieve the required degree of mixing.
Mixing may be accomplished by mechanical mixers, by digester gas
recirculation, by sludge recirculation or by a combination of these. Me-
chanical mixing has been accomplished using multiblade turbines driven by 4-
10 HP mixers in a 23 m (75 ft) diameter digester. (23) The turbine blades
were four feet in diameter mounted three feet below the surface. Mixing
horsepower is less than 0.334 HP per 1,000 cu ft or 0.045 HP per 1,000 gals
of digester volume. This was employed primarily to break up the scum layer.
Sludge recirculation was also practiced.
Examination of plants where mechanical mixers are used to provide
mixing for activated sludge processes showed that energy requirements ranged
from 0.186 to 0.37 HP per 1,000 gals of aeration tank volume. This amount
of energy results in intensive mixing, when suspended solids concentrations
are only in the 1,000 to 3,000 mg/1 range. Higher concentrations could be
maintained but the limit is unknown. Energy, at least in the range of 0.2
to 0.4 HP per 1,000 gals will provide complete and thorough mixing with
liquid depths 10 to 12 feet deep.
An estimate of possible energy requirements can be made also by com-
parison with the energy required to give good mixing in diffused air aeration
systems. A review of several aeration systems which do provide good mixing
shows that with diffused air systems available, energy ranges from 0.155 HP
to 0.54 HP per 1,000 gals of tank volume. Experience has shown that this
will maintain up to three percent solids in suspension and result in inten-
sive mixing. Increasing these values by 50 percent is believed necessary to
provide complete and intensive mixing when solids concentrations increase to
five to ten percent.
Energy and specific design considerations using gas recirculation as a
means of mixing is neglected by most texts and the USEPA Process Design
Manual. The manuals suggest obtaining specific information from various
manufacturers.
A summary of energy requirements of five different gas recirculation
systems manufactured by different companies is given in Table 23. The
50
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Table 23
COMPARISON OF HORSEPOWER NEEDS FOR VARIOUS EQUIPMENT
FOR ANAEROBIC DIGESTER GAS RECIRCULATICN*
(horsepower/1,000 cu ft)
Digester
Diameter,
feet
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
105
110
Pearth
(a)
0.375
0.252
0.210
0.210
0.149
0.149
0.115
0.115
0.120
0.120
0.074
0.074
0.051
0.051
0.042
0.042
0.049
0.049
Pearth
v, x
(b)
0.730
0.320
0.270
0.170
0.160
0.120
O.C90
0.110
0.090
0.070
Carter
Aero-Hyd
(b)
0.220
0.190
0.110
0.067
0.049
0.035
0.027
0.022
0.017
0.014
Catalytic .
Reduction^ ;
0.250
0.200
0.200
0.150
0.120
0.086
0.111
0.091
0.077
0.063
0.050
0.043
0.058 '
0.050
0.043
0.043
0.036
Walker
Process
CN
iH
•
O
S
*Manual of Wastewater Operations prepared by The Texas Water Utilities
Assoc. (1971)
(a) Actual HP used per 1,000 cu ft of digester capacity
(b) Nameplate HP per 1,000 cu ft of digester capacity at 22' SWD
(c) Required HP per 1,000 cu ft of digester capacity at depths from 19" for a
20' diameter to 30' for a 110' diameter
51
-------
horsepower per 1,000 cu ft varies fron 0.730 for a 20 foot diameter digester
to 0.014 for a 110 foot digester. Generally, all of the manufacturers
lecontend higher unit horsepower for smaller digesters. Sane have inulti-
pcint diffusers and others have single point. Presumably, they all claim to
provide a similar degree of mixing.
When the energy inputs, especially for digesters greater than 20-30
feet in diameter, are compared to energy inputs required to provide inten-
sive or complete mixing, the conclusion may be drawn that only enough energy
is provided to break up any scum layer. The degree of mixing required for
an anaerobic digester may not be as great as an aerobic digester; however,
that provided to date appears inadequate. As an example, the power to give
complete mixing in an aerobic digestion tank is on the order of 1.0 to 4.0
HP/1,000 cu ft, while the power to provide so called complete mixing in a
large anaerobic digester, say 80 feet in diameter, is in the order of 0.027
to 0.090 HP/1,000 cu ft, depending on the manufacturer as shown in Table 23.
While 1.0 to 4.0 HP/1,000 cu ft may be too high, values of 0.027 to 0.090
are questioned as being too low.
The complete development of mixing theory is beyond the scope of this
presentation. The horsepower needed for mixing not only depends on the type
of mixing, but also on how the digester contents are recirculated and heated
and how raw sludge is introduced. Mixing only may require horsepower in the
range of 1.0 to 4.0 or more as discussed earlier when attempting to mix two
slurries. Mixing the upper portions of the digester contents to prevent a
scan layer, based on experience, is on the order of 0.30 to 0.40 HP/1,000
cu ft. This value may be modified somewhat by successfully entraining the
digester gas. Considerable evidence should be provided before the values
are significantly reduced.
An idealized mixing concept is proposed on Exhibit 17. The digester
contents would be recirculated with the discharge of the recirculating pump
introduced tangenti ally at various points around the perimeter of the
digester. Suction and discharge points would be at several elevations with
the suction being from the center of the tank. This would provide a circular
mixing motion to the tank contents. Becirculation capacity should be suf-
ficient to recirculate the entire digester in four to eight hours.
Gas recirculation would also be employed to provide complete vertical
mixing and prevent any scan development. About 0.2 to 0.6 HP/1/000 cu ft
should be available to provide adequate recirculation. Diffusers or eductors
would be located in the quadrants of the digester. In very large digesters,
additional points of diffuser location and recirculation discharges may be
required.
The proposed mixing features and energy inputs, when considered with
the typical design criteria as given in Table 24, should improve the effec-
tiveness of anaerobic digesters. Table 25 gives the proposed energy in
horsepower which is thought to be definitive in establishing the degree of
mixing.
52
-------
SLUDGE IN
SLUDGE TO
RECIRCULATION
Exhibit No. 17
An Idealized Anaerobic Digester Mixing Concept
-------
Table 24
TYPICAL DESIGN CRITERIA FOR STANDARD RATE
AND HIGH RATE ANAEROBIC DIGESTERS (9)
Parameter Low Rate High Rate
Solids Retention Time (SFT), days 30 to 60 10 to 20
Solids loading, Ib VSS/cu ft/day 0.04 to 0.1 0.15 to 0.40
Volute Criteria, cu ft/capita
Primary Sludge 2 to 3 1 1/3 to 2
Primary Sludge + Trickling Filter Sludge 4 to 5 2 2/3 to 3 1/3
Primary Sludge + Waste Activated Sludge 4 to 6 2 2/3 to 4
Combined Primary + Waste Biological
Sludge Feed Concentration, percent solids
(dry basis) 2 to 4 4 to 6
Digester Underflow Concentration, percent
solids (dry basis) 4 to 6 4 to 6
As noted, the high rate process requires considerably less detention time
and volume, and operates successfully with a higher solids loading compared
to the conventional process. This is attributed to the greater use of the
digestion tank for biological activity and improved mixing.
Ten State Standards permits volatile solids loading of up to 0.080
Ibs/cu ft for completely mixed systems. In moderately mixed digesters where
mixing is accomplished only by circulating sludge through an external heat
exchanger, the loading may increase to 0.040 Ibs/cu ft in the active digestion
units.
Table 25
PROPOSED HP REQUIREMENTS FOR ANAEROBIC DIGESTER
MIXING PER 1,000 GALLONS OF DIGESTER TOLUME
Moderate Complete
or or
Method of Mixing Low Rate High Rate
Gas recirculation 0.03-0.05 0.30-0.50
Mechanical mixers 0.04-0.06 0.40-0.60
54
-------
Guidelines for the design of aerobic digesters are given in Table 26.
While this alternative is attractive, particularly for small connunities,
additional data are needed to fully evaluate the pathogen reductions. One
of the major advantages of the aerobic process is the ataost conplete ab-
sence of any objectionable odors during the stabilization process. This
method is particularly applicable where primary sedimentation is emitted.
Other advantages and disadvantages are cited in the literature.
55
-------
Table 26
AEROBIC DIdSTICN DESIG* PARAMETERS
(9)
Parameter
Value
Remarks
10-15*
15-20^
3-4
0.024-0.14
Solids Retention Time, days
Solids Retention Time, days
Volume Allowance, cu ft/capita
VSS Loading, pcf/day
Air Requirements
Diffuser System, cfm/1,000 cu ft 20-35a
Diffuser System, cfip/L,000 cu ft 60^
Mechanical System, HP/1,000 cu ft 1.0-1.25
Minimum DO, mg/1
Temperature, °C
1.0-2.0
15
VSS Reduction, percent
Tank Design
35-50
Depending on temperature, type
of sludge, etc.
Depending on temperature, type
of sludge, etc.
Enough to keep the solids in
suspension and maintain a DO
between 1-2 mg/1.
This level is governed by
mixing requirements. Most
mechanical aerators in aerobic
digesters require bottom
mixers for solids concentra-
tion greater than 8,000
mg/1, especially if deep tanks
( 12 feet) are used.
If sludge temperatures are
lower than 15° C, additional
detention time should be pro-
vided so that digestion will
occur at the lower biological
reaction rates.
Aerobic digestion tanks are
open generally require no
special heat transfer equip-
ment or insulation. For
small treatment systems (0.1
rogd), the tank design should be
flexible enough so that the di-
gester tank can also act as a
sludge thickening unit. If
thickening is to be utilized
in the aeration tank, sock
type diffusers should be
used to minimize clogging.
Power Requirement, BHP/10/000
Population Equivalent 8-10
?Excess activated sludge alone.
Primary and excess activated sludge, or primary sludge alone.
56
-------
HEAT TREATMENT
There is little doubt that heat treatment processes, whether called
pasteurization or low pressure oxidation, destroy pathogens and other bac-
teria found in sludge. A summary of work done by others and presented in
the latest USEPA Process Design t'Sanual^) is reproduced here in Table 27.
This data shows that temperatures in the range of 50° C. to 70° C. for 30 to
60 minutes is effective for pathogen kill.
Table 27
EFFECT OF TIME AND TEMPERATURE ON THE SURVIVAL
OF TYPICAL PATHOGENS FOUND IN SLUDGE*
Temperature °C
Organism 50 55 60 65 70
minutes
Cysts of Entamoeba histolytica 5
Eggs of Ascaris lumbricoijdes 60 7
Brucella abortus 60 3
Corynebacterium diphtheria 45 4
Salmonella typhosa 30 4
EscherichTa coli 60 5
Micrococcus pyrogene var. aursus 20
Mycobacterium tuberculosis var. promixis 20
Viruses 25
*Pathogens completely eliminated at indicated time and temperature.
Test on digested liquid sludge conducted at the National Environmental
Itesearch Center in Cincinnati, Ohio showed that pathogenic organisms can be
destroyed or inactivated at a temperature of 70° C. when maintained for 30
to 60 minutes &) although coliform indicator concentrations sometimes
remained above 1,000 count/100 ml. The results are included in Table 28.
The basic components of the pasteurization process are a steam boiler
and steam contact tank. Since each sludge particle must receive the pas-
teurization temperature for complete effectiveness, good mixing of the steam
and sludge is essential. Most of the work done on pasteurization has been
done outside the United States. A flow schematic of a plant in Germany is
reproduced on Exhibit 18. The basic steps as given by Stern(2) are: " (1)
sludge from a concentrated digester sludge tank is pumped into a preheater
and heated from 18° C. to 38° C. by the vapors from the blow-off tank under
0.1 atmosphere; (2) the preheated sludge is pumped, at 1 atm (atmosphere),
to the pasteurizer where direct steam injection heats the sludge to about
70° C; (3) the sludge is then transferred to a retention tank where it is
held for 30 minutes at 70° C; (4) next, the sludge is transferred to the
blow-off tank and cooled at 45° C under 0.1 atm (the vapor from this blow-
57
-------
PREHEATER.O.I ATM.
TO THE VACUUM PUMPS
O.I ATM.
BLOW-OFF
TANKS
/PASTEURIZED
)SLUDGE
/-CONCENTRATED
(. DIGESTED SLUDGE
\ I8°C
STORAGE BASIN
PUMPS
PUMP
STORAGE BASIN PUMP
— SLUDGE
— HEATING STEAM
»— VAPORS
— VACUUM (AIR)
— WATER
Exhibit 18
Diagram of sludge pasteurization in the Group-Sewage
Plant of the Niersverband Viersen illustrating one-stage heat recuperation
(After Stern, reference 3 )
-------
Table 28
PASTEURIZATION TEST RESULTS
(3)
Organisms/100 ml
Test Tenp.
No. (1) °C
13.5^
L-l 59-04 ( '
-> 15
^ 60-69
i 7 1G it\
^3 63-66 (6)
15
L-4
67-75
L-5 3°
^J 68-73
L-U 1B
L U 77-85
L-7 14
Ir/ 37-91
Using Stear.i Gun
26
P-l 33-55
Through Copper Tube
3/16 inch holes
25
p_2 70-83
(7)
59 * '
Tijne
(hours)
1
2
-
1
1
_
1
2
-
1
-
1
-
1
_
1.5
with 12
—
1
1.5
-
Salmonella
sp.
N!D.(4)
N.D.
23
N.D.
9.3
N.D.
23
N.D.
N.D.
29
N.D.
3
N.D.
240
N.D.
240
240
240
N.D.
N.D.
N.D.
Pseudomonas
aeruginosa
20
N.D.
N.D.
9.1
N.D.
21
20
150
N.D.
N.D.
1,100
N.D.
7.3
N.D.
43
N.D.
93
N.D.
16
N.D.
N.D.
N.D.
Total
Aerobic
Counts
2.5x10^
2x10^
lxlOJ
3.4x10®
7x10 J
6 . 3x10°
2.5x10®
6. 4x10 C
1 . 3x10
1.7x10;!
3xl06
1.2x10®
6xlOJ
1x10®
3x10°
7.9x10^
1.7x10
1.8x10®
4.4x10;?
4.5x10?
3. 8x10 J
Fecal
Coliform
6xl05
9,000
B.D.L.
1.5xl06
B.D.L.
7.7xl06
6,000
2xlOC
B.D.L.
B.D.L.
9.9x10°
5,000
1.9x10°
B.D.L.
IxlO6
B.D.L.
5x10^
5x10
8.4xl06
B.D.L.
E.D.L.
B.D.L.
Fecal % Dilution
Streptococci After Past
16xl04
,r. B.D.L. 18
(5) B.D.L.
30xl04
B.D.L.
2.3x10^
9xl04 14
5xl06
B.D.L. 22
B.D.L.
2.7xl06
5,000 i2
6.5xl04
B.D.L.
6.5x10'*
B.D.L.
1.7x10^ ..
4.2X104 10
2.1xl05
B.D.L.
B.D.L.
B.D.L.
(1) L-numLers = laljoratory tests
P-numbers = large scale tests
(2) Oriyinal digested sludcje
temtjerature (topical)
(3) Pasteurization temperatures
(typical)
(4) K.D. = none detected ( 3/100 ml)
(5) Below detectable lijnits of analysis ( 1,000/100 ml)
(6) Presence of Pseudanonas aeruginosa and relatively
high fecal streptococci suggests that heat diu not
penetrate the sludge.
(7) After cooling with air to 59° C.
-------
off tank is used to preheat the incoming sludge); (5) the pasteurized sludge
is further cooled to 35° C at 0.051 atm in a second blow-off tank."
Capital costs for equipment and energy costs would be significant for
this process. Costs are given by Stern, (2) but details as to assumptions
and what is included are lacking. Good comparisons are thus beyond the
scope of this presentation. Odor problems are also inentioned and effective-
ness of sludge digestion preceding pasteurization is a factor.
Heat treatment by low pressure oxidation uses temperatures in the range
of 350° F. to 400° F., with pressures of 180 to 210 psi and retention tines
of 20 to 30 minutes. The wet air oxidation process uses temperatures greater
than 500° F., with pressures in the range of 1,500 psi. This higher temp-
erature oxidizes practically all the organics to a relatively inert ash.
Two serious problems are encountered in heat treatment. One is the
inherent problem of solubilizaticn of organics. Ihe liquid decant from the
heat treated sludge is very high in BCD, chemical oxygen demand, ammonia,
and phosphorus. Thus, the recycle of the decant and filtrate liquors can
represent a sizeable load when returned to the raw wastewater flow for
treatment. In an activated sludge plant, the BCD and solids loading of the
heat treatment liquor recycle steam can represent 30 to 50 percent of the
loading to the aeration system. Ihe second problem is the operation and
reliability of equipment. The characteristics of wastewater treatment plant
sludges make processing at high temperatures and pressures difficult.
Serious problems have been encountered with grinders, pumps, pipes, valves,
and heat exchangers resulting in much more downtime than originally esti-
mated. Because of these equipment problems, costs have been iruch greater
than anticipated and the process abandoned in sane cases. Part of the
problem can be attributed to inadequately trained operators for this level
of sophistication in equipment and processing.
The objective in this discussion is not to discourage the use of heat
treatment as a sludge stabilization process, but to make design engineers
and operators fully aware of the problems and disadvantages of these pro-
cesses as well as the advantages. A second objective is to show that when
comparing different alternatives for sludge disposal, factors such as sludge
characteristics, equipment, operating personnel, and total cost must be
evaluated.
60
-------
OTHER STABILIZATION AND DISAFFECTION SYSTEMS
Chlorination, long-term lagooning, composting, and drying are other
processes used to stabilize or disinfect sludges. The chlorination process
subjects the sludge to very high doses of chlorine. Long-term lagooning
results in holding the liquid sludge for a long period of time. Corposting
employs biological action at low temperatures. The drying process involves
drying the sludge with heat to a dry solid.
Other means of disinfection are known but have little or no application
on a large scale. Among these are radiation, ozonation, ultraviolet light,
ultrasonics, thermoradiation, addition of carbolic acid, coal tar distillage,
formalin, and sunlight. These can be used to disinfect very small quantities
of sludge.
All of the above systems can be used, but each has technological prob-
lems or prohibitive costs which prevents widespread application, except
long-term lagooning. This method has considerable use; however, it is sel-
dom mentioned because it is generally not recognized as a stabilization or
disinfection system.
Chlorinaticn
This process requires large doses of chlorine (approximately 500 mg/1
of chlorine added to each percent solids concentration) to effect disinfec-
tion. Chlorine dosage could be up to 2,000 nig/1 or more. The pH is reduced
to 2-3 which results in an acidic slurry. Dewatering and ultimate disposal
are thus greatly affected. Only limited data and information are available
on the method.
long-term Lagooning
Plant operators may not admit it, but many employ them. When all else
fails, the sludge is dumped into a lagoon or the low area "out back" of the
plant. Long-term lagoons will concentrate sludge and provide storage and
time for additional stabilization and reduction in pathogenic organism
concentrations. About 99.9 percent reduction of fecal coliforms after 30
days storage at ambient temperature has been reported. Long-term storage of
liquid sludge for 60 days at 20° C. or for 120 days at 4° C. also reduces
the concentration of pathogenic organisms. \2' Relatively large land areas
are required and care must be exercised to control odor problems.
The Ten State Standards ' require at least two lagoons not more than
24 inches in depth. The soil must be reasonably porous and the bottom of
the lagoon at least 18 inches above the maximum groundwater table. The area
required depends on local climatic conditions. Adequate consideration must
be given to prevention of pollution of ground and surface waters and isola-
tion to avoid nuisance situations.
61
-------
A number of plants in Ohio use long-tern lagoons with satisfactory
results. One plant uses the conbination of a storage lagoon at the waste-
water treatment plant site with pumping to another storage lagoon in the
vicinity of the land disposal area. Land disposal is by tank truck fror, the
second lagoon.
The use of composting has not been widely practiced in the United
States. While recognized as a means of stabilizing and reducing the number
of pathogenic organisms in sludges, it nay be difficult and costly. Table
29 by Stern (2) and others shows the effectiveness of corposting for des-
troying pathogenic organisms in sludge.
Table 29
TEMPERATURE AND TIME FOR PATHOGENIC DESTRUCTION
IN COMPOSTING DEWATERED SEWAGE SLUDGE
Exposure Time (Minutes) for Destruction
at Various Tenperatures (° F (0°C)
Microorganisms 140 (60) 158 (70)
Salmonella newport 30
Candida aTbicans 60
60+
Poliovlrus Type I 5
+Result is based on TOP (tine is a constant and tenperature is varied) . All
other results are based en TDT (tenperature is a constant and tine is varied)
Conposting of wastewater sludge with other drier organic material such
as municipal solid wastes and wood chips may offer sane possibility of
reducing costs. Much development is needed to make this a practical alter- fq.
native which can be applied in many areas. The USEPA Process Design Manual1 '
has a limited discussion on the composting process, effectiveness, and
costs. There are also a number of proprietary systems. Table 30 summarizes
the hygienic quality of conpost O) showing general types of composting,
materials used, moisture content, and temperature achieved.
62
-------
Table 30
HYGIENIC QUALITY OF COMPOST
w
Treatment Method
Material
Water Maximum Temp.
Content (%) Achieved (° C)
Hygienic
Evaluation
Remarks
Contour spreading sludge + solid
waste
Windrow spreading sludge
Windrow spreading solid waste
Rotating drum
(Dano process)
Rotating drum
Rotating tower
(multibacto
process)
Rotating tower
Contour Composting
55 46
60
40-60
Windrow spreading sludge + solid 40-60
52
55
55
Mechanical Cotiposting
solid waste 45-55 60
sludge + solid approx.
waste 50
solid waste 40-50
sludge + solid 45-55
waste
60
65
65
Not pathogen-free
after 5 months
Not pathogen-free
after 6 months
Pathogen-free
after 3 weeks
Pathogen-free
after 3 weeks
Pathogen-free
after 6-7 days
Pathogen-free
after 6-7 days
Pathogen-free
after 1 day
Pathogen-free
after 1 day
Spore-free after 1
week of windrow
composting
Spore-free after 1
week of windrow
composting
Spore-free after 1
week of windrow
composting
Spore-free after 1
week of windrow
composting
-------
Flash
This process is also discussed in the USEPA Process Design Manual. The
process does render wastewater sludges into a highly desirable state. If
drying could be accomplished on a competitive basis with other processes, it
probably would be mace widely used than any other process. With today's
energy costs and current technology, drying of sludge is simply not competi-
tive, in most cases.
Other Disinfectants
Disinfectants such as radiation, ozonation, ultraviolet light, ultra-
sonics, carbolic acid, coal tar distillates, and formalin are not practical
on a plant scale. These are used only on a very small scale in limited
application. The major problem is the cost and difficulty with ultimate
disposal.
64
-------
The assistance of Tim Cppelt, Jon Bender, the staff of the National
Environmental Research Center Pilot Plant, Lebandon, Chio, Jack Wiitaker,
and the staff of the Lebanon Kastewater Division was greatly appreciated
during the completion of the lime stabilization project. FT ITS C. Thoipson
of Lebanon was more than cooperative in donating the use of his property and
equipment for the sludge disposal and growth studies. Parasite analyses
were performed by Tulane University, School of Medicine, New Orleans,
Louisiana. The lime stabilization project officer was Steven W. Hathaway,
under the direction of Dr. J. B. Farrell of the U. S. Eovircnaental Protection
Agency, National Environmental Research Center, Cincinnati, Chio.
Hark Kipp of Burgess & Niple, T.imii-prf operated the line stabilization
facilities. Kay Wilson was responsible for typing the final manuscript.
65
-------
LIST CF REFERENCES
1. Farrell, J. B. and Stern, G., "Methods for Inducing the Infection
Hazard of Wastewater Sludges," presented at the Symposium on the Use
of High Level Radiation in Waste Treatment, Munich, Germany,
Mar. 17-21, 1975.
2. Love, Gary J., Thompkins, Edythalena, and Galke, Warren A., "Potential
Health Impacts of Sludge Disposal on the Land," Municipal Sludge
Management and Disposal, 1975.
3. Stern, Gerald, "Reducing the Infection Potential of Sludge Disposal."
4. Farrell, J. B., Smith, J. E., Hathaway, S. W., "Line Stabilization
of Primary Sludges," Journal Water Pollution Control Federation,
Vol. 46, No. 1, January 1974, pp 113-122.
5. Counts, C. A., Shuckrow, A. J., Smith, J. E., "Stabilization of
Municipal Sewage Sludge by High Lime Dose," UNPUBLISHED REPORT by
Pacific Northwest Laboratories, Battelle Memorial Institute, Richland,
Washington.
6. USEPA, "Methods for Chemical Analysis of Wastes," USEPA, Cincinnati,
Olio, 1974.
7. Standard Methods for Examination of Water and Wastewater, 13th & 14th
Editions, AWWA, APHA, WPCF, American Public Health Association,
Washington, D.C.
8. "Enumeration of Salmonella and Pseudomonas aeruginosa,** Journal WPCF,
Vol #46, No. 9, Sept. 1974, pp 2163-2171.
9. USEPA, "Process Design Manual for Sludge Treatment and Disposal,"
USEPA Technology Transfer, Oct., 1974.
10. Brown, R. E. et al, "Ohio Guide for Land Application of Sewage Sludge,"
Ohio Agricultural Research and Development Center, Wooster, Ohio, 1976.
11. National Lime Association, "Lime Handling Application and Storage in
Treatment Processes Bulletin 213," National Lime Assoc., Washington,
D.C., pp 1-3.
12. Badger and Banchero, "Introduction to Chemical Engineering," page 614,
McGraw-Hill, 1955.
13. Hicks, R. W. et al, "How to Design Agitators for Desired Process
Response," Chemical Engineering, April 26, 1976, pp 103-106 ff.
14. Fair, G. M. and Geyer, J. C., "Water Supply and Wastewater Disposal,"
John Wiley & Sons, New York, 1956.
66
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15. Riehl, M. L. et al, "Effect of Lime Treated Water on Survival of
Bacteria," Journal American Water Works Assn., 44,466 (1952).
16. Grabow, W.O.K. et al, "The Bactericidal Effect of Lime Flocculation
Flotation as a Primary Unit Process in a Multiple System for the
Advanced Purification of Sewage Works Effluent," Water Resources
3, 943 (1969).
17. Buzzell, J. C., Jr., and Sawyer, C. N., "Removal of Algal Nutrients
from Raw Wastewater with Lime," Journal WPCF, 39, R16, 1967.
18. "How Safe is Sludge?" Compost Science 10 March-April 1970.
19. Kempelmacher, E. H. and Van Noorle Lansen, L. M., "Reduction of
Bacteria in Sludge Treatment," Journal WPCF 44, 309 (1972).
20. Evans, S. C., "Sludge Treatment at Luton," Journal Indust. Sewage
Purification 5, 381, 1961.
21. Noland, R. F., Edwards, J. D., Kipp, M. A., "Project Cl-74-0294
Full Scale Demonstration of Lime Stabilization - unpublished draft
of final report.
22. Personal comniunication - Steven W. Hathaway, February, 1977.
23. Oldshue, J. Y., "Mixing in Anaerobic Digesters, Tonawanda, New York,"
American City, Feb. 1974, p. 80.
24. Farnham, Richard - Personal comtnunication, March, 1977.
25. The Texas Water Utilities Association, Manual of Wastewater
Operations, 1971.
26. Recommended Standards for Sewage Works, Great Lakes-Upper Mississippi
River Board of State Sanitary Engineers.
67
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REVIEW OF CGKDITICNIKG TuICK^KIHG
Alii) DENATURING OF SLUDGE
JOHN R. HARRISON, b.S.ChE., P.E.
PREPARED FOR ThE
ENVIRONKEKTAL PROTECTION AG^nCY
TECHNOLOGY TRANSFER
SEHIHAfi SERIES ON
SLUDGE TREATMENT AND DISPOSAL
1977
FEBRUARY, 1977
68
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OUTLINE
1 - Introduction - Sludge Conditioning, Thickening £ Dewatering
1.1 - Purposes
1.2 - Method
1.3 - Rationale-Successful Innovative Design
1.4 - Sources-Design Information
1.5 — Special Considerations-Design Information
1.6 - The Total System Approach to Design
1.7 - The QFD & Material Balance Concepts
1.8 - Broad Definition of Unit Processes
1.9 - Specific Definition of Sludge Conditioning
1.10- Specific Definition of Sludge Thickening
1.11- Specific Definition of Sludge Dewatering
2 - Developments in Sludge Conditioning
2.1 - Chemical - Inorganic
2.2 - Chemical - Organic
2.3 - Thermal Conditioning
2.4 - Case Histories - Heat Treatment
2.4l - Colorado Springs
2.42 - Port Huron
2.4-3 - Status Summary - Heat Treatment Plants
2.44 - Perth, Scotland
2.45 - Round Hill
2.46 - Overall Status of British II.T. Plants
3 - Developments in Sludge Thickening
3.1 - DAF - Recent Results
3.2 - Disc Centrifuge Results - Colorado Springs
3.3 - Newly Developed M.S. - H.B.F.'s
69
-------
OUTLINE
- Developments in Sludge Dewatering
4.1 - Horizontal Belt Filters
4,11 - General Comment
4.12 - B.F. Carter - Series 31
4.13 - Komline Sanderson Unimat
4.14 - Infilco Degremont Floe-Press
4.2 - Pressure Filters
4.21 - U.S. Case Histories
4.22 - Conclusions on U.S. Results to Date
4.23 - Other Developments in Pressure Filters
4.3 - Centrifuges
4.31 - General Comment
4.32 - Most Recent & Definitive Experiences - Germany
4.33 - Side by Side Evaluation of New Low Speed Concurrent
Flow Solid Bowl Centrifuge and the Older High Speed
Counter-Flow Type
70
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LIST OF TABLES AND FIGURES
PAGE
11
12
15
18
20
21
22
23
24a
25
27
28
30
35
36
37
41
43
44
46
NUMBER
Table I
Table II
Table III
Table IV
Table V
Table VI
Figure I
Table VII
Figure II
Table VIII
Table IX
Table X
Table XI
Figure III
Table XII
Table XIII
Table XIV
Table XV
Table XVI
Table XVII
CONTENT
Summary of Average Downtimes - Heat
Treatment Plants
Recycle Loads, Heat Treatment Plants
Reported Costs, Colorado Springs Unit
Cost of Sludge Treatment Using Different
Types of Plant at Perth
Plant Results - Flotation Thickening
Plant Results - Disc Centrifuge -
Thickening
Horizontal Lelt Filter - Original Concept
tiBF's - List of Manufacturers
Carter Automatic Belt Filter Press System -
Series 31
Types and Dimensions of S-Presses
Unimat Series Design Data
Dry Solids Cake & Polymer Dosage - Unimat
Cost - Pressure Filtration - Kenosha
Farnham Plant-Sludge Conditioning and
Pressing Flow Diagram
Operating Conditions for Various Condition-
ing Agents
Summary of United Kingdom Results - Various
Conditioning Systems
Effect of Speed Differential on Throughput
and Dry Solids
Side by Side Comparison - Process Results
Side by Side Comparison - Machine Parameter;
Side by Side Comparison - Annual Cost Profii
71
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1 - Introduction - Sludge Conditioning, Thickening, and Dewatering.
1.1 - Purposes
- Review operating experiences of past 3-^ years in sludge
conditioning, thickening, and dewatering.
- Review recent applicable research and development activities
in these same unit process areas.
- Particularly emphasize innovative results achieved in
operating plants.
- Stimulate discussion of the above topics in this session.
1.2 - Method
- Formal presentation (prefer questions during discussion period)
- Discussion as required.
1.3 - Rationale - Successful Innovative Design
- Development and maintenance of a thorough knowledge of the
various sludge treatment unit processes.
- Continual study of plant operational results to provide
feedback for cost saving modifications and future design.
- Adequate pilot plant study of alternate prescreened treatment
plant systems as required by the particular circumstances.
- Use of the systems analysis method for comparing alternate
complete systems (both liquid treatment and sludge processing)
for treatment plants.
72
-------
1 - Introduction - Sludge Conditioning, Thickening, and Dewatering. (Cont'd.)
l»*f - Sources - Design Information
- Texts and Literature must be reviewed but rarely give all
the answers,
•• Laboratory and Pilot Studies are almost always necessary.
- Suppliers recommendations; Equipment and product firms,
because of their interest, have their internal R & D work
which can provide data.
- Previous Experience; Is all too seldom available.
- Visitation to Other Plants; Helpful but sometimes misleading.
1.3 - Special Considerations - Design Information
- Adequacy of available literature.
- Reliability of suppliers recommendations.
- Plant data; fact versus folklore.
1.6 - The Total System Approach to Design
- Evaluation of variations or changes in a sub-system (unit
process such as conditioning, thickening, etc.) only as
part of a total system evaluation.
- The Cardinal Sin examples:
- Evaluation of dewatering costs without evaluating
side-stream recycle and total system effects.
- Considering autothermic combustion as being related
only to cake solids contents (not calorific value).
73
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1 - Introduction - Sludge Conditioning! Thickening, and Dewatering. (Gout
1,7 - The Quantitative Flow Diagram and Material Balance Concepts
- A detailed comparison of alternate treatment process systems
should always include a flow diagram (s) with quantitative data
on composition of the various liquid and sludge streams.
- Preparation of such QFD's requires use of material balance data
including any changes of state involved.
1.8 - Broad Definition of Unit Processes
The following categorization of processes used in treatment
and disposal of sludges is used.
Thickening (Blending)
Stabilization (Reduction)
Conditioning (Stabilization)
Dewatering
Heat drying
Reduction (Stabilization)
Final disposal
In classifying and describing sludge processing methods, the
potential of a process to accomplish more than one task must
be taken into account. Accordingly, this nomenclature attempts
to recognize that four of the major categories (Thickening,
Conditioning, Dewatering, and Reduction) have primary as well
as secondary objectives,
1.9 - Specific Definition - Sludge Conditioning
Sludge conditioning is pretreatment of a sludge to facilitate
removal of water in a thickening or dewatering process.
74
-------
1 - Introduction - Sludge Conditioning, Thickening, and Dewatering (Cont'd.)
1.9 - Specific Definition - Sludge Conditioning (Cont'd.)
Methods are as follows:
Chemical (Inorganic and Organic)
Elutriation
Heat Treatment
Chemical methods involve the use of inorganic or organic
flocculants to promote formation of a porous, free-draining
cake structure. In this way, the flocculants improve sludge
dewaterability, alter sludge blanket properties, and improve
solids capture. In dewatering, flocculants increase the
degree of solids capture both by destabilization and agglomeration
of fine particles and facilitate cake formation. The
resultant cake becomes the true filter media. In thickening
processes, the flocculants promote more rapid phase separation,
higher solids contents, and a greater degree of capture.
Elutriation is the process of washing the alkalinity out
of anaerobically digested sludge to decrease the demand
for acidic chemical conditioners and to improve settling
sludge, the process is cost-effective and does not create
undesirable effects. When elutriation is used in a plant
which combines primary and excess activated sludge prior to
digestion, the mixed sludge fractionates during the elutria-
tion process, producing a highly polluted elutriate. The
process has been criticized because this elutriate was
bypassed into the plant effluent at some plants. However,
use of flocculants in elutriation can eliminate the problem
of the polluted elutriate.
75
-------
1 - Introduction - Sludge Conditioning, Thickening, and Dewatering (Cont'd,]
1.9 - Specific Definition - Sludge Conditioning (Cont'd.)
Heat treatment, herein, refers to the pressure cooking of
sludges in such a manner that little sludge oxidation occurs.
The Porteous, Farrer, Zurn, and some Zimpro systems fall
into this category. Thus, heat treatment is distinct from
wet air oxidation which generally involves high temperatures
and pressures, with air injection to promote a major degree
of sludge oxidation.
1.10 - Specific Definition - Sludge Thickening
The term thickening, herein, will be used to describe an
increase in solids concentration, whether it occurs as the
objective of a separate process, or as a secondary effect
of a process provided essentially for a different purpose.
Thickening Methods (Blending) are as follows:
Gravity
Flotation
Centrifugation
1.11 - Specific Definition - Sludge Dewatering
Dewatering Methods
Any process which removes sufficient water from sludge so
that its physical form is changed from essentially that of a
fluid to that of a damp solid, is a dewatering process.
Methods used in dewatering are best described by the equip-
ment employed and some major types are listed below.
Rotary vacuum filters
Centrifuges
Drying beds
Filter presses
Horizontal belt filters
Rotating cylindrical devices
Lagoons
76
-------
2 - Developments in Sludge Conditioning
2»1 - Chemical - Inorganic
New availability of by-product Ferric Chloride
- Previous major suppliers:
Pennwalt - 30,000+Tons/Year
Dow - Withdrew from business
New suppliers:
E.I.duPont deNeraours - Ultimate capacity -
150,000 Tons/Year
K. A. Steel (Gary, Indiana) - Keposted
capacity - 70,000 Tons/Year
- Sources:
Pickle liquor from steel processing and
pigment manufact'iro.
- Double dip contribution
Solution to waste acids pollution problem.
Improvement in supply/price situation particularly
in view of nutrient removal usage,
- Other potential sources
Aluminum chloride from catalyst wastes.
- Precautions
Trace contaminants.
77
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2 - Developments in Sludge Conditioning
2.2 - Chemical Organic
Cationic Polyelectrolytes
- New high functionality (high charge density products)
polyelectrolytes - dry powders,
- New liquid lower priced products.
- New emulsion type products.
Anionic Polyelectrolytes
- New, extremely high and uniform molecular weight
products.
2,21 - New Cationics (high charge density and high molecular
weight - dry powders)
- Conditioning of particularly difficult and high
activated sludge content mixed sludges for
dissolved air flotation thickening and dewatering
(Most major suppliers have one).
- Evaluations on specific sludges required - High
cost per pound.
- Used on newer filter belt presses with high
shear sections and in pressure filters.
2.22 - New liquid "Hannich" products
- Lower cost cationic functionality on polyacrylamide
backbone.
- 5% to 20% active ingredient, so reasonably local
manufacture required.
78
-------
2 - Developments in Sludge Conditioning
2.2 - Chemical Organic (Cont'd.)
2.22-New liquid "Mannich" products (Cont'd.)
- Make a flocculated sludge with, a relatively small
particle size with a slow dewatering rate ala ferric
chloride.
Use in pressure filters to replace inorganics.
2.23 -New Emulsion Polyelectrolytes - Cationic
- Very high molecular weight dispersible polymers in
emulsion form.
Water-in-oil emulsions, 20-50% by weight of polymer.
- Monomer is polymerized in an emulsion form in presence
of hydrophobic liquid and emulsifying agents.
Shipped in emulsion form.
- High molecular weight and not subjected to drying
process.
- Reputed to be very effective in dewatering but no
widespread results; still relatively new.
- Precaution; makeup of hydrophobic portion (in some
cases - kerosene).
2.2^- -New Ultra High Molecular Weight Anionics
- Radiation catalysis instead of chemical catalysis.
Uniformity of degree of polymerization and ultra
high molecular weight.
79
-------
2 - Developments in Sludge Conditioning (Cont'd.)
2,2 - Chemical Organic (Cont'd.)
2«2*f-New Ultra High Molecular Weight Anionics (Cont'd.)
Uses in primary and final basins with metal salts
with 40-60% lower dosages required,
- Also new and being now proven in - available in
gel or dry powder form.
2»3 - Thermal Conditioning (Heat Treatment)
- Definition
ox
High temperature (300-500 F) and high pressure
(150-400 PSIG) cooking of sludges to facilitate
dewatering.
- Mechanism
Re-dissclves a significant portion of the sludge,
particularly the biomass portion, generally resulting
in a sludge which will dewater fairly readily, but
simultaneously creating a major side stream or recycle
stream (Cooking Liquor) which must again be treated
biologically thus producing more biomass which must
again be heat treated and so on.
- Suppliers of Note
Zimpro low and intermediate type processes.
Envirotech/BSP-Porteous systems.
Dorr Oliver-Farrer systems (Believe Farrer process
is now with Neptune/Nichols).
80
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2 - Developments in Sludge Conditioning (Cont'cU)
2.3 - Thermal Conditioning (Heat Treatment) - (Cont'd.)
- Equipment and Process Changes
Heat exchangers, high pressure pumps, boilers and
odor control devices have been the object of some research
due to serious maintenance problems encountered to date
in U.S. plants. Downtime from maintenance problems has
frequently been 30-50% of available operating tin.e.
Several plants (Ft. Lauderdale, Cambridge/Maryland)
have had to replace stainless steel heat exchanger systems
with titanium units due to corrosion.
Severe odor and hydrocarbon emission problems have
also plagued operations of these systems. After trying
catalyltic and gas fired after-burners, one manufacturer
now recommends a dry packed granular carbon absorption
tower with subsequent steam regeneration of the carbon.
Cooking liquor treatment and the recirculation load
from sludge solubilized during heat treatment has also
been a major problem.
In Great Britain, where the use of heat treatment had
previously gone on for a number of years, (essentially
all British Heat Treatment plants have now been shut
down), the authorities had banned discharge of cooking
liquors back through the plant and/or separate biological
treatment and discharge into any stream.whic' was rr-V-
sequently ^.o be used as a source of potable water, for
health reasons.
81
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2 - Developments in Sludge Conditioning (Cont'd.)
2.3 - Thermal Conditioning (Heat Treatment) - (Cont'd.)
- Operation and Maintenance Problems
Listed below is a table showing average downtimes
encountered as listed in a recent review.
TABLE I - SUMMARY OF AVERAGE DOWNTIMES - HEAT TREATMENT PLANTS
Plant
Average Downtime
50
35
Bedford, Ohio
Columbus, Ohio
(Jackson Pike)
Gloversville/ 40
Johnson City, N.Y.
Cincinnati, Ohio 84
(Muddy Creak)
Terre Haute, Indiana 57
Denton, Texas > 50
Portland, Oregon 32
Colorado Springs 33
Current
Status
Shut down in 1975
.rtill operating in
"Irregular Fashion"
Still operating -
Vent supernatant
Working on special
cooking liquor
treatment.
Cost = $ll6.29/ton
(f83.00 = Maintenance)
Only 10% of sludge
now heat treated
Now shut down
- The Sludge Solubilization (Cooking Liquor) Problem
Heat treatment processes have always been plagued, to
some degree, with the problem of solubilization of a
portion of the sludge during the process and the sub-
sequent effects of the side-stream or recirculation load
on the aeration system proper and the plant effluent
quality.
The great debate on the relative amounts of sludge
solubilized and re-circulated has gone on for years.
82
-------
2 - Developments in Sludge Conditioning (Cont'd.)
2.3 - Thermal Conditioning (Heat Treatment) - (Cont'd.)
- The Sludge Solubilization (Cooking Liquor) Problem (Cont'd.)
Brooks-Fischer and Swanwyck (1) had carried out controlled
and documented experiments showing:
"Up to 66 percent of the suspended solids can be
dissolved and recycled in heat treatment".
"Solubilization is most marked in the case of
activated sludge (biomass)".
"About 33 percent of the cooking liquor is not
amenable to normal biological treatment".
While these general statements are based on controlled
experiments on specific sludges, and must be considered
in that context, recent experiences reported in a survey
of U.S. operating plants should be noted:
TABLE II - RECYCLE LOADS, HEAT TREATMENT
Effect of
Plant Recycle Load
Millville, N.J. Actual primary flow = 50% of
design but 100% of secondary
aeration capacity in use.
Gloversville/ Tried recycling to bio-filter,
Johnstown, N.Y. primary tanks, and aeration tanks
all unsuccessful so now vent
untreated supernatant to river.
Cincinnati Only 5 months operation in 2-J years
(Muddy Creek) since start-up due to maintenance
problems but plan special anaerobic
treatment system test work on cook-
ing liquor.
Gresham, Oregon Recycled cooking liquor loads:
BOD = 41%; Suspended Solids = 59%.
Vancouver, Wash. Recycled BOD load = 35%
S.S. = 11% (?)
Kalamazoo, Mich. BOD to secondary increased by
35-4-0% from heat treatment.
Plant was averaging 75-80% BOD
removal despite very high aeration
capacity.
83
-------
2 - Developments in Sludge Conditioning (Cont'd.)
2,5 - Thermal Conditioning (Heat Treatment) -(Cont'd.)
- The Sludge Solubilization (Cooking Liquor) Problem (Gont'd»)
Despite the information listed above, the firm which
carried out the survey felt constrained to make the follow-
ing statement in their report:
"Very little information on the indirect costs of or
requirements for treatment of liquors and off-gases was forth-
coming from the surveys. Engineering estimates, information
from the literature review, and information from manufacturers
were used almost exclusively to arrive at the indirect
costs,"
The surveying fire, then carried out an extensive paper
study to evolve detailed cost data on cooking liquor
treatment.
However, a basic assumption of the cost study was
that BOD loading to the aeration system would only be
increased by 20% due to the recycle of cooking liquor.
The question must be asked: What is the basis of the
20% recycle figure in light of the data listed above from
the same report plus other published data?
- Processing Discontinuity and Storage Effects on Degree
of Sludge Solubilization in Heat Treatment.
The material balance data on treatment plant systems
contained in design and cost analyses assumes steady
state operation and no effect from discontinuity of
sludge processing.
Unfortunately, as graphically revealed in the
preceding Table II, operation of heat treatment systems
has been largely subject to interruption due to operating
and maintenance problems, and inevitably, sludge piles up
in the plant.
84
-------
2 - Developments in Sludge Conditioning (Cont'd.)
2.3 - Thermal Conditioning (Heat Treatment) - (Cont'd.)
- Processing Discontinuity and Storage Effect on Degree
of Sludge Solubilization in Heat Treatment. (Cont'd.)
This has a double-barreled effect. It means that the
"Sludge Removal Rate" from the plant must be dramatically
increased after a period of sludge processing shut down
just to clean out the plant and then get back to a normal
equilibrium removal rate. Moreover, since the heat treat-
ment process causes a significant recycle load via solubili-
zation, the aeration system of the plant will, during the
period of operation at higher than normal sludge removal
rate, be extremely over-loaded due to the much greater
volume of recycle load arising from the "Glean-Out" period
rate of sludge processing.
The "other barrel" of discontinuity in sludge removal
is the effect of sludge storage on the degree of sludge
solubilization and hence the magnitude of the amount of
the cooking liquor recycle load. It is an unfortunate fact
that accumulation of sludge in a plant renders it more
soluble and generally less amenable to thickening and
dewatering. Thus the assumption of a fixed rate of sludge
solubilization in the cooking liquor, even when it has some
factual basis, has no practical significance when dis-
continuity of sludge removal occurs.
2.k - Case Histories - Heat Treatment
- Colorado Springs, Colorado
First BSP/Porteous Unit in 1968
(Trickling filter plant - 1^ MGD)
Second BSP Porteous unit in 1973
(Activated sludge expansion - 30 MGD)
85
-------
2 - Developments in Sludge Conditioning (Cont'd.)
2»4 - Case Histories - Heat Treatment (Cont'd.)
2.4l- Colorado Springs, Colorado (Cont'd.)
- Technical papers on the operation of the first unit (for
trickling filter sludge) have been published by Sherwood
and Phillips (3) and Kochera (*f). A technical paper on
the 1973 unit (primary and activated sludges) was published
by Boyle and Grunewald (5) in October, 1975* The evolution
of reported cost data and changes in perspective is of parti-
cular note.
- The first two papers and immediately subsequent data
yield the following cost pattern for the first unit:
TABLE III - REPORTED COSTS, COLORADO SPRINGS - UNIT I
Cost Elements Cited
Operating - Porteous/V.F.
Operating - Porteous/V.F.
Operating/Maintenance of
Porteous/V.F./Land
I/Ton
2
15
30
Source
Sherwood &
Kochera
Subsequent
Phillips
Plant Data
The paper by Boyle & Grunewald acknowledged "hidden costs"
of heat treatment associated with the second (primary and
activated sludge) unit as being kBc/o of the previously
estimated direct costs. Further, the recycle sludge solids
load from heat treatment increased the amount of sludge to
be processed by 30%.
Costs for heat treatment capital, operating and maintenance,
excluding dewatering capital costs, thickening and cake
disposal costs were stated to be
86
-------
2 - Developments in Sludge Conditioning (Cont'd.)
2.4 - Case Histories - Heat Treatment (Cont'd.)
2.41 •Colorado Springs, Colorado (Cont'd.)
- As of February, 1976, the heat treatment unit was to be
shut down and plant work commenced using chemical condition-
ing. It was noted that chemical conditioning costs of
$50/ton would be tolerated in light of experiences with
heat treatment.
- Over the past three years significant operational studies
have been carried out at Colorado Springs by the plant
staff.
2.42 -Port Huron, Michigan
- Activated sludge plant with Dorr Oliver Farrer system.
- Use centrifuges to dewater heat treated mixed sludge
after gravity thickening to 10%.
- Problems encountered with corrosion and scaling of heat
exchanger tubes.
- Routinely use flocculants in dewatering at rate of $8
worth per ton of sludge.
2.43 - Summary Status - U.S. Heat Treatment Plants
- Shut Down (5)
Coors Golden/Colo.
Bedford Heights/Ohio
Chattanooga, Tenn.
Colorado Springs, Colo.
Santee, California
87
-------
2 - Developments in Sludge Conditioning (Cont'd.)
2.k - Case Histories - Heat Treatment (Cont'd.)
2.^3 - Summary Status - U.S. Heat Treatment Plants
- Intermittent Operation (7)
Columbus, Ohio
Cincinnati, Ohio (Muddy Creek)
Gresham, Oregon
Cambridge, Maryland
Denton, Texas
Rockland County, N.Y,
Terre Haute, Indiana
- Reasonably Regular Operation (10)
Canton, Ohio
Lucas County, Ohio
Lancaster, Pa.
Millville, New Jersey
Levittown, Pa.
Wausau, Wise.
Muskogee, Okla.
Gloversville/Johnstown, New York, (Vents supernatant)
Indio, Calif. (Primary Sludge only)
South Milwaukee, Wise.
2.44. Perth, Scotland (6)
- Primary sedimentation and greatly over designed surface
aeration activated sludge plant - Effluent standards
100 PPM BOD and 100 PPM S.S.
- Porteous heat treatment system installed during 1972 -
Recycling of cooking liquor to head of plant - plate &
frame filter presses - land disposal.
88
-------
2 - Developments in Sludge Conditioning (Cont'd.)
2.4 - Case Histories - Heat Treatment (Cont'd.)
2.44-Perth, Scotland (6) (Cont'd.)
- Despite extremely high capacity of aeration system
bulking sludge problems experienced due to recycle.
- Very high fuel consumption and legal actions on
odor problems.
Evaluated Alternate Methods
TABLE IV - COSTS OF SLUDGE TREATMENT USING DIFFERENT
TYPES OF PLANT AT PERTH
Type of Plant
Heat Treatment
Centrifuge (A)
Centrifuge (B)
Centrifuge (C)
Filter belt press (A)
Filter belt press (B)
Cost/dry
Electricity
£
1.60
0.50
0.50
0.40
0.21
0.609
tonne solids
Fuel Chemicals
£ £
6.50
3.4o
4.00
3.79
1.165
7.406
Total
£
8.10
3.90
4.50
4.19
1.375
8.015
- Shut down heat treatment about end of 1973.
- Now use Satec horizontal uelt filter presses and flocculant
conditioners.
89
-------
2 - Developments in Sludp;e Conditioning (Cont'd.)
2.4 - Case Histories - Heat Treatment (Cont'd.)
2,45- Round Hill Plant/Severn-Trent Water Authority
- The case of the still-born heat treatment/incineration
plant system.
- Ordered by small local authority prior to formation of
regional water authorities,
- Completed in late 1975 but new water authority decided
to use the digestion process. Even with the added
capital expenditure for digestion the Severn/Trent
Authority claimed savings of $500,000/year would
accrue (Even without considering increased fuel costs)
by use of digestion.
2.46 -Overall Status of British Heat Treatment Plants
Over the past five years nearly all of the approxi-
mately 26 heat treatment plants in the U.K. have been shut
down.
The closing down of these plants coincided with the
reorganization of British water and sewage treatment agencies
from a large number of relatively unsophisticated small local
authorities to larger regional water authorities with signifi-
cant professional engineering staff capability.
The process of closing them down had started well
before the energy crisis.
As of late 19?6t there were only four heat treatment
plants still operating, to some degree, in the U.K. Of these
four, one was not processing any activated sludge, and one
(14) reported partial costs of |ll6 per ton of sludge processed
via heat treatment in 1971-72, (before the energy crisis), as
well as reporting many operational and maintenance problems.
At the moment, there are no new installations planned.
89A
-------
3 - Developments in Sludge Thickening
3.1 - Dissolved Air Flotation
British Results
Paper by Burfitt of Severn-Trent Water Authority - 1975 (7)
Aycliffe Sewage Works - Thickening of excess activated
sludge
Design Basis:
p
Loading - 9175 kg/ra /h
Influent Solids - 5,000 mg/1
Effluent Solids - k%
Polymer Dosage - 1.63 kg/h
TABLE V - PLANT RESULTS - FLOTATION THICKENING
Influent
Flow Rate
850 m3/d
SS (mg/1)
Mean - 5080
Max. - 7110
Min. - 247C
Std. Deviation
Effluent
SS (mg/1)
18
46
7
- 1475 7
Float
Loading
7.8 kg/m/h
Total Solids (%)
4.5
7.6
2.0
0.8
- In general, results on dissolved air flotation sludge
thickening in the U.S. are very similar to the published
data noted above.
90
-------
3 - Developments in Sludge Thickening (Cont'd.)
3.2 - Use of Disc Centrifuges
- Most significant work done by Grunewald at Colorado
Springs (8).
- Dorr Oliver units thickening excess activated sludge,
TABLE VI - DISC CENTRIFUGE RESULTS - THICKENING
Polymer
Cost #/Ton
Nil
10
Thickened Sludge
Solids (%)
k
5-6
Solids
Capture (%)
85
98
- Final selection of type and amount of polyelectrolyte to
be used and level of solids capture to be selected is tiie
subject of continuing plant study,
- Particularly significant equipment needs for successful
use of disc centrifuges noted by Grunewald:
1 - DSM hydraulic screens required ahead of centri-
fuges to eliminate nozzle plugging.
2 - Centricleaners also required to eliminate
abrasives and prevent excessive wear, even
though excess activated sludge being processed.
- Newly Developed Multi-Stage Horizontal Belt Filters
- The first stage of these units are designed, in some cases,
to both condition and thicken sludges of lower concentra-
tion (0<>5-2,5% solids) then what is normally considered
adequate for successful dewatering (3/°)«
91
-------
3 - Developments in Sludge Thickening (Cont'd.)
3.3 - Newly Developed Multi-Stage Horizontal Belt Filters (Cont'd.)
- Results on U.S. sludges are currently being obtained.
- These units are described under the "Developments in
Sludge Dewatering" section.
4 - Developments in Sludge Dewatering
4.1 - Horizontal celt Filter Presses
11 - General Comment
- The continuing development and improvement of this type
of dewatering device has been most extensive in Europe,
and particularly in West Germany. The initial U.S. unit
was the original Klein device as introduced by 8. F. Carter
in 1971.
FIGURE I - Horizontal Belt Filter - Original Concept
—k-Draining zone-*!—Press zone •'• Shear zone—J
This type unit has been very successful for most normal
mixed sludges. Typical results for dewatering digested
mixed sludges with initial feed solids of 5«7% to a final
cake solids content of 19% at a rate of 6.7 Ib/hr/ft with
a chemical conditioning cost of |&.10/ton are cited.
92
-------
- Developin_ents_j.n_ Sludge Dewatering (Cont'd.)
- Horizontal Belt Filter Presses (Cont'd.)
.11 - General Comment (Cont'd.)
- While these results are satisfactory for many install-
ations and the filter belt press (in some form) has in the
past five years become the most widely used dewatering
device outside the U.S., much of the success of the basic
horizontal belt filter concept is due to the continuing
refinement of the units. There have been continuing
developments beyond the original Klein/Carter single pass
unit.
Because of the widespread acceptance of the horizontal
belt filter press units, (*tl? units by Klein of Germany
alone as of 1975) » several equipment firms have developed
and successfully applied various refinements of the original
unit.
- Among these are:
TABLE VII - HORIZONTAL BELT FILTERS - LIST OF MANUFACTURERS
Company Name of Device Comment
B.F.Carter
(German Origin)
B.F.Carter
(German Origin)
Komline Sanderson
(German Origin)
Infilco Degremont
(French Origin)
Simon Hartley
(German Origin)
Passavant
Series JO-Two Level
Belt Filter Press
Series 31 (Similar
to Klein S Press)
Unimat-Model S,
Model SM & Model
SMH
Floe Press
Winklepress
Sibamat
93
Higher throughput
than original unit
Separate cylindri-
cal screen "Reactor-
Conditioner" before
3 zone pressing
Three models with
one, two and three
successive stages,
respectively.
Horizontal belt
followed by press-
ure drum.
Horizontal and then
Vertical drainage
sections followed by
Shear Zones
Gravity, vacuum
§. mechanical
ure
-------
- Developments in Sludge Dewatering (Cont'd.)
4.1 - Horizontal Belt Filter Presses (Cont'd.)
*f,12 - B. F. Carter - Series 31 Device
- Referring to Figure 2 below this device functions
as follows:
1. The reactor conditioner (a rotating cylindrical
screen) removes free draining water, usually
increasing sludge solids content from 0.5-5% to 5-12%.
(Note possible replacement of a separate sludge
thickening stage).
2. The sludge then passes into the first or low
pressure zone with the top belt being solid and the
lower one being a sieve. Herein further water
removal occurs and a sludge mat with significant
dimensional stability is forming.
3. In the second or high pressure zone (4 atmospheres)
the sludge is sandwiched between two sieve belts.
Large mesh openings are possible because the sludge
has developed structural intergrity at this point.
4. A serpentine configuration makes up the Shear
Zone at the end of the second pressure zone wherein
by stretching the belts and sludge cake over smaller
rollers, a squeezing action expels more water from the
cake.
94
-------
4 - Developments in Sludge Dewatering (Cont'cU)
*r_«l - Horizontal Belt Filter Presses (Cont'd.)
4.12-B. F. Carter - Series 31 Device (Cont'd.)
FIGURE II - Carter Automatic Belt
Filter Press System - Series 31
CARTER AUTOMATIC BELT-FILTER PRESS SYSTEM
WITH INTEGRAL SLUDGE REACTOR CONDITIONER"
SCHEMATIC (CONCEPTUAL ONLY)
POLYMER
—-SLUDGE
rWASH WATER
(EFFLUENT OR
! CITY WATER)
I—(optional)
CLEAN FILTRATE
DISCHARGE
SOLIDS
BELT PRESS
(LOW PRESS./HIGH PRESS./
SHEAR PRESS.)
— - - - k PROCESSED
------ -7* X. CAKE
DISCHARGE
|
DIRTY WASH WATER,
FILTRATE, AND
RECYCLE POLYMER
PATENTS APPLIED FOR
95
-------
- Developments in Sludge Dewatering (Cont'd.)
- Horizontal Belt Filter Presses (Cont'd.)
4.12- B. F. Carter - Series 31 Device
- While few details on equipment sizing and results to
date have been published in the U.S., the following
size data is available from Europe using Wm. Jones Chemical
Engineers Ltd., London's nomenclature system for the
Carter Series 31 unit which is known as the "S" Press
in Europe.
TABLE VIII - TYPES AND DIMENSIONS FOR S-PRESSES
Type Filter Active Overall Dimension-Press/Reactor Complete
Belt Filter Length Width Height Weight Plant
Width
m
Area
m m
m m Tonnes
KwHrs.
S.8 0.8
S.15 1.5
S.25 2.5
17 3.3/1.6 1.3/0.75 2.2/1.3 3.5/0.5 5
32 3.3/2.2 2.0/1.8 2.2/1.4- 5.0/1.0 7
53 3.3/2.2 3.0/1.8 2.2/1.4 7.0/1.0 9
Typical capacity and results for the largest S P)ess (S.25)
are that it will dewater a 4-6% solids feed of mixed
digested primary and excess activated sludges at a rate of
6-18 tons/day while producing a cake with a dry solids
content of 30-4-0% and using 4—10 pounds/ton of cationic
polyelectrolyte.
In mid 1975 there were 50 world-wide installations of the
Klein S Press similar to the Carter Model 31 Type Unit
with many more being designed into other installations.
Processing of 50 dry tons per day of a typical mixed
primary/excess activated sludge is estimated to require
3 S Presses which would cost about ^300,000 for a completely
automated system including polyelectrolyte facilities.
96
-------
4 - Developments in Sludge Dewatering (Cont'd.)
4.1 - Horizontal Belt Filter Presses (Cont'd.)
*t,12- B. F. Carter - Series 31 Device (Cont'd.)
- The ability to obtain a significantly drier dewatered
cake (30-^-0% solids) and low power consumption are
significant performance characteristics of this latest
generation horizontal belt filter press.
An additional consideration is the potential use on
lower solids content feed sludges.
4,13 - Komline Sanderson Unimat Belt PMlter Press
- This device also features three stages of processing:
Gravity drainage; medium pressure pressing; and lastly,
high pressure pressing.
- The Unimat Belt Filter Press is a unique system designed
to provide optimum dewatering of municipal and industrial
wastes. The Unimat Press offers exceptional flexibility
in operation, since each stage in the system operates
independently, thus allowing optimum control. Separate
modules provide for gravity separation in the initial
stage. After the waste has been dewatered to its maximum
in these modules, it is distributed on a continuous belt,
where additional water is allowed to drain from the solidst
Pressure is then applied to these solids as the cloth
carries the sludge cake around the pressure rolls. If
required, a third stage is provided where a sustained
high pressure is applied by slatted plates, continuously
applying high pressure for further dewatering, Additional
area may be added to the middle pressure stage or nigh
pressure stage to increase the final solids content if
additional time and pressure will result in further
dewateringo
97
-------
4 - Developments in Sludge Dewaterin^ (Cont'd.)
4.1 - Horizontal Belt Filter Presses (Cont'd.)
- Komline Sanderson Unimat Belt Filter Press (Cont'd.)
Control of the unit feed, dewatering time and cake thick-
ness can be effected through the wide range of operating
times and pressures of the belt press. The press operates
continuously and automatically and is able to apply
extremely high pressures on the cake solids while being
free from the disadvantages of batch processing.
The following table lists the design features of the
Unimat Series*
TABLE IX - ACTIVE FILTRATION SURFACE AREAS & RETENTION
TIMES
Machine
Model
S
M
H
Machine
Width
(Meter)
1
2
3
1
2
3
1
2
3
Active Filtration
Surface Area (Sq. Ft
S
~5ff
136
204
5 roll 7
101
203
305
ALL
32.8
65.6
98.4
L
104
208
312
roll
190
380
570
Retention
.) Time (Minutes)
S L
1.2 to 6 2 to 9
5 roll 7 roll
5 to 19 10 to 36
ALL
2 to 6
Note: When using 2 or more sections, the retention time
and active surface areas are cumulative.
Example:
SMH 1/5 = 68 sq.ft. +101 sq.ft. +32.8 sq.ft. =201.8 sq.ft.
SMH 1/5 = 1.2 min.+ 5 min.+ 2 min.= 8.2 min. in Unimat at
maximum speeds*
SMH 1/5 = 6 min.+ 19 min.+ 6 min.= 31 min. in Unimat at
minimum speeds.
98
-------
- Developments in Sludge Dewatering (Cont'd.)
k.l - horizontal belt Filter Presses (Cont'd.)
- Komline Sanderson Unimat Belt Filter Press (Cont'd.)
- Typical results for the various Unimat models appear below:
TABLE X - DRY SOLIDS OF CAKE AND POLYMER DOSAGE
UNIMAT:
Type of Sludge
Feed Cone.
(% D.S.)
Fresh-Primary
(Raw)
4 - 6%
Fr. Prim &
Trickling
Filter
5 - 5%
Fr, Primary
& Activated
3 - 5%
Anaerobically
Model S.
After
Gravity
Stage
(%D.S.)
12-18
10-15
10-15
JA-24
Model SM
After Gravity
& Medium
Pressure
(#D.S.)
25-35
22-32
17-27
25-35
Model SMH
After
Gravity &
Medium &
High Press-
ure
30-45
28-JfO
25-35
30-^5
Typical
Polymer
Dosage
/ton D.S
6.0 - 8.5
6.0 - 10.0
6.0 - 10.0
5.0 - 8.5
Dig. Prim. &
Act. k -
-------
- Developments in Sludge Dewatering (Cont'd,)
4.1 - Horizontal Belt Filter Presses (Cont'd.)
40l4 - Infilco - Degremont Floe-Press
- This unit originated in France where there are
46 installations,.
- The Floe-Press is a two stage unit with a horizontal
belt free drainage area followed by a pressure belt
section.
- U.S. installations are at:
Medford, New Jersey
Fayetteville, North Carolina
Bell County, Texas
Harris County, Texas
Madwaska, Maine
- It appears to be well constructed device which will produce
cakes comparable to centrifuges and rotary vacuum filters
with a lowered power consumption.
4.2 - Developments in Pressure Filters
4.21 - U. S. Case Histories - Conventional Units (9)
- Kenosha, Wisconsin
- Plant Design
26 MGD Primary & Activated Sludge
Sludges mixed, gravity thickened, anaerobically
digested, dewatered in Nichols (Edwards & Jones)
pressure filters and disposed of to farmers as
dewatered cake for land application via manure
spreader.
- Dosage of chemicals is J>% Ferric Chloride (based on
dry solids) and 25% lime, in slurry form.
100
-------
- Developments in Sludge Dewatering (Cont'd.)
4.2 - Developments in Pressure, Filters (Cont'd.)
^•2.1- U. S. Case Histories - Conventional Units (9) (Cont'd.)
- Kenosha, Wisconsin(Cont'd.)
- Digested sludge at 3-7% solids is dosed in line with
Ferric Chloride and lime is added in a subsequent
mix tank with slow speed mixing,
- Two Moyno pumps feed the two press simultaneously.
The Hoynos have worked very well. Filtrate is
returned to head of plant.
- Try to maintain 100 PSIG for 30 minutes and total
cycle time is 2-y -2-g- hours - Operate 16 hours per
day, 7 days per week to produce 12 tons per day of
dry solids cake at 35-38% solids. Cake thickness
is one inch.
- Results: Good handleable press cake and clear filtrate.
TABLE XI - COSTS - PRESSURE FILTRATION, KENOSHA
Costs |/Ton
Labor 7.^3
Chemicals 20.17
Power 1.71
Maintenance 3»25
32.56
Problems
High chemical dosage and costs. Cake is actually
about 25% added chemical so analysis is really
about 65% water, 26% sewage sludge and 9% inorganic
101
-------
- Developments in Sludge Dewatering (Cont'd.)
4.2 - Developments in Pressure Filters (Cont'd.)
4.21-U. S. Case Histories - Conventional Units (9) (Cont'd.)
- Kenosha, Wisconsin (Cont'd.)
- Problems
chemical. Net sludge production must be reduced
by 25% to get actual figures.
Excessive wear in cloths and stay bosses causing
serious maintenance problems. Filter cloths
replaced 3 times in 2 years (3,000^ per press
per change).
Severe ammonia odor problems in press room,
(effect of lime and high pH).
- Comment
Despite above problems there have been no
extensive forced downtime periods in the
2 years of operation.
Much of the chemical consumption might be
eliminated if the alkalinity of the digested
sludge were washed out in a properly designed
and operated elutriation system using flocculants.
Why use pressure filters when the wet cake is
disposed of on land by a manure spreader?
- Brookfield, Wisconsin - Fox River
Water Pollution Control Center
- Plant Design
2 MGD - Primary + Activated Sludge + Contact
Stabilization.
102
-------
k - Developments in Sludge Dewatering (Cont'd.)
4.2 - Developments in Pressure Filters (Cont'd,)
4.21-U. S. Case Histories - Conventional Units (9) (Cont'd.)
- Brookfieldt Wisconsin - Fox River
Water Pollution Control Center (Cont'd.)
- Plant Design (Cont'd.)
80% Primary Sludge + 20% Secondary Sludge is
mixed, pumped through a grinder, diluted with
recycled incinerator ash (O.^/W sludge),
conditioned with lime (15-18%) and Ferric
Chloride, pressed and fed to a 5 hearth incinerator.
95% of incinerator ash is recycled. The incinera-
tion is not autotherraic and uses natural gas.
Pressure filters are standard Passavant design
with 52" diameter plates of steel and have been
operated for 1-J years.
- Results: Plant personnel claim that no major
operating problems have been encountered. There
have only been two "Sludge Blowing Incidents" in
the 1-jy years of operation.
Press cloths have had to be replaced every 6
months at a cost of $3,600 per shot.
Comments:
1. The mixed sludge being processed is a relatively
easily dewaterable material which is high (80%)
in primary content and high in fibrous material.
Indeed the high fiber content has caused problems
in the press cake breaking operation,.
103
-------
- Developments in Sludge Dewatering (Cont'd.)
402 - Developments in Pressure Filters (Cont'd.)
*f«21-U. S. Case Histories - Cocventional Units (9) (Cont'd.)
- Brookfield, Wisconsin - Fox River
Water Pollution Control Center (Cont'd.)
)
- Comments: (Cont'd.)
2. No records are available on natural gas con-
sumption and no cost data on the system has been
made available.
3. The system appears to be a complex high capital
and high operating and maintenance cost one which
is difficult to rationalize, particularly at a
plant with such an easily processable sludge.
4. The plant has two components of interest to other
potential press filter designs: the wet sludge
grinder and the slow speed cake breaker.
4.22 - Conclusions on U. S» Results to Date
- Reference 9 t from which the above results came, is
an excellent review of the current U. S. installations.
- The conclusions from reference 9 are as follows:
1. In looking at the two types of presses, we found
some advantages with the lower pressure design.
Essentially, it is a much simpler operation. The
recycling of incinerator ash seemed to provide few
benefits, particularly because it only complicated
the operation with additional material handling
equipment.
104
-------
Developments in Sludge Dewatering (Gont'd,)
k»2. - Developments in Pressure Filters (Cont'd.)
4.22 - Conclusions on U« S« Results to Date (Cont'd.)
2, In general, we found that filter presses are an
acceptable method for dewatering sludge. Theoreti-
cally, they should always produce an autocombustible
sludge cake. But, practically, we know of no installa-
tion anywhere that can achieve this. The ash
recirculation is probably the limiting factor,
3, Filter presses seem to be quite capable of handling
different sludge concentrations and different types
of sludge feed. Proper conditioning, especially
with lime, is the key to good operation. Vacuum
filters are not quite so adaptable,
4. The necessity of using high lime for conditioning
could be a drawback. Lime handling is always
difficult,
5, Prior to a large scale installation, pilot plant
work should always be performed to evaluate the
dewatering characteristics and chemical require-
ments.
6, Filter presses have a higher capital cost than
vacuum filters. The presses also usually have a
higher operational cost. Their real advantage is
in greatly reducing the costs of final disposal for
the sludge cakes0 A detailed economic analysis of
the total system is needed before deciding for or
against filter presseso
105
-------
- Developments in Sludge Dewatering (Cont'd.)
4.2 - Developments in Pressure Filters (Cont'd.)
4.23 -Other Developments in Use of Pressure Filters
Polyelectrolyte Conditioning
Due to the much more prevalent previous incidence of the
use of filter presses in continental Europe and the
United Kingdom, and also due to innovative work there,
the successful use of certain polyelectrolytes in
conditioning sludges for dewatering in plate and frame
presses has been realized at a number of locations.
Farnham Water Pollution Control Works,
Thames Water Authority, U.K. (10)
- Primary and Trickling Filter sludges.
- Humus sludge recirculated to primaries, mixed
sludge thickened, dewatered on two filter presses,
operating pressure = 586 - 690 kPa (85-100 PSIG).
- Initial operation with aluminum chlorohydrate as
conditioner.
FIGUBE III - Farnham Plant-Sludge Conditioning & Pressing
Flow Diagram
FILTRATE
RAW MIXED
SLUDGE
I SUPERNATANT
4 LIQUOR
MOLDING
TANK
MONO
TRANSFER BAR
PUMPS SCREEN
wren
rxjwJ
V J \ cU 7 MONO
N S V^X DOSING
CHEMICAL
STORAGE
TANK
CHEMICAL PUMPS
! DILUTION
/-1
.TANK
V-
-c:~>-
CAKE
DISCHARGED
t
FK.TER PRESSES
FILTRATE
T
CAKE
DISCHARGED
x-_-
y
ALUMINIUM CHLOROHYDRATE
BATCH CONDITIONING.
— »• ZETAG 63 IN-LINE
CONDITIONING.
106
-------
- Developments in Sludge Dewatering (Cont'd.)
4.2 - Developments in Pressure Filters (Cont'd.)
4.23- Other Developments in Use of Pressure Filters (Cont'd.)
- Farnham Water Pollution Control Works,
Thames Water Authority, U.K. (10) (Cont'd.)
- Severe filter cloth blinding problem encountered and
various diagnostic test work done (Reference 10 ).
- By converting to use of Allied Colloids Zetag 63 liquid
polyelectrolyte, the cloth blinding problem was alleviated
sufficiently to permit the two presses to cope with the
sludge load.
- Chemical costs of alternate systems are depicted below*
TABLE XII - OPERATING CONDITIONS FOR VARIOUS CONDITIONING
AGENTS
GST Range Pressing Cycle
Conditioning Dose Cost during cycle Time Range
Agent (% on ds) (£/tonne (seconds) (hours)
ds)
Aluminium
Chlorohydrate 2.5
(batch)
Aluminium
Chlorohydrate 2.5
(in-line)
Zetag 63 0.2-
(batch) 0.3
Zetag 63 0.2-
(in-line) 0.3
Ferric Chloride 3
11.00
11.00
3.35-
5.05
3.35-
5.05
7.40
10-65
.Results not
Available
10-32
8-14
8-45
6-18
6-12
6-9
3-6
3-13
& Lime (batch) 25
Ferric Chloride 3
& Lime (in-line) 25
8-15
3-5
107
-------
4 - Developments in Sludge Dewatering (Cont'd,)
4.2 - Developments in Pressure Filters (Cont'd.)
4.23- Other Developments in Use of Pressure Filters (Cont'd.)
TABLE XIII - SUMMARY OF UNITED KINGDOM RESULTS -
VARIOUS CONDITIONING SYSTEMS (11)
Type % Dry
Sludge Solids
Primary + 4
Humus +
Excess
Activated
it ii /j.
Primary + 3-4
Excess
Activated
Sludge
« n 3.^
- Comments on
Cake
Conditioning Thickness
System (mm)
3-5$ Ferric 25-32
Chloride +
20% Lime
0.3-0.5% 25-32
Cationic
Polymer
5% Ferric 25
Chloride +
20-25% Lime
0.3-0.5% ^5
Cationic
Polymer
European Experiences
Properties
% Dry Cycle
Solids Time(Hrs.)
35-40 4-7
35-40 4-7
30-35 7
30-35 7
The U.S. continues to lag behind Europe in adapting
pressure filters to the use of polyelectrolytes. There are
many European plants which have successfully replaced the
inorganic conditioners and thereby materially reduced
operating and maintenance costs.
108
-------
- Developments in Sludge Dewatering (Cont'd.)
km2 - Developments in Pressure Filters (Cont'd.)
4»23- Other Developments in Use of Pressure Filters (Cont'd»)
- Comments on European Experiences (Cont'd,)
Successful adaptation to polyelectrolyte usage
usually involves a change to "in-line" flocculant
dosage, proper regulation of the press loading cycle,
and in some cases, the use of two or three filter
cloths of varying mesh opening size in the press.
4,3 - Developments in Centrifuge Dewatering of Sludge
4,31 -General Comment
- Adaptation of older counter-flow types of
horizontal solid bowl centrifuges designed for
various relatively easy to dewater raw primary
or industrial sludges to the more difficult munici-
pal sludges containing biomass.
- Initial attempts = higher speeds and greater
"g" forces (1000+) were largely counter-productive
due to shear effects on the sludge floes,
- Problems were to achieve a greater degree of
dewatering/clarification (higher cake solids and
clean centrate) and to reduce operating and main-
tenance costs.
109
-------
- Developments in Sludge Dewatering (Cont'd.)
*j>j__ - Developments in Centrifuge Dewatering of Sludges (Cont'd.)
^.31- Genoral Comment (Cont'd.)
- Five steps taken which have proven to be beneficial.
- Longer bowls with smaller diameters.
- Lower rotational speeds to reduce turbulence,
electrical costs and wear and tear.
- Concurrent flow to minimize turbulence.
- Adjustable variation of speed differential
between the bowl and the sludge removal scroll.
- Use of new high molecular weight cationic
polyelectrolytes.
- Various manufacturers have combined some of the
first four features in their latest models. All of
them are using the new high molecular cationic
polyelectrolytes.
4.52 - Host Recent and Definitive Experiences in Germany
- Reference 12 is a comprehensive article relating results
obtained at Wuppertal-Buchenhofen plant with a low speed
con-current flow type unit.
- A combined municipal-industrial treatment plant treat-
ing 1,200,000 population equivalent.
- After primary and biological treatment the mixed sludges
are thickened to J>-k% and anaerobically digested, followed
by sludge settlement and decantation, thence dewatering.
110
-------
- Developments in Sludpe Dewatering (Cont'd,)
*f»3 - Developments in Centrifuge Dewatering of Sludges (Cont'd,)
4,32-Most Recent and Definitive Experiences in Germany (Cont'd,)
- After initial trial work the authority asked for com-
petitive tenders from various suppliers of centrifuges
with performance requirements as follows:
1. Capacity of each centrifuge: ^0-60 m /hour of
sludge with feed of 2,5-3fr dry solids,
2. Minimum cake solids: 20%,
3, Centrate maximum suspended solids of 0,2%,
4. Maximum polyelectrolyte dosage.permissible of
3.3 kg/ton of dry solids (100 gm/nT).
5« Maximum permissible power consumption of 1 KWH
per cubic meter of sludge feed including ancillary
equipment such as pumps, flocculant metering
stations, etc,
6, Guaranteed life of screw conveyor = 10,000 hours.
7, Provision of a package plant with a minimum
capacity of 4-0 m /h for a k month trial period under
a leasing arrangement,
- KHD Industrieanlagen AG Humboldt-Wedag of Cologne won
the contract and initially installed two S3-2 type low
speed concurrent flow centrifuges with capacities of
20-30 m /h each. These units met the agreed performance
guarantees but when the full civil installation was com-
pleted they were replaced, as planned, by two of the
larger Bk-1 units (of the same basic type) but with
capacities of 40-60 m /h each.
Ill
-------
- Developments in Sludge Dewatering (Cont'd.)
*f»3 - Developments in Centrifuge Dewatering of Sludges (Cont'd.)
4,52- Most Recent and Definitive Experiences in Germany (Cont'd.)
- KHD Industrieanlagen AG Humboldt (Cont'd.)
Power consumption for the complete dewatering plant
was 0,9-0,95 KWH/m with SJ-2 units and improved to
0.75-0.8 with the larger S4-1 units.
Dosage of Zetag 92 polymer (Allied Colloids) averaged
60-80 gm/ra.
- The article contains much data on the effect of centri-
fuge dewatering variations on overall process performance
and sludge disposal costs.
- A significant factor studied was that of the effect of
the differential in speed between the scroll and the bowl.
TABLE XIV - EFFECT OF SPEED DIFFERENTIAL ON THROUGHPUT
AND DRY SOLIDS
Speed Differential 2 *t 6
Flocculent dosage (g/m^) 60 80 60 80 60 80
Dry Solids carried by
discharge (90 26 28.5 2k 2J> 20. $ 20
Dry solids carried by
centrate (undissolved 0.35 0.25 0.17 0.07 0.12 0.07
solids)
Ideal throughput (m5/h) 33 37 ^3 ^5 ^0 48
- As can be seen, a 28.5% dewatered cake at a reasonable
throughput of 37 m /hour and centrate suspended solids of
0.2536 can be obtained with flocculant dosage of 80 g/m by
using a speed differential of 2 instead of 6.
112
-------
Developments in Sludge Dewatering (Cont'd.)
4.3 - Developments in Centrifuge Dewatering of Sludges (Cont'd.)
k»32 - Host Recent and Definitive Experiences in Germany (Cont'd.)
The paper claims and purports to show that very large
capacity centrifuges of the improved low speed-concurrent
flow type, when operated in a lower differential speed
mode can offer significant capital and 0/M cost savings
where large volumes of sludges are to be processed.
- Unit costs are given as follows:
Operating - DM 36.^0/ton dry solids
Annual Capital - DM ^7.60/ton dry solids
^33- Side by Side Evaluation of New Low Speed Concurrent Flow
Solid Bowl Centrifuge and the Older High Speed Counter-
Flow Type (13)
- Stockholm, Sweden has operated three high speed centri-
fuges for a three year period and also have operated
a new low speed concurrent flow unit on the same sludge
for one and one-half years.
- Table 15 below shows the results obtained with the two
different types of centrifuge:
113
-------
- Developments in Sludge Dewatering (Cont'd.)
3 - Developments in Centrifuge Dewatering of Sludges (Cont'd.)
4,33 - Side by Side Evaluation of New Low Speed Concurrent Flow
Solid Bowl Centrifuge and the Older High Speed Counter-
Flow Type (13) (Cont'd.)
TABLE XV - SIDE BY SIDE COMPARISON PROCESS RESULTS
Centrifuge Design Low Speed
Sludge Identification
No, of Operation Units
Flow Rate Per Unit
% Feed Consistency
% Cake Solids
% Solids Recovery
Polymer Type
Polymer Dosage 6 Ibs/ton
High Speed
Anaerobically Digested Primary
Plus Waste Activated with Alum
Sludge
one (1)
190 GPM
16-18%
95-98%
three (J)
90 GPM
16-18%
95-98%
Allied Colloids Percol
Cationic
12 Ibs/ton
- While the above table only shows the improvement realized
by reduction in polyelectrolyte costs by about JS(9/ton
(which is a considerable savings), the following Table 16
illustrates the additional advantages for the low speed
design.
114
-------
Developments in Sludge Dewatering (Cont'd.)
4.3 - Developments in Centrifuge Dewatering _qf_ Sludges (Cont'd.)
4-.33 - Side by Side Evaluation of New Low Speed Concurrent Flow
Solid Bowl Centrifuge and the Older High Speed Counter-
Flow Type (13) (Cont'd.)
TABLE XVI - SIDE BY SIDE COMPARISON MACHINE PARAMETERS
Centrifuge Design
Bowl Diameter
Bowl Length
Centrifugal Force
Unit Flow Rate
Unit Pool Volume
Sigma Factor
Unit Motor Size Rating
Absorbed Horsepower
Noise Level @ 3 ft.
Wear @ 2000-Hour
Inspection
Low Speed
36"
96"
511 x G
190 GPM
196 Gallons
1.15 x 107 cm2
100 HP
.3 HP/GPM
80-85 dBA
1/2 mm
High Speed
25"
90"
18?8 x G
90 GPM
73 Gallons
5.3 x 107 cm2
180 HP
.6 HP/GPM
95-100 dBA
9 mm
- Wear played an important part in displacing the high speed
centrifuges in favor of the low speed centrifuges at this
particular plant. The low speed centrifuge was inspected
after 2000 hours of operation and found to have only 1/18
of the wear of the high speed alternative. The abrasive
protection on the low speed machine conveyor blades is
tungsten carbide, while the protection on the high speed
machine is equivalent to an alloy called Stellite 1016.
The Stellite material is considered inferior to the tung-
sten carbine and posseses a relative hardness value of Rc-6lt
115
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- Developments in Sludge Dewatering (Cont'd.)
4.3 - Developments in Centrifuge Dewatering of Sludges (Cont'd.
4. 33 -Side by Side Evaluation of New Low Speed Concurrent Flow
Solid Bowl Centrifuge and the Older High Speed Counter-
Flow Type (13) (Cont'd.)
whereas the tungsten carbide hardness values approach
fic-69o Experience shows that if both materials had been
similar that the wear rate would still have favored the
low speed design by as much as a five to one ratio.
Summarized in Table 1? is the annual cost analysis of the
operation of these two types of centrifuges installed side
by side* The low speed unit clearly has the edge in all
categoriese Power consumptions are one-half (1/2) that of
the high speed unit. With respect to polymer consumption,
the low speed centrifuge in this particular case utilized
44% less cationic polymer than the high speed centrifuge.
With respect to conveyor maintenance, we have modified the
high speed centrifuge figure to reflect a ratio of con-
veyor resurfacings more in the category of five to one
than the 18 to one margin indicated by the actual side by
side installation. The category entitled "Amortized
Equipment" includes the cost of the centrifuge, the motor,
and the starter, and is expressed on a tonnage basis and
reflects an amortization rate of 1% interest over a 20-
year period. Electrical usage rate was assumed to be
fi.02/KWH and polymer (Allied Colloids Percol^?28) was
figured at S1.50/lbe
116
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k - Developments in Sludge Dewatering (Cont'd,)
4,3 - Developments in Centrifuge Dewatering of Sludges (Cont'd,)
4»33- Side by Side Evaluation of New Low Speed Concurrent Flow
Solid Bowl Centrifuge and the Older High Speed Counter-
Flow Type (13) (Cont'd.)
TABLE XVII - SIDE Bi' SIDE COMPARISON ANNUAL COST - PROFILE
Centrifuge Design Low Speed High Speed
Tons/Year Per Unit 12,483 5,913
Power Expenditure $0.Ob/ton $1.19/ton
Polymer Expenditure $9.00/ton $l6.00/ton
Maintenance Expenditure $1.21/ton S8.30/ton
Amortized Equipment #1.50/ton S2,44/ton
Total Annual Cost S12.33/ton 027.93/ton
- While the larger size of the low speed unit would account
for a minor portion of the above noted superiority, it is
abundantly clear that the lower speed concurrent flow unit
is superior from a cost-effectiveness standpoint.
117
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BIBLIOGRAPHY
1 - Fischer, W. J., and Swanwick, J. D., "High Temperature Treatment
of Sewage Sludges", Water Polio Cont., (1971), pp.355-373.
2 - Process Design Manual For Sludge Treatment and Disposal -
EPA 625/1-74-006.
3 - Sherwood, R., and Phillips, J., "Heat Treatment Process Improves
Economics of Sludge Handling and Disposal, Water & Wastes Eng,,
42, (1970).
k - Kochera, B., Operation of a Thermal System for Sludge, WPCF Meeting,
Atlanta, Georgia, 1972.
5 - Boyle and Grunewald, WPCF Journal, 1976.
6 - McLeod, J., Operating Experiences at the City and Royal Burgh of
Perth Sewage Treatment Works, Water Poll. Cont., 1976, pp. 311.
7 - Burfitt, Dissolved Air Flotation at Aycliffe Sewage Works, Water
Poll. Cont., 1975
8 - Personal Communication - Grunewald, D., Colorado Springs, 1977.
9 - Cassel, A. F., Review of U.S. Filter Press Operations, Paper presented
at Chesapeake WPCF, June, 1976.
10 - Charlesworth, B. R., et.al., Polyelectrolytes in Pressure Filtra-
tion: Experiences at Farnham, Effluent & Water Treatment Journal,
August, 1975» pp.4ll.
11 - Personal communication, Allan Jones, Technical Sales Mgr., Johnson
Progress Ltd., Stoke on Trent, U.K.
118
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BIBLIOGRAPHY (Cont'd.)
12 - Reimann, D., Kommunalwirtschaft, No0 9, Sept., 197^, pp.3^3-352,
13 - Guidi, E, J., Why Low Speed Centrifugation, Presented at Ohio
WPCF, Columbus, June 16, 19?6.
l^f - Whitehead, C. R., and Smith, E. J., Sludge Heat Treatment:
Operation and Management, Water Poll. Cont.f 1975, 1976, (l),
PP. 31.
119
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ANAEROBIC DIGESTER GAS
SOLAR ENERGY AND SLUDGE COMPOSTING
IN MUNICIPAL WASTEWATER TREATMENT
by
G. M. Wesner
CULP/WESNER/CULP
Clean Water Consultants
prepared for
ENVIRONMENTAL PROTECTION AGENCY
TECHNOLOGY TRANSFER
120
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TABLE OF CONTENTS
Page No.
INTRODUCTION 125
ANAEROBIC DIGESTER GAS 126
GAS PRODUCTION 130
GAS UTILIZATION 132
COST ESTIMATES - DIGESTER GAS UTILIZATION 134
ANAEROBIC DIGESTION HEAT REQUIREMENTS 136
SOLAR ENERGY 138
ACTIVE SOLAR COLLECTION 138
PASSIVE SOLAR COLLECTION 139
EXAMPLE - SOLAR SYSTEM FOR SPACE HEATING 139
SOLAR HEATING F.OR ANAEROBIC DIGESTERS 139
SOLAR SYSTEM COSTS 140
ENERGY REQUIREMENTS - DIGESTER GAS AND SOLAR ENERGY USE 141
SLUDGE COMPOSTING 142
PROCESS DESCRIPTION 142
WINDROW COMPOSTING 146
121
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TABLE OF CONTENTS (CONTINUED)
Page No.
STATIC PILE COMPOSTING 147
COMPOSTING EXPERIENCE 148
COMPOSTING COSTS 151
122
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LIST OF TABLES
TABLE NO.
1 DIGESTER GAS ANALYSES
2 SUMMARY OF PLANT OPERATIONS
3 INTERNAL COMBUSTION ENGINE EFFICIENCY OPERATING ON
DIGESTER GAS
4 TYPICAL HEAT RECOVERY RATES FOR DUAL FUEL ENGINES
5 ANAEROBIC DIGESTER GAS PRODUCTION AND USE
6 DIGESTER GAS CLEANING AND STORAGE COSTS
7 SOLAR HEATING EXAMPLE DETROIT MICHIGAN
8 ENERGY REQUIREMENTS 30 mgd ACTIVATED SLUDGE PLANT
IN SOUTHERN U.S.
9 COMPOST PILE PERFORMANCE - BANGOR MAINE
123
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LIST OF FIGURES
FIGURE NO.
1 ANEROBIC DIGESTER GAS UTILIZATION SYSTEM
2 INTERNAL COMBUSTION ENGINE - CONSTRUCTION
AND MATERIAL COSTS
3 INTERNAL COMBUSTION ENGINE - 0 & M LABOR AND
ALTERNATE FUEL REQUIREMENTS
4 DIGESTER GAS UTILIZATION SYSTEM - CONSTRUCTION
AND MATERIAL COSTS
5 DIGESTER GAS UTILIZATION SYSTEM - LABOR AND
ENERGY REQUIREMENTS
6 ANAEROBIC DIGESTER HEAT REQUIREMENTS FOR PRIMARY
PLUS WASTE ACTIVATED SLUDGE
7 TYPICAL SOLAR ENERGY SYSTEM
8 SCHEMATIC DIAGRAM - SOLAR HEATING ANAEROBIC
DIGESTER
9 PROCESS SCHEMATIC - ACTIVATED SLUDGE SYSTEM
10 STATIC PILE COMPOSTING
124
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INTRODUCTION
This paper evaluates the potential for use of anaerobic digester gas, solar
energy and sludge composting in municipal wastewater treatment facilities.
The section on digester gas is limited to gas use applications and does not
include information on digester design or operation. Anaerobic digester de-
sign and operation data is available in several publications by the Environ-
mental Protection Agency (EPA) and others.1'5 The use of anaerobic digester
gas has been practiced to some extent in wastewater treatment plants for many
years. Digester gas is currently being used at several plants to heat digesters
and buildings and as fuel for engines that drive pumps, blowers and generators.
Solar energy has not been used in operating treatment plants. Research has been
conducted in Florida5 and Maryland7 on heating digesters and one small plant in
Maine8*9 will use solar energy for water, space and digester heating.
Sludge composting has received renewed interest recently. In an ongoing program
supported by EPA and the Maryland Environmental Service at Beltsville, Maryland,
the U.S. Department of Agriculture, Agriculture Research Service has developed
significant new data and demonstrated an innovative composting system. Municipal
sludge composting operations are planned or in operation at several locations in
the United States.
125
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ANAEROBIC DIGESTER GAS
Digester gas is utilized in the United States in municipal wastewater treatment
plants at the following locations:
Atlanta, Georgia Los Angeles County Sanitation District
Bloom Township, Illinois Madison, Wisconsin
Buffalo, New York Orange County Sanitation District (California)
Cincinnati, Ohio Philadelphia, Pennsylvania
Cleveland, Ohio Racine, Wisconsin
Fort Worth, Texas San Jose, California
Los Angeles, California Tucson, Arizona
This is not a complete list of all plants using digester gas in the United States
but it does include several large installations and the following summary describes
conditions at some of the plants.
Atlanta, Georgia
A 90 mgd treatment plant was recently completed and digester gas will be used
in three dual fuel engines to drive blowers.
Bloom Township, Illinois
Digester gas is not now used in internal combustion engines in this plant because
of high maintenance costs.
Buffalo, New York
Internal combustion engines are not used at this plant. Sludge digester gas
is used as fuel for: (a) two boilers to heat digesters, (b) an incinerator
which burns sludge cake, and (c) building heat. There are no gas cleaning
or storage facilities.
Cincinnati, Ohio
Digester gas is utilized at the Mill Creek Treatment Works in four 1910 hp turbo-
charged dual fuel internal combustion engines to drive four 1350 kw generators.
Heat recovery units are used to furnish steam for heating the digesters. Data
from 1973-75 indicate that an average of 17.8 scf of digester gas was required
to produce one kwh of electricity. Data from other plants in Cincinnati indicate
that digester gas produced ranged from 10.9 to 13.4 cu ft per Ib of VS destroyed.
126
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Cleveland, Ohio
The sludge digester gas system will be removed from this plant in the near future
in connection with the expansion and installation of a different solids handling
system. Digester gas is not used in internal combustion engines, but is used
to heat the digesters and as fuel for a sludge incinerator. Digester gas is
produced at the rate of about 500,000 cu ft per day and about 5 cu ft per Ib
of VS destroyed.
Fort Worth, Texas
The following information is based on the period October 7, 1973 through September
30, 1974.
Average flow treated 38.8 mgd
Average VS destroyed 47 percent
in digesters
Gas produced 4.2 scf/lb of VS destroyed
Average power generated 19.7 scf digester gas required to
generate 1 kwh electricity
Two 1620 hp White Superior dual fuel engine generator sets were installed in June
1972. The generators are rated at 1180 kw each. One 1440 hp gas engine is used
to drive one blower. The engines are equipped with heat recovery units which
are used to heat the digesters. Gas is compressed and stored at 35 to 45 psi
in a 50 ft diameter sphere. An iron sponge type scrubbing system was installed
with the engines but is not used because the hydrogen sulfide concentration is
less than 1,000 ppm. The White Superior engines are turbo-charged and gas must
be supplied at a minimum pressure of 35 psi.
Los Angeles, California
The Hyperion Plant treats an average flow of 340 mgd all of which receives
primary treatment and 100 mgd receives conventional activated sludge treatment.
Sludge treated in the digesters is about 92 percent primary and 8 percent waste
activated. There are 18 digesters, 15 operate at 95°F and three at 122°F. Follow-
ing is a summary of engine operation and gas production data during three fiscal
years:
1971 - 72 1972 - 73 1973 - 74
Gas Production
million cu ft per day 4.186 3.843 3.548
Heat Value, Btu/cu ft 590 590 590
cu ft gas produced/lb . 17.7 13.4 11.7
VS destroyed
Engine Operation
Btu/hp-hr 6,469 6,428 7,675
Electricity Generated
kwh/day 58,533 59,349 56,847
* Low heat value from laboratory tests
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Engineers at the Hyperion Treatment Plant believe that the reduction in gas
production indicated in the last two years is the result of poor metering and
does not represent a change in actual gas production. The gas is compressed
to 35 psi and stored. The hydrogen sulfide content is about 800 ppm and scrub-
bing has never been used.
The digester gas is used primarily in 10 supercharged 8 cylinder Worthington
internal combustion engines rated at 1688 hp. The engines are dual fuel and
continuously utilize about 5 percent fuel oil. Five of the engines operate
generators each rated at 1190 kw. The other five engines are direct coupled
to blowers rated at 40,000 cfm each. The engines are equipped with heat re-
covery units which are used to heat the digesters.
Los Angeles County Sanitation District
A primary plant treats an average flow of about 385 mgd and is equipped with
30 digesters. An average of 16 cu ft of gas is produced per Ib of VS destroyed.
The digester gas is about 60 percent methane with a high heat value of 607 Btu.
A summary of digester gas analyses from December 1973 through May 1975 is shown
in Table 1. Since the low heat value of methane is 963 Btu per cu ft, the low
heat value of the digester gas would be about 577 Btu per cu ft. This data also
shows that the average hydrogen sulfide concentration was very low, about 28
ppm, with 147 ppm the highest value reported.
Gas is transferred directly from the digesters to internal combustion engines
without any treatment, compression or storage. There is an emergency waste gas
burner on site, but normally any excess gas is taken by a contractor at $0.15
per 1,000 cu ft. The gas is utilized in 12 Ingersoll-Rand internal combustion
engines. Five of the engines are direct coupled to pumps rated at 97,000 gpm
each; the other seven engines are connected to generators as follows:
Rated Engine, bhp Rated Generation Capacity, kw
2 engines at 2280 835
1 engine at 1100 775
2 engines at 888 615
2 engines at 800 560
Total 6836 4795
The engines operate at low rpm (330 to 360) and some have been operating for
20 years with no significant down time. The standby fuel is propane and the
engines are not equipped with heat recovery units.
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Orange County Sanitation District (California)
During the 1972-73 fiscal year digester gas production in two plants with a flow
of about 135 mgd averaged 2,214,000 cu ft/day. The gas is used in (a) natur-
ally aspirated internal combustion engines coupled to influent and effluent pumps,
(b) boilers, and (c) rag incinerators. All engines are spark ignited with
natural gas for standby fuel. Heat recovery systems on the engines are utilized
to heat the digesters. The plant is also equipped with a gas turbine-generator
set which is used for standby power. The gas turbine is equipped with a heat
recovery unit which furnished steam to a turbine and another generator. This
heat recovery system has not performed satisfactorily and has been removed from
service.
A 45 mgd activated sludge plant is currently under construction and two 1500
hp Enterprise-Del aval engines will be installed to drive blowers rated at 35,000
scfm at 7 psi discharge pressure. The engines will be spark ignited and will
operate at 350 rpm. Two White Superior 1200 hp engines will be installed for
effluent pumping and two 250 hp White Superior engines will be installed for
in-plant pumping. Natural gas will also be the standby fuel for these new en-
gines.
Gas withdrawn from each digester passes through a sediment trap and is conveyed
to gas compressors. The compressors normally compress the gas to 40 psi with
a maximum capability of 50 psi. Compressed gas is stored at a maximum pressure
of 50 psi in two 32 ft diameter spheres. Gas pressure is reduced from the stor-
age pressure of 40 - 50 psi to 2 - 5 psi prior to use in the engines, boilers
and incinerators. The digester gas has a high hydrogen sulfide concentration
of as much as 3,000 ppm, but scrubbers have never been used.
The District estimates that present work equivalent performed per day using di-
gester gas as fuel amounts to 74,300 hp-hr. This amounts to 58 percent of the
total energy required for collection and treatment based on actual work performed.
Other energy sources used in the two plants are electrical, which accounts for
38 percent of the work and natural gas, which accounts for 4 percent.
Philadelphia, Pennsylvania
Digester gas is used to heat buildings and digesters, but no internal combustion
engines are operated on digester gas. The gas is not cleaned, compressed or
stored before use. A yearly average of 6.4 cu ft of gas is produced per Ib of
VS destroyed.
San Jose, California
This 160 mgd plant has eight primary digesters heated to 95°F and three unheated
129
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secondary digesters. The digesters reduce VS by 50 to 55 percent. Primary di-
gesters are heated with an external heat exchanger by hot water from internal
combustion engine heat recovery units.
Average heat value of the digester gas is 550 Btu/cu ft and is mixed with natu-
ral gas to produce a blend with a heat value of 700 Btu/cu ft. No cleaning or
scrubbing, except water removal, is provided. Digester gas is compressed to
60 psi before blending and no storage is provided before use in engines. Gene-
rally 85 to 90 percent of digester gas is used and 10 to 15 percent is flared.
The blended gas is used as fuel for 11 internal combustion engines. Five dual
fuel Enterprise-Del aval engines drive electrical generators: 2 - 800 hp and
3 - 2500 hp. Six tri fuel spark ignited Cooper-Bessemer engines drive blowers:
3 - 2400 hp and 3 - 1800 hp.
Tucson, Arizona
Digester gas is used as fuel for 300 hp Waukesha internal combustion engines
which are direct coupled to blowers. Data from two years operation was taken
from the 1973-74 Annual Report and is summarized in Table 2. There is no ex-
planation for the high gas production reported.
GAS PRODUCTION
Perhaps the most important design criterion that must be selected is the volume
of gas produced per unit of organic material destroyed in the digester. Virtu-
ally all operating data, as well as data in the literature, is reported in cu
ft of gas produced per Ib of VS destroyed. In some cases the gas production
is recorded in total Ib of VS supplied to the digester. An EPA report10 dis-
cusses the volume of gas produced as follows:
"The volume of gas produced per Ib of VS destroyed is reported as 17-18
scf/lb at the larger and better instrumented plants. Smaller plants re-
port lesser values, sometimes as loa as 6 scf per Ib VS destroyed, but
these lover values are probably due to poor measurement techniques."
The Water Pollution Control Federation's Manual of Practice on Anaerobic Sludge
Digestion3 gives the following data on anaerobic conversions of the chief types
of organic matter in sewage sludge:
Type and Average Gas Produced
Concentration (cu ft gas/lb organic matter digested)
Carbohydrate (C6Hi005)n 14.2
Fat C50H9006 24.6
Insoluble Soap Ca(Ci5H3102)2 22-3
Protein 6C»2NH3«3H20 9.4
130
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These data were developed from extensive experimental work conducted at the
Los Angeles County Sanitation Districts.
The WPCF manual on sewage treatment plant design4 gives the following gas pro-
duction data:
"In terms of solids digested, the average yield adjusted to standard
temperature of 60 F is about 15 cu ft of gas per Ib of VS destroyed.
These gas volumes are for normal plant operating pressures of 6 to 8
inches of water."
The EPA Process Design Manual for Sludge Treatment and Disposal gives the follow-
ing sludge and digester gas data:1
"In general, treatment of 1 mgd of municipal wastevater will provide
1 ton of mixed primary and activated sludge solids which translates
to 0.2 to 0.3 Ib solids/capita/day. An unheated digester will typically
produce 0.32 to 0.56 cu ft of gas/capita while a heated digester will
produce from 0.56 to 0.74 cu ft of gas/capita. This is equivalent to
a maximum gas production of approximately 11 to 12 cu ft of gas/lb of
total solids digested. The heat value of sludge gas is approximately 566
Btu/cu ft."
A range of 14 to 19 cu ft of digester gas produced per Ib of VS destroyed was
reported for Chicago.11
Data collected from operating plants by the author indicates that 17 to 18
scf/lb of VS destroyed is not routinely obtained even at some well operated
facilities and much lower values are reported in some presumably well operated
plants. Therefore, 15 scf/lb VS destroyed is recommended for sizing typical
digester gas utilization systems, unless data are available for a specific waste
to be treated.
The amount of sludge produced in a wastewater treatment plant, the VS content
of the sludge, and the gas produced by anaerobic digestion varies with influent
suspended solids concentration, BOD and type and efficiency of the biological
treatment processes. A published review12 of sludge quantities produced in
municipal wastewater treatment plants concludes that 915 and 1,085 Ib/million
gallons treated are typical quantities of sludge produced by primary and secon-
dary treatment respectively. The following sludge quantities are based on a
review of data from several sources and are considered representative of typical
primary and activated sludge plants:
Sludge Solids
(Ib/million gallons) Volatile
Total Volatile (percent of total)
Sludge Type
Primary 1,155 690 60
Waste Activated 945 756 80
TOTAL 2,100 1,446 69
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A review of the literature and data collected from operating plants indicates
that about 50 percent of the volatile solids are destroyed by anaerobic diges-
tion and that the gas produced has a heat value of about 600 Btu/scf.
These criteria give the following estimates for gas and heat available from
anaerobic digestion.
Waste
Primary Activated
Sludge Sludge Total
Gas Produced, scf per million 5,175 5,670 10,845
gallons treated
Heat Available, Btu per million 3,105,000 3,402,000 6,507,000
gallons treated
For planning purposes, and in the absence of more specific information, it may
be assumed that about 6.5 million Btu per million gallons of wastewater treated
are available from gas produced by anaerobic digestion of primary and conven-
tional activated sludge treatment.
GAS UTILIZATION
Digester gas can be used for on-site generation of electricity and/or for any
in-plant purpose requiring fuel. Digester gas could also be used off-site in
a natural gas supply system.
Off-Site Use
Off-site use of digester gas will usually require treatment to remove trace im-
purities such as hydrogen sulfide and moisture; in most cases the heat value of
the digester gas must be increased by removal of carbon dioxide before it could
be used in a natural gas system. Carbon dioxide removal is not commonly prac-
ticed at wastewater treatment plants but information on systems used in the chemi-
cal industry is available.13 The estimated cost in 1974 to treat digester gas,
from a 125 mgd plant in Dallas, Texas, or use in a natural gas system was $0.46
per 1,000 scf of methane.1'* This cost included a carbon dioxide removal system
manufactured by Union Carbide that uses a monoethanolamine absorbent. In-plant
energy requirements for primary and secondary treatment always exceed the energy
available from digester gas; therefore, the remainder of this section is devoted
to on-site use as fuel in internal combustion engines.
Use In Internal Combustion Engines
Diesel or gas internal combustion engines can be used to drive electric generators,
air blowers or pumps in a wastewater treatment plant. A typical system illus-
trating these potential uses is shown in Figure 1.
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Diesel engines operate on fuel oil that is ignited entirely by the heat result-
ing from the compression of the air supplied for combustion. Gas-Diesel engines
operate on a combustible gas (anaerobic digester gas in this case) as primary
fuel; the ignition of the digester gas is accomplished by the injection of a
small amount of pilot fuel oil. Commonly 5 to 10 percent fuel oil is required
to operate a dual fuel engine. Dual fuel Diesel engines are equipped to operate
on fuel oil only or as a gas-Diesel. Fuel oil is normally used in the alternate
fuel system for dual fuel engines in a wastewater treatment plant; however,
it is possible to equip this type of engine to also operate on natural gas or
propane.
A gas internal combustion engine operates on a combustible gas fuel (anaerobic
digester gas in this case) that is ignited by an electric spark. Natural gas
or propane could be used as an alternate source of fuel in a gas engine.
There are many variations in engine design, and auxiliary equipment required,
for these two basic engine types. The operating speed and turbocharging are
basic differences between engines supplied by different manufactuers. These
variations in engine types result in equipment cost and operation and mainten-
ance cost variations.
The EPA report10 assumes that work can be produced by an engine operating on
digester gas at the rate of one hp-hr per 7000 Btu (since 1 hp-hr = 2547 Btu,
the assumed efficiency is 36.4 percent). The efficiency of engines varies de-
pending on the basic engine design and method of operation. In general, low
speed, turbocharged or dual fuel engines require less fuel per hp-hr than higher
speed naturally aspirated engines. However, capital costs are greater for the
more efficient engines. Fuel required at an engine-generator set efficiency
of 30 percent is about 11,400 Btu/kwh. Average efficiencies obtained at the
Hyperion Treatment Plant during three years of operating 10 dual fuel engines
are compared with other estimates in Table 3.
The use of heat recovery equipment will increase the overall efficiency. One
manufacturer estimates energy supplied to internal combustion engines is used
as follows:
Energy Use
(percent)
Jacket water and lube oil 45
Exhaust 15
Radiation 10
Work 30
Heat recovery has been used successfully for many years particularly with large
slow speed engines. Typical heat recovery rates for dual fuel engines manufac-
tured by White Superior are shown in Table 4. This data shows that recovered
133
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heat varies from 20 to 31 percent of fuel input. Typical heat recovery rates
in percent of fuel supplied to the engine are: jacket water, 18 to 20 percent;
exhaust, 10 to 13 percent; combination of both jacket water and exhaust heat
recovery, 20 to 33 percent. This recovered heat added to the 30 to 37 percent
efficiency of the engine results in a total thermal efficiency ranging from 50
to 70 percent.
One generally used method of recovering jacket water heat is through ebullient
cooling, that is, raising the jacket water temperature to just above the boiling
point (215° to 220°F) and collecting the steam in an external separator. The
low pressure steam thus produced may be used for digester heating, sludge dry-
ing, building heating or other purposes. Exhaust heat is typically recovered
by use of combination exhaust silencer and heat recovery boilers. In some in-
stallations the jacket water and exhaust heat are recovered in a single combined
unit. The cost of heat recovery equipment varies considerably, but usually in
proportion to the size of the engine, with lower unit costs for larger engines.
Table 5 is a summary of gas, heat and power available for various size treatment
plants based on the following criteria:
1. Total dry solids to digester = 2,100 Ib/million gallons and VS =
1,446 1 fa/million gallons from primary and conventional activated
sludge treatment.
2. Fifty percent of VS destroyed in digester.
3. Digester gas produced = 15 scf/lb VS destroyed.
4. Heat available = 600 Btu/scf gas or 9,000 Btu/lb VS destroyed.
5. 1C engine efficiency = 36.4 percent (7,000 Btu/hp-hr).
6. Engine-generator efficiency = 30 percent (11,400 Btu/hp-hr).
COST ESTIMATES - DIGESTER GAS UTILIZATION
Construction costs in this paper include all elements of construction cost a
contract bidder would normally encounter in furnishing a complete facility.
Construction costs include materials, labor, equipment, electrical, normal ex-
cavation and contractor overhead and profit. Construction costs do not include
costs for land, engineering, legal, fiscal and administration services or in-
terest during construction. Equipment costs were obtained through quotes from
various suppliers and manufacturers. Construction costs include allowances for
the following: overhead and profit (25 percent), equipment installation (35
percent), electrical (15 percent), piping and miscellaneous items (15 percent)
and, other site work and contingency (15 percent). Operation and maintenance
is broken down into three categories: (1) operating and maintenance labor in
hr/yr, (2) materials and supplies in $l,000/yr, and (3) energy in kwh/yr
or Btu/yr. <
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Estimated costs to clean and store digester gas are summarized in Table 6. Hy-
drogen sulfide can be removed from digester gas by treatment in a chemical scrub-
bing system using sodium hypochlorite or other oxidizing agents. Estimated costs
include scrubbing with NaOCl in a packed tower to remove 1,000 ppm H2S and on-
site hypochlorite generation. It is possible to use activated carbon for H2S
removal but the carbon must be regenerated with steam. Chemical scrubbing sys-
tems appear to be more economical and simpler to operate. It may be possible
to use other chemicals, or other sources of hypochlorite, to furnish less ex-
pensive scrubbing systems than shown in Table 6. Iron sponge scrubbers have been
installed in some treatment plants. Construction costs for cleaning and storing
digester gas are greatly influenced by the storage capacity provided. The stor-
age capacity used in these estimates is based on one sphere per plant, up to
plant sizes of 100 mgd.
Estimated costs for 600 rpm internal combustion engines equipped with heat re-
covery and alternate fuel systems are shown in Figures 2 and 3. These cost
curves include data for both dual fuel and gas engines. Operation and mainten-
ance costs are greatly affected by the alternate fuel consumed. Propane alter-
nate fuel systems are more costly than fuel oil systems; however, gas engines
that would require propane are less costly than dual fuel engines that require
fuel oil. Dual fuel engines require about 10 percent fuel oil on an averaqe
annual basis. Gas engines could operate without using any alternate fuel. How-
ever, for these estimates, it is assumed that 10 percent propane would be con-
sumed. Propane would have to be used (or at least paid for) to obtain contracts
for a firm supply.
Estimated costs for complete systems to generate electricity with digester gas
are shown in Figures 4 and 5. These costs are for a system as shown in Figure
1. The cost curves may be used to estimate on-site electricity generation costs
as shown in the following example for a 100 mgd plant:
Construction cost (Figure 4) $2,500,000
Material (Figure 4) 55,000/yr
Labor (Figure 5) 5,800 hr/yr
Electricity (Figure 5) 1,500,000 kwh/yr
Fuel (Figure 5) 23 x 109Btu/yr
Annual costs:
• Construction
$2,500,000 plus 35 percent for engineering, administration,
interest during construction and other costs = $3,375,000 total.
Amortize for 20 years at 7 percent interest,
($3,375,000) (0.09439) = $319,000.
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• Operation and Maintenance
Labor 5,800 hr G> $10/hr $58,000
Material 55,000
Electricity 1,500,000 kwh @ $0.025/kwh 38,000
Fuel 23x109 Btu/yr @ $3/mil Btu 69,000
• Total Annual Cost = $537,000 per year
Column (7) in Table 5 shows that there are 2400 kw (21,000,000 kwh/yr) available
from a 100 mgd plant. This gives a unit electricity production cost of $0.026
per kwh. If the generating facility operates only 80 percent of the time, the
unit cost increases to $0.032/kwh. These costs do not take credit for recovered
heat. Column (8), Table 5 estimates that 162.5 mil Btu/day (59 x 109 Btu/yr)
could be recovered in a 100 mgd plant. Valuing this waste heat at $1.50/mil
Btu reduces the unit costs to $0.022/kwh and $0.028/kwh for 100 percent and 80
percent operating time respectively.
ANAEROBIC DIGESTION HEAT REQUIREMENTS
Heat is required in the anaerobic digestion process to (1) raise the tempera-
ture of the influent sludge to the level of the digester, and (2) compensate
for heat losses from the digester through its walls, bottom and cover. The op-
timum temperature for sludge digestion in the mesophilic range is about 95°F.
The heat required to raise the influent sludge temperature can be calculated
from the following relationship:
Q = WC (TD - Ts)
Where
Q = heat required, Btu
W = weight of influent sludge, Ib
C = specific heat of sludge, 1.0 Btu/lb/°F
for 1 to 10% solids sludge
TD = temperature in digester, °F
T~ = temperature of influent sludge, °F
The WPCF Manual of Practice No. 8, gives the following criteria for digester
heating:1*
Data accumulated from numerous digester installations have made it con-
venient to use factors for estimation of heat losses from digesters
without considering separately the loss through each element of the
digester. For the normal installation it is assumed that a 1°F drop
in temperature occurs for the entire tank contents in 24 hr. A correction
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factor is applied for outside temperature, depending upon location
and special conditions, such as the presence of ground water. For each
1,000 cu ft of contents, this amounts then to 1,000 x 62.5 x 1.0 =
62,500 Btu per day; or 62,500 = 2,600 Btu per hr. Correction factors
24
for geographical location by which the value of 2,600 Btu per hr is mul-
tiplied are as follows:
Northern United States 1.0
Middle United States 0.5
Southern United States 0.3
The WPCF Manual of Practice No. II5 gives the following loadings for anaerobic
digesters:
Loading, Ib VS/da.y/cu ft
Standard Rate 0.03 to 0.1
High Rate 0.1 to 0.4
Digester heat requirements for this paper are based on loadings of 0.05 and 0.15
Ib/VS/day/cu ft. These criteria give the following digester capacities:
Digester Capacity
(cu ft/mil gal)
Solids Total Volatile Total Loading
Sludge Content Solids Solids Sludge (Ib/VS/day/cu ft)
Type (percent) (Ib/mil gal) (Ib/mil gal) (Ib/mil gal) 0.05 0.15
Primary 5 1155 690 23,100 13,800 4,600
Primary 4.5 (thickened)2100 1446 46,600 28,900 9,600
+WAS
The total heat required for digestion at 95°F at the two loadings is shown in
Figure 6 for primary plus waste activated sludge. These heat requirements are
based on the above criteria for sludge heating and digester heat loss and a 75
percent heat transfer efficiency.
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SOLAR ENERGY
The solar energy, or solar insolation, available at a particular location on
the earth varies greatly throughout the year due to atmospheric absorption and
angle of the sun above the horizon. Data on solar insolation are compiled by
the U.S. Weather Bureau and are available in several publications.15'16
Solar energy may be used for space and process heating in wastewater treatment
plants through three different types of collector systems:
1. Active solar collection (water collectors)
2. Passive solar collectors (insulated translucent panels)
3. Atmospheric solar collection (to be used by heat pump outside coil)
ACTIVE SOLAR COLLECTION
The most common use of solar energy is by active solar collection. This type
of system in general is composed of solar collector, heat storage system, heat
exchanger and various pipes and pumps for circulating a working fluid which
transfers the heat absorbed at the collector to the storage device. Common
working fluids used are water, a water and glycol mixture and air. Typical
storage devices are a large tank of water, a bed of rocks or a combination of
the two. The working fluid is pumped through the collectors to the storage de-
vice throughout the day as long as the temperature of the fluid coming from the
collector is higher than the temperature of the fluid in storage. For space
and water heating purposes, fluid is circulated from storage through a heat ex-
changer and back to storage. A schematic of the general concept for space heat-
ing is shown in Figure 7.
Flat plate collectors are the most common type. Other types of collectors such
as concentrating and sun tracking have been used and are available. Concentrating
collectors use reflective devices or lenses to focus a large amount of solar
radiation upon a relatively small collection area. These devices normally re-
quire accurate tracking systems so that the sun's rays always strike the concen-
trating equipment at the proper angle. Because only direct radiation can be
concentrated these devices are not very effective on cloudy days when diffuse
radiation prevails. Due to many variables such as the amount of solar insolation,
heat losses from reflection and radiation, differences in glazing surfaces and
fluctuations in ambient temperature, collectors operate at continuously varying
efficiencies throughout the day.
Materials with a fairly high heat capacity are used to store heat during periods
of darkness or cloudiness. Water, with a specific heat of 1.0 Btu/lb/°F, is most
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often used to store heat and concrete or steel tanks are the most common storage
devices. Water is also usually the fluid circulated in collectors. Rocks have
a specific heat of about 0.2 Btu/lb/°F and are also used, especially if the cir-
culating fluid is air.
PASSIVE SOLAR COLLECTION
Passive solar collectors consist of translucent panels of glass, fiberglass,
or plastic located in the wall or roof of a building. Solar energy passing
through these panels is absorbed by surfaces and objects below. This concept
was used in the design of the wastewater treatment plant in Wilton, Maine, for
the passive collection of solar energy into the clarifier and onto darkly painted
masonry and concrete surfaces for the retention of heat in a building. 8»9 The
heat collected from such a system depends on solar energy available and size
and characteristics of the panels.
EXAMPLE- SOLAR SYSTEM FOR SPACE HEATING
Determination of the actual useful amount of solar radiation collected is a
somewhat involved procedure. The continuously changing solar input to the col-
lector plus the constantly varying collection efficiency suggest that an hourly
or even minute by minute calculation for the entire year is necessary for accu-
rate determination of the solar energy collected. Computer programs are available
to do such calculations. A simplified approach is used in this example by aver-
aging the daily variations into monthly variations.
The treatment plant location used in this example is 40 deg latitude in the vi-
cinity of Detroit, Michigan. Solar insolation data for this location, collector
output and heat requirements for 2,000 sq ft floor area are summarized in Table
7. These data show that about 3,000 sq ft of collector area are required to heat
a 2,000 sq ft building in December and January and virtually no heating is re-
quired in the summer.
SOLAR HEATING FOR ANAEROBIC DIGESTERS
A study in Annapolis, Maryland7 concluded that: (1) it is technically and
economically feasible to heat digesters with solar energy, (2) the lowest
cost method is to supply about 90 percent of the digester annual heat load with
solar energy, and (3) preheating raw sludge before it enters the digester is
the best method of utilizing solar energy. A schematic diagram of the proposed
system is shown in Figure 8.
A supplemental study to the feasibility study for Annapolis concluded that:
(1) solar heating of anaerobic digesters is economically feasible at all loca-
tions in the United States, including Alaska, (2) the degree nf economic at-
tractiveness of solar digester heating is approximately proportional to the
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average annual solar radiation multiplied by the difference between digester tem-
perature (35°C) and average annual air temperature, and (3) the optimum-size
solar heating system, expressed as percentage of annual heat requirement sup-
plied by solar energy, varies with location from about 82 to 97 percent.
SOLAR SYSTEM COSTS
Costs for solar systems vary considerably at the present time. For custom de-
signed systems, costs as high as $80 per square foot have been reported.17
Commercial flat plate collectors ranging from $4 to $15/sq ft or more are avail-
able. The less expensive units have no glazing or cover glass and are generally
used for swimming pool heating. The more expensive units are applied to space
and process heating and cooling. The glazed collectors generally range from
$12 to $15/sq ft. Costs for other system components and installation increase
the cost to about $25 sq ft for a complete flat plate collector system.17
The present worth of gas conserved less the present worth of an optimum size
solar system for digester heating (25 year project life) was calculated for 18
locations in the United States.7 The calculated cost difference varied from
about $37,000 in Corpus Christi, Texas to $108,000 in Fairbanks, Alaska.
Passive solar collector costs vary from about $5 to $7/sq ft, depending on the
size of each panel, thickness and material. Installation costs are about $1.50
sq ft.
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ENERGY REQUIREMENTS - DIGESTER GAS AND SOLAR ENERGY USE
Figure 9 is a flow diagram for a typical activated sludge plant with anaerobic
digestion. Energy requirements for this process in a 30 mgd plant are shown
in Table 8. The energy requirements are taken from a report that will be pub-
lished by EPA.18 The heat requirement of 31,755 million Btu/yr for anaerobic
digestion is shown in Figure 6 for a standard rate digester.
Using the data summarized in Table 5, it can be calculated that: (1) about
71.2 billion Btu/yr are available in the digester gas produced in a 30 mgd plant;
(2) total electrical energy that could be produced by on-site generation is
6.3 million kwh/yr, and (3) heat that could be recovered from the engine driving
the generator is about 17.7 billion Btu/yr. Electricity generated with digester
gas could supply about 67 percent of the 9.4 million kwh/yr required and heat
recovered from the engines could supply about 44 percent of the 40.4 billion
Btu/required. These data also indicate that: (1) there is more than enough
digester gas available to supply all of the fuel requirements, (2) a major re-
quirement in this type of treatment plant is for electricity and/or energy to
operate the aeration system, and (3) the application of solar energy appears
limited to building heating (a relatively minor requirement) and digester heating.
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SLUDGE COMPOSTING
Much of the early work on sludge composting at the University of California19
and other places was concerned with composting of municipal refuse. In a pro-
ject supported by EPA, the U.S. Department of Agriculture, Agricultural Research
Service (USDA) in cooperation with the Maryland Environmental Service (MES) and
the Blue Plains Wastewater Treatment Plant began investigating sludge composting
in 1972.20 This project is located on the grounds of the USDA Agricultural Re-
search Center at Beltsville, Maryland and the studies have demonstrated new tech-
niques in sewage sludge composting.21.22
Composting of wastewater sludges differs significantly from composting solid
wastes. There are several advantages of composting sewage sludge compared to
solid waste and the past poor publicity and problems associated with solid waste
composting need not discourage the use of composting as an alternative in the
treatment and reuse of wastewater sludge.
1. Composting solid wastes requires a complex materials handling and separation
process that is not necessary in sludge composting.
2. Solid wastes vary widely in composition and as a result the composting
process is usually more difficult to operate than a sludge composting sys-
tem.
3. Several past solid waste composting operations were evaluated on the basis
of their profit making potential rather than as an alternative disposal
method.
4. The per capita quantity of solid waste is several times the wastewater sludge
quantity; therefore, marketing or disposal of solid waste compost is a more
difficult task.
5. Sewage sludge compost is a more uniform product because plastics, metals and
other materials often remain in solid waste compost.
PROCESS DESCRIPTION
Present day composting is defined as the aerobic thermophilic decomposition of
organic solid wastes to a relatively stable humus like material.23 The basic
composting mechanism is similar for any organic material and is described in
more detail in several publications.23.21* Modern composting actually involves
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both mesophilic and thermophilic temperatures, and, since it is a biological
process, is subject to the constraints of any biological system.
Proposed sludge regulations in California define sludge composting as follows:
"Compost means to process day a tared sat age sludge in a manner
that (a) exposes all portions of the sludge to air and to a
temperature at least 60 degrees centigrade for at least 48 hours;
(b) subsequently reduces the water content of the sludge to
40 percent or less, by weight; and (c) sufficiently decomposes
the sludge so that it will not produce excessive odor or reheat
above 40 degrees centigrade in the center of a pile that is one
meter high, one meter wide, and one meter long, in a test wherein
the sludge is remoistened to a water content of 55 percent, by
weight, and held for four days, after having undergone steps
(a) and (b) above."
Sludge compost is a natural organic product with high humus content. It has
a slight musty odor, is moist, dark in color and can be bagged. The texture
of compost varies depending on the degree of screening. Because of its high
organic content it is similar in appearance to peat. Compost increases the water
holding capacity of sandy soils, improves the structure of heavy clay soils,
and increases the air content of fine soils. The organic matter in compost
improves the workability of the soil and makes it easier for plant roots to
penetrate. Compost has relatively little fertilizer value; however, a signi-
ficant percentage of the nitrogen content is in the organic form. This organic
nitrogen is released slowly providing long term benefits to the plant life.
The composition of compost varies widely, but typically is 1 to 3 percent nit-
rogen, 1 to 2 percent phosphoric acid, with small amounts of potash and several
trace elements.
Decomposition is accomplished by various microorganisms including bacteria
actinomycetes and fungi. The principal by-products of this aerobic decomposi-
tion are carbon dioxide, water and heat. The composting process may be physi-
cally achieved in basically three types of systems; (1) windrow, (2) aerated
static pile, and (3) mechanical units of various designs which usually supply
continuous mixing and positive aeration. The windrow and static pile methods
have been used almost exclusively for composting sewage sludge because of their
low cost and demonstrated performance. The windrow and static pile methods will
be discussed in more detail in this paper. There are several mechanical pro-
cesses marketed by various manufacturers that are not discussed herein; how-
ever, these mechanical processes may be useful in certain applications.
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The general composting method is very similar for both static pile and windrow
processes. Dewatered sludge (typically 20 percent solids) is delivered to the
site and usually mixed with a bulking agent. The purpose of the bulking agent
is to increase porosity of the sludge and to assure aerobic conditions during
composting. Various bulking agents can be used including wood chips, bark chips,
rice hulls and cubed solid waste. Unscreened finished compost has also been
used. Generally one part sludge (20 percent solids) is mixed with three parts
bulking agent. The sludge-bulking agent mixture is then formed into windrows
or static piles. After composting, which requires three weeks or longer, the
product is removed from the windrow or static pile and allowed to further stabi-
lize in storage, or curing, piles for about another 30 days, or longer. Prior
to or following curing, compost may be screened to remove a portion of the bulk-
ing agent for reuse or for applications requiring a finer product. Compost
may also be used without the screening.
The early research at the University of California and other locations developed
some fundamentals of composting and these are summarized by Golueke.21*
1. Obtaining thermophilic temperatures requires no input of external energy
when the composting mass is sufficiently insulated and favorable environ-
mental conditions are maintained for the biological organisms.
2. No innoculation with external microbial cultures is necessary either before
during or after the composting process. This fact was demonstrated repeatedly
at the major research centers.
3. The relations between environmental factors and the course of the process
were shown to be those that are characteristic of any biological process.
4. The early research developed little information on the survival of viruses
and other pathogens, fate of heavy metals, and the long term effect of using
compost on the soil.
Composting is a dynamic process representing the combined activity of a succes-
sion of mixed bacterial and fungal population associated with a diverse succes-
sion of environments, one overlapping the other and each emerging gradually
as a result of continual changes in temperature and substrate. The principal
environmental factors in composting are moisture, temperature, pH, nutrient
concentration and availability, and oxygen concentration.
Moisture
The minimum moisture content at which bacterial activity takes place is from
12 to 15 percent. As a rule of thumb, the moisture content becomes a limiting
factor in the range of 45 to 50 percent. Most sludge composting experience
has been with solids concentrations of 10 to 30 percent.
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Temperature
Modern composting processes are designed to operate within the mesophilic and
thermophilic ranges. The range of optimum temperatures for the composting pro-
cess as a whole is quite broad, probably from about 35°C to 65°C. The tempera-
ture of a reasonably large composting mass will gradually rise to within the
thermophilic range due to excess energy from microbial activity. This increase
will inevitably take place unless positive measures are taken to dissipate the
heat or improper composting procedures are used.
Sludge composting should reach thermophilic temperatures for a significant per-
iod of time for several reasons: (1) the optimum temperature for some of the
organisms involved in the composting process is within the thermophilic range,
(2) most pathogenic organisms and weed seeds cannot survive long exposure to
thermophilic temperatures, and (3) composting mass will reach thermophilic
temperatures unless definite countermeasures are taken to dissipate heat.
In practical operations little can be or needs to be done to alter the pH in
a composting mass.
Nutrients
One of the more important nutrient requirements in composting is the carbon-
nitrogen balance or ratio (C/N ratio). Part of the carbon is lost as C02 and
carbon is present in the cellular material in greater concentration than is
nitrogen; therefore, the amount of carbon required is considerably greater than
nitrogen. The optimum C/N ratio for most wastes falls within the 20 to 25 to
1 range.
The more the carbon-nitrogen balance deviates from the optimum, especially
in the upper range, the slower the process proceeds. However, the actual upper
limit for an individual application depends upon the degree of availability
of the carbon. The principal deleterious effect of too low a C/N ratio is the
loss of nitrogen through the production of ammonia and its subsequent volati-
lization. Apparently, any excess nitrogen ends up as-ammonia. As far as the
composting process itself is concerned excess nitrogen is not detrimental.
Nutrient concentrations and balances in most sludges are adequate and not li-
miting to the composting process.
Oxygen
Optimum oxygen levels in a composting mass are believed to be between about
5 and 15 percent. Some method must be employed to achieve these levels in
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either the static pile or windrow method. Since the composting process is
aerobic, low oxygen levels will slow down the process and may precipitate an-
aerobic conditions in some parts of the composting mass. Excessively high oxygen
concentrations increase aeration expense and may reduce temperature.
Degree of Stabilization
The net result of the composting process is the partial stabilization of or-
ganic material. Sludge is not completely stabilized or rendered inert by com-
posting because this would result in end products of carbon dioxide, water and
mineral ash. Obviously this is not possible nor desireable in a composting
system. The desired degree of stability is one in which the product will not
give rise to nuisances when stored even if moisture is added. It was observed
in studies at the University of California that attainment of a satisfactory
degree of stabilization was always accompanied by a final decline in tempera-
ture. It was observed that once the temperature had declined to about 45 to
50°C the material had become sufficiently stabilized to permit indefinite stor-
age.
WINDROW COMPOSTING
The windrow process is conducted in the open air and relies on natural venti-
lation plus periodic turning to maintain aerobic conditions. The sludge-bulking
agent mixture is spread in windrows with a triangular cross section normally
6 to 10 feet wide and 3 to 5 feet high. An alternative method to mixing the
bulking agent and sludge before forming the windrow is placing the bulking agent
as a base for the windrow. The sludge is dumped on top of the bulking agent
and spread. A composting machine (similar to a large rototiller) then mixes
the sludge and bulking agent and forms the mixture into a windrow. Several
turnings (about 8 to 10 times) are necessary to adequately blend the two materials.
The windrow is normally turned daily using the composter; however, during rainy
periods turning is suspended until the windrow surface layers dry. Temperatures
in the windrow under proper composting conditions range from 50°C to 65°C.
Turning moves the surface material to the center of the windrow for exposure
to higher temperatures. Turning also aids in drying and increases the porosity
for greater air movement and distribution.
The windrows are turned for a three week period or longer depending on the weather
and efficiency of composting. The windrow is then spread and flattened for
further drying. The compost is moved to a curing area when the moisture con-
tent has decreased to approximately 30 to 40 percent. Proper windrow composting
should produce a relatively stable product with a moisture content of 30 to
40 percent which has been exposed to temperatures of at,least 50°C for several
days during the process.
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The composting process requires longer detention times in cold or wet weather,
therefore climate is a significant factor with the windrow process in open
spaces. Covering the composting area would significantly reduce the effects
of cold weather and nearly eliminate the problems of wet weather.
In the initial studies by the USDA at Beltsville, Maryland, digested sludge
was successfully composted in windrows.20'22 Fifty tons of wet sludge (23 per-
cent solids) was composted daily. The windrow process was found to be unsatis-
factory for composting undigested primary and waste activated sludges because
offensive odors were produced. Also, survival of coliforms and salmonellae
was extensive, with indications of regrowth, as material in the center of the
compost windrows was shifted to the exterior when the windrows were turned.
The unsatisfactory performance of the windrow process for composting undigested
sludges led USDA researchers Epstein, Will son and their co-workers to develop
a forced aeration, static pile method.21*22
STATIC PILE COMPOSTING
In this process, the pile remains fixed, as opposed to the constant turning
of the windrow, and a forced ventilation system maintains aerobic conditions.
The static pile system developed by USDA for composting undigested sludge is
illustrated in Figure 10 and includes:
1. A 12 inch thick base consisting of bulking agent or previously composted
unscreened product.
2. Approximately 40 tons of sludge in each pile 20 feet wide, 40 feet long
and 8 feet high in a triangular cross section.
3. The entire pile is covered by a 12 to 18 inch layer of previously composted
material to prevent escape of odors and provide insulation.
4. Aeration system consisting of 4 inch diameter pipe in the base material
connected to a 0.33 hp centrifugal blower. Air is drawn through the pile
at a rate necessary to provide oxygen concentrations from 5 to 15 percent
throughout the pile. Normally the blower is operated on an on-off cycle
to maintain proper oxygen levels and temperatures within the pile. Air
is drawn through the pile and discharged into a small pile of previously
composted material. Aeration is continued in this manner for 21 days.
5. Water condenses in the piping system outside the pile. This water and
drainage from the pile should be collected and may be recycled to the
treatment plant.
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This system operates at Beltsville without causing odors. The results indicate
that by varying such parameters as the pile size and geometry, the direction
and rate of air flow, and the thickness of the cover of finished compost, a
procedure for uniform destruction of coliform and salmonella bacteria may be
developed.
COMPOSTING EXPERIENCE
Composting operations and marketing activities are in progress at several loca-
tions in the United States.
Beltsville, Maryland
Approximately 3,650 dry tons of Washington, D.C. sludge from the Blue Plains
plant is composted annually at this site using the static pile method. This
program is supported by EPA and operated jointly by the Maryland Environmental
Service and USDA. Most of the Beltsville compost is provided free of charge to
public agencies and it must be picked up at the site. Compost is not available
to individual private users. Demand exceeds supply, but only a portion of the
Blue Plains sludge production is composted at Beltsville.
As previously described, digested sludge was successfully composted at Belts-
vine by the windrow process. Static pile composting studies at Beltsville
have been conducted with: (1) combination of primary and secondary undigested
sludges, (2) 75 percent undigested and 25 percent anaerobically digested
sludge, and (3) anaerobically digested sludge. The results of these studies
were reported by Epstein, et al.21 It was concluded that:
1. Either digested or undigested sludge can be composted in an aerated pile
without releasing objectionable odors.
2. Destruction of total coliforms, fecal coliforms, and salmonellae was much
greater than with windrow composting. Survival of microorganisms in the
lower corner of the triangular shaped piles was believed to be a result
of the lack of insulation, or compost depth, and resulting heat loss in
this section.
Work is continuing at Beltsville in a cooperative effort between MES and USDA.
Construction is underway to add improvements to the site. A summary paper has
been prepared by USDA that contains some virus F2 indicator and pathogen results,
An engineering manual is also being prepared by USDA but the publication date
has not been established.
Bangor, Maine
The City of Bangor, Maine, population 38,000, generates approximately 50 cubic
yards of raw, dewatered sewage sludge each week. The sewage treatment facility
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is a primary plant constructed in the late 1960's. Sludge is composted using
the aerated static pile method with bark as the bulking agent. The Bangor pro-
ject is in its second year of operation under an EPA Office of Solid Waste Manage-
ment Programs grant. Composting began in 1975 and is in the second winter of
operation.
The compost has not been marketed or disposed of to date. It is intended that
it will be used by public agencies within the area. Potential uses in Bangor
include the municipal golf course, municipal parks, municipal forest areas, and
other municipal landscaped areas.
The composting site is located three miles from the plant on an abandoned taxiway
at Bangor International Airport. Sludge is stored in thickeners and is dewatered
to approximately 25 to 30 percent solids by vacuum filters immediately prior to
delivery to the composting site. Lime and polymer are used as conditioners prior
to vacuum filtration and sludge pH is 11 to 12. This high pH may be detrimental
to the composting process and operations will be tested at pH 10.
None of the compost site is covered and the operation is carried out with mobile
equipment. No fixed equipment has been used to date. Down time due to rain,
snow, and cold weather has been minimal. Aside from visibility and wind chill
problems with personnel, cold and snow do not hamper composting operations.
Mixing of compost cannot be accomplished satisfactorily during significant rain.
Generally severe weather only lasts a day or two and operations can be rescheduled
or postponed a day or so either way when severe weather is expected or encountered.
No odors are noticeable at the site and no complaints have been reported.
There is a slight odor when the sludge is dumped, but the odor disappears as
soon as it is mixed with the bark. Mixing the sludge immediately upon arrival
at the site helps to minimize odors. Generally, the pile is completed in the
afternoon after sludge delivery and composting commences. The blower is started
and runs continuously the first few days and then is operated on an on-off cycle
as required. The air flow is not reversed during the composting process. The
piles compost for approximately 21 days and are then moved to a separate area
for curing.
Performance data are summarized in Table 9 for 18 piles which were composted
during the grant period. The moisture content of the bulking agent varied widely
from 40 to over 60 percent. Bulking agent used in piles 10B, 11C, and 12A
was wet, very fine, and somewhat decomposed. When bulking agent of more uniform
size (without the fines content) is available as screening is implemented,
more consistent results may be achieved.
Durham, New Hampshire
The city operates a primary treatment plant and produces approximately 15 cu
yd per week of raw dewatered (15 percent solids) primary sludge. The plant
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is to be expanded to secondary treatment and the projected land requirements
for sludge spreading were greater than presently available. As a result, the
city set up a test program for evaluating aerated static pile composting and
obtained a grant through the New Hampshire Department of Public Health small
grants program. The purpose of the test was to determine: (1) whether proper
composting could be accomplished outdoors in a severe northern climate, and
(2) composting costs.
Approximately 15 cu yd per week of raw primary sludge was composted on a temporary
1.75 acre site. The site was not improved to any extent for the operations
because of the limited project life. The site did have a gravel base and blower
housings were constructed. Operations were conducted similar to those at Belts-
vine except air was drawn from the piles for 12 days and then blown into the
piles for the rest of the period. It was found that temperatures would drop
after 12 days if the air flow were not reversed. Wood chips were used as a
bulking agent. Sludge-bulking agent mixing was accomplished with a combination
of a front loader and motor grader. It was felt that this provided a superior
mix compared to use of a front loader alone.
The test operation was considered successful and has been suspended until the
treatment plant is upgraded and expanded. This expansion will include a mechanized
aerated static pile composting operation which will incorporate a number of
materials handling features. Much of the materials handling will be accomplished
with fixed equipment as opposed to the mobile equipment used previously. General
operations will include the following:
• Mechanized movement of sludge and bulking agent and measuring of the
components to a specified ratio.
• Mechanized mixing of sludge and bulking agent with fixed equipment to
obtain adequate and consistent results independent of weather.
• Mechanical movement of the mixture to the designated composting area
and rapid construction of the pile.
• Mechanical screening of compost and direct placement in curing bins
(five months storage in year 2025).
• A front loader will be used to form the piles, dismantle the piles, load
the compost into the screen, transfer bulking agent from the storage bin
to the mixer feed hopper and transfer finished compost from the curing
bins to trucks.
The new Durham facility will be designed for producing approximately 10 cu yd
of compost per day initially and 17 cu yd by 2025. The area required for com-
posting is 15,000 sq ft, but with all appurtenant requirements such as sludge
ISO
-------
processing building, storage areas, roadways, and truck washing area the total
requirement is 3.5 acres. The total estimated construction cost for the facility
is $658,000 not including land and sludge dewatering equipment.
It is anticipated that the dewatering and composting facility will be staffed
by two persons based on an eight hour shift. For two or three days a week,
these people will operate the facility with five hours a day for operations
and the other three hours for clean-up, start-up and shut-down. The remaining
days will be devoted to clean-up, maintenence and compost screening and testing.
The work force will increase to an anticipated six persons in the year 2025
for the dewatering and composting operation.
Los Angeles County Sanitation District
About 45,000 dry tons per year are currently composted by the windrow process.
Anaerobically digested and centrifuged primary sludge with about 10 percent
solids concentration is placed in windrows in 12 ton increments with 12 tons
of previously composted material. Mobile equipment is used to turn the windrows
once per day for 21 days. Kellogg Supply Company hauls the compost to its nearby
plant for further processing and packaging and pays for the compost on a royalty
basis. The composted sewage sludge is blended with other ingredients to form
various specialized soil conditioners. The basic product is marketed under
the trade name Nitrohumus. Kellogg has developed a complete line of garden
soil conditioning and fertilizer products as well as offering soil testing and
analysis services. These products and services are marketed within a radius of
about 300 miles directly to large users such as golf courses, commercial nurseries,
and stadiums and through retail outlets such as nurseries, garden stores, and
chain stores.
COMPOSTING COSTS
Composting costs may be considered in two components (1) capital, operation
and maintenance costs of producing the compost, and (2) cost of (or income
from) disposal of the compost product. Sludge composting may be a viable alter-
native for many locations but the basic processes are still in the development
and demonstration phase. Consequently, it is not possible to prepare generalized
cost estimates at this time. Some cost considerations and estimates prepared
in several studies are presented.
A recent market study25 found several successful municipal sludge composting
operations where all of the end product was sold or otherwise successfully used.
The study concluded that the current upper price limit for bulk sludge compost
is about $4 to $10/ton and for packaged, bagged, sludge compost, about $60/ton.
Bagging costs could approach $30/ton. Sludge compost marketing operations that
have been successful have generally: (1) had favorable local publicity, (2) had
the product available for pick-up (or made deliveries), (3) offered guidelines
for its use, or at least suggestions, (4) offered the product at no or low
cost, and (5) given the product a trade name.
151
-------
The cost of producing compost includes: (1) amortization of land, capital
site improvements, and structures, (2) amortization of major mobile equipment
costs, and (3) operation and maintenance costs including bulking agent, typi-
cally $2 to $4/cu yd. Land requirements are affected by several factors but
are typically 0.2 to 0.4 acres/dry ton for the static pile technique. Windrow
techniques require 2 to 3 times more area.
The required site improvements and structures will vary depending on process
used, availability of existing facilities, degree of mechanization of the process,
and to a degree, the demands of the climatic region. Site improvements related
to composting will generally include site access and improvements, bulking agent
storage, bulking agent-sludge mixing area or mechanical fixed equipment, composting
pads and appurtenances such as blowers, screening area, compost storage area,
support facilities such as electrical, and fixed materials handling equipment.
A study26 of the sludge disposal alternatives for the New York-New Jersey Metro-
politan area developed a cost of $40 to $45 per dry ton for composting large
quantities of dewatered sludge without any hauling or land costs included.
The USDA and MES estimate the total cost for static pile composting of approxi-
mately 600 wet tons per day of sludge (20 percent solids) would be $20 to $40
per dry ton excluding land and hauling. A recent study by USDA27 estimates total
costs for composting in 10 and 50 dry ton per day facilities to be $51 and $36 per
dry ton respectively. Camp, Dresser and McKee28 estimated a cost of $45 per
dry ton including land, but excluding hauling, to windrow compost 600 wet tons
per day of sludge.
Preliminary studies indicate that total costs to a municipality for static pile
composting should be in the range of $30 to $60 per dry ton of sewage sludge
solids excluding dewatering and hauling, but including land at $10,000 per acre.
This cost varies with local conditions and with the size of the operation.
Windrow composting costs would be somewhat higher.
152
-------
REFERENCES
1. "Process Design Manual for Sludge Treatment and Disposal", U.S.
Environmental Protection Agency, Technology Transfer, October 1974.
2. "Process Design Manual for Upgrading Existing Wastewater Treatment
Plants", U.S. Environmental Protection Agency, Technology Transfer,
October 1974.
3. "Anaerobic Sludge Digestion", WPCF Manual of Practice No. 16, 1968.
4. "Sewage Treatment Plant Design", WPCF Manual of Practice No. 8, 1967.
5. "Operation of Wastewater Treatment Plants", WPCF Manual of Practice
No. 11, 1976.
6. Story, A. H., "The Application of Solar Heating to Sludge Digesters",
M.S. Thesis, University of Florida, August 1958.
7. Cassel, D. E., "An Anaerobic Digester Heated by Solar Energy", EPA
Contract No. 68-03-2356, June 1976.
8. "Wastewater Plant Design Reduces Off-site Energy Needs", Water and
Sewage Works, February 1976.
9. Wilke, D. A., "There j_s_ Something New Under the Sun!", Water and
Wastes Engineering, March 1976.
10. Smith, R., "Electrical Power Consumption for Municipal Wastewater Treat-
ment", EPA-R-2-73-281, July 1973.
11. Graef, Steven P., "Anaerobic Digester Operation at the Metropolitan
Sanitary Districts of Greater Chicago", Proc. National Conference
on Municipal Sludge Management, Pittsburgh, Pa., pp. 29-35, June 1974.
12. Kormanik, Richard A., "Estimating Solids Production for Sludge Handling",
Water and Sewage Works, pp. 72-74, December 1972.
13. Strelzoff, S., "Choosing the Optimum Oh Removal System", Chemical
Engineering, pp. 115-120, September 15, 1975.
14. "Digester Gas Reclamation, City of Dallas Central Wastewater Treatment
Plant", Black and Veatch, 1974.
15. Duffie & Beckman, "Solar Energy Thermal Processes", Wiley & Sons,
New York, 1974.
16. Yellott, J. I., "Solar Energy Utilization for Heating and Cooling",
NSF, U. S. Government Printing Office, 1974.
153
-------
17. Clark, J. A., "Solar Energy System for Heating and Cooling", Seminar
at California State University, Los Angeles, April 1976.
18. "Energy Conservation in Municipal Wastewater Treatment", Culp/Wesner/Culp,
draft report for EPA.
19. McGauhey, P. H. and C. G. Golueke, "Reclamation of Municipal Refuse by
Composting", Tech. Bull. No. 9. Sanit. Eng. Res. Lab., University of
California, Berkeley, June 1953.
20. Epstein, E. and Willson, G. B., "Composting Sewage Sludge", Proc.
National Conference on Municipal Sludge Management, Pittsburgh, Pa.,
pp. 123-128, June 1974.
21. Epstein E., et al., "A Forced Aeration System for Composting Wastewater
Sludge", Journal WPCF, pp. 688-694, April 1976.
22. Epstein, E. and Willson, G. B., "Composting Raw Sludge", Proc. 1975
National Conference on Municipal Sludge Management and Disposal,
pp. 245-248, August 1975.
23. "Utilization of Municipal Wastewater Sludge", WPCF Manual of Practice
No. 1, 1971.
24. Golueke, C. G., "Composting, A Study of the Process and its Principles",
Rodale Press, Emmaus, Pa., 1973.
25. "User Survey for Sewage Sludge Compost", EPA Contract No. 68-03-2186,
May 1976.
26. Kalinske, A. A., et al., "Study of Sludge Disposal Alternatives for the
New York-New Jersey Metropolitan Area", paper presented at 48th WPCF
Conference, Miami Beach, Florida, October 1975.
27. Colacicco, D., et al., "Costs of Sludge Composting", USDA, Agricultural
Research Service, ARS-NE-79, February 1977.
28. "Draft Report, Alternative Sludge Disposal Systems for the District of
Columbia Water Pollution Plant at Blue Plains, District of Columbia",
Camp, Dresser & McKee, Inc., September 1975.
154
-------
TABLE 1
DIGESTER GAS ANALYSES
Los Angeles County Sanitation District
Date
December 1973
March 1974
April 1974
May 1974
July 1974
August 1974
September 1974
October 1974
November 1974
December 1974
January 1975
February 1975
March 1975
April 1975
May 1975
Average 36.9 59.9 607
Note: Data from March 1974 through February 1975 indicates that the
average H2S concentration is 28 ppm +_17 ppm. The highest
figure reported for this period was 147 ppm or 0.015% by
weight per cu ft of digester gas.
* Based on a high heat value of 1013 Btu/cu ft
155
Number
Days Sampled
17
18
22
21
21
22
18
22
16
19
22
10
21
20
21
Average
la CO 2
36.9
37.1
37.0
37.0
36.4
36.2
36.0
36.5
37.2
36.7
36.8
36.9
37.2
37.7
37.2
Average
% Methane
59.9
60.0
59.8
59.6
60.0
60.3
60.3
59.9
59.8
60.2
60.0
59.9
59.6
59.1
59.6
Average
Btu/cu ft
607
608
606
604
608
611
611
607
606
610
608
607
604
600
604
-------
TABLE 2
SUMMARY OF PLANT* OPERATIONS
Tucson, Arizona
1972-73 1973-74
Population served 325,318 341,930
Average daily flow, mgd 33 32
Average influent suspended solids, mg/1 211 236
Average influent BOD5, mg/1 227 235
Average suspended solids to digester, Ib/day 38,192 35,589
Average volatile solids
To digesters, percent of SS 72 79
To digesters, Ib/day 27,452 28,137
Destroyed, Ib/day 12,490 14,430
Reduction, percent 45.5 51.3
Average digester gas produced
Thousand cu ft/day 341,970 367,668
cu ft/lb volatile solids to digester 12.5 13.1
cu ft/lb volatile solids destroyed 27 4 25 5
*
Sewage is treated in three plants: two activated sludge and one
trickling filter.
156
-------
TABLE 3
INTERNAL COMBUSTION ENGINE EFFICIENCY
OPERATING ON DIGESTER GAS
Engine
Rating Efficiency
. (Btu/hp-hr) (percent)
Hyperion Plant
1971-72 6469 39.4
1972-73 6428 39.6
1973-74 7675 33.2
10
EPA Report 7000 36.4
Engine Manufacturers
Catepillar 8500 30.0
Del aval 6630 38.4
White Superior
Gas fuel, naturally aspirated, 8300 30.7
spark ignited
Gas fuel, turbo-charged, 7700 33.1
spark ignited
Dual fuel 7000 (or less) 36.4
157
-------
TABLE 4
TYPICAL HEAT RECOVERY RATES FOR DUAL FUEL ENGINES
Type of
Engine Size Exhaust Fuel Input
(kw) Cycle Manifold (Btu/kwh)
H1
cn
oo
1500-2000
1000-1500
1000-2500
3000-6000
4
4
2
2
Wet
Dry
Dry
Dry
9950
9950
9520
9450
Recovery
Power
3563
3563
3563
3563
At Full Load
Jackets
1700
700
800
1180
(Btu/kwh)
Exhaust
1400
1900
2100
700
Total
6663
6163
6463
5443
Overall
Efficiency
(Percent)
67
61.9
67.9
57.6
-------
TABLE 5
ANAEROBIC DIGESTER GAS PRODUCTION AND USE
01
(1)
Plant
Capacity
(mgd)
1
5
10
25
50
75
100
(2)
Total
Dry
Solids to
Digester
(Ib/day)
2,100
10,500
21,000
52,500
105,000
157,500
210,000
(3)
Volatile
Solids
Destroyed
(Ib/day)
723
3,615
7,230
18,075
36,150
54,225
72,300
(4)
Gas
Produced
(scf/day)
10,845
54,225
108,450
271,125
542,250
813,375
1,084,500
(5)
Heat
Available
(mil Btu/day)
6.5
32.5
65.0
162.5
325.0
487.5
650.0
(6)
Power
Available
From 1C
Engines
(hp)
38
190
380
950
1,900
2,850
3,800
(7)
Power
Available
From Engine-
Generator set
(kw)
24
120
240
600
1,200
1,800
2,400
(8)
Heat
Recovered
From 1C
Engine
(mil Btu/day)
1.6
8.1
16.2
40.6
81.2
121.8
162.5
Column (2) Primary and conventional activated sludge treatment
(3) Primary sludge solids 60% volatile, WAS 80% volatile; 50% volatiles destroyed
(4) 15 scf per Ib VS destroyed
(5) Net heat = 600 Btu/scf (9,000 Btu/lb VS destroyed)
(6) Efficiency = 36.4%; 7000 Btu/hp-hr
(7) Efficiency = 30%; 11,400 Btu/kw-hr
(8) 25% recovery
-------
TABLE 6
DIGESTER CAS CLEANING AMD STORAGE COSTS
Plant
Capacity
o>
o
S
to
25
SO
75
100
200
300
Scrub and Compress
Scrub i
Compress
(aefm)
yu <• k tu /
50
100
200
350
6(0
1050
1400
2100
HjS
Removed
9 1000 ppn1
(Ib/day)
5.1
10.2
25.3
50.5
75.6
101
202
303
. Cai
Compressed2
(10QO
cu ft/day)
24
48
96
168
307
504
672
1008
Equipment Coat
(51,000)
Scrub Compress
14
16
20
25
34
44
51
63
20
22
25
35
45
55
90
110
Construct-
ion
Cost
($ 1,0001
88
99
117
156
205
257
367
450
Storage Spheres
Volume Construc-
1000 tion Cost
(cuft) (no.idla) ($1,000)
17
24
50
74
113
113
226
339
1-32
1-36
1-46
1-36
1-46
1-60
1-60
2-60
3-60
65
90
IBS
275
400
400
800
1200
Total
Construe-,
tion Coat
($*1.000)
153
189
302
431
605
657
1168
1650
1 Labor Material
hr/yr $1,000/TT
240
470
1000
2000
2900
3750
5750
7500
2
4
10
20
30
40
60
80
Energy
1000
kvh/ii
102
219
371
63*
1092
1593
2533
3600
(I) Assumes digester gas - 0.071 Ib/ft1.
(2) Css compressed and stored 8 45 pal (scfn x 1440/3).
(3) Total Construction Cost - conatruction-cost of scrubbers, compressors
and storage spheres in a complete system.
-------
TABLE 7
SOLAR HEATING EXAMPLE DETROIT MICHIGAN
Month
Jan
Feb
Mar
Apr
May
June
July
Aug
Sept
Oct
Nov
Dec
No. Days
31
28
31
30
31
30
31
31
30
31
30
31
Solar
Insolation
(Btu/sq ft/month)
56110
60536
72230
69600
70184
66720
69130
69998
66840
63860
53340
50654
Fraction of
Monthly Sunshine
0.35
0.46
0.53
0.59
0.65
0.69
0.72
0.72
0.69
0.65
0.42
0.40
Hourly
Mean Solar
Insolation
(Btu/hr/sq ftl
242
240
265
238
211
212
204
224
246
223
237
220
Collector
Efficiency
0.42
0.43
0.49
0.51
0.50
0.55
0.56
0.57
0.57
0.50
0.46
0.40
Collector
Output
(Btu/sq ft/month)
8250
11970
18760
20940
22810
25320
27870
23730
26290
20750
10310
8100
Mean Temp.
(°F)
25
30
35
50
60
70
75
70
65
55
40
30
Deg-Day
(0F-day/month)
1330
1198
1066
639
319
90
16
40
159
465
843
1212
Heating
Requirement
for
2,000 sq ft
(mil Btu/month)
25.0
22.6
20.1
12.0
6.0
1.7
0.3
0.8
3.0
8.8
15.9
22.8
Solar Collector
Area Required
For Heating
2,000
(sq ft)
3030
1890
1070
573
263
68
11
26
IK
422
1540
2810
-------
TABLE 8
ENERGY REQUIREMENTS
30 mgd ACTIVATED SLUDGE PLANT IN SOUTHERN U.S.
(See Flow Diagram, Figure 8)
PROCESS
ENERGY REQUIRED
TREATMENT PROCESSES
Raw Sewage Pumping
Preliminary Treatment
Bar Screen
Comminutor
Grit Removal- Aerated
Primary Sedimentation - Circular
Aeration - Mechanical
Secondary Sedimentation
Chlorination
Sub Total
Gravity Thicken
Air Flotation Thicken
Anaerobic Digestion
Sludge Drying Bed
Land Disposal - Truck
Sub Total
Building Heat
Building Cooling
Sub Total
Total Treatment Process Energy
ENERGY RECOVERY PROCESS
Anaerobic Digester Gas
Utilization System
Total Energy with Recovery
Facilities
Electricity
(thousand
kwh/yr)
470
102
2,773
100
100
510
9,425
Fuel
or
Heat
(million
Btu/yr)
31,755
150
1.400
33,305
500
500
162
-------
TABLE 9
COMPOST PILE PERFORMANCE
BANGOR MAINE
1975-76
Pile
No.
1A
2B
3C
4A
5B
6C
7A
8B
9A
10B
11C
12A
13B
14C
15A
16B
17C
ISA
Compost
Period
8/19 -
8/26 -
9/2 -
9/10 -
9/23 -
10/2 -
10/8 -
10/15 -
11/7 -
11/13 -
12/3 -
12/10 -
1/13 -
1/15 -
2/12 -
2/23 -
3/1 -
3/9 -
9/10
9/15
9/25
10/2
10/10
10/17
10/31
10/31
12/4
12/23
12/23
12/23
2/5
2/5
3/8
3/12
3/29
3/30
Days To
Peak
Temp
4
7
5
8
15
8
7
13
11
17
20
14
20
11
20
20
15
17
Days
Above
55°C
8
14
21
17
9
12
18
10
18
0
1
3
15
10
7
9
17
10
Peak
Temp,
°C
67
83
65
67
72
76
76
67
62
50
61
60
66
58
60
74
71
70
Avg
Temp,
°C
58
60
60
62
63
75
73
62
58
50
61
60
60
58
58
71
68
68
Avg
Ambient
Temp,
°C
15
15
16
15
11
10
7
7
3
-5
-11
-12
-5
-6
-2
-5
0
5
Avg
02
(percent)
17
17
18
17
13
13
12
12
12
12
9
14
15
15
14
11
10
10
163
-------
GAS FROM DIGESTER
0.2 psi 95° F
TJ
O
c
TO
m
STEAM OR
HOT WATER
TO DIGESTER
OR OTHER USE
HEAT
RECOVERY
UNIT
SCRUBBER
ALTERNATE
FUEL
SYSTEM
INTERNAL
COMBUSTION
ENGINE
EXCESS GAS
BURNER
ELECTRICAL GENERATOR
AIR BLOWER
WATER PUMP
ANAEROBIC DIGESTER GAS
UTILIZATION SYSTEM
-------
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INTERNAL COMBUSTION ENGINE
CONSTRUCTION AND MATERIAL COSTS
600 rpm ENGINE WITH HEAT RECOVERY
AND ALTERNATE FUEL SYSTEM
165
FIGURE 2
-------
1,000
100
7891,000 2
1C ENGINE, hp
100
56789 10,000
INTERNAL COMBUSTION ENGINE
0 8 M LABOR AND ALTERNATE FUEL REQUIREMENTS
600 rpm ENGINE WITH HEAT RECOVERY
AND ALTERNATE FUEL SYSTEM
166
FIGURE 3
-------
MAINTENANCE MATERIAL, $ 1,0007 yr
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TREATMENT PLANT CAPACITY, mgd
DIGESTER GAS UTILIZATION SYSTEM
LABOR AND ENERGY REQUIREMENTS
COMPLETE SYSTEM FOR ELECTRICAL GENERATION
AS SHOWN IN FIGURE 1
168
FIGURE 5
-------
7.0
-
a
:
I
6.0
5.0
-
-
•
-
-
.
4.0
3.0
2.0
1.0
DIGESTER LOADING
0.05 Ib VS/doy/cu ft
0. 15
DIGESTION
TEMPERATURE
: 95°F
30
40 50 60 70
SLUDGE TEMPERATURE TO DIGESTER, °F
ANAEROBIC DIGESTER HEAT REQUIREMENTS FOR
PRIMARY PLUS WASTE ACTIVATED SLUDGE
169
FIGURE 6
-------
SOLAR
ENERGY
HEAT
STORAGE
HOT WATER COIL
i
COLD HOT
IN OUT
HOT AIR OUT
FOR SPACE
HEATING, ETC.
COLD
AIR IN
FROM
HOT WATER
SYSTEM
TO
HOT WATER
SYSTEM
AUXILIARY HEAT
o
c
rn
•>i
TYPICAL SOLAR ENERGY SYSTEM
-------
SOLAR HEAT COLLECTORS
COLLECTOR
PUMP
COLD RAW
SLUDGE
DIGESTER
PREHEATED SLUDGE
SOLAR HEAT
STORAGE TANKS
L.7D
AUXILIARY HEAT
CIRCULATING PUMP
COLLECTOR PUMP ON WHEN :
AUXILIARY
BOILER
T | GREATER THAN T£
T3 LESS THAN 37°C
AND
AUXILIARY HEAT CIRCULATING PUMP ON WHEN:
T3 LESS THAN 33°C
SCHEMATIC DIAGRAM
SOLAR HEATING ANAEROBIC DIGESTER
(FROM REFERENCE 7)
171
FIGURE 8
-------
INFLUENT
WASTE WATER
PRELIMINARY
TREATMENT
to
PRIMARY
SEDIMENTATION
* '
AERATION
o
c
to
SECONDARY
SEDIMENTATION
FLOTATION
THICKEN
ANAEROBIC
DIGESTION
CHLORINATION
TREATED
EFFLUENT
•WASTEWATER
SOLIDS
LAND DISPOSAL
PROCESS SCHEMATIC
ACTIVATED SLUDGE SYSTEM
-------
COMPOST PILE
WATER
REMOVAL
40'
20'
SCREENED
COMPOST
DEODORIZING
PILE
0.33 hp
BLOWER
BULKING AGENT
AND SLUDGE
SCREENED COMPOST-
UNSCREENED COMPOST;
OR BULKING AGENT
PERFORATED PIPE-
CROSS SECTION
STATIC PILE COMPOSTING
( DEVELOPED BY THE U.S. DEPARTMENT OF AGRICULTURE,
AGRICULTURAL RESEARCH AT BELTSVILLE, MARYLAND,
REFERENCES 21 AND 22 )
173
FIGURE 10
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LIST OF ABBREVIATIONS AND SYMBOLS
ammonia/ammonium NH3/NH^
average avg
Baum6 B6
bed volume(s) BV
biochemical oxygen demand BOD
British thermal unit Btu
calcium hydroxide (hydrated lime) Ca(OH)2
calcium oxide (quick lime) CaO
carbon dioxide C02
chemi cal oxygen demand COD
chlorine C12
coefficient of performance COP
cubic foot (feet) cu ft
cubic feet per minute cfm
cubi c yard cu yd
degree(s) deg
degree Celsius °C
degree Fahrenheit ° F
diameter di am
feet (foot) ft
feet per second fps
ferric chloride Fed 3
174
-------
List of Abbreviations and Symbols (Continued)
f 1 ow rate Q
food to microorganisms ratio F/M
gallon(s) gal
gallons per day gpd
gallons per day per square foot gpd/sq ft
gal1ons per mi nute gpro
gal 1 ons per mi nute per square foot gpm/sq ft
horsepower nP
horsepower hour(s) hp-hr
hour(s) hr
hydrogen sulfide ^2S
inch(es) in-
independent physical-chemical IPC
internal combustion •• IC
Jackson turbidity unit JTU
kilogram(s) kg
kilowatt kw
kilowatt hour kwh
mercury : 9
methanol CH3°H
micron(s) **
miles per gallon mpg
miles per hour mp
milligram(s) per liter mg/1
175
-------
List of Abbreviations and Symbols (Continued)
mi 11 imeter mm
million mil
million gallons mil gal
million gallons per day mgd
minute(s) min
mixed liquor suspended solids MLSS
mixed liquor volatile suspended solids MLVSS
most probabl e number MPN
nitrate N03
nitrogen N
oxygen 02
percent %
phosphorus P
pound(s) Ib
pounds per square foot psf
pounds per square i nch ps i
pounds per square i nch absol ute ps i a
pounds per square inch gage psig
publicly owned treatment works POTW
sodium hydroxide NaOH
solids retention time SRT
square foot (feet) sq ft
suspended sol ids SS
standard cubic foot (feet) scf
176
-------
List of Abbreviations and Symbols (Continued)
standard cubi c feet per mi nute scfm
sulfur dioxide S02
sul furi c aci d H2SQ
temperature
temp
temperature change AT
total dissolved soli ds IDS
total dynami c head TDH
total solids TS
vacuum fi1ter VF
vel oci ty grad i ent G
volatile solids VS
waste activated siudge WAS
wei ght wt
year(s) yr
177
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CHEMICAL FIXATION OF WASTES
by
Robert E. Landreth1 and Jerome L. Mahloch2
Sanitary Engineer, EPA Municipal Environmental Research Laboratory
Cincinnati, Ohio
2Sanitary Engineer, Environmental Effect Laboratory, U.S. Army Engineer
Waterways Experiment Station, Vicksburg, Mississippi
178
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CHEMICAL FIXATION OF WASTES
INTRODUCTION
A major consideration inherent in the plans for installing pollu-
tant abatement systems is the necessity for disposing of or utilizing
the by-products or resultant wastes. The rapid increase in the volume
of wastes requiring disposal to the land has caused concern over the
potential buildup of pollutants from long-term application. Alterna-
tives to the disposal of raw wastes are being assessed and in the more
promising cases, demonstrated. One alternative under consideration is
the chemical fixation of wastes.
Chemical fixation may be defined as a process to limit or minimize
the movement of contaminants away from the disposal site and to improve
the physical characteristics of the waste. Fixation usually imparts
increased physical strength and protects the potential pollutants of
the waste from dissolution by rainfall or by groundwater. If fixation
slows the rate of release of pollutants from the wastes sufficiently
so that no serious stresses are exerted on the environment, then the
wastes have been rendered essentially harmless and restrictions on
where the disposal site may be located will be minimal.
The bulk of the data base for chemical fixation technology has
been developed using inorganic industrial wastes and air abatement
residues. Selected processors are now addressing the municipal
sewage sludge for chemical fixation but data are limited. Municipal
sewage sludge data discussed in this paper were obtained from un-
published processor data. ERA has become involved with evaluating
chemical fixation technology because of the almost non-existent
independent evaluations of fixation technology and an insufficient
published data base to verify long-term durability.
Current EPA research on chemical fixation is being conducted through
an interagency agreement with the U.S. Army Corps of Engineers at the Water-
ways Experiment Station (WES). This research includes a (1) literature
review to identify known commercially available processors or processors
far enough along in the development of a process to be considered for
testing; (2) a laboratory phase, Teachability and durability, to evaluate
selected sludges; and (3) a field evaluation phase consisting of lysimeters
and actual subsurface monitoring of fixed waste disposal sites. This re-
search is being performed utilizing inorganic industrial wastes and air
abatement residues. The laboratory phase of the research has recently been
expanded to include municipal sewage sludges.
179
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LEACHING PHENOMENON
The degree to which contaminants will leach from a fixed waste is
strongly dependent on the chemical properties of that waste. In general,
fixation of a solid waste, or sludge, proceeds by the mixing of one or
more additives with the waste. The resultant product is one which may
possess chemical and physical properties which differ drastically from
the parent waste. The two major chemical properties which may be altered
by chemical fixation are the concentration and solubility of a particular
contaminant. In this case a distinction will be made between availability
of a contaminant and solubility.
Alterations in the concentration of contaminants in the fixed waste
occurs by virtue of the mass dilution by the admixed materials. This
assumes that initial concentration within the admixed materials are
lower than the waste; this may not necessarily be true and a reverse
effect may occur. In many cases the availability of a contaminant
from a fixed waste is directly proportional to its concentration;
consequently, dilution by admixing may be beneficial. The degree to
which this factor affects contaminant availability has not been ex-
plored in great deal, and in many cases is overshadowed by solubility
properties and therefore would not be critical in design.
Chemical fixation may affect the solubility of contaminants in a
variety of ways such as (1) alteration of the pH of the waste, (2)
altering the form of the contaminant (i.e. precipitation), or (3) com-
plexing or sequestering the contaminant in a matrix, generally provided
by the additive. Solubility of the contaminants is generally the con-
trolling factor which will govern the leaching process. The interaction
of solubility with chemical, physical, and biological mechanisms associ-
ated with leaching dictate the availability of the contaminants. Because
of the dominant influence of solubility on the leaching process, the
stability of any solubility changes caused by fixation becomes a critical
aspect of the long-term potential environmental impacts of fixed waste
for disposal.
The major groups of contaminants which are of interest and could
possibly be leached from municipal sewage sludges are organics, nutrients,
and selected anions and trace metals.
Leaching of Industrial Materials
Leaching of fixed wastes is a function of physical, chemical, and
biological mechanisms and principally occurs in the following two ways:
1. External leaching which occurs primarily as surface washing
and/or as diffusion into surface flow.
2. Internal leaching which is primarily a function of the
solubility of the material.
180
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To place these two leaching methods in perspective for fixed wastes,
most fixed wastes are characterized as being highly impermeable; conse-
quently, in a field disposal situation, the internal leaching contributes
an insignificant mass of contaminants to the environment. External leach-
ing is the major route of contaminant availability from fixed wastes.
Internal leaching may become significant if the physical stability of the
fixed waste is poor. Under long-term exposure and weathering, the fixed
waste may crack a deteriorate to a point where significant leaching may
be internal in nature.
External leaching is the predominant mechanisms for contaminant mobility
from fixed waste disposal areas as indicated by EPA research studies conducted
at the WES. As primarily stated this external leaching is a combination of
surface washing and/or diffusion to surface flow. Surface washing is pre-
dominantly a function of the solubility of the individual contaminants, con-
sequently, availability or leaching is related to the chemistry of the fixed
waste. Diffusion from the internal mass of the fixed waste to the surface
is a physical phenomenon, and related to solubility of the contaminant.
Typically, diffusion of contaminants from the fixed waste will be
less than from the initial surface washing. Comparison of these two
mechanisms of leaching for individual contaminants and when diffusion
will become dominant is dependent on the initial concentrations of
these contaminants in the fixed waste.
A representation of a typical leaching curve from a fixed specimen
is presented in Figure 1. This curve resembles a classical leaching
curve and demonstrates both mechanisms associated with external leaching.
The appearance of these curves for various types of contaminants present
is largely dependent on the initial concentration of the contaminants
and their respective solubilities. For those contaminants present in
large concentrations and highly soluble (e.g. chloride) the curve may
reach a diffusion limited situation rapidly, Case A, Figure 2. In the
case of high initial concentrations and relatively low solubilities (e.g.
calcium, sulfate), the initial surface washing may persist for a long
period of time before reaching the diffusion situation, Case B, Figure 2.
Finally, for those contaminants present in low initial concentrations and
low solubilities (e.g. lead), a curve similar to Case A is expected when
the curve may read a diffusion limited situation rapidly, except that
lower concentrations will generally occur, Case C, Figure 2. In actual
practice examples of all situations may be observed, and because of
differing chemical reactions and solubilities, variations between these
examples will generally be noted.
The interaction of biological mechanisms with leaching as it affects
contaminant mobility from fixed wastes is not too well documented. Possi-
ble biological mechanisms which may be critical include (1) biological
transformation of contaminants resulting in a more mobile form, and (2)
biological deterioration of the fixed waste which may expose more waste
for leaching or affect the additives reducing their effectiveness.
181
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The extension of these concepts to field disposal requires examina-
tion of the design of the disposal site. Typically the fixed waste will
be placed in a cell and be free draining on the top surface. Because
of the low permeability of fixed waste, the flow of water will be around
the material through the soil. Depending on the amount of recharge for
the site, the fixed waste will be subjected to alternate cycles of
saturated and unsaturated flow at the soil-fixed waste interface. The
flow will be subject to dispersion by the soil particles, and it is
expected that a certain degree of attenuation by the soil of some
contaminants will occur. The combination of the recharge and leaching
mechanism will typically give a leaching curve as shown in Figure 3.
In most cases this curve will be depressed (attentuation), and will
appear to approach a diffusion limited case (dispersion) faster as
compared to leaching only.
Fixation of sludges will generally result in an improvement in
leachate quality because of the inherent physical and chemical properties
of the fixed wastes as compared to the raw sludges. The primary factor
contributing to improvement in leachate quality from fixed wastes is the
reduction in raw waste surface exposed to leaching. This fact generally
results, not only in lower leachate concentrations, but also in a signifi-
cant improvement in the total mass of contaminants released to the environ-
ment. This latter advantage of fixation is directly proportional to the
quantity of waste (or initial amount of any particular contaminant) for
disposal. Equal consideration of the alteration of chemical properties of
the sludge must also be considered when evaluating fixation. In some cases
the alteration of chemical properties may be more significant than altera-
tion of physical properties, but this is extremely process dependent.
Leaching of Fixed Municipal Sewage Sludges
Currently there is limited data available concerning the leachate
quality from fixed municipal sewage sludges. Data that are available,
from a number of laboratory experiments, have been summarized in Table 1.
The major contaminants of interest, organics, nutrients, trace metals,
and selected anions, all show significant improvement in leachate quality
for the fixed wastes. In most cases, this improvement amounts to 1-2
orders of magnitude with respect to concentrations.
Since municipal wastewater sludges contain residual organic materials,
the possibility of biological action must be considered. Currently there
has been very little research on the long-term stability of fixed material
subject to biological attack. However, one processor has indicated that
digested sewage sludge presented no deterioration after fixation while un-
digested sewage sludge had to have a pretreatment step (liming and
dewatering) before fixation.
182
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Table 1. Comparison of Leachate Quality for Raw
and Fixed Municipal Sewage Sludge*
Parameter Raw Sludge Leachate** Fixed Sludge Leachate
(mg/1) (mg/1)***
Organics
a. BOD 4500-6000 930-25
b. COD 45,000-200,000 3100-300
Nutrients
a. Phosphate, ortho 4000-9500 7-1
b. Nitrogen, NH3 1000-1900 10-2.5
Selected Anions
a. Chloride 15,000-75,000 700-25
Trace Metals
a. Chromium, total 150-320 < 0.10
b. Lead 0.9-18 < 0.10
c. Nickel 8-53 2.5-0.10
d. Cadmium 4-14 < 0.10
Notes:
* Based on laboratory leach testing of representative products.
** Values given represent a range.
*** Values given represent a range from initial to terminal leach
cycles, if only one value is cited it was constant throughout
the test.
PHYSICAL CLASSIFICATION
At the WES fixed and raw industrial wastes were subjected to a series
of standard tests commonly used in determining the properties of soil and/
or concrete. The use of these standard tests and procedures allows for
comparison of waste properties with those common materials whose properties
are available in the literature. The data resulting from these tests indi-
cate that raw and fixed wastes exhibit a wide range of properties, many of
which were waste and/or process-dependent. It should be noted that some
fixed wastes were soil-like in appearance while others were solid masses
resembling low strength concrete. A discussion of the tests and results
are given below in order to indicate the types of results one might expect.
It should be emphasized that these tests were conducted on wastes other
than municipal sewage sludges except where specifically noted.
183
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Grain size distribution curves were determined for combined sieve and
hydrometer analysis. The wastes studies were generally well-graded with a
smooth distribution of grain size curves. Average grain size curves ranged
from 0.0076 to 0.125 mm suggesting a silt type soil. A high percentage of
one processor's fixed wastes passed the #200 sieve indicative of low per-
meability and strength and high compressibility. Fixed municipal sewage
sludge exhibited properties similar to a silty loam or loam with 60-75%
of the material passing the #200 sieve.
In some cases attempts to determine grain size distribution were
only partially successful due to flocculation during the hydrometer
analysis. Since the raw waste was tested in identical procedures it
was concluded that the test failure was attributed to the fixation
additive.
The fixed wastes generally decreased in plasticity. Valves for
liquid limit, plastic limit, and plasticity index were determined.
One can assume that since the grain size distributions and atterburg
limits exhibit properties characteristic of silty soils, the behavior
of these sludges would be similar to that of silty soils.
Specific gravity of raw wastes that WES studies ranged from 2.41 to
3.96 and for fixed wastes from 1.74 to 3.68. These valves of specific
gravity are within the range of common minerals and soils. Generally,
the raw wastes were higher than comparable fixed specimens. However,
changes in specific gravity due to fixation are process dependent.
COMPACTION AND STRENGTH
The water content of samples indicate that the relative amount of
available interstitial water after fixation is process-dependent. Data
for void ratio and porosity indicate fixed wastes are process dependent.
Bulk and oven-dry weights were determined to be within the range of soils.
The data generated from the 15 blow compaction test indicate no sub-
stantial increase in the dry unit weight of fixed wastes as composed to
raw wastes and that the optimum moisture content for maximum compaction
of the fixed wastes were waste dependent.
Results from the unconfined compression tests indicate that the com-
pressive strengths of fixed wastes are highly dependent on waste type and
fixation process. Some wastes exhibited compressive strengths typical of
silts and clays while others had strengths comparable to soil-cement
mixtures or Tow-strength concrete. Of those wastes studied at WES uncon-
fined compressive strengths ranged from 8 to 4500 psi. This is within
the range of values reported by the individual processors for municipal
sewage sludges. The higher values could probably be obtained for a
majority of the wastes if sufficient additive were added. Of course
this increase in additive would be reflected in the cost.
The results of the compaction and unconfined compression tests
indicate that the fixed wastes are viable candidates for bearing
capacities and embankment construction.
184
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PERMEABILITY
Permeabilities for fixed waste were generally "ower than that of raw
wastes although there was a very wide range of valves, i.e., 4.5 x 10~11
to 7.9 x lO"1* cm/sec. This range of permeability is comparable to range
of soils from a fat clay to a silty sand. Municipal sewage sludge had a
permeability in the 10~6 to 10~7 range. Permeability becomes an important
parameter if one considers the Teachability of the fixed mass.
DURABILITY
The durability, i.e., the ability to withstand repeated freeze-thaw
and wet-dry/cycles, testing of the fixed wastes was performed using the
standard ASTM tests. These tests utilized a steel brushing which was
very severe on the test specimens. Few of the specimens survived the
test. This test has since been modified to eliminate the steel brushing.
There were some data obtained to indicate that the durability of the
fixed wastes were a function of the process rather than waste. The test
results, including sewage sludge, suggest that continual exposure to
weathering will break down, physically, the solidified masses.
The breaking down of the mass will have an influence on the per-
meability of the material and subsequently the Teachability. It would
be inappropriate to discuss or conclude how the laboratory data could
be extrapolated to long-term field conditions without field verification.
Data from field disposal sites are being collected to develop correlations
between laboratory and field performance.
SUMMARY OF RESEARCH TO DATE
Chemical fixation of wastes is being evaluated. Reducing the leach-
ing of pollutants by chemical fixation is process dependent, but appears to
be successful for selected industrial wastes. Fixation of wastes also re-
sults in physical alterations which is process and waste dependent. Labora-
tory and field studies are continuing to better define and evaluate the
pollutant potential chemically fixed wastes.
ECONOMICS
The assessment of costs for chemical fixation of sludges is very
complicated. Because of the competiveness between fixation processors,
it is extremely difficult to pinpoint all costs to arrive at a total
disposal cost. Companies are willing to give only general cost ranges
for various types and conditions of sludges. They would rather discuss
the individual disposal problem in a more business like atmosphere
where all factors can be considered. This hesitation on the part of
the fixation processor is in part justified because of the site and
sludge specific conditions that affect the ultimate cost.
185
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Air Abatement Wastes
The Aerospace Corporation has evaluated costs for disposal of fixed
flue gas cleaning (FGC) wastes. The resulting costs were in the $7 to $11
per dry waste ton (1975 dollars) range. These values were based on a
1000-Mw power plant, 30-year plant life, 50% average annual load factor
and 5 miles to the disposal site. Included in these costs are capital
equipment, land and operating costs.
To illustrate the complexity of determining costs the following infor-
mation was used to arrive at the above costs. Capital equipment life time
factors range from 10 to 30 years with average operating load factors of 70
to 100%. The capital changes were amortized to include depreciation, in-
surance, cost of capital, replacements and taxes. The average annual charge
on capital investment was 18% based on 50-50 debt-equity funding and 30-year
straight-line depreciation. Land cost were estimated at $1,000 per acre
resulting in an estimate of $0.13 per ton of dry waste charge.
Dewatering of the waste can have a significant impact on the final
cost. An increase in solids content from 35 to 50 percent resulted
in a disposal cost reduction of $30 to $10 per dry waste ton. Capital
costs for dewatering FGC wastes were about $0.50 per dry ton of waste with
an additional $0.12 per dry ton estimated for labor and power.
Operating costs that were included were: fixation additive costs,
labor, maintenance, materials, space, parts and power costs. Site main-
tenance, monitoring, truck, hauling, placement and compaction were also
included in the final disposal cost. A waste disposal site located 0.5
miles from the plant instead of 5 miles was calculated to reduce the total
cost 5 to 13%.
Other factors which would affect disposal costs include access roads,
rights-of-way and the effect of higher solids content of the waste.
Municipal Sewage Sludge
Sewage sludge fixation costs have not been well defined. Due to the
low solids content drying or conditioning of the sludge may have to be
performed. In some cases this drying is a requirement because of the
process of fixation. In comparison to other disposal methods chemical
fixation at least is a viable alternative. Table 2 presents ranges of
costs for selected disposal alternatives. One should view the table
with extreme care as site and sludge specific conditions may change
the costs considerably.
Industrial Wastes
There have been insufficient detail studies to assess the cost for
disposing of a variety of industrial wastes. Due to the similarity of
these wastes and the air abatement wastes it is expected that disposal
costs are comparable.
186
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Table 2. Comparative Costs for Sewage Sludge
Disposal Alternatives
Disposal Alternative Costs $/Dry Ton
Ocean $20
Landfill ing, Composting
Landspreading $40-$100
Incineration $90-$180
Chemical Fixation* $50-$100
*Volume dependent among other costs.
CANDIDATE PROCESSORS
There are several potential processors located throughout the
country. Table 3 lists those identified in a recent literature search
and by personal communication. This list is not known to be complete
nor does it represent an endorsement of any one processor. Some pro-
cessors listed are well established and have been practicing chemical
fixation for several years. Others have recently developed a process
which may or may not have a sufficient data base for a variety of sludge
fixation. A potential user of chemical fixation should investigate
several candidates for technical and economic effectiveness.
Most additives used by the processors are proprietary and patented.
In some cases the additives themselves are a waste material and could be a
source of pollutant potential. A few processors will discuss their
additives but will not divulge the mixing ratios or mixing techniques.
Some fixation techniques require adjustment of waste pH levels and most
prefer a relatively high solids content, e.g., 50-80% solids. Lower
solids content require more additives making the process more expensive.
Dewatering of sludges is also performed for those with low solids content.
Not all processors will fix or attempt to fix all types of sludges.
Certain processors are known to accept only selected sludge while others
are known to at least investigate the majority of waste sludges.
187
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Table 3. Chemical Fixation Processors
Company (Processor) Name and Address
I. U. Conversion Systems, Inc.
Research Center
P.O. Box 331
Plymouth Meeting, PA 19462
215/825-1555
Contact: Dr. Steve Taub
Wehran Engineering Corp.
East Main Street Extended
Middletown, NY 10940
914/342-5881
Contact: Mr. Dennis Fenn
Protective Packaging, Inc. (NECO)
328 Production Court
Jeffersontown, KY 40299
502/491-8300
Contact: Mr. Bruce Goreham
DRAVO Corporation
Product Research
Neville Island
Pittsburg, PA 15225
412/771-1200
Contact: Mr. Laszlo Pasztor
Chemfix, Inc.
505 McNeilly Road
Pittsburgh, PA 15226
412/343-8611
Contact: Mr. Douglas Wagner
Air Frame Mfg. and Supply Company (TACSS)
7407 Fulton Avenue
North Hollywood, CA 91605
213/875-2094
Contact: Mr. Robert F. Jensen
Werner & Pfeiderer Corp.
160 Hopper Avenue
Waldwick, NJ 07463
201/652-8600
Contact: Mr. John E. Stewart
188
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Aerojet Energy Conversion Company
P. 0. Box 13222
Sacramento, CA 95813
916/355-2255
Contact: Mr. Roy E. Jones
Chem Nuclear Systems, Inc.
P. 0. Box 1866
Bellevue, Washington 98009
206/747-5331
Environmental Technology Corp.
289 Casa Drive
Pittsburg, PA 15241
412/431-8586
Contact: Mr. Albert R. Kupiec
ANEFCO Company
151 East Post Road
White Plains, NY 10601
914/946-4631
Contact: Mr. John Murphy
United Nuclear Industries Commerical Div.
1201 Jadwin Avenue
Richland, Washington 99352
509/946-7661
Contact: Mr. Harold W. Heacock
Sludge Fixation Technology, Inc.
P.O. Box 32
Orchard Park, NY 41427
716/662-1005
Contact: Mr. Richard E. Valiga
Todd Research and Technology
P. 0. Box 1600
Galveston, TX 77550
713/744-7141
Contact: Mr. Cliff Winters
Hittman Nuclear and Development Corp.
9190 Red Branch Road
Columbia, MD 21045
301/730-7800
Contact: Mr. Pete Tweet
189
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John Sexton Contractors
900 Jorie Boulevard
Oak Brook, ILL 60521
312/654-1280
Contact: Mr. Dennis Johnson
TRW Systems Group
One Space Park
Redondo Beach, CA 90278
213/535-2715
Contact: Mr. H. R. Lubowitz
190
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REFERENCES
1. Mahloch, J. L., D. E. Averett, and M. J. Bartos, Jr., Pollutant
Potential of Raw and Chemically Fixed Hazardous Industrial Wastes
and Flue Gas Desulfurization Sludges, U. S. Environmental Protection
Agency, EPA-600/2-76-182, July 1976.
2. Fling, R. B., W. M. Graven, F. D. Hess, P. P. Leo, R. C. Rossi, and
J. Rossoff, Disposal of Flue Gas Cleaning Wastes: EPA Shawnee Field
Evaluation - Initial Report, U. S. Environmental Protection Agency,
EPA-600/2-76-070, March 1976.
3. Personal Communication, H. Mullin, W. Minnick, and S. I. Taub,
I. U. Conversion Systems, Inc., Philadelphia, Pa.
4. Memorandum, Fujisash Industries, Ltd., Seikichi Furuya to A. W. Lindsey
OSW, U. S. Environmental Protection Agency, March 1976.
5. Personal Communication, D. Wagner, Chem Fix, Inc., Pittsburg, Pa.
6. Bartos, M. J., Jr., M. R. Palermo, Physical and Engineering Properties
and Durability of Raw and Chemically Fixed Hazardous Industrial Wastes
and Flue Gas Desulfurization Sludges, U. S. Environmental Protection
Agency (to be published).
191
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Figure 1. Generalized Leaching
of Fixed Materials.
DIFFUSION
CONTROLLED
ro
TIME
-------
Figure 2. Leaching Patterns from
Fixed Materials.
TIME
-------
Figure 3. Raw and Fixed Leaching.
TIME
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Introduction to the
Principles of Land Application of Sludge
by
Bruce R. Weddle
Prepared for the
Environmental Protection Agency
Technology Transfer
Design Seminar Series
for
Sludge Treatment and Disposal
1977
1 Chief, Special Wastes Branch, Office of Solid Waste,
U. S. Environmental Protection Agency, Washington, D. C.
195
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INTRODUCTION to the
PRINCIPLES OF LAND APPLICATION OF MUNICIPAL SLUDGE
As the introductory speaker to this session on land application of
municipal sludge, I have been asked to touch upon three major topics.
The first deals with the current status of several EPA sludge programs.
Specifically, I will address the municipal sludge technical bulletin,
the recently enacted solid waste legislation and the development of an
Agency-wide municipal sludge strategy paper. I will then briefly
discuss sludge landfilling practices and conclude with an overview of
agricultural landspreading of sludge.
I would like to begin with the proposed technical bulletin "Municipal
Sludge Management: Environmental Factors," which was published in the
June 3, 1976 Federal Register. The sludge technical bulletin, as it is
commonly referred to, is intended to assist the Agency's Regional
Administrators and their staffs in evaluating grant applications for
construction of publically owned sewage treatment works under Section
203(a) of PL 92-500. The bulletin, while not a regulatory document,
addresses factors important to the environmental acceptability of
particular sludge management options and does so in a general manner in
order to allow maximum flexibility to the Regions. Detailed information
on costs and cost-effectiveness analysis procedures, pretreatment
guidelines and regulations, as well as in-depth reviews of the somewhat
controversial potential impacts of land application are or will be
covered in additional supporting documents.
The sludge technical bulletin is based on current knowledge and
will be modified from time to time as any new regulations are developed
and additional information becomes available from current and future
research, development, and demonstration projects. The document emphasizes
land application alternatives since no Agency guidance has been issued
on this subject in the past, and some Agency guidance (and in some cases
regulations) is already available on the other major options—incineration,
landfill, and ocean disposal.
The proposed bulletin is divided into two distinct parts, one
including methods in which the sludge is utilized as a resource and the
second including those methods not utilizing the sludge for any beneficial
purpose. Appendices are also available that cover the preparation of
environmental impact statements, groundwater requirements of BPT,
guidance for the land (filling) disposal of solid wastes, incinerator
emission and performance standards, and criteria established for ocean
dumping of municipal sewage sludges.
196
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The proposed bulletin places primary reliance on FDA and USDA to
establish recommendations for acceptable tolerances or limits for heavy
metals and other contaminants in human foods and animal feeds, and the
best agricultural practices for sludge use in agriculture. Until the
necessary human food and animal feed quality standards are established,
strict regulation of crops produced on sludge amended soils and design
criteria for new projects will, out of necessity, have to be based upon
rather arbitrary values. There are currently no acceptable tolerances
or limits available for control of most contaminants in sludges for
human foods and animal feeds that can be applied to crops grown on
sludge amended soils for human or animal use.
The proposed bulletin will apply some control to the design and
proper management of this practice—at least to the extent that eligibility
for capital funds from the Construction Grants Program is concerned.
While the technical bulletin is not a regulatory document, new
solid waste legislation (the Resource Conservation and Recovery Act of
1976) may result in the regulation of some municipal sludge. This law
provides the Federal Government with the authority to protect health and
the environment and facilitate resource recovery and conservation in the
face of the growing solid waste disposal problem. Under the Act, a
permit program is established to manage the disposition of potentially
hazardous materials from their point of origin to their final disposition.
The legislation also mandates state and regional solid waste plans aimed
at phasing out open dumps. The Agency has the authority to provide
technical and financial assistance to help states develop and implement
solid waste, resource recovery and resource conservation plans and
systems. In addition, the Act expands EPA's current research, development,
and demonstration of solid waste management technologies.
How will this new piece of legislation affect sludge? We can begin
to answer this question by looking at the definition section of the Act
(Subtitle A, Section 1004). There are three definitions that are of
importance to sludge management:
Solid waste is defined as "any garbage, refuse, sludge from a
waste treatment plant, water supply treatment plant, or air
pollution control facility..."
Disposal is defined as "the discharge, deposits, injection,
dumping, spilling, leaking, or placing of any solid waste or
hazardous waste into or on any land or water so that such
solid waste or hazardous waste or any constituent thereof may
enter the environment or be emitted into the air or discharged
into any waters, including groundwater."
Hazardous waste is defined as a solid waste that may "pose
a substantial present or potential hazard to human health
or the environment when improperly treated, stored, transported,
or disposed of or otherwise managed."
197
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These definitions suggest that anything in the Act that refers to
solid waste or solid waste management also refers to sludge and sludge
management. Furthermore, the definition of disposal, which includes
placing waste into or on any land, clearly encompasses both sludge
landspreading and sludge disposal in a landfill. The definition of
hazardous waste also leaves open the possibility that some sludges, like
some solid wastes, may be hazardous and may, therefore, be covered under
the hazardous waste control program of PL 94-580 (Subtitle C).
Our preliminary analysis of the Act, then, suggests a major emphasis
on residual sludge management. Specifically, we now envision the
following:
Guidelines (Section 1008) - We are required to write guidelines
for solid waste management that will be mandatory for federal
facilities and advisory for states. We plan to write guidelines
for sludge utilization and disposal that would fall under this
section. The guidelines will likely include descriptions of
alternative sludge management practices which will achieve
acceptable environmental performance levels.
Technical Assistance (Section 2003) - We are required to
provide teams of personnel to assist states and localities with
solid waste management problems, including sludge. A minimum
of 20 percent of the total general appropriation must be
allocated to this section.
Hazardous Wastes (Subtitle C) - We are required to define
parameters for determining which solid wastes are hazardous,
and to establish a permit program and write guidelines to
enable the states to control such hazardous wastes. To the
extent that some sludges due to their chemical constituents
or other characteristics may be defined as hazardous wastes,
this subtitle will affect sludge management.
Planning and Open Dumps (Subtitle D) - We are required to
approve and fund state solid waste plans and through this
mechanism prohibit open dumping of solid wastes. Residual
sludge management may be included in such plans,
perhaps by a permit program at the state level. We also
believe that some current sludge disposal practices may fall
under the definition of open dumps, and therefore be
phased out within 5 years of the approval date of the state
plan.
Public Participation (Section 6004) - The legislation provides
for public participation in the development and implementation
of the Act. We are taking this language very seriously. We
will be involving the public in every major step of the process
through advisory groups, public meetings, and public information
dissemination.
198
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I realize that what I have just said may seem very broad and
sweeping. It should, nevertheless, give some indication of what our
present plans are vis-a-vis sludge utilization and disposal.
Before moving on to the land disposal of sludge, I want to discuss
the Agency's Residual Sludge Working Group. In January of 1976, John Quarles,
then Deputy Administrator of EPA, issued a memo giving the Office of Solid
Waste the overall responsibility for "coordinating the development of
Agency policy, planning and guidance in the area of the utilization and
disposal of sludge." Our first action under this mandate was to form a
Residual Sludge Working Group, composed of representatives of the many
program offices within EPA that have an interest in the sludge issue.
Membership in the group thus includes not only the Office of Solid
Waste, but also the Office of Water Program Operations, the Office of
Research and Development, the Office of Enforcement, the Office of
Planning and Management, and last, but perhaps most important, a repre-
sentative of EPA's regional offices.
Working Group activities center around four major tasks:
Identification of technical, scientific and programmatic
problems and issues,
Coordination of on-going programs addressing those problems,
Development and recommendation of future programs, and
Development, coordination and recommendation of residual
sludge management policy.
The first major activity of the Sludge Working Group was to prepare
an Action Plan for Residual Sludge Management. This plan was designed
to identify the constraints to Agency sludge management, and to propose
particular action items for the resolutions of the problems identified.
The plan was signed on October 19, 1976 by John Quarles, and work is now
under way on the immediate action items proposed in the plan.
Briefly, the plan identifies four major problem areas as barriers
to implementation of an effective sludge program: (1) a lack of data on
public health and environmental issues related to sludge utilization and
disposal, as well as an absence of interpretation of existing data;
(2) problems associated with the technologies for sludge processing
treatment and disposal; (3) a lack of consistency in air, water and land
use guidance with respect to sludge and its constiuents; and (4)
social, economic and institutional constraints.
Now moving from Washington's paper filled world of technical bulletins,
rules, regulations and guidelines, I would like to briefly touch on the
199
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practice of landfilling sludge. The envrionmental effects of sludge
landfilling have not been thoroughly investigated. This is particularly
true with respect to the effects on groundwater quality. For the past
year and half we have been monitoring groundwater at 8 municipal sludge
landfills (3 sludge only, 5 sludge mixed with solid waste). The sites
selected (shown in Figure 1) reflect varying soils, age, and precipitation
rates, etc. Further description of each site is included in Table 1.
Wells were drilled at each site to sample leachate (if present) and
groundwater downgradient from the disposal site. Samples for background
water quality were obtained from nearby existing wells. The general
well locations are shown in Figure 2. Two wells, one shallow and one
deep were established to sample groundwater downgradient, local con-
ditions permitting. Rather than further describing the scope of this
project, I have included a copy of a paper presented by Dale Mosher at
the conference, held in St. Louis in September 1976. However, a brief
discussion of the interim results of this monitoring program is appropriate.
The total content of selected metals with the sludge presently
entering each site is shown in Table 2. Due to the lack of historical
sludge data we are forced to assume that the metals content of the
sludge analyzed was representative of that entering the site during its
lifetime. This assumption is probably reasonable for sites 1 through 5
where industrial input is apparently limited.
The range of leachate concentrations of selected parameters is
shown in Table 3. These were compared to leachate concentrations at
municipal solid waste only sites, developed under USEPA contract 68-01-2923
submitted by SCS Engineers of Long Beach, California. The only apparent
difference was a higher upper limit of metal contents at sludge sites.
No conclusions, however, could be drawn due to limited amount of data and
site to site variability. In general, it appeared that the affect of
leachate on groundwater quality would be the same whether the leachate
is from municipal solid waste, sewage sludge or a combination of both.
This, however, does not appear to be the case. While each of the
11 solid waste only sites and each of the 8 sites accepting sludge show
groundwater contamination (based on indicated parameters such as specific
conductance in chemical oxygen demand), those sites accepting sewage
sludge show a definite trend towards contamination of groundwater with
heavy metals, while those that do not accept sludge do not show this
trend. Data for selected metals are shown in Table 4. Because the
metal contamination shown in this table was found at the disposal sites
accepting sewage sludge and generally not a solid waste only sites, we
believe that some factor or factors other than metals concentration in
the sludge or leachate are responsible for the observed results. Such
factors could be chelation or other changes in chemical equilibrium
brought about by the presence of sludge.
200
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- l .ll...___ .,.-__.
Figure 1
LOCATION OF SLUDGE MONITORING SITES
•':
-------
N)
O
Table I
Waste Characteristics for Sites Studied
Site
Criteria 1
Sludge Type Raw
primary
and
secondary
Solids 25-30%
Contents
Annual 13,555m
Sludge
Quantity
Total 76,500m3
Annual Solid
Wastes Quantity
Proportion 18%
of Sludge to
2 3
Raw Raw
primary primary
and and
secondary secondary
paunch
manure
20-25% 25-40%
26,224m3 Variable
354,100m3 None
7% Sludge
Only
4
Raw
primary
and
secondary
18-25%
7 , 300m3
None
Sludge
Only
5
Raw
Digested
and
incinerated
sludge ash
20-25%
125,700m3
760,420m3
17%
6
Digested
and
septic
tank
pumpings
3-5%
8,000m3
127,700m3
6%
7
Raw
primary
and
secondary
and
Zimpro
sludge
40% Zimpro
20% where
down
15,200m3
585,000m3
3%
8
Raw
primary
and
secondary
15%
19,900m3
None
Sludge
Only
Solid Waste
Received
(Volume basis)
-------
Leachate Sampling Well
Shallow Well
Deep Well
N)
o
Ul
Groundwater Flow
Figure 2. Generalized Location of Monitoring Wells
-------
Table 2
Metals Content of Sludges
Site
1
2
3
4
5
6
7
8
Cd
4
9
3
10
22
3
23
1
ppm (i
Cr
111
65
150
120
780
2,750
43,300
33,300
(dry weight basis)
Fe Pb
4,100
13,000
4,700
23,800
67,000
75,000
6,700
2,000
170
220
170
110
1,100
100
1,000
90
Table 3
Range of Leachate Characteristics
Parameter
Leachate Source
MSW * SS +
TKN
Cl
COD
Cd
Cr
Fe
Pb
11-758
139-568
165-13,000
.007-. 05
.33-. 65
15-679
.09-. 29
115-2513
3-1201
3,000-20,000
.009-. 1
.14-21
14-172
.1-1.55
*
+
Municipal Solid Waste Only - 5 sites
Sewage Sludge W/Wo MSW - 6 sites
SCS Contract No. 68-01
SCS Contract No. 68-01-3108
204
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Table 4
Average Increase over Background Level of
Selected Parameters
Parameters
Site Cd Cr Fe Pb
Increase in ppm
1
2
3
4
5
6
7
8
.02
.65*
.65*
.02
-
-
.10*
.10* .38*
.46*
539*
28*
1.10
.29
3.8*
374*
.03
.79*
.09*
.07*
_
.02
_
.34*
* Increase is at or above applicable Drinking Water Standards
While the presence of these metals in groundwater should be of
concern to each of us, it must be remembered that the groundwater
samples obtained in this study were within 61 meters (200 feet) of the
working face of the landfill. The data do not predict what effect this
contamination could have on groundwater further downgradient from the
site. This question will require further study.
The limited scope of this study does not justify abandonment of
subsurface sewage sludge disposal. It does, however, justify greater
emphasis in groundwater resource evaluation for sites which will accept
sewage sludge. This should include quality, quantity, direction and
rate of flow, present and potential use downgradient to the disposal
site. Where the water resource has a "high" value, site design and
operation should offer protection of that water resource.
In summary, the landfilling of sludge like the disposal of any
waste material, carries with it the potential for environmental de-
gradation. Therefore, in order to minimize such degradation, it is
encumbent on each of us to exercise the appropriate management control.
In this case, additional care should be taken in the design and operation
of any site which accepts municipal sludge. Specifically such sites
should closely follow the guidance contained in EPA's publication
"Sanitary Landfill Design and Operation."
Like landfilling, ocean dumping or any other disposition option,
the landspreading of municipal sludge carries certain environmental
risks. I would like to spend the remainder of my time identifying
management schemes to minimize some of those risks.
205
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While there are several controversial questions concerning sludge
agricultural utilization including pathogens, organic contamination of
food or forage and heavy metals uptake by crops, I will only be address-
ing the latter issue.
Sludge borne metals such as zinc, copper, nickel, and lead, generally
become toxic to plants before they reach levels that can be harmful to
man. Cadmium, on the other hand, being less toxic to plants can reach
potentially harmful levels to man within the crops. Therefore, I will
focus on the potential environmental and health problems surrounding
cadmium uptake by crops.
A 1974 study conducted by the US Food and Drug Administration
indicates that the mean intake of cadmium from food and drinking water
in the United States is approximately 72 ug/day. While there are no
standards for the allowable cadmium content in foods, a joint FAO/WHO
expert committee on food additives proposed a tolerable daily intake
level of 57 to 71 ug/day. A comparison of these numbers shows that our
average daily intake of cadmium currently approximates that proposed
tolerable limit. Compounding that concern is the fact that FDA generally
uses a safety factor of 100 for food additives while the FAO/WHO commit-
tee used a safety factor of only 4. While both the average daily intake
number and the proposed tolerable daily intake numbers are subject to
debate, FDA scientists indicated in the December 1975 issue of Environ-
mental Health Perspectives that "Further increases in the cadmium
content of foods should be avoided."
I would like to emphasize at this point that my reason for pointing
out the above figures is not to suggest that municipal sludge should
never be placed on agricultural land, but rather to point out that
prudence is advisable.
Research conducted by Lars Linnman on cadmium uptake in wheat
illustrates that site management is the key to proper agricultural
utilization of municipal sludge. Linnman*s work shows that cadmium can
and is assimilated by plants from the soil, and that cadmium uptake is
closely associated with the pH of that soil as well as to the total
amount of cadmium added. His data also shows that through the agronomic
application of 19 ton/ha (based on nitrogen and soil pH), the cadmium
level in the crop increased by 70 percent. This could be compared to
the 100 percent increase which some scientists consider to be an interim
goal. Indeed, it is the speaker's opinion that until further health
research on cadmium effects on man is completed, site management procedures
should be employed which minimize the translocation of cadmium from
sludge to crops.
Further support for the total annual and cumulative cadmium addi-
tion and pH controls can be found in the data which we gathered at 16
farms which have accepted sludge over a varying period of years.
206
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TABLE 5
CADMIUM UPTAKE BY WHEAT GRAIN (ug/g)
pH Range
Sludge
Applied
(t/ha)
0
6.5
19
58
Source: L. Linnman, Et.Al. 1973
5.0
0.067
0.119
0.170
0.257
6.1
0.045
0.086
0.123
0.134
7.2
0.029
0.033
0.050
0.068
o
-J
TABLE 6
CITY
M
N
O
PH
5.4
7.0
5.1
Cd/Zn
%
0.9
70
0.6
SLUDGE
Cd
(ppm)
6.5
3,200
5.9
ANNUAL
LOADING
(MT/ha)
12
17
16
CROP
SOYBEAN
WHEAT
HAY
CONTROL
Cd
(ppm)
0.24
0.32
0.13
CROP
Cd
(ppm)
0.52
2.3
1.7
INCREASE
117
620
1,200
-------
Table 6 shows selected data from the 3 communities showing the
greatest uptake of cadmium. In communities M and O, pH is apparently
the major factor influencing the cadmium increase since the incremental
increase of cadmium concentration in the sludged crops was the highest
of all sites examined (with the exception of one community which utilized
a sludge containing 3200 ppm cadmium).
Rather than focusing on what everyone agrees are poor practices,
let us examine the effects of following the aforementioned controls.
Table 7 shows two sites where a relatively high cadmium sludge was
applied with little impact on crop cadmium levels. In the case of City
A, the cadmium levels actually decreased following the addition of
sludge and raising the soil pH. The data from City F clearly shows
that high cadmium sludges can be applied to farm land as long as the pH
is controlled and the annual application rate is minimized. Dr. Lee
Sommers will provide a more detailed look into the effectiveness of
these controls following my presentation.
Data from 4 additional sites is shown in Table 8. In each case,
proper management control at the site resulted in achieving the goal of
minimizing cadmium uptake. In each case a low cadmium sludge was
applied to neutral soils at agronomic rates.
In summary, almost any sludge can be either a resource or pose an
environmental problem. The key lies in proper management of the site.
Each of the subsequent speakers will elaborate on the various management
techniques I have mentioned. It was my intent to impress upon each of
you the need to seriously consider their guidance and the potential
risks implicit in ignoring that guidance.
208
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TABLE 7
Control Sludged
pH Soil pH
City
A 5.8 6.8
F 7.5 7.1
SLUDGE
Cd/Zn Cd
CITY pH % (ppro)
D 6.4 0.3 6
E 7.0 0.4 16
H 7.4 0.4 4
K 6.5 0.5 - 18
Sludge Annual cd
Cd Application Increase
(ppm) Rate in Crop
(t/ha) %
54 6.5 -50
80 5.4 23
TABLE 8
ANNUAL CONTROL CROP
LOADING Cd Cd
(MT/ha) CROP (ppm) (oom)
2 SOYBEAN 0.33 0.34
12 POPCORN 0.14 0.17
18 GRASS 0.27 0.4
14 HAY 0.12 0.22
INCREASE
3
21
48
88
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A Preliminary Assessment of the Effects of
Subsurface Sewage Sludge Disposal on
Groundwater Quality *
Dale C. Mosher
Based in part on the results of a study conducted for the
Environmental Protection Agency by SCS Engineers of
Long Beach, California, under Contract No. 68-01-3108
210
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INTRODUCTION
The environmental effects of subsurface sewage sludge disposal have
not been thoroughly investigated. This is particularly true with
respect to effects on groundwater quality. This paper presents the
results of a preliminary evaluation of the effects of sewage sludge
disposal on groundwater quality. The term "subsurface sewage sludge
disposal" as used here means the burial of sewage sludge with or without
municipal solid waste in trenches, pits or area type landfills.
A study conducted at Oceanside, California (1) on leachate from
municipal solid waste and mixed sewage sludge/municipal solid waste was
completed in 1973. This study concluded that other than a lower pH and
higher BOD in the leachate from mixed sewage sludge/municipal solid
waste no other differences occurred. A continuing study of sewage sludge
only disposal was initiated in 1972 by the U. S. Department of Agricul-
ture, Agricultural Research Service at Beltsville, Maryland. The data
from this study (2) shows groundwater has been affected after only 19
months. The testing has been limited to chloride and nitrogen compounds.
These studies did not allow projection of the total effect of
subsurface sewage sludge disposal on groundwater resources. The Oceanside
study, for example, was limited to leachate analysis only. This data
then could only yield a determination of potential pollutants. The USDA
study did not include analysis for toxic metals. Toxic metals analysis
at the USDA field plots will be started in the near future.
Sewage sludges, however, are being generated in ever increasing
quantities and state regulatory agencies must determine what methods of
211
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sludge disposal are acceptable. la order to provide a broader data base
on which to issue guidance to state regulatory agencies, Environmental
Protection Agency's Office of Solid Waste awarded a contract to SCS
Engineers in Long Beach, California to monitor the effects of subsurface
sewage sludge disposal on groundwater quality. This paper will briefly
describe and report the results of that contract, drawing comparisons
where appropriate to a similar and somewhat more comprehensive study of
municipal solid waste only sites.
212
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Project Description
One objective of this project was to determine differences in
groundwater contamination resulting from subsurface sewage sludge
disposal at eight land disposal sites where location and operational
conditions ranged from optimal to unacceptable.
Further, a similar and somewhat more comprehensive study of ten
solid waste sites was being conducted. Thus the second objective of the
study was to compare these two sets of data to determine if differences
in groundwater contamination occurred between solid waste only and
sewage sludge land disposal practices.
Site Selection and Description - The acceptability of any given site
relative to groundwater protection is dependent upon many interrelated
factors such as permeability, depth to groundwater, subsurface soil,
geologic characteristics, climatology, etc. The major factors con-
sidered in site selection for this study were as follows:
Factor Range
Soils/Geology Sand to clay
Precipitation 59 to 115 cm/year
Operation poor to excellent
Age 3 to 5 years
It was expected that all sites would generate some leachate given a
minimum annual precipitation of 59 cm. It was also expected that sites
with clayey soils and excellent operations would show less groundwater
213
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contamination (if any) compared to sites with sandy soil and/or poor
operations. Other factors such as quantity of waste received, depth of
wastes disposal and depth to groundwater would also be expected to
influence the affect a specific site could have on groundwater quality.
In selecting sites to cover the above factors, a wide geographic dis-
tribution was necessary. The approximate location of study sites is
shown in Figure 1. The sludge quantities received at mixed sites varied
from 1 to 18% of the solid waste received on a weight basis (dry weight
for sludge and as received weight for solid waste). At sludge only
disposal sites the loading rates varied from 2241-5603 tonnes/ha (1000-
2500 tons/ac) on a dry weight basis. Further description of the sludge
and solid waste received at each site is given in Table 1.
Monitoring Program - Wells were drilled at each site to sample leachate
(if present) and groundwater downgradient from the disposal site.
Samples for background water quality were obtained from nearby existing
wells. The general well locations are shown in Figure 2. Two wells,
one shallow and one deep, were established to sample grandwater down-
gradient, local conditions permitting.
Starting one month after the wells were established three samples
of leachate and groundwater downgradient and one sample of background
water were taken during a five month period in 1975 from May to November.
An additional sample was obtained in June of 1976 from most wells. The
relationship of samples taken during this time period to the hydrologic
cycle is unknown. This sampling program was admittedly limited, however,
214
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it must be remembered that the objectives were limited to (1) determining
types of contamination occurring, (2) compare contamination from sewage
sludge to contamination from solid waste only. The data for the latter
being generated by a somewhat more comprehensive monitoring program. In
addition to the water samples, sludge at each site was analyzed, once in
1975 and once in 1976.
Before presenting the results obtained, it may be beneficial to
briefly discuss the method of data presentation. Figure 3 shows a
theoretical distribution over time for some contaminant concentration in
both background and downgradient groundwater. The variation over time
shown is a function contaminant source. The curve representing down-
gradient groundwater varies then, according to the quality and quantity
of leachate produced over time. The variation shown for background
water quality is exaggerated compared to "normal" uncontaminated ground-
water. This was done for illustrative purposes. From examination of
this figure, it is obvious that when only three or four samples down-
gradient are compared to one or two samples of background groundwater,
as in this study, examination of individual data points can be confusing.
In order to avoid a confusing picture, I have averaged all available
data points from each well. In this manner it is possible to subtract
background levels from downgradient levels and display the "average"
increase. This method is obviously subject to inaccuracy, however,
since normal background variation is generally quite small the probability
of showing an increase which is not real is minimal.
215
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Results and Discussion - The presentation of results is being limited to
heavy metals. This is because contaminants such as sulphates, chloride,
etc., have rarely exceeded their suggested drinking water standard.
Secondly, although increases in such parameters often exceeded industrial
standards, discussion of groundwater contamination is most often related
to drinking water standards. Because standards on groundwater do not
exist, I will in general only, refer to increases above background
levels. Where it is necessary for comparative purposes, increases will
be compared to drinking water standards.
The data generated in this study will be presented in the following
sequence: the source of metals, the leachate characteristics; and the
nature of groundwater contamination. Where appropriate the discussion
will compare this data to unpublished data from a similar but somewhat
more comprehensive study of solid waste only land disposal sites.
Source of Contaminants - The total content of selected metals for the
sludge presently entering each site is given in Table 2. Due to the
lack of historical sludge data we are forced to assume that the metals
content of the sludge analyzed was representative of that entering the
site during its life time. This assumption is probably reasonable for
sites one thru five where industrial input is apparently limited.
The range of leachate concentrations of selected parameters is
shown in Table 3. These are compared to leachate concentrations from
municipal solid waste only sites. The municipal solid waste only
leachate analysis comes from the draft final report of U.S.E.P.A. contract
216
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68-01-2923 submitted by SCS Engineers of Long Beach, California. The
ranges for sewage sludge only and mixed sewage sludge/solid waste are
not separated as no differences were apparent. The only apparent
difference is a higher upper limit of metal contents at sludge sites. No
conclusion, however, can be drawn due to the limited amount of data and
site to site variability. In general, it appears that the effect of
leachate on groundwater quality should be the same whether the leachate
is from municipal solid waste, sewage sludge or a combination of both.
This, however, does not appear to be the case. Data from this
study and the previously mentioned study of solid wastes only show
contamination of groundwater has occurred at all sites based on indicator
parameters such as specific conductive and chemical oxygen demand (COD).
Unlike solid waste only sites, however, the subsurface sewage sludge
sites show a definite trend toward contamination of groundwater with
heavy metals. Data for selected metals are show in Table 4.
In examining the data in Table 4, a logical conclusion would be
that sites 5 and 6 are sanitary landfills and all other sites are dumps.
This, however, is not the case. Using "Sanitary Landfill Design and
Operation" as a guide, site 5 would be called a sanitary landfill and
site 6 a dump. The latter is largely due to poor operation. Further,
site 3, which shows rather significant contamination, would also be
classified as a sanitary landfill. I should point out that the reference
used discusses factors related to the potential for ground water con-
tamination but does not give specific recommendations. Classifying any
site then is a matter of professional judgment. I believe that few
217
-------
people would disagree with the above classification of sites 3, 5 and 6.
Because metals contamination as shown in Table 4 was found at disposal
sites accepting sewage sludge and generally not at solid wastes only
sites, suggests that some factor or factors other than concentration are
responsible for the observed results. Such factors could be chelation
or other changes in chemical equilibrium brought about by the presence
of sludge. It must be remembered that the groundwater samples obtained
here were within 61 meters (200 feet) of the landfills studies. The
data do not predict what effect this contamination could have on groundwater
users further downgradient. This question will require further study.
This study was designed to determine the types of contaminants
found in groundwater as the result of subsurface sewage sludge disposal.
In developing this study it was assumed that no greater effect would be
observed than would occur from municipal solid waste only. This was not
found to be the case. The limited scope of this study, however, does
not justify abandonment of subsurface sewage sludge disposal. It does,
however, justify greater emphasis in groundwater resource evaluation for
sites which will accept sewage sludge.
It is obvious that more work is needed in the area of subsurface
sewage sludge disposal to better define the extent of the problems and
provide solutions. A contract has been awarded to SCS Engineers to
conduct further study of the sites discussed today. Detailed infor-
mation is being obtained on soils, geology, etc. to better define the
cause and effect relationships that exist.
218
-------
At the present time, good site selection practices should include
a comprehensive ground and surface water resource evaluation. This
should include quality, quantity, direction and rate of flow, present
and potential use downgradient from the disposal site. Where the
water resource has a "high" value site design and operation should
offer protection of the water resources.
Groundwater investigations are expensive to conduct, difficult to
evaluate and can provide answers only after years of study. We, there-
fore, cannot expect definitive solutions rapidly. We can, however,
periodically adjust our activities as more information becomes available.
219
-------
Figure 1
LOCATION OF SLUDGE MONITORING SITES
-------
to
t-J
Leachate Sampling Well
/ Shallow Well
y
Fill Area
V
,
f
5 i
/
1
I/"* Deep Well
V
Y
n
Groundwater Flow
Figure 2. Generalized Location of Monitoring Wells
-------
ij
g
w
E-i
2
2
O
U
JFMAMJJASOND
TIME
Figure 3. Theoretical Variation of Contaminant Levels
in Groundwater over time
222
-------
N>
Table I
Waste Characteristics for Sites Studied
Site
Criteria 1
Sludge Type Raw
primary
and
secondary
Solids 25-30%
Contents
Annual 13,555m3
Sludge
Quantity
Total 76,500m3
Annual Solid
Wastes Quantity
Proportion %
of Sludge to
2 3
Raw Raw
primary primary
and and
secondary secondary
paunch
manure
20-25% 25-40%
26,224m3 Variable
354,100m3 None
% Sludge
Only
4
Raw
primary
and
secondary
18-25%
7,300m3
None
Sludge
Only
5
Raw
Digested
and
incinerated
sludge ash
20-25%
125,700m3
760,420m3
10%
6
Digested
and
septic
tank
pump ings
3-5%
8,000m3
127,700m3
6%
7
Raw
primary
and
secondary
and
Zimpro
sludge
40% Zimpro
20% where
down
15,200m3
585,000m3
26%
8
Raw
primary
and
secondary
15%
19,900m3
None
Sludge
Only
Solid Waste
Received
(Volume basis)
-------
Table 2
Metals Content of Sludges
ppm (dry weight basis)
Site Cd Cr Fe Pb
1
2
3
4
5
6
7
8
4
9
3
10
22
3
23
1
111
65
150
120
780
2,750
43,300
33,300
4,100
13,000
4,700
23,800
67,000
75,000
6,700
2,000
170
220
170
110
1,100
100
1,000
90
224
-------
Table 3
Range of Leachate Characteristics
Leachate Source
Parameter MSW * SS +
11-758
139-568
165-13,000
.007-. 05
.65-. 33
15-679
.09-. 29
115-2513
3-1201
3,000-20,000
.009-. 1
.14-21
14-172
.1-1.55
TKN
Cl
COD
Cd
Cr
Fe
Pb
Municipal Solid Waste Only - 5 sites SCS Contract No. 68-01
Sewage Sludge W/Wo MSW - 6 sites SCS Contract No. 68-01-3108
225
-------
Table 4
Average Increase over Background Level of
Selected Parameters
Site
1
2
3
4
5
6
7
8
Parameters
Cd Cr Fe
Increase in ppm
.02
.65*
.65*
.02
_
-
.10*
.10* .38*
.46*
539*
28*
1.10
.29
3.8*
374*
Pb
.03
.79*
.09*
.07*
-
.02
-
.34*
* Increase is at or above applicable Drinking Water Standards
226
-------
Reference Cited
1. "Sewage Sludge Disposal into a Sanitary Landfill" - Ralph Stone
and Company, SW-71d, U. S. Environmental Protection Agency, 1974.
2. Trench Incorporation pf Sewage Sludge in Marginal Agricultural
Land. J. M. Walker et al. Agricultural Research Service, U. S.
Department of Agriculture, Environmental Protection Technology
Series, PB 246 561, U. S. Environmental Protection Agency, 1975
3. Sanitary Landfill Design and Operation - D. R. Burnner and
D. J. Keller. Environmental Protection Publication SW-65 ts
Washington, U. S. Government Printing Office, 1972.
227
-------
PRINCIPLES OF LAND
APPLICATION OF SEWAGE SLUDGE
by
L. E. Sommers
Prepared for the
Environmental Protection Agency
Technology Transfer
Design Seminar for Sludge Treatment and Disposal
Cincinnati, OH
Associate Professor of Agronomy, Purdue University, West
Lafayette, IN 4790?
228
-------
INTRODUCTION
The application of sewage sludge on land can be viewed from
two standpoints—firstly, the rates of application are consistent
with utilization of the plant nutrients in sludge by a growing
plant (i.e., recycling approach), and secondly, the maximum pos-
sible amount of sewage sludge is applied in a minimum amount of
time (disposal approach). From the standpoint of maintaining a
quality environment, the recycling approach should be adopted
when considering application of sewage sludges on agricultural
land. The successful operation of a program utilizing applica-
tion of sewage sludge on land is dependent on a knowledge of
sludge, soil, and crop characteristics and of the management
required to maintain environmental quality. The approach adopted
in this discussion is to present information on (l) sludge sampl-
ing and analysis; (2) soil properties and the fate of constituents
added to soil in sewage sludge; (3) nutrient requirements of
crops and techniques for assessing soil and crop interactions;
(4) management methodologies; and (5) application techniques.
SLUDGE SAMPLING AND ANALYSIS
Sampling
All programs utilizing application of sewage sludge on land
depend on a knowledge of sewage sludge composition. Obviously,
the composition of sewage sludge will depend upon the process
used in generating the sludge. At present, the majority of
sewage sludges are produced by an anaerobic digestion of primary
and/or secondary sludges. Unstabilized primary sludges are not
recommended for use in agriculture. However, lime (CaO)treated
and composted primary sludges may be of increasing significance.
Other types of materials that may be encountered include lagoon,
trickling filter, activated or wet-air oxidized sludges. The
advent of tertiary treatment of waste water for phosphorus re-
moval will increase the quantity of sludge -requiring disposal.
Not only will the chemical composition of sludges vary with
the type of sludge treatment process employed, but it will also
be dependent upon the composition of sewage entering the treatment
plant. For example, the presence of industries using metals
(e.g., Cu, Zn, Ni, Pb, Cd; within the sanitary district will
result in sewage sludges containing elevated metal concentrations.
Furthermore, the influence of industrial metal inputs on sludge
composition is not constant due to (1) varying degrees of industrial
229
-------
pretreatment; (2) differing efficiencies of metal removal from
sewage by various treatment plants and (3) varying concentra-
tions of metals entering sewage from native sources (e.g.,
plumbing systems, urban runoff, etc.). An additional factor in
determining sludge composition is the handling methods employed.
For example, the concentration of soluble constituents in sludge
(e.g., Na+, K+, NH^*) will be decreased by dewatering (vacuum
filtration, centrifugation, etc.) while metal concentrations
will be unaltered. Alternatively, heat drying of sludges will
decrease NH^+ levels but will not influence K+ or Na+. As an
example, the effect of wet-air oxidation on sludge composition
is shown in Table 1.
The diversity of sewage sludge composition is indicated by
the data presented in Table 2. It is apparent that the composi-
tion of sludge is extremely variable from one treatment plant to
another. Not only does the composition of sludge vary with the
treatment plant but it also varies with time at the same treat-
ment plant. A recent study involving analysis of sludges from
& treatment plants in Indiana suggests that a sound sampling
program is needed to assess accurately the composition of sludges,
Representative data on the variability of sludge components is
shown in Table 3. The variation found at a given treatment plant
often times exceeded that found between plants.
Several approaches can be used to obtain a representative
sample of sewage sludges for chemical analysis. The most de-
sirable method, but the most difficult to implement, is to obtain
flow weighted average data on chemical composition. This
approach requires continuous measurement of flow in conjunction
with periodic sampling for chemical analysis. The median con-
centration can also be used to evaluate chemical composition.
Using the median tends to minimize data from samples exhibiting
abnormally high or low concentrations. The number of samples
needed to estimate the median concentrations should be based
on the residence time of the sludge in the digester or process
used. If seasonal inputs to the plant are known, this will
influence the time and frequency of sampling. A third possi-
bility, and the least desirable, is to evaluate composition
based on a single grab sample of sludge. Available results
suggest that values for a grab sample will fall within one stan-
dard deviation of the true mean approximately 50^ of the time.
In all cases, the above assumes that the form of sludge applied
to land is sampled. Due to changes in composition resulting
from sludge handling procedures, it is essential that the
material applied is analyzed. For example, it is not valid to
sample and analyze liquid sludge exiting a digester and extra-
polate that data to sludge further processed by heat-drying or
dewatering. This is especially critical for N and K.
230
-------
Table 1. Effect of Wet-Air Oxidation on the Chemical Composi-
tion of Sewage Sludgesa
Parameter
Volatile solids
Soluble P
Part icul ate P
Soluble total N
Soluble organic N
Part icul ate total N
Particulate organic N
Total Cu
Total Zn
Total Ni
Total Cd
Total Pb
Plant
Before
47.1
0.032
1.074
1.356
0.293
2.120
1.837
1090
1996
70
11.4
451
No. 1
After
36.7
0.004
1.219
0.471
0.173
0.356
0.863
1011
1974
70
11.3
471
Plant No.
Before
*b
/u
57-2
0.153
1.401
1.354
0.131
2.839
2.490
g/kg
649
1814
911
53.4
686
2
After
36.3
0.010
2.315
0.427
0.170
1.348
1.329
852
2497
1064
77.2
973
*2
aAdapted from Sommers and Curtis
Percent or mg/kg oven-dry solids basis
231
-------
Table 2. Chemical Composition of Sewage Sludgesa
Component Ns^piesf Range Median Mean
Total N
NH.-N
4
N03-N
P
K
Ca
Mg
Fe
Mn
B
Hg
Cu
Zn
Ni
Pb
Cd
191
103
45
189
192
193
189
165
143
109
78
205
208
165
189
189
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
IS -
4 -
0.5 -
34 -
101 -
2 -
13 -
3 -
- 17.6
- 6.8
- 0.5
- 14.3
- 2.6
- 25.0
- 2.0
- 15.3
7,100
760
10,600
10,400
27, 800
3,520
19,700
3,410
^b
3.3
0.1
0.1
2.3
0.3
3.9
0.5
1.1
V.
260
33
5
850
1,740
82
500
16
3.9
0.7
0.1
2.5
0.4
4.9
0.5
1.3
380
77
733
1,210
2,790
320
1,360
110
a 3
Adapted from Sommers. Data are from numerous types of sludges
(anaerobic, aerobic, activated, lagoon, etc.).
Percent or mg/kg oven-dry solids basis.
232
-------
Table 3. Variability of Cd, Cu and Ni in Sewage Sludges'
Metal
Cd
Cu
Ni
Sludge
No.
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
Range
109-3 72
4- 39
483-1,177
3-150
24-756
12-163
22-256
11- 32
4,083-7,174
5,741-11,875
2,081-3,510
452-802
391-6,973
300-1,800
422-1,392
979-1,475
1,932-4,016
663-1,351
468-812
75-219
40-797
46- 92
47-547
65- 93
Median
•5
170
15
806
40
663
12
154
11
6,525
8,386
2,390
683
476
682
894
1,144
3,543
1,053
651
95
86
88
367
79
Mean
210
19
846
53
503
42
136
16
6,079
8,381
2,594
662
1,747
778
871
1,154
3,184
1,015
649
119
252
81
349
80
Coefficient
of Variation
c
45
67
27
95
63
160
69
54
19
27
21
18
167
67
47
15
27
29
21
50
144
22
55
12
a 1
Adapted from Sommers et al.
Oven-dry basis.
cStandard deviation expressed as a percentage of the mean.
233
-------
The pertinent points of sludge sampling can be summarized
as follows:
1. Develop a sound sampling program. A minimum effort is
3-6 samples obtained over a one-year period. The number
of samples required can vary from plant to plant and
can be altered based on past experience. Obviously,
the validity of recommendations for application rates
is directly proportional to the knowledge of sludge
composition.
2. Sample the form of sludge being considered for land
application.
3. Consider the residence time of sludge in the treatment
plant when deciding the frequency of sampling.
4« Samples must be preserved to prevent changes in compo-
sition from the time of collection to analysis. Freezing
and low temperature storage (4°C) are recommended for
samples analyzed >7 and <7 days, respectively, after
collection.
Sludge Analysis
Based on current research results, the key components in
sludges needing analysis are solids (or moisture), total N, NH.+,
NO}-, P, K, Cu, Zn, Ni, Cd and Pb. The above analyses are re-^
quired on all sludge materials to develop recommendations for
application rates on agricultural soils.
Upon obtaining a sample of sludge, several pretreatments may
be required prior to analysis. In order to obtain accurate N
analyses, the sludge must be analyzed at the moisture content
of sampling. For liquid sludges (<10$ solids), subsampling is
facilitated by placing the sample in a blender to disrupt solid
particles. For sludges containing >10$ solids, dilution of the
sludge sample with ^0 and then disruption in a blender may
alleviate subsampling problems. All other analyses can be per-
formed on samples dried at room temperature or in an oven. After
drying, the sludge must be ground to < 60 mesh to allow accurate
subsampling. The percent solids content of each sludge analyzed
is obtained in order to express all data on an oven-dry basis.
Total Inorganic N (NH^+ and N0o~). From the standpoint of
developing recommendations for application rates on agricultural
soils, the inorganic N content of sludge is a significant para-
meter. Ammonium may be present in sludge as either a soluble or
234
-------
exchangeable cation. If the pH >3, significant amounts of NE,
are also present. The determination of inorganic N is accom-
plished by extracting a sludge sample with_2 M KC1 to remove
both soluble and exchangeable NHi + and NOo . Once extracted,
several analytical procedures can be used to quantify the inor-
ganic N present, including steam distillation and acidimetric
titration and colorimetry.
Total N. The conventional Kjeldahl type digestions are used
to determine the total N content of sludges. Digestion of sludges
with concentrated I^SO/,. in the presence of salts (e.g., K2SO^)
and catalysts (e.g., Se and CuSO^) results in the conversion of
sludge organic N into NH^. The NH^ thus released is commonly
determined by colorimetry or steam distillation and acidimetric
titration.
Organic N. The organic N content of sludge is estimated
by difference as follows:
Organic N = Total N - (NH,+ + NO ~)
where NH^ + NO^" is the total inorganic N content of sludge.
For anaerobically digested sludges, the N0o~ fraction will be
present at very low concentrations ( < 10 mg/kg) and total in-
organic N is nearly equal to the NHA + concentration. It is
essential to determine both inorganic N and total N in sludges
because inorganic N may constitute from 25 to 50$ of the total
N in anaerobically digested sludge, depending on the solids
content of the sludge.
Phosphorus, Potassium, Copper, Zinc, Lead, Nickel, and
Cadmium. The analysis of these constituents are described to-
gether because a single extraction procedure can be used for all
elements listed. Extraction procedures commonly used include
(1) wet oxidation with HNOj-HClOi ; (2) dry ashing at 400-500°C
followed by treatment with KNOT, HC1 or HF; (3) refluxing with
Z»M HN03. For most sludges, wet- and dry-oxidation procedures
give comparable results. Following digestion, P is determined
by colorimetry, K by atomic absorption or flame emission and
Cu, Zn, Pb, Ni and Cd by atomic absorption. Background cor-
rection should be employed with Ni, Pb and Cd analyses to
minimize interferences present in sludge extracts. Other
analytical procedures are amenable to sludge analysis such as
neutron activation analysis, polarography, emission spectros-
copy, etc. In general, either these techniques are time con-
suming or the equipment is too expensive for use in routine
analyses of sludges. Analytical methods applicable to analysis
of sludges are described in several publicatioris.lt 4» 5» o, 7
235
-------
Other Analyses. Based on current information, the above
analyses allow development of recommendations for rates of sludge
application on agricultural soils. However, as new research data
is accumulated, information may be needed about the concentrations
of other elements; i.e., B, Se, Mo, Be, etc. Another special
category of compounds that may require analysis is chlorinated
hydrocarbons. The most recent example is the presence of poly-
chlorinated biphenyls (PCB) in sludges. If proper management is
used when applying sludges containing PCB's to soils, it is un-
likely that plant uptake of recalcitrant chlorinated hydrocarbons
will occur. Nevertheless, organic compounds can be absorbed
on the surface of forage crops and/or vegetables and thus,
consumption of surface contaminated crops may allow such organic
compounds to enter animal or human diets. As stated above,
proper management can alleviate these types of problems. Ana-
lytical procedures used for chlorinated hydrocarbon analysis
involve extraction with a non-aqueous solvent, clean-up and gas
chromatography. Laboratories specializing in pesticide residues
are equipped to perform these, types of analyses.
SOIL PROPERTIES
Overview of Soils
Soil is a complex mixture of inorganic and organic compounds,
whose proportions and properties depend upon the time, climate,
topography, vegetation and parent material involved in soil
formation. In a well aggregated soil, soil particles and pore
space each constitute 50^ of the volume. Optimum conditions for
plant growth exist when water and air each occupy 50$ of the
pore space. With respect to the solid phase, the texture of a
soil is defined by the relative proportion of particles found
in the sand (> 20 >u), silt (2-?C>u) and clay « 2>u) size frac-
tions, based on effective diameter. Through use of a texture
triangle, a soil containing a certain percentage of sand, silt
and clay is assigned a name, such as sandy loam, silt loam,
silty clay loam, etc. In this context, the term clay is used
to define a size fraction, which may contain inorganic compounds
in addition to clay minerals.
The inorganic components in soils may be subdivided into
the following categories: (1) clay minerals; (2) other silicate
minerals, (3J oxides, and (4) carbonates. Clays, or layer
silicates, are composed of sheets of Si tetrahedra and Al octa-
hedra present in 1:1 or 2:1 configuration. Kaolinite is a
typical 1:1 clay mineral while montmorillonite and vermiculite
are 2:1 clays. Isomorphous substitution of Al3+ or Fe3+ for Si
in the tetrahedral layer and Mg^+ or Fe^+ in the octahedral
layers results in clays possessing a net negative charge or a
236
-------
cation exchange capacity. This negative charge is satisfied ~
by surface retention of a cation such as H+, K+, Ca^+, Mg2+, Al-3 ,
etc. The magnitude of the negative charge is measured by
determining the cation exchange capacity (CEC), which is com-
monly expressed in meq/lOOg. The CEC arising from isomorphous
substitution is not pH dependent. However, clay minerals possess
some pH dependent CEC arising from the dissociation of OH groups
present at the edges of broken clay crystals. In addition to
CEC, additional properties of clays include a high surface area,
the capacity to sorb metals and organics, and the ability to
swell or shrink depending on water content.
Silicate minerals, oxides and carbonates are the other
major inorganic components in soils. In addition to clays,
soils may contain silicate minerals such as quartz, mica,
feldspar, etc. These types of silicates are less important than
clays from the standpoint of chemical reactivity because of their
minimal or no CEC and low surface area.
The predominant types of oxide minerals are compounds of
Fe, Al, and Mn. A significant part of the Fe and Al oxides in
soils may be present as amorphous rather than crystalline com-
pounds, depending on soil pH, organic matter and other properties,
Amorphous compounds possess a higher surface area and greater
chemical reactivity than their crystalline counterparts. Recent
research indicates that Fe and Al hydrous oxides can sorb Zn2+,
Cd^+, and probably other trace metals. It has been well estab-
lished that Fe and Al compounds in soil are important sites for
fixation of P. In addition, Fe and Al oxides may interact with
clay minerals resulting in the general trend observed for a
direct relationship between clay, Fe and Al content of soils.
The solubility of Fe3+ and Al3+ in soils is depressed with in-
creasing pH. Since Fe and Mn can undergo oxidation-reduction
reactions, the forms and subsequent solubility of Fe and Mn
are controlled by soil aeration. In addition to oxides, soils
may contain carbonates of Ca and Mg. In alkaline soils, CaCO^
and MgC03 are stable but with continued leaching soils become
acid due to the dissolution of carbonates and movement of Ca2+.
Acid soils are commonly limed with CaCO-^ to increase pH and
promote crop growth.
The other major component of the solid phase in soil is
organic matter (i.e., humus). Soil organic matter can be
grouped into two major categories, namely humic and non-humic
substances. Briefly, humic substances are a complex, high_
molecular group of organic compounds that result from chemical
and enzymatic reactions of degradation products from plant,
animal and microbial residues. Humic substances are subdivided
into the following categories: fulvic acid (acid and alkali
soluble), humic acid (acid insoluble, alkali soluble), and
humin (acid and alkali insoluble). Although quantitative
237
-------
differences exist in chemical composition, all 3 fractions are
characterized by possessing a non-polar (aromatic rings) core
with attached polar functional groups. The non-polar nature
results in the strong affinity of soil organic matter for added
organic compounds such as herbicides, pesticides, etc. Func-
tional groups found in soil organic matter include carboxyl
(-COOH), phenolic and alcoholic hydroxyl (-OH), amino (-NHo)
and sulfhydryl (-SH) groups. All of these functional groups
exhibit acid-base character and thus, soil organic matter is
involved in the buffering of soil pH. Furthermore, the ioniza-
tion of functional groups results in soil organic matter pos-
sessing a net negative charge or CEC. Soil pH strongly influences
the CEC of soil organic matter with increasing pH resulting in
increasing CEC. Metals may also interact with functional groups
through chelation and ion exchange mechanisms.
Non-humic substances are intact or partialy degraded
compounds found in plant, animal or microbial residues. Types
of compounds included are proteins, polysaccharides, fats,
waxes, nucleic acids, etc. With time, the majority of these
compounds will be subject to decomposition with a portion of
the degradation products becoming incorporated into humic sub-
stances. In general, non-humic substances account for <25$
of soil organic matter.
Soil organic matter is in a continual state of flux with
synthesis and degradation occurring concurrently. Both humic
and non-humic fractions contain N, P and S which are essential
for plants. As a general rule, the C:N:P:S ratio in soil
organic matter is 100:10:1:1. Since soil organic matter con-
tains N, P, and S in excess of that required to synthesis
microbial protoplasm, microbial degradation results in release
of inorganic Nf P, and S (i.e., mineralization) . A generalized
description of the N, P, and S distribution in soils is shown
in Table 4-
Soil acidity results from the presence of free H and ex-
changeable H+ and Al3 + . Acidity is generated when exchangeable
is displaced by another cation:
A1(OH) + 3H+
where X represents an exchange site on a clay mineral or soil
organic matter. In addition, the dissociation constants for
soil organic matter cover a broad range for a given functional
group resulting in a large buffering capacity. Hence, measure-
ment of soil pH in 1^0 followed by a simple calculation of the
amount of CaCCh needed to reach a desired pH is not valid in
soils. Current methods for obtaining lime requirements are
based on measuring pH in water (or a dilute salt solution)
and in a buffer solution to estimate the buffering capacity
of a soil. In some cases, exchangeable Al3+ is also estimated.
238
-------
Table 4. Distribution and Forms of N, P, and S in Soils
Element
Total
Organic
Forms
Inorganic
Forms
N
0.05-5.0
95-99
Amino acids
Hexosamines
i° of Total -
1-5
N0
2,
Fixed NH,
0.01-2.0
10-50
Inositol P
Phospholipids
Nucleic acids
50-90
Apatite
Fe-, Al-P
Occluded P
0.02-2.0
90-95
Amino acid
SO, esters
5-10
SO,2"
4
Reduced inorg. S
239
-------
Fate of Sludge N in Soils
An understanding of the N cycle in soils is useful in
understanding the fate of N added to soil in sewage sludge. A
simplified version of the N cycle is presented in Fig. 1. Both
organic and inorganic forms of N will be added to soil in sludges.
Ammonium and N03~ present in sludges will be immediately avail-
able for plant uptake. In addition, a portion of the organic N
will be decomposed releasing NH^"*" which will be available to
plants. It appears that the percentage of organic N mineralized
is approximately 20$ the 1st year, 10$ the 2nd year, and 5$ the
3rd year. Other estimates of organic N mineralization for the
first three years after application range from 10-3-3$ to 30-15-
7»5$« Further research is needed to quantify the residual
effects of organic N mineralization. When developing recommenda-
tions for application rates, it is essential that the quantity
of residual N be taken into account.
Ammonium-N added to soil in sludge is subject to several
chemical and microbial interactions (Fig. 1). With respect to
chemical reactions, soluble NHj^+ may displace a cation (e.g., K+)
present on the exchange complex of soil. In soils containing
micaceous minerals, NH/^+ may penetrate between the mineral plates
causing collapse of the mineral and NH^ fixation. This form of
NJfy is relatively inert and will not participate to a great ex-
tent in further chemical or microbial reactions. Of most sifni-
ficance, especially when considering surface application of
sludges, is NH^ volatilization. In excess of 50$ of the NH^-H is
commonly volatilized during air-drying of sewage sludges.8 The
extent of NH^ volatilization after surface application of sludge
will depend on the following factors: (1) soil pH (NHj favored
at pH>8); (2) soil CEC; (3) climate (temperature, relative hu-
midity); and (4) soil conditions (water content, rate of infil-
tration). Laboratory experiments indicate that the extent of NH-^
volatilization is related inversely to CEC and directly to pH .
Volatilization of NH^ can be reduced to < 5$ of applied NH^-N by
incorporation of sludge into the soil. Unfortunately, quantita-
tive data are not available concerning the magnitude of NH3
volatilization under field conditions. At present, recommenda-
tions based on N application rates assume that 50$ of the plant
available N is lost via NH3 volatilization when sludge is surface
applied.
Ammonium added to soils in sludge will be converted to NO^
through nitrification. Nitrification is a two-step process
involving oxidation of NH^* to N02~ by Nitrosomonas followed by
oxidation of N02~ to IKh" by Nitrobacter. In neutral soils,
essentially all NH^"4" added will be converted to N03~ within 2
weeks after application. Depressed nitrification rates may
occur in sludge amended soils at N application rates approaching
1000 Ibs/acres, amounts in excess of those recommended for
240
-------
Sludge N
N)
Organic
Decomposition
Exchange
NH4+
Clay-Fixed
NH4+
Leaching
NOf in
Ground Water
Volatilization
NH3 in
Atmosphere
Plants
Denitrification
N2 in
Atmosphere
Fig. 1. Nitrogen cycle in soils
-------
agricultural soils. In contrast to NH, which is held as an
exchangeable cation, N0o~ remains as a soluble anion in the soil
solution. The formation of NO^" is of significance because NO-}"
can be lost from the soil through leaching and denitrificationC
In humid regions, N applied to soils in excess of crop require-
ments may leach and result in NO^ contamination of ground water.
Systems developed for land treatment of waste water are based
on the premise that a growing crop will reduce the NO-5 concen-
tration in the soil solution to levels acceptable for drinking
water. Thus, the annual amount of N applied to soils in sludge
is based on the N required by the crop grown.
In addition to leaching, N0o~ may be lost from soils through
denitrification. Denitrification occurs when facultative
anaerobic bacteria utilize NO-^~ as a terminal electron acceptor
in place of ©2 under anaerobic conditions (i.e., saturated or
excessive water contents). In an "aerobic" soil, it is also
possible that denitrification can be occurring because the center
of soil aggregates may be water-saturated and anaerobic. The
end-product of denitrification is generally N2» which diffuses
into the atmosphere. Denitrification may be a significant
mechanism for N loss in soils treated with liquid sludge because
of localized increases in soil 1^0 content. Thus, NH,* may be _
oxidized to N0o~ in an aerobic zone followed by diffusion of NO-^
into anaerobic microsites where denitrification occurs (Fig. 2).
Phosphorus Cycle in Soil
Chemical rather than biochemical reactions control the
behavior of P in soils. In general, 50$ of the total P in
soils is present in organic matter while 90$ of total N and S
is present in organic combinations. The majority of P in sludges
is in inorganic compounds (70-90$ of total P). Thus, even though
mineralization of organic P will occur during decomposition of
sludge organic matter, the reactions of inorganic P are of
greater significance after sludge application.
The dynamics of P in soils are illustrated in Fig. 3. The
P immediately available for plants is present in the soil solu-
tion. As plants deplete the soil solution, the equilibria with
sorbed P and P minerals are shifted resulting in replenishment
of the soluble P pool. The quantity of soluble P in soil is
referred to as an "intensity" factor whereas the total amount of
P present that may enter the soil solution is a "capacity factor.'
Thus, the concentration of soluble P in soils may not be related
to the ability of a soil to supply P to crops throughout the
entire growing season. The majority of soils possess the ability
to "fix" P through sorption and/or precipitation reactions.
As a result, the concentration of P in the soil solution is
generally *r0.1 mg/1, resulting in minimal losses of P from soils
242
-------
Aerobic
(+02)
Soil Aggregate
Fig. 2. Schematic representation of denitrification
in anaerobic microsites in soil
243
-------
Sorbed P
Fe + Al
Oxides
Occluded P
Fe203j AI2O3
Leaching
Fig. 3. Phosphorus cycle in soil
244
-------
through leaching. In fact, land treatment of waste waters is
based on retention of P as waste water percolai;-?7 through a
soil profile.
Reactions of Metals in Soil
The majority of sludges add appreciable amounts of trace
metals to soils. The metal content of soils and plants is quite
variable depending on the soil type and plant species (Table 5).
Trace elements such as B, Co, Cu, Mn, Mo, Se and Zn are essential
for plant growth; however, if excessive concentrations are ap-
plied to soil, metal toxicities may develop and crop yields
will decrease. Often times, the interpretation of a metal toxi-
city to plants is not straightforward because of interactions
between nutrients (e.g., P induced Zn deficiency). Non-essential
metals (e.g., Cd, Ni, Pb) may be toxic to plants and decrease
yields. Of greater concern is the enrichment of food and fiber
with metals potentially harmful to humans and animals. Because
As, Pb and Hg are not taken up from soils by most plants, the
element of greatest concern is Cd. In general, the rationale
of sludge application guidelines is to minimize (1) decreased
crop yields caused by metal additions to soil; and (2) increased
concentrations of non-essential metals (e.g., Cd) in the plant
part consumed by man or animals. The fate of sludge metals in
soils and plants has been reviewed recently.10
The chemistry of metals in soils is quite complex and
incompletely understood at the present time. The fate of metals
added to soils in sewage sludge is depicted in Fig. 4» Metals
available to plants and susceptible to leaching are present in
the soil solution as the free metal ion (M^+), complexes (MOH+,
MC1+, etc.) and chelates (M-EDTA, M-Fulvic acid, etc.). As
plant uptake or leaching occurs, the soil solution re-equili-
brates with the solid phases present, resulting in a relatively
constant concentration in the soil solution. The equilibrium
concentration will be controlled by soil properties such as pH,
Ej^, solution composition, etc. In general, the solubility and
plant availability of metals decreases with increasing pH
(Fig. 5).
Metals in the soil solution are continuously interacting
with metals present in precipitates (carbonates, hydroxides,
etc.), bound with soil organic matter, sorbed by clay minerals
and retained by hydrous oxides. Furthermore, the properties
of clay minerals in soil are influenced to a great extent by
interaction with organic matter and hydrous oxides. In
general, the organic matter present in clay-organic matter com-
plexes is more resistant to decomposition than "free" organic
matter resulting in the common trend for the clay and organic
matter contents of soils to increase proportionately. The
245
-------
Table 5- Metal Content of Soils and Crops'
Element
As
B
Cd
Cr
Co
Cu
Pb
Mn
Mo
Ni
Se
V
Zn
Cone.
Common
6
10
0.06
100
8
20
10
850
2
40
0.5
100
50
in soils
Range
0.1-40
2-100
0.01-7
5-3000
1-40
2-100
2-200
100-4000
0.2-5
10-1000
0.1-2
20-500
10-300
Cone, in
— diagnostic
Normal
7i
0.1-5
30-75
0.2-0.8
0.2-1.0
0.05-0.5
4-15
0.1-10
15-100
1-100
1
0.02-2.0
0.1-10
15-200
plant
tissue
Toxicb
_
>75
—
—
—
>20
—
—
—
>50
50-100
>10
>200
a 11
Adapted from Allaway.
Toxicities listed do not apply to certain accumulator plant
species.
246
-------
Clay Minerals
MnO2
MC03
M(OH)2
MS
Soluble
Leaching
Soil
Organic
Matter
Plant
Uptake
Fig.
Reactions of metals in soil (M + represents
Cu, Zn, Ni, Cd, Pb, etc.)
247
-------
0
o
£4
c
g
u
c
o
O 8
O)
Q
I
10
12
O
Zn
Cu
I
Q
pH
8
10
12
Fig. 5. Effect of pH on the activity of Zn2+
and Cu + in the soil solution (adapted
from Lindsay1^)
248
-------
presence of acidic functional groups in soil organic matter is
responsible for metal retention through both exchange and
sorption mechanisms. Considerable evidence is accumulating
concerning the importance of metal retention by Fe and Al hydrous
oxides. As shown in Fig. 4, hydrous oxides may also be sorbed
onto clay minerals but they still retain the ability to sorb
metals. The Fe and Al hydrous oxide content of soils also tends
to increase \vith increasing clay content. As a result of these
interactions between clay, hydrous oxides, and organic matter,
CEC has been used as an index of the metal retention capacity
of a soil. This does not imply that metals added to soils are
retained through an ion exchange mechanism. Metals present in
soil as an exchangeable cation are readily available for plant
uptake but it has been demonstrated in numerous studies that
only a small fraction of metals added to soil are present as
an exchangeable ion. The above use of CEC for recommending
metal loadings is still open to question.
SOIL TESTING AND NUTRIENT REQUIREMENTS OF CROPS
The basic goal of recommendations for sludge application
rates is to supply a crop with adequate nutrients and to prevent
detrimental effects on crop yield and quality. Thus, informa-
tion is needed concerning the crop and its nutrient needs and
the level of existing soil fertility.
Nutrient Requirements of Crops
Fertilizer recommendations for crops are based primarily
on the amount of major nutrients (N, P and K) needed by a crop
and the yield desired. Since the application of sludges on
vegetable crops is not recommended, this discussion will focus
on cereal and forage crops.
The amounts of N, P and K required by the major agronomic
crops are shown in Table 6. As shown for corn, the yield
desired will determine the amount of N, P and K required.
Since cropping systems alter the level of-plant available nutrients
to different extents, the previous crop exerts an influence on
the N recommendations for corn at different yield levels (Table
7). These differences arise because crops such as legumes
actually increase the N availability in soils through symbiotic
N2 fixation. Primary emphasis in developing sludge guidelines
is placed on the ability of sludges to satisfy the N needs of
a crop.
249
-------
Table 6. Annual N, P and K Utilization by Selected Crops
a
Crop
Corn
Corn silage
Soybeans
Grain sorghum
Wheat
Oats
Barley
Alfalfa
Orchard grass
Brome grass
Tall fescue
Bluegrass
Yield
150 bu.
180 bu.
32 tons
50 bu.
60 bu.
4 tons
60 bu.
80 bu.
100 bu.
100 bu.
8 tons
6 tons
5 tons
3«5 tons
3 tons
N
185
240
200
257b
336b
250
125
186
150
150
450b
300
166
135
200
P
^^^ I r"\ G / Q O'V* Q j
35
44
35
21
29
40
22
24
24
24
35
44
29
29
24
K
1?8
199
203
100
120
166
91
134
125
125
398
311
211
154
149
Values reported are from reports by the Potash Institute of
America and are for the total above-ground portion of the
plants. For the purpose of estimating nutrient requirements
for any particular crop year, complete crop removal can be
assumed.
Legumes obtain N from symbiotic N2 fixation so fertilizer N
is not added.
250
-------
Table 7. Influence of Previous Crop on N Fertilization
Rates for Corna
Yield level, bu/acre
Previous crop ioo-110 111-125 126-150 151-175 176-200
Good legume
(alfalfa, red
clover, etc.)
Average legume
(legume-grass
mixture or
poor stand)
Corn, soybeans,
small grains,
grass sod
Continuous corn
60
100
120
70
100
120
140
Ibs N/acre
100
140
160
170
120
160
150
180
190
200
220
230
Purdue University Plant and Soil Testing Laboratory Mimeo, 1974.
251
-------
Soil Testing
Soil testing is utilized to assess the ability of a soil
to supply N, P, K and trace elements to plants. In addition,
plants vary in their ability to tolerate acid conditions so soil
pH and lime requirement are routinely determined. Because a
good plant available N soil test does not exist for most crops,
P and K are the principle plant nutrients determined in soils.
The approach used in soil testing is to determine the amount of
P or K extracted from soil with a specific reagent. Knowing the
relationship between crop yield and nutrient concentration in
the soil, it is possible to recommend the amount of fertilizer
required to attain a specific yield. The relationship between
the concentration of a plant nutrient in soil and crop yield
is shown in Fig. 6. With increasing levels of a nutrient in
soil, both yield and concentration of the element in plant
tissue increases. Crop yield will plateau and, for some elements
(e.g., metals), decreasing yields are encountered when increas-
ing amounts of an element are added to soil. Although yields
are not changing at high (subtoxic) rates of nutrient addition
to soil, the concentration in plant tissues continually increases.
The concentration of elements in plant tissues can be used to
assess both deficiencies and toxicities.
Development of soil testing procedures involves evaluating
a range of extractants and soils in greenhouse and/or field
experiments with a particular crop and the extract ant showing
the best correlation with plant yields and/or composition is -.~
used as a soil test. The reader is referred to Walsh and Beaton
for additional information about the approaches used in soil
and plant testing.
Regional variations in soil properties have led to the
development of P soil tests for different parts of the U. S.
For the sake of brevity, soil tests for P will be subdivided
on the basis of calcareous and acid soils. The following ex-
tractants are commonly used to evaluate available P in soils:
Calcareous soils - 0.5 M NaHCO-j
Acid soils - 0.025 N HC1 + 0.03 N NH^F (Bray PI)
- 0.05 N HC1 + 0.025 N H
The similarities of K reactions in acid and calcareous soils
result in the majority of states using IN NH^ acetate (pH 7)
as an extractant for plant available K. Recommendations for
fertilizer P and K applications tend to vary from region to
region because yield potentials depend on soil, crop and
climatic factors. As an example, the P and K recommendations
currently used in Indiana for corn are shown in Table 8.
Similar tables are used for other crops.
252
-------
Concentration
in Plant
t
cu
c
O
2
+->
c
-------
Table 3. Fertilizer P and K Recommendations for Corn'
to
en
Yield level, bu/acre
100-110
P
0-10
11-20
21-30
31-70
71+
K
0- 80
31-150
151-210
211-300
301+
P
44
31
22
13
0
K
33
58
42
25
0
111-125
P
43
35
26
13
0
K
100
75
50
25
0
126-150
P
53
40
26
18
4
K
125
100
58
33
0
151-175
P
57
44
31
22
4
K
149
116
75
50
0
176-200
P
66
53
35
22
4
K
166
133
100
66
0
f\
Purdue University Plant and Soil Analysis Laboratory Mimeo, 1974.
-------
Soil tests are also used to assess the availability of
Ca, Mg, S, B, and trace elements. Plant available Ca and Mg
is extracted with IN NIL acetate, S with water or CaCE^POi^,
and Zn, Cu, Mn and Fe with numerous salts, acids or chelating
agents. A procedure used in many of the western states employs
DTPA (diethylenetriaminepentacetic acid) buffered at pH 7.3 as
an extractant for Fe, Zn, Cu and Mn availability.^ In the
case of applying sewage sludges, the major concern is accumu-
lation of excessive metals rather than detecting deficiencies.
Nevertheless, the DTPA procedure may also serve as a technique
for evaluating plant available metals in soils treated with
sludges over a period of years.
A soil property routinely determined in soil testing
and one that is essential for soils receiving sludge is the
determination of soil pH and lime requirement. As discussed
previously, determination of soil pH in a water system cannot
be used to calculate the amount of lime required to increase
soil pH to a specified value due to the buffering capacity of
soils. The lime requirement is routinely determined by meas-
uring the pH of a soil-buffer mixture. The extent of pH
depression of the buffer caused by adding soil is proportional
to the amount of lime needed. The SMP buffer is used by many
laboratories and contains p-nitrophenol, K^CrOi , CaCl2> Ca
acetate, triethanolamine and 1^0 (pH 7.5). The buffer method
is described in detail by McLean. 1* The relationship between
soil + buffer pH and lime requirement is shown in Table 9-
Soil pH must be maintained at 6.5 or above in soils treated
with sludge so determination of lime requirement is essential.
Cation Exchange Capacity (CEC)
One approach for guidelines concerning metal additions
to soil in sludge is based on soil CEC. Several approaches are
used in determining soil CEC. One approach involves saturating
.g., NH^"1", Mg2+), washing out
the soil with a common cation (e
excess salt, replacing the saturating cation with a similar
cation (e.g., K+, Ca2+), and determining the amount of satur-
ating cation retained by the soil. By definition, exchangeable
cations can be displaced from a soil by a neutral salt. How-
ever, the salt chosen cannot react with soils through non-
exchange mechanisms (e.g., sorption). An alternative method
for evaluating CEC involves summing exchangeable H+ ions and
the cations removed by IN NHj^ acetate (pH 7)> i.e., K+, Na+,
Ca2+ and Mg^*. Both procedures give valid estimates of soil
CEC.
255
-------
Table 9. Amount of Lime (CaCOo) Required to Adjust Mineral
Soils to pH 6.5a
Soil pH determined Lime required for
in SMP buffer soil pH 6.5b
7.0
6.8
6.6
6.4
6.2
6.0
5. S
5.6
5.4
5.2
5.0
4.8
tons/acre
0
1.0
2.4
3.9
5.3
6.7
8.1
9.6
11.1
12.5
14.0
15.5
a 15
Adapted from McLean. '
Applies to mineral soils only,
255A
-------
DEVELOPMENT OF APPLICATION RATE RECOMMENDATIONS
The following discussion will pertain to application of
sludges on agricultural soils used for growing agronomic crops.
The only sludges considered are those that have been stabilized
by aerobic or anaerobic digestion, CaO, wet-air oxidation, etc.
Raw, undigested sludges should not be applied to agricultural
soils. Furthermore, vegetable crops should not be grown on
sludge amended soils since these crops, in general, are metal
accumulators. Numerous aspects of applying sludges on land
are discussed by Miller and Knezek.l"
The information needed to develop annual application rate
recommendations is based on the N and Cd content of the sludge
and the crop being grown. The length of time sludge can be
applied is limited by metal additions. The metals of primary
concern are Pb, Zn, Cu, Ni and Cd. This approach can be de-
picted as follows:
Annual rate Total amount
tons/acre
N required Cd tons/acre
by crop 2 Ibs/acre
\ /
Lower of Controlling metal
two amounts (Pb, Zn, Cu, Ni, Cd)
With respect to an annual application rate, the N required
by the crop is applied in sewage sludge. The plant available
N content of the sludge is used in these calculations:
Available N = NH, + + N03~ + 20$ organic N
assuming that 20$ of the organic N is mineralized during the
first year after application. As discussed earlier, more or
less than 20$ of the organic N may in fact' be mineralized during
the first year and thus, this percentage may be altered based
on new research data. In the case of surface applied sludge,
1.5 to 2 times the crop requirement may be applied to soil be-
cause a large percentage of the NHi will be lost through
volatilization as the sludge dries. Addition of sludge at N
utilization rates will minimize contamination of ground water
through N0q~ leaching.
256
-------
The application of Cd to soil is limited to 2 Ibs/acre
per year. Based on research in Wisconsin, the addition of 2
lbs.-Cd/acre did not significantly increase the concentration
of Cd in corn grain (Table 10). Although all possible crops
have not been studied to evaluate the uptake of Cd applied at
2 Ibs/acre, the available data suggest that this level of Cd
will rovide rotection from excessive metal contamini
provide protection from excessive metal contamination of
crops.
The total amount of sludge applied to soils is controlled
by metal additions. These limits are designed to allow the
growth of crops at any future date provided that soil pH>6.5.
The metal limits suggested are shown in Table 11.
It should be re-emphasized that the metal limits require
a soil pH>6.5. Since metal availability increases with de-
creasing pH, metal toxicity to or contamination of crops may
occur if soils treated with sludge become acid.
Following calculation of the annual application rate, the
amounts of P and K added are compared to the fertilizer recom-
mendations for P and K. In general, sludge will add sufficient
P to satisfy nearly all crops but K may have to be added as an
inorganic fertilizer to insure an optimum yield. Optimizing
crop yields and concurrent N uptake is important to minimize
N0o~ leaching into ground water.
Residual N, i.e., N added in previous years, is considered
for soils receiving sludge for three consecutive years. The
Ibs. of N released 1, 2 and 3 years after sludge application
is shown in Table 12 for sludges containing different organic
N contents. The amount of N added in the current season by
sludge application is then corrected for the amount of residual
N mineralized during the growing season.
The steps involved in calculating application rates can
be summarized as follows:
Calculation of Annual Application Rate
Step 1. Obtain N requirement for the crop grown from
Table 6.
Step 2. Calculate tons of sludge needed to meet crop's
N requirement.
a. Available N in sludge
% Inorganic N (N±) = (% NH^-N) + '^NC^-N)
% Organic N (N_) = (% total N) - (% inorganic
0 N)
257
-------
Table 10. Cadmium Uptake by Crops From Application of Sewage
Sludgea
Year
Applic.
1971
1972
1973
of
Harvest
1972
1972
1973
1973
1973
1974
1973
1974
1 Crop0 -
Rye
Corn
Corn
Rye
Corn
Corn
Sorghum-
Sudan
Corn
Rate
0
0.10
0.09
0.06
0.23
0.08
0.07
0.53
0.07
of sludge application,
2
0.25
0.09
0.05
0.25
0.06
0.07
0.50
0.07
4
Cd cone.
0.30
0.13
0.05
0.35
0.07
0.07
0.75
0.07
8
in crop
0.25
0.08
0.08
0.45
0.07
0.07
0.75
0.07
tons/acreb
16
(rag/kg)
0.30
0.11
0.05
0.40
0.02
0.07
0.85
0.07
32
0.30
0.09
0.05
0.50
0.05
0.19
0.95
0.12
a 17
Adapted from Keeney et al. '
Application of 0, 2, 4, 8, 16 and 32 tons/acre added 0, 0.28,
0.56, 1.12, 2.24 and 4.48 Ibs Cd/acre, respectively.
Refers to rye and sorghum-sudan forage and corn grain.
258
-------
Table 11. Total Amounts of Pb, Zn, Cu, Ni, and Cd Suggested
for Agricultural Soils Treated with Sewage Sludgea
Soil CEC, meq/100 g
I'ltiOcL-L
Pb
Zn
Cu
Ni
Cd
<5
500
250
125
50
5
5-15
1000
500
250
100
10
>15
2000
1000
500
200
20
o
Developed by cooperative efforts of regional research projects
NC-118 and W-124 and ARS, USDA.
259
-------
Lb. available N/ton sludge = (% Ni x 20) +
(% NQ x M
b. Residual sludge N in soil
If the soil has received sludge in the past 3
years, calculate residual N from Table 12.
c. Annual application rate
i) Tons sludge/acre = crop N req'ment - resid. N
Ib. available N/ton sludge
If sludge is surface applied, this rate
can be doubled.
ii) Tons sludge/acre =
iii) The lower of the two amounts is applied.
Step 3. Calculate total amount of sludge allowable.
a. Obtain maximum amounts of Pb, Zn, Cu, Ni,
and Cd allowed for CEC of the soil from Table
11.
b. Calculate amount of sludge needed to exceed Pb,
Zn, Cu, Ni, and Cd limits, using sludge analy-
sis data.
Metal
Pb: Tons sludge/acre =
Zn: Tons sludge/acre =
Cu: Tons sludge/acre =
Ni: Tons sludge/acre =
Cd: Tons sludge/acre =
(Note: Sludge metals are expressed on a dry
weight ppm (mg/kg) basis.)
260
-------
Table 12. Release of Residual N in Soils Treated with Sewage
Sludge
Years Organic N content of sludge, %
after sludge —
application 2.0 2.5 3.0 3.5 4-0 4-5 5.0
Ibs. N per ton sludge added
1 1.0 1.2 1.4 1.7 1.9 2.2 2.4
2 0.9 1.2 1.4 1.6 1.8 2.1 2.3
3 0.9 1.1 1.3 1.5 1.7 2.0 2.2
261
-------
The lowest value is chosen from the above
five calculations as the maximum tons of
sludge per acre which can be applied.
Step 4. Calculate amount of P and K added in sludge.
Tons of sludge x % P in sludge x 20 = Ib. of P added
Tons of sludge x % K in sludge x 20 = Ib. of K added
Step 5. Calculate amount of P and K fertilizer needed.
Ib. P fertilizer needed = (Ib. P recommended
for crop)a - (Ib. P in sludge)
Ib. K fertilizer needed = (Ib. K recommended
for crop)a - (Ib. K in sludge)
Sample Calculations to Determine Sludge Application Rates on
Agricultural Land "~~~ '
Sludge: 2% NH^-N, 0% NOo-N, 5% total N, 2% P, 0.2% K
Zn, 10,000 ppm; Cu, 1,000 ppm; Ni, 50 ppm; Pb, 5,000
ppm; Cd, 10 ppm
Soil: Silt loam, CEC = 20 meq/100 g; fertilizer recommenda-
tions from soil tests are 25 Ib. of P per acre and
100 Ib. of K per acre.
Previous applications: 10 tons/acre for 2 previous years.
From Table 6: 180 bu. corn — 240 Ib. N
A. Calculate annual sludge application rate based on N and CM
1. Available N in sludge
2% NH, -N + 0% N03-N = 2% N±
59& total N~ 2% N± 3% N0
Lb. available N/ton sludge = 20 x 2% + 4 x
=40+12
= 52
52 Ib. available N/ton sludge.
2. Residual N
P and K recommendations based on soil tests for available P
and K.
262
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B
From Table 12 for 3% organic N
a) Sludge added 1 year earlier
10 tons/acre x 1.4 Ib. N/ton = 14 Ib. N
b) Sludge added 2 years earlier
10 tons/acre x 1.4 Ib. N/ton = 14 Ib. N
c) Residual N = 28 Ib.
3. Sludge Application Rate
a) 240 Ib. N needed - 28 Ib. residual N = 212 Ib. N
from sludge
, ^ 212 Ib. N Q. „ _ /
b) 52 Ib. N/ton sludge = 8*7 tons/acre
c) Calculate application rate for 2 Ib. Cd/acre
2 Ib. Cd/acre .,nr. . /
-iri ^—p / v—7T7=^T = 100 tons/acre
10 ppm Cd x .002
4. The lower amount is applied = 8.7 tons sludge/acre
Calculate total sludge amount which may be applied.
Based on Table 11, maximum amounts are calculated as
follows:
1)
2)
3)
4)
5)
Metal
Pb
Zn
Cu
Ni
Cd
Maximum
Amount
Ib./acre
2,000
1,000
500
200
20
Cone, in
Sludge
ppm
5,000
10,000
1,000
50
10
Tons of
Sludge/Acre
9DD
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2. K fertilizer
8.7 tons/acre x 0.2?° K x 20 = 34-8 Ib. K/acre
Fertilizer recommendation is 100 Ib. K/acre
Fertilizer K needed = 65 Ib./acre
D. Summary
Annual application rate is based on N required by
crop - 8.7 tons sludge/acre. To obtain optimum yield
65 Ibs. K/acre would be applied in a fertilizer. A total
of 50 tons sludge could be applied. If continuous corn
is grown, 8.7 tons sludge/acre could be applied for ap-
proximately 6 years. Use of small grains and other crops
would alter the annual rate and thus, the lifetime of the
disposal site.
MANAGEMENT AND MONITORING OF SOILS RECEIVING SEWAGE SLUDGE
Monitoring Crops
The constituents of most concern in crops growing on sludge
amended soils are metals. Monitoring of plant composition in
soil fertility studies involves analysis of a diagnostic tissue
obtained at a specified stage of plant development. A summary
of crops, diagnostic tissues and number of samples needed is
presented in Table 13• Although the use of vegetable crops is
not recommended on soils treated with sludge, diagnostic tis-
sues for these crops are also presented. From the standpoint
of metal impact on the human food chain, sampling the mature
grain or forage is the preferred method of monitoring. Plant
analyses can be performed by the methods described previously
for sludge. The major emphasis is placed on analysis of Zn,
Cu, Ni, Cd and Pb. In some cases, analysis of the diagnostic
tissue may allow prediction of the eventual metal concentration
in the grain; however, insufficient data is presently available
for most crops to develop general predictive relationships.
The principles of plant analyses and their interpretation are
summarized by Walsh and Beaton.^3
Soil Monitoring
Procedures have not been established for monitoring soils
treated with sludge. Irrespective of the constituent monitored,
valid sampling techniques are essential. All soil testing
laboratories describe procedures that should be used for obtain-
ing soil samples. In essence, composite soil samples are ob-
tained for the area receiving sludge. The sampling design
should take into account changes in soil type as the area is
264
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Table 13. Suggested Procedures for Sampling Diagnostic Tissue
of Crops3-
Crop
Corn
Soybeans
and other
beans
Small
grains
Hay, pas-
ture or
forage
grasses
Alfalfa,
clover &
other
legumes
Sorghum-
milo
P.A-t-.-l-nn
Stage of
growth13
1. Seedling
2. Prior to
tasselling
3. From tassel-
ing to
silking
1. Seedling
2. Prior to or
during
early
flowering
1. Seedling
2. Prior to
heading
1. Prior to
seed
emergence
1. Prior to or
at 1/10
bloom
1. Prior to or
at heading
1 . Prior to or
Plant part sampled °
O
All the above ground
portion.
Entire leaf fully devel-
oped below whorl.
Entire leaf at the ear
node (or immediately
above or below) .
All the above ground
portion.
Two or three fully de-
veloped leaves at top
of plant.
All the above ground
portion.
The 4 uppermost leaves.
The 4 uppermost leaf
blades.
Mature leaf blades taken
about 1/3 of the
way down the plant.
Second leaf from top of
plant .
Youngest fully mature
^ifts/
20-30
15-25
15-25
20-30
20-30
50-100
50-100
40-50
40-50
15-25
30-40
Potato
at 1st leaves on main stem.
bloom, or
at 1st
square
Prior to or
during
early bloom
3rd to 6th leaf from
growing tip.
20-30
265
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Table 13. Continued
Crop Stage of Plant nart ssrrml Pd No* Plants/
growth6 Flant part samPled sample
Head crops 1. Prior to 1st mature leaves from 10-20
(e.g., cab- heading center of whorl.
bage)
Tomato 1. Prior to 3rd or 4th leaf from 20-25
or during growth tip.
early bloom
stage
Beans 1. Seedling All the above ground por- 20-30
tion.
2. Prior to 2 or 3 fully developed 20-30
or during leaves at the top of
initial plant.
flowering
Root crops 1. Prior to Center mature leaves. 20-30
root or
bulb en-
largement
Celery 1. Mid-growth Petiole of youngest mature 15-30
(12-15" leaf.
tall)
Leaf crops 1. Mid-growth Youngest mature leaf. 35-55
(12-15"
tall)
Peas 1. Prior to or Leaves from 3rd node down 30-60
during ini— from top of plant.
tial flow-
ering
Melons 1. Prior to Mature leaves at base of 20-30
fruit set plant on main stem.
aAdapted from Jones and Steyn.
Seedling stage signifies plants less than 12 inches tall.
266
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traversed. Due to the natural variability in ^vtal content of
soils, it is essential that samples be obtained from an adjacent
area of the same soil type which has not received sludge. Pre-
ferably, soil samples are obtained prior to sludge application,
enabling an evaluation of metal concentrations in soil with
subsequent sludge applications. The P, K and lime requirements
of sludge amended soils can be monitored by conventional soil
testing techniques.
A major goal of monitoring soils is evaluating the extent
of metal accumulation. Total metal content (HNOo-HClOi digestion)
or plant available metals (DTPA or 0.1 N HC1 extract able) are
possible alternatives for monitoring metal concentrations in
soils.
The movement of N0^~ into ground water may require monitor-
ing in some instances. If sludge applications are based on the
N requirement of the crops grown, N leaching will be minimized.
One approach to N monitoring involves obtaining soil cores to a
depth of 3—5 feet at the end of the growing season and analyz-
ing each 1 foot increment for NR^+ and N03~. Suction lysimeters
can also be used to obtain a sample of the soil solution at a
3-5 foot depth. Alternatively, monitoring wells can be in-
stalled and water samples obtained therefrom. This approach
requires a knowledge of ground water movement. Site monitoring
considerations have been discussed by Blakeslee.19
Other Considerations
The majority of sludges contain coliforms, Salmonella,
Ascaris cysts and viruses and some concern has been expressed
about the health effects of applying sludges to agricultural
land. The presence of these types of organisms is responsible,
in part, for not permitting sludges on soils where vegetable
crops are grown. In general, more research data is needed to
assess the potential threat due to pathogens. Since these organ
isms are not indigenous to soils, their survival tends to be
minimal but it is a function of soil chemical and physical
properties. Contamination of crops with pathogens is very un-
likely when sludges are incorporated prior to growing crops.
Furthermore, experiments conducted in Georgia indicated that
coliforms added to forages in a surface application of sludge
had disappeared within 2 weeks. 20 At the present time, the
survival and significance of viruses added to soil in sludge
remains open to question. In summary, although questions arise
concerning the impact of pathogens in land disposal systems,
the lack of problems encountered by the numerous ongoing
projects using land application of sludges suggests that patho-
gens are not as serious a consideration as contamination of
soils with metals.
267
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In some sludges elevated concentrations of chlorinated
hydrocarbons are found. Based on research with chlorinated
hydrocarbon insecticides (e.g., DDT), a minimal amount of uptake
by and translocation in plants is anticipated. The major com-
pounds of concern are PCS's, which are not rapidly degraded in
soils. Sludge constituents (e.g., PCB) may enter animals if
sludge is surface applied on forages and grazed after applica-
tion. In excess of 80-90$ of the sludge is probably washed
from the forage by rainfall but detectable concentrations of
PCB's may be retained by the forage. Essentially no impact of
PCB* s on crop quality is anticipated when sludges are incor-
porated prior to planting. The above comments are the author's
opinion only because essentially no research data are available.
APPLICATION TECHNIQUES
The two types of techniques used for liquid sludge appli-
cation are surface and subsurface (incorporation) application.
The principle types of surface application methods are irriga-
tion and tank truck. Incorporation procedures are favored
because less N is lost from the soil via NHo volatilization.
For solid or semi-solid sludges, conventional surface spreading
equipment can be used. Obviously, the economics involved in
transporting liquid versus dried sludges are compared to the
costs of dying when developing a system for land application
of sludge. The characteristics of application systems as pre-
sented by V/hite21 are shown in Tables 14, 15, and 16.
268
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Table 14. Surface Application Methods and Equipment for Liquid Sludges
a
Method
Characteristics
Topographical and
Seasonal Suitability
to
C7>
VO
Irrigation
Spray
(Sprinkler)
Ridge and
Furrow
Overland
Tank Truck
Farm .Tank
Wagon anH
Large orifice required on nozzle; large
power and lower labor requirement; wide
selection of commercial equipment avail-
able; sludge must be flushed from pipes
when irrigation completed.
Land preparation needed; lower power
requirements than spray.
Used on sloping ground with vegetation
with no runoff permitted; suitable for
emergency operation; difficult to get
uniform areal application.
Capacity 500 to more than 2,000 gallons;
larger volume trucks will require flota-
tion tires; can use with temporary ir-
rigation set-up; with pump discharge
can spray from roadway onto field.
Capacity, 500 to 3,000 gallons; larger
volume will require flotation tires;
can use with temporary irrigation set-
up; with pump discharge can spray from
roadway onto field.
Can be used on sloping land; can
be used year-round if the pipe is
drained in winter; not suitable
for application to some crops dur-
ing growing season; odor (aerosol)
nuisance may occur.
Between 0.5 and 1.5^ slope depend-
ing on percent solids; can be used
between rows of crops.
Can be applied from ridge roads.
Tillable land; not usable with
row crops or on soft ground.
Tillable land; not usable with
row crops or on soft ground.
aAdapted from White.21
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Table 15. Subsurface Application Methods and Equipment for Liquid Sludges'
Method
Characteristics
Topographical and
Seasonal Suitability
N)
-J
O
Flexible irri-
gation "hose
with plow fur-
row or disc
cover
Tank truck
with plow fur-
row cover
Farm tank
wagon and*
tractor
Plow furrow
cover
Subsurface
injection
Use with pipeline or tank truck with pres-
sure discharge; hose connected to manifold
discharge on plow or disc.
500-gallon commercial equipment available;
sludge discharged in furrow ahead of plow
mounted on rear of 4-wheel-drive truck.
Sludge discharged into furrow ahead of
plow mounted on tank trailer—application
of 170 to 225 wet tons/acre; or sludge
spread in narrow band on ground surface and
immediately plowed under—application of 50
to 125 wet tons/acre.
Sludge discharged into channel opened by a
tillable tool mounted on tank trailer;
application rate 25 to 50 wet tons/acre;
vehicles should not traverse injected area
for several days.
Tillable land; not usable on
wet or frozen ground.
Tillable land; not usable on
wet or frozen ground.
Tillable land; not usable on
wet or frozen ground.
Tillable land; not usable on wet
or frozen ground.
aAdapted from White.21
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Table 16. Methods and Equipment for Application of Semi-Solid
and Solid Sludgesa
Method
Characteristics
Spreading
Piles or windrows
Reslurry and
handle as in
Table 14 or 15
Truck-mounted or tractor-powered box
spreader (commercially available); sludge
spread evenly on ground; application rate
controlled by over-the-ground speed; can be
incorporated by discing or plowing.
Normally hauled by dump truck; spreading
and leveling by bulldozer or grader needed
to give uniform application; 4 to 6-inch
layer can be incorporated by plowing.
Suitable for long hauls by rail transporta-
tion.
aAdapted from White.2
271
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REFERENCES
1. Sommers, L. E., D. W. Nelson, and K. J. Yost. 1976.
Variable nature of chemical composition of sewage
sludges. J. Environ. Qual. 5:303-306.
2. Sommers, L. E., and E. H. Curtis. 1977. Effect of wet-
air oxidation on the chemical composition of sewage
sludge. J. Water Poll. Control Fed. (In press)
3. Sommers, L. E. 1977- Chemical composition of sewage
sludge and analysis of their potential use as ferti-
lizers. J. Environ. Qual. (In press)
4. Black, C. A. 1965. Methods of Soil Analysis, Part II.
American Society of Agronomy, Madison, WI.
5. EPA. 1974. Methods for Chemical Analysis of Water and
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6. Allen, S. E. 1974 « Chemical analysis of ecological mater-
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7. Ellis, R., J. J. Hanway, C. Holmgren, D. R. Keeney, and
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plants, wastewater and sludge. North Central Regional
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8. Ryan, J. A., D. R. Keeney, and L. M. Walsh. 1973- Nitrogen
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9. Ryan, J. A., and D. R. Keeney. 1975. Ammonia volatiliza-
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11. Allaway, W. H. 1968. Agronomic controls over the environ-
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12. Lindsay, W. L. 1972. Inorganic phase equilibria of micro-
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13. Walsh, L. M., and J. D. Beaton. 1973. Soil Testing and
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14. Viets, F. G., Jr., and ¥. L. Lindsay. Testing soils for
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L. M. Walsh and J. D. Beaton (ed.), Soil Testing and
Plant Analysis.
15. McLean, E. 0. 1973. Testing soils for pH and lime re-
quirement, p. 77-96. In L. M. Walsh and J. D. Beaton
(ed.), Soil Testing and Plant Analysis.
16. Knezek, B. D., and R. H. Miller. 1976. Application of
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17. Keeney, D. R., K. W. Lee, and L. M. Walsh. 1975. Guide-
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18. Jones, J. B., Jr., and W. J. A. Steyn. 1973. Sampling,
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Central Regional Publication No. 235•
ft ILS. GOVDIMCKT PIRNTING OFFICE: 1977—7 S7 - 508
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