vvEPA
United States
Environmental Protection
Agency
TECHNOLOGY TRANSFER
Environmental
Regulations
and Technology
Use and Disposal of
Municipal Wastewater Sludge
fell
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TECHNOLOGY TRANSFER
EPA 625 710-84-003
Environmental
Regulations
and Technology
Use and Disposal of
Municipal Wastewater Sludge
September 1984
This guidance was prepared by
U.S. Environmental Protection Agency
Intra-Agency Sludge Task Force
Washington DC 20460
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This guidance document was prepared by the U.S. Environmental
Protection Agency's Intra-Agency Sludge Task Force,
Washington, D.C., and Jan Connery, Elaine.Burke, and Frank
Lowenstein of Eastern Research Group, Inc., Cambridge,
Massachusetts.
EPA thanks the following organizations for providing information
and technical review: the Association of Metropolitan Sewerage
Agencies; the Association of State and Interstate Water Pollution
Control Administrators; the Association of State and Territorial
Solid Waste Management Officials; the Municipality of
Metropolitan Seattle; the North Shore Sanitary District; and the
Zirnpro Corporation.
EPA also thanks the following organizations for contributing
photographs to this document: City of Philadelphia Water
Department; E&A Environmental Consultants, Inc.; Institute of
Forest Resources, University of Washington; Kellogg's Supply
Company; Los Angeles County Sanitation Districts Joint Water
Pollution Control Plant; North Shore Sanitary District; Recovery
Associates, Inc.; University of California, Riverside; U.S.
Department of Agriculture; and the Zimpro Corporation. Cover
photo by Eastern Research Group, Inc.
This report has been reviewed by the U.S. Environmental
Protection Agency and approved for publication. The process
alternatives, trade names, or commercial products are only
examples and are not endorsed or recommended by the U.S.
Environmental Protection Agency. Other alternatives may exist or
may be developed.
This guidance was published by
U.S. Environmental Protection Agency
Center for Environmental Research Information
Office of Research Program Management
Office of Research and Development
Cincinnati OH 45268
COVER PHOTOGRAPH: Municipal wastewater sludge compost.
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Contents
1. Introduction
1
2. Municipal Wastewater Sludge
2.1 What is Wastewater Sludge? 3
2.2 Sludge Quantity 4
-2.3 Sludge Constituents 6
2.4 Sludge Characteristics 8
3. Land Application
3.1 Introduction 10
3.2 Process and Performance 10
3.3 Key Parameters 19
3.4 Case Study: Agricultural Application 23
3.5 Case Study: Land Reclamation 25
4. Distribution and Marketing of
Sludge Products
4.1 Introduction 27
4.2 Process and Performance 29
4.3 Key Parameters 33
4.4 Case Study 43
5. Landfilling
5.1 Introduction 37
5.2 Process and Performance 37
5.3 Key Parameters 41
5.4 Case Study 43
6. Incineration
6.1 Introduction 46
6.2 Process and Performance 47
6.3 Key Parameters 51
6.4 Case Study 54
7. Ocean Disposal
7.1 Introduction 56
7.2 Process and Performance 57
7.3 Key Parameters 58
8. Evaluating Alternatives
8.1 Introduction 61
8.2 Key Parameters 62
8.3 Sample Evaluation 70
9. Trends and Prospects 72
10. Sources of Further Information 73
11. References
75
III
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Abbreviations
ac = acre Ib
BTU = British thermal unit m
cm = centimeter m3
cu yd = cubic yard mil gal
°C = degree Celsius meq
°F = degree Fahrenheit mg
ft = foot mgd
gat = gallon mi
ha = hectare mt
hr = hour no
in = inch ppm
kg = kilogram sq ft
kJ = kilojoule yr
km = kilometer %
kW = kilowatt $
I = liter
pound
meter
cubic meter
million gallons
milliequivalent
milligram
million gallons per day
mile
metric ton
number
parts per million
square feet
year
percent
dollar
iv
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1. Introduction
The Clean Water Act requires municipalities to cleanse their
wastewaters prior to discharging them into the environment. This
cleansing process—wastewater treatment—generates sludge which
in turn must be used or disposed of. Sludge management begins
with sludge generation and continues through sludge treatment
and sludge use and disposal (Figure 1). It is an integral
consideration in the planning and design of wastewater treatment
plants, and can be the most complex and costly part of wastewater
management. This document provides guidance on the final step in
the sludge management process—the ultimate use and disposal of
municipal wastewater sludge.
The need for effective sludge management is continual and
growing. The quantity of municipal sludge produced annually has
almost doubled since 1972, when the Clean Water Act imposed
uniform minimum treatment requirements for municipal
wastewater. In addition, the sludges generated by more advanced
treatment are more difficult to handle than the sludges produced by
less advanced treatment. Municipalities currently generate
approximately 6.2 million dry metric tons (mt) (6.5 million dry tons)
of wastewater sludge a year, or approximately 26 kilograms (kg)
(56 dry pounds [Ib]) per person per year. Sludge production is
expected to about double to approximately 12 million dry mt
(13 million dry tons) per year by the year 2000 as the population
increases, as more municipalities comply with Clean Water Act
requirements, and as more sophisticated wastewater treatment
systems are developed and installed.
When properly used, sludge can be a valuable resource as a soil
conditioner and partial fertilizer and as a source of methane for
producing energy. The U.S. Environmental Protection Agency
(EPA), the primary Federal regulatory agency responsible for sludge
management, encourages the beneficial use of sludge wherever
environmentally feasible (Figure 2).
This guidance document describes the five major sludge
use/disposal options currently available—land application,
distribution and marketing of sludge products, landfilling,
incineration, and ocean disposal—and factors influencing their
selection and implementation. The document is intended for a '
broad audience of individuals and organizations, including state and
local officials, managers and operators of wastewater treatment
systems, planners, resource managers, and concerned citizen
groups.
The document provides an initial framework for evaluating sludge
use/disposal alternatives. It describes accepted and proven use/
disposal technologies and Federal regulations pertinent to sludge
management (Table 1). Additional sources must be consulted for
more detailed information and design criteria, and for the most
current information on emerging technologies. In addition, state
and local authorities should be consulted to determine regulations
and good management practices applicable to local areas.
WASTEWATER
WASTEWATER
TREATMENT
SLUDGE
TYPE
SLUDGE
TREATMENT
Odor Control and
Pathogen Reduction
• Stabilization
Water Removal,
Volume Reduction,
and Possibly
Mass Reduction
• Thickening
• Conditioning
• Dewatering
• Drying
SLUDGE
USE/DISPOSAL
Land Application
Distribution and
Marketing
Landfilling
Incineration
Ocean Disposal
Wastewater
Sludge
Figure 1. Generation, Treatment, and Disposal of Municipal Wastewater Sludge
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INTRODUCTION
Tho U.S. Environmental Protection Agency (EPA) will actively
promoto those municipal sludge management practices that provide
for the beneficial use of sludge while maintaining or improving
environmental quality and protecting public health. To implement
this policy, EPA will continue to issue regulations that protect public
health and other environmental values. The Agency will require
Slates to establish and maintain programs to ensure that local
governments utilize sludge management techniques that are
consistent with Federal and state regulations and guidelines. Local
communities will remain responsible for choosing among alternative
programs; for planning, constructing, and operating facilities to meet
thoir needs; and for ensuring the continuing availability of adequate
and acceptable disposal or use capacity.
SOURCE: Reference (1).
Figure 2. EPA Policy on Municipal Sludge Management
Tabte 1. Sludge Management Regulations of the
U.S. Environmental Protection Agency
This document has 11 chapters. Chapter 2, Municipal Wastewater
Sludge, describes the different types of municipal sludges and how
their characteristics affect their suitability for various use/disposal
options. Chapters 3 through 7 present the five basic sludge
use/disposal options: Land Application, Distribution and Marketing
of Sludge Products, Landfilling, Incineration, and Ocean Disposal.
Chapter 8, Evaluating Alternatives, describes key factors involved in
evaluating the sludge use/disposal alternatives. Chapter 9 discusses
Trends and Prospects in sludge use/disposal, Chapter 10 presents
Sources of Further Information, and Chapter 11 lists References.
Coverage
Reference
Application
Polychlorinatod
Biphenyls (PCBs)
40 CFR 761
All sludges containing
more than 50 milligrams
per kilogram
Ocean Dumping
40 CFR 220-228
The discharge of sludge
from barges or other
vessels
Now Sources of
Air Emissions
40 CFR 60
Incineration of sludge
at rates above 1,000
kilograms per day
Mercury
40 CFR 61
Incineration and heat
drying of sludge
Cadmium, PCBs,
Pathogenic
Organisms
Extraction
Procedure Toxicity
40 CFR 257
40 CFR 261
Appendix II
Land application of
sludge, landfills, and
storage lagoons
Defines whether sludges
are hazardous
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2. Municipal Wastewater Sludge
2.1 What Is Wastewater Sludge?
Sludge is a by-product of municipal wastewater treatment. It
usually contains 93 to 99.5 percent water as well as solids and
dissolved substances that were present in the wastewater and that
were added or cultured by wastewater treatment processes. Usually
these wastewater solids are treated prior to ultimate use/disposal to
improve their characteristics for these processes (Figure 1 and
Table 2).
The characteristics of a sludge depend on both the initial
wastewater composition and the subsequent wastewater and
sludge treatment processes used. Different treatment processes
generate radically different types and volumes of sludge (Figure 3
and Table 2). At an individual plant, the characteristics of the
sludge produced can vary annually, seasonally, or even daily
because of variations in incoming wastewater composition and
variations in the treatment processes. This variation is particularly
pronounced in wastewater systems that receive a large proportion
of industrial discharges.
The characteristics of a sludge affect its suitability for the various
use/disposal options. Thus, when evaluating sludge use/disposal
alternatives, a municipality should first determine the amount and
characteristics of its sludge and the degree of variation in these
characteristics.
PRIMARY SLUDGE. Generated during primary wastewater
treatment, which removes the solids that settle out readily. Primary
sludge contains 3 to 7 percent solids; usually its water content can
be easily reduced by thickening or dewatering.
SECONDARY SLUDGE. Often called biological process sludge
because it is generated by secondary biological treatment processes,
including activated sludge systems and attached growth systems
such as trickling filters. Secondary sludge has a low solids content
(0.5 to 2 percent) and is more difficult to thicken and dewater than
primary sludge.
TERTIARY SLUDGE. Produced by advanced wastewater treatment
processes, such as chemical precipitation and filtration. The
characteristics of tertiary sludge depend on the wastewater
' treatment process that produced it. Chemical sludges result from
treatment processes that add chemicals, such as lime, organic
polymers, and aluminum and iron salts, to wastewater. Generally,
lime or polymers improve the thickening and dewatering
characteristics of a sludge, whereas iron or aluminum salts usually
reduce its dewatering and thickening capacity by producing very
hydrous sludges which bind water.
Figure 3. Types of Raw (Untreated) Sludge
A typical wastewater treatment plant. Municipal wastewater enters through the rectangular pre-aeration basin on the right and receives
primary treatment in a clarifier (bottom center). Four large trickling filters (center) provide secondary treatment, and six clarifiers (top right)
remove the solids formed by secondary treatment before discharging the clarified water to the pond on far right. Sludges from the primary
and secondary clarifiers are thickened in the two smaller circular tanks just above the trickling filters, then pumped to digesters (upper left)
and, from there, to one of the three storage lagoons (center left).
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MUNICIPAL WASTEWATER SLUDGE
Table 2. Effects of Pretreatment and Sludge Treatment Processes on Sludge and Sludge Use / Disposal Options
Treatment process and definition
Effect on sludge
Effect on use /disposal options
Protroatmont: Reduction in contaminant
levels in industrial wastowater discharge.
Reduces levels of heavy metals and organics
in industrial wastewater discharge, thereby
lowering the concentration of these
constituents in the sludge.
Increases the viability of land application,
distribution and marketing, and ocean
disposal. Reduces need for pollution control
devices during incineration, and prevents
problems with incinerator ash disposal.
Thickening: Low-force separation of water
and solids by gravity or flotation.
Increases solids concentration of sludge by
removing water, thereby lowering sludge
volume.
Lowers sludge transportation costs for all
options.
Digestion (Aerobic and Anaerobic):
Biological stabilization of sludge through
conversion of some of the organic matter to
water, carbon dioxide, and methane.
Reduces the volatile and biodegradable
organic content of sludge by converting it to
soluble material and gas. Reduces pathogen
levels and controls putrescibility.
Reduces sludge quantity. Preferred stabiliza-
tion method prior to landfilling and land
application. Reduces heat value for incinera-
tion, but anaerobic digestion produces
recoverable methane.
Lime Stabilization: Stabilization of sludge
through the addition of lime.
Raises sludge pH. Temporarily decreases
biological activity. Reduces pathogen levels
and controls putrescibility. Increases the dry
solids mass of the sludge.
May be used prior to land application and
landfilling. High pH of lime-stabilized sludge
tends to immobilize heavy metals in sludge
as long as the high pH levels are maintained.
Conditioning: Alteration of sludge
properties to facilitate the separation of
water from sludge. Conditioning can be
performed in many ways, e.g., adding
inorganic chemicals such as lime and
ferric chloride; adding organic chemicals such
as polymers; or briefly raising sludge
temperature and pressure. Thermal condi-
tioning also causes disinfection.
Improves sludge dewatering character-
istics. Conditioning may increase the
mass of dry solids to be handled and
disposed of without increasing the
organic content of the sludge.
Increases the amount of auxiliary fuel
required in incineration if the amount of
inert material in the sludge is increased.
Downtorlng: High-force separation of water
and solids.
Increases solids concentration of sludge by
removing much of the entrained water,
thereby lowering sludge volume. Some
nitrogen and other soluble materials are
removed with the water.
Reduces fuel costs for incineration. Reduces
land requirements and bulking soil require-
ments for landfilling. Lowers sludge trans-
portation costs for all options. Dewatering
may be undesirable during land application in
regions where the water itself is a valuable
agricultural resource. Reduction of nitrogen
levels may or may not be an advantage.
Composting: Aerobic process involving the
biological stabilization of sludge in a windrow,
in an aerated static pile, or in a vessel.
Lowers biological activity. Can destroy all
pathogens. Degrades sludge to a humus-like
material. Increases sludge mass due to
addition of bulking agent.
Useful prior to land application and distribu-
tion and marketing. Often not appropriate for
other use or disposal options due to cost.
Heat Drying: Application of heat to kill
pathogens and eliminate most of the water
content.
Disinfects sludge. Slightly lowers potential
for odors and biological activity.
Generally used only prior to distribution
and marketing.
2.2 Sludge Quantity
The amount of sludge that must be used or disposed of affects the
economic and technical feasibility of the various use/disposal
options. Two ways to look at sludge quantity are the volume of the
wet sludge, which takes into account both the water content and
solids content, and the mass of the dry sludge solids.
Sludge volume is expressed as liters (gallons) or cubic meters.
Sludge mass is usually expressed in terms of weight, in units of dry
metric tons (tons). Because the water content of sludge is large and
highly variable, the mass of the dry sludge solids is often used to
compare sludges with different proportions of water.
Key factors affecting sludge volume and mass are sources of the
wastewater, wastewater treatment processes, and sludge treatment
processes.
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MUNICIPAL WASTEWATER SLUDGE
10
° 5
o
o>
3
WET SLUDGE
Primary
Settling
PRIMARY
TREATMENT
Trickling Activated Chemical
Filters Sludge Treatment
Treatment (Lime)
SECONDARY
TREATMENT
TERTIARY
TREATMENT
150
100
1 50
o
w
T3
DRY SLUDGE
Primary
Settling
PRIMARY
TREATMENT
Trickling Activated Chemical
Filters Sludge Treatment
Treatment (Lime)
SECONDARY
TREATMENT
TERTIARY
TREATMENT
1 m3 = 264.2 gal
1 kg = 2.205 Ib
SOURCE: Reference (2).
Figure 4. Typical Sludge Quantities Generated by Various
Wastewater Treatment Processes
In activated sludge treatment, air is continuously injected into
wastewater in aeration basins, which stimulates the growth of
microorganisms to form an active mass of microbes called
"activated sludge."
Wastewater Sources. Industrial contributions to wastewater
influent streams can significantly increase the sludge quantity
generated from a given amount of wastewater. Pretreatment
provided by an industrial facility can greatly reduce sludge quantity
by removing industrial contamination such as metals and organic
chemicals.
Wastewater Treatment. Higher degrees of wastewater treatment
generally increase sludge volume (Figure 4). For example, primary
treatment typically produces 2,500 to 3,500 liters of sludge per
million liters of wastewater treated. Biological secpndary treatment
produces an additional 15,000 to 20,000 liters per million liters of
wastewater treated. Use of chemicals for phosphorus removal
during tertiary treatment increases sludge volume another
10,000 liters per million liters treated.
Sludge Treatment. Some sludge treatment processes reduce sludge
volume, some reduce sludge mass, and some actually increase
sludge mass while improving other sludge characteristics. For
example, dewatering processes reduce the amount of water in a
sludge without significantly reducing the mass of solids; dewatering
is thus purely a volume reduction process. Anaerobic digestion of
sludge results in a loss of solid material through biodegradation; it
is thus a mass reduction process. Although anaerobically digested
sludges have less mass than the original raw sludges, they are
equally as difficult to dewater, which means they tend to have a
large volume. Inorganic chemical addition generally increases
sludge mass while improving other characteristics for subsequent
treatment, use, or disposal. For example, lime and ferric chloride
are added to enhance a sludge's dewatering characteristics; in this
case, sludge mass is increased although, at a subsequent
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MUNICIPAL WASTEWATER SLUDGE
Thickening—a sludge treatment process—reduces sludge volume
by removing water from the wastewater solids, which sink and are
col/ected from the center of the thickener. Shown here is the
effluent weir of a circular gravity thickener.
dewatering step, sludge volume will be decreased. Composting,
another type of sludge treatment, significantly increases mass
through the addition of a bulking agent such as wood chips.
2.3 Sludge Constituents
The composition of a sludge can limit a municipality's choice of
sludge use/disposal options or make certain options more
appealing. The five constituents that are usually the most important
in decision-making are:
• Organic content (usually measured as volatile solids).
• Nutrients.
• Pathogens.
• Metals.
• Toxic organic chemicals.
Figure 5 shows the importance of these constituents for the various
sludge use/disposal options.
The major sources of toxic organic chemicals and metals are
industrial discharges. Pretreatment can be an effective way to
reduce the levels of these constituents. The EPA requires
Plate and frame filter press and resulting sludge cake.
Sludge rolling off vacuum filters is checked for consistency.
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MUNICIPAL WASTEWATER SLUDGE
wastewater treatment plants to implement industrial waste
pretreatment programs to control the entry of potentially harmful
wastes into the system. One of the primary methods for
implementing industrial pretreatment is the sewer ordinance, which
sets upper concentration limits for certain pollutants in wastewater.
2.3.1 Organic Content
Sludge organic content is most often expressed as the percent of
the total solids (TS) that are volatile solids (VS). VS are organic
compounds that are removed when the sludge is heated to 550°C
(1,022°F) under oxidizing conditions. Most unstabilized sludges
contain 75 to 85 percent VS on a dry weight basis. Organic content
is an important determinant of thermal value (in incineration),
potential for odor problems (in storage and land application), value
as a soil conditioner (in land application), and potential for gas
generation (in digesters).
Table 3. Comparison of Nutrient Levels in Commercial Fertilizers
and Wastewater Sludge
Nutrients (%)
CD
I ||
o -S ^
i£ fe§
j< Q <
Volatile Solids 9 O
Nutrients • Q
Pathogens • •
Metals • •
Toxic Organic O 9
Chemicals
a Based on current EPA information;
however, assessment of potential
effects continues.
•z.
CD O
-* P
d DC
11 III
Q "Z.
?; O
< Z
« •
0 O
a
0 0
9 Q
0 Very Important
_i
O Q
O
O
oa
Q
Q Moderately Important
O Not Important
Nitrogen Phosphorus Potassium
Fertilizers for Typical
Agricultural Use3
Typical Values for
Stabilized Municipal
Wastewater Sludge (3)
5
3.3
10
2.3
10
0.3
Figure 5. Importance of Sludge Constituents to Sludge
Use/Disposal Options
a Rates of application vary to reflect soil and crop needs, and the relative con-
centrations of nutrients in a fertilizer may range up to 82 percent nitrogen, up
to 10 percent phosphorus, and up to 25 percent potassium.
2.3.2 Nutrients
Municipal sludges contain three essential nutrients for plant
growth: nitrogen, phosphorus, and potassium. Typical sludge
nutrient levels are considerably lower than those of commercial
fertilizers (Table 3) although some sludges can contain more than
10 percent nitrogen and 8 percent phosphorus by dry weight.
Potassium rarely occurs in sludge in significant concentrations.
A nutrient may be present in sludge in one of several chemical
forms. For example, nitrogen may occur as organic nitrogen,
ammonium and nitrate ions, and phosphorus may occur as
phosphate and ortho-phosphate ions. Both the form and the
concentration of nitrogen and phosphorus affect the fertilizer value
of the sludge for land application. Reactions in the soil slowly
convert most of the organic nitrogen forms into nitrate ions, which,
like nitrates from fertilizers, is either used by plants or leached
away. Nitrate is the most soluble form of nitrogen and therefore
presents the most potential for contamination.
2.3.3 Pathogens
A significant proportion of the bacteria, viruses, protozoa, and eggs
of parasitic worms in wastewater become concentrated in sludge
during wastewater treatment. A small percentage of these
organisms may be pathogenic (disease-causing). Pathogen"
abundance is difficult to measure directly, but pathogen reduction
can be estimated from the reduction in concentration of indicator
organisms (e.g., total fecal coliform bacteria). Pathogen levels can
be substantially reduced by sludge treatment processes such as
anaerobic digestion (Table 4). Note that the numbers of the parasite
Ascaris are not reduced by this treatment method.
To preclude potential human exposure problems, EPA specifies two
tiers of pathogen reduction prior to land application (see subsection
3.3.10). These are currently included in 39 state regulations, and
EPA is seeking the nationwide incorporation of these controls into
state regulations and enforcement efforts (5).
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MUNICIPAL WASTEWATER SLUDGE
Table 4. Typical Pathogen Levels in Unstabilized
and Anaerobically Digested Sludges
Pathogen
Typical concentration
in unstabilized
sludge
(No./100mil1iliters)
Typical concentration
in anaerobically
digested sludge
(No./100milliliters)
Virus
Focal Coliform Bacteria*
Salmonella
Ascatis lumbflcoldes
2,500 - 70,000
1,000,000,000
8,000
200-1,000
100 - 1,000
30,000 - 6,000,000
3-62
0-1,000
"Although not pathogenic, they are frequently used as indicators.
SOURCE: Reference (4).
2.3.4 Metals
Sludges may contain varying amounts of heavy metals and
Inorganic ions such as boron, cadmium, chromium, copper, lead,
nickel, mercury, silver, and zinc. At low concentrations in soil,
some of these elements are essential micronutrients required by
plants and animals, and are often added to inorganic commercial
fertilizers and feed supplements. However, at high concentrations
they may be toxic to humans, animals, and plants. The metals
concentrations in a sludge are among the foremost considerations
in land application because of their potential to damage crops and,
in the case of cadmium, to enter the human food chain. Acceptable
metal levels for land application have been a subject of considerable
debate (6,7). Concentrations of metals are used as controls only in
distribution and marketing. Table 5 lists ranges and medians for
metals in sludges. Metals may also be a concern in landfilling, if
Table 5. Metals in Sludge
conditions are acidic and promote leaching of metals, and in
incineration, if improper design or operating procedures result in
the release of metals into the atmosphere.
Concentrations of metals are primarily a function of the type and
amount of industrial waste that is discharged into the municipal
wastewater treatment system. Industrial pretreatment and source
control programs can control or reduce the metals content of
sludge. Good management practices in land application, landfilling,
and incineration may minimize or eliminate the potential for adverse
effects.
Regulations under the Resource Conservation and Recovery Act
(RCRA) (44 FR 53438) identify listed hazardous wastes and
hazardous waste characteristics. Municipal wastewater sludge is
neither excluded nor specifically listed as hazardous waste.
However, sludges from highly industrialized areas may need to be
evaluated for the characteristics that designate hazardous waste.
The test most appropriate to municipal wastewater sludge is the
Extraction Procedure (EP) toxicity test. States administering the
hazardous waste program may have additional criteria for
identifying and handling hazardous wastes. If a sludge fails the EP
test (i.e., demonstrates metal toxicity), it must be handled as a
hazardous waste according to the requirements of RCRA.
Nonhazardous sludges are subject to RCRA solid waste
regulations.
2.3.5 Toxic Organic Chemicals
Sludges can contain synthetic organic chemicals from industrial
wastes, household chemicals, and pesticides. Most sludges contain
low levels of these substances and do not pose a significant human
health or environmental threat. Exposure to these chemicals is a
concern in land application, distribution and marketing, and
landfilling, but adherence to good practices as described in
Chapters 3, 4, and 5 will prevent detrimental effects.
Dry sludge (mg/kg)
Moial
8 Reference (6).
Range8
Median3
Zmc
Lead
Copper
Nickel
Cadmium
Mercury
Arsenic
Cobalt
Chromium
Iron
Manganese
Molybdenum
Tin
Selenium
101 -49,000
13 - 26,000
84 - 17,000
2 - 5,300
1-3,410
0.6 - 56
1.1 -230
11.3-2,490
10 - 99,000
1,000 - 154,000
32 - 9,870
0.1 - 214
2.6 - 329
1.7-17.2
1,700
500
800
80
10
6
10
30
500
17,000
260
4
14
5
2.4 Sludge Characteristics
Sludge is usually treated with the aim of improving its
characteristics for ultimate use/disposal. The importance of sludge
characteristics for each sludge use/disposal option is illustrated in
Figure 6. Typical goals of sludge treatment include reducing water
content, reducing sludge mass, controlling odors, and destroying
pathogens. Major sludge treatment processes and their benefits are
described in Table 2.
Water Content. Sludges typically contain 93 to 99.5 percent water.
The concentration varies significantly depending on the type of
sludge. Sludge water content affects:
• Size of sludge treatment and disposal facilities.
• Sludge transportation costs.
• Type of land application equipment used.
• Amount of auxiliary fuel needed to evaporate water during
incineration.
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MUNICIPAL WASTEWATER SLUDGE
• Size and lifespan of a sludge landfill.
• Leachate formation in landfilling.
Sludge water content is inversely related to sludge solids content,
which is usually expressed as percent TS. The higher the percent
solids, the lower the water content. Treatment processes such as
thickening, conditioning, dewatering, composting, and drying can
lower sludge water content and thus raise the percent solids.
Doubling the solids content of a sludge (e.g., raising it from 5 to 10
percent TS) halves the volume of sludge that must be used or
disposed of (see Figure 7).
Degree of Stabilization. Stabilization refers to a number of
processes that reduce the potential for odor. Stabilization
processes also reduce pathogen levels and, usually, volatile solids
content. Major methods of stabilization include anaerobic
digestion, aerobic digestion, lime stabilization, and composting.
Anaerobic digestion is the most common method of sludge
stabilization, and generally biodegrades about 50 percent of the
volatile solids in a sludge. Because much of the organic matter has
already been eliminated, stabilized sludges tend not to have odor
problems. Low pathogen levels and low odor potential are often
desirable and sometimes required prior to ultimate use/disposal (for
example, in land application).
pH. The acidity of a sludge (measured by pH) affects the availability
of heavy metals, the pathogen content of the sludge, and the
corrosivity of the sludge. High pH (greater than 11) sludges destroy
o ^ •
< <
£ zg
2 < °
o g£
? O Q
Water Content
Degree of Stabilization
PH
a Biological stabilization may reduce the
fuel value of sludge by as much as
one half.
bLow pH is corrosive.
• O
O
9 Very Important
O Moderately Important
O Mot Important
40-
_ 30-
e
e>
Q
20-
10-
This example is for a sludge with a mass
of 910 kg (2,000 Ib) of dry sludge solids.
This mass remains constant at every
point on the curve. Other sludge masses
would show similar reductions in volume
with increasing solids concentration.
SOURCE: Reference (8).
10 20 30 40 50
SLUDGE SOLIDS CONCENTRATION (%)
60
Figure 7. Change in Sludge Volume with Increase.in Sludge
Solids Concentration
many bacteria and, in conjunction with soils of neutral or high pH,
can inhibit movement of heavy metals through soils and uptake of
heavy metals by plants. Conversely, low pH (less than about 6.5)
sludges promote leaching of heavy metals and promote greater
crop uptake of metals. Leaching of heavy metals can occur at
landfills because acid conditions often prevail. Thus, pH affects the
suitability of sludge for land application, distribution and marketing,
and landfilling. Low pH sludges are also corrosive, and must be
treated to prevent equipment damage during incineration.
Figure 6. Importance of Sludge Characteristics to Sludge
Use/Disposal Options
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3. Land Application
3.1 Introduction
Land application, defined as the spreading of sludge on or just
below the surface of the land, is the most widely employed sludge
use option. The sludge can serve both as a soil conditioner and as a
partial replacement for commercial fertilizers. Usually, sludge is
applied to land in one of four settings: on agricultural lands, forest
lands, drastically disturbed lands (land reclamation), or land
dedicated to sludge disposal (dedicated land disposal).
Throe of the four types of land application—agricultural application,
forest application, and land reclamation—use sludge as a valuable
resource to improve the characteristics of the land. Sludge acts as a
soil conditioner by facilitating nutrient uptake, increasing water
retention, permitting easier root penetration, and improving soil
texture (which in turn reduces runoff and erosion and makes the
soil easier to work).
Sludge also serves as a partial replacement for expensive chemical
fertilizers. The major constituents of chemical fertilizers—nitrogen,
phosphorus, and even small amounts of potassium (see Table 3) —
as well as many trace elements required by plants are found in
wastewater sludge, though usually not in optimal proportions.
Based on 1983 fertilizer prices in the South-Central United States a
metric ton of dry sludge solids would contain approximately $9.08
worth of nitrogen, $28.33 worth of phosphorus, and $0.66 worth of
potassium.
Concurrent with improving soil productivity, land application also
functions as a sludge treatment system. Sunlight, soil micro-
organisms, and desiccation help to destroy pathogens and many
toxic organic substances in the sludge. Heavy metals and, to some
extent, nutrients in sludge are trapped by soil as a result of soil's
various physical and chemical characteristics. Nutrients, which can
cause eutrophication and other problems if released into surface
waters, are instead largely converted into useful biomass such as
crops or wood. However, the capacity of the land: to treat sludge
constituents is finite, and land application systems must be
designed and managed to work within the assimilative capacity of
the land and the crops grown on it.
Municipalities in every part of the country are successfully using
land application and have been doing so for many decades. Land
application has been used successfully by both small towns and
large cities. Currently about 25 percent of the nation's sludge is
land applied.
This breadth of experience has shown land application to be a safe
and effective wastewater sludge use option. In particular, research
during the last 10 years has produced new knowledge which allows
the full benefits of sludge application to be achieved with negligible
Impacts (9).
Many states have begun to promote land application as the sludge
use/disposal option of choice. For example, Pennsylvania now
requires the application of wastewater sludge to be considered as
one alternative in any disturbed land reclamation plan, and New
Jersey is promoting the reduction of toxic organic chemical and
metal concentrations in all municipal sludges, so that they can be
recycled by land application.
10
3.2 Process and Performance
Three aspects of a land application system greatly affect its
success: site characteristics, application rates, and the sludge
application system. Together these three conditions determine both
the potential for environmental or health problems and the
economics of sludge application.
All three conditions are intimately intertwined. Site selection is
influenced by the amount of land required to apply all the sludge.
The amount of land needed depends on the sludge loading rate,
which in turn depends on the sludge's characteristics, on which
application alternative (e.g., forest land application) is to be used,
and on the sludge application method (e.g., injection of liquid
sludge). Site characteristics may also influence sludge application
rates.
3.2.1 Site Characteristics
Site characteristics greatly affect the potential environmental
impacts of sludge application; consequently, site selection is an
important aspect of all land application systems. Factors of concern
include depth to ground water, distance to surface waters, slope of
the site, soil permeability, soil pH, soil cation exchange capacity,
and depth and type of bedrock.
The greater the depth to ground water and distance to surface
waters, the less potential for contamination exists. Guidance on
appropriate depths and distances can be found in reference (9).
The slope of a site affects the rate and amount of runoff from the
site. For agricultural application, slopes of less than 6 percent are
generally considered acceptable, and slopes of less than 3 percent
are ideal. Slopes of up to 15 percent can be managed safely, but on
steeper sites high runoff velocities may carry sludge constituents
and soil into nearby lakes or streams if runoff controls are not
installed. Sites with extremely low soil permeability should not be
used for land application as ponds may form during high rainfall.
Soil characteristics, particularly pH and cation exchange capacity,
affect the potential for contamination of the food chain by heavy
metals. High soilpH immobilizes most metals and reduces their
absorption by plants. For agricultural application, the pH of the soil
must be at or above 6.5 at the time of sludge application (see
subsection 3.3.10). This requirement has been questioned by
researchers who note that acceptable programs can be conducted
at lower, naturally occurring pH levels, and that other controls such
as crop monitoring can be used. In some situations, such as
application to forest lands where soils are naturally acid, it may be
impractical to raise the pH to 6.5. However, since the products of
forest lands are usually not major components of the human diet,
heavy metals in forest soils are of concern only as they affect the
health of forest plants and animals and can contaminate aquifers
and surface waters.
The cation exchange capacity, which is an indirect measure of the
soil's ability to capture positive ions (the form in which most metals
are found in the soil), can also be important in planning land
application systems. Soils with a high cation exchange capacity can
generally receive higher levels of metals than soils with a low cation
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LAND APPLICATION
exchange capacity. Other soil characteristics, such as clay-mineral
content and organic matter content, can greatly influence metal
retention.
Other site characteristics of importance are the proximity of the site
to social and cultural facilities such as homes, schools, and other
public buildings. A strip of land between the sludge application site
and such facilities may be desirable to enhance public acceptance
of the sludge application program. Such a buffer zone may also be
desirable on unfenced sites to reduce the chances that children,
adults, or pets will directly contact the sludge.
Unless special precautions are taken, application sites should not be
located in areas underlain by fractured bedrock or containing
sinkholes, as these types of geologic formations may provide a
route for rapid transport of pollutants to nearby aquifers.
3.2.2 Application Rates
As with commercial fertilizers, the primary means of managing land
application is by controlling the application rate to optimally
disperse sludge constituents. The two constituents that are usually
most important to control are nitrogen and cadmium; however,
several other sludge constituents may also govern application rates.
Rates of application are calculated based on crop needs,
permissible sludge constituent concentrations (based on health and
environmental effects), and soil characteristics. Application rates
are designed so that the limiting constituent is applied in
appropriate quantities.
Limiting constituents vary with how the sludge will be used. In
agricultural application, crop nutrient needs and potential
contamination and phytotoxicity from heavy metals are major
concerns; therefore, nitrogen, cadmium, and/or another heavy
metal often limit application levels. In dedicated land disposal,
where the crops grown are typically not food chain crops, metals
are usually of much less concern.
The application rate is the primary factor to be considered in
determining the amount of land required—the higher the
application rate the less land needed to handle sludge production.
In dedicated land disposal, sludge is applied at high rates to a small
piece of land under intensive management to preclude detrimental
environmental effects. In agricultural application, the sludge is
applied to a larger land area at much lower rates, which reduces the
danger of environmental degradation and, consequently, the need
for intensive management. In forest land application and land
reclamation, large quantities of sludge are applied at infrequent
intervals. Cumulative application rates are usually as low as those
for agricultural application.
3.2.3 Application of the Sludge
Both liquid and dewatered sludge can be applied beneficially to
land. The sludge can be spread onto the surface or incorporated
into the soil. Each of these choices has advantages and
disadvantages.
Thickening or dewatering processes reduce both the water content
and the soluble nitrogen content of sludge. Because nitrogen
usually limits application rates, reducing nitrogen levels may be an
advantage if only a small area of land is available, since greater
quantities of wastewater solids can be applied without exceeding
the nitrogen loading capacity of the soil. On the other hand, a high
nitrogen content in sludge may be of value for promoting plant
growth.
The decrease in water content may be beneficial, since it reduces
handling costs, including those for transportation. Generally the
reduction in transportation costs is more important for large
municipalities, which often must transport the sludge a greater
distance to reach a suitable site. Many small communities will not
need to invest in dewatering equipment.
Dewatered sludge is ordinarily surface applied. Dewatered sludge is
first spread on the soil surface and subsequently incorporated into
the upper layer of soil by plowing or discing. With specially
designed equipment, dewatered sludge can be injected below the
soil surface, provided the sludge solids content does not exceed
about 20 percent.
Sludges may also be applied to land in composted, air-dried, or
heat-dried forms. These dried forms are easier to store and, in the
case of composted sludge, are more stabilized than the liquid or
dewatered sludges.
Liquid sludge may be injected into the soil, sprayed or spread over
the soil surface, or applied by ridge-and-furrow irrigation. The
subsurface methods—injection of liquid sludge and incorporation of
dewatered sludge—reduce the potential for contact between the
sludge and crops, grazing animals, or people, and reduce the
potential for sludge erosion. In addition, subsurface application can
eliminate significant odors. Surface application allows ammonia
and volatile toxic organic chemicals to disperse into the
atmosphere. Surface-applied sludge is also exposed to sunlight and
air, which helps destroy toxic organic chemicals and pathogens.
The choice of application method may be limited by locally specific
factors. For example, ridge-and-furrow irrigation requires flat land
that is carefully graded.
A key factor affecting the scheduling of sludge application is
climate. Sludge application to saturated soils or to frozen or snow-
covered ground greatly increases sludge runoff and erosion and
should be avoided. Consequently, municipalities must have
sufficient capacity to store sludge during unfavorable conditions.
Figure 8 shows an estimate of the number of days of storage
required in various parts of the country based on climatic factors
alone. For some crops that make the application site inaccessible
(e.g., corn), sludge storage is required. Additional storage may be
required during the crop harvesting period, to provide system
backup, or to equalize application rates over the course of the year.
11
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LAND APPLICATION
Shading denotes regions where the
principal climatic constraint to
application is wet spells.
SOURCE: Reference (10).
Figure 8. Estimated Number of Days that Sludge Storage is Required Based Solely on Climatic Factors
(Temperature, Precipitation, and Snowcover)
3.2.4 Agricultural Use
Agricultural use of sludge is the most widely used of all land
application methods. Sludges may be applied to a wide range of
crops, including grains, animal feeds, and nonfood crops.
Municipalities should retain enough control over the process to
ensure that safe practices are followed in order to preclude adverse
effects on the food chain.
Agricultural application does not usually require the municipality to
purchase any land. The responsibilities of the farmer and the
municipality can be laid out in a contract, which may cover liability
for any damages, whether the farmer will pay for the sludge or be
paid to take it, when the sludge may be applied, how much sludge
can be applied, and under what conditions sludge application can
be terminated by one of the parties to the contract. Figure 9 shows
a sample contract. This was developed as part of an EPA
demonstration project with the Ohio Farm Bureau. The contract
can be adapted for local use by changing the costs, the application
rate, and other terms.
Agricultural application is often extremely economical. In most
cases the farmland to which the sludge is applied is kept on the tax
rolls, in contrast to incineration, landfilling, and dedicated land
disposal, where the municipality usually owns the land. Farmers
participating in land application may save money by reducing their
dependence on expensive chemical fertilizers. In some regions of
the country the water added to the soil during sludge application is
also a valuable resource.
Soil Conservation Service officials and the county agricultural
extension agent are usually a municipality's prime contact with local
farmers. These officials are familiar with the opportunities
presented by sludge use and the operational needs and concerns of
local farmers, and can assist in designing and implementing a land
application program. Local farm bureaus may also assist. Such
contacts are usually essential to generate farmer support for an
agricultural application program.
12
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LAND APPLICATION
THIS CONTRACT, made this.
.day of.
CONTRACT
_, 19 , by and between .
hereinafter referred to as Owner, and , hereinafter referred to as City, witnesseth that,
WHEREAS, Owner is the owner of a parcel of agricultural real property located in (PARCEL NO.) r (TOWNSHIP) r (COUNTY) t
Ohio, which can be reached as follows: , and
WHEREAS, City operates a waste treatment or disposal plant which after processing produces a product known as sewage sludge, and
WHEREAS, Owner will allow sewage sludge from City to be placed on the above-mentioned real property only on the terms set out below,
NOW THEREFORE, Owner and City mutually agree as follows:
1. The "Ohio Guide for Land Application of Sewage Sludge,"
Bulletin 598 of the Cooperative Extension Service of the Ohio State
University, as revised in May, 1976, shall be used as a guideline for
responsible management practices. Hereinafter Bulletin 598 will be
referred to as "The 1976 Guide."
2. The City will deliver sewage sludge to the above-mentioned
property of Owner and will properly spread or otherwise deposit said
sewage sludge on said property without charge to the Owner. City shall
be responsible for all equipment used to deliver and spread such sewage
sludge.
3. The Owner and the City will mutually agree on the specific portion
of said property which is to receive sludge. In the absence of unusual
factors, they will abide by the site election criteria of the 1976 Guide.
4. The Owner or his representative may decline to receive sludge on
said property when, in Owners's or his representative's judgement, the
sludge application equipment would damage the soil structure because
of excessive soil moisture at the disposal site. When possible, the
Owner will give the City notice of poor field conditions 24 hours prior to
the appointed application time. However, the City does realize that this
is not always possible and that there will be some days when untimely
excessive rainfall will require termination of spreading activities at a
moment's notice on a given field.
5. The Owner will notify City in writing of the dates between which
City may deliver and spread sewage sludge. The City may deliver said
sewage sludge only during the period thus described. The Owner will
make himself or his representative available to City or its employees
during such ppriod to ensure said sewage sludge is deposited on the
proper location on said property.
6. Owner shall specify the access to be used by the City when
sewage sludge is applied to a specific portion of said property. The
Owner shall provide and maintain an access for use by the City without
charge to the City, and the City shall not be liable for any damages
thereto, except damage caused by City's negligence.
OWNER:
Address:
7. Using the criteria of the 1976 guide, the Owner and the City have
mutually agreed on the rates and amounts per acre said sewage sludge
is to be applied during the Contract period. For the term of this
Contract, Owner will adhere to mutually agreed upon application rates
listed in Attachment A which is included as a part of this Contract.
8. The City shall properly analyze its sewage sludge on a monthly
basis for the total nitrogen, ammonia and nitrate nitrogen, phosphate,
potassium, lead, zinc, nickel, copper, and cadmium content. The results
of such analysis will be provided to the Owner or his representative
upon request without charge before sludge is applied to said property.
9. City shall keep and maintain records of the following items, and
shall make such records available to Owner or his representative upon
request:
(a) All analyses of the composition of sewage sludge produced by the
City.
(b) All reports concerning the operation or production of sewage
sludge by the City.
(c) All applications to agricultural land of sewage sludge produced by
City including dates of application, amounts applied, specified
rates of application, specific parcels of land upon which sewage
sludge has been applied.
(d) All required governmental permits or approvals for the application
of sewage sludge on agricultural land.
10. City will deliver and apply sludge which is well stabilized and
which does not present a severe odor nuisance to Owner or other rural
residents whcrlive in the vicinity of the sludge disposal site. The Owner
may refuse to accept any sludge which is exceptionally odorous.
11. The Contract shall continue in effect for a period of three years
following the date first above written. The Parties hereto may renew this
Contract in writing. Either party may cancel this Contract by giving
written notice to the other party of the intention to do so. Cancellation
will be effective five days after receipt of such notice. Such notices shall
be delivered personally or by certified mail to the address(es) listed at
the end of this Contract.
CITY:
By_
Title
By_
Title
Address:
Figure 9. Sample Contract Between a Farmer and a Municipality
13
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LAND APPLICATION
Agricultural application and incorporation of sludge.
a. Subsurface injection of sludge.
Agricultural application rates generally range from 2 to 70 dry
metric tons per hectare per year (mt/ha/yr). This is equivalent to a
rate of 1 to 30 dry tons per acre per year (tons/ac/yr). A typical rate
would be 15 dry mt/ha/yr (6.7 tons/ac/yr}. Application rates are
usually limited by either the nitrogen needs of the crop grown or by
the annual or cumulative metals addition to the soil. Less
frequently, application rates are limited by the phosphorus needs of
the crop. Phosphorus-based rates are generally lower than metal- or
nitrogen-based rates due to the relatively low phosphorus needs of
most crops.
b. Incorporation of sludge into the soil surface by discing.
,'^
c. Surface application of liquid sludge by truck. Balloon tires
prevent soil compaction in wet conditions.
d. Surface application of liquid sludge by tractor.
14
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LAND APPLICATION
The heavy metal contact of sludge has been extensively studied as
a potential source of human exposure through the food chain.
Research has shown that several factors act as barriers to human
exposure to heavy metals in land-applied sludge. Because metals
have low solubility, uptake by plants is minimal. Metals that are
taken up tend to remain in the roots, preventing buildup of toxic
metal concentrations in edible plant parts. In addition, most metals
visibly damage crops at concentrations far lower than those that
affect human health (14). However, cadmium does not have
phytotoxic effects and, for this reason, is subject to strong
regulatory controls.
A 1981 joint statement by the U.S. Environmental Protection
Agency (EPA), U.S. Food and Drug Administration, and U.S.
Department of Agriculture recommended that only "good" sludges
[i.e., those containing less than 25 milligrams per kilogram (mg/kg)
of cadmium, 10 mg/kg of polychlorinated biphenyls (PCBs), and
less than 1,000 mg/kg of lead on a dry weight basis] be used for
growing fruits and vegetables (13).
References (9,11,12,13) should be consulted for further information
on agricultural application. Many states have also published
documents containing guidance for the particular climates, soils,
and cropping patterns found within their boundaries, as well as
detailed regulations affecting agricultural use. Federal regulations
on agricultural application are discussed in subsection 3.3.10.
3.2.5 Forest Land Application
Sludge application can greatly improve forest productivity. Studies
at the University of Washington on the use of sludge as a fertilizer
in silviculture showed height increases of up to 1,190 percent and
diameter increases of up to 1,250 percent compared to controls in
certain tree species.
Forest soils are in many ways well suited to sludge application.
They have high rates of infiltration (which reduce runoff and
ponding), large amounts of organic material (which immobilize
metals from the sludge), and perennial root systems (which allow
year-round application in mild climates). Although forest soils are
frequently quite acid, research at the University of Washington has
found no problems with metal leaching following sludge
application.
One major advantage of forest application over agricultural
application is that forest products (e.g., wild edible berries,
mushrooms, game, and nuts) are an insignificant part of the human
food chain. The primary environmental and public health concern
associated with forest application is therefore pollution of water
supplies. In many areas, particularly in the western states, forest
lands form crucial watersheds and groundwater recharge areas.
Contamination of water supplies by nitrates can be prevented by
limiting sludge application rates according to the nitrogen needs of
the trees, which usually is equivalent to a rate of 10 to 220 mt/ha
(4 to 100 tons/ac) in a single application every 3 to 5 years.
A typical application rate would be 40 mt/ha every 5 years
(18 tons/ac every 5 years), which is equivalent to an average yearly
Municipal wastewater sludge is being incorporated into a slope as
one of the first steps in a forest application program. The site was
then planted with Douglas fir.
Once the seedlings have been planted, sludge must be sprayed
onto the land in order not to disturb their growth. Here sludge is
being sprayed in early spring while the trees are dormant in order to
avoid damaging new foliage.
Douglas fir seedling about 6 weeks after over-the-canopy sludge
application, with grasses reappearing.
15
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LAND APPLICATION
Young Douglas fir trees about 10 weeks after over-the-canopy
sludge application. Rain has washed away much of the sludge from
older foliage, and new foliage is emerging.
Comparable branches from control Douglas fir tree (no sludge
application) on the left, and sludge-treated tree on the right.
Note the differences in foliage cover and branch size (white ruler is
12 in long).
application rate slightly less than that for agricultural application
(4,11).
As in any fertilizer use, residual nutrient loadings from the previous
sludge and fertilizer applications must be considered. Trees take up
nitrogen and other nutrients and incorporate them into leaves,
branches, and trunks. Unless the trees are cut for lumber or
pulpwood, the leaves and eventually the trees themselves fall and
decay, releasing the nutrients into the soil. Thus, successive sludge
applications on forest lands should be controlled to provide only the
level of nutrients that can be used beneficially.
Currently, few municipalities are using forest application as their
principal means of sludge use/disposal, and guidance on this
option is limited. As in agricultural application, the Soil
Conservation Service and county extension agents may be able to
ho!p with program design and implementation.
Forest lands are often extremely rough, so special application
vehicles may be required unless the land contains an adequate road
system. Seattle, Washington, has purchased such vehicles for its
forest application program. These vehicles have four-wheel drive,
are hinged in the middle, can traverse 25 percent slopes, and have
flotation tires for use on wet soils. Each vehicle cost about $175,000
in early 1983.
3.2.6 Land Reclamation
Sludge can help return barren land to productivity. According to
preliminary results of a 1982 survey by the U.S. Soil Conservation
Service, 1.6 million ha (4 million ac) of land disturbed by mines,
quarries, or sand and gravel pits remains unreclaimed (15).
Unreclaimed lands are often barren and frequently harmful to the
surrounding environment. They may have such problems as acid
runoff, high erosion rates, low nutrient levels, and toxic levels of
trace metals. Application of wastewater sludge can improve all
these characteristics.
16
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LAND APPLICATION
Spraying sludge under the canopy of an older Douglas fir stand. The cannon-mounted sludge application vehicle
can pump sludge 30 to 50 m (100 to 160 ft).
The amount of sludge applied at one time during land reclamation
can be relatively large, ranging from 7 to 450 dry mt/ha (3 to 200
ton/ac). This is necessary to ensure that sufficient organic matter
and nutrients are introduced into the soil to support vegetation until
a self-sustaining ecosystem is established; A typical one-time
application would be 112 mt/ha (50 ton/a'c). Usually the sludge is
applied and incorporated into the soil, the land is reseeded, and no
further sludge is applied. Depending on site topography and sludge
treatment prior to application, some contamination of ground and
surface waters might occur immediately following sludge
application, particularly by nitrate nitrogen. Similar problems occur
during land reclamation with chemical fertilizers, and such effects
are usually negligible compared to the environmental problems
present prior to reclamation. Since sludge is usually applied only
once, the cumulative amount of metals and persistent organic
chemicals applied during land reclamation may be less than the
cumulative amount applied during agricultural application or forest
land application, assuming a 20-year lifetime for forest and
agricultural sites.
Good practices reduce the potential for adverse effects from sludge
application during land reclamation, and also maximize the
likelihood of success. For example, the type of sludge applied may
be important. Research has suggested that large applications of
composted sludge minimize the quantity of nitrogen leached to
ground water or lost to surface waters (since the nitrogen in
composted sludge has low solubility), while providing sufficient
organic matter and nutrients to sustain vegetative growth for at
least 10 years (16). Large applications of digested sludge, on the
other hand, provide sufficient organic matter, but pose a greater
threat to water supplies due to the presence of large quantities of
soluble nitrogen in the sludge which can be readily oxidized to the
nitrate form and enter the ground water. Smaller applications of
digested sludge may provide insufficient organic matter to restore
soil fertility (16). The benefits of applying composted sludge must
be weighed against the cost of composting, and against the lower
availability of nitrogen during the critical early stages of vegetation
growth.
17
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LAND APPLICATION
b. Application of sludge to strip-mined land.
Incorporation of the sludge.
Use of sludge to reclaim strip-mined land.
a. An active strip mine.
Other important aspects of good practice include prompt
rovegetation to prevent erosion, and site preparation prior to sludge
application to improve infiltration rates and reduce site slopes,
thereby further reducing the potential for runoff and erosion
(11,16).
Categories of land appropriate for reclamation efforts include
surface mine spoils, mine tailings, borrow pits, quarries, cleared
forests, dredge spoils, fly ash, completed land fills, and
construction sites. These sites are often extremely difficult to
revegetate due to the poor characteristics of the soil. Historically,
land reclamation with sludge has been very successful. A recent
summary reported that of 20 projects using sludge for land
reclamation all but one were successful in a short period of time
f 16). The one failure was apparently due to a severe drought and,
with irrigation, this program later achieved success.
d. Reclaimed land after sludge application. Vegetation growth
can reach this level in as little as 5 months.
18
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LAND APPLICATION
A municipality contemplating sludge-based land reclamation should
be certain that there is sufficient land requiring such treatment
within economical transport distance. The site management
considerations in land reclamation are frequently more complex
than in other land application schemes, due to the drastic alteration
in soil characteristics desired and the need to satisfy regulations
pertaining both to sludge use and mine land reclamation.
3.2.7 Dedicated Land Disposal
In dedicated land disposal relatively large quantities of sludge are
applied to a land area for many years. The objective of this practice
is to employ the land as a treatment system by using soil to bind
metals, and soil microorganisms, sunlight, and oxidation to destroy
the organic matter in the sludge. Often, no attempt is made to
productively use the sludge nutrients.
Dedicated land disposal allows a municipality considerable control
over the ultimate fate of the sludge, at the cost of more intensive
management. Because the application area usually is owned or
leased by the municipality, there is no need to convince farmers,
lumber companies, or mining companies to participate in the
program. The dedicated land disposal site may be located on the
wastewater treatment plant grounds, thus reducing transportation
costs.
Application rates range from 220 to 900 dry mt/ha/yr (100 to 400
tons/ac/yr), approximately 20 times those of agricultural lands.
Dedicated sites where crops are grown will have application rates
toward the lower end of this range.
To prevent environmental degradation, Federal regulations require
that the sites not contaminate any ground or surface waters outside
site boundaries. Necessary precautions at dedicated sites may
include physical barriers to control runoff and leaching, careful
monitoring for contamination of ground and surface waters, and
remedial efforts in the event of contamination. Often leachate and
runoff water must be captured and treated prior to release.
After completion of a dedicated land disposal program, the soil
should be analyzed for heavy metals levels. Should high levels of
heavy metals have built up, it may be necessary to either prohibit
future production of food chain crops on the land; manage the site
permanently as a park or other facility that will preclude crop
production; cover the site; or remove the top layer of soil. Any of
these options will increase the cost of the operation, either by
requiring expenditures after closure, or by reducing the value of the
land for resale. However, since dedicated land disposal requires
relatively little land, and savings in transportation costs can be
substantial, this option may result in overall economic savings
compared to other land application systems.
While it is not required, vegetation should be grown on the disposal
site. Because of the potential for high rates of metal uptake
associated with high application rates, the plants grown should not
be used for human consumption. Suitable crops can include sod,
pulpwood, and animal feeds. Vegetation will help remove nutrients
and heavy metals from the soil, and thereby reduce the
groundwater contamination potential presented by the high
application rates. Plants will also increase soil aeration, promote
good drainage, and reduce odors. Vegetation on the site improves
aesthetics and working conditions at the site. In addition, crops will
reduce erosion and runoff from the site and, through transpiration,
will reduce the amount of water that must be captured and treated.
3.3 Key Parameters
3.3.1 Treatment Requirements
Federal regulations require stabilization of sludge prior to land
application in order to reduce odors and lower pathogen levels.
Details of sludge stabilization methods are provided in Federal
regulations and in reference (4).
Thickening or dewatering processes are also often considered
during the design of a land application system. Decreasing the
volume of sludge to be handled generally reduces transportation
costs. On the other hand, dewatering beyond 8 to 10 percent solids
content rules out pipelines, spray application, and irrigation as
application methods. Dewatering also reduces the nitrogen content
of the sludge because much of the soluble nitrogen is removed with
the water. Thus the need for dewatering depends on the objectives
of the particular application program.
3.3.2 Community Size
Land application is practiced successfully by communities of all
sizes.
3.3.3 Land Requirements
The amount of land required varies with sludge quality, climate, the
crops grown, and site characteristics.
Site characteristics influence the potential for adverse
environmental and public health effects from a sludge application
program, public acceptance of the program, and the cost of its
operation. Evaluation of site characteristics is detailed in
reference (11).
Sludge application must also be compatible with current and future
land uses. For example, the crops to be grown on sludge-amended
soil must be compatible with traditional cropping patterns used in
the area. Conservative application rates should be used when future
land use is difficult to predict. For example, on agriculture lands
that move in and out of production as demand rises and falls, and
on forest lands that may ultimately be developed for agriculture,
some states limit cumulative heavy metals to the same levels used '
for agricultural lands that are in continual production.
3.3.4 Storage Requirements
All land application programs require some storage facilities. The
volume of storage needed may range from the equivalent of 15
19
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UNO APPLICATION
days' production in hot, arid climates where the weather rarely
prevents sludge application, to 160 days in cold, damp climates
where sludge application may be impossible over much of the year
(see subsection 3.2.3). Storage should also be provided in the event
of equipment failures and other service disruptions.
3.3.S Good Practices
No factor is more crucial to successful, economical, and safe land
application than good practice in system management. The aspects
of good practice are myriad, and beyond the scope of this
document. A few have been described in Sections 3.1 and 3.2.
More detailed guidance on appropriate practice should be sought
from EPA and state agencies as plans are made to implement a land
application program. ;
One important factor in good practice is runoff and erosion control.
Even on relatively level sites, good soil conservation practices must
be followed to prevent sludge constituents from entering surface
waters. This is particularly important in agricultural application,
where new crops with new root structures must be established
each year, and at dedicated land disposal sites where poor soil
conservation greatly increases the expense of recovering and
treating runoff. Application of sludge to saturated, snow-covered,
or frozen ground greatly increases runoff, and is strongly
discouraged.
Good range management practices are essential on sludge-
amended pastureland. On overgrazed, poorly managed pastures,
the amount of soil consumed by livestock may rise to over 10 times
its normal level, greatly increasing the amount of sludge they
ingest.
Monitoring requirements also vary greatly among options and site
conditions, but some monitoring should always be considered a
part of good practice. Dedicated land disposal sites may require the
same degree of monitoring as landfills. Land reclamation, forest
application, and agricultural application sites generally require
intermittent monitoring. Groundwater monitoring should be
conducted at sites where nitrogen is applied at rates in excess of
crop needs. Land application monitoring may include soil metal
levels and soil pH. Surface water and crop monitoring are often
also required.
3.3.6 Sludge Quality
Land application employs soil as a treatment system and offers a
means of utilizing sludge as a source of nutrients for plants and as a
source of humus in conditioning soils. To use land application
successfully, care must be taken with pathogenic organisms and
toxic levels of certain organic chemicals and heavy metals. Each of
these factors can be managed successfully.
Four approaches to land application have been described, each
with special notes on the sludge quality factors that are important.
In each approach, nitrogen loading limits should.be considered,
although they may not be the limiting factor. In agricultural land
Dedicated land disposal sites may require the same degree of
monitoring as landfills. Here a soil auger is used to extract a soil
sample at a dedicated land disposal site located next to a
wastewater treatment plant.
application, additional elements must be considered (see
subsection 3.2.4).
3.3.7 Public Acceptance
Public acceptance—crucial to the success of any sludge
use/disposal option—is particularly important when the voluntary
use of sludge is being promoted. Public acceptance is gained by
stressing the proven value of sludge as a resource, and is
maintained by conscientious management and performance of
operations. Public involvement in the decision-making process will
help to minimize opposition and to identify the major roadblocks to
local acceptance.
In agricultural application, the acceptance of local farmers is also of
paramount concern. As mentioned earlier, the local Soil
Conservation Service, county extension agents, and Farm Bureau
can provide vital links with the farm community. However,
continuing acceptance depends on maintaining a perception of
quality in both management and product. Some cities, such as
Milwaukee and Los Angeles, have been so successful in gaining
public acceptance that they have created a product following, with
demand often exceeding supply.
20
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LAND APPLICATION
Site access is a key factor in public acceptance. Land application
requires transport of sludge over good roads that are passable in
most or all seasons. Trucking sludge through residential
neighborhoods may generate public concern about traffic
congestion, sludge spills, and dripping of sludge on the streets.
Steps can be taken to assuage these concerns—for example,
scheduling truck traffic at hours that will neither conflict with rush-
hour traffic nor disturb sleeping residents, and washing trucks
before they leave the site. One community fined trucks that dripped
sludge, which has proven effective in reducing sludge spills.
3.3.8 Transportation Requirements
Transportation is a major expense in most land application systems.
In agricultural application, where the sludge is often destined for
many parcels of land, trucks are usually the most economical
means of transport. For liquid sludge, tank trucks are commonly
used. Even dewatered sludge requires watertight closed trucks.
Open trucks with a tarp or similar covering can be used for
composted and dried sludge. For dedicated land disposal sites
pipeline transport may be possible. All transportation options are
highly energy dependent, and none is cheap. The most appropriate
mode of transport depends on the nature of the sludge and the
distance to its destination.
3.3.9 Energy Usage
Except for transportation, energy usage in land application is low.
3.3.10 Regulatory Approval
Federal regulations pertaining to land application of sludge are
contained primarily in 40 CFR 257—Criteria for Classification of
Solid Waste Disposal Facilities and Practices. Many states also
regulate sludge land application—some more stringently than the
Federal government. Other requirements are contained in 40 CFR
761 and in hazardous waste rules under the Resource Conservation
and Recovery Act.
In 40 CFR 257, land application is considered to be a form of solid
waste disposal, as are landfilling and sludge lagooning. The same
regulations, in several general sections, apply to all three practices.
• Floodplains. Land application sites, landfills, and lagoons may
be located in a floodplain; however, they must not "restrict the
flow of the base flood, reduce the temporary water storage
capacity of the floodplain, or result in washout of solid waste,
so as to pose a hazard to human life, wildlife, or land or water
resources." A base flood is a 100-year flood.
• Surface Waters. Discharges that would violate Sections 402,
404, and 208 of the Clean Water Act are prohibited.
• Ground Water. Facilities must not "contaminate an
underground drinking water source beyond the solid waste
boundary." States may establish an alternative boundary for a
facility if such a change would not contaminate drinking water
resources. EPA is currently examining more stringent controls
on land application to protect particularly vulnerable and
valuable groundwater resources such as irreplaceable aquifers.
• Public Health. Waste cannot cause a risk of infection by the
enteric organisms which are concentrated in the sludge. For
this reason, controls on pathogenic organisms are required.
To protect public health, sewage sludge or septic tank pumpings
that are applied to the land or incorporated into the soil must be
treated by a "Process to Significantly Reduce Pathogens" (PSRP)
prior to application or incorporation (see Table 6). The success of a
PSRP can be determined by measuring the reduction in the number
of organisms present. A one-log (90 percent) reduction in the
number of pathogens present, or a two-log (99 percent) reduction
in indicator bacteria (fecal coliforms) can be used to show that an
unlisted process attains equivalent pathogen reduction. Also to
protect public health, public access to the facility must be
controlled for at least 12 months, and grazing by animals whose
products are consumed by humans must be prevented for at least
one month unless "Processes to Further Reduce Pathogens"
(PFRP) are used (see Table 7).
Food-Chain Crops
Food-chain crops are: tobacco, crops grown for human
consumption, and feed for animals whose products are consumed
by humans. Land application of sludge for growth of food-chain
crops is subject to additional requirements, and to restraints
imposed by good practices and state regulations. For example, to
prevent nitrate contamination of ground water, the usual practice is
Table 6. Regulatory Definition of Processes
to Significantly Reduce Pathogens
Aerobic Digestion: The process is conducted by agitating sludge with air
or oxygen to maintain aerobic conditions at residence times ranging from 60
days at 15°C to 40 days at 20°C, with a volatile solids reduction of at least
38 percent.
Air Drying: Liquid sludge is allowed to drain and/or dry on underdrained
sand beds, or on paved or unpaved basins in which the sludge depth is a
maximum of 9 inches. A minimum of 3 months is needed, for 2 months of
which temperatures average on a daily basis above 0°C.
Anaerobic Digestion: The process is conducted in the absence of air at
residence times ranging from 60 days at 20 °C to 15 days at 35 °C to 55 °C,
with a volatile solids reduction of at least 38 percent.
Composting: Using the within-vessel, static aerated pile, or windrow com-
posting methods, the solid waste is maintained at minimum operating con-
ditions of 40°C for 5 days. For 4 hours during this period the temperature
exceeds 55 °C.
Lime Stabilization: Sufficient lime is added to produce a pH of 12 after
2 hours of contact.
Other Methods: Other methods of operating conditions may be
acceptable if pathogens and vector attraction of the waste (volatile solids)
are reduced to an extent equivalent to the reduction achieved by any of the
above methods.
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UNO APPLICATION
Tnbto 7. Regulatory Definition of Processes
to Further Reduce Pathogens
Composting: Using the within-vessel composting method, the solid waste
Is maintained at operating conditions of 55°C or greater for three days.
Using tho static aerated pile composting method, the solid waste is main-
tained at operating conditions of 55°C or greater for three days. Using the
windrow composting method, the solid waste attains a temperature of 55°C
or greater for at least 15 days during the composting period. Also, during
tho high temperature period, there will be a minimum of five turnings of the
windrow.
Heat drying: Dewatered sludge cake is dried by direct or indirect contact
with hot gases, and moisture content is reduced to 10 percent or lower.
Sludge particles reach temperatures well in excess of 80°Cr or the wet bulb
temperature of the gas stream in contact with the sludge at the point where
it leaves tho dryer is in excess of 80°C.
Heat treatment: Liquid sludge is heated to temperatures of 180°C for
30 minutes.
Thormophillc aerobic digestion: Liquid sludge is agitated with air or
oxyoon to maintain aerobic conditions at residence times of 10 days at 55 °C
to CO'C, with a volatile solids reduction of at least 38 percent.
Other methods: Other methods or operating conditions may be
acceptable if pathogens and vector attraction of the waste (volatile solids)
oro reduced to an extent equivalent to the reduction achieved by any of the
above methods.
Any of tho processes listed below, if added to a PSRP, further reduce
pathogens.
Beta ray Irradiation: Sludge is irradiated with beta rays from an
accelerator at dosages of at least 1.0 megarad at room temperature
(ca. 20*C).
Gamma ray Irradiation: Sludge is irradiated with gamma rays from certain
isotopes, such as "Cobalt and "'Cesium, at dosages of at least 1.0
megarad at room temperature (ca. 20°C).
Pasteurization: Sludge is maintained for at least 30 minutes at a minimum
temperature of 70*C. ;
Other methods: Other methods or operating conditions may be accep-
table if pathogens are reduced to an extent equivalent to the reduction
achieved by any of the above add-on methods.
Food-chain application is also subject to regulations designed to
prevent excessive human exposure to cadmium. Annual cadmium
applications to sites growing tobacco, root crops, and leafy
.vegetables are limited to 0.5 kg/ha/yr. Cadmium application to
sites growing other crops are limited to 1.25 kg/ha/yr until 1987,
when the limit will drop to 0.5 kg/ha/yr. The cumulative application
of cadmium is also limited, based on soil pH and soil cation
exchange capacity. In general, soil pH must be at least 6.5 or
greater at the time of planting, and EPA recommends that pH be
permanently maintained at or above 6.2. Future regulations may
reflect greater flexibility in this requirement.
Alternatively, if the crop is exclusively animal feed, cadmium
applications need not be limited, but pH must be consistently
maintained at or above 6.5. Thus the production of animal feed is
ideal at dedicated land disposal facilities. However, such facilities
do require a facility operating plan which demonstrates how the
animal feed will be distributed to preclude ingestion by humans and
which describes measures to safeguard the public health from the
hazards of cadmium entering the food chain. Also, future property
owners must be notified, by means of a stipulation in the land
record or property deed, that the property has received solid waste
at high cadmium application rates and that food-chain crops should
not be grown.
Sludges containing greater than 10 mg/kg but not more than 50
mg/kg of PCBs must ordinarily be incorporated into the soil when
applied to land used for producing animal feed, including pasture
crops for animals raised for milk. Sludges containing greater than
50 mg/kg of PCBs must be treated under the strict requirements of
40 CFR 761.60 which allows only incineration (in compliance with
Part 761.70) or disposal in a chemical waste landfill (defined under
Part 761.65). These requirements are separate from hazardous
waste requirements specified under RCRA. Substitute methods of
disposal may be approved by EPA Regional Offices.
Sludges that contain high concentrations of metals and thus qualify
as hazardous wastes are controlled under provisions of the
Resource Conservation and Recovery Act (see subsection 2.3.4).
to apply sludge at a rate that just satisfies the nitrogen requirement
of the crop to bo grown on a site. Similarly, some states protect
surface waters against phosphorus contamination by limiting
application rates to the phosphorus needs of the crops. Key Federal
regulations affecting land application to food-chain crops focus on
pathogen reduction, cadmium limitations, and PCB content.
If the sludge will not contact the edible portions of the crop,
pathogen reduction to PSRP levels is acceptable. However, if crops
for direct human consumption are grown within 18 months of
sludge application, sludge must be treated with a PFRP. These
processes destroy pathogenic bacteria, viruses, and protozoa, as
w@ll as parasites, in most cases by exposing the sludge to elevated
temperatures over a period of time.
3.3.11 Cost Factors
Land application may be a low-cost sludge use option. Capital
expenditures are frequently low, particularly if the municipality does
not need to buy land. Capita/ costs include:
Trucks
Sludge storage facilities
Dewatering/drying equipment
Stabilization /composting equipment
Spreading equipment
A small amount of land on which to set up or store the
equipment and facilities.
Dewatering, drying, and composting may all require high capital
expenditures, but are often not used in land application.
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LAND APPLICATION
Operating and maintenance costs are generally a substantial part of
the overall cost of a land application program. In particular,
because of the predominance of transportation costs, recent
increases in energy prices have raised the overall operating costs of
land application. Despite such setbacks, land application is still the
lowest cost option for many communities.
3.4 Case Study: Agricultural Application
Salem, Oregon, generates 121,120 cubic meters (m3) [32 million
gallons (mil gal)] of 2.7 percent solids, anaerobically digested
sludge per year. In 1976, it initiated a program of sludge application
to agricultural land. Known as BIOGRO, this program now recycles
90 to 95 percent of Salem's sludge to local farmland.
Typical sludge characteristics are shown in Table 8. The sludge
nitrogen levels are raised by the addition of ammonia during the
treatment process.
In 1982, sludge was applied to approximately 1,200 ha (3,000 ac) of
local agricultural land. Application sites are located as far as
32 kilometers (km) [20 miles (mi)] from the treatment plant, but the
majority are located within an 11-km (7-mi) radius of the treatment
plant. At virtually all sites, the sludge is applied only once per year.
Sludge application rates are based on the nitrogen needs of the
crop and the nutrient content of the sludge. They average
approximately 3.4 dry mt/ha (1.5 dry tons/ac), and vary from
2.2 dry mt/ha (1 dry ton/ac) to 6.3 dry mt/ha (2.8 dry tons/ac).
Table 8. Characteristics of Digested Sludge at Salem, Oregon,
Willow Lake Wastewater Treatment Plant3
Constituent
Concentration15
PH
Total solids
Total nitrogen
Ammonia-nitrogen
Phosphorus
Potassium
Zinc
Copper
Nickel
Cadmium
Iron
Lead
Barium
Chromium
Magnesium
Calcium
Sodium
Arsenic
Cobalt
7.3
2.5%
10.3%
5.9%
2.0%
0.96%
980 mg / kg
470 mg / kg
43mg/kg
7 mg / kg
21,000mg/kg
230 mg / kg
720 mg / kg
60 mg / kg
200 mg / kg
12,200 mg/kg
3,000 mg/kg
0.1 mg/kg
Smg/kg
a All constituents except pH reported on a dry weight basis.
b Based on samples from early 1983.
SOURCE: Reference (11).
3.4.1 Crop Choice and Site Selection
The sludge is applied primarily to fields used to produce grains,
grasses, pasture, and silage corn. Sludge-amended sites are also
used to produce seed crops, Christmas tree farms, commercial
nurseries, and filbert orchards. No sludge is applied to fruit and
vegetable crops. For poorly drained soils, sludge can generally only
be applied from April 15th through October 15th. For well-drained
soils, sludge can be applied anytime except during or immediately
after rainstorms. Schedules for application of sludge to soils with
intermediate drainage capacity fall between these two extremes.
Cation exchange capacity is used to limit cumulative metal loadings
added by sludge application (see Table 9). However, if soil pH is
less than 6.5, as it is in most of the Salem area, then cumulative Cd
addition is limited to 4 kg/ha (4.5 Ib/ac), regardless of soil cation
exchange capacity. Since the sludge generated by Salem is very
low in metals, application sites generally have a life well over
25 years. The BIOGRO program keeps records of the annual sludge
application to each site, including quantities per hectare of dry
solids, total nitrogen, ammonia nitrogen, and the various heavy
metals.
Table 9. Maximum Cumulative Heavy Metal Loadings
Recommended3 for Sludge Application to Privately
Owned Agricultural Land at Salem, Oregon
Cation
exchange
capacity
(milli-
equivalents/
100 grams)
<5
5-15
>15
Metal loading
[kg/ha (Ib/ac)]
Pb
500 (447)
1,000 (893)
2,000(1,786)
Zn
250 (223)
500(447)
1,000(893)
Cu
125(112)
250 (223)
500 (447)
Ni
50(45)
100 (89)
200 (179)
Cdb
5(45)
10(9)
20 (18)
aOregon Administrative Rules, Chapter 340, Division 50.
blf soil pH is below 6.5, maximum Cd limitation is 4 kg/ha (4.5 Ib/ac)
regardless of soil cation exchange capacity.
Each sludge application site is investigated by the Oregon
Department of Environmental Quality (DEQ), which makes
recommendations on a case-by-case basis. General guidelines are
as follows:
• Minimum distance to domestic wells = 61 m (200 ft).
• Minimum distance to surface water = 15 m (50 ft).
• Minimum rooting depth (effective depth of soil) = 0.61 m
(2ft).
• Minimum depth to ground water at time that sludge is applied
= 1.22m (4ft).
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LAND APPLICATION
» Minimum distance of sludge application to public access areas
varies with the method of sludge application:
- If sludge is incorporated Into soil = 0.
- If sludge is not incorporated into soil = 30.5 m (100 ft).
- If sludge is pressure-sprayed ("big gun"-type sprayer) over
the soil » 91 to 152 m (300 to 500 ft).
• Sludge application is not approved close to residential
developments, schools, parks, and similar areas.
» Minimum slope is largely left to the investigator's discretion.
Where no surface waters are endangered, slopes as high as
30 percent have been approved. Generally, however, the
maximum allowable slope is 12 percent and, in cases where
sensitive surface waters are nearby, maximum slopes may be
held to 7 percent or less.
3.4.2 Sludge Application
Sludge is hauled and applied to agricultural land virtually year round
in the Salem BIOGRO program. All hauling is done by a fleet of
four tanker trucks with a useful capacity of 20,000 I
(2,500 gal) each.
In general, pasture and grass land receive sludge applications
during the winter months; agricultural land growing seasonal crops
receives sludge during the warmer months, before planting or after
harvesting. When weather prevents sludge application, the sludge
is stored in lagoons at the treatment plant.
Sludge is usually applied by haul trucks themselves. If the
application site soil is too wet or otherwise unsuitable for direct
truck access, then the sludge is sprayed onto the application site. In
this procedure, the haul truck is parked as close to the application
site as practical and connected sequentially to a short discharge
hose, a portable pump, portable aluminum pipe (if necessary), a
200-m (600-ft) long hose, and a big gun sprinkler capable of
spraying liquid sludge in a 37-m (120-ft) radius.
City employees do all the sludge hauling and spreading. Three
drivers are used year round, and two additional temporary drivers
are added during the summer months when sludge volume and
distribution activity increase.
Application of liquid sludge from a tanker truck to agricultural land in Salem's BIOGRO program.
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LAND APPLICATION
3.4.3 Monitoring
During the early years of the B1OGRO program, the city routinely
analyzed the sludge-amended soil. Results showed virtually no
change in soil chemical and physical characteristics, so the city no
longer routinely monitors soils, but many farmers have their soils
tested periodically by laboratories as a prudent agricultural practice.
During the early years of the BIOGRO program, ground water from
wells on or within 150 m (500 ft) of sludge application sites was
sampled and analyzed before and after application. Since results
showed no significant changes in groundwater quality over a period
of 3 years, the groundwater monitoring program has been gradually
reduced. Selected wells are now sampled approximately every
3 years.
The City of Salem and the Oregon DEQ report that background
levels of nitrate nitrogen were very high in groundwater samples
obtained from many wells in the area north of the treatment plant.
These high nitrate nitrogen levels are thought to be due to the soil
characteristics in this area and the application of commercial
fertilizers over long periods. To avoid future claims of groundwater
degradation, the BIOGRO program does not apply sludge in this
area.
The BIOGRO program conducted some limited crop tissue sampling
and analysis during the initial years of the program. Constituents
analyzed included boron, cadmium, copper, magnesium, nickel,
zinc, arsenic, lead, molybdenum, and selenium. Results showed no
significant difference between crops grown on sludge-amended
soils and control crops.
Application sites are selected to avoid the possibility of surface
water contamination, and no surface water monitoring is routinely
conducted.
3.4.4 Costs
Annual costs for the BIOGRO program are approximately $320,000,
including depreciation on capital equipment. This translates to a
cost of about $106/mt ($97/ton) of sludge solids.
3.5 Case Study: Land Reclamation
In Venango County, Pennsylvania, sludge from local towns was
used to reclaim a bank of bituminous coal strip mine spoil —
unwanted materials removed from the ground during mining and
discarded on the surface. The site had been mined for coal and,
prior to this project, was essentially barren despite three previous
attempts to reclaim the area using commercial fertilizer. Sludge was
initially applied on a small scale to demonstrate the feasibility of
sludge-based land reclamation. The pilot project was so successful
that the mine owner decided to reclaim the entire site. The positive
results of this reclamation effort and several other demonstration
projects were factors in the State of Pennsylvania's decision to
allow the use of wastewater sludge to reclaim more than 1,200 ha
(3,000 ac) of mined land, and to actively encourage this as a means
of land reclamation.
3.5.1 Preliminary Preparations
Liquid and dewatered sludges for the demonstration project were
obtained from three local treatment plants and analyzed to
determine their acceptability for land application. Four 1-ha (2.5-ac)
plots were laid out and marked for sludge application. Two of these
plots received liquid digested sludge, the other two received
dewatered sludge. Prior to application, a portion of the
demonstration area was scarified with a tractor and chisel plow to
loosen the compacted spoil material and decrease the potential for
sludge runoff during heavy rains.
Soil analyses indicated that the average site soil pH was 3.9. The
Pennsylvania Department of Environmental Resources requires that
soil pH be at least 6.5 for use of sludge in land reclamation projects.
Therefore, agricultural lime was applied at an average rate of
12.3 mt/ha (5.5 ton/ac) to raise the soil pH to 6.5.
Diversion ditches were installed to prevent sludge runoff in the
direction of the two lakes on the property. A berm was constructed
on three sides of the dewatered sludge unloading and storage area
to prevent sludge migration.
3.5.2 Sludge Application and Incorporation
The liquid and dewatered sludges were mixed on site prior to
application. Average solids content for the liquid digested sludge
was 3 percent and for the dewatered sludge was 52 percent.
Average total nitrogen content was 1.3 percent for the dewatered
sludge and 2.7 percent for the liquid digested sludge.
Metals loading rates were well within EPA- and state-recommended
levels, except for copper which slightly exceeded the Pennsylvania
recommendation of 112 kg/ha but was well within the EPA
guideline of 250 kg/ha. The highest sludge application rate was
equivalent to applying 10 mt/ha (4.5 ton/ac) of an 11-9-0 (N-P-K)
commercial fertilizer.
In May 1977, liquid digested sludge was hauled in tank trucks from
the towns of Farrell and Oil City, mixed on site in a plastic-lined
holding pond, and spread onto two plots with a vacuum tank liquid
manure spreader at rates of 7 and 11 dry mt/ha (3 and 5 tons/ac),
respectively.
A total of 588 wet mt (647 tons) of dewatered sludge was
transported by coal trucks to the site, mixed with a farm manure
spreader, and applied to two plots at rates of 90 and 184 dry mt/ha
(40 and 82 tons/ac) respectively. The dewatered sludge was then
incorporated into the surface with a tractor to a depth of 10 cm
(4 in).
3.5.3 Seeding and Mulching
The sludge-treated areas were broadcast seeded with a mixture of
two grasses and two legumes. The two grass species germinated
quickly, and provided a complete protective cover during the first
year, allowing time for the two legume species to become
established and develop into the final vegetative cover.
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UNO APPLICATION
3.5.4 Monitoring
Vegetation growth responses were evaluated at the end of each
growing season. All sludge-treated areas had a complete cover of
vegetation within 3 months of sludge application, and vegetation
growth continually increased during the following 4 years with no
additional sludge applications. In comparison, untreated portions of
the site remained barren.
The two grass species were dominant initially; however, legumes
had begun to predominate by the third season. Within 5 years the
grass species were almost completely replaced by permanent
legume species.
Samples of vegetation showed trace metal concentrations well
below the levels that might impair crop growth.
Spoil samples were collected at various locations and depths at the
end of each year. Surface spoil pH generally increased during the
5 years following sludge application. Even at the highest sludge
application rate [184 mt/ha (82ton/ac)], the trace metal
concentrations in the surface spoil [0 to 15 cm (0 to 6 in)] were only
slightly increased, and were low in comparison to normal ranges for
soils. Nitrate nitrogen levels in soil percolate water at a 90-cm depth
increased to up to 34 mg/l shortly after application, but decreased
to well below 10 mg/l within 5 months of application, by which
time vegetative cover was well established.
Groundwater analysis taken at the edge of the site for a 4-year
period indicated that metals concentrations, fecal coliforms, and
nitrate nitrogen levels in ground water did not increase, even at the
highest application rates.
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4. Distribution and Marketing of
Sludge Products
4.1 Introduction
Distribution and marketing (D&M) of sludge products is a widely
employed sludge use option, and its use is growing. Like land
application, distribution and marketing employs the soil
conditioning and fertilizer value of sludge beneficially. In a typical
D&M program, sludge products are sold or distributed free to
commercial growers, landscaping firms, parks, highway
departments, cemeteries, and the public.
Many of the benefits and, concerns associated with land application
also apply to distribution and marketing. No Federal regulations
currently cover this activity; the practices recommended here are
advisory, based on reviews of many successful programs. Because
of the high potential for public contact with the sludge, only
sludges that meet PFRP criteria (Table 7) should be used in D&M
programs. Heat-dried or composted sludges usually meet these
criteria and are typically used because they have a high solids
content and are therefore more easily handled by the user.
Application of sludge compost in September to landscape a road
shoulder in Maryland.
By November, lush grass had entirely covered the site.
Use of sludge compost to recondition a tourist-worn lawn
surrounding Maryland's state cap/to/ at Annapolis.
Sludge products are applied to lawns, shrubs, ornamental plants,
and vegetable gardens. Application to vegetable gardens is not
usually recommended because the amount applied cannot be
controlled as it is in large-scale land application programs, raising
the possibility that high levels of heavy metals might be applied to a
given plot of ground. Sludge products are distributed in bulk or in
bags. Bags are common since they facilitate distribution. For
example, Milorganite, a heat-dried sludge produced in Milwaukee,
Wisconsin, is sold as a bagged product in every state as a soil
conditioner. Other cities that distribute heat-dried sludge include
Chicago, Illinois; Houston, Texas; Largo, Florida; Newport News,
Virginia; and the Greater Atlanta, Georgia, area. Municipalities that
distribute composted sludge include Philadelphia, Pennsylvania; the
District of Columbia; Kittery, Maine; Topeka, Kansas; Salt Lake
City, Utah; Columbus, Ohio; Missoula, Montana; Portland, Maine;
27
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DISTRIBUTION AND MARKETING OF SLUDGE PRODUCTS
28
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DISTRIBUTION AND MARKETING OF SLUDGE PRODUCTS
Portland, Oregon; and the Greater Los Angeles, California, area.
Some of these municipalities contract with an intermediary for
distribution.
Because dried or composted sludge may be used on urban open
spaces such as lawns, golf courses, nurseries, cemeteries, or
school fields, distribution and marketing is a particularly appropriate
option for localities that do not have the land available for
conventional land application. Although the municipality may
receive some return on the sale of sludge products, these revenues
do not usually cover the costs of treating, distributing, and
marketing the sludge product. Consequently, a decision on the area
to be included in the marketing effort should take into account such
factors as the cost of shipping and the possibility of reaching
buyers who may be willing to pay a higher price for the product.
In most D&M programs, the municipality has little control over
what is ultimately done with the slQdge, so only generalized
analysis of the environmental impacts of sludge application is
possible. Due to the low level of control achievable, D&M is most
appropriate for sludges with low levels of heavy metals and toxic
organic compounds. If bagged, use instructions should be printed
on the bag. If the product is distributed in bulk, literature on
appropriate uses should be provided to all recipients.
The problems and concerns involved in setting up a distribution and
marketing program center around ensuring that a high quality
product is available, and effectively developing a market for that
product. Other important concerns include maintaining good public
relations and ensuring that the operations are acceptable to the
community.
The key factor in the success or failure of a distribution and
marketing program is product demand. Many D&M programs use
surveys to identify potential users, and some hire people with
experience in setting up similar marketing efforts. Distribution and
marketing programs usually assign a trade name to the dried or
composted sludge to enhance its marketability. Some of these
names include ComPRO, Eko-Kompost, ComTil, Hou Acnite, Earth
Life, and Philorganic in addition to Milorganite.
Product quality is a key factor in maintaining product demand (see
subsection 4.3.5). In most communities using D&M, sludge
products have competed successfully against other soil
conditioners, topsoil substitutes, and potting media. In some
localities, demand for the product has exceeded supply. But in
other municipalities D&M programs have failed due to poor or
inconsistent product quality or due to operations that were not
acceptable to the community.
The demand for sludge products tends to be highly seasonal, with
peaks in the spring or fall. However, local factors such as climate or
a year-round specialized market may serve to either accentuate or
alleviate the seasonality of the market.
4.2 Process and Performance
Typically, either composted or heat-dried sludge products are used
in distribution and marketing. Air-dried sludge is sometimes used,
but is considered less suitable because it is unlikely to meet the
PFRP criteria specified (see Table 7) without additional processing.
4.2.1 Composting
In wastewater sludge composting, the sludge is dewatered, mixed
with a bulking agent, such as wood chips, bark, shredded tires, rice
hulls, straw, or previously composted sludge, and allowed to
decompose aerobically for a period of time. Three composting
processes are employed in the United States: windrow composting,
aerated piles, and in-vessel composting (Figure 10).
In windrow composting, the sludge-bulking agent mixture is
formed into long, open-air piles. The sludge is turned frequently to
ensure an adequate supply of oxygen throughout the compost pile
and to ensure that all parts of the pile are exposed to temperatures
capable of killing all pathogens and parasites. Windrow composting
may be adversely affected by cold or wet weather and is difficult to
control when raw sludge is used.
Sewage sludge composting at Beltsville, Maryland. Sludge is first
mixed with wood chips 11), then either placed into windrows (2)
and aerated by two large machines (3), or placed into static piles (4)
and aerated with pumped air which exits through odor control piles
(5).
29
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DISTRIBUTION AND MARKETING OF SLUDGE PRODUCTS
W = Windrow
P = Aerated Pile
V = In-Vessel
Facilities enclosed in parentheses are
either pilot facilities or full-scale facilities
that are not yot completed. Symbols do
not Indicate the precise locations of the
facilities.
SOURCE: Reference (17).
Figure 10. Location of Wastewater Sludge Composting Facilities in the Contiguous United States
Aerated piles, also called static piles, are rectangular piles that are
supplied with air via blowers connected to perforated pipes running
under the piles. The blowers draw or blow air into the pile, assuring
even distribution of air throughout the composting sludge (18).
A layer of previously composted sludge placed over the surface of
tho pile helps to insulate the pile and assure that sufficient
temperatures are achieved throughout the pile (Figure 11). Because
the piles do not have to be turned, and because the sludge is
Insulated by the outer layer of previously composted sludge, static
pile composting is less affected by inclement weather than windrow
composting. As in windrow composting, the sludge must be mixed
with a bulking agent to lower the moisture content and to enhance
sludge porosity so that air can be drawn through the entire pile.
Aerated pile composting has been studied extensively at the U.S.
Department of Agriculture in Beltsville, Maryland; at Rutgers—the
State University of New Jersey; at Ohio State University; and at the
University of California at Berkeley.
;: ••;;rrs
The first step in aerated pile composting is mixing the sludge and
bulking agent—in this case, wood chips. Here sludge is laid out on
a bed of wood chips in preparation for mixing.
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DISTRIBUTION AND MARKETING OF SLUDGE PRODUCTS
Bui/dozers are commonly used to mix and build aerated piles.
After 21 to 30 days of composting, the sludge is formed into curing
piles to allow additional stabilization. Typically, the composted
mixture will remain in a curing pile like this one for approximately
30 days.
Piles are constructed atop perforated pipes connected to blowers
which draw or blow air through the piles.
In-vessel composting takes place in completely enclosed
containers, where environmental conditions such as temperature
and oxygen supply can be closely monitored and controlled. This
process is particularly viable for municipalities in cold climates or
where land is limited. Many in-vessel systems are operational in
Europe and, as of 1984, several in-vessel systems are under
construction in the United States.
The objective in all composting systems is to allow thorough
aerobic decomposition of sludge to produce a humus-like product
resembling soil. Sludge is typically composted for 21 to 30 days,
during which time pile temperatures typically reach 55°C in a
properly run operation. (The exact amount of time required varies
with the composting method.) The compost is then allowed to cure
for an additional 30 days, and is often stored for 60 to 90 days
following curing to ensure that the final product has no residual
odors. The product is screened before or after curing to remove as
much bulking agent as possible. The high temperatures achieved
Compost is screened before or after curing to separate the compost
from the bulking materials.
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DISTRIBUTION AND MARKETING OF SLUDGE PRODUCTS
Composted
Sludge
Air
Bulking Agent/
Sludge Mixture
Porous Base:
Wood Chips or
Compost
Filter Pile of
Composted Sludge
Rgure 11. Aerated Static Pile Composting
/n-vesse/ composting system in Horn, Federal Republic of
Germany.
Interior of Compost Systems Company in-vessel composting
system in South Charleston, Ohio.
during composting destroy virtually all pathogens and parasites;
however, compost is a suitable medium for the regrowth of
bacteria, and care must be taken to keep it from becoming
contaminated (see subsection 4.3.5).
During composting, the organic material in the sludge is degraded
to a humus-like material that makes an excellent soil conditioner.
Tha bulking agent is also partially digested (19) and, despite
screening, adds appreciably to the volume of the material that must
bo marketed. Compost has a lower level of available nitrogen than
other forms of sludge due to preprocessing of the sludge via
conditioning and dewatering, dilution of nutrients by bulking
material, and loss of ammonia nitrogen during the composting
process. However, it is an excellent soil conditioner and its
nutrients become available slowly over several years. Additionally,
by promoting a healthy soil microflora, compost can help to prevent
plant diseases (12).
Additional details of the various composting methods can be found
in references (4,12,20,21).
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DISTRIBUTION AND MARKETING OF SLUDGE PRODUCTS
Proper composting of municipal wastewater sludge results in an
earth-like product that resembles fertile soil in both texture and
odor.
4.2.2 Heat Drying
Heat drying involves removing water from the sludge at high
temperatures. Energy costs are a major consideration in the
selection of this process. Some municipalities have used the waste
heat from thermal processes, such as solid waste incineration, to
dry sludge.
Heat drying at above 80°C (176°F) for very short periods destroys
all pathogens in sludge and greatly reduces sludge volume by
removing most of the water. Heat-dried sludge contains 4 to 6
percent nitrogen—a level comparable to.liquid digested sludge.
Most of the nitrogen is in the form of organically bound nitrogen
that is present in high levels in raw waste-activated sludge—the
sludge most commonly used for heat drying. Ammonia nitrogen is
lost in the drying process. Guidance on design of heat-drying
processes is provided in reference (4).
4.2.3 Air Drying
Air drying rapidly reduces sludge water content in dry climates. The
process is usually inexpensive; however, it does not destroy
pathogens as effectively as do the listed PFRP technologies (see
Table 7). For this reason, air-dried sludges should not be distributed
or marketed to the general public. They are, however, suitable for
application to land under more controlled conditions.
4.3 Key Parameters
4.3.1 Treatment Requirements
If food-chain crops are to be grown on sludge-amended soil very
shortly after the sludge application. Federal regulations require that
the sludge be subjected to a process that reduces pathogens to
PFRP levels (Table 7). Sludge products used in D&M programs
may present these same exposures and should be subjected to the
same level of treatment. The sludge product should usually be fairly
dry to facilitate handling by the user. Dewatering is therefore
generally employed prior to heat drying and composting.
4.3.2 Community Size
Distribution and marketing is most widely used by mid-sized to
large municipalities. Small municipalities often rely on the informal
giveaway of air-dried sludge or are likely to find direct land
application a more economically acceptable option.
4.3.3 Land Requirements
Distribution and marketing requires only a small amount of
land—that needed for composting or heat-drying facilities. If drying
beds are used, between 9 and 20 m2/mt (90 and 200 sq ft/ton) of
dry sludge solids are required in the northern United States (2).
4.3.4 Storage Requirements
Significant storage capacity is present in the composting process
itself. Often, however, 6 to 9 months' worth of storage beyond that
provided by the process may be necessary. The amount of storage
needed is highly site specific and depends on such factors as
climate and the presence of year-round markets such as nurseries.
To maintain product quality, storage facilities should protect the
finished compost from contamination and precipitation. Wet
compost is heavy and generally less desirable to end-users.
Some storage of sludge prior to composting may also be necessary
to facilitate system operation and to allow greater flexibility in
transporting the sludge from the treatment plant to the composting
facility. In addition, storage capacity for the untreated sludge is
desirable as a contingency in case of system malfunctions, unless
there are alternative options for sludge use/disposal during periods
of disrupted operations.
4.3.5 Good Practices
Quality control is crucial to maintaining a strong demand for the
product. Since even a well-run composting program may
occasionally encounter quality control problems, all products
should be monitored for quality, and provisions should be made for
disposing of compost that does not meet the quality control
standards. The key factors of good practices in composting are
ensuring the quality of incoming sludge; using trained and
33
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DISTRIBUTION AND MARKETING OF SLUDGE PRODUCTS
conscientious operators; allowing adequate composting and curing
times; maintaining aerobic conditions and adequate temperatures
during composting; and keeping the finished product dry during
storage.
Heat drying, like incineration, is a high technology process that
requires careful equipment maintenance and well-trained operators.
Controlling dust during sludge handling can be a problem. In
addition, extremely dry sludge is quite flammable, and when dried
to form dust, is explosive.
Quality control for pathogen reduction can be achieved by
monitoring the high temperatures achieved in the process. In both
composting and heat-drying operations, care should be taken to
prevent contamination of the finished product. Procedures to
accomplish this objective include using different equipment for
handling the raw sludge and the finished product, washing
equipment regularly, and promptly cleaning up sludge spills.
Reoontamination in air-dried sludge is less of a problem than in
compost because bacteria do not survive well in such dry material.
A laboratory technician at the Agricultural Research Center in
BeftsvillBf Mar/land, measures water uptake of grasses and
soybeans fertilized with composted sludge applied to soil at
different rates. These tests enable scientists to determine the
proper amounts of composted sludge for fertilizing various crops.
4.3.6 Sludge Quality
Because sludge products may be applied at very high rates and may
be handled by users, sludge quality is very important. Only sludges
with low metal concentrations should be distributed or marketed,
and these should be processed to eliminate pathogenic organisms.
When pathogen levels are reduced below detectable levels and the
end product is applied in small quantities, there is little potential for
harmful effects on human health or the environment from these
products.
Since garden produce forms a significant portion of the diet of
some families, there is a slight potential health hazard from the
continued use of sludge products containing high metals levels.
Some distribution and marketing programs recommend not
applying sludge to vegetable gardens; others offer guidelines for
garden application.
Lead levels are particularly important. Some children consume
nonfood substances such as soil and paint chips—a behavior
known as pica. Use of sludge products in lawns and parks increases
the potential for exposure of these children to the heavy metals in
sludge. Given the well-documented adverse effects of lead on the
development of children, sludges with low lead levels are preferable
for D&M.
Maximum levels of heavy metals considered suitable for
unrestricted distribution of wastewater sludge compost have been
published by USDA (12), by the Maryland Environmental Service
(MES) (19), and others. These concentrations are:
• cadmium—12.5 to 30 mg/kg
• copper—500 to 900 mg/kg
• lead-285to 1,000 mg/kg (MES)
• nickel —100 to 200 mg/kg
• zinc—1,250 to 1,800 mg/kg
• mercury—5 mg/kg.
One occupational health concern that may be raised in connection
with composting is the presence of Aspergillus fumigatus.
Aspergillus fumigatus is a very common fungus found in many
. locations such as basements, farm buildings, and wooded areas.
During certain composting operations, particularly woodchip
handling, elevated levels of Aspergillus may occur (22). In
susceptible individuals, such as chronic asthmatics and patients
receiving immunosuppressive therapy, infection by Aspergillus
spores can deteriorate respiratory function, resulting in a condition
known as aspergillosis. In a few such cases, this condition has led
to serious illness and even death. However, aspergillosis is not
normally observed in healthy individuals. When it does occur in
healthy individuals, the symptoms are usually mild and disappear
after exposure to the spores is eliminated (23).
Elevated Aspergillus levels have been observed at composting sites
when mixing sludge with the bulking agent and when mixing
compost piles; these levels are comparable to those encountered in
walking through a pile of decaying leaves (22). Levels rapidly return
34
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DISTRIBUTION AND MARKETING OF SLUDGE PRODUCTS
to background concentrations after such operations are completed.
Composting presents little additional risk of aspergillosis to citizens
living near the site; however, as a precaution composting facilities
should not be located in the immediate vicinity of nursing homes or
hospitals (22). To protect workers at the facility, individuals who
have a history of allergic sensitivity, have had recent renal or
cardiac disease, or are undergoing immunosuppressive therapy
should not be hired. As an additional precaution, front-end loaders
can be equipped with enclosed, air-conditioned cabs, or workers
can be provided with dust-filtering masks (22).
4.3.7 Public Acceptance
Distribution and marketing programs have generally been well
accepted by the public and by horticultural professionals. Public
concerns over environmental problems are generally low. Many
localities have demonstrated a high demand for composted or
dried-sludge products.
4.3.8 Transportation Requirements
Transportation is important in large-scale distribution and marketing
operations. In addition to considering the cost of transportation of
the sludge or sludge product from the wastewater treatment plant,
planners must consider the transportation of bulking materials and
the distribution of the finished product.
4.3.9 Fuel Usage
Heat drying requires large amounts of energy. Composting uses
less fuel and electric power than heat drying, but fuel and power for
dewatering the sludge, and constructing and aerating the piles are
significant costs in these operations.
4.3.10 Regulatory Approval
Distribution and marketing of sewage sludge is technically covered
under the same regulations as land application (subsection 3.3.10),
but EPA plans to promulgate regulations better adapted to the
uncontrolled use and frequent human contact that characterize the
use of these products. These regulations may detail more specific
criteria for sludge quality in D&M programs.
4.3.11 Cost Factors
The costs of a distribution and marketing program may be high
relative to the costs of direct land application. Major cost factors
include:
Dewatering
Composting or heat drying
Market development
Shipping.
The first two components involve significant capital expenditures,
and all components can generally affect total operating costs.
As part of a public acceptance program, site personnel take air
samples from a windrow at the Los Angeles County Sanitation
District facility. Samples are checked for odors.
4.4 Case Study
"Site II" is an aerated static-pile composting facility located in
Silver Spring, Maryland, and operated by the Washington
Suburban Sanitary Commission (WSSC). Currently the facility is
operating below its designed capacity of 360 wet mt (400 wet tons)
of dewatered sludge per day. This is due to moisture problems in
the sludge resulting in slightly lower solids content than expected.
The sludge is trucked to the site from the Blue Plains Sewage
Treatment Plant in Washington, D.C.
The plant is located in a densely populated suburb of Washington,
D.C. and faced considerable public resistance during site selection.
Consequently, the facility is designed and operated with constant
attention to neighborhood concerns such as odors, noise, and
appearance.
4.4.1 Operations
To minimize odors and maintain sludge quality, much of the facility
is partially or fully enclosed. The sludge is mixed with wood chips at
a ratio of 3.8 m3 wood chips/wet mt of sludge (4.5 cu yd wood
chips/wet ton sludge). [The facility was designed to operate at a
ratio of 2 to 2.5 m3 wood chips/wet mt sludge (2.5 to 3 cu yd wood
chips/wet ton sludge), but wetter-than-expected sludge has
required the higher ratio. This operational change underscores the
importance of sludge moisture content in operations.] The sludge/
wood chip mixture is formed into piles 31 m (100 ft) long, 6 m
(20 ft) wide, and 3 m (11 ft) tall. A 0.5-m (1.5-ft) thick layer of
finished compost is spread on top of the piles.
Fifty-six 11-kilowatt (15-horsepower) blowers provide a maximum
aeration rate of 110 to 125 m3/hr/dry mt of sludge (3,500 to
4,000 cu ft/hr/dry ton). The piles require this maximum rate during
the first week of composting to assure aerobic decomposition and
minimize odors, and again during the last 2 days of the composting
35
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DISTRIBUTION AND MARKETING OF SLUDGE PRODUCTS
cycle to lower pile temperature and minimize odors prior to
screening and curing. A backup generator is available to provide
aeration in the event of a power failure.
After the first week of composting, aeration demands of the piles
decrease. Pile temperatures are maintained at about 60°C (140°F)
for the entire composting cycle except the last 2 days.
Air drawn through the compost piles from the blowers is directed
Into one central pipe and released into a filter pile of previously
composted sludge to trap odorous gases, such as hydrogen sulfide.
WSSC personnel are also considering installing a backup chemical
odor control system to absorb the hydrogen sulfide.
After composting for 3 weeks, the piles are broken down and
screened in a fully enclosed building to minimize dust generation.
Approximately 70 percent of the wood chips are recovered during
screening. The screened compost is then placed in open-air curing
piles. Small blowers maintain aerobic conditions during curing.
(Other composting facilities postpone screening until after curing,
In which case the lower density provided by the wood chips
eliminates the need for blowers during curing. However, some of
tho wood chips decompose during curing, which reduces recovery
rates.)
Golf Courses
1.3%
Nurseries
2%
.Topsoil Dealers
r8.4%
Landscapes
and
Contractors
40%
Solos are given on a percent by volume basis.
SOURCE: Reference (24).
4.4.2 Marketing
The composted product is marketed by the Maryland
Environmental Service (MES) (a state agency), under the trade
name of ComPRO. Suggested uses of the product are as a fertilizer
and soil conditioner for alkaline-loving shrubs and trees, for
vegetable and flower gardens, and for lawns. ComPRO is also
recommended as a component of potting mixes for house plants.
At the outset of the marketing program, MES conducted a market
survey to determine who would be interested in purchasing
composted sludge. MES continues to employ agricultural
professionals as sales agents, and to advertise in professional
journals and the mass media.
As of late 1983, more than 99 percent of MES's sales were bulk
sales (Figure 12). Buyers include landscapers, contractors,
universities, military installations, school districts, and a network of
about 50 retail outlets in the Washington, D.C., area that in turn
sell the product to home owners and other small users: MES sells
the compost for $5.25/m3 ($4.00/cu yd) at Site II, but
transportation and handling costs raise the retail price to between
$19.60/m3 and $39.25/m3 ($15.00/cuyd and $30.00/cu yd).
MES sales of composted sludge from 1981 to mid-1984 totaled
about 115,000 m3 (150,000 cu yd), and were sufficient to handle the
volume of compost generated. The revenue generated by sales at
the 1984 rate of 46,000 m3 (60,000 cu yd) per year at Site II are just
sufficient to cover the costs of the marketing program.
4.4.3 Costs
The total capital costs for Site II were about $27 million. Operating
and maintenance costs when the site operates at full capacity are
expected to average about $38.50/mt ($35/ton) of dewatered
sludge cake treated (25).
Figure 12. Distribution of ComPRO Sales in 1983
by User Category
36
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5. Landfilling
5.1 Introduction
Landfilling is a sludge disposal method in which sludge is deposited
in a dedicated area, alone or with solid waste, and buried beneath a
soil cover. Landfilling is primarily a disposal method, with no
attempt to recover nutrients and only occasional attempts to
recover energy from the sludge. Currently, about 25 percent of the
municipal wastewater sludge generated in the United States is
landfilled.
To a certain extent landfilling, like land application, is an extension
of sludge treatment. However, there is an important difference.
When sludge is landfilled, anaerobic degradation occurs because
insufficient oxygen is available for aerobic decomposition, such as
occurs during land application and composting. Anaerobic
conditions degrade the sludge more slowly and less completely
than aerobic processes.
Adherence to proper sanitary landfilling procedures minimizes many,
potential health, environmental, and aesthetic problems associated
with sludge landfilling. However, groundwater contamination by
constituents in landfilled sludge remains a concern. Groundwater
contamination may be difficult to detect until the damage has
occurred, and even if contamination is detected, it may be
extremely difficult to correct. Proper planning and site management
can help to avoid these problems.
Landfilling has been and continues to be a popular sludge disposal
option, but increasing competition for available landfill space has
diminished interest in this disposal option. Nevertheless, landfilling
can be viable for municipalities that have available land with
hydrogeologic characteristics that protect ground water and other
drinking water supplies. If landfilling operations are properly
planned and executed, a completed landfill site can be sold or used
by the municipality for other purposes, such as recreational space.
Thus, even if a large area needs to be devoted to filling for several
years, it need not be permanent use of the land.
5.2 Process and Performance
Two major types of landfilling are currently practiced:
« Sludge-only disposal, in which sludge is buried, usually in
trenches.
• Codisposal, in which sludge is disposed of at a municipal
refuse landfill.
In both cases, adherence to proper sanitary landfill procedures
helps to maximize successful performance and minimize potential
problems.
5.2.1 Sludge-Only Disposal
Most sludge-only landfills consist of a series of trenches, dug into
the ground, into which dewatered sludge is deposited and then
covered with soil. Other sludge-only landfill designs exist (area fill
mounds, area fill layers, and diked containment) in which the
sludge is deposited on the ground surface, but these are not
commonly used. Reference (26) provides further information on all
methods.
Dewatered sludge is pumped into a narrow trench from a haul
vehicle in Montgomery County, Maryland. Sludge must contain
less than 30 percent solids and the trench floor must be nearly level
to ensure even spreading of sludge.
Sludge landfill trenches range from 1 to 15 m (3 to 50 ft) in width.
At narrow trenches [1 to 3 m (3 to 10 ft) wide], dewatered sludge is
usually dumped into the trench from a haul vehicle alongside the
ditch. The sludge must be less than 30 percent solids and the
trench floor must be nearly level to ensure that the sludge will
spread evenly throughout the narrow trench. A wide trench [3 to
15 m (10 to 50 ft) wide] allows the haul vehicle to work within the
trench itself (Figure 13). In this case, the sludge should be at least
30 percent solids (this may include bulking material, such as fine
sand) to ensure that it will stay in piles and not slump. The addition
of a bulking agent is generally not cost effective if sludge solids
content is less than about 20 percent. Instead, further dewatering
of the sludge should be done at the treatment plant.
The sludge should be covered with soil the same day it is deposited
in order to minimize odors and to prevent insects, birds, and other
vectors from contacting the sludge and spreading contaminants.
As each new trench is dug, the^ excavated soil can be used to cover
the sludge in a nearby trench. If the sludge is solid enough to
support a vehicle (greater than about 30 percent solids), soil cover
can be applied by a track dozer within the trench. For sludges less
than about 30 percent solids, cover must be applied by a front-end
loader or dragline next to the ditch.
Sludges must contain at least 20 percent solids in order to support
cover material. Narrow trenches can handle sludges down to
15 percent solids because the ground on either side helps support
the cover. Table 10 summarizes sludge characteristics related to
different methods of landfilling.
37
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LANDFILLING
Tha sludga haul vehicle Is working within the trench. The bulldozer is spreading excavated soil as a cover over the deposited sludge layer.
Rgure 13. Wide Trench Landfill
Toblo 10. Sludge Characteristics for Landfilling
Tronch
Narrow trench
Wide trench
Codisposal
Sludge/ refuse
mixture
Sludge /soil
cover
Solids
content
15-28%
2:30%
2:3%
2:20%
Bulking
agent
required?
No
No
Occasionally
Occasionally
Stabilization
recommended?
Yes
Yes
Yes
Yes
Sludge/soil mixture, 'in which sludge and soil are mixed and
spread on top of refuse.
Sludge I Refuse Mixture
Most sludge/refuse operations use sludges with at least 20 percent
solids, although sludges as low as 3 percent solids have been
codisposed by spraying the sludge on the refuse from a tank truck.
However, low-solids sludge requires large refuse volumes—as
much as 7 tons of refuse for every wet ton of sludge sprayed. The
excess moisture in low-solids sludge increases the rate of solid
waste decomposition; however, it also increases the likelihood of
leachate and methane formation, and is therefore not a
recommended method of operation.
Narrow trenches are relatively land intensive. Sludge applications
range from about 460 to 2,120 dry metric tons per hectare
(dry mt/ha) [200 to 940 tons per acre (tons/ac)] including areas
between trenches. Wide trench operations are less land-intensive
than narrow trenches, with sludge applications ranging from about
1,200 to 5,400 dry mt/ha (530 to 2,440 tons/ac).
5.2.2 Codlsposal
In codisposal, wastewater sludge is deposited in a landfill together
with municipal solid waste. In this way, the absorption
characteristics of the solid waste and soil conditioning
characteristics of the sludge can complement each other. The solid
wasta absorbs excess moisture from sludge and reduces leachate
migration. Sludge can also aid revegetation of the completed
codisposal site. The two categories of codisposal are:
• Sludge/refuse mixture, in which sludge is deposited on top of
refuse and then mixed in.
Dewatered sludge being mixed with refuse at a codisposal landfill.
38
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LANDFILLING
The liquid nature of sludge makes sludge/refuse codisposaf
operations prone to operational problems, including a tendency for
the sludge to flow away from the working area and for equipment
to slip and stick in the sludge. Long periods of wet weather
compound these problems. These difficulties are minimized by
depositing only as much sludge as the refuse can handle.
The amount of sludge that can be disposed of at a sludge/refuse
codisposal site is low compared to other landfilling processes but
high compared to agricultural land application of sludge. It ranges
from 180 to 1,600 dry mt/ha (80 to 700 tons/ac). The rate of sludge
disposal that a solid waste landfill can handle depends on the rate
of refuse delivery and the solids content of the sludge.
Sludge/ Soil Mixture
Spreading a sludge/soil mixture over completed refuse fill areas
promotes revegetation of the site. (See subsection 3.2.6 for further
discussion.) Use of well-stabilized sludges reduces odors that could
result if sludge is not completely buried. Sludge/soil covering
operations have high manpower and equipment requirements.
Advantages and Disadvantages
Advantages of codisposal include:
• Shorter time delay. Permits to allow sludge disposal at an
existing refuse landfill are usually processed more quickly than
permits for a sludge-only site. Also, because most or all the
site preparation required for sludge disposal has been
completed, construction delays are unlikely.
• Lower costs. Due to the economy of scale, the cost of one
codisposal site will probably be lower than the combined costs
of two separate sites.
Disadvantages of codisposal include:
• Ma/odor. Odors may be greater than at a solid waste landfill,
depending on sludge stabilization.
• Operational problems. Because of the relatively liquid nature of
sludge and the need to coordinate its disposal with that of
refuse, operations become more difficult. When public access
to refuse disposal areas is allowed, codisposal operations may
not be possible.
• Unpredictable site capacity. Wet weather can decrease the
bulking capacity of solid wastes and thus decrease the capacity
of the site for sludge.
• Leachate. Organic acids, formed during the anaerobic
decomposition of the landfilled sludge, could enhance the
leaching of metals from the solid waste/sludge mixture.
Therefore, leachate collection and treatment systems may have
to be installed, enlarged, or upgraded to handle increased
leachate quantity.
• Sludge storage. In some cases sludge may be delivered around
the clock, whereas refuse delivery may be confined to certain
hours. In such situations, on-site storage may be needed for
sludge until sufficient refuse for bulking has been delivered.
This procedure necessitates an additional sludge handling step.
Table 11. Range of Constituent Concentrations in Leachate
from Sludge Landfills
Constituent
Concentration3
Chloride
S04
Total organic carbon
Chemical oxygen demand
Calcium
Cadmium
Chromium
Zinc
Mercury
Copper
Iron
Lead
TKN°
Fecal coliform
Fecal streptococcus
20 - 600
1 -430
100 - 15,000
100-24,000
10-2,100
0.001 - 0.2
0.01 - 50b
0.01 - 36
0.0002-0.0011
0.02 - 37
10-350
0.1 - 10b
100-3,600
2,400 - 24,000
MPN/100mld
2,100 - 240,000
MPN/100mld
a Concentration is in milligrams per liter unless otherwise noted.
bThe maximum concentrations shown exceed the limits specified in
40 CFR 261.24 Table I. These limits define hazardous wastes under RCRA.
°Total Kjeldahl nitrogen.
dMPN/100mI = Most Probable Number/100ml.
SOURCE: Reference (26).
5.2.3 Leachate
Leachate is generated from the excess moisture in the sludge,
usually with some contribution from rainfall. The type and amount
of constituents in leachate from a sludge landfill depend on the
nature of the sludge. Table 11 gives the range of constituent
concentrations in leachate from several study sites.
If landfill leachate reaches an aquifer, heavy metals and toxic
organic chemicals are of particular concern because of their
possible adverse health effects. If leachate enters surface waters,
the resultant elevated nutrient levels can cause eutrophication and
concomitant undesirable algal blooms and fish kills. Pathogen
contamination of drinking water supplies could also have adverse
health effects.
The potential for groundwater contamination can be reduced by
properly covering landfills and installing liners to contain any
leachate within the fill area and to attenuate harmful contaminants.
The majority of states (72 percent) require or can require that
soil-based liners, synthetic liners, or both be installed in a sludge
landfill (5).
A leachate collection system should be installed in any landfill
where leachate is being contained or where water tends to pond in
the fill area. The two types of collection systems are:
A sump into which leachate collects and is subsequently
pumped to a holding tank or pond.
39
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LANDFILLING
i A series of drain pipes or tiles that intercept and channel the
leachate to the surface or to a sump. (See Figure 14 for an
example.)
5.2.4 Surface Water Containment
All upland drainage should be directed away from the landfill.
Working areas of the landfill should have a grade greater than
2 percent to promote runoff and prevent ponding, but less than
5 percent to reduce flow velocities and minimize erosion. Straw
bales, berms, or vegetation can be used to reduce flow velocities.
Siltatlon ponds will probably be necessary to settle the solids
contained in the site runoff.
5.2.5 Gas Control
The decomposition of organic matter in sludge and solid waste
produces methane and other gases, including trace amounts of
hydrogen sulfide. Methane is the gas of primary concern. It can
scop by diffusion through sludge and other materials into nearby
buildings or underground structures, such as utility tunnels, where
it may accumulate to explosive concentrations (5 to 15 percent). To
prevent this hazard, systems to collect gases are usually installed in
landfills located near buildings or underground structures
(figure 15). Reference (26) contains details on gas control
methods.
Collected gas can be vented to the atmosphere or incinerated.
A third option Is to recover and use the methane as an energy
source. This is being done successfully at a growing number of
solid waste sanitary landfills. However, the minimum landfill size
required for economical gas recovery ranges from about 11 ha
(28 ac) for a site with a 45-m (150-ft) fill depth to 31 ha (78 ac) for a
site with a 15-m (50-ft) fill depth (27). Thus, gas recovery is
presently not practiced at sludge-only landfills because they are
normally much smaller.
5.2.6 Monitoring
Approximately 60 percent of the states require landfill operators to
perform some form of monitoring and keep some form of records
(5).
Ground Water
Groundwater monitoring is important if the landfill is located in the
vicinity of an aquifer that is a potential drinking water source.
Ground water travels slowly along a gradient. Wells located
upgradicnt provide samples of water unaffected by landfill leachate.
Wells downgradiont from the landfill are used to detect leachate
migration from the fill area. A hydrogeologist should assist in
designing a groundwater monitoring program. Monitoring should
begin 6 months to a year before any landfilling to establish
background groundwater quality, including seasonal fluctuations.
Once the facility is In operation, an ongoing monitoring program
should be established. The frequency of sampling and the
15 cm Clay
1 cm = 0.39 in
Perforated
Plastic Pipe
Figure 14. Underdrain for Leachate Collection at a Landfill
..Slope,
Gas Venting
or Collection
System
.COVERS^
/~S
Figure 15. Permeable Method of Gas Migration Control
parameters analyzed depend on state regulatory requirements and
site-specific characteristics. For example, if the local ground water
is potable, parameters that have drinking water standards should be
measured.
Surface Water
A surface water monitoring program is necessary if surface runoff
or a leachate release could contaminate nearby water bodies.
40
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LANDFILLING
Gas
If buildings or underground structures are located on or near the
site, periodic gas monitoring should be performed to detect
methane migration and accumulation.
5.3.2 Community Size
Landfilling can be successfully practiced by communities of all
sizes, if appropriate disposal sites are within economical hauling
distance.
5.2.7 Contingency and Mitigation Plans
Because of their reliability, landfills are often essential elements of
contingency plans for other use/disposal options. However, landfill
operations themselves may be disrupted for several hours to several
weeks because of vehicular accidents, inclement weather, or labor
strikes. To prepare for such emergencies, the wastewater treatment
plant should have sludge storage facilities that can accommodate
sludge production until landfill operations resume. It is also
desirable, although not always feasible, to have a backup sludge
use/disposal system.
Another type of emergency that can occur at a landfill operation is
a leachate release that threatens ground water or surface waters. A
mitigation plan should be prepared that specifies the actions to be
taken in the event of such a release—for example, pumping
downstream wells to contain the leachate, and treating the
extracted water prior to discharge. A plan of action should also be
in place in the event methane is detected inside a structure.
5.2.8 Site Closure
After a landfill site is completed, it may be used for various other
purposes. Such uses should be planned during site selection. Every
step of the landfill process—initial site preparation, installation of
screens and buffers, placement of the final landfill cover, and
revegetation — should be steps towards achieving the final use.
These preparatory steps enhance the ultimate value of the site and
reduce redevelopment costs.
Proper site closure procedures should be followed when closing a
site or a segment of the landfill (26). After closure, the site should
be inspected at monthly to quarterly intervals for several years.
5.3 Key Parameters
5.3.1 Sludge Treatment Requirements
Reference (26) presents guidance on the suitability of various
sludges for landfilling. Sludges should be stabilized to preclude
odor problems and faciliate handling. Almost half of all states
require sludge stabilization prior to landfilling (5).
Sludge dewatering is an important step prior to landfilling to reduce
the potential for leachate formation and to reduce sludge volume.
Dewatering is essential prior to sludge-only disposal, where there is
no refuse for bulking and where the sludge must support a soil
cover. Half of all states require that sludge be dewatered prior to
landfilling (5).
5.3.3 Land Requirements
Landfilling can require substantial amounts of land. For example, a
municipality generating 25 dry mt (28 dry tons) of sludge per day
(i.e., population of about 230,000) will require approximately 2 to
20 ha (4 to 50 ac) of land per year for sludge-only landfilling,
depending on trench width, fill area depth, and sludge solids
content. This range is important because the areas suitable for
landfilling are limited by land use concerns in the community.
Finding and gaining access to an adequate landfill site capacity is
often the most significant problem in implementing a sludge landfill
operation.
Amount of Land
A landfill has a finite size and therefore a finite operating life. This
operating life must be long enough to justify purchase, site
preparation, and other capital costs, which become less significant
when amortized over time.
A landfill's lifespan can be estimated by dividing the volume of
sludge it can hold by the volume of sludge landfilled each year.
Landfill capacity is the product of the usable fill area (generally 50
to 70 percent of the total site surface area) times the depth of the
landfill. The remaining 30 to 50 percent of the site is used for buffer
zones, access roads, and soil stockpiles. In calculating landfill size
requirements, the projected increase in sludge volume during the
lifetime of the site must be considered. This will be a function of
community growth and the construction of additional wastewater
treatment capacity.
Soil Availability
Soil is often used to increase the solids content of a sludge and to
provide interim and final cover. Bulking and cover soil may be
present on site, and may be readily available from trench
excavation. If sufficient soil is hot available on site, or if its physical
and chemical properties are not suitable, soil may have to be hauled
to the landfill, a costly procedure.
Hydrogeology
Pollution of ground and surface waters are the major environmental
concerns associated with sludge landfilling. The depth to ground
water, the type of bedrock, and the soil environment affect the
potential for groundwater contamination. Any currently used or
potentially potable ground water should be protected from landfill
leachate.
41
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LANDFILLING
Sfte Preparation
The time and cost necessary to prepare a site for landf filing can
influence the desirability of that site. For example, a highly
vegetated area may require extensive logging or clearing, which can
greatly increase capital costs. Varied terrain will increase the cost of
constructing sludge haul roads, while a site with an appropriate
slope (2 to 5 percent) will help to keep capital costs down by
minimizing the need for grading. Varied terrain can, however, offer
deep fills to increase site capacity.
Site Access
The physical adequacy of public roadways for truck traffic; the
number of residences, parks, and schools fronting the roads; and
the effect of traffic congestion must be considered when evaluating
the landfill alternative.
5.3.4 Storage
Storage space to accommodate at least several days' or more
production of sludge should be provided at the treatment plant and
elsewhere in case transportation or labor problems prevent hauling
sludga to the landfill site. On-site storage is also desirable in case
inclement weather or other problems disrupt site operations. These
disruptions can be minimized if special fill areas close to the landfill
entrance are designated for use only during inclement weather.
5.3.5 Good Practices
Proper sanitary landfill site planning and management procedures
wiH minimize the potential for leachate formation and migration;
methane generation; and surface runoff, erosion, and siltation.
5.3.6 Sludge Quality
The physical characteristics of sludge are important for landfilling.
Sludges should be stabilized, dewatered, and mixed with bulking
agents to facilitate handling. The chemical composition of sludge is
rarely a concern. Sludge chemical characteristics are important only
if the sludges are classified as hazardous under the provisions of
RCRA. For this reason, sludges that are too highly contaminated
for other use/disposal options, but not contaminated enough to be
classified as hazardous, may be landfilled.
5.3.7 Public Acceptance
Public acceptance is a key factor in implementing a sludge
landfilling operation. Public concerns over landfilling generally
focus on potential odors, land values in the neighborhood,
increased traffic, and the potential for groundwater contamination.
Tho closer the landfill is to residential or commercial areas, the
greater will be the level of public concern. To mitigate public
concerns, residents should be involved in the siting, planning, and
design of the landfill. The bulk of public involvement should be at
the beginning of the planning process. Although early input may
cause some project delays, it will help minimize public opposition in
later planning stages which can be both lengthy and expensive.
42
The importance of public acceptance of landfilling may be
particularly critical if a community must periodically develop new
landfill sites. In that case, public acceptance will be an ongoing
issue.
Figure 16 illustrates several basic design features that can help gain
public acceptance. The fill areas avoid the stream and pond.
Groundwater and surface water monitoring stations are in place,
and gas control/venting trenches protect the on-site building.
Woods visually shield the landfill from the road, railroad, and local
residences, and buffer other nuisance effects, such as dust, noise,
and odor. The prevailing winds also tend to blow any odors away
from the road and inhabited areas.
5.3.8 Transportation Requirements
Transportation of sludge from the treatment plant to the site must
be considered from both an economic and a practical standpoint.
The costs of sludge hauling can be a major contributor to the costs
of landfill operations.
Prevailing Wind
Woods
Surface Water Monitoring
Groundwater Monitoring
Qas Control Venting Trenches
\//\ Operational Facilities'
•fj- Residences
= Road
-t—i- Railroad
Stream
Figure 16. Schematic of a Typical Landfill Site in Relation to the
Surrounding Environment
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LANDFILLING
Transport vehicles should be leakproof and should be able to dump
sludge easily. Large, enclosed vehicles, such as concrete mixers,
have been used. Specialized trucks may not be needed; often,
municipalities already have adequate vehicles for sludge transport
within their existing fleet.
The most appropriate transportation route should be considered
from the standpoint of traffic congestion and public acceptability.
In addition, the public roads along the route must be able to
accommodate the weight and number of trucks required.
5.3.9 Energy Usage
The primary energy inputs into landfilling are fuel for sludge
transport from the treatment plant to the landfill site, for the heavy
equipment used in landfilling and, if necessary, for operation of
dewatering equipment.
5.3.10 State and Federal Regulatory Approval
The same general Federal regulations that govern land application
of sludge (see Chapter 3) also govern sludge landfills. State
regulations for sludge landfilling are more specific. Some states,
such as Minnesota and Vermont, openly discourage sludge
landfills, while New Jersey is considering a ban on the option (5).
5.3.11 Cost Factors
The major capital costs associated with sludge landfilling are:
Land acquisition
Site preparation
Equipment purchase.
The major operating and maintenance costs are:
Transportation of sludge from the treatment plant to the site:
fuel, equipment, maintenance, parts, labor
On-site operations: fuel, equipment, maintenance, parts, labor
Utilities
Laboratory analysis of water samples
Bulking and cover materials.
In general, the dominant costs for landfilling are dewatering and
transportation. These costs are interrelated. The drier the sludge,
the higher the dewatering costs but the lower the transportation
costs. As the haul distance to a landfill increases; the drier the
sludge must be for landfilling to be economical.
Aerial view of a sludge-only narrow trench landfill in Lake County,
Illinois. Completed, covered cells that are being revegetated with
grass can be seen in the upper right. The working area, where new
trenches are being dug and filled, is the striated area, center left.
5.4 Case Study
The North Shore Sanitary District (NSSD) of Lake County, Illinois,
treats wastewater from 11 municipalities and unincorporated areas
(approximately 230,000 people) and two major military bases at
three advanced wastewater treatment plants and one pretreatment
facility. The advanced treatment plants consist of conventional,
primary, and secondary waste-activated sludge systems, followed
by biological nitrification and sand filtration. One of the advanced
treatment plants has capabilities for anaerobic digestion of sludge.
Sludges from all plants are pumped or hauled to one plant, in
Waukegan, where they are conditioned with lime and ferric chloride
and dewatered to at least 20 percent solids. The dewatered sludge
is then transported 16 km (10 mi) in standard 30-cubic-yard (23-m3)
dump trailers to the sludge-only landfill.
During 1982 to 1983, NSSD treated over 68.9 million m3 (18.2 billion
gal) of wastewater (about 20 percent industrial effluent), producing
136,000 m3 (36 mil gal) of liquid sludge. Of that, 128,700 m3 (34 mil
gal) were dewatered, producing over 36,000 wet mt (40,000 wet
tons) or about 9,000 dry mt (10,000 dry tons) of sludge. The
dewatered sludge was transported in 2,700 trailer trips to the
landfill. The remaining 7,600 m3 (2 mil gal) was digested sludge that
was not dewatered, but was directly injected into surrounding
agricultural land.
5.4.1 History
Before the NSSD landfill was implemented, sludge was treated and
disposed of in several ways: lagoons, sand drying beds, trucking
out of the district for disposal, and land application within Lake
County. None were satisfactory long-term solutions.
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LANDFILLING
In the late 1960s, four methods of sludge use/disposal were
considered:
• Incineration.
• Land application of digested dewatered sludge on cropland,
followed by discing or plowing.
» Land application of digested liquid sludge on cropland by
irrigation.
• Landfilling.
On the basis of cost evaluation studies and what was
environmentally acceptable to local and state governments,
landfilling appeared to be the best alternative. Incineration was
ruled out, Fn part because of concern about how stringent the
ultimate air quality standards would be. Expanding the land
application program was not feasible.
Potential landfill sites were selected on the basis of short-haul
distances of about 15 km (10 mi) from the dewatering facility,
availability of land for purchase, and greatest public acceptance.
The final site selected was 114 ha (282 ac) with 81 ha (200 ac)
suitable for landfill operations. The soils consisted of 0.5 m (2 ft) of
topsoil, followed by 6 to 7.5 m (20 to 25 ft) of silty clays, and finally
2 to 4.5m (6 to 15ft) of tight, blue clays. NSSD, its consultants,
the Lake County Soil and Water Conservation District, and the
U.S. Department of Agriculture's Soil Conservation Service
developed a plan for site preparation and use that met the
requirements of the State of Illinois "Rules and Regulations to
Refuse Disposal Sites and Facilities." In addition, the plan included
the following requirements:
• Maintain a 45-m (150-ft) buffer between sludge deposits and
adjacent residential properties or state highway.
» Landfill only dewatered sludge conditioned with lime and ferric
chloride.
» Install 10 groundwater monitoring wells at state-approved
locations, and monitor for 22 contaminants annually and
5 contaminants quarterly.
• Install gas monitoring wells at state-approved locations, and
monitor for methane, carbon dioxide, and oxygen.
Other design considerations included:
• Relatively low-solids sludge (20 percent).
• Adequate protection of the existing, potable aquifer.
» Soil stability for trenching operations.
• Maximum use of the site acreage.
There were no major public acceptance problems. People living
near the landfill site were apprehensive when the project began.
Because of the control and care taken by the NSSD with regard to
safety, odor control, and appearance, these fears were virtually
eliminated.
5.4.2 Landfill Operation
The NSSD landfill consists of a series of trenches, each about
4.5 m wide and 245 m long (15 ft by 800 ft). Each trench is dug
with a backhoe and filled in sections, called cells, that are 15 to
55 m (50 to 180 ft) in length. A minimum of 3 m (10 ft) of
impervious clay is maintained between the bottom of a trench and
any continous water-bearing strata.
During fill operations, temporary protective berms built from
excavated trench material (trench spoil) prevent surface runoff from
entering the cells. A final 1.5-m (5-ft) layer of soil covers each cell.
When a fill area is complete, the area is graded and grassed. If a cell
settles after a few years, additional soil is added and the area
regrassed.
Sludge is generally deposited in 0.5-m (2-ft) layers and covered with
0.3 m (1 ft) of trench spoil. Although the percent solids is
maintained above 20 percent, small variations in sludge consistency
cause large changes in its ability to support cover. Because of this
phenomenon, the depth of sludge and the quantity of spoil used to
cover it become critical, and those are left to the judgment of the
site operator. To date, monitoring has not detected any
contamination of ground water in on-site wells.
5.4.3 Costs
The annual costs for NSSD landfill operations, based on fiscal year
1982-1983 and a sludge production rate of about 9,000 dry mt/yr
(10,000 dry tons/yr), are summarized in Table 12.
5.4.4 The Future
The landfill was started in 1974 with an anticipated lifespan of
20 years. In mid-1984, the capacity of the site was about half used
and the initial estimate of lifespan appeared to be correct.
The NSSD is considering several options for land use after site
closure, including:
• Silviculture. For example, hybrid poplars could be grown to
provide wood chips for possible future sludge composting
programs.
• Recreational facilities, such as a park, golf course, or forest
preserve area.
• Agriculture.
Although the landfill site still has about 10 years of operation,
future sludge use/disposal options are under investigation. NSSD's
options include:
• Continuing present landfilling practice.
• Initiating projects such as:
- expanded use of liquid sludge
- pilot sludge cake surface incorporation
- pilot compost operations.
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LANDFILLING
Table 12. North Shore Sanitary District Costs for Fiscal Year 1982/83
Summary:
$/dry mt $/dry ton
Dewatering
Hauling
Landfill
capital
Landfill O&M
Total
Dewatering sludge:
$/dry mt $/dry ton
Labor $ 32.42 $ 29.47
Chemicals 25.01 22.74
Allocated
overhead 21.87 19.88
Supplies 11.28 10.25
Depreciation 5.84 5.31
Electricity 2.32 2.11
Fuel 1.83 1.66
Misc. direct
costs 0.09 0.08
Total $100.66 $ 91.50
$100.66 $ 91.
53.08 48.
.50
.25
5.45 4.95
57.10 51,
$216.29 $196.
,91
,61
Hauling dewatered sludge:
Labor
Allocated
overhead
Transpor-
tation
Supplies
Depreciation
Misc. direct
costs
Total
$/dry mt
$ 32.62
15.02
4.42
0.66
0.35
0.01
$ 53.08
$/dry_ton
$ 29.65
13.65
4.02
0.60
0.32
0.01
$ 48.25
Economically, the NSSD's present practice of landfilling dewatered
sludge remains their most cost-effective use/disposal method.
However, at the time the NSSD acquired the landfill site, the
average cost of land was $4,940/ha ($2,000/ac). A recent survey of
available land indicated costs of $14,820 to $24,700/ha ($6,000 to
$10,0007ac). If landfilling continued to be their sludge disposal
optipn, an additional 185 ha (460 ac) would have to be purchased in
1990 at a projected cost of $3,722,000. Thus the availability of
suitable land at a reasonable cost would be an important factor.
Further information on this case history is available in
reference (28).
Landfill capital3:
Landfill O&M:
$/dry mt $/dry ton
$/drymt $/dryton
Land $ 2.48
Site prep-
aration 1 .80
Monitoring
wells 1.17
Total $ 5.45
$ 2.25
1.64
1.06
$ 4.95
Allocated
overhead
Labor
Vehicles & fuel
Materials &
supplies
Depreciation15
Maintenance
Equipment
rental &
services
Utilities
Miscellaneous
Total
$ 14.37
13.52
10.71
7.25
5.32
2.62
2.56
0.73
0.02
$ 57.10
$ 13.06
12.29
9.74
6.59
4.84
2.38
2.33
0.66
0.02
$ 51.91
a Initial capital expenditures are divided by the total amount of sludge received
over the life of the site.
b Equipment costs were depreciated on a straight-line basis for 10 years for
heavy equipment and 6 years for automotive.
CSOURCE: Reference (28).
45
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6. Incineration
6.1 Introduction
6.1.1 What Is Incineration?
Incineration is the burning of volatile materials in sludge solids in
tho presence of oxygen. Strictly speaking, incineration is not a
sludge disposal or use method, but a treatment method that
converts sludge into an ash, which is then disposed of or used.
Nevertheless, because incineration drastically reduces the volume
and mass of residual solid materials, it has traditionally been
regarded as a disposal method, and is evaluated alongside land
application, distribution and marketing, landfilling, and ocean
disposal as a use/dispbsal option. Additional information on sludge
Incinerator design can be found in reference (4).
Other thermal processes for the destruction or treatment of sludge
exist, but only incineration is in wide use today. Starved-air
combustion—the burning of sludge in insufficient oxygen to
completely degrade the sludge constituents—may eventually enable
substantial reductions in fuel usage and particulate emissions
compared to incineration, but is only now being introduced on a
plant scale. Coincineration—the burning of municipal sludge and
refuse together—has been employed in full-scale projects but, with
few exceptions, has proven impractical. In contrast, incineration is
a proven sludge disposal technique, and is currently used on
25 percent of the nation's wastewater sludge (29).
Recent experience with applying the latest in energy recovery
technology and efficient operating techniques to wastewater sludge
incinerators, including older incinerators, has shown that
incineration can be an affordable and competitive sludge disposal
alternative under the right circumstances. Details of some of these
techniques are included in the case study of Hartford, Connecticut
(Section 6.4). Similar experiences in retrofitting older systems as
well as in designing new systems are in references (29,30,31).
Wastewater sludge incinerators.
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INCINERATION
6.1.2 Advantages and Disadvantages
Incineration offers significant advantages over other use/disposal
options: it reduces the sludge to a compact residue consisting of
about 20 percent of the original volume of the sludge solids, and it
eliminates some potential environmental problems by completely
destroying pathogens and degrading many toxic organic chemicals.
Metals, however, are not degraded, but are concentrated in the ash
and in particulate matter entrained in the exhaust gases generated
by the process. High-pressure scrubbers or other pollution control
devices are needed to prevent degradation of air quality, and
appropriate means of ash disposal may occasionally be difficult to
find.
A major potential problem with all incineration systems is
operational reliability. Because incineration is much more highly
mechanized than other sludge use/disposal alternatives, it is
particularly subject to varying sludge quality and quantity,
equipment failure, and operator error. Inconsistent quality of sludge
feed, poor maintenance, and insufficient operator training can
greatly increase the frequency of these problems and,
consequently, the expense of sludge incineration. Although many
municipalities are successfully operating sludge furnaces, many
others have had to shut down operations due to repeated
equipment breakdowns and operating costs much higher than
originally predicted.
Municipalities that may wish to consider incineration include those
where:
• Surrounding land is unsuited to landfilling or land application.
• There is strenuous local opposition to other alternatives.
• State and local regulations impose stringent requirements on
other alternatives.
• The sludge contains high levels of pathogens or organic
chemicals that interfere with the use or disposal of sludge by
other methods.
6.2 Process and Performance
When sludge is burned in incinerators in the presence of sufficient
oxygen, the flammable constituents are converted to their basic
chemical components (mainly carbon dioxide and water). A
conceptual diagram of incineration is provided in Figure 17.
Three factors determine how much energy must be added to the
incineration process or, in a few cases, how much excess energy
can be recovered from the process. These three factors are the
thermal content of the sludge, the amount of excess air (above the
theoretical minimum required for combustion) required, and the
water content of the sludge. High thermal content, low rates of
excess air use, and low percentages of water in the sludge make
incineration more energy efficient and economical.
Sludge with a high thermal content burns readily with reduced
supplementary fuel and requires less dewatering to burn
autogenously (i.e., burn by itself with no supplementary fuel). The
thermal content of the sludge depends largely on the sources of the
wastewater, but can be lowered during treatment by such
processes as inorganic chemical conditioning, which adds large
quantities of material with no fuel value to the sludge. Sludges
containing large amounts of grease or oil generally have a high
thermal content; burning such materials has sometimes produced
higher temperatures than the incinerator was designed for.
Dry raw sludge solids typically are comparable in fuel value to
low-grade coals, wood, and municipal refuse, with typical heat
values of 1,700 to 5,000 kilo Joules per dry kg (kJ/dry kg [5,000 to
16,000 British Thermal Units (BTU) per dry Ib]). Table 13 compares
the heat values of several sludge materials against various fuels. In
order to burn without auxiliary fuel, sludge usually must contain 25
to 35 percent solids, a level that is achievable with some sludges
through conventional mechanical dewatering.
Conventional sludge incineration systems use 20 to 150 percent
excess air above the theoretical amount needed because it is
virtually impossible to ensure complete and even mixing of air and
sludge. In the absence of energy recovery equipment, the heated
air exits at high temperatures and represents a significant energy
drain on the system. The amount of excess air required is partially a
function of the type of system chosen, but is also highly dependent
on operating procedures. Well-trained operators and appropriate
process controls can significantly lower the amount of excess air
required, resulting in reduced costs. For example, decreasing
excess air flow from 100 percent to 20 percent can cut the use of
auxiliary fuel by almost half.
Nearly all the auxiliary fuel used in incineration goes to evaporate
water from the sludge. The need for auxiliary fuels can be greatly
reduced by efficient dewatering. At 25 to 35 percent solids, most
sludges will burn without supplementary fuel.
Table 13. Typical Heat Values for Several Sludge Materials
and Various Fuels
Heat value
Materials
Sludge material:
Grease and scum
Raw sludge solids
Digested sludge
Fuels:
No. 2 oil
No. 6 oil
Natural gas
Bituminous coal
Wood (air-dried)
Refuse-derived fuel
Dry solids
combustibles (%)
88.5
74.0
59.6
—
—
—
_
—
—
kJ/kg
dry solids
5,400
3,350
1,720
6,390
5,700
7,430
4,430
1,790
2,440
BTU/lb
dry solids
16,700
10,285
5,290
19,600
17,500
22,800
13,600
5,500
7,500
SOURCE: References (32,33).
47
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INCINERATION
Gas Exhaust
Shaft Cooling Air Discharge
Shaft Cooling
Air Return
Sludge
Food
Precooler
and Venturi
Furnace
Exhaust
Shaft
Cooling Air
Boiler
Exhaust
Recoverable Heat
Auxiliary
Fuel
Heat Radiation
Wet Scrubber
Scrubber
Water
Drain
Precooler and
Venturi Water
Combustion Air
Connected Power (Input to All Components)
Ash
Discharge
Flguro 17. Flowsheet for Multiple-Hearth Sludge Incineration Furnace
The sludge solids content also affects the loading rates of the
system, which fn turn influences system efficiency. Although
dowatcring Is expensive, it can substantially reduce the overall
costs of Incineration both by reducing fuel consumption and by
reducing the volume of sludge to be burned, thereby reducing the
size of the incinerator needed (see Section 6.4). Dewatering also
reduces emissions by reducing the amount of excess air used
during incineration and by reducing the amount of steam in the
exhaust gases. The reduction in excess air usage means that fewer
particulates will be entrained. Furthermore, since steam may entrap
organic compounds from the sludge and carry them into the
exhaust gases, steam reduction reduces the amount of toxic
organics present in the off-gases.
-------
INCINERATION
There are three basic approaches to removing water from the
sludge in incineration systems:
• Chemical and/or thermal conditioning and dewatering before
incineration.
• Burning additional fuel during incineration.
• Using heat from exhaust gases to dry incoming sludge or
preheat incineration air.
Many types of incinerators have been developed, but only two—the
multiple-hearth furnace and the fluidized-bed furnace—are widely
used in the United States. Other less widely used incineration
processes include single-hearth cyclonic furnaces, electric furnaces,
and rotary kilns. The relative use of different types of incineration
facilities is shown in Figure 18.
6.2.1 Multiple-Hearth Furnace
The multiple-hearth furnace (MHF) is the most commonly used
sludge incineration system. It is durable, simple to operate, and
tolerant of variations in sludge quality and loading rates. The MHF
consists of a cylindrical, ceramic-lined steel drum, from 1.4 to 8.8 m
(4.5 to 29 ft) in diameter, containing 4 to 14 horizontal hearths
(Figure 19).
Sludge enters the furnace near the top and is pushed alternately to
the center or the periphery of each hearth, where the sludge drops
Fluidized-Bed
Facilities
12%(22)
Multiple-Hearth Facilities
81% (150)
SOURCE: Reference (29).
Fish-eye view inside one hearth of a multiple-hearth furnace.
Sludge drops into this hearth from the periphery of the hearth
above and is shunted by the rabble arms into the center, where it
drops down to the hearth below.
Cooling Air Discharge
Floating Damper
Discharge
Combustion
Air
Sludge-Feed
Auxiliary
Fuel
Rabble Arm
. at Each Hearth
' Solids Flow
Cooling Air
Return
Rabble Arm Drive
Figure 18. Relative Prevalence (and Numbers) of Sludge
Combustion Facilities Operating in the United States
Figure 19. Cross-Section of a Multiple-Hearth
Sludge Incineration Furnace
49
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INCINERATION
down to the next hearth. Incineration takes place on the middle
hearths, where temperatures generally range from 769°C to 816°C
(1,400°F to 1,500°F) (4). The hot gases from incineration rise
through the upper hearths, drying the incoming sludge before it
drops to the hearth where combustion takes place. After
incineration, ash is pushed onto still lower hearths where it cools,
giving off heat to incoming air.
Tho MHF has several disadvantages. For instance, to avoid
cracking the ceramic lining, MHFs must be heated or cooled very
slowly, which makes them impractical for intermittent use. Some
communities use the MHF for intermittent sludge flows by burning
supplementary fuels during slack times, but this is also costly.
Another strategy is to store sludge until enough has accumulated
to justify a period of continuous operation, but this requires
invostment in storage facilities and presents manpower scheduling
problems.
Also, because hot exhaust gases are used to dry incoming sludge,
they may pick up toxic volatile organics, hydrocarbons, or odorous
compounds. The temperature of the exhaust gases at this point is
not high enough to destroy these compounds, and they may need
to be removed from the exhaust gases prior to release. Gas removal
Is accomplished with an afterburner, which raises the temperature
of the exhaust gases momentarily to 800°C (1,472°F), thus
destroying the organic substances. The use of an afterburner can
ralso fuel and capital costs significantly. Another disadvantage of
MHFs is that they usually require more excess air than other
incinerators, raising fuel costs still further. This disadvantage can
be avoided by careful operation. Under strict operating practices
(sea Section 6.4) the amount of excess air required can be reduced
to as low as 20 percent above the theoretical minimum.
6.2.2 Fiuldized-Bed Furnace
The fluidized-bed furnace (FBF) is the other commonly used type of
incinerator. Consisting of a vertical, ceramic-lined, steel drum, the
FBF contains a sand bed into which air is injected, expanding the
bod and reducing its density to the point where it responds as a
fluid. The temperature of the bed is maintained at between 769°C
and 816°C (1,400°F and 1,500°F). Sludge is fed either directly into
the bed or just above it, and ash, some sand, and stack gases exit
through the top of the unit (Figure 20). The exhaust gases can be
used to indirectly preheat incoming incineration air through a heat
exchanger.
Because of the high exit temperature of the gases, odorous
compounds and toxic organic compounds are usually destroyed in
tha incineration chamber, and no afterburner is needed. However,
pollution control devices are necessary to remove sand, ash, and
heavy metals from the stack gases. Use of too much air blows
excess sand and incomplete incineration products into the
off-gases. Ordinarily, sand losses from the bed are about 5 percent
of bed volume for every 300 hours of operation. The dust content
of the untreated stack gases can be as high as 200 grams/m3.
The FBF requires only 20 to 45 percent excess air; thus, for the
same exit gas temperature, the FBF is more fuel-efficient than all
but the best-run MHFs. Additionally, use of stack gases to preheat
the incoming air can lower fuel costs up to 61 percent. The heat
storage capacity of the sand bed itself allows for quick startup after
relatively short shutdowns (i.e., overnight). Finally, the FBF has
approximately three times the incineration capacity of a similarly
sized MHF; however, capital cost estimates for the same sludge-
burning capacity are comparable. In current practice, the FBF
furnaces are more frequently chosen for smaller plants, whereas
larger plants use MHFs.
Although the FBF is conceptually simple, contains few moving
parts, and is relatively easy to operate, there have been problems
with breakdowns of temperature controls, jamming of sludge
injection equipment, and sand damage to pollution control devices.
Sludge
Feed
Air Inlet
Exhaust Sand and
Ash Discharge
Auxiliary
Fuel
Figure 20. Cross-Section of a Fluidized-Bed
Sludge Incineration Furnace
50
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INCINERATION
6.2.3 Ash Disposal
Ash disposal is the last step in the incineration process. Because
incinerator ash is sanitary, odorless, and free from toxic organic
chemicals, its disposal may be less complicated than the disposal of
the sludge itself. The ash often contains heavy metals, which are
generally immobilized in soils due to the high pH of the ash. In only
a few cases has the metal content of the ash caused problems in
finding a final disposal site. For example, Salem, Massachusetts,
chose to cease incinerating its sludge because of high chromium
levels in the wastewater discharges by the large local tanning
industry. The chromium was converted to hexavalent chromium
during incineration. Ash from this process failed to meet the criteria
of the EP test (see Section 2.3) and was required to be treated as a
hazardous waste.
Incinerator ash can be applied to land as a soil conditioner, where it
can take the place of phosphate and ground limestone
supplements. The ash can also provide necessary trace metals to
the soil. Other uses of ash, such as addition to soil to improve the
freeze-thaw characteristics of road grades or to partially replace
sand in cement manufacturing, have been tried on an experimental
basis. Ash from some communities has been evaluated as an ore
for gold and silver recovery (34).
6.3 Key Parameters
6.3.1 Sludge Treatment Requirements
Because the water content of the sludge is one of the most
important factors in determining incineration costs, dewatering is
an essential part of modern incineration systems.
Stabilization, however, is unnecessary since incineration destroys
pathogens, and is undesirable since it reduces the thermal content
of sludge. In some areas the digester gases, from stabilization are
used as an auxiliary fuel in incineration or in other plant operations,
in which case the energy penalty of stabilization is reduced.
Stabilization also reduces sludge mass, which reduces the capital
cost of the facility and provides a sludge which is easier to dispose
of when the incinerator is out of service. ;
6.3.2 Community Size
Larger municipalities can often absorb the capital costs of
incineration systems. Furthermore, because incineration systems
are more efficient when operated continually, a large volume of
waste is necessary for economical incineration. Some small
communities have achieved continuous incineration by storing
several weeks' worth of sludge and then burning it in a relatively
short period of time; however, larger incineration facilities
historically have been more successful than smaller ones (see
Figure 21).
NG INCINERATION FACILITIES
at o
0 0
I i
F OF OPERAT
D
T
Vc
s
he bars represent the percent of incineration
srious size categories that were operating as
OURCE: Reference (29).
\ ••
%;. *" ^
\ ^
/ '
y ,>
faciiitie
of 1983
""i"""!
^ .. \
f /'
s w
thin
• \? *<
;% s \
\ ^\
g 0-1 1-5 5-10 10-25 25-50 50 +
g: SIZE OF WASTEWATER TREATMENT PLANT (mil gal /day')
°- 1 million gallons/day = 3,785 m3/day
Figure 21. Success of Incineration by Plant Size
6.3.3 Land Requirements
Very little land is required for the incinerator itself; however, land is
required for the ultimate disposal of the incinerator ash. The mass
of ash is about 15 or 20 percent that of the dry solids in the original
sludge, or higher if inorganics are used in dewatering.
6.3.4 Storage
Incineration is not weather dependent and can be carried out year
round, so extensive sludge storage is not required. Often the
storage capacity provided by thickening and dewatering steps is
sufficient for the entire system. However, since incinerator repairs
may take days or weeks if parts are not inventoried, it is essential to
have backup storage capacity, a backup incinerator, or an available
alternative use/disposal method, if adequate storage is not
provided.
6.3.5 Good Practices
Good operating practices are often the key to successful sludge
incineration. Perhaps the single most important factor in good
practice is thorough operator training. An operator who
understands the system and knows how to respond to an
unexpected situation in the most appropriate manner can prevent
damage from excessive temperatures or rapid temperature change,
can conserve fuel usage, and can keep pollutant emissions low.
Even highly trained operators, however, will be helpless without
appropriate instrumentation with which to monitor the situation
inside the incinerator. Such instrumentation is not necessarily
expensive. By monitoring and manipulating the flow of air and the
51
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INCINERATION
temperature at different hearths within the incinerator, an operator
can optimize system efficiency by controlling where combustion
takes place within the furnace. Provision should also be made for
monitoring of stack emissions from the facility and correlating them
to operating variables such as scrubber pressure drop and the
oxygen content of the off-gases.
Finally, consistent and conscientious maintenance is also crucial to
tho proper operation of incinerators. In the absence of good
maintenance practices, efficiency and effectiveness decline, and
operating costs rise.
6.3.6 Sludge Quality
Many of the pathogens and toxic organic chemicals that must be
carefully managed when sludge is land applied or landfilled are
destroyed during sludge incineration. Metals, such as cadmium and
load, are not destroyed, however, and are associated with the ash
and fine particulates in the stack emissions. In modern incinerators,
tho paniculate content of stack emissions can be easily reduced to
the levels required by EPA regulations (see subsections 6.3.3 and
6.3.10). However, cadmium and lead tend to be associated with
fine particulates, which are not as efficiently removed by the high
pressure scrubbers as large particulates (35). Cadmium and lead
stack emissions are under continuing regulatory review.
Mercury Is another metal that may occur in sludge. It is currently
controlled as a hazardous air pollutant because, unlike cadmium
and lead, it is considered to be completely volatilized within sludge
incinerators.
Tho metals in sludge incinerator ash are rarely of concern. In a few
Instances, however, state regulations may require that ashes with a
high metal content be treated as a hazardous waste. In these cases
the cost of ash disposal may be very high.
6.3.7 Public Acceptance
Gaining public acceptance of sludge incinerators requires assuring
adequate air quality impacts and acceptable costs.
6.3.8 Transportation Requirements
If an incineration facility serves several wastewater treatment
plants, transportation of sludge to the facility may be an important
factor. Provisions must be made for the additional traffic from these
transfers.
If the Incineration facility is located at the wastewater treatment
plant, as Is often the case, transportation requirements will be
limited to transporting the ash for land application or landfilling.
6.3.9 Energy Usage
Fuel usage is generally the primary operating cost of an incineration
system. The amount needed depends on the water content of the
sludge, the efficiency of the particular system, volatile sludge solids
content, the cost of fuel, and operator skill. Energy is required in
every step of the incineration process:
• Sludge dewatering prior to incineration.
• Auxiliary fuel during incineration.
• Heating of incineration air prior to use.
• Operation of air pollution control equipment.
• Transportation of sludge to the facility and ash to an ultimate
disposal site.
Electrical requirements for incinerators vary between 14,000 and
90,000 kilowatthours (kWh) per dry ton of daily capacity. The lower
amount is for a multiple-hearth unit, and the higher amount for a
fluidized-bed incinerator.
Fuel requirements for sludges containing 20 percent solids are
about 13.7 x 103mJ (13 million BTU), or about 341 I (90 gal) of fuel
oil.
6.3.10 State and Federal Regulatory Approval
Incineration of municipal sludge is regulated under the Clean Air
Act (CAA). The cornerstone of the act is a set of National Ambient
Air Quality Standards (NAAQS) for specific pollutants. The CAA
also specifies particular technological requirements that must be
met regardless of whether emission controls are necessary to meet
specific air quality standards.
There are national ambient air quality standards for six pollutants:
• Ozone
• Total suspended particulates
• Sulfur oxides
• Lead
• Nitrogen dioxide
• Carbon monoxide.
Parts of the country that do not meet one or more of these
standards are designated as nonattainment areas. Sludge
incinerators contribute primarily to ambient paniculate loadings.
Figure 22 shows the locations of nonattainment areas for
particulates as of 1982.
Before a new incinerator can be built in a nonattainment area,
emissions offsets greater than or equal to the increment in
emissions that the new incinerator would cause must be
demonstrated. Often these offsets can be found on site. For
example, a major wastewater treatment facility in Los Angeles was
able to acquire sufficient offsets simply by replacing diesel engines
located on site with lower emission turbines.
52
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INCINERATION
Incinerators constructed or significantly modified since June 11,
1973, are subject to additional regulation under the New Source
Performance Standards, which limit discharge of particulates to
0.65 g/kg (1.30 Ib/ton) dry sludge input (Subpart 0, 40 CFR 60).
These standards apply to any incinerator that burns more than
10 percent wastewater sludge at a rate greater than 1,000 kg
(2,205 Ib) per day. Usually incinerators will have to use high
pressure scrubbers to meet these requirements, but some
incinerators have been able to meet the standard solely through
strict operating practices.
The emission of mercury and beryllium from sludge incinerators and
drying equipment is regulated under 40 CFR 61. However, this
regulation rarely causes concern, since most sludges have low
concentrations of these elements.
State Implementation Plans may require a facility to demonstrate
that air quality impacts will be within acceptable levels. To
accomplish this, mathematical models may be used to predict
emission levels.
SOURCE: Reference (36).
Figure 22. Designated Nonattainment Areas (Counties and Portions of Counties) for Total Suspended Particulates as of 1982
53
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INCINERATION
6.3.11 Cost Factors
Tho costs of sludge incineration are frequently higher than for other
use/disposal options. Capital, labor, and energy costs are all often
high and may be unpredictable. High capital costs are due to the
necessity for complex facilities capable of operating reliably at
extremely high temperatures. Labor costs for system operation and
maintenance may also be relatively high due to the need for skilled
personnel.
Tho major capital costs for incineration are:
Dcwatedng equipment
Incinerator
Pollution control equipment
Fuel storage facility.
The major operating and maintenance costs are:
Labor
Fuel
Replacement mechanical equipment, duct work, and fire bricks
Electric power (for dewatering operations and incinerator
mechanical power)
Transportation (for ash transport)
Landfilling or land application (for ash disposal).
6.4 Case Study
Tho City of Hartford, Connecticut, has been incinerating its sludge
since 1968. Prior to 1978, the sludge was dewatered using vacuum
filters before being fed into the multiple-hearth incinerator.
However, this process generated a sludge cake of only 13.8 percent
solids, and the plant suffered from frequent breakdowns, high fuel
consumption, and the lack of a common operating procedure used
by incinerator operators on each shift.
In 1978, Hartford initiated a major effort to reduce operating costs.
Between 1978 and 1982, new dewatering equipment and improved
operational procedures lowered fuel consumption by 83 percent,
which reduced operating costs by $1,300,000 per year.
6.4.1 Belt Filter Press Conversion
Belt filter presses were tested in 1978 and, despite numerous
mechanical problems and excessive downtime (25 percent),
produced a significantly drier sludge cake than did the vacuum
filters. The first press was installed in 1979. It paid for itself in
reduced fuel costs in only 6 weeks. By 1982, three additional
presses had been installed.
Uso of the drier sludge cake reduced fuel consumption by almost
3401 oil/dry mt sludge (82 gal oil/dry ton sludge), increased the
incineration rate (dry solids burned per operating hour) by
57 percent, and decreased the average use of incinerators by
23 percent.
6.4.2 New Incinerator Operating Mode
The dramatic success with the belt filter presses encouraged the
City of Hartford to pursue other innovative changes to further
improve their operations, so the City hired a consultant to develop -
more fuel-efficient operating procedures. Preliminary analysis of
existing incinerator operations found no standard operating
procedures. Further, several existing practices were contributing to
excessive fuel consumptions, including:
• Combustion in the wrong part of the incinerator.
• High exfiaust gas temperatures.
• Use of too much auxiliary air.
• Lack of remote operator controls for airflow dampers and
burners.
Based on operational analyses and trial tests, new operating
procedures with specific instructions and furnace operating settings
were developed. The new procedures were then demonstrated in
full plant operation for a 2-week test period. On-the-job operator
training was accomplished at the same time. After the
demonstration period, the operating procedures were standardized
for routine use.
The new operating procedures were characterized by the following
general operating guidelines:
• Maximum use of preheated combustion air.
• Lowest possible draft to minimize air leakage.
• Combustion on a low hearth within the incinerator to maximize
the drying area.
• Minimization of excess air.
T!
•8 500 -
§3
|_ (/)
| 1 400 -
| s,
pi 300-
O M
-J "S
UJ °
ID t:
u- E. 200 -
LU >•
C3 -a
<^
S S. 100-
"o
— 0
_/
-
>
•" :
f \
'\
* :
1 I oil /dry mt =
0.24 gal oil /dry ton
83%
k
Fuel
Reduction
>
t
1978 1979 1980 1981 1982
Figure 23. Average Fuel Consumption of Hartford, Connecticut,
Incinerators: 1978 to 1982
54
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INCINERATION
The specific operating instructions for the new operating
procedures were given to the incinerator operators and included
procedures for loading sludge into the furnace, incinerator control,
controlling combustion zone location, and standby and startup
operations.
The average fuel consumption using the new operating procedures
was 87.8 I oil/dry mt sludge (21.1 gal oil/dry ton) as compared to
181 I/dry mt (43.5 gal/dry ton) previously—a 51.5 percent
reduction. With this improvement, the total fuel reduction achieved
by Hartford between 1978 and 1982 amounted to 433 I/dry mt
(104 gal/dry ton) or 83 percent which, at the 1982 production level,
represented a savings of 4,075 m3 (1,076,504 gal) of No. 2 fuel oil
(see Figure 23).
In addition to reducing direct fuel consumption, the new operating
mode provided increased furnace operating flexibility, since the
incinerators could now be operated efficiently at loading rates of 50
to 60 percent of capacity. Incinerator operation is also now
characterized by cooler maximum operating temperature, more
steady state control, fewer particulate emissions, and reduced
maintenance on internal incinerator parts.
6.4.3 Cost Savings
The nominal cost savings from fuel reduction were estimated at
over $1,076,000 per year assuming a No. 2 fuel oil price of $0.26/1
($1.00/gal). Other energy savings were realized from the belt filter
press conversion. An almost 50 percent reduction in air usage
reduced the electrical energy requirements of the air compressor by
20 percent, resulting in $200,000 annual savings in electricity costs.
Also, the belt presses required less energy than the vacuum filters,
resulting in an estimated savings of $25,000 per year. Elimination of
the vacuum pumps saved $6,000 per year. The estimated operating
cost savings from belt filter press conversion and implementation of
the new incinerator operating mode totalled $1,300,000 per year.
55
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7. Ocean Disposal
7.1 Introduction
In ocean disposal, municipal wastewater sludge is released into a
designated area of the ocean, either from vessels at the ocean
surface or through outfall pipes. Currently, about 4 percent of the
municipal wastewater sludge produced in the United States is
ocean disposed. All this volume comes from several large
municipalities in the New York City metropolitan area that barge
sludge to an offshore disposal site, and from the cities of Los
Angeles, California, and Boston, Massachusetts, which discharge
wastowater sludge through ocean outfall pipes. However, pipe
discharge of sludge is not legal under the Clean Water Act and is
being phased out. For this reason, guidance on pipe discharge will
not be included in this document.
For communities near the sea, ocean disposal is a relatively
Inexpensive sludge disposal option. However, it can face the same
local public opposition often encountered when siting land-based
facilities, and it has generated great concern at state and Federal
levels.
When conducted in areas close to shore, ocean disposal can
degrade near-shore and shoreline environments; at shallow sites,
where there is little dispersion of sludge materials, sludge disposal
will degrade the local marine environment. The Marine Protection
Research and Sanctuaries Act (MPRSA) which regulates ocean
disposal, requires that the EPA select appropriate ocean disposal
sites. Attempts to find more suitable areas for sludge disposal have
recently led to a deepwater site farther offshore and away from
areas of competing ocean uses, which should allow more
environmentally acceptable disposal of sludge.
Nsw York City's tanker North River discharging sewage sludge at the 12-mile sludge dump site in the New York Bight.
56
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OCEAN DISPOSAL
7.2 Process and Performance
The barging of municipal wastewater sludge to an offshore disposal
site is currently practiced by several municipal sewerage authorities
in the New York City/northern New Jersey area. The process is
relatively simple. Self-propelled tankers or towed barges go out to
the site where the sludge is released. The sludge immediately
begins to disperse, aided by the wake of the vessel. Some sludge
constituents, such as volatile hydrocarbons, rapidly evaporate from
the water surface and are diluted in the atmosphere. Floatable
materials such as grease, oil, and scum tend to remain on the water
surface and can be transported long distances from the disposal
site by winds and currents.
The rest of the sludge material generally sinks in the ocean as an
expanding cloud, which increases in volume as it entrains
surrounding water (Figure 24). Heavy particles may sink directly to
the ocean floor independently of the cloud. The remaining cloud
may proceed directly, although more slowly, to the ocean bottom.
The extent to which sinking sludge constituents are dispersed from
the disposal area depends on local conditions, such as water depth
and currents.
In the ocean, water density often varies from the surface to the
seafloor due to changes in temperature and salinity with depth.
Even slight density gradients in the water column at a sludge
disposal site may cause sludge particles to accumulate at these
density fronts. Many contaminants, such as metals and chlorinated
hydrocarbons, tend to be associated with fine particles in the
sludge, and thus can accumulate at various depths within the water
column; the organisms that congregate in these areas have an
increased exposure to contaminants.
The fate of particle-associated contaminants that reach the seafloor
is difficult to assess. If the area is subject to major storms, currents,
or erosional processes, the particles and the associated
contaminants may disperse. In less turbulent or shallow areas,
particle-associated contaminants could gradually accumulate on the
ocean bed.
Figure 24. Generalized Schematic of the Fate of Sludge Solids Disposed of at Sea
57
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OCEAN DISPOSAL
7.2.1 Nutrients
Tho fate and effect of nutrients contained in sludge depend on local
conditions. The nutrients may result in eutrophication if sludge is
disposed of near shore or carried near shore by currents. Nutrients
may also have a biostimulatory effect in deeper waters. The
addition of nitrogen to marine ecosystems may be particularly
deleterious. Under normal conditions, nitrogen tends to be the
limiting nutrient in biomass production in the water column and in
tho benthos. Thus, surplus nitrogen could result in the increased
production of phytoplankton and other plant life, with concomitant
changes in local water quality and species composition.
7.2.2 Pathogens
Pathogens contained in ocean-disposed sludge are a potential
human-health risk. Marine organisms, especially filter feeders, can
accumulate pathogens. Shellfish are of particular concern because
many are sessile organisms that dwell on the ocean floor where the
greatest and most persistent accumulation of pathogens, metals,
and toxic organic chemicals may occur. In addition, sludge
materials discharged near shore may contaminate recreational
beaches and pose a public health hazard.
7.2.3 Metals
The effects of the metals contained in sludge on marine ecosystems
Is not well known. The accumulation of toxic metals into the food
chain is a concern because of possible health effects to man from
eating contaminated seafood. However, except for methyl mercury,
most metals do not appear to biomagnify—that is, to increase in
concentration up the food chain. Regulations specifically prohibit
the disposal of sludge containing levels of mercury and mercury
compounds that would, after initial mixing, raise on-site mercury
concentrations by more than 50 percent over background levels.
7.2.4 Organic Chemicals
A number of synthetic organic contaminants sometimes found in
sludge are persistent and have the potential for long-term effects in
tho marine environment. As with metals, food-chain accumulation
of toxic organic chemicals is a public health concern. Some organic
chemicals, such as halogenated hydrocarbons, tend to
bioaccumulate up the food chain, whereas others, such as
polycyclic aromatic hydrocarbons, degrade more readily and do not
biomagnify.
7.3 Key Parameters
7.3.1 Sludge Treatment Requirements
Tho floatable fractions of sludge should be extracted prior to ocean
disposal in compliance with regulations. This is most efficiently
done by not including sludges high in floatables (e.g., scum) in the
materials destined for ocean disposal.
Thickening and dewatering may reduce barging costs. However,
the savings in transportation costs must be weighed against the
cost of installing and operating the sludge treatment equipment. In
general, thickening and dewatering are economical when haul
distances are greater than about 160 km (100 mi) round trip.
Increasing the solids concentration may change the dispersal
patterns of the sludge.
Stabilization is not required prior to ocean disposal. However, it
reduces the odor potential of stored sludge, which is particularly
important in urban areas. By reducing the number of pathogenic
organisms, sludge stabilization also increases the number of
use/disposal options available should ocean disposal operations be
disrupted. Stabilization through anaerobic digestion also allows
methane recovery from the sludge in the digester.
7.3.2 Community Size
Barging is currently practiced only by several large communities in
the New York metropolitan area. Many large communities are
located on the seacoast and have limited access to land-based
alternatives. Their rates of sludge production are high and suited to
the capacity of vessels and the associated transportation costs. In
addition, large communities can afford the studies needed for
permitting and the monitoring programs required for ocean
disposal.
Several factors limit the feasibility of ocean disposal for small
communities. A small community often does not generate enough
wastewater sludge to fill a vessel frequently enough for efficient
operations. A small community may also find the costs of program
administration difficult to absorb. For these reasons, small
communities can only consider ocean disposal in association with
other communities.
7.3.3 Land Requirements
The only land requirements for ocean disposal might be for sludge
storage, barge docking, and loading facilities (see subsection
7.3.4).
7.3.4 Storage Requirements
Spare barges or, more likely, land and tank capacity are needed for
sludge storage during periods when the vessels are in transit and
during times when disposal operations are disrupted. Storage
requirements vary with the time between sludge hauling trips, the
holding capacity of the barges, and the rate of sludge generation.
The interval between successive trips is a function of haul distance
and vessel availability. In addition, sufficient storage should be
available to accommodate several days to several weeks of sludge
generation in the event of inclement weather, vehicle breakdown,
labor disagreements, or other conditions that could delay barge
trips. Sludge thickening, dewatering, and digestion facilities may
assist in providing sufficient storage capacity.
58
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OCEAN DISPOSAL
7.3.5 Good Practices
The most critical aspect of good practices for ocean disposal is
discharging sludge at the correct location. If sludge is discharged
elsewhere, the environmental and health effects may be greater and
monitoring these effects will be more difficult. Thus, operator
responsibility is a significant factor in the successful performance of
this disposal alternative.
Another important aspect of good practices is proper program
management. In the past, minimal program management has been
required for ocean disposal. Management will become more
complex as EPA requirements for site monitoring are intensified.
7.3.6 Sludge Quality
EPA regulations (40 CFR 227) only allow ocean disposal of sludges
which meet certain standards as demonstrated by several different
tests. For example, sludge must be evaluated in tests to
demonstrate the absence of undesirable floatable materials and to
characterize the waste's physical properties, such as density and
solids content. Mercury, cadmium, oil, and grease must be below
levels which have undesirable effects on the ecosystem through
either toxicity or bioaccumulation. After sludge disposal, synthetic
organic chemicals must become diluted to concentrations below
marine water quality criteria (where they exist). Organic chemicals
that are immiscible or slightly soluble in seawater cannot exceed
concentrations above their solubility limits. Regulations require
tests to examine the fate of pathogenic organisms in sludge, and to
assess the toxicity of the waste and the bioaccumulation of certain
sludge contaminants up the marine food chain.
Failure of a sludge to pass these environmental tests does not
automatically preclude ocean disposal. If a municipality can
demonstrate that ocean disposal poses the least amount of
environmental degradation of all the available sludge use/disposal
options, an ocean disposal permit may be granted (see subsection
7.3.10).
7.3.7 Public Acceptance
Ocean disposal generally has more favorable public acceptance
than land-based sludge use/disposal alternatives. Any opposition to
disposal at a specific site is usually encountered during site
designation (see subsection 7.3.10) when conflicting site uses, such
as fisheries or recreation, must be resolved.
7.3.8 Transportation Requirements
Sludge must first be transported from the treatment plant to the
vessel loading facility. In a coastal community, these may be very
close or at the same location. However, for an inland town,
overland sludge transport would be an important consideration.
Sludge is hauled to the disposal site either by self-propelled tankers
or in standard bulk container barges that are hauled by tugboats.
7.3.9 Energy Usage
The primary energy requirement of ocean disposal is fuel
consumption by the tugboats or self-propelled vessels.
7.3.10 Regulatory Approval
Federal controls on ocean disposal were instituted in the early 1970s
under the Clean Water Act and the Marine Protection Research and
Sanctuaries Act (MPRSA). Regulations promulgated under
MPRSA define the circumstances under which the EPA will grant a
permit for ocean disposal of sludge. This is the only instance in
which the EPA becomes directly involved in sludge management
planning.
The regulatory structure of the MPRSA consists of two phases:
(1) EPA designates sites for disposal of specific materials, and
(2) EPA issues permits to dispose of materials at these sites. These
regulations are currently being refined.
Site designation is based on such factors as proximity to beaches
and the effect of disposal on the marine environment. Permitting
decisions for sludge disposal are based on such factors as the
volume and characteristics of the sludge and the availability and
effect of alternative disposal methods. A permit to ocean dispose
sludge at a site is granted only if the applicant can clearly
demonstrate that no practicable alternative is available that has less
impact on the total environment. Because the long-term costs of a
degraded marine environment may be greater than the short-term
savings to municipalities, EPA does not sanction a choice of ocean
disposal based solely on economic considerations.
Shortly after the passage of MPRSA in 1972, EPA designated the
"12-Mile" Site off the New York/New Jersey metropolitan area for
use on an interim basis, but that designation expired at the end of
1981. Sludge disposal has continued at that site under court orders.
EPA has designated a replacement site. Known as the "106-Mile"
Site, it is located off the Outer Continental Shelf 217 km (135 mi)
southeast of the entrance to New York Harbor and 212 km (132 mi)
from Atlantic City, New Jersey.
EPA selected the "106-Mile" Site over the closer "12-Mile" Site for
several reasons. The primary concern was the degradation of the
quality of the New York Bight, which is the section of the Atlantic
Ocean within the bend of the coastline between Long Island and
New Jersey. Although sludge disposal is not the only cause of the
degraded condition of this area, it is a contributor to the problem,
and one that can be removed by moving the disposal site.
There is greater potential for dispersion at the "106-Mile" Site than
there is at the "12-Mile" Site. Although the "106-Mile" Site has a
permanent density stratification at about 200 m (650 ft), other
hydrographic features increase dispersion and the transport of
materials out of the disposal area. These features include prevailing
currents, and large eddies that break off from the Gulf Stream and
traverse the site about 70 days per year. The "106-Mile" Site has
been used for the disposal of various materials since 1961, and no
59
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OCEAN DISPOSAL
long-term adverse ecological effects from these activities have been
detected.
Ocean disposal is the sludge use/disposal option least favored by
EPA. The administrative and technical aspects of the permitting
process are usually difficult and costly to a municipality, although
they are still possible when ocean disposal is the preferred
alternative. The emerging Federal policy to promote the productive
use of sludge and to encourage states to assist local communities in
finding adequate land-based sludge disposal capacity will provide
capacity lost by EPA restrictions on ocean disposal.
7.3.11 Cost Factors
Ocean disposal has been a relatively low-cost sludge disposal
option. However, current and projected requirements related to
hauling sludge to deepwater sites, permitting, and site monitoring
increase the cost of ocean disposal programs. These costs tend to
make ocean disposal most feasible for large municipalities.
Other capital and operating costs associated with ocean disposal
are still relatively low, because fuel consumption during vessel
transport is low, and tugboats that may be used in ocean disposal
operations are generally rented.
60
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8. Evaluating Alternatives
8.1 Introduction
Five methods are widely employed to use or dispose of wastewater
sludge: land application, distribution and marketing, landfilling,
incineration, and ocean disposal. Their applicability to a particular
municipality depends on many factors, including the source and
quantity of wastewater sludge, geographic location of the
community, hydrogeology of the region, land use, economics,
public acceptance, and regulatory framework. Often, a community
must select and implement more than one sludge use/disposal
option, and must develop contingency and mitigation plans to
ensure reliable capacity and operational flexibility.
Determining which of the various use/disposal options is most
suitable for a particular community is a multistage process. The first
step is to define the needs—that is, to determine the quantity and
quality of sludge that must be handled and estimate future sludge
loads based on growth projections. Then alternative sludge
use/disposal options, that meet these needs and that comply with
applicable environmental regulations, must be broadly defined.
Unsuitable or noncompetitive alternatives must be weeded out in a
preliminary evaluation based on readily available information. For
example, seldom would a rural rnidwestern agricultural community
elect to ocean dispose or incinerate its wastewater sludge.
Resources are then focused on a more detailed definition of the
remaining alternatives and on their evaluation. Final selection of an
option may require a detailed feasibility study.
Several systems are available for evaluating alternatives. For
example, "Cost-Effectiveness Analysis" is used to compare
alternatives on the basis of their cost. Cost-effectiveness analysis is
essential for sludge management projects that are to be supported
with the aid of EPA's Construction Grant funding. Details of its
requirements can be found in reference (38).
One planning approach for tallying the nonmonetary and often
subjective factors is a "System of Accounts," which allows the
proposed alternatives to be evaluated from different "accounts"
(39), including:
• Compatibility with land uses in close proximity to the proposed
site.
• Energy usage.
• Recovery of resources.
• Reliability.
• Demonstrated ability to operate.
• Operating life of the facility.
In this approach, the different accounts selected for evaluation are
scored numerically to tally the comparative strengths and
weaknesses of the various alternatives. The "System of Accounts"
is a valuable tool for demonstrating the objectivity of the planning
to groups that may oppose project alternatives.
In the recent past, sludge management has had to deal specifically
with the issue of risk, and a "Risk Assessment" has been advanced
as a tool to aid local decision-making (40,41). Because of the
Sludge Treatment Requirements
Dewatering
Stabilization
Community Size
Land Requirements
Land Availability
Hydrogeology
Storage
Good Practices
Sludge Quality
Pathogens
Toxic Organic Chemicals8
Metals
Nutrients
Public Acceptance
Odors, Aesthetics
Traffic
Transportation Requirements
Energy Usage
State and Federal
Regulatory Approval
Cost Factors
a Based on the most current EPA
information; however, assessmer
impact continue.
b Heavily influenced by transportat
costs.
CD
._ ZC Z
g oC g o
.§ I! i i ii
-------
EVALUATING ALTERNATIVES
difficulty In collecting the data needed for such an assessment, and
tha difficulty In making needed assumptions and interpreting the
results of the analyses, risk assessment is only recommended for
large-scale planning processes.
Preparing for implementation involves securing permits; financing;
contracting; demonstrating to regulatory agencies compliance with
environmental standards; and verifying that the project meets
program design expectations.
Chapters 3 through 7 of this guidance document describe the five
major sludge use/disposal options individually and discuss the key
parameters that affect their implementation. These parameters are
summarized for comparison in Figure 25. This chapter provides a
basis for a preliminary comparison of the options through a broad
overview of the key parameters. However, each community must
ultimately tailor its evaluation strategy to meet its local needs and
conditions. Reference (42) provides additional guidance.
Although the emphasis of this guidance document is sludge
use/disposal, sludge management actually encompasses a series of
activities, starting with the production of sludge in wastewater
treatment, continuing through sludge treatment and transportation,
and ending with sludge use/disposal, the treatment process and
transportation options and requirements for the five use/disposal
options are shown in Figure 26. Ideally, these processes should be
selected and designed as a unit to optimize efficiency and cost
effectiveness. However, this can only be done under ideal
situations. Municipalities usually have parts of a sludge
management system already in place, and this will influence their
selection of new or additional processes. Clearly, the possibility of
replacing or modifying existing wastewater and sludge treatment
facilities should not be overlooked, since it may result in long-term
cost savings and more acceptable sludge management.
8.2 Key Parameters
8.2.1 Sludge Treatment Requirements
Sludge use/disposal options require some form of prior sludge
treatment: thickening, stabilization, conditioning, and dewatering.
The costs of treatment can be significant. To illustrate this, typical
costs for anaerobic digestion and dewatering processes are
provided in Figure 27. These costs assume no prior processing of
the sludge before it enters the stated treatment process.
Sludge Type
Primary
Secondary
*•*•*
Tortlary
Sludge Treatment
Thickening Stabilization Dewatering /Drying
Gravity
Flotation
A0A«*
Anaerobic Digestion
• n
Aerobic Digestion
• ••
Lime Treatment
• D
Composting
Filter Press
A+H
Belt Press
A**B*
Drying Beds
Centrifuge
Vacuum Filter
Heat Drying
Transportation
Rail
Truck
• *•
Pipeline
Barge
*
Key
Q Land Application
A Distribution
^ and Marketing
• Landfilling
A Incineration
*jf Ocean Disposal
Rgure 26. Typical Sludge Treatment and Transportation Processes Used Prior to Sludge Use/Disposal Options
62
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EVALUATING ALTERNATIVES
These costs do not include costs for
chemical conditioning, which typically
range from $5 to $30/dry mt.
1 mt = 1.1 tons
a SOURCE: Reference (43).
20-
20
40
60
80
100
RAW SLUDGE GENERATION
(dry mt/d)
Figure 27. Typical Costs for Anaerobic Digestion and Dewatering
as a Function of Sludge Generation
Sludge treatment processes, however, produce sidestreams which
must be treated to remove contaminants prior to discharge.
Sidestreams are generally reintroduced to the wastewater stream
entering a treatment plant. Treatment of solids in the sidestreams
may represent a large additional load and a considerable expense to
the wastewater treatment system. Thus, the impacts of any new
sidestream on wastewater treatment facilities must be considered
when evaluating the merits of a new or additional sludge treatment
process.
8.2.2 Community Size
The economics of sludge management are highly influenced by the
size of the municipality. Wastewater treatment plants and the
communities they serve can be divided into three categories based
on the volume of wastewater inflow: small plants that process less
than 1 million gallons of wastewater per day (1 mgd)a, medium
plants that process between 1 and 10 mgd, and large plants that
handle more than 10 mgd. The vast majority (12,000) of wastewater
treatment plants are small, with 2,700 medium-sized and only 500
large. The volume of sludge a community produces is related to the
31mgd = 3,785m3/d.
volume of wastewater and types of treatment processes. As a rule
of thumb, wastewater treatment plants generate approximately 240
grams of sludge solids for every cubic meter (m3) of wastewater
processed to secondary levels (11).
Based on current practice (44), small and medium-sized wastewater
treatment plants tend to land apply or landfill sludge, whereas
larger plants choose from among all five options. Almost all ocean
disposal and most incineration systems currently operating are used
by large plants (Figure 28). Incineration has been the method of
choice for many large communities because they generate a large
volume of sludge and have limited land available for land
application or landfilling. In addition, the initial capital costs of an
incinerator, the need for highly trained operators, and continuing
high costs for equipment and maintenance are more easily
absorbed by large communities.
8.2.3 Land Requirements
The proximity of disposal or use sites is a major factor in evaluating
alternatives. For land application and landfilling, an adequate
amount of suitable land must be available within an affordable
transportation distance (see subsection 8.2.8).
The amount of land needed is a direct function of sludge quantity,
its characteristics, how it has been treated, and the use/disposal
option chosen. Figure 29 compares the total leased or purchased
land that is needed to accommodate all the sludge production from
treatment plants of various sizes for a period of 10 years at typical
sludge loading rates. Table 14 gives the information used in
preparing Figures 29 and 30. In every situation portrayed, the raw
sludge is anaerobically digested, which reduces by 50 percent the
mass of sludge solids to be further processed. Note that wide
trench landfills, codisposal landfills, dedicated land disposal, and
composting typically require the least amount of land; narrow
trench landfills require slightly more land; and agricultural
application, land reclamation, and forest application require the
most land.
The range of land requirements for land application and landfilling
based on extreme sludge loading rates are shown in Figure 30.
Situation-specific factors, such as sludge nitrogen, sludge metal
concentrations, and climatic limitations on sludge application, will
determine where in this range a particular system would fall. The
land requirements are for sites that are suitable for land application
or landfilling—that is, that have appropriate hydrogeology, zoning
and adjacent land use, and proposed future use.
Since composted sludge is frequently applied in suburban or
nonagricultural commercial operations, it may be a feasible
alternative where adequate land is not available for other sludge
disposal options. Also, because composted sludge may have a
higher value to users than other forms of sludge, the municipality
may be able to charge a fee for the compost, and users may have
incentive to transport the sludge themselves, allowing more distant
sites to be considered.
63
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EVALUATING ALTERNATIVES
SMALL
TREATMENT
PLANTS
MGD)
Distribution
and Marketing
11%
MEDIUM
TREATMENT
PLANTS
(1-10 MGD)
LARGE
TREATMENT
PLANTS
(>10 MGD)
Incineration
1%
Ocean Incineration
Disposal 1%
1%
Based on a random survey of 1,011
treatment plants (6.5 percent of all
treatment plants nationwide) that
generate 36 percent of the municipal
wastowator sludge in the United States.
The category "other" Includes options
such as storage lagoons.
SOURCE: Reference (44).
Distribution
and Marketing
19%
Distribution
and Marketing
13%
Distribution
and Marketing
18%
Ocean
Disposal
4%
1 MGD = 3,785 mVday
Figure 28. The Relative Distribution of Sludge (Dry Weight) to the Five Use/Disposal Options
Among Small, Medium, and Large Treatment Plants
Ocean disposa/\s probably viable only if the community is located
within about 40 km (25 mi) of a suitable dock site that can offer
barga transport of sludge, and if there is an approved offshore
dumpsite within economical transport range.
Land availability is occasionally a limiting factor in incineration if a
suitable site for ash disposal does not exist within a reasonable
distance of the treatment plant.
8.2.4 Storage
Sludge storage is usually a component of all sludge management
systems. For land application, storage is necessary because climatic
conditions and variations in agricultural activity prevent year-round
application. For incineration and landfilling, climatic constraints are
toss important, but storage is still necessary to accommodate
fluctuations in sludge voldme, operational difficulties, and
Drying beds—a method of sludge dewatering—can be used to
store sludge. The bed on the left contains dried sludge. The bed on
the right contains partially dried sludge.
64
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EVALUATING ALTERNATIVES
t/3
oc
IT
O
C/3
§
LLI
cc
a
0 1
RAW SLUDGE GENERATION
(dry mt/day)
11 12M3 14 15
Composting
Wide Trench Landfill
Dedicated Land Disposal
In every case illustrated, the sludge generated during wastewater
treatment is anaerobically digested prior to land application or
land-filling (see Table 14).
Incineration and ocean disposal, not shown here, have insignificant,
but finite, land requirements.
OLD = dedicated land disposal 1 mt = 1.1 tons 1 ha = 2.471 ac
Figure 29. Typical 10-Year Land Requirements
for Land Application, Landfilling, and Composting
of Municipal Wastewater Sludge
as a Function of Sludge Generation
equipment failures. Sludge storage may also be necessary because
wastewater treatment, sludge treatment, and sludge use/disposal
sometimes operate on different schedules.
Some storage is provided by thickening, stabilization, and
dewatering systems—particularly drying beds, drying lagoons and
digestion facilities. Specialized storage facilities may also be
needed.
8.2.5 Good Practices
Site management encompasses all the operations of a sludge
management program. Depending on the use/disposal option, site
management may include preparing the site; training operators;
Monitoring is a key element of good sludge use/disposal
operations. Shown here are several types of monitoring.
a. Collection of leaf samples from soybeans fertilized with
composted sludge. These samples will be analyzed for water,
nitrogen, and heavy metals to help determine the fertilizer
value of the sludge compost.
b. Collection of forage samples from strip-mined land that has
been reclaimed with sludge compost. The samples will be
analyzed for heavy metals.
c. Extraction of a groundwater sample from a land application
site.
65
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EVALUATING ALTERNATIVES
500
400-
|300-
ffi 200 •
100
AGRICULTURAL
LAND APPLICATION
500-
400-
en
HI
oc
o
jjj 200-
100-
FOREST LAND
APPLICATION
10
15
500
400-
300
LU 200
100-
0
LAND
RECLAMATION
SLUDGE GENERATION (DRY METRIC TONS/DAY)
20-
15-
S
K
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EVALUATING ALTERNATIVES
Table 14. Assumptions for Figures 29 and 30.
For every m3 of wastewater treated with primary and activated sludge processes, 230 g of raw sludge solids are produced (1,900 Ib /mil gal). The raw
sludge is then anaerobically digested.
Of the initial raw solids content, 75 percent is volatile. Fifty percent of the volatile solids are removed during anaerobic digestion, and 75 percent of the
remaining solids are captured from the effluent stream.
After digestion, 108 g of sludge solids remain to be treated and disposed for every m3 of wastewater treated.
Application frequency
Low loading
Typical loading
High loading
Agricultural application
Forest application
Land reclamation
Dedicated land disposal
Composting3
Wide trench landfill
Narrow trench landfill
Codisposal
Apply repeatedly
to the same sites
ever year
Apply to each site
one time every 5 years
Apply to a site
one time only
Apply repeatedly
to the same site
Apply to static piles
with a 28-day
extended detention
Apply 20% solids
content sludge to a site
one time only
Apply 20% solids
content sludge to a site
one time only
Apply 20% solids
content sludge to a site
one time only
2 dry mt/ha/yr
10dry mt/ha/5yr
7 dry mt/ha
220 dry mt/ha/yr
4.2 dry mt/ha
1,200 dry mt/ha
460 dry mt/ha
900 dry mt/ha
15dry mt/ha/yr
40 dry mt/ha/5yr
112dry mt/ha
227 dry mt/ha/yr
6.7 dry mt/0.07 ha/day
3,439 dry mt/ha
482 dry mt / ha
1,800 dry mt/ha
70 dry mt/ha/yr
220drymt/ha/5yr
450 dry mt/ha
900 dry mt/ha/yr
11.2 dry mt/ha
5,480 dry mt/ha
2,120 dry mt/ha
7,900 dry mt / ha
"Only composting and storage facility land is required.
SOURCE: References (4,9,11,16,43).
8.2.7 Public Acceptance
Public acceptance is crucial to the success of any sludge
use/disposal option. All five options may encounter public
resistance. This resistance is often rooted in a lack of understanding
of the problems, and in a feeling by the community that they have
been excluded from the decision-making process. However, it may
also stem from justified concerns about effects. Frequently raised
concerns include odors, poor aesthetics, noise and traffic
congestion in residential areas, and health or environmental risks.
To minimize public opposition, the evaluation process should
include some form of public involvement. This program should be
tailored to the scope of the project and the potential for public
concern. Goals of such a program may include:
• Informing the public about the evaluation process and any
decisions that are made.
f>
Involving the public in the decision-making process helps pave the
way for a successful sludge use/disposal program.
67
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EVALUATING ALTERNATIVES
• Educating the public about the problems and solutions of
sludgs management.
* Involving the public in the decision-making process.
Whatever its scope, a public participation program should be
implemented early in the evaluation process. This allows time for
compromise, accommodation, and changes to the plan in case of
any serious public opposition. Further information on such
programs can be found in references (26) and (42). Once a sludge
management system is in place, proper operation and management
are essential to maintain public support for the program. In some
cases, public dissatisfaction has closed down operations and
required the selection and construction of a replacement system.
Any concessions made to the public during the selection process
must be honored. For example, in Dickerson, Maryland, sludge
haulers were ticketed and fined if they violated any of the rules for
transportation of sludge agreed upon with the community.
Table 15. Metal Reduction in Sludge by Industrial Pretreatment
Chicago
Level (mg/kg)
Motol
Cadmium
Chromium
Copper
Load
Nickel
Zinc
Before
190
2,100
1,500
1,800
1,000
5,500
After
54
790
282
486
77
2,800
Removal
(%)
71.6
62.4
81.2
73.0
92.3
49.1
Buffalo
Level (mg/kg)
Before
100
2,540
1,570
1,800
315
2,275
After
50
1,040
330
605
115
364
Removal
(%)
50.0
59.1
79.0
66.4
63.5
84.0
SOURCE: Reference (45).
8.2.8 Transportation Requirements
Sludge can be transported by truck, pipeline, rail, or barge. The
choice of transportation method depends on the use/disposal
method chosen, the volume and solids content of the sludge, and
the distance to and number of destination points. Trucks and
pipelines are the most common form of transport. Barge transport
is used almost exclusively for ocean disposal. Rail transport,
although potentially useful, is rarely used in the United States, due
to the difficulty in unloading rail cars and the system's fixed
location. Pipelines can be used cost effectively for long-distance
pumping of liquid sludge (usually less than 8 percent solids) but
have been used for sludges of up to 20 percent solids over short
distances.
Truck transport allows greater flexibility than any other transport
method. Destinations can be changed with little advance notice,
and the sludge can be distributed to many different destinations. If
trucks must be routed along residential or secondary streets, then
public concern about congestion and the risk of sludge spills must
be considered. Most land application programs use truck transport,
either alone or after sludge transport by pipeline or rail to an
intermediate storage facility. Liquid sludge of up to a 10 percent
solids concentration (depending on its viscosity) can be transported
in tank trucks. Dewatered sludge with a greater than 10 percent
solids concentration can usually be transported in open trucks with
watertight seals if precautions are taken to prevent spillage. Dried
and composted sludges of an approximately 50 percent or greater
solids concentration can be transported without watertight seals or
splash guards.
The practical limit for a truck haul distance is about 16 to 32 km
(10 to 20 mi) one way (42). For land application of liquid sludge, the
land must generally be within about a 16-km (10-mi) radius of the
treatment plant for transportion to be economical. Mechanically
Table 16. Estimated Metal Loadings from Indirect Industrial Dischargers Into U.S. Municipal Sewer Systems [1,000s of kg (Ib) /yr]
Metal
Cadmium
Chromium
(trfvalont)
Inorganic
chemicals
5
(11)
684
(1,504)
Chromium —
(hcxovatent)
Copper
Lead
Nickel
Zinc
32
(70)
176
(388)
2.3
(5)
201
(443)
Metal
finishing
42
(92)
2,871
(6,316)
1,052
(2,315)
2,037
(4,482)
67
(147)
2,472
(5,439)
1,860
(4,092)
Steel
0.9
(2)
191
(421)
16
(36)
55
(121)
48
(106)
170
(374)
355
(782)
Ore
mining
2.7
(6)
15
(33)
—
248
(545)
23
(51)
58
(128)
636
(1,400)
Coil Porcelain
coating enameling
0.05
(0.1)
160
(352)
0.14
(0.3)
0.9
(2)
0.9
(2)
45
(98)
3.2
(7)
1.4
(3)
2.7
(6)
25
(54)
47
(103)
54
(118)
Foundries
-
—
0.5
(1)
3.6
(8)
0.04
(0.08)
11
(24)
Petroleum
Pesticides refining
- 0.003
(0.006)
- 62
(137)
- 1.4
(3)
- 7
(15)
- 2.2
(5)
14
(3)
1.4 36
(3) (80)
Ink
-
0.5
(1)
0.14
(0.3)
1.4
(3)
—
—
Pulp & Leather
Paint paper tanning
- - 2,055
(4,522)
— — —
0.09 - -
(2)
— — —
— — —
25 20 -
(56) (44)
SOURCE: Adapted from Temple, Barker and Sloan summary of EPA data, January 31, 1983.
68
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EVALUATING ALTERNATIVES
Sludge transportation requirements are a key consideration when
evaluating sludge treatment, use, and disposal alternatives. Trucks
are the most common method of sludge transportation. Shown
here is a 24,600-1 (6,500-gal) liquid sludge tank truck.
least 1 month and often longer. A long regulatory review may delay
investment and thus increase the capital costs of a use/disposal
option. The management effort needed to gain approvals may
render the option less attractive than it originally seemed. In
addition, state and local regulations may directly limit the feasibility
of an option. For example, Massachusetts regulations as of 1984
require that specific site approval be obtained prior to land
application of any sludge or sludge product that contains more than
2 milligrams per kilogram (mg/kg) of cadmium. This
requirement—far more stringent than Federal
regulations—essentially eliminates distribution and marketing as a
sludge use/disposal option for sludge products of greater than
2 mg/kg cadmium because the destination of the sludge product is
generally not known.
8.2.11 Cost Factors
The major cost elements for each option are shown in Figure 31.
For ease of comparison, these costs have been broken down into
dewatered sludge can generally be economically transported to a
land application or landfill site up to about 22 km (20 mi). Air-dried
sludges, which can have solids concentrations in excess of 55 to
60 percent, can be economically transported a greater distance. In
evaluating transportation costs, the cost of dewatering must be
weighed against the cost savings that can result from transporting
a drier sludge.
8.2.9 Energy Usage
Energy usage is a concern because of the unpredictable nature of
fuel costs. The most significant energy uses in sludge management
are:
• Auxiliary fuel in incineration.
• Transportation costs in land application, landfilling, ocean
disposal.
• Sludge treatment—particularly dewatering.
• Heating and mixing sludge in anaerobic digesters.
• Aerating sludge during aerobic digestion.
• Moving, aerating, and turning sludge during composting.
8.2.10 State and Federal Regulatory Approval
Most sludge management options are subject to minimum Federal
regulations, and usually to state regulations and local permit
requirements. The regulatory climate at each level can significantly
influence the cost and feasibility of a sludge management option.
Several different state and local agencies may have jurisdiction over
sludge management. The types of regulations and the feasibility of
obtaining the requisite permits vary dramatically from jurisdiction to
jurisdiction. The review period for any permit application will vary
depending on the regulatory agency, its procedures, the backlog of
applications preceding it, and other factors. This process takes at
Sludge Treatment
Transportation
Capital
Operation and
Maintenance
Administration
0
LAND
APPLICAT
0
•
o
o
0
CD
|1 i
<§< 3
*2 1
WZ |
Q < -J
• 0
0 •
• •
• 0
0 0
g
INCINERAl
O
o
•
»
o
OCEAN
DISPOSAL
O
•
o
o
o
• Very Important
O Usually Less Important
Figure 31. Major Cost Factors for the Five
Sludge Use/Disposal Options
69
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EVALUATING ALTERNATIVES
five categories: sludge treatment costs, sludge transportation
costs, capital costs, operating costs, and administration. Sludge
treatment and transportation costs are featured separately because
they vary considerably from one municipality to another. In the
case of land application, cost evaluation should also consider any
Income from the sale of sludge, sludge products, or energy.
Economic comparison of use/disposal alternatives is a relatively
specialized task, generally performed by an engineering consulting
firm. However, Rgure 32 provides a rough idea of comparative
economics of the different use/disposal alternatives. Actual costs
may vary considerably depending on the local situation. References
(38,43) and engineering economics texts provide more detailed
information on comparative economic evaluations.
Ono factor to consider in evaluating costs is system reliability.
Unplanned service disruptions and the management time necessary
to resolve them can result in unexpected cost increases. Price
changes will also impact the operating costs of any long-term
project, and the sensitivity of operating costs to price changes must
bo carefully assessed. In particular, energy costs and contractor
escalator clauses should be carefully considered.
In some cases, part of the costs of feasibility studies and
construction are eligible for funding under the EPA Construction
Grants program and under individual state programs. For more
information about funding, consult reference (38) and state water
pollution control programs.
8.3 Sample Evaluation
The following hypothetical example is intended to illustrate the
types of Issues and considerations that must be addressed when
evaluating sludge use/disposal alternatives. The example is a
hypothetical situation; however, it does demonstrate the
complexity of the decision-making process. Although several key
factors enable the field of potential alternatives to be narrowed
down early in the decision-making process, there is rarely one
clearly preferable alternative. Final selection may take months and
often years of study and negotiation among municipal officials,
concerned citizens, and regulators to arrive at an acceptable
compromise.
Green Valley, USA
Green Valley, a community with a population of about 2,500, is
located in a rural agricultural area of the midwest. The town's
primary and secondary treatment plant is located on the outskirts of
town. Handling 1,900 m3 (0.5 mil gal) of wastewater per day, the
plant produces 12.5 wet mt (13.7 wet tons) of liquid sludge
(2 percent solids) each day, or about 90 dry mt (110 dry tons) of
sludge solids each year. The town was meeting its sludge
management needs by anaerobically digesting the liquid sludge,
thickening it to a solids content of 5 percent, and storing it in
lagoons with occasional removal to a landfill or sporadic land
application to either municipal or agricultural land. However, with
community growth, and more stringent state and Federal treatment
requirements that Increased sludge generation, residents and their
elected officials needed to choose a more environmentally sound
500'
400-
E 300-
fr
200-
100-
Incineration
Ocean Disposal
1 1 1 1 1 1 1
10 20 30 40
RAW SLUDGE GENERATION (dry mt/d)
—T
50
fc-
W
8
30-i
20-
10-
Narrow Trench Landfilling
—l—
10
Wide Trench Landfilling
T 1 r~
—r—
20
T
30 40
RAW SLUDGE GENERATION (dry mt/d)
50
Prior to land application of the liquid sludge, the raw sludge was
anaerobically digested.
Prior to landfilling, the raw sludge was anaerobically digested and
dewatered on a belt filter press to a 20 percent solids concentration.
Prior to incineration, the raw sludge was conditioned with an organic
polymer and dewatered on a belt filter press to a 20 percent solids
concentration.
Costs do not include the costs of sludge treatment prior to final use
or disposal.
1 mt = 1.1 tons
Figure 32. Typical Costs for Land Application, Landfilling,
Incineration, and Ocean Disposal of Municipal
Wastewater Sludge as a Function of Sludge Generation
70
-------
EVALUATING ALTERNATIVES
use/disposal option. Because of a local industry—the predominant
livelihood of the town—the digested sludge contains approximately
25 mg/kg of cadmium, which exceeds the state's regulatory limit of
20 mg/kg for land application to private farmland. No other
chemicals or metals occur in the sludge in significant
concentrations.
Town officials undertook a study to evaluate the relative economic,
environmental, health, and technological merits of various
use/disposal options. Two alternatives were eliminated at the
outset. Incineration was eliminated because of the poor history of
small-scale incinerators, and because of the high capital outlay
required, which the town felt unable to raise or justify. Ocean
disposal was clearly not an option for this inland town. The three
remaining options were land application, distribution and
marketing, and landfilling.
Land application appeared to be a highly attractive option. At
standard agricultural application rates of 15 dry mt/ha/yr
(6.7 dry tons/ac/yr) approximately 6 ha (15 ac) of farmland were
needed to apply all the town's sludge. Plenty of productive
farmland was available within 32 km (20 mi) of the treatment plant.
Some of that farmland was within 8 km (5 mi) of the plant, making
transportation of liquid sludge economical. The ability to land apply
liquid sludge would save the town the cost of installing and
operating dewatering equipment, which would be necessary to
produce a higher solids content sludge for transport to more distant
areas. Total costs of land application, including transport and
application equipment costs, labor, and fuel, were estimated at
$100/dry mt. Land application of liquid sludge was therefore an
economically attractive option. Local farmers expressed interest in
the sludge as a soil conditioner and fertilizer; however, they were
concerned about the potential health effects associated with high
cadmium concentrations. In addition, the cadmium concentration
of 25 mg/kg exceeded the state regulatory limit of 20 mg/kg for
land application of sludge to cropland even though it was clearly
within the Federal criteria.
Distribution and marketing was not an attractive alternative for
several reasons. Although a limited market existed for sludge
products among residential homeowners and some farmers, the
costs of implementing and maintaining a sludge composting
facility, and hiring additional personnel to run the facility and
administer the program, were too large. In addition, the cadmium
concentration exceeded the state limits for application of sludge to
agricultural crops, and the final destination of sludge product would
be difficult to monitor and control in a distribution and marketing
program.
Landfilling met with some objection. Many of the local citizens
opposed the idea of landfilling. The town's sanitary solid waste
landfill was going to run out of space within the next 2 years, and,
despite the availability of potential landfill sites, the town had not
yet been able to site a new sanitary landfill because of public
opposition. This opposition stemmed from environmental and
public health concerns. Much of the area was underlain by an
aquifer from which local drinking water was drawn. Geohydro-
logical conditions would necessitate the installation of liners in a
landfill to minimize the potential for groundwater contamination.
Because of the environmental concerns, a relatively shallow [1-m
(3-ft) depth] wide trench landfill with liners was felt to be the most
suitable design. This design had a relatively low sludge loading of
2,000 dry mt/ha (890 tons/ac). For this design, the amount of land
needed for the next 20 years of sludge production was estimated to
be about 1 ha (2.5 ac). Because landfilled sludge should have about
20 percent solids to reduce leachate formation, dewatering
equipment would have had to be installed. Total costs were
estimated to be very similar to those estimated for land application.
Land application of the digested liquid sludge appeared to be the
most attractive option if the cadmium problem could be eliminated.
Municipal officials considered passing an industrial sewer ordinance
that would set a maximum level of cadmium in industrial
wastewater discharge; this would require the local industry to
install pretreatment facilities. Citizens expressed concern that this
requirement might cause the industry to relocate, leaving a large
proportion of the town jobless. Negotiations were begun with the
industry, and a compromise was reached in which the town agreed
to assist the industry in finding a suitable pretreatment system.
Pilot studies will be run and, when cadmium levels in sludge are
adequately reduced, land application will be implemented as the
town's primary sludge use method.
However, the long-term storage of any sludge, especially liquid
sludge, during the nongrowing season and inclement weather was
still a concern. Municipal authorities agreed that another
use/disposal option would have to be available as a backup for land
application. Landfilling appeared to be a good contingency option.
Officials are examining the rate of solid waste generation to see if it
would provide sufficient bulk for codisposal of the liquid sludge,
and they are investigating the cost of drying beds and mechanical
dewatering equipment, which would be necessary for sludge-only
landfilling. The officials held preliminary town hearings on the
subject because they recognized that a concerted public
participation program is necessary for an Unpopular option, sludge
landfilling, to become a feasible contingency.
71
-------
9. Trends and Prospects
Sludge management Is characterized by extreme complexity. The
interplay of technology, public relations, resource management,
health and environmental concerns, and economics makes any
projections of future sludge management options difficult. Changes
in economic conditions and public perception of sludge
management, and innovations in process and equipment, modify
tho way communities evaluate the choices available to them and
the basic nature of these options.
New technologies are emerging, including pyrolysis, making bricks
from sludge, using sludge for asphalt production, coincineration
with municipal waste, earthworm conversion, and recovering
precious metals from sludge incinerator ash. The ultimate
usefulness of these technologies will depend on many factors,
including technical success, environmental soundness, public
acceptability, and cost. The history of sludge management
suggests that new ideas are accepted only cautiously. Processes
that employ biological systems similar to those that take place
during natural decay of wastes have generally proven the most
successful options. Composting is one example of this.
Research into the health and environmental effects of sludge
uso/disposal helps to provide more refined management techniques
to prevent, detect, and resolve problems. This information will
enable future Federal requirements for sludge management to
specify planning techniques and operating procedures in greater
detail than in the past. While this will impose some constraints on
the options available to states and municipalities, it may also permit
higher sludge use/disposal rates, with close and careful scrutiny for
the environmental or health effects. In response to these more
specific Federal guidelines, local governments will probably rely
more on advanced planning. States will also be refining their
programs to include Federal technical requirements, and to require
more specific local government planning.
Changes in public attitudes will also have a dramatic effect on
future sludga management options. The Federal emphasis on
sludge use as a resource rather than as a waste may provide subtle
pressure to alter public attitudes and clarify the distinction between
municipal sludge and industrial wastes. As EPA regulation of
industrial discharges to sewers takes effect, the concentration of
metals and toxic organic chemicals in sludge should decline,
making its use in agriculture more economical and more acceptable
to the general public. Consequently, land application will become
even more prevalent in the future.
Public acceptance is crucial to the success of any sludge
management technique and cannot be secured solely by technical
improvements or research into health effects. Careful and
enlightened state regulation of sludge use and disposal will be
essential to improved public perception of sludge management.
However, the largest responsibility for fostering favorable public
attitudes lies with local operating agencies and their contractors.
A history of responsibility and concern in the execution of sludge
management will go far towards clearing the way for any future
changes.
72
-------
10. Sources of Further Information
Additional documents provide further guidance or information on
the various aspects of sludge management discussed in this
guidance document. The additional documents for each chapter are
listed below. To obtain further guidance, contact the EPA sludge
coordinators in the EPA regional offices (Table 17), and the state
agency responsible for sludge management.
2. Municipal Sludge
EPA. 1979. Environmental pollution control alternatives. EPA
625/5-79-012. Center for Environmental Research Information, U.S.
Environmental Protection Agency, Cincinnati, Ohio.
3. Land Application
EPA. 1980. A guide to regulations and guidance for the utilization
and disposal of municipal sludge. EPA 430/9-80-015. Office of
Water, U.S. Environmental Protection Agency, Washington, D.C.
EPA. 1983. Technology Transfer process design manual: land
application of municipal sludge. EPA-625/1-83-016. Center for
Environmental Research Information, U.S. Environmental
Protection Agency, Cincinnati, Ohio.
Table 17. EPA Regional Sludge Coordinators
REGION I
Municipal Facilities Branch
Water Division
EPA — Region I
JFK Federal Building
Boston, MA 02203
REGION II
NY Project Management Station
Water Division
EPA — Region II
26 Federal Plaza
New York, NY 10007
REGION 111
Water Division
EPA — Region III
6th and Walnut Streets
Philadelphia, PA 19106
REGION IV
Facility Requirement Branch
Water Management Division
EPA - Region IV
345 Courtland Street, NE
Atlanta, GA 30308
REGION V
Water Division
Facility Planning, Unit 1
EPA — Region V
230 South Dearborn Street
Chicago, IL 60604
REGION VI
Water Division
EPA - Region VI
First International Building
1201 Elm Street
Dallas, TX 75270
REGION VII
Construction Grants Branch
Water Division
EPA - Region VII
324 East 11th Street
Kansas City, MO 64106
REGION VIII
Water Management Division
EPA - Region VIM
1860 Lincoln Street
Denver, CO 80295
REGION IX
Water Division
EPA - Region IX
215 Fremont Street
San Francisco, CA 94105
REGION X
Construction Grants Section
Water Division, Mail Stop 429
EPA - Region X
1200 6th Avenue
Seattle, WA 98101
EPA/FDA/USDA. 1981. Land application of municipal sewage
sludge for the production of fruits and vegetables: a statement of
Federal policy and guidance. SW-905. Office of Solid Waste. U.S.
Environmental Protection Agency; U.S. Food and Drug Adminis-
tration; and U.S. Department of Agriculture, Washington, D.C.
National Fertilizer Development Center, Tennessee Valley
Authority, Muscle Shoals, Alabama.
4. Distribution and Marketing
EPA. 1981. Composting processes to stabilize and disinfect
municipal sewage sludge. EPA 430/9-81-011. Office of Water
Program Operations, U.S. Environmental Protection Agency,
Washington, D.C.
Hornick, S.B., L.J. Sikora, S.B. Sterrett, J.J. Murray,
P.O. Millner, W.D. Burge, D. Colacicco, J.F. Parr, R.L. Chaney,
and G.B. Willson. 1984. Utilization of sewage sludge compost as a
soil conditioner and fertilizer for plant growth. Agricultural
Information Bulletin 464. Agricultural Research Service, U.S.
Department of Agriculture, Beltsville, Maryland.
MES. 1984. Operations manual for sewage sludge composting:
Blue Plains wastewater treatment plant. Maryland Environmental
Service, Annapolis, Maryland.
USDA/EPA. 1980. Manual for composting sewage sludge by the
Beltsville aerated-pile method. EPA-600/8-80-022. Agricultural
Research, Science, and Education Administration, U.S.
Department of Agriculture, Washington, D.C.;, and Municipal
Environmental Research Laboratory, U.S. Environmental Protection
Agency, Cincinnati, Ohio.
5. Landfilling
Byers, H.W., and G.D. Lukasik. 1983. Design, operating and
monitoring a sanitary landfill for the exclusive disposal of
wastewater treatment plant sludges. North Shore Sanitary District,
Gurnee, Illinois.
EPA. 1978. Technology Transfer process design manual: municipal
sludge landfills. EPA 625/1-78-010. Center for Environmental
Research Information, U.S. Environmental Protection Agency,
Cincinnati, Ohio; and Office of Solid Waste, U.S. Environmental
Protection Agency, Washington, D.C.
6. Incineration
Bennett, R.L., K.T. Knapp, and D.L. Duke. 1984. Chemical and
physical characteristics of municipal sludge incinerator emissions.
EPA 600/3-84-047. NTIS PB-84-169 325.
73
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SOURCES OF FURTHER INFORMATION
EPA. 1979. Technology Transfer process design manual: sludge
treatment and disposal. EPA 625/1 -79-011. Municipal
Environmental Research Laboratory and Center for Environmental
Research Information, U.S. Environmental Protection Agency,
Cincinnati, Ohio.
EPA. 1984. Technology Transfer seminar publication on municipal
sludge combustion. Center for Environmental Research
Information, U.S. Environmental Protection Agency, Cincinnati,
Ohio.
Gerstte, R.M., and D.N. Albrinck. 1982. Atmospheric emissions
from sewage sludge incineration. J. Air Pollution Control Assoc.
8. Evaluating Alternatives
EPA. 1980. Innovative and alternative technology assessment
manual. EPA 430/9-78-009. Office of Water Program Operations,
U.S. Environmental Protection Agency, Washington, D.C.; and
Office of Research and Development, U.S. Environmental
Protection Agency, Cincinnati, Ohio.
EPA. 1980. Evaluation of sludge management systems: evaluation
checklist and supporting commentary. EPA 430/9-80-001. Office of
Water Program Operations, U.S. Environmental Protection
Agency, Washington, D.C.
Wall, H.O., and J.B. Farrell. 1979. Particulate emissions from
municipal wastewater sludge incinerators. Presented at Mid-
Atlantic States Section, Air Pollution Control Association, Newark,
New Jersey, April 27, 1979.
7. Ocean Disposal
Duke, T.W. (ed.). 1982. Impact of man on the marine environment.
EPA 600/8-82-021. Office of Research and Development, U.S.
Environmental Protection Agency, Washington, D.C.
EPA. 1984., Report to Congress January 1981-December 1983. On
Administration of the Marine Protection, Research, and
Sanctuaries Act of 1972, as Amended (P.L. 92-532) and
Implementing the International London Dumping Convention.
Office of Water Regulations and Standards, U.S. Environmental
Protection Agency, Washington, D.C.
Goldberg, E. (ed.). 1979. Proceedings of a Workshop on
Assimilative Capacity of U.S. Coastal Waters for Pollutants.
National Oceanographic and Atmospheric Administration,
Washington, D.C.
NAS. 1976. Disposal in the marine environment. An oceanographic
assessment. Commission on Natural Resources, National Academy
of Sciences, Washington, D.C.
NRC/NAS. 1983. Report of the Workshop on Land, Sea, and Air
Disposal of Industrial and Domestic Wastes. Board on Ocean
Science and Policy, National Research Council and National
Academy of Sciences, Washington, D.C.
NOAA. 1975. Ocean dumping in the New York Bight. NOAA Tech.
Rept. ERL321-MESA.
74
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11. References
(1) 49 FR 24358, June 12, 1984. EPA Policy on Municipal Sludge
Management.
(2) Metcalf and Eddy, Inc. 1972. Wastewater engineering —
collection, treatment, and disposal. McGraw Hill, Inc.
(3) Sommers, L.E. 1977. Chemical composition of sewage sludges
and analysis of their potential use as fertilizers. J. Environ.
Qual. 6:225.
(4) EPA. 1979. Technology Transfer process design manual:
sludge treatment and disposal. EPA 624/1-79-011. Center for
Environmental Research Information, U.S. Environmental
Protection Agency, Cincinnati, Ohio.
(5) Peirce, J.J., and L. Cahill. 1984. State programs to control
municipal sludge. J. environ. Engng 110(1):15-26.
(6) Chaney, R.L. 1983. Potential effects of waste constituents on
the food chain. In: J.F. Parr, P.B. Marsh, and J.M. Kla (eds.).
Land treatment of hazardous wastes. Noyes Data Corp., Park '
Ridge, New Jersey, pp. 152-140.
(7) Chaney, R.L., and P.M. Giordano. 1977. Microelements as
related to plant deficiencies and toxicities. In: L.F. Elliot and
F.J. Stevenson (eds.). Soils for management of organic
wastes and waste waters. American Society of Agronomy,
Madison, Wisconsin, pp. 234-279.
(8) EPA. 1982. Technology Transfer design manual: dewatering
municipal wastewater sludges. Municipal Environmental
Research Laboratory, U.S. Environmental Protection Agency,
Cincinnati, Ohio.
(9) Page, A.L., T.L. Gleason III, J.E. Smith, Jr., I.K. Iskandar,
and L.E. Sommers (eds.). 1983. Utilization of municipal
wastewater and sludge on land. University of California,
Riverside, California. I
Ji
(10) Loehr, B.C., W.J. Jewell, J.D. Novaki W.W. Clarkson, and
G.S. Friedman. 1979. Land application of wastes. Vol. 2. Van
Nostrand Reinhold, New York. 431 pp.
(11) EPA. 1983. Technology Transfer process design manual: land
application of municipal sludge. EPA 625/1-83rQ16. Center for
Environmental Research Information, U.S. Environmental
Protection Agency, Cincinnati, Ohio.
(12) Hornick, S.B., L.J. Sikora, S.B. Sterrett, J.J. Murray,
P.O. Millner, W.D. Surge, D. Colaciccp, J.F. Parr,
R.L. Chaney, and G.B. Wilson. 1984. Utilization of sewage
sludge compost as a soil conditioner arid fertilizer for plant
growth. Agricultural Information Bulletin 464. Agricultural
Research Service, U.S. Department of Agriculture, Beltsville,
Maryland.
(13) EPA/FDA/USDA. Land application of municipal sewage
sludge for the production of fruits and vegetables: a statement
of Federal policy and guidance. SW 905. Office of Solid
Waste, U.S. Environmental Protection Agency, Washington,
D.C.
(14) Chaney, R.L. 1980. Health risks associated with toxic metals in
municipal sludge. In: G. Bitton etal. (eds.). Sludge—health
risks of land application. Ann Arbor Science Publishers, Inc.,
Ann Arbor, Michigan.
(15) SCS. 1984. Preliminary results of the 1982 National Resources
Inventory. Soil Conservation Service, U.S. Department of
Agriculture, Washington, D.C.
(16) Jewell, W.J. 1982. Use and treatment of municipal wastewater
and sludge in land reclamation and biomass production
projects—an engineering assessment. In: W.E. Sopper,
E.M. Seaker, and R.K. Bastian (eds.). Land reclamation and
biomass production with municipal wastewater and sludge.
Pennsylvania State University Press, University Park,
Pennsylvania.
(17) Wilson, G.B., and D. Dalmat. 1983. Sewage sludge
composting in U.S.A. BioCycle 24(5) :20-23.
(18) Olver, W.M., Jr., and R.E. Shou. 1982. Static pile composting
of municipal sewage sludge: the process as conducted by the
City of Bangor, Maine. The City of Bangor, Maine. 75 pp.
(19) MES. 1984. Operations manual for sewage sludge composting:
Blue Plains wastewater treatment plant. Maryland
Environmental Service, Annapolis, Maryland.
(20) EPA. 1981. Composting processes to stabilize and disinfect
municipal sewage sludge. EPA 430/9-81-011. Office of Water
Program Operations, U.S. Environmental Protection Agency,
Washington, D.C.
(21) Editors of BioCycle Magazine. 1981. Managing sludge by
composting. The I.G. Press, Inc., Emmaus, Pennsylvania.
322pp.
(22) Energy Resources Co. Inc. 1980. Monitoring of Aspergillus
fumigatus associated with municipal sewage sludge
composting operations in the State of Maine. Portland Water
District, Portland, Maine.
(23) Taffel, W.F. 1979. Health risk assessment. A position paper.
In: Proceedings of the workshop on health and legal
implications of sewage sludge composting. NTIS PB 296 56.
(24) Maryland Environmental Services, Annapolis, Maryland.
(25) Goldstein, N. 1983. "Odor free" sludge in a high density
suburb. BioCycle 24(5):24-27.
(26) EPA. 1978. Technology Transfer process design manual:
municipal sludge landfills. EPA-625/1-78-010. SW-705.
Environmental Research Information Center, U.S. Environ-
mental Protection Agency, Cincinnati, Ohio; and Office of
Solid Waste, U.S. Environmental Protection Agency,
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