Biosolids Generation,

Use, and Disposal in

The United States

Agency

www.epa.gov

1EPA

(5306W)

2 Printed on paper that contains at least 30 percent postconsumer fiber.
Biosolids Generation, Use, and Disposal

in the United States

U.S. Environmental Protection Agency

Municipal and Industrial Solid Waste Division

Office of Solid Waste

EPA530-R-99-009

September 1999
Contents

Executive Summary 1

Section One Introduction 4

1.1 How This Report Can Be Used 5

1.2 Sources of Information 5

Section Two Background 7

2.1 Wastewater Treatment 8

2.2 Biosolids Treatment 10

2.2.1 Stabilization Processes 10

2.2.2 Dewatering 15

2.3 Biosolids Use and Disposal Practices 17

2.3.1 Land Application and Other Beneficial Use Options for Biosolids 17

2.3.2 Incineration of Biosolids 20

2.3.3 Surface Disposal and Landfilling 22

Section Three Generation, Use, and Disposal of Biosolids in 1998 25

3.1 Generation of Biosolids in 1998 25

3.2 Biosolids Management Practices in 1998 26

3.2.1 Beneficial Use of Biosolids in 1998 26

3.2.2 Disposal of Biosolids in 1998 28

3.2.3 Amount of Biosolids Managed by MSW Facilities in 1998 28

Section Four Trends and Projections for Biosolids Generation, 29

Use, and Disposal

4.1 Generation 29

4.2 Use and Disposal 31

4.2.1 Use Trends 31

4.2.2 Disposal Trends 34

4.2.3 Use and Disposal Projections 35

ii
Section Five Beneficial Use of Biosolids 38

5.1 Overview of Beneficial Use 38

5.2 Potential Barriers to Increased Beneficial Use 39

5.2.1 Public Acceptance 39

5.2.2 Liability Concerns 43

5.2.3 Costs 44

5.2.4 Crop Considerations 47

5.3 Examples of Beneficial Use 47

5.3.1 King County, Washington 47

5.3.2 Los Angeles County, California, Sanitation Districts 49

5.3.3 City of Austin, Texas 50

5.3.4 Columbus, Ohio 51

5.3.5 Charlottesville, Virginia 52

References 54

Appendix Biosolids Generation, Use, and Disposal Methodology 57

and Results

Contents

iii
List of Tables

Section Two

2-1 Types of Wastewater Treatment and Resulting Types of Biosolids 9

2-2 Benefits of Using Compost 14

2-3 Stabilization Technologies and Associated Use or Disposal Methods 16

Section Three

3-1 Estimates of Biosolids Generation for Use or Disposal (1998) 25

3-2 Estimates of Biosolids Use and Disposal 27

Section Four

4-1 Projections of Biosolids Generation for Use or Disposal in 2000, 30

2005, and 2010

4-2 Projections of Use and Disposal in 2000, 2005, and 2010 35

4-3 Projections of Biosolids Use and Disposal in 2000, 2005, 37

and 2010 (million U.S. dry tons)

Section Five

5-1 Biosolids Composting Costs (1997 data from 100 composting facilities) 45

Appendix

A-1 Estimate of Biosolids Generation Factor 63

A-2 Estimate of Biosolids Generated by POTWs in 1996 and 1998 63

A-3 Adjustment for Biosolids Generation From Privately and Federally 64

Owned Treatment Works

A-4 Biosolids Use and Disposal Based on WEF Survey Data (million U.S. dry tons) 66

A-5 Comparison of WEF (1997) and BioCycle (1998) Data on Use 67

and Disposal Practices

A-6 Estimates of Biosolids Use and Disposal With Adjustments for 69

Biosolids Receiving Advanced Treatment (million U.S. dry tons)

A-7 Trend Analysis of Flow (1984 to 1996) 71

A-8 Wastewater Flow Projections for POTWs and Privately and 72

Federally Owned Treatment Works in 2000, 2005, and 2010

A-9 Projected Percentages of Biosolids Use and Disposal in 2000, 2005, and 2010 73

A-10 Projected Quantities of Biosolids Use and Disposal in 2000, 2005, 73

2010 (million U.S. dry tons)

iv
List of Figures

Executive Summary

ES-1 Estimates of Biosolids Use and Disposal (1998) 3

Section Three

3-1 Estimates of Biosolids Use and Disposal (1998) 27

Section Four

4-1 Projections of Biosolids Generation for Use and Disposal in 31

2000, 2005, and 2010

4-2 Projections of Use and Disposal for 2000, 2005, and 2010 36

v
Executive Summary

The purpose of this report is to broaden the U.S. Environmental Protection

Agency’s (EPA) series of solid waste studies by quantifying the amount of

biosolids managed by municipal solid waste (MSW) facilities. Biosolids are

the byproduct of municipal wastewater treatment and also are known as sewage

sludge. This report focuses on biosolids generated by publicly owned treatment

works (POTWs) and the subsequent management practices used by POTWs for

treating and then recycling or disposing of biosolids. The quantity of biosolids

processed by POTWs and the treatment methods they select are likely to affect

MSW decision-makers regarding their involvement in biosolids management.

EPA hopes to support MSW operators and state and local solid waste decisionmakers in developing coordinated biosolids management programs with local

POTWs and other generators to encourage the cost-effective, beneficial use of

biosolids. In beneficial use, biosolids are used for their soil-conditioning and

nutrient-containing properties. This report also examines the advantages to

MSW operators of using biosolids in composting operations for land application

and sale to the public. The key areas discussed in this report regarding the 

beneficial use or the disposal of biosolids, particularly at MSW facilities, are

detailed below:

• The use or disposal of biosolids

— The use or disposal of biosolids begins with wastewater treatment. The type

and level of wastewater treatment has an effect on the type, quantity, and

quality of biosolids generated. Pretreatment of wastewater by industry can

improve biosolids quality considerably.

— Biosolids treatment is inherent in the proper use of wastewater solids.

Various stabilization processes control odor, pathogens (e.g., disease-causing bacteria and viruses), biodegradable toxins (e.g., hydrocarbons), and 

vectors (e.g., rodents and flies) and can bind heavy metals. Composting is a

highly effective way of stabilizing and reducing pathogens in biosolids, 

resulting in a valuable soil conditioning product that often has many useful

properties (e.g., slower and steadier nutrient availability unmatched by 

conventional chemical fertilizers). Dewatering is necessary for landfilling and

1
incineration of biosolids and can be a critical step in preparing biosolids for

composting.

— Biosolids management practices primarily involve land application, which can

include the use of compost or other highly treated biosolids and other beneficial uses (e.g., landfill cover). Other biosolids management options include

landfilling and other forms of surface disposal and incineration.

• Quantities of biosolids generated, used, and disposed of between

1998 and 2010

— This report estimates that approximately 6.9 million tons of biosolids were

generated in 1998, of which about 60 percent were used beneficially (e.g.,

land applied, composted, used as landfill cover) and 40 percent disposed of

(i.e., discarded with no attempt to recover nutrients or other valuable properties). This report further estimates that at least 20 percent of biosolids were

managed by MSW facilities through either landfilling (17 percent) or as landfill

cover (3 percent). An estimated additional 6 percent were managed by MSW

facilities in composting programs. “MSW facility” defined here includes any

commercial, noncommercial, or municipal entity that composts organic MSW

(e.g., yard trimmings) with biosolids. Thus, about a quarter of all biosolids

have been managed by MSW facilities, mostly by MSW landfill operators

(see Figure ES-1).

— We expect that the use of biosolids will increase in the future due to the benefits from recycling, cost considerations, and public perception issues associated with disposal. In 2000, we estimate that 7.1 million tons of biosolids will

be generated for use or disposal, growing to 7.6 million tons in 2005 and to

8.2 million tons in 2010. We anticipate that the percentage of biosolids used

(rather than disposed of) will grow from 63 percent in 2000 to 66 percent in

2005 and to 70 percent in 2010. A trend away from disposal and toward use

would result in a decline in biosolids disposed of in MSW landfills and an

increase in the use of biosolids as landfill cover and in composting programs

at MSW facilities. In 2000, we estimate that at least 14 percent of biosolids

will be landfilled and 3 percent used as landfill cover. An estimated additional

6 percent might be used in composting programs, for a total of at least 

17 percent to a possible 23 percent of all biosolids managed by MSW facilities. We expect that changes will occur in 2005 due to increasing reuse of

biosolids and a corresponding decrease in landfilling, primarily because of

cost and siting considerations. An estimated 13 percent will be landfilled, 

3 percent will be used as landfill cover, and 6.5 percent will be composted at

MSW facilities, for a total of at least 16 percent to possibly 22 percent of

biosolids being managed by MSW facilities by 2005. In 2010, we estimate

that 10 percent might be landfilled, 3 percent used as landfill cover, and possibly 7 percent used in composting programs, for a total of at least 

13 percent to possibly 20 percent of biosolids managed by MSW facilities 

(as defined above). 

Executive Summary

2
• Concerns about beneficial use and ways to address them

— The beneficial use of biosolids is hindered by public opposition in some areas

of the country. The public acceptance issues involve concerns about pollutants in the biosolids, risk of disease, and nuisance issues such as odors.

When properly treated and managed in accordance with existing regulations

and standards, biosolids are safe for the environment and human health.

Furthermore, over time, as industrial pretreatment of wastewater has

advanced, the quality of biosolids has continued to improve. Public acceptance concerns can be effectively addressed through a combination of

approaches, including careful assessment of public attitudes, modifications to

biosolids management programs, aggressive outreach and education, and

strong marketing of biosolids products. These approaches are successfully

employed by a number of biosolids managers (as presented in the case studies in Section 5.3), resulting in highly effective programs that emphasize costeffective beneficial use of biosolids. In addition, a new Environmental

Management System for biosolids management is being developed, with the

support of Congress, by the National Biosolids Partnership program.

Voluntary membership in the National Biosolids Partnership program includes

the public, generators, land appliers, farmers, academics, federal, state, and

local governments, and other interested parties.

Executive Summary

3

Figure ES-1 

Estimates of Biosolids Use and Disposal (1998)

COMBINED

DISPOSAL

2.8 MDT (40%)

COMBINED

BENEFICIAL USE

4.1 MDT (60%)

Land Applicationa

2.8 MDT (41%)

Other Disposal

0.1 MDT (1%) Incineration

1.5 MDT (22%)

Surface Disposal/Landfill

1.2 MDT (17%)

Other Beneficial Use

0.5 MDT (7%)

Advanced Treatment

0.8MDT (12%)

MDT (1998) = millions of dry tons

Source: See Appendix A.3. a

Without further processing or stabilization such as composting.
4

Section One

Introduction

Biosolids (historically known as sewage sludge) are the solid organic matter produced from private or community wastewater treatment processes

that can be beneficially used, especially as a soil amendment. The

amount of biosolids generated and the use or disposal of biosolids, as discussed in this report, are of interest to municipal solid waste (MSW) facility

operators and others (e.g., farmers, foresters, land reclaimers, landscapers) for

several reasons, including:

• Disposal of biosolids commonly occurs in MSW landfills

• Ash from biosolids incineration might be disposed of in MSW landfills

• Biosolids can be composted (recycled) with other organic MSW materials

• Biosolids can be used as a soil amendment and fertilizer

• Biosolids can be used as daily cover or part of a final landfill cover

This report discusses the amount of biosolids generated in the United States

and their subsequent use or disposal. Section Two summarizes the various

treatment, use, and disposal practices for biosolids and includes brief references to regulatory requirements influencing these practices. Section Three provides actual estimates of the amount of biosolids generated, recovered, and

disposed of in the United States. Section Four discusses current and possible

future trends in the generation, use, and disposal of biosolids through 2010.

Section Five discusses beneficial uses of biosolids, addresses concerns about

beneficial use, and presents several case studies that illustrate a variety of successful biosolids management programs. The Appendix provides the full

methodology and detailed results of the data analyses summarized in Sections

Three and Four.
1.1 How This Report Can Be Used 

This report contains information on biosolids treatment and management that

may be useful to MSW managers who are considering the impact of biosolids

on their operations, as well as for other varied users of biosolids. MSW managers can use the generation, use, and disposal figures in this report, for example, to gain a better perspective of the various management options available

for biosolids and what the current trends are in the use and disposal of

biosolids. MSW managers can also use this report to explore what trends may

affect future biosolids management practices over the next 15 years, including

the potential markets for composted biosolids. This report also may help clarify

the relationship between MSW facility operators and POTW operators and

encourage them to work cooperatively. By showing how solid wastes, such as

yard trimmings, and biosolids can be managed together in a composting operation, for example, this report might help various municipal groups, such as solid

waste and wastewater treatment departments, deal more efficiently and cooperatively with recycling and waste handling issues. Federal, state, and local solid

waste decision-makers can use this report to help determine the amounts of

biosolids potentially available for beneficial use projects and facilitate planning

for future use and disposal operations.

The data estimates made in this report target the quantities of biosolids that are

likely to be generated by POTWs whose management practices ultimately affect

the quality of resulting biosolids and, therefore, MSW facilities’ management

options. For that reason, this report does not include information on domestic

septage that is not treated at POTWs. Domestic septage is the liquid or solid

material removed from septic tanks, cesspools, portable toilets, Type III marine

sanitary devices, or similar systems. This report also does not quantify the

amount of biosolids incinerator ash generated and disposed of, although up to

22 percent of total biosolids generated in 1998 were incinerated. Biosolids incineration as a disposal practice, however, is discussed in this report.

1.2 Sources of Information

To estimate biosolids generation, use, and disposal and to prepare this report, a

number of information sources were used. The 1988 National Sewage Sludge

Survey (NSSS) surveyed 479 POTWs in 1988 and provided a statistically valid

estimate of the amounts of biosolids used or disposed of by POTWs using secondary or tertiary treatment in that year (U.S. EPA, 1993a). EPA’s Needs Survey

(1986 through 1996 data) also was used in this report and assesses the number

of wastewater treatment facilities in operation, their existing and projected

wastewater flow, and the number of people they serve. In addition, the results of

the following recent studies and surveys were used: a 1995 inventory conducted

by the Water Environment Federation (WEF) and the Association of Metropolitan Sewerage Agencies (AMSA) on biosolids generation, beneficial use, and

disposal (WEF, 1997); a 1996 survey of state regulators (Bastian, 1997); and

1991, 1997, and 1998 surveys of state regulators (BioCycle, 1991, 1997, and

1998). In the near future, however, data on biosolids quality and management

5

Introduction Section One
6

will be more readily available through EPA’s Biosolids Data Management

System, which is a data program that allows for electronic reporting (and access

of data) among treatment facilities, states, and EPA. 

These sources and the information used are discussed in more detail in the

Appendix. Additional sources of information are cited as referenced; full citations

can be found in the references section at the end of this report.

Introduction Section One
Section Two

Background

The Clean Water Act requires that communities treat their wastewater to

return this resource safely to the environment. When wastewater is treated, the process produces a semisolid, nutrient-rich byproduct known as

biosolids. When treated and processed properly, biosolids can be recycled and

applied to crop land to improve soil quality and productivity because of the nutrients and organic matter that they contain. Historically called sewage sludge,

biosolids is the term now used to emphasize the beneficial nature of this recyclable material.

Biosolids often contain approximately 93 to 99 percent water, as well as solids

and dissolved substances present in the wastewater or added during wastewater or biosolids treatment processes. The quantity of municipal biosolids produced annually in the United States has increased dramatically since 1972, from

roughly 4.6 million dry tons in 1972 (Bastian, 1997) to 6.9 million dry tons in

1998. This is a 50 percent increase from 1972, when the Clean Water Act first

imposed minimum treatment requirements for municipal wastewater, and is

greater than the 29 percent increase in U.S. population from 1972 to 1998

(Council of Economic Advisors, 1999). 

Treatment works treat both wastewater as well as the resulting biosolids, often

using different technologies designed specifically for each treatment process.

This section, therefore, divides the discussion of treatment into wastewater

treatment and biosolids treatment. The influence of wastewater treatment on

biosolids generation is addressed first, followed by a discussion of biosolids

treatment. The different types of biosolids use and disposal practices are then

discussed, including practices that might involve MSW facilities. Additionally, the

regulatory requirements found in The Standards for the Use or Disposal of

Sewage Sludge (Title 40 of the Code of Federal Regulations [CFR], Part 503),

which was published in the Federal Register in 1993, are discussed and will be

referred to in this document as “the Part 503 Biosolids Rule” or “Part 503.” This

rule establishes the regulations limiting the pollutants and pathogens in

biosolids. Also discussed are the municipal solid waste landfill regulations, published in 1991 under Title 40 CFR Part 258, as they apply to the disposal of

biosolids in MSW landfills. Discussion of landfill regulations in this document will

be referred to as “the Part 258 Landfill Rule.”

7
8

2.1 Wastewater Treatment

Domestic, commercial, and industrial wastewater are collected through an

extensive network of sewers and transported to wastewater treatment plants

(usually POTWs).1

Prior to the release of wastewater into the municipal sewer

network, most industrial plants must pretreat their wastewater to remove certain

contaminants (including metals, such as copper, lead, cadmium, and chromium,

and other pollutants such as chlorinated hydrocarbons). Over the past 20 years,

industrial pretreatment and pollution prevention programs have substantially

reduced levels of metals and other pollutants going into POTWs, resulting in

noticeable improvements in biosolids quality (Walker, 1998). At the POTW,

before it is discharged into the environment, wastewater undergoes preliminary,

primary, secondary, and, in some cases, tertiary treatment (see Table 2-1). The

quantity and characteristics of the biosolids generated at a POTW depend on

the composition of the wastewater, the type of wastewater treatment used, and

the type of subsequent treatment applied to the biosolids. Even within an individual plant, the characteristics of the biosolids produced can change annually,

seasonally, or even daily because of variations in the incoming wastewater composition and variations in treatment processes.

Generally, higher degrees of wastewater treatment can increase the total volume of biosolids generated. Higher levels of treatment also can increase the

concentrations of contaminants in biosolids, because many of the constituents

removed from the wastewater end up in the biosolids. Furthermore, wastewater

processes that involve the addition of chemicals to precipitate the solids (such

as ferric chloride, alum, lime, or polymers) can result in increased concentrations of these chemicals in the biosolids. Other, indirect effects also can occur,

such as when alum (as aluminum hydroxide) adsorbs phosphorus or causes

trace metals (e.g., cadmium) to precipitate out of the wastewater and into the

biosolids. Industrial pretreatment regulations for wastewater, required by federal

and state agencies, as well as pollution prevention programs can reduce levels

of metals and other pollutants in the wastewater treated at POTWs and in the

subsequent biosolids produced. Thus, the type of wastewater treatment or pretreatment used affects the characteristics of biosolids, which in turn can affect

the types of biosolids treatment chosen. The marked improvements in biosolids

quality resulting from pretreatment and pollution prevention programs, for example, can encourage POTWs to process their solids further, such as by composting them. When biosolids achieve the low levels of pollutants that make the

widest distribution of biosolids products possible, processes such as composting

become more attractive.

1

Although the focus of this report is on biosolids generated by POTWs, quantities of biosolids generated by privately and federally owned treatment works are included in estimates presented in

Sections Three and Four. Operations at these treatment works, although smaller than those at

many POTWs, are similar to POTWs.

Background Section Two
Table 2-1

Types of Wastewater Treatment and Resulting Types of Biosolids 

9

Background Section Two

Wastewater Treatment Level

Wastewater screening removes

coarse solids that can interfere with

mechanical equipment. Grit

removal separates heavy, 

inorganic, sandlike solids that

would settle in channels and 

interfere with treatment processes.

Usually involves gravity 

sedimentation of screened, 

degritted wastewater to remove

suspended solids prior to 

secondary treatment.

Generally relies on a biological

treatment process (e.g., suspended

growth or fixed growth systems), in

which microorganisms are used to

reduce biochemical oxygen

demand and remove suspended

solids. Secondary treatment is the

minimum treatment level required

for POTWs under the Clean

Water Act.

Used at POTWs that require higher

effluent quality than that produced

with secondary treatment. Common

types of tertiary treatment include

biological and chemical 

precipitation and processes to

remove nitrogen and phosphorus.

Types of Biosolids Produced

Screenings and grit are handled as

a solid waste and nearly always

landfilled. This material is excluded

from the definition of biosolids and

from the 40 CFR Part 503 

regulation governing the use or 

disposal of biosolids.

Biosolids produced by primary

wastewater treatment usually

contain 3 to 7 percent solids; 

generally their water content can be

easily reduced by thickening or

dewatering.

Biosolids produced by secondary

wastewater treatment usually have

a low solids content (0.5 to 

2 percent) and are more difficult to

thicken and dewater than primary

biosolids.

Lime, polymers, iron, or aluminum

salts used in tertiary wastewater

treatment produce biosolids 

with varying water-absorbing 

characteristics. Also, high-level lime

precipitation produces alkaline

biosolids.

Screening and Grit Removal

Primary Wastewater Treatment

Secondary Wastewater Treatment 

Tertiary (Advanced) Wastewater Treatment
2.2 Biosolids Treatment

Most biosolids undergo additional treatment on site before they are used or disposed of to meet regulatory requirements that protect public health and the

environment, facilitate handling, and reduce costs. Biosolids characteristics can

determine a municipality’s choice of use or disposal methods. Only biosolids

that meet certain regulatory requirements for pathogens, vector attraction reduction, and metal content (discussed in Section 2.3.1), for example, can be land

applied or used as compost. Even those biosolids that are disposed of rather

than land applied must meet regulatory requirements (see Sections 2.3.2 and

2.3.3). Also, with regard to handling and cost, the water content of biosolids can

affect many aspects of biosolids management, such as transportation and the

size of treatment and use or disposal operations. Some biosolids treatment

processes reduce the volume or mass of the biosolids (such as biosolids digestion processes), while others increase biosolids mass (for example, when lime is

added to control pathogens.) The two most common types of biosolids treatment processes are stabilization and dewatering.2

Stabilization refers to a number of processes that reduce pathogen levels, odor,

and volatile solids content. Biosolids must be stabilized to some extent before

most types of use or disposal. Major methods of stabilization include alkali

(lime) stabilization, anaerobic digestion (digestion of organics by microorganisms in the absence of oxygen), aerobic digestion (digestion of organics by

microorganisms in the presence of oxygen), composting, and/or heat drying

(described in more detail in Section 2.2.1).

Dewatering removes excess water from biosolids and generally must be performed before biosolids are composted, landfilled, dried (e.g., pelletized or heat

dried), or incinerated. A number of dewatering processes can be used, including

air drying, vacuum filters, plate-and-frame filters, centrifuges, and belt filter

presses (discussed in Section 2.2.2). 

2.2.1 Stabilization Processes

Alkaline Stabilization

The improved structural characteristics of stabilized biosolids (compared to

dewatered biosolids cake without lime stabilization) generally reduce pathogens

and odors, allow for more efficient handling operations, and provide a source of

lime to help neutralize acid soils. While lime is most commonly used, other alkaline materials, such as cement kiln dust, lime kiln dust, Portland cement, and fly

ash, have also been used for biosolids stabilization.

Background Section Two

2

Most of the information discussed in Sections 2.2.1 and 2.2.2 has been taken from the

Regulatory Impact Analysis of the Part 503 Regulations (U.S. EPA, 1993a), Process Design

Manual on Land Application of Sewage Sludge (U.S. EPA, 1995a), A Plain English Guide to the

Part 503 Biosolids Rule (U.S. EPA, 1994a), and Use and Disposal of Municipal Wastewater

Sludge (U.S. EPA, 1984).

10
Historically, alkaline stabilization has been implemented using either quicklime

(CaO) or hydrated lime (CA[OH]2), which is added to either liquid biosolids

before dewatering or dewatered biosolids in a contained mechanical mixer.

Traditional lime stabilization processes are capable of producing biosolids 

meeting the minimum pathogen and vector attraction reduction requirements

found in the 40 CFR Part 503 rules governing land application of biosolids; sufficient lime is added so that the pH of the biosolids/lime mixture is raised to 12.0

or above for a period of 2 hours. The elevated pH helps to reduce biological

action and odors.

In recent years, a number of advanced alkaline stabilization technologies have

emerged, some of which use other chemical additives to replace the lime (in

part or fully). Many of the newer technologies use similar biosolids handling and

mixing equipment as traditional lime stabilization (although some use special

equipment), but the precise chemical formulas of the stabilization additives

and/or the processing steps used are generally proprietary. Thus, many of these

technologies are available only to POTWs as procurements from private firms.

The most common modifications used in these newer technologies include the

addition of other chemicals, a higher chemical dose, and/or supplemental 

drying, which: 1) increase solids content and granularity; 2) reduce mobility of

heavy metals; 3) increase the agricultural lime value; 4) achieve a higher degree

of pathogen reduction, including the production of a biosolids product with

pathogens below detectable levels; and/or 5) achieve long-term stability of the

product to allow for storage with minimum potential for odor production or

regrowth of pathogens. Potential markets for advanced alkaline-stabilized

biosolids products include agricultural, slope stabilization, structural fill, and

MSW landfill cover operations.

Anaerobic Digestion

Anaerobic digestion involves biologically stabilizing biosolids in a closed tank to

reduce the organic content, mass, odor (and the potential to generate odor),

and pathogen content of biosolids. In this process, microorganisms consume a

part of the organic portion of the biosolids. Anaerobic bacteria that thrive in the

oxygen-free environment convert organic solids to carbon dioxide, methane

(which can be recovered and used for energy), and ammonia. Anaerobic 

digestion is one of the most widely used biosolids stabilization practices, 

especially in larger treatment works, partly because of its methane recovery

potential. Anaerobic digestion is typically operated at about 35o C (95o F), but

also can be operated at higher temperatures (greater than 55o C [131o F]) to 

further reduce solids and pathogen content of the stabilized biosolids.

Aerobic Digestion

Aerobic digestion involves biologically stabilizing biosolids in an open or closed

vessel or lagoon using aerobic bacteria to convert the organic solids content to

carbon dioxide, water, and nitrogen. Pathogens and odors (and the potential to

generate odors) are reduced in the process. Aerobic digestion is commonly

used by smaller POTWs and often is accomplished using wastewater treatment

11

Background Section Two
12

lagoons containing aeration equipment. The high-temperature operation 

(i.e., higher than 55o C [131o F]) of aerobic digestion is becoming more popular

because it can produce biosolids with lower pathogen levels and higher 

solids content.

Composting

Composting is the decomposition of organic matter by microorganisms in an

environment that controls the size and porosity of the pile, thereby facilitating an

increase in temperature (typically to about 55o to 60o C [131o to 140o F]) to

destroy most pathogens. The moisture and oxygen levels of this process are

also controlled to reduce the potential for processing odors. During the process,

biosolids are degraded to a humus-like material with excellent soil conditioning

properties at a pH range of 6.5 to 8, which is conducive to growing healthy

plants and reducing the mobility of metals. Composting involves mixing dewatered biosolids with a bulking agent (such as wood chips, municipal yard 

trimmings, bark, rice hulls, straw, or previously composted material) and 

allowing the biosolids mixture to decompose aerobically (in the presence of 

oxygen) for a period of time. The biosolids mass is initially increased due to the

addition of the bulking agent. The bulking agent is used to lower the moisture

content of the biosolids mixture, increase porosity, and add a source of carbon.

Depending on the method used, the biosolids compost can be ready in about 

3 to 4 weeks of active composting followed by about one month of less-active

composting (curing). 

Three different composting processes are typically used: windrow composting,

aerated static piles, and in-vessel composting. In windrow composting, the

biosolids and bulking agent mixture are formed into long, open-air piles. The

piles are turned frequently to introduce oxygen into the pile, ensure that adequate moisture is present throughout the pile, and ensure that all parts of the

pile are subjected to temperatures of 55o C (131o F) for destruction of pathogens. Aerated static piles (or windrows) are rectangular piles supplied with

oxygen via blowers connected to perforated pipes or grates running under the

piles. In-vessel composting takes place in a completely enclosed container

where temperature and oxygen levels can be closely monitored and controlled.

In-vessel composting also helps contain process and building air so that it can

be captured and treated for odors.

Various odor control measures, such as frequent turnings, are used in conjunction with most composting operations (see Section Five). Frequent turnings help

reduce odor-producing anaerobic pockets in the composting biosolids by introducing oxygen and remixing pile ingredients. This approach, however, might not

work well for large operations near residential areas because the turnings themselves (while adding more oxygen to the process) generate more odors initially.

In these cases, timing the turnings to occur when conditions are ideal (such as

when climate conditions are most advantageous) is used to minimize odors as

well as collecting and scrubbing the off-gasses chemically or biologically

(through packed towers, mist towers, or constructed biofilters).

Background Section Two
Biosolids composting might interest MSW facility operators because biosolids

can be composted in combination with various organic components of MSW

such as yard trimmings (e.g., leaves, grass clippings, brush), paper, and

chipped wood debris. The benefits of composting (see Table 2-2) include diverting these resources from landfills while producing a high-quality soil amendment. If biosolids are included as part of the compost, the processing and

product are subject to the 40 CFR Part 503 Biosolids Rule. Furthermore, if the

finished compost product meets 40 CFR Part 503 Biosolids Rule Class A specifications for the highest level of pathogen and vector control (as described in

Section 2.3.1) and specific metals limits, the compost product can be widely

used, like any other fertilizer or soil-conditioning product. MSW operators who

compost can simply meet these Part 503 Biosolids Rule requirements for Class

A pathogen status and vector attraction reduction by using good management

practices, careful documentation, and high-quality biosolids (that meet the

pollutant concentration limits in Table 3, Section 503.13). Important end uses for

biosolids compost include landscaping projects, nursery operations, and applications to parks, lawns, and home gardens. Additionally, biosolid compost is

often used for soil blending, landfill cover, application to golf courses, mine

reclamation, degradation of toxics, pollution prevention, erosion control, and

wetlands restoration. It also is used for agricultural purposes, such as application to citrus crops (BioCycle, 1997 and U.S. EPA, 1997a). Composts made

from biosolids can also be tailored to remediate contaminated soils (U.S. EPA,

1997a; U.S. EPA 1998a).

Although biosolids compost has less total nitrogen than most other forms of

treated biosolids (due to processing and dewatering, dilution of nutrients by

bulking material, and loss of ammonia during the composting process), this

nitrogen is released more slowly and, thus, is available to plants over a longer

period of time, which is more consistent with plant uptake needs. Biosolids compost also is an excellent soil conditioner, and the slow release of nitrogen in

compost reduces leaching of nitrogen into the water table—a common problem

with other types of soil conditioners and conventional fertilizers. Also, by promoting a healthy soil microflora, compost can help prevent plant diseases. For more

information on the composting process, see Section Five, as well as the

sources Composting of Yard Trimmings and Municipal Solid Waste (U.S. EPA,

1993b), Compost—New Applications for an Age-Old Technology (U.S. EPA,

1997a), and An Analysis of Composting as an Environmental Remediation

Technology (U.S. EPA, 1998a). A number of communities have highly successful, cost-effective composting programs. In 1997, 198 biosolids composting facilities were in operation in the United States (BioCycle, 1998). Some of these

programs are profiled in Section Five.

13

Background Section Two
14

Table 2-2

Benefits of Using Compost

Background Section Two

Soil Enhancement

Plant Growth

Pollution Prevention

Compost aerates the soil and

improves the soil’s water-holding

capacity and structure by adding

organic materials.

Compost provides a slowly released,

long-term source of nutrients, 

promotes faster root development,

and can reduce plant disease by

promoting beneficial microorganisms

that reduce plant parasites.

• The soil and plant improvements

that composting provides can

result in reduced use of fertilizers

and pesticides. 

• When compost is used, 

fertilizers, metals, organic 

chemicals, and pesticides are

less able to migrate to and 

contaminate ground water and

surface water. 

• Compost also can help prevent

soil erosion by increasing water

infiltration. 

• Composting instead of landfilling

reduces methane gas formation

in landfills, which can contribute

to global warming if not 

appropriately captured and

utilized. 

Benefit Description

Source: Adapted from Garland, et al., 1995.
Heat Drying and Pelletizing

Heat drying involves using active or passive dryers to remove water from

biosolids (solar drying is used in some locations). It is used to destroy

pathogens and eliminate most of the water content, which greatly reduces the

volume of biosolids. Heat-dried biosolids from secondary treatment processes

generally do not have objectionable odors, especially when stored dry, whereas

heat-dried primary biosolids can have objectionable odors even when stored

dry. Several highly successful products are prepared using this process 

(e.g., Milorganite®, produced and sold by the city of Milwaukee since the 1920s)

(U.S. EPA, 1995a). Heat drying has the advantage of conserving nitrogen but

does require fuel for processing. In some cases, the heat-dried biosolids are

formed into pellets. These products are very dry and, therefore, can save 

significantly on transportation costs over compost or other forms of biosolids

with higher moisture contents. Thus, heat drying and pelletizing might be

processes of choice for urban communities where distances to agricultural land

can be substantial. Boston, Massachusetts, and New York City, for example,

pelletize and transport their biosolids out of state.

2.2.2 Dewatering

Dewatering decreases biosolids volume by reducing the water content of

biosolids and increasing the solids concentration. Dewatering often is a necessary process before treatment or use, such as before composting, heat drying,

or biosolids preparation for land application, although liquid biosolids can be

land applied using common or specialized application methods (see Section

2.3.1). Dewatering also is necessary for biosolids destined for incineration to

prevent damage to boilers and decrease the energy required for biosolids 

combustion. Additionally, landfilled biosolids are required to be dewatered

because disposal of liquids in landfills is prohibited. Dewatering makes handling

of the biosolids easier by converting liquid biosolids to a damp cake and

reduces transportation costs, although cost savings should be weighed against

the cost of dewatering. Dewatering might be undesirable for land application of

biosolids in regions where water itself is a valuable agricultural resource.

Prior to dewatering, biosolids are usually conditioned and thickened. In 

conditioning, chemicals, such as ferric chloride, lime, or polymers, are added to

facilitate the separation of solids by aggregating small particles into larger 

masses or “flocs.” In thickening, part of the water bound to biosolids particles is

removed to concentrate the solid materials. Gravity thickening is a common

practice (Walker, 1998).

Typical dewatering methods include air drying and mechanical systems. 

Air drying involves placing biosolids on a sand bed and allowing them to dry

through evaporation and drainage. This process can produce a solids content in

primary biosolids of as high as 45 to 90 percent. Air drying systems are relatively simple in terms of operation but require large land areas and relatively long

periods of time and, therefore, tend to be used by small POTWs that generate

15

Background Section Two
16

small amounts of biosolids. Larger POTWs rely on mechanical dewatering systems such as vacuum filters, plate-and-frame filter presses, centrifuges, and belt

filter presses. Vacuum filters, which typically achieve 12- to 22-percent solids

content, involve rotating a drum submerged in a vat of biosolids and applying a

vacuum from within the drum, drawing water into the drum, and leaving the

solids or “filter cake” on the outer drum filter medium. The dewatered biosolids

are scraped off the filter. This form of dewatering is now being replaced by belt

filter presses, centrifuges, and, in some cases, plate-and-frame presses.

Centrifuges spin biosolids in a horizontal, cylindrical vessel at high speeds, with

the solids concentrating on the outside of the vessel. These solids are then

scraped off. Centrifuging can result in a 25- to 35-percent solids content. Belt filter presses can achieve 20- to 32-percent solids content. They work by exerting

pressure on biosolids placed between two filter belts, which are passed through

a series of rollers. The pressure forces water out of the biosolids, and the dried

biosolids cake is retained on the filter belt. Plate-and-frame presses are the

most expensive system to operate and can produce 35- to 45-percent solids

content. They work by squeezing the biosolids between two porous plates or

diaphragms. The pressure forces water out of the biosolids, and the dried

biosolids cake is retained on the plates. 

Table 2-3 presents some of the common stabilization technologies and the use

or disposal method typically associated with each process.

Table 2-3

Stabilization Technologies and Associated Use or Disposal Methods

Background Section Two

Aerobic or Anaerobic Treatment

(Digestion)

Alkaline Treatment

Composting

Heat-Drying/Pelletizing

Produces biosolids used as a soil

amendment and organic fertilizer on

pasture and row crops, forests, and

reclamation sites; additional 

treatment, such as dewatering, also

can be performed (see note below).

Produces biosolids useful for land

application and for use as daily 

landfill cover.

Produces highly organic, soil-like

biosolids with conditioning properties

for horticultural, nursery, and 

landscape uses.

Produces biosolids for fertilizers 

generally used at a lower rate

because of higher cost and higher

nitrogen content.

Treatment Process Use or Disposal Method

Note: Two or more processes are often used for treating biosolids (e.g., anaerobic digestion with

dewatering and composting).

Source: Adapted from U.S. EPA, 1997b.
2.3 Biosolids Use and Disposal Practices

The most common destinations for biosolids include various types of land 

application sites (after the biosolids have been treated to meet regulatory

requirements), landfills, and incinerators.

2.3.1 Land Application and Other Beneficial Use Options for

Biosolids

Land application involves the spreading of biosolids on the soil surface or 

incorporating or injecting biosolids into the soil. Land application has been practiced for decades and continues to be the most common method for using

biosolids. Biosolids serve as a soil enrichment and can supplement or replace

commercial fertilizers. Nutrients (e.g., nitrogen and phosphorus), micronutrients

including essential trace metals (e.g., copper, zinc, molybdenum, boron, calcium, iron, magnesium, and manganese), and organic matter in the biosolids are

beneficial for crop production, gardening, forestry, turf growth, landscaping, or

other vegetation.

Biosolids generally have lower nutrient contents than commercial fertilizers.

Biosolids typically contain 3.2 percent nitrogen, 2.3 percent phosphorus, and 

0.3 percent potassium, while commercial fertilizers might contain 5 to 10 percent

nitrogen, 10 percent phosphorus, and 5 to 10 percent potassium (Metcalf &

Eddy, 1991). Nevertheless, the use of biosolids conditions the soil and reduces

or eliminates the need for commercial fertilizers, thereby reducing the impacts of

high levels of excess nutrients entering the environment. Furthermore, although

biosolids contain metals, so do fertilizers, although data on metals in fertilizers

are not comprehensive. States are only now starting to look at regulating metals

levels in fertilizers, whereas metals in biosolids have been regulated for years.

See Box 1 for a discussion of regulations affecting the land application and

other beneficial uses of biosolids. 

Biosolids treatment before land application can involve digestion, composting,

alkaline treatment, heat treatment, or other methods. Biosolids are treated to different levels, depending on the end use. In many cases, land application of

biosolids is less expensive than disposal methods (Federal Register, Vol. 54,

No. 23, pp. 5476-5902, February 6, 1989). Biosolids composting adds cost, but

the resulting compost has a wide variety of uses, and a composting program

has the potential to reduce municipal funding normally spent on purchasing soil

amendments and/or provide a high-quality compost to many other users.

Furthermore, composting offers ease of storage and ease of application

because of its semidry product, less odors, and more flexibility in land application due to its high quality.

Some of the uses for biosolids and biosolids composts include their application

to various types of land including agricultural lands, forests, mine reclamation

sites and other drastically disturbed lands, parks, and golf courses. Composted

and treated biosolids are used frequently by landscapers and nurseries and by

17

Background Section Two
18

Background Section Two

Box 1: Regulations Affecting Beneficial Use of Biosolids

Biosolids must meet the requirements specified in the 40 CFR Part 503

Biosolids Rule, “The Standards for the Use or Disposal of Sewage Sludge”

before they can be beneficially used. The Part 503 Biosolids Rule land

application requirements ensure that any biosolids that are land applied

contain pathogens and metals that are below specified levels to protect the

health of humans, animals, and plants. Part 503 also requires that the

biosolids are applied at an “agronomic rate,” which is the biosolids application rate designed to provide the amount of nitrogen needed by the crop or

vegetation and to minimize the amount of nitrogen in the biosolids that

passes below the root zone of the crop to the ground water. In addition,

Part 503 requires that vector (e.g., flies and rodents) attraction be reduced

and includes specific management practices, monitoring frequencies, and

recordkeeping and reporting requirements. 

More specifically, the Part 503 Biosolids Rule sets metals limits in land

applied biosolids for nine metals. Four sets of limits are provided: the ceiling limits for land application, more stringent high-quality pollutant concentration limits, the cumulative loading limits, and the annual limits for bagged

products not meeting the high quality pollutant concentration limits.

Biosolids that meet pollutant concentration limits can be applied to sites

without tracking cumulative loading limits, as long as the rate does not

exceed the agronomic rate. Biosolids that meet the ceiling limits but not the

pollutant concentration limits can only be applied until the amount of metals

on the site have accumulated up to the cumulative limits. 

The Part 503 Biosolids Rule divides biosolids into “Class A” and “Class B”

biosolids in terms of pathogen levels. It also imposes a vector attraction

reduction requirement, providing specific alternatives for meeting the

requirement. Whether biosolids are Class A or Class B can affect MSW

facility operators in several ways. Class A biosolids must undergo treatment that reduces pathogens (including pathogenic bacteria, enteric viruses and viable helminth ova) in the biosolids below detectable levels. Once

these goals are achieved, Class A biosolids can be land applied without

any pathogen-related restrictions at the site. Class A biosolids (but not

Class B) can be used as bagged biosolids marketed to the public. Some of

the treatment processes described earlier, such as composting, heat drying, and high-temperature aerobic digestion, can meet the Part 503

Biosolids Rule Class A pathogen reduction requirements if they are conducted to meet operating conditions also specified in the rule. Biosolids

having the least further restrictions on beneficial use are those meeting the

Class A pathogen and vector attraction reduction requirements, and the

high-quality pollutant concentration limits for metals. Once these requirements are met, the biosolids can be used with no more restrictions than

any other fertilizer or soil amendment product.
homeowners for lawns and home gardens. Agricultural land application of

biosolids has worked well for many communities. Application of biosolids to forest lands, which currently involves a relatively small percentage of biosolids, can

help shorten pulp wood and lumber production cycles by accelerating tree

growth (U.S. EPA, 1994c). At reclamation sites, biosolids help revegetate barren

land and control soil erosion; relatively large amounts of biosolids are used to

achieve these goals at reclamation sites. A growing market is the use of

biosolids in manufactured soils, which can be used for erosion control, roadway

construction, and parks (U.S. EPA, 1998a). Composted and heat dried or pelletized biosolids used on public lands, lawns, and home gardens are often sold

or given away in bags or bulk quantities; these forms are usually of excellent

quality (with very low levels of metals and pathogens below detection levels),

are easy to store and handle, and are usually in high demand. 

The value of crop or other vegetation improvements from using marketed

biosolids products (such as bagged or other containerized biosolids) has been

estimated at between $35 to $50 per dry ton more than the value generated by

other potting media (U.S. EPA, 1995a). In some areas, such as King County,

Washington, a high demand for composted biosolids products exists. Some

communities, such as Austin, Texas, give away some of their composted

biosolids (although a nominal cost is strongly recommended to support regional

compost markets). Biosolids also have valuable properties that many commercial fertilizers cannot duplicate (e.g., the slow release of nutrients providing longterm nourishment to plants). A number of communities, such as Milwaukee with

its well-known Milorganite® brand biosolids product (heat dried, not composted),

19

Background Section Two

Class B biosolids ensure that pathogens in biosolids have been reduced to

levels that are protective of public health and the environment under the

specific use conditions. Site restrictions apply to Class B biosolids, which

minimize the potential for human and animal contact with the biosolids until

environmental factors have reduced pathogens to very low levels. Class B

biosolids cannot be sold or given away in a bag or other container for land

application at public contact sites, lawns, and home gardens. Class B

biosolids can be used in bulk at appropriate types of land application sites,

such as agricultural lands, forests, and reclamation sites, if the biosolids

meet the limits on metals, vector attraction reduction, and other management requirements of Part 503. Biosolids can be used as MSW landfill

cover, as long as they meet regulatory requirements in 40 CFR Part 258,

which governs MSW landfills (the Part 503 Biosolids Rule does not cover

biosolids that are disposed of in MSW landfills but states that biosolids disposal in MSW landfills must meet the Part 258 Landfill Rule requirements).

See 40 CFR Part 503 for specific requirements, including which biosolids

treatment processes are approved for Class A and B biosolids, and the

Part 258 Landfill Rule for specific MSW landfill requirements. Section 2.3.3

discusses the Part 258 MSW landfill requirements specific to biosolids 

disposal in more detail.
20

have successfully marketed brand-name biosolids fertilizers or soil conditioning

products. Although ventures in developing composted or further processed

biosolids products involve additional costs for communities over direct land

application, the sale of these products can generate revenue that offsets some

of the costs. Also, communities with existing composting operations, such as for

yard trimmings, may easily incorporate biosolids into their operation using yard

trimmings as a bulking agent. Combining these materials to produce a biosolids

compost could avoid additional costs, since a composting operation is already in

place. Federal and state regulations regarding biosolids composting, however,

must be taken into consideration.

Liquid or dewatered biosolids can be applied by surface spreading or, in the

case of liquid biosolids, by subsurface injection. Surface application methods

include spreading by farm manure spreaders, tank trucks, or special applicator

vehicles. After being applied to the surface and allowed to dry partially, biosolids

are commonly incorporated into the soil by plowing, discing, or other methods.

Liquid biosolids may be malodorous but can be injected below the soil surface

by tank trucks with injection shanks to minimize odors. At forest sites and reclamation sites, spray irrigation of liquid biosolids and special flinging of dewatered

biosolids are common.

2.3.2 Incineration of Biosolids

Incineration of biosolids involves firing biosolids at high temperatures in a combustor or combustion device. The volatile organic materials in the biosolids are

burned in the presence of oxygen. Incineration reduces biosolids to a residue

primarily consisting of ash, which is approximately 20 percent of the original volume. The incineration process destroys virtually all of the volatile solids and

pathogens and degrades most toxic organic chemicals, although compounds

such as dioxin may be formed, and products of incomplete combustion must be

controlled. Metals are not degraded and are concentrated in the ash and in the

particulate matter that is contained in the exhaust gases generated by the

process. Air pollution control devices, such as high-pressure scrubbers, are

required to protect air quality. See Box 2 for information on the regulations

affecting biosolids incineration. Nonhazardous biosolids incinerator ash can be

disposed of in a MSW landfill as allowed by 40 CFR Part 258 Landfill Rule. The

ash also can be used in aggregate (e.g., concrete) production, as a fluxing

agent in ore processing, or for other purposes such as an athletic field amendment (see Section Five).

The types of incinerators most commonly used are multiple-hearth and fluidizedbed furnaces. Fluidized-bed furnaces, however, are known to have fewer problems with emissions than multiple-hearth units because of their more advanced

technology resulting in more uniform combustion of biosolids. Common types of

air pollution control devices include wet scrubbers, dry and wet electrostatic precipitators, fabric filters (all of which control particulates), and afterburners (which

can control releases of partially burned organics). Some municipalities opt for

biosolids incineration when land is scarce or unsuitable for land application. 

Background Section Two
21

Background Section Two

In some cases, municipalities use incinerators as standby units on an 

as-needed basis for use when other biosolids management options cannot 

be implemented.

The type of biosolids incinerated affects incineration efficiency. Due to their higher volatile solids content (i.e., heat content), for example, biosolids from primary

wastewater treatment processes (see Table 2-1) are more suitable for incineration than those that have undergone secondary treatment or above. Biosolids

from secondary wastewater treatment processes are more difficult to incinerate

because of their lower volatile solids content and the higher water content.

Biosolids dewatering is required prior to incineration. Biosolids incinerator ash

can be recovered and used in aggregate or can be used for other products such

as an athletic field amendment (see case studies in Section Five).

Only a few facilities in the United States currently cofire biosolids with MSW

(communication with Steven Levy, U.S. EPA, October, 1997). This practice 

is so rarely used that, for the purposes of this report, we assume all incineration

of biosolids discussed in Sections Three and Four to take place in biosolidsonly incinerators.

Although biosolids incinerators require auxiliary fuel, many facilities that incinerate biosolids include energy recovery as part of the process (communication

with Bob Bastian, U.S. EPA, October, 1997). Most of these facilities use the

Box 2: Regulations Affecting the Incineration of Biosolids

Several regulatory considerations apply to facilities that incinerate

biosolids. The 40 CFR Part 503 Biosolids Rule includes pollutant limits for

metals in emissions that effectively become site-specific limits on metals in

biosolids that are incinerated; limits on total hydrocarbons or carbon

monoxide in emissions; general requirements and management practices;

frequency of monitoring requirements; and recordkeeping and reporting

requirements. If biosolids incinerator ash is applied to land other than in a

MSW landfill, regulations in 40 CFR Part 257 must be followed. Any incinerated waste that meets the definition of a hazardous waste must meet

regulations in 40 CFR Parts 261 through 268 for hazardous wastes.

Additionally, if biosolids and MSW are cofired and MSW accounts for less

than 30 percent of the mixture, the mixture is considered auxiliary fuel and

must meet Part 503 requirements for incineration. If the percentage of

MSW in a biosolids/MSW mixture is greater than 30 percent, then the mixture is not regulated as an auxiliary fuel under the Part 503 Biosolids Rule

but rather is regulated as MSW under 40 CFR Parts 60 and 61. The equipment used in incinerators that cofire biosolids with other wastes generally

must be specially designed for this purpose (e.g., include flash dryers and

separate burners) to handle the moisture content and odor potential of

biosolids successfully. In the near future, incinerators also will be subjected

to regulation under provisions of the Clear Air Act that are more stringent

and are based on what is technically achievable.
22

energy generated within the facility for the incineration process itself (some facilities have claimed to be autothermal, or self-sufficient in producing and using

their own energy) or for energy for other facility processes. A few facilities have

in the past sold at least part of the energy they produced from the incineration

process. In many cases, air quality requirements determine incinerator operation

to some extent because the requirements are temperature-based (i.e., an afterburner to raise the temperature of exit gases might be needed to destroy

unburned hydrocarbons) and often cannot be met economically unless energy

recovery is included in the process. Numerous facilities that incinerated

biosolids have closed over the past decade because other biosolids management options became more publicly acceptable or less expensive, even when

the facilities recovered energy.

To the extent that biosolids are successfully being used for energy recovery and

to the extent that energy recovery might be considered a beneficial use, the

quantities of biosolids that are estimated in this report to be beneficially used

might be somewhat understated. Defining incineration as a disposal method,

however, is consistent with the Part 503 Biosolids Rule, which categorizes

biosolids incineration as a disposal method, since that is the primary purpose of

incinerating biosolids.

2.3.3 Surface Disposal and Landfilling

Most biosolids that are disposed of in or on land are landfilled with MSW. This

report combines most discussions of surface disposal (as covered by the Part

503 Biosolids Rule for biosolids-only disposal in or on land) and landfilling

(defined here as disposal of biosolids in MSW landfills, which is covered by the

Part 258 Landfill Rule rather than by Part 503). See Box 3 for information on the

regulations affecting surface disposal on land and landfilling of biosolids in 

MSW landfills. 

Surface disposal is defined by the Part 503 Biosolids Rule as biosolids placed

on an area of land where only biosolids are placed for final disposal. It does not

include biosolids that are placed on land for either storage (generally less than 2

years) or treatment (e.g., lagoon treatment for pathogen reduction). It involves

landfilling of biosolids in monofills (biosolids-only landfills), disposal in permanent piles or lagoons used for disposal (rather than treatment or temporary storage), and dedicated surface disposal practices. The difference between surface

disposal and land application primarily involves the application rate. If biosolids

are spread on land at greater than the agronomic rate, then the ability of the

cover crop to retain nitrogen might be exceeded, and the excess nitrogen could

migrate through the soil and contaminate ground water. Any time the application

rate exceeds the agronomic rate (except as permitted by the permitting authority

for reclamation sites), EPA considers the practice to be surface disposal, and

the site must comply with all of the management practices outlined for surface

disposal in the Part 503 Biosolids Rule, including ground-water monitoring. If,

however, the applier reduces the application rate or changes the cover crop

from a low-nitrogen-demand crop to a high-nitrogen-demand crop, and the 

Background Section Two
practice meets Part 503 requirements for land application (assuming the land

application criteria for metals concentrations and pathogens and vectors are

met; see Box 1), then the practice is considered land application. 

At the time the National Sewage Sludge Survey was conducted, biosolids from

most POTWs practicing surface disposal were determined to be able to meet

the Part 503 pollutant concentration criteria for land application, and, in many

cases, the biosolids were being applied at rates that could be considered agronomic rates (U.S. EPA, 1993a). Therefore, the practice of spreading biosolids

on land for disposal purposes was nearly eliminated by the Part 503 Biosolids

Rule because: 1) the cost of meeting surface disposal management requirements (including ground-water monitoring) is usually much higher than that for

meeting land application requirements and 2) most operations could be easily

adapted to meet the Part 503 definitions of land application.

The vast majority of biosolids currently reported as either surface disposed or

landfilled are likely to be disposed of in MSW landfills.3

The small amounts of

biosolids reported as surface disposed or landfilled that are not disposed of in

MSW landfills are likely primarily disposed of in biosolids-only monofills 

(i.e., landfills dedicated to accepting only biosolids). Monofilling, possibly the

most common surface disposal technique covered by the Part 503 Biosolids

Rule, typically is undertaken using a series of unlined trenches dug into the

ground, into which dewatered biosolids (meeting concentration limits imposed

by Part 503 for unlined surface disposal units) are placed and then covered with

soil. Other techniques less commonly used include fill mounds, area fill layers,

and diked containment.

23

Background Section Two

3

This conjecture is further substantiated by communication with Bob Bastian, U.S. EPA, May, 1997

and by information in BioCycle (1998), which indicates that among the 34 surveyed states that

provided adequate data, less than 2 percent of biosolids are reported to be surface disposed in

biosolids-only monofills.
24

Background Section Two

Box 3: Regulations Affecting the Surface 

Disposal and Landfilling of Biosolids

The Part 503 Biosolids Rule regulates the surface disposal of biosolids

other than landfilling of biosolids with MSW in an MSW landfill, which is

required to meet the Part 258 Landfill Rule. According to Design, Operation

and Closure of Municipal Solid Waste Landfills (U.S. EPA, 1994b), all

biosolids disposed in MSW landfills must pass the paint-filter liquids test

(dewatering biosolids to about 20 percent solids or more will generally

meet this goal). Furthermore, the biosolids cannot contain more than 50

parts per billion of polychlorinated biphenyls (PCBs) (40 CFR Part 761)

and must not meet the definition of hazardous wastes under the Resource

Conservation and Recovery Act (RCRA) (that is, they must not meet the

definition of hazardous waste as defined by RCRA or the Toxicity

Characteristic Leachate Procedure test). 

Biosolids used as MSW landfill cover should be dewatered to achieve soillike characteristics. The Part 258 Landfill Rule requires that the daily MSW

landfill cover consist of 6 inches of earthen material (or alternative materials or thickness approved by the state) and that the solid waste be covered

at the end of each day or more frequently as needed to control disease

vectors, fires, odors, blowing litter, and scavenging. Biosolids can be used

as part of a final MSW landfill cover, which must meet the Part 258 Landfill

Rule cover criteria for permeability, infiltration, and erosion control. 

For surface disposal in biosolids-only facilities, Part 503 requires that the

site meet certain locational restrictions similar to the site restrictions in the

Part 258 Landfill Rule. Provisions for closure and postclosure care must be

made, and a plan for leachate collection (if the unit is lined), methane monitoring, and public access restrictions must be developed. If the surface

disposal unit is unlined, the biosolids must meet concentration limits on

arsenic, chromium, and nickel. Also, the surface disposal unit must meet

management requirements similar to those for MSW landfills. These management practices include requirements for runoff collection, leachate collection and disposal (if the unit is lined), vector control, methane

monitoring, and ground-water monitoring or certification, and restrictions on

public access, growing of crops, and grazing of animals. See the Part 503

Biosolids Rule and U.S. EPA, 1994a for more details.
Section Three

Generation, Use, and Disposal of

Biosolids in 1998

3.1 Generation of Biosolids in 1998

This report uses the National Sewage Sludge Survey (NSSS) estimate of

the quantity of biosolids used or disposed of in 1988 and data on wastewater flow between 1988 and 1996 from the Needs Surveys conducted

during those years to estimate the quantity of biosolids generated in 1998. This

estimate was made on the basis of increased wastewater flow since 1988 and

on the assumption that biosolids generation per gallon of wastewater has

remained approximately the same from 1988 to 1998. (See the Appendix for a

detailed discussion of the methodology used in this report, the sources used,

the assumptions made to derive this estimate, and a presentation of intermediate results.) On the basis of this approach, we estimate that 6.9 million dry tons

of biosolids were generated in 1998. Table 3-1 presents a breakdown of this

estimate to show the quantities of biosolids estimated to have been generated

by primary-only treatment POTWs or secondary-or-above treatment POTWs

and by privately or federally owned treatment works. 

25

Treatment Group

Primary-Only Treatment POTWs

Secondary-or-Above Treatment POTWs

Privately and Federally Owned Treatment Works

Total

Table 3-1

Estimates of Biosolids Generation for Use or Disposal (1998)

1998 Biosolids

Generation (million

U.S. dry tons)

0.5

6.3

0.1

6.9

Source: See Appendix A.2.2.
26

3.2 Biosolids Management Practices in 1998

This report primarily used the 1997 Water Environment Federation (WEF) report

results (with some modifications; see the Appendix) to divide biosolids management practices into use and disposal categories (see Section 1.2). Categories of

management practices considered beneficial use include land application, composting and other approaches to further processing, and other beneficial use.

Composting and further processing and stabilization is a special category partly

created out of WEF survey responses indicating “treatment” or other related

management practices including responses such as fertilizer, lawns and gardens, potted growing media, soil amendments, composting, or pelletizing.

Generally, biosolids receiving further processing (also referred to as “advanced

treatment” in this report) are considered likely to have met Class A pathogen

and vector reduction requirements (see Box 1 in Section Two). We consider the

ultimate end use of these biosolids to be primarily land application. We included

survey responses indicating landfill cover or aggregate in the “other beneficial

use” category. The Part 503 Biosolids Rule does not regulate landfill cover if it is

being placed on MSW landfills; however, we consider landfill cover to be a beneficial use for the purposes of this report. Therefore, the amount of biosolids

used for landfill cover or as aggregate is accounted for within the total amount

of biosolids beneficially used and not within the disposal totals.

Disposal, for the purposes of this document, as discussed in Section Two,

includes surface disposal, landfilling, and incineration. Additionally, in this report,

we have defined an “other” category, which includes WEF survey responses of

any unidentified processes. We have placed quantities included in this very

small category within the disposal totals. 

3.2.1 Beneficial Use of Biosolids in 1998

Table 3-2 and Figure 3-1 present a breakdown of the various biosolids management options, which are categorized as either a beneficial use option or a disposal option. As the table shows, 60 percent of all biosolids generated in 1998

were land applied, received advanced treatment and then land applied, or were

otherwise beneficially used. This category of “other beneficial use,” which

accounts for 7 percent of all biosolids generated, intends to capture and include

as beneficial use the fraction of biosolids that might be used as alternative daily

landfill cover, as part of a final landfill cover, or as aggregate.4 We assume for

the purposes of this report that the land application category is generally associated with Class B biosolids and the advanced treatment category is associated

with Class A biosolids. Out of a total of 6.9 million dry tons, we estimate that 2.8

million dry tons have been land applied after being treated to a Class B

pathogen status. We estimate an additional 0.8 million dry tons to have been

beneficially used after further treatment, such as composting, advanced alkaline

Generation, Use, and Disposal of Biosolids in 1998 Section Three

4

This total differs from the estimate, made by Bastian in 1997, that only 54 percent of all biosolids

generated were beneficially used. The difference is due to the inclusion in this report of an "other

beneficial use" category (i.e., landfill cover and aggregate) accounting for 7 percent of the total

amount contributing to the beneficial use total of 60 percent.
stabilization, or heat treatment, and that 0.5 million dry tons have been beneficially used in another manner for a total of 4.1 million dry tons. See the

Appendix for how we estimated these quantities. 

Other Surface

Estimate Land Advanced Beneficial Disposal/ Inciner-

(millions) Applicationa Treatmentb Use Total Landfill ation Other Total Total

1998 Dry 2.8 0.8 0.5 4.1 1.2 1.5 0.1 2.8 6.9

Tons

Percent of 41% 12% 7% 60% 17% 22% 1% 40% 100%

Total

Beneficial Use Disposal

27

Generation, Use, and Disposal of Biosolids in 1998 Section Three

Table 3-2

Estimates of Biosolids Use and Disposal

Note: Numbers may not add up properly due to rounding.

Source: See Appendix A.3. a

Without further processing or stabilization such as composting.

b

Such as composting.

Figure 3-1 

Estimates of Biosolids Use and Disposal (1998)

COMBINED

DISPOSAL

2.8 MDT (40%)

COMBINED

BENEFICIAL USE

4.1 MDT (60%)

Land Applicationa

2.8 MDT (41%)

Other Disposal

0.1 MDT (1%) Incineration

1.5 MDT (22%)

Surface Disposal/Landfill

1.2 MDT (17%)

Other Beneficial Use

0.5 MDT (7%)

Advanced Treatment

0.8MDT (12%)

MDT (1998) = millions of dry tons

Source: See Appendix A.3. a

Without further processing or stabilization such as composting.
28

3.2.2 Disposal of Biosolids in 1998

Table 3-2 also presents a breakdown of the disposal categories. We estimated

that 17 percent of all biosolids were surface disposed or landfilled, 22 percent

were incinerated, and 1 percent were disposed of in some unidentified manner.

Thus, 40 percent (2.8 million dry tons) of all biosolids generated in 1998 were

disposed of primarily in landfills (1.2 million dry tons) or incinerated (1.5 million

dry tons).5

3.2.3 Amount of Biosolids Managed by MSW Facilities in 1998

Out of the total 6.9 million dry tons of biosolids generated in 1998, we estimate

that a total of 1.2 million dry tons were disposed of at MSW landfills, and 0.2

million tons of treated biosolids were handled at MSW facilities as landfill cover

(daily or final). Additionally, MSW facilities6 might have composted biosolids

either on or off a landfill site. The total amount of biosolids that might have been

composted by MSW facilities is not known at this time, but we estimate the total

amount to have been 0.4 million dry tons based on the assumptions listed

below. Thus, we estimate that possibly 1.4 to 1.8 million dry tons, or 20 to 26

percent of biosolids generated in 1998, might have been managed by MSW

facilities after processing by POTWs. As noted, these estimates depend on the

following assumptions:

• All surface-disposed or landfilled biosolids are disposed of in MSW landfills.

This assumption is reasonable given the small amount of biosolids believed

to be disposed of in monofills, piles, or surface disposal sites (see Section

Two).7

• No biosolids are coincinerated with solid waste. This is a reasonable

assumption because coincineration is not a common practice.8

• We assume that the advanced treatment category is split such that half is

managed at MSW facilities (landfill, commercial, noncommercial, or municipal

operations, as defined above). MSW facilities are assumed to include any

composting facilities that handle both organic MSW (e.g., yard trimmings)

and biosolids. The actual percentage of the advanced treatment category

(composted) biosolids managed by MSW facilities is not known at this time,

and further research is recommended. 

Generation, Use, and Disposal of Biosolids in 1998 Section Three

5

The quantity of biosolids incinerated might be overstated, but supporting information is inadequate to adjust the data; see discussion in the Appendix.

6

An MSW facility is defined for the purposes of this report to include: 1) any facility, such as an

MSW landfill, that handles MSW; 2) any commercial or noncommercial operation that composts

biosolids and organic MSW suitable for composting (e.g., yard trimmings); and 3) municipal operations not associated with MSW landfills, such as parks departments, public works departments,

or POTWs, that manage composting programs using both organic MSW and biosolids.

7

Also based on communication with Bob Bastian, U.S. EPA, May, 1997.

8

Based on communication with Steven Levy, U.S. EPA, October 1997, and Bob Bastian, U.S.

EPA, October 1997.
Section Four

Trends and Projections for

Biosolids Generation, Use, and

Disposal

Avariety of factors have influenced biosolids generation and use over the

years. Advancements in wastewater and biosolids treatment technologies,

including wastewater pretreatment, pollution prevention programs, and

population growth, have resulted in increased volumes of higher quality

biosolids (Stehouwer and Wolf, 1998). Increases in biosolids amounts and

improvements in quality are only part of the story, however. Federal and state

regulations and guidance, in particular the Part 503 Biosolids Rule, have

encouraged recycling and use of biosolids rather than disposal.9 Additionally, a

number of factors have contributed to increased biosolids use (see Section

Five). These factors include outreach and marketing efforts, high costs for disposal of biosolids in some locations, bans on disposal of biosolids in landfills

(such as in New Jersey), landfill capacity concerns, closures of landfills following

implementation of landfill regulations, bans of yard trimmings in landfills, and

continuing research into the safe beneficial use of biosolids. In some areas of

the country, however, biosolids use has temporarily decreased. In these areas,

landfill costs are relatively low because of the presence of very large landfills

(megafills). This situation is causing some beneficial use operations to begin

landfilling their biosolids. It is not yet clear, however, whether this factor will

affect the overall trend away from disposal of biosolids. This section presents a

summary of these and other factors affecting current trends in biosolids management and includes specific projections for biosolids generation, use, and disposal through 2010.

4.1 Generation

The U.S. population and the population served by municipal sewers have

increased dramatically over the past 20 years. These increases have 

29

9

Three federal beneficial use policies have had an important influence. See U.S. EPA, FDA, and

USDA 1981; Federal Register, Vol. 49, No. 114, pp. 24358-59, July 12, 1984; and Federal

Register, Vol. 50, No. 138, pp. 33186-88, July 10, 1991. 
30

contributed to an increase in the volume of biosolids produced since 1972

(nearly a 50 percent increase; see Section Two). As population levels continue

to increase, we expect the generation of biosolids to increase (Bastian, 1997).

Moreover, during the past 20 years, POTWs increasingly have been treating

wastewater at more advanced levels. By 1988, over 75 percent of the U.S. population was served by POTWs providing secondary wastewater treatment as

mandated by the Clean Water Act. By 1996, this figure had increased to over 90

percent (U.S. EPA Needs Surveys, 1988 to 1996). Also, some secondary wastewater treatment methods can produce additional amounts of biosolids over that

generated by primary treatment alone. The total amount of biosolids produced

annually has increased at a somewhat greater rate than the increased U.S. population being served by sewers (see Appendix calculations and projections).

These increases in quantity have been accompanied by improved environmental quality of biosolids due to the greater prevalence of pretreatment and pollution prevention programs undertaken by industrial wastewater generators. The

physical quality of biosolids also has improved because of advanced mechanical dewatering equipment, automated process control systems, aeration systems, and odor control systems. New technologies such as these have allowed

for lower water content, less odor, and easier handling of biosolids. 

The trends in wastewater flow increases during 1986 to 1996 show an average

of a 4 percent per year decrease in wastewater flow at POTWs using only primary treatment, while wastewater flow at POTWs using secondary or higher levels of treatment has increased about 2 percent per year (see the Appendix).

Assuming that these trends will continue into the future, and using the same

methodology used to estimate 1998 biosolids generation, the expected biosolids

generation amounts in 2000, 2005, and 2010 are shown in Table 4-1 and Figure

4-1 (see the Appendix for methodology). Future biosolids production is expected

to increase from 6.9 million dry tons in 1998 to 7.1 million dry tons in 2000, 7.6

million dry tons in 2005, and 8.2 million dry tons in 2010. This represents a 19

percent increase from 1998 to 2010. These increases are largely due to anticipated increases in population served and, to a lesser extent, the increase in

POTWs using secondary treatment and the subsequent slight increases in

quantities of biosolids produced.

Trends and Projections for Biosolids Generation, Use, and Disposal Section Four

Table 4-1

Projections of Biosolids Generation for Use

or Disposal in 2000, 2005, and 2010

1998

2000

2005

2010

6.9

7.1

7.6

8.2

Source: See Appendix A.5.

Total (million

U.S. dry tons) Year
4.2 Use and Disposal

The following sections discuss general trends in use and disposal that are

expected to continue into the future. 

4.2.1 Use Trends

Just as the generation of biosolids has increased over the past 20 years, so has

the use of biosolids. There are three major reasons for this increase. First, regulatory influences on both the federal and state levels have encouraged the beneficial use of biosolids, either directly through guidance and federal policies on

beneficial use or indirectly because of stringent and higher-cost requirements for

disposal practices (e.g., incineration and landfilling). Second, better biosolids

research and technology also have helped alleviate public concern regarding

the human health and environmental impacts of biosolids. Third, outreach, education, and marketing efforts have been improving public perceptions in some

31

Trends and Projections for Biosolids Generation, Use, and Disposal Section Four

Figure 4-1

Projections of Biosolids Generation for Use

or Disposal in 2000, 2005, and 2010

0

2

4

6

8

10

2000 2005 2010

Year

Total Biosolids Generation

(Million U.S. dry tons)

7.1

7.6

8.2

Source: See Appendix A.5.
32

areas of the United States about the beneficial use of biosolids, although public

acceptance problems persist in other areas. The potential for a growing positive

acceptance of beneficial use of biosolids could lead to increasing biosolids

recovery in the future. 

Regulatory influences on biosolids use include the indirect effects from the

Clean Water Acts of 1977 and 1986 and the more direct effects of the Part 503

Biosolids Rule. The Clean Water Act mandated more active federal involvement

in biosolids management, which previously had been handled primarily at a

state level. Effluent restrictions were set by the National Pollutant Discharge

Elimination System (NPDES) program for industrial facilities discharging to

POTWs. As a result, POTW influent and the resulting biosolids now have lower

levels of contaminants. Biosolids quality has dramatically improved since the

1970s. Regulations promulgated in response to the 1988 Ocean Dumping Ban

Act and the Clean Water Act (i.e., Part 503) prohibited ocean dumping of

biosolids and imposed comprehensive controls on biosolids use and disposal

practices. 

More importantly, Part 503, codified in 1993, clearly defines biosolids quality

requirements for use or disposal and has become a useful tool for biosolids

managers in marketing efforts (U.S. EPA, 1994a). The Part 503 Biosolids Rule

helps biosolids managers identify “exceptional quality biosolids” (i.e., biosolids

that meet the most stringent metals limits and Class A pathogen and vector control requirements—see Box 1 in Section Two). Exceptional quality biosolids are

subject only to the same regulations as any other fertilizer product; thus, the rule

provides a useful public relations tool that has opened the door for greater use

of biosolids as fertilizer and soil conditioner and has also expanded potential

markets for products such as compost made from biosolids. The Part 503 rule

has encouraged POTWs to treat biosolids to a higher quality level and provide

for the least constraints on use. Furthermore, for disposal methods, Part 503

requires relatively expensive pollution control equipment and/or management

practices, such as ground-water monitoring, further encouraging biosolids recycling and use options rather than disposal. 

The increase in biosolids use associated with the implementation of the Part

503 Biosolids Rule is measurable according to a study performed by BioCycle

magazine. This study notes that 37 states have regulations in place that are the

same or more stringent than Part 503 (BioCycle, 1997). Thirty-four states regulate exceptional quality biosolids in the same way they do fertilizers. Both of

these regulatory conditions provide incentives for biosolids recovery and reuse.

Thirty states have increased the beneficial use of biosolids, and many community programs have encouraged biosolids use. Composting programs on the community level, such as in Portland, Oregon; Palm Beach County, Florida; and

Hampton, New Hampshire, have lowered the cost of composting biosolids

(Snow, 1995) by combining biosolids with yard trimmings in their composting

operations. Additionally, composting facilities often charge a tipping fee to

receive yard trimmings, which offsets processing costs.

During the development of the Part 503 Biosolids Rule, EPA extensively

researched the risks of beneficially using biosolids and determined that risks

Trends and Projections for Biosolids Generation, Use, and Disposal Section Four
from properly managed biosolids are negligible (U.S. EPA, 1992a). This

research has allowed EPA to set standards that are protective of human health

and the environment. An independent report by the National Research Council

in 1996 titled Use of Reclaimed Water and Sludge in Food Crop Production concluded that established numerical limits (in the Part 503 rule) on concentrations

of pollutants added to cropland by biosolids are adequate to ensure the safety

of crops produced for human consumption (National Research Council, 1996).

These findings also tend to encourage beneficial use.

Another factor influencing biosolids recycling is public perception, which plays

an important role in biosolids marketability. With the evolution of regulatory standards for biosolids, marketing and promotion of biosolids or products made from

biosolids have been made possible. Although public education on the attributes

of beneficial use has increased public acceptance, increased public awareness

also has the tendency to generate skepticism about the risks of biosolids use,

public health, and the environment. Public opposition to biosolids use, whether

legitimate or unfounded, can arise from any change to the status quo. 

The ability to market biosolids products will be determined by the public’s perception of the safety and value of biosolids recovery. In an effort to improve public acceptance on a national scale and to increase the beneficial use of

biosolids, the National Biosolids Partnership has been established and, with the

support of Congress, will be working with stakeholders to develop an

Environmental Management System (EMS) for Biosolids. The National Biosolids

Partnership consists of representatives from the Water Environment Federation,

the Association of Metropolitan Sewerage Agencies, EPA, states, the U.S.

Department of Agriculture, and other stakeholders. The EMS is a voluntary program designed to help ensure the responsible management of biosolids from

generation of solid wastewater treatment residuals through the further treatment,

transport, storage, and use of the resulting biosolids. Successful EMS development and ultimate implementation depends in great part on the participants and

the development process. Those stakeholders involved in this process include

the public; generators; land appliers; farmers; academics; federal, state, and

local governments; and other interested parties. At a minimum, entities who

pledge to follow the EMS code must be in compliance with all applicable rules

as well as managing nutrients and controlling nuisances such as odors, noise,

and traffic. It is envisioned that the EMS will have:

• A code of good practices that defines broad goals to guide the operation of

biosolids management programs at all facilities and for all projects that adopt

an EMS.

• A manual of good practice that describes the full range of practices available

to facilities and projects that choose to implement an EMS. Each project or

facility will select from the manual those specific practices that are appropriate to its situation.

• A set of procedures that can be used by all entities who pledge to meet the

code in designing and implementing their own EMS.

33

Trends and Projections for Biosolids Generation, Use, and Disposal Section Four
34

• An ongoing program of one or more forms of independent third-party verification and advisory input to insure continuing effective implementation based

on the code.

• A training program to help entities understand what meaningful participation

in the EMS will be.

For more information regarding public acceptance, Section Five of this report

presents a number of issues concerning biosolids use that can negatively affect

public perceptions (e.g., human health risks). Section Five also addresses how

these issues can be dealt with effectively with a careful and well planned

biosolids management program. In addition, several case studies are presented

that highlight successful beneficial use/composting programs.

4.2.2 Disposal Trends

Disposal of biosolids is expected to decrease because of regulatory influences,

voluntary improvements in biosolids quality, and the resulting increase in

biosolids use. Regulatory influences include the increased restrictions on incineration, surface disposal, and landfilling in the Part 503 Biosolids Rule, the Part

258 Landfill Rule, and various state requirements, which also have driven up the

costs of these disposal methods (U.S. EPA, 1993a). In some municipalities,

however, decreases in landfill costs are causing shifts toward increased landfilling and reductions in biosolids recycling. This trend is evident primarily among

municipalities using landfills with excess capacity. The long-term effects of this

factor on biosolids beneficial use is not yet known at this early stage.

As incineration becomes more costly, disposal of biosolids through this method

is expected to decrease. Incineration is a costly means of disposal and is primarily used in large urban areas (proposed Part 503 rule, Federal Register, Vol.

54, No. 23, February 6, 1989, pp. 5476-5902; U.S. EPA, 1993a). Public concern

about the environmental and health impacts of incineration has made this disposal option even more costly and difficult to undertake. Public resistance to

incineration is so great that no new incinerators have been built in recent years,

and expansions or upgrades to existing incinerators are difficult to get approved

(Bastian, 1997). 

Any increased costs of biosolids disposal also are expected to promote beneficial use. MSW landfills built to meet the Part 258 Landfill Rule requirements

incorporate liners, gas control, leachate control, and plans and funding for monitoring and long-term care after closure, which makes them more expensive than

landfills built prior to issuance of the Part 258 Landfill Rule (Regulatory Impact

Analysis (RIA) for 40 CFR Part 258 [U.S. EPA, 1991]). The national average tipping fee is expected to rise from $35 per ton (prior to the Part 258 Landfill Rule

implementation in 1997 dollars) to $38 per ton (U.S. EPA, 1998b). Other analyses, however, have shown no increase in tipping fees in 1998, and according to

these analyses, a very slight downward trend is expected to hold for the next

few years (Glenn, 1998). Where local increases in tipping fees are occurring,

however, communities will be encouraged to consider diverting high-volume,

Trends and Projections for Biosolids Generation, Use, and Disposal Section Four
35

readily compostable organic residues from their landfills. Tipping fees around

the country range anywhere from $15 per ton (Texas) to over $100 per ton (New

Jersey) (U.S. EPA, 1999).

4.2.3 Use and Disposal Projections

Based on the above discussion of expected trends in biosolids use and disposal, Table 4-2 provides projections on the percentages of biosolids that will be

used or disposed of in 2000, 2005, and 2010. The use and disposal of biosolids

were estimated in dry tons for those years (see Table 4-3) in an effort to characterize trends in biosolids use and disposal methods more accurately. As shown

in Table 4-2, beneficial use of biosolids is expected to increase from 60 percent

in 1998 to 63 percent in 2000, 66 percent in 2005, and 70 percent in 2010.

Thus, by 2010, we estimate that disposal might only account for about 30 percent of all biosolids generated. 

Trends and Projections for Biosolids Generation, Use, and Disposal Section Four

Table 4-2

Projections of Use and Disposal

in 2000, 2005, and 2010

Other Surface

Land Advanced Beneficial Disposal/

Year Application Treatment Use Total Landfill Incineration Other Total

1998 41% 12% 7% 60% 17% 22% 1% 40%

2000 43% 12.5% 7.5% 63% 14% 22% 1% 37%

2005 45% 13% 8% 66% 13% 20% 1% 34%

2010 48% 13.5% 8.5% 70% 10% 19% 1% 30%

Beneficial Use Disposal

Source: See Appendix A.5.

Table 4-3 and Figure 4-2 below show estimated quantities of biosolids, in millions of U.S. dry tons, projected to be used or disposed of based on the percentages in Table 4-2 and the quantities of biosolids projected to be generated. The

amount of biosolids estimated to be used beneficially is expected to increase to

4.5, 5.0, and 5.7 million dry tons in 2000, 2005, and 2010, respectively, with 2.6,

2.6, and 2.5 million dry tons, respectively, being disposed of. A positive trend in

the beneficial use of biosolids is expected to continue in the future, while the

trend toward disposal decreases slightly. 
36

Trends and Projections for Biosolids Generation, Use, and Disposal Section Four

0

10

20

30

40

50

60

70

80

90

100

Other

Advanced Treatment

Land Application

1996 2000 2005 2010

Other

Incineration

Surface Disposal/Landfill

1996 2000 2005 2010

BENEFICIAL USE DISPOSAL

YEAR YEAR

41 43 45 48 22

22 20

19

17 14 13 10

12

7

7.5

8

8.5 60

63

66

70

37

40

34

30

12.5 13

13.5

1

1

1

1

PERCENT

Figure 4-2

Projections of Use and Disposal for 2000, 2005, and 2010

Source: See Appendix A.5.
The amount of biosolids going to MSW facilities, as defined in Section Three,10

in the years 2000, 2005, and 2010 reach 1.6, 1.7, and 1.6 million dry tons,11

respectively, with declines in landfilled biosolids being offset by increases in use

of biosolids for landfill cover and in composting. 

Therefore, MSW facilities are likely to be handling about 1.6 million dry tons of

the 7.1 million dry tons generated in 2000 (23 percent), 1.7 million dry tons of

the 7.6 million dry tons generated in 2005 (22 percent), and only about 1.6 million dry tons of the 8.2 million dry tons generated in 2010 (20 percent). These

figures include amounts of biosolids disposed of in MSW landfills, used for landfill cover, or composted for sale or given away to farmers, contractors, or the

general public. 

37

Trends and Projections for Biosolids Generation, Use, and Disposal Section Four

Table 4-3

Projections of Biosolids Use and Disposal in

2000, 2005, and 2010 (million U.S. dry tons)

Other Surface

Land Advanced Beneficial Disposal/ IncinerYear Application Treatment Use Total Landfill ation Other Total Total

2000 3.1 0.9 0.5 4.5 1.0 1.6 0.1 2.6 7.1

2005 3.4 1.0 0.6 5.0 1.0 1.5 0.1 2.6 7.6

2010 3.9 1.1 0.7 5.7 0.8 1.5 0.1 2.5 8.2

Beneficial Use Disposal

Note: Numbers may not add up properly due to rounding.

Source: See Appendix A.5.

10An MSW facility is defined for the purposes of this report to include: 1) any facility, such as an

MSW landfill, that handles MSW, 2) any commercial or noncommercial operation that composts

biosolids and organic MSW suitable for composting (such as yard trimmings), and 3) municipal

operations not associated with MSW landfills, such as parks departments, public works departments, or POTWs, that manage composting programs using both organic MSW and biosolids.

11The quantity of biosolids handled by MSW facilities is estimated to rise slightly by 2005 because

the upward trend in beneficial use offsets declines in disposal, but at varying rates over the years.

The categories of biosolids considered to be managed by MSW facilities include the surface disposal and landfill category and half of the advanced treatment category. See Appendix for more

details of these calculations.
38

Section Five

Beneficial Use of Biosolids

5.1 Overview of Beneficial Use

The beneficial qualities of biosolids as a soil enhancement are generally

recognized. When added to soil, biosolids contribute nutrients and

improve soil properties. Depending on agricultural needs, these benefits

can be even greater with composted biosolids, which enhance the physical,

chemical, and biological properties of soil. Noncomposted biosolids have a high

nutrient availability and decompose and mineralize quickly and easily in soils.

This rapid decomposition of land-applied biosolids can provide large amounts of

nitrogen and phosphorous for immediate use by crops. Composted biosolids, on

the other hand, retain highly stable organic materials that decompose at a slow

rate, therefore releasing nutrients at a slower and steadier rate than noncomposted biosolids (USDA, 1998). Composted biosolids thus provide a long-term

source of slow-release nutrients.

Biosolids compost helps ensure pH stability; improves soil water-holding capacity, aeration, and structural stability; increases resistance to water and wind erosion; and improves root penetration. By promoting beneficial microorganisms,

compost reduces attack by parasites, promotes faster root development, contributes to higher yields of agricultural crops, and reduces reliance on pesticides,

herbicides, and fungicides. Furthermore, compost’s ability to improve the waterholding capacity of soil and fix nitrogen into a form that can be used by plants

reduces the potential for nonpoint-source pollution, such as that associated with

applications of commercial fertilizers. Compost also contributes to water conservation by reducing water loss from percolation, evaporation, and runoff. In addition, compost can be used to bioremediate many toxic contaminants in soil

(Garland, et al., 1995; U.S. EPA, 1997a; U.S. EPA, 1998a). 

According to the Organic Materials Management Strategies report (U.S. EPA,

1998b), the Composting Council estimated the potential demand for compost to

be over 1 billion cubic yards per year (based on 1992 data). The report

describes nine markets for compost: agriculture, silviculture (forests), sod production, residential retail, nurseries, delivered topsoil, landscaping, landfill cover,

and surface mine reclamation. In practice, biosolids compost is more commonly

used by nurseries, landscapers, and soil blenders rather than for agricultural

purposes. Nevertheless, in its analysis, the Composting Council concluded that

the demand for compost in agriculture and silviculture alone could exceed 
39

current and potential supplies. While cost is a constraint with regard to processing, transportation, and bulk application equipment, the primary constraint to

increased use of compost by these markets is the generation of odors during

production. 

Compost is just one form of biosolids that can be beneficially used, however.

The combined potential of using either composted or noncomposted biosolids is

great. By addressing the environmental and public health issues related to

biosolids, the Part 503 Biosolids Rule also has greatly encouraged land application of many other types of biosolids, including advanced alkaline stabilized,

heat-treated, and pelletized biosolids, as well as less highly processed liquid

biosolids and biosolids cake. While there is a trend toward the beneficial use of

biosolids, this trend is sometimes constrained, principally by lack of public

acceptance, as described below.

5.2 Potential Barriers to Increased Beneficial Use

Several factors limit the potential for expanding the beneficial use of biosolids.

These factors include limited public acceptance especially with regard to odors,

liability concerns of landowners, certain cost factors, and the type of crop grown.

This section discusses these barriers as well as ways that these barriers might

be overcome, such as through increasing public outreach efforts and ensuring

the availability of diverse biosolids products for a variety of uses (e.g., both

advanced treatment [such as composted] biosolids as well as less highly

processed Class B biosolids products [to which site restrictions and use restrictions apply]).

5.2.1 Public Acceptance 

Some public resistance to the beneficial use of biosolids persists based primarily on concerns about potential health, environmental, or nuisance impacts. The

public’s perceptions of biosolids treatment and application can affect whether a

facility is built, where it is sited, and how it is operated. Although public perception is often not based on science and can be irrespective of the degree of risk

to human health or the environment, it can present a significant deterrent to

increased beneficial use. Understanding what the public concerns are can allow

biosolids managers to address these concerns as part of their biosolids management program. Overcoming public resistance to the beneficial use of

biosolids involves a combination of sensitivity to public perception issues, a

framework within which the concerns can be addressed, and a willingness to

address these issues through management practices and technologies, effective

outreach programs, and active marketing of biosolids products.

The public’s concerns can be addressed and alleviated in part by increasing

their understanding of how advancements in biosolids technologies and regulations governing the use and disposal of biosolids have resulted in high-quality

products that are safe and suitable for use. One very effective approach toward

Beneficial Use of Biosolids Section Five
40

accomplishing public education is to assemble a biosolids “team” that includes

representatives from all key community stakeholders including university or

other scientists, water quality professionals, public health officials, agricultural

groups and farmers, the environmental community, regulatory officials, and the

media. Although some in the environmental community may oppose biosolids

use, obtaining the involvement of an environmental group can result in a more

successful effort. For example, consider the experience of existing groups that

have addressed public concerns about biosolids, including the Information

Sharing Group in New Jersey and New York, whose efforts included researching

the use of biosolids in an ecologically sensitive area, and the Northwest

Biosolids Management Association (NBMA), in which a member conservation

organization, the Mountains to Sound Greenway Trust, conducts a highly successful public education campaign (Walker, 1998) (see the case study on King

County, Washington, in Section 5.3 for more information on the NBMA).

In addition to implementing a good public education campaign, it appears that

going beyond the requirements of the Part 503 Biosolids Rule (such as conducting additional site monitoring or using Class A biosolids), which is occurring in a

number of locations, can increase the public’s acceptance of biosolids use. It is

important to note that a number of biosolids projects are currently being placed

on hold until states and counties develop their own more stringent rules or ordinances for biosolids use.

Public concern also persists regarding the perceived lack of oversight of

biosolids regulations. Successful oversight can be provided in part by incorporating an operation fee into a biosolids management program that is designated

specifically for third-party inspectors who ensure compliance with the regulations. Also, the biosolids community is now working to develop an

Environmental Management System (EMS) for biosolids that will encourage

good management and community practices that go beyond basic compliance

with the applicable federal, state, and local rules and will include third-party

oversight. The EMS concept for biosolids helps generators, processors (e.g.,

composters), and others focus on critical control points. For example, a critical

control point for odor is at the POTW, and proper management would involve

analyzing how the biosolids are conditioned, thickened, dewatered, and stabilized at the POTW. In addition, conducting demonstration projects that illustrate

good biosolids management and the benefits and safety of using biosolids may

also improve public acceptance of biosolids use (Walker, 1998). 

Odors

The potential for offensive odors can be a significant obstacle, if not the greatest

obstacle, to increasing the beneficial use of biosolids. Not only do the odors

themselves cause a public concern, but odors also trigger fears that ‘foulsmelling’ residues from municipalities and industry must be toxic and harmful. In

some parts of the country, where rapid suburbanization of former farmland has

occurred, biosolids application might no longer be used on the remaining farmland because proximity to residential areas makes actual or potential odor concerns unacceptable to the new neighbors. In other areas, treatment and good

management practices can control most odor problems keeping them to a 

Beneficial Use of Biosolids Section Five
41

minimum; however, occasionally even the best run operations may emit offensive odors. In these instances, there are a number of odor-control methods,

from biofilters to neutralizing solutions, that can help. The composting process

may generally be able to reduce biosolids odors, although the composting

process itself could generate offensive odors if not managed properly. 

Considerable information is available on abating or controlling odors generated

from composting or other biosolids use operations, and new methods are being

developed. Odors can be controlled by treating malodorous biosolids with lime

prior to shipping to an application site, minimizing anaerobic conditions, maximizing the ability of microbes to break down substances, injecting biosolids into

the soil rather than spreading them on the land surface, and collecting, treating,

and dispersing any odors that are formed (USDA, 1997; Walker, 1998).

Mitigating odor problems is another opportunity for the successful implementation of an EMS where generators, processors, and recyclers of biosolids products will decrease the generation of odors in addition to minimizing other

nuisances impacting public acceptance and perceived oversight. Thus, odor

problems can be prevented or mitigated with technology, advanced planning,

and/or good management practices.

Environmental and Health Concerns

Environmental and health concerns are often the major issues that biosolids

managers must address. The public’s concerns about biosolids often focus on

infectious diseases, bioaerosols, water quality, and the introduction of pollutants

into the environment. A large number of disease-causing bacteria, viruses, and

parasites, including Salmonella and Shigella, are found in untreated wastewater

and biosolids. To the extent that people are unaware of how thoroughly

biosolids are treated to control pathogens, public concern over exposure to

pathogens can impede beneficial use projects. Increasing the public’s awareness of the regulatory requirements of the Part 503 Biosolids Rule for pathogen

reduction can help mitigate this concern. Box 4 summarizes the two levels of

pathogen reduction, other requirements, and typical uses of Class A and Class

B biosolids. These requirements include treatment of the biosolids (e.g., through

heat drying, composting, or other methods) to reduce pathogens to below

detectable levels and reduce odor and vector attraction (Class A); in some

cases, site restrictions are required that allow further pathogen destruction and

reduce potential public exposure (Class B).

Beneficial Use of Biosolids Section Five
42

Beneficial Use of Biosolids Section Five

Box 4: Biosolids Classifications

The Part 503 Biosolids Rule classifies biosolids on their level of pathogen

reduction.

Class A Biosolids undergo advanced treatment to reduce pathogen levels

to below detectable levels. Heat drying, composting, and high-temperature

aerobic digestion (described in Section 2.2) are treatment processes that

typically achieve Class A pathogen reduction requirements. Class A

biosolids, often sold in bags, can be beneficially used without pathogenrelated restrictions at the site. If they also meet vector reduction requirements and Part 503 concentration limits for metals, Class A biosolids can

be used as freely and for the same purposes as any other fertilizer or soil

amendment product. 

Class B Biosolids are treated to reduce pathogens to levels protective of

human health and the environment, but not to undetectable levels. Thus,

Class B biosolids require crop harvesting and site restrictions, which minimize the potential for human and animal contact until natural attenuation of

pathogens has occurred. Class B biosolids cannot be sold or given away

for use on sites such as lawns and home gardens, but can be used in bulk

on agricultural and forest lands, reclamation sites, and other controlled

sites, as long as all Part 503 vector, pollutant, and management practice

requirements also are met.

Concerns also have been raised about the possible health effects associated

with inhalation of airborne dust (“bioaerosols”) originating from composting facilities. According to research published in Compost Science & Utilization (Millner,

et al., 1994), bioaerosols (e.g., Aspergillus fumigatus) from composting do not

impose any unique endangerment to the health and welfare of the general public. The report acknowledges, however, that further research into the occupational hazards of workers at composting sites is needed. Use of proper worker

protection (e.g., dust masks or respirators) at composting sites during screening

would reduce such risks considerably.

The Part 503 Biosolids Rule also provides numerous safeguards for protecting

water quality (for example, when Class B biosolids are applied in bulk, Part 503

states that they cannot be applied less than 10 meters from any surface

waters). Nevertheless, public concerns remain about the potential for biosolids

to pollute water resources. As explained in EPA’s technical support documents

for Part 503 for land application and pathogen control (U.S. EPA, 1992a; U.S.

EPA, 1992b), the potential for contaminants in land-applied biosolids, such as

heavy metals, volatile and semivolatile organic compounds, pesticides, nutrients, PCBs, and pathogens, to reach surface water and ground water was

extensively evaluated, and limits for metals were established that ensure protection of surface waters. (EPA’s risk assessment showed that of all potential toxins, only metals were potentially present in biosolids at levels that might be of

environmental concern.) 
43

The limits set for metals in the Part 503 Biosolids Rule ensure that risks of contaminants entering surface or ground water will be minimal. Additionally, even at

these minimal levels set for metals, composting binds the existing metals in the

biosolids and prevents them from migrating to water resources, being absorbed

by plants, or becoming bioavailable to humans (U.S. EPA, 1997a). Furthermore,

under most circumstances, biosolids must be land applied only at rates that

meet the nitrogen needs of a crop and minimize leaching of nitrogen to ground

water, thus protecting ground water from possible nitrate contamination. Also,

many states go beyond the Part 503 requirements in terms of management

practices and setback requirements, and a few states have more stringent metal

limits than those set in Part 503. Increasing public awareness about the low risk

of contamination of ground water or surface water by nutrients, pathogens, or

chemicals in biosolids and composted biosolids is an important component of a

biosolids beneficial use program.

Public concerns also persist regarding the presence of pollutants and pathogens

in biosolids that might find their way to humans through plant uptake, direct contact, and animal ingestion. Although considerable independent research exists

to demonstrate that the risks to humans are negligible, the public might perceive

higher risks due to the origin of biosolids and past management practices

(USDA, 1997). The Part 503 Biosolids Rule was designed specifically to protect

human health and the environment from these types of risks. EPA’s technical

support document for the rule presents the data, assumptions, and methodologies EPA used to set limits on pollutants in land applied biosolids (U.S. EPA,

1992a). The Agency investigated 14 pathways of exposure including plant and

animal uptake of metals with subsequent ingestion by humans and direct ingestion of biosolids by children. The limits set in Part 503 are protective of human

health and the environment under all likely ways that plants, animals, or humans

can be exposed to pollutants in biosolids.

Informative outreach programs that deal directly with health and environmental

issues and that present the ways in which the Part 503 Biosolids Rule and state

pollutant limits and management practices minimize these risks can help to

increase public acceptance, as demonstrated by the example programs highlighted in Section 5.3. A useful document for reference on the protection provided by the Part 503 rule is EPA’s Guide to the Biosolids Risk Assessments for

the EPA Part 503 Rule (U.S. EPA, 1995b).

5.2.2 Liability Concerns

Property owners, lending institutions, and others involved in biosolids land application have expressed concerns about liability under laws such as the

Comprehensive Environmental Response, Compensation, and Liability Act

(CERCLA) of 1980 and nuisance lawsuits. Adherence to the requirements of the

Part 503 Biosolids Rule, however, addresses these concerns. Persons who land

apply and beneficially use biosolids in accordance with Part 503 are not subject

to CERCLA liability or other federal enforcement actions (Walker and Albee,

1994). The pollutant limits and management practices required in the Part 503

Beneficial Use of Biosolids Section Five
44

rule for land application of biosolids ensure that land-applied biosolids are nonhazardous. Also, the records maintained as part of meeting the Part 503

Biosolids Rule requirements provide evidence that the biosolids placed on a site

are nonhazardous.

5.2.3 Costs

The Part 503 Biosolids Rule regulates numerous biosolids management options,

but communities must decide which options are most appropriate and costeffective given their circumstances. Data developed for the proposed Part 503

rule (Federal Register, Vol. 54, No. 23, pp. 5476-5902, February 6, 1989) indicated that the least expensive management options were surface disposal and

crop application. (Surface disposal has become significantly less prevalent

because of the additional costs imposed by the Part 503 Biosolids Rule; crop

application, prior to the promulgation of either the municipal solid waste landfill

regulations or Part 503, was roughly equal to an assumed average cost for

landfilling [including transportation].) Land application costs (due to suburbanization and possible increases in hauling distances to agricultural land in some

areas) may have increased in the intervening years. Monofilling of biosolids was

roughly 20 percent more expensive than either surface disposal or land application on average and most likely is still more expensive following the implementation of Part 503. Furthermore, landfilling, since the municipal solid waste landfill

regulations came into effect, has generally increased in cost disproportionately

in comparison to these other methods, although landfill costs in some areas are

very inexpensive due to the construction of increasingly large landfills, sometimes called “megafills.”

Cost information for different types of composting processes, researched by

BioCycle magazine is shown in Table 5-1, including capital and operating and

maintenance costs for different types of composting methods. The wide variations in costs are due to vast differences in size from the smallest to largest

facilities. Small facilities will generally incur the smallest capital costs, but can

incur relatively higher operation and maintenance costs on a per-ton basis. A

high cost per ton is typical of facilities that compost only a few tons per year. 

Beneficial Use of Biosolids Section Five
45

Beneficial Use of Biosolids Section Five

Table 5-1

Biosolids Composting Costsa

(1997 data from 100 composting facilities)

Aerated Static Pile

In-Vessel

Windrow

Aerated Windrow

Static Pile

$36,000 - $20 million

$850,000 - $33 million

$50,000 - $8 million

$450,000c

not reported

$12 - $500/dry ton

$18.24 - $540/dry ton

$2.15 - $245/dry ton

$50 - $325/ton

$25 - $165/ton

Source: Goldstein and Block, 1997.

a

Does not reflect revenue generated from the sale of composted products.

b

Costs reported by operations are estimates in many cases. The wide range reflects management

differences at sites, as well as what each facility factors into the operating costs.

c

Only one facility reported a capital cost.

Based on the research, distribution and marketing of biosolids products (e.g.,

composting operations) was, on average, more than three times the cost of the

least expensive options, although this does not take into account revenue from

the sale of the compost, which will offset some of these costs (100 composting

facilities reported revenues of from $1 to $35 per cubic yard, according to

Goldstein and Block, 1997). Also, with reductions in nearby agricultural land in

some areas and the fact that many users of compost provide their own transportation, the difference in cost between composted biosolids and land application of less highly processed biosolids is likely to be decreasing. Furthermore,

there are considerable economies of scale involved in composting, and some

communities might find that composting operations using both biosolids and

organic MSW materials, especially yard trimmings, might become more economical on a cost-per-ton basis than disposing of either waste individually.

Incineration and land reclamation were, prior to 1989 and most likely still are,

the most expensive options on a unit cost basis. The cost of land reclamation as

presented in the Federal Register, however, includes the cost of the reclamation

process itself. If one compares the cost of reclamation with biosolids to the cost

of reclamation without biosolids (that is, using soils purchased or obtained from

other locations), the cost of reclamation using biosolids could be relatively much

lower, and might even represent a cost savings. In land reclamation, it is the

expense of landshaping using costly earth-moving equipment, and not the

biosolids use, that drives costs. Also, three times the amount of biosolids can be

applied for land reclamation as for land spreading at the agronomic rate for crop

growth. Furthermore, the costs of land reclamation reported in the Federal

Register also do not take into consideration the difference between the costs of

Type of Composting

Method Capital Costsb Operation and

Maintenance Costs
46

unused, unproductive land and reclaimed productive land through enrichment by

biosolids or composted biosolids. 

Although land application of biosolids is one of the least-cost management

options, the cost to municipalities or farmers of applying biosolids, monitoring,

recordkeeping, and meeting the management practices of federal, state, and

local regulatory agencies can impede biosolids use. Although biosolids are valuable to farmers as a soil amendment, and some or all of these costs can be

incurred by the contractor or POTW, the availability of low-cost commercial fertilizers may limit farmers’ willingness to pay for biosolids (National Research

Council, 1996). In some municipalities, however, such as Seattle, Washington,

and Madison, Wisconsin, users pay for their biosolids. In others, POTW managers can promote biosolids use by setting up demonstration projects using

biosolids, assisting in the recordkeeping tasks, and covering the cost of applying

the biosolids. In several localities, marketing of biosolids for beneficial use is not

a problem at all; in Madison, Wisconsin, for example, as well as other areas, the

demand for biosolids as a soil amendment exceeds the local supply (see

Section 5.3).

In comparison, composting is considerably more expensive than land application, based on EPA’s Regulatory Impact Analysis (RIA) for the proposed Part

503 Biosolids Rule (U.S. EPA, 1989), although, as discussed above, the cost

differential may be shrinking in some areas. The cost of composting operations

can affect whether this particular beneficial use option is chosen, but the desirability of the composted product and the potential market for a sellable product

that is proven to be safe can offset some of this cost. In Columbus, Ohio, for

example, the city’s compost product, which is sold to the general public as a soil

amendment, has been so successful that on various occasions demand has far

exceeded supply. The case studies presented in Section 5.3 illustrate the

demand for biosolids and the process that can be used to market composted

and other types of biosolids.

Transportation of biosolids is also a substantial cost category for POTWs, and

these costs can have the most significant effect on the total costs of land application. Furthermore, the distance to land application sites is increasing as available land closer to the point of generation becomes more developed (thus

requiring biosolids to be hauled farther). Reducing biosolids volume through

thickening, dewatering, conditioning, and drying can reduce these costs.

Preparation and long-distance shipping of pelletized biosolids, for example, generally can be less expensive than for nonpelletized biosolids because the

reduced water weight results in lower transport costs (communication with

Massachusetts Water Resources Authority, February, 1998). Transportation

costs also can be greatly reduced by finding local markets for biosolids

compost.

Beneficial Use of Biosolids Section Five
47

Beneficial Use of Biosolids Section Five

5.2.4 Crop Considerations

In a number of locations, fiber crops are being replaced with food crops. When

Class B biosolids are applied to land where food crops are raised, waiting periods before harvesting are imposed, which can reduce the usefulness of Class B

biosolids. Municipalities applying biosolids in these areas might need to have

their treatment plants change their treatment process to produce Class A

biosolids (i.e., nondetectable pathogen levels), which require no waiting period

before crop harvest, to encourage farmers to continue to use biosolids; transport

biosolids farther to land apply; or landfill biosolids instead of land apply them.

These trends highlight a need for municipalities to: 1) continue identifying new

locations suitable for land application of Class B biosolids or 2) consider adding

Class A treatment processes.

5.3 Examples of Beneficial Use

The following five examples illustrate how some communities have successfully

addressed the management and beneficial use of biosolids, often in cooperation

with municipal solid waste operations. Each of the programs stresses the importance of education and outreach to obtain public acceptance. The programs

also rely on a variety of disposal and use options, which ensures that biosolids

will be properly managed even in the event that any one option is no longer

viable. Some of the case studies were summarized from applications submitted

to EPA’s Office of Water for its annual Biosolids Beneficial Use Awards Program

for Operating Projects, Technology Development, Research, and Public

Acceptance. These summaries were updated in 1998 with information provided

by key operating personnel in the municipalities.

5.3.1 King County, Washington

King County operates a highly successful biosolids management program that

results in the beneficial use of all biosolids produced at the West Point

Treatment Plant in Seattle and the East Division Treatment Plant in Renton. In

1996, these two wastewater treatment plants, with secondary treatment capabilities, processed a combined 100,000 wet tons (20,000 dry tons) of biosolids,

which were eventually digested anaerobically, dewatered using a centrifuge or a

belt-filter press, and land applied. In 1995, one of the biosolids products originating from these two plants, a Class B biosolids cake, was used for agricultural

land fertilizer and forest applications (such as reclaiming and regreening scars

left from logging roads). A portion of the biosolids is composted by a private

contractor and marketed under the name GroCo® as a general compost for a

variety of applications including those in Seattle parks. 

King County receives revenues from its biosolids cake product provided to farmers and forest owners at $15 to $25 per acre and $35 to $60 per acre, respectively. These prices reflect what each buyer would pay for equivalent chemical
48

fertilizers. In fact, land application of King County’s biosolids cake product,

accounting for 90 percent of the county’s biosolids, has proven to be so effective as a soil fertilizer or amendment that current demand significantly exceeds

the supply. The county also receives $5 per dry ton from the contractor who

composts and markets the other 10 percent of the county’s biosolids. In 1995,

King County received over $100,000 in revenues from selling biosolids, which

helps offset the cost of hauling biosolids from the treatment plant to the contractor. King County also pays to have the biosolids land applied. These hauling and

application costs are less expensive than disposal in a landfill. 

In the early 1980s, the King County biosolids management program suffered a

series of setbacks due to organized public resistance to land purchases for

long-term biosolids cake application projects. As a result of the public’s resistance, most land application projects receiving treated biosolids were halted. The

King County Council then required that the staff of the Biosolids Management

Program be accountable to the council and the public regarding the issuance of

permits and informing the public of projects. Augmenting this shift in accountability from private contractors to the county staff was the formation of the

Northwest Biosolids Management Association (NBMA), an association of 150

municipal biosolids agencies and private firms that work together to share management strategies and initiate research and public education programs.

Together, these developments helped improve public acceptance and provided

information to regulatory agencies, elected officials, and the public.

The current success of King County’s biosolids management program is mainly

due to the county’s extensive outreach and education efforts through NBMA, the

program’s excellent performance record (i.e., no contamination events or regulatory compliance issues), and the development of an efficient and reliable

biosolids and biosolids compost market. 

Public trust and interest has been solidified through the Mountains to Sound

Greenway Biosolids Forestry Program, a comprehensive effort to restore and

protect logged-over mountain slopes and road scars in the I-90 corridor of

Washington State by the Washington Department of Natural Resources,

Weyerhaeuser Company, University of Washington, King County, and the

Mountains to Sound Greenway Trust. The Weyerhaeuser Company will increase

its use of King County biosolids from 2,000 dry tons to 5,000 dry tons per year

to stimulate accelerated vegetative growth in this region. The Greenway Trust, a

respected conservation organization, promotes the use of biosolids, conducts

public education on biosolids recycling and environmental sustainability, and

manages the compost land application program. This project represents a new

way of doing business for wastewater treatment utilities, offers a creative way to

reduce ratepayer costs, and helps the public realize the value of the services

and products created by wastewater treatment. 

Beneficial Use of Biosolids Section Five
49

5.3.2 Los Angeles County, California, Sanitation Districts

Use of biosolids in Los Angeles County began in 1928 with a contract between

a fertilizer supply company and the Joint Water Pollution Control Plant (JWPCP)

in Carson, California, to distribute dewatered, digested biosolids cake from the

plant. Since that time, the County Sanitation Districts of Los Angeles County

(CSDLAC) system, which operates the JWPCP, has grown to seven POTWs

linked by a common sewer system serving 5 million people in Los Angeles

County and treating 500 million gallons per day (MGD) of wastewater. 

Residual solids from six upstream treatment plants with a combined flow of 170

MGD are returned to the sewer system for centralized processing at the

JWPCP, where an additional 330 MGD of wastewater are also treated. All solids

are anaerobically digested at 35° C (96° F) for 20 days and dewatered using

scroll centrifuges to 26 percent total solids. CSDLAC has adopted a strict pretreatment program that helps ensure all biosolids meet the Part 503 requirements for quality. In 1997, the JWPCP generated 119,000 dry tons of Class B

biosolids that meet the Part 503 Biosolids Rule high-quality pollutant concentration limits. 

JWPCP operation and maintenance costs in 1997 were approximately $50 million. These costs would have been considerably higher if not for various cost

saving measures implemented on site, such as using digester gas to produce

steam for heating, fuel pump engines, and generate electrical power. These

measures allowed JWPCP to be energy self-sufficient and save nearly $5 million in 1997. Another cost saving measure has been to enhance the dewatering

performance of the centrifuges, resulting in a major reduction in cake production

and a savings of several million dollars. 

Because of the tremendous volume served by JWPCP, the county developed

various ways to manage biosolids in the last several years. This diversity

ensures that no one contractor, locality, or management practice is relied on so

heavily that its absence in the program would threaten the CSDLAC’s ability to

handle its biosolids. The program currently consists of four different management practices in five counties at seven independent sites that are located up to

200 miles from JWPCP. The four biosolids management practices include: land

application, which accounts for 76 percent of the system’s biosolids; injection

into a cement kiln, which accounts for another 12 percent of the biosolids and

helps reduce the levels of nitrogen oxide (NOx) air emissions from the cement

making process; composting, which has been moved off site to two privately

operated facilities; and landfilling, which accounts for approximately 12 percent

of the system’s biosolids. CSDLAC is in an advantageous position because it

owns and operates a sanitary landfill. The landfill adds flexibility to the entire

biosolids system by providing disposal capacity when conditions might be

unsuitable for land application.

Diversity thrives on a continuous evaluation of new alternatives. The CSDLAC

has a long history of biosolids processing research and development. An example is the construction of a demonstration (2 dry tons per day) in-vessel composting unit combined with a CSDLAC-patented air pollution control system that

Beneficial Use of Biosolids Section Five
50

produces virtually no odors or pollutant emissions. CSDLAC also plays an active

role in local and statewide organizations that promote biosolids use and guide

the development of new regulations that address the public’s needs while

encouraging beneficial use.

5.3.3 City of Austin, Texas

The City of Austin Water and Wastewater Utility has operated a successful

biosolids recycling program since 1986. Austin’s biosolids recycling program

receives approximately 500,000 gallons, or 50 dry tons, of biosolids daily from

the city’s three wastewater treatment plants. The biosolids are mixed in a flow

equalization basin and thickened to 6 to 8 percent solids content before being

anaerobically digested. After anaerobic digestion, the biosolids are dried in a

mechanical dewatering unit or directed to one of five, 5-acre, open-air concrete

drying basins and dried to a solids concentration of 15 to 25 percent. 

About 55 percent of the dried biosolids are mixed with bulking agents (including

yard and tree trimmings), windrow composted, and sold as Dillo Dirt® to the general public through registered vendors. This compost product is used as a soil

conditioner for residential lawns and flower gardens and complies with Part 503

Biosolids Rule requirements for Class A pathogen and vector attraction reduction. Approximately 20,000 cubic yards of Dillo Dirt® are produced annually, with

95 percent sold for $7 per cubic yard to registered vendors including landscapers, nurseries, and garden centers. The remaining 5 percent is given away to

other city departments and local nonprofit organizations. Due to the success of

marketing efforts, the demand for Dillo Dirt® often exceeds the supply.

The remaining 45 percent of dewatered biosolids cake meets Part 503 requirements for Class B pathogen and vector attraction reduction and is land applied

to a farm where hay and pecans are grown.

The Austin program enjoys strong public acceptance resulting from public education and outreach efforts, tours, positive media coverage, and strict adherence to permit requirements. The city has demonstrated the benefits of

biosolids-based soil amendments in various local projects. Also, in a jointeffort

with the Texas Department of Transportation, the city has demonstrated the

benefits of using compost to increase vegetation along Texas highway

roadsides.

The annual operating budget for the Hornsby Bend Biosolids Management

Plant, the city’s centralized biosolids treatment and use facility serving a population of 550,000, is approximately $3 million. Revenues generated through the

sale of Dillo Dirt® and the land application of dried biosolids exceeds $150,000

annually. In addition, all of the city’s yard and tree trimmings are recycled by the

program, resulting in approximately $500,000 in avoided landfill disposal costs

per year.

Austin’s biosolids recycling program has prospered through many challenges,

including the lack of usable equipment and bulking agents for compost and the

Beneficial Use of Biosolids Section Five
51

lack of space for a compost pad. A unique and successful partnership between

the multiple city departments, including solid waste services, electric utility,

parks and recreation, and water and wastewater, has allowed the program to

expand by sharing costs for additional equipment and personnel. 

5.3.4 Columbus, Ohio 

Several years ago, when federal funding for new incinerators was unavailable,

EPA encouraged the city of Columbus to establish a biosolids beneficial use

program. In response, the Columbus Department of Public Utilities established a

biosolids recycling program through three city-owned facilities: Columbus

Compost Facility, Southerly Wastewater Treatment Plant, and the Jackson Pike

Wastewater Treatment Plant. 

The Jackson Pike facility handled 78 MGD of wastewater and produced approximately 15,400 dry tons of biosolids in 1997. Biosolids are stabilized in an anaerobic digester on site with a 58 percent volatile solids reduction. A portion of the

biosolids from the Jackson Pike Plant, locally distributed as Bio-Rich®, is applied

to agricultural areas using a subsurface injection process. The remainder of the

biosolids is incinerated. Biosolids produced by the Jackson Pike Plant are categorized as Class B biosolids products under Part 503. 

In 1997, the Southerly facility treated 82 MGD of wastewater and produced

28,400 dry tons of biosolids, of which 3.8 percent was stabilized using alkaline

treatment on site, 30.5 percent was composted, 8 percent was landfilled, and

the remainder was incinerated during production of “Flume Sand.” A product of

incineration, Flume Sand is a fine red sand that absorbs water more readily,

costs less, and is less abrasive than natural sand. It is used throughout the

Columbus area as an athletic-field amendment. Sales and distribution of Flume

Sand were suspended in June 1997 once the pilot project came to an end,

because the city failed to acquire state approval to finalize the program due to a

lack of state environmental standards. The city is currently preparing a plan for

distribution of Flume Sand that will be submitted to the state for approval.

A portion of the biosolids is diverted from the dewatering centrifuges to lime stabilization, then land applied by subsurface injection at 6 percent total solids. The

remaining biosolids and raw primary biosolids are blended and dewatered to 20

percent total solids for composting or 24 percent total solids for incineration. In

the composting operation, the dewatered biosolids cake is composted using

aerated static piles. It is then placed in windrows to cure for 60 days, producing

a Class A product according to the Part 503 Biosolids Rule. The compost is sold

in bulk and bags as Com-Til® to the general public for use as a soil amendment.

From 1994 to 1997, the city of Columbus averaged 9,800 dry tons of Com-Til®

sales per year. 

The city’s biosolids management program has proved to be cost-effective and

adaptable. From 1994 through 1996, Flume Sand use resulted in $92,000 per

year in avoided landfill disposal costs and generated $18,190 per year in revenues. During that same period, Com-Til® also generated $263,250 per year in

Beneficial Use of Biosolids Section Five
52

additional revenues. Com-Til® has been so successful that on various occasions

the product has been sold out.

The city’s biosolids recycling program is well accepted throughout the community, and there is high demand for all the biosolids products. This situation is primarily due to the various marketing programs, education, and outreach efforts of

the city’s Department of Public Utilities. Educational programs have focused on

the environmental and neighbor-friendly aspects of the various biosolids products. The program, however, initially had to overcome some obstacles.

Problems with excessive biosolids stockpiling on farmland, low market demand

for biosolids products, odor, and poor public perception (stemming from potential contamination events brought about by runoff) were encountered. These

problems were solved by diverting a large portion of the biosolids to land application without centrifuge dewatering. The biosolids, at 6 percent solids, were

lime stabilized and land applied by injection, which reduced odors (when compared to surface-applied cake biosolids), reduced concerns about runoff, and

eliminated field stockpile problems. Diverting a large portion of biosolids from

the dewatering process also helped improve the performance of the centrifuges

and, indirectly, the incinerator, as a result of the higher solids content of the final

dewatered cake. Furthermore, by increasing the total solids content of the

biosolids, the centrifuges also reduced compost material handling costs.

5.3.5 Charlottesville, Virginia

The Rivanna Water and Sewer Authority oversees the operation of the Moores

Creek Advanced Wastewater Treatment Plant in Charlottesville, Virginia, which

is located approximately 120 miles southwest of Washington, DC. The plant

began operating in 1981 and today serves a population of 75,000 (26,000 connections) from the city of Charlottesville and portions of surrounding Albemarle

County. The plant treats 11 MGD of wastewater and has a design capacity of 15

MGD. The plant is equipped with primary, secondary, and tertiary treatment systems, which produce a total of approximately 7,500 cubic yards of dewatered

biosolids per year on average. Wanting to be on the cutting edge of wastewater

management, the city of Charlottesville began to look into ways it could use its

biosolids beneficially while saving landfill disposal costs. As a result, the Moores

plant began composting its biosolids in 1984. Today, the facility produces and

sells 5,700 cubic yards of compost annually for use as a soil amendment. The

remaining 1,500 cubic yards (25 percent) of biosolids is land-applied or used as

landfill cover. The plant hopes to begin composting 100 percent of its biosolids

in the future. 

Once filtered from wastewater, the solids are anaerobically digested. Methane

gas, approximately 95,000 cubic feet per day produced by the digestion

process, is used to operate gas engines that run the blowers providing air for

the aeration basins used in the secondary and tertiary treatment stages. Water

heated using waste heat from these engines also helps heat the digesters and

Beneficial Use of Biosolids Section Five
53

some of the buildings at the plant. After digestion, the solids are dewatered in a

diaphragm filter press (plate-and-frame filter press), which removes about 

65 percent of the water. From there, the biosolids are ready for use in the composting process.

The biosolids are transported to an adjoining compost area on the plant premises. Biosolids from the wastewater treatment plant are mixed with wood chips at

a ratio of three parts wood chips to one part biosolids. The facility annually uses

4,000 cubic yards of wood chips that come from chipped pallets purchased from

a pallet company located in Richmond, Virginia, for $5 per cubic yard ($18 to

$22 per ton). The biosolids/wood chip mixture is placed on a bed of fresh wood

chips covering an asphalt pad in a series of static piles protected from the

weather. The compost temperature is monitored and maintained between 55° C

and 77° C (131° F and 170° F) for 5 days. The temperature probes are then

removed and the piles are left to compost for an additional 10 days, for a total of

15 days to complete the active composting process. The compost is then cured

for 1 month and is tested for salmonella and metals on a quarterly basis. 

The Moores Creek plant’s compost is made available for sale once a month to

the public, selling for $12 per cubic yard in bulk and $15 per cubic yard for small

purchases. Some compost is also manually bagged and sold for $3.50 per 

40-pound bag. It is sold to individuals, nurseries, farmers, and local park and

recreation departments for use on lawns, flowers, house plants, trees, shrubs,

and vegetables.

Beneficial Use of Biosolids Section Five
54

References

Bastian, R., 1997. “The Biosolids (Sludge) Treatment, Beneficial Use, and

Disposal Situation in the USA.” European Water Pollution Control

Journal. Vol. 7, No. 2, pp. 62-79. March.

BioCycle, 1991. “Sludge Management Practices in the U.S.” March.

BioCycle, 1997. “Biosolids Management Practices in the U.S.” May.

BioCycle, 1998. “Biosolids Management Update.” January.

Council of Economic Advisors, 1999. Economic Report of the President: 1999.

U.S. Government Printing Office, Washington, DC.

Garland, G., Grist, T., and R. Green, 1995. “The Compost Story: From Soil

Enrichment to Pollution Remediation. BioCycle. October.

Glenn, Jim, 1998. “State of Garbage.” BioCycle. April.

Goldstein, N. and D. Block, 1997. “Biosolids Composting Holds its Own.”

BioCycle. December.

Metcalf & Eddy, 1991. Wastewater Engineering. 3rd ed. New York: McGraw Hill

Publishing.

Millner, P.D, S.A. Olenchock, E. Epstein, R. Rylander, J. Haines, MD, J. Walker,

B.L. Ooi, E. Horne, and M. Maritato, 1994. “Bioaerosols Associated

with Composting Facilities,” Compost Science & Utilization. Autumn.

National Research Council, 1996. Use of Reclaimed Water and Sludge in Food

Crop Production. National Academy Press, Washington, DC.

Snow, Darlene, 1995. “Getting Down to Earth with Trash and Sludge.” MSW

Management. January/February.

Stehouwer, R. and A. Wolf, 1998. Pennsylvania Sewage Sludge Quality Survey:

1978-1998. Pennsylvania State University.

USDA, 1997. Interagency Agreement between the U.S. EPA and USDA

Agricultural Research Service with Respect to Beneficial

Management of Municipal Biosolids and Other Municipal and

Agricultural Organic and Inorganic Recyclable Products.
55

USDA, 1998. Agricultural Uses of Municipal, Animal, and Industrial Byproducts.

Agricultural Research Service: Conservation Research Report

Number 44. January.

U.S. EPA, FDA, and USDA, 1981. Land Application of Municipal Sewage

Sludge for the Production of Fruits and Vegetables: A Statement of

Federal Policy and Guidance.

U.S. EPA, 1984. Environmental Regulations and Technology. Use and Disposal

of Municipal Wastewater Sludge. EPA625-10-84-003. September.

U.S. EPA, 1989. Regulatory Impact Analysis of the Proposed 40 CFR Part 503

Rule. PB89-136634. February.

U.S. EPA, 1991. Regulatory Impact Analysis for Final Criteria for Municipal Solid

Waste Landfills. PB92-100847. September.

U.S. EPA, 1992a. Technical Support Document for the Land Application of

Sewage Sludge. PB93-110583. November.

U.S. EPA, 1992b. Technical Support Document for Pathogens and Vector

Attraction Reduction in Sewage Sludge. PB93-110609. November.

U.S. EPA, 1993a. Regulatory Impact Analysis of the Part 503 Sewage Sludge

Regulation. PB93-110625. February.

U.S. EPA, 1993b. Composting of Yard Trimmings and Municipal Solid Waste.

Office of Solid Waste and Emergency Response. November.

U.S. EPA, 1994a. A Plain English Guide to the EPA Part 503 Biosolids Rule.

EPA832-R-93-003. September.

U.S. EPA, 1994b. Seminar Publication: Design, Operation, and Closure of

Municipal Solid Waste Landfills. EPA625-R-94-008. September.

U.S. EPA, 1994c. Biosolids Recycling: Beneficial Technology for a Better

Environment. EPA832-R-94-009. June. 

U.S. EPA, 1995a. Process Design Manual: Land Application of Sewage Sludge

and Domestic Septage. EPA625-R-95-001. September.

U.S. EPA, 1995b. A Guide to the Biosolids Risk Assessments for the EPA Part

503 Rule. Office of Wastewater Management. EPA832-B-93-005.

September.

U.S. EPA. Needs Survey, Report to Congress, 1984, 1986, 1988, 1992, 1996.

Assessment of Needed Publicly Owned Wastewater Treatment

Facilities in the United States. Office of Municipal Pollution Control.

U.S. EPA, 1997a. Compost—New Applications for an Age-Old Technology.

Office of Solid Waste and Emergency Response. EPA530-F-97-047.

October. 

References
56

U.S. EPA, 1997b. Biosolids Management, Use and Disposal. Office of Water.

U.S. EPA, 1998a. An Analysis of Composting as an Environmental Remediation

Technology. EPA530-R-98-008. April. 

U.S. EPA, 1998b. Organic Materials Management Strategies. Office of Solid

Waste and Emergency Response. EPA530-R-97-003. May.

U.S. EPA, 1999. Cutting the Wastestream in Half: Community Record Setters

Show How. Institute for Local Self-Reliance. Unpublished document.

Walker, J., 1998. “Biosolids Management, Use and Disposal.” In: Encyclopedia

of Environmental Analysis and Remediation.” Robert A. Meyers, ed.

John Wiley & Sons, Inc.

Walker, J. M. and R. N. Albee, 1994. Yes, But What About the Liability? EPA

and Farm Credit Bank Find Fertile Ground for Dealing with Land

Application Liability Issues. In “Water Connection.” Newsletter of the

New England Interstate Water Pollution Control Commission. Vol 11,

2:10-11, Fall.

Water Environment Federation (WEF), 1997. National Outlook: State Beneficial

Use of Biosolids Activities. June.

References
57

Appendix

Biosolids Generation,

Use, and Disposal

Methodology and Results

A.1 Introduction

Biosolids generation, use, and disposal estimates made in this report in

Section Three and projections of generation, use, and disposal in Section

Four are based on a number of information sources. Estimates of

biosolids generation were based primarily on the 1988 National Sewage Sludge

Survey (NSSS) and the 1984 through 1996 Needs Surveys, as discussed in

detail in Section A.2 and A.4 of this appendix. Several other sources of information on generation rates and use and disposal methods were also investigated,

such as the Water Environment Federation’s (WEF) 1997 report and Robert

Bastian’s 1997 paper, which provide data estimates on biosolids generation,

use, and disposal in 1995 and 1996, respectively. BioCycle (1991, 1997, and

1998) also provides information on generation and use and disposal methods.

The biosolids generation estimates from the WEF report or Bastian (1997) were

considered, but this report also made additional estimates as described in this

appendix to verify the results of these other studies. This appendix discusses

the major data sources used for estimating generation, use, and disposal of

biosolids; the strengths and weaknesses of the data sources; and the methodologies and results of this analysis.

In 1988, EPA conducted the NSSS, a survey of a random sample of 479 publicly owned treatment works (POTWs) to support the development of the Part

503 Biosolids Rule. The survey produced a statistically valid estimate of the

amounts of biosolids used or disposed of by POTWs using at least secondary

wastewater treatment processes. At that time, the number of POTWs using at

least secondary wastewater treatment totaled approximately 11,400. The survey

was stratified on the basis of POTW size (amount of wastewater processed

daily) and principal use or disposal method. The survey also collected data on

pollutant concentrations in biosolids, from which EPA could determine whether

biosolids would meet the criteria being developed under the Part 503 Biosolids
58

Rule. At the time, EPA considered the NSSS estimate of the amount of biosolids

used or disposed of as the most accurate estimate to date. The NSSS, however, is no longer current and also does not provide estimates of biosolids generation by POTWs using primary wastewater treatment processes12 or by privately

or federally owned treatment works. Most importantly, the NSSS cannot provide

an estimate of current practices because the survey was undertaken before the

Part 503 Biosolids Rule was finalized. The Part 503 rule has had an impact on

POTWs’ choices of use or disposal methods, since it generally was written to

encourage POTWs to choose beneficial use rather than disposal if the biosolids

were of sufficiently high quality (U.S. EPA, 1993a).

The WEF (1997) report, which was conducted in cooperation with the

Association of Metropolitan Sewer Agencies (AMSA) using an EPA grant, is an

inventory of biosolids generation, beneficial use, and disposal practices for

1995. WEF surveyed 162 AMSA members and received 117 responses. Twentyfive states and federal regulators also responded to the survey. Additionally, the

report presented information on biosolids beneficial use practices, appropriate

regulations, and attitudes. Although the information in this report is current and

represents half the wastewater flow in this country, the survey primarily captured

data from AMSA members, which tend to be the largest POTWs. The POTWs

associated with the other half of the flow might not operate like the POTWs represented by the WEF data, although the addition of data from other sources

might have helped reduce the large-POTW bias in the data. Despite possible

drawbacks, the WEF data does provide breakdowns of biosolids quantities by

use and disposal methods that can easily be adapted to the categories of use

and disposal methods used in this report.

Data from Bastian (1997) are current for 1996. That paper, published in

European Water Pollution Control (March 1997) presented results of a survey of

state regulators who were asked for 1996 data on total biosolids production and

the percentage of biosolids used or disposed of by land application, surface disposal, incineration, and other means. The paper also describes changes in

biosolids management and treatment and discusses obstacles to biosolids management, such as public acceptance and liability issues. Unless the state is

authorized as the permitting authority, however, it might not have detailed

records of biosolids generation, use, and disposal that would best support a

national estimate. Furthermore, some states do not have easy access to permit

information (i.e., in database form) from which viable aggregate data might be

drawn. Finally, much of the more detailed data are kept primarily at the POTW

level (particularly among the smaller POTWs, which are not required to report

any of their recordkeeping data to the states unless specifically requested or

unless their biosolids quality triggers specific reporting requirements). Therefore,

although some states have excellent data from which to compile state estimates

of biosolids generation, use, and disposal, other states may only be able to estimate roughly the amounts of biosolids generated, used, or disposed of.

Additionally, the WEF report further refines the breakdown of use and disposal

Methodology and Results Appendix

12For purposes of this appendix, the term primary processes means those considered less than

secondary and the term secondary processes means those considered at least secondary.
59

categories, originally presented in Bastian (1997), in a way that is effective for

the purposes of this report. 

Researchers at BioCycle, a journal that covers recycling and management of

biosolids and other organic wastes, surveyed state regulators regarding

biosolids generation and management in 1989, 1996, and 1998. The surveys

provide a state-by-state breakdown of management practices according to land

application, composting, lime stabilization, heat drying or pelletizing, landfilling,

incineration, or surface disposal. The journal also conducts an annual survey of

biosolids composting operations. Again, because these are state data, the information can vary from sketchy to excellent, depending on the level of data collection and management at the state level. As discussed below, the most recent

survey (1997 data) provides data on both total quantities of biosolids generated

(in dry tons) and use and disposal practices for 34 states (BioCycle, 1998).

Because only 34 states with adequate data for the purposes of this report are

represented in the data, any conclusions drawn from these data may be somewhat limited. 

All these sources of information on generation, use, and disposal of biosolids

have their relative strengths and weaknesses. Ultimately, the choice was made

to estimate biosolids generation using the NSSS to provide one more data point

for consideration in addition to analyzing data from the 1997 WEF report and

Bastian (1997) and to use the 1997 WEF report for the distribution of use and

disposal methods. The BioCycle (1998) data and the NSSS were also used as

additional support for the estimates of use and disposal methods. As the results

show later in this appendix, the biosolids generation estimates from the WEF

(1997) report, Bastian (1997), and this report are remarkably similar. We estimate that 6.7 million U.S. dry tons of biosolids were generated for use or disposal in 1996 (both 1996 and 1998 estimates are made in this report). Our

estimate falls between the 1995 WEF estimate of 6.4 million dry tons and the

1996 Bastian (1997) estimate of 6.9 million U.S. dry tons. This estimate is used

in this report for biosolids generated by POTWs practicing secondary or above

wastewater treatment (the major source of biosolids in this country), along with

additional information from other sources about primary treatment biosolids and

those generated by privately and federally owned facilities (U.S. EPA, 1993a).

This report uses the 1997 WEF study primarily as the basis for determining use

and disposal practices in 1998, because the combined data from POTWs and

states are likely to be more accurate than data strictly from the states alone.

The WEF data were also chosen because of how the use and disposal categories are broken out.

A.2 Estimate of Biosolids Generation in 1998

This section describes our estimate of the quantities of biosolids generated in

1996 and then further estimates the quantities generated in 1998. These estimates are primarily based on the 1988 NSSS (results of which are reported in

the Regulatory Impact Analysis (RIA) for the Part 503 Biosolids Rule [U.S. EPA,

Methodology and Results Appendix
60

1993a]) and the 1988 through 1996 Needs Surveys.13 The NSSS does not

address biosolids generation at POTWs using only primary treatment processes

or biosolids generation at privately or federally owned treatment works, therefore, additional information was incorporated from the RIA and the Needs

Surveys to estimate these quantities. To determine quantities of biosolids generated by POTWs using primary treatment processes, this report used an estimate of primary biosolids generation from the RIA (U.S. EPA, 1993a), which

also was based on the 1988 Needs Survey. For POTWs using at least secondary treatment processes, this report used the NSSS and the Needs Surveys.

We estimated privately and federally owned treatment works biosolids quantities

using information developed in the RIA (U.S. EPA, 1993a). This stratification

also was necessary to account for differences in biosolids generation rates at

POTWs using either primary or secondary treatment processes, because primary processes can generate different amounts of biosolids per gallon of wastewater processed than secondary processes. The following discussion shows the

development of an estimate of biosolids generation at POTWs, then follows with

the development of an estimate of biosolids generation at privately and federally

owned treatment works.

A.2.1 Estimate of 1998 Biosolids Generation at POTWs

Methodology

This report begins with an estimate of 1996 biosolids generation because 1996

is the most recent year for which data on total U.S. wastewater flow is available.

The 1998 estimate is based on a projection from this 1996 base year. 

The key assumption in this report for first estimating 1996 biosolids generation

at POTWs is that once biosolids quantities are split between primary and secondary processes, the quantity of biosolids generated per gallon of wastewater

treated at POTWs would not be substantially different in 1996 than it was in

1988.14 Two Biosolids Generation Factors (BGFs), therefore, were created for

estimating biosolids quantities resulting from each process, one for primary

treatment and one for secondary and above. Each of the BGFs (BGFprimary and

BGFsecondary) is equal to the biosolids estimated to be generated by each treatMethodology and Results Appendix

13The 1984 and 1986 Needs Surveys also are used to identify trends in wastewater flow over time

later in this appendix.

14Tertiary processes create additional biosolids per gallon of wastewater treated than either primary or secondary processes, and to the extent that wastewater going to tertiary treatment

processes has increased since 1988, this approach could slightly underestimate biosolids generation rates. This underestimation was not corrected because summary data for the NSSS did not

distinguish between biosolids generated in secondary treatment processes and those generated

in tertiary treatment processes. The amount of wastewater going to tertiary treatment is, however,

relatively small compared to that going to secondary treatment. Furthermore, biosolids generation

might be slightly overstated (particularly for projections made later in this section) because dewatering processes are changing from ferric and lime processes to polymer processes, which

reduce the volume of biosolids generated. Also, with bans on phosphates in detergents, fewer

chemicals are needed for removing phosphates from wastewater, leading to further reductions in

biosolids volume.
61

Methodology and Results Appendix

ment group in 1988 divided by the 1988 annual flow of wastewater treated by

each treatment group. The formula below illustrates an example of this 

calculation:

Biosolids Generated in 1988 Primary Processes (U.S. dry tons) = BGF

primary (1) Total 1988 Annual Primary Wastewater Flow (MGD)

For this calculation, estimates of primary and secondary biosolids generation in

1988 were obtained from the RIA supporting the Part 503 Biosolids Rule (U.S.

EPA, 1993a). For POTWs using secondary processes, the estimates of

biosolids disposal and use from the 1988 NSSS (as reported in U.S. EPA,

1993a) were used to represent the amount of biosolids generated from secondary and above treatment operations.15 The 1988 NSSS data were not used to

estimate primary treatment process biosolids because the survey did not gather

data on biosolids generated exclusively from primary processes. To identify

quantities of biosolids generated from primary processes in 1988, the estimate

of primary biosolids amounts that was developed in the RIA (U.S. EPA, 1993a)

was used. This estimate was based on information obtained from the 1988

Needs Survey and engineering estimates. 

Annual wastewater flow numbers associated with primary and secondary treatment were then obtained. The amount of 1988 annual flow for each treatment

group (both primary and secondary) was taken directly from the 1988 Needs

Survey. The 1996 Needs Survey data did not distinguish the flow rate by level of

wastewater treatment process, however. We assumed that the flow for each

treatment group was proportionate to the total population served for each treatment level reported in 1996.16 For example:

Population Served by Primary Treatment = Percent of Total Flow Attributable (2)

Total Population Served to Primary Treatment

and

Population Served by Secondary Treatment = Percent of Total Flow Attributable (3)

Total Population Served to Secondary Treatment

15Biosolids can be generated in one year and used or disposed of in another year. It is assumed

that the NSSS estimate of use or disposal in 1988 is roughly equivalent to generation, since some

biosolids that were used or disposed of in 1988 were generated in previous years, whereas some

biosolids that were generated in 1988 were not used or disposed of until later years. Although the

NSSS did ask for data on generation, this information did not appear to be presented in any summary document reviewed. NSSS data on biosolids generation might have been of limited accuracy, since respondents with treatment lagoons who did not dispose of biosolids in 1988 would have

needed to estimate generation rates.

16In making this calculation, the 1996 Needs Survey treatment levels were collapsed into two

groups, primary treatment and secondary treatment. The primary treatment group is the same as

the “less than secondary treatment” category, and the at-least-secondary treatment category

includes the “secondary,” “tertiary,” and “no discharge” categories.
62

The percentages of population served for each treatment group in 1996 were

applied to the total 1996 flow to estimate the flow attributable to POTWs in each

treatment category. The applicable BGFs were then multiplied by the estimated

1996 flow for each treatment group (primary and secondary). For example: 

BGF Primary X Total 1996 Annual Flow = Biosolids Generated in 1996 from (4)

for Primary Treatment (MGD) Primary Flow (U.S. dry tons)

and

BGF Secondary X Total 1996 Annual Flow = Biosolids Generated in 1996 from (5)

for Secondary Treatment (MGD) Secondary Flow (U.S. dry tons)

These results provided an estimate of the quantity of biosolids generated in

1996 for both the primary and the secondary treatment groups, the sum of

which gave the total biosolids (in U.S. dry tons) generated by POTWs in 1996. 

The estimate for 1996 was extrapolated to 1998 on the basis of an analysis presented in Section A.4. As Section A.4 discusses, primary treatment wastewater

has been declining on average about 4 percent per year, and secondary and

above treatment wastewater has been increasing on average about 2 percent

per year. These increases and decreases are incorporated into projections of

wastewater flow in those two treatment categories to derive estimates of

biosolids generation in 1998.

Results17

As shown in Table A-1, we estimate (using Equation 1) that the BGFprimary is

203. The BGFsecondary is 206.18 We also estimate that, in 1996, primary flow

was 2,900 MGD and secondary flow was 29,200 MGD using Equations 2 and 3

(see Table A-2). These flow numbers and the BGFs calculated in Table A-1 are

Methodology and Results Appendix

17Throughout the tables in this appendix, totals might not appear to compute exactly because of

rounding.

18Both factors fall within the expected ranges of biosolids generation from wastewater treatment

processes, although generally one might expect the difference between BGFprimary and

BGFsecondary to be somewhat greater because of the ability of secondary processes to remove

additional pollutants from wastewater. There are several reasons for this result, however. The primary reason is that many POTWs with secondary wastewater treatment also treat their biosolids

in biosolids treatment processes such as digesters that can dramatically reduce (by up to 90 percent in some cases) the volume of biosolids initially generated in the wastewater treatment

process. Thus, the BGFsecondary factor is associated with the ultimate, not the initial, biosolids volume generated. Biosolids generated by POTWs that use only primary treatment are much less

likely to be treated in costly biosolids treatment processes that result in large volume reductions.

Another major reason is that BGFprimary and BGFsecondary might not be directly comparable numbers. That is, BGFsecondary, rather than being a true estimate of a generation rate, reflects a way

to relate two very different databases (Needs Survey and NSSS), which have very different data

collection methods and sampling approaches, and use them to approximate an increase in

biosolids amounts over time. BGFprimary, on the other hand, relies on engineering estimates and

reflects an engineering-based estimate of a generation rate. Furthermore, the volumes of

biosolids reported in the NSSS reflect the huge variation in the generation of biosolids by secondary wastewater treatment processes. Primary wastewater treatment processes generate biosolids

within in a much narrower range of rates.
63

used in Table A-2 to calculate the estimate of biosolids generated by POTWs in

1998 using Equation 4 and the projections discussed above. As shown in Table

A-2, we estimate that 0.5 million dry tons of biosolids were generated by

POTWs using primary treatment processes in 1998 and 6.3 million dry tons of

biosolids were generated by POTWs using secondary and above treatment

processes in 1998, for a total of 6.8 million dry tons of biosolids.

Methodology and Results Appendix

Table A-1

Estimate of Biosolids Generation Factor

Treatment Category

Primary

Secondary

1988 Biosolids

Generation (million

U.S. dry tons)

0.875

5.018

1988

Wastewater Flow

(MGD)

4,300

24,400

Biosolids

Generation Factor

(U.S. dry tons/MGD)

203

206

Source: U.S. EPA, 1993a; 1988 Needs Survey (U.S. EPA, 1988).

Table A-2

Estimate of Biosolids Generated by POTWs in 1996 and 1998

Treatment

Group

Primary

Secondary

Total

Population

Served

17,177,500

172,533,400

189,710,900

% of Total

Population

Served

9.05%

90.95%

100.00%

1996

Estimate of

Flow by

POTW Type

(MGD)

2,910

29,300

32,200

1998

Estimate of

Flow by

POTW Type

(MGD)

2,700

30,400

33,100

BGF (U.S.

dry tons/

MGD)

203

206

—

1996

Estimated

Biosolids

Generated

by POTWs

(million U.S.

dry tons)

0.6

6.0

6.6

1998

Estimated

Biosolids

Generated

by POTWs

(million U.S.

dry tons)

0.5

6.3

6.8

Source: 1996 Needs Survey (U.S. EPA, 1996).

A.2.2 Estimate of Biosolids Generation in 1998 from Privately and

Federally Owned Treatment Works 

Methodology

The NSSS also did not collect data from privately or federally owned treatment

works, therefore, an estimate of flow from privately and federally owned treatment works presented in the Part 503 RIA (U.S. EPA, 1993a) was used. This

source indicates that flow from these types of treatment works averaged 
64

0.09 MGD in 1991 and that about 5,080 treatment works of this type were

known to exist in that year. Thus, 460 MGD of wastewater were estimated to be

processed by privately and federally owned treatment works in 1991. We then

determined that this flow was 1.5 percent of the flow from POTWs in 1992,

according to the 1992 Needs Survey. Also, we assumed that privately and federally owned treatment works operate like POTWs, with the same proportion of

wastewater going to primary and secondary treatment processes and with the

same BGFs. Therefore, the amount of biosolids estimated for POTWs in 1996

and 1998 was increased by 1.5 percent to account for biosolids generation in

1996 and 1998 by this group of treatment works.

Results

As Table A-3 shows, increasing the 1998 estimates of biosolids generated by

POTWs by 1.5 percent produces a 1998 biosolids generation estimate of 6.9

million U.S. dry tons, with about 0.1 million dry tons attributable to privately and

federally owned treatment works, or about 0.2 million U.S. dry tons more than

that estimated for 1996.

Methodology and Results Appendix

Table A-3

Adjustment for Biosolids Generation From Privately

and Federally Owned Treatment Works

Treatment

Group

Primary

Secondary

Total

1996 Estimate of

Biosolids

Generated by

POTWs (million

U.S. dry tons)

0.6

6.0

6.6

1998 Estimate of

Biosolids

Generated by

POTWs (million

U.S. dry tons)

0.5

6.3

6.8

Factor for

Privately and

Federally Owned

Treatment

Works

1.5%

1.5%

1.5%

Total 1996

Estimate of

Biosolids

Generated by All

Treatments

Works (million

U.S. dry tons)

0.6

6.1

6.7

Total 1998

Estimate of

Biosolids

Generated by All

Treatments

Works (million

U.S. dry tons)

0.6

6.4

6.9a

a

Note: Numbers may not add up properly due to rounding.

Source: Table A-2 and U.S. EPA (1993a).

A.2.3 Total Estimate of Biosolids Generation in 1998

Using these above approaches, we estimate that a total of 6.9 million dry tons

were generated in 1998 (see Table A-3). Note that the 1996 estimate is about

6.7 million dry tons, which falls between the two previous estimates of total 1995

and 1996 biosolids production; WEF (1997) estimated 6.4 million dry tons for
65

1995, while Bastian (1997) estimated 6.9 million dry tons for 1996. Thus, all

these recent estimates tend to support each other.19

A.3 Estimates of Biosolids Use and Disposal in 1998

Methodology

To estimate the amount of biosolids going to various use or disposal methods,

the WEF (1997) survey data were used and applied toward this report’s estimate of 1998 biosolids generation total of 6.9 million dry tons (see Section

A.2.3). The WEF study was chosen over other data sources to calculate percentages of biosolids going to various use or disposal methods primarily

because it provides fairly current 1995 data and also is broken down into various use and disposal categories in such a way as to provide data that are relevant to this report. It also is the most complete source of current data on use

and disposal practices because it combines state data with POTW data. This

combination of data is useful because some states do not have complete

records of biosolids generation, use, and disposal. The data presented in WEF’s

report also are arranged in categories that correspond most appropriately to the

categories of most interest, allowing biosolids management practices to be

divided into the use and disposal categories discussed in Sections Two and

Three of this report.20

WEF divided biosolids management into four categories: land application, surface disposal, incineration, and other. The “other” category included biosolids

used for landfill cover, landfill, composting, and other further stabilized or

enhanced products. The percentages presented in the WEF report were further

adjusted by incorporating the narrative portion of WEF’s survey responses to

characterize use and disposal methods more precisely for this report. Specifically, since WEF requested and received detailed responses associated with the

“other” category on a state basis, it was possible to distribute these responses

to the “other” category into the use and disposal categories of interest. Therefore, these responses were distributed into the following categories: surface disposal and landfilling (including landfill, codisposal, and lagoons), incineration

Methodology and Results Appendix

19Although the WEF (1997) estimate is for 1995, the difference between the 1996 estimate made

in this report and WEF's estimate is about 0.1 million dry tons (using generation trends developed

later in this appendix to compare across years).

20A drawback to this approach is that WEF's sample of POTWs was composed primarily of larger

facilities, as discussed earlier. Smaller POTWs tend to have different use and disposal patterns

than larger POTWs. Therefore, using data based on samples of large POTWs could tend to overstate some percentages and understate other percentages of biosolids going to various use and

disposal methods. Incineration, for example, is more often practiced by larger POTWs, and smaller POTWs are often located in rural areas where landfill space is still available and land application has been in use for many years. Larger POTWs are often located in urban areas where

dwindling landfill space and public perception have prompted some POTWs to institute land application as a method of biosolids management, despite the transport distances involved. Thus, a

survey favoring larger POTWs might slightly overstate incineration and might also slightly overstate shifts from landfilling to land application since 1988. WEF, however, has supplemented its

POTW data with data from state agencies, lessening the potential for bias.
66

Methodology and Results Appendix

(including incineration and combustion stabilization processes), advanced treatment (including fertilizer, compost, lawn and garden, potted growing media,

lime-stabilized fertilizer, soil amendment, and pelletizing), other beneficial use

(including landfill cover and aggregate), and other (all other unidentified

processes). This adjustment resulted in a total list of six categories for EPA’s

needs, including the beneficial use categories of land application, advanced

treatment, and other beneficial use as well as the disposal categories of surface

disposal and landfilling, incineration, and other (i.e., unidentified processes).

Percentages of biosolids use and disposal for the adjusted categories were

applied to the total amount of biosolids generated in 1998, providing an estimate

of the dry tons of biosolids going to each use and disposal method (see Table 

A-4). According to these estimates, 60 percent of biosolids generated in 1998

were beneficially used. Broken down further, 53 percent of biosolids generated

in 1998 were land applied or received advanced treatment, such as composting,

and were land applied. An additional 7 percent were otherwise beneficially used

(3 percent were used as landfill cover and 4 percent were used as aggregate).21

Table A-4 presents this breakdown of use and disposal methods based on the

WEF data. BioCycle (1998) also notes a national trend toward beneficial use of

biosolids, with 34 states indicating overall that 61 percent of their biosolids are

beneficially used. 

21The beneficial use category might be somewhat understated since this report does not distinguish between incineration for disposal and incineration where energy recovery or ash use is

practiced, as discussed in Section Two.

Table A-4

Biosolids Use and Disposal Based on WEF Survey Data (million U.S. dry tons)

Other Surface

Land Advanced Beneficial Disposal/ IncinerYear Application Treatment Use Total Landfill ation Other Total Total

1998 3.6 0.07 0.5 4.1 1.2 1.5 0.07 2.8 6.9

Percent of 52% 1% 7% 60% 17% 22% 1% 40% 100%

Total

Beneficial Use Disposal

Source: WEF (1997) and estimates of the distribution of “other” use or disposal method responses in the WEF survey (see

text).

The 52 percent of biosolids going to land application without advanced treatment probably includes some biosolids that did, in fact, receive advanced

treatment (defined here as heat treated, lime stabilized, composted, pelletized,

or otherwise generally meeting Class A pathogen and vector control
67

requirements—see Section Two), since the WEF survey did not specifically ask

respondents to identify amounts of biosolids that received advanced treatment.

Thus, we adjusted this figure further, using BioCycle (1998) data on composted

biosolids, to account more accurately for the amount of biosolids that received

advanced treatment before land application.

In BioCycle (1998), a total of 34 states provided adequate data for the purposes

of this analysis. Data were excluded from some states, such as Louisiana, that

reported biosolids volumes in wet tons or that provided breakdowns but no total

quantities or total quantities with no breakdowns. Several caveats associated

with these data must be noted, however. First, BioCycle’s data collection effort

for biosolids receiving advanced treatment is likely to be the most extensive of

all current efforts, since this journal specifically tried to capture data on

advanced treatment from the states. Not all states, however, provided sufficient

data to clearly break out composted biosolids from biosolids that are normally

land applied without advanced treatment because a large portion of advanced

treatment biosolids are ultimately land applied.

Second, these data can be used for extrapolation only with the assumption that

the “missing” states are not significantly different from the ones that did provide

data (an assumption that might not be true). Finally, the data are only as good

as the states’ records. Some states have accurate recordkeeping, while others,

as mentioned in the article, are still in the process of developing accurate

recordkeeping. Nevertheless, state data are likely to become more accurate

over time.

BioCycle columns “land application,” “composting,” “lime stabilization,” and “heat

treatment/pelletizing” were grouped into a beneficial use category and the “landfill,” “surface disposal,” “incineration,” and “other” columns were grouped into a

disposal category. A total of 61 percent of the biosolids fall into the beneficial

use category and 39 percent fall into the disposal category (compared to the

WEF data that indicate that 60 percent could be considered beneficial use and

40 percent disposal, using similar assumptions about classifications). Table A-5

shows how these two sets of data overlap in the area of advanced treatment

and other beneficial use. 

Methodology and Results Appendix

Table A-5

Comparison of WEF (1997) and BioCycle (1998)

Data on Use and Disposal Practices

Data 

Source

WEF

BioCycle

Land

Application

52%

47%

Advanced

Treatment

1%

Other

Beneficial

Use

7%

Surface

Disposal/

Landfill

17%

19%

Incineration

22%

20%

Other

1%

14%a 1%

Sources: WEF (1997); BioCycle (1998). a

6.8 percent is composted, 2.7 percent is lime stabilized, and 4.8 percent is heat dried/pelletized.
68

According to BioCycle’s data, about 14 percent of the total biosolids appear to

receive advanced treatment. As discussed earlier, it is clear from footnotes in

the tables, as well as caveats in the text, that the land application category in

the BioCycle data includes some biosolids that were lime treated or received

advanced treatment. Thus, the quantity of biosolids listed in BioCycle data treatment categories are underestimated. Even so, these quantities of biosolids that

received advanced treatment, according to BioCycle, are still larger than the

estimates based solely on WEF data. Using this assumption, we estimate that

of the 14 percent of the biosolids that BioCycle presents as receiving advanced

treatment, 7 percent received advanced treatment and were later land applied

while an additional 7 percent received advanced treatment and were beneficially

used (as landfill cover and aggregate).

Even the BioCycle-based estimate might understate the amount of biosolids that

receive advanced treatment, therefore, one more approach was used to estimate this figure. According to the NSSS, in 1988 an estimated 1,519,700 U.S.

dry tons of biosolids were land applied, of which 329,900 U.S. dry tons were

composted, sold, or otherwise likely to have been applied to public contact sites.

Biosolids that were composted, sold, or applied to public contact sites (which

implies advanced treatment),22 therefore, constituted 22 percent of all landapplied biosolids in 1988 (U.S. EPA, 1993a). This percentage of biosolids going

to land application may actually belong in the advanced treatment category.

Thus, we estimate that 12 percent (12 percent is 22 percent of the 53 percent of

biosolids that are land applied or receive advanced treatment) of all biosolids

generated in 1998 might have been treated and land applied.23 The percentages

presented in Table A-4 were then adjusted to reflect this assumption, as discussed below. 

Results

Based on the adjustments to WEF data, out of the total 6.9 million dry tons, 2.8

million dry tons are estimated to have been land applied without any special

treatment, such as composting or pelletizing, 0.8 million dry tons are estimated

to have been land applied after special treatment, and 0.5 million dry tons are

estimated to have been beneficially used in some other manner (i.e., as landfill

cover or aggregate), for a total of 4.0 million dry tons estimated to have been

beneficially used. It also is estimated that 1.2 million dry tons were surface disposed, 1.5 million dry tons were incinerated, and 0.1 million dry tons were

disposed of in another manner.

Methodology and Results Appendix

22Given the public access restrictions outlined in the Part 503 Biosolids Rule associated with

applying biosolids to public contact sites that have not been further treated (for example, by composting), it is assumed that most biosolids currently applied to public contact sites are likely to

have received advanced treatment.

23This estimate might still understate the quantity of biosolids treated, since any trend toward

advanced treatment of biosolids is not captured using this approach. It is believed, however, that

12 percent receiving advanced treatment and land applied might be a better estimate than 7 percent receiving advanced treatment and then land applied.
69

The amount of biosolids likely to be going to municipal solid waste facilities can

be estimated after some assumptions are made. First, we assumed that all surface-disposed biosolids are disposed of in municipal solid waste landfills.24 This

assumption is reasonable given the small amount of biosolids believed to be

disposed of in biosolids monofills, piles, and lagoons or applied to land strictly

for disposal (see discussion in Section Two of this report), and given the results

of the BioCycle (1998) survey, which indicate less than 2 percent of biosolids

are surface-disposed among the 34 states with adequate data. Second, for the

purpose of this report, it is assumed that no incinerated biosolids are coincinerated with solid waste, although this might occur in rare instances.25 The

advanced treatment category is the only category that is likely to be split

between municipal solid waste facilities and others, where municipal solid waste

facilities are defined as commercial, noncommercial, or municipal entities that

compost municipal solid waste (including yard trimmings) with biosolids. It is

estimated that, based on the percentage of biosolids estimated to be used as

landfill cover as reported in the WEF (1997) report (3 percent), 0.2 million dry

tons of biosolids were used as landfill cover (landfill cover was included in the

“other beneficial use” category). At a minimum, 1.4 million dry tons, or 20 percent of total biosolids generated in 1998, are likely to have been managed at

municipal solid waste facilities through landfilling or use as a landfill cover.

Some additional amount of biosolids might be composted at municipal solid

waste facilities (as defined above) for land application, but this quantity is not

known. Numbers presented in Section Three include an assumption that half of

the advanced treatment category biosolids (0.4 million of the 0.8 million dry tons

shown in Table A-6) might be composted at municipal solid waste facilities or at

Methodology and Results Appendix

Table A-6

Estimates of Biosolids Use and Disposal With Adjustments for Biosolids

Receiving Advanced Treatment (million U.S. dry tons)

Other Surface

Land Advanced Beneficial Disposal/ IncinerYear Application Treatment Use Total Landfill ation Other Total Total

1998 2.8 0.8 0.5 4.1 1.2 1.5 0.01 2.8 6.9

Percent of 41% 12% 7% 60% 17% 22% 1% 40% 100%

Total

Beneficial Use Disposal

Source: Table A-5 with adjustments for advanced treatment.

24Based on communication with Bob Bastian, U.S. EPA, May 1997.

25Based on communication with Bob Bastian, U.S. EPA, October 1997, and with Steven Levy, 

U.S. EPA, October 1997.
70

facilities that manage both biosolids and municipal solid waste, including yard

trimmings. Adding the 0.4 million dry tons to the 1.4 million dry tons estimated

above to be handled by municipal solid waste or composting facilities brings the

total to 1.8 million dry tons or 26 percent of the amount of biosolids estimated to

be generated in 1998.

A.4 Projections of Biosolids Generation in 2000, 2005, and 2010

Methodology

This report based projections of biosolids generation for 2000, 2005, and 2010

on trends in wastewater flow rates, which were obtained from available Needs

Surveys from the years 1984 to 1996. The amount of flow for each treatment

method (primary or secondary treatment) was not available in the Needs

Surveys for most years. We, therefore, estimated the flow for each treatment

group using the population served for each treatment level as a percentage of

the total population served. This calculation is similar to calculations discussed

in Section A.2 to determine the Biosolids Generation Factor for each treatment

method for a given year’s flow.

In each year of the Needs Survey for which data on total flow and population

were available (1988, 1992, and 1996), the percentage of those served by primary treatment or secondary treatment to the total population served by all

POTWs was calculated.26 These percentages then were applied to the total flow

to estimate the flow attributable to POTWs in each treatment category, as was

done earlier for estimating 1996 flow. The trend in flow across the years for

which data were available was calculated, and the trend factors were applied to

1996 flows to calculate the flows in 2000, 2005, and 2010 using the estimate of

percent change per year and the number of intermediate years.

The BGF for each treatment level was multiplied by flow to estimate the dry tons

of biosolids generated, as discussed in Section A.2, for developing the initial

estimate of 1996 biosolids generation.

Flow Projection (MGD) x BGF = Biosolids Generation (U.S. dry tons) (6)

This calculation was repeated for each of the years 2000, 2005, and 2010 and

for each treatment level. 

Results

Table A-7 presents the calculations of trends. Given the overall increase in flow

due to steady increases in the population served, flow from POTWs using only

primary treatment was estimated to be decreasing at an annual rate of about 4

percent, while flow from POTWs using at least secondary treatment methods

Methodology and Results Appendix

26Again, secondary treatment for this discussion includes secondary, tertiary, and no discharge

categories.
71

was estimated to be increasing at an annual rate of about 2 percent. With these

rates of change, flow was projected for 2000, 2005, and 2010 (see Table A-8).27

Based on the above methodology, we estimate that the percentage of total

biosolids production attributable to POTWs using primary treatment levels will

fall from 8 percent in 1998 (see Table A-3) to 4 percent in 2010. Concurrently,

we estimate that total biosolids production will increase by 19 percent from 1998

to 2010. By 2010, a total of 8.2 million dry tons of biosolids are expected to be

used or disposed of annually (see Table A-8).

Methodology and Results Appendix

27Over total flow, some variation in the trend was seen over time, with the mid-1980s associated

with greater flow increases than the early to late 1990s. After the early 1990s, however, increases

picked up again. This is consistent with the accelerating and delaying of wastewater treatment

projects that might have occurred. These variations could have been driven by several factors. In

the mid-1980s, POTWs were aware that the Construction Grants Program was being eliminated

and, thus, might have accelerated some building programs into those years. The Construction

Grants Program, which was being phased out in the late 1980s, received its last appropriation in

the fiscal year 1990. In the late 1980s and early 1990s, the acceleration of the mid-1980s could

have led to a slowdown in wastewater programs, (since many would have been completed), while

other POTWs, which had delayed their projects, further delayed them as they investigated new

sources of funding. With the onset of the recession in the early 1990s, further delays were likely.

Finally, by the mid-1990s, the improving economic conditions and the accumulation of construction programs that could no longer be delayed might have led to the greater increases in flow

seen in these years. Taking these factors into account, it is believed that smoothing these trends

by averaging them over the years of data available is appropriate.

Table A-7

Trend Analysis of Flow (1984 to 1996)

Year

1984

1986

1988

1990

1992

1994

1996

Trend

(1-year)

Total Flow

(MGD)

27,095

27,692

28,736

29,113a

29,490

30,833a

32,175

—

Primary as

% of Total

Population

15%

12%

9%

—

Secondary

as % of

Total

Population

85%

88%

91%

—

Primary

Flow

4,320

3,545

2,913

—

Secondary

Flow

24,416

25,945

32,175

—

Primary

—

-0.18

-0.13

-0.04

Secondary 

—

+0.03

+0.10

+0.02

Total

—

+0.02

+0.04

+0.01

+0.01

+0.05

+0.04

+0.015

Trend

Note: Blanks indicate years with missing data.

Source: 1984-1998 Needs Surveys.

a

Computed as the midpoint between years when data were unavailable.
72

A.5 Use and Disposal of Biosolids in 2000, 2005, and 2010

Methodology

The percentages of biosolids going to the various use and disposal methods

were estimated on the basis of expected future trends in factors affecting

biosolids use and disposal. As discussed in Section Four, we expect factors

favoring the increased recovery of biosolids, including the regulatory environment, technological development, and public acceptance, to contribute to a continuing increase in the beneficial use of biosolids. Concurrently, we anticipate

the amount of biosolids going to surface disposal and incineration to decrease,

partially due to the rising costs of incineration and, in some locations, landfilling.

Amounts incinerated are not expected to decrease rapidly, since this category

has grown since 1988.28 Some small decline in incineration is expected, however, given public concerns about environmental impacts of incineration. (See

Section Four for a more detailed discussion of trends.) We then determined the

quantities of biosolids going to each use or disposal method on the basis of the

projected quantities of biosolids generated in 2000, 2005, and 2010 and the percentage assigned to each method. To account for trends and the projections of

biosolids generation for 2000, 2005, and 2010, we first developed percentage

estimates for those years (see Table A-9) and then applied these percentages

against our previously estimated flow data (Table A-8).

Methodology and Results Appendix

Table A-8

Wastewater Flow Projections for POTWs and Privately

and Federally Owned Treatment Works in

2000, 2005, and 2010

Treatment

Group

Primary

Secondary

Total

2000

2,430

32,280

34,710

2005

2,000

35,085

37,085

2010

1,640

38,130

39,780

Biosolids

Generation

Factor

203

206

— 

2000

0.5

6.6

7.1

2005

0.4

7.2

7.6

2010

0.3

7.9

8.2

Wastewater Flow (MGD) Biosolids Generated

(million U.S. dry tons)

Source: Tables A-2 and A-7. Includes 1.5 percent additional flow to account for privately and federally owned treatment works

under the assumption that these treatment works will follow the same trends as POTWs. 

28A total of 16.1 percent of biosolids were estimated to have been incinerated in 1988 while 22

percent were estimated to have been incinerated in 1995 (WEF, 1997); note, however, that the

WEF (1997) data might somewhat overstate amounts incinerated, as discussed earlier in Section

A.3. This conjecture might be supported by BioCycle (1998). The data presented in this source

indicate that 20 percent of biosolids generated (in the 34 states with sufficient data) were 

incinerated.
73

Based on this assessment of likely trends, we estimate the amount of biosolids

to be beneficially used to increase to 4.4, 5.0, and 5.7 million dry tons in 2000,

2005, and 2010, respectively, with 2.6, 2.6, and 2.5 million dry tons, respectively, being disposed of. Compared to current breakdowns between use and disposal methods, a positive trend in the use of biosolids continues in the future,

Methodology and Results Appendix

Table A-9

Projected Percentages of Biosolids Use and Disposal

in 2000, 2005, and 2010

Other Surface

Land Advanced Beneficial Disposal/

Year Application Treatment Use Total Landfill Incineration Other Total

1998 41% 12% 7% 60% 17% 22% 1% 40%

2000 43% 12.5% 7.5% 63% 14% 22% 1% 37%

2005 45% 13% 8% 66% 13% 20% 1% 34%

2010 48% 13.5% 8.5% 70% 10% 19% 1% 30%

Beneficial Use Disposal

Source: EPA estimates.

Results

As Table A-10 shows, we expect beneficial use of biosolids to increase from 60

percent in 1998 to 63 percent in 2000, 66 percent in 2050, and 70 percent in

2010. Thus, by 2010, disposal might only account for about 30 percent of all

biosolids generated. 

Table A-10

Projected Quantities of Biosolids Use and Disposal

in 2000, 2005, and 2010 (million U.S. dry tons)

Treatment/ Other Surface

Land Land Beneficial Disposal/ IncinerYear Application Application Use Total Landfill ation Other Total Total

2000 3.1 0.9 0.5 4.5 1.0 1.6 0.1 2.6 7.1

2005 3.4 1.0 0.6 5.0 1.0 1.5 0.1 2.6 7.6

2010 3.9 1.1 0.7 5.7 0.8 1.5 0.1 2.5 8.2

Beneficial Use Disposal

Source: Tables A-9 and A-10.
74

but the trend in disposal becomes slightly negative. The amount of biosolids

going to municipal solid waste facilities is projected to be 1.2, 1.2, and 1.0 million dry tons (not including composted biosolids managed by municipal solid

waste facilities, as defined earlier, that are not used as landfill cover) in 2000,

2005, and 2010, respectively.29 Declines in landfilled biosolids are offset slightly

by small increases in use of biosolids for landfill cover, but not enough to

change the overall decline rate at municipal solid waste facilities. Municipal solid

waste facilities, therefore, are likely to be handling at a minimum 17 percent of

the 7.1 million dry tons generated in 2000, 16 percent of the 7.6 million dry tons

generated in 2005, and 12 percent of the 8.2 million dry tons generated in 2010. 

As discussed in Section Four, some portion of the amount estimated to receive

advanced treatment might be prepared by municipal solid waste facilities. As

much as half (approximately 0.5 million dry tons of the 0.9, 1.0, and 1.1 million

dry tons shown in Table A-10) might be handled by these facilities. When these

amounts are added to the above estimates, municipal solid waste facilities might

manage 1.6 million dry tons of the 7.1 million dry tons generated in 2000 (23

percent), 1.7 million dry tons of the 7.6 million dry tons generated in 2005 (22

percent), and 1.6 million dry tons of the 8.2 million dry tons generated in 2010

(20 percent). These figures include amounts of biosolids disposed of in municipal solid waste landfills, used for landfill cover, or composted for sale or distribution to farmers, contractors, or the general public.

Methodology and Results Appendix

29Using the same assumption as above about the relative ratios of landfill cover to aggregate in

the other beneficial use category.
1EPA

Penalty for Private Use $300Official BusinessWashington, DC 20460(5306W)Environmental Protection AgencyUnited States