United States
Environmental Protection
Agency
Solid Waste and
Emergency Response '
(5305)
EPA530-R-94-003
May 1994
Composting
Yard Trimmings and
unicioal Solid Wast
i*
KA
J»f
*'f
«a#fS,Jl
-
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Composting of yard
Trimmings and
Municipal solid Waste
U.S. Environmental Protection Agency
Office of Solid Waste and Emergency Response
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Acknowledgments
EPA would like to thank the following individuals for their contributions to the manual:
Jan Beyea National Audubon Society
Charlie Cannon Solid Waste Composting Council
Steve Diddy Washington State Department of Ecology
Dr. Melvin Einstein Rutgers University
Dr. Charles Henry University of Washington
Francine Joyal Florida Department of Environment Regulation
Jack Macy Masshusettts Department of Environmental Protection
Randy Monk Composting Council
Dr. Aga Razvi University of Wisconsin
Dr. Thomas Richard Cornell University
Connie Saulter Northeast Recycling Council
Dr. Wayne Smith University of Florida
Roberta Wirth Minnesota Pollution Control Agency
In addition, EPA thanks Wayne Koser of City Management Corporation and Steve Diddy
for their contributions to Appendix B: Composting Equipment.
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Chapter Overview
Chapter 1- Planning
Describes the importance of planning and discusses some
of the preliminary issues that decision-makers should ex-
amine before embarking on any type of composting pro-
gram including waste characterization, operation plans,
facility ownership and management, community involve-
ment, vendors, and pilot programs.
Chapter 2- Basic Composting Principles
Provides a brief scientific overview of the composting
proms. Discusses the physical, chemical, and biological
factors that influence composting including the type and
number of microorganisms present, oxygen level, mois-
ture content, temperature, nutrient levels, acidity/alkalin-
ity, and particle size of the composting material.
Chapter 3-Collection Methods
Describes options for collecting yard trimmings and
municipal solid waste (MSW) along with the advantages
and disadvantages associated with each option. Highlights
the critical role that source separation plays when
composting MSW
Chapter 4- Processing Methods,
Technologies, and Odor Control
Discusses the three stages of composing (preprocessing,
processing, and postprocessing). Introduces the types of
equipment associated with each stage, which are examined
in detail in Appendix B. Describes the methods currently
used to compost yard trimmings and MSW in the United
States, and provides a detailed discussion of odor control.
Chapter 5- Facility Design and Siting
Describes factors to consider when siting and designing a
composting facility including location, site topography
and land requirements. Also discusses design considera-
tions for preprocessing, processing and postprocessing ar-
eas; buffer zones; access and onsite roads; and site facilities
and security.
Chapter 6 - The Composting Process:
Environmental, Health, and Safety Concerns
Focuses on how to prevent or minimize the potential en-
vironmental impacts associated with composting includ-
ing the potential for water pollution, air pollution.odor
Vector, fires, noise, and litter. Dicsusses the safety and
health risks including bioaerosols to workers at compost-
ing facilities and ways to minimize these risks.
Chapter 7- State Legislatian and Incentives
Presents an overview of state legislation activity through-
out the country. Also discusses state incentives to stimu-
late yard trimmings and MSW composting.
Chapter 8- Potential End Users
Describes the potential end users of compost derived from
yard trimmings and MSW (agriculture, landscaping nurs-
eries, silviculture, public agencies, and residents). Dis-
cusses how compost is currently utilized by these end
users as well as the potential for expanded use.
Chapter 9- Product Quality and Marketing
Emphasizes the importance of securing markets for the
finished compost product. Provides a detailed discussion
of quality and safety concerns that could affect the mar-
ketability of compost. Also discusses key factors associated
with marketing including pricing, distribution, education
and public relations, and program assessment.
Chapter 10- Community Involvement
Discusses the importance of developing strong local support
for a composting operation. Also discusses ways to involve
and educate the community throughout the planning siting,
operation, and marketing phases of a composting program.
Chapter 11- Economics
Introduces the economic and financial issues that must be ex-
amined when planning a composting facility Discusses capital
cost, operation and maintenance costs, and potential benefits
associated with starting up and maintaining facility.
Appendix A - Additional Sources of
Information on Composting
Lists publications related to composting as well as EPA
contacts.
Appendix B - Composting Equipment
Describes the cost, efficiency, and major advantages and dis-
advantages of the equipment commonly used at a compost-
ing facility.
Appendix C- Glossary of Composting Terms
Defines terms used throughout the guidebook.
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Contents
Page
Introduction . 1
Composting as a Component of Integrated Solid Waste Management 1
What Is Composting? 2
Status of Composting Yard Trimmings and MSW in the United States 3
Chapter One - Planning H
Goal Setting 11
Waste Characterization 11
Operational Plans . 12
Community Involvement 12
Facility Ownership and Management 13
Composting Vendors 14
Pilot Programs 14
Summary 14
Chapter Two - Basic composting Principles 16
Overview of the Composting Process 16
The Role of Microorganisms 16
Factors Influencing the Composting Process 17
Oxygen 18
Particle Size 18
Nutrient Levels and Balance 19
Moisture 19
Temperature 19
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Table of Contents
Chapter Two - Basic composting Principles (Continued)
Acidity/Alklalinity(pH) 19
Summary 20
Chapter Three - Collection Methods 21
Factors in Yard Trimmings Collection 21
Public Drop-Off Sites for Yard Trimmings 21
Curbside Collection of Yard Trimmings 22
Factors in MSW Collection 28
Source-Separated MSW 28
Commingled MSW 29
Summary 30
Chapter Four - Processing Methods, Technologies, and Odor Control 31
Preprocessing 31
Sorting 31
Reducing the Particle Size of the Feedstock 37
Treating Feedstock Materials to Optimize composting Conditions 37
Mixing 39
Processing 40
The composting Stage 40
The Curing Stage 47
Odor Control 47
Process Control 48
Engineering Controls 48
Postprocessing 51
Summary 53
Chapter Five - Facility Siting and Design 56
Siting .- 56
Location . 56
Topography 59
Land Area Requirements .- 59
VI
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Table of Contents
Chapter Five - Facility Siting and Design (Continued)
Other Factors Affecting Siting Decisions 60
Design , 60
Preprocessing Area 60
Processing Area 60
Postprocessing Area 62
Buffer Zone 63
Access and Onsite Roads 63
Site Facilities and Security 64
Summary 64
Chapter Six - The Composting Process: Environmental, Health, and Safety Concerns ... 65
Environmental Concerns During composting 65
Water Quality .... 65
Run-On/Ponding 68
Air Quality 68
Odor 70
Noise 70
Vectors 70
Fires 70
Litter 71
Occupational Health and Safety Concerns During composting 71
Bioaerosols 71
Potentially Toxic Chemicals 72
Noise Control 73
Other Safety Concerns 73
Worker Training 73
Summary .... 74
Chapter Seven - State Legislation and Incentives ?6
Composting Legislation Overview 76
Permit and Siting Requirements 77
vn
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Table of Contents
Chapter Seven - State legislation and Incentives (Continued)
Facility Design and Operations Standards 77
Product Quality Criteria 78
Bans Landfilling Combustion 79
Recycling Goals 79
Requirements for Local Governments to Implement composting 79
Requirements for State Agencies to Compost 79
Separation Requirement 79
Yard Trimmnings and MSW composting Incentives 79
State Encouragement and Local Authority to Implement Programs 80
Grants 80
Procurement 80
Encouragement of Backyard Composting 80
Education Programs 80
Summary 81
Chapter Eight - Potential End Users 87
The Benefits of Finished Compost 87
Agricultural Industry 87
Landscaping Industry 91
Horticultural Industry 92
Silviculture 92
Public Agencies 93
Residential Sector 94
Summary 96
Chapter Nine - Product Quality and Marketing . 98
Product Quality 98
Yard Trimmings Compost Quality 98
MSW Compost Quality 99
Product Specifications , 102
Vlll
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Table of Contents
Chapter Nine - Product Quality and Marketing (Continued)
Product Testing 102
Market Assessment 103
Private vs. Community Marketing 104
Pricing 104
Location/Distribution Issues . ,107
Education and Public Relations 108
Updating the Market Assessment 108
Summary 108
Chapter Ten - Community Involvement 111
Planning the Composting Project.. Ill
Community Involvement in Siting Decisions .112
Public Participation in the Composting Project ,113
Community Education at the Marketing Phase 114
Summary 114
Chapter Eleven - Economics .115
Cost/Benefit Analysis 115
Capital Costs -116
Site Acquisition . -116
Site Preparation/Land Improvements 116
Vehicle and Equipment Procurement ,116
Training , ,117
Permits , ,117
Operating and Maintenance (O&M) Costs .117
Collection Costs .117
Labor Costs 118
Fuel, Parts, and Supplies -118
Outreach and Marketing Costs .119
Other Costs .119
IX
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Table of Contents
Chapter Eleven - Economics (Continued)
Benefits from Composting 119
Avoided Costs 119
Revenues 119
Summary, , 120
Appendix A - Additional EPA Sources of Information on Composting 124
Appendix B- Composting Equipment 126
Appendix C- Glossary of Compost Terms 138
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Introduction
Composting is a firm of recycling. Like other recycling effort, the composting of yard trimming and munici-
pal solid waste can help decrease the amount of solid waste that must be sent to a landfill or combustor,
thereby reducing disposal costs. At the same time, composting yields a valuable product that can be used by
farmers, landscapers, horticulturists, government agencies, and property owners as a soil amendment or mulch.
The compost product improves the condition of soil reduces erosion, and help suppress plant diseases.
The purpose of this manual is to aid decision-makers in planning, sitting, designing and operating composting
facilities. It also will be useful to managers and operators of existing facilities, as well as to citizens, regulators,
consult-anti, and vendors interested in the composting process. The manual discusses several approaches to com-
porting and outlines the circumstances in which each method should be considered
AS detailed in the manual a composting operation should be designed according to the need and resources of the
community. For example, a municipal composting effort can entail simply collecting yard trimmings on a sea-
sonal basis and using a simple "windrow and turn" technology to produce the compost, or it can mean siting and
designing a large facility that is capable of handing several tons of mixed municipal solid waste a dry.
When considering any type of composting effort, however decision-makers must plan ahead to avoid potential
obstacles that could hinder the operation. The most common challenges are siting the facility ensuring that the
facility is properly designed mitigating and managing oak, controlling bioaewsols and investing adequate
capital to cover unforeseen costs. This manual helps decision-makers understand and prepare for these challanges
so that they can develop a successful composting program in their community
In 1990, Americans generated over 195 million tons of
municipal solid waste (MSW). The amount of waste gen-
erated annually in this country has more than doubled in
the past 30 years (EPA, 1992). While MSW generation
rates have increased, however, the capacity to handle these
materials has declined in many areas of the country. Many
landfills have closed because they are full. Others are
choosing to shut down rather than meet stringent new
regulations governing their design and operation. In addi-
tion, new landfills and combustors are increasingly diffi-
cult to site. In conjunction with this growing gap in
disposal capacity, tipping fees at solid waste management
facilities are rising in many communities, and the trend
does not appear to be changing. As communities search
for safe and effective ways to manage MSW, composting
is becoming a more attractive management option.
in some communities, composting has proven to be more
economical than landfilling, combustion, or constructing
new landfills or combustors, especially when considering
disposal costs avoided through composting and reduced
expenditures on soil amendments for municipal parks and
lawns. In addition, composting can help communities
meet goals to recycle and divert substantial portions of the
MSW stream from disposal. Many states are now setting
ambitious recycling goals for their jurisdictions. Because
composting can potentially handle up to 30 to 60 percent
of a community's MSW stream (EPA, 1993), it can play a
key role in helping communities meet these goals. Finally,
as a type of recycling, composting in many ways repre-
sents a more efficient and a safer use of resources than
landfilling or combustion.
Composting as a Component of
Integrated Solid Waste Management
EPA encourages communities to use a mix of managem-
ent techniques (an approach called integrated solid
waste management) to handle their MSW stream since no
-------
Introduction
single approach can meet the needs of all communities.
EPA suggests a hierarchy of management methods for of-
ficials to consider when developing a solid waste manage-
ment plan. Source reduction is the preferred management
option. Source reduction can be defined as the design,
manufacture, purchase, or use of materials or products
(including packages) to reduce their amount and toxicity
before they enter the MSW stream. Recycling, including
composting is the next preferred management option.
While lower on the hierarchy than source reduction and
recycling combustion (with energy recovery) and landfill-
ing also are options to manage materials that cannot be
reduced, reused, recycled, or composted. Combustion
reduces the amount of nonrecyclable materials that must
be landfilled and offers the benefit of energy recovery.
Landfillng is needed to manage certain types of nonreus-
able, nonrecyclable materials, as well as the residues gener-
ated by composting and combustion.
In any case, consideration of a composting program
should be part of a community's comprehensive approach
to solid waste management. AS decision-makers evaluate
their options for managing solid waste, many will look to
composting as an attractive and viable option for han-
dling a portion of their MSW stream,
What Is Composting?
Biological decomposition is a natural process that began
with the first plants on earth and has been going on ever
since. As vegetation falls to the ground, it Slowly decays,
providing minerals and nutrients needed for plants, ani-
mals, and microorganisms. Composting is often used
synonymously with biological decomposition. As the term
is used throughout this guidebook, however, composting
refers to the controlled decomposition of organic (or carb-
on-containing) matter by microorganisms (mainly bacte-
ria and fungi) into a stable humus material that is dark
brown or black and has an earthy smell. The process is
controlled in that it is managed with the aim of accelerat-
ing decomposition, optimizing efficiency, and minimizing
any potential environmental or nuisance problems that
could develop.
Composting programs can be designed to handle yard
trimmings (e.g., leaves, grass clippings, brush, and tree
prunings) or the compostable portion of a mixed solid
waste stream (e.g., yard trimmings, food scraps, scrap pa-
per products, and other decomposable organics). These
materials are the feedstock or "find" for the composting
process. Composting programs also have been designed
for sewage biosolids, agricultural residues and livestock
manures, food processing by-products, and forest industry
by-products. Because these materials are not considered
part of the MSW stream, however, they are not discussed
at length in this guidebook. Some facilities compost
'Larry's Markets composts almost 500 tons of Suits,
ivegctables, food, and flowers that can't be sold and
would ollierwise be thrown away. This organic mate-
has begun to
landscaping
re-
uced the amount of materials being landfilled: !>f
nearly 40 percent. This project, has also sigru'ficandy
j "f J * , 11 t it Jf t fft M "" "' '
cat Jjjrry's disposal costs. Composting a ton of material
costs tariff's $67, while running compactors, hauling
material to local landfills, and paying landfill fees and
taxes com $100 per ton. The difference between com-
posting and landfilling for Larry's is a total savings of
approximately $15,000 each year. _. ,
MSW with sewage biosolids, which is a form of co-com-
posting. Co-composting is not discussed in detail in this
guidebook.
During the composting process, feedstock is placed in a
pile or windrow (an elongated pile) where decomposition
takes place. The rate of decomposition depends on the
level of technology used as well as on such physical,
chemical, and biological factors as microorganisms, oxy-
gen levels, moisture content, and temperature. Compost-
ing works best when these factors are carefully monitored
and controlled.
The end products of a well-run composting process are a
humus-like material, heat, water, and carbon dioxide.
Compost is used primarily as a soil amendment or mulch
by farmers, horticulturists, landscapers, nurseries, public
agencies, and residents to enhance the texture and appear-
ance of soil, increase soil fertility, improve soil structure
and aeration, increase the ability of the soil to retain water
and nutrients and moderate soil temperature, reduce ero-
sion, and suppress weed growth and plant disease. Figures
1-1 and 1-2 at the end of this introduction illustrate the
steps involved in composting yard trimmings and MSW.
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Introduction
Status of Composting Yard
Trimmings MSW in the
United States
Nationwide, nearly 35 million tons of yard trimmings
were generated in 1990, accounting for nearly 18 percent
of the MSW stream (EPA, 1992). About 2,200 facilities
for the composting of yard trimmings were operating in
the United States in 1991 (Goldstein and Glenn, 1992).
Approximately 12 percent or 4.2 million tons of the yard
trimmings generated in 1990 were composted by these fa-
cilities (This estimate> however, does not include the
amount of yard trimmings composted through "back-
yard" composting projects and other individual efforts.)
(EPA, 1993).
In 1990, the United States also generated over 16 million
tons of food scraps, 12 million tons of scrap wood, and 73
million tons of paper waste, which together account for
51 percent of the MSW stream (EPA, 1992). Although
over 28 percent of all paper waste was recycled in 1988, a
negligible amount of this material is currently composted
(EPA, 1992). While composting of MSW has been prac-
ticed in other countries for many years, interest and com-
mitment to MSW composting on a large scale is a recent
development. As of 1992,21 full-scale MSW composting
facilities were in operation in the United States (Goldstein
and Steuteville, 1992). Capacities of most of these facili-
ties range from 10 to 500 tons of MSW feedstock per day.
Minnesota leads the way with eight operational facilities;
Florida has three, and Wisconsin maintains two MSW
composting facilities (see Table 1-1). Minnesota's leading
position is due, in part, to available state funds and tech-
nical assistance for MSW composting systems (Crawford,
1990). A number of facilities also are in the planning or
construction stages (see Table 1-2). Table 1-3 provides a
brief comparison of the composting of yard trimmings
and MSW in reference to several operational and program
parameters.
AS these numbers indicate, composting is currently receiv-
ing a substantial amount of attention. Among other
factors, this interest is due to regulatory and economic
factors. In recent years, a number of communities and
states have banned yard trimmings from disposal in land-
fills. As mentioned earlier, some states also have estab-
lished ambitious landfill diversion goals, along with
financial assistance programs that support alternative
management projects. Several states also have adopted
MSW compost regulations and more states are likely to
follow. Another important legislative development is that
several states currently require state agencies to purchase
and use compost if it is available and if it is equivalent in
quality to other soil amendments (Crawford, 1990).
Another indication of the headway being made in
composting is the increasing number of vendors market-
ing their composting systems to public offcials, haulers,
and landfill operators (Goldstein and Glenn, 1992). In
addition, many companies that are in the process of
constructing new waste management facilities are plan-
ning to incorporate composting into their operations to
reduce the amount of residuals that must be landfilled
(Goldstein and Glenn, 1992). Additionally many com-
munities and commercial establishments are now at-
tempting to compost a larger portion of the MSW stream
in an effort to reuse materials, rather than landfill or com-
bust them. Several municipalities have established pilot or
ongoing programs to collect mixed MSW for composting.
Others are conducting pilot projects for collecting source-
separated food scraps. In addition, many restaurants and
grocers are composting leftover or unusable food scraps at
their operations.
Introduction Resources
Crawford, S. 1990, Solid waste/sludge composting Inter-
national perspectives and U.S. opportunities. Proceedings
of the sixth international conference on solid waste man-
agement and secondary materials. Philadelphia, PA. De-
cember 4-7.
Glenn, J. 1992. The state of garbage in America Part I.
BioCycle. April, 33(4):46-55.
Goldstein, N., and J. Glenn. 1992. Solid waste compost-
ing plants face the challenges. BioCycle. November,
33(ll):48-52.
Goldstein, N., and R Steuteville. 1992. Solid waste com-
posting in the United States. BioCycle. November,
33(ll):44-47.
METRO. 1989. The art of composting A community
recycling handbook. Portland, Oregon Metropolitan
Service District.
Taylor, A., and R. Kashmanian. 1989. Yard Waste Com-
posting A Study of Eight Programs. EPA1530-SW-89-
038. Washington, DC: Office of Policy, Planning and
Evaluation and Office of Solid Wrote and Emergency
Response.
U.S. Environmental Protection Agency (EPA). 1992. U.S.
Environmental Protection Agency. Characterization of
Municipal Solid Waste in the United States. EPA/530-R-
019. Washington, DC: Office of Solid Wrote and Emer-
gency Response.
U.S. Environmental Protection Agency (EPA). 1993. U.S.
Environmental Protection Agency. Markets for compost.
Washington, DC: Office of Solid Waste and Emergency
Response and Office of Policy, Planning and Evaluation.
-------
Introduction
Table 1-1. Summary of operating MSW plants.
Plant Name
Lakeside, AZ
New Castle, DE
Escambia County, FL
Pembroke Pines, Ft.
Sumter County, FL
Buena vista County, IA
Coffeyville, KS
Mackinac Island, Ml
Fillmore County, MN
Mora, MN (East
Central SWC)
Lake of the woods
County, MN
Bennington County, MN
St Cloud, MN
Swift County, MN
Truman, MN
(Prairieland SWB)
Wright County, MN
Sevierville, TN
Hidalgo County, TX
Ferndale, WA
Columbia County, WI
Portage, WI
Year
started
1991
1984
1991
1991
1988
1991
1991
1992
1987
1991
1989
1987
1988
1990
1991
1992
1992
1991
1991
1992
1986
Current Amount of Proprietary
MSW Composted Technolgy or
(tons/day) System(l) Ownership/Operation
10-12
200-225
200
200
50
4000/yr.
50
8 (inc. MSW,
Sludge, manure) (2)
12
250
5
12
60
12
55
165
150 (design)
70
100
40-45
20
bedminster
Bioconversion
Fairfield
digesters
»
Buhler
Lundell (for
processing)
«
Daneco
Lundell (for
processing)
Eweson digester
w/Royer ag. bed
OTVD
Buhler
Bedminster
Bioconversion
Royer ag. bed
^^m
Joint Venture
Public/Private
Public/Public
Private/Private
Public/Private
Private/Private
Private/Private
Public/Public
Public/Pubic
Public/Private
Public/Public
Public/Private
Private/Private
Public/Public
Public/Public
Public/Private
Public/Private
Public/Public
Private/Private
Public/Public
Public/Public
(1) This category is limited to compost system vendors and not other proptietary technologies/equipment
in use at these facilities.
(2) Amount for Mackinac island indicates average daily flow due to park population during the summer
months,
Source: Goldstien and Glenn, 1992.
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Introduction
Table 1-2. Nationwide listing of MSW composting facilities.
Facility Status System
ARIZONA
1. Pinetop-Lakeside Operational Digester (Bedminster)
ARKANSAS
I, Madison Pilot Windrow
LTnowcnil Planning Windrow (enclosed)
(Madera County
2 San Diego (City Vendor negotiation A-SP (Daneco)
, Tulare Cbunty7 Proposal review, , , Windrow or in-vessel
4, Ventura County Proposal review for solid
waste management
CONNECTICUT n ,
1, Northeastern Conn, Proposal review in-Vessel/Enclosed
Res, Rec, Auth,
(Brooklyn)
DELAWARE
LTM Reclamation Project Operational In-vessel (Fairfield)
T\T n ii \ J ^ '
(New Castle)
FLORIDA
1, Cape Coral vendor negotiation Windrow
AtnprrpfVflp)
2, Charlotte County Proposal review
, Escambia County Operational Windrow
4, Manatee County Vendor negotiation Windrow
J o i , , \
AmprprvnP
InlllclciyilcJ
5, Monrofi County , Proposal review
6, PaWeacn County PiWotonned «) Agitated bed (IPS)
(RDr RDr rejects,
mixed paper)
7, Pembroke Pines Operational Enc aerated windrow
S.Sumter County Operational Windrow (Amerecycie)
IOWA
1, Buenvista County Operational Windrow (w/ Lundell
. . , n , processing line
2,Cedar Rapids Feasibility study (for v 8
wet/dry separation)
3, Council Bluffs Consideration
4, Harden County Planning Windrow (w/ Lundell
(w/Butler,Wnght processing line
counties)
LCoffeyville Operational Windrow
1 , Tri-Pairish SWC Consideration of pilot
(St. Martin, Iberia (Cocomposttno)
Lafayette)
MAINE
1, Bowdoinham A-SP
(Source sep. organics)
2, Machias
(Source sep, Orangnics
MARYLAND I/ACU\
1, Baltimore <*$$$<$ > In-vessel A'S-H 2
(FERST Co,)
2, Brandywine Z.Brandywine Enc, A-SP (Rader Co,)
3, Salisbury Consideration of plot In-vessel (Sewdrum)
(wicomico Cty, (byAmertewlWeriali
1 mllVIk Ommr 1
Tons/Day
(Unless noted)
12-14 (w/6 wet tpd
sludge)
40(100-150 at full scale
500-800 (wMudge)
300,000/vear
9ffi-l,pOOw/sludge
3,01)0 (total StrearfiJ
200
200-225 (w/1 50-200 wet
tpd sludge)
200
400 (w/sludge)
MI400 design)
IjjOO (total Stfeam)
75,600yr, (total Stream)
550 (650 design))
50
4,000/yr,
75-80
60
50
700 (total stream)
lAnontfi
2,500 pop,
520(700 design)
340
20(300 design)
-------
Introduction
Table 1-2. (Continued).
FacOity
MASSACHUSETTS
1, Berkshire .county
Southern
r\ p\ T fi / i
z.Franklm county
INantucket
4. Northampton
5. NorthfieU
6. Somersat
7, Wrentham
WOMAN
LMacMnac Island
MINNESOTA
1, Filimore County
2, Freeborn/Mower
counties
3. Goodhue
4, Randiyoni County
5, Lake of the wood
County
6. Mora (East Central 1C)
lEenniflgton County
S.RiceUsunty J
9. Rosemount
10. StCloud
11. StLouis County
12, Swift County
13, Truman (Praineland
Solid Waste Board)
14, Wright County
Mssoum
1. Springfield
NEW HAMPSHIRE
1, Ashuelot Valley
Refuse Disp, Dlst,
2, Hooksat
l. Atlantic wunty
2. Cape May County
3. Ocean County
4, Ocean Township
NEW TQM
LCarrihtt
2. Delaware County
M fm&L U«MW^«M«
A tan Hampton
4, Eastern Rennselaer
County SWMA
5, Madison County
6, Monroe County
Status
Systm
consideration (Market/odor
control studies needed)
siting(for source sep,
organics; shidoe)
Proposal r.eview
Consideration
Proposed by Bennett
Construction, Inc,
Proposed by ERS
Propose by ERS
Operational
Operational
Planning(source
ssDt OToanics)
Proposed by ERS
Operational
Operational
In-Vessel
Enc. -aerated
Tim&Diy
(Unless noted)'
15
100
100
Tunnel w/enc, windows 200
A-SP
A-SP;Enc.windrow(in
construction)
Aerated Windrow
i>M JBI
mnorow
Enc,A-SP (Danco)
700
§00(W/180 tpd slud£
8 (w/sludge, manure)
12
80
450
20-40
5
250
e)
Operational , Windrow 40(80 tpd disign))
Plaining (w/ addtl, Aeratedwindrow
Counties
P uuu.nu.vuy
lanmne (by Ceres
for RDF residuals
MSW, other organics)
Mndrow
Operational Digester* agitated bed
by Recomp
A-SP
Operational lerated Windrow
Operational In-vassal (OTVD)
Operational , ,
TO residuals
from Anola County)
inc, aerated Windrow
(Buhler)
Permitting Enc. A-SP (Damn)
Consideration
Proposed by Aware Corp, \
Vindrow
Design(Source Sep, In -Vessel (agitated bed)
Permitting
Pilot (source sep,
oganics by Otean Cty,
_ Landfill Corp.)
Proposal review
Planning
Consideration
Feasibility studyn
(source sep, Organics:
MRF under construction)
Vendor negotiation
Plot (Residential source V
sep. organics)
Consideration \
inc. A-SP (Daneco1
n-Vessel
n-Vessel
n-Vessel
n-Vessel
inc, A-SP(Daneco)
IBnitatfMii
viiMinjw
I&«A««M
nwiuw
100
60(100tpd design)
12 [5,5 to Composting)
55 (100 design] 8
165
500
800
159 (w/sludge)
300 (design)
400400
5HPP ,
lOOldesgn ^
110 (Totafstream)
100-150 (w/sludge,
ssplage)
Zrwk.
300
-------
Introduction
Table 1-2. (Continued).
Facility
1. NewYork City
8, Riverhead
9,South Hampton
NORTH CAROLINA
1. Buncombe County
I, Portland
PENNSYLVANIA
I, Adams County
2 .Blair County
TENNESSEE ,
I, Sevierville (Sevier)
Solid Waste)
TEXAS
I.Big Sandy
2, Hidalgo County
3. Houston
4,StephenvilIe
VERMONT
l,Cei|ral Vermont
VIRGINIA
lloudon County
WASHINGTON
I, Ferndale
WEST VIRGINIA
I, Leestown
WISCONSIN
I.Adams County
2, Burnett & Washburn
Counties
3, Columbia County
4, Portage
5, Vilas tounty
Status
Pilot (Residential source
Permitted by pmni
Tech Serv, (Procuring
waste contracts
Consideration
voter ref.on
n/31/92)
Plot
Temporarily closed
(vendor negotiation)
Feasibility study
Consideration
Opentfoml
Operational by
Bedminster (research)
tacility)
Operational
Proposal by WPF Corp,
Consideration
Planning (Source sep,
Orgaracs by priv, co.)
Operational by Recomp
Pilot (Source sep,
Organics)
Consideration (wet/dry)
Consideration
Operational
Operational , >
Fflofp planning)
System
Windrow
Agitated bed (Koch)
Windrow
In-vessel
Digester w/aerated
Windrows (Bedminst
Digester*/
ttAmttiwtt
WlnuiwW
AerateTwindrow
Windrow
fjx. aerated
windrow
Digester w/agitated
red Royen
\ j !
Static pile,
Windrows
Windrow
Windrow & A-SP
Drum w/enc, curing
Drum w/windrows
A-SP
Tons/Dty
(Unless noted)
4,5-5/wk
250(500 design)
200(tota for pilot)
\ MM np^ion
JUU JJU lUCJliilll
600 (design)
ISO tola stream
240 tola Stream
. I50fw/75wettpd
er) Sludge)
35 w/ sludge
(seasonal)
70 (300 design)
3 Jpwk total stream
368,500 cy/yr,
125-180
100
11
40-45w/sludge
f fcm \
20 (w/sludge)
30-50 for pilot
20 tpd (total stream)
Source: Goldstein and Glenn, 1992.
-------
Introduction
Table 1-3. A brief comparison of yard trimmings and MSW composting.
Parameter
Planning
separation
Technology
Leachate Control
Odor Control
Regulations
Product Quality
Economics
Yard Trimmings composting
Yard trimmings composting often requires planning for
seasonal variations in tfie flow of feedstock.
MSW composting
Large-scale MSW composting will require a detailed
waste stream assessment that will require planning and
resources to complete.
Easy to separate yard trimmings feedstock from the rest Feedstock for MSW composting can be separated by
of the MSW stream for collection and composting since residents or at the facility into recyclable, compostable,
yard trimmings are normally gathered by the and/or noncompostable components.
homeowner separately from other materials.
Yard trimmings composting can be done using relatively MSW composting requires mare complex technology
simple technologies. because it processes a mixed feedstock that can include
varied contaminants.
Leachate collection systems might be required,
particularly for larger facilities and those in areas of
moderate to high rainfall.
Yard trimmings compost facilities can often employ
simple siting, process, and design controls to minimize
Colors.
yard trimmings composting is not governed by stringent
regulations.
medium- to high-quality compost can be produced
using relatively simple technology and can be easily
marketed to end users
A low-technology yard trimmings composting facility
can be financed with a relatively small capital
investment and low operating casts (mostly labor).
Due to the diversity of materials in MSW feedstock,
leachate collection systems ore generally required.
MSW composting facilities are likely to require
sophisticated technologies to control odors. More
stringent siting and design measures also are typically
needed.
MSW composting is more stringently regulated or
controlled than yard trimmings composting, and may
require compliance with state or local permitting
procedures.
Extensive preprocessing is required to achieve medium-
to high-quality compost that can overcome public
perception problems of impurity and be marketed easily,
Siting, equipment, and permitting costs can add up to a
large initial and ongoing investment for a MSW
composting facility, particularity for a large operation.
-------
Introduction
l^^H
I
) *
^
Planning
. Goal Setting
Operational Plans
Facility Ownership/Managi
Finding Composting Ven
^
Siting
Odor Control
Land Area Requlremer
t
Facility Design Requir
sment
dors
1
its
ements
^
Collection Methods
| Public Drop-Off Sites | | Curbside Collection |
1 | Bag'ged
"I | Loose |
^
t
Processing Methods
sorting
Process Selection
I \ *~
I . ' . i
1 Passive Piles 1 1 Turned Windrows 1
1 , 1 1 , 1
)-*
h
^M^MM
1 1
| Curing/Storage |
Aerated Static
Piles
t
Environmental Concerns
. Odor Control
. Leachate Control
. Occupstional Health and Safety
t
Product Qualit
Compost Quality
. product Specification
Product Testing
/
s
f
Marketing
Product Demand
End User Requirements
Pricing
Location/Distribution Issues
Education and Public Relations
t
Potential End Users
| Agriculture | | Landscaping | |
Horticulture |
| Silviculture | | Public Agencies |
[ Residential Sector
.
'
Figure 1-1. Overview of a yard trimmings composting program.
-------
Introduction
Community Involvement
Planning
Goal Setting
Waste Characterization
Operational Plans
Facility Ownership/Management
Finding Composting Vendors
Siting
Odor Control
Land Area Requirements
Facility Design Requirements
Collection Methods
I Curbside Collection I
| Source-Separated MSW | | Commingled MSW |
| Recydables |
Processing Methods
| Sorting [
I Separation Technologies J
"^""^^^^^^^^^^"i
]
Size Reduction
Process Selection
J
Aerated Static Piles
T [ In-Vassal Systems [
Turned
Windrows
Suction
System
1 1
Positive
Pressure
System
±
Rotating
Drum
Tank
System
Curing/Storage
^ Household
Hazardous Waste
and
Moncompostables
Environmental Concerns
Odor Control
Vector Control
Leachate Control
Occupational Health and Safety
Product Quality
Compost Quality
Product Specifications
Product Testing
Marketing
Product Demand
End User Requirements
Pricing
Location/Distribution Issues
Education and Public Relations
Potential End Users
| Agriculture | | Landscaping | | Horticulture |
| Silviculture ~| | Public Agencies [
Residential Sector
Figure 1-2. Overview of an MSW composting program.
-------
Chapter One
Planning
[ ommunities that are considering incorporating composting into their solid waste management strategy need
I to conduct thorough planning to decide what type of program best fits the needs and characteristics of their
\J locality Because each community possesses its own set of financial climactic, socio-economic, demographic,
and land use characteristics, there is no formula dictating how to incorporate composting into an integrated waste
management plan; these issues must be decided on a case-by-case basis for each community or region. This chap-
ter describes some of the preliminary steps that a community should take before embarking on any composting
program. Addition planning requirements are addressed throughout the guidebook.
Goal Setting
An important first step for public officials considering a
composting program is to determine what they want the
program to achieve. Typical goals of a composting pro-
gram include
Reducing the flow of materials into landfills or
combustors.
Diverting certain types of materials from the MSW
stream.
Complying with state or local regulations or recov-
ery goals.
Providing a practical management option for a sin-
gle community or a larger region.
Once a community has clearly defined the goals of its pro-
gram, it will be easier to evaluate available technologies and
determine the role that composting will play in the commu-
nity's overall management strategy. In addition to goal-set-
it is important to evaluate the economic and technical
feasibilty of composting in the context of other waste man-
agement techniques, such as landfilling and combustion, to
determine which alternatives are most suitable for the com-
munity The costs and benefits of each option as well as rele-
vant political and public opinion considerations can be
evaluated to ascertain which mix of solid waste management
approaches will best serve the community
Waste Characterization
A municipal composting program must be implemented
with a full understanding of the MSW stream. Identifying
and quantifying the components of the local MSW
stream should be an integral part of preliminary planning
for every program. One way to obtain this information is
to conduct a waste stream characterization study. These
studies range in price from $35,000 to $400,000, depend-
ing on the type and quality of information needed. A
co-reprehensive waste characterization study involves ana-
lyzing the local MSW stream by separating and sampling
waste. Sampling can take place at the local waste manage-
ment facility or at a transfer station. If a large-wale MSW
composting facility is being contemplated, a detailed
waste stream characterization study is necessary to ensure
proper design (this would not be necessary in advance of a
large-scale yard trimmings composting program). Publica-
tions, including the Solid Wrote Composition Study 1990-
1991: Part 1 published by the Minnesota Pollution
Control Agency, are excellent references for more detailed
information on conducting MSW stream assessments
(this document is cited in the resources list at the end of
this chapter). While a waste stream characterization study
can provide information on the anticipated quantity of
materials generated, it will not necessarily discern the
amount of materials that will actually be collected or
dropped off in the composting program since that will de-
pend on factors such as the percent of homes or facilities
that provide organic material for composting.
Although a comprehensive waste characterization study is
the most accurate way to obtain data on the local MSW
stream, the analysis involved can be very expensive and
time consuming, Therefore, many communities might
simply want to examine state or national MSW genera-
tion patterns, using these figures as a basis for determining
local waste flow and characterization. Planners should,
11
-------
Planning
however, take into consideration any local factors that
could influence the composition and amount of their
MSW stream including
Season and climate - In certain parts of the country,
the amount and type of yard trimmings generated
will vary dramatically from season to season and as
the climate changes. For example, an abundance of
leaves are generated in autumn in many localities.
Climate also can affect the composition and
amount of the MSW stream. During warm sea-
sons, for example, the quantity of beverage contain-
ers might be expected to rise. During the
December holiday season, municipalies might ex-
pect a large amount of gift-wrapping paper or
Christmas trees.
Regional differeces - Communities in Florida, for
example, might discover that palm fronds consti-
tute a large amount of their local MSW stream,
while municipalities along the Maine seacoast must
take into account large amounts of fish scraps gen-
erated in their region.
Demographics - Population variations can have a sig-
nificant impact on the MSW stream. These include
temporary population changes (particularly in popu-
lar tourist or seasonal resort areas and college towns);
the average age, income and education of the popula-
tion, age of neighborhoods; and population densities.
State of the economy - The economic state of an area
also can affect the composition of the MSW
stream. For example, the increase in consumption
that can be associated with good economic times
might be reflected in an increase in packaging and
other goods in the MSW stream.
Locall source reduction and recycling programs - Pro-
grams that aim to reduce or divert certain compo-
nents of the MSW stream from disposal can affect
the amount and type of materials that can be col-
lected for composting.
For more accurate estimates, information from communi-
ties with similar demographic characteristics and sources
of discards can be extrapolated to fit the local scene. Local
collection services and facility operators also can be con-
sulted. These individuals might have written records of
the amount and type of discards collected on a yearly or
even a monthly basis.
Operational Plans
An operational plan should be drafted to assist local offi-
cials and community members in understanding the
proposed composting program and their roles in that pro-
gram. An operational plan can be used as the basis for
community discussion about the proposed program and
for developing strong political support and consensus.
The operational plan will be the community's road map
for implementing and operating a successful composting
program. Therefore, the more detailed the plan, the more
useful it will likely be. The operational plan can be revised
throughout the planning process as necessary to reflect
major changes or alterations.
The operational plan should stipulate the chosen com-
posting technology (e.g., turned windrows, aerated static
piles, in-vessel systems, etc.); the equipment needed; pro-
posed site design; and the pollution, nuisance, and odor
control methods that will be employed. In addition, it
should specify the personnel that will be required to oper-
ate the program as well as the type and extent of training
they will require. The plan also should contain procedures
for marketing or otherwise distributing the compost
product.
When developing a plan, it is important to remember that
all of the elements of a composting program (e.g., buying
equipment, siting a facility, marketing the finished prod-
uct, etc.) are interrelated. For this reason, all elements of a
composting program should be chosen with other ele-
ments in mind. For example, composting site design can
be influenced by a variety of factors. Site design might be
influenced by the type of material that the site will proc-
ess. A site which processes large quantities of a readily pu-
trescible material and has close neighbors can require an
enclosed design. Site design might also be influenced by
compost markets. A site with screening capabilities and
flexible retention time could be needed to meet the de-
mands of end users. In addition, site design might be in-
fluenced by long-term considerations. A site with the
potential to expand can be more appropriate for the com-
munity that expects its materials stream to grow in vol-
ume. As this example makes clear, decision-makers should
accommodate the interrelated nature of the elements of a
composting program throughout the planning process.
Community Involvement
Throughout the planning process, officials should work
closely with collectors, haulers, processors, the recycling
industry, local utilities, private citizens, and others to
develop a safe, efficient, and cost-effective program.
Providing these groups with a forum to express their con-
cerns and ideas about composting will build a sense of
ownership in the project as a whole. In addition, coopera-
tion will enhance the understanding of the concerned
groups about the compromises needed to make the pro-
gram work; as a result, objections to siting or collection
programs, for example, should be lessened. These groups
also can provide invaluable information on vital aspects of
12
-------
Planning
a composting operation (see Chapter 10 for more infor-
mation on community involvement).
Facility Ownership and
Management
One of the basic decisions that must be addressed in the
early planning stages is composting facility ownership and
management. There are essentially four options for site
ownership and operations, as shown in Table 1-1. These
are municipal facilities, merchant facilities, privatized fa-
cilities, and contract services.
The option chosen for ownership and management of the
composting facility will depend on many factors such as
feedstock supply land size and location, personnel re-
sources, experience, costs, liability, financing methods,
and political concerns, composting facilities can be
located on municipally or privately owned land, for
example. When a community has available land and re-
sources, it might consider owning and operating the facil-
ity itself If the municipality has the land but not the
resources for operation, it could contract out to an inde-
pendent management firm. Communities might also con-
sider encouraging the development of a privately owned
and operated facility that works on a long-term contract,
with the municipality guaranteeing tipping fees and feed-
stock. This facility might be owned and operated by a
landfll owner or a refuse hauler that could serve the needs
of all the communities it services. For larger facilities, in
Table 1-1. A comparison of facility ownership options.
Facility
Type Owner Operator Arrangement
Municipal Municipality Municipality
Privatized Private
vendor
Municipality Municipality
and provides its own
equipment.
Private Vendor works under long-term
vendor service agreement with
municipa lity to compost
feedstock. Vendor designs
and constructs facility an the
basis of private capital
attracted by the predictable
revenue stream created by the
long-term contract.
Private Private vendor designs,
vendor finances, constructs, and
operates facility on
expectation of sufficient
revenue from tipping fees and
service charges. No contract
between vendor and
municipality exists, however.
Contract Municipality Private firm Long-term Contract With
services community for operation and
maintenance of facility. Private
company receives tipping fee.
Municipality might staff me
site or me private company
might bring its own labor
resources.
Merchant
facility
Private
vendor
Advantages
Municipality has full control of
operations.
Municipality uses franchises
and operating licenses to
minimize competition far the
vendor and thereby minimize
investment risk for the vendor.
Municipality carries no
financial or operafional risk.
Municipality retains significant
cord since it can change
service company upon
expiration of the contract.
Disadvantages
Municipality shoulders all
financial and performance
risks associated with starting
and operating the facility, if
problems occur with the
facility (e.g.,traffic,odor,etc
the municipality might have to
oddress political issues as well.
Municipality does not have full
control over operations.
High risk to vendor because of
absence of contract
guaranteeing feedstock and
ripping fees. The public risk 'is
tied to the possibility of the
vendor failing and leaving the
community with reduced waste
management capacity. Also
community has no input on the
level of service and no control
of costs.
Municipality shoulders funding
of facility.
Source: Gehr and Brawn, 1592.
13
-------
Planning
particular, municipalities should consider regional ap-
proaches to ownership and management. For example,
one town might supply the site with others providing
equipment and staffing. Such approaches offer both large
and small communities advantages in financing, manage-
ment, marketing and environmental protection. Regional
approaches also can help communities accomplish to-
gether what they cannot attain alone.
Composting Vendors
Many communities do not have the technical personnel
and resources to develop and design a composting pro-
gram and facility. It is not uncommon therefore to so-
licit this expertise from the private sector through a
Request For Proposals (RFP). The purpose of an RFP is
to encourage the submission of proposals from vendors
that can conduct composting operations for the com-
munity. A well thought out and carefully worded RFP
should include the broad operational plan for the com-
munity's composting program. This will give potential
vendors the proper frame of reference for proposal de-
velopment. In addition, the RFP should encourage the
vendors to develop creative as well as low-cost options
for composting. Finally, the RFP must provide a strong
basis for reviewers to evaluate the different proposals
and choose the vendor that offers the best mix of tech-
nical expertise, program design, and cost effectiveness
for the community (Finstein et al, 1989).
Officials should consider hiring outside services to per-
form meticulous technical and economic analyses of
any RFPs to determine their suitability to the commu-
nity's specific solid waste characteristics. Given the
plethora of source reduction, recycling, composting,
and disposal options, many experts recommend the use
of an RFP particularly for more complex composting
operations, in order to identify opportunities to maxi-
mize cost effectiveness and ensure the resulting com-
posting operation will meet its goals.
Pilot Programs
Before implementing a full-fledged composting pro-
gram, many communities first conduct pilot programs
to determine the costs and prospects for success of a
full-scale project. Pilot programs enable communities to
experiment with different components of a program
(such as composting technologies, collection strategies,
and marketing techniques) to ascertain the most effec-
tive approaches for the community. Start-up costs for a
pilot program are greater than for an ongoing compost-
ing program, however, and should not be used to esti-
mate the start-up costs of a fill-scale or long-term
program.
Pilot Program in Seattle, Washington
From 1980 until 1989, the City of Seattle, Washing-
ton, conducted a yard trimmings composting^ pilot
program consisting of a variety of demonstration pro-
jects aimed at determining the success of composting
as a management option. Demonstration projects in-
cluded community education on composting, Christ-
mas tree recycling, and a 3-month "Clean Green"
drop-off program for yard trimmings at the city's two
transfer stations. In October 1988, Seatde passed an
ordinance requiring residents to separate yard trim-
mings from recyclables and refuse. Based on the results
of the city's pilot program, today Seattle maintains a
three-pronged composting program: "Clean Greea"
drop-off centers for yard trimmings, backyard com-
posting, and curbside collection of yard urimmings
(ILSR, 1992).
Summary
In order to ensure a successful composting progwm,
communities must plan ahead Thorough plan-
ning will enable communities to detect any major
problems with a composting operation that could
jeopardize its success, such as an unacceptable siting
decision, a lack of consistent feedstock, or a shortage
of demand for the final product. Among the prrlimi-
nary planning steps that a community should under-
take are setting gosh, conducting a waste stream
characterization study or assessment, devloping in an
operational plan, soliciting the viewpoints of affected
parties, determining site ownership and manage-
ment, securing a vendor and considering the value of
conducting a pilot program. Official should view
composting as one alternative in their MS W man-
agement program and analyze its effectiveness in
comparison with management alternatives including
source reduction, landfilling and combustion.
Chapter One Resources
Finstein, M., P. Strom, F. Miller, and J. Hogan. 1990.
Elements of a request for proposal (RFP) for sludge and
municipal solid waste composting facilities Scientific and
technical aspects. New Brunswick NJ: Rutgers Coopera-
tive Extension, New Jersey Agricultural Experiment
Station.
14
-------
Planning
Gehr, W., and M. Brown. 1992. When privatization
makes sense. BioCycle. July, 33(7): 66-69.
International City/County Management Association
(ICMA). 1992. Composting Solutions for waste man-
agement. Washington, DC: ICMA
Institute for Local Self-Reliance (ILSR). 1992. In-depth
studies of recycling and composting programs: Designs,
costs, results. Volume III.
Minnesota Pollution Control Agency (MPCA). 1992.
Solid Waste Composition Study 1990-1991: Part 1. St.
Paul, MN: Ground Water and Solid Waste Division.
O'Leary P., P. Walsh, and A. Razvi. 1990. Composing
and the waste management plan. Waste Age. February,
21(2): 112-117.
U.S. Environmental Protection Agency (EPA). 1989. De-
cision-Maker's Guide to Solid Waste Management.
EPA1530-SW-89-072. Washington, DC Office of Solid
Waste and Emergency Response.
Walsh, P., A. Razvi, and P. O'Leary. 1990. Operating a
successful compost facility. Waste Age. January, 21(1):
100-106.
15
-------
Chapter Two
Basic Composting
Principles
omposting relies on a natural process that results from the decomposition of organic matter by microorgan-
I isms. Decomposition occurs wherever organic matter is provided with air and moisture; it occurs naturally
w on the forest floor and in open field composting, as the term is used in this guidebook, is distinguished
from this kind of natural decomposition in that certain conditions parameters such as temperature and mois-
ture.) are controlled to optimize the decomposition process and to produce final product that is sufficiently sta-
ble for storage and application to land without adverse environmental impacts. This chapter provides a brief
introduction to the biology involved in composting It also describes the physical and chemical parameter that influ-
ence the process. Chapter 4 of guidebook discusses how to control these parameter to optimize composting.
Overview of the Composting Process
The composting process occurs in two major phases. In
the first stage, microorganisms decompose the compost-
ing feedstock into simpler compounds, producing heat as
a result of their metabolic activities. The size of the com-
posting pile is reduced during this stage. In the second
stage, the compost product is cured" or finished. Micro-
organisms deplete the supply of readily available nutrients
in the compost, which, in turn, slows their activity. As a
result, heat generation gradually diminishes and the com-
post becomes dry and crumbly in texture. When the cur-
ing stage is complete, the compost is considered
"stabilized" or "mature." Any further microbial decompo-
sition will occur very slowly.
The Role of Microorganisms
Composting is a succession of microbial activities whereby
the environment created by one group of microorganisms
invites the activity of successor groups. Different types of
microorganisms are therefore active at different times in
the composting pile. Bacteria have the most significant ef-
fect on the decomposition process, and are the first to
take hold in the composting pile, processing readily de-
composable nutrients (primarily proteins, carbohydrates,
and sugars) faster than any other type of microorganism.
Fungi, which compete with bacteria for food, play an im-
portant role later in the process as the pile dries, since
fungi can tolerate low-moisture environments better than
bacteria. Some types of fungi also have lower nitrogen
requirements than bacteria and are therefore able to de-
compose cellulose materials, which bacteria cannot. Be-
cause fungi are active in composting piles, concern has
arisen over the growth of opportunistic species, particu-
larly those belonging to the genus Aspergillus. Chapter 6
discusses the potential health risks associated with this
fungus.
Microorganisms also play a role in the composting proc-
ess. Rotifers, nematodes, mites, springtails, sowbugs, bee-
tles, and earthworms reduce the size of the composting
feedstock by foraging, moving in the compost pile, or
chewing the composting materials. These actions physi-
cally break down the materials, creating greater surface
area and sites for microbial action to occur.
The microorganisms necessary for composting are natu-
rally present in most organic materials, including leaves,
grass clippings, and other yard trimmings, and other or-
ganic materials. Products are available that claim to speed
the composting process through the introduction of se-
lected strains of bacteria, but tests have shown that inocu-
lating compost piles in this manner is not necessary for
effective composting of typical yard trimmings or MSW
feedstock (Rynk et al., 1992; Haug, 1980; Gray et al.,
1971a).
The bacteria and fungi important in decomposing the
feedstock material can be classified as mesophilic or
thermophilic. Mesophilic microorganisms or meso-
philes (those that grow best at temperatures between 25
and 45°C [77 to 113°F]) are dominant throughout the
16
-------
Basic composting Principles
70
55
o
e
UJ
<
a:
in
o.
UJ
25
10
10
9
0
7
6
5
r
a
Source: Gray et al., 1971 a.
TIME
Figure 2-1. Temperature and pH variation with time phases of microbial activity.
A = mesophilic, B = thermophilic, C = cooling, D = maturing.
composting mass in the initial phases of the process when
temperatures are relatively low. These organisms use avail-
able oxygen to transform carbon from the composting
feedstock to obtain energy, and, in so doing, produce
carbon dioxide (C02) and water. Heat also is generated
as the microorganisms metabolize the composting feed-
stock. As long as the compost pile is of sufficient size to
insulate internal layers from ambient temperatures and
no artificial aeration or turning occurs, most of the heat
generated by the microorganisms will be trapped inside
the pile. In the insulated center layers, temperatures of
the composting mass will eventually rise above the tol-
erance levels of the mesophilic organisms. Figure 2-1
shows a typical temperature pattern for natural com-
posting processes. When the temperatures reach toward
45°C (113°F), mesophiles die or become dormant,
waiting for conditions to reverse.
At this time, thermophilic microorganisms or thermo-
philes (those that prefer temperatures between 45 and
70°C [113 and 158°F]) become active, consuming the
materials readily available to them, multiplying rapidly,
and replacing the mesophiles in most sections of the com-
posting pile. Thermophiles generate even greater quanti-
ties of heat than mesophiles, and the temperatures reached
during this time are hot enough to kill most pathogens
and weed seeds. Many composting facilities maintain a
temperature of 55°C (131°F) in the interior of the com-
post pile for 72 hours to ensure pathogen destruction and
to render weeds inviable. (See Chapter 6 for a detailed dis-
cussion of pathogens and Chapter 7 for a discussion of
different states' requirements for ensuring pathogen and
weed destruction.)
The thermophiles continue decomposing the feedstock
materials as long as nutrient and energy sources are
plentiful. As these sources become depleted, however,
thermophiles die and the temperature of the pile drops.
Mesophiles then dominate the decomposition process
once again until all readily available energy sources are
utilized. Table 2-1 shows the density of microorganisms as
a function of temperature during composting.
Factors Influencing the Composting
Process
Because microorganisms are essential to composting, envi-
ronmental conditions that maximize microbial activity
will maximize the rate of composting. Microbial activity is
influenced by oxygen levels, particle sizes of the feedstock
material, nutrient levels and balance (indicated by the
carbon-to-nitrogen ratio), moisture content, temperature,
and acidity/alkalinity (pH). Any changes in these factors
are interdependent; a change in one parameter can often
17
-------
Basic Composting Principles
result in changes in others. These factors and their interre-
lationships are discussed briefly below and in more detail
in Chapter 4.
Oxygen
Composting can occur under aerobic (requires free oxy-
gen) or anaerobic (without free oxygen) conditions, but
aerobic composting is much faster (10 to 20 times faster)
than anaerobic composting. Anaerobic composting also
tends to generate more odors because gases such as hydro-
gen sulfide and amines are produced. Methane also is pro-
duced in the absence of oxygen.
Microorganisms important to the composting process re-
quire oxygen to break down the organic compounds in
the composting feedstock. Without sufficient oxygen,
these microorganisms will diminish, and anaerobic
microorganisms will take their place. This occurs when
the oxygen concentration in the air within the pile falls
below 5 to 15 percent (ambient air contains 21 percent
oxygen). To support aerobic microbial activity, void spaces
must be present in the composting material. These voids
need to be filled with air. Oxygen can be provided by mix-
ing or turning the pile, or by using forced aeration sys-
tems (Chapter 4 discusses mixing and aeration methods
in more detail).
The amount of oygen that needs to be supplied during
composting depends on:
n The stage of the process - Oxygen generally needs to
be supplied in the initial stages of composting; it
usually does not need to be provided during curing.
n The type of feedstock - Dense, nitrogen-rich materi-
als (e.g., grass clippings) will require more oxygen.
The particle size of the feedstock - Feedstock materi-
als of small particle size (e.g., less than 1 or 2 inches
in diameter) will compact, reducing void spaces
and inhibiting the movement of oxygen. For this
reason, the feedstock should not be shredded too
small before processing (see below and Chapter 4
for information on size reduction).
The moisture content of the feedstock - Materials with
high moisture content (e.g., food scraps, garden
trimmings) will require more oxygen.
Care must be taken, however, not to provide too much
aeration, which can dry out the pile and impede
composting.
Particle Size
The particle size of the feedstock affects the composting
process. The size of feedstock materials entering the com-
posting process can vary significantly. In general, the
smaller the shreds of composting feedstock, the higher the
composting rate. Smaller feedstock materials have greater
surface areas in comparison to their volumes. This means
that more of the particle surface is exposed to direct mi-
crobial action and decomposition in the initial stages of
composting. Smaller particles within the composting pile
also result in a more homogeneous mixture and improve
insulation (Gray et al, 197 Ib). Increased insulation ca-
pacity helps maintain optimum temperatures in the com-
posting pile. At the same time, however, the particles
should not be so small as to compact too much, thus ex-
cluding oxygen from the void spaces, as discussed above.
(Chapter 4 describes techniques for size reducing com-
posting feedstock prior to processing.)
Table 2-1. Microbial populations during aerobic compacting!
Microbe
Bacteria
Mesophilic
Thermophilic
Actinomycetes
Thermophilic
Fungi
Mesophilic
Thermophilic
Number per Wet Gram of Compost
Mesophilic Initial
Temp (40°C)
108
104
104
Thermophilic
(40-70°c)
106
10'
108
Mesophilic
(70°C to Cooler)
10"
107
105
105
106
Numbers of
Species Identified
6
1
14
18
16
"Composting substrate not stated but thought to be garden-type meterials composted with little mechanical agitation.
'Actual number present is equal to or less than the stated value.
Source: Haug, 1980.
18
-------
Basic Composting Principles
Nutrient Levels and Balance
For composting to proceed efficiently, microorganisms re-
quire specific nutrients in an available form, adequate
concentration, and proper ratio. The essential macronutri-
ents needed by microorganisms in relatively large amounts
include carbon (C), nitrogen (N), phosphorus (P), and
potassium (K). Microorganisms require C as an energy
source. They also need C and N to synthesize proteins,
build cells, and reproduce. P and K are also essential for
cell reproduction and metabolism. In a composting sys-
tem, either C or N is usually the limiting factor for effi-
cient decomposition (Richard, 1992a).
Composting organisms also need micronutrients, or trace
elements, in minute amounts to foster the proper assimi-
lation of all nutrients. The primary micronutrients needed
include boron, calcium, chloride, cobalt, copper, iron,
magnesium, manganese, molybdenum, selenium, sodium,
and zinc (Boyd, 1984). While these nutrients are essential
to life, micronutrients present in greater than minute
amounts can be toxic to composting microorganisms.
Even if these nutrients are present in sufficient amounts,
their chemical form might make them unavailable to
some or all microorganisms. The abilty to use the avail-
able organic compounds present depends on the microor-
ganism's "enzymatic machinery" (Boyd, 1984). Some
microorganisms cannot use certain forms of nutrients be-
cause they are unable to process them. Large molecules,
especially those with different types of bonds, cannot be
easily broken down by most microorganisms, and this
slows the decomposition process significantly. As a result,
some types of feedstock break down more slowly than
others, regardless of composting conditions (Gray et al,
197la). For example, lignin (found in wood) or chitin
(present in shellfish exoskeletons) are very large, complex
molecules and are not readily available to microorganisms
as food. These materials therefore decompose slowly.
The C:N ratio is a common indicator of the availability of
compounds for microbial use. The measure is related to
the proportion of carbon and nitrogen in the microorgan-
isms themselves. (Chapter 4 discusses the C and N con-
tent of different types of feedstock.)
High C:N ratios (i.e., high C and low N levels) inhibit the
growth of microorganisms that degrade compost feed-
stock. Low C:N ratios (i.e., low C and high N levels)
initially accelerate microbial growth and decomposition.
With this acceleration, however, available oxygen is
rapidly depleted and anaerobic, foul-smelling conditions
result if the pile is not aerated properly. The excess N is re-
leased as ammonia gas. Extreme amounts of N in a com-
posting mass can form enough ammonia to be toxic to
the microbial population, futher inhibiting the compost-
ing process (Gray et al., 1971b; Haug, 1980). Excess N
can also be lost in leachate, in either nitrate, ammonia, or
organic forms (Richard, 1992b) (see Chapter 6).
Moisture
The moisture content of a composting pile is intercon-
nected with many other composting parameters, includ-
ing moisture content of the feedstock (see Chapter 4),
microbial activity within the pile, oxygen levels, and tem-
perature. Microorganisms require moisture to assimilate
nutrients, metabolize new cells, and reproduce. They also
produce water as part of the decomposition process. If
water is accumulated faster than it is eliminated via either
aeration or evaporation (driven by high temperatures),
then oxygen flow is impeded and anaerobic conditions re-
sult (Gray et al., 1971 b). This usually occurs at a moisture
level of about 65 percent (Rynk et al., 1992).
Water is the key ingredient that transports substances
within the composting mass and makes the nutrients
physically and chemically accessible to the microbes. If
the moisture level drops below about 40 to 45 percent,
the nutrients are no longer in an aqueous medium and
easily available to the microorganisms. Their microbial ac-
tivity decreases and the composting process slows. Below
20 percent moisture, very little microbial activity occurs
(Haug, 1980).
Temperature
Temperature is a critical factor in determining the rate of
decomposition that takes place in a composting pile.
composting temperatures largely depend on how the heat
generated by the microorganisms is offset by the heat lost
through controlled aeration, surface cooling, and moisture
losses (Richard, 1992a) (see Chapter 4). The most effec-
tive composting temperatures are between 45 and 59°C
(113 and 138°F) (Richard, 1992a). If temperatures are
less than 20°C (68°F), the microbes do not proliferate and
decomposition slows. If temperatures are greater than
59°C (138°F), some microorganisms are inhibited or
killed, and the reduced diversity of organisms results in
lower rates of decomposition (Finstein et al., 1986; Strom,
1985).
Microorganisms tend to decompose materials most effi-
ciently at the higher ends of their tolerated temperature
ranges. The rate of microbial decomposition therefore in-
creases as temperatures rise until an absolute upper limit is
reached. As a result, the most effective compost managing
plan is to maintain temperatures at the highest level possi-
ble without inhibiting the rate of microbial decomposi-
tion (Richard, 1992a; Rynk et al., 1992).
Acidity/Alkalinity (pH)
The pH of a substance is a measure of its acidity or alka-
linity (a function of the hydrogen ion concentration), de-
scribed by a number ranging from 1 to 14. A pH of 7
indicates a neutral substance, whereas a substance with
pH level below 7 is considered to be acidic, and a sub-
stance with a pH higher than 7 is alkaline. Bacteria prefer
19
-------
Basic composting Principles
apH between 6 and 7.5. Fungi thrive in a wider range of
pH levels than bacteria, in general preferring a pH be-
tween 5.5 and 8 (Boyd, 1984). If the pH drops below 6,
microorganisms, especially bacteria, die off and decompo-
sition slows (Wiley, 1956). If the pH reaches 9, nitrogen is
converted to ammonia and becomes unavailable to organ-
isms (Rynk et al, 1992). This too slows the decomposi-
tion process.
Like temperature, pH levels tend to follow a successional
pattern through the composting process. Figure 2-1, on
page 17, shows the progression of pH over time in a com-
posting pile. As is illustrated, most decomposition takes
place between pH 5.5 and 9 (Rynk et al., 1992; Gray et
al., 197 Ib). During the start of the composting process,
organic acids typically are formed and the composting
materials usually become acidic with a pH of about 5. At
this point, the acid-tolerating fungi play a significant role
in decomposition. Microorganisms soon break down the
acids, however, and the pH levels gradually rise to a more
neutral range, or even as high as 8.5. The role of bacteria
in composting increases in predominance again as pH
levels rise. If the pH does not rise, this could be an
indication that the compost product is not fully matured
or cured.
Summary
omposting is a biological process influenced by a
I variety of environment factors, including the
\J number and species of microorganisms present
oxygen levels.particle size, of the composting materials
a/5 nutrient levels, moisture content, temperature,
and pH. All of these factor are interrelated, and
must be monitored and controlled throughout the
composting process to ensure a quality product.
Chapter Two Resources
Alexander, M. 1961. Introduction to soil microbiology.
New York, NY: Wiley Publishing Co. As cited in: Gray,
K.R., K. Sherman, and AJ. Biddlestone, 1971b. A review
of composting Part 2- The practical process. Process Bio-
chemistry. 6(10):22-28.
Boyd, RF. 1984. General microbiology. Wirtz, VA: Time
Mirror/Mosby College Publishing.
Finstein, M. S., F.C. Miller, and P.P. Strom. 1986. Waste
treatment composting as a controlled system. As cited in:
HJ. Rehm and G. Reed, eds.; W. Schonborn, vol. ed.
Biotechnology A comprehensive treatise in 8 volumes
Volume 8, microbial degradations. Weiheim, Germany
Verlagsangabe Ver. Chemie (VCH).
Golueke, C.G. 1977. Biological reclamation of solid
wastes. Emmaus, PA: Rodale Press.
Gray K.R., K. Sherman, and AJ. Biddlestone. 197la. A
review of composting Part 1- Process Biochemistry.
6(6):32-36.
Gray, K. R., K Sherman, and AJ. Biddlestone. 1971b. A
review of composting Part 2- The practical process. Proc-
ess Biochemistry. 6(10):22-28.
Haug, R.T. 1980. Compost engineering principles and
practice. Ann Arbor, MI: Ann Arbor Science publishers,
Inc.
Massachusetts Department of Environmental Protection
(MA DEP). 1991. Leaf and yard waste composting guid-
ance document. Boston, MA: MA DEP, Division of iolid
Waste Management.
May, J. H., and T.W. Simpson. Virginia Polytechnic Insti-
tute and State University. 1990. The Virginia yard waste
management manual. Richmond, VA: Virginia Depart-
ment of Wrote Management.
McGaughy, P.M., and H.G. Gotaas. Stabilization of mu-
nicipal refuse by composting. American Society of Civil
Engineers. Paper No. 2767. As cited in Haug, 1980.
Compost engineering principles and practice. Ann Arbor,
MI: Ann Arbor Science Publishers, Inc.
Poincelot, R.P. 1977. The biochemistry of composting. As
cited in: composting of Municipal Residues and Sludges:
Proceedings of the 1977 National Conference. Rockville,
MD: Information Transfer.
Richard, T.L. 1992a. Municipal solid waste composting
Physical and biological processing. Biomass & Bioenergy.
Tarrytown, NY: Pergamon Press. 3(3-4):163-180.
Richard, T.L. 1992b. Personal communication. College of
Agriculture and Life Sciences. Cornell University. Ithaca,
NY.
Rynk, R, et al. 1992. On-farm composting handbook.
Ithaca, NY: Cooperative Extension, Northeast Regional
Agricultural Engineering Service.
Strom, P.P. 1985. Effect of temperature on bacterial species
diversity in thermophilic solid waste composting. Applied
Environmental Microbiology 50(4): 899-905. As cited in
Richard, 1992a. Municipal solid waste composting Physi-
cal and biological processing. Biomass & Bioenergy. Tarry-
town, NY: Pergamon Press. 3(34):163-180.
Wiley, J.S. 1956. Proceedings of the llth industrial waste
conference. Purdue University, series 91, p. 334.
20
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Chapter Three
Collection Methods
The cost, ease, and effectiveness of implenenting a composting program is affected by the method chosen for
collecting the compost feedstock. Communities can select from a variety of collection systems to develop a
composting progam to meet their specific needs. Programs can be designed to collect just yard trimmings, or
yard trimming and MSW. Collection can occur at curbside, where the municipality picks up the materials di-
rectly from household or through drop-off sites, where residents and commercial producers deliver their com-
postable material to a designated site. Most communities will want to build on their existing refuse collection
infrastructure when implementing a composting program. This will ease the implementation of composting into a
community overall MS W management program and help contain costs. This chapter describes the advantages
and disadvantages of various collection methods and examines some of the factors that decision-makers should
consider when examining the applicability of different systems. Because collection is very different depending on
whether yard trimming, MSW or both am being collected this chapter is divided two babes. The first portion of
the chapter discusses yard trimmings collection; the second section focuses on source-separated and commingled MSW
Collections.
Factors in Yard Trimmings Collection
When developing a yard trimmings collection program,
officials must take into account the length of the growing
season, which affects both the amount of feedstock to be
collected as well as the duration of collection. In the more
temperate climates of the southern and southwestern re-
gions of the United States, collection can take place
throughout the year. In other areas of the United States,
collecting yard trimmings is largely a seasonal matter.
Grass can be collected from spring through fall (the aver-
age growing season is 24 to 30 weeks). Leaves usually can
be collected from mid-October through December and
once again in the spring. Brush typically is collected in
spring and fall. Depending on the season and the region,
the brush, grass, and leaves can be collected together or
separately. Ideally, brush should not be mixed with grass
cuttings and leaves during collection without first being
processed into smaller pieces because large branches tend
to decompose more slowly. Because large volumes of
leaves are generated within a relatively short time span,
many communities find it cost-effective to collect and
compost them separately from other yard trimmings.
Leaves can be composted with other materials, usually
grass, whose high nitrogen content can accelerate the
composting process and result in a higher quality finished
product (see Chapters 2 and 4). The high nitrogen con-
tent of grass can, however, cause odor problems during
the composting process if not balanced with sufficient car-
bonaceous material and managed properly (see Chapters 4
and 6 for more information).
There are two basic options for collecting yard trimmings:
public drop-off sites and curbside collection. When estab-
lishing a collection program, community leaders must
consider the program's convenience for the public, as well
as the level of interest displayed by citizens participating
in the program. A drop-off program in a small, densely-
populated community with residents well-educated about
the importance of composting might garner high partici-
pation rates. By contrast, in a community that is uninter-
ested or uneducated about composting, even a curbside
program-which is typically more convenient for com-
munity residents-might fail to bring in large amounts of
yard trimmings. Drop-off and curbside collection meth-
ods are described below.
Public Drop-Off Sites for Yard Trimmings
Public drop-off sites are specified locations where residents
and businesses can take their yard trimmings. Drop-off sites
can be an effective, low-cost option for some municipalities
since they allow communities to operate a composting pro-
gram while avoiding the labor and capital investment costs
associated with curbside collection operations.
21
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Collection Methods
Home Composting and "Don't Bag
It" Programs
Residents can be encouraged to let grass clippings
remain on the lawn. The clippings will decompose
and add nutrients to the soil. This eliminates the
need to bag and remove the cuttings. Although exact
recommendations depend on the variety of grass, it is
generally advisable to not cut more than one-third of
the blade, and not more than 1 inch total at any time.
Leaves also can be mulched with a lawn mower into
the lawn if cut finely enough.
Home composting of yard trimnings also serves to di-
vert material from being collected and recovered or dis-
posed of, Additionally, residents are provided with
compost for gardening and landscaping. Home com-
posting is particularly appropriate for residential lots of
one-half acre or larger. Many types of food scraps can
be composreci as well
To encourage individual to leave clippings on the
lawn, perform mulching, or compost at home, munici-
palities must educate residents about the "whys" and
"hews" of these procedures. Many towns and cities,
states, anti university extension service across the
country have published local guides and brochures on
how to mulch and compost. Also, incentives such as
providing simple compost bins at no cost ear encour-
age residential composting.
Drop-off stations can be located at established recycling
centers, landfills, and transfer stations or at the compost-
ing facility itself In addition, some localities employ a sys-
tem of collection trailers, which can travel to different
locations in the community for added convenience to area
residents, in all cases, yard trimmings should be collected
frequently from drop-off centers to prevent the formation
of odors and attraction of vectors (see Chapters 4 and 6).
Drop-off collections typically have low participation rates
primarily because residents must assume the responsibility
for collection (Richard et al, 1990). In communities
where citizens are accustomed to delivering their house-
hold waste to landfills or transfer stations, drop-off collec-
tions of yard trimmings are more likely to succeed.
Drop-off programs in communities with curbside collec-
tion of MSW however, could witness lower collection
rates at first due to residents' lack of familiarity with this
collection method. To encourage participation, communiti-
es should strive to make the collection as convenient as
possible, some programs, for example, allow participants to
pick up finished compost, firewood or d chips on the
same day they drop off compostable materials. In addition,
the public should be informed of the specifics of the
community's collection program, as well as the rationale
for and benefits of composting (see Chapter 10 for more
information on community involvement).
In addition to residents, other sectors of the community
can be encouraged to participate in yard trimmings drop-
off programs. For example, businesses that generate a sub-
stantial amount of yard trimmings (such as landscape
contractors) might be allowed to drop off the material. In
areas where tipping fees are charged for municipal solid
waste disposal, businesses might be offered a recked fee
as an incentive for bringing in yard trimmings for com-
posting. This would mean, however, that incoming ship-
ments would need to be measured. To eliminate the need
for measuring shipments on site, communities could cal-
culate the average amount of yard trimmings per truck-
load (based on tons or pounds per cubic yard) for each
business and draft permits for a limited number of drop-
offs based on these calculations. Figure 3-1 presents a
sample yard trimmings drop-off permit.
Curbside Collection of Yard Trimmings
In a curbside collection program, the municipality picks
up the yard trimmings that residents have placed outside
of their homes. Curbside collection of yard trimmings
typically offers the advantage of higher participation rates
than drop-off programs. Overall, curbside collection is
more expensive than drop-off colleetion due to the added
equipment and labor resources needed. Nevertheless, ad-
ditional costs are frequently justified by the volume of
yard trimmings that is diverted and recovered.
The frequency of pickup will depend on such factors as
the type and amount of yard trimmings being collected,
the size and makeup of the community, and the budget.
Schedules for curbside collection can range from weekly
collections for grass in the summer to a single annual col-
lection for brush.
Communities also must decide which collection method
to employ for curbside yard trimmings collection. The
material either can be collected in a container set out by
the household or collected loose with the aid of a front
loader or other equipment (see Appendix B). Several pro-
grams, such as those in Columbia, South Carolina, and
Sacramento, California, have been collecting loose yard
trimmings since the 1950s or earlier (Glenn, 1989). Col-
lection of containerized yard trimmings, on the other
hand, is relatively new. The advantages and disadvantages
of both collection strategies arc examined below.
Loose Yard Trimmings
Picking up loose yard trimmings at the curbside, a prac-
tice known as bulk collection, is most frequently used for
collecting leaves during fall when communities generate
large volumes of this material. Bulk collection avoids the
cost of providing bags or special containers to residents
22
-------
Collection Methods
Permit #
Last Name First
Mo. Day Yr.
( 1 1 \
Disposal
Quantity
Purchased
Cu. Yd.
Amount
Paid (S)
(Cu. Yd.
Quantity
used
Unused
Cu. Yd.
Name
Street
P.O. Box
city
( ) 1.individual residence
( ) Z.commericial
( ) 3, tree surgeon
( ) 4. school/college
Zip Phone
Classification of yard waste scarce fmarie (xl
( ) 5. commercial property
( ) 6. public Utility
( ) 7. local goverment ^
( ) 8. other goverment
( ) 9. other (specify)
Leaf Disposal Information for CommcerciaHaulers-
There will be a petmit fee of $ per each vehicle for dumping at this site. The permit
will be affixed on the inside of the windows of the driver's side, and be in plan view upon
entering the composting site.
Permits may be obtain at the compost site or city hall, Monday through Friday from
9:OOAM to ll:00)AMody. Payment shall be a certified check or money order made out
the Town of NO r ASH WILL BE AClkH 1 bD.
the hours of operation will be Monday through Friday from 7:OOAM to 5 PM beginning
There will be no dumping on Veteran's Day and Thanks-
giving Day. Dumping will terminate on or sooner, at the discretion
of the public works superintendent if the yard becomes full.
Haulers depositing yard waste will enter and exit from.
The DPW requests the cooperation of all permit holders and reminds everyone that no plastic
bags or any other foreign are to be included with the yard waste. Failure to follow
any of the above mentioned, or the instructions of the site attendant, may result in the forei-
ture of one's permit.
Permits are granted as an exclusive right of the DWP and are to be used only at the compost
site. Said permits are non-transferrable and may be revoked for just cause at any time.
Source: Richard et al., 1990.
Figure 3-1. Yard trimmings drop-off permit application farm from New York State.
23
-------
Collection Methods
(or requiring residents to purchase these items). In addi-
tion, bulk collection facilitates the unloading of material
at the facility since no debagging is necessary.
Bulk collections are a long labor-intensive process, how-
ever, and could require the community to purchase new
Collection Strategies in Two
Massachusetts Towns
Melrose, Massachusetts, opened a leaf composting Fa-
cility in October 1990 in response to a state landfill
ban on leaves and other yard trimmings. To cover
costs, the Boston suburb invited other regional com-
munities to send leaves to the facility for a moderate
tipping fee with one stipulation-that the leaves be de-
livered loose or in biodegradable paper bags.
several towns and cities its the area responded immedi-
ately, including Stoneham and Burlington. Stoneham
officials decided to collect leaves at the curbside
throughout the entire town on two Saturdays at the
beginning of November and December, respectively.
Six biodegradable paper bags would be provided at no
cost to each household, with extra bags available at the
Stoneham Department of Public Works are the cost of
three for $1. Stoneham also established a 40-cubic-
yard container at the Department of Public Works
where residents could drop off leaves from October 1
through December 15,1990. Because of Stoneham's
compact size-no household was located more than 5
minutes from the drop-off sitethe combination of
limited curbside collection and a drop-off container
worked to capture about 60 percent of the estimated
leaf stream available.
Burlington officials, on the other hand, decided against
a drop-off center in favor of more frequent curbside
collections, This was due primarily to the more dis
persed population of the town. (A central drop-off lo-
cation would make it inconvenient for some
households to drive the 20 minutes necessary to de-
posit their leaves.) Burlington officials contracted with
the town collector to pickup all available leaves for 6
weeks in the fall and 3 weeks in the spring each year.
The paper bags were distributed through the town's
public work department. Like their neighbors in
Stoneham, Burlington residents recovered about 60
percent of&e leaves that normally went to the landfill
in the first year of the program. Both Stoneham and
Burlington officials carefully examined the factors that
could influence the outcome of their collection pro-
grams. In each case, they tailored the programs to the
conditions in their respective towns to recover a major-
ity of the leaves.
equipment. AS a result, the community might be able to
afford only a reduced pickup schedule. Many different
types of equipment are used to pick up unbagged leaves
mechanically. Vacuum trucks are commonly used to col-
lect piles of leaves. These trucks often can mix leaves with
glass, sand, and other undesirable substances found on the
road, however, and are not effective when the leaves be-
come wet or frozen (See Appendix B for more informa-
tion). Front-end loaders can be used under these
conditions but are not effective with dry leaves. Special-
ized vehicles, such as tractors equipped with a claw or leaf-
loaders that quickly sweep material from the curb to the
transportation truck, are becoming available for bulk col-
lections of yard trimmings. (See Appendix B for descrip-
tions and costs for specialized equipment.)
Communities must consider several potential problems
inherent in bulk leaf collections. First, loose leaves are sus-
ceptible to being mixed with unwanted objects such as
glass, cans, and ear batteries (Richard et al, 1990). The
leaves also become difficult to collect after they have
blown around or children have played in them. In addi-
tion, loose leaves can catch fire from hot automobile ex-
haust systems.
Bulk collection of unbagged brush and grass clippings is
problematic. Piles of grass left on the sidewalk are very
difficult to collect, and in most communities this op-
tion is not cost-effective. Brush collections require spe-
cial handling. Because brush does not readily compact,
mobile wood chippers might be needed to reduce the
volume of brush, thereby facilitating collection and cut-
ting down on handling and transportation costs. Alter-
natively, brush can be collected in bundles and taken to
a central processing facility for chipping. While brush is
produced year round, it is impractical to have a year-
round collection program because of the relatively small
amount of material involved. Many communities have
organized monthly or annual brush collection days
(Mielkeetal.,1989).
Bagged or Containerized Yard Trimmings
Collecting bagged or containerized yard trimmings at the
curbside is typically a neater and more efficient operation
than collecting in bulk. Moving the materials to the trans-
portation vehicle is relatively quick and the bags or con-
tainers are not affected seriously by weather conditions.
Communities generally can use a standard compactor
truck for collection. Furthermore, existing programs have
found that bagged yard trimmings typically contain less
noncompostable material than unbagged yard trimmings.
Several types of containers can be used for collection.
Common containers include plastic and degradable plas-
tic bags, paper bags, and specialized marked trash contain-
ers. Table 3-1 lists the major advantages and disadvantages
of each type of bag and bin. Another alternative the
24
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Collection Methods
Table 3-1. A comparison of yard trimmings collection containers.
Type of Container Cost
Plastic Bags $0.12/bag
"Biodegradable" $0.20/bag
Plastic6 Bags g
Paper Bogs
$0.25-0.45/bag
Rigid plastic Bins $50-60/bin
Advantages
Inexpensive and readily available.
Reduce the amount of time collection vehicles
spend on routes because the yard trimming
workers; a so true for other types of bogs.
Materials in bags are less likely to contain
unwanted materials since they are not
exposed; also true far other types of bags,
Supposed to degrade by microbial action or
in me presence of sunlight, eventually
becoming port of the compost.
Can offer additional holding strength over
lightweight plastic bags.
If paper bags get torn or crushed early in the
composting process, such as in the
compactor truck, the composting process is
enhanced because paper bags are
degradable.
Bins are large enough to be practical yet
small enough to be handled by the collection
crews and residents without undue strain.
Bins range in size from small, basket-sized to
30- and 90-gallon well-marked containers.
Disadvantages
Can be torn open, scattering materials; also
true for for other types of bags, Require an
extra debagging step because plastic con
clog he tines on the turning eqipment and
bla
were out grinding blades in oilier machines.
plastic does not decompose and is
considered undesirable in the compost.
As grass clippings decompose in plastic
bags, they will Became anaerobic and
therefore malodorous. Workers and nearby
residents might find these odors
unacceptable when these bogs are opened
at the composting site.
Deqrodability is uncertain. Some studies
have shown that these bags Can take Several
years to fully degrade, so its of plastic still
will be visible when the compost is finished.
These contaminants can reduce the
marketability of finished compost.
Can be more expensive than plastic bags.
The initial costs of the bins might represent a
prohibitive expenditure for some
cummities, however. Fees are
frequently passed on to homeownersto pay
far the start-up cask.
Bins allow for neat storage of yard trimmings Might require extra collection time to empty
while awaiting collection. bins and collect materials.
The time that yard trimmings spend in
anaerobic conditions is often minimized
(depending on how long the material is in
the bin) since the yard trimmings are emptied
from the bin and transported unbaaged.
This, is turn reduces the potential for odor
problems.
Source Wagner, 1991.
community can choose is to require residents to separate
yard trimmings into color-coded or otherwise marked
bags that can be sorted easily at the processing facility.
Some communities provide bags at no cost to residents
and cover the cost as part of their solid waste manage-
ment budget. Others sell bags to the residents at full
price or at a discount. If bags are sold to residents, in-
centives to purchase the bags and participate in the pro-
gram must be provided to discourage individuals from
mixing their yard trimmings with refuse. In areas of the
country that charge for general refuse collection by the
barrel and maintain a bagged yard trimmings collection
program, residents might be tempted to conceal noncom-
postable materials in composting bags as a way to decrease
their own disposal costs. To minimize this problem, trans-
parent plastic bags can be used. This strategy is being
employed by a number of communities, including
Brookline, Massachusetts. These bags allow sanitation
workers to easily identify the contents of the bag, as
well as any undesirable objects that might be readily
visible. Town ordinances prohibiting the mixing of yard
trimmings with refuse also might be considered. Figure
3-2 provides an example of a town ordinance.
25
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Collection Methods
AN ORDINANCE.
AMENDING TITLE 7, CHAPTER 7.16 OF THE REVISED ORDINANCES OF THE
CITY OF SPRINGFIELD, 1986, AS AMENDED
Be it ordained by the City Council of the City of Springfield, as follows:
Title 7, Chapter 7.16 of the Revised. Ordinaces. of the City of
Springfield, 1986, as amended, is hereby further amended by inserting the
following new section 7.16.041 Mandatory Yard and Leaf Waste Composting.
7.16.041 ManndatoryLeaf and Yard Waste Composting
A. There is hereby established a program for the mandatory separation
of certain compostable leaf and yard waste material from garbage or rubbish
by the residents of the City of Springfield and the collection of these
compostable leaf and yard waste materials at the residents" curbside. The
collection of separated compostable leaf and yard waste material shall be
made periodically under the supervision of the Director of Public Works.
B. For the purposes of this ordinance the following definitions
apply:
1. Leaves- Deciduous and coniferous seasonal deposition.
2. Yard Waste- grass clippings, weeds, hedge clippings, garden
waste, and twigs and brush not longer than two (2) feet in length
and on-half (1/2) inch in diameter.
3. Paper Leaf Bag- A paper leaf bag "shall be a Sanitary Kraft
Paper Sack or equal of thirty (30) gallon capacity, two (2) ply
fifty (50) pound wet strength with decomposing glue and reinforced
self-supporting square bottom closure.
4. Leaf and Yard Waste collection season- the autumn leaf season
beginning the first full week of October and ending the second
full week of December.
C. Separation of Compostable Leaf and Yard Waste Material and
Placement for Removal.
During the Leaf and Yard Waste Collection Season Residents shall place
their leaf and yard waste material into paper leaf bags as defined in
Section 7.16.041.B. of barrels. These paper bags or barrels shall be place
on the curbside or treebelt in accordance with section 7.16.060 on the
special leaf and yard waste collection days specified by the Department of
Public Works and advertised in the Springfield daily newspapers.
Figure 3-2. Mandatory yard trimmings and leaf composting ordinance from the City of Springfield, NewYork.
26
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Collection Methods
No material other than that specified in Section 7.16.041.B shall be
placed in these paper bags or barrels.
Compostable leaf and yard waste material shall not be placed in
plastic trasn bags during the Leaf and Yard Waste Collection Season. Leaves
and yard waste shell not be placed in the same refuse Container as or
otherwise mixed with other fores of solid waste for collection, removal, or
disposal during Leaf and Yard Waste Collection Season. Any violation of
this Section C or any part thereof shall be punishable by a fine not to
exceed fifty dollars.
When the Owner has failed to comply with the requirements of Section C
of this Ordinance, the Director of trie Department of Public works in his
discretions, my refuse to collect the leaf and yard waste material and all
garbage, or paper, ashes, or rubbish of the owner until the next regular
pick- up, and the owner shall remove from the curb such garbage, leaf and
yard waste material, and all other paper, ashes, and rubbish.
1). Ownership of Compostable Leaf and Yard Waste Materials.
Upon placement of Compostable leaf and yard waste material for
collection by the City at the curbside or treebeit in accordance with the
special collection day, pursuant to this ordinance, such materials shall
become the property of the City. It shall be a violation of this ordinance
for any person; other than authorized agents of the City acting in the
course of their employment, to collect or pick up or cause to be collected
or picked up any Compostable leaf and yard waste material so placed. Each
and every such collection or pick up in violations hereof from one or more
locations shall constitute a separate and distinct offense. The Compostable
leaf and yard waste material collected by the City shall be transported to
and composted at a designated Leaf and Yard Waste Composting Site. Any
violation of this paragrapn D or any part thereof shell be punishable by a
fine not to exceed one hundred ($100.00) dollars.
E. All ordinance, resolutions, regulations or other documents
inconsistent with the provisions of this ordinance are hereby repealed to
the extent of such inconsistency.
F. This ordinance and the various parts, sentences, and clauses
thereof are hereby declared to be severable. If any part, sentence, or
clause is adjusted invalid, it is hereby provided that the remainder of this
ordinance shall not be affected thereby.
G. This ordinance shell take effect for the Leaf and Yard Waste
Collection Season commencing in 1988.
Approved: October 3, 1988
Effective: October 7, 1988
Attest: f. Vf0«/""-?ttjrZr7iA City Clerk
Source: Richard., 1990.
Figure 3-2. (Continued).
27
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Collection Methods
Whichever curbside collection system is used, if the con-
tainerized yard trimmings are collected on the same day as
discards, provisions must be made for keeping the com-
postable materials separate after pickup. Compartmental-
ized vehicles can be used to accommodate this need; they
are especially efficient if all factions of the collected mate-
rial will be processed at the same facility. Since the late
1980s, a number of compartmentalized trucks have come
on the market, some of which have compaction devices
for each compartment (see Appendix B). Using compart-
mentalized trucks can avert the expense of an extra pickup
crew. The amount of yard trimmings must be estimated
fairly accurately however, to prevent one compartment of
the truck from falling up before the other, forcing the crew
to deliver the materials before the entire vehicle is full.
(Although, on average, yard trimmings constitute 18 per-
cent of the nation's municipal discards, local factors such
as climate and demographics can affect the amount of
leaves or grass generated. Collection offficials often have
information pertaining to waste stream composition.) An-
other alternative that the community can choose is to re-
quire residents to separate yard trimmings into
color-coded or otherwise marked bags that can be sorted
easily at the processing facility.
Factors in MSW Collection
Communities that decide to collect MSW for composting
can opt to source separate or commingle this material.
Source-separated MSW involves varying degrees of mate-
rials segregation, which is performed where the MSW is
generated. Commingled MSW is not separated by the
generator. The decision to collect source-separated or
commingled MSW is a significant one and affects how
the material is handled at the composting facility, the pre-
processing and processing costs, and the quality and mar-
ketability of the finished compost. Table 3-2 summarizes
the major advantages and disadvantages of each collection
method.
Source-Separated MSW
Source separation of MSW entails the segregation of com-
postables, noncompostables, and recyclable by individu-
als at the point of generation. The community then
collects and transports the separated materials accordingly.
Source-separation strategies can remove:
Compostable materials, such as certain grades of pa-
per, that can be more economically recycled than
composted. In some areas, markets for certain
grades of paper are strong. Therefore, a community
could opt to sell collected paper for its resource
value rather than compost it.
Noncompostable recyclable such as aluminum,
glass, and plastic beverage containers.
Avoiding Undesirable Materials in
Feedstock Collections
Both yard trimmings and collected MSW can contain
materials that might affect processing and product
quality. These materials can include glass, metals, bev-
erage containers, plastics, household hazardous waste,
and other undesirable materials. Collecting crews
should be trained to recognize and separate these types
of materials whenever possible. Because of the variety
of materials collected, MSW feedstock is likely to con-
tain larger amounts of undesirable materials than yard
trimmings feedstock. Although yard trimmings can
contain pesticides and herbicides commonly used by
residents and businesses, the composting process will
break down many of these substances, limiting their
impact on the final product (see Chapter 6 for a more
detailed discussion).
Communities can take steps to reduce the amount of
undesirable materials in the feedstock. These include
passing ordinances, posting warning notices, and issu-
ing fines for mixing noncompostables with compost-
ables. In addition, bagged yard trimmings and MSW
bins can be opened at the curb to detect undesirable
materials. Facility employees can look for and separate
out unwanted materials (see Chapter 4),
Materials that are difficult to compost such as
brush.
Household hazardous waste such as paints, batter-
ies, pesticides, and used oil.
Noncompostable nonrecyclables such as light bulbs
and toothpaste tubes.
The primary benefit of source separation is that the feed-
stock tends to contain fewer unwanted materials, particu-
larly heavy metals (Glaub et al, 1989). In addition, source
separation can help remove those items from the waste
stream that are difficult to separate at the facility, such as
plastic, which is often shredded; and glass, which can
shatter into small, hard-to-remove pieces. This produces a
higher quality compost, Most MSW composting facilities
in communities with source-separation programs peform
an additional sorting of incoming materials to produce a
still cleaner compost feedstock. Communities with MSW
composting facilities can combine source separation of
compostable materials with source separation of other re-
cyclable materials such as glass, aluminum, and plastic.
A study conducted in 1990 revealed that a majority of
MSW composting facilities prefer processing source-sepa-
rated over commingled MSW (Goldstein and Spencer,
1990). The study indicated that recycled materials are
cleaner and more marketable if source separated since they
28
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Collection Methods
Table 3-2. Source separation vs. commingling of MSW.
Advantages
Source Separation of MSW
Less chance of collecting unwanted object, which can result in a
higher quality compost product.
Less money and time spent an handling and separation at facility
Provides an educational benefit to residents and might encourage
source reduction.
Collection of Commingled MSW
Usually done with existing equipment and labor resources.
Convenient to residents since no separation is required.
Disadvantages
Can be less convenient to residents.
Might require the purchase of new equipment and/or conjoiners.
Might require additional labor for collection.
Higher potential for collecting unwanted objects, which can result in
a lower quality compost product.
Higher processing and facility costs.
are not mixed with undesirable materials. Moreover, the
amount of noncompostable material received at the com-
posting facility is reduced. This means freer noncom-
postables must be separated out on site and sent to
landfills or recycling centers, resulting in lower transporta-
tion and labor expenditures. Finally, the quality and ap-
pearance of the compost can be improved and therefore
command a higher price. (Chapter 4 discusses the role of
source separation on preprocessing at the composting fi-
cility in more detail; Chapter 9 discusses the role that
source separation can play in reducing heavy metals and
other contaminants in the final compost product.)
Source separation of MSW for composting can be done in
bins or bags. Some programs require that compostables,
noncompostables, and recyelables be placed in different
bins for curbside collection. While a large number of col-
lection containers can be unsightly to some citizens, the
containers themselves are usually small since each one
holds small volumes of materials. Some municipalie.s
even use small baskets (similar to milk crates) to collect
glass, paper, and metals.
While source separation can avert many of the expenses
associated with preprocessing compostables, other costs
must be considered. The community very likely will have
to devote more labor to the collection process. In addi-
tion, containers or bins must be purchased either by the
municipality or citizens. The degree of participation is a
variable also, so a thorough public education and aware-
ness campaign is necessary to encourage residents and
businesses to separate out noncompostables (see Chapter
10).
Commingled MSW
Commingled MSW collection is the method that munici-
palities traditionally have used to pick up materials from
residents and businesses. Commingling allows residents to
combine trash, compostables, and recyelables in the same
containers. The municipality then collects and transports
the materials to the composting facility. Commingled
MSW collections usually can be done with existing equip-
ment. Collection time and cost per ton often are less than
Wet/Dry Separation Strategies for
Composting
Some communities in Canada and Europe are using or
experimenting with the separation of materials into
wet and dry components. The City of Gueiph in On-
tario, Canada, reported a diversion rate of more than
60 percent using this collection strategy (Hoornweg et
al., 1991).
The wet stream includes all organic kitchen scraps,
yard trimmings, nonrecyclable paper, and some non-
compostable elements. The dry stream comprises all
dry noncompostables and recyelables. The dry waste
stream is sent to a landfill or materials recovery facility
(MRF) where recyelables are removed for recovery, ^tftt
materials are sent to a compost facility.
Since 1989, Gueiph has been conducting a pilot pro-
gram to test four different materials separation tech-
niques in over 500 households. The city has found that
the highest diversion rates were achieved by citizens di-
viding the MSW stream into wet and dry components
and placing diese components in green and blue plastic
bins, respectively. The city currently is investigating
odier aspects of the program, including separation in
multi-family dwellings and commercial and educa-
tional institutions.
As of August 1993, plans were underway to open a
139,000 ton per year facility, including a 44,000 ton
per year "wet" composting plant and an 85,000 ton
per year "dry" MRF (Darcey et al., 1993).
29
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Collection Methods
those for separated materials since sanitation collectors
can fit more into single unit packer trucks at a faster rate.
Commingled commercial materials are deposited in large
metal or plastic bins equipped with hinged lids. These
bins are designed for easy transport to the processing facil-
ity. Some bins are equipped with a compactor, making it
possible to increase the capacity of each container.
Compaction can make separation more dificult, however,
and can greatly complicate the procedures and equipment
that will be used to compost.
The primary disadvantage of a commingled MSW collec-
tion program is that the separation must be performed as
soon as possible once the material arrives at the facility. At
the facility, the organic materials are typically separated by
both manual and mechanical means (see Chapter 4) in or-
der to remove them from the recyclable and other non-
compostable materials-a process that requires significant
labor and specialized equipment. Additionally commin-
gling does not require individuals to change their behavior
thereby becoming more aware of the resource value of ma-
terials they discard,
Summary
Wi
'hether designing a yard trimmings or MSW
composting program, collection is a key fac-
tor in ensuring the program's success. Not
only does collection have a direct bearing on the will-
ingness of household to participate in and endorse a
program but the collection strategy chosen also influ-
ences the way that the feedstock is handled and proc-
essed at the facility as well as the quality and
marketability of the final product. Additionally col-
lection can be one of the most expensive aspects of a
composting program and influences labor equip-
ment, processing, and other resource needs. For these
reasons, decision-maken should carefully examine
and weigh all possible collection methods to deter-
mine the best approach for their community.
Chapter Three Resources
Appelhof, M., and J. McNelly. 1988. Yard waste compost-
ing guide. Lansing, MI: Michigan Department of Natural
Resources.
Ballister-Howells, P. 1992. Getting it out of the bag. Bio-
Cycle. March, 33(3):50-54.
Cal Recovery Systems (CRS) and M. M. Dillon Limited.
1989. composting A literature study. Ontario, Canada:
Queen's Printer for Ontario.
Darcey, S. 1993. Communities put wet-dry separation to
the test. World Wastes. 36(98):52-57.
Glaub, J., L. Diaz, and G. Savage. 1989. Preparing MSW
for composting. As cited in: The BioCycle Guide to Com-
posting Municipal Wastes. Emmaus, PA: The JG Press, Inc.
Glenn, J. 1992. Integrated collection of recyclable and
trash. BioCycle. January, 33(l):30-33.
Glenn, J. 1989. Taking a bite out of yard waste. BioCycle.
September, 30(9):31-35.
Goldstein, N., and B. Spencer. 1990. Solid waste com-
posting facilities. BioCycle. January, 31(l):36-39.
Hoornweg, D., L. Otten, and W. Wong. 1991. Wet and
dry household waste collection. BioCycle. June, 32(6):
52-54.
Mielke, G., A. Bonini, D. Havenar, and M. McCann.
1989. Management strategies for landscape waste. Spring-
field, IL: Illinois Department of Energy and Natural Re-
Richard, T., N. Dickson, and S. Rowland. 1990. Yard waste
management A planting guide for New York State. Albany,
NY: New York State Energy Research and Development
Authority, Cornell Cooperative Extension, and New York
State Department of Environmental conservation.
U.S. Environmental Protection Agency (EPA). 1989. De-
cision-Maker's Guide to Solid Waste Management.
EPA1530-SW-89-072. Washingron, DC: Office of Solid
Waste and Emergency Response.
Wagner, T.C. 1991. In search of the perfect curbside sys-
tem. BioCycle. August,
Wirth, R. 1989. Introduction to composting. St. Paul,
MN: Minnesota Pollution Control Agency, Ground
Water and Solid Waste Division.
30
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Chapter Four
Processing Methods,
Technologies, and
Odor Control
Ms chapter describes the three stages of composting (preprocessing, processing and postprocessing) for both yard
trimming and MSWcomposting. It examines the operations that must be performed at each step in the process
and describes ways for optimizing those conditions that influence the process. In addition, this chapter discusses
the differnt technologies currently used to compost yard trimmings and MSW feedstocks in the United States. These
can range simple, low-technology systems that require minimal attention and maintenance to complex systems
that use sophisticated machinery and require daily monitoring and adjustment. The design and complexity ofa com-
posting operation are determined by the volume, composition, and size distribution of the feedstock; the availability of
equipment the capital and operating funds; and the end-use specification for the finished product. This chapter also
examines the potential problems associated with odor and describes the measures a composting facility can take to pre-
vent or minimize odor. A system now chart for a typical operation that compost yard trimmings is shown in Figure 4-
1. Figure 4-2 outlines a process diagram for a typical MSW composting facility. For more information on costs
and effectiveness of the equipment described in this chapter, see Appendix B. Two case studies illustrating the process of
composting yard trimmings and MSW are included the back of this chapter.
Preprocessing
During preprocessing feedstock is prepared for composting.
Preprocessing has a significant impact on the quality of the
finished compost product and the speed at which processing
can be conducted. In general, the more effective the preproc-
essing the higher the quality of the compost and the greater
the efficiency of processing. Three procedures are typically
peformed during preprocessing 1) sorting feedstock mate-
rial and removing materils that are difficult or impossible to
compost; 2) reducing the particle size of the feedstock mater-
ial; and 3) treating feedstock to optimize composting condi-
tions. These composting procedures are described below for
both yard trimming and MSW
Sorting
The level of effort required to sort and remove unwanted
materials from the composting feedstock depends on sev-
eral factors, including the source of the feedstock, the end
use of the product, and the operations and technology
involved. The more diverse the feedstock material, the
more sorting and removal will be required. For this rea-
son, yard trimmings (which tend to be relatively uniform)
generally require little sorting while MSW (which com-
prises heterogeneous materials] can require extensive sort-
ing and separation. The end-use specifications for the
finished compost product also affect the level of effort in-
volved as some end uses require a higher quality product
than others. For example, compost that will be used as
landfill cover can have higher levels of unwanted materials
than compost that will be used on food crops. Compost-
ing operations designed to produce landfill cover can
therefore utilize simpler and less thorough sorting and re-
moval methods.
Sorting Techniques for Yard Trimmings Feedstock
Upon delivery to a composting site, yard trimmings
should be visually inspected to detect any materials that
could affect the composting process. Visual inspection can
be readily accomplished by spreading out the material on
31
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Processing Methods, Technologies, and odor Control
Figure 4-1, Typical yard trimmings composting operation.
c
MSW
C
End Market*
Preprocessing
Sorting
(Degree of sorting
will depend on
whether and how
thoroughly the
materials have
been source
separated)
Screening
tConveyor/Hand
Separation
SeparationTechniques
. Magnetic Recovery
. Eddy Current
separation Systems
Air Classification
.Wet separation
Technologies
Ballistic or Inertial
separation
^-
Size Reduction
Hammermills
Shear Shredders
. Rotating Drums
To Recycling
Facility
Postprocessing
Post-Processing
Shredding
Screening
. Bagging
Curing
Composting
Control Temperature
Control Oxygen
Control Moisture
Figure 4-2. Typical MSW composting operation.
32
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Processing Methods, Technologies, and odor Control
the tipping floor where the feedstock is unloaded. Work-
ers can then physically remove any undesirable objects
present. Materials that should be removed are those that
would interfere with mechanical composting operations,
inhibit the decomposition process, cause safety problems
for those working with or using the compost, or detract
from the overall aesthetic value of the finished compost
product. Plastic bags are the chief problem at most yard
trimmings composting facilities.
Feedstock with a significant amount of unwanted objects
can be hand-sorted more efficiently with a mechanical
conveyor belt. With this approach, the feedstock material
is loaded into a hopper that discharges at a slow speed
onto a conveyor belt. Workers on either side of the mov-
ing belt manually pick out glass, plastic, and other visible
noncompostables. To facilitate sorting, the belt width
should allow the workers to reach the center of the belt,
and the trimmings should not be more than 6 inches
deep. Materials removed from the conveyor belt are de-
posited into storage containers that can be moved easily to
other storage/processing areas. These noncompostable
materials are considered residuals from the composting
process and generally are recycled or disposed of by land-
filling.
For reasons of health and safety, it is important that work-
ers avoid physical contact with undesirable materials dur-
ing manual sorting and removal. The sorting area should
be well-lit and properly ventilated, and the conveyor belt
should be setup to minimize motion injuries such as back
strain. Those handling the materials should wear heavy
gloves and follow specified hygiene practices (see Chapter
6 for more information on worker health and safety).
Sorting Techniques for MSW Feedstock
In general, sorting of MSW prior to composting requires
more labor and machinery than sorting yard trimmings
because of the diversity of MSW. As mentioned earlier,
MSW is extremely heterogeneous in size, moisture, and
nutrient content, and the organic fractions can contain
varying degrees of noncompostable and possibly hazard-
ous waste. Both physical and chemical materials found in
the feedstock can have a negative impact on the market-
ability of the finished product, and their removal forms a
large part of the expense of modern MSW composting fa-
cilities (Richard, 1992). Both manual and mechanical
techniques can be used to sort feedstock materials and re-
move unwanted items.
Many items in the MSW composting feedstock are recy-
clable, such as aluminum cans, ferrous materials, and plas-
tic bottles. Because of the potential value of these
recyclable, the separation, removal, and collection of
these items should be pursued. Although the MSW feed-
stock can be sorted after being subjected to size-reduction
processes, it is advisable to remove recyclable before size
reduction (this also will improve the value of recyclable).
Sorting before size reduction also will prevent recyclable
from being pulverized and mixed into the feedstock,
which can cause a variety of problems. For example, plas-
tics are difficult to remove after they are shredded and
mixed with compostable materials. Shattered glass gener-
ates shards that can remain in the compost and devalue
the finished product as well as present a safety hazard both
to workers sorting the compost and to compost users.
Materials targeted during manual separation include recy-
clable and inert materials. As in the case of yard trim-
mings, manual separation along a conveyor belt represents
the most effective method to remove noncompostable
materials and chemicals from feedstock. Health and safety
provisions for manually sorting are particularly important
in the case of MSW feedstock, which might contain po-
tentially dangerous items such as syringe needles, patho-
genic organisms, broken glass, or other materials that
could cause injury or infection (see Chapter 6).
Mechanical sorting and removal techniques are based on
the magnetic and physical (i.e., weight and size) properties
of the feedstock materials. Magnetic-based systems separate
ferrous metals from the rest of the feedstock eddy-current
machines separate out nonferrous metals; size-based systems
such as screens separate different sizes of materials; and
weight-based systems separate out heavier noncompostable
materials such as metals, glass, and ceramics.
Table 4-1 outlines mechanical separation technologies
that are currently used in MSW composting. These tech-
nologies are discussed briefly below and in more detail in
Appendix B.
Screens - Screens are used in most MSW compost-
ing facilities to control the maximum size of feed-
stock and to separate materials into size categories.
The main purpose of this size fractionation is to Fa-
cilitate further separation. Screens separate small
dense materials such as food scraps, glass, and
small, hard plastic pieces from the bulky, light frac-
tion of the feedstock. The type of screen used de-
pends on the moisture content, cohesiveness,
heterogeneity, particle shape, and density of the
feedstock to be segregated. Trommel screens are
commonly used for initial materials processing at
MSW facilities. Figure 4-3 illustrates a trommel
screen.
Magnetic-based separators - Magnetic separators cre-
ate magnetic fields that attract ferrous metals and
remove them from the rest of the feedstock stream
as it travels along conveyors. Magnetic separators
are among the most effective and inexpensive unit
processes available for sorting and removing con-
taminants from the feedstock. The economic bene-
fits of these devices are enhanced by selling the
33
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Processing Methods, Technologies, and Odor Control
Table 4-1. Processing MSW feedstock separation
techniques.
Technology
Screening
Magnetic
Separation
Eddy-Current
Separation
Air Classification
Wet Separation
Ballistic Separation
Materials Targeted
Large: Film plastics, large paper,
cardboard.
Mid-sized: Recyclables, most organics.
Fine: Organics, metal fragments.
Ferrous metal.
Nonferrous metals.
Light: Paper, plastic.
Heavy: Metals, glass, organics.
Floats: Organics.
Sinks: Metals, glass, gravel.
Light: Plastic undecomposed paper.
Heavy: Metals, glass, gravel.
Source: Richard, 1992.
scrap metals these units separate from the com-
postable materials. The efficiency of magnetic sepa-
rators depends primarily on the quantity of
materials processed and the speed at which they
pass through d-se magnetic field. The size and shape
of the ferrous objects, as well as the distance be-
tween the magnet and the objects, also are impor-
tant variables. To increase the efficiency of the
separation process, more than one magnetic separa-
tion technology can be used in series with another.
Applying air classification (described below) prior
to magnetic separation minimizes the contamin-
ants in the scrap ferrous even further.
Eddy-current machines - Eddy-current machines
separate aluminum and other nonferrous metals
from MSW. These machines generate a high-en-
ergy electromagnetic field that induces an electrical
charge in nonferrous metals (and other materials
that conduct electricity). The electrical charge
forces these materials to be repelled from non-
charged fractions of the feedstock material. The
feedstock should be conveyed to eddy-current ma-
chines after magnetic separation to minimize con-
tamination by ferrous metals. Recovery rates for
eddy-current separators vary with the depth of the
material on the conveyor belt, belt speed, the de-
gree of preprocessing and the strength of the mag-
netic field. Full-wale trials and manufacturer
estimates of separation efficiency in MSW applica-
tions range from 50 to 90 percent. Figure 4-4 illus-
trates an eddy current separator.
Air classifiers - Air classifiers separate feedstock ma-
terials based on weight differences; for example, the
heavier fractoions (metals, glass, ceramics, and
rocks) are removed from the lighter materials. The
heart of an air classification system is an air column
or throat into which the materials stream is fed at a
metered rate. A large blower sucks air up through
the throat, carrying light materials such as paper
and plastic. These then enter a cyclone separator
where they lose velocity and drop out of the air
stream. Heavy materials fall directly out of the
throat. An important consideration when using air
classifiers is that although most of the heavier mate-
rials separated out are noncompostable, some mate-
rials that fall out (e.g., certain food materials and
wet paper) can be composted (Glaub et al, 1989).
Air classifiers typically are used after the feedstock
has been size-reduced. Separation efficiency in ex-
perimental application of air classification systems
has reached 90 percent for plastics and 100 percent
for paper materials. In combination with screening
and size reduction, air classification can be used to
significantly reduce metal contaminant levels. Fig-
ure 4-5 illustrates an air classification system.
Wet separation technologies - Wet separation tech-
nologies are similar to air classification systems in
that they separate materials based upon density, but
water replaces air as the floating medium in these
technologies. After entrainment in a circulating
water stream, the heavy fraction drops into a sloped
tank where it moves to a removal zone. The lighter
organic matter floats and is removed from the recir-
culating water using stationary or rotating screen-
ing systems similar to those employed by
wastewater treatment facilities. This technology is
particularly effective for removing glass fragments
and other sharp objects.
Ballistic or inertial separation - This technology sepa-
rates inert and organic constituents based upon
density and elasticity differences. Compost feed-
stock is dropped on a rotating drum or spinning
cone and the resulting trajectories of glass, metal,
and stones, which depend on density and elasticity,
bounce the materials away from the compost feed-
stock at different lengths. Figure 4-6 illustrates a
ballistic separator.
34
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'recessing Methods, Technologies, and Odor Control
f
m
Fine
*^/rz?w3%$W*x^'wn
>v% ?# rft\ pirn**,!? M M ^*
^!.y-w^*^M^»fe»ft
^l^^l^lpP^P^
Medium
Undersize
Source: Richard, 1992.
Oversize
Figure 4-3. Trommel screen.
o o
O
O
O
External Drum
(rotates at Slow speed)
Alternating Polarity Rotor
(rotates at high speed)
Non-Conductors Conductors
(wood, paper (aluminum, brass,
plastic, glass) copper, etc.)
Source: Richard, 1992.
Figure 4-4. Eddy-current separator.
35
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Processing Methods, Technologies, and Odor Control
MSW Infeed
Light
i
tttt
Airstream
Rotary Airlock
Heavj
Source: Richard, 1992.
iBIoweir
Exhaust Air
Cyclone Separator
Fraction
Light Fraction
Figure 4-5. Air classification system.
Source: Richard, 1992,
Light Organic Dense Organic
inorganic
Figure 4-6. Ballistic separator.
36
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Processing Methods, Technologies, and Odor Control
Reducing the Particle Size of the Feedstock
Size reduction usually is performed after noncompostables
have been separated from the compostable feedstock.
Some separation technologies, including magnetic separa-
tion, air classification, and wet separation, achieve greater
levels of removal only after size reduction, however. The
exact order of steps varies in different composting opera-
tions depending on the type and volume of feedstock to
be composted. Proper sequencing of the-se preparation
processes can have a significant impact on system
performance.
The primary reason for performing size reduction is to in-
crease the surface area to volume ratio of the feedstock
materials. This enhances decomposition by increasing the
area in which microorganisms can act upon the compost-
ing materials. If composting materials are too small, how-
ever, air flow through the compost pile will be reduced.
This reduced oygen availability has a negative impact on
decomposition. Maximizing composting efficiency re-
quires establishing a balance between reducing particle
size and maintaining aerobic conditions. A study of the
tradeoff between increased surface area for decomposition
and reduced pore size for aeration concluded that particle
sizes of 1.3 to 7.6 cm (0.5 to 3.0 inches) are most efficient
(Gray and Biddlestone, 1974). The lower range is suitable
for forced aeration systems while the larger range is pre-
ferred for windrows and other systems supplied with oxy-
gen by passive diffusion and natural convection.
Yard Trimmings
Size reduction of most types of yard trimmings can help
accelerate the composting process. Size reduction is war-
ranted for woody material mixed with other yard trim-
mings since wood decomposes at a very slow rate and
might delay the development of the compost end prod-
uct. Some facilities have found that shredding leaves as
well will reduce the time required to produce finished
compost from 18 months to 9 months (Richard et al,
1990). Excessive size reduction of leaves and grass could
prove undesirable, however, because small particles can in-
hibit aerobic conditions and impede release of heat from
the composting masses. If grass clippings become com-
pacted, they can restrict oxygen flow and create anaerobic
pockets in the composting mass. Finely shredded yard
trimmings must be turned more frequently to prevent
these anaerobic conditions. Tub grinders are a common
piece of size reduction machinery at large Facilities for com-
posting yard trimmings. These grinders use a rotating tub to
feed a horizontal hammermill (see following section).
MSW
Size reduction homogenizes MSW feedstock materials,
achieving greater uniformity of moisture and nutrients to
encourage even decomposition. A variety of size-reduction
devices are available, the most common of which are
hammermills, shear shredders, and rotating drums. This
equipment is outlined below and described in more detail
in Appendix B.
Hammermills - Hammermills reduce the size of
feedstock materials by the action of counter rotat-
ing sets of swinging hammers that pound the feed-
stock into smaller sized particles. The hammer axles
can be mounted on either a horizontal or a vertical
axis and usually require material to pass through a
grate before exiting. Mills that lack the exit grate
are termed flail mills. Figure 47 illustrates a
hammermill.
Shear shredders - Shear shredders usually consist of
a pair of counter rotating knives or hooks that ro-
tate at a slow speed with high torque. The shearing
action tears or cuts most materials, which helps
open up the internal structure of the particles and
enhances opportunities for decomposition.
Rotating drums - Rotating drums use gravity to
tumble materials in a rotating cylinder. Material is
lifted by shelf-like strips of metal along the sides of
the drum, which can be set on an incline from the
horizontal. Some of the variables in drum design in-
clude residence time (based on length, diameter,
and material depth), inclination of the axis of rota-
tion, and the shape and number of internal vanes
(which lift materials off of the bottom so they can
fall through the air). Figure 4-8 illustrates a rotat-
ing drum.
If materials such as gas cylinders and ignitable liquids are
present in MSW feedstock, there is a potential for explo-
sions during size reduction. Visual inspection, along with
sorting and removal procedures, can minimize this poten-
tial. Nevertheless, size reduction equipment should be iso-
lated in an explosion-proof area within the composting
facility, and proper ventilation for pressure relief should be
provided.
Treating Feedstock Materials to Optimize
Composting Conditions
To enhance composting, both yard trimmings and MSW
feedstock can be treated before processing. Such treatment
can optimize moisture content, carbon-to-nitrogen (C:N)
ratio, and acidity/alkalinity (pH). (These parameters were
introduced in Chapter 2.)
Moisture Content
Maintaining a moisture content within a 40 to 60 percent
range can significantly enhance the composting process.
Before composting begins, the feedstock should be tested
for moisture content. The "squeeze test" is a simple
37
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Processing Methods, Technologies, and Odor Control
method of determining whether the moisture content falls
within the proper range. If just a few drops of water are
released from a handful of the feedstock when squeezed,
the moisture content is acceptable. If a more definitive de-
termination of moisture content is needed, a sample of
the feedstock can be weighed, oven-dried at about 104°C
-Free Swin ing
Hammer
Grate
Source: Richard, 1992.
Rotating Hammermill
Figure 4-7. Hammer-mill.
(219°F) for 8 hours, and weighed again. The moisture
content can be derived by the following formula:
moisture content = (wet weight - dry weigh)wet weight
With yard trimmings, the moisture content of leaves
tends to be lower than optimal. The moisture content of
grass tends to be higher than optimal. Moisture, therefore,
should be added to dry leaves, generally at a level of about
20 gallons of water per cubic yard of leaves (Richard et al,
1990). During the early stages of composting leaves must
be mixed during wetting to prevent the water from run-
ning off the pile surface. On the other hand, grass should
be mixed with drier materials (such as leaves or wood
chips) or turned more frequently during the initial stages
of processing to facilitate the evaporation of excess water.
Moisture content in the MSW feedstock varies widely.
Significant attention, therefore, should be paid to assess-
ing moisture levels of MSW and mixing materials streams
to optimize moisture content of the composting feed-
stock. For high-rate MSW composting, a minimum mois-
ture content of 50 to 55 percent is recommended
(Goluek, 1977). Since MSW feedstock is often drier
than this, water must be added during the composting
and curing singes to bring the moisture content into the
optimal range. MSW compost mixtures usually start at
about 55 percent moisture and dry to 35 percent moisture
(or less) prior to find screening and marketing (CC, 1991).
Mechanical aeration and agitation directly influence the
moisture content of the composting pile. Aeration in-
creases flow through the composting pile, inducing
evaporation from the interior spaces. Turning compost-
ing piles exposes the interior of the piles, releasing
heated water as steam. This moisture loss can be benefi-
cial, but if excess moisture is lost (i.e., the moisture
content falls to 20 percent), rewetting might be re-
quired (Richard, 1992). MSW composting piles usually
require additional water.
Infeed
I Source: Richard, 1992.
Outfeed
Figure 4-8. Rotating drum.
38
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Processing Methods, Technologies, and Odor Control
Finally temperature determines how much moisture will be
lost with turning and aeration; the higher the temperature,
the more water will be lost via evaporation. In turn, moisture
loss afects the temperature of the piles.
Carbon-to-Nitrogen (C:N) Ratio
Most of the nutrients needed to sustain microbial decom-
position are readily available in yard trimmings and MSW
feedstocks. However, carbon and nitrogen might not be
present in proportions that allow them to be used effi-
ciently by microorganisms, composting proceeds most ef-
ficiently when the C:N ratio of the composting material is
from 25:1 to 35:1. When the C:N ratio is greater than
35:1, the composting process slows down. When the ratio
is less than 25:1, there can be odor problems due to an-
aerobic conditions, release of ammonia, and accelerated
decomposition.
Generally, the C:N ratio for yard trimmings can be
approximated by examining the nature of the feedstock;
green vegetation is high in nitrogen and brown vegetation
is high in carbon. While the diversity of MSW feedstock
material makes an estimation of the C:N ratio somewhat
difficult, a precise C:N ratio can be determined by labora-
tory analysis. Feedstock materials with different C:N ratios
can be mixed to obtain optimal levels of carbon and nitro-
gen when necessary (see Table 42 for carbon-to-nitrogen
ratios for various organic materials).
Acidity/Alkalinity (pH)
The closer the pH of the feedstock material is to the neu-
tral value of 7, the more efficient the composting process
will be. Fresh leaves tend to have pH levels of approxi-
mately 7 (Strom and Finstein, 1989). Fruit scraps gener-
ally are acidic with a pH below 7 (CRS, 1989). Kits to
test pH levels are readily available and easy to use. If pH
levels are significantly higher than 8 (an unusual situ-
ation), acidic materials, such as lemon juice, can be added
to the feedstock. If the feedstock has a pH significantly
below 6, buffering agents, such as lime, can be added. Be-
cause pH levels are largely self-regulating, actions to bring
pH to optimum levels are rarely necessary (CRS, 1989;
Strom and Finstein, 1989).
Mixing
Mixing is often required to achieve optimal composting
conditions. Mixing entails either blending certain ingredi-
ents with feedstock materials or combining different types
of feedstock materials together. For example, bulking
agents (such as wood chips) are often added to feedstock
materials that have a fine particle size (such as grass).
Bulking agents have the structural integrity to maintain
adequate porosity and help to maintain aerobic condi-
tions in the compost pile. Bulking agents are dry materials
and tend to have a high carbon content. Therefore,
Table 4-2. Carbon-to-nitrogen ratio of various materials.
Type of Feedstock Ratio
Bark
Corn Stalks
Foliage
Leaves and Weeds (dry)
MixedMSW . ...
Paper
Sawdust
Straw (dry)
Wood
Cow Manure
Food Scraps
Fruit Scraps
Grass Clippings
Hay (dry)
Horse Manure
Humus
Leaves (fresh)
Mixed Grasses
Nonlegume Vegetable Scraps
Poultry Manure
Biosolids
Weeds (fresh)
Seaweed
High tarbom Contonf
100-130:1
60:1
40-80:1
90:1
50-oO:l
170:1
500:1
100:1
700:1
High Mi'frofm Confrnf
18:1
15:1
35:1
12-20:1
40:T
25:1
10:1
30-40:1
19:1
11-12:1
15:1
11:1
25:1
19:1
Source: Golueke, 1977; Richard et al., 1990; Gray et al., 1971b.
whenever bulking agents are used, are should be taken to
ensure that C:N ratios do not become too high.
Mixing is most efficient when it is conducted after feed-
stock sorting and size reduction and before processing be-
gins. This can minimize the quantity of materials that
must be mixed because noncompostables have been re-
moved. In addition, once piles have been formed for proc-
essing adequate mixing becomes extremely difficult.
For simple composting operations that do not require
high levels of precision, mixing can be performed during
size reduction or pile formation by feeding different
ingredients or types of materials into these operations.
When higher levels of precision are required, mixing
equipment (such as barrel, pugmill, drum, and auger
39
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Processing Methods, Technologies, and Odor Control
mixers) Mbe used (see Appendix B). Most mixers also
compress materials, which can reduce pore space in the
feedstock and inhibit aeration in the compost pile. Mixers
also have relatively high capital and operating and mainte-
nance costs so it might be impractical for smaller facilities
to use them, particularly those that compost only yard
trimmings.
Processing
After yard trimmings and MSW feedstock materials are
preprocessed, they can be introduced into the compost
processing operations. During processing, various m&h-
ods can be employed to decompose the feedstock materi-
als and transform-them into a finished compost product.
Processing methods should be chosen to maximize the
speed of the composting process and to minimize any
negative effects, such as odor release and leachate runoff.
The level of effort required for processing composting
feedstock depends on the nature of the feedstock, the de-
sired speed of production, the requirements for odor and
leachate control, and the quality requirements for the fin-
ished compost. A facility's financial resources and available
space also are important. In general, the greater the speed
of the process, the more odor and leachate control neces-
sary. Where greater space or level of effort is needed, more
financial resources will be required.
In general, more resources and higher levels of effort are
necessary to compost a MSW feedstock than a yard
trimmings feedstock, largely because of the diverse na-
ture of MSW. For composting either yard trimmings or
MSW, processing occurs in two major phases: the com-
posting phase and the curing phase. These stages are dis-
cussed below.
The Composting Stage
Microorganisms decompose the readily available nutrients
present in the feedstock during composting. Because most
of the actual change in the feedstock occurs during this
stage, the most intensive methods and operations tend to
be used here. Compost processing can occur in simple en-
vironments that are completely subject to external forces
or in complex and highly controlled environments. The
composting methods currently employed are (in order of
increasing complexity):
Passive piles
Turned windrows
Aerated static piles
In-vessel systems
Passive Piles
Although this method is simple and generally effective, it
is not applicable under all conditions or to all types of
materials, composting under these conditions is very slow
and is best suited to materials that are relatively uniform
in particle size. Although passive piles theoretically can be
used for composting either yard trimmings or MSW, the
propensity for odor problems renders them unsuitable for
MSW feedstock materials or even large quantities of grass
or other green materials that have a high nitrogen content.
Passive piles require relatively low inputs of labor and
technology. They consist of piles of composting material
that are tended relatively infrequently usually only once
each year. Tending the piles entails turning them (i.e.,
physically tearing clown and reconstructing them), Figure
4-9 illustrates the proper method of turning a compost
pile. Such an effort requires only a few days use of per-
sonnel and equipment, making this a relatively low-cost
composting method.
Before piles are turned, the moisture content of internal
and external layers of the compost pile should be checked
using the methods discussed in the preprocessing section
of this chapter. If the moisture content is too low, water
can be added by manually spraying the pile with hoses or
by using automatic sprinklers or irrigation systems. If the
moisture content is too high, turning can be conducted
more frequently to increase evaporation rates.
With all composting methods, regular monitoring of the
temperatures of composting materials is recommended. A
variety of long-stem (3-foot) digital and dial-type ther-
mometers and infrared scanners are available that can read
temperatures up to 93°C (199°F).
Passive piles should be constructed large enough to con-
serve sufficient heat but not so large as to overheat. If tem-
peratures of the composting mass exceed 60°C (HOT),
composting materials can combust, and/or microorgan-
isms needed for decomposition can be killed. Compost
piles should be turned if this temperature is exceeded.
Even if temperature and moisture are not monitored with
the passive pile composting method, the periodic turning
of the piles will adjust the oxygen level, moisture content,
and temperature to some degree. The movement created
by turning aerates the pile, and the anaerobic center is re-
placed with oxygen-rich external layers of the material. In
addition, dry internal materials are exposed to the outer
layers of the pile where they are more susceptible to wet-
ting by rain or snow. The increased aeration and wetting
caused by turning also serve to reduce temperatures in the
internal layers, preventing excessive heat buildup. Tem-
perature and oygen levels also can be controlled some-
what by forming piles of the appropriate size. The larger
the pile, the greater the insulation and the higher the tem-
perature levels that can be reached. The larger the pile,
however, the lower the degree of oxygen penetration and
the greater the potential for anaerobic conditions forming
in the center of the pile.
40
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Processing Methods, Technologies, and Odor Control
Lift compost high with bucket loader and let compost fall to new
location to create a cascading mixing effect.
Note:
Adapted from: UConn CES, 1989.
The principle of the mixing technique is to
move the top of the pile to the bottom of
the pile being formed mixing the material
well during this process.
Figure 4-9. Pile turning for aeration and mixing.
Several disadvantages are associated with passive pile meth-
ods. Unlike more intensive composing processes that can
produce a finished product in a few weeks to a few months,
passive piles can require over 1 year for the composting proc-
ess to be completed. In addition, the minimal turning of
passive piles results in the formation of anaerobic conditions
so that when piles are eventually turned (especially for the
first year or two of the process) significant odors result. Pas-
sive piles consequently cannot be placed in densely popu-
lated areas, and a large buffer zone is recommended between
residents and composting operations (Strom and Finstein,
1989). The untended passive piles also might resemble
dump sites to community members who might discard trash
at the site. Some means of controlling access to the passive
pile site is, therefore, recommended. Finally large, untended
piles have the potential to overheat and combust, creating a
possible fire hazard.
Turned Windrows
Tinnedwindrows are a widely used method for compost-
ing yard trimmings and MSW. This method generally is
not appropriate, however, for MSW containing significant
amounts of putrescible materials due to odor concerns.
Tuned windrows are elongated composting piles that are
turned frequently to maintain aerobic composting condi-
tions. The frequent turning promotes uniform decom-
position of composting materials as cooler outer layers
of the compost pile are moved to inner layers where
they are exposed to higher temperatures and more inten-
sive microbial activity. The turned windrow method re-
sults in the completion of the composting process for yard
trimmings in approximately 3 months to 1 year (UConn
CES, 1989).
Turned windrow operations generally can be conducted
outdoors. To increase the operator's ability to control
composting conditions, however, windrows can be placed
under or inside shelters. Leachate problems should be
minimized by constructing windrows on firm surfaces
surrounded by vegetative filters or trenches to collect run-
off (see Chapter 6). (A paved surface might be helpful, de-
pending on the size and location of the facility and how
muddy it might get.) Run-on controls also are helpful as
is careful balancing of the C:N ratio. Progressive decom-
position of the composting materials reduces the size of
the windrows, allowing them to be combined to create
space for new windrows or other processes,
As with passive piles, forming windrows of the appropri-
ate size helps maintain appropriate temperature and oxy-
gen levels. The ideal height for windrows is from 5 to 6
feet (CRS, 1989). This height allows the composting mat-
erials to be insulated properly but prevents the buildup of
excessive heat. Windrow heights vary, however, based on
the feedstock, the season, the region in which the
composting operation is being conducted, the tendency of
the composting materials to compact, and the turning
equipment that is used. Windrow widths generally are
41
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Processing Methods, Technologies, and Odor Control
twice the height of the piles. Factors such as land availabil-
ity, operating convenience and expedience, type of turn-
ing equipment used, and interest in the end product
quality also affect the chosen windrow width. Careful
monitoring of width is unnecessary, however, to ensure
that proper oxygen and temperature levels are maintained;
windrow height determines aeration levels to a far greater
degree than windrow width. Windrow length also has lit-
tle impact on the composting process.
Windrow shapes can be altered to help maintain appro-
priate composting conditions (primarily moisture levels).
For example, windrows with concave crests are appropri-
ate during dry periods and when the moisture content of
the composting material is low to allow precipitation to
be captured more efficiently. Peaked windrows are prefer-
able during rainy periods to promote runoff of excess
water and to prevent saturation. Illustrations of these
windrow shapes are presented in Figure 4-10.
The same types of operations used to monitor critical
composting conditions in the passive pile method also can
be used with turned windrow composting. The more fre-
quent turning of composting materials with the turned
windrow technique does tend to maintain oxygen, mois-
ture, and temperature at appropriate levels, however.
Where odor control and composting speed are a high pri-
ority, oxygen monitoring equipment can be installed to
alert operators when oxygen levels fall below 10 to 15
percent, which is the oxygen concentration required to
encourage aerobic decomposition and minimize odor
problems (Richard, 1992).
Turning frequencies for this method can range from twice
per week to once per year. In general, the more frequently
that the piles are turned, the more quickly the composting
process is completed. Some materials do not need to be
turned as frequently to maintain high levels of decomposi-
tion. For example, structurally firm materials have greater
porosity and therefore can maintain aeration for greater
periods of time without turning. Ideal turning patterns
should move the outside layers of the original windrow to
the interior of the rebuilt windrow (this pattern is shown
in Figure 411). If this pattern is not feasible, then care
should be taken to ensure that all materials spend suffi-
cient time in the interior of the pile. Inefficiencies in the
turning pattern can be compensated for by increasing the
frequency with which the windrows are turned.
The turning equipment used will, in part, determine the
size, shape, and space between the windrows. Front-end
loaders are commonly used in smaller operations. The
quantity of materials that they can handle as well as the
control that they can exercise over the turning process is
limited, however. When this equipment is used, enough
space must be maintained between windrows to allow the
front-end loaders to maneuver and turn the piles. Wind-
row turners are larger machines that are often used at
Landspreading
Land spreadhg involves the placement of organic
materials on the ground for decomposition under
uncontroled conditions. A few simple interven-
tions, however, such as reducing feedstock particle size
or periodically turning materials with a plow, can be
used to accelerate decomposition. Landspreading re-
quires very low inputs of labor and technology and is;
therefore relatively inexpensive.
Unlike composting, material that have been land-
spread are first degraded by the actions of soil dwelling
microorganisms such as worms and insects. Once the
feedstock is size reduced by these Macroorganisms,
mesophilic microorganisms begin decomposition
which proceeds at low temperatures and slow rates
(CRS, 1989). Since the feedstock is applied to the
land before any processing is conducted, this method is
not appropriate for MSW, which is more likely to con-
rain pathogenic and chemical materials than yard trim-
mings. Yard trimmings that have been exposed to high
pesticide levels also should not be landspread.
To increase the efficiency of the landspreading the ,
feedstock materials can be shredded prior to applica-
tion. This increases the uniformity of the particle size
of the materials, thereby accelerating composting,
Some states govern the level of application of materials
to acreage according to water quality concerns and ag-
ronomic soil tests. Siting the operations as close to the
source of the feedstock materials as possible also should
be pursued to minimize transportation costs, For these
reasons, careful consideration should be given to siting
landspreading operations,
Landspreading of materials that decompose rapidly
can enhance plant growth. If the feedstock is applied
at the appropriate time, the decomposition process
will be completed before crops are planted, The de-
composed feedstock materials will then act as a soil
amendment product and assist in crop growth. If
however, crops are planted before the decomposition
is completed, landspread leaves can reduce crop yield
by tying up otherwise available nitrogen and reduc-
ing oxygen availability. Also, extensive separation op-
erations might be needed to remove unwanted
materials such as brush and glass. Finally, raw leaves
and grass can be diffcult to handle and have a ten-
dency to clog farm machinery.
facilities that compost large volumes of material. These
machines can be either self-propelled or mounted to
front-end loaders. Self-propelled windrow turners can
straddle windrows, minimizing the required space be-
tween windrows and consequently reducing the space
42
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Processing Methods, Technologies, and Odor Control
requirements for the composting process. Windrow turn-
ers should peform several functions including increasing
porosity of the pile, redistributing material to enhance proc-
ess homogeneity, and breaking up clumps to improve prod-
uct homogeneity.
Aerated Static Piles
Aerated static piles, sometimes called forced aeration
windrows, are a relatively high-technology approach that
can be used to compost both yard trimmings and MSW.
This approach is effective when space is limited and the
composting process must be completed within a year. In
this method, piles or windrows are placed on top of a grid
of perforated pipes. Fans or blowers pump or pull air
through the pipes and, consequently through the com-
posting materials. This maintains aeration in the compost
pile, minimizing or eliminating the need for turning. In
some operations, the pipes are removed her 10 to 12
weeks of composting and the piles or windrows are then
turned periodically.
Aerated static piles are 10 to 12 feet high on average. To
facilitate aeration, wood chips (or other porous materials)
are spread over the aeration pipes at the base of the pile.
The feedstock is then added on top of the wood chips. It
might be necessary to top off the pile with a layer of fin-
ished compost or bulking agent. This protects the surface
of the pile from drying, insulates it from heat loss, dis-
courages flies, and filters ammonia and potential odors
generated within the pile (Rynk et al, 1992). It can take
as little as 3 to 6 months to produce finished compost
with this method.
Air can be supplied to the process through a suction sys-
tem or a positive pressure system. The suction system
draws air into and through the pile. The air then travels
through a perforated pipe and is vented through a pile of
finished compost, which acts as an odor filter (see Figure
4-1 1). With this system, condensate from water vapor
drawn from the pile must be removed before the air
reaches the blower. The ability to contain exhaust gases
for odor treatment is an important advantage of suction
aeration. The presence of this odor filter, however, more
than doubles the pressure losses of suction aeration.
The positive pressure aeration system uses a blower to
push air into the compost pile. The air travels through the
pile and is vented over its entire surface. Because of the
way air is vented, odor treatment is difficult with positive
pressure aeration. The absence of an odor filter, however,
means lower pressure losses with this system, which results
in greater air flow from the same blower power. Therefore,
positive pressure systems can be more effective at cooling
the pile and are preferred when warm temperatures are a
major concern (Rynk et al., 1992).
To ensure that decomposition proceeds at high rates, tem-
perature and oxygen levels must be closely monitored and
maintained with aerated static pile composting. Aeration
management depends on how the blower is controlled.
The blower can be run continuously or intermittently.
Continuous operation of the blower permits lower air flow
rates because oxygen and cooling are supplied constantly
however, this leads to less uniform pile temperatures. Inter-
mittent operation of the blower is achieved with a
I
Concave Shape - Traps Water
Source: Richard et al., 1950
I
Peak Shape- sheds water
Figure 4-10. Windrow shapes for maximum and minimum water adsorption.
43
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Processing Methods, Technologies, and odor Control
Suction
Pressure
Cover layer
finished compost
Well-mixed
raw material
Porous
base
Condensate trap
A
Pile width
W=2H
(10-16 feet)
l/3w "
to
1/4W
1
*
1
1 1
I 1
1 U *1 1
70-90 feet maxium
Compost
1 cover
| Vie w A-A1
PUe height
H ~ 5 o TB8i
6-inch cover layer
Pile width
H 5-8feet
Source: Rynk et al, 1992.
Figure 4-11. Aerated static pile.
44
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Processing Methods, Technologies, and Odor Control
programmed timer or a temperature feedback system.
Triers are a simple and inexpensive method of control-
ling blowers to provide enough air to satisfy oxygen re-
quirements and control temperatures. This approach does
not always maintain optimum temperatures, however. A
temperature feedback system does attempt to maintain
optimum pile temperatures, for example, within the range
of 54 to GOT (129 to 140°F) (Rynk et al, 1992). Elec-
tronic temperature sensors, such as thermocouples or ther-
mistors, switch the blower on or off when the temperature
exceeds or falls below a predetermined level. The blower
switches on to provide cooling when the temperature rises
above its high temperature, usually around 57°C (135°F),
and switches off when the pile cools below a set point (Rynk
etal.,1992).
In general, the aerated static pile method is best suited for
granular and relatively dry feedstock materials that have a
relatively uniform particle size of less than 1.5 to 2 inches in
diameter. This is because large or wet materials and materials
of diverse sizes have a tendency to clump. Clumping con-
stricts air flow through the piles, leads to short circuits of air
pumping equipment, produces anaerobic pocks, and oth-
erwise limits the rate of decomposition. Aerated static piles
are commonly used for composting wet materials (such as
biosolids), however. Clumping is controlled by proper mix-
ing of bulky materials that adjust porosity and moisture.
In-Vessel Systems
In-vessel systems are high-technology methods in which
composting is conducted within a fully enclosed system.
All critical environmental conditions are mechanically
controlled with this method, and, with most in-vessel
systems, they also are fully automated. These systems are
rarely used to compost yard trimmings because it is ex-
pensive to maintain this degree of control. More and
more facilities are selecting in-vessel systems for their
MSW composting program. An in-vessel system can be
warranted for MSW if 1) the composting process must
be finished rapidly, 2) careful odor and leachate control
are a priority, 3) space is limited, and 4) sufficient re-
sources are available.
In-vessel technologies range from relatively simple to ex-
tremely complex systems. Two broad categories of in-ves-
sel technologies are available: rotating drum and tank
systems. Rotating drum systems rely on a tumbling action
to continuously mix the feedstock materials. Figure 4-12
illustrates a rotating drum composter. The drums typically
are long cylinders, approximately 9 feet in diameter,
which are rotated slowly, usually at less than 10 revolu-
tions per minute (CRS, 1989). Oxygen is forced into the
drums through nozzles from exterior air pumping sys-
tems. The tumbling of the materials allows oxygen to be
maintained at high and relatively uniform levels through-
out the drum. The promotional literature for rotating
drums indicates that composting materials must be re-
tained in the drums for only 1 to 6 days (CRS, 1989).
Complete stabilization of the composting material is not
possible within this timeframe, however, and further com-
posting and curing of from 1 to 3 months is necessary
(CRS, 1989),
Tank in-vessel systems are available in horizontal or verti-
cal varieties. Rectangular tanks are one type of horizontal
in-vessel system. These tanks are long vessels in which
aeration is accomplished through the use of external
pumps that force air through the perforated bottom of the
tanks. Mixing is accomplished by mechanically passing a
source: Rynk et al.,1992.
Second stage
Figure 4-12. Rotating drum composter.
45
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Processing Methods, Technologies, and Odor Control
moving belt, paddle wheel, or flail-covered drum through
the composting material. This agitates the material, breaks
up clumps of particles, and maintains porosity. Compost-
ing materials are retained in the system for 6 to 28 days
and then cured in windrows for 1 to 2 months.
The agitated-bed system is an example of this type of
horizontal in-vessel system. Figure 4-13 illustrates a rec-
tangular agitated-bed composting system, composting
takes place between walls that form long narrow channels
(called beds). A rail or channel on top of each wall sup-
ports and guides a compost-turning machine. Feedstock is
placed at the front end of the bed by a loader, and the
turning machine mixes the composting material and
discharges it behind the machine as the material moves
forward on rails. An aeration system in the floor of the
bed supplies air and cools the composting materials. In
commercially available systems, bed widths range from 6
to 20 feet, and bed depths are between 3 and 10 feet. Sug-
gested composting periods for commercial agitated-bed
systems range from 2 to 4 weeks (Rynk et al, 1992).
Vertical tank in-vessel systems use a vertical tank orienta-
tion. Forced aeration and stirring also are used with this
method. These systems can consist of a number of tanks
dedicated to distinct stages of the composting process or
of one tank (which might be divided into different
"floors"). Vertical tank in-vessel systems might use conveyors,
Compost discharged
Air plenum or grave*
base with aeration
Dioe underneath
M
Blowers
(one for each aeration
zone in every bed)
Turning machine
(moves towards raw
materials loading end)
Raw materials loaded
to transport the turning
machine to the next bed
Sources Rynk et al., 1992.
Figure 4-13. Rectangular agitated-bed composting system.
46
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Processing Methods, Technologies, and Odor Control
rotating screws, air infeeds, or air outfeeds to agitate com-
post, move compost between tanks, and maintain proper
levels of oxygen and moisture. A problem with vertical
tank in-vessel systems is the difficulty of maintaining an
equilibrium of moisture and air between the layers inside
the tank. In an attempt to adequately aerate the top layers
of the compost, these systems can cool down the bottom
layers of compost. Furthermore, excessive condensation
can form at the top of vertical tanks where moisture and
temperature levels are uncontrollable.
The Curing Stage
Once the materials have been composted, they should be
cured. Curing should take place once the materials are
adequately stable. While testing for stability is an inexact
science, oxygen uptake and Convolution tests can be
considered to discern the degree of maturity of compost
derived from MSW feedstock. For compost derived from
yard trimmings, simpler methods can often suffice. One
method is to monitor the internal temperature of the
compost pile after it is turned. If reheating of the pile oc-
curs, then the material is not ready for curing. Another
method is to put the compost material in a plastic bag for
24 to 48 hours. If foul odors are released when the bag is
opened, the materials are not ready for curing.
During the curing stage, compost is stabilized as the re-
maining available nutrients are metabolized by the micro-
organisms that are still present. For the duration of the
curing stage, therefore, microbial activity diminishes as
available nutrients are depleted. This is a relatively passive
process when compared to composting stage operations so
less intensive methods and operations are used here. In
general, materials that have completed the composting
stage are formed into piles or windrows and left until the
specified curing period has passed. Since curing piles un-
dergo slow decomposition, care must be taken during this
period so that these piles do not become anaerobic. Cur-
ing piles should be small enough to permit adequate natu-
ral air exchange. A maximum pile height of 8 feet often is
suggested (Rynk et al, 1992). If compost is intended for
high-quality uses, curing piles should be limited to 6 feet
in height and 15 to 20 feet in width (Rynk et al., 1992).
Curing operations can be conducted on available sections
of the compost storage or processing area. In general, the
area needed for the curing process is one-quarter of the
size needed during the composting process. The curing
process should continue for a minimum of 1 month
(Rynk et al., 1992). A curing process of this duration will
allow decomposition of the composting materials to be
completed and soil-dwelling organisms to colonize the
compost. It is important to note, however, that curing is
not just a matter of time, it also depends on the favorabil-
ity of conditions for the process to be completed.
Once the curing process is completed, the finished com-
post should not have an unpleasant odor. Incompletely
cured compost can cause odor problems. In addition,
compost that has not been cured completely can have a
high C:N ratio, which can tie up otherwise available ni-
trogen in the soil and be damaging when the compost is
used for certain horticultural applications since immature
compost can deprive plants of needed oxygen (Rynk et al.,
1992). The C:N ratio of finished compost should not be
greater than 20:1. C:N ratios that are too low can result in
phytotoxins (substances that are toxic to plants) being
emitted when composts are used. One group of phytotox-
ins is produced when excess nitrogen has not been utilized
by microorganisms. Nitrogen reactions ultimately can oc-
cur, causing the release of ammonia and other chemicals.
These chemicals "burn" plant roots and inhibit growth.
Therefore, proper end uses for incompletely cured com-
posts are limited (see Chapters 8 and 9).
Odor Control
While odor might seem to be a superficial measure of a
composting Facility's success, odor is potentially a serious
problem at all types of composting facilities and has been
responsible for more than one MSW composting plant
shutdown. In the planning stage of a facility, decision-
makers should examine composting conditions and odor
prevention and control approaches at existing facilities to
develop a control strategy for their operations. If nuisance
odors still develop, a facility will need to:
Identity the principal sources of odor.
Identify the intensity, frequency, characteristics,
and meteorological conditions associated with the
odors. A facility might consider establishing an
"odor standard" above which residents consider the
odor a nuisance. An odor panel, made up of com-
munity members who volunteer (or are chosen) to
represent the community's level of acceptability,
can help judge the odor intensity and detectability
at their residences.
Develop limits for odor emissions on site based on
maximum allowable odors off site.
Measure odor release rates from suspected sources
for comparison with emission limits.
Select suitable controls for each source of odor.
Source.s of odors include various compounds that maybe
present in composted organic wastes (such as dimethyl di-
sulfide, ammonia, and hydrogen sulfide). These odors
can be produced during different stages of the composting
process: conveying, mixing processing, curing, or storage.
Methods exist for measuring the quantity, intensity perva-
siveness, emission rate, and transport of odors and for es-
tablishing odor standards. For example, odor quantity
can be expressed as the number of effective dilutions (ED)
required so that 50 percent of a panel of 10 people can
47
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Processing Methods, Technologies, and Odor Control
Case Studies: Odor Problems
Facility managers should anticipate potential odor
problems and incorporate odor prevention and
control methods from the start. The following are
examples of how complaints about odor can lead to
setbacks or even failure:
In Illinois, a state law banning yard trimmings from
landfills nearly failed when hastily built composting fa-
cilities produced unacceptable odor. The Illinois Com-
posting Council was formed to address odor and
management issues.
Neighbors of the St. Cloud, Minnesota, MSW com-
posting facility complained about the odors emanating
from die facility, resulting in a year-long suspension of
large-scale production while the facility constructed an
enclosed system and engineered odor controls.
An MSW composting facility in Florida was forced to
shut down, pardy because of odor complaints. Neigh-
bors would not allow the facility to remain in opera-
tion long enough to retrofit die plant and install
engineering controls.
still detect the odor; this quantity is known as the Eo50.
Odor standards can be based on odor measurements (e.g.,
an ED,J, the number of odor complaints, or an existing
legal standard. Data on relevant meteorological condi-
tions, such as wind speed and direction, temperature, and
inversion conditions, often can be obtained from local
weather stations. For more information on methods of
measuring odors and setting odor standards, see Control of
composting Odors (Walker, 1993) and EPA's Draft Guide-
lines for Controlling Sewage Sludge Composting Odors (U.S.
EPA, 1992).
The types of odor controls chosen depend on the odor
sources, the degree of odor reduction required, and the
characteristics of the compounds causing the odor. Odor
reduction efforts should incorporate both prevention and
control measures. In addition to the process and engineer-
ing controls described below, careful monitoring and con-
trol of the composring process will help avoid anaerobic
conditions and keep odors to a minimum. In-vessel com-
posting tends to cause fewer odor problems, but in-vessel
systems still must be operated and monitored carefully.
Proper siting (discussed in Chapter 5) and effective public
involvement (see Chapter 10) also will help minimize
problems resulting from odors.
Process Controls
At facilities that compost yard trimmings, facility manag-
ers can implement a number of procedures to minimize
odors in the tipping and staging areas. Assuming that
grass is cut over the weekend, managers that have control
over the collection schedule can arrange for feedstock to
be delivered at the beginning of the week to minimize the
amount of time that grass is held in closed containers. If
grass coming to the facility is already odorous, it should
be mixed with a bulking agent (e.g., wood chips) as
quickly as possible so that the C:N ratio is approximately
30:1 (Glenn, 1990).
At facilities that compost yard trimmings and/or MSW
procedures that can help prevent or minimize odors include
Forming incoming materials into windrows
promptly.
Making sure windrows are small enough to ensure
that oxygen can penetrate from the outside and
guard against the formation of a foul-smelling an-
aerobic core but large enough for the interior to
reach optimal temperatures. For an aerated pile
composting system, the pile height should be lim-
ited to 9 feet high (Walker, 1993).
Providing aeration by completely mixing the feed-
stock and regularly turning the piles (see Engineer-
ing Controls below). Because turning can release
odors, however, a windsock can be used for
determining when conditions are right for turning
so as to keep odors from leaving the site.
Breaking down piles that are wet and odorous and
spreading them for drying. Mixing in dried com-
post that has been cured also can help.
Covering compost piles with a roof to help control
temperature and moisture levels.
Avoiding standing pools of water or pending
through proper grading and use of equipment (see
Chapters 5 and 6).
Engineering Controls
Facilities that compost yard trimmings typically rely on
regular turning of windrows to mitigate odors. Many
MSW composting facilities, however, are beginning to use
sophisticated odor control technologies to treat exhaust
gases from decomposing feedstock. Some facilities collect
and treat odorous gases from the tipping and composting
areas. Such systems are necessary if simpler odor control
measures are unsuccessful. Table 4-3 describes and com-
pares the effectiveness of several odor control methods:
odor piles, biofilters, wet scrubbers, adsorption, dispersion
enhancement, and combustion. Combustion is effective
but can be expensive (Ellis, 1991). Biofilters and air scrub-
bers, however, are gaining acceptance as effective means
for odor control. These two methods are described below.
48
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Processing Methods, Technologies, and Odor Control
Table 4-3. Effectiveness of composting odor control technologies.
Technology
Odor Pile
Biofilter
Wet Scrubbers
Pocked tower
Mist scrubbers
Adsorption
Dispersion Enhancement
Site modification
Tall stack
Combustion
Description
Odorous gases from composting pile are diverted to flow over
finished compost.
Controlled application of odor pile approach, incorporating filter
media to which microorganisms are attached.
Odorous compounds are absorbed into a liquid then extracted with
chemicals.
casses are oassed aver an inert medium to which the odor-causing
compounds attach, thereby "cleaning" the gases.
Facilitates greater dispersion of odorous gases.
Gases are captured and odorous compounds burned.
Effectiveness
Questionable.
90%+ removal.
Up to 70% per sloge.
<90%.
Effective for polishing and
control of volatile organic
compounds.
Moderate.
Potentially good.
99% removed.
Biofilers
Biofilters have been used to treat odorous compounds and
potential air pollutants in a variety of industries. The
composting industry is expanding its use of biofilters as
engineering design criteria for this technology have be-
come increasingly available (Willams and Miller, 1992a).
In a biofiltration system, a blower or ventilation system
collects odorous gases and transports them to the biofilter.
The biofilter contains a filtration medium such as finished
compost, soil, or sand. The gases are evenly distributed
through the medium via a perforated piping system sur-
rounded by gravel or a perforated aeration plenum (an en-
closure in which the gas pressure is greater than that
outside the enclosure). The incoming gas stream is usually
moisturized to keep the filter medium from drying out
(Williams and Miller, 1992a).
As the gases filter up through the medium, odors are re-
moved by biological, chemical, and physical processes.
Biofilters have an enormous microbial population. For ex-
ample, soil biofilters contain 1 billion bacteria and
100,000 fungi per gram of soil. These microorganisms
oxidize carbon, nitrogen, and sulfur to nonodorous carb-
on dioxide, nitrogen, sulphate, and water before those
compounds can leave the filter medium (Bohn and Bohn,
1987). The biofilter medium acts as a nutrient supply for
microorganisms that biooxidize the biodegradable con-
stituents of odorous gases. Biofilters also remove odorous
gases through two other mechanisms that occur simulta-
neously adsorption and absorption (Naylor et al, 1988;
Helmer, 1974). Adsorption is the process by which odor-
ous gases, aerosols, and particulate accumulate onto the
surface of the faltering medium particles. Absorption is the
process by which odorous gases are dissolved into the
moist surface layer of the biofilter particles (Williams and
Miller, 1992a). As microorganisms oxidize the odorous
gases, adsorptive sites in the filtering medium became
available for additional odorous compounds in the gas
stream. This makes the process self-sustaining (Willams
and Miller, 1992a) and results in long-term odor removal.
Several different biofilter designs have been used in the
composting industry. Figure 4-14 illustrates open and en-
closed biofilter systems. In an open system, the biofilter is
placed directly on the soil surface, or portions can be
placed below the soil grade. Typically an appropriate area
of soil is excavated, an aeration pipe distribution network
is placed in a bed of washed gravel, and the area is filled
with the filter medium. A closed system consists of a ves-
sel constructed of concrete or similar material with a per-
forated block aeration plenum. The vessel is filled with
the biofilter materials.
The type of design chosen depends on the amount of land
available, climate, and financial resources. Both open and
closed systems can be covered to minimize the effects of
precipitation (Williams and Miller, 1992a).
For successful odor control using biofilters, only a few de-
sign limitations must be kept in mind:
The vessel and the medium must be designed to en-
sure a suitable environment for microbial growth.
The moisture content in the biofilter must be opti-
mal for the resident microorganisms to survive and
metabolize gases (Williams and Miller, 1992b). It
can be very challenging to maintain the proper
moisture conditions within the biofilter.
The biofilter medium must have a large reactive
surface area, yet be highly porous. These two char-
acteristics tend to be mutually exclusive in natu-
rally occurring soils and compost therefore, porous
material is often mixed with the soil or compost to
49
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Processing Methods, Technologies, and Odor Control
Open Blofliter System
Compost Filter Bid
(about 1 meter dtap)
Ground Gravel
Note: Precipitation cover and sprinkler system can be added
closed Biofliter System
Exhaust Air
A A A A A
Water Sprinkler
to Moisten Air
Compost Filter Bed
Foul Air
Perforatad
Support
Plate
Steam injector
source: Williams and Miller, 1992a.
Heat Exchange
Drain
Figure 4-14. Bulk media fiber designs.
50
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Processing Methods, Technologies and Odor Control
obtain a more suitable biofilter medium (Williams
and Miller, 1992a).
The filtration medium should have a significant
pH buffering capacity to prevent acidification from
the accumulation of sulfates.
Compaction of the medium over time should be
minimized.
Uniform air distribution should be designed into
the system. If the odorous gases are not distributed
evenly throughout the filter medium, "short circuit-
ing" of exhaust gases and inadequate odor control
can result (Kissel et al, 1992; Williams and Miller,
1992a).
Table 4-4 presents the maximum removal capacities of
various compounds through biofilters. To effectively re-
move ammonia from composting exhaust gases, other re-
moval technologies such as acid scrubbing (discussed
below) might be needed in addition to biofilters.
The initial cost of biofilters is usually less than the instal-
lation costs of other odor control methods, and the sav-
ings in operation and maintenance are even greater
because biofilters require no fuel or chemical input and
little maintenance (Bonn and Bohn, 1987). The initial
cost of biofilters is $8-10 per cubic foot of air passing
through the filter per minute (cfm).
Air Scrubbers
Air scrubbers use scrubbant solutions to remove odorous
compounds through absorption and oxidation. A variety
of air scrubbers exist. In packed tower systems, the scrub-
bant solution is divided into slow-moving films that flow
over a packing medium. The air stream being treated is
usually introduced at the bottom of the packing vessel
and flows upward through the medium (Lang and Jager,
1992). The scrubbant solution is recirculated to minimize
chemical usage (Ellis, 1991). In mist scrubber systems,
the scrubbant solution is atomized into very fine droplets
that are dispersed, in a contact chamber, throughout the
air stream being treated. Mist scrubbers use a single pass
approach: the chemical mist falls to the bottom of the
chamber and is continuously drained (Lang and Jager,
1992; Ellis, 1991).
Recent evidence suggests that multiple stages of scrubbers,
called multistage scrubbers, often with different chemical
solutions, are required to achieve adequate odor removal
effciency (Ellis, 1991). Figure 4-15 illustrates a multistage
odor-scrubbing system for a compost operation.
Research by the Washington Suburban Sanitary Commis-
sion at the Montgomery County Regional composting
Facility has identified dimethyl desulfide (DMDS) as the
primary odorant in air from the composting process
(Hentz et al., 1991). This research has led to the develop-
ment of a three-stage scrubbing process shown to remove
97 percent of the odor in composting exhaust gases. This
process involves an acid/surfactant wash in the first stage
to remove ammonia and certain organics, a hypochlorite
oxidation stage to remove DMDS and other organic sul-
fides, and a final hydrogen peroxide wash to dechlorinate
and furher remove organics (Murray, 1991).
Multistage scrubbing systems require effective operation
and maintenance procedures to ensure optimum perform-
ance. Therefore, before selecting a multistage scrubbing
system for odor control, it is important to consider its
maintenance requirements in comparison to other odor
control technologies.
Postprocessing
Postprocessing is optional but normally is performed to
refine the compost product to meet end-use specifications
Table 4-4. Removal capacities of various compounds
through biofilters.
Compound
Methyl Formiate
Hydrogen Sulfide
Butylacetate
Butanol
N-butanol
Ethylacetate
Toluene
Methanol
Methonethiol
Dimethyl Disulfide
DimeriiyUulfide
Ammonia
Maximum
Removal Rat.
35.0 g/kg dry
media/day.
5.0g s/kg dry
2.14g/kgdry
peat/day.
2.41 /kg dry
peat/day.
2.40 g/kq dry
compost/day.
2.03 /kg.dry
, ,| 01 J
peat/day.
1.58 g/kg dry
peat/day.
1.35£/kgdry
media/day.
0.90 g S/kg dry
peat/day.
0.68 e S/kg dry
peat/cloy.
0.38 g S/kg dry
peat/day.
O.lGgN/kgdry
peat/day.
Reference
Van lith et cJ.,
1990.
Cho etal.,1991.
Ottengrof, 1 986.
Helmer, 1984.
Ottengraf, 1986.
Oltengrof, 1986.
Van Lith et al.,
1990.
Cho etal.,1991.
Cho etal.,1991.
Choetal., 1991.
Shoda, 1991.
'Converted from g/m3/hr, assuming a media bulk density
of401b/CF
Sources Williams and Miller, 1992a.
51
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Processing Methods, Technologies, and Odor Control
or market requirements. During postprocessing, compost
can be analyzed to ensure that stabilization is complete.
Compost also can be tested for chemical or pathogenic
contamination and tested to determine nutrient levels,
cleansed of unwanted material, sorted by size, screened,
size reduced, blended with other materials, stored, and/or
bagged.
Sorting and removal operations can be conducted to re-
move any remaining large particles that could lower the
quality of the compost or be aesthetically displeasing.
Sorting and removal also may be performed to generate
composts of uniform size for end uses where such uni-
formity is important (such as in horticultural applica-
tions). The same equipment can be used in both
preprocessing and postprocessing, but for composting op-
erations with continual rather than seasonal inputs of
feedstock materials, dedicated equipment provides for a
more reliable and convenient systems flow. Where size re-
duction of finished compost particles is desired for aes-
thetic or marketing reasons, the use of simple shredding
mechanisms should suffice.
Proper storage is necessary to maintain the quaky of the
compost product. The most common storage problem is
inadequate drainage controls, causing the compost to be-
come saturated. Overly wet compost can become mal-
odorous and is heavy and difficult to handle. Provision for
adequate drainage is essential when storing compost. In
general, the storage area should be large enough to hold
25 percent of the compost produced by the facility each
year as well as a large supply of bulking agent, if needed
(Alexander, 1990).
During postprocessing, compost that will be used as soil
amendment should be tested to ensure that it has been
properly cured. Compost stability can be assessed by seed
germination tests or by analyzing factors that indicate the
level of compost maturity. In seed germination tests, sen-
sitive plant species are planted in the compost and in a
soil medium. Germination rates for the plants grown in
the compost are compared to those grown in the soil and,
if the rates are comparable, they show that the compost
has been properly stabilized. Laboratory analyses of im-
portant compost parameters such as oxygen consumption,
Stage
Ammonia
Removal
S 1
-age
Oxidation with
Stage II
Final wash
- 0.5-1.0% Bleach C^OuQ
Solution 3 gpm \
Retirculation SO gpm
(Fogging Nozzle)
Recirculation
f f
60 gpm (Fogging Nozzle)
i
Air In
nil III
I3BD
>
^
J
M^M^
j 1 >
r-^-l
-re_.
^
y
M
j :
1 i-:
|
2-3.0KSulfuricAcid
Solution 3" gpm
(Atomizing Nozzle)
- -
'\
iBleacft
!
Source: Goldstein,
1989.
k
" I
!
1
i
"
\
N
]
0-1.1
Solu
(Ato
-
1 1
1
-,
I^Acid
1
JljBk
//n\^
fin \\\
N
h ^_ 1
t
s,
^
)%SulfuricAcid 1
tion 3 gpm
mizing Nozzle) I
--
b-
1
lliwttw
Ml
b
Figure 4-15. Process odor-scrubbing system for compost operation.
52
-------
Processing Methods, Technologies, and Odor Control
carbon dioxde production, C:N ratios, and cation ex-
change capacity also can be conducted (see Chapter 9).
Laboratory analyses also ears be conducted to determine if
phytotoxic or pathogenic contaminants are present in the
compost. Nutrient levels can be determined through
laboratory tests as well. Several states and localities have
imposed compost quality requirements (see Chapter 7'),
and laboratory analysis is often needed to ensure that
these requirements are met.
Once contaminant and nutrient levels have been deter-
mined, results can be incorporated into compost labels.
This will allow end users to obtain composts with
contaminant and nutrient levels that fall within ranges ac-
ceptable to their specific needs. Labels also can include in-
formation on the types of feedstocks used for composting,
weight or volume of container contents, suggested uses for
the compost, appropriate application rate, warnings or re-
strictions on compost use, and the name and address of
the compost producer.
Finally compost can be bagged before it is distributed if it
is economically feasible. Bagging facilitates transporting,
marketing, and labeling of compost. Because it is rela-
tively labor intensive (and therefore costly), however, bag-
ging should be conducted only if buyers for the compost
have been secured and the cost of bagging can be justified
by an increase in expected revenues.
Summary
There are three stages in the composting process:
preprocessing, processing and postprocessing.
Different method, operations, and and equipment
are associated with each of these stages. Th e level of
effort applied at each stage depends on the desired
quality of the final product, the type and amount of
feedstock, the speed at which the process must be com-
pleted the emphasis placed on odor and leachate con-
trol, the resources available, and the level of effort
applied at the other composting stages. An under-
standing of the range of methods and operations that
can be used during compost processing will facilitate
planning and development as well as maintenance
and improvement, composting facility managers aslo
must consider the potential for odor problems when
designing processing operations. Odor is a potentially
serious problem that has led to the closure of several
composting facilities in recent years. Many steps can
be taken, nowever to address odor formation before
it becomes a public nuisance.
Chapter Four Resources
Alexander, R 1990. Expanding compost markets. BioCy-
cle. August, 31(8):54-59.
Appelhof, M., and J. McNelly. 1988. Yard waste compost-
ing guide. Lansing, MI: Michigan Department of Natural
Resources.
Bohn, H. L, and R. K. Bohn. 1987. Biofiltration of odors
from food and waste processing. As cited in Proceedings
of Food Processing Waste Conference, Georgia Techno-
logical Research Institute, Sept. 1-2,1987.
Buckner, S.C. 1991. High volume yard waste composting.
BioCycle. April, 32(4):48-49.
Cal Recovery Systems (CRS) and M.M. Dillon Limited.
1989. composting A literature study. Ontario, Canada:
Queen's Printer of Ontario.
composting Council (CC). 1991. Compost facility plan-
ning guide. Washington, DC: composting Council.
Ellis, S. 1991. Air pollution and odor control methods.
Proceedings of the Northeast Regional Solid Wrote Com-
porting Conference, June 1991. Washington, DC: Com-
porting Council, pp. 23-26.
Glaub, J., L. Diaz, and G. Savage. 1989. Preparing MSW
for composting. The BioCycle Guide to composting Mu-
nicipal Wastes. Emmaus, PA: The JG Press.
Glenn, J. 1990. Odor control in yard waste composting.
BioCycle. November, 3 1(11):38-40.
Glenn, J. 1991. Upfront processing at MSW composting
facilities. BioCycle. November, 32(ll):30-33.
Goldstein, N. 1989. New insights into odor control. Bio-
Cycle. February, (30)2:58-61.
Golob, B. R., R. Spencer, and M. Selby. 1991. Design ele-
ments for solid waste composting. BioCycle. July,
32(7):50-53.
Golueke, C.G. 1977. Biological reclamation of solid
wastes. Emmaus, PA: Rodale Press.
Gray, K.R., K. Sherman, and A.J. Biddlestone. 1971a. A review
of composting Part 1- Process Biochemistry 6(6): 32-36.
Gray, K.R., K. Sherman, and A.J. Biddlestone, 1971b. A
review of composting: Part 2 - Process Biochemistry
6(10): 22-28.
Gray, K.R., and A.J. Biddlestone. 1974. Decomposition
of urban waste. As cited in: Richard, 1992. Municipal
solid waste composting: Physical and biological process-
ing. Biomass & Bioenergy. Tarrytown, NY: Pergamon
Press. 3(3-4): 195-211.
53
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Processing Methods, Technologies, and Odor Control
Processing Yard Waste
The Town of blip, New York has been operating a large-scale yard trimmings composting facility on a 40-acre site since '
1988. Approximately 60,000 tons of grass leaves, and wood debris is collected from town residents, municipal agen-
cies, and commercial landscapers every year and transported via packer trucks to the facility.
Isip's composting facility comprises preprocessing, processing, and postprocessing operations. During the preprocessing::
stage, a shredder debags the composting feedstock and size reduces larger materials. This machine is capable of processing
25 tons of yard waste per hour. Once shredded, the feedstock is conveyed to a trommel screen where it is sorted and aer-
ared. A high percentage of plastic is removed during this preprocessing stage. Once size reduced and screened, moisture is
added to the feedstock to obtain an initial moisture content of 50 percent.
During processing, the feedstock is transported via dump trucks to the composting area, where it is formed into windrows
on a woodchip base. This base absorbs leachate, increases porosity, and improves drainage conditions at the bottom of the
windrows. Twenty-five acres of the facility has been sited for windrow formation. The size of the windrow formed depends
upon the nature of the feedstock material and the time of year composting takes place. Feedstock containing mostly leaves
can be formed into windrows 12 feet high by 26 feet wide. The size of the windrow formed from feedstock containing
predominancy grass depends on the bulking material used, however, these are generally no larger than 6 feet high by 14
feet wide. To maintain aerobic composting conditions, smaller windrows are turned with a rotary-drum turning machine,
while a front-end loader is used to turn larger windrows. The frequency of turning varies depending on the windrow size,
feedstock composition, stage of decomposition, and moisture content and is adjusted so that aerobic conditions are
maintained.
Leaves usually remain in windrows for at least 16 weeks before being placed in curing piles for further stabilization. Grass
remains in windrows from 6 to 8 weeks before being placed in curing piles where it will stay for another 4 to 6 weeks, The
facility ensures continual processing of fresh material delivered to the site by closely controlling the decomposition rate
and windrow size.
Once cured, postprocessing takes place to produce the final product. This involves screening the material to remove wood-
chips and any plastic fractions remaining in the compost. An air classifier is to be added to the system to separate the plas-
tic from the woodchips so that the chips can be recycled back to the windrows.
The finished compost is available to residents of Islip free of charge and can be purchased by landscape contractors, turf
growers, topsoil suppliers, and nurseries for $6 per yard (Buckner, 1991).
Source: Buckner, 1991.
Helmer, R 1974. Desodorierung von geruchsbeladener
abuft in bodenfiltern. Gesundheits-Ingenieur. 95(1):21.
As cited in: Williams and Miller, 1992a. Odor control us-
ing biofilters, Part I. BioCycle. October, 33(10):72-77.
Hentz, L. H., C.M. Murray, J.L. Thompson, L. Gasner,
and J.B. Dunson. 1991. Odor control research at the
Montgomery County regional composting facility. Water
Pollution Control Federal Journal v. 26, Nov/Dec. As
cited in: Murray, 1991. Controlling odor. Proceedings of
the 1990 Solid Waste composting Council Conference,
November 1990. Washington, DC: composting Council.
pp. 93-96.
Illinois Department of Energy and Natural Resources
(IDENR). 1989. Management strategies for landscape
waste. Springfield, IL Office of Solid Waste and Renew-
able Resources.
Kissel, J.C., C.H. Henry, and R.B. Harrison. 1992. Po-
tential emissions of volatile and odorous organic com-
pounds from municipal solid waste composting facilities.
Biomass & Bioenergy. Tarytown, NY: Pergamon Press.
3(3-4):181-194.
Lang, M. E., and R.A. Jager. 1992. Odor control for mu-
nicipal sludge composting. Biocycle. August, 33(8):76-85.
Murray C.M. 1991. controlling odor. Proceedings of the
1990 Solid Waste composting Council Conference, No-
vember 1990. Washington, DC: composting Council, pp.
93-96.
Naylor, L.M., G.A. Kuter, and PJ. Gormsen. 1988. Biofil-
ters for odor control: the scientific basis. Compost Facts.
Hampton, NH: International Process Systems, Inc.
Richard, T., N. Dickson, and S. Rowland. 1990. Yard
waste management: A planning guide for New York State.
Albany NY: New York State Energy Research and Develop
ment Authority, Cornell Cooperative Extension, and New
York State Department of Environmental Conservation.
Richard, T.L. 1992. Municipal solid waste composting
Physical and biological processing. Biomass & Bioenergy.
Tarrytown, NY: Pergamon Press. 3(3-4):195-211.
54
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Processing Methods, Technologies, and Odor Control
Composting Municipal Solid Waste Using Enclosed Aerated Windrows
The MSW composting facility in Wright County, Minnesota has been operational since 1991. This facility processes ap-
proximately 165 tons per day (TPD) of MSW and its composting, curing, and storage areas are sized m accommodate
up to 205 TPD. Incoming MSW is weighed and discharged onto the concrete tipping floor of the receiving area
where some hand separation of recyclables occurs. The receiving area has a storage capacity of approximately 330 tons.
The preprocessing operations at the facility include screening handsorting, size reduction, and mechanical sorting. The '
composting feedstock is transferred from the receiving building to a preprocessing building where it is discharged into a
trommel screen equipped with knives to facilitate bag opening. Two conveyors transfer the screened material to the hand-
sorting area. One conveyor transports the fines that pass through the screen openings, and the other transports oversized
materials. During this stage, handsorting personnel remove recyclables such as high-density polyethylene and polyethylene
terephthalate plastics and aluminum arts. Once handsorted, the feedstock is size reduced by a hammermill located in an
explosion-proof enclosure with explosion venting. Following this, the shredded feedstock passes underneath an overhead
electromagnet to remove ferrous metals.
At this stage the feedstock material is discharged into a mixing drum and water is added to raise the moisture content to
an optimal level. The purpose of the mixing drum is to adjust the moisture content, homogenize the waste stream, and
screen oversized and nondegradable material that would inhibit downstream process steps. Three separate feedstock
streams are generated by this operation. Material less than 2 inches in size is transported to thecomposting area, material
greater than 2 inches but less than 8 inches undergoes additional shredding and screening, and material greater than 8
inches is disposed of in a sanitary landfill.
Composting takes place in an open-sided covered hangar, sired to contain 12 windrows. Feedstock material is placed in
one of two primary windrows formed in the middle of the hangar by a central belt conveyor equipped with a traveling
tripper and cross belt conveyor assembly. When one primary windrow has been formed, a windrow turning machine will
move through the pile and reposition it to the second row, and from there to the third row, and so on. An aeration system
draws air through the primary and secondary windrows. The exhaust air passes through a biofilter for odor control (see
Section 6). The facility has an extensive leachate collection system.
The composting feedstock remains in the composting area for approximately 60 days after which it is transferred to a
hammermill for further size reduction. A screening drum is then used to separate nondegraded materials from this mate-
rial. The finished compost is stored on an asphalt pad.
Source: Golob et al., 1991.
Rynk, R., et al. 1992. On-farm composting handbook.
Ithaca, NY: Cooperative Extension, Northeast Regional
Agricultural Engineering Service.
Strom, P.F., and M.S. Einstein. 1989. Leaf composting
manual for New Jersey municipalities. New Brunswick,
NJ: Rutgers State University.
University of Connecticut Cooperative Extension Service
(UConn CES). 1989. Leaf composting: A guide for
municipalities. Hartford, CT: State of Connecticut De-
partment of Environmental Protection, Local Assistance
and Program Coordination Unit, Recycling Program.
U.S. EPA. 1992. Draft guidelines for controlling sewage
sludge composing odors. Office of WasteWater Enforce-
ment and Compliance, Washington, DC.
Walker, J.M. 1993. Control of composting odors. In: Sci-
ence and engineering of composting. Hoitink and Keener,
eds. Worthington, OH: Renaissance Publications.
Williams T.O., and E.G. Miller. 1992a. Odor control us-
ing biofilters, Part I. BioCycle. October, 33(10):72-77.
Williams T.O., and E.G. Miller. 1992b. Biofilters and fa-
cility operations, Part II. BioCycle. November, 33(11):
75-78.
Wirth, R 1989. Introduction to composting. St. Paul,
MN: Minnesota Pollution Control Agency.
55
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Chapter Five
Facility Siting and
Design
Proper siting and design are prerequisites to establishing safe and effective composting facilities. Decision-
makers should take care in selecting a suitable site and developing an appropriate design so as to control
both construction costs and operational probems over the life of the facility This chapter describes factors
that should be considered when siting and designing facilities for the composting ofMSWoryard trimmings. In
general the primary issues to consider involve odor control (see Chapter 4) and bioaerosol concerns (ice Chapter
6). While both types of facilities have similar siting and design requirements, more stringent measures are typi-
cally needed at MSW composting facilities. Throughout the siting and design process, it is crucial that the needs
of the community be accommodated since public acceptance of a facility is key to its success. Local and state
requirements aso should be reviewed prior to siting and designing composting facilities. Many states have estab-
lished specific criteria that composting facilities must address during siting and design. The criteria address many
technical concerns, including those rekzted to protecting human health and the environment, and can have an
impact on facility location, land use, size, and other considerations. In general detailed engineering plans typi-
cally must be approved by the state environmental protection agency in order to obtain a permit to construct and
operate a MS W compost facility (Chapter 7 discusses state legislation including the specific siting, design, and
permitting requirements of several states.)
Siting
Finding a suitable location for a composting facility will
help a community achieve its composting goals while
avoiding a variety of complications that could slow the
composting process. A number of technical, social,
economic, and political factors will shape decisions on
locating a facility. Some of the major factors in facility
siting include:
Convenient location to minimize hauling distances.
Assurance of an adequate buffer between the facil-
ity and nearby residents.
Suitable site topography and soil characteristics.
Sufficient land area for the volume and type of ma-
terial to be processed.
These factors are described in more detail below. Figure 5-
1 presents a site assessment form used in New York State
for the composting of yard trimmings. This form is
designed to obtain an objective assessment of proposed
sites for facilities that compost yard trimmings. Various
factors affecting siting are rated from 1 to 5, with 1 be-
ing least desirable and 5 being most desirable. These
ratings are then added to give a total rating for each
site. This rating evaluation makes it easier to choose the
most appropriate site for a facility that composts yard
trimmings. The same form also could be used for a
MSW composting facility.
Location
Potentially suitable locations for composting facilities
include areas adjacent to recycling drop-off centers and
in the buffer areas of existing or closed landfills, transfer
stations, and wastewater treatment plants. Current Fed-
eral Aviation Administration (FAA) guidelines prohibit
siting any type of solid waste facility, including com-
posting facilities, within 10,000 feet (almost 2 miles) of
an airport. This is to prevent birds, which could be at-
tracted to the site by potential food sources, from inter-
fering with airplanes.
56
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Facility Siting and Design
Site Name Date of Inspection.
Site Location Description Inspected by:
This form is designed for use in the field, to obtain an objective assessment of the proposed site.
The various "factors" considered at each site receive a rating from 1 to 5, with 1 being least desirable
and 5 being most desirable.
RATING COMMENT
1. Site Preparation Costs
a) compost area development..
b) access road construction
c) security set-up,
2. Site Characteristics
a) soil characteristics
b) proximity to water; streams, lakes,
c) Slope and topography
d) acreage
e) drainage
3. Access by Public Roads
4. Infrastructure
a) water
b) existing access road,
c) storage
d) telephone
e) electric
f) scale
5. Proximity to Homes
6. Proximity to Town in Need
7. Regional Site Potential
Figure 5-1. Yard trimmings site assessment form.
57
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Facility Siting and Design
RATING
COMMENT
8. Land Ownership
9. Environmental Impact
a) tree removal
b) habitat disturbance,,,,
10. Impact on Current Use
a) visual
b) physical...,
11. Impact on Future Use
a) visual
b) Physical
12. DEC Criteria (minimum distances)
a) property line, 50 ft
b) residence or business, 200 ft
c) potable water well, 200 ft
d) surface water supply, 200 ft
e) drainage swale, 25 ft
f) water table, 24 inches *,
TOTAL RATING
General comments relative to suitability of site to serve as a municipal composting facility:
Source: Richard et al, 1990.
Figure 5-1. (Continued).
A centrally located facility close to the source of the compost
feedstock will maximize efficiency and convenience while re-
ducing expeses associated with hauling these materials and
distributing the finished compost product. Siting a facility
that can be accessed via paved, uncrowded roads through
nonresidential areas will further contain transportation ex-
penses. If necessary, however, a busy local road network
can be compensated for by scheduling feedstock and com-
post product deliveries during off-peak road use times, A
centrally located facility can offer a further advantage to
communities operating drop-off collections since conven-
ient siting often encourages greater resident participation
in such programs.
Often, however, the concerns of local residents (particu-
larly about potential odors) force a composting facility to
be sited away from ideal collection and distribution loca-
tions. This is especially true for MSW composting facili-
ties. Locating a site with an extensive natural buffer zone,
planted with trees and shrubs, is an effective way to re-
duce the potential impacts that a new composting facility
might have on the surrounding neighborhoods. If natural
buffers do not exist, artificial buffer zones might need to
be constructed, visual screens, such as berms or landscap-
ing, can be designed to protect the aesthetic integrity of
the surrounding neighborhoods. (Buffer zones are dis-
cussed in more detail later in this chapter.)
58
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Facility Siting and Design
Odor Evaluation
A most important consideration in the siting and
design of a composting facility is the potential for
odors and for odor transport to the community.
When planning a facility, it is important to predict po-
tential sources of odors along with their emission rates,
detectability, and intensity. This information can be ob-
tained from Literature studies and visits to other com-
posting sites. In order to predict how these odors will
be transported, information on meteorological condi-
tions (e.g., wind speed and direction, temperature, and
inversion conditions) in the vicinity of the site can be
obtained from a local weather station. This informa-
tion then can be used to conduct dispersion modeling
to predict how odors could be transported into the
community and how potentially bad they will smell.
Data from the modeling can assist decision-makers in
choosing a suitable site and in selecting a composting
system whose design will help minimize odors (Walker,
1992). (See Chapter 4 for a more in-depth discussion
of odor control and management.)
Topography
Potential sites should be evaluated in regard to the
amount of alteration that the topography requires. Some
clearing and will be necssary for proper composting,
but minimizing this work is desirable in order to reduce
expenses and maintain trees on the perimeter of the site,
which act as a buffer. A composting site should be appro-
priately graded to avoid standing pools of water and run-
off. To avoid pending and erosion, the land slope at a
composting site should be at least 1 percent and ideally 2
to 4 percent (Rynk et al, 1992). U.S. Geological Survey
topographic maps and a plot plan survey can provide in-
formation on the natural drainage characteristics of a site.
The type and structure of the soil present at the site
should be assessed to control run-on and runoff. If the site
is unpaved, the soil on the site should be permeable
enough to ensure that excess water is absorbed during pe-
riods of heavy precipitation and that the upper layers of
the soil do not become waterlogged (this can create pool-
ing and limit vehicular access). If the soil is impermeable
or the site is paved, a range of drainage devices can be
used to divert precipitation away from the composting
pad and storage areas (see Chapter 6 for more information
on these devices).
Proximity to certain water sources also must be consid-
ered. Floodplains, wetlands, surface waiters, and ground
water all need to be shielded from runoff or leachate that
can originate at the site. The height of the water table is a
crucial factor in protecting these water sources. The water
table is the upper surface of the "zone of saturation,"
which is defined as the area where all available spaces or
cracks in the soil and rock are filled with water. In general,
the water table should be no higher than 24 inches below
the soil surface. Otherwise, flooding can occur during
times of heavy precipitation, which can potentially wash
away windrows and carry compostable materials off site.
Pooling also can result, slowing composting significantly
(Richard et al., 1990). In addition, leachate from com-
posting operations is more likely to contaminate ground
water when there is less soil to naturally falter the leachate
as it seeps downward (Richard, 1990).
Some states have stringent regulations concerning the pro-
tection of ground water at a composting site (see Chapter
7). The state of Illinois does not allow the placement of
compost within 5 feet of the high water table North
Carolina requires composting pads and storage areas to be
at least 2 feet above the seasonal high water table and
Pennsylvania does not allow a composting facility to be
sited in an area where the seasonal high water table is less
than 4 feet from the surface (WDOE and EPA, 1991).
Flood hazard maps, available from local soil conservation
offices, can help show the hydrologic history of a site. In
addition, municipalities should research the guidelines
that apply in their area as many states have regulations re-
stricting composting operations on floodplains or wet-
lands. In areas where no local or state regulations exist,
Section 404 of the Clean Water Act, administered by the
U.S. Army Corps of Engineers, regulates siting issues in
proximity to wetlands.
The composting site should have a water source for prop-
erly controlling the moisture content of the composting
process. The amount and source of the water to be sup-
plied depends on the nature of the compostables, the
composting technology used, the size of the operation,
and the climate. For example, dry leaves generally require
20 gallons of water per cubic yard of leaves (Richard et al.,
1990). Feedstocks with high moisture content (e.g., food
scraps) will require less water (see Chapter 2).
Onsite water sources are needed for composting that re-
quires substantial water use. Possible sources include city
water hookups, stormwater retention facilities, and wells
or surface pumping from nearby lakes or streams. For
smaller sites or those requiring minimal amounts of water,
mobile water sources can be used. Potential sites should be
able to accommodate both the present and future water
requirements of the composting program.
Land Area Requirements
To operate efficiently, a composting facility must allot
sufficient space to the preprocessing, processing, and
postprocessing compost stages as well as to the
surrounding buffer zone. Typically, the bulk of the site
will be occupied by the composting pad and the buffer
zone. (The size of the composting pad and buffer zone
59
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Facility Siting and Design
are discussed in more detail later in this chapter.) Admin-
istrative operations and equipment also need to be housed
on site and should be planned for when determining land
area requirements for the facility.
Communities should be careful not to locate a facility on
too small a site as this can decrease plant efficiency and in-
crease operational costs. The land area of a composting fi-
cility must be large enough to handle both present and
future projected volumes. Ideally a composting facility
should have, at a minimum, enough acreage to accommo-
date an entire year's projected volume of incoming feed-
stock on the site (Richard et al, 1990).
Other Factors Affecting Siting Decisions
Municipalities must consider a number of other factors
when siting a composting facility. These factors include
The existing infrastructure - The presence of
existing utiliy hookups, storage space, and paved
access roads could significantly reduce costs of site
preparation.
Zoning issues - Themconstruction of composting facili-
ties is permitted only on certain tracts of land within
a community as dictated by local zoning laws.
Site ownership - Potential sites could be owned by a
public or private entity ownership will affect cost
and control of the composting facility.
Nearby land uses - Sites near schools or residential
areas could provoke objections from citizens con-
cerned about potential odor or noise.
Design
Once a site has been identified, a facility must be designed
to meet the community's composting needs. It is a good
idea to visit other composting facilities to view different
designs and operations first-hand. (Figures 5-2 and 5-3 il-
lustrate sample composting site designs.) When develop-
ing the initial facility design, future expansion possibilities
should be considered in the configuration. Different
scenarios should be developed to account for feedstock
type and volume changes, facility modifications, system
alterations, and other potential revisions in facility design
or capability (CC, 1991).
The following are critical to the design of a facility
Preprocessing area
Processing area
Postprocessing area
Buffer zone
Access and onsite roads
Site facilities and security
Preprocessing Area
A preprocessing or staging area offers room to receive col-
lected feedstock and sort or separate materials as needed.
Receiving materials in a preprocessing area will eliminate
the need for delivery trucks to unload directly into wind-
rows in poor weather conditions. The size and design of
the preprocessing area depends on the amount of incom-
ing materials and the way the materials are collected and
sorted (see Chapters 3 and 4). Some facilities also find it
advantageous to use a staging area to store separated mate-
rials and to wet and hold the materials briefly to prepare
them for windrow formation.
The tipping area (the part of the preprocessing area where
incoming feedstocks are unloaded) is often roofed in areas
subject to severe weather conditions. The floor should be
strong enough to support collection vehicles and
hardened to withstand the scraping of equipment such as
front-end loaders. The tipping floor also should contain
no pits, which can attract vermin. Concrete floor slabs
and pushwalls to run the front-end loaders against when
scooping MSW will increase the efficiency of the opera-
tion. The minimum ceiling height of an enclosed tipping
area depends on the clearances that the various types of
hauling vehicles require to discharge their MSW The tip-
ping floor area should allow a minimum maneuvering dis-
tance of no less than one-and-a-half times the length of
the delivery vehicle.
The preprocessing area is also frequently used to shred the
compostable material or separate the bags in which the
feedstock has been collected. The size of this area depends
on the volume of material that the site handles and the so-
phistication of the system design. For example, the re-
quired floor area for a simple system consisting of infeed
and discharge conveyors, a single shredder, and a trommel
is approximately one-half of that required for a more
complex system that also includes vibratory screens, a
preshredding flail mill, and postprocessing equipment. A
composting site that will sort out recyclable from the
MSW received will require additional space and contain-
ers for holding these materials.
Some composting facilities use a truck weigh scale to keep
track of the weight of feedstock being hauled into the facility
as well as the amount of finished compost produced and dis-
tributed. Weigh scales of varying lengths can be purchased to
accommodate large vehicles. Designed to operate under a
variety of weather conditions, they often are located out-
doors on the entrance roadway. A scale should be used unless
the composting operation is very small.
Processing Area
The processing area, composed of the composting pad
and the curing area, must be carefuly designed for effi
cient composting. Design specifications for this area will
60
-------
Facility Siting and Design
BUFFER
ZONE
Staging Area
Gais
X«{<(KW<&((<.;»'. ''(
bWfoWWKWfiW
ltiH( and bcrai
canprovfct**
vlMMl and sound
barrtor
Surteo*
Water
(not to scale)
Direction of slope
m
Source: Richard et al,
Figure 5-3. Compost facility site layout.
61
-------
Facility Siting and Design
differ considerably depending on whether the composting
facility processes yard trimming or MSW feedstocks.
The composting pad surface in a yard trimmings com-
posting facility does not have to be paved; however, it
must be firm and absorbent enough to prevent pending
around the windrows or erosion from runoff. Grading the
surface of the pad to meet the optimal slope also will help
prevent erosion by allowing for gentle drainage. Mainte-
nance of the composting site should include annual re-
grading to preserve this slope. As a further protection
against erosion, windrows should be arranged parallel to
the grade to allow runoff to flow between the piles instead
of through them (Richard et al, 1990; Mielke et al,
1989). Precipitation moving onto the composting pads
can be diverted from compost piles through the use of
drains and conduits. Adequate drainage at composing
facilities is essential. Poor site drainage leads to pending of
water, saturated composting materials, muddy and unsightly
site conditions, bad odors, and excessive runoff and leachate
from the site (Rynketal, 1992).
Some states have additional requirements for the process-
ing area. For example, to minimize leachate from migrat-
ing into subsurface soils, ground water, or surface water,
Minnesota requires MSW composting operations to be
placed on liners made of synthetic materials, such as high
density polyethylene plastics, or natural soils, such as clay.
Soil liners must beat least 2 feet thick and compacted to
achieve a permeability of no greater than 1 x 10-7 centi-
meters per second (WDOE and EPA, 1991). Minnesota
regulations also require that MSW composting facilities
be designed to collect and treat leachate. The preferred
method is to collect, pump, and haul the leachate to the
municipal wastewater treatment plant if the plant accepts
the leachate. Iowa regulations require composting facilities
to use an impervious composting pad with a permeability
coefficient of 1 x 10'centimeters per second (WDOE
and EPA, 199 1). Florida regulations require MSW com-
posting facilities to conduct their composing operations
on surfaces such as concrete and asphalt. They also require
a leachate collection system. Municipalities should check
with their state to be sure composting pad designs comply
with existing guidelines (see Chapter 7).
The size of the composting pad depends primarily on the
amount of material that the facility receives for compost-
ing and the level of technology that will be used. The re-
quired area also depends on the characteristics of the
feedstock; the initial and final density of the composting
material and the moisture content will affect the amount
of material that will fit on the pad. The windrow turning
equipment influences aisle width, which in turn influ-
ences the size of the composting pad (see Chapter 4). A
common design is to line the windrows in pairs 5 feet
apart with 15-foot aisles between each pair. This method
uses space efficiently but is only possible when straddle-
type turning equipment is available (Mielke et al., 1989).
Operations that use a front-end loader to turn the mate-
rial require individual rows and aisles between the wind-
rows of 15 to 20 feet. Some composting pad areas are
housed under structures with movable side walls. In dry
climates, where water is scarce or expensive, a roof over
the composting area reduces evaporation and process
water requirements. In areas of high precipitation, a roof
prevents overly wet compost and anaerobic conditions
from developing. In regions that experience severe win-
ters, all or part of the composting area can be located
within a heated or insulated building to avoid arresting
the biological process due to freezing. Because the com-
posting process requires the use of moisture and enclosed
composting operations can create extremely damp condi-
tions, wood structures are not recommended unless they
are well treated to withstand high moisture levels.
Proper ventilation is required in enclosed preprocessing and
processing areas because the air within the structure can be a
source of bioaerosols, odors, dust, and excess moisture. Air
filters can be used to clean the exhaust air. Biofilters can be
used to absorb odor-producing compounds (see Chapter 4).
Adequate vents situated over preprocessing equipment can
reduce dust and odors, and fires can be used to help disperse
nonpervasive odors in the facility
A curing and also should be part of the design of the
processing site. This area is used to hold the compost for
the last phase of the composting process, to allow the ma-
terial to stabilize and mol. The space requirement for cur-
ing is based upon the amount of organic material
composted, the pile height and spacing and the length of
time that the compost is cured (Rynk et al., 1992). Locat-
ing this operation is less problematic than finding a suit-
able site for the composting pad provided that the
composting process has been carried out properly. If this is
the ease, the material should be fairly stable and many of the
runoff, ground-water contamination, and other siting con-
cerns are mitigated. In addition, the curing area needs less
space, requiring only about one quarter of the area of the
compost pad (Richard et al., 1990 UConn CES, 1989).
Postprocessing Area
A postprocessing area at composting facilities can be used
to conduct quality control testing of compost to perform
screening, size reduction, and blending operations; to
compost in preparation for market; and to store the com-
post. A space about one- fifth the area of the composting
pad is sufficient (Richard et al., 1990).
If the finished compost will not be delivered to the end
user within a relatively short period of time, the compost
should be covered. Otherwise, winds can transport weed
seeds into the piles, which can support the growth of un-
wanted plants and devalue the product. Backup storage
and disposal capacity also should be planned for seasonal
markets. Cured compost should be stored away from sur-
face water and drainage paths. A storage capacity of at
62
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Facility Siting and Design
least 3 months should be incorporated into site designs
for composting Facilities. Cured compost, which is a
source of odors in some meteorological conditions, might
be better stored away from the site.
Buffer Zone
The buffer zone frequently needs to be several times the
size of the composting pad, particularly when the com-
posting operation is adjacent to residential areas or busi-
nesses. Enclosed or higher technology facilities might
require less of a buffer zone, since many of the operations
are by design closely controlled and contained.
During site design, the direction of the prevailing wind (if
one exists) should be noted and the buffer zone extended
in this direction. This will help minimize the transport of
odor and bioaerosols downwind of the facility Figure 5-4
shows a sample buffer zone design.
In general, the larger the buffer zone, the greater the ac-
ceptance of the facility among residents. The buffer zone
required by a composting facility depends largely on the
type of feedstock being composted and the level of tech-
nology (in terms of monitoring and odor control) em-
ployed at the facility. State and local regulations frequently
require minimal buffer zone sizes or specify the distances
that composting operations must be from property lines,
residences, or adjacent businesses and from surface water
or water supplies (see Chapter 7).
New Jersey regulations recommend a buffer zone for leaf
composting facilities of 150 feet (high-level technology,
less than one-year cycle) to 1,000 feet (minimal technol-
ogy, two- to three-year cycles) (WDOE and EPA, 1991).
Buffer zone recommendations are wider in New Jersey
(from 150 to 1,500 feet) when grass is included in the
composting feedstock because of the greater potential for
odors. Iowa regulations require MSW composting facili-
ties to be located at least 500 feet from any habitable resi-
dence. Table 5-1 lists the minimal separation distances
allowed by the State of Wisconsin for facilities that com-
post yard trimmings or MSW.
Municipalities should check state and local regulations to
be sure all applicable guidelines are being incorporated
into their buffer zone design. Because odor problems can
force a multimillion dollar facility to shut down, commu-
nities might extend composting buffer zones beyond the
minimum required. (Other steps to control odors are dis-
cussed in Chapter 4.)
Access and Onsite Roads
The type and amount of traffic into and out of a facil-
ity should be considered in the design process. Traffic at
a site is largely dependent on the volume of materials
that flows through the facility and the type of collection
system in place. For example, operations that compost
municipal yard trimmings will involve intensive use of
SMMM
i Off 10
JP^^£
«Oi
Note: Depending on site constraints such as property
lines, buildings and surface water, available
acreage for composting will vary. Area loss
could oe significant.
Source UConn CES, 1989.
Figure 5-4. Site setback distances.
the roads during periods of peak collections. MSW com
posting operation, on the other hand, will usually receive a
more consistent schedule of deliveries. Although an extensive
onsite road network usually is not necessary, there should be
permanent roads leading to the tipping and storage areas.
These access roads should be graveled or paved to handle
large vehicles during adverse weather conditions. This surfac-
ing is expensive, however, and the resulting run-on and run-
off must be managed to prevent erosion.
If drop-off collections will occur at the facility, the design
should accommodate a greater flow of automobile and
light truck traffic. A circular traffic flow can accommodate
rapid deliveries, effectively reducing congestion. A
Table 5-1. Setback requirements for Wisconsin
composting facilities.
Navigable lake or pond
Navigable river or stream
Stale, federal, or interstate
highway or public park
boundary
Airport runway
Public or private water supply
well
Source: WDOE and EPA, 1991.
1,000 feet
300 feet
1,000 feet
1,000 feet
1,200 feet
63
-------
Facility Siting and Design
separate access road to the tipping area also can be con-
structed for these vehicles (Richard et al, 1990, Strom and
Finstein, 1989). Ideally the road used by the public to de-
liver materials or to pick up finished compost should be dif-
ferent from the heavy equipment access road. Roads should
also be designed to provide adequate turning and dumping
areas to accommodate delivery by all types of vehicles.
Site Facilities and Security
composting operations might require one or more build-
ings to house various site functions, from maintenance
and administrative work to personnel facilities. This is
true even for smaller operations such as sites that compost
yard trimmings, which might need only a small receiving
post. Site buildings should have, at a minimum, electric-
ity, heat, air conditioning a toilet, and drinking water. All
facilities should have a telephone or radio in case of emer-
gencies. In larger facilities (sites with a daily capacity
greater than 50 tons), a personnel area containing an of-
fice, shower, locker room, and lunch room might be ap-
propriate. A maintenance area that includes a workshop
and storage rooms to keep parts and other maintenance
materials also might be needed.
Access to the site must be controlled to prevent vandal-
ism, especially arson, and illegal dumping. At a mini-
mum, the access roads must be secured with a fence,
cable, locked gate, or other type of constructed barrier.
Usually the surrounding buffer zone will eliminate off-
road vehicular access, but if natural geographic barriers do
not exist, fencing the entire site might be necessary
Summary
Today municipalities face major challages when
attempting to site and design compost processing
facilities. When developing a composting facility
municipalities must consider a number of factor in-
eluding location, topography zoning laws, land
availability and ownership. The facility needs to be
designed to accommodate both current and projected
operations. To ensure that the facility is well sited
and designed input should be sought regarding the
technical and economic aspects of a composting sys-
tem from a range of specialists including engineers,
biologists, system managers, and equipment suppliers.
Municipalities also must accommodate the needs of
local residents throughout the siting and design proc-
ess to ensure the construction of a facility that the
whole community will find acceptable. Community
involvement is critical since one of the major factors
in the shutdown of many composting operations has
been complaints from neighboring household and
businesses about odors.
Chapter Five Resources
Albrecht, R. 1992. National Solid Waste Management As-
sociation (NSWMA). Seminar on composting. Ft. Lau-
derdale, FL. November 19-20.
Appelhoff, M, and J. McNelly. 1988. Yard waste com-
posting Guidebook for Michigan communities. Lansing,
MI: Michigan Department of Natural Resources.
composting Council (CC). 1991. Compost facility plan-
ning guide. Washington, DC: composting Council.
Darcey, S. 1993. Communities put wet-dry separation to
the test. World Wastes. 36(98):52-57.
Mielke, G., A. Bonini, D. Havenar, and M. McCann.
1989. Management strategies for landscape waste. Spring-
field, IL: Illinois Department of Energy and Natural Re-
sources, Office of Solid Waste and Renewable Resources.
Richard, T., N. Dickson, and S. Rowland. 1990. Yard
waste management A planning guide for New York State.
Albany, NY: New York State Energy Research and Devel-
opment Authority, Cornell Cooperative Extension, and
New York State Department of Environmental
Conservation.
Rynk, R, et al. 1992. On-farm composting handbook.
Ithaca, NY: Cooperative Extension, Northeast Regional
Agricultural Engineering Service.
Strom, P., and M. Finstein. 1989. Leaf composting man-
ual for New Jersey municipalies. New Brunswick, NJ:
New Jersey Department of Environmental Protection, Di-
vision of Solid Wrote Management, Office of Recycling.
University of Connecticut Cooperative Extension Services
(UConn CES). 1989. Leaf composting A guide for mu-
nicipalities. Hartford, CT: State of Connecticut Depart-
ment of Environmental Protection, Local Assistance and
Program Coordination Unit, Recycling Program.
Washington Department of Ecology (WDOE) and U.S.
Environmental Protection Agency (EPA). 1991. Summary
matrix of state compost regulations and guidance.
Minneapolis, MN.
Walker, J. 1992. Control of composting odors. As cited in
Hoitink, H., and H. Keener, eds. Science and engineering
of composting An international symposium. Worthington,
OH: Renaissance Publications. March 27-29,1992, Colum-
bus, OH.
64
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Chapter Six
The Composting Process:
Environmental, Health,
and Safety Concerns
ome aspects of the composting process can pose potential environmental, health, and safety problems. Deci-
sion-makers must be aware of these possible complications before proceeding with composting facility plan-
ning so that measures can be taken to avert difficulties. This chapter will help official understand the
potential risks involved with composting. Over the past several yearn several composting facility closures have
occurred due to some of the problems mentioned in this chapter, particularly odor The firrst portion of this chapter
describes the possible environmental concerns associated with the composting process such as water and air pollu-
tion. The second section discusses potential worker health and safety issues. Potential environmental health, and
safety concerns associated with the compost product are discussed in Chapter 9.
Environmental Concerns During
composting
If not carefully controlled, the composting process can
create a number of environmental concerns including air
and water pollution, odor, noise, vectors, fires, and litter.
Many of these concerns can be minimized through the
proper design and operation of a facility. In addition, sim-
ple procedures often can be implemented to reduce the
impact of the facility on the environment.
Water Quality
Water pollution from leachate or runoff is a potential con-
cern at composting facilities. Leachate is liquid that has
percolated through the compost pile and that contains ext-
racted, dissolved, or suspended material from the pile. If
allowed to run untreated and unchecked from the com-
posting pile, leachate can seep into and pollute ground
water and surface water. Runoff is water that flows over
surfaces without being absorbed. Contaminated runoff
from composting sites can be a problem (particularly at
MSW composting facilities) in areas with high rainfall or
during periods of heavy rain. Both runoff and leachate
also can collect in pools around the facility, producing
odor problems. In addition, runoff can cause erosion.
There are many ways to prevent and control leachate and
runoff at composting operations, as described in the fol-
lowing sections.
Leachate
Leachate from the composting of yard trimmings can
have elevated biochemical oxygen demand (BOD) and
phenols, resulting from the natural decomposition of or-
ganic materials. High BOD depletes the dissolved oygen
of lakes and streams, potentially harming fish and other
aquatic life. Naturally occurring phenols are nontoxic but
can affect the taste and odor of water supplies if they
reach surface water reservoirs. Natural phenols and BOD
do not appear to pose a problem to ground water sup-
plies, however, as they are substantially reduced by soil bi-
ota through degradation processes (Richard and Chadsey,
1990). Table 6-1 shows elevated levels of phenols and
high BOD in leachate from a leaf composting facility in
Croton Point, New York.
Another potential water contamination problem at facili-
ties that compost yard trimmings is nitrate generation
caused by composting grass clippings along with leaves.
Because grass clippings have a low carbon to nitrogen
(C:N) ratio, an initial burst of microbial activity depletes
oxygen in the composting pile before the grass is
completely composted. The lack of oxygen causes aerobic
65
-------
The Composting Process: Environmental, Health, and Safety Concerns
Table 6-1. Croton Point, New York, Yard trimmings
compost leachate composition.
Compost Leachate (16 samples)
cd
Cu
Ni
Cr
Zn
Al
Fe
Pb
K
NH4-N
NO3-N
NOrN
Phosphorus
Phenols (total)
COD
BOD
pH
Color
Odor
Avarage
(mg/L)
ND
ND
ND
ND
0.11
0.33
0.57
0.01
2.70
0.44
0.96
0.02
0.07
0.18
56.33
>41a
7.75
ND
ND
Standard
Deviation (mg/L)
0.13
0.38
0.78
0.02
0.99
0.35
1.00
0.02
0.08
0.45
371.22
>60
0.36
Includes 3 samples above detection limit of 150 mg/L.
ND - Not Determined.
COD - Chemical Oxygen Demand.
Source: Richard and Chadsey,1990.
microorganisms to die, releasing nitrates in their cells.
One way to avoid nitrate generation is to monitor the
C:N ratio, adjusting the feedstock to keep it at optimum
levels (see Chapters 2 and 4). At the Croton Point facility
(Table 6-1), nitrates were not a problem because grass was
not included in the feedstock. Grass clippings can be
composted successfully, however, if appropriate material
mix ratios, methodology, and equipment are used. In a 3-
year study conducted in Massachusetts, very little leaching
of nitrate was noted from windrows consisting of one part
grass to three parts leaves. Leaching did occur, however,
when windrows consisting of grass and leaves in ratios of
(or higher than) one part grass to two part leaves were
subjected to heavy precipitation or watering (Fulford et
al, 1992).
Leachate from yard trimmings and MSW composting
operations can also contain potentially toxic synthetic
compounds, including polychlorinated biphenyls (PCBS)
from treated wood; chlordane, a pesticide and polycyclic
aromatic hydrocarbons (PAHs), combustion products of
gasoline, oil, and coal. PCBS and chlordane are resistant
to biodegradation and so generally are not broken down
during the composting process (Gillett, 1992). While mi-
croorganisms can degrade PAHs during the composting
process, the compounds formed as a result of this process
can be more toxic than the original PAHs (Chancy and
Ryan, 1992; Menzer, 1991). Monitoring incoming feed-
stock to remove pesticide containers and other foreign
materials can help reduce the occurrence of synthetic
chemicals in leachate.
Leachate generation can be reduced or prevented by
monitoring and correcting the moisture levels in the com-
posting pile. In addition, the windrows or piles can be
placed under a roof to prevent excessive moisture levels
due to precipitation. If the composting materials contain
excess moisture, leachate will be released during the first
few days of composting even without added moisture or
precipitation. Following this initial release of leachate, the
amount of leachate formed will decrease as the compost
product matures and develops a greater capacity to hold
water.
The age of the pile also affects the composition of
leaehate. As the pile matures, microorganisms break down
complex compounds and consume carbon and nitrogen.
If the C:N ratio is maintained within the desired range,
little excess nitrogen will leach from the pile since the mi-
croorganisms will use this element for growth. A study
conducted by Cornell University researchers supports this
theory (Rymshaw et al., 1992). Table 6-2 summarizes the
results of the one portion of the Cornell study in which
water was added to columns of manure-bulking agents
and the leachates tested for nitrogen content. The leachate
produced from 19 weeks of composting and longer was
much lower in total nitrogen content than it was in the
begining of the study. Table 6-3 shows concentrations of
nitrogen from leachate collected under an actual compost-
ing windrow of manure and sawdust. This portion of the
study shows an initial peak of nitrogen concentration fol-
lowed by a subsequent decrease over time. Therefore, as il-
lustrated by this study the older the composting pile, the
less nitrogen will leach from the pile.
Many composting Facilities use a concrete pad to collect
and control any leaehate that is produced (see Chapter 5).
The primary task here is to watch the edges, catching any
leachate before it leaves the pad. The simplest way to han-
dle leachate is to collect the water and reintroduce it into
the compost pile. This should not be done once the com-
posting materials have passed the high-temperature phase,
however, as any harmful microorganisms that were inacti-
vated by the high heat can be reintroduced with the
leaehate (CC, 1991).
66
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The Composting Process: Environmental, Health, and Safety Concerns
Excess amounts of leachate beyond the moisture needs of
the composting facility can be transported to a municipal
wastewater treatment plant if the plant will accept them.
If the plant indicates that the contaminant levels in the
leachate are too high, an onsite wastewater pretreatment
system might be needed. If leachate is stored, treated on
site, or discharged to a municipal wastewater treatment
facility, facility operators must comply with federal, state,
and local requirements such as regulations covering stor-
age, pretreatment, and discharge permits. It is unlikely
that pretreatment will be necessary, however, if the feed-
stock is monitored carefully. Measures to control leachate
include
Diverting leachate from the compost curing and
storage areas to a leachate holding area.
Installing liner systems made of low-permeability
soils such as clay or synthetic materials.
Using liners under drain pipes to collect the
leachate for treatment.
Curing and storing compost indoors to eliminate
infiltration of leachate into the ground (With,
1989).
Table 6-2. A summary of column study concentrations.
i/l
Nitrate
Ammonia
Organic Nitrogen
Total Nitrogen
Total Organic Garbon
% Water Retained
Chip/Newspaper
Initial/Final
0.0/13.0
239.4/1 1.2
975.4/17.5
1,1 96.8/28.7
1,780.8/1,318.1
92.00/85.00
straw
Initial/Final
0.0/526.0
293.1 /17.5
702.6/25.9
995.7/45.4
829.1/1,201.6
6.67/70.00
Sawdust
Initial/Final
7.0/134.0
800.8/8.71
747,3/71.0
1,548.2/79.7
1^43.8/995.4
781.00/71.25
Laboratory experiment used 10-inch diameter, 24-inch deep columns of manure-bulking agent (woodchips and newpaper, straw, or sawdust) to which
water was added. Volumes of water applied corresponded to 2.1 to 12.4 cm of rainfall. Samples were collected from the bottom of the columns over 20
weeks, 21 week, or 19 weeks (for chips/newspaper, straw, and sawdust, respectively.
Source: Rymshaw et al., 1992.
Table 6-3. A summary of windrow leaehate concentrations.
Weeks
1.0
1.5
2.0
2.5
3,0
5.0
8.0
8.5
N03
10.00
13.00
10.50
9.00
15.00
3.00
3.00
4.00
NH4
28.35
12.95
21.00
25.20
8.40
29.80
39.91
14.84
I
Organic
Nitrogen
109.90
115.50
105.00
86.80
134,40
32.20
58.80
A
Total
Nitrogen P04
138.25
128.45
126.00
112.00
142.80
62.00
39.91 75.90
73.64 50.80
Total Organic
Carbon
8,743.71
9,384.00
6,258,96
5,372.81
14,174.92
3,715.66
2,459.63
Leachate was collected from under a composting windrow of manure and sawdust.
Source: Rymshaw et al., 1992.
67
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The Composting Process: Environmental, Health, and Safety Concerns
Runoff
Runoff can be caused both by heavy precipitation and by
the many aspects of the composting process that use
water. For example, the water used to wash trucks and sta-
tionary machinery can contribute to runoff. Highly pol-
luted water can be spilled in the tipping area of MSW
composting facilities when packer trucks and compaction
boxes from restaurants, grocery stores, and food processors
are emptied. While MSW facilities are more prone to pol-
luted runoff problems, operations that are composting
yard trimmings can also produce runoff containing small
quantities of heavy metals, pesticides, and inorganic
nutrients.
For both yard trimmings composting facilities and MSW
composting facilities, water that has come into contact
with incoming raw materials, partially processed materi-
als, or compost should not be allowed to run off the site.
Figure 6-1 shows several options for diverting water from
composting windrows and for containing runoff from the
piles. The facility design must include provisions for iso-
lating, collecting, treating and/or disposing of water that
has come in contact with the composting feedstock. These
provisions can include:
Maintaining sealed paving materials in all areas.
Grading facility areas (1 to 2 percent grade) where
contaminated water will be collected.
Erecting containment barriers or curbing to pre-
vent contaminated water from coming in contact
with adjacent land areas and waterways.
Covering processing areas (composting beds and
compost product processing areas).
Percolating contaminated water through soil so as
to absorb and break down organic compounds.
Creating detention ponds to prevent the discharge
of runoff to surface water.
If runoff contains significant amounts of solids (often the
case for truck or floor wash-down water), screening, set-
tling, or skimming might be necessary. If runoff is stored,
treated on site, or discharged to a municipal wastewater
treatment facility, facility operators must comply with fed-
eral, state, and local requirements such as regulations cov-
ering storage, pretreatment, and discharge permits.
Because runoff can contribute to soil erosion at and
around a facility, some simple steps can be taken to avoid
soil loss:
Choosing erosion control measures that are appro-
priate for the given soil type more stringent meas-
ures are needed for less permeable soil.
Avoiding sites with steep slopes.
Grading the site properly (see Chapter 5).
Minimizing the disruption of existing surfaces and
retaining as much vegetation as possible when clear-
ing the site.
Using proper fill and compaction procedures.
Prompt seeding and mulching of exposed areas.
Using erosion screens and hay or straw bales along
slopes.
Using grass filter strips to intercept the horizontal
flow of runoff When runoff passes through the
grass strip, pollutants usually settle out of the water
or are physically filtered and adsorbed onto the
grass.
Run-On/Ponding
Run-on also can be a problem at yard trimmings and
MSW composting facilities if the water enters the facility
during storms. The site should have a slight slope with
windrow piles oriented parallel to the slope to prevent
pending of rainwater among compost piles (Walsh et al,
1990). (See Chapter 5 for more guidance concerning sit-
ing and site design.) Pending or pooling of water on the
site also can be a problem if the composting piles rest on a
soft suface. Loaders can dig up the dirt base with the
piles as they are turned, forming pits that allow water to
stand. To remedy this, new fill (e.g., soil, sand, or gravel)
should be brought in to replace the excavated material.
Equipment that is operated in mud also can create ruts in
which pending can occur. Avoiding work during wet con-
ditions can prevent this problem, although the best way is
to compost on paved surfaces.
Air Quality
In general, air pollution is not a major concern at com-
posting facilities, with the exception of the odor problems
discussed in the next section. Minor problems could arise,
however, from vehicle traffic. The amount of air pollution
from vehicle emissions can be reduced by organizing
drop-off points to minimize queuing or by restricting
feedstock delivery to compaction trucks. Finally any mo-
bile equipment used at the facility should be well main-
tained to keep it operating cleanly.
Dust can frequently be a problem at composting facilities,
particularly in the dry summer months. Dust is generated
from dry, uncontained organic materials, especially during
screening and shredding operations, and from vehicle traf-
fic over unimproved surfaces. Dust from composting op-
erations can clog equipment, and carries bacteria and
fungi that can affect workers at the facility (see Occupa-
tional Health and Safety Concerns During composting
on page 71). As long as there is an adequate buffer zone
around the facility, however, residents near the Facility
68
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A
/
Runoff diversion
channel
Compacted sand
or gravel pad
(6 inches minimum)
Composting pad cross section
Runoff diversion
channel
paH mn/\ff *rM***.nr.
Pad length and windrow/pile length Pad runoff collection
2-4% slope _ channel*
Possible holding pond
View through the composting pad length
(a) Interceptor trench
Clean runoff
Sub-Surface drain
leading to open surface
outlet away from pad
As needed
Diversion terrace
(dike and channel)
(b) Dike
Composting pad
Source: Rynk et al., 1992.
(c) Diversion channel i-to 3-foot depth
I
'width determined
by runoff volume
69
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The Composting Process: Environmental, Health, and Safety Concerns
generally will not be affected by dust (Lembke and Knise-
ley 1980), and environmental effects are not likely. Meth-
ods for controlling dust on site are discussed later in this
chapter.
Odor
As discussed elsewhere in this manual, odor is a significant
concern. Many stages in the composting process can re-
lease odors. The feedstock can contain odorous com-
pounds; odors can be produced during collection,
transport, and storage of the feedstock or discards; and
improper composting procedures can encourage the for-
mation of odorous compounds (Kissel et al, 1992). An-
aerobic conditions encourage generation of odorous
compounds like organic acids, mercaptans, alcohols,
amines, and hydrogen sulfide gas, and other odorous
sulfur compounds (Williams and Miller, 1992a; Diaz,
1987). Ammonia can be released under anaerobic con-
ditions and aerobic conditions if the C:N ratio is less
than 201 (Kissel et al., 1992). The compounds thought
to be responsible for odors at composting facilities are
listed in Table 6-4. Chapter 4 discusses process and en-
gineering controls for reducing nuisance odors.
Table 6-4.
Compounds either specifically idc
implicated in composting odors.
identified or
Sulfur Compounds
Hydrogen Sulfide
Carbon Oxysulfide
Carbon Disulfide
Dimethyl Sulfide
Dimethyl Disulfide
Dimethyl Trisulfide
Methanethiol
Ethanethiol
Ammonia and Hitrogon-Containing Compounds
Ammonia Trimethytamine
Aminomethane . 3-methylindole (skatole)
Dimethylamine
Volatile Fatty Acids
Methanoic (formic) Butanoic (butyric)
Bhanoic (acetic) Pentanoic (valeric)
Propanoic (propionic) 3-methylbutanok (isovaleric)
Ketones
Propanone (acetone) 2-pentanone (MPK)
Butanone (MEK)
Other Compounds
Benzotfiiozole Phenol
Ethanal (ocetaldehyde)
Source: Williams and Miller, 1992a,
Noise
Noise is generated by trucks entering and leaving a
composting facility and by equipment used in compost-
ing operations. Hammermills and other shred-
ding/grinding machines are the noisiest of this
equipment, generating about 90 decibels at the source.
Many states have noise control regulations that limit
noise at the property line.
Measures that can reduce noise emanating from the facil-
ity include
Providing an adequate buffer zone around the Facil-
ity with plenty of trees.
Including specifications for noise-reducing design
features, such as mufflers and noise hoods, when
procuring equipment.
Properly maintaining mufflers and other equip-
ment components.
Coordinating hours of operation with adjacent
land uses.
Taking steps to limit traffic to and from the facility
(see "Controlling Air Pollution").
These measures will not always protect workers from ex-
posure to excessive noise on site, however. Further noise
control methods are described below under "Occupa-
tional Health and Safety."
Vectors
Vectors are small animals or insects that can carry diseases.
Mice, rats, files, and mosquitoes are potential visitors to
facilities that compost yard trimmings and/or MSW. Ro-
dents can be attracted by the food and shelter available at
composting facilities (particularly MSW composting op-
erations) and can be difficult to eliminate. Where proper
operating procedures do not control rodents, the help of a
professional exterminator might be required.
Flies, which can transmit salmonella and other food-borne
diseases, are often carried in with the incoming material and
are attracted to windrows that have become anaerobic. Re-
search has shown that all life stages of the housefly are killed
by the temperatures reached in the comparing pile
(Golueke, 1977). Mosquitoes, which can transmit disease,
breed in standing water. Insects can be controlled by keeping
the processing area neat, maintaining aerobic conditions and
proper temperatures in the windrows, and grading the area
properly to prevent pending.
Fires
If the compost material dries out and becomes too hot,
there is a potential for spontaneous combustion to occur
at composting facilities. Organic material can ignite
spontaneously at a moisture content of between 25 and
70
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The Composting Process: Environmental, Health, and Safety Concerns
45 percent. This is unlikely however, unless the material
reaches temperatures higher than 93°C (199°F), which
typically requires a pile over 4 meters high. Keeping the
windrows about 3 meters high and turning the compost
when temperatures exceed GOT ( 140°F) will prevent
fires. In addition to these precautions, the site must be de-
signed for access by firefighting equipment, including
clear aisles among windrows, and must have an adequate
water supply (see Chapter 5) (Richard et al, 1990).
Other steps that can reduce the risk of fire include pre-
venting accumulation of dust produced by shredding op-
erations and preventing in-vessel composting systems
from becoming too dry. Adequate site security is necessary
to ensure that composting sites do not become a target for
arson. Site security will also ensure that the facility does
not become a dumping ground for used oil, appliances, or
other unacceptable materials.
Litter
Littter from the composting facility can be a source of
complaints from nearby residents. Litter can come from
yard trimmings and MSW brought to the facility in open
loads, plastic and paper blowing from windrows, and re-
jects (such as plastic) blowing away during screening. Lit-
ter can be controlled by:
Requiring loads of incoming material to be covered.
Using movable fencing or chain link fences along
the site perimeter as wind breaks and to facilitate
collection of litter.
Enclosing receiving, processing, and finishing
operations.
Collecting litter as soon as possible before it
becomes scattered off site.
Removing plastic bags before windrowing or
collecting in paper bags, in plastic bins, or in bulk
(for leaves and woody materials) (Wirth, 1989).
Occupational Health and Safety
Concerns During composting
Potential health and safety problems at facilities for com-
posting yard trimmings and MSW include exposure to
bioaerosols, potential toxic chemicals, and other sub-
stances. Excessive noise and injuries from equipment used
at the facility also can be concerns. These problems can be
minimized by proper siting, design, and operation of the
facility and by adequate worker training and education.
Additional information about recognizing and controlling
job risks can be obtained from Occupational Safety and
Health Administration (OSHA) regional offices or from
state agencies responsible for occupational health and
safety.
Bioaerosols
A variety of biological aerosols (bioaerosols) can be gener-
ated during composting. Bioaerosols are suspensions of
particles in the air consisting partially or wholly of micro-
organisms. These microorganisms can remain suspended
in the air for long periods of time, retaining viability or
infectivity. The bioaerosols of concern during composting
include actinomycetes, bacteria, viruses, molds, and fungi.
Aspertgillus fumigatus is a very common fungus that is
naturally present in decaying organic matter. The spores
of this fungus can be inhaled or can enter the body
through cuts and abrasions in the skin. The fungus is not
considered a hazard to healthy individuals. In susceptible
individuals, however, it can inhabit the lungs and produce
fungal infections. Conditions that predispose individuals
to infection by Aspergillus fumigatus or other molds and
fungi include a weakened immune system, allergies,
asthma, diabetes, tuberculosis, a punctured eardrum, the
use of some medications such as antibiotics and adrenal
cortical hormones, kidney transplants, leukemia, and lym-
phoma (Epstein and Epstein, 1989; Wirth, 1989; USDA
and EPA, 1980). Effects due to Aspergillus fumigatus expo-
sure are hard to predict because infection depends on
worker susceptibility.
Aspergillus fumigatus often colonizes the incoming mate-
rial at both yard trimmings and MSW composting facili-
ties, and is readily dispersed from dry and dusty compost
piles during and after mechanical agitation. The levels of
Aspergillus fumigatus decrease rapidly only a short distance
from the source or a short time after activity stops
(Epstein and Epstein, 1989). Table 6-5 shows levels of
Aspergillsu fumigatus in different areas of a biosolids com-
posting facility in Windsor, Ontario. While these data are
not from yard trimmings or MSW composting facilities,
Table 6-5. Levels of Aspergillus fumigatus at a sewage
biosolids composting facility.
Location
Mix Area
Near Tear Down Pile
Compost Pile
Front-End Loader Operations
Periphery of Compost Site
Centrifuge Operating Room
Grit Building
Pump House
Background Level
CPU = Colony-forming units,
Source: Epstein and Epstein, 198
Concentration
(CFU/m2)
notoi20
8 to 24
12to15
11 to 79
2
38 to 75
2
10
2
71
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The Composting Process: Environmental, Health, and Safety Concerns
they do demonstrate the direct relationship between fun-
gus levels and activity levels (Roderique and Roderique,
1990). Similar results have been seen in MSW compost-
ing plants in Sweden (Clark et al, 1983).
Another health concern at composting facilities is expo-
sure to endotoxins. Endotoxins are toxins produced
within a microorganism and released upon destruction of
the cell in which it is produced. They can be carried by
airborne dust particles. Table 6-6 shows the levels of endo-
toxins in composts from various sources (Epstein and Ep-
stein, 1989). The levels of endotoxins in the air at one
yard trimmings composting facility ranged from 0.001 to
0.014 mg/m3 (Roderique and Roderique, 1990).
Because bioaerosols and endotoxins are both carried as
dust, dust control measures should be incorporated into
the design and operation of the facility. These measures
help control worker exposure to and reduce the the risk of
disease from these airborne hazards. Several steps can be
taken to minimize dust generation at the Facility
Keeping compost and feedstock moist.
Moistening compost during the final pile tear-
down and before being loaded onto vehicles, taking
care not to over wet the material, which can pro-
duce leachate or runoff.
constructing driving surfaces from asphalt or con-
crete (or water can be applied to roadways to mini-
mize dust) (Roderique and Roderique, 1990).
Minimizing dust from enclosed operations through
engineering controls such as collection hoods, nega-
tive air pressure at dust generation points, and bag-
house technology. These controls, however, tend to
be expensive.
Isolating workers from spore-dispersing compo-
nents of the composting process such as mechani-
cal turning (for example, using tractors or
front-end loaders with enclosed air-conditioned or
heated cabs).
Table 6-6. Comparison of endotoxin levels in composts
from Various sources.
Source
Biosolids Compost
Cattle Manure Compost
Sheep Manure Comport
leaf Compost
Levels ng/g)
3.9-6.3
2.3
4.9
4.5
Using aeration systems instead of mechanical
turning.
In addition to these control measures, workers should be in-
formed that disease-producing microorganisms are present
in the composting environment and that, although the risk
of infection is low in healthy individuals, the following pre-
cautions should be adhered to for personal protection
Workers should wear dust masks or respirators un-
der dry and dusty conditions, especially when the
compost is being turned (charcoal-filled respirators
also reduce odor perception).
Uniforms should be provided to employees, and
workers should be instructed to wash hands before
meals and breaks and at the end of the work shift.
Shower facilities should be available, and clean
clothing and shoes should be worn home by each
employee.
Cuts and bruises should receive prompt attention
to prevent contact with the incoming loads or
feedstock.
If the facility is enclosed, proper ventilation i
required.
is
Souce: Epstein and Epstein, 1989.
Individuals with asthma, diabetes, or suppressed immune
systems should be advised not to work at a composting fa-
cility because of their greater risk of infection.
Potentially Toxic Chemicals
Some volatile organic compounds (VOCs), such as ben-
zene, chloroform, and trichloroethylene can present po-
tential risks to workers at MSW composting facilities
(Gillett, 1992). Certain solvents, paints, and cleaners con-
tain VOCs. The combination of forced aeration (or peri-
odic turning in the ease of window systems) and elevated
temperatures can drive VOCs from the composting mate-
rial into the surrounding atmosphere, much as the aera-
tion and heating of activated biosolids does. Workers are
more likely than compost users to be exposed to VOCs.
Modeling suggests that this is because most of the VOCS
in the feedstock should volatilize from mechanically aer-
ated composting piles within 1 or 2 days (Kissel et al.,
1992). To avoid worker exposure to VOCs in enclosed
spaces, adequate ventilation is required. Control technolo-
gies developed for odor control also apply to VOC con-
trol. While misting scrubbers have been used to control
VOCs (Li and Karrell, 1990), biofilter design for remov-
ing VOCs is not fully developed, however (Kissel et al.,
1992). The best method of controlling VOC emissions is
to limit their presence in the feedstock. Limiting MSW
composting to residential and high-quality commercial
feedstocks, instituting source separation, and implement-
72
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The Composting Process: Environmental, Health, and Safety Concerns
ing effective household hazardous waste collection and
education programs can minimize the amount of VOCs
in MSW (see Chapter 3).
More persistent organic compounds also pose a potential
threat to workers. Workers can be exposed to polychlori-
nated biphenyls (PCBs), dioxins, pesticides, and polyaro-
matic hydrocarbons (PAHs) from the composting
feedstock and compost itself, although the extent of expo-
sure varies and is hard to determine (Gillett, 1992). Ef-
fects on worker health have not been observed from
exposure to metals during composing or from the fin-
ished compost itself Mozzon et al. (1987) found that air-
borne lead and cadmium concentrations were below levels
of concern at MSW processing sites (less than 0.003
mg/m3. Gillett (1992) suggests that compared to work-
ers' exposure to metals in polluted air and food, exposure
to metals in compost can be insignificant.
Noise Control
The best way to prevent health effects from excessive
noise is to use engineering controls that reduce worker ex-
posure to noise. Regional OSHA offices can provide in-
formation to workers and employers regarding sources
and control of noise. To prevent hearing loss, workplace
noise levels should not exceed 85 decibels (dB). Table 6-7
shows that noise levels in some areas of yard trimmings or
MSW composting facilities can exceed 85 decibels. Com-
posting equipment that creates excessive noise should be
avoided. It is often possible to purchase screening plants,
shredders, and other equipment that do not necessitate
the use of ear protection for workers (Appelhof and
McNelly 1988). Simple design control measures such as
lowering the height from which feedstock is dropped into
processors, rearranging machinery inside the facility, and
installing mufflers, can bring noise levels down. Hearing
protection should be provided until noisy equipment is
repaired or replaced.
Other Safety Concerns
Safe design and operation of equipment used at the com-
posting facility are essential. For example, specialized wind-
row turning equipment typically has mixing flails that rotate
at high speeds and must be well shielded from human con-
tact. Because stones and other objects can be thrown a long
distance from turning equipment, operators must ensure a
safe clearance around and behind this equipment. Devices
that prevent access to equipment undergoing servicing or
maintenance might be necessary since unexpected ignition
could cause injury to workers. The potential for shredder ex-
plosions is discussed in Chapter 4.
Table 6-7. Reported noise levels in resource
recovery plants.
location
Tipping Floor
Shredder Meed
Primary Shredder
Magnetic Separator
Secondary Shredder
Air Classifier Fan
Shop
Control Room
Offices
Maintenance Laborer
Shredder Operator
Noise Level
(dBA)
85-90
85-90
96-98
90-96
91-95
95-120
78
70
67
89
83
OSHA Hearing Conservation Requirements 85
OSHA 8-hr Standard 90
OSHA 4-hr Standard 95
dBA - A-weighted sound-pressure level.
Adapted from: Robinson, 1986.
Worker training is an essential part of ensuring a safe
workplace. The objectives of employee safety and health
training are
To make workers aware of potential hazards they
might encounter.
To provide the knowledge and skills needed to per-
form the work with minimal risk to health and
safety.
To make workers aware of the purpose and limita-
tions of safety equipment.
To ensure that workers can safely avoid or escape
from emergencies
Topics that should be covered in health and safety training
include the rights and responsibilities of workers under
OSHA and/or state regulations; identification of chemi-
cal, physial, and biological risks at the site; safe practices
and operating procedures; the role of engineering controls
and personal protective equipment in preventing injuries
and illnesses; procedures for reporting injuries and ill-
nesses; and procedures for responding to emergencies.
Worker Training
Chapter Six Resources
73
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The Composting Process: Environmental, Health, and Safety Concerns
Summary
Environmental and worker health and safety
^problems can arise during processing. Environ-
; mental problems during composting such as
water and air pollution, odor, noise, vectors, fires,
and litter can be prevented or minimized through
proper facility design and operation. Facility plan-
ners and managers must also take steps to ensure a
safe workplace by reducing potential exposure to
pathogens, hazardous substances in composting feed-
stock, and excessive noise; by ensuring that equip-
ment is design and maintained to prevent injuries;
and by providing worker training in safety and
health concerns.
Appelhof, M., and J. McNelly. 1988. Yard waste compost-
ing; Guidebook for Michigan communities. Lansing; MI:
Michigan Department of Natural Resources.
Canarutto, S., G. Petruzzelli, L. Lubrano, and G. Vigna
Guidi. 1991. How composting affect heavy metal con-
tent. BioCycle. June, 32(6):48-50.
composting Council (CC). 1991. Compost Facility plan-
ning guide. Washington, DC: composting Council.
Chancy, RL, and J.A. Ryan. 1992. Heavy metals and
toxic organic pollutants in MSW composts: Research re-
sults on phytoavailability, bioavailability, fate, etc. As cited
in H.A.J. Hoitink et al, eds. Proceedings of the Interna-
tional composting Research Symposium. In press.
Chancy, R.L. 1991. Land application of composted mu-
nicipal solid waste Public health, safety, and environ-
mental issues. As cited in: Proceedings of the Northeast
Regional Solid Waste composting Council Conference,
June 24-25,1991, Albany NY. Washington, DC.
Cimino, J.A. 1982. Carbon monoxide levels among sani-
tation workers. Proceedings of the 42nd annual AMA
congress on occupational health. Tampa, FL. As cited in:
J.A. Cimino and R. Mamtani. Occupational Hazards for
New York City Sanitation Workers. Journal of Environ-
mental Health. 50(1):8-12.
Clark, C. S., R Rylander, and L. Larsson. 1983. Levels of
gram-negative bacteria, Aspergillus fumigatus, dust, and
endotoxins at compost plants. Applied Environmental
Microbiology. 45(5): 1501-1505.
de Bertoldi, M., F. Zucconi, and M. Civilini. 1988. Tem-
perature, pathogen control and product quality. BioCycle.
February, 29(2):43-47.
Diaz, L.F. 1987. Air emissions from compost. BioCycle.
August, 28(8):52-53.
Dunovant, V.S. et al. 1986. Volatile organics in the waste-
water and airspaces of three wastewater treatment plants.
Journal of the Water Pollution Control Federation. Vol.
58.
Epstein, E., and J.I. Epstein. 1989. Public health issues
and composting. BioCycle. August, 30(8):50-53.
Fulford, B.R, W. Brinton, and R DeGregorio. 1992.
composting grass clippings. BioCycle. May, 33(5):40.
Gillett, J.W. 1992. Issues in risk assessment of compost
from municipal solid waste: Occupational health and
safety, public health, and environmental concerns.
Biomass & Bioenergy. Tarrytown, NY: Pergamon Press.
3(3-4):145-162.
Golueke, C.G. 1977. Biological reclamation of solid
wastes. Emmaus, PA: Rodale Press.
Gordon, R.T., and W.D. Vining. 1992. Active noise con-
trol: A review of the field. American Independent Hy-
giene Association Journal. 53:721-725.
Kissel, J. C., C.H. Henry, and R.B. Harrison. 1992. Po-
tential emissions of volatile and odorous organic com-
pounds from municipal solid waste composting facilities.
Biomass & Bioenergy Tarrytown, NY: Pergamon Press.
3(3-4):181-194.
Lembke, L. L., and RN. Kniseley 1980. Coliforms in
aerosols generated by a municipal solid waste recovery sys-
tem. Applied Environmental Microbiology. 40(5):888-
891.
Li, R, and M. Karen. 1990. Technical, economic, and
regulatory evaluation of tray dryer solvent emission con-
trol alternatives. Environmental Progress 9(2):73-78. As
cited in: Kissel, J. C., C.H. Henry, and R.B. Harrison.
1992. Potential emissions of volatile and odorous organic
compounds from municipal solid waste composting facili-
ties. Biomass & Bioenergy. Tarrytown, NY: Pergamon
Press. 3(3-4): 181-194.
Menzer, R.E. 1991. Water and soil pollutants. As cited in:
Amdur, M. 0., J. Doull, and C.D. Klaassen, eds. Casarett
and Doull's Toxicology The Basic Science of Poisons, 4th
ed. New York, NY: Pergamon Press, pp. 872-902.
Mozzon, D., D.A. Brown, and J.W. Smith. 1987. Occu-
pational exposure to airborne dust, respirable quartz and
metals arising from refuse handling, burning, and landfill-
ing. Journal of the American Industrial Hygiene Associa-
tion^):! 11-116.
Naylor, L.M., G.A. Kuter, and PJ. Gormsen. 1988. Biofil-
ters for odor control: The scientific basis. Compost Facts.
Hampton, NH: International Process Systems, Inc.
Pahren, H.R. 1987. Microorganisms in municipal solid
waste and public health implications. Critical reviews in
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Richard, T., N. Dickson, and S. Rowland. 1990. Yard
waste management A planning guide for New York
State. Albany, NY: New York State Energy Research and
Development Authority, Cornell Cooperative Extension,
and New York State Department of Environmental
Conservation.
Richard, T., and M. Chadsey. 1990. Environmental im-
pact of yard waste composting. BioCycle. April, 31(4):42-
46.
Robinson, W. D., cd., 1986. The solid waste handbook.
New York John Wiley and Sons.
Roderique, J.O., and D.S. Roderique. 1990. The environ-
mental impacts of yard waste composting. Falls Church,
VA: Gershman, Brickner & Bratton, Inc.
Rymshaw, E., M.F. Walter, and T.L. Richard. 1992. Agri-
cultural composting Environmental monitoring and
management practices. Albany, NY: New York State Agri-
culture and Markets.
Rynk, R, et al. 1992. On-firm composting handbook.
Ithaca, NY: Cooperative Extension, Northeast Regional
Agricultural Engineering Service.
U.S. Department of Agriculture (USDA) and U.S. Envi-
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composting sewage sludge by the Beltsville aerated-pile
method. EPA1600-8-80-022. Washington, DC: EPA.
U.S. Environmental Protection Agency (EPA). 1989.
Characterization of Products Containing Lead and Cad-
mium in Municipal Solid Waste in the United States,
1970-2000. EPA/530-SW-89-015B. Washington, DC:
Office of Solid Waste and Emergency Response.
Walsh, P., A. Razvi, and P.O'Leary. 1990. Operating a
successful composting facility. Waste Age. January,
Williams, T. 0., and F.C. Miller. 1992a. Odor control us-
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75
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Chapter Seven
State Legislation
and Incentives
Because of the lead role that states have assumed in regulating composting, this chapter focuses on state activi-
ties. State legislation has greatly influenced the development of composting approaches in many areas of the
country and a Ml understanding of early state legislative activity will confer a broad appreciation of legis-
lation issues throughout the country related to the composting of yard trimmings and MSW This chapter pre-
sents an overview of existing state legislation on both yard trimmings and MS W composting and discusses state
incentive programs to stimulate yard trimmings and MS W composting. The chapter discusses permit and siting
requirements, facility design and operational standards, product quality criteria, bans on landfilling or combus-
tion of organic material, recycling gosh, requirements directed at local governments to implement composting
programs, requirements directed at state agencies, and requirements the separation of yard trimmings and or-
ganics from MSW
Composing Legislation Overview
Adoption and implementation of composting legislation
is a cumbersome process, and the status of composting
legislation generally lags behind public and legislative in-
terest in the issue. Very few states have composting laws
that have been fully implemented, but many states are in
the process of enacting legislation or promulgating regula-
tions. In recent years, a surge in legislative activity con-
cerning recycling and composting has occurred, and more
composting legislation can be expected in the near future.
In the absence of specific composting legislation, many
states and localities regulate yard trimmings and MSW
composting facilities under related environmental statutes.
For example, many jurisdictions have already imple-
mented regulations governing the composting of sewage
biosolids. These jurisdictions often use these regulations
to control yard trimmings and MSW composting and, in
addition, usually borrow from EPA and state biosolids
composting laws when developing specific legislation for
the composting of yard trimmings and MSW. In Novem-
ber 1992, EPA issued 40 CFR Part 503, which pertains to
the land application, surface disposal, and combustion of
biosolids (sewage sludge). Many of the standards promul-
gated in this rule can be applicable to MSW compost.
Many states, in lieu of specific composting standards for
MSW, are using these standards as guidelines or as models
for regulations. State water and air pollution control laws,
solid waste management laws, and environmental protec-
tion laws also can be utilized to regulate composting. Of
special relevance is Part 503, which governs land applica-
tion of biosolids and biosolids composting. In addition, a
wide range of local ordinances often are applicable, in-
cluding zoning and building codes, regulations governing
materials that can be landfilled or incinerated, fire codes, and
safety regulations.
The use of a wide variety of nonspecific local and state or-
dinances to manage yard trimmings and MSW compost-
ing can create a complex regulatory framework. Because
of the benefits that can be accrued from composting (e.g.,
landfill diversion and production of valuable soil amendm-
ent products), some states and localities are seeking to
stimulate composting by minimizing this regulatory
complexity.
There are notable differences between legislation for
MSW and yard trimmings composting. The composting
of yard trimmings is much more widespread than MSW
composting. Consequently, more states have adopted spe-
cific legislation regulating the composting of yard trim-
mings. In general, however, because the composting of
yard trimmings poses freer problems than MSW
76
-------
State Legislation and Incentives
composting, requirements for the composting of yard
trimmings are less stringent than those developed for
MSW. Legislation for the composting of yard trimmings
is usually general in scope and applies to operations that
handle leaves, grass clippings, brush, or some combination
of these materials. Legislation in a few states (such as New
Jersey), however, targets specific yard trimmings, such as
leaves. State MSW composting legislation generally covers
household MSW. When any amount of sewage biosolids
is co-composted with other materials such as yard trim-
mings or mixed MSW, it is regulated under EPA's 40 CFR
Part 503 regulations.
Table 7-1 presents a summary of legislation at the state
level to encourage or mandate composting Table 7-2 de-
scribes specific state legislation used to regulate yard trim-
mings and MSW composting. These tables can be found
at the end of this chapter. The remainder of this chapter
discusses specific examples of state legislation pertaining
to yard trimmings and MSW composting.
Permit and Siting Requirements
To date, most states (especially those in the central and
western United States) have not established specific per-
mit or siting requirements for facilities that compost yard
trimmings. In addition, because of minimal environ-
mental impacts generally associated with the composting
of yard trimmings, a few states (Delaware, Michigan, and
Pennsylvania) have expressly exempted these facilities
from any requirements (CRS, 1989). Other states exempt
certain types of composting operations from permit and
siting criteria. For example, Florida has exempted back-
yard composting and normal farm operations from com-
posting regulations (FDER, 1989). Wisconsin does not
require permits for operations that compost yard trim-
mings and that are less than 38 m3in size (Wk. Stat,
1987-1 988). New York also exempts small operations as
well as operations that compost only food scraps or live-
stock manure (N.Y. Gen. Mun. Law, 1990). Illinois does
not require permits for composting operations that are
conducted on sites where yard trimmings are generated.
composting operations that compost materials at very
low rates and most on-farm composting operations also
are exempt from permitting (111. Rev. Stat., 1989).
Those states that do have siting and permitting require-
ments for yard trimmings and MSW composting attempt
to minimize the impact of composting operations on sur-
rounding property and residences, ensure appropriate
composting operations are conducted, and prevent envi-
ronmental problems associated with leachate runoff. For
example, Illinois prohibits siting of facilities for the com-
posting of yard trimmings within 200 feet of a potable
water supply or within 5 feet of a water table, inside the
10-year floodplain, or within 200 feet of any residence. In
addition, the legislation states that the location of a com-
posting facility shall "minimize incompatibility with the
character of the surrounding area" (111. Rev. Stat., 1989).
New Jersey legislation requires every Soil Conservation
District in the state to develop site plans for leaf compost-
ing facilities that are to be constructed within their juris-
dictions. These site plans must include any information
required by the state's Department of Environmental Pro-
tection (NJ. Stat., 1990).
Permitting and siting regulations for MSW composting
are usually more stringent than those for yard trimmings.
Florida regulates mixed MSW composting facilities to the
same degree as solid waste disposal sites. These regulations
prohibit siting MSW composting facilities in geologically
undesirable areas (such as in open sink holes or gravel
pits), within 500 feet of a shallow water supply well,
within 200 feet of a water body, in an area subject to
flooding, within public view from any major thoroughfare
without proper screening, on the right-of-way of a public
road, or near an airport (FDER, 1990).
Pennsylvania has also adopted a strict set of standards for
permitting and siting MSW composting facilities. In order
to receive a permit for MSW composting plans must be
submitted to the state's Environmental Quality Board. These
plans must describe facility siting and design; facility access;
control of leachate, soil erosion, sedimentation, odor, noise,
dust, and litter alternative management of feedstocks or
compost in case processing operations or end-use markets;
ground-water monitoring and revegetation and postclosure
land use for the site (Penn. Env. Qual. Board, 1988). Strict
siting regulations to prevent contamination of surface or
ground-water resources are also included in the Pennsylvania
rules. For example, siting a facility within the 100-year
floodplain or within 300 feet of "an important wetland" is
prohibited (Penn. Env. Qual. Board, 1988).
Facility Design and Operations
Standards
Most states have not adopted specific regulations for the
design and operation of yard trimmings and MSW com-
posting facilities. The legislation that has been adopted at-
tempts to minimize negative impacts associated with
composting and to protect public health and the environ-
ment. New Jersey has adopted a relatively extensive set of
regulations concerning leaf composting operations. These
regulations restrict access to composting facilities; limit
the maximum quantity of leaves to be composted per
acre; limit windrow size, govern windrow placement; re-
strict the grade of compost pads; establish a minimum
turning frequency for windrows; limit the quantity of
compost that can be stored on the site; and require the use
of leachate, odor, dust, noise, and fire controls. In addi-
tion, representatives from the Soil Conservation Districts
are required to conduct annual inspections of leaf
77
-------
State Legislation and Incentives
composting facilities operating within their jurisdiction to
ensure that the facilities are properly managed and main-
tained. Other states have adopted portions of these regula-
tions for facilities that compost leaves and yard trimmings
in general.
Florida regulations are similar to those that have been
implemented in New Jersey but include some specific
requirements geared toward controlling the potential
safety, health, and environmental impacts that might be
associated with operations that compost mixed MSW.
These requirements include prohibitions on the compost-
ing of biohazardous wastes and hazardous wastes, except
for small quantities of household hazardous wastes. The
Florida regulations also include requirements for tempera-
ture monitoring and recordkeeping and specify the fol-
lowing that appropriate stormwater management systems
must be implemented at composting facilities; all-weather
access roads to the facility must be provided; detailed
signs indicating the name and telephone number of the
operating authority, hours of operation, charges, etc.,
must be posted; and litter control devices must be in-
stalled (FDER, 1989). In addition to operational require-
ments similar to those of Florida, Pennsylvania's
regulations require that feedstocks are weighed when re-
ceived, composting equipment is properly maintained,
salvaging of materials is strictly controlled, unloading of
feedstocks is conducted in a safe and efficient manner,
point and nonpoint source pollution of water resources is
prevented, soil erosion and sedimentation does not occur,
soil and ground-water monitoring is conducted, and resi-
dues from composting operations are "disposed or proc-
essed at a permitted facility for municipal or residual
waste" (Penn. Env. Qual. Board, 1988).
New Jersey regulates mixed MSW composting under the
same rules as sewage biosolids composting. Pathogen con-
tamination is consequently regulated in a strict manner
and only three specific methods of mixed MSW compost-
ing can be used:
windrow composting- Under this method, aerobic
conditions must be maintained, temperatures
within 6 to 8 inches of the surface of the windrow
must remain above 55°C (131 T) for at least 15
consecutive days, and the windrow must be turned
at least five times during this 15-day period.
Aeratedstatic pile - With this method, the pile must
be insulated and temperatures of at least 55°C
(131°F) must be maintained for a minimum of 3
consecutive days.
In-vessel composting - In this method, the compost-
ing mixture must be maintained at a minimum
temperature of 55°C (13 1°F) for at least 3 consecu-
tive days (NJ. Dept. Env. Prot, 1986).
Product Quality Criteria
A few states have adopted a variety of criteria to classify
different grades of compost. Criteria covering yard trim-
mings and MSW composts have been developed that con-
cern the degree of stabilization, particle size, moisture
content, levels of organic vs. inorganic constituents, and
contaminant content. Florida's regulations governing
compost product quaky are some of the most well-devel-
oped to date. Under these regulations, finished compost
products must be tested by approved methods and infor-
mation must be recorded on the following parameters:
percent moisture content; percent of total dry weight of
nitrogen, phosphorus, and potassium percent organic
matter pH; percent foreign matter mg/kg dry weight of
cadmium, copper, lead, nickel, and zinc; and most prob-
able number of feed coliform. After testing, the quality of
the compost is classified based on the type of feedstocks
processed as well as strict specifications concerning the
maturity of the product, the foreign matter content, the
particle size, and metal concentrations. Seven levels of
compost quality have been specified:
Type Y composts use yard trimmings as the only feed-
stock; are mature or semimature have fine, me-
dium, or coarse particle size; and have a low foreign
matter and metal content.
Type YM composts have the same characteristics as
Tpye composts but can also use livestock manure
as a feedstock.
Type A composts use MSW as the feedstock, are ma-
ture, have a fine particle size, and have a low for-
eign matter and metal content.
Type B composts use MSW as the feedstock, are ma-
ture or semimature, have a fine or medium particle
size, have an intermediate foreign matter content,
and have low or intermediate metal concentrations.
Type C composts use MSW as the feedstock are ma-
ture or semimature, have free, medium, or coarse
particle size, have high foreign matter content, and
have high, intermediate, or low metal
concentrations.
Type D composts use MSW as the feedstock; are
fresh; have fine, medium, or coarse particle size
have a high foreign matter content; and high, me-
dium, or low levels of metals.
Type E composts use MSW as the feedstock and
have very high metal concentrations (FDER, 1989).
Under Florida regulations, distribution of compost Types
Y, YM, and A are not restricted. Distribution of Type B
or C compost is restricted to commercial, agricultural,
78
-------
State Legislation and Incentives
institutional, and governmental use. In addition, accord-
ing to the regulations, if the compost "is used where con-
tact with the general public is likely, such as in a park,
only Type B maybe used" (Fla. Stat, 1989). Distribution
of Type D is restricted to landfills or land reclamation
projects with which the general public does not generally
come into contact. Finally, Type E composts must be
disposed of in a solid waste facility (FDER, 1989).
Approaches of this kind to regulate compost quality cur-
rently are being pursued by several other states.
Pennsylvania has adopted a case-by-case approach for
regulating the quality of MSW compost. The state re-
quires that a chemical analysis of MSW compost prod-
ucts be performed and submitted to the Department of
the Environment before sale and distribution of the
material. The regulations state that "if the Department
determines that the compost has the potential for caus-
ing air, water, or land pollution," the compost facility
operator will be informed that the compost must be
"disposed of at a permitted disposal facility" (Penn.
Env. Qual. Board, 1988).
Bans on Landfilling or Combustion
Several states have restricted the use of certain disposal op-
tions (particularly landfilling and combustion) for yard
trimmings. Usually, legislation of this kind is coupled
with state efforts to implement composting programs.
Even where no overt state efforts exist to initiate the com-
posting of yard trimmings, however, disposal bans indi-
rectly stimulate the composting of yard trimmings.
Currently 21 states have enacted a disposal ban on yard
trimmings or components of yard trimmings. Wisconsin
and Iowa, for example, have adopted legislation that bans
both the landfilling and combustion of yard trimmings
(FDER, 1989; Iowa Adv. Legis. Serv., 1990). Illinois,
Florida, Minnesota, and Missouri ban disposal of yard
trimmings in landfill (111. Rev. Stat., 1989; Fla. Stat.,
1989 Minn. Stat, 1990; Mo. Adv. Legis. Serv., 1990).
New Jersey has banned disposal of leaves in landfills (N.J.
stat., 1990).
Recycling Goals
Recycling goals have been established at the state or local
level in many areas. It is generally not mandated that
composting be performed in order to meet these goals; the
establishment of such goals, however, enhances the attrac-
tiveness of composting to states and localities. Some ex-
perts believe that without composting it will be difficult
to achieve recycling goals of 20 percent or more. Maine
and West Virginia are examples of states that have set re-
cycling goals that specifically mandate the composting of
yard trimmings (W.Va. Code Ann., 1990, Me. Rev. Stat.,
1989).
Requirements for Local Governments to
Implement Composting
Some states do require local governments to implement
composting programs. For example, state legislation in
Minnesota mandates that local governments develop pro-
grams for the composting of yard trimmings as part of
their overall recycling strategy (Minn. Stat., 1990). Simi-
larly, New Jersey legislation directs localities to develop
programs for collecting and composting leaves (N.J. Stat.,
1990).
Requirements for State Agencies to
Compost
In several states, legislation requires state agencies to par-
ticipate in composting. For example, Wisconsin legisla-
tion mandates that state agencies comply with the state's
100 percent yard trimmings ban (WI Stat 1.59). Some
agencies, like the University of Wisconsin-Stevens Point,
have complied by creating onsite composting Facilities.
Other agencies, like the State Capitol Building have com-
plied by contracting with existing composting facilities.
Wisconsin's Department of Administration is responsible
for seeing that agencies meet the 100 percent requirement
and that no yard trimmings go to landfills from state
agencies. Alabama and New Mexico require state environ-
mental departments to evaluate their state agencies' recy-
cling programs (including the composting of yard
trimmings) and develop new programs if necessary
(Michie's Code of Ala., 1990; N.M. Ann. Stat).
Separation Requirement
bother method of stimulating the composting of yard
trimmings without directly mandating that it occur is to
require that yard trimmings be separated from MSW be-
fore they are collected. Household separation of yard
trimmings facilitates composting by minimizing the need
for intensive sorting and removal procedures during com-
post preprocessing. Legislation in Delaware requires the
state's solid waste authority to consider the separation of
yard trimmings for potential recycling programs (Michie's
Del. Code Ann.). Iowa legislation directs local govern-
ments to require residents to separate yard trimmings.
Under this legislation, local governments are also in-
structed to collect yard trimmings if they normally collect
other forms of MSW (Iowa Adv. Legis. Serv., 1990).
Yard Trimmings and MSW
Composting Incentives
Several states have opted to stimulate yard trimmings and
MSW composting through a variety of incentive pro-
grams, whether they also subscribe to legislative mandates.
State composting incentives include encouraging localities
79
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State Legislation and Incentives
to implement programs ardor giving them specific
authority to do so; providing grants to local governments
or private firms to develop composting programs; empha-
sizing market development for compost products; and de-
veloping educational programs on backyard composting.
State Encouragement and Local Authority
to Implement Programs
MSW management has traditionally been handled at the
local level. Many states have consequently opted to main-
tain and promote such local control. Some of these states
have also passed legislation that clearly communicates
their support of composting to local governments,
however. For example, legislation in both Florida and
North Carolina does not mandate that the composting of
yard trimmings occur at the local level, but encourages lo-
cal governments to recycle yard trimmings (Fla. Stat,
1989; Michie's Gen. Stat. of N.C.). Similarly Iowa legisla-
tion does not require composting at the local level, but di-
rects the state to "assist local communities in the
development of collection systems for yard waste ... and...
the establishment of local composting facilities" (Iowa Adv.
Legis. Service, 1990).
Other states have supported local control by specifically
granting local governments the authority to mandate yard
trimmings and MSW composting. For example, legisla-
tion in New York gives municipalities the authority to
adopt laws requiring that materials, including garden and
yard trimmings, be "separated into recyclable, reusable or
other components" (N.Y. Gen. Mun. Law, 1990). Massa-
chusetts' legislation has a similar clause that applies to
MSW which states that local governments may establish
recycling programs mandating the separation, collection,
and processing of recyclable including "compostable
waste" (Mass. Ann. Laws, 1990).
Grants
Many states have sought to promote yard trimmings and
MSW composting by providing grants to local govern-
ments and private businesses to establish composting fa-
cilities. For example, Iowa law authorizes the state to
"provide grants to local communities or private individu-
als" that are establishing recycling facilities, including fa-
cilities for the composting of yard trimmings (Iowa Adv.
Legis. Serv., 1990). In Minnesota, those entities that de-
velop yard trimmings and MSW composting projects can
receive "grant assistance up to 50 percent of the capital
cost of the project or $2 million, whichever is less" (Minn.
Stat., 1990). The state of Washington provides funds, as
available, to local governments submitting a proposal to
compost food scraps and yard trimmings (Wash. Rev.
Code, 1990).
Procurement
State agencies that work to build roads, control erosion,
construct buildings, and maintain land consume large
quantities of topsoil and organic materials. Many states
have committed to developing markets for yard trim-
mings and MSW compost by setting procurement poli-
cies for these agencies. Procurement policies encourage
state agencies to buy compost by (1) requiring that state
agencies give preference to compost when making pur-
chase decisions or (2) requiring that a given percentage of
a state's topsoil/organic material purchases are purchases
of compost.
As of April 1993, agencies in Georgia are required to give
preference to compost when purchasing topsoil and or-
ganic material. The legislation even specifies that the state
of Georgia give preference to compost made from source-
separated, nonhazardous organics. Several states require
agencies to give preference to compost when it is cost
effective to do so. These agencies include Florida, Maine,
Minnesota, and North Carolina.
Encourgement of
Backyard Composting
Several states are encouraging backyard composting or
ganics. Legislation in Connecticut requires regionaljuris-
dictions to foster recycling through a variety of
mechanisms, including backyard composting. These juris-
dictions are directed to develop and then implement recy-
cling plans that will facitate backyard composting of
organics. States such as Massachusetts, New Jersey, New
York, and Rhode Island have published manuals and bro-
chures that explain backyard composting operations.
Education Programs
Several states encourage yard trimmings and MSW
composting through educational and public awareness
programs. Massachusetts has initiated a technical assis-
tance program for yard trimmings and MSW compost-
ing. The state conducts hands-on workshops and
provides guidance materials on designing and operating
municipal compost facilities. In addition, state officials
visit compost facilities and potential composting sites
to provide expert guidance. In Seattle, Washington, an
urban, organic gardening organization, Seattle Tilth As-
sociation, trains volunteers to teach other city dwellers
how to compost yard trimmings and food scraps. The
volunteer educators, called "master composers," are
thoroughly trained in basic composting methods, com-
post biology, system design, and troubleshooting. The
Seattle Tilth Association also operates a hotline to an-
swer questions about composting.
80
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State Legislation and Incentives
Summary
Significant legislative activity has occurred at the
state level in recent years on both yard trim-
mings and MSW composting. States have
adopted legislation concerning permitting and siting
of compost facilities, compost facility design and op-
eration, compost product quality, landfilling or com-
bustion of organic material, recycling goals, local
government implmentation of composting programs,
state agency composting policy and the separation of
yard trimmings and other organics from MSW. In
addition, many states have promoted yard trimmings
and MSW composting through a variety of incentive
programs that encourage heal development of com-
posting and grant localgovernment the authority to
implement such programs, provide find to local gov-
ernments or private firms to develop composting pro-
grams, stimulate market development for compost
products, encourage backyard composting and ad-
vance educational programs.
Chapter Seven Resources
Cal Recovery Systems (CRS) and M. M. Dillon Limited.
1989. Composting A literature study. Ontario, Canada
Queen's Printer for Ontario.
Florida Department of Environmental Regulation
(FDER). 1990. Florida Administrative Code. Solid Waste
Management Facilities. Rule 17-701.
Florida Department of Environmental Regulation (FDER).
1989. Florida Administrative Code. Criteria for the Produc-
tion and Use of Compost Made from Solid Waste. Rule 17-
709.
Florida Statutes (Fla. Stat). 1989. Title XXIX, Public
Health. Chapter 403, Environmental Control. Part IV,
Resource Recovery and Management, Fla. Stat. 403.70.
Glenn, J. 1992. Solid waste legislation: The state of gar-
bage in America. BioCycle. May, 33(5):30-37.
Harrison, E. Z., and T.L. Richard. 1992. Municipal solid
waste composting policy and regulation. Biomass &
Bioenergy. Tarrytown, NY: Pergamon Press. 3(3-4):127-
141.
Illinois Revised Statutes (111. Rev. Stat.). 1989. Chapter
111 1/2, Public Health and Safety Environmental Protec-
tion Act.
Iowa Advance Legislative Service (Iowa Adv. Legis. Serv.).
1990. Seventy-Third General Assembly. la. ALS 2153;
1990 la. SF 2153.
Maine Revised Statutes (Me. Rev. Stat.). 1989. Title 38,
Waters and Navigition. Chapter 13, Wrote Management.
Subchapter I, General Provisions, 38 M.R.S. 1302.
Annotated Laws of Massachusetts (Mass. Ann. Laws).
1990. Part I, Administration of the Government, Title
VII, Cities, Towns and Districts. Chapter 40, Powers and
Duties of Cities and Towns, §8H.
Michie's Code of Alabama (Michie's Code of Ala.). 1990.
Title 22, Health, Mental Health and Environmental Con-
trol. Subtitle 1, Health and Environmental Control Gen-
erally. Chapter 22B, Recycling by State Agencies, Code of
AM. 22-22b-3.
Michie's Delaware Code Annotated (Michie's Del. Code
Ann.). Title 7, Conservation. Part VII, Natural Resources.
Chapter 64, Delaware Solid Wrote Authority. Subchapter
II, Recycling and Waste Reduction, 7 Del. C. 6453.
Michie's General Statutes of North Carolina (Michie's
Gen. Stat. of N.C.). Chapter 130A, Public Health. Article
9, Solid Materials Management. Part 2A, Nonhazardous
Solid Materials Management, N.C. Gen. Stat. 130A-309.
Minnesota Statutes (Minn. Stat.). 1990. Environmental
Protection. Materials Management, Ch. 115A.
Missouri Advance Legislative Service (Me. Adv. Legis.
Serv.). 1990. 85th General Assembly, Second Regular Ses-
sion. Conference Committee Substitute for House Com-
mittee Substitute for Senate Bill No. 530. 1990 Mo. SB
530.
New Jersey Department of Environmental Protection
(N.J. Dept. Env. Prot), Division of Solid Materials Man-
agement. 1986. Compost Permit Requirements, August 1.
New Jersey Statutes (N.J. Stat.). 1990. Title 13, Conserva-
tion and Development-Parks and Reservations. Chapter
IE, Solid Materials Management, 13:1 E-99.12.
New Mexico Annotated Statutes (N.M. Ann. Stat.).
Chapter 74, Environmental Improvement. Article 9, Solid
Materials Act, N.M. Stat. Ann. 74-9.
New York General Municipal Law (N.Y. Gen. Mun.
Law). 1990. Article 6, Public Health and Safety, NY CLS
Gen Mun 120-aa.
Pennsylvania Environmental Quality Board (Penn. Env.
Qual. Board). 1988. Municipal Materials Management
Regulations. Chapter 281, composting Facilities. Penn-
sylvania Bulletin, April 9.
Revised Code of Washington (Wash. Rev. Code). 1990.
Title 70, Public Health and Safety. Chapter 70.95, Solid
Materials Management-Reduction and Recycling, RCW
70.95.810.
Washington Department of Ecology (WDOE) and the
U.S. Environmental Protection Agency (EPA). 1991.
Summary Matrix of State Compost Regulations and
81
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State Legislation and Incentives
Guidance. Prepared for the Focus Group Meeting on and Regional Solid Materials Authorities, W. Va. Code
Compost Quality and Facility Standards. Minneapolis, 20-9-1.
MN.November 6-8.
Wisconsin Statutes (Wis. Stat). 1987-1988. Chapter 144,
Water, Sewage, Refuse, Mining and Air Pollution. Sub-
West Virginia Code Annotated (W.Va. Code Ann.). chapter IV, Solid Materials, Hazardous Waste and Refuse,
1990. Chapter 20, Natural Resources. Article 9, County wk. stat. 144.79.
82
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State Legislation and Incentives
Table 7-1.
State
[j Alabama
Arkansas
B :
: California :
£--. -.-...-.*. :! ::' '- -.-.-. X- !-.-.. :.-.-:,
Connecticut
So:* '-.fXiW- .*:"*.- :V' ,:.: ":: -:-:.
I Delaware
District of
Columbia
I Florida
Georgia
: Hawaii IS
Illinois
; Indiana ;
Iowa
I Kentucky
Louisiana
1 Maine ;.j;;?:rH
Maryland
1 Massachusetts
Michigan
i Minnesota
Mississippi
Missouri
Montana
Nebraska
Nevada
State legislation to encourage or mandate yard trimmings and MSW composting,
Solid Waste Management Goals
(includes source reduction, recycling, and composting unless
otherwise specified; mandated unless otherwise specified)
^25^|;t[:ilf||lf|||^^ii^i4fratiBii
40%
'- 50% ! . ' ; S!ff.«' . : '..': ; .;'; : ' : : '-".'
25% recycling alone, which includes yard trimmings
composting.
21% recycling alone, which includes yard trimmings
composting; not mandated.
45% recycling alone, which includes yard trimmings
composting.
30% source reduction and recycling, which includes yard
trimmings composting.
25%
.:..::..-:-: .:: -::.: : . .. :-... .. . :-- : --. - . - :- --.- :-.--.:: :-.- ;- -.<,., '-.
'''''':'ff^nj' '- -'-' '' ' '-- ": :: ": : : : :: : ".':'-1: ::. :: ': : ::":.:.:::.'ffi:
25% recycling alone, which includes yard trimmings
composting.
50% E ; ff f : :
50%
;: 25% : m
25%
1 50% recycling and composting; not mandated. t
. ': : '. .' .' " : --:'' ': .'. '':'. . ''' .-'' "'' : '. '-'. ' ' '-' ' "'
25% recycling alone, which includes yard trimmings
composting.
21% composting specifically; : '-,' \ i 4
8-12% composting specifically; not mandated.
25%
J/VV :"' -:,.'-'-:'.? ....-' :." -::.:..^ i:" :::^:V:" .-:: '?' A;,;',..'*,;*; '? /v.S1' .?:"J::>₯"1111?:'1 i :' ?.'''% - "'':" ::: >*--.$':
25%; not mandated.
: A*/A : - . ."::'' ":: w;. ^^yj^^^^f-^.' :- ~\~ ':"".;" V"; :""; .:"": ." ;. ":" ": : -.
'25%
Yard
Trimmings
Bans
; : : - : ;. : S::::;y -':
Yes
' - ' - . "US
Yes
: { Yes; : ; f : ;
:v^Kij
l>B»:':;n^:
Yes
liSlil;.;
v ':;:' :;; :!:..::: :V i :--:;:;">
: :. ::: - :: _.: ;::;
Yes
''"feS^': f'vhK
Yes
!->»^SIii
p Yss ;";' -' !1|;1
ill^yili'lii
Procurement
Funds spent on lopsoil/Organic materials must -;i
be spent on compost (20% by 1993; 40% by 1;
i??^f}LHn^-i-:K-u=Bi4;i]isiiiiii
State agencies and local governments must :
procure compost when price is equivalent, M
especially for highways, reactivation, and ,
erosion control. : : ; ; : ; ; ! :>::-:
State agencies must give preference to compost
for all road building,lana development, and
land maintenance.
;:i.n.iiiI!iiliL!I^T"i^H!!rl!'^f^
h^i^nuH; iM-riH^-^WrffffffiB
State and local agencies are directed to give
preference to the use of compost in land
maintenance.
; State agencies must give preference to compost.;
All state agencies and public-funded - s
construction/land maintenance activities will I :
use composted and recycled organic material
where economically feasible and
environmentally sound. ; ? ;
State agencies and local governments must give
preference to compost in any public-funded
land maintenance activity.
.;:::.v. '.. : ; .;: :;.
State agencies must use compost where cost 1 1 ;
effective. : : : :; : ;i
- .;: ^: I! :. - : -: :;. :>.::-:: w -;::^ ^ :: .-y.:;: .^.::v.::y,:;:, ,v: , |, ;:, ^ ^|: ,|. :fc. :.:^: . :^v|:. : :v.^, :| ::
Slate agencies and local governments must give
preference to compost. '-;,.; ; . i.|.;,:J |:|- ,;..,; { ,
83
-------
State Legislation and Incentives
Table 7-1. (Continued).
State
New
Hampshire
Solid Waste management Goals
(includes source reduction, recycling, and composting unless
otherwise specified; mandated unless otherwise specified)
40%
New Jersey 25% recycling, which includes yard trimmings composting
but excfudesieaf composting as port of the goal.
New Mexico 50%
New York
North
Carolina
Norfh
Dakota
Ohio
Oregon
60%; not mandated.
25%
40%
25%
50%
Pennsylvania 25% recycling alone, which includes yard trimmings
composting.
Rhode Island 15% recycling alone, which includes yard trimmings
composting.
South
Carolina
30%
South Dakota 50%; not mandated.
Tennessee 25%
Texas* 40%
Vermont 40%; not mandated.
Virginia 25% recycling alone, which includes yard trimmings
composting.
Washington 50%
West
Virginia
Wisconsin
50%
Yard
Trimmings
Bans
Yes (leaves
only).
Yes
Yes
Yes (leaves
and brush
only).
Yes
Yes
Yes
Yes
Yes
"The Department of Health must compost 15% of the state's solid waste stream by 19
Sources Glenn, 1992; WDOE and EPA, 1991.
Procurement
State agencies and local governments must
give preference to compositor public-funded
land maintenance activities.
State and bed agencies are directed to give
preference to the use of compost in land
maintenance.
State agencies must give
recycled materials, including compost.
Stole agencies and local agencies must give
preference to compost if it does not cost more.
State agencies must purchase compost to the
"maximum extent economically feasible".
State agencies and public funded projects
must purchase compost where economically
practicable.
The State Department of General
Administration must spend a* least 25% of its
budget on compost products for use as
landscape materials and soil amendments; in
July 1994, this figure will be raised to 50%;
for contracts that use soil cover on stale and
local rights-of-way, compost products must
comprise 25% of the materials purchased; in
July 1993, this figure will rise to 50% for
state roods and in July 1994, the figure will
rise to 50% for focal roads.
Agencies and instrumentalities of the state
must use compost in al| landscaping and
land maintenance activities.
84
-------
State Legislation and Incentives
Table 7-2. Legislation to regulate the composting of yard trimmings and MSW.
State
California
Connecticut
Delaware
Florida
Illinois
Iowa
Maine
Massachusetts
Minnesota
Missouri
New Jersey
New York
North Carolina
Requirements for Operating
Compost Facilities
Must be promulgated by Hie
Department of General Services.
Specific requirements far leaf
composting; leaf composting is
exempt from solid waste permitting
requirements.
separate requirements exist for yard
trimmings and MSW composting.
Requirements exist for operating
landscape composting operations.
separate, extensive requirements far
yard trimmings and MSW composting.
Specific requirements for "vegetative
requirements apply to biosoolids
composting, co-composting and
composting of vegetative trimmings.
MSW composting subject to state
solid waste management regulations
as for landfills); guidance is available
for yard trimmings composting.
Separate requirements for yard
trimmings and MSW composting.
Minimal requirements for yard
trimmings composting.
Criteria for yard trimmings
composting; separate criteria for leaf
composting alone.
Facilities that compost yard trimmings
or MSW must comply wifh regulations
for solid waste management racilities
ond must also comply with specific
yard trimmings and MSW composting
requirement.
Specific requirements for operating
MSW composting facilities; also
requirements for yard trimmings,
agricultural, and silvicultural
composting.
Requirements for
Designing/Siting Compost
Facilities
Compost Classification/Quality
Standards
same requirements exist far yard
trimmings and MSW composting
additional restrictions are place on
MSW composting.
Design and siting criteria exist for
landscape composting.
Design criteria far MSW composting;
siting criteria far bath yard trimmings
and MSW comnposting (slightly mare
restrictive for MSW composting).
Requirements for buffer distances and
impermeable ground surfaces.
MSW composting, some requirement
as landfills; separate requirements
and guidelines far facilities that
compost yard trimmings.
Requirements MSW composting
but not yard trimmings compacting.
Siting criteria for facilities that
compost yard trimmings.
Requirements and guidelines for yard
trimmings composting.
separate yard trimmings and MSW
facility design requirements; siting
criteria far solid waste management
facilities.
Specific requirement for designing
and siting MSW composting facilities;
also siting and design requirements
far yard trimmings, agricultural, and
silvicultural composting.
Contaminant Standards.
Compost must be classified based an
type of material composted, maturity
or compost, foreign matter content,
particle size, an neavy metal
content; restrictions on use of certain
categories of compost exist; compost
testing required.
pathogen control standards far
finished compost; finished compost
must be innocuous and free of
sharp-edged objects.
Classifications for animal manures
and vegetative trimmings.
Reauirement for MSW compost;
guidelines for yard trimmings compost.
Classification standards and use
restrictions for some categories.
Only yard trimmings can be used in
the compost; compost from yard
trimmings is regulated as fertilizer or
soil conditioner, depending on how it
is labeled.
Classification requirement for MSW
composting but not far yard trimmings.
itemand
v jtandards far MSW compost;
Jso requirement far yard trimmings,
agricultural, and silvicultural compost.
85
-------
State Legislation and Incentives
Table 7-2. (Continued).
State
Pennsylvania
South Carolina
Virginia
Wisconsin
Requirements for Operating
Compost Facilities
operating all compost facilities, but
these are to targeted at biosolids
composting; specific requirements
exist for operations that compost yard
trimmings.
Separation operations criteria exist for
yard trimmings and MSW
composting, and no mixing is allowed.
Separate operations criteria exist far
yard trimmings composting on a small
scale, yard trimmings composting on
a large scale (over 20.000 cubic
yards annually), MSW composting,
and biosolids and livestock manure
composting.
lta|irirmiwt« for
Designing/Siting Compost
Facilities
General requirements exist for siting
and designing all compost facilities,
but these are targeted at biosolids
composting; specific siting
requirements exist for yara trimmings
composting but no specifi
requirements tor facility d
esign.
separate design and siting criteria
exist far yard trimmings and MSW
Composting.
Siting criteria exist far all compacting
operations; in addition, operations
that compost yard trimmings and are
20,000 cubic yards per year must
submit a design plan to state.
Compost Clasaification/Quality
Standards
_r on system or
quality standards exist far MSW
composting, although some standards
exist for biosolids composting and the
biosolids can be composted with
MSW; a classification scheme for
yard trimmings compost is in place.
Quality standards for yard trimmings
compost are being promulgated.
Yard trimmings and MSW must be
composted separately; MSW may be
composted witn biosolids..
Composting is classified into the
.ollowing categories: household
composting, neighborhood
composting, community yard
trimmings composting, solid waste
composting, and biosolids and
livestock manure composting; yard
trimmings compost may be used
without a permit, but a permit is
required to landspread MSW compost.
Sources: WDOE and EPA, 1991: Harrison and Richard,
86
-------
Chapter Eight
Potential End
Users
f ompost currently is used in a variety of application in the United States, from agriculture and landscaping
I to reforestation projects and residential gardening. When planning a composting facility, decision-makers
\J should identify potential end users to determine the type of compost that is required For example, if a facil-
ity only produces low-quality unscreened compost and end users demand high-quality screened compost the prod-
uct might not be used. By identifying potential end users, a facility can ensure that the compost product can be
marketed MSW composting facilities and large yard trimmings composting facilities might identi- market for a
spectrum of end uses, from low- to high-quality compost, since the finished product does not always meet the de-
sired specifications. This chapter discusses the potential end users ofcompost derived from MSW or yard trimming.
The Benefits of Finished Compost
Compost can benefit the biological, chemical, and physi-
cal properties of soil. Biologically compost enhances the
development of fauna and microflora, renders plants less
vulnerable to attack by parasites, and promotes faster root
development of plants. Chemically, compost benefits soil
in a number of ways. Compost increases nutrient content,
turns mineral substances in soil into forms available to
plants, and regulates the addition of minerals to soil, par-
ticularly nitrogenous compounds. In addition, compost
serves as a buffer in making minerals available to plants
and provides a source of micronutrients. Furthermore,
compost improves many physical properties of the soil,
including the soil's texture, water retention capacity, infil-
tration, resistance to wind and water erosion, aeration ca-
pacity, and structural and temperature stability. Table 8-1
summarizes potential end users and their quality require-
ments for finished compost. These end-use markets are
examined in more detail in this chapter.
Agricultural Industry
A market assessment was conducted in 1991 to estimate
the potential demand for compost in the United States
(Slivka, 1992). This survey identified agriculture as the
largest potential end-use market for compost, accounting
for over 85 percent of potential use. At present, however,
the amount of compost used in large-scale agricultural ap-
plications is small. According to a 1992 composting
Council survey of 126 yard trimmings and 20 MSW
composting programs, only four yard trimmings and three
MSW facilities mentioned the agricultural sector as an
end-use market.
Agricultural use of compost remains low for several rea-
sons. One, the product is weighty and bulky, which can
make transportation expensive. The nutrient value of
compost is low compared to fertilizers. In addition, agri-
cultural users might have concerns regarding potential lev-
els of heavy metals (particularly lead) and other possible
contaminants in compost, particularly mixed MSW com-
post (see Chapter 9). The potential for contamination be-
comes an important issue when compost is used on food
crops. This concern is mitigated if compost is applied well
in advance of planting. Many experiments examining the
effects of MSW compost application on the physiochemi-
cal characteristics of soils have indicated positive results as
outlined in Table 8-2 (Shiralipour et al, 1992).
To successfully market a compost product to the agricul-
tural sector, therefore, the compost must be available at
the appropriate time of year, be consistent in composition
and nutrient content, contain low levels of potentially
toxic substances, and be offered at a low cost. Additionally
difficulties associated with bulkiness must be resolved,
distribution channels established, and the positive effect of
compost on crop yields demonstrated (EPA 1993).
If these issues are addressed, compost has the potential to
be used in large quantities by the agricultural industry.
Compost can be used to increase the organic matter, tilth,
and fertility of agricultural soils. Compost also improves
87
-------
Potential End Users
the aeration and drainage of dense soils, enhances the
water-holding capacity and aggregation of sandy soils, and
increases the soil's cation exchange capacity (i.e., its ability
to absorb nutrients) (Rynk et al, 1992). In addition, com-
post enhances soil porosity, improves resistance to erosion,
improves storage and release of nutrients, and strengthens
disease suppression (EPA, 1993). The near-neutral pH of
compost also is beneficial for growing most agricultural
crops.
An important potential use of compost in the agricultural
industry is its application as a soil amendment to eroded
soils. Farmers in the United States are increasingly concerned
about the depletion of organic matter in soil and are acutely
aware that fertilty is dependent upon maintaining a suffi-
cient amount of organic matter in the soil (EPA, 1993).
Compost is an dent source of organic matter that can
enrich soil and add biological diversity. When applied to
eroded soils, compost can help to restore both organic
content and the soil structure Kashmanian et al., 1990).
The use of compost can help restore and build up nutri-
ents in soil. The nutrients in compost are released slowly
to the roots of plants through microbial activity over an
extended period of time, thereby reducing the potential
for nutrients to leach from the soil. The gradual dissipa-
tion of nutrients from compost also indicates that only a
fraction of the nitrogen and phosphorus available in com-
post is available to the crop in the first year. When applied
continuously, the supply of plant nutrients from compost
is enough to keep plants healthy for several years. Studies
on the residual properties of compost on agricultural soils
have reported measurable benefits for 8 years or more af-
ter the initial application (Rynk et al., 1992).
Effects of Compost Application on Crop Yields in Johnson City, Tennessee
Aompost has been demonstrated to improve crop yields. A study was conducted in Johnson City, Tennessee, from 1968
to 1972 that involved applying compost made from mixed MSW to test plots. During the period of the study 13 suc-
\J cessful corn crops were produced and yield increases due to compost application were noted. The total increase in
yield ranged from 55 percent with an application rate of 40 tons of compost per acre to 153 percent with an application
rate of 1,000 tons per acre (Mays and Giordano, 1989). The figure below outlines the increases in crop yields following
compost application over a 14-year period.
Effects of MSW Compost Application on Test Plots
-*- 200 T/A annually 1969-1973
-«- 8 T/A annually 1969-1973
- No compost applied 1(
1969 1971
Source: Mays and Giordano, 1989,
1973 1975
1977
1979 1981
1983
-------
Potential End Users
Table 8-1. Potential users and uses of compost.
User Group
Agricultural and residential
Primary Uses for Compost Products Compost Products1
Forage and field-
crop growers
Fruit and vegetable
farmer's
Homeowners
Organnic farmers
Turf growers
Commercial
Discount stores,
supermarkets
Garden centers,
hardware/lumber outlets
Golf courses
Greenhouses
Land-reclamation
contractors
Landscapers and
land developers
Nurseries
Municipal
Landfills
Public works
departments
Schools, park
and recreation
departments
Soil amendment, fertilizer supplement top
dressing for pasture and hay crop maintenance
soil amendment fertilizer
supplement, mulch for fruit trees
Soil amendment, mulch, fertilier supplement,
and fertilizer replacemant for home gardens
and lawns
Fertilizer substitute, soil amendment
Soil amendment for turf establishment, top
dressing
Top dressing for turf, soil amendment for
turf establishment and landscape plantings
Resale to homeowners
Resale to homeowners and small-volume users
Top dressing for turf, soil amendment for greens
and tee construction, landscape plantings
Potting mix component, peat substitute,
soil amendment for beds
Topsoil and soil amendment for disturbed
landscapes (mines, urban renovation)
Topsoil substitute, mulch, soil amendment,
fertilzier supplement
Soil amendment and soil replacement for
field-grown stock, mulch, container mix
component, resale to retail and landscape clients
Landfill cover material, primarily final cover
Topsoil for road and construction work, soil
amendment end mulch for landscape plantings
Topsoil, top dressing for turf and ball fields,
soil amendment and mulch for landscape
plantings
Unscreened and
screened compost
Unscreened and
screened compost
screened compost,
high-nutrient compost,
mulch
Unscreened and
screened compost,
high-nutrient compost
Screened compost,
topsoil blend
Screened compost
General screened
compost product
screened compost,
mulch
screened compost
topsoil blend
High-quality, dry,
screened compost
Unscreened compost,
topsoil bland
screened compost
topsoil bland, mulch
Unscreened and
screened compost
composted bark mulch
Unscreeneded low-
quality compost
Unsreened and screened
compost, topsoil bland
Screened compost.
topsoil blend, mulch
Note: Unscreened compost with a consistent texture and few large particles maybe used in place of screened compost.
Topsoil blend is a mixture of compost, soil, or sand to make a product with qualities similar to topsoil or loam. Mulch includes
unscreened, coarse-textured compost such as composted wood chips or bark.
Source: Rynk et al., 1992.
89
-------
Potential End Users
Table 8-2. Effect of MSW compost application an physiochemical characteristics of soil.
Compost compost
Type Rate (mt/ha)
MSW±N-P-K 35,70
fertilizer
MSW±N 4.4,44
MSW 37-99
Pelletized 8,16,32,64
MSW, N-P-K
fertilizer
MSW + SS 80,112,143
MSW±N 224480,
(ammonium 160,325
nitrate)
MSW+SS 124,248,496
+ N
MSW
MSW 112,224,448
MSW+SS
MSW+SS
MSW+SS
MSW 25
MSW 6, 15,40
MSW 15,30
MSW, MSW+-
ss
Duration of
Experiment
2 years
2 years
3 years
16 months
2 years
2 years
5 years
5 years
3 years
^
"""*
3 years
2 years, 6
months
24 pars
Experiment
Condition
Field
Field
Field
Greenhouse
Field
Field
Field
Field.
Field
Field
(mulching
Field
Greenhouse
Field and
climate
controlled pots
Field.
Field,
greenhouse
Field
Soil Type
Phosphate
mine sand
tailings
Sandy soil
Cloy
Arredondo
Songo silt
loom, cloy
loom
Songo silt
loam, clay
loam
Hdston loam
Redish-brown
clay
Myokka-
Basinger fine
sand
Sandy loam
Alluvial, loamy
Loamy sand
Loamy and
sand/vermiculite
mixture
Luvisol derived
from Less
Changes in Soil
Physiochemical
Characteristics
Increased C.E.C.0, E,C>, O.M.C,
and K, Ca, Mg levels..
Increased water holding
capacity,O.M.,pH
exchangeable Co, Mg, and K
Mode the heavy soil more
friable, promoted a crumbly
structure, permitted better
moisture absorption, reduced
erosion, improved aeration, and
increased pH.
Increased water holding
capacity, C. E.G., N, K, Ca,
Mg, B, Mn, and Zn levels.
Increased water holding
capacity, O.M., pH, and K, Ca,
Mg, Zn levels. Decreased bulk
density and compression
strength.
Increased water holding
capacity. O.M., oH, and K, Co,
Mg, Zn levels. Decreased bulk
density and compression
strength.
Increased K, Ca, Mg, Zn, but
decreased P levels in the soil.
Increased O.M. and water
holding capacity.
About 50% of the applied
inorganic P was converted to
organic P and remained in ihe
zone of compost placement.
Metals were distributed in 0 to
23 cm depth.
Increased H and P, K, Co, Mg
levels. Reduced erosion.
Increased C, N, P, K levels.
Increased , O.M., and Cd,
Cu, Mn, Pb, Zn levels.
Did not excessively increase the
heavy metals. Increased pH.
Increased pH, O.M., and total N.
Increased macro and micro
elements, pH, EC., and O.M.
Increased total C and total N.
Reference
Hortenstine
and Rothwell,
1972
Cornette, 1973
Duggan, 1973
Hartenstine
and Rothwelll,
1972
Mays et al.,
1973
Terman and
Mays, 1973
Duggan and
Wiles, 1976
Wang, 1977
Fiskdl and
Prifchett, 1980
Sanderson,
1980.
del Zan et at.,
1987
Chu and
Wong, 1987
Bauduin etal.,
1987
Paris et al.,
1987
Monies and
Syminis, 1 988
Werner et al.,
1988
90
-------
Potential End Users
Table 8-2. (continual).
Compost
Type
MSW+SS +
N-P-K fertilizer
MSW
MSW
Compost
Rate(mt/ha)
98.8 to 2,470
14
15, 30, 60
Duration of
Experiment
5yeors
7,90,180
days
Experimental
Condition
Field
Field
In chambers
Soil Type
Alluvial, loamy
Alluvial
fypic
Haploxeralt
Changes in Soil
Physiochemical
Characteristics
Increased O.M., C.E.C., pH,
macro and micro elements, and
heavy metals. Decreased bulk
density.
No change in available P levels,
but increased K, and available
levels of Cu.Zn.
Increased aggregate stability,
water holding capacity, ana pH.
No change in C.E.C
Reference
Mays and
Giordano,
1989
Cabrera et al.,
1989
Hemandoet
al., 1989
Source: Shiralipour et al., 1992.
'C.E.C. = cation exchange capacity
"E C.= electrical conductivity
'O.M. = organic matter content
Applying compost to soils reduces the likelihood of plant
diseases. This is due to several factors. First, the high temp-
eratures that result from the composting process kill patho-
gens and weed seeds. The frequent turning of windrows and
the insulating layers in static piles ensure uniform high tem-
perature exposure and, therefore, uniform pathogen reduc-
tion. Second, beneficial microorganisms in compost kill,
inhibit, or simply compete with pathogens in soil, thereby
suppressing some types of plant disease caused by soil-borne
plant pathogens and reducing the need to apply fungicides
or pesticides to crops. Microorganisms use the available nu-
trients in compost to support their activity. Organic matter
within compost can replenish the nutrients in soil that has
low microbial activity and, as a result, is susceptible to devel-
oping soil-borne diseases. Finally, physical and chemical
characteristics such as particle size, pH, and nitrogen content
also influence disease suppression. Research indicates that
some composts, particularly those prepared from tree barks,
release chemicals that inhibit some plant pathogens (Hoitink
and Fahy 1986; Hoitink et al., 1991).
Another potential use of compost in the agricultural in-
dustry is the prevention of soil erosion. Soil erosion has a
direct financial impact on food production and the econ-
omy, composting is one of the few methods available for
quickly creating a soil-like material that can help mitigate
this loss. Soil erosion also has a serious impact on the
quality of the nation's surface water supply. Agricultural
runoff fromcroplands, pasture lands, rangelands, and live-
stock operations is estimated to be responsible for over 50
percent of the nonpoint source-related impacts to lakes and
rivers (Kashmanian et al, 1990). Encouraging farmers to use
compost made on and off the farm can bath reduce erosion
and improve water quality. Some counties in Tennessee and
Minnesota are allowed to "east-share" the agricultural use of
compost. The state helps farmers in these areas defray the
cost of purchasing or transporting the compost Kashma-
nian et al., 1990).
Landscaping Industry
The landscaping industry is another potential outlet for
compost. According to the composting Council survey,
the majority of composting facilities surveyed sell com-
post to landscapes (79 yard trimmings facilities and 12
MSW facilities market to this industry). Landscapers use
compost in direct soil incorporation, in the production of
outdoor growing mixes, in the manufacture of topsoil for
new planting, as a soil amendment, and in turf estab-
lishment and maintenance projects. Landscapers require a
premium compost. In general, this means that the prod-
uct should have minimal odor, particle sizes of no greater
than 1/2 inch in diameter, less than 50 percent moisture
content, and no plant or human pathogens (see Table 8-
3). Compost with a near-neutral pH is most suitable for
this industry. Every effort should be made, therefore, to
avoid using liming or acidifying agents during compost-
ing. Landscapers must have the flexibility of raising or
lowering pH themselves so the compost can be useful for
growing plants with different pH requirements.
The landscaping industry also requires that the materials
used in its projects meet the specifications of the land-
scape architect or inspector. Therefore, compost marketed
to this sector must be demonstrated to meet these specifi-
cations. Since landscapers also have expressed concern
about the possible presence of potentially toxic com-
pounds in MSW compost and of viable seeds, herbicides,
and pesticides in yard trimmings compost, tests should be
conducted on the final compost product and the results
made available to potential users.
91
-------
Potential End Users
The amount of compost used by the landscaping industry
depends on economic cycles in the construction and hous-
ing industries. For example, new construction projects such
as residential housing developments and commercial build-
ings can create a high demand for compost. The amount of
compost used by landscapers also is affected by price, avail-
ability and ease of compost application (EPA, 1993).
Landscapers have successfully used compost as a top dress-
ing to reduce weed growth and improve the appearance of
soil and as a mulch to reduce evaporation and inhibit
weed growth. Compost is used in the manufacture of top-
soil due to its ability to improve the quality of existing
soil, which is beneficial to new planting. This use of com-
post is attractive to landscapers because it can reduce the
amount of new topsoil needed, thereby reducing costs.
Other uses of compost in the landscaping industry in-
clude maintenance of lawns and parks, highway landscap-
ing, and sod production. Athletic field maintenance,
renovation, and construction are other strong potential
uses for compost in this industry (Alexander, 1991).
Compost can be used as a soil amendment in the renova-
tion of athletic fields, as a turf topdressing to help main-
tain the quality of the turf surface, and as a component of
athletic field mixes, which are used in the construction of
new fields.
Horticultural Industry
The horticultural industry is one of the largest potential
markets for compost of uniform consistent high quality.
Compost is attractive to the horticultural industry because
it is a source of organic matter and essential trace plant
nutrients, increases the water-holding capacity of soil, im-
proves the texture of soil, and enhances a soil's ability to
suppress plant diseases. The use of compost in potting
mixtures and in seedling beds has helped to reduce the
need to apply soil fungicides in the production of certain
horticultural crops (Rynk et al, 1992).
The use of compost by the horticultural industry depends
upon the quality of the compost, the consistency and
availability, and the cost. As is the case with landscapers,
the use of compost in this industry also depends upon the
state of the economy, particularly the housing industry.
The number of new single-family dwellings built and the
number of homes sold have a direct impact on the demand
for horticultural products. When home sales rise, the de-
mand for nursery products increases as well (EPA, 1993).
The products distributed to the horticultural industry
must be of the highest quality and almost always must be
unlimed. Because of its higher pH, limed compost has
fewer applications than unlimed compost (Gouin, 1989).
To improve the quality of compost earmarked for the hor-
ticultural industry, the compost should be thoroughly
stabilized, composting in smaller piles and for longer pe-
riods of time aid the stabilization process. It is also impor-
Using Yard Trimmings Compost in
Landscaping
Montgomery County, Maryland, sells most of its
compost to landscapers and nurseries in mini-
mum loads of 10 cubic yards (EPA, 1993). The
facility screens its finished compost, which is derived
from leaves and grass clippings, and tests it for weed
seeds and heavy metals. Montgomery County has
found the peak market demand for its finished product
occurs in the spring and fall.
tant for the compost to be odor free. This can be achieved
by ensuring that the compost does not become anaerobic
during curing or storage. In addition, the compost should
be stored either under cover or outdoors in low windrows
not to exceed 6 feet in height. Table 8-4 outline compost
quality guidelines based on certain horticultural end uses.
These suggested guidelines have received support from
producers of horticultural crops (Rynk et al., 1992).
One of the primary uses of compost in horticulture is as a
growing medium for plants. Approximately 60 percent of
all nursery and greenhouse plants currently marketed are
grown in containers. Because 60 to 70 percent of the con-
tainer-growing medium is organic matter, the potential
market for high-quality compost is substantial (Gouin,
1991). As with farmers, however, the high value of the
horticultural industry's crops also make this sector very
cautious and resistant to change (Alexander, 1990; Gouin,
1989). In addition, the horticultural industry already has
a dependable supply of products containing organic mate-
rial. One of these products is peat moss. Significant
amounts of peat moss are used by nurseries for potting
mixes. Compost could be used as a substitute for peat
moss because it is a relatively inexpensive local source of
organic matter. In order for compost to take over a sub-
stantial amount of the market share currently held by peat
moss, laboratory analyses and field tests must be conducted
to demonstrate the benefits, safety, and reliability of the ma-
terial (see Chapter 9).
Silviculture
Silviculture or forestry applications area potentially large
market for compost. A national study estimated that the
aggregate potential for silviculture application was 50 mill-
ion metric tons annually (Slivka, 1992). Four segments of
this market present viable opportunities: forest regenera-
tion, nurseries, Christmas tree production, and established
forest stands.
Regenerating forests represents the largest potential mar-
ket for compost in a silvicultural application (Shiralipour
et al., 1992). Results from limited experimentation with
92
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Potential End Users
Table 8-3. (Continued).
Potenial Compost
Users
Agricultural Industry
Landscaping Industry
Horticultural
Industry/Nurseries
Public Agencies
Residential Sector
Other
Land reclamation
Dedicated land
Golf courses
Sod farms
Quality Requirements
High:
low concentration of physical/chemical contaminants"
High organic content
'/2* particle size
High:
Minimal odor
pH 6.0-7.0; adjustable
* 1/2 "particle size
2% moisture content
High:
pH 6.0-7.0
<'/2" particle size
Low soluble salts
High:
Mature (stable) compost
Low concentration or physical/chemical contaminants0
isize
Good nutrient content
No weed seeds
High:
Minimal odor
<'/2" particle size
<40% moisture content
Low:
Able to support grass
Low
Medium-high
Medium-low
No phytotoxicity
Low soluble salts
Good water-holding capacity
Low soluble salts
No plant/human pathogens
No weed seeds
Dark color
Good nutrient content
Low concentration of physical/chemical contaminants0
Low:
Able to support grass/wildflowers
Low concentration of physical/chemical contaminants"
Dark color
sical contaminants are visible, noncompostable particles; chemical contaminants include heavy metals and toxic substances,
Sources: EPA, 1993;Rynk et al., 1992.
compost applications during forest regeneration have
shown that compost applications have improved the
physiochemical properties of soil and have led to excellent
seedling survival and sustained growth advantages (Shi-
ralipour et al., 1992). One long-term study, in which
MSW compost was applied during forest planting deter-
mined that MSW compost can provide forest growth ad-
vantages while causing no detectable problems
(Shiralipour et al., 1992).
Forest nurseries and Christmas tree production represent
potentially low-volume/high-value applications of com-
post. Organic amendments increase plant vigor, facilitate
improved root proliferation, and enhance survival in out-
planning (Shiralipour et al., 1992). Approximately 123.5
acres of forest nurseries in Florida produced approxi-
mately 106 million seedlings for a 1990 planting of
150,670 acres of new plantations (Shiralipour et al.
1992). An average of 53.5 tons per acre of organic matter
are added annually to maintain Productivity of the seed
beds. Compost could be used in such applications (Shi-
ralipour et al, 1992).
The option to use compost in established forests is not as at-
tractive as those opportunities outlined above due to difficul-
ties associated with gaining adequate access to these areas
with compost spreading machinery Recently planted forests,
however, could be treated before canopy closure and while
access still is possible (Shiralipour et al., 1992).
Public Agencies
Compost uses that are applicable to the public sector in-
clude land upgrade, parks and redevelopment, weed
abatement on public lands, roadway maintenance, and
median strip landscaping. Municipalities that produce
compost should examine their internal needs for soil
amendments, fertilizers, topsoil, and other products. Since
many communities have this built-in market for compost,
they can avoid spending funds on such products, adding
to the overall cost-effectiveness of implementing a com-
posting program. Some states have established standards
(e.g., Florida, Iowa, Maine, Minnesota, NeW Hampshire,
New York, and North Carolina) anchor procurement
93
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Potential End Users
The Use of Yard Trimmings Compost
in the Horticultural Industry
Many facilities for the composting of yard trim-
mings successfully market their compost to the
horticulture industry. Some municipalities have
designed innovativmarketing arrangements that
benefit both the community and the user. For example,
in Scarsdale, New York, the city works with a local
nursery in the composting of approximately 35,000
cubic yards of yard trimmings per year and in the dis-
tribution of the final compost. In return for a share of
the product, the nursery assists with turning the wind-
rows and provides storage space for the finished com-
post. Twice a year, the compost is available free of
charge to residents in a "giveaway" program. The re-
remaining compost is marketed by the nursery as mulch
and also blended into potting soil and topsoil.
A composting facility located in Carver County,
Minnesota, has set up an enterprising arrangement
with the University of Minnesota. The composting
facility is located at the university landscape arbore-
tum. In exchange for the site, the arboretum receives
approximately one-half of the finished compost
product,
preferences (e.g., California, Florida, Illinois, Iowa, Ken-
tucky, Maine, Maryland, Minnesota, Missouri, Nebraska,
New Jersey, North Carolina, Pennsylvania, South Caro-
lina, Washington, and West Virginia) for using compost
in public land maintenance activities funded by the state
(Kashmanian, 1992) (see Chapter 7).
Public agencies can use both high- and low-quality com-
posts. High-quality composts should be used in locations,
such as parks and playing fields, where people or animals
come in direct contact with the material or in the upgrade
of public lands. Upgraded land requires less water to irri-
gate, has an increased resale value, and has a higher quality
of soil (EPA 1993). In parks, high-quality compost can
be used primarily to build and maintain turf. A coarse
compost that has low water-retention capability can be
applied to areas where weed control is necessary.
Lower quality compost can be used for purposes such as
land reclamation, landfill cover, and, possibly large high-
way projects (EPA, 1993). Lower quality compost can be
used by public agencies (as well as private companies) to
establish vegetative growth and restore or enhance the soil
productivity of marginal lands. Uses of compost in land
reclamation include restoring surface-mined areas, cap-
ping landfills, and maintaining road shoulders polluted
with heavy metals and organic pollutants.
Reclamation of mine-spoil areas can be an excellent end-
use option for large quantities of compost. Compost is
valuable for these sites because of its high water-holding
capacity. When using MSW compost in mine-spoil recla-
mation, soil-plant ecology must be considered in regard to
intended land use. For example, if the land is reclaimed
for a natural area, the compost will be required to aid in
the reestablishment of a natural ecosystem (Shiralipour et
al., 1992). If the land is reclaimed for future home sites,
the compost should aid in the support of typical land-
scape plantings and should not contain any pathogens.
Compost with excessive levels of heavy metals can be used
only for landfill cover. The composting Council's 1992
survey reports that several communities across the nation
are using compost in the final capping of landfills. Escam-
bia county, Florida, has been composting mixed MSW
since September 1991. From the outset, the county
planned to use the compost product for daily and final
landfill cover. The material is suitable for use as landfill
cover after four weeks of composting.
Most road shoulders are already polluted with heavy met-
als and organic pollutants from motor vehicles (Shi-
ralipour et al., 1992). Therefore, the use of mixed MSW
compost would not substantially contribute to the dete-
rioration of environmental quality and could reduce the
bioavailability of existing contaminants (Chancy, 1991).
The compost must be capable of supporting roadside
growth with minimal erosion, and the compost must
comply with both state and federal standards for land ap-
plication. Federal and state highway departments have
standards or guidelines for reseeding and landscaping of
highway shoulders that might need to be modified to en-
able use of compost. The growth of this end use depends
on the amount of road construction and maintenance.
Residential Sector
The residential sector represents a substantial market for
compost. Gardeners frequently use compost as a soil amend-
ment to improve the organic matter and nutrient content of
Municipalities Utilizing Compost for
Public works Projects
Mount Lebanon, in Allegheny County Pennsylva-
nia, uses compost in parks and on the city's golf
course (EPA, 1993). The compost is made from
leaves collected in the community. The county also is
planning to set up a series of composting areas in city
parks and to make the finished compost available to
municipalities and park departments. Compost pro-:
duced in Hennepin County Minnesota, is used by the
county's _parks department or redistribured to munici-
palities, which make the compost available to residents
in bulk form free of charge (EPA, 1993). The compost
is made from yard trimmings collected from residents
and landscapers.
94
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Potential End Users
Table 8-4. Examples of compost quality guidelines based on end use.*
End use of compost
Characteristic
Recommened uses
Potting grade
As a growing medium
without additional
blending
Potting media
amendment grade '
For formulating growing
media for pottea crops
withapHlbelow7.2
Top dressing
grade
Primarily for top-
dressing turf
soil amendment
grade a
Improvement of agricultural
soilds, restoration of disturbed
soils, establishment and
maintenance of landscape
plan tings withpH
requirements below 7.2
Color
Odor
Particle size
pH
Soluble salt
concentration
(mmhos per centimeter)
Foreign materials
Heavy metals
Respiration rate
(milligrams par
kilogram per hour)b
Dark brown to black
Should have good,
earthy odor
Less than 1/2 inch
(13 milliliters)
5.0-7.6
Less than 2.5
Should not contain
more than 1% by dry
weight of combined
glass, plastic, and
other foreign particles
1/8-1/2 inch
(3-13 centimeters)
Should not exceed
EPA standards for
unrestricted use
Less than 200
Dark brown to black
Should have no
objectionable odor
Less than 1/2 inch
(13
Dark brown to black Dark brown to black
Range should
be identified
Less than 6
Should not contain
more than 1% by dry
weight of combined
glass, plastic, and
other foreign particles
1/6-1/2 inch
(3-13 centimeters)
Should not exceed
EPA standards for
unrestricted use c
Less than 200
would have no
objectionable odor
Leas than 1/4 inch
(7 millimeters)
Range should
be identified
Less than 5
Should not contain
more than 1% by dry
weight of combined
glass, plastic, and
other foreign particles
1/6-1/2 inch
(3-13 centimeters)
Should not exceed
EPA standards for
unrestricted usec
Leas than 200
Should have no
objectionable odor
Less than 1/2 inch
(13 millimeters)
Range should
be identified
Less than 20
Should not contain
more than 5?'. by dry
weight of combined
glass, plastic, and
other foreign particles
Should not exceed
EPA standards far
unrestricted use
Less than 400
"Far craps requiring a pH of 6.5 or greater, use lime-fortified product. Lime-fortified soild amendment grade should have a soluble salt
concentration less than 30 mmhos per centimeter.
'Respiration rate is measured by the rate of consumed. It is an indication of compost stability.
These are EPA 40 CFR Part 503 standards for sewage biosolids compost. Although they are not applicable to MSW compost, they can be
used as a benchmark.
1 These suggested guidelines have received support from producers of horticultural craps.
Sources: Rynketal., 1992.
95
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Potential End Users
the soil and to increase the soil's moisture-holding capac-
ity. Compost also can be used as a top dressing and as a
mulch. The amount of compost used by the residential
sector depends on the ability of suppliers to consistently
produce a quality product at a reasonable cost. For exam-
ple, only high-quality compost with low soluble salt con-
centrations should be used for home gardens (Rynk et al,
1992). Such compost should have a goad earthy color and
odor and be free of clods. See Table 8-3 for a list of quality
requirements for the residential sector.
Homeowners are becoming increasingly familiar with the
composting of yard trimmings through community yard
trimmings collection programs and promotional backyard
composting campaigns. This familiarity encourages accep-
tance of yard trimmings compost as a high-quality prod-
uct. Developing residential markets for mixed
MSW-derived compost, however, might prove more diffi-
cult due to the reluctance of the residential sector to ac-
cept mixed MSW compost as a high-quality product.
In addition to product quality, other factors that affect the
quantities of compost used by the residential sector include
population growth, the economy and the housing induts-
try Communities that have a large percentage of single-
family homes typically have a higher demand for soil
amendments than areas of high-density housing (EPA,
1993).
Summary
ompost provides a stabilized form of organic
matter that improves the physical chemical
w and biological properties of soils. It is currently
used by a wide range of end users, including com-
mercial industries (e.g., agriculture, landscaping
horticulture, and silviculture), public a agencies, and
private citizens. There is great potential for expand-
ing these end-use markets. To market compost success-
Mly,yard trimmings and MSWcomposting facilities
must learn the specific requirements of potential end-
users for quality composition, appearance, availabil-
ity and price of the product.
Using Compost as a Growing Medium
Researchers at the University of Florida conducted an experiment using mixed MSW-derived composts as growing me-
dium for plains. The plants used in the experimentthe Cuban royal palm, orange jessamine, and dwarf oleander-
are grown commercially in tropical and subtropical climates, primarily for landscaping. The study found that the
growth rates of the palm and jessamine grown in mixed MSW compost were not significantly different than those grown
in the potting mix used as a control medium; the oleander performed better in mixed MSW composts than in the control
soil (see table below). The study concluded that the mixed MSW composts were no better or worse in terms of plant
growth than the commercial potting mix, which is sold for $35 per cubic yard.
Growth of Three Tropical Landscape Crops as influenced by MSW-Growing Media
. height cm to. On iratftf
-------
Potential End Users
Chapter Eight Resources
Alexander, R. 1991. Sludge compost use on athletic fields.
BioCycle. July, 32(7):69-70.
Cal Recovery Systems (CRS). 1989. composting tech-
nologies, costs, programs, and markets. Richmond, VA:
U.S. Congress, Office of Technology Assessment. As cited
in: U.S. Congress, Office of Technology Asessment.
1989. Facing America's trash: What next for municipal
solid waste? OTA-0-424. Washington, DC: U.S. Govern-
ment Printing Office.
Cal Recovery Systems (CRS). 1988. Portland area com-
post products market study. Portland, OR: Metropolitan
Service District.
Chancy, R.L. 1991. Land application of composted mu-
nicipal solid waste Public health, safety, and environ-
mental issues, p.61 -83. As eked in Shirahpour et al,
1992. Uses and benefits of municipal solid waste com-
post. Biomass & Bioenergy. Tarrytown, NY: Pergarnon
Press. 3(3-4):267-279.
composting Council (CC). 1992. Quarterly Newsletter.
October. Washington, DC: composting Council.
Gouin, F.R. 1989. Compost standards for horticultural
industries. BioCycle. August, 30(8):42-48.
Gouin, F.R. 1991. The need for compost quality stand-
ards. BioCycle. August, 32(8):44-47.
Hoitink, H.A.J., and P.C. Fahy. 1986. Basis for the Con-
trol of Plant Pathogens with Compost. Annual Review of
Phytopathology. Vol. 24:93-114.
Hoitink, H.A.J., Y. Inbar, and M.J. Boehm. 1991. Status
of compost-amended potting mixes naturally suppressive
to soilborne diseases of floricultural crops. Plant Disease.
November, Vol. 75.
Kashmanian, R. 1992. composting and Agricultural
Converge. BioCycle. September, 33(9):38-40.
Kashmanian, R.M., H.C. Gregory, and S.A. Dressing.
1990. Where will all the compost go? BioCycle. October,
31(10):38-39,80-83.
Mays, D.A., and P.M. Giordano. 1989. Landspreading
municipal waste compost. BioCycle. March, 30(5):37-39.
Mecozzi, M. 1989. Soil salvation. Wisconsin Natural Re-
sources Magazine. PUBL-SW-093-89. Madison, WI: De-
partment of Natural Resources, Bureau of Solid and
Hazardous Waste Management.
Rynk, R., et al. 1992. On-fare composting handbook,
Ithaca, NY: Cooperative Extension, Northeast Regional
Agricultural Engineering Service.
Shiralipour A., D.B. McConnell, and W.H. Smith. 1992.
Uses and benefits of municipal solid waste compost.
Biomass & Bioenergy. Tarrytown, NY: Pergarnon Press.
3(3-4):267-279.
Slivka, D.C. 1992. Compose United States supply and
demand potential. Biomass & Bioenergy. Tarrytown, NY:
Pergarnon Press. 3(3-4):281-299.
Spencer, R, and J. Glenn. 1991. Solid waste compacting op
erations on the rise. BioCycle. November. 32(ll):34-37.
U.S. Congress, Office of Technology Assessment. 1989.
Facing America's trash: What next for municipal solid
waste? OTA-0-424. Washington, DC: U.S. Government
Printing Office.
U.S. Environmental Protection Agency (EPA). 1993.
Markets for compost. EPA1530-SW-90-073b. Washing-
ton, DC: Office of Policy, Planning and Evaluation; Of-
fice of Solid Waste and Emergency Response.
97
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Chapter Nine
Product Quality
and Marketing
Marketing plays a critical role in any composting operation. It is important to identify end users for the
compost product early in the planning stages of a compost facility since a customer's requirements will
have a significant impact on the dessign and operation of the facility This chapter provides information
about the quality of compost that can be expected from yard trimmings and MSW composting programs. It also
discusses the importance ofspecifications and testing when marketing a compost product. In addition, this chap-
ter examines the factors that must be considered when attempting to tap into identified markets, including mar-
ket assessment, pricing distribution, user education, and public education.
Product Quality
Consistent and predictable product quality is a key factor
affecting the marketability of compost. Each compost user
has different requirements for quality, however. These re-
quirements must be understood and planned for when de-
signing a composting system so that compost quality can
be matched to a user's specific requirements. For example,
certain end uses of compost (e.g., application to crops) re-
quire the production of a high-quality product that does
not pose threats to plant growth or the food chain. Other
uses of compost (e.g., landfill cover) have less rigorous re-
quirements (Section 8 discusses various end uses of com-
post). Some of the key concerns about the potential risks
of composted yard trimmings and MSW are discussed in
this chapter. It should be noted, however, that although
the potential risk associated with biosolids compost has
been extensively studied, less is known about mixed MSW
composts. More studies and field demonstrations are nec-
essary to address research gaps concerning potential envi-
ronmental and health effects of MSW-derived compost.
Yard Trimmings Compost Quality
Compost derived from yard trimmings contains fewer nu-
trients than that produced from biosolids, livestock ma-
nure, or MSW (Rynk et al, 1992); at the same time, it
contains fewer hazardous compounds and other contamin-
ants than compost derived from biosolids, manure, or
MSW (see below). Nevertheless, concerns about the pres-
ence of heavy metals (e.g., lead, Cadmium, zinc, copper,
chromium, mercury, and nickel) and pesticides in finished
yard trimmings compost could affect its marketability.
In general, the levels of heavy metals in MSW compost
made from yard trimmings are well below those that cause
adverse environmental and human health impacts
(Roderique and Roderique, 1990). Table 9-1 shows data
on heavy metal content in yard trimmings compost from
two facilities. The content of heavy metals in the compost
varied, but in all cases was below soil concentrations of
trace elements considered toxic to plants, as well as the
maximum levels established in Minnesota and New York
for co-composted MSW and municipal sewage biosolids
(Table 9-2).
Yard trimmings compost also might contain pesticide or
herbicide residues as a result of lawn and tree spray appli-
cation, High levels of these chemicals could result in a
phytotoxic compost (a compost that inhibits or kills plant
growth). Generally however, pesticides tend to have a
stronger attraction to roots and soil than to yard trim-
mings. In addition, pesticides and herbicides that are
found in yard trimmings feedstock are usually broken
down by microbes or sunlight within the first few days of
composting (Roderique and Roderique, 1990). This is
supported by several recent studies.
A 1990 study found low levels of four pesticides (captan,
chlordane, lindane, and 2,4-D) in leaf compost; all levels
were below U.S. Department of Agriculture tolerance lev-
els for pesticides in food (Table 9-3). Low levels of pesti-
cides also were found in yard trimmings compost in
Portland, Oregon, in 1988 and 1989 (Hegberg et al.,
98
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Product Quality and Marketing
Quality Characteristics in Compost
Product quality depends upon the biological, chemi-
cal, and physical characteristics of die material. Some
of the most desirable characteristics include.
Maturity (e.g., properly cured and stabilized).
High organic matter content.
Absence of viable weed and crop seeds, pathogenic
organisms, and contaminants (such as bits of glass,
plastic, and metal).
Proper pH for the designated end use (usually
between 6,0 and 7.8).
Available nutrients (e.g., nitrogen, phosphorus, and
potassium).
Low or undetectable levels of heavy metals and toxic
organic compounds.
Low concentrations of soluble salts (less than 25
mmhos [a measure of electrical conductivity]).
Uniform particle size of less than 1/2 inch in
diameter.
Dark color and earthy odor.
Moisture content below 50 percent.
Absence of visual, noncompostable contaminants
such as pieces of glass or plastic (Rynk et al, 1992;
CRS, 1990).
It is important to note that storage practices can influ-
ence the quality of MSW and yard trimmings com-
post that is eventually marketed to end users. If piles
of compost are not kept dry and aerated, anaerobic
conditions prevail and odors and harmful anaero-
bic by-products will result (Rynk et al., 1992) (see
Chapter 4).
1991) (see Table 9-4). The chlordane concentration in
the Portland compost were believed to be a result of ter-
mite treatment around houses. Because chlordane is now
banned from general use, the presence of this compound
in compost should decrease in the future. The pentachlo-
rophenol concentrations might be due to treatment of
outdoor wood such as fenceposts. Preliminary studies
conducted in Portland have shown that the presence of
these compounds does not interfere with seed germina-
tion or plant growth (Hegberg et al., 1991).
As these studies indicate, levels of heavy metals and pesti-
cide residues detected in yard trimmings compost have
generally been insignificant. Nonetheless, compacting fa-
cilities should test their product for these and other vari-
ables (including soluble salts, viable weed seed, and
pathogens), as described later in this chapter.
MSW Compost Quality
In order to market MSW compost successfully to many
end users, concerns about potential threats to plants, live-
stock wildlife, and humans must be addressed. One of
the primary concerns is the presence of heavy metals (par-
ticularly lead) and toxic organic compounds in the MSW
compost product, To date, where problems have occurred
with MSW compost, they have resulted from immature
composts, not metals and toxic organics (Chancy and
Ryan, 1992; Walker and O'Donnell, 1991). Manganese
deficiency in soil and baron phytotoxicity as a result of
MSW compost application ears be potential problems,
however. Nevertheless, measures (including effective
source separation) can be taken to prevent all of these
problems and produce a high quality compost.
Heavy Metals and Organics
The bioavailability of contaminants in MSW compost de-
scribes the potential for accumulation of metals or or-
ganics in animals from ingested compost, or from
food/feed materials grown on compost-amended soils.
While research on the ingestion of MSW compost has
only begun recently, field studies on biosolids and MSW
Table 9-1. Heavy metals in yard trimmings compost.
Heavy
Metals
Cadmium
(ppm)
Nickel
Lead
Copper
Chromium
Zinc
Cobalt
Manganese
Beryllium
Titanium (%)
Sodium
Ferrous
Aluminum
Croton
Point New
York
ND
10.1
31.7
19.1
10.5
81.6
4.2
374.0
15.0
0.09
1.51
2.67
3.38
Montgomery
n P **
County,
Maryland1 Standard"
<0.5
102.7
35.5
33.6
153.3
1,100.0
0.02
0.96
0,66
10
200
250
1,000
1,000 <
2,500
NS
NS
NS
NS
NS
NS
NS
'Average of 11 samples, 1984-1985.
"For pesticides, standards are derived from USDA tolerance levels for
pesticides in food (40 CFR Chapter 1, Part 180). Far metals, standards
are Class 1 Compost Criteria for mixed MSW compost, 6 NYCRR Part
60-5-3.
Source: Roderique and Roderique, 1990.
99
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Product Quality and Marketing
Table 9-2. Contaminant Limits for MSW compost (mg/kg).
ConhmiiMMt
Cadmium
Chromium
Copper
Lead
Mercury
Nickel
PCB
Zinc
Minnesota
10
1,000
500
500
5
100
1
1,000
New York
10
1,000
1,000
250
10
200
1
2,500
Source: Hegberg et al., 1991.
composts suggest that a small percentage of metals in
compost-amended soil are bioavailable to plants and other
organisms.
The bioavailability of lead in mixed MSW compost is of
concern to some end users. Lead can present a potential
risk to children who inadvertently ingest compost-
amended soil. A study that examined the levels of heavy
metals in MSW compost from five operating facilities
found somewhat higher lead levels in MSW composts
than the median level in biosolids (Walker and O'Don-
nell, 1991). Studies are necessary to determine if the
bioavailability of this lead is reduced because of binding
with hydrous iron oxide and phosphate in sewage
biosolids compost. Based on available research, Chancy
and Ryan (1992) conclude that lead concentrations in
mixed MSW compost products should be limited to 300
mg/kg. MSW compost prepared from MSW separated at
a central facility often contains lead concentrations of 200
to 500 mg/kg. Source separation of products containing
lead should help reduce the concentration of lead in the
compost product (see below). Diverting these materials
from the MSW stream in the first place (through house-
hold hazardous waste collection programs) should further
help reduce the level of lead in compost.
Researchers also have been concerned with food chain and
dietary risks posed by another heavy metal, cadmium. AS
a result of research on cadmium risk conducted during re-
cent years, it can be concluded that uncontaminated
biosolids and mixed MSW composts pose no cadmium
risk, even in extremely worst-case risk scenarios (Chancy
and Ryan, 1992). Research also indicates that the
bioavailability of cadmium is low, even in acidic soils. In
general, absorption of heavy metals by plants increases if
the soil is acidic (i.e., pH 7.0). In addition, because zinc
(which is found along with cadmiun in biosolids and
MSW composts) interferes with cadmium uptake by
plants, mixed MSW compost is even less likely to
contribute cadmium to human and animal diets via plants
(Chancy, 1991).
It should be noted that heavy metals also appear to be-
come less soluble (therefore less bioavailable to plants)
over time during full-scale mixed MSW composting. If
the composting process is performed properly, metals be-
come bound to humic compounds, phosphates, metal ox-
ides, etc. in the compost and stay bound when mixed
with soil (Chancy, 1991).
Toxic organic compounds, including polychlorinated
biphenyls (PCBs), polycyclic aromatic hydrocarbons
(PAHs), and polychlorinated aromatics (PCAs), are po-
tential concerns with MSW compost. Research has shown
that PCBs are quite stable in the presence of both natural
soil bacteria and fungi (Nissen, 1981); therefore, any
PCBs that do find their way to the feedstock will most
likely be present in the compost. The concentration of
PCBs in MSW compost has been found to be low, how-
ever. PAHs are another potential concern in MSW com-
post, degrading to acids that contribute to the
phytotoxicity of unstable composts. PCAs also can pose
some risk. While they have been found to bind to the or-
ganic fraction of compost, little information is available
regarding their availability to organisms in the compost
product (Gillett, 1992). More studies are needed to better
determine the risks posed from toxic organic compounds
in MSW compost.
Boron Phytoxicity
MSW compost contains substantial levels of soluble boron
(B), Which can be phypotoxic (Chancy and Ryan, 1992).
Much of the soluble B found in MSW compost is from
glues, such as those used to hold bags together (Volk, 1976).
Table 9-3. Pesticides in yard trimmings compost.
Heavy
MotOlS
Captan
Total
Chlordane
Undone
Total 2,4-D
Crotoa
Point, Now
York
0.0052
0.0932
0,1810
0.0025
Montgomery
County,
Maryland"
<1.0C
<1.0
Standard11
0.05-100
0.03
1.00-7.00
0.05-1.00
'Average of 11 samples, 1984-1985.
"For pesticides, standards are derived from USDA tolerance levels for
pesticides in food (40 CFR Chapter 1, Part 180). For metals, standards
are Class 1 Compost Criteria for mixed waste compost, 6 NYCRR Part
60-5-3.
'Average of 2 samples.
Source: Roderique and Roderique, 1990.
100
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Product Quality and Marketing
Table 9-4. Pesticide analysis of Portland, Oregon, yard trimmings compost.
Pesticide
Classification
Chlorophenoxy
herbicides
Chlorinated
Hydrocarbons
.Residue
2,4-D
2, 4-D8
2,4, 5-T
silvex
MCPA
MCPP
Dichloroprop
Dicamba
Pentachlor-
phenol
Chlordane
DDE
DDT
opDDT
ppDDT
Aldrin
Endrin
Number
Of
Samples'
16
16
16
16
16
16
14
16
14
19
14
14
14
16
16
Samples Above
Detection
Limit*
0
0
0
0
0
0
0
0
9
17
3
0
2
4
1
0
Mean'
(mg/kg)
ND'
ND
ND
ND
ND
ND
0.229
0.187
0.011
0.005
0.016
0.007
ND
Range'
(mg/kg)
0.001-0.53
0.063-0.370
0.005-0.019
0.004-0.006
0.002-0.035
0.007
Organo-
phosphates
Miscellaneous
Malathion
Parathion
Diazinon
Dursban
Dieldrin
Trifluralin
Dalapon
Dinoseb
Casoron
PCBs
16
14
14
14
15
13
10
4
5
0
0
0
1
1
0«
0
1
V
0
ND
ND
ND
0.039
0.019
0.129
0.039
0.019
0.129
a. The number of samples is the combined total for 2 sources of compost, which were sampled in June
1988, October 1988, Apti/1989, July 1989 and October 1989. The number of samples taken each time
was not uniform (mostly 2 per period per source in 1988 and 1 per period per source in 1989).
b. The minimum detection limit is 0.001 ppm for pesticides and 0.01 ppm for PCBs.
c. Dry basis.
d. Not detectable (ND),
e. Residue detected but not measureable.
Source: Hegberg et al., 1991.
In general, B phyroxicity has occurred when MSW com-
post was applied at a high rate to B-sensitive crops (e.g.,
beans, wheat, and chrysanthemums). It appears to be
more severe when plants are deficient in nitrogen, when
low humidity conditions are present, or when a great deal
of transpiration occurs (e.g., as in greenhouses) (Chancy
and Ryan, 1992). Because soluble B is more phytotoxic to
acidic soils, liming can correct the problem. In addition, B
phyrotoxicity has been shown to be short lived; it seems to oc-
cur only in the first year of application (Chancy and Ryan,
1992).
Manganese Deficiency
Mixed MSW compost has been found to cause a lime-in-
duced manganese (Mn) deficiency in soils in some eases
(de Haan, 1981). Whether Mn deficiency will occur when
mixed MSW compost is applied to soil depends on such
factors ax
The pHofthe soil- Mixed MSW compost usually
raises the pH of soil; when it is added to naturally
low Mn acidic soils, the resultant high pH can
cause Mn deficiency.
The susceptibility of the crop - Crops that are suscep-
tible to Mn deficiency include soybeans and wheat.
The clay content of the soil - Mn concentration ap-
pears to increase with increasing clay content.
The height ofthe water table - Soils that have been
submerged during formation leach Mn and are
101
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Product Quality and Marketing
more susceptible to Mn deficiency (Chancy and
Ryan, 1992).
MSW compost producers need to consider the potential
of mixed MSW compost to induce Mn deficiency, par-
ticularly if soils or crops in the area that the compost will
be marketed are susceptible to Mn deficiency. If necessary,
Mn can be added during composting to ensure that Mn
deficiency does not occur.
The Effect of Source Separation
Many researchers support the use of source separation (see
Chapter 3) to remove recyclable and nonrecyclable/non-
compostable components from the compostable compo-
nents. Source separation is key to reducing the heavy
metal and visual contaminant concentrations in the fin-
ished compost. In a four-season discard characterization
study in Cape May, New Jersey, at least 86 percent of met-
als found in MSW were attributable to noncompostable
materials (plastic, wood, aluminum and tin cans, house-
hold batteries, etc.) (Rugg and Hanna, 1992). Another
study examined the influence of preprocessing techniques
on the heavy metal content in MSW compost. Looking at
the level of heavy metals in finished compost and at dif-
ferent separation techniques, the study concluded that fin-
ished compost contained the lowest levels of zinc, lead,
copper, chromium, nickel, and cadmium when source
separation occurred (see Table 9-5). In practice, however,
it might be very difficult to remove many of the materials
containing heavy metals. Extensive separation once these
materials have been mixed with organics can be very
costly.
Product Specifications
Developing and utilizing appropriate compost product
specifications ensures that high-quality compost will be
produced. Specifications can be established for a number
of parameters, including organic matter content, particle
size, nutrient content (especially carbon-to-nitrogen ra-
tio), presence of toxic compounds, nontoxic contaminant
levels, concentration of weed seeds, seed germination and
elongation, soluble salts, color, odor, and water-holding
capacity (EPA, 1993).
All of these characteristics are critical to buyers. For exam-
ple, high moisture content means customers receiving
bagged compost receive bagged water as well. Particle size
affects aeration, drainage, or water-holding capacity. The
compost's pH, nutrient concentrations, or heavy metal
concentrations restrict its usefulness for certain plants. If
the compost is not stable, storage will be difficult and
might affect the compost quality, Compost stability also
has an impact on plant growth. Finally presence of visible
noncompostable contaminants might influence the
buyer's perception of quality.
Table 9-5. Heavy metal concentrations in MSW-derived
compost.
Metal
Processing method (mg/kg dry weight)
A B c D
zinc
Lead
Copper
Chromium
Nickel
Cadmium
1,700
800
600
180
110
7
800
700
270
70
2.5
520
420
100
40
1.8
230
180
50
30
1.0
A, Mixed household Waste are composted without preparation, the
process takesapproximately 12 month, After composting, the product
is screened and Insert are removed,
B. The collected household waste are separated into two fractions.The
material container most the easily degradable organic material,
between two and-a-half and five months are needed for this
composting process,
C, The collected waste are shredded, then processsed,resulting in a
fraction to be composted, This fraction is free of most inerts, such as
glass and plastics,
D, Wastes are separated at the source, The organic components are
collected separately at households, All necessary steps are taken to
insure that components Containing heavy metals do not enter the
organic components,
Source: Oosthnoek and Smit, 1987.
Uniform product specifications have not been developed
for compost. A few states, however, have developed speci-
fications and regulations for yard trimmings and MSW
compost (see Chapter 7 for more information on legisla-
tion). During the planning stages of a composting facility,
communities should determine what regulations and
specifications, if any, have been established in their state.
Specifications of bordering states also could be investi-
gated in order to expand marketing options. Where a state
has not established specifications, minimum acceptable
product standards should be determined based on antici-
pated end uses.
The final compost product should exhibit the charac-
teristics that are important to the customer. Prospective
clients also can be provided with samples of the compost
product and specification sheets listing the parameters
tested and the results of the tests (a sample specification
sheet is shown in Figure 9-1).
Product Testing
To ensure product quality, the compost product should be
laboratory tested frequently, Many environmental labora-
tories test compost. A composite sample, composed of
many small samples from different locations in the curing
piles, will provide the most representative result.
102
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Product Quality and Marketing
Average Concentration of Essential Plant Netrients
(h permit)
Kjeldahl Nitrogen (TKN)
Phosphorus
Potash
1.40%
1.56%
0.30%
Average Heavy Metal and KB Concentrations
(in mkroorganisms/g, dry weight basis)
Cadmium
Copper
bad
Mercury
Nickel
Zinc
PCBs
Source: Rohrbach, 1989.
2.9
332.0
499.0
4.6
449.0
929.0
4.6
Figure 9-1. Sample specifications sheet.
Among the tests most commonly conducted are those
that determine the concentration of plant nutrients and
toxic compounds. The compounds that are tested for will
depend on the feedstock and any applicable regulations.
Facility managers should be aware of possible heavy metal
contamination in mixed MSW compost, or other con-
taminants introduced by specific sources. Some facilities
also test for maturity and stability (by using growth
germination tests and root lengths). The present of weed
seeds and phytotoxic compounds also should be moni-
tored. Respiration rate determinations indicate the rate of
decomposition to be expected; a reduction/oxidation test
that measures aeration status of the compost can predict
odor problems. Some composts actually suppress soil-
borne plant diseases, and that possibility should be as-
sessed as well (see Chapter 8). The laboratory equipment
requirements for tests of moisture content, pH, and parti-
cle size are minimal; an outside laboratory will be needed,
however, to determine characteristics such as nutrient and
heavy metal concentrations. Larger facilities perform res-
piration rate tests in house smaller facilities will need to
seek an outside laboratory. Finally, as an added selling
point to potential users, field tests can be conducted,
often by university staff or extension specialists at land
grant schools, to demonstrate product utility and
effectiveness.
It would be useful to carefully record the test data (on a
computerized spreadsheet, if possible) to facilitate any re-
porting requirements that might have to be met and to
provide a basis for comparing information collected over a
long period of time. In this way, subtle changes in com-
post quality or properties can be observed.
Market Assessment
The best way to identify end users for a product is
through a market assessment. The market assessment pin-
points potential consumers, along with their product re-
quirements. Conducting this assessment in the early stages
of the planning process and using the data as the basis for
program design will increase the likelihood of widespread
use of the final compost product and long-term stability
of the composting program. In addition, a market assess-
ment can estimate potential revenues from the sale of the
compost. While the sale of compost is in general not a
highly profitable activity, any revenues earned can help
offset the cost of processing. Estimating revenues is also
important in determining what equipment will be needed
and what the facility's total budget will be. Figure 9-2 pro-
vides a sample market assessment form.
Once the market assessment is performed, potential users
must be turned into real compost users. Many Factors af-
fect this transformation. The product must be priced,
A Successful Market Assessment for
MSW Compost in Wright County,
Minnesota
In Wright County, Minnesota, a product end-use
market assessment was conducted as part of the
county's plans to develop a state-of-the-art compost-
ing facility to manage a substantial portion of its
MSW. Through the assessment, the county accom-
plished the following:
Projected total county demand for compost
products.
Identified end-user specific requirements such as
transportation, chemical and physical specifications,
product pricing, application considerations, de-
mand seasonability, and delivery schedules.
Reviewed compost products' chemical and physical
characteristics and related these to the various end
uses and to applicable regulations.
Identified market development activities such as
field and laboratory testing tailored to local
end-user requirements.
To identify end users, a questionnaire was mailed to
over 130 potential users in a 15-mile radius of the pro-
posed compost facility site. Data from local Chambers
flf Commerce were used to compile the list of potential
end users. Twenty-two end users returned tie ques-
tionnaire; these individuals were tben personally inter-
viewed (Selby et aL, 1989).
103
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Product Quality and Marketing
Company Name.
contact Person _
Address
Phone Number
Type of Business.
1. If you use or sell any of the materials listed below, please indicate the amount used or sold an an annual basis,
as well as the cast per ton.
Product Used Amount Used (in tons) Amount Sold (in tons) cost Per Ton
Composted manures
Fresh manure
Sewage sludge compost
Mushroom compost
Peat
Loam
Organic fertilizers
Topsoil
Potting soils
Custom soil mixes
Bark mulch
Wood chips
2. At what percentage are your annual needs for the above items increasing or decreasing?
3. What are your current terms of purchase?
Figure 92. Sample market assessment farm.
104
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Product Quality and Marketing
4. If yard waste or MSW compost were available in quantity on an ongoing basis, how much would you purchase?
would the purchase terms differ from your current terms?
5. Under what conditions would you be prepared to negotiate a purchase agreement for compost?
6. What are your concerns when purchasing a compost product (for example, odor, price,
nitrogen/phosphorus/potassium, fineness, packaging)?
7. When are your peak demands?
8. What are your transportation/delivery needs?
9. Would you be prepared to guarantee acceptance of a minimum quantity of Compost?
Additional comments:
Please return to:
J. Compost Farmer
100 Dairy Road
Poultryville, MA 00000
Adapted from: Rynk et al., 1992.
Figure 9-2. (Continued).
105
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Product Quality and Marketing
sold, and distributed, and the buyers must be educated so
they can optimize their sales efficiency.
Private vs. Community Marketing
Communities ears market compost themselves or rely on
private companies that are in the business of marketing
compost. Private marketers can advertise the product by
attending trade shows, field demonstration days, and other
events, developing a good public relations campaign;
suggesting appropriate equipment for handling the compost
and pricing the compost competitively
Municipalities also can perform all of these functions, but
this might put a burden on available resources. Some
communities find that the revenues received from market-
ing compost can offset administrative and promotional
costs. Others find, however, that they do not have the in-
house marketing expertise or a suitable infrastructure to
administer a program and thus choose to enlist the serv-
ices of a professional marketing company.
Communities that opt to market the compost them-
selves should check whether they have the legislative
authority to market compost products. Cities with their
own programs also enter into the sensitive area of com-
peting for business in the private sector. Municipal em-
ployees who sell compost to markets such as chain
stores and nurseries can be at a disadvantage compared
to salespeople who work for private firms, especially in
terms of flexibility in dealing with potential customers.
Another approach to marketing compost that is becoming
increasingly popular is to market the product through a
broker (CRS, 1990). The broker buys the compost at
a low price and takes responsibility for product testing,
compliance with regulatory constraints, and promotion.
A compost broker in the Northeast buys compost from
a number of municipalities in the region and resells it to a
network of landscapers and major topsoil users.
Table 9-6. Prices received for compost.
Free Compost
Some facilities build a customer base by giving away
compost. Middlebush Compost, Inc., has been
composting leaves in Franklin Township, New Jer-
sey, since early 1987. At first, in order to establish mar-
kets, the company gave the product away as part of its
marketing campaign. By die end of 1989, they were
able to sell all of their product at $ 10 per cubic yard
screened and $6 per cubic yard unscreened. The com-
post was sold to landscapers, developers, nurseries, gar-
den centers, and home owners for use as a potting soil,
a soil amendment, or a mulch for water retention and
weed control, and was also used to cap landfills
(Meade, 1989).
Pricing
A number of factors play a role in determining the final
price of the compost product, including compost qual-
ity and availability the cost of the composting
program; costs of transportation, production, market-
ing, and research and development the price structure
of competing products; and the volume of material
purchased by an individual customer. Since the main
objective of marketing is to sell the compost that has
been produced, the price of the compost should be set
to help achieve this. A logical strategy is to price the
product modestly at first to establish it in the market-
place and then increase the price based on demand.
Table 9-6 provides examples of prices established for yard
trimmings and mixed MSW compost.
Several communities have not charged for compost in
order to increase community awareness of the benefits
of compost. Providing compost free of charge also pro-
motes good will in a community and is an effective way
to find commercial users who might be willing to try the
Facility or Community
St. Cloud, Minnesota
Portage, Wisconsin
New Castle County, Delaware
Sumter County, Florida
Skamania, Washington
Montgomery County, Maryland
Seattle, Washington
Materials Composted
Mixed MSW and Biosolids
Mixed MSW and Biosolids
Mixed MSW and Biosolids
Mixed MSW
Mixed MSW
Yard Trimmings
Yard Trimmings
Market
Farm Fields, Landscapers
City-Owned Industrial park
Landscapers, Horticulture
Nurseries, Sod Farms
Homeowners
Landscapers, Nurseries
Landscapers, Residents,
City/County
Price
None or $4 per yard0
$20 per ton
$8 per Yard'
$4.50 per yard"
Planning on $9-12 per yard'
$5-10 per yard"
$19.20 per tonb
$7.50-12.50 per yardb
Sources: "Goldstein and Spencer, 1990; 'Taylor and Kashmanian, 1989.
106
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Product Quality and Marketing
product. Some experts warn against "giveaway" programs,
however, because these can give the impression that the
compost has no value. Many recommend charging at least
$1 per cubic yard to associate value with the product.
Some communities charge a nominal fee to bulk users
and nonresidents but give the product free to residents.
Other communities charge residents a small fee. In
Cleveland, Ohio, the Greater Cleveland Ecological As-
sociation, which serves 16 communities and composts
approximately 250,000 cubic yards of leaves each year,
sells compost to residents. Discounts might be given for
large-volume buyers and for early payment. The pricing
structure and whether to give the compost away are de-
terminations that should be made on a community by
community basis, depending on the amount of material
available, its quality, and the opportunities for use
(Mielke et al, 1989).
Location/Distribution Issues
Market location is of key importance for both product ac-
ceptance and transportation issues. Generally, the price of
compost does not cover the cost of transportation over
long distances (EPA, 1993). In most eases, therefore, the
market for compost is within 25 or 50 miles of the
Cleveland's Options for Compost
Distribution
"^f^ie Greater Cleveland Ecological Association oper-
I ates six facilities for composting yard trimmings
I and serves 16 communities in Cleveland, Ohio.
The association sells compost in the following ways:
Customers bring dieir own containers (bags or bush-
els) to the composting site; the cost is $0.75 per
bushel.
Customers pick up bulk loads of compost at the
composting site. Customers' trucks are loaded for
$13.50 per cub'ic yard.
Compost is home delivered. There is a 2 cubic yard
minimum, which is sold for $55.10, and a 10 cubic
yard maximum, which is sold for $178.30. These
prices include delivery and taxes. There is art addi-
tional charge of $20 for out-of-county delivery.
Compost is bagged in 1 cubic yard plastic bags.
These are sold dirough distributors who deal with
the nursery and landscaping industries.
A discount is given for semi-truckloads delivered to
landscapers and commercial growers to encourage the
use of compost on lawns and in potting media for
nursery stock. The compost has sold out every year.
composting facility (Rynk et al., 1992). Proximity to com-
posing facilities promotes trust in the product through
name recognition, increases buyers' access to the product,
and enables the compost to be sold at a competitive price
due to low transportation costs. Bagging the compost
product can expand the potential market area. While bag-
ging requires a higher capital investment in machinery
and bags, the bagged product sells at a considerably higher
price than most bulk compost. The higher price might
justify higher transportation costs and, therefore, a larger
market area (Rynk, et al., 1992). Municipalities are usu-
ally better off selling in bulk.
The cost of transporting compost also depends on its
weight and bulkiness. Many compost products are mar-
keted only locally because the bulkiness of the compost
(400 to 600 kg/m3[700 to 1,000 lb/yd3]) makes transpor-
tation expensive. Communities need to monitor available
transportation funds carefully during facility planning
stages so that the distance between potential markets and
the manufacturing facility can be set accordingly.
Distribution systems for compost are diverse and often
creative. A system should be developed based on a survey
of the needs of the potential users. Most compost is dis-
tributed in the following ways:
Direct retail sale or free distribution of bulk com-
post by truckload or in small quantities on site.
Direct sale or free distribution of bagged compost
on site or at special distribution centers.
Direct sale or free distribution to wholesalers for
processing in bulk or in bags to retailers (EPA,
1993).
Municipalities that perform composting should examine
their own public sector markets and determine how much
money is spent annually on fertilizer, top soil, and other
soil amendments by governmental agencies in the region.
A fair amount of demand often can be created internally
by passing procurement ordinances specifying recycled
materials. For example, bid proposals could require that
the topsoil used for land reclamation contain a minimum
level of compost.
Many facilities rely on local residents to transport the
compost from the composting site. This approach is not
always successful, as most residents can transport and use
compost only in small quantities. Residential users also
prefer bagged compost. Bagging requires additional in-
vestment in capital costs, which in turn requires higher
pricing. A successful marketing program for bagged com-
post requires a high-quality product and intensive adver-
tising to overcome price competition from competing
products.
107
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Product Quality and Marketing
Product Diversity
For both yard trimmings and MSW composting op-
erations, producing a variety of products broadens
the potential market base, increasing the amount of
compost sold and the revenues earned. Producing
more than one product can alleviate shortfalls during
peak demand periods, thereby improving distribution
and reducing the amount of storage space required,.
Producing several products from the feedstock also
guards against generating an oversupply. Several grades
of compost products (that would be significantly dif-
ferent in chemical or biological properties) could be
manufactured by segregating portions of the feedstock.
For example, a facility could offer soil amedment-
grade and potting media-grade composts.
If such segregation is not possible, the compost pro
duced at the facility could be modified to make several
grades of compost. For example, the compost's nutri-
ent properties could be supplemented, the pH adjusted
to suit different market needs, or the particle size could
be varied by using coarser or finer screens to manufac-
ture a rough-grade and a fine-grade compost. Whole-
salers and retailers of compost sometimes add other
ingredients, like lime or sand, for special uses or mar-
kets. The costs of these options will vary according to
region.
Education and Public Relations
The results of a marketing study carried out in Port-
land, Oregon, indicate that the quantity of compost
used by residents is largely a function of public educa-
tion and the capability of a facility to produce a high-
quality product consistently (CRS, 1988). It is therefore
important to work closely with potential end users to
educate them about the product's benefits and how it
should be used.
Product credibility as recognized by an independent third
party could help improve sales. Communities can obtain
several independent expert opinions to assure the user of
the benefits of the product. These might include a repre-
sentative of a university, an extension service, an agricul-
tural experiment station, or even a large greenhouse,
nursery, or farmer who has used the product and is willing
vouch for it. Landscape or nursery associations might pro-
vide opportunities for composting facility representatives
to speak at monthly meetings and offer educational infor-
mation to their members. Once educational material is
developed, the involvement of an educational network is
vital (Tyler, 1992). The United States Department of
Agriculture offers an educational program to farmers
through the Cooperative Extension Service; communities
can contact the Cooperative Extension Service to assist
them in marketing finished compost to area farmers.
Throughout the marketing process, it is critical to present
the compost as a usable product, not as a waste material
that must be disposed of. It is imperative to realize the im-
portance of a positive attitude and how contagious enthu-
siasm can be when presenting ideas on the uses of
compost (Tyler, 1992). A positive approach can help re-
duce the potential stigma that users might assign to cer-
tain types of compost and promote acceptance of compost
in the marketplace.
Updating the Market Assessment
Marketing requires continuous effort and does not stop
once end users are secured. End users must become repeat
customers if there is to be continued success of a market-
ing strategy. Monitoring of the marketplace is necessary to
determine if all of the compost produced is being distrib-
uted, if users are satisfied with the product, and if the
publicity strategies being employed are effective. Re-sur-
veying potential users to determine whether they are now
willing to use the compost is beneficial, as is updating the
market assessment to identify any new market that might
have emerged since the last survey. Ongoing marker surveys
allow customers to participate in program development. Un-
derstanding customers' feelings and emotions paves the way
for building trust in the compost product (Tyler, 1992).
Summary
The marketing of compost should be undertaken
in the early stages developing the composting
facility in order to identifiy potential end users of
compost and quality of compost they demand This
will assist decision-makers in all facets ofplanning
from desiging the size of the facility to marking fi-
nancial projections of revenues. Communities should
consider all aspects of marketing including packag-
ing, distribution, and applicable regulations. Mar-
keting can be conducted in house or through
marketing companies and brokers. Finally commu-
nity officials should keep in mind the constant need
to gauge customer satisfaction and attitudes so that
potential problems can be isolated and solved before
they affect facility performance.
Chapter Nine Resources
Appelhof M, and J. McNelly. 1988. Yard waste compost-
ing Guidebook for Michigan communities. Lansing MI:
Michigan Department of Natural Resources.
108
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Product Quality and Marketing
Cal Recovery Systems (CRS) and M.M. Dillon Limited.
1990. composting A literature study. Ontario, Canada:
Queen's Printer for Ontario.
Cal Recovery Systems (CRS). 1988. Portland-area com-
post products market study. Portland, OR: Metropolitan
Service District.
Chancy, R.L., and J.A. Ryan. 1992. Heavy metals and
toxic organic pollutants in MSW composts: Research re-
sults on phytoavailability, bioavailability, Fate, etc. As cited
in. H.A.J. Hoitink et al, eds. Proceedings of the Interna-
tional composting Research Symposium. In press.
Chancy, R.L. 1991. Land application of composted mu-
nicipal solid waste Public health, safety, and environ-
mental issues. As cited in Proceedings of the Northeast
Regional Solid Waste composting Conference, June 24-
25, 1991, Albany, NY. Washington, DC composting
Council, pp. 34-43.
composting Council (CC). 1992. Personal communica-
tion. Washington, DC.
de Haan, S. 1981. Results of municipal waste compost re-
search over more than fifty years at the Institute for Soil
Fertility at Haren/groningen, the Netherlands. Nether-
lands Journal of Agricultural Science. 29:49-61. As cited
in Chancy and Ryan, 1992. Heavy metals and toxic or-
ganic pollutants in MSW composts Research results on
phytoavailability, bioavailability, fate, etc. As cited in:
H.A.J. Hoitink et al., eds. Proceedings of the Interna-
tional composting Research Symposium. In press.
Gillett, J.W. 1992. Issues in risk assessment of compost
from municipal solid waste Occupational health and
safety, public health, and environmental concerns.
Biomass & Bioenergy. Tarrytown, NY: Pergamon pres.
3(34):145-162.
Goldstein, N., and B. Spencer. 1990. Solid waste com-
posting facilities. BioCycle. January, (31)1:36-39.
Harrison, E.B., and T.L. Richard. 1992. Municipal solid
waste composting policy and regulation. Biomass &
Bioenergy. Tarrytown, NY: Pergamon Press. 3(3-4):127-
141.
Hegberg, B.A., W.H. Hallenbeck, G.R. Brenniman, and
R.A. Wadden. 1991. Setting standards for yard waste
compost. BioCycle. February 32(2):58-61.
Meade, K 1989. Waiting for the leaves to fall. Waste Al-
ternatives. March: 34-38.
Mielke G., A. Bonini, D. Havenar, and M. McCann.
1989. Management strategies for landscape waste. Spring-
field, IL: Illinois Department of Energy and Natural Re-
sources, Office of Solid Waste and Renewable Resources.
New York Legislative Committee on Solid Waste Manage-
ment. 1992. Earth for sale: Policy issues in municipal
solid waste composting. Albany, NY
Nissen, T.V. 1981. Stability of PCB in soil. As cited in:
M.R. Overcash, ed. Decomposition of toxic and nontoxic
organic compounds in soil. Ann Arbor, MI: Ann Arbor
Science Publishers, pp. 79-87.
Oosthnoek, J., and J.P.N. Smit. 1987. Future of compost-
ing in the Netherlands. BioCycle. July 28(7):37-39.
Pahren, H.R. 1987. Microorganisms in municipal solid
waste and public health implications. Critical reviews in
environmental control. Vol. 17(3).
Portland Metropolitan Service District (PMSD). 1989.
Yard debris compost handbook. Portland, OR: PMSD.
Roderique, J. 0., and D.S. Roderique. 1990. The environ-
mental impacts of yard waste composting. Falls Church,
VA Gershman, Brickner & Bratton, Inc.
Rohrbach, J. 1989. Delaware Solid Wrote Authority New
Castle, DE.
Rugg, M., and N.K. Hanna. 1992. Metals concentrations
in compostable and noncompostable components of mu-
nicipal solid waste in Cape May County, New Jersey. Pa-
per presented at the Second U.S. Conference on
Municipal Solid Waste Management, Arlington, VA.
Rynk, R, et al. 1992. On-farm composting handbook.
Ithaca, NY: Cooperative Extension, Northeast Regional
Agricultural Engineering Service.
Selby, M., J. Carruth, and B. Golob. 1989. End use mar-
kets for MSW compost. BioCycle. November, (30)11:56-
58.
Smit, J.P.N. 1987. Legislation for compost in the Nether-
lands-Part II. As cited in de Bertoldi, M. et al., eds.
Compost: Production, quality and use. New York, NY:
Elsevier Applied Science.
Taylor, A., and R Kashmanian. 1989. Yard waste com-
posting A study of eight programs. EPA1530-SW-89-038.
Washington, DC: Office of Solid Waste and Emergency
Response, Office of Policy, Planning and Evaluation.
Tyler, R 1992. Ground rules for marketing compost. Bio-
Cycle. July, 33(7):72-74.
U.S. Environmental Protection Agency (EPA). 1989.
Characterization of Products Containing Lead and Cad-
mium in Municipal Solid Waste in the United States,
1970-2000. EPA/530-SW-89-015B. Washington, DC:
Office of Solid Waste and Emergency Response.
U.S. Environmental Protection Agency (EPA). 1993.
Markets for compost. EPA/530-SW-90-073b. Washing-
ton, DC: Office of Policy, Planning and Evaluation, Of-
fice of Solid Wrote and Emergency Response.
109
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Product Quality and Marketing
VolkV.V. 1976. Application of trash and garbage to agri- Walker, J.M., and M.J. O'Donnell. 1991. Comparative
cultural lands, pp. 154-164. As cited in Chancy and Ryan, assessment of MSW compost characteristics. BioCycle.
1992. Heavy metals and toxic organic pollutants in MSW August, 32(8):65-69.
composts: Research results on phytoavailability, bioavail-
ability, fate, etc. As cited in: H.A.J. Hoitink et al, eds. Williams, T.O., and E. Epstein. 1991. Are there markets
Proceedings of the International composting Research for compost? Waste Age. April, 22(1):94100.
Symposium. In press.
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Chapter Ten
Community
Involvement
Decisions involving solid waste management can generate considerable controversy among local residents,
who are concerned about the safety and health of their friends and family as well as the welfare of their lo-
cal environment. Therefore, it is crucial local official to develop strong support among their constituents
whenever embarking on solid waste policy-making; planning a composting facility no exception. Local support
ofa composting operation determines the ease with which the facility can be sited and the willingness ofthe pub-
lic to participate in the program. Decision-makers can involve the public by inviting constituent to participate
in many decisions surrounding composting facility siting design, and operation. In addition, an educational and
public relations program must be conducted to maintain citizen enthusiasm in the program once operation has
commenced
Planning the Composting Project
A well-run public information program can help generate
support for a composting program in the planning stages.
Local officials can undertake a publicity campaign to edu-
cate citizens and the media about how composting works
and why it can be an effective waste management strategy.
The publicity campaign can also point to the planned
composting program as a source of civic pride because it is
an indication that the community is environmentally
aware. Publicity techniques can include
Paid advertising - Television or radio ads, newspa-
per ads or inserts, magazine ads, outdoor ads.
Public service advertising - Radio announcements,
free speech messages, community calendar notices,
utility bill inserts.
Press coverage - Briefings, news conferences, feature
stories, press releases, press kits.
Non-media communications - Presentations to civic
organizations or schools, newsletters, exhibits/dis-
plays, mailings of key technical reports, promo-
tional materials (brochures, door hangers, leaflets).
while promoting the benefits of composting the public
information program should also foster realistic expecta-
tions. Officials must provide honest and detailed informa-
tion about issues such as:
Odor- It is important to acknowledge that com-
posting can generate odors, but that-steps can be
taken to minimize their impact on the surrounding
community (see Chapter 6).
mThe portion ofthe waste stream that can be composted -
While as much as 30 to 60 percent of the MSW
stream could potentially be composted, compost-
ing is not a panacea for managing all that a commu-
nity discards.
Costs of composting - The sale of compost will not
generate enough revenue to support all the costs of
a municipality's composting program. It is the cost
savings from avoiding combustion or landfilling
and the beneficial reuse of materials that make com-
posting financially attractive.
Once the public has been informed about composting in
general and about the proposed facility, the next step is to
provide avenues through which members of the public
can express their concerns. A variety of techniques are
available for soliciting feedback from members of the Pub-
lic, including advisory groups/task forces, focus groups,
telephone hotlines, public hearings, town meetings,
referendums, interviews with people representing key
groups or neighborhoods, and workshops to resolve spe-
cblic "issues. Some of these techniques give community
111
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Community Involvement
members decision-making roles, while others give them
advisory roles or simply provide information. The degree
of decision-making authority might depend on what local
laws require (some require that all policy and budgetary
decisions be made by local officials) or what element of
the composting program is under discussion and if it is
controversial (for example, siting might require more
decision-making by members of the community than
details of processing technologies). Cornell University is
currently doing a study on this subject, supported by
funds from the Compost Council Research Foundation.
Commnity Involvement in Siting
Decisions
Siting a composting facility can be a sensitive process for
solid waste managers and site designers. The search for
sites can be stalled by local residents who do not want a
Planning a composting Facility
Through Teamwork
Disposing of fish scraps from processing plants was
a perennial problem for communities on the
Maine shoreline until a consortium of public and
private organizations found a solution through com-
posting, The consortium included fish processors, the.
local water company the U.S. Department of Agricul-
ture, and the Maine Departments of Transportation,
Environmental Protection, and Agriculture. By involv-
ing these groups in the planning process, adversarial re-
lationships were minimized and a sense of joint
ownership of the project developed.
One of the first steps of the consortium was to develop
clearly stated goals. The groups also formed special ac-
tion committeesmanagement, budget and funding,
public relations, and research-to carry out important
tasks identified in the team planning sessions. The
publicity committee, for example, was charged with
addressing the concerns of local residents about com-
posting. The committee developed a slide show for the
public that depicted the process and benefits of large-
scale composting an educational project display for
municipal offices, and a high-quality brochure. In ad-
dition, the publicity committee organized two public
field days at the site and promoted the usefulness of
finished compost through an information campaign.
Today, due in part to this educational campaign, the
facility continues to compost and has gained accep-
tance for its finished product. Many groups, such as
the Maine Department of Transportation, along with
towns and private citizens use the compost for land-
scaping and soil amendment purposes (York and Laber,
1988).
composting facililty in their community (the Not In My
Backyard, or NIMBY, syndrome). People might be espe-
cially opposed to siting a facility in populated areas or in
areas located near residences, schools, and hospitals.
Residents near a site proposed for a composting facility
might be concerned about potential problems with the
operation, particularly about the potential for odor gen-
eration. Noise, traffic, visual impacts, and potential health
threats might be additional concerns of residents. Officials
should be prepared to listen to the public's concerns and
to negotiate the site selection or the design of the facility.
Many communities have changed site or facility design on
the basis of citizens' concerns. Involving the public in sit-
ing decisions builds a greater sense of community solidar-
ity in the project and facilitates compromise among the
participants in the project.
Officials should assure residents that serious problems do
not occur at properly managed facilities, and that effective
corrective measures are available for any complications
that do arise. However, it is important to communicate
that composting is not risk free, just as combustion and
landilling are not risk free. Offering information about
the experiences of other communities might help to allay
concerns about the facility. Communicating information
about any risks associated with the program is critical in
building consensus for siting decisions. Because many
misgivings among the public about solid waste manage-
ment facilities are based on perceived risk, officials should
be prepared to provide information dispelling or putting
into perspective any fears that arise among community
members. (Siting considerations and techniques for solv-
ing potential environmental problems are discussed in
more detail in Chapters 5 and 6.)
Site selection committees should draft a set of objective
criteria for choosing an appropriate location for the com-
posting facility. A site selected on the basis of objective
analysis of these criteria will be more acceptable to the
public and will help counter any perceptions that the se-
lection process is arbitrary.
Other guidelines for successful siting include:
Accepting the public as a legitimate partner.
Listening to the concerns of the different interests.
Planning a siting process that permits full consid-
eration of policy alternatives.
Setting goals and objectives for public involvement
and risk communication activities in each step of
the siting process.
Creating mechanisms for involving the public early
in the decision-making process.
Providing risk information that the public needs to
make informed decisions.
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Community Involvement
Siting a Co-Composting Facility in
Wisconsin
fficials in Columbia County, Wisconsin, learned
I the importance of public participation while at-
\J tempting to site a dual materials recovery facility
(MRF) and in-vessel co-composting facility in 1989
and 1990. The officials selected a site for the facilities
in Pacific Township. Meanwhile, the township board
decided to exercise an ordinance granting it authority
to approve the siting of any solid waste authority
within township lines. When county officials pur-
chased an option on the property prior to obtaining
township approval and applied for a Wisconsin De-
partment of Natural Resources permit, many township
residents felt the county was trying to force the board
to accept the site selection.
County officials were cordfronted with a grave public
perception and credibility problem. To avert further
misunderstanding, the county notified residents in the
area surrounding the proposed site and organized pub
lie hearings on the matter, At the same time, residents
of the township established a citizens' committee to
block the siting.
Eventually the county received a permit for the facicility
from the state Department of Natural Resources with
the condition that the county agree to a number of
clauses requested by local citizens. The county agreed,
for example, to put a plastic membrane lining under
the tipping floor-of the MRF and to provide free col-
lection of Pacific Township's garbage. Pacific Township
also obtained authority to inspect the facility at any
time during business hours and issue citations if any-
thing was out of order. Thanks to the willingness of the
county to listen to citizens' concerns and compromise
on facility site and design, the MRF opened in the
spring of 1991, and the co-composting facility opened
in the fall of 1991 (ICMA and EPA, 1992).
Being prepared to mitigate negative impacts on the
community.
Evaluating the effectiveness of public involvement
and risk communication activities (EPA, 1990).
Public Participation in the
Composting Project
To ensure that the composting project runs smoothly
members of the public must have a clear idea of their role
in the program. Facility or community officals must
communicate information such as the collection schedule,
acceptable and unacceptable materials, and how the mate-
rials will get to the facility. Residents can be notified of
collection dates by letter or through announcements in
newspapers or on the radio.
Municipalities also can provide information to the public
about home composting or leaving grass clippings on the
lawn. This information can help reduce the amount of
yard trimmings that a community needs to collect. For
facilities that compost either yard trimmings or MSW,
information also should be provided about the availability
of finished compost and whether the product is free or for
sale (Wish et al, 1990).
At the composting facility, attractive and informative signs
can communicate salient information to the public, in-
cluding the nature of the project, the facility name, the
hours of operation, and the business address and tele-
phone number of the operator. Other signs can direct col-
lection vehicles to unloading areas and indicate traffic
circulation patterns. If there is a drop-off site, signs should
guide people to the site and clearly present the rules for
delivery of the materials. The facility operator should con-
sider including a reception area in the plant and arranging
for tours for interested members of the public and the me-
dia. Officials also can recruit volunteers from the commu-
nity to participate in monitoring incoming materials and
assisting at the drop-off facility.
Educating Citizens About a
Composting Program
Information that can be provided to citizens in a no-
tification about a composting program (and their
role in the program) might include:
A statement of the intent and community benefits
of a composting program.
A description of the intended uses of the compost.
A statement that compostable materials must not
contain materials such as glass, metal, or household
hazardous waste.
Instructions regarding the piling of yard trimmings,
or if bags are used, the type of bag and bag closure
to include information about source separation or
commingling of compostables.
Instructions regarding the placement of the material
at the curb or in the street.
The dates when materials will be collected in desig-
nated districts and the locations and hours of com-
munity collection stations and other drop-off
locations.
A map showing designated drop-off collection areas
(UConn CES, 1989).
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Community Involvement
Another way to maintain a positive relationship with the
community is to establish a complaint response proce-
dure. Some municipalities, for example, recruit residents
to participate on "odor panels" that report to the facility
the detection of any odors originating from the compost-
ing site. (Most composting facilities receive some com-
plaints, primarily about odors.) Complaints should be
logged, along with the time, name of the complainant, ac-
tion taken in response to the complaint, and the date of
followup communication to the complainant. This proce-
dure is designed to ensure that small problems are solved be-
fore they become larger ones, and will reassure neighbors
that their concerns are taken seriously (Walsh et al, 1990).
community education about composting should continue
after the composting operation begins to ensure that support
does not wane. Ongoing publicity can describe successes in
the composting project and remind the community that
composting is an important tool to manage organic materi-
als. The effectiveness of the publicity techniques should be
evaluated periodically
Community Education at the
Marketing Phase
Community education also is important in marketing, es-
pecially if the compost will be distributed to residents.
Literature can be developed explaining the merits and uses
of the compost, how the compost will be distributed (e.g.,
in bags or in bulk), and any restrictions on use. Samples
of the product also can be provided to potential users. In
addition, some communities give away compost to resi-
dents or neighbors of the composting facility (or provide
it at a nominal charge). This can be promoted as a public
service. Such programs foster goodwill and build support
for the composting facility, although communities should
be aware that giving compost away could create the im-
pression that it has no monetary value. Many giveaway
programs require residents to pick up compost at a cen-
trally located site, which is sometimes combined with a
recycling center. This approach helps to raise public
awareness about composting and recycling, and provides a
tangible reward to residents for their efforts. If the com-
post will be distributed or sold to users other than resi-
dents, marketing research should be conducted and sales
strategies devised (see Chapter 8).
Chapter Ten Resources
International City Management Association (ICMA) and
U.S. Environmental Protection Agency (EPA). 1992.
Summary
Successful management of community relations
requires the same degree of attention, systematic
planning and expertise as do the more technical
elments of designing and operating a composting
program. Officals should strive to involve the public
directly in planning and siting the facility Commu-
nity involvement in decision-making builds a sense
of ownership among local residents and minimizes
confrontation among concerned parties.
A strong educational program should accompany
each phase of facility planning and operation. Pub-
lic outreach should include risk communication, in-
formation on program logistics such as collection
times and places, and pubic service announcements
and advertisements aimed at raising public partici-
pation in the program.
Case studies of municipal solid waste facility sitings: Suc-
cess in your community (revised draft report). 73-80.
Logsdon, G. 1991. Slowing the flow to the landfill. Bio-
Cycle. May, 32(5):74-75.
Richard, T. L, N.M. Dickson, and SJ. Rowland. 1990.
Yard waste management: A planning guide for New York
State. Cornell, NY: New York State Energy Research and
Development Authority, Cornell Cooperative Extension,
and New York State Department of Environmental
Conservation.
U.S. Environmental Protection Agency (EPA). 1990. Sites
for Our Solid Waste: A Guidebook for Effective Public In-
volvement. EPA/530-SW-90-0 19. Washington, DC: Of-
fice of Solid Waste and Office of Policy, Planning and
Evaluation.
University of Connecticut Cooperative Extension Service
(UConn CES). 1989. Leaf composting A guide for mu-
nicipalities. Hartford, CT: State of Connecticut Depart-
ment of Environmental Protection, Local Assistance and
Program Coordination Unit, Recycling Program.
Walsh, PA., A.S. Razvi, and P.R. O'Leary. 1990. Operat-
ing a successful compost facility. Waste Age. March,
21(3):137-144.
York, C. E., and D. Laber. 1988. Two c's overcome
NIMBY BioCycle. October, 29(10):60-61.
114
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Chapter Eleven
Economics
Sound financial planning is a crucial step in the successful development ofa composting program. When con-
sidering the mulitude of options available for tailoring a composting program to the needs and resources of
the community decision-makers must weigh the costs and benefits involved and determine whether compost-
ing represents a feasible management option for their community This section describes economic factors that a
community will need to examine when designing a composting program. To give decision-makers a clear frame-
work ofthe costs and benefits involved in setting up and managing a composting facility the primary assumption
used throughout this chapter is that the community owns and operates the facility. Communities might want to
examine other options, such as forming partnerships with other municipalities or private companies, hiring a
contractor to run the facility or trying to attract a private company to establish the facility (see Chapter 1 for
more information on planning). A financial worksheet also is included at the back ofthe Chapter that can be
used to analyze cost information (Figure 11-1).
Cost Benefit Analysis
Costs for developing a composting program typically in-
clude 1) capital costs for establishing and equipping a fa-
cility and 2) operation and maintenance (O&M) costs
associated with such activities as collection, transporta-
tion, processing, program administration, and marketing,
Communities also must keep in mind the revenue-gener-
ating or cost-avoiding aspects of the various composting
choices. Composting can offer several potential economic
benefits to communities:
Extended landfill longevity.
Avoided costs from reducing or eliminating the
need for soil amendment purchases.
Reduced or avoided landfiil or combustor tipping
fees.
Environmental benefits from reduced landfill and
combustion use.
Creation of new jobs.
Revenues from selling the finished product.
Revenues from sale of recyclable.
The net cost of a composing program can be projected
by estimating all capital and O&M costs and subtracting
any revenue ardor avoided costs generated from running
the program. This type of economic assessment, called a
cost/benefit analysis, is used widely throughout the gov-
ernment and private industry to determine the cost-
effectiveness of implementing a social program or making
an investment. To be effective, cost/benefit analyses
should be as comprehensive and derailed as possible.
Many communities, therefore, hire consultants to conduct
this analysis.
Decision-makers should not expect to earn money from
composting. Most community owned and operated man-
agement facilities function at some expense to the taxpay-
ers in the area. This should not diminish the feasibility of
instituting a composting facility, however. Instead, deci-
sion-makrs should compare the costs of composting
against the costs of landfilling and combustion. With the
rising costs of landfilling and combusting, composting
programs frequently prove to be economically sensible
management options.
Communities can choose from a host of collection meth-
ods, site designs, and equipment technologies when plan-
ning a composting program. For instance, implementing
a simple composting program for yard trimmings that re-
quires residents to drop off their materials would require
minimal capital and operating expenses from the commu-
nity. In contrast, MSW composting programs typically
entail far greater start-up and operating expenditures and
are often constructed to serve more than one community.
Typically the program design that a community selects
for a composting project depends on the desired level of
115
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Economics
capital expenditure and on resources, such as equipment
and labor, that are already available and can be partially or
wholly allocated to the composting program.
Capital Costs
Capital expenses must be evaluated when establishing a
compost facility. First, the community must apply re-
sources to plan the composting facility. This involves allo-
cating resources to hire staff or consultants to design the
facility, to hold community meetings, and to conduct out-
reach measures to communicate with the community on
such issues as siting. Suitable land then must be located
and purchased, the site must be prepared for the compost-
ing activity, and vehicles and equipment might need to be
purchased. Some states might require composting facili-
ties (particularly MSW facilities) to obtain an operating
permit, a process that can involve considerable assistance
from staff and/or consultants. When projecting yearly
costs of a composting operation, communities should an-
nualize capital expenses for equipment and site prepara-
tion on the basis of the depreciation rate and the discount
rate.
Site Acquisition
The first capital expense that a municipality must con-
sider is site acquisition. The cost of purchasing a site will
depend on local real estate costs and on how centrally it is
located. More remote sites likely will require less capital to
obtain, but transportation costs will be higher. Communi-
ties that have land available should base the cost of using
the site for a composting facility on the rental market
value of the land.
Site Preparation/Land Improvements
Site preparation costs can vary widely, depending on the
size of the planned facility and natural characteristics of
the land. Communities will need to engage an engineer to
design the site and the facility itself. Decision-makers
must include in the economic analysis for the program the
engineer's salary, even when assigning a staff engineer to
design the composting facility.
Most sites for composting yard trimmings will require
grading to give the processing area the ideal gradual slope
to facilitate proper drainage and efficient composting. It
might be necessary to construct drainage channels to im-
prove control of any runofff The state of Michigan esti-
mates that these minimal preparation measures for a
facility that composts yard trimming will total about
$17,000 on average for a small operation on a 4-acre site
(Appelhof and McNelly, 1988). Significant variables in
this estimate include the size of the site, the cost of labor,
and the difficulty of grading the slope of the site. Infra-
structure and construction costs are additional expenses to
consider. Simple, seasonally oriented operations for the
composting of yard trimming are the least expensive to
build, since minimal infrastructure is required. Road sys-
tems can be limited and unsurfaced, and fencing can be
limited to the processing area to protect onsite equip-
ment. For security, a gate on the access road can be con-
structed, as well as a simple gate house and office for
onsite administration. Construction on this scale, for a
medium-sized operation of 12 acres, has been estimated
to cost $72,000 (Mielke, et al, 1989). These costs can
vary widely however. Paving the surface is the largest
component in this estimate, but this cost might not be
necessary, depending on the soil conditions at the site.
Larger facilities for composting yard trimmings will need
to construct more road systems; to construct a fence
around most of the perimeter of the property, and to
maintain several buildings for equipment, maintenance,
and administration. Many facilities opt to cover the com-
post pad to provide shelter from inclement weather. These
operations will require higher capital expenditures. In ad-
dition, utility hookups will be needed. The main variable
in this expense is the distance of the site from local serv-
ices such as power lines and water mains. Finally, if a
community chooses to implement drop-off collection in
its composting program for yard trimmings, it also must
consider the land needed for a drop-off area, including an
area situated at the composting facility itself or areas lo-
cated at several transfer stations where residents can de-
liver leaves, grass, and/or brush.
MSW facilities require significant site preparation to
guard against runoff and leachate (see Chapter 6). These
facilities will need to construct a drainage system to direct
leachate away from the composting pad to a treatment
area. In addition, a typical 300-to 400-ton per day MSW
composting facility would require an office or administra-
tion area, a mixed processing building, and a composting
area, which might or might not be fully enclosed. Typical
MSW windrow composing facilities require 9 to 24 acres
for the total facility. Capital outlays easily can exceed $1
million when preparing a site for MSW composting (Re-
source Systems, Inc. et al., 1990).
Vehicle and Equipment Procurement
Once the site has been prepared, communities must pro-
cure equipment. Again, lower technology operations for
the composting of yard trimmings will have minimal
start-up costs. Many small facilities that compost yard
trimmings can operate with only a front-end loader for
windrow turning, depending on the size and horsepower
of the selected model, front-end loaders cost from
$55,000 to $125,000 (UConn CES, 1989; Appelhof and
McNelly, 1988). For higher throughput operations de-
signed to accelerate the compost process, grinders or
shredders for particle reduction are necessary these cost
approximately $40,000 to $90,000 (Wirth, 1989; UConn
CES, 1989), depending on capacity. Screening equipment
might be necessary for programs that seek to produce a
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Economics
high-quality compost; these units typically range from
$25,000 for portable screens to $50,000 for stationary
units (Appelhof and McNelly 1988).
Municipalities planning small- or medium-sized opera-
tions for the composting of yard trimmings can share ex-
isting equipment with their public works department or
other communities to reduce start-up costs. In addition,
they might examine the possibilities of renting equip-
ment. Large-scale facilities that compost yard trimmings
might be interested in specialized windrow-turning equip-
ment, which can process material more quickly than
front-end loaders. While such equipment can increase ef-
ficiency, these units can cost well over $125,000.
MSW composting facilities, especially those with on-site
MSW separation, typically require significant equipment
purchases. Magnetic separators and vibratory screens,
which are basic units commonly used in the separation
process, can cost $5,000 and $20,000, respectively
(Wirth, 1989). Shredders, grinders and trommels to
process the feedstock each cost over $100,000. Input and
output conveyors, which move feedstock to and from the
different preprocessing equipment, vary in cost according
to length, but can cost well over $100,000 for a 300 to
400-ton per day facility (Wirth, 1989). Other equipment
that can be used for MSW composting includes odor con-
trol equipment (see Chapter 6), in-vessel windrow turn-
ing systems, and aeration equipment. Each of these
systems are priced over $100,000 for the most simple ver-
sions of the technology. Equipment costs, advantages, and
disadvantages are listed in Tables B-l through B-8 in
Appendix B.
Training
There are also start-up costs associated with personnel
training. Whether a site is small and needs only a few
part-time workers or has a large, onsite staff, training in
equipment operations, administration, and, most impor-
tantly, quality control will be required. It is crucial that
employees recognize the role they play in the production
of consistent, highly marketable compost. Employee in-
terest in the compost product begins with training, and
proper training prevents extensive, costly trial-and-error
learning periods (Appelhof and McNelly, 1988). (Chap-
ter 6 contains more information on safety and health
training.)
Permits
Communities must consider outlays associated with per-
mitting. Permitting requirements vary from state to state,
but usually a municipality seeking to open a composting
facility must submit a comprehensive application detail-
ing site design and operations. Permit applications typi-
cally include provide an engineering design report and a
description of the site layout, facilities, and equipment.
Information on specific site activities, such as active
composting monitoring, and product marketing, as well
as a plan for preventing any environmental contamination
of the site also should be included. Applications also
might include personnel training information. Experts in
the fields of engineering, compost science, finance, and
law are usually needed to prepare applications. Planners
should cheek with their state to determine the exact per-
mit applications requirements.
Operating and Maintenance (O&M)
Costs
O&M costs are those expenses that are incurred from
running and managing a composting facility. Typical
O&M costs include dark, utilities, insurance, and
equipment repair. These costs should be estimated during
the planning process to determine the feasibility of the
composting program for the community.
Collection Costs
One of the largest cost factors connected with any com-
posting program is the type of collection system used. For
a management system to be successful, the costs of collec-
tion must not exceed available resources. Solid waste man-
agers should become familiar with all of the various
options for separating and transporting materials to their
management facility in order to select the method that
will optimize their available resources (see Chapter 3).
The O&M costs of a collection program vary according
to the features of the collection method employed and
certain variables unique to each community. These vari-
ables include local labor costs and the presence or lack of
existing collection equipment and infrastructure.
Drop-Off Collection Costs for yard Trimmings
Limited operating costs are associated with drop-off col-
lection programs. Decision-makers must consider ex-
penses for an ongoing education and communication
program to encourage participation. Public offcials can
notify residents about the program via press releases and
public service announcements. Informational pamphlets
or brochures also can be mailed directly to residences, and
public meetings can be held to discuss the program. Pub-
licity campaigns can become expensive, however, since the
process must be continuous in order to maintain the com-
munity's interest and participation (see Chapter 10 for
more information on community outreach).
MSW Curbside Collection Cost for Yard
Trimmings
Communities looking at curbside collection as a way to
encourage greater participation must decide if such a pro-
gram will be cost-effective by calculating the capital and
O&M costs associated with the various types of curbside
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Economics
collection programs (bulk or containerized). Curbside col-
lection is a more costly collection method than drop-off
programs, but often the additional feedstock reduces unit
processing costs.
Bulk collection systems for yard trimmings are a fairly
labor-intensive undertaking. Personnel must spend con-
siderable time per stop to collect the yard trimmings, re-
sulting in higher operating costs than for containerized
collections. This method also involves additional training
expenses. Since bulk collections are more prone to con-
tamination than containerized collections (particularly in
communities in which tipping fees are charged to resi-
dents for their solid waste), collection personnel must be
trained to spot and remove noncompostables hidden in
curbside piles of yard trimmings. A curbside collection
program that picks up containerized yard trimmings is a
less labor-intensive operation. Such a program, however,
does involve the purchase of the containers and their dis-
tribution to local residents. Chapter 3 contains detailed
cost information on the various types of bags and bins.
With some bins, collection trucks might require special
lifting equipment.
MSW curbside collections can be conducted with source-
separated or commingled MSW. Onsite separation will
result in a large volume of recyclable and noncompostable
material, and the latter must be transported off site for
proper disposal. Source-separated MSW collection in-
volves the costs of a continuing education program to in-
form residents on which components should be separated
out. Commingled collection entails intensive sorting and
removal prior to composting. Significant labor and capital
expenditures will be incurred from installing and operating
the needed preprocessing equipment. In addition, this col-
lection procedure is not entirely free of added hauling costs.
Labor Costs
The labor required at a compost facility is contingent
upon the volume and type of material handled, as well as
the level of technology used. At a minimum, most opera-
tions require workers to receive and prepare compostable
material for windrowing form and turn the windrows;
prepare the compost product for delivery and perform
monitoring maintenance, and administration functions.
A low-technology leaf composting site, one that processes
about 3,000 to 5,000 cubic yards of leaves per acre with
windrows turned by a front-end loader, could function
with just two people working part time-one to operate
the front-end loader and one to monitor the site and to
water the windrowsor one full-time staff person. It has
been estimated that such a facility would need about 135
to 150 labor hours to produce compost.
AS the complexity of the facility and the program grows,
more employees will be needed to perform various func-
tions in the process. A high-technology site that composts
yard trimmings and uses forced aeration and windrow
turners to compost 80,000 cubic yards of feedstock per
year, for instance, might need a plant manager or supervi-
sor to oversee the site; equipment operators to handle the
machinery and vehicles; and workers to empty bagged
material, wet incoming compostable material, and main-
tain the site. Other workers could include a tipping floor
operator, scale operator, and maintenance personnel. For
a facility of this size, much of the staff would likely be em-
ployed full time.
Because of the amount of separation and preparation in-
volved, mixed MSW composting facilities usually incur
the greatest labor costs. In addition, at mixed MSW facili-
ties, more extensive administration and maintenance is
needed over all site operations. The compost process, in
particular, must be overseen carefully and detailed records
on each composting phase must be kept in order to ensure
that a consistent product is produced. This labor drives up
costs. For example, the Delaware Reclamation Project, a
1,000-ton per day mixed MSW composting site that sorts
out noneompostable material with mechanical sorting
and uses an in-vessel system for composting, requires an
annual personnel budget of several million dollars.
Fuel, Parts, and Supplies
The O&M costs for facility equipment also can be signifi-
cant. To operate as cost effectively as possible, fuel.il,
parts, and other supplies must be available to keep site
machinery functioning at capacity. AS a rule of thumb,
municipalities can calculate these expenses for a yard trim-
mings facility as a percentage of the initial equipment
capital costs, with estimates likely ranging around 15 per-
cent. MSW composting will have higher equipment oper-
ating costs than yard trimmings facilities, since much of
the composting is dependent on processing equipment.
A Public/Private Co-Composting
Venture
In 1988, Gardener's Supply, a national mail order
firm located in Burlington, Vermont, proposed to
the city that it convince residents to drop off their
leaves and lawn clippings at a 2-acre plot near the
firm's headquarters. To supplement the yard trim-
mings, Gardener's Supply brought in 70 truckloads of
cow and chicken manure and supervised the laying out
of long windrows across the plot. A vigorous public
education campaign consisting of flyers and signs com-
bined with incentives from Gardener's Supply, such as
Coupons for free finished compost and discounts on
the company's products, brought enough materials to
create 500 tons of compost during the first year of op-
eration. The public relations campaign cost about
$2,400 (ICMA, 1992).
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Economics
For example, at a 300- to 400-ton per day MSW in-vessel
composting facility, these expenses could reach about
$150,000 (Wirfh, 1989). O&M costs for odor control
equipment alone can range up to $360,000 annually, de-
pending on the type of equipment used (see Table B-8 in
Appendix B). These costs include those for biofilter med-
ia, chemical solutions for wet scrubbers, and carbon re-
placement for carbon absorption systems.
Outreach and Marketing Costs
The success of any composting program relies heavily on
the individuals contributing the feedstock. The impor-
tance of public education in developing a composting
program should not be underestimated; the composting
program should be kept in the public's attention con-
stantly in order for a community to maintain good par-
ticipation and recovery levels. Education can take on a
multitude of forms, from radio and television an-
nouncements to newspaper press releases. Communities
should take advantage of as much "free press" as possible.
Expenditures on public outreach often depend on the
level of sophistication communities choose for their publi-
cations and other informational activities. A simple bro-
chure or Fact sheet can be written and printed for only a
few cents per copy, for example. (Chapter 10 describes
public outreach techniques, and Appendix A contains ex-
amples of public outreach material.)
Communities also can choose to market their finished
compost to a variety of potential end users (see Chapters 8
and 9). Marketing efforts should commence with a mar-
ket assessment to identify such factors as the transporta-
tion needs and desired chemical and physical
specifications of each potential buyer. Municipalities often
engage private companies to conduct these surveys and to
develop creative advertising campaigns.
Other Costs
Lesser O&M costs, from utility payments to building and
grounds maintenance, are inherent in any composting
program and should be anticipated. Laboratory testing for
monitoring the quality of the compost produced is an-
other O&M cost. In addition, virtually all composting
operations produce residual waste that must be disposed
of. Large mixed MSW composting sites that receive com-
mingled solid waste and sort out the noncompostable
fraction will generate substantial volumes of reject mate-
rial, often between 10 and 30 percent of incoming materi-
als (Goldstein and Spencer, 1990). Yard trimmings facilities
usually receive compostable yard trimmings separated from
solid waste, and therefore extract a smaller percentage of re-
sidual waste, ranging from 1 to 10 percent (Kashmanian and
Taylor, 1989). The specific costs of rejection disposal depend
on the distance of the composing facility from the landfill,
as well as on the tipping fees for the local landfill.
Benefits From composting
Avoided Costs
The potential for avoided costs must be incorporated into
the cost/benefit analysis of a composting facility. There are
five major avoided costs associated with composting.
First, because composting reduces the need for landfilling
or combustion, some tipping fees are avoided. The
amount of money saved through composting can be sub-
stantial, especially in communities where landfill or com-
bustion capacity is scarce. In some areas, landfill or
combustor tipping fees exceed $100 per ton. Second, a
composting program extends current landfill life and de-
lays the construction of a more expensive replacement
landfill or incinerator. This is particularly significant for
municipalities whose landfills are nearing capacity. Third,
composting avoids the environmental costs of landfilling
operations. For example, risks such as the production of
leachate or methane gas are often not reflected by the tip-
ping fees paid to dispose of solid waste; composting re-
duces these risks, although quantifying the amount of risk
reduction might be a difficult task. Fourth, with compost-
ing the community saves money it currently spends on
soil amendments, topsoil, mulch, wood chips, and other
products for municipal landscaping, landfill cover, and
reclamation programs. If a community uses the finished
compost it produces for these purposes, it will avoid such
expenditures. Folly, composting might result in costs that
can be avoided through reduced trash collection. If drop-off
or curbside programs divert enough yard trimming or com-
postable MSW sanitation personnel might spend less rime
collecting waste destined for the landfill or combustor.
Revenues
It is possible for communities to produce and market a
high-quaky product as a result of their composting ef-
forts. These revenues can help defray some of the costs as-
sociated with a composting program; it is very unlikely,
however, that these revenues alone will offset start-up and
O&M costs. Compost from yard trimmings currently is
more marketable, although markets for MSW compost
might be opening up.
If revenue from the sale of compost is reported as the
price per ton of finished compost, communities should
calculate the ratio of tons of finished compost to tons of
compost feedstock (e.g., $50/ton of finished compost
where 5 tons of feedstock are used to produce 1 ton of
finished compost would translate into $10/ton of feed-
stock revenue stream).
Limited additional revenues might be earned by separat-
ing out recyclable materials during the collection process
or at a mixed MSW composting Facility. Finally, if a com-
munity accepts yard trimmings or MSW for composting
from neighboring communities, revenue can be generated
by collecting ripping fees.
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Economics
Summary
The cost components of the various composting sys-
tems are the major determinants in choosing a
composting system. Judging whether a compost-
ing program will save money is difficult and and
as much on local circumstances as on the chosen com-
bination of collections and processing. A municipal-
ity's size in proportion to its labor rates, land lease or
purchase costs, and equiment cost and operating
rates will determine much of its composting costs.
While it is impossible to consider every contingency,
planners must approach the issue of costs and benefits
from this perpective, drawing all relevant fators
into the equation to make a sound decision on com-
posting in their community. To determine the savings
and thus the economic feasibility o a composting fa-
cility planners should evaluate { e cost per ton of
material composted and compare these numbers with
the costs of alternative management options.
Chapter Eleven Resources
Appelhof, M, and J. McNelly. 1988. Yard waste compost-
ing guide. Lansing, MI: Michigan Department of Natural
Resources.
Dickson, N., T. Richard, and S. Rowland. 1990. Yard waste
management: A planning guide for New York State. Albany,
NY: New York State Energy Research and Development
Authority, Cornell Cooperative Extension, and New York
State Department of Environmental Conservation.
Goldstein, R and B. Spencer. 1990. Solid waste compost-
ing facilities. BioCycle. January, 31(l):36-39.
International City/County Management Association
(ICMA). 1992. composting solutions for waste manage-
ment. Washington, DC: ICMA.
Kashmanian, R., and A. Taylor. 1989. Costs of compost-
ing vs. landfliing yard waste. BioCycle. October,
30(10):60-63.
Massachusetts Department of Environmental Protection
(MA DEP). 1991. Leaf and yard waste composting guid-
ance document. Boston, MA: Division of Solid Waste
Management.
Mielke, G., A. Bonini, D. Havenar, and M. McCann.
1989. Management strategies for landscape waste. Spring-
field, IL: Illinois Department of Energy and Natural Re-
sources, Office of Solid Waste and Renewable Resources.
Resource Systems, Inc., Tellus Institute, and E&A Envi-
ronmental Consultants. 1990. Lowell-Chelmsford Co-
Composting Feasibility Study.
University of Connecticut Cooperative Extension Service
(UConn CES). 1989. Leaf composting A guide for mu-
nicipalities. Hartford, CT: State of Connecticut Depart-
ment of Environmental Protection, Local Assessment and
Progress Coordination Unit, Recycling Program.
U.S. Environmental Protection Agency (EPA). 1993.
Markets for compost. EPA1530-SW-90-073b. Washing-
ton, DC: Office of Policy, Planning and Evaluation, Of-
fice of Solid Waste and Emergency Response.
Wirth, R. 1989. Introduction to composting. St. Paul,
MN: Minnesota Pollution Control Agency.
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Economics
I. START-UP (CAPITAL) COSTS
Site Preparation
Engineering design
Site clearing
Grading
Drainage
Pad material
Equipment
Thermometers(2)
(For other equipment, see optional costs)
TOTAL ONE-TIME START-UP COSTS: $
TOTAL AMORTIZED START-UP COSTS/YR: $
II. OPERATIONAL COSTS
Labor
Monitoring incoming materials
and directing vehicles
Forming windrows (loader operator)
Turning windrows (loader operator)
Watering windrows
Monitoring temperature
Fuel and Maintenance
Front end loader
Related Coats
Lab analysis of Compost
Marketing/distribution compost
Public education
Other
TOTAL OPERATIONAL COSTS/YRS $
Figure 1-1. Composting economics worksheet.
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Economics
III . OPTIONAL OPERATIONAL COSTS
Equipment. Related Labor and O&M
AMORTIZED
PRICE OF
EQUIPMENT LABORO&M
Shredder
Screener
Chipper
Windrow turner
Other
Subtotal: _ + _ +
Othar Otional
Debagging
Other
Subtotal:
TOTAL OPTIONAL OPERATIONAL COSTS/YR: $
IV. OPTIONAL COLLECTION COSTS
Equipment. Related Labor and O&M
AMORTIZED
PRICE OF
EQUIPMENT LABORO&M
Compactor truck
Loader w/claw
Vacuum truck
Dump truck
Street sweeper
Other
Subtotal:
TOTAL OPTIONAL COLLECTION COSTS/YR: $.
Figure 11-1. (Continued).
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Economics
v. COST/BENEFIT ANALYSIS: COMPOSTING VS. CURRENT DISPOSAL
TOTAL COSTS
A. Total amortized start-up costs/yr $_
B. Total operational costs/yr $_
C. Total optional operational costs/yr $_
D. Total optional collection costs/yr $_
E. Total Costs/Yr (A + B + C + D) $.
TOTAL BENEFITS
F. Avoided disposal cost/yr $.
G. Avoided purchases of soil amendment/yr $_
H. Projected income from sale of compost/yr $_
I . Total Benefits/Year (F + G + H) $.
TOTAL NET SAVINGS OR COST
1. Net Savings Year (I-EifI>E)
K. Net Cost/Year (E - I if E > I)
Source: MA DEP.1991
Figure 11-1. (Continued).
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Appendix A
Additional EPA
Sources of
Information on
Composting
EPA Publications on Topics Relating to Composting
The following publications are available at no charge from
the EPA RCRA/Superfund Hotline. Call 800-424-9346,
or TDD 800-553-7672 for the hearing impaired, Monday
through Friday, 8:30 a.m. to 730 p.m., EST. In Washing-
ton, DC, call 703-412-9810 or TDD 703-412-3323.
Decision-Maker's Guide to Solid Waste Management.
EPA/530-SW-89-072. 1989.
Markets for compost. EPA/530-SW-90-073b. 1993.
Promoting Source Reduction and Recydability in the Mar-
ketplace. EPA/530-SW-89-066. 1989.
Recycling Grass Clippings. EPA/530-F-92-012.
Residential Leaf Burning: An Unhealthy Solution to Leaf
Disposed EPA/452-F-92-007.
Sites for Our Solid Waste: A Guidebook for Effective Public
Involvement. EPA/530-SW-90-019. 1990.
Yard Waste Composting: A Study of Eight Programs.
EPA/530-SW-89-038. 1989.
Yard Waste Composting. EPA/530-SW-91-009.
The following publications are available from the Na-
tional Technical Information Service (NTIS). Call 800-
553-6847, Monday through Friday, 8:30 a.m. to 5:30
p.m. In Washington, DC, call 703-487-4650.
Characterization of Municipal Solid Waste in the United
States. PB92-207 166.1992.
gmg Households Waste Colletion and Disposal The
Effects of Weight- or Volume-Based Pricing on Solid Waste
Management. PB91-111 484.1990.
Variable Rates in Solid Waste: Handbook for Solid Waste
Offical. PB90-272 063.1990.
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Additional EPA Sources of Information on Composting
U.S. Environmental Protection Agency
Regional Offices
Region 1
U.S. EPA Region 1
J.F.K Federal Building
Boston, MA 02203
617-565-3420
Region 2
U.S. EPA Region 2
26 Federal Plaza
New York, NY 10278
212-264-2657
Region 3
U.S. EPA Region 3
841 Chestnut Building
Philadelphia, PA 19107
215-597-9800
Region 4
U.S. EPA Region 4
345 Courtland Street, NE
Atlanta, GA 30365
404-347-4727
Region 5
U.S. EPA Region 5
77 West Jackson Boulevard
Chicago, IL 60604-3507
312-353-2000
Region 6
U.S. EPA Region 6
First Interstate Bank Tower
1445 Ross Avenue
Dallas, TX 75202-2733
214-655-6444
Region 7
U.S. EPA Region 7
726 Minnesota Avenue
Kansas City, KS 66101
913-551-7000
Region 8
U.S. EPA Region 8
Denver Place (811WM-RI)
999 18th Street, Suite 500
Denver, CO 80202-2405
303-293-1603
Region 9
U.S. EPA Region 9
75 Hawthorne Street
San Francisco, CA 94105
415-744-1305
Region 10
U.S. EPA Region 10
1200 Sixth Avenue
Seattle, WA 98101
206-553-4973
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Appendix B
Composting
Equipment
Different types of equipment are used during composting
to collect and transport the feedstock materials, to remove
noncompostable materials for recycling or disposal, to in-
crease the rate at which materials compost, to improve the
quaky of the finished compost product, to improve
worker safety and working conditions, and to prepare the
finished compost for marketing. Although the same types
of equipment can be used to compost both yard trim-
mings and MSW, in many cases certain types of equip
ment are more appropriate for one type of composting
than the other.
This appendix discusses the wide variety of equipment
that is available for use in composting operations. The
types of equipment discussed are divided into the follow-
ing categories:
Yard trimmings feedstock collection equipment
Debagging equipment
Sorting/separation equipment
Size reduction equipment
Mixing equipment
Turning equipment
Process control equipment
Odor control equipment
Yard Trimmings Feedstock Collection
Equipment
A variety of equipment exists for the collection of yard
trimmings for processing and disposal. In most communit-
ies, yard trimmings are collected at curbside or citizens
transport their materials to a specified drop-off area or
transfer station. The main types of equipment used are
trash collection vehicles and storage containers, because
compactors and containers are so common, this equip-
ment is not discussed here.
There are several types of equipment available for yard
trimmings collection today mechanical scoops, which use
either a bucket-like system to scoop yard trimmings or
pincer-like systems to grab yard trimmings; and vacuum
machines, which suck leaves through a nozzle for collec-
tion (Barkdoll and Nordstedt, 1991). These types of
equipment are briefly described below
Bucket Attachments - These are standard attachments
that can be fitted to a front-end loader and are used
to scoop up yard trimmings and place them into
holding containers.
Pincer Attachment - These attachments can be fitted
to front-end loaders or skid/steer loaders. Pincer
buckets grab, rather than scoop up, the yard trim-
mings and place them into holding containers, usu-
ally on dump trucks or garbage packers.
Self-Contained Mechanical Scoops - These systems use
a series of rotating paddles that scoop yard trim-
mings off the ground and onto a conveyor that car-
ries the yard trimmings to dump trucks. Mechanical
scoops are usually mounted on small tractor trucks.
Vacuum Loaders - Vacuum pressure is used to suck
leaves directly into a separate enclosed container, usu-
ally built onto dump trucks.
Vacuum Collectors - These self-contained units in-
clude both the vacuum equipment and the collec-
tion/storage units.
For more information on yard trimmings feedstock collec-
tion equipment, see Table B-l.
Debagging Equipment
For yard trimmings and MSW placed in plastic bags for
collection, some system must be used to release the feed-
stock materials from the plastic bags and to remove the
plastic so that it does not interfere with the composting
process or diminish the quality of the finished compost
product. Although manual opening and removal of bags is
acceptable and widely used, a wide variety of commercial
debagging equipment is now available.
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Composting Equipment
Table B-l. A Comparison of yard trimmings collection equipment.
Type of Equipment Cost
Bucket Attachments
Usually included in
price of front-end
loader.
Pincer Attachments $2,300 to $12,0
Self-Contained
Mechanical Scoops
Vacuum Loaders
>85,000 to
hoo.ooo.
to $25,C
Vacuum Collectors $15,000 to $40,000.
Source: Barkdoll and Nordstedt, 1991.
Major Advantages
Many public works agencies have therti
availablejwork we'lfon hard surface
Well suited for collecting trimmings,
particularly leaves; good for wet leaves.
Well suited for collecting yard trimmings,
particularly leaves; the unit is self-contained
and no front-end loader is necessary.
Well suited for collecting leaves; can be
detached from the collection vehicle to dump;
can remounted to the front of the
collection/storage vehicle.
Well suited for collecting leaves; the system is
self-contained and includes a self-dumping
collection unit along with the vacuum
machine; a compactor is available through
at least one manufacturer.
Major Disadvantages
Not very efficient for collecting loose yard
trimmings; must be fitted to a ant-end
loader or similar vehicle; pick up dirt and
gravel.
Must be fitted to a front-end loader or similar
vehicle: might need street sweeper to follow,
depending on type of pincer.
Must be fitted to a front-end loader or similiar
vehicle.
Must be mounted to a collection/storage
vehicle; labor intensive.
Not good for grass and leaves when they
become wet or frozen; must be mounted to a
collection/storage vehicle; labor intensive.
There are two general categories of commercially available
debagging devices: slitter trommel devices and augers. AU
of these debagging systems can be used for both yard
trimmings and MSW. Debagging can occur at the facility
or at curbside. All the equipment described below is em-
ployed at the facility, except for the compactor truck with
auger, which is attached to a collection vehicle
Slitter/Trommel Devices - A wide variety of slitter and
trommel equipment are commercially available to-
day. With these systems, the bags are either fed di-
rectly into the slitter or are transported by conveyors
to the slitter unit. Slitters generally use counter-rotat-
ing blades to slice open the bags. The bags and their
contents then fall or are transported by conveyors
into the trommel unit. Feedstock is screened from
the bags in the trommel unit, either through vibrat-
ing action of flat screens or rotating action of drum-
like screens. Bags are removed from the trommel by
hand or by air or water classifying units. Slitter/trom-
mel systems can be used in conjunction with separa-
tion devices to remove metals, plastics, glass, etc.
Augers - With auger systems, bags are loaded into the
auger unit where a sharp-edged, screw-iii shaft ro-
tates and slices open the bags. The bags are turned
and mixed by the auger so that their contents are re-
leased. The auger units generally are on an angle
with the infeed end higher than the discharge end.
Gravity moves the bags and feedstock materials
through these systems. The materials are released at
the discharge end and bags are removed by hand or
by classifiers.
Trash Compactor Trucks with Augers - Although the
primary purpose of these units is trash compaction,
most bags loaded into these units break during proc-
essing. The bags are dropped into the unit and are
ripped when they pass into the compactor. The turn-
ing of the auger futher rips the bags, compacts the
materials, and releases much of the material from the
bags.
Spike and Conveyor Debagging Systems - One com-
pany has developed a system where bags are loaded
into a hopper where a spiked chain grabs and drags
the bags into a trough with two counter-rotating
wheels edged with vertical spikes. The bagsy press
down on each other and the pressure causes the bags
to be gripped by the spikes and ripped open by the
counter-rotating motion. Contents of the bags spill
onto a conveyor and the bag clings to the spikes. A
vacuum machine removes the bags from the spikes.
Specially Designed Windrow Turners - The elevating
face of these windrow turners lifts the plastic bags
with paddle-like extensions. The bags are hooked by
trencher teeth on the front of the windrow turner
and ripped open. As the bags flip over the top, their
constents are spilled out and the bags remain hung
on the teeth. Common systems can be adapted with
a bar containing cutting blades to enhance bag open-
127
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Composting Equipment
ing and with spiked teeth (rather than the normal
cup-like teeth) to increase bag retrieval. Certain
windrow turners also can be adapted to keep mate-
rial in the windrow away from the bearings and can
be fitted with a radial arm to cut bags off the drum
of the windrow turner when they get wrapped
around it.
Mechanical Jaw Debagging Systems -Front-end load-
ers or in-line conveyors are used to feed bags into
these systems. When the upper jaws of the unit
open, the bags fall into the processing area. When
the upper jaws close, new bags cannot enter the proc-
essing unit until processing of the original bags is
completed. Bags are held in a&d position while
rippers slash them open. The lower jaws open and
drop the material and bags onto a conveyor. A sys-
tem is being developed to mechanically remove the
bags, but currently manual separation of the bags is
required.
Saw-ToothedBlade Debagging Systems - These rela-
tively small units can be used as stationary systems
or they can be pulled by tractors. Power is supplied
from the tractors, or the units can be adapted for
electric motors. Bags are manually fed onto a con-
veyor, which is at a 45° angle. The conveyor is
equipped with heavy, metal bars that are perpendicu-
lar to the conveyor and spaced 18 inches apart. Each
bar has two tines that hook the bags. Hooked bags
must pass under a saw-toothed blade, which tears
them open. At the top of the conveyor, the contents
of the bag are dropped into a bin. A blower blows
the materials from the bags into a hopper or a truck
or directly into a windrow for mobile systems. The
bags stay attached to the tines and dangle down until
they are caught by a double roller that pulls them
from the tines and feeds them into a baler.
For more information on debagging equipment, see
Table B-2.
Sorting/Separation Equipment
Sorting and separation of both yard trimmings and MSW
usually are warranted to remove noncompostable materi-
als and contaminants from the compost feedstock. A vari-
ety of sorting systems are available, ranging from
technologically simple and labor intensive methods like
manual removal of noncompostables and contaminants
from a conveyor to technologically complex systems that
mechanically separate noncompostables from com-
postables on the basis of physical characteristics such a
weight, size, conductivity, and magnetic properties. Al-
though all sorting/separation equipment can be used for
both yard trimmings and MSW feedstock, certain types of
equipment are more appropriate for one type of
composting than another. The main types of sorting/sepa-
ration equipment are briefly defined below.
Conveyors - Conveyors are mechanical systems with
belts that slowly pass over rotating wheels. Conveyor
belts are used in the sorting/separation phase of com-
posting to allow a constant stream of feedstock to
pass by workers who manually remove noncom-
postables and other contaminants. The conveyor belt
must be narrow enough for the workers to reach its
center. Conveyors are needed primarily at MSW
composting facilities.
Screens - There are many types of screens, but all sort
materials based on their size. The following types of
screens are used in yard trimmings and MSW com-
posting (Richard, 1992 Rynk et al, 1992):
Stationary screen - These are grates that are held
in place while feedstock materials are dropped
onto them. They retain materials that are larger
than the mesh on the grate, while materials that
are smaller than the mesh fall through. Screens
with different mesh sizes can be positioned to
separate materials into different size categories.
Shaker screens - Mechanical action causes these
screens to move with an up and down motion.
This movement helps to sift the materials through
the mesh on the screens. The motion minimizes
blinding. Heavy balls can be placed on the screen
to help dislodge materials that are clogging the
screen. Screens with different mesh sizes can be
used with shaker screens to separate materials into
different sizes.
Vibrating screens - These are similar to shaker
screens except that the rate of motion is much
more rapid. Vibrating screens are placed on an an-
gle to remove oversized materials. Like shaker
screens, different mesh sizes and cleaning balls
can be used.
Trommel screens - These are long, cylindrical
screens that are placed on an angle so that materi-
als flow through them. Materials that are smaller
than the grate fall through. As trommel screens ro-
tate, a brush is passed over the top of the screen to
remove lodged materials and prevent clogging of
the screen. Trommel screens can separate items of
different sizes by having a mesh gradient that in-
creases away from the infeed end of the screen.
128
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Composting Equipment
Table B-2. A comparison of debagging equipment.
Type of
Equipment
Efficiency
Sifter/Trommel 95% of the bogs are opened; 75 to
Devices 99% of the bag contents are
removed; 15 to 40 ton* of material
are processed per hour (some
systems can process up to 90 tons
per hour for just yard trimmings);
1,700 bags per hour can be
processed^
Augers
. _r r ately 98% of bag contents
are removed; up to 25 tons of
material can be processed per hour.
Cost
$90,000 to
$270,000.
$65,000 to $75,000.
Major Advantages
Bogs are left whole or in
large pieces; a wide variety
of systems are commercially
available with different
adaptations for specific
requirements.
Models are available with
augers that reverse direction
when jammed; bogs are left
whole or in large pieces;
companion baling sytems for
bag and separation devices
Major Disadvantages
Monuol seporation or
another bag removal
mechanism must be used; up
to 30% of the shredded
plastic or paper bag pieces
can remain in composting
material, making a
screening step necessary.
Small bags can squeeze
through the system without
being opened: manual
separation of bags is
required
Trash
: Compactor
Trucks with
Augers
Spike and
Conveyor
Debagging
Systems
Specially
Designed
Windrow
Turners
Data not available.
Debagging
Attachments
for
Compactor
rp i 1
Trucks
Mechanical
Jaw
Debagging
Systems
2,000 bags are opened pe r hour;
approximately 10 tons of material
can be processed per hour.
Approximate 90% of the bags
were removed with three passes of
the windrow turner with one model
investigated; with another model,
80% the bags were removed with
four passes; approximately 41 tons
of material can be processed per
hour; 1,172 bags were opened per
hour with one of the systems.
of the bugs are removed.
90% of the bogs are opened; 99% of
the bag contents are removed; 1,200
to 1,500 bogs per hour can be
processed.
Saw-Toothed 1,200 bags per hour can be
Blade process
Debagging
Systems
Approximately
$69,000.
Approximately
$95,000.
Approximately
$57,000'$100,000
to$15,bOOto
retrofit certain
models with a radial
arm to remove bags
wrapped around the
drum.
Approximately
$8,750.
Approximately
$49,500.
Approximately
$88,000.
Excellent safety features,
including automated lifting
of carts and me auger
compaction combine, which
reduce injuries to collection
personnel.
After processing, bags are
whole or in large pieces; a
vacuum component removes
thekigsand there is no
need for manual separation;
virtually all bags are
retrieved with is method.
The unit also can be used for
windrow turning; some
windrow turners can be
purchased or retrofitted with
a radial arm for removing
bogs that become wrapped
around the windrow turner
drum.
All bogs are removed; less
labor and handling are
required at the composting
site, because all bags hove
been removed; can be
mounted on an rear-load
Compactor truck,
Removes almost all bag
contents.
Can be used as a stationary
unit or pulled by a tractor; self
adjusts lor different sized bags;
with mobile units, material'can
be blow from the bags
directly into the windrows; a
mechanical device
automatically bales the bags.
To be efficient enough for use
with a composting operation,
only paper bags can be
processed; with plastic bags,
further screening is required
to remove bags.
It will be necessary to
customize the system to tailor
it to a specific facility.
For maximum debae
Hpr maximum debagging
efficiency, bags shoura only
be placed three deep in a
windrow; plastic bags can
become wrapped around the
drum of the windrow turner.
Labor is required to hold the
bags in place while they are
being processed; a rear-load
compactor truck is needed to
use this system; it is only
appropriate for small
communities with 10,000 to
25,000 residents.
Must be fed by conveyor or
front-end loader.
Must be fed by conveyor.
Source: Ballister-Howells, 1992.
129
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Composting Equipment
. Disc screens - These systems consist of many rotat-
ing scalloped-shaped, vertical discs. Small items
fall through the spaces between the discs, and
large items are moved over the discs to the dis-
charge end of the system. These systems remove
large items but do not separate the smaller pieces
by size.
Rotary screens - Feedstock is loaded onto spinning,
perforated discs with this system. Oversized mate-
rials are thrown from the screen because of the
spinning action. Undersized materials fall through
the perforations in the discs.
Flexing belt screens - Belts with dots or some other
type of perforation are used with these systems.
Segments of the belt are flexed and snapped in an
alternating pattern, or the belt moves with a wave-
like motion. This movement helps undersized ma-
terials to fill through the belt and removes
materials that are clogging the screen.
Auger and trough screens - These systems use a per-
forated trough to screen materials, An auger ro-
tates in the trough, helping fine material fall
through the perforations and moving oversized
material out of the trough. Auger and trough
screens with perforations of different sizes can be
used to separate materials by size. This type of
screen is primarily used to sort fine materials from
wood chip.
i Magnetic Recovery Systems - With these systems, a
magnetic field removes ferrous metals from the rest
of the feedstock material. The following types of
magnetic separators are commonly used with yard
trimmings and MSW composting systems:
Overhead belt magnets - Cylindrical magnets are
installed over a conveyor belt, which carries feed-
stock. A belt is secured around the magnets,
which rotate to move the belt. The belt is made of
a material that becomes magnetized by the mag-
nets, allowing the belt to attract ferrous metals
and remove them from the conveyor belt below.
The magnetized belt is either positioned directly
over the conveyor belt or perpendicular to the
conveyor belt. Generally, the magnetized belt
moves more quickly than the conveyor belt to im-
prove the efficiency of the magnetic separation.
Drum magnets - Drum magnets are placed over a
conveyor at the end of a mechanism used to feed
the separation system. Ferrous metals in the
feedstock that pass under the rotating drum are
attracted to the magnet and stick to the drum. An
operation must be conducted to periodically
scrape the ferrous metals from the drum.
Eddy-Current Separation Systems - These systems are
used to separate nonferrous metals from feedstock
materials. A high-energy electromagnetic field is cre-
ated, which induces an electrical charge in materials
that conduct electricity, primarily nonferrous metals.
The charge causes these materials to be repelled from
the rest of the feedstock materials.
Air Classifiers - With this technology, feedstock mate-
rials are fed through an air column at a specified rate.
The air column is created by a vacuum that sucks
light materials into a cyclone separator. As materials
lose velocity in the cyclone, they are separated out by
volume. Heavy materials are not even picked up by
the sucking action and fall directly though. Air classi-
fiers target light objects like paper and plastic and
heavy objects like metals, glass, and organics.
Wet Separation Systems - These systems use water
rather than air to separate materials. Materials enter
a circulating water stream. Heavy materials drop into
a sloped tank, some of which vibrate. The heavy
items then fall into an area where they can be re-
moved. The lighter materials float and are removed
from the water with stationary or rotating screens.
These systems target organics and other floatable ma-
terials and sinkable materials like metal, glass, gravel,
etc.
Ballistic or Inertial Separation Systems - These separa-
tors are based on the density and elasticity charac-
teristics of the feedstock materials. They use rotating
drums or spinning cones to generate a trajectory dif-
ference that bounces heavy materials away from
lighter materials. These systems separate materials
into three categories: light materials, such as plastic
and undecomposed paper medium materials, such
as compost and heavy materials, such as metals,
glass, gravel, etc.
For more information on sorting/separation equipment,
see Table B-3.
Size Reduction Equipment
Size reduction of feedstock materials is done with both
yard trimmings and MSW composting, primarily to in-
crease the surface area to volume ratio of the material to
speed up the composting process. Size reduction also can
improve the effectiveness of certain sorting/separation
technologies. Although the available size reduction equip-
ment can be used for both yard trimmings and MSW
130
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Composting Equipment
Table B-3. A comparison of sorting/separation equipment.
Type of Equipment Major Advantages
Conveyors
Major Disadvantages
Relatively low cost; enables separation of all categories Requires manual separation of materials.
of materials.
Stationary Screens
Shaker Screens
Vibrating Screens
Trommel Screens
Disc Screens
Rotary Screens
Flexing Belt Screens
Lack of mechanization makes them relatively
inexpensive; screens of different mesh sizes can be
used to sort materials into different size categories.
Screens of different mesh sizes can be used to sort
materials into different size categories, movemenf and
use of cleaning balls limits clogging of the screens.
some models have been adapted specifically for
compost use; screens 9f different mesh sizes can be
usedto sort materials into different size categories;
slope of screen helps move oversized materials to
discharge paint; movement and use of cleaning balls
limits clogging of the screens.
A screen of varying mesh size can be used to sort
materials info different size categories; slope of unit
helps move oversized materials to discharge point;
movement and use of cleaning brush limits clogging of
the screen.
Targets and eliminates large items; long history of use
in other industries.
Movement helps limit clogging of the screen.
Movement, particubrly snapping and wave action,
helps limit clogging or the screen.
Auger and Trough Screens Troughs with perforations of varying sizes can be used
to sort materials into different size categories;
movement of tfte auger helps move oversized materials
to discharge point; movement limits clogging of the
screen; designed to remove wood chips from finer
materials.
Overhead Belt Magnets Very effective at separating ferrous metals from the rest
of the feedstock materials; relatively inexpensive
system far separating ferrous matals.
Drum Magnets
Very effective at separating ferrous metals; relatively
inexpensive; a second belt is not required.
Eddy Current Separation Effective at recovering nonferrous material (these
Systems cannot be separated or recovered with traditional
magnet systems).
Air Classifiers
Light materials that are larger in size (such as plastic
and paper) can be removed.
Screens easily became blinded; only separates b size
and does not remove small pieces of glass, metal
plastic, and other noncompostables.
Only separates by size and does not remove small
pieces of glass, metal, plastic, and other
noncompostables; mechanization increases expense.
Only separates by size and does not remove small
pieces of glass, metal, plastic, and other
noncompostables; mechaniztion increases expense.
only separates by size and does not remove small
pieces of glass, metal, plastic, and other
noncompostables; mechanization increases expense.
Only target and eliminates large items; does not sort
materials by sizs; does not remove small pieces of
glass, metal, plastic, and other noncompostables;
mechanization increases expense.
Only targets and eliminates large items; does not sort
materials by size; does not remove small pieces of
glass, metal, plastic, and other noncompostables;
mechanization increases expense.
Only targets and eliminates large items; does not sort
materials by size; does not remove small pieces of
glass, metal, plastic, and other noncompostables;
mechanization increases expense.
Only separates by size and does not remove small
pieces of glass, metal, plastic, and other
noncompostables; mechanization increases expense.
Can only be used to separate ferrous metals from the
rest of the feedstock materials; relatively ineffective far
feedstock laced on conveyors in thick layers; a
second belt is required.
sly ineffctive for feedstock placed on conveyors
in thick layers.
If magnetic se ration is not conducted prior to this
process, high levels of contamination with ferrous
metals occurs; can on be used to separate nonferrous
metals from the rest of the feedstock materials;
relative ineffective far feedstock placed on conveyors
in thick layers.
Only targets and eliminates relatively light or heavy
items; does not remove medium-weight
noncompostables; mechanization increases expense.
131
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Composting Equipment
Table B-3. (Continued).
Type of Equipment
Wet Separation Systems
Ballistic or Inertial Separation
Systems
Major Advantages
Particularly effective at removing organic* because
they float; allows heavy, sharp objects (such as
glass pieces) to be safely removed.
sorts and separates inorganics (glass, metal, and
stone fall into separate bins); can use lasers or
optical scanners to target certain inorganics,
improving recovery rate.
Major Disadvantages
Size reduction is needed before this technology is
used; only targets and separates relatively lignt
materials; does not remove lightweight
noncompostables.
Only targets and eliminates relatively dense items;
does not remove dense noncompostables;
mechanization increases expense.
Source: Rynk et al., 1992; Richard, 1992; Glaub et al., 1989.
composting, certain type of equipment are preferable de-
pending on the type of feedstock. In the following list, the
most common types of size reduction equipment available
for use with yard trimmings and MSW composting ate
briefly described:
Hammermill - With these systems, either free-swing-
ing hammers strike and crush the feedstock materials
or the feedstock materials are ground against fixed
hammers and broken into smaller pieces. Hammer-
mills must be well ventilated to prevent explosions
that could arise from clogging. The following types
of hammermills are most commonly used for
composting
Horizontal hammermil - These systems use
counter-rotating hammers to crush feedstock ma-
terials. The free-swinging hammers are attached
to horizontal shafts. Size-reduced feedstock must
pass through a grate before exiting the system.
Vertical hammermills- These systems are similar
to horizontal hammermills, except that the free-
swinging hammers are attached to vertical
shafts.
Flail mills - with these hammermills, size reduced
materials do not have to pass through a grate be-
fore exiting the system.
Tub grinders - This type of size reduction equip-
ment is used primarily for yard trimmings. Feed-
stock materials are loaded into the tub, which
rotates and moves the material across a fixed floor
that holds the hammers. The movement of the
tub grinds feedstock against the hammers.
Shear Shredder - These systems use either fixed or
free-swinging knives to slice feedstock materials into
smaller sizes. Shredders typically require little
maintenance.
Fixed-knife shear shredders - With these shred-
ders, a cleated belt is used to force feedstock ma-
terials against fixed knives. The materials are
raked and shredded by the movement. With this
type of equipment, adjustable fingers catch over-
sized materials and push them back into the shred-
der. Glass items are rejected and fall through a
trash chute.
Rotating-knife shear shredders - This type of shred-
der has two shafts with hooked cutter discs at-
tached to them. The shafts are counter rotating
and the discs interconnect. The discs slice the ma-
terials until they are small enough to fall through
the spaces between the discs. The size of the re-
duced materials is dependent on the size of the
cutter discs.
Rotating Drums - These systems consist of a rotating
cylinder that is positioned at an angle. Materials are
fed into the drum and the rotating motion causes
them to tumble around the cylinder. The tumbling
action breaks up the materials as dense and abrasive
items pulp the softer materials.
For more information on size reduction equipment, see
Table B-4.
Mixing Equipment
Mixing is performed in both yard trimmings and MSW
composting operations to optimize several characteristics
of the composting feedstock such as moisture content,
carbon-to-nitrogen ratios, pH, and particle size. Mixing
can be done when the compost piles or windrows are be-
ing turned, which does not necessarily require special mix-
ing equipment (this probably depends on feedstock and
odor concerns, however). When more complete mixing is
warranted, special mixing equipment can be obtained.
This mixing equipment can be used for composting both
yard trimmings and MSW Because of the expense in-
volved, however, mixing equipment tends to be used more
frequently for MSW composting because the heterogene-
ity of these feedstock increases the need for mixing before
composting.
132
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Composting Equipment
Table B-4. A comparison of size reduction equipment,
Type of Equipment
Hammermills
Tub Grinders
Shear Shredders
Capacity
4(0 75 tons per
hour (or 60 to 450
cubic yards per
hour, depending on
the measure used).
5 to50 tons per
hour (or 80 To 100
cubic yards per
hour, depending on
the measure used).
0.4 to 110 tons per
hour (or 50 to 250
cubic yards per
hour, depending on
the measure used).
Cost
$14,000
$450,000.
$20,000 to
$191,400.
$11,000 to
$360,000.
Major Advantages
Tend to reduce materials into
smaller sizes than other
size-reducfion equipment.
A wide variety of tub grinders
are available; portable or
stationary unit are available.
A wide variety of shear
shredders are available;
materials tend to be torn apart,
which opens up their internal
structure and speeds the
Major Disadvantages
Care must be taken in selecting
on appropriate hammermill for
MSW; create more noise than
other types of size reduction
equipment.
Can require careful maintenance.
Thin, flexible items (like plastic
sheeting) might not be cut or
torn; might not be able to
process oversized equipment.
Rotating Drums
One model claims
75 tons per hour.
$135,000.
composting process; often can
be mounted on a trailer.
Materials are mixed while being
size-reduced.
Actual size reduction varies with
feedstock mix; long
noncpmpostable items (like
plastics sheeting and cables)
usually must be manually
removed.
Source: Barkdoll and Nordstedt,1991.
Some facilities use the same equipment for size reduction
and mixing. Mixing equipment is typically divided into
batch systems and flow-through systems. Batch systems
work with one load of material at a time. They are usually
mounted on a truck or wagon so that mixed material can
be placed directly on the windrow or composting pile.
Flow-through systems are always stationary. Usually fed
and emptied with a conveyor, they can process a continu-
ous stream of material. Both types of mixing systems
blend material by employing one of the technologies (or a
combination of the technologies) described below
Auger Mixers- These consist of one or a number of
rotating screws that chop, turn, and mix materials;
used primarily in batch systems.
Barrel Mixers - These mixers use paddles attached to
a rotating shaft to stir material. Material is continu-
ously fed into a vertical or inclined stationary drum;
used primarily in flow-through systems.
Drum Mixers - These are slowly turning, inched
drums that tumble and blend material. Sometimes
the drums are divided into chambers for each stage
of the mixing process.
Pugmill Mixer - These mixers blend material with
hammers attached to counter-rotating shafts; used
primarily in flow-through systems.
For more information on mixing equipment, see
Table B-5.
Turning Equipment
Because large quantities of feedstock materials must be
handled, even with small composting operations, some
type of equipment is needed to turn compost piles or
windrows with almost any municipal composting opera-
tion. This equipment can range from machinery not spe-
cifically meant for composting operations, such as
front-end loaders, to highly specific types of windrow
turners. The same types of equipment can be used to
compost both yard trimmings and MSW The following is
a list of the most common types of turning equipment
used in composting operations:
Front-End Loaders - These vehicles have a shovel-like
attachment at the front of the machine. The attach-
ment can be raised by a hydraulic mechanism to lift
feedstock materials and tipped to release the materi-
als into piles or windrows.
Bucket Loaders - These loaders are similar to front-
end loaders except that the attachment used to raise
and tip the feedstock materials is bucket-shaped.
Manure Spreaders - With these vehicles, feedstock is
loaded in a hopper at the rear of the cab. Rotating
paddles push materials out of the back of the storage
133
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Composting Equipment
Table B-5. A comparison of mixing equipment.
Type of Equipment Major Advantages
Batch Mixers
Barrel Mixers
Pugmill Mixers
Drum Mixers
Agger Mixers
After mixing, the materials can be discharged directly
into a composting pile or windrow; most mixers can be
mounted on an available truck or wagon; good for
smaller facilities.
High capacity because of continuous operation; good
fonarge facilities.
Achieves best size reduction; produces high-quality mix Maintaining hammers can be costly.
Major Disadvantages
If the mixer is operated for too long, compaction occurs;
fibrous materials, such as straw, can wrap around the
mixing mechanism; limited capacity.
Do not significantly compress materials; high capitol
costs.
Facilites composting since microbial decomposition
can begin in drum.
When used in botch system, materials can be moved to
curing pad or windrow while being mixed; produces
uniform mix.
Wet material might stick to drum at high speeds or form
clumps at low speeds.
Can shred materials and therefore reduce the
effectiveness of bulking agents.
Source: Higgins et al., 1981.
container, mixing the materials as they are released.
The materials can be released while the spreader is in
a stationary position into a pile or while the spreader
is slowly moving.
TractorfTrailer-Mounted Windrow Turners - These
turners must be pushed or pulled by a tractor or
another vehicle. They ride on the side of the vehicle
and rotating paddles or other extensions flip and
turn the material in the windrow.
Tractor-Assissted Windrow Turners - These turners are
similar to tractor/trailer-mounted windrow turners
except that they require the tractor to provide a
power source to rotate their turning mechanism.
The tractor must have a power gear or hydrostatic
drive to power the turners.
Self-Driven Windrow Turners -A wide variety of
self-driven, self-powered turners exist. Some mod-
els have turning mechanisms that ride to the side
of the vehicle. Others straddle the windrow while
the turning mechanism flips and turns the com-
posting materials.
For more information on turning equipment see
Table B-6.
Process Control Equipment
Two of the factors most commonly controlled with com-
post operations are temperature and oxygen levels. Tun-
ing of windrows and compost piles is a common way to
control these factors. Specially designed forced aeration
equipment is available to control temperature and oxygen
levels in compost piles and windrows. The primary cate-
gories of forced aeration equipment areas follows:
Suction System -A vacuum device is used to draw air
through the composting mass. The air is collected in
an exhaust pipe and can be treated for odor control.
Leachate also is removed.
Positive Pressure Systems - With this equipment, a
blower pushes air into the composting mass.
Three types of methods can be used to control the aeration
of the composting mass. These are described below:
Continuous Aeration - With these systems, aeration
devices are run without interruption (although they
can be turned off manually).
Timer Control - With these systems, empirical data is
gathered to determine when and for how long forced
aeration equipment should be run. Timers ate then
used to turn the aeration equipment on and off
Automatic Feedback Control - With these systems,
temperature or oxygen monitoring equipment is
used to determine when critical levels of these pa-
rameters have been reached. When a critical level has
been reached, the sensors trigger a mechanism that
turns the aeration equipment on or off.
For more information on process control equipment, see
Table B-7.
Odor Control Equipment
Numerous odor control methods are used at composting
facilities, ranging from simple and inexpensive procedures
(such as adding wood ash to the compost or increasing di-
lution of compost exhaust air with ambient air by install-
ing fans or raising stack height) to the more complex and
costly equipment discussed below. Appropriate odor con-
trol methods will vary for different Facilities depending on
134
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Composting Equipment
the type and amount of control needed and on financial
resources.
Biofilters - The exhaust air from the compost process
is passed through a biological falter medium, such as
soil or sand. The air is evenly distributed through the
medium by either an open system, consisting of per-
forated pipes set in gravel over which the biofilter
medium is placed, or by a closed system, consisting
of a vessel (with a perforated aeration plenum) filled
with the biofilter medium. Odorous compounds in
the exhaust air are removed by the biofilter through
various physical, biological, and chemical processes.
For example, odorous compounds are broken down
into non-odorous materials such as carbon dioxide,
water, and nitrogen, or are absorbed or adsorbed by
the biofilter. Some researchers have recommended
Table B-6. A comparison of turning equipment.
Type of Equipment Capacity
Loaders
Cost
3 '4 to 4 yd3 bucket. $120,000 to
$170,000.
Manure Spreaders
300 to 350 bushel
loads.
Major Advantages
Readily available in many
municipalities; self-powered and
self-driven; materials are not
loaded into the vehicle; can be
fitted with buckets or other
attachments according to facility
needs.
$9,500 to $11,000. Mixes materials thoroughly.
Tractor/Trailer- 300 to 3,000 tons
Mounted Windrow per hour.
Turners
$15,000 to
$100,000,
Tractor-Assisted
Windrow Turners
300 to 1,200 tons
per hour.
$7,400 to $68,1
Self-Driven Windrow 1,000 to 4,000 tons
Turners per hour.
$89,000 to
$250,000.
Very efficient for turning
windrows and mixing materials;
self-powered; a variety of
models exist with different
turning mechanisms.
Very efficient far turning
windrows and mixing materials;
a variety of models exist with
different turning mechanisms.
Very efficient for turning
windrows and mixing materials;
self-driven; self-powered; a
variety of models exist with
different turning mechanisms;
some models straddle the
windrows and require minimal
space between windrows.
Major Disadvantages
A space the width of the loader
is required between every pair of
windrows; poor mixer.
Materiels must be loaded into
the spreader before the can be
turned; a space the width of the
spreader (end the vehicle that is
used to load materials into the
spreader) is required between
every pair of windrows; it takes
significantly mare time to
conduct the mixing operation
than with other equipment
alternatives.
Must be mounted to a tractor or
another vehicle; for most models,
a space the width of the tractor
and the turner is required
between each windrow or pile;
for single-pass turner models,
however, a space the width of
the tractor and the turner is
required between every pair of
windrows.
Requires a separate power
source; must Be mounted'to a
tractor or another vehicle; for
mast models, a space the width
of the tractor andthe turner is
required between each windrow
or pile; far single-pass turner
models, however, a space the
width of the tractor and the
turner is require between every
pair of windrows.
For some models, a space the
size of the turner is required
between every windrow or pair
of windrows.
source: Barkdoll and Nordstedt, 1991.
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Composting Equipment
Table B-7. A comparison of process control equipment.
Type of Equipment
Suction Systems
Capacity
Medium.
Positive Pressure Systems Medium.
Continuous Aeration Low.
Timer Control Medium.
Automatic Feedback Control High.
source: Richard, 1992; Rynketal., 1992.
Major Advantages
Exhaust gas can be captured and treated to
control odors.
provides more efficient and uniform aeration
than suction devices.
Lower airflow rates are required; no timer or
feedback mechanism is required.
More uniform temperature or oxygen levels
can be achieved than with continuous
aeration systems.
Relatively uniform temperature or oxygen
levels in the compost pile or windrow can be
achieved; optimal temperature or oxygen
levels can be maintained.
Major Disadvantages
Water vapor must be removed from the
exhaust gas before it reaches the suction
device; continuous use can lead to variable
temperature, oxygen, and moisture levels in
the compost pile or windrow.
Odor prevention is difficult; continuous use
can lead to variable temperature, oxygen
and moisture levels in the compost pil e or
windrow; tends to create an unpleasant
working environment.
variable temperature and oxygen levels that
are disruptive to the composting process are
likely inside the composting pile or widrow.
Temperatures are not necessary maintained
at optimal levels; experimentation is needed
to determine the best time schedule for
aeration.
More poweHul aeration equipment is
necessary.
that further research, such as measurements of odor
pervasiveness and intensity before and after air passes
through the biofilter, be conducted to verify the
odor removal efficiency of biofilters.
Wet Scrubbers-Air from the composting process is
exposed to a scrubbing solution, which reacts with
and removes the odorous compounds in the air (e.g.,
through oxidation). Multistage scrubbers are gener-
ally needed to achieve adequate odor control. It is es-
sential that chemical reactions in scrubbers occur in
the correct sequence.; otherwise the correct reactions
may not occur, or other, odor-forming reactions
might result. The two most common types of wet
scrubbers are packed tower and mist scrubbers.
Packed tower scrubbers pass the air through packing
media through which the scrubbing solution circu-
lates. Mist scrubbers atomize the scrubbing solution
into droplets that are dispersed through the exhaust
air stream.
Carbon Adsorption- Air from the compost process
enters a vessel containing beds of granular activated
carbon and is dispersed across the face of the beds.
The activated carbon adsorbs the odorous com-
pounds in the air stream.
n Thermal Regenerative Oxidation - The compost air
stream is exposed to temperatures of approximately
1,400 'F for one second. The high temperature re-
duces odors.
For more information on odor control equipment, see
Table B-8.
Appendix B Resources
Barkdoll, A.W., and R.A. Nordstedt. 1991. Strategies for
yard waste composting. BioCycle. May, 32(5):60-65.
Ballister-Howells, P. 1992. Getting it out of the bag. Bio-
Cycle. March, 33(3):50-54.
Glaub, J., L. Diaz, and G. Savage. 1989. Preparing MSW
for composting. As cited in The BioCycle Guide to Com-
posting Municipal Wastes. Emmaus, PA: The JG Press, Inc
Higgins, A.J., et al, 1981. Mixing systems for sludge
composting. Biocycle. May 22 (5): 18-22.
Richard, T.L. 1992. Municipal solid waste composting
physical and biological processing. Biomass & Bioenergy.
Tarrytown, NY: Pergamon Press. 3(3-4):195-211.
Rynk, R., et al., 1992. On-farm composting handbook.
Ithaca, NY: Cooperative Extension, Northeast Regional
Agricultural Engineering Service.
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Composting Equipment
Table B-8. A comparison of odor control technologies.
Typo of Equip
Biofilters
Multistage Wet Scrubbers
Packed Tower
Mist scrubber
Carbon Adsorption
Cost
Capital cost:
$240,000
(1,600 CFM).
Annual O&M costs:
$140,000.
Capital cost
$1,000,000
(65,000 CFM).
Annual O&M costs:
$240,000 to
$360,000.
Capital cost:
1000,000
CFM).
Annual O&M costs:
$240A000 to
$366,000,.
Capital cosh
$600,000.
Annual O&M costs:
$100,000.
Major Advantages
High removal rates at moderate cost.
Effective for ammonia removal;
recirculation of solution enhances process
efficiency.
"Once-through" passage of solution
removes odorous compounds from air
stream permanently.
Capable of removing a broad range of
compounds.
Major Disadvantages
Possible short-circuiting of exhaust gases;
tendency of media to dry out, reducing
effectiveness; need to maintain pH
buffering capacity in media.
Plugged media in
recirculation of solution may reintroduce
odors into air stream.
Difficulty in maintaining effective chemical
Feedrates; plugged nozzles and filters.
Carbon capacity will be exhausted,
requiring costly regeneration or
replacement; thus standby unit is
recommended; susceptible to plugging
from particulates in air stream;
recommended as secondary system only.
Thermal Regeneration
Capital cosh
$1,500,000.
Annual O&M costs
$240,000 to
$360,000.
Recaptures heat, reducing fuel costs.
Numerous mechanical problems.
Source: Based primarily on estimates from pilot tests at the Concord, NH, biosolids composting facility (total exhaust air flow rate ranging from 24,(
CFM to 65,000 CFM), as reported in Biocycle, August 1992, and on personal communications with odor control researchers.
CFM = cubic feet/minute of air
137
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Appendix C
Glossary of
Compost Terms
actinomycetes - Family of microorganisms belonging to
a group intermediary between bacteria and molds (fungi);
a form of filamentous, branching bacteria.
aerated static pile - composting system using control-
led aeration from a series of perforated pipes running un-
derneath each pile and connected to a pump that draws or
blows air through the piles.
aeration (for composting) - Bringing about contact of
air and composted solid organic matter by means of turn-
ing or ventilating to allow microbial aerobic metabolism
(biooxidation).
aerobic - composting environment characterized by
bacteria active in the presence of oxygen (aerobes); gener-
ates more heat and is a faster process than anaerobic
composting.
agricultural by-products or residuals - By-product
materials produced from plants and animals, including
manures, bedding, plant stalks, leaves, and vegetable
matter.
air classification - The separation of materials using a
moving stream of air light materials are carried upward
while heavy components drop out of the stream.
anaerobic - composting environment characterized by
bacteria active in the absence of oxygen (anaerobes).
bacteria - Unicellular or multicellular microscopic
organisms.
bioaerosols - Biological aerosols that can pose potential
health risks during the composting and handling of or-
ganic materials. Bioaerosols are suspensions of particles in
the air consisting partially or wholly of microorganisms.
The bioaerosols of concern during composting include
actinomycetes, bacteria, viruses, molds, and fungi.
biochemical oxygen demand (BOD) - The amount of
oxygen used in the biochemical oxidation of organic mat-
ter; an indication of compost maturity and a tool for
studying the compost process.
biodegradability - The potential of an organic compo-
nent for conversion into simpler structures by enzymatic
activity.
biooxidation - Aerobic microbial metabolism of organic
or inorganic compounds.
biosolids - Solid, wet residue of the wastewater purifica-
tion process; a product of screening, sedimentation, filter-
ing, pressing, bacterial digestion, chemical precipitation,
and oxidation; primary biosolids are produced by sedi-
mentation processes and secondary biosolids are the prod-
ucts of microbial digestion.
bulking agent - Material, usually carbonaceous such as
sawdust or woodchips, added to a compost system to
maintain airflow by preventing settlement and compac-
tion of the compost.
carbon to nitrogen ratio (C:N Ratio) - Ratio repre-
senting the quantity of carbon (C) in relation to the quan-
tity of nitrogen (N) in a soil or organic material;
determines the composting potential of a material and
serves to indicate product quality.
cation exchange capacity (CEC) - A routine measure
of the binding potential of a soil; measures the soil's abil-
ity to remove negative ions from metals and other com-
pounds, allowing the ions to form insoluble compounds
and precipitate in the soil; determined by the amount of
organic matter and the proportion of clay to sand-the
higher the CEC, the greater the soil's ability to bind
metals.
cellulose - Carbon component of plants, not easily di-
gested by microorganisms.
co-composting - composting process milking carbon-
rich organic material (such as leaves, yard trimmings, or
mixed municipal solid waste), in combination with a ni-
trogen-rich amendment such as biosolids.
compost - The stabilized product of composting which is
beneficial to plant growth; it has undergone an initial,
rapid stage of decomposition and is in the process of
humification.
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Glossary of Compost Terms
compostable - Organic material that can be biologically
decomposed under aerobic conditions.
composting - The biodegradation, usually aerobic and
thermophilic, that involves an organic substrate in the
solid state; evolves by passing through a thermophilic
stage with a temporary release of phytotoxins; results in
the production of carbon dioxide, water, minerals, and
stabilized organic matter.
composting municipal - Management method whereby
the organic component of municipal discards is biologi-
cally decomposed under controlled conditions; an aerobic
process in which organic materials are ground or shredded
and then decomposed to humus in windrow piles or in
mechanical digesters, drums, or similar enclosures.
curbside pickup - The curbside collection and transport
of used household materials to a centralized handling fa-
cility (municipal or private) such as a transfer station, a
materials recovery facility (MRF), an incinerator, or land-
fill. Materials at curbside might be mixed together in
common containers or source separated by the house-
holder into separate fractions such as newspapers, glass,
compostables, or any variation of mix and separation.
curbside recycling- Residents separate recyclable from
their trash and leave the recyclable on their curbside for
collection.
cured compost - A stabilized product that results from
exposing compost to a prolonged period of humification
and mineralization.
curing - Late stage of composting, after much of the
readily metabolized material has been decomposed, which
provides additional stabilization and allows further de-
composition of cellulose and lignin.
decomposition - Conversion of organic matter as a result
of microbial and/or enzymatic interactions; initial stage in
the degradation of an organic substrate characterized by
processes of destabilization of the preexisting structure.
denitrification - The biological reduction of nitrogen to
ammonia, molecular nitrogen, or oxides of nitrogen, re-
sulting in the loss of nitrogen into the atmosphere.
digester - An enclosed composting system with a device
to mix and aerate the materials.
drop off- Individuals take recyclable materials to a recy-
cling center.
drum compostings ystem - Enclosed cylindrical vessel
which slowly rotates for a set period of time to break up
and decompose material.
endotoxins - A toxin produced within a microorganism
and released upon destruction of the cell in which it is
produced. Endotoxins can be carried by airborne dust
particles at composting facilities.
enclosed system -See "in-vessel composting."
erosion - The removal of materials from the surface of
the land by weathering and by running water, moving ice,
and wind.
feedstock - Decomposable organic material used for the
manufacture of compost.
finished product - Compost material that meets mini-
mum requirements for public health, safety, and environ-
mental protection and is suitable for use as defined by
finished product standards.
foodscraps - Residual food from residences, institutions,
or commercial facilities; unused portions of fruit, animal,
or vegetable material resulting from food production.
fungi - Saprophytic or parasitic multinucleate organisms
with branching filaments called hyphae, forming a mass
called a mycelium; fungi bring about celluolysis and hu-
mification of the substrate during stabilization.
green materials- Portion of the municipal discards con-
sisting of leaves, grass clippings, tree trimmings, and other
vegetative matter.
hammermill - Machine using rotating or flailing ham-
mers to grind material as it falls through the machine or
rests on a stationary metal surface.
heavy metals - Elements having a high specific gravity
regulated because of their potential for human, plant, or
animal toxicity, including cadmium (Cd), copper (Cu),
chromium (Cr), mercury (Hg), nickel (Ni), lead (Pb) and
zinc (Zn).
household hazardous waste - Products containing haz-
ardous substances that are used and disposed of by indi-
viduals rather than industrial consumers; includes some
paints, solvents, and pesticides.
humus - A complex aggregate of amorphous substances,
formed during the microbial decomposition or alteration
of plant and animal residues and products synthesized by
soil organisms; principal constituents are derivatives of
lignins, proteins and cellulose; humus has a high capacity
for cation exchange (CEC), for combining with inorganic
soil constituents, and for water absorption; finished com-
post might be designated by the general term humus.
hydromulching - An application method using a water
jet to spread a mulch emulsion on a land surface.
in-vessel composting - (also "enclosed" or "mechanical")
A system using mechanized equipment to rapidly decom-
pose organic materials in an enclosed area with controlled
amounts of moisture and oxgen.
insert - Nonbiodegradable products (glass, plastics, etc.).
inorganic - Substance in which carbon-to-carbon bonds
are absent mineral matter.
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Glossary of Compost Terms
integrated waste management - The complementary
use of a variety of practices to handle municipal solid waste
safely and effectively; techniques include source reduction,
recycling/composting, combustion, and landfilling.
land reclamation - The restoration of productivity to
lands made barren through processes such as erosion,
mining or land clearing.
landfilling - The disposal of discarded materials at engi-
neered facilities in a series of compacted layers on land
and the frequent daily covering of the waste with soil; fill
areas are carefully prepared to prevent nuisances or public
health hazards, and clay and/or synthetic liners are used to
prevent releases to ground water.
leachate - Liquid which has percolated through materials
and extracted dissolved and suspended materials; liquid
that drains from the compost mix.
macronutrient - Nutritive elements needed in large
quantities to ensure normal plant development.
mature compost- Compost that has been cured to a sta-
bilized state, characterized as rich in readily available
forms of plant nutrients, poor in phytotoxic acids and
phenols, and low in readily available carbon compounds.
mesophili stage - A stage in the composting process
characterized by bacteria that are active in a moderate
temperature range of 20 to 45°C (68 to 113°F); it occurs
later, after the thermophilic stage and is associated with a
moderate decomposition rate.
metabolism - Sum of the chemical reactions within a cell
or whole organism, including the energy-releasing break-
down of molecules (catabolism) and the synthesis of com-
plex molecules and new protoplasm (anabolism).
micronutrients - Nutritive elements needed in small
quantities for healthy plant development trace elements.
microorganims - Small living organisms only visible
with a microscope.
moisture content - The mass of water lost per unit dry
mass when the material is dried at 103°C (217°F) for 8
hours or more. The minimum moisture content required
for biological activity is 12 to 15 percent it generally be-
comes a limiting factor below 45 to 50 percent expressed
as a percentage, moisture content is water weight/wet
weight.
mulch - Any suitable protective layer of organic or inor-
ganic material applied or left on or near the soil surface as
a temporary aid in stabilizing the surface and improving
soil microclimactic conditions for establishing vegetation;
mulch reduces erosion and water loss from the soil and
controls weeds.
municipal solid waste (MSW) - Discarded material from
which decomposable organic material is recovered for
feedstock to make compost. Municipal solid waste origi-
nates from residential, commercial, and institutional
sources within a community.
nematodes - Elongated, cylindrical, unsegmented worms;
includes a number of plant parasites (a cause of root dam-
age) and human parasites.
nitrification - The oxidation of ammonia to nitrite and
nitrite to nitrate by microorganisms.
organic - Substance that includes carbon-to-carbon
bonds.
organic contaminant - Synthetic trace organics in-
clude pesticides and polychlorinated biphenyls (PCBs).
organic matter - Portion of the soil that includes mi-
croflora and microfauna (living and dead) and residual de-
composition products of plant and animal tissue; any
carbon assembly (exclusive of carbonates), large or small,
dead or alive, inside soil space; consists primarily of hu-
mus.
organic soil condition - Stabilized organic matter
marketed for conditioning soil structure it also improves
certain chemical and biological properties of the soil.
oxidation - Energy-releasing process involving removal
of electrons from a substanc; in biological systems, gener-
ally by the removal of hydrogen (or sometimes by the ad-
dition of oxygen); chemical and/or biochemical process
combining carbon and oxygen and forming carbon diox-
ide (C02).
pathogen - An organism, chiefly a microorganism, in-
cluding viruses, bacteria, fungi, and all forms of animal
parasites and protozoa, capable of producing an infection
or disease in a susceptible host.
persistence - Refers to a slowly decomposing substance
which remains active in the natural cycle for a long period
of time.
pH- The negative logarithm of the hydrogen ion concen-
tration of a solution, a value indicating the degree of acidity
or alkalinity; pH 7 = neutral, pH <7 = acid, pH >7 =
alkaline (basic).
phytotoxic - Detrimental to plant growth; caused by the
presence of a contaminant or by a nutrient deficiency.
polychlorinated biphenyls (PCBs) - A class of chlorin-
ated aromatic hydrocarbons representing a mixture of
specific biphenyl hydrocarbons which are thermally and
chemically very stable; some PCBs are proven
carcinogens.
putrescible waste - organic materials prone to degrade
rapidly, giving rise to obnoxious odors.
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Glossary of Compost Terms
recydaWe - Products or materials that can be collected,
separated, and processed to be used as raw materials in the
manufacture of new products.
recycling- Separating, collecting, processing, marketing,
and ultimately using a material that would have been
thrown away.
runoff- Water that flows over the earth's surface that is
not absorbed by soil.
screening - The sifting of compost through a screen to
remove large particles and to improve the consistency and
quality of the end product.
shredder - Mechanical device used to break materials
into small pieces.
size reduction - Generic term for separation of the ag-
gregate or for breaking up materials into smaller pieces
through abrasion, thermal dissociation, tearing, screening,
tumbling, rolling, crushing, chipping, shredding, grind-
ing, shearing, etc.; the process makes materials easier to
separate andean increase surface area for composting.
soil amendmend soil conditioner - Soil additive which
stabilizes the soil, improves resistance to erosion, increases
permeability to air and water, improves texture and resis-
tance of the surface to crusting, eases cultivation, or other-
wise improves soil quality.
source reduction - The design, manufacture, purchase,
or use of materials to reduce their amount or toxicity be-
cause it is intended to reduce pollution and conserve re-
sources, source reduction should not increase the net
amount or toxicity generated throughout the life of the
product techniques include reusing items, minimizing
the use of products that contain hazardous compounds,
using only what is needed, extending the useful life of a
product, and reducing unneeded package.
source separation - Separating materials (such as paper,
metal, and glass) by type at the point of discard so that
they can be recycled.
stability- State or condition in which the composted
material can be stored without giving rise to nuisances or
can be applied to the soil without causing problems there;
the desired degree of stability for finished compost is one
in which the readily decomposed compounds are broken
down and only the decomposition of the more resistant
biologically decomposable compounds remains to be
accomplished.
stabilization - Stage in composting following active de-
composition; characterized by slow metabolic processes,
lower heat production, and the formation of humus.
static pile system - An aerated static pile with or with-
out a controlled air source.
thermophilic stage - A stage in the composting process
characterized by active bacteria that favor a high tempera-
ture range of 45 to 75°C (113 to 167°F); it occurs early,
before the mesophilic stage, and is associated with a high
rate of decomposition.
tilt - The physical state of the soil that determines its
suitability for plant growth taking into account texture,
structure, consistency, and pore space; a subjective estima-
tion, judged by experience.
topsoil - Soil, consisting of various mixtures of sand, silt,
clay, and organic matter, considered to be the nutrient-
rich top layer of soil that supports plant growth.
toxicity - Adverse biological effect due to toxins and
other compounds.
vector - Animal or insect-including rats, mice, mosqui-
toes, etc.that transmits a disease-producing organism.
volatilization - Gaseous loss of a substance to the
atmosphere.
windrow system - Elongated piles or windrows aerated
by mechanically turning the piles with a machine such as
a front-end loader or specially designed equipment.
wood scrap - Finished lumber, wood products and prun-
ings, or stumps 6 inches or greater in diameter.
yard trimmings - Grass clippings, leaves, brush, weeds,
Christmas trees, and hedge and tree prunings from resi-
dences or businesses.
Appendix C Resources
composting Council. 1991. Compost facility planning
guide. Washington, DC: composting Council.
*U.S. GOVERNMENT PRINTING OFFICE: 1994-520-790/81120
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