USDA
oEPA
United States
Department of
Agriculture
Agricultural Research
Science and Education Administration
Washington DC 20705
United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
EPA-600/8-80-022
May 1980
Research and Development
Manual for
Composting Sewage
Sludge by the
Beltsville
Aerated-Pile Method
-------
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the "SPECIAL" REPORTS series. This series is
reserved for reports targeted to meet the technical information needs of specific
user groups. The series includes problem-oriented reports, research application
reports, and executive summary documents. Examples include state-of-the-art
analyses, technology assessments, design manuals, user manuals, and reports
on the results of major research and development efforts.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
-------
EPA-600/8-80-022
May 1980
MANUAL FOR COMPOSTING SEWAGE SLUDGE BY THE
BELTSVILLE AERATED-PILE METHOD
by
G. B. Willson, J. F. Parr, E. Epstein, P. B. Marsh
R. L. Chaney, D. Colacicco, W. D. Burge
L. J. Sikora, C. F. Tester, S. Hornick
U.S. Department of Agriculture
Beltsville, Maryland 20705
Grant No. S803468
Project Officer
James A. Ryan
Wastewater Research Division
Municipal Environmental Research Laboratory
Cincinnati, Ohio 45268
This study was conducted in cooperation with
U.S. Department of Agriculture
Beltsville, Maryland 20705
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
-------
DISCLAIMER
Trade names are used in this publication to provide specific
information. Mention of a trade name does not constitute a
guarantee or warranty of the product or equipment by the U.S.
Department of Agriculture or the U.S. Environmental Protection
Agency nor an endorsement over other available products.
-------
FOREWORD
The U. S. Environmental Protection Agency was created because of in-
creasing public and governmental concern about the dangers of pollution of
air, water, and land to the health and welfare of the American people. Its
personnel are charged with the responsibility of alleviating, correcting,
and when possible preventing problems of that nature.
The U. S. Department of Agriculture is broadly concerned with all
aspects of U. S. agriculture. Its personnel endeavor to facilitate the
efforts of the U. S. farmer to supply food and fiber to populations at home
and abroad, but always with the minimum practical hazard to the environment.
The work here reported was aimed at the furtherance of the purposes of
both agencies. It originated from an urgent need of both large and small
municipalities for better methods to dispose of ever-increasing amounts of
sewage sludge. Composting offers a double-barreled solution to that problem.
It not only disposes of sludge but also converts it into a product which is
more aesthetically acceptable, safer from a health standpoint, and useful in
many important practical applications as a soil amendment beneficial to the
growth of plants. The present manual discloses details of the Beltsville
Aerated Pile Method of Composting sewage sludge. Research conducted at
Beltsville by USDA in cooperation with the Maryland Environmental Service
with the support of EPA, has shown that composting is a cost-effective and
environmentally acceptable alternative to such ultimate disposal methods as
incineration, ocean dumping, and landfilling.
TTj^Eclminster Stephen J.\Gage
Deputy Director for Agricultural Assistant Administrator for Research
Research . and Development
Science and Education Administration U. S. Environmental Protection Agency
U. S. Department of Agriculture
o
111
-------
PREFACE
In the early 1970's, the Blue Plains Wastewater Treatment
Plant in Washington, D.C., serving seven jurisdictions, was
producing about 300 wet tons (23% solids) of digested sludge per
day. Construction for advanced wastewater treatment facilities
displaced existing sludge storage. Disposing of the sludge by
discharging it into the Potomac River or barging it for off-shore
dumping into the Atlantic Ocean were both rejected as environ-
mentally unacceptable. The consulting firm of Metcalf and Eddy,
Inc. recommended sludge incineration as the best disposal system
for Blue Plains. Until the incinerators could be constructed,
the Maryland Environmental Service (MES), assumed the responsi-
bility for disposing of the sludge by land application.
In 1971, the Biological Waste Management Laboratory at the
U.S. Department of Agriculture's Beltsville Agricultural Research
Center initiated research on land application of sludge in cooper-
ation with MES and the Metropolitan Washington Council of Govern-
ments. Several methods were investigated, including trenching
and landspreading. In 1972, at the request of MES and the Blue
Plains participants, this Laboratory began research on composting
of sewage sludge. By early 1973, a successful windrow method
utilizing woodchips as a bulking and moisture-absorbing agent had
been developed for composting digested sludge. During 1973 and
1974, the Beltsville facility windrow composted in excess of 50
wet tons of digested sludge each day (Figure 1).
By 1975, the Blue Plains Wastewater Treatment Plant had in-
creased its capability for removal of solids from the wastewater.
This resulted in the production of an additional 200 wet tons of
undigested or raw sludge (a mixture of primary and activated
secondary sludges), for a total output of about 500 wet tons of
sludge per day. Meanwhile, digestion capacity remained at 300
tons per day.
Difficulties were encountered when the windrow method was
applied to raw sludge, because of the greater level of malodors
associated with this type of sludge. Moreover, raw sludge gener-
ally contains a higher level of pathogens and there was concern
that some of these organisms might survive in the outer layers
of the windrow, where temperatures would be lower. The need for
disposal of the raw sludge resulted in the development of the
composting process now referred to as the Beltsville Aerated
Pile Composting Method described in this manual.
iv
-------
Figure 1. Screening woodchips from sewage sludge compost for recycling,
Beltsville, 1973. Stock pile of screened compost in left foreground.
Air-dried compost before screening in right foreground.
-------
The Environmental Protection Agency has issued a deadline of
1981 or sooner to cities that are presently ocean dumping their
sludge to cease using that method of disposal. This manual was
developed for the assistance of those sewage authorities that
must find acceptable new outlets for their sludge on short
notice. The manual has been written during the early stages of
research; improvements can be expected as development continues
and communities adopt the process.
VI
-------
ABSTRACT
In producing clean water from sewage, wastewater treatment
plants also produce sludge. Most of the commonly used methods
to dispose of this material are now considered to be either
environmentally unacceptable, wasteful of energy, or very
expensive. To ease this situation, a relatively simple, rapid,
and inexpensive sludge composting process has been developed at
Beltsville. The method makes possible the conversion of undi-
gested sludge into a composted product that is aesthetically
acceptable and meets environmental standards. The material has
demonstrated usefulness as a soil amendment stimulative to plant
growth. If relatively simple control procedures are followed,
the compost appears to be free of primary human pathogens because
of the lethal effect of heat generated during the composting
process on such organisms.
The new Beltsville composting procedure, detailed here in
respect to both principles and practice, represents a major
advance over previously known composting methods. It is adapt-
able to practical use in municipalities of widely varying size.
In many situations its short startup time will allow its use as
an emergency interim solution for sludge management. Key infor-
mation is presented on the economics of the process, and on the
marketing and use of the product as a soil conditioner to improve
plant growth.
This report was submitted in partial fulfillment of Grant
No. S803468 by the Maryland Environmental Service under spon-
sorship of the U.S. Environmental Protection Agency. Work was
done under subcontract by the U.S. Department of Agriculture.
This report covers the period July 1975 to December 1977, and
work was completed as of June 1978.
vii.
-------
CONTENTS
Pas
Disclaimer ii
Foreword iii
Preface iv
Abstract vii
Contents ix
Figures xii
Tables xiv
Conversion Factors- xv
Acknowledgments xvi
1. Introduction 1
2. Definition of the Problem and Key Facts
on Composting as a Solution 1
The Problem 2
Benefits of Composting 2
Composition of the Sludge 4
Economic Feasibility of Composting 7
3. The Composting Process 11
Factors Affecting the Composting Process 11
Temperature 11
Carbon:Nitrogen Ratio 13
Moisture Content 13
Aeration and Oxygen Supply 13
Use of Inocula 13
pH of Sludge 14
Site Selection and Design Criteria 14
Bulking Materials to Condition the Sludge
for Composting 15
The Mixing Operation 17
ix
-------
CONTENTS (continued)
The Aerated Pile 22
The Extended Aerated Pile 26
Temperatures Attained During Composting 29
Aeration and Oxygen Supply 29
Condensate and Leachate Control 32
Sequence of Operations for Composting
Sludge - 32
Dry ing 33
Screening 33
Curing and Storing 36
Monitoring Operations 36
Odor Control 38
The Mixing Operation 39
Aerated Pile Surface 39
Air Leakage Between Blower and Filter
Pile 39
Odor Filter Piles 39
Condensate and Leachate 39
Removal of Compost from Aerated Pile to
Curing Pile 39
Curing Piles 40
Storage Piles 40
Aggregates or Clumps of Sludge 40
Ponding of Rainwater 40
Health Aspects of Sludge Composting 40
4. Utilization of Compost 43
Potential Markets 43
Beneficial Effects as a Fertilizer and
Soil Conditioner 43
Constraints on Uses 55
Pathogens 55
Heavy Metals 55
References ; 60
-------
CONTENTS (continued)
Appendix 62
Analytical Methods 62
Monitoring Equipment 63
English to Metric Unit Conversions 65
xi
-------
FIGURES
Number Page
1 Screening woodchips from compost, Beltsville, 1973 v
2 Cost of Aerated Pile Composting, 1977 9
3 Flow diagram for composting operation 12
4 Aerial view of compost research site 16
5 Unloading of sludge 18
6 Spreading sludge over woodchip bulking agent
prior to mixing 19
7 Mixing operation with Terex-Cobey windrow composter.... 20
8 Mixing operation with Roto-Shredder 21
9 Schematic diagram of aerated pile 23
10 Orientation of aeration pipe in pile 23
11 Aerated pile construction 24
12 Aerated pile construction 25
13 Forced aeration system showing odor filter pile 27
14 Schematic diagram of extended aerated pile 28
15 Typical sequence of sludge additions to extended pile.. 30
16 Temperatures recorded during the composting operation.. 31
17 Screening woodchips from compost 34
18 Screening operation 35
19 Effect of sludge compost amendment to clay subsoil
on growth of Kentucky bluegrass 45
20 Effect of sludge compost amendment on tulip
poplar seedlings 46
• •
XII
-------
FIGURES (continued)
Number Page
21 Effect of sludge compost on dogwood seedlings 47
22 Response of weeping lovegrass to increasing amounts
of compost added to acid strip-mine spoil 52
23 Mixed grasses and legumes grown on compost-amended
acid strip-mine spoil 53
xiii
-------
TABLES
Number Page
1 Percentage estimates of use of different management
methods for municipal wastewater sludges in the
U.S. in 1975 3
2 Relative effects of various wastewater treatment
processes on pathogen destruction and sludge
stabilization 5
3 Composition of raw and digested sludges and their
composts 6
4 Comparative costs for various sludge disposal
processes in 1976 7
5 Suggested parameters and time sequences for monitoring.. 38
6 Examples of pathogens encountered during the composting
process 41
7 Recommended compost application rates for various soil
conditions 49
8 Available N in KG from a single application of sludge
compost at indicated rates 54
9 Metal content of digested sewage sludges 58
10 Maximum allowable cumulative metal loadings from
sludge or sludge compost applied to privately
owned land 59
xiv
-------
CONVERSION FACTORS
Length
1 1 inch
1 foot
Area
1 square inch
1 square foot
1 acre
Volume
1 cubic inch
1 cubic foot
1 cubic yard
1 gallon
Weight
1 pound
1 ton
Application rate
1 pound per 1000 square feet
1 ton per acre
1 pound per acre
Temperature
v Fo
2.54 centimeters
30.48 centimeters
6.45 square centimeters
0.0929 square meters
0.405 hectares
16.39 cubic centimeters
0.0283 cubic meters
0.765 cubic meters
3.79 liters
454 grams
0.907 metric ton
4.89 grams per square meter
2.24 metric tons per hectare
1.12 kilograms per hectare
= 9/5 C + 32
xv
-------
ACKNOWLEDGEMENTS
We wish to acknowledge financial support from the
Metropolitan Washington Council of Governments (COG), The Blue
Plains Participants, and the Maryland Environmental Service (MES)
throughout our research and development of sewage sludge compost-
ing at Beltsville.
The U.S. Environmental Protection Agency, Office of Research
and Development, Cincinnati, Ohio, provided a 2-year grant
(effective July 1, 1975) for research and development of process
technology for composting municipal sewage sludges, and for
investigating the use of sludge composts on land.
The U.S. Environmental Protection Agency, Region III, Phila-
delphia, Pennsylvania, provided a 2-year grant (effective December
1, 1975) for construction, improvements, and operations at the
Beltsville Composting Facility.
We also acknowledge grants from the USEPA, Office of Research
and Development, Cincinnati, Ohio, which have enabled ARS and MES
to continue research on the effects of sludge entrenchment on
soil chemical, physical, and biological properties.
Grants from the Food and Drug Administration, Department of
Health, Education, and Welfare, the USEPA Office of Solid Waste
Management Programs, Washington, D.C., and the Washington
Suburban Sanitary Commission (WSSC) provided further support for
research on the toxicity of sludge-borne heavy metals to plants,
and their uptake and accumulation by plants when sludges and
sludge composts were applied to soils.
xvi
-------
SECTION 1
INTRODUCTION
Many municipalities are looking for solutions to their
problems of disposal of sewage sludge. As energy costs continue
to increase and as wastewater treatment plants across the nation
produce larger amounts of sludge, composting will be considered
as an alternative to land-fill, ocean dumping, and incineration.
Moreover, as abatement and pretreatment measures are implemented,
many municipalities now producing sludges with an undesirable
content of heavy metals and industrial chemicals will produce
sludges that are environmentally safe and acceptable for land
application.
Composting of sewage sludge is now being conducted success-
fully by an increasing number of municipalities throughout the
country, while others are seriously considering the practice.
This has resulted in an urgent need for a state-of-the-art docu-
ment on the various aspects of sludge composting and compost
utilization.
This manual attempts to fulfill the above-mentioned need.
It was written with three principal objectives in mind: 1) to
provide municipal planners and decision-makers with information
which would assist them in deciding whether composting would be
adaptable and economically practical in their local situation,
2) once having made a decision to compost, to provide design
information on a rapid aerobic, thermophilic composting method
of demonstrated reliability, moderate cost and high environment-
al acceptability, and 3) to present information on the benefi-
cial use of the compost product as a soil conditioner and source
of nutrients for plant growth.
-------
SECTION 2
DEFINITION OF THE PROBLEM AND KEY FACTS ON COMPOSTING AS A
SOLUTION
THE PROBLEM
Efforts to reduce the pollution of rivers, lakes, and oceans
by treating sewage are generating a rapidly growing amount of
sludge, solid material that is removed from a wastewater to
produce a clean effluent. Present national production of 5 mil-
lion dry tons of sludge annually is expected to double by 1985.
The increase will be largely due to implementation of Federal
legislation that prohibits disposal of sewage into fresh waters
(Water Pollution Control Act Amendments of 1972) and oceans
(Marine Protection Research, and Sanctuaries Act of 1972).
Implementation of these laws will require progressively better
treatment through 1985.
Table 1 shows the USEPA estimates of the percentages of
1975 sludge production disposed of by various methods. The U.S.
Environmental Protection Agency has ordered that municipalities
shall cease all dumping of sewage into the oceans by 1981. As
ocean dumping is phased out, use of other methods must increase.
Air pollution, which may result during incineration, is subject
to stringent regulations imposed by the Air Quality Act of 1967.
These restrictions, together with rapidly increasing costs and
decreasing supply of petroleum products, reduce the cost-effec-
tiveness of incineration and other thermal methods of sludge
processing, and will probably reduce the number of communities
that will convert from ocean dumping to this disposal action.
To make matters even more difficult, land costs for landfill
sites are increasing rapidly and new sites are difficult to
obtain.
Since the choice of acceptable management alternatives is
decreasing at the same time that sludge production is increasing,
the use of land application systems will probably increase sub-
stantially. The conversion of sludge to composts is expected to
accelerate this trend, especially in large metropolitan areas
surrounded by extensive suburbs.
BENEFITS OF COMPOSTING
Sludge composting is the microbial conversion of this
material in the presence of suitable amounts of air and moisture
-------
TABLE 1. PERCENTAGE ESTIMATES OF USE OF DIFFERENT MANAGEMENT
METHODS FOR MUNICIPAL WASTEWATER SLUDGES IN THE U.S.
IN 1975.
Disposal method Use in % of total
Landfill 35
Landspreading 20
Ocean dumping 20
Incineration 25
Pyrolysis 0
Composting <1
Thermal dehydration
-------
Advantages of the Beltsville Aerated Pile Composting Method
over the windrow method previously developed are the following:
(1) Satisfactory processing of raw sewage sludge, there-
by eliminating the need for expensive digesters or
other means of sludge stabilization.
(2) Greater flexibility in scale of operation.
(3) Lower capital costs.
(4) Greater reduction of pathogenic organisms.
(5) Greater flexibility in the ratio of labor to
capital.
Aerated pile composting can be used as a permanent sludge
management method, or it can be used as a temporary method while
a permanent solution to sludge management is being developed. A
composting operation may be started on very short notice if a
site is available. In many areas, sites could be found that
would need little or no preparation. No permanent facilities are
required for the process. The only essential major equipment—a
front-end loader—can readily be rented. Other equipment, such
as the blowers, are stock items. If electricity is not available,
portable generators can be rented until service is provided. On
a moderate scale and a temporary basis, operations could be com-
menced on an acceptable undeveloped site within hours. Usually,
however, some grading, runoff control, and paving would signifi-
cantly increase the dependability of the operation.
The relative effects of different wastewater treatment
processes on the destruction of pathogens and stabilization of
sludge were compared by Farrell and Stern (Table 2). Processes
such as pasteurization, ionizing radiation, and heat treatment
can eliminate pathogens; however, they leave sludges that are
unstabilized and subject to putrefaction when applied to land.
Anaerobic and aerobic digestion stabilize sludge, as does com-
posting. However, composting is the only process that provides
both good pathogen control and stabilization. Additionally, the
compost can be handled and stored easily.
SLUDGE COMPOSITION
The suitability of sewage sludges for processing into compost
depends on the characteristics of the wastewater and on the treat-
ment process. The composition of the sludge depends on the type
of wastewater treatment (primary, secondary, digestion, etc.),
chemical used for flocculation, and sludge source (industrial or
domestic). The composting process is not particularly sensitive
to the added chemicals, so both digested and undigested or raw
sludges can be composted satisfactorily within the pH range of 5
-------
TABLE 2. RELATIVE EFFECTS OF VARIOUS WASTEWATER TREATMENT
PROCESSES ON DESTRUCTION OF PATHOGENS AND STABILIZATION
OF SEWAGE SLUDGES (ADAPTED FROM FARRELL AND STERN. 1975)
Processes
Pathogen
reduction
Putrefaction
potential
Odor
abatement
Anaerobic digestion
Aerobic digestion
Chlorination, heavy
Lime treatment
Pasteurization (70°C)
Ionizing radiation
Heat treatment (195°C)
Composting (60°C)
Long-term lagooning of
digested sludge
Fair
Fair
Good
Good
Excellent
Excellent
Excellent
Good
Good
Low
Low
Medium
Medium
High
High
High
Low
Good
Good
Good
Good
Fair
Poor
Poor
Good
to 11. Digested sludge, however, has less energy available for
raising the temperature to the thermophilic range. Moisture
content appears to be the most important characteristic of the
sludge for composting. The drier the sludge, the less material
there will be to handle in the composting operation and the less
it will cost.
Heavy metals content of sludges will vary with the level of
industrial contribution. However, we have not found the metal
content to affect the composting process. Bulking materials will
to some extent dilute the heavy metals content of the sludge.
Under certain conditions heavy metals (zinc, copper, nickel)
can kill plants and cadmium can be taken up by plants in concen-
trations that may be harmful in the human diet. Even domestic
wastewater may yield sludges containing enough metals to warrant
limiting continuous application. It is apparent therefore, that
heavy metal analyses are needed to assess the marketability of
the compost to be produced. If levels are high, a source control
program may need to be developed in conjunction with the compost-
ing program. Analyses and monitoring can be pursued (Appendix)
to estimate safe application rates. Table 3 shows the properties
of raw and digested sludge compost. The sludges were obtained
from the Washington, D.C. Blue Plains Wastewater Treatment Plant
-------
and composted with woodchips. Because these sludges are mostly
from domestic sources, the derived compost is relatively low
in heavy metals and pesticides and, therefore, suitable for land
application.
TABLE 3. COMPOSITION OF RAW AND DIGESTED SLUDGES FROM WASHINGTON,
D.C., BLUE PLAINS WASTEWATER TREATMENT PLANT AND THEIR
RESPECTIVE COMPOSTS PROCESSED AT THE USDA COMPOSTING
FACILITY, BELTSVILLE, MD
Component
pH
Water, %
Organic carbon,
Total N, 7o
NH4+-N, ppm
P 7
JT , /o
K, 7=
Ca, 7o
Zn , ppm
Cu , ppm
Cd, ppm
Ni, ppm
Pb , ppm
PCBs- , ppm
BHC-/, ppm
DDEl/
DDT, ppm
Raw Raw sludge
sludge compost
9.5
78
7o 31
3.8
1540
1.5
0.2
1.4
980
420
10
85
425
0.24
1.22
0.01
0.06
6.8
35
23
1.6
235
1.0
0.2
1.4
770
300
8
55
290
0.17
0.10
<0.01
0.02
Digested Digested sludge
sludge compost
6.5
76
24
2.3
1210
2.2
0.2
2.0
1760
725
19
-
575
0.24
0.13
-
-
6.8
35
13
0.9
190
1.0
0.1
2.0
1000
250
9
-
320
0.25
0.05
0.008
0.06
I/ Polychlorinated biphenyls as Arochlor 1254.
?/ The gamma isomer of benzene hexachloride is also called
lindane.
3_/ DDE results from the dehydrochlorination of DDT.
6
-------
ECONOMIC FEASIBILITY OF COMPOSTING
To evaluate the economic desirability of composting for a
municipality, one must first evaluate the costs of converting raw
sludge into compost and then the benefits the compost will furnish
to the community. Benefits will partially offset costs and the
net cost of composting may then be compared with the cost of
other forms of sludge management.
The cost of composting will vary among projects. Much of
the variation will result from differences in physical inputs
(i.e., equipment and site preparation) in response to (1) the
amount of sludge composted, (2) the topography of the composting
site, (3) state and local restrictions, (4) local institutional
constraints, and (5) amounts of already existing public works
equipment available for the composting. The unit prices of the
physical inputs will also differ among localities, adding another
cost variable.
Table 4 compares costs of various sludge disposal methods.
The wet sludge actually composted contained 23% solids. The dry
ton figures presented may be converted to approximate wet tons
by dividing by 4.
TABLE 4. APPROXIMATE COMPARATIVE COSTS FOR VARIOUS SLUDGE
DISPOSAL PROCESSES. 1976.
Process Range of costs
in dollars per dry ton!' A/
Digested sludges by:
Ocean outfall 10 to 35
Liquid landspreading- 20 to 54
Digested and dewatered sludges by:
Ocean barging 31 to 44
Landfilling 23 to 53
Landspreading 26 to 96
Dewatered sludges:
Trenching!/ 116 to 134
Incineration*/ 57 to 93
Heat drying*/ _ ___ 62 to 115
Composting!' 35 to 50
I/ Costs exclude transportation of sludge to disposal site.
-------
Table 4 (continued)
2_/ Costs exclude cost of removal of residues from the site and
benefits from resource recovery.
3_/ Cost comparisons require careful interpretation. For example,
the cost of digestion should be included in the cost of land-
spreading. However, digestion reduces mass of sludge solids
by about one-half so there is less sludge to process.
4/ 1 dry ton = 0.908 metric ton (or tonne).
Composting compares favorably in cost with other sludge
disposal processes. Landfilling and ocean-dumping may be cheaper
in some instances, but they offer no benefits and have serious
disadvantages. Incineration is likely to be more expensive than
composting and offers benefits only if heat is recovered. Compost-
ed and heat-dried sludge will improve the soil. Heat-drying,
however involves a large use of energy. Both heat-drying and
composting produce a product that is more easily handled and less
offensive than digested sludge for use on land. The optimal
sludge management system will differ between municipalities due
to the variability of the relative environmental, social, and
economic ramifications of the alternatives.
Composting dewatered sludge is estimated to cost between $35
and $50 per ton of dry sludge. The higher cost is based on
an operation that processes 10 dry tons per day, the lower one
on 50 dry tons per day. Economies of size in equipment and labor
use decrease the unit cost as the size of the operation increases.
These calculations include all on-site expenditures but exclude
costs of (1) dewatering the sludge to 20% solids, (2) transport-
ing the sludge to the composting site, (3) treating the runoff
from the site, and (4) transporting the compost to the location
of its use.
Operating costs account for about 807o of the composting cost
per dry ton, with labor accounting for about half of these oper-
ating costs and the bulking agent for about a quarter.
The capital costs of composting are not large in relation to
such costs in other sludge management options. Capital costs of
composting are estimated to be $30,000 to $40,000 per dry ton of
daily capacity, although this figure may vary considerably
between sites. If these capital costs were increased 10 percent,
it would increase the unit cost of composting by less than $1.00
per dry ton.
A cost function for aerated pile composting as practiced at
Beltsville, Maryland is presented in Figure 2. It is apparent
that operating costs are subject to economies of size which are
attained by facilities that compost over 70 dry tons per day.
8
-------
80
5270
§
r-
r»
o>
60
Z50
Q40
e
30
ui
10
COST OF AERATED PILE COMPOSTING, 1977
10 20 30 40 60 60 70 80 90 100
SLUDGE QUANTITY
-------
There will be beneficial uses for all sludge compost that
might be produced by including the use of compost for fertilizer
on farm land. Compost contains small amounts of nutrients, so
the Beltsville compost has a value of about $4 per cubic yard in
terms of 1977 prices in Maryland for nitrogen and phosphate. A
market study is necessary to determine the net benefits or cost
to a community from the distribution of the sludge compost. Some
refuse composting operations have closed because of the lack of a
developed market for compost in their area and because they
expected to show a profit on the production and distribution of
the compost. Composting will benefit the sewage authority eco-
nomically if the net cost of production and distribution is
less than that of any other environmentally acceptable disposal
system. A well-planned and -managed marketing program is essent-
ial to derive a profit over distribution costs, as is the case
in Los Angeles'County. If the sludge compost is used for its
fertilizer value alone, there .could be a net cost of distribut-
ion, depending on the hauling distance.
Compost may be used in place of peatmoss or topsoil in
certain horticultural applications. During preparation for the
National Bicentennial, the National Park Service used Beltsville
sludge compost to construct Constitution Gardens in the Mall area
of Washington, D.C. The Park Service saved over $200,000 by
making an artifical topsoil with the compost instead of buying
topsoil, which was selling at about $5 per cubic yard undelivered
in 1976. The yield of compost is about 5 cubic yards per ton of
dry sludge solids, so the net profit or loss on distribution per
yard must be multiplied by 5 to obtain the effect per ton of
sludge solids.
Composting may be a cost-effective alternative for some
municipal sludge management problems. The net cost of composting
will vary among municipalities because the production costs and
the utilization benefits will also vary. Therefore, a feasi-
bility study of sludge composting must include not only a cost
analysis of the process but also a comprehensive analysis of the
potential market for the product.
10
-------
SECTION 3
THE COMPOSTING PROCESS
Composting is an ancient practice used by farmers to convert
organic wastes into soil amendments that supply available
nutrients to crops and replenish depleted soil organic matter.
The practice remained more of an art than a science until about
40 years ago when Sir Albert Howard, a British agronomist in
India, developed the Indore Process for composting. Named after
the state in India where Howard developed it, the method utilizes
a 5- to 6-foot layered pile of various organic wastes such as
leaves, night soil, animal manure, sewage sludge, straw, and
garbage. The pile is turned after 2, 4, and 8 weeks, and compost-
ing is complete in about 3 to 4 months. The method is essential-
ly a combination of aerobic and anaerobic composting. Howard
demonstrated that composting is a beneficial alternative to the
burning and dumping of refuse and sewage sludge.
The Beltsville Aerated Pile Composting Method stimulates a
natural biological process. Complex organic molecules are
decomposed into simpler compounds through the growth and activity
of bacteria, actinomycetes, and fungi. While these organisms
utilize a portion of the carbon and nitrogen fraction in the
composting biomass for synthesis of cellular materials, they also
convert chemical energy into heat through respiration. This heat
raises the temperature of the biomass, evaporates moisture, and
raises the temperature of air passing through the biomass. Heat
is also lost at the pile surface by radiation, conduction, and
convection. A flow diagram for the process, explained at a later
point in detail, is presented in Figure 3.
FACTORS AFFECTING THE COMPOSTING PROCESS
A number of factors influence the rate at which composting
can proceed and the quality of the finished product.
Temperature Temperature profoundly affects the growth and
activity of microorganisms and, consequently, determines the
rate at which organic materials are composted. Most of the micro-
organisms in sewage sludge are mesophilic; that is, they grow
best in the temperature range of 20 to 35°C. However, as temper-
atures increase during composting, a specialized group of micro-
organisms becomes predominant. These are thermophilic aerobic
organisms that develop only at higher temperatures and grow
11
-------
WOOD CHIPS
RECYCLED
OPTION A
DRYING
-» SCREENING
AERATED
PILE
(21 DAYS)
WOOD CHIPS
(2 VOLUMES)
CURING
(30 DAYS)
t
STORAGE
COMPOST
MARKETING
OPTION B
DRYING
i
-•»
SCREENING
WOOD CHIPS
RECYCLED
*J
Figure 3. Flow diagram for composting operation.
-------
fastest at 45 to 65°C. They generate sufficiently high temper-
atures to destroy human pathogens.
Carbon:Nitrogeri Rat io The C/N ratio is an important parameter in
composting because it provides a useful indication of the proba-
ble rate of organic matter decomposition. Microorganisms use
about 30 parts of carbon for each part of nitrogen. Thus, an
initial C/N ratio of 20 to 35 would be most favorable for rapid
conversion of organic wastes into compost. Sewage sludges usu-
ally have C/N ratios of less than 15. Although decomposition
will be rapid at this ratio, .nitrogen may be lost as ammonia. In
the process described here, the addition of woodchips or other
organic bulking materials raises the C/N ratio, ensuring the con-
version of available nitrogen into organic constituents of the
biomass. The subsequent removal of the woodchips for reuse then
lowers the C/N ratio, allowing N to mineralize.
Moisture Content Sewage sludges can be composted aerobically
over a wide range of moisture contents, 30% and higher, if aer-
ation is adequate. However, excessively high moisture contents
should be avoided in most aerobic composting systems, because
water displaces air from the pore spaces and can quickly lead to
anaerobic conditions. On the other hand, if the moisture content
is too low (less than 40%) stabilization will be slowed because
water is essential for microbial growth. The most favorable
moisture content for composting sludge (22% solids) with wood-
chips by the aerated pile method is from 55 to 65% in the sludge-
chip mixture.
Aeration and Oxygen Supply In composting sewage sludge, aera-
tion is essential for the development of thermophilic microorgan-
isms to ensure rapid decomposition, odor abatement, and stabili-
zation of the residual organic fraction which remains as compost.
Aeration also provides for lowering the moisture content of com-
posting materials that may have initially been too high. The
forced aeration system used with the Aerated Pile Composting
Method provides for internal oxygen levels of from 5 to 15%.
Within this range, maximum temperatures are attained to ensure
pathogen destruction and rapid stabilization. Proper control of
the aeration rate is essential because too high a rate can lead
to excessive heat loss, cooling of the pile, and incomplete
stabilization.
Use of Inocula Wherever composting has been practiced, there
has been considerable debate as to whether special strains of
microorganisms, or other biological factors such as chemical
activators, enzymes, and hormones, are necessary to ensure suc-
cessful composting. A number of these products are commercially
available, the contents of which are known only to the manu-
facturers. However, most organic wastes and residues are already
colonized with large numbers of indigenous microorganisms (bacte-
ria, actinomycetes, and fungi) with a wide range of physiological
13
-------
capabilities, and most composting studies indicate that inoculants
and other additives to accelerate or activate the composting pro-
cess are ineffective and unnecessary.
pH of the Sludge Sewage sludges can be composted over a pH
range of from pH 5 to 10. The most favorable pH range for rapid
aerobic composting of sludge would be from 6 to 8, because most
microorganisms exhibit maximum growth and activity in that range.
Nevertheless, initial pH values as extreme as 5 or 11 do not seem
to retard microbiological activity for more than 1 or 2 days.
Generally, as composting proceeds the pH shifts toward neutrality.
SITE SELECTION AND DESIGN CRITERIA
Locating the composting site near the wastewater treatment
plant results in lower costs for hauling and transportation of
sludge, bulking materials, and equipment; a possible reduction of
manpower requirements; and more effective utilization of the space
allocated for the composting operation. Adverse public reaction
to sludge haulage through residential areas may also be avoided.
A sludge-composting facility should comprise the following
areas: (a) receiving and mixing, (b) composting pad, (c) drying
and screening, (d) curing, (e) compost storage, (f) storage of
woodchips or other bulking materials, (g) administrative and
maintenance buildings, and (h) driveways. These facilities can
be provided for a 10-dry-ton-per-day production rate on a 3.5-
acre site.
The sludge and bulking material can be mixed directly on the
composting pad with a front-end loader. This mixing procedure is
quite satisfactory for small municipalities and requires only a
small area for handling materials and maneuvering the equipment.
Larger amounts of sludge, i.e., more than 15 dry tons per day,
would best be mixed in a stationary mixer (drum mixer or pugmill)
located near the filtering equipment. This will substantially
decrease the area required for mixing, and also minimize
potential problems.
The composting pad should be large enough to accommodate 4
weeks of sludge production by the treatment plant. This will
provide for the usual 21-day composting period and the necessary
space for operating the equipment. It also will provide a safety
margin to allow for extending the composting period beyond 3
weeks if necessary due to low temperatures, excessive precipita-
tion, or equipment malfunction. The odor filter pile will
occupy a space equivalent to about 1070 of the pile area.
14
-------
Fad area = (l.l)(Vol- of 4 wks sludge production) (R-fl)
^-~ ^ sludge layer
where R = volume of bulking agent
volume of sludge
The size of the processing area for drying and screening
depends on climatic factors, the bulking material used, and the
potential use of the product. A considerably smaller area will
suffice in hot, dry climates, where the material is relatively
dry after composting, than in cool, humid climates. If fine,
granular bulking materials are used, the compost may not require
screening. For a climate similar to Washington, B.C. ,
Processing area = pad area
The curing area should accommodate 30 days of compost pro-
duction. In regions where compost application is restricted to
spring, summer, and fall, the compost must be stored during
winter. Thus, the area required for compost storage would be
considerably larger in the Northern than in the Southern United
States. For Washington, D.C. , where compost was stored during
the winter,
Curing and storage area = 2 x pad area
In addition to the areas specified earlier, access roads,
turnaround space, and a truck-wash area are needed. If the com-
posting site is not near the treatment plant, or if runoff from
the site cannot be drained into a sewer system, a runoff collect-
ion pond must be provided. Figure 4 shows most of the ARS-MES
sludge -compos ting facility at Beltsville, Maryland, which can
compost 20 dry tons of sludge per day.
A buffer zone around the compost site is desirable. Although
the Beltsville Aerated Pile Composting Method effectively con-
tains most of the sludge odor, a faint earthy or musty odor of
compost remains. Under most weather conditions, this odor dis-
sipates in a very short distance. A screen of trees and shrub-
bery around the site may reduce the likelihood of odor com-
plaints.
BULKING MATERIALS TO CONDITION THE SLUDGE FOR COMPOSTING
To ensure rapid aerobic composting, the sludge must be mix-
ed with a suitable bulking material to provide the necessary
structure, texture, and porosity for mechanical aeration. The
bulking material, which is usually organic, can also function as
a carbon carrier to provide extra energy for the microorganisms
during composting. While some decomposable carbon in the ^bulking
material is desirable, it is not essential to the composting
process.
15
-------
Figure 4. Aerial view of sludge-composting research site.
Windrows in foreground are being used to dry compost prior to
screening. Extended pile adjacent to windrows contains as much
sludge as five of the individual aerated piles. Piles in upper
portion of picture are stored compost. Weather has caused no
interruptions in the processing rate of 60 T/day, 5 days per week
during the 4 years that aerated pile composting has been the
major mode of operation.
16
-------
The amount of bulking material needed is related to moisture
content of the sludge. For example, liquid sludge at 6 to 8%
solids would require about 5 to 7 times as much of a given bulk-
ing material as partially dewatered sludge at 22 to 24% solids.
Bulking materials should have sufficient wet strength to allow
the necessary porosity for air movement when mixed with the
sludge and placed in the pile. These materials also should have
sufficient moisture absorptive capacity to induce crumbling of
the sludge. Because most of the decomposition during composting
occurs at exposed surfaces, crumbling speeds stabilization by
increasing the surface-to-volume ratio. The upper limit for good
crumbling of sludge is at a moisture content of about 607o.
Many materials frequently considered wastes have the proper-
ties of a suitable bulking agent in some degree, e.g. woodchips,
wood shavings, sawdust, peanut hulls, corncobs, leaves, refuse
(garbage), cotton gin trash, sugarcane bagasse, pelleted refuse-
derived fuel (RDF), rice hulls, cereal straws, shredded bark, and
various air-classified fractions (mainly paper) from solid waste
recovery plants.
Landfill operators may have valuable information on sources
and amounts of waste materials that might be used as bulking
materials for the composting of sewage sludge. The amount of
bulking material needed will vary with the material selected and
the sludge. For a partially dewatered sludge of 20% solids, the
most effective bulking material-to-sludge ratio has ranged
between 1:1 and 4:1 on a loose volume basis. The mixture should
be porous and contain no free liquid. Some bulking materials can
be recovered by screening and used several times; others might
need to be screened out and landfilled; some might become a part
of the compost. The influence of the bulking material on the
value of the compost should not be overlooked.
Woodchips have been the most commonly used bulking material
for composting sewage sludges at USDA's Composting Research
Facility at Beltsville, Md., because of their low cost and
guaranteed availability.
THE MIXING OPERATION
The sludge and bulking material must be thoroughly mixed so
that lumps of sludge are no larger than 3 inches (7.5 cm) in
diameter. If sludge aggregates are larger than this, a slow rate
of decomposition and suboptimal temperatures may result.
A number of different machines (Figures 5-8) can be used
to achieve this desired degree of mixing, for example, a front-
end loader. Another method is to spread the bulking material and
sludge in layers, and then to mix with a rototiller. Windrow
turning machines can also be used effectively, but their cost
17
-------
Figure 5. Dump truck load of vacuum filter cake sludge from
the Blue Plains Waste Water Treatment Plant being unloaded onto
a bed of woodchips with which it will be mixed.
18
-------
Figure 6. Front-end loader distributing sludge uniformly over
bed of woodchips prior to mixing. The loader may also be used
for the entire mixing operation.
19
-------
Figure 7. Terex-Cobey windrow composter mixing sludge with
woodchips. This method of mixing might be suitable for treatment
plants producing 100 dry tons of sludge daily.
20
-------
Figure 8. Roto-shredder, another windrow composting machine,
mixing sludge with woodchips.
21
-------
makes their use more applicable to operations that handle
several hundred tons of sludge (22% solids) per day.
Drum mixers and pugmills may also be used in the mixing
operation. However, the stickiness of the sludge and the flow
characteristics of the bulking material are important consider-
ations in designing systems that can successfully feed and unload
them. With such mechanization it may be necessary to increase
the bulking material:sludge ratio to compensate for variations
in proportioning.
THE AERATED PILE
A three-dimensional schematic diagram of the Beltsville
Aerated Pile Method for composting sewage sludge is shown in
Figure 9. In their simplest form, the individual aerated piles
are constructed as follows:
1. A loop of 4-inch-diameter (10-cm) perforated plastic
pipe is placed on the composting pad lengthwise and
directly under what will become the ridge of the pile
(Figure 10). The perforated pipe should not extend
under the end slopes of the pile because too much air
may be pulled through the sides, causing localized "cold
spots" that do not reach the thermophilic range.
2. A 6- to 8-inch (15- to 20-cm) layer of woodchips or
other bulking material is placed over the pipe and
the area to be occupied by the pile. This layer
comprises the pile base and facilitates the move-
ment and distribution of air during composting.
The base material also absorbs excess moisture
that may condense and leach from the pile.
3. The mixture of sludge and woodchips is then placed
loosely upon the prepared base with a front-end
loader or conveyor system (Figures 11 and 12) to
form a pile with a triangular cross section 15 feet
wide (5 m) and 7.5 feet high (2.5 m).
4. Excess woodchips are removed from around the base and
the pile is completely covered with a 12-inch (30-cm)
layer (often referred to as the "blanket") of cured,
screened compost or an 18-inch (45-cm) layer of cured,
unscreened compost to provide insulation and prevent the
escape of malodorous gases during composting. If finish-
ed compost is not available, as would be the case for
the first piles of a new operation, the bulking material
can be used. However, the blanket thickness may have to
be increased to achieve the same degree of insulation
and odor control as obtained with cured compost.
22
-------
COMPOSTING WITH FORCED AERATION
SCREENED
COMPOST
WOODCHIPS
AND SLUDGE
PERFORATED
PIPE
WATER TRAP
FOR CONDENSATES
FILTER PILE
SCREENED COMPOST
Figure 9. Schematic diagram of an aerated pile, showing
location of aeration pipe. The piping under the pile is
perforated for air distribution.
|(Mor FIMW
PLAN VIEW
CROSS SECTION A-A
x-ETV
» *> i S 9 f >
H»"*f-
I——2H <
CROSS
SECTION
B-B
Figure 10. Orientation of aeration pipe in pile, indicating
recommended edge distances and spacing for extended piles.
23
-------
Figure 11. Front-end loader placing sludge-woodchips mixture
on aerated pile. Note air conditioner on top of cab which
enables operator to work in relatively dust-free environment.
24
-------
Figure 12. Front-end loader about to place sludge-woodchips
mixture on aerated pile. Loader wheels ride up on the woodchip
base but not on the mixture since they would compact it, thus
blocking air movement.
25
-------
5. During construction of the pile base, the perforated
pipe is connected to a section of solid plastic pipe ex-
tending beyond the pile base. The solid pipe is connect-
ed to a blower rated at 160 cfm with 5" water head pow-
ered by a 1/3 - hp motor and controlled by a timer
(Figure 13). The actual air resistance of this entire
system has been less than 5" so that the actual air
delivery has been 200 to 250 cfm. Aerobic composting
conditions are maintained by drawing air through the
pile intermittently. The exact aeration schedule will
depend on pile geometry and the amount of sludge to be
composted. For a pile with the dimensions described (20
mx 5 mx 2.5 m), the timing sequence for the blower is
4 minutes on and 16 minutes off. The composting begins
when the blower is turned on.
6. The effluent air stream discharged from the compost pile
blower is conducted into a small cone-shaped pile of
cured, screened compost approximately 4 feet high (1.3
m) and 8 feet in diameter (2.7 m), where malodorous
gases are absorbed. These are commonly referred to as
odor filter piles. The moisture content of compost in
the filter pile should not exceed 50% because the odor
retention capacity tends to decrease at higher contents.
A 6-inch (15-cm) base layer of woodchips or other bulk-
ing material around the perforated pipe will minimize
back pressures, which could cause leakage of malodorous
gases around the blower shaft. The odor filter pile
should contain about 1 cubic yard.of screened compost
for each 10 wet tons of sludge being composted.
With new operations, where screened compost is not yet
available, some bulking material or soil (or a mixture
thereof) could be used in the filter piles.
Variations in pile shape and size can adapt the process to
differences in the rate of sludge production by most treatment
flants. The individual pile method described here is suitable
or operations ranging from as little as 5 tons.of sludge (20%
solids) from a single weekly dewatering operation in a cone shap-
ed pile to more than 100 tons per week.
THE EXTENDED AERATED PILE
Another version of the aerated pile is the aerated extended
pile illustrated in Figure 14. Each day's sludge production is
mixed with a bulking material and added against the slope of the
previous day's pile, thus forming a continuous or extended pile.
The extended pile offers certain advantages for larger munici-
palities on a daily sludge production schedule. For example, the
area of the composting pad can be reduced about 50% as compared
26
-------
Figure 13. Axial vane centrifugal fan powered by a 1/3 horse-
power electric motor. Steam is escaping from the odor filter
pile on the right. Fan is controlled to operate intermittently
by a time clock. Typically, the time clock is set to operate
motor for 4 minutes out of 20 when serving 50 tons of vacuum
filter cake.
27
-------
SCREENED
COMPOST
COMPOSTING EXTENDED
PILES WITH FORCED
AERATION
FILTER
SCREENED
COMPOST
Figure^14. Schematic diagram of extended aerated pile showing
construction of pile and the arrangement of aeration pipe.
28
-------
with that required to accommodate, an equal amount of material
in individual piles. Moreover, the amount of screened compost
blanket material needed for insulation and odor control and the
amount of bulking material for the pile base are decreased 50%,
In constructing an extended pile, the first day's sludge
production is placed In an individual pile with triangular cross
section as described earlier, but only one side and the ends are
blanketed. The remaining side is dusted with about an inch (2.5
cm) of screened compost for overnight odor control. On the
second day, additional aeration pipe is placed on the pad surface
parallel to the dusted side, the pile base is extended, and the
sludge-woodchips mixture is placed in such a manner as to form an
extended pile with a trapezoidal cross section as shown in Figure
15. Also on the second day, the flat top and ends are blanketed
with screened compost and the remaining side receives a thin lay-
er of compost as before. The pile is extended in this fashion
each day for 28 days. However, after 21 days the first day's
section is removed for either drying and screening or placing in
a curing pile. After the removal of seven sections in chronolog-
ical sequence, sufficient space is freed for operating the equip-
ment so that a new extended pile can be started where the old one
had been. Thereafter, a section is removed each day from the old
pile and a section is added to the new one.
TEMPERATURES ATTAINED DURING COMPOSTING
The transformation of sludge into compost is essentially
complete after 3 weeks in the aerated pile. Microbial decomposi-
tion of the volatile organic fraction of the sludge in an aerobic
atmosphere soon raises the temperature throughout the pile to
above 140 F (60°C), which effectively destroys pathogenic organ-
isms that might cause disease in humans. Typical temperatures
recorded during the composting of raw sludge by the Beltsville
Aerated Pile Method are shown in Figure 16. Temperatures in t^e
pile increase rapidly into the thermophilic range of 176 F (80 C)
or higher. Temperatures begin to decrease after about 16 to 18
days, indicating that the microflora have used the more decompos-
able organic constituents and that the residual sludge has been
stabilized and transformed into compost. Figure 16 also indi-
cates that if piles are constructed properly, neither excessive
rainfall nor low ambient temperatures affect the composting
process.
AERATION AND OXYGEN SUPPLY
Centrifugal fans with axial blades are usually the most
efficient mechanism for developing the necessary pressure to move
air through the compost piles and into the odor filter piles.
About 5 inches (12.5 cm) of water pressure across the fan has
29
-------
COMPOST
REMOVED
HERE
SLUDGE ADDED
.HERE
GJ
o
Figure 15. Cross section of an extended pile showing a typical sequence
of sludge additions to the pile. Numbers indicate the age of the compost
in days.
-------
80-
70 -
60-
O
ui 50
cc
£ 40
CL
5
H 30 -
20 -
10-
MEAN
o
u.
Z
-5.0
13 15 17
TIME-DAYS
19 21
23
25 27
Figure 16
operation.
Temperatures recorded during the composting
Bars at bottom indicate rainfall events.
-------
been adequate when woodchips are used as the bulking material.
However, when finer textured materials such as sawdust are used
for composting sludge, a substantial increase in pressure may be
needed.
o
An aeration rate of about 500 cubic feet (14m ) per hour per
ton of sludge (dry weight basis) should maintain the oxygen level
in the pile between 5 and 15% and provide for rapid decomposition
of the sludge and extended thermophilic activity. Continuous
aeration results in rather large temperature gradients within the
pile. Cycles of 20 to 30 minutes, with the fan operating 1/10 to
1/2 of the cycle, have given more uniform temperature distribu-
tion.
The air under the compost piles is collected and delivered
to the odor filter piles by 4-inch (10-cm) flexible plastic drain
pipe. The pipe is damaged beyond reuse when the piles are taken
down, but since it is relatively inexpensive it is considered
expendable. Rigid steel pipe has also been used and can be pull-
ed lengthwise out of the pile without damage for reuse. Pipe
spacing for the extended piles should not exceed the pile height.
The pipe should be large enough so that the air velocity does not
exceed 2,000 ft. per minute to prevent excessive pressure varia-
tion. Manifolding the outer ends of the pipe will equalize
pressure should the pipe be damaged.
CONDENSATE AND LEACHATE CONTROL
As air moves down through the composting sludge, it is warm-
ed and picks up moisture. However, as a result of heat loss to
the ground, temperatures near the base of the pile are slightly
cooler. As the air reaches this area, it is cooled slightly,
causing moisture to condense. When enough condensate collects,
it will drain from the pile, leaching some sludge with it. Con-
densate will also collect in the aeration pipes and, if not
drained, can accumulate and block the air flow. Leachates and
condensate combined may amount to as much as 5 gallons per day
per ton of dry sludge. If the bulking material is sufficiently
dry when mixed, however, no leachate will drain from the pile.
Since the leachate contains sludge, it can be a source of odor if
allowed to accumulate in puddles, so it should be collected and
handled in the same manner as runoff water from the site.
SEQUENCE OF OPERATIONS FOR COMPOSTING SLUDGE
A flow diagram for the Beltsville Aerated Pile Method for
composting sewage sludge is shown in Figure 3. After 21 days of
composting, there are two options which provide considerable
flexibility for the process. If weather and climatic conditions
are favorable and labor and equipment are available, option A is
32
-------
usually followed, whereby windrow drying and screening are per-
formed before a 30-day curing period is imposed. The compost
and woodchip mixture is usually dried to about 40 to 45 percent
moisture to facilitate clean separation of compost from chips by
screening. The recovered woodchips are recycled with new batches
of sludge. If the weather is inclement or labor and equipment
are not available, option B can be followed, whereby the compost-
ed biomass is taken directly from the aerated pile and placed in
a curing pile for 30 days before drying and screening. Not only
does this provide processing flexibility but it offers the choice
of two kinds of compost - users of compost for land reclamation
and erosion control often prefer the unscreened compost contain-
ing woodchips.
The curing and any subsequent storage can be considered as
an extension of the composting process and are associated with
elevated temperatures, though somewhat lower than the mean tem-
peratures attained during the initial composting. Curing ensures
total dissipation of phytotoxic gases and offensive odors, and
allows for total destruction of any remaining pathogens.
Drying The moisture content of the compost can substantial-
ly influence its handling characteristics. When the moisture
content is 4570 or less, the compost will flow freely and can be
handled or screened without difficulty. Good handling character-
istics are also advantageous for the users of the product. The
moisture content should not be below 357o, since dusting becomes
a problem at lower moisture contents.
Two methods of mechanically assisted drying have been used
at Beltsville. In the first method, the compost is spread out in
a 12-inch layer and harrowed frequently with a spring tooth har-
row mounted on a small farm tractor. In the second method, the
compost is placed in a windrow 3 feet high and turned frequently.
Generally, 1 to 2 days of drying by either method is adequate if
the compost is worked hourly. Regularly updated weather fore-
casts are essential when drying the compost by either of these
methods. When precipitation is predicted, the compost should be
piled to minimize the surface exposed. Heavy precipitation will
increase moisture only slightly in storage piles more than 10
feet (3 m) high. The same methods can be used for drying wet
bulking material when necessary.
Screening Depending on the bulking agent used, operators
may find it desirable to screen the compost to improve its mar-
ketability or to remove the bulking material for reuse (Figures
17 and 18). These choices are largely governed by economics.
When a coarse bulking agent is used, some screened compost is
desirable for blanket material. Both rotary screens (trommels)
and vibrating screens have been used satisfactorily. _The rotary
screens, however, have been less susceptible to clogging when^
screening compost at higher moisture contents. A 1/4 to 1/2-inch
screen opening wjlll produce a product that is attractive for most
33
-------
Figure 17. Rotary drum (trommel) screen separating woodchips
from composted sludge. Conveyor in foreground is delivering
compost. Moisture content of compost must be less than 50%
to prevent bridging in feed hopper.
-------
Figure 18. Still-warm woodchips steaming in foreground.
Reclaimed woodchips are reused as bulking material until they
decompose and become part of the compost after about 4 to 5
uses .
35
-------
soil conditioning uses.
Curing and Storage After the compost has been cured for
about 30 days(screened or unscreened), it may have to be kept in
a storage pile. Use of the compost will be somewhat seasonal,
i.e., most of it will be applied either in the spring or fall.
Thus, a storage capacity to accommodate 3 to 6 months' production
will be needed.
During storage, the compost will continue to decompose slow-
ly. Usually, this does not present any problem because by this
time the compost is well stabilized. Decomposition in storage
can be largely curtailed by drying the compost to a moisture con-
tent of about 157o. If it is stored in large piles at a moisture
content of, say 4570, temperatures will increase to the thermo-
philic range, and additional composting will occur. The compost
can be stored without cover and may be piled as high as is con-
venient with the equipment available. The tops of the storage
piles should be rounded so that wet pockets do not develop.
MONITORING OPERATIONS
The aerated pile composting process is relatively insensi-
tive to changes in operating conditions and materials. However,
to achieve economy of operation, produce a product of adequate
quality, and reduce potential for pollution, control and monitor-
ing of operating parameters is necessary. Since microbiological
activity during composting is mainly influenced by temperature,
oxygen, and moisture content, these parameters should be monitor-
ed so that improper composting conditions can be corrected. Com-
posting as described here is a batch process, making it important
to collect some data on each pile or each section of an extended
pile.
The most common cause of difficulties is excessive moisture
in the composting mixture. The maximum moisture content for
consistently good composting activity will be about 607o wet basis
of the sludge-bulking agent mixture. A skilled operator will
soon learn to identify this limit by appearance, as well as by
the moisture content of the bulking material needed to produce a
compostable mix.
Temperature will reveal more about the process than any
other single measurement. Temperatures should be measured at
several locations in the pile. Continuous measurement is not
needed, but remote recording of temperature from several thermo-
couple or thermistor probes may be more cost-effective than
periodically sending out an operator to take measurements.
Most of the compost pile should reach 130°F (55°C) within 2
to 4 days, indicating satisfactory conditions with respect to
36
-------
moisture content, bulking material ratio, mixing, and pH. If
substantial portions of the pile exceed 175°F (80°C), the aera-
tion rate can be increased to remove additional moisture from the
pile. Temperature also is an excellent indicator of the probable
extent of pathogen destruction or survival. Pathogens die off
rapidly when temperatures are 130°F (55°C) or higher for several
days. Some temperature measurements should be taken just inside
the blanket, where cold spots are most likely to occur. Cold
spots may result from a thin place in the blanket, from the
placement of an aeration pipe too close to the edge of the pile,
from excessive pad material not covered by the blanket, or from
incomplete mixing. If the average temperature in the pile is
below 140°F (<60DC) after 5 to 7 days, the cause should be deter-
mined and corrected. If, as is most likely, the moisture content
is too high, additional dry bulking material can be mixed in and
the pile rebuilt. Two other possible causes of low temperatures
are an excessive aeration rate (also indicated by high oxygen
levels) and high sludge pH (>11.0). Equipment recommended for
monitoring temperatures is listed in the appendix.
Oxygen analysis of gas samples drawn from the center of the
piles is useful for locating problems and optimizing the aeration
system. The oxygen level should be in the range of 57o to 15% the
first week. Scattered readings below 570 indicate poor distribu-
tion or movement of air, probably due to excessive moisture or
incomplete mixing. If a gas sample cannot be obtained, there are
no voids for oxygen movement and the sampling location is proba-
bly anaerobic. If all readings are low, the aeration rate should
be increased. High aeration rates to maximize drying will in-
crease the oxygen level to as much as 2070 during the third week
of composting. Equipment recommended for monitoring oxygen
levels during composting is listed in the appendix.
The maximum allowable level of pathogens or heavy metals in
the compost may eventually be set by federal or state regulations,
in which case the sampling procedures and frequency will be pres-
cribed by the regulatory agency. However, a record of operating
temperatures showing that the temperature of the coldest part of
the pile had exceeded 60°C would indicate that most pathogens
were killed.
Site operators should pay particular attention to odors.
Whenever unpleasant odors are noted, the source should be located
and corrected. Exposed sludge, ponding around compost piles, and
partially composted sludge are potential odor sources. Improper-
ly constructed odor filter piles or leaky pipes between the
blower and the filter pile can also contribute odors. Over time,
the odor filter piles tend to collect condensate, which lowers
their capacity to absorb and retain odors. When the moisture
content of the odor filter piles becomes excessive (i.e., 75 to
80%), they should be removed and rebuilt with dry (50% moisture
content or less) compost. The used filter pile compost can be
37
-------
placed in a curing pile for reconditioning. A recommended pro-
cedure for measuring the moisture content of compost or bulking
materials is described in the appendix.
The blowers should be checked daily to see that they are
operating. Whenever the bulking agent or the air distribution
system is changed, the air delivery rate should be checked.
Table 5 lists parameters that should be monitored during the
composting operation, and the suggested frequency of measurement
in accordance with the size of operation.
Table 5. Suggested parameters and time sequences for monitoring
Parameter
Moisture content
Temperature
Oxygen
<25
monthly
daily
optional
Size of operation in tons
week (dry solids)
25 to 250
weekly
daily
weekly
per
>250
daily
daily
daily
Pathogen survival as required by local regulations
Heavy metals as required by local regulations
Process odors daily daily daily
V
Blower operations daily daily daily
pH of sludge^ monthly monthly monthly
1 Qualitative "by eye" estimation of moisture of the compost mix
should be done daily. Moisture content of sludge should be
obtained from sewage plant operator.
2 Good communications should be maintained with sewage plant
operators, so that the compost plant operator is informed of
any process change or condition that will effect the quality
of the sludge.
ODOR CONTROL
Although sewage sludge can emit a strong unpleasant odor,
this odor gradually disappears as the sludge is stabilized by
composting. All odor cannot be eliminated during composting,
38
-------
however. Even well-cured sludge composts have an earthy odor
that fortunately is pleasant to most people.
Each of the unit operations can be a potential source of
odors. Some of the odors are emitted intermittently and others
continuously. Odor potential increases considerably during and
immediately after heavy precipitation. To minimize the odor
potential throughout the composting process, one must manage each
operation as follows:
1. The mixing operation — Prompt mixing of sludge and
bulking material and placement of the mixture in the
aerated pile reduces the time for odor generation. Lime
added to the as a conditioner for dewatering or added
with the bulking material will help to lower the odor
intensity. An enclosed mechanical mixer could eliminate
the release of odors during this operation.
2. Aerated pile surface — This will not be a source of
strong odors if the blanket of compost is adequate for
insulation. Thin spots or holes in the blanket will be
a potential source of odors. The effectiveness of the
blanket for odor control decreases when its moisture
content exceeds 60%.
3. Air leakage between the blower and odor filter pile --
Since air leakage can occur at this point,all pipe
joints should be sealed. Back pressure from the odor
filter pile should be minimized to prevent gaseous
losses around the blower shaft. A layer of woodchips
over the perforated pipe will minimize back pressures.
4. Odor filter piles — Odor filter piles should be cone-
shaped and symmetrical, and should contain about 1
cubic yard of dry (5070 moisture or less) screened com-
post per 10 wet tons of sludge being composted. A
small cone of woodchips over the pipe outlet will re-
duce pressure through the pile.
5. Condens ate and 1eachate --As these liquids drain from
the compost pile, they should be collected into a sump
and conveyed in a pipe to the sewer system or runoff
pond.
6. Removal of compost from the aerated pile to the curing
pTle — Excessive odor during this operation can prob-
ably be attributed to inadequate stabilization of the
compost due to too high a moisture content of the bulk-
ing material. The situation is prevented by using
drier materials in the initial mixing operation. See
item 7 (below) for overcoming the problem if it occurs.
39
-------
7. Curing piles -- These also can be a source of odors if
the material removed from the aerated pile has not been
completely stabilized. Blanketing the curing pile with
dry cured compost will help to contain any odors. If
sludge is incompletely composted after 21 days because
of excess moisture, low temperatures, improperly con-
structed piles, or improperly treated sludge, it should
not be put on a regular curing pile. Instead it should
be mixed with additional bulking material and composted
another 21 days with aeration, or put into a separate
isolated pile, heavily blanketed with screened compost,
and allowed to compost anaerobically for 6 to 8 months.
8. Storage piles — Piles should not be constructed with
excessively wet compost (above about 55% moisture. The
compost should be dried by the procedures outlined
above (see "Sequence of Operations - Drying") before
piling for storage.
9. Aggregates or clumps of sludge -- When aggregates of
sludge,even though small,are allowed to remain on the
compost pad after mixing and processing, they soon emit
unpleasant odors. All sludge aggregates should be
carefully removed from the mixing areas as soon as
possible.
10. Ponding of rainwater -- When rainwater is allowed to
pond on "the site,anaerobic decomposition can result
and cause unpleasant odors. Therefore, the site must
be graded and compost piles located so that no ponding
will occur.
HEALTH ASPECTS OF SLUDGE COMPOSTING
Workers at sludge composting facilities encounter disease
risks: (a) from the pathogens normally present in sewage sludges,
and (b) from fungi and actinomycetes that grow during composting.
The former are often referred to as primary pathogens because
they can initiate an infection in an apparently healthy individ-
ual. The latter are referred to as secondary pathogens because
they usually infect only people weakened by a primary infection
or by some other trauma such as lung surgery. Densities of
secondary pathogens generally are increased by composting. The
growth of secondary pathogens is not peculiar to composting
sewage sludge but occurs also in many farm and garden operations,
such as during the composting of leaves or other materials.
Examples of primary and secondary pathogens, along with the
diseases they cause, are presented in Table 6.
Studies to define the risk of infection by primary pathogens
to people working with sewage wastes are not as extensive as
40
-------
Table 6. Examples of pathogens found in or generated during
composting of sewage sludge, together with human diseases
associated with these pathogens.
PRIMARY PATHOGENS
GROUP
Bacteria
Protozoa
Helminths
Viruses
EXAMPLE
Salmonella enteritidis
En't amoeba histolytica
Ascaris lumbricoides
Hepatitis virus
SECONDARY PATHOGENS
Fungi AspergilTus fumigatus
Actinomycetes
Micromonospora spp
DISEASE
Salmonellosis
(food poisoning)
Amoebic dysentery
(Bloody diarrhea)
Ascariasis
(worms infecting
the intestines)
Infectious hepatitis
(jaundice)
Aspergillosis
(growth in lungs
and other organs)
Farmer's lung
(Allergic response
in lung tissue)
might be desired, but available data indicate that the risk is
probably low. The predominant route of infection from the waste
material is through the mouth. Prevention of infection involves
such precautions as thorough washing of the hands before eating
to prevent ingestion of the pathogens. The exposure of workers
to primary pathogens in a composting operation is limited to the
pile building operation because the temperatures reached in the
next processing step (composting) reduce primary pathogen densi-
ties to insignificant levels. The mixing operation presents
little hazard, because the high moisture levels prevent dust
formation.
Medical difficulty from secondary pathogens may result from
inhalation of air containing a high density of spores. The pro-
bability that individuals in good health will be infected by
secondary pathogens encountered in composting is very^small. How-
ever, people who are predisposed because of such conditions as
diabetes, asthma, emphysema, or tuberculosis, or who may be
41
-------
taking such medication as corticosteroids, broad-spectrum anti-
biotics, or immunosuppressive drugs may be more susceptible to
infection.
The help of local medical authorities should be obtained in
compiling a medical history questionnaire for work applicants so
that predisposed people are screened out. Individuals who are
"atopic," i.e., prone to severe allergies, should also be exclud-
ed from employment at composting facilities. Moreover, a com-
plete physical examination is recommended, plus inoculations for
typhoid, tetanus, and polio.
The following recommendations and provisions are advisable
to ensure the health and safety of employees:
1. Rules pertaining to personal cleanliness should be post-
ed in appropriate areas. For example, the following
items should be emphasized:
a. Wash hands before eating, drinking, and smoking.
b. Wash hands before returning home after work.
c. Never store food in close proximity to sludge or
compost samples taken for analysis.
d. If accidentally contaminated with sewage sludge or
effluent, immediately take a hot shower, and put on
clean clothing.
2. Showers and lockers should be provided at the composting
facility.
3. The municipality should provide protective clothing,
e.g., coveralls and safety shoes for all workers.
4. Workers should change from protective clothing to street
clothes at the end of each day. Protective clothing
should not be worn home.
5. As necessary, protective clothing should be cleaned and/
or sterilized.
6. During periods of dry weather, the area should be sprin-
kled periodically to ensure that workers do not inhale
the dust. During such weather, workers should be en-
couraged to wear face masks or respirators.
42
-------
SECTION 4
UTILIZATION OF COMPOST
POTENTIAL MARKETS
The success of a composting operation will depend greatly on
the market developed for the product. It is important to
appraise the value of the compost for its potential uses; both
beneficial and detrimental characteristics should be considered.
A realistic evaluation of the potential market relative to the
amount of compost produced is especially important. Some munici-
palities may find it advantageous to distribute compost to con-
sumers at no cost, since this may be a least-cost option to the
municipality.
Livestock manures and their composts, peat, topsoil, and
chemical fertilizers already hold significant portions of the
potential market. There are, however, possibilities for increas-
ing the market by developing new uses.
The potential market can be classified into three broad
categories: (1) a very high-profit, but usually small, market
for intensive plant culture practices (luxury garden market); (2)
a market for restoration of disturbed lands by mixing compost
into the unproductive soil of strip mines, gravel pits, road con-
struction sites and areas of urban or suburban development, and
(3) a market for use as a fertilizer-soil conditioner for farm
crops.
Some promotional effort will be necessary to distribute a
steady volume of compost in any of the above markets. Since the
cost of composting is very competitive with the cost of alterna-
tive disposal practices even with no credit for value of the
compost, it will rarely be essential to show a profit on market-
ing. However, it will be necessary to develop a market suffi-
cient to handle the planned production.
BENEFICIAL EFFECTS AS A FERTILIZER AND SOIL CONDITIONER
Sludge compost applied at a rate to supply the nitrogen re-
quirements of the crop will supply most of the plant nutrients
except potassium, thus it may be necessary to apply supplemental
Eotash. However, it is unlikely that sewage sludge composts_will
e used to supply the total nutrient requirements of agronomic
crops because of the large amounts that would have to be applied.
43
-------
The maximum value is realized when they are employed in combina-
tion with inorganic fertilizers; they partly meet the crop's
nutrient requirements and also serve as a valuable organic soil
conditioner for maintaining soil productivity.
Nearly all of the nitrogen in sewage sludge compost is in
the organic form and must be mineralized to inorganic ammonium
or nitrate before it is available for crops. Research indicates
the compost from the Beltsville Aerated Pile Method mineralizes
only about 1070 of the organic nitrogen (N) during the first crop-
ping period after the compost is applied. Thus, sludge compost
can indeed be considered as a slow-release N fertilizer.
The application of sludge compost alone, at fertilizer rates
(i.e., the N requirement of the crop), to marginal soils can
produce significantly higher yields than commercial fertilizers
applied alone at the same N level. The higher yields are
attributed to an improvement in soil physical properties by the
compost. Sludge compost is known to improve soil physical
properties, as evidenced by enhanced aggregation, increased soil
aeration, lower bulk density, less surface crusting, and in-
creased water infiltration, water content, and water retention.
Sludge compost added to sandy soils will increase the moisture
available to the plant and reduce need for irrigation. In heavy
textured clay soils, the added organic matter will increase per-
meability to water and air, and increase water infiltration into
the profile, thereby minimizing surface runoff. The soils also
will have a greater water storage capacity. Addition of sludge
compost to clay soils has also been shown to reduce compaction
(i.e., lower the bulk density) and increase root development and
depth.
Large quantities of the sludge compost produced at Belts-
ville have been mixed with subsoil and used successfully as a
topsoil substitute. A number of public agencies, including the
National Capital Park Service and the Maryland State Park
Service, have used the compost for land reclamation and develop-
ment research at Beltsville indicates that sewage sludge compost
can be used to great advantage in the commercial production and
establishment of turfgrasses (Figure 19), trees (Figures 20 and
21), and ornamental plants. Plants and turfgrasses produced
with sludge compost were of better quality, had developed more
extensive root systems, were transplanted with lower mortality,
and were marketable earlier than those grown with inorganic
fertilizer alone. It is likely that large amounts of sludge
compost will eventually be used on golf courses and cemeteries,
and for landscaping the grounds of public buildings.
In addition to the above uses, sludge compost has a major
potential for use in the revegetation and reclamation of lands
disturbed by surface mining, by removal of topsoil, and by
44
-------
Figure 19. Effect of sludge compost amendment to an infertile
soil with clay subsoil on growth of Kentucky bluegrass. Control
plot on right received 2 t/1000 sq. ft. of lime, 240 lb/1000 sq.
ft. of phosphate, and straw mulch, treated plot on left received
1.5 cu. yd. compost/1000 sq. ft. in addition. Courtesy Dr. Jack
Murray, ARS-USDA, Beltsville, Maryland.
45
U.S EPA Headquarters Library
Mai' code 3404T
1200 Per; ••;; Avenue NW
Washington, DC 20460
202-566-0556
-------
T POPLAR
Figure 20. Tulip poplar seedlings showing effects of (N)
commercial nursery fertilization; (0) unfertilized control (100
S) 100 T/A screened sludge compost amendment. Courtesty of
Frank Gouin, University of Maryland. (See Hort. Sci.
12 (1): 45-47. 1977, for details).
46
-------
Figure 21. Dogwood seedlings showing effects of (N) commercial
nursery fertilization; (0) unfertilized control; (50 S) 50 T/acre
sludge compost amendment. Courtesy of Dr. Frank Gouin, Univer-
sity of Maryland. (See Hort. Sci. 12 (1): 45-47. 1977 for
details).
47
-------
excavation of gravel deposits. Eastern stripmined lands are
among the most hostile environments for the establishment and
growth of plants because of (a) extremely low pH (often below
3.0), (b) extreme droughtiness from lack of organic matter, (c)
very high surface temperatures, (d) lack of nutrients, and (e)
very poor physical conditions. Research by USDA has shown that
through the proper use of sewage sludge compost and dolomitic
limestone, a wide variety of agronomic and horticultural crops
can be grown on such lands (Figures 22 and 23). With proper
management, such disturbed lands can be reclaimed in a surprising-
ly short time and restored to a high production level.
Recommended compost application rates for various uses to
achieve fertilizer benefits and soil improvement are shown in
Table 7. In the disturbed soils, higher application rates than
listed may be warranted if groundwater contamination is not con-
sidered the major factor. For example, if the watershed has
little other N inputs and the resulting contamination would be
small and/or temporary. Thus, a heavy single application of com-
post could supply the fertilizer requirements for several seasons.
Heavy application rates might also be desirable for disposal
purposes during the market development phase of a project.
The fertilizer benefit to the crop from nitrogen contained
in the compost may be approximated by appropriate calculations.
Several facts must be established to make such calulations:
1. The crop requirement for nitrogen should be estimated.
County Agricultural Extension Agents can usually provide nitrogen
requirements for crops grown in their particular area, taking in-
to account soil fertility and predicted yield levels.
2. The amount of nitrogen available to the crops during the
initial growing season from the applied compost can be estimated
as follows:
% available N = 0.1 x % organic N
The inorganic N in the compost immediately available to the
plant is accounted for in the 10% mineralization rate prediction.
Alternatively, the percent mineralizable nitrogen may be deter-
mined more accurately by an incubation technique, using the
specific soil to which the compost will be added.
3. The amount of nitrogen supplied from the soil (including
previously applied compost, crop residues, manures, and chemical
fertilizers) should be estimated.
Mineralization of organic N from earlier compost applica-
tions will supply a considerable portion of the N requirement
along with that which is available from the current application.
The second year mineralization of sludge compost is about 5% of
48
-------
TABLE 7. VARIOUS USES AND APPLICATION RATES OF SEWAGE SLUDGE
COMPOST TO ACHIEVE FERTILIZER BENEFITS AND SOIL IMPROVEMENT
(ADAPTED FROM HORNICK ET AL 1979)
Use
Compost per , ,
1,000 square feet-7
Remarks
Pounds
Turfgrasses:
Establishment:
Soil incorporated--2,000-6,000
Surface mulch 600-700
Maintenance 400-800
Incorporate with top 4-6 inches
of soil. Use lower rate on
relatively fertile soil and
higher rate on infertile soil.
Broadcast uniformly on surface
before seeding small seeded
species (bluegrass)or after
seeding large seeded species
(fescues).
Broadcast uniformly on surface
On cool-season grasses apply
higher rate in fall or lower
rate in fall and again in early
spring.
Sod production:
Incorporated -
•3,000-6,000
Incorporate with top 4-6 inches
of soil.
Unincorporated 6,000-18,000 Apply uniformly to surface.
Irrigate for germination and
establishment.
Vegetable crops:_'
Establishment
-1,000-3,000
Maintenance 1,000
Rototill into surface 1-2 weeks
weeks before planting or in
previous fall. Do not exceed
recommended crop nitrogen rate.
Rate is for years after initial
garden establishment. Rototill
into surface 1-2 weeks before
planting or in previous fall.
_. ., 21
Field crops :—
Barley, oats, rye
wheat
•1,000-1,300 Incorporate into soil 1-2 weeks
before planting or in previous
fall.
49
-------
TABLE 7 (continued)
Corn
Legumes:!
3Z.
-3,000-3,800 Incorporate into soil 1-2 weeks
before planting. Supplemental
potash may be required depend-
ing on soil test.
Legumes can be grown in rota-
tion with corn, oats, or other
nitrogen-requiring crops.
Forage grasses:
Establishment-
-4,000-7,000
Maintenance 1,000-1,300
Nursery crops and ornamentals
(shrubs and trees):
Establishment 1,900-7,000
Maintenance 200-500
Incorporate with top 4-6 inches
of soil. Use lower rate on
relatively fertile soil and
higher rate on infertile soil.
Supplement during first year's
growth with 1/2 pound per 1,000
square feet (25 pounds per acre)
of soluble nitrogen fertilizer
when needed.
Broadcast uniformly on surface
in fall or early spring 1 year
after incorporated application.
Incorporate with top 6-8 inches
of soil. Do not use where acid-
soil plants (azalea, rhododen-
dron, etc.) are to be grown.
Broadcast uniformly on surface
soil. Can be worked into soil
or used as a mulch.
Potting mixes-
--Equal ratio Thoroughly water and drain mix-
of material^./ es several times before plant-
ing to prevent salt injury to
plants.
Reclamation:
Conservation
planting—
Up to 9,200
Incorporate with top 6 inches
of soil. Use maximum rate only
where excessive growth for
several months following estab-
lishment is desirable. For
each inch beyond 6 inches of
incorporation, add 1,000 pounds
per 1,000 square feet on soils
50
-------
TABLE 7 (continued)
where ground-water nitrogen
will not be increased.
Mulch 300-700 Broadcast screened or unscreen-
ed compost uniformly on surface
after seeding; unscreened is
more effective.
I/ 1,500 pounds per 1,000 square feet is equal to 1/2 inch of
compost per 1,000 square feet or 33 wet tons per acre based
on 40 percent moisture content and 1/2 inch mesh-screened
material.
2_/ When food crops are grown, careful consideration must be given
~~ to the "constraints on uses" described on pages 55 to 59.
3_/ Legumes, such as alfalfa and soybeans, do not need all the
nitrogen fertilizer supplied by the compost. Maximum benefit
of compost as fertilizer can be realized by growing legumes
in rotation.
4/ Effective potting mixes have been prepared using equal volumes
~ of sludge compost + peatmoss + vermiculite, compost + peat +
sand, or compost -I- infertile loamy subsoil. After several
months' growth, supplemental nitrogen fertilizer may be
required.
51
-------
Figure 22 Response of weeping lovegrass to increasing amounts
of sewage sludge compost added to an infertile acid strip-
mine spoil.
52
-------
Figure 23. Scientists examining heavy yield of mixed grasses
and legumes grown on infertile acid strip-mine spoil amended
with 50 tons per acre of sewage sludge compost.
53
-------
TABLE 8. AVAILABLE N IN KG FROM A SINGLE APPLICATION OF SLUDGE
COMPOST AT INDICATED RATES.*
Sludge Application Total N Available N (kg)
dry metric tons/ha Applied (kg) 1st yr 2nd yr Subsequent yrs
20
40
100
200
200
400
1000
2000
20
40
100
200
9
18
45
89
3
7
17
34
* Mineralization rates are 10%, 5%, and 2% for the first, second,
and subsequent years, respectively.
the remaining organic N and it is estimated that 2% of the re-
maining organic N will mineralize per year after the second year.
Table 8 contains the available N levels for a designated appli-
cation of compost containing 1.070 organic N. If a user were to
use compost only as the N source for his crop and the crop re-
quired 100 kg N/ha, he would apply 100 metric tons/ha the first
year, about 60 metric tons/ha the second, third and fourth years,
and 30 metric tons/ha thereafter until a mineralization equili-
brium would be established; at that time, the amount of available
N would equal the total N applied. The number of years of suc-
cessive compost applications required to reach equilibrium has
not yet been established by research. The user might also con-
sider supplementing nitrogen needs with fertilizer, depending on
availability and cost. The user should be aware that, in addi-
tion to N availability, heavy metal and salt accumulation will
also be factors in the determination of a beneficial cumulative
loading rate for sludge compost.
In potting soil mixes, sludge compost can supply organic
matter, the macronutrients nitrogen (N), phosphorus (P), potas-
sium (K), calcium (Ca), magnesium (Mg), and iron (Fe), and the
micronutrients copper (Cu), zinc (Zn), manganese (Mn), molybdenum
(Mo), and boron (B). In such mixes, it can be used in various
combinations with peat-vermiculite, peat-sand, and mixed with
infertile subsoil. To ensure optimum plant growth, some inorgan-
ic N fertilizer and potassium may have to be applied.
Use of high rates (>50% by volume) is wasteful of the
nutrients in the sludge compost, and can cause salt toxicity.
Leaching of the mix during watering, a normal horticultural prac-
tice, removes excessive soluble salts. A very successful potting
mix developed at Beltsville consists of equal parts by volume of
54
-------
compost, peat, and vermiculite. With, this mix, no salt problems
occurred during the growth. of several crops twatered to achieve
leaching). However, some additional nitrogen was needed after 4
weeks of growth.
CONSTRAINTS ON USES
Pathogens Because of its origin, compost made from sewage sludge
may not be readily accepted by the public from the standpoint of
esthetic or health aspects. Esthetic reservations will generally
be dispelled upon direct examination of the compost itself, which
the observer will perceive as being free from offensive odors
and having the appearance of a highly fertile soil. Reassurance
on health safety may depend more on an explanation of the com-
posting process and the high temperature disinfection involved,
reinforced perhaps by approval from local health authorities. If
composting is properly done, as described in this manual, it
destroys or reduces to insignificant levels all primary pathogens
present in sewage sludges. Once destroyed, viruses, helminths,
protozoans, and most bacteria will not repopulate the compost,
since they cannot grow external to their hosts. Salmonella, one
of the most common organisms causing food poisoning, can regrow
to a limited extent in the finished compost, but it does not
compete well with other microorganisms present.
Salmonella bacteria are frequently found in the environment.
They are often present in fecal material of wild and domestic
birds and animals, including pets, and have been isolated from
streams and vegetation of mountainous areas remote from human
population centers. No significant hazard should be associated
with their presence in compost so long as the compost does not
come into contact with food.
HeaVy metals Many sewage sludges contain large amounts of heavy
metals which may reduce the value as a fertilizer for either
direct application to land or for composting. Excessive amounts
of these metals are often found in sludges where industrial
effluent is discharged into the sanitary sewers without pretreat-
ment. Application of high metal sludges on land results in soil
enrichment in heavy metals. Experiments on sludge application
have shown that soil enrichment by zinc, copper, and nickel can
cause direct phytotoxic effects manifested as decreased growth
and yield, especially where soil pH is low (pH 5.5) and rates of
application are high. Heavy metals may also accumulate in plant
tissues and enter the food chain through direct ingestion by
humans or indirectly through animals.
The element of greatest concern to human health where sewage
sludges and sludge composts are applied to land is cadmium (Cd),
since it is readily absorbed by most crops and is not generally
55
-------
phytotoxic at the concentrations normally encountered. There-
fore, Cd can accumulate in plants and enter the food chain more
readily than, for example, lead (Pb) or mercury (Hg), which are
not readily absorbed and translocated to the edible portion of
crops. However, since Hg is accumulated by mushrooms, sludge
compost should not be used for mushroom culture. Most human ex-
posure to Cd comes from food (principally grain products, vege-
tables, and fruits) and results in an accumulation of the element
in the liver and kidneys. Approximately 3 to 5 percent of die-
tary Cd is retained by humans. If dietary Cd is substantially
increased over long periods of time, Cd can accumulate to levels
that might be expected to cause kidney injury. Among the sources
that contribute to the level of Cd in food are (a) soils and
surface waters contaminated by disposal of wastes, (b) soils in-
herently high in Cd because of geochemical factors, (c) indus-
trial fallout, and (d) phosphatic fertilizers containing Cd, and
(e) industrial contamination of soil and/or food.
The World Health Organization (WHO) has recommended that the
maximum level of dietary Cd should not exceed 70 yg/person/day.
Workers in the U.S. Food and Drug Administration (FDA) advance
the view that any further increase in dietary intake of Cd seems
undesirable. However, the extent of the hazard is debated be-
cause current data are incomplete about human exposure to Cd and
risk through their lifetime. Thus, in order to limit this risk,
the utilization of organic wastes on land is restricted by regu-
latory agencies to control the level of Cd in food chain crops.
Plant species, as well as varieties, have been found to dif-
fer markedly in their ability to absorb and translocate heavy
metals, to accumulate them within edible organs of the plant,
and to resist their phytotoxic effects. Leafy vegetables are
usually sensitive to the toxic effects of metals and accumulate
them; cereal grains, corn, and soybeans are less sensitive; and
grasses are relatively tolerant. Uptake studies with corn, soy-
ean, and cereal grains have shown that heavy metals accumulate
less in the edible grain than in the leaves; similar results are
found for edible roots, as radish, turnip, carrot, and potato,
and fruits, as tomato, squash, etc.
The availability to and uptake of heavy metals by plants
are influenced by certain chemical and physical properties of
soil, especially pH, organic matter content, cation exchange
capacity (CEC), and texture (i.e., the proportions of sand, silt,
and clay). Phytotoxicity and plant availability of sludge-borne
metals are higher in acid soils than in those with neutral or
alkaline pH. Maintaining soil pH in the range of 6.5 or above by
liming reduces the availability of heavy metals to plants. Appli-
cation of organic amendments such as manures and crop residues
can also decrease the availability of heavy metals to plants.
The CEC is a measure of the soil's capacity to retain cations;
higher CEC is usually associated with higher clay and organic
56
-------
matter contents. Heavy metals are generally less available to
plants in soils of high CEC (e.g., organic matter rich soils or
clay loams) compared with soils of low CE(T(e.g., loamy sands).
Recent research at Beltsville suggests that, on a total metal
basis, heavy metals are less available to plants in composted
sewage sludges than in uncomposted raw and digested sludges, al-
though the reason for this is not yet known.
The metal contents of digested sewage sludge in terms of the
range of observed levels, the maximum levels recommended for
landspreading and the median levels found in several surveys are
presented in Table 9. The levels of heavy metals for raw or un-
digested sewage sludges would be approximately one-half of those
shown in the table, since anaerobic digestion reduces the vola-
tile solids and thus tends to increase the metal content. In the
view of the present writers, the Cd/Zn ratio of sludges used on
cropland should not exceed 0.015; that is, the Cd content of
sewage sludge should not exceed 1.5 percent of the zinc content.
The reasons for this are as follows: a) if Zn levels in the soil
are much higher than Cd, plant Zn will accumulate to phytotoxic
levels before sufficient Cd can be absorbed to endanger the food
chain, b) Zn reduces absorption of Cd in animal intestines, and
c) Zn inhibits uptake of Cd by dicotyledonous plants at low Cd/Zn
ratios. Limited experimental evidence has shown a low Cd/Zn
ratio reduces potential impact of soil Cd wheii soil pH drops be-
low the recommended limits, while cumulative Cd application
limits control Cd effects at pH 6.5 or above. At present, regu-
lation of Cd/Zn ratio is not universally accepted, but no other
method has been proposed which limits impact of Cd in acid soils.
Median sludge Cd was 13 or 16 ppm, and Cd/Zn >_ 1%. Metal
contents indicated in Table 9 as "Typical Domestic Level" are
achieved by many large cities in the United States, e.g. Washing-
ton, D.C., Baltimore, MD, Denver, CO, and Philadelphia, PA.
Sludge metal contents in cities with higher levels could be re-
duced by industrial pretreatment. It has not yet been shown
that pretreatment will produce acceptable sludge metal levels at
all locations, although most evidence supports pretreatment.
To limit the buildup of heavy metals on agricultural land
resulting from the landspreading of either sewage sludges or
sludge composts, USDA proposed certain recommendations in 1976.
Two categories of land were delineated: (1) privately owned
land and (2) publicly owned or leased land dedicated to sludge
application. (Copies of the draft document are available from
the Office of Environmental Quality Activities, USDA, Washington,
D.C.). Such recommendations hopefully will encourage the use of
sludges of low heavy metal content for composting and direct land
application on privately owned land. The recommendations were
based on the best information available at the time from scien-
tists at a number of state universities and agricultural experi-
ment stations, as well as from USDA sources.
57
-------
TABLE 9. METAL CONTENT OF SEWAGE SLUDGE BASED ON SEVERAL SURVEYS.
t_n
00
Element
Cd,
Zn,
ppm
ppm
Cd/Zn, %
Cu,
Ni,
Pb,
ppm
ppm
ppm
Maximumi'
Domestic
25
2500
1.0
1000
200
1000
NC-118-/
Median
16
1740
1.0
850
82
500
Mean
110
2790
4.8
1210
320
1360
Range
3- 3410
101-27800
0.1-100
84-10400
2- 3520
13-19700
3/
Northeast"
Median
13
1430
0.84
790
42
500
Mean
72
2010
3.64
1080
129
735
0
228
0
240
10
52
Range
.6 - 970
-6430
.26- 78
-3490
-1260
-4900
I/ Digested sludge, Chaney and Giordano, 1977.
2_/ 169-208 sludges, Sommers, L. E. 1977. Chemical composition of sewage
sludges and analysis of their potential use as fertilizers. J. Environ.
Qual. 6 (2):225-232.
3_/ 43 treatment plants, (digested sludge), Chaney, R. L., S. B. Hornick, and
P. W. Simon. 1977. Heavy metal relationships during land utilization of
sewage sludge in the Northeast, p. 283-314. In R. C. Loehr. (Ed.). Land
as a waste management alternative. Ann Arbor Science Publishers, Inc.,
Ann Arbor, Mi.
-------
Table 10 shows the recommended maximum cumulative sludge
metal loadings for privately owned agricultural land according
to the soil cation exchange capacity (USDA recommendations) .
Soils in the 0 to 5 CEC range are characteristically sands
through sandy loams; the 5 to 15 range includes sandy loams,
loams, silt loams; and > 15 includes silty clay loams and clays.
Higher metal loadings would be considered reasonably allowable on
heavier textured soils. Cadmium loadings on land should not
exceed 2 kg/ha/year for dewatered1sludge or sludge compost and
should not exceed the total cumulative loadings shown in Table
10. When sludges are applied, the soil should be limed to pH 6.5
and maintained at 6.2 or higher. Sludges and sludge composts
should not be applied to land used to grow tobacco as this crop
allows high transfer of Cd to humans; sludges and composts used
on land used to grow leafy vegetables should be low in Cd and
Cd/Zn ratio to minimize any effects on humans.
On publicly controlled land, a maximum of up to 5 times the
amount of sludge-borne metals listed in Table 10 seems to re-
present a reasonable limit if the sludge is incorporated into
the soil to a depth of 15 cm. With deeper incorporation, total
metal applications may be proportionally higher. These metal
loadings are permissible only when the pH is maintained at pH
> 6.5; cropping with Cd-excluding grains (e.g. corn) minimizes
the impact of this practice.
TABLE 10. RECOMMENDED MAXIMUM CUMULATIVE METAL LOADINGS FROM
SLUDGE OR SLUDGE COMPOST APPLICATIONS TO PRIVATELY OWNED LAND.
Metal Soil cation exchange capacity (meq/100g)~
0-5 5-15 >15
(Maximum metal addition, kg/ha)
Zn
Cu
Ni
Cd
Pb
250
125
50
5
500
500
250
100
10
1000
1000
500
200
20
2000
I/ CEC determined prior to sludge application using 1 N neutral
ammonium acetate and is expressed here as a weighted average
for a depth of 50 cm.
59
-------
REFERENCES
1. Anonymous. 1956-61. International Research Group on Refuse
Disposal (IRGRD) Information Bull. Nos. 1-12. United States
Public Health Service. 308 p.
2. Anonymous. 1976. Application of sewage sludge to cropland:
Appraisal of potential hazards of the heavy metals to plants
and animals. Council for Agricultural Science and Technol-
ogy Report No. 64.
3. Breidenbach, A. ¥. 1971. Composting of municipal solid
wastes in the United States. USEPA Publ. SW-47r. 103 p.
4. Chaney, R. L. and P. M. Giordano. 1977. Microelements as
related to plant deficiencies and toxicities. p. 235-279.
In Soils for Management and Utilization of Organic Wastes
and Wastewaters. Soil Sci. Soc. Amer. Madison, Wisconsin.
5. Farrell, J. B. and G. Stern. 1975. Methods for reducing
the infection hazard of wastewater sludge, pp/ 19-28. In
Radiation for a Clean Environment. International Atomic
Energy Agency, Vienna, Austria.
6. Ettlich, W. F. and A. K. Lewis. 1976. Is there a 'sludge
market1? Water and Waste Engineering. 13:40-45.
7. Goldstein, J. (Ed.). Compost Science, Journal of Waste
Recycling. Rodale Press, Inc. Emmaus, Pa.
8. Golueke, C. G. 1972. Composting: a study of the process
and its principles. Rodale Press, Inc. Emmaus, Pa. 110 p.
9. Gotaas, H. B. 1956. Composting: Sanitary disposal and re-
clamation of organic wastes. WHO Monograph No. 31. Geneva,
Switzerland. 205 p.
10. Hornick, S. B., J. J. Murray, R. L. Chaney, L. J. Sikora, J.
F. Parr, W. D. Burge, G. B. Willson, and C. F. Tester.
1979. Use of Sewage Sludge Compost for Soil Improvement
and Plant Growth. USDA, SEA ARM-NE-6. 10 p.
11. Jerris, J. S., R. Regan, and R. Gasser. 1968. Cellulose
degradation in composting. Civil Engineering Dept.,
Manhattan College, Bronx, N.Y. 134 p.
60
-------
12. Poincelot, R. P. 1975. The biochemistry and methodology of
composting. Conn. Agr. Exp. Sta. Bull. 754. 38 p.
13. Satriana, M. J. 1974. Large scale composting. Noyes Data
Corp., Park Ridge, N. J. and London, Eng. 269 p.
14. Stone, G. E. and C. C. Wiles. 1972. Interim report with
operational data. Joint USPHS-TVA Composting project,
Johnson City, Tenn. 212 p.
61
-------
APPENDIX
ANALYTICAL METHODS
A compendium of analytical methods for sewage sludges and
sludge composts has not yet been published. Nevertheless, a
number of references are available which will be helpful in the
chemical and microbiological analyses of these materials. These
are listed as follows:
a. A Manual of Methods for Chemical Analysis of Water and
Wastes. 1974. (EPA-625-16-74-003).
b. Standard Methods for the Examination of Water and Waste-
water- -Including Bottom Sediments and Sludges. 1975.
14th edition, published jointly by the American Public
Health Association, the American Water Works Association,
and the Water Pollution Control Federation. Available
from the American Public Health Association, 1790 Broad-
way, New York, N.Y.
c. Sampling and Analysis of Soils, Plants, Wastewaters, and
Sludge: Suggested Standardization and Methodology. 1976.
North Central Regional Publ. No. 230. Available from
Kansas State University Agricultural Experiment Station,
Manhattan, Kansas. 20 p.
d. Methods of Soil Analysis. 1965. Part I: Physical and
Mineralogical Properties, including Statistics of Meas-
urements and Sampling. Agronomy J. No. 9, American
Society of Agronomy, Inc., Madison, Wisconsin. 768 p.
e. Methods of Soil Analysis. 1965. Part II: Chemical and
Microbiological Properties. Agronomy J. No. 9, American
Society of Agronomy, Inc., Madison, Wisconsin, p. 768r
1569.
f. Recommended Procedure for the Isolation of Salmonella
Organisms from Animal Feeds and Feed Ingredients. Agri-
cultural Research Service, U.S. Department of Agricul-
ture. ARS 91-68-1, July 1971. 15 p.
Methods generally accepted for analyzing components needed
in calculating compost application rates are: total N by Kjeldahl;
62
-------
NH4-N by analysis of NH4 in the filtrate of an extract of 1 g of
sludge or compost with 50 ml of 2N KC1 for 60 minutes; total P,
K, Ca, Mg, Zn, Cu, Ni, Cd, Pb, and Fe in a dry-ashed or wet-ashed
sample using colorimetric or atomic absorption analysis (atomic
absorption is the preferred method, especially for important
elements like Cd, but background correction is required for anal-
ysis of Cd, Ni, and Pb by this method). If Hg, Se, or As anal-
yses are needed, only wet ashing is acceptable; for Hg analyses,
a wet^sample should be used, as heat drying (105°C oven) causes
volatilization of Hg. CaCO^ is measured by consumption of acid
using a pH meter titration method; soluble salts are measured as
conductivity of the saturated extract.
f
A plant germination and early growth test in which a mix of
compost soil is used at a typical loading rate (<_ 50 T/ha) and
compared to a control will demonstrate whether improper compost-
ing, or the salts, introduced with the compost could interfere
with planned uses. Customarily, seeds of several species (corn,
bean, cucumber) are sown; percent germination and growth patterns
are observed.
MONITORING EQUIPMENT
Note: All equipment with exception of pH meter should be
portable and rugged.
Temperature reading devices; Must have temperature range of
at least 0°C to 100°C. Probe should be 1.5 meters long for in-
sertion into compost pile. Some typical equipment is listed
below:
1. Thermistemp Tele-thermometers—Yellow Springs Instru-
ments, Model 42. (Available through Fisher Scientific
or Curtis-Matheson Scientific). General purpose, with
three overlapping scales to continuously monitor temper-
ature in range from -40°C to 150°C. Probe to be used
with this instrument listed below.
2. Thermistor probe. Atkins Technical Inc., Model PK-35.
To be used with above Tele-thermometers. General
purpose and moderately heavy duty.
3. Compact, portable, temperature-calibrated potentiometer.
James G. Riddle Co., Cat. Nos. 606115 and 604116, Leeds
and Northrup. Suited for making accurate temperature
measurements from thermocouples, checking and measuring
thermocouples, as well as checking other thermocouple
pyrometers, recorders, and controllers.
4. Insulated thermocouple wire--Fisher Scientific, Leeds
and Northrup Co. 16-gauge wire capable of handling
63
-------
temperatures up to 195°F (90°C) used.
Oxygen reading devices
1. Portable oxygen analyzer--Teledyne Analytical Instru-
ments Model 320 B/RC, Taylor Servomex Type OA 250.
Used in field or laboratory situation for instant Q£
determination in air medium. A probe for collecting
gas samples for analysis may be made from 0.6-cm steel
tubing. The tube is capped or pinched off and small
holes are drilled near the tip.
Moisture content determination devices
1. Moisture determination balance--Ohaus Model Nos. 6109,
Mettler Model LP 11. Combination balance and heat lamp
for taking original weight, drying out sample, and
taking final weight. The instrument is calibrated to
read in percent moisture content.
Air velocity determination devices
1. Thermo-anemometer and probe -- Alnor Instrument Co.,
Type D 500 K. For use in determining air flow velocity
in pipe. Range from 10 to 2000 feet per minute. Port-
able, for field use.
Pressure determination device
1. Magnehelic pressure gauges--Dwyer Instruments Inc.
Portable, for measuring pressure in pipe flow in field
or laboratory. Can be obtained to cover various ranges
and pressures.
pH determination devices
Compost is prepared for analysis by making a slurry with
distilled water (1:1) and allowing slurry to stand for 30 minutes
before the determination. Many suitable pH meters are available,
two are listed below:
1. Laboratory expanded scale research pH meter--Fisher
"Accumet" Model 320, Corning Model 110 (Digital)
Scientific. For use in laboratory situation. Models
vary in type of readout and precision.
2. pH meter, pocket size, analytical--VWR Scientific. For
on the spot readings in the field. Completely self-
contained in waterproof carrying case.
64
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
REPORT NO.
EPA-600/8-80-022
2.
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
MANUAL FOR COMPOSTING SEWAGE SLUDGE BY THE BELTSVILLE
AERATED-PILE METHOD
5. REPORT DATE
May 1980 (Issuing Date)
6. PERFORMING ORGANIZATION CODE
AUTHOR(S) e. B. Willson, J. F. Parr, E. Epstein,
P. B. Marsh, R. L. Chaney, D. Colacicco, W. D. Burge,
L. J. Sikora, C. F. Tester, S. Hornick
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
U. S. Department of Agriculture
Beltsville, Maryland 20705
10. PROGRAM ELEMENT NO.
C36B1C
11. CONTRACT/GRANT NO.
S803468
12. SPONSORING AGENCY NAME AND ADDRESS
Municipal Environmental Research Laboratory-Cin., OH
Office of Research and Development
U. S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
EPA/600/14
15. SUPPLEMENTARY NOTES
Project Officer: James A. Ryan (513) 684-7653
16. ABSTRACT
In producing clean water from sewage, wastewater treatment plants also produce
sludge. Most of the commonly used methods to dispose of this material are now con-
sidered to be either environmentally unacceptable, wasteful of energy, or very expen-
sive. To ease this situation, a relatively simple, rapid, and inexpensive sludge
composting process has been developed at Beltsville. The method makes possible the
conversion of undigested sludge into a composted product that is aesthetically
acceptable and meets environmental standards. The material has demonstrated useful-
ness as a soil amendment stimulative to plant growth. If relatively simple control
procedures are followed, the compost appears to be free of primary human pathogens
because of the lethal effect of heat generated during the composting process on such
organisms.
The new Beltsville composting procedure, detailed here in respect to both prin-
ples and practice, represents a major advance over previously known composting methods
It is adaptable to practical use in municipalities of widely varying size. In many
situations its short startup time will allow its use as an emergency interim solution
for sludge management. Key information is presented on the economics of the process,
and on the marketing and use of the product as a soil conditioner to improve plant
growth.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
COSATI Field/Group
Aerobic processes
Sewage disposal
Composts
Beltsville static-pile
composting
Agronomic utilization of
sewage compost
13B
6D
2A
8. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)'
ASSTFTED
21. NO. OF PAGES
81
20. SECURITY CLASS (Thispage)
22. PRICE
ASSTFTFtl
EPA Form 2220-1 (9-73)
65
4 U.S. GOVERNMENT PRINTING OFFICE: 1980-657-146/5649
------- |