A project of Volunteers in Asia ay: Letitia A. Obeng and Frederick W. .Wright
WB TP#7/UNDP PMR##7
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UNDP Project Management Report
INTEGRATBD RESCURCE RECDVBR’I SERIES
This is the seventh in a series of reports being prep&red by the
Resource Recovery Project as part of a global effort to realize the goal of the United Nations International Drinking
Sanitation Decade, which is to eF;end domestic and community water supply and sanitation services throughout the developing world during 1981 to 1990. The project objective is to encourage resource recovery a3 a means of off setting some of the costs of community sanitation.
Other volumes published to date include:
Annotated et al. from !4unicipal
A State-of-th? Art Review and
Paper No. 30) by S. Cointreau
R. T. Lund. for
The Experience of the United States and
Developing Countries (Technical Paper
A Component of Low Cost Sanitation
TTechnical Paper No. 36) by P. Edwards.
Status Report on Selected
Materials and Energy Recovery Projects (Technical
No. 37) by
J. C. Abert.
TTechnical Paper No.
Principles and Practices for Biogas Systems
49) by C. G. Gunnerson and 0, C. Stuckey et al.
Wastewater Irrigation in Developing Countries: Health Effects and
Technical Solutions (Technical Paper No, 51) by ii. Shuval et al.
Photographs (from top to bottom, left to right): Workers show how compost can be used to improve the quality of soil for agricultural purposes. A range of different waste materials can be efficiently composted if the right mix of carbon and nitrogen is provided in the materials. Here garbage is placed on a conveyer belt for sorting out noncompostible matter , and sludge from a septic tank is mixed with paper wastes and wood chips for co-compostfng.
Aeration of composting materials can be carried out in a variety of ways.
These include by hand-turning, provided proper protective clothing is worn; by using wlndrow machines or tractors to turn windrows of composting materials, here made up of garbage and sludge; and by forced aeration in which air is blown or drawn through a static pile by a small horsepower motor.
The large amount of heat generated destroys disease-causing organisms.
WORLD BANK TECHNICAL PAPER NUMBER !57
The World Bank
The I&mational Bank for Reconstruction
Washiqton D.C. 20433, USA.
Ail rights reserved
Man&ctured in the United States of America
First printing March 1987
Technical Papers are not formal publications of the World Bank, and are circulated to encmrage discussion and comment and to communicate the results of the Rank’s work quickly to the development community; citation and the use of these papers should take account of their provisional character. The findings, interpretations, and conclusions expressed in this paper are entirely those of the author(s) and should not be attributed in any manner to the World Rank, to ik affiiiated organizations, or to members of ik Board of Executive Directors or the countries they represent. Any maps that accompany the text have been prepared solely for the convenience of readers; the designations and presentation of material in them do not imply the expression of any opinion whatsoever on the part of the World Rank, its affiliates, or its Board or member countries concerning the legal status of any country, territory, city, or area or of the authorities thereof or concerning the delimitation of its boundaries or ik national affiliation.
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The most recent World Bank publications are described in the catalog Nnu
IWicutim, a new edition of which is issued in the spring and fall of each year. The complete bacldist of publications is shown in the annual In&x of Rcblicdms, which contains an alphakztical title list and indexes of subjeck, authors, and countries and regions; it is of value principally to libraries and institutional purchasers. The continuing shrdia, which is issued annually. The latest edition of each of these is available free of charge from the Publications Sales Unit, Department F, The World Rank, 1818 H Street,
N.W., Washington, D.C. 20433, U.S.A., or from Publications, The World Bark 66, avenue d%na, 75 116 Paris, France.
Letitia A. Obeng is an economist and Frederick W. Wright a project officer in the
Applied Technology Unit of the Water and Urban Development Department at the
Library of congnsS Chtaloging-in-Publiation
Letitia A., 1954-
Co-compoeting of domestic solid and human wastes.
Bank technical paper, ISSN 0253-7494 ; no. 57)
Bibliography : p.
2. Recycling (Waste, etc.)--Developing countries. I. Wright, Frederick W.,
II. Title. III. Series.
! TD796.5.024 1987
87-6091 t .-.
This report is part of a joint global research, development, and demonstration effort of the United Nations Development Progransne and the world
It reviews current literature and practices on the co-cornposting of human waste (fresh nightsoil or sewage sludge) together with the organic fraction of domestic solid waste (as well as with other wastes].
The report describes the composting process, reviews various co- composting systems, and discusses health aspects such as pathogen destruc- tion. The uses of compost as a soil conditioner, mulch, fertilizer or for land reclamation are also described.
The report also develops several cost/benefit models for economic analysis of co-composting operations and outlines the economics of the process as a whole. The focus of the analytical methodology is on developing coun- tries.
The computer models are written for use on widely available micro- computers and are designed so that they can be adapted to site-specific economic conditions. A copy of the computer models is available on request. discussed.
Key issues for consideration
Decision makers reference on co-composting and planners in when addressing planning will find waste for this composting report management a valuable and are also resource recovery issues in the developing countries.
- vii -
This is the seventh of a series of generic reports produced by the joint UNDP/World Bank Global Research and Development Project on Integrated
Resource Recovery CGL0/84/007, GLO/80/004). The primary project goal is to achieve economic and social benefits through sustainable resource recovery activities in the developing countries by recycling liquid wastes from municipal and comrcial sources and reusing within the solid context and of appropriate waste management.
Increasing recognition ciency in allocating and utilizing of the need for technical and economic effi- resources and the role that appropriate resource recovery can play in the water and sanitation sector have led this project
International to be included in the formal activities
Drinking Water Supply and Sanitation of
Decade. the United Nations
Urban areas are finding it increasingly of human wastes and domestic solid wastes. difficult to safely dispose
It is also becoming increasingly important worldwide to improve the nutrient and physical qualities of agricul- tural soils. This is especially true in the food production areas surrounding growing urban centers in developing countries.
This report presents a review and analysis framework of co-composting, which is a process that can convert more than one waste, such as human and domestic solid wastes, into a useful resource l
The report describes composting and examines ways of co-composting of human waste (fresh nightsoil or sewage sludge) together with the organic fraction of domestic solid waste. It discusses the procedures entailed, the health aspects, and the uses of compost based on a literature review.
Furthermore, an economic analysis methodology is developed using computer models that perform cost-benefit calculations of co-composting operations.
These models are suitable for analysis of specific co-composting investmen when modified to reflect local conditions.
Copies of the
Et template are available on request.
The authors would like to thank J. Pickford, G. Willson, C. Golueke,
L. Diaz, 0. Mara, !4. Thalmann, and S. Cointreau and World Bank staff members
M. Cohen, G. Tschannerl, D. de Ferranti, C. Bartone, S. Arlosoroff, H. Garn,
We Walters, A. Elwan, and R. Overby, who have reviewed this report and whose assistance has been invaluable to its production. They would also like to thank all others who have assisted in the preparation of this report.
Your comments on this report would be welcome, and we would be grateful to receive any case study information the resource recovery series could benefit. from which future editions of
Please send your comments to
WUDAT, The Uorld Bank, 1818 R Street, N.WI, Washington, D.C. 20433, USA.
Chief, Applied Research and Technology Unit
UNDP Projects Manager
Water and Urban Development Department
A/ Registered Trademark of LOTUS Corporation.
- ix - tist of Tables and Figures
. . . . . . ..*..................*.....*.......
. . . ..e....*..........................*......
Aim ......................................................... biight Soil ..................................................
Solid Waste .................................................
Co-Composting of Garbage with liuman Waste ...................
Qmpter 2 The Comporting Procerr l . . . . . . . . . . . . . . ..*................
Rate-Related Factors ........................................
Xoirrture Content .........................................
Particle Site ............................................
WEi- SUPPlY ............................................
................................................ pH Control
Other Factors ...............................................
Quptcr 3 Comportirmg Sy8tcrl
. . . . . . ..*.............................
Reactor Systmm ............................................. lIonreactor Systems ..........................................
Choice of System ............................................
Sewage Sludge and Night Soil
Co-Composted with Refuse
Siting and Mixing .........................................
Qhepter 4 Cmttol of Bxcreted and
Veterinary Pathogens ........................................
Secondary Pathogen8 .........................................
Plant Pathogens .............................................
5 u8e8 Of -8t
. . . . . . . . . . . . . . . ..*.....*........e...*....
Quality of Cumpost ..........................................
Application of Compost to Land ..............................
Other Uses of Compost .......................................
Chapter 6 lkthodology for Rvaltmting the lltconmic Fearibility of Co-cmpo8tily .a.......*.......................,...
Composition of Waste and Value of Resources Recovered .......
Scale and Technology of Co-Composting Plant .................
Capital and Operating Gouts .................................
Land Value and Lendfill Requirements Corta ..................
Other Factors Affecting Financial Caste and Revenues ........
From Financial co8t6/hm.LueS
56 to Economic Coats/Benefits
Result8 from Hypothetical Model Calculationa
7 mry ..*.........,..............,.................*...
Market ...................................................... compost Plant ...............................................
Pilot Scale Composting ......................................
Benefits and Justification
Other Methods of Co-comporting with Sewage Sludge . . . . . . . . 75 and Night Soil
Sewage Sludge and Night Soil Composted with Bark . . . . . . . . . . . . 75
Sewage Sludge and Night Soil Comported with Straw . . . . . ...*..
Sewage Sludge and Night Soil Composted with Wood Chipa . . . . . . 75
Sewage Sludge and Night Soil Comported with Other
Sewage Sludge and Night Soil Comported without the Addition of Bulking Agents . . . . . . . . . . . . . . . . . . . . . ..a.................
Annex B: Pathogen Survival
. . . . . . . . . . . . . . . . ..*................*....
References . . . . . . . . . . . . . . . . . ..C....................~................
- xi -
Refuse Content from Various Nunicipalities ..............
Hicrofloral Population during Aerobic Composting ........
Maximum, Optimum, and Ninimum Temperature Ranges for Nesophils and Thermophila
Feedback Loops in the Composting Ecosystem
Approximate Nitrogen Content and C/N Ratios for Some Compostable Materials
Methods of Odor Control
Using Compost Filters
Sunxnary of Different Nonreactor Composting Systems ......
Comparison of Reactor and Nonreactor Systems ............
Composting of Sewage Sludge with Refuse .................
Comparative Costs for Various Sludge Disposal Processes., 23
Factors To Consider in Planning a
Survival Times of Rxcreted Pathogens in Feces,
Night Soil, and Sludge at 20030°C .....................
Survival Times of Excreted Pathogens On Crops
25 at 20030°C ............................................
Bacterial Pathogens Excreted in Feces ...................
Viral Pathogens Excreted in
Protozoa1 Pathogens Excreted in Feces ................... fX
Relminthic Pathogens Excreted in Feces ...................
Animal Pathogens Capable of Causing Infections in Naz ...
Concentrations of Thermophilic Actinomycetes
Different Naterials ...................................
Plant Pathogens in
Differences between Rature and Raw Compost ..............
Netal Concentrations in Compost and Human Waste .........
Physical Effects of the Addition of Compost to Clay or Sandy Soils ........................................
Criteria for the Specific Applications of Compost .......
Compost Application Rates:
Uses and Application Rates of Sewage
Sludge Compost to Achieve Fertilizer
Benefits and Improve Soil .............................
Application Rates for Sewage Sludge Compost in the
Year of Use Based on N or P Fertilizer Recommendations 44
Domestic Solid Waste Composition ........................
Resource Recovery Coefficients ..........................
Recovered Material Values ...............................
Revenue/Ton of Domestic Solid Waste
Material Balance Per
1 Ton Domestic Solid Waste .........
Description of Base Case
Estimated Capital Costs (Base Case) •o~~.~~gg~~~-~~~~C~~~ 54
- xii -
Estimated Staffing Requirements (base case) .............
Miscellaneous Base Case Operating Requirements
Financial Input Prices (base case) ......................
Operating Cost Bstimata (base case) .....................
Compost Markets and Prices (base case) ..................
Economic Input Prices (bare case) .......................
Baergy Used to Process Virgin and Recycled Materials .... 63
Recycled Material Valuation - Energy Based ..............
1984 Fertilieer Prices ..................................
Base Case Results .. Financial ..........................
Case Results -- Bconomic
-- Results (Economic Values) ... 68
Sensitivity Tests -- Multiple
Change .................... 69
Table A-l. Composting of Sludge and Night Soil with Bark . . . . . . . . . . . 75
Sludge and Night Soil with Straw . . . . . . . . . .
Description of the Beltsville Aerated Static Pile and Windrow Composting . . . . . . . . . ..*.......+............
Table A-4. Rethods of Composting Sewage Sludge with Other
Bulking Agents . . . . . . . . . . . . . . . ..*....................*.
Table A-5. Methods of Composting Sewage Sludge and Night Soil Alone.
Table B-l. Survival of Bacterial Pathogens during Composting .......
Table B-2. Survival of Viral Pathogens during Composting ...........
Protosoal Pathogens during Composting .......
Table B-4. Survival of Lielminthic Pathogens during Composting ......
Figure 1. Typical time/temperature relationships using mode valuea of readings taken at 14 monitoring points within each of 12 static piles . ..*...............*....
Figure 4. Survival of pathogens at different temperature/time regimes ..*...................................,.....*..
A typical time/temperature relationship for composting sewage sludge by the aerated pile method . . .
Figure 3. Elements of aerated pile composting system . . . . . . . . . . . . . . 15
The recycling of human waste has been an accepted practice throughout the which world for many years.
One method of reusing human waste is composting, means converting it into
material that is safe to use, usually on land.
The purpose of this report is to describe methods of co-composting
I r-k-,& with human waste in various places (using selected literature) and some of the health aspects, uses, and the economics of composting.
The report also suggests ways in which planners and operators in developing countries can co-compost these two wastes (garbage and human) to best suit their needs and requirements.
NIGHT SOIL toilet
Human waste may be deposited into buckets, pits, vaults, or flush basins.
When it is deposited into buckets, pits, or vaults, it is referred to as night soil. If the night soil is deposited into buckets
vaults, it has to be removed and tr;ated away from the site of collection. If the night soil is deposited into pits or vaults, they become full. emptying of these pits is often these have to be emptied hazardous because full when pits contain fresh excrete.
If twin or double pits are in use, the night soil in one pit is usually stored for at Least one year (preferably two) before the pit is emptied.
During this time, most of the disease-causing organisms are destroyed.
However, hardy pathogens such as Ascaris eggs may survive.
soil that is removed from the pits (either fresh
be reused in agriculture,
it contains many nutrients.
It can be mixed with
biogas plant or it can be used as a raw material in
During the composting process, most disease-causing organisms that may be present in the night soil will be destroyed. The resulting compost is a humus-Like material properties
it contains many nutrients with good soil-conditioning and minerals essential for pLant growth.
Waste that is flushed away into
is transported to sewage- treatment plants.
The solid waste matter produced by this treatment is known
sludge. This material can be further treated by anaerobic digestion to produce digested sludge.
Many countries in Europe and in North America either use sewage sludge directly uses. on the land or convert it into compost, which is put to many
The use of sewage sludge compost on land is restricted in some indus- trialized areas because it contains relatively high concentrations of heavy metals.
Sewage sludge and night soil are similar in their moisture and nutrient content.
The advantage of night soil over contain heavy metals, but there has been little sludge is that experience in it does not night soil composting.
Nevertheless, provide some information the experience that may be of with sewage sludge composting can use in night soil composting. This review focuses primarily there on co-composting of garbage and human wastes, but
also other ways of co-composting with sludge and night soil (see annex A).
Any of these systems could be a useful guide to plant planners wishing to find a suitable method of composting human waste.
In this report garbage refers to the organic material present in refuse or solid waste.
Refuse also contains metals, glass, plastics, and other such materials.
In most industrialized countries, cloths, solid waste consists the waste primarily of non-compostable can be composted. matter that has to be sorted out before
Very of ten the main costs of refuse composting plants arise from these sorting activities. In many developing countries the sorting is done by sea-:engers before the refuse reaches the treatment plant.
Diat and Colueke (1985) discuss scavenging in relation solid waste management, including the social, political,
In some countries to other aspects and economic of ones. the waste is mainly organic and does not need to be sorted, but in others sorting information is required (see table 1). There is a wealth of on the sorting of refuse, but that subject is beyond the scope of this report.
CO-COMPOSTING OF GARBAGE WITH HUMAN WASTE materials
The term co-composting together. means
Many exampl e 8 of the composting different of materials two or being more raw composted together are available. Some are cited in Annex A. In the case of human waste and garbage advantageous because
(the organic part the two waste of refuse), materials this kind of composting is complement each other well.
The human waste is high in nitrogen content and moisture and the garbage is high in organic (carbon) content and has good bulking quality.
Furthermore, both these waste materials can be converted into a useful product.
Table 1. Refuse Content from Various Municipalities
Dhabi, Accra, dria,
Moisture of crude refuse
- = not measured
Sources: Weber (1983); Hughes (1986).
Camposting can be defined as the biological decomposition of the organic constituents of wastes under controlled conditions. This process can take place in the presence or absence of oxygen. The former is called aerobic composting composting and the latter can rapidly anaerobic.
If efficiently produce a pathogen-free carried out, aerobic product, as this review attempts to show. decomposition times
Anaerobic composting and is seldom free by contrast of pathogen requires much longer and odor problems.
The material being composted decomposes as a result of the activity of the bacteria, fungi, actinomycetes, and protozoa present material and of those that are seeded from the atmosphere. in the
The densities waste of the different organisms are a function of the nature of the waste in which they are found. various
Table 2 shows typical numbers of some organisms present in
of composting. The efficiency of the process depends to a large extent on temperature since microbial succession occurs with the temperature changes brought about by microbial activity. Figure 1 shows a typical temperature pattern in a compost pile over a period of 25 days. When a composting mixture is prepared, mesophilic microbial activity within the mass generates heat, which raises the temperature the temperature reaches a certain level, the within the mixture.
When q esophilic activity begins to subside and thermophilic activity begins to increase. This process continues until declines. the temperature thermophils, and their conditions population become declines. limiting to the
Subsequently, survival of the temperature
At this point mesophilic organisms (mainly fungi and acti,lomycetes) the
0nCe again increase. As the process approaches completion, the concentration
Microfloral Population during Aerobic
Numbers per gram wet compost
Mesophilic initial tem- perature - 40°C
Numbers of microorganisms identified
Source: adapted from Poincelot (1974).
1 number less than or equal to number stated.
1. mica1 time/temperature relationship using mode values of readings taken at 14 monitoring points within each of 12 static milea.
et ali 11981).
-69 of nutrients also becomes rate limiting to its ambient value. Table 3 indicates and the temperature typical temperature ranges for mesophils and thermephils. mini-l, eventually optimal, returns and maximal
Maximum, Optimum, and Minimum Tern erature Ranges for
Mesophils and Thermophils ( a C)
Source: Glathe and Parkasdi (1966).
7 S.-80 destroyed
Excreted pathogens or inactivated during present in the raw waste material the thermophilic will be phase (see table 4). Since the composting process is aerobic, structure and porosity for efficient the sewage sludge and night soil conposting, raw materials decomposition organic to or must occur, have sufficient
In the case of inorganic materials normally have to be added so as tc increase air spaces to allow for proper aeration, mixture, provide structural and, in the support, reduce the bulk weight of the composting
of organic additives, increase the quantity of degradable materials. this purpose, as
The organic part of garbage or refuse is suitable for
other types of materials that can be added, such as wood chips, shredded tires, peanut shells, rocks, bark, rice hulls, peat, straw, sawdust, manure, and grass.
Various rate-related parameters or
affect the efficiency the comporting process and the quality of the product.
The most important of ones are briefly described in this section. The optimal ranges given are not always found in practice as different ezperience to be the best suited to operators their may particular use conditions raw shown materials by and composting process.
The moisture content of a composting mixture should be much greater than the lowest level at which bacterial activity will occur
(which is about
12-15 percent 1. The optimum moisture usually in the range of SO-60 percent. content
efficient composting is
Sewage sludge and night soil contain a great deal of ‘moisture
> 92 percent)
their untreated state. Even when dewatefed, they may still be too wet to be composted on their own and amendments or bulking
Table I. Feedback Loops In the Camposting Ecosystam
Tmrature optma foe the popuIatloa
Fmltivo feedback (a’
Amblent teeperatur e at assembly of rlxture
I&mph1 Is generate heat; temperature
Increases; aesophi Is increase
Above 40’ C
(awrox 1 at start of thermphi I ic phase of self- heat i ng
Thermphi Is generate heat; teaperature
Increases; thermoph i I s i ncrease
Neqat I vo feedback
Component i ntaract lm
Above 40* c, self-heatlng passes from aesophI I Ic phsse to thermophlllc
Above SSO C
Marophfl Ic tmrature tolerance Iirlt emesded; popu-
Iatlons collapse; accompanying heat outputs decl In0
The-hi I ic taperature tolerance limit approached ; population and acampanylng heat output decl Ines a. Posittva. The microbial succession progresses. b. NagHive. The microbial succession is regressed.
Finstein et al. (1980).
*.rill then be required structural integrity as well to reduce as increase the the moisture carbon content content. and
Typical provide amend- ments include sawdust, straw, garbage, grass, etc. Typical bulking agents include wood chips, shredded tires, rocks, peanut shells, etc.
The moisture content of a composting mass will tend to decrease as decomposition mainly because of evaporation losses during the thermophilic phase, proceeds, and in some cases water may have to be added to maintain optimal conditions. Process performance can be evaluated during the drying out of a composting mixture since it is relatively simple to measure moisture and can easily be done even with poor laboratory facilities.
Temperature including between
20 the and important
35’ C. composting has different thermophilic one,
Most microorganisms thrive at temperature body grow stages, best temperature
Temperatures above 50’ C achieved during thermophilic composting should be high enough to destroy these pathogens if maintained for a suff i- cient period of time. This, however, is only possible if the tempersture maintained above SO0 C throughout the composting mass and there are no pockets is of low tempe,.-ature during that time.
The temperature changes observed during the decomposition of organic matter can be used as an indication malfunctioning) of the process. of the proper functioning
Temperature is perhaps a more reliable
(or indicator directly than moisture, aeration, affects pathogen control, or nutrient which is important good compost.
Figure 2 shows typical time-temperature concentrations, to prcfiles the production for since composting it of sewage sludge scales to by the aerated attain thermophilic pile method. temperatures.
Other methods use different
In addition, the time maximum temperatures materials operators achieved vary from system to system, depending on the raw used and operational and design factors.
Many compost plant believe that it is important to maintain very high temperatures
(>6S” C), but this has been shown to be counterproductive microbial activity rapidly becomes limited at these because temperatures. thermophilic
The quality of a product greatly depends on the length of time that a mixture is composted. If high composting temperatures (optimum SO-55’ C) are not days), maintained resistant pathogen throughout destruction pathogens the material will not for reach a sufficient the required length of time (> 2 level.
(Some heat may survive this temperature range.)
Reactor retention times and curing times may vary from system to system.
Composting material that consists of small particles is more readily decomposed than material with larger particles is greater. At the same time, if particles oxygen diffusion. Furthermore, as the surface are too fine, area there will of contact be less very fine material tends to lose some of its
60 lima (day31
Figure 2. A typical time/temperature sludge by the aerated pile method. conditiona of mirture, temperature, relationship
Curve 1 depicts for comporting rewage
situation where and aeration are at optimum levela for rapid transition
Curve 2 represent8
from the merophilic condition where certain outside their optiur and activity range, of theOindigenous rerulting organisms. into the thermophilic parameters in adverse effectr are deficient rtage. or on the growth
Saurce: Parr, Bpatein, and Yillson (1978).
- 10 - usefulness as a soil amendment. Typical particle sizes of material used for composting range from 10 to 50 millimeters, the lower value being appropriate for forced aeration or agitated system and the upper one for static piles or windrows.
The optimum levels of oxygen required microorganisms range
the growth of aerobic
5 to 15 percent of the air, with 5 percent being the minimum essential for the growth of mesophils.
The oxygen consumption in a composting mass depends on several factors: (a) the stage of the
(b) the temperature; composition
(c) the degree of agitation of the comporting mass; of the mass;
size of the mass; and
(f) the moisture content. logarithmically with changes
Oxygen consumption in temperature appears to increase
, and the moisture and decrease content affects the air spaces within the composting mass.
at which the compost material is aerated also affects the process.
(33-78 cubic feet of air
If the aeration rate is high
day per pound of volatile solids) the excess flow of air causes the compost mixture to cool down. If this rate is low (4-6 cubic feet of air per day per pound of volatile solids), aerobic activity will decline and the process may become anaerobic.
Carbon and nitrogen are two elements required for microbial
The carbon-to-nitrogen (C/N) ratio provides a useful indication growth. of the rate of decomposition of organic matter. l4icroorganisms generally require 30 parts of carbon to each part of nitrogen for their metabolism. This ratio is therefore commonly used in the composting process; the most frequently used value is between 25 and 30. Sewage sludge and night soil are both relatively high in nitrogenous compounds, and the C/N ratio is normally less than 15 for these wastes (see table 5 for the nitrogen wastes).
The addition of amendments content and C/N ratios of various
bulking agents material that have a high C/N ratio compared with that of sewage sludge
night soil can be used to adjust is too high, the final however , ratio to one within the decomposition the optimal range,
If the C/N ratio process slows down as nitrogen becomes growth limiting; if ;he ratio is too low, the large amount of nitrogen present is rapidly lost by volatilization as molecular anrnonia.
Since nitrogen is a valuable plant nutrient, its levels in mature compost need to be kept reasonably process. high; thus , maintaining an optimum C/N ratio is advantageous to the pH Control
The optimal pH for the growth of bacteria and other composting organisms is in the range of 6.0 to 8.0.
At a pH of 8-9, nitrogen may be lost through volatilization of molecular ammonia; if the pH is too acidic (< 5 1, microbial malfunction; activity will cease.
In some cases9 pH may reflect if, for example , a composting mass begins to turn anaerobic, process the pH may fall
Conversely, to about 4.5 owing to the accumulation as the process approaches stability, of organic the pH shifts acids. toward neutrality (pH 7).
- 11 -
Approximate Nitrogen Content and C/M Ratios for Some
X dry weight
Night soil wastea
Digested sewage sludge
Young grass clippings
Farmyard manure (average)
This indicator is not only an index of the efficiency of the process, but it also affects public acceptance of and support for composting plants, especially in areas of high population density.
There are various methods of controlling are effective or removing foul odors from composting materials. unless the process goes totally anaerobic,
These usually for example, and garticblarly foul odors are produced. In forced aeration systems a relatively simple and inexpensive method of deodorizing the exhaust air is to use some of the previously filter composted materials as
filter, since organisms present in the readily absorb and decompose the malodorous compounds present in the air. Simple filters consist of is blown. (Some compost filters
small pile of compost through which the air
described in table 6.)
- 12 -
Table 6. Methods
Odor Control Using Compost Filters
A bed of perforated covered with compost piping
Composting plants at Duisburg and Heidelberg (Fed. Rep. of
Germany) (Jiiger and JPger 1978)
Beringen Composting Plant
A windrow constructed perforated pipe through which air from a reactor is blown over
Cone-shaped pile of screened compost contain- ing 1 cubic yard of dry material per 10 tons of wet sludge being composted lb-inch diameter perforated asbestos cement pipes
8 feet apart are covered with l-2 inches of gravel to a thickness of 16 inches and this is then covered with fresh compost
a depth of 5 feet
Beltsville Cornposting Plant
United States (Willson et al.
Increasing ammonia concentration and rising levels of carbon dioxide have been shown to correlate
(Japan Sewage Uorks Agency with different
1980). stages of the composting process
At composting installations with well- equipped laboratories, be used as indicators these parameters can be continuously of process operation. monitored and thus
- 13 -
The composting systems described in this report can be divided into two main categories: (a) reactor systems in which at least the initial composting occurs within a mechanical reactor and
(b) nonreactor systems in which the entire composting process occurs outside a reactor.
Most composting systems developed up to now have been used for composting refuse; however, since human wastes in the form of sludge and night soil are the main raw materials of interest in this report, systems that can be used to treat these wastes are described here as well as systems for their combined treatment with garbage.
The different usually classified types as vertical of reactor flow, systems inclined flow, used for composting and horizontal flow are in which aeration occurs with or without agitation of the composting mass. There are many different reactor systems for composting. These systems can compost a combination of human waste (sludge or night soil) and garbage, provided the waste has been adequately prepared (presorted, days in the reactor, windrows to mature. the waste material pulverized, etc.). After a few
(raw compost) is put in piles or
A few of the more common reactor systems are described below.
A vertical flow system may have vertically stacked floors or decks in a silo or tower-type reactor.
Aeration is effected by allowing the composting mass to drop from one level to the next over a period of days.
The raw compost is then stored outside to mature.
The Dano system is a typical comprises a drum that is slightly inclined inclined from flow the type horizontal of system. and can
It be rotated. Air is introduced into the drum by forced aeration. The composting mass stays in the drum for up to 5 days, after which it is placed in windrows to mature. horizontal
A typical horizontal screw moves the waste bottom of each cell. After flow reactor consists of a series of cells. from cell to cell. a few days in the cells,
Air is introduced the compost matures out
A at the in the open for several weeks.
There are two types of nonreactor systems: (a) those in which the waste being composted is agitated or turned and (b) those in which the waste remains static during composting. system will
The degree of mixing in the nonreactor depending on the technology used and the degree of control applied.
In situations where the waste being composted is agitated or turned, this may be done by placing it in a windrow that is turned by a windrow-turning machine, by a front-end loader on a tractor, or manually by
- 14 - using shovels.
The static pile system relies on two methods forced aeration of the composting mass and natural ventilation of
(air aeration: diffu- sion).
A comparison of different nonreactor systems
(1982) has shown that turning is a less efficient by method de Bertoldi of producing et al. good compost than forced aeration of a static pile. This is mainly because of the difficulty
Periero-Neto, of attaining
Stentiford, thorough mixing and Mara (1986j by turning. in which
A study windrows conducted were compared by with aerated static piles showed that a better quality compost
(good pathogen removal) was produced by the forced aeration static piles. Table 7 describes briefly four different shown in figure 3, nonreactor systems.
A typical forced aeration pile is
Summary of Different Nonreactor Composting Systems
The waste material is placed in alternate pile.
It is turned frequently by shovel layers in a trench or over a 3 to 6 month period.
The waste material is formed into a windrow (triangular section) using a front-end loader or windrower. This in cross is then regularly turned by machine for 4 to 6 weeks.
The waste material is extruded into pellets (each with a l/cm diameter), pressed into briquettes or formed into bales, stacked in piles, and aerated by natural ventilation.
The material is constructed into a pile (static aerated pile) through which air is either blown or drawn over a period of about 3 weeks. cxorce
The major differences between reactor and nonreactor the capital and operating costs of the two systems. This systems is of great are in impor- tance if financial resources are a constraint in the choice of a composting system. technically
Because of their complexity skilled operators, in hardware and their need for highly reactor systems have high construction, tion, and maintenance costs, whereas nonreactor systems that are less opera- complex and can rely on fewer technically skilled staff tend to cost less. Reactor systems for composting have been popular in industrialized countries, where there has been increasing need to compost solid and human waste.
In addition, complex equipment has been required to sort out the large amounts of noncom- postable waste material in areas with limited space availability.
In many developing basis countries, of limited there is no need to opt for the reactor system on the space availability. In addition, the waste often comprises more than 60 percent compostable material.
Often this is because scavengers have removed most of the noncompostable material. Comparison is made of some of the management and operational differences between reactor and nonreactor systems in table 8.
Some of the important points to consider in planning for composting are discussed later.
caamsnN0 mm H)nclD AmAnoN
- 15 -
World BIllk - 18069
Figure 3. Elements of aerated pile composting system.
Land requirement control of air supply
Heed for subsequent drying
Aerated pile generally low
- 16 -
Comparison of Reactor and Nonreactor Systems generally low in small systems; can become high in large systems
High, depending largely on amendment or bulking agents
Limited unless forced aeration is used
Drying usually occurs in wlndrow but depends on cl imate
Ccmp I ete
Drying can be achieved in pile with high air supply; wlndrow drying may be required
Forced aeration, agitation
Forced aeration, no agitation generally high
Generally low, depending on power source
Low for reactor but can be high where windrow drying Is required
Camp I ete general ly low, depend i ng on amendment or bulking agent
Low, but can increase if wlndrow drying is required
Camp I ete
Drying achieved tor; can be final in reac- drying in windrow or heat dryer may be required
Demonstrated in cold and wet climates
Less drying potential frcm lower air flow- rates; final drying In wind- row or heat dryer usually required
Demonstrated in cold and wet climates
Sensftivlty to cold or wet weather
Sensltlve unless in housing; demon- strated mainly in wara, dry cl imates
Demonstrated in cold and wet c ‘r imates
Cwms+fng demonstrated on digested sludge
Coposting duonstrated on raw sludge
Yes, but odor problems observed
- 17 -
Table 8 (cont.1
Aerated p I lo
Control of odors Depends largely on Handling of raw raw ataterials sludge is poten- tial ly odorous; filter nay be requ i red
Source : Adapted fran Haug (1980).
Forced aeration, agitation
Forced aeration, no agitation
SEWAGE SLUDGE AND NIGHT SOIL CO-COMPOSTED WITH REFUSE
Several European countries, most notably Holland (Oosthoek 19811,
France (Hirscheydt 19751, Austria (Ingerle 19781, and the Federal Republic of
Germany (Tabasaran 19761, have a long history of refuse cornposting. of preparing refuse for camposting have been described in the literature
(see, for example, Breidenbach 1971; Spohn 1978; Rabbani et al. 1983; Savage and
Golueke 1986). Sorting processes for refuse and composting are not discussed in detail here as they are also well described in the literature.
In West Germany, the co-cornposting of sewage sludge with garbage originated out of the need to treat and dispose of ever-increasing amounts of sludge.
Co-composting now is a viable alternative in many developing coun- tries where great concern exists about the large amounts of garbage and poorly disposed and treated human wastes that are being produced in urban areas.
These waste materials can be reused and recycled through cornposting, to improve the urban environment soils. and to increase the quality and productivity of
Co-cornposting of garbage with human waste can be carried out both in reactor systems (Ingerle 1980) and nonreactor systems.
Nonreactor systems are best used wherever the refuse does not require much sorting and pulverizing and where funds and other resources are scarce. The different reactor and nonreactor systems for composting already have been described. examples of different reactor and nonreactor systems
Table 9 gives and how they have been used to co-compost garbage and human waste.
Different types night soil can be mixed with the garbage (or sorted refuse). of sludge and
Temperatures reached at cornposting time are indicative of efficient pathogen control.
- 18 -
Table 9. Examples of Co-composting of Sewage Sludge with Refuse
PI ant type/ raw materials
Woreactor cell system; dewatered digested sludge and refuse
Hstemag drum system with forced aeration; refuse and ml xed raw/d i gested sewage sludge dewatered to 25 percent solids
After refuse is separated and pulverized, it is nixed in a drum together with the sludge for 24 hours; then the raw compost is matured In forced ‘aeration piles for up to 5 months. Temperatures of up to 50’ C are attained within the drum.
A compost filter is used to control odor.
Grote ( 1978 1
(Heidelberg) system; a tower reactor con- sisting of several levels; refuse and dewatered dfgested sludge
(Du i sberg 1
Dano drum/ reactor; refuse and d i gested sludge
Experimental study. The sewage sludge is first pelletized (to a diameter of
10 millimeters) and then aixed together with the sorted pulverized refuse in bioreactor ccl Is. Temperatures of up to 80’ C are attained over a number of days.
The sludge is dewatered to 40 percent solids before addftion to the sorted pulverized refuse. The mixture falls from level to level wfthin the tower during a period of 24 hours to 1 week during which temperatures of up to
70’ C are reached, Maturation occurs in tunneled wlndrows (I.e., plled with
@*tunnels” to aid aeration and drying).
Experiments using the towers demonstrate the varlatlon In mesophilic and thermo- philic populations (described in chapter
2) at the temperatures occurring at different levels within the tower. A compost filter is used to control odor.
Refuse is sorted before being put into the drum, where it is mixed with the sludge. Rstention tima is about 3 days, after which the raw ccmpost mix is put in windrows to mature. Temperatures up to 72’ C are reached and maintained in the drum.
A canpost filter is used to control odor.
Farkasd I fexperimentel,
19681, Sander fl%f), Hart
- 19 -
Table 9 (cont.)
PI ant type/ raw mater i a I s
(F lensburg 1
Rheinstatil process drum reactor; refuse and dewatered mixed sludge
(Dar i ngsn 1 reactor; refuse and dewatered digested sewage slLdge
The refuse is milled and sorted. it is then mixed with the sludge in a drum for
24 hours. The raw compost is then matured in a windrow for J-4 months.
Temperatures of 60-70’ C are main- tained in the drun during the 24 hours.
A ccmpost filter Is used to control odor.
The refuse is sorted and milled and fed into a Dano drum together with the sludge.
The retention time is 48 hours and a temperature of at least 40° C is main- tained throughout. The raw compost is matured in windrows for 8-10 months
(temperatures of up to 70’ C are ccamion).
A ccmpost filter is used to control odors from the drum.
Hardma i or
Eng I and
(Leicester 1 and digested sewage sludge
The refuse is sorted, homogenized, and mixed with the sludge. The mixture is fed into the drum where it stays for about 3 days; then the raw compost is screened and matured in w i ndrous.
Vertical reactors each divided
Into stages by paraliei steel bars; refuse and dewatered sludge and night soil
Experimental plant. The refuse is sorted and milled and is then mixed with the sludge and night soil. The mixture is added to a vertical reactor consisting of five stages. The retention time is 5 days and the the average temperature is 5S” C.
(Toyohash I ) drums and verti- tlcal reactors; refuse and raw/ digested night soil fend poul- try wastes 1
The refuse is sorted and milled. The night soil is either digested aerobically first or dewatered and mixed with the ret use.
The mixture is fed into Dano drums for 2 days, is kept in vertical reactors for another 2 days, and then stored. A tamperslure of 60’ C is reeched in both reactors. The raw c-post is then stockpiled for 2 weeks before use.
Table 9 (cont.1
Plant type/ rau materfals
Refuse and sludge are c-posted using a biotunnel. Temperatures of 65-70’ C are observed.
Austr I a
(Wiesbaden) bales; refuss and raw sludge grikollare pro- cess briquettes
20 x 25 x 50 centimeters are formad; refuse and dwatered digested sewage t I udge
Same as above briquettes
20 x 25 x 50 centimeters; refuse and dwatered sewage sludge
(platform ronpostirq); refuse end sewage si udge
Experfmental plant. me refuse Is sorted and mllled and then mixed with the sludge.
Waxt, the mixture is formed into bales uslng a press and then stored
In the open to mature for about 14 mths before being broken up. Temperatures
(typical of windrow compost temperatures) sf between 36’ C and 72’ C have been measured. Odor Is not a problem.
Refuse Is sorted, ground, end then mixed Hart (19671, with the sewage sludge. The mixture is
Sander then compressed into briquettes have holes for aeration).
They are stored Nordsiek on pallets In a curing shed. Temperatures (1976) of 55-60’ C are attained during curing
(2-3 weeks 1.
The briquettes are broken up before marketing.
The process is similar to the one above except that higher (60-65’ C) tempera- tures are observed In the briquettes durlng 3 weeks of curing. The briquettes are broken up and seived Into dlfferent fractions before marketing.
Refuse Is sorted and ground and then mixed with sludge.
The mix Is laid on a plat- form to a depth of 3-4 meters and ccxn- posted with forced aeration
Then the compost Is matured on open-air platforms for up to 4 months. for 3-4 weeks.
- 21 -
Table 9 (cont.1
Plant type/ ram naterials
Eng I and
I ndones i a
Refuse and sewage sludge in forced aeration pi Is
Refuse and night soi I
Windrows; refuse, manure, night soil
Night soil and refuse
Nlght soil and refuse
Experimental study. Refuse “fines,” which pass through a 50 IIUI mesh, are mixed uith sewage sludge (l-g% solids) with front-end loader, and the mixture
Is piled over a perforated aeration pipe for canposting for ,about 30 days and then allowed to nature.
Stentiford et al.
The refuse and night soil mixture is placed in brick-lined pits that have aeration and drainage channels. The mixture Is turned at least twice during the 30-day c-posting period.
The raw materials are mixed and put in wlndrows, which are then left for 4-7 months.
Refuse (70-80 percent by weight) and night soil (20-30 percent by weight) are mixed and heaped in piles 4 meters at the base, 2 meters at the top,
1.5 maters high and 4 meters long.
Bamboo poles for aeration are inserted at 30-centimeter levels and removed on day 2. The pile is sealed with a 40:60 percent soil-cinder paste. Temperatures of 50-55’ C are achieved and malntalned for 25 days.
Ch i nese
Pilot plant, 175 cubic asters of preheated Dalmat shredded refuse from a refuse treatment et al. plant is mixed with 3.5 cubic meters of
(1982) pit latrins wasts using a front-end loader.
Pi Ies are constructed over a system of perforated pipes for forced aeration.
Air Is drawn through the pipes and exhaust gases conducted into a compost filter (Beltsvil Ie Aerated Pile Method).
Siting and Mixing
Many counttier traditionally collect rafure reparately from night soil and their refure treatment production and dirpoaal riter. and dirporal
The logiaticr rites of locating differ a night from sludge aoil/eludge- garbage co-cwrting rite muat be carefully conridered.
A refure disposal site ir often suitable becaure of land availability.
After the refuee is sorted and the reject6 dirpored sludge.
it must be mixed with the night soil or
Where windrour are to be ured instead of aerated pilea or reactors, experiments have rhown that rpetially derigned ahtedder machines are far more efficient at mixing than front-end loaderr (Colueke et al. 1980).
Many factor8 need to be considered
To begin with, the planner must carefully before opting for one ryrtem or another. when
Table planning rtudy a composting the local
10 compares situation some sludge disposal methods and give. an idea of the torts involved.
According to the figurer in table 10, the cortr of composting are lower than the corta for treatment procersea such aa heat drying and incineration landrpreading, treating but comparable to dirporal-reure and ocean dirporal. and dirporing of uarter
Am noted are often protearer earlier, compared. ruch aa landfilling, different
Compoating methods of may not always be the most economically viable method of treating waste, sludge, and/or refume, and thur
often faced with the difficult city councila
, and private companies tart of deciding whether or not to compost. are
Comparative Coats for Variour Sludge Dirposal Proceesea
(1974 U.S. dollara)
per dry ton (US$/ton)
Wyatt and White (1975),
Carroll et al. (19751,
Smith and Bilera (1975),
Digested and dewatered rludae
Wyatt and White (19751,
(1975) and White (19751,
Camp Dresser & McKee
Camposting b/ r,b/
Camp Dresser and
Van Note et al. (1975)
Camp Drerwer and
Colacicco, Derr, and Kaoper (1977) a. Costs exclude tranrportation of rludge to rite. b. Coats exclude cost of removal of reriduer and benefits from resource recovery I
Dew, and Karper (1977).
- 24 -
It is important to note, however, that significant
(even though difficult to quantify) derive from converting health benefits these highly pathogenic organic wastes into compost that is relatively
Furthermore, the application of compost to poor soils helps pathogen-free. to improve their fertility and general condition.
Another important factor is the nature of the raw material(s) to be used, as this determines the complexity of the treatment plant required. the raw material is refuse containing little organic matter, for example,
If a considerable amount of sorting and pulverization -- by machinery or manpower, or both -- will be required before the refuse can be composted. Other factors that need to be taken extensive expenditure, into consideration, especially are summarized in table 11. since they may require
Table 11. Factors To Consider in Planning a Compoating Plant
Compost demand quantity and composition of waste type of waste collection of waste pretreatment required cost of bulking material transport of raw wastes to plant transport of compost disposal of noncompostible materials marketing possibilities alternative disposal options location of plant capital costs land requirement (also for storage) site development equipment costs expansion possibilities applicability of existing types system required choice of equipment energy/fuel requirements laboratory needs maintenance needs maintenance costs personnel costs market research market promotion marketing costs
As table 11 indicates, planners must weigh many factors in deciding how to best compost garbage and human waste. They should not just pick any system and hope that it can be operated efficiently under local conditions.
(Some of the questions on costs are discussed in Chapter 6.)
-4 eolsTBOL OF EXCUTBD AND OTHER PATEoGgNS
Excreted pathogens occur in sewage sludge at varying concentrations depending on their ability to survive the various sewage treatment processes and whether they accumulate in the sludge. Concentrations in night soil depend almost entirely on the levels being excreted at any one time and on the ability of the pathogens to survive in the external environment.
Table 12 suxrsarises the survival times of pathogens excreted in feces, night soil, and sludge, and table 13 suaxnarixes survival timea on crops. Golueke (1983) has reviewed their survival in soil.
The literature on the survival of enteric pathogens during various treatment processes has been thoroughly reviewed by
Peachem et al. (19831, who present detailed information aspects of excreta-related infections. Furthermore, on health and other
Blum and Feachem (1985) review the health aspects of night discuss survival and health risks. soil and sludge use in agriculture and
Table 12. Survival Times of Excreted Pathogens in Feces,
Night Soil, and Sludge at 20-30°C
Pathogens Survival time (days)
Cl00 but usually <20
<90 but usually C50
<60 but usually (30
<30 but usually cl0
(30 but usually <5
Entamoeba histolytica cysts
Ascaris lumbricoides eggs
<30 but usually cl5
* Includes polio , echo, and coxsackieviruses.
Source: Feathem et al. (19831, p, 66.
- 26 -
Survival Times of Excreted Pathogens on Crops at 20-30°C
Bnteroviruses* <60 but usually <15
<30 but usually
<30 but usually
<lo but usually
<5 but ususlly cysts
Ascaris lumbricoides eggs
<lo but usually ~2
<60 but usually <30
* Includes polio, echo, and coxsackieviruses.
Feachem et al. (19831, p*
Some pathogens msy not survive the sludge production process. open-air drying of sludge and night soil eliminates pathogens,
In addition, depending on the length of drying time. The key factors in determining the survival of pathogens sre the temperature-time
(1983) have suggested various temperature-tim interactions. regimes
Peachem et al. for selected pathogens to ensure their death in sewage sludge snd night soil. These have been based on an evaluation of survival times for numerous pathogens over a wide range of temperatures (see figure 4).
Samples of sludge or night soil should be free of excreted pathogens
(with the possible exception of hepatitis
A virus and heat-resistant bacterial spores such as those of clostridium perfringens) if they are heated for 1 hour at > 62’ C, 1 day at
> 50” C, or 1 week at > 46’ C.
These regimes are all within the safety zone shown in f igurc 4.
Smsll-scale studies using 20-30 tons of compost msterisl have shown that e* coli and salmonella spp+ are destroyed by heat more easily than fecal streptococci, and that even cm perfringers
Stentiford, numbers decrease during comporting and maturation (Pereira-Neto, and Mara 1986).
Other workers have proposed different criteria for determining pathogen destruction in compost on the basis of work using
- other media as well as compost.
Burge, Cramer, and Epstein
(1978) and [email protected], Colacicco, and Cramer (1981) suggest that F2 bacteriophage be used as an indicator of pathogen destruction since this organism is more resistant to heat than many excreted pathogens.
[email protected] of work done on this organism have shown that a 150log reduction in F2 bacteriophage numbers can be expected reduction if they are of an infective maintained at dose of 10
5’ C for 2 days (for example, a I-log
- Vibrio [email protected] would leave 1 Vibrio cholera bacterium). Maintaining pathogens at 55” C for 2 days as a minimum is within the safety zone shown in figure 4. This figure is a reliable of survival times, especially since the use of standard fecal coliform indicator counts may not be reliable (these have been shown to multiply in msture compost
([email protected] et al. 1981)).
The main bacterial pathogens of interest are listed in table 14. The survival rate of excreted bacterial pathogens in night soil and sludge is variable involved. and depends in part on the temperature
At and the length of time temperatures above 20’ C, these pathogens will generally survive up to one month in samples of sludge and night soil. cates survival times for various bacteria.
(Annex table B-l indi- are based mainly on the absence of pathogens in the compost at the end of the sampling time, and in many cases there ir no indication of the initial concentrations, which would
Table 14. Bacterial Pathogens Excreted in Feces
Pathogenic Escherichia coli Castroenteritis
Disease of diarrhea
Salmonelloais and other types of food poisoning
Vibrio [email protected]
Paratyphoid fever dysentery
- 20 -
1 ~osk 1 month
Figure 4. gumrival of pathogens at different
Peachem et al. (1983). tmperature/tirc rcgimss.
- 29 - have an effect on the time for complete destruction or of frequences of sampling.) temperatures
However, above in general,
50’ when the cornposting
C, complete destruction
2 weeks (see examples in annex B table B-1). mass was maintained was shown to occur within at
The main viral pathogens of interest here are listed in table 15.
Data on the survival of viruses in sludge and night soil are less abundant than in the case of bacteria, principally because the methods used to determine unreliable. viruses in samples are difficult to carry out and are of ten
Survival of viral pathogens in compost of different materials is reduced to low levels within 2 weeks at temperatures between 35 and 70’ C for most of the pathogens presented in annex table B-2.
Table 15. Viral Pathogens Excreted in Feces
Hepatitis A virus
Diarrhea or gastroenteritis childre;
The main protoeoal pathogens of interest here are listed in table 16.
Reported survival of some of these pathogens in compost is presented in annex table B-3.
The figures there indicate that in general the protozoa1 pathogens survive for short pfriods.
- 30 -
Protoeoal Pathogens Excreted in Feces
Amoebic dysentery and liver abrcess
Diarrhea and malabsorption
Mild diarrhea and colonic ulceration
The main helminths of interest are presented in table 17.
Certain helminths can survive in night soil and sludge up to a period of 3 months or longer, especially at cooler temperatures (<25’ C).
The most resistant are Ascaris and hookworm ova (annex table B-4). In compost, survival ones is generally very low at temperatures maintained over 35’ C for a few days (annex table B-4).
Because the survival times for the different pathogens vary gre.at!.y at the different temperature-time cornposting plant operators, it regimes is extremely measured important by researchers to establish and reliable temperature-time criteria for pathogen destruction during composting. The regimes within the safety zone proposed by Feachem et al. (1983) and Burge,
Colacicco, and Cramer (1981) may be of great ure in this regard.
Pathogens excreted by animals may find their way into sludge or night soil if the wastes containing them become mixed with human wastes. Several infections can be transmitted from animals to man (see table 18). Only some of these diseases are enteric and are of interest here. bacteria,
Enteric pathogens that mey’be isolated from animal waste include viruses, protoeoa,*and helminths. They occur in varying numbers depending on the type of disease and the physical and chemical composition of the waste. Since these pathogens are enteric, their optimum growth occurs around body temperature. Thus the thermophilic temperature (> 45 C) achieved during aerobic composting should be sufficient enteric pathogens, especially if the to destroy temperatures are or inactivate msintained sufficient the for lengths of time.
Some exceptions to this may be spores of apore- forming bacteria found in animal wastes (such as Bacillus anthracis and some clostridia), which survive at high temperatures.
Ancylostoma [email protected]
Diphyllobothrium felineus viverrini latum
Gastrodiscoides buski hominis
Helminthic Pathogens Excreted in Feces
- 32 -
Table 18. Animal Pathogens Capable of Causing Infections in Man
Infection Rode of infection sacter i a
Direct contact, excreta
Cow to man, direct
Swlnr to aan, contact goats to non, ingestion
Cattle/dogs to aan, direct contact
Arbov i ruses
Pox virus cowpoxa
Togav i rus
(cow to man)
Ronkey to man, direct contact
Toxoplasmosis Mammals/birds to man, ingestion/inhalation feces
Fast iI ol iasis
Tam i asis
Taen i asrs
Sheap and cattle to man
Cow to man
Pig to man
Bog to man, d irrct contact
Secondary pathogens affect people whose defense systems have been weakened by certain diseases or therapies. They may be present in sewage sludge secondary or night soil pathogens and some are are able some thermophilic to grow in compost. fungi
Examples of and actinomycetes.
These infect people who have had respiratory infections or prolonged antibiotic or steriod treatment (Hart, Russell, and Remington
The p.cobability of
- 33 - people in good health becoming infected is very low (Olver 1979; Willson et al. 1980; gurge and Millner 1980).
The main thermophilic fumigatus, which causes a respiratory thermophilic actinomycetes (for fungus of concern here is Aspergillus disease example, known as asperigillosis.
Micromonospora vulgaris) cause allergic reactions such as
1974; Marsh, Miller, actinomycetes reported and Kla 1979). to grow at the
(1982) lists several other temperatures attainable during ubiquitous the composting process (SO' C).
These secondary pathogens are and are very common in agricul turaj situations.
Asperigillus fumigatus, for example, is found in soils, hay, wood, cereals, forage, and various moldy farm wastes. thermophilic actinomycetes
From the data on maximal concentrations in different materials (see table 19), it of appears that the concentrations in compost are generally lower than those in the othe materials
(more mature compost usually has higher concentrations - up to 10 B per gram of dry weight ). Compost is able to support the growth of fumigatus and the actinomycetes because of the temperatures achieved during the pro- cess.
Aspergillus fumigatus grows at temperatures of Less than 20’ C to about
60’ C (Cooney and Kmerson 1964; Kane and Mullins 1973a,b) and has been readily isolated from wood chips at 50’ C (Tansey 1971). The actinomyecetes have a similar temperature (Lacey 1974). High concentrations have been isolated between 55’ la::1 60’ C (Millner 1982).
Certain factors can inhibit the growth of these secondary pathogens: excessive moisture and high temperatures (> 63’ low
C). pH, anaerobic conditions,
Toward the end of a composting process, when the compost is cooling down and becoming drier, the secondary pathogens may predominate.
Their spores are readily dispersed from dry and dusty compost piles especially during and after mechanical agitation (Millner, Bassett, and Marsh 1980).
Table 19. Concentrations of Thermophilic Actinomycetes in Different Materials
(numbers per gram, dry weight)
Pl-day sewage sludge compost
4-month sewage sludge compost gagasse
1.7 x 107
5.7 x 109
1.8 x lo8
9.6 x lo6
6.6 x 106
- 34 -
The degree of dispersal also depends on meteorological factors such as wind and rain (Millner et al. 1977).
Experiments carried out to measure concentrations of these secondary pathogens at Locations downwind of compost piles at treatment plants have shown that conditions differ for each compost plant, but that concentrations secondary infections tend to be lower from moldy hay (Burge than and Millner those associated
1980; Millner 1982). with
As already noted, the risk of infection in healthy individuals is low.
Certain measures can be taken, however, to improve the general health standards at a composting pla3 and thus reduce the risk of these secondary infections even further:
Workers should be encouraged to maintain high standards of hygiene.
2. During periods of dry weather, sprinkled periodically with water the composting to reduce area dust dispersal. should be
During adverse weather conditions, wear masks or respirators or workers some other should covering be encouraged to reduce to dust inhalation.
Workers should be isolated from the spore-dispersing process, such as mechanical turning. parts of the
5. The composting plant should be Located at “discreet” hospitals and residential areas (the distance will distances vary from plant from to plant, but in general should be at Least 1 kilometer).
Numerous pathogens cause plant diseases. Most agricultural soils are infested with nematodes, bacteria, viruses, and fungi (Sasser 1971).
Some of these may be present in compost made from garbage, vegetable, and other gardening wastes. Knoll (1980) has described standard laboratory methods that can be used to isolate and measure the concentrations of indicator plant pathogens in comport.
Table 20 Lists some pathogens that have been associated with compost as an indicator or that have been isolated from it.
The most important ones are those that produce heat-resistant spores, such as the fungi listed in table
20 or some viruses. would therefore be inactivated
Most other under thermophilic pathogens composting are mesophils temperature-time and regimes (although heat resistant spores present in compost may persist in the soil for long periods after being spread on Land). Recent research has revealed that compost may have a beneficial diseases. The application of compost to soils effect on plants containing and soil-borne diseased plants has been followed by inmediate and Long-term reduction in the incidence and severity of certain diseases such as root rot of beans, cotton, and radish.
- 35 -
(various) tobacco nematodes
Plant Pathogens in Compost mosaic meloidogyne
Fungi, Plasmodiophora brassicae
Olipidium brassicae type,
- 36 -
This chapter briefly reviews the uses of compost. The degree of use depends greatly on whether or not material of fecal origin ie culturally and socially acceptable.
QUALITY OF COMPOST
A well-produced, mature compost is free from odor and easy to handle, store, and transport. these qualities,
A raw compost (one that but will acquire them with has time if not it matured) is allowed does not have to mature.
Table 21 lists some of the differences between raw and mature compost.
Mature compost contains trace and essential elements, of which the most important are nitrogen, phosphorus, potassium, and sulphur. These are available to the soil and plants, depending on their initial concentrations in the raw compost materials and on the degree of mineralization
(Tester, Parr, and Paolini 1980). (Concentration that occurs in compost from sludge/night soil and garbage compost are considered equivalent, although concentrations other elements will vary depending on the raw materials.) These elements of are released by the compost and become available in the years following applica- tion. The compost can therefore be used in somewhat the same way as an inorganic fertilizer (except that in many cases the concentrations elements are 50 low that excessively Large application rates of these would be required).
As a result, compost is often considered a low analysis fertilizer or soil conditioner (Golueke 1972; Hand, Gerahman, and Navarro 1977; Parr et al. 1978). However, the NPK values (and other mineral content) of compost can be fortified with chemicals to enhance its fertilizing capacity (Hileman
1982). Unlike inorganic fertilizers, compost has a humuslike quality that makes it even more useful, especially in areas of the world where the humus content of soil is being rapidly depleted as a result of excessive cultivation and land erosion (Tietjen 1975; compost can replace lost humus.
Pagliali et al. 1981). That is to say,
Compost may contain high concentrations the source of the raw materials. If sludge of heavy metals, depending from a mixed industrial-domestic on source is used, concentrations of lead, zinc, and nickel may be very high.
Some typical heavy metal concentrations in compost, night soil, and sludge are presented in table 22. Concentrations in night soil are negligible. Garbage and human waste plants metals, especially if utilizing the night soil will produce compost low in heavy refuse is largely organic.
Other hazardous chemicals such as detergents and those in certain industrial wastes that may be composted will appear in the product if they are nonbiodegradable.
- 37 -
Table 21. Differences between Mature and Raw Compost compost
Nitrogen as nitrate ion
Sulphur as sulphate ion
Lower oxygen demand
No danger of putrefaction
Nutrient element5 are in part available to plants
Higher concentrations of vitamin5 and antibiotic5
Higher concentrations of soil bacteria, fungi, which are decomposed, easily degradable substances
50 percent is about
Higher water retention ability
Clay-humus complexes are built
Compatible with plants
Nitrogen as ammonium ion
Sulphur still in part as sulphide ion
Higher oxygen demand
Danger of putrefaction
Nutrient element5 not available
Lower concentrations and antibiotics of vitamin5
Higher concentration of bacteria and fungi, which decompose organic materials
High proportion mineralized
Not compatible of organic
Lower water retention complexes with ability generated plants substances not
APPLICATION OF COMPOST TO LAND
The most important use of compost is its application takes several forms:
It can be applied to land as a to land. fertilizer,
This soil conditioner, or mulch, or can be used as a means of Land reclamation.
Furthermore, the use of compost can range from domestic applications by the home gardener to Large-scale cropland or by municipalities applications for parklands. by conrmercial farmers to their positive
The application effects on plant of compost to land has several advantages. growth, compared with the effects of fertilizers fruit, crop alone yields, are well and other documented factors
Its for example, Arditti 1973; Hornick et al. 1979; Tokyo Metropolis 1979; Kurzweil
Table 22. MeteI Concentrstions in Coapost and Hwsn Waste
Rmf uwh I udge carport
Refuse/sludge sewago/ I udga
Ccmcbntrat ions c8dn i urn Chrunlun Copper Nickel Lead
0.24 lsO.0 77.0
Mixed damtic/ industrial sludge
Mixad daestic/ industrial sludge
Sludge, digested, industrial
Mixed domestic/ industrial s I udge
- 3 not measured.
Zinc Ref oronce
34.0 Rhode (19721
0.77 6ucller ( 1974 I
(19701 and fbmano
0.25 Japan Samgo
Uorks Agency (19gg)
Japan Seuage tbrks Agmy (19m)
Japan Sowaga works Agency (I980)
Works Agency 119110)
WIllson et al. w8o)
Willson et al.
Stentiford et al.
- 39 -
1980; Angle, Wolf, and Hall 1981; and Sridhar et al. 1985). The advantages it has over inorganic fertilizers lie in itr cffecta on the soil.
Table 23 zusssarizea some of these effects with respect to clay or sandy soils.
In both cases, the quality of the soil ir improved and it is more productive. recommendations and criteria for the application of compost to land
Some are presented in tables 24-26.
Compost may not only amend the physical properties of the soil, but it may have other beneficial effects, such as raising the pH of acid soils.
Production of compost may be of great countries with poor, arid soils. interest, especially in
Table 23. Physical Effects of the Addition of Compost to Clay or Sandy Soils
Sandy soil + compost Clay soil + compost
Water content is increased
Water retention is increased
Aggregation of soil particles is enhanced
Erosion is reduced
Aeration of soil increased
Permeability increased of soil to water
Potential crusting of soil surface is decreased
Compaction is reduced horticulture,
Compost may be used on land for the following purposes: home gardening, vegetable gardening, viticulture, landfill, forestry, soil conditioner, or cosssercial farming. or fertilizer
It is usually for many of these applications. applied agriculture, landscaping, as mulch,
OTHER USES OF COI’4POST
Apart from the traditional other uses.
For example, sewage applications sludge to land, or refuse compost compost has some can be fed to piglets. Pigs are omnivores and so compost is palatable to them. The compost has to be ground into a fine material (< 4m) and is fed only to piglets. In
Switzerland it is bagged and sold on the market at about 120 SF per cubic meter Olelfer 1975). As noted earlier, animal enteric pathogens should in general be inactivated or destroyed.
Compozt from night soil and vegetable matter has been used in fish farming experiments, where the compost has acted not only as a nutrient for the growth of algae but also as fish feed (Polprasert has also been used to make bricks bricking material before firing; porous. during leaving the fired bricks porous, as desired. firing
It is incorporated the st al. 1981). Compost organic matter into the burns,
- 40 -
Criteria for the Specific Applications of Compost
Compost type Frequency
Quantities per hectare)
Grassland and cultivation fodder plants of
SO-100 (light soils) *
Special mix with iron
(30 kilograms per farrow in first three weeks) up to 300
Control of erosion
Special compost has added minerals or is very fine in texture.
Adapted from Bundesrepublik (1979) and Tabasaran, Bidlingmaier,
Bickel (1981). and
- 41 -
Table 25. Compost Application Rates:
Uses and Application of Sewage Sludge Compost to Achieve Fertilizer Benefits
Ratea and Improve Soil
(metric tons per hectare)
Barley, oats, rye, wheat
Rototill into surface l-3 weeks before planting or in previous fall. Do not exceed recommended crop nitrogen rate.
Rate is for years after ini- tial garden establishment.
Rototill into surface l-2 weeks before planting or in previous fall.
Incorporate into soil
1-2 weeks befqre planting or in previous fall.
Incorporate into soil l-2 weeks before planting.
Supplemental potash may be required, depending on soil test.
Legumes can be grown in rotation with corn, oats, or other nitrogen-required crops b
Incorporate with top
4-6 inches of soil. lower rate on relatively
Use fertile soil and higher rate on infertile soil.
Supplement during first year's growth with l/2 pound per 1,000 square feet
(25 pounds per acre) of soluble nitrogen fertil- izer when needed.
- 42 -
Table 25 (cont.)
Uursery crops and ornamental8
(shrubs and trees)
Establishment (soil incorporation)
(metric tons per hectare)
Broadcast uniformly on surface in fall or early spring 1 year after incorporated application.
Potting mixes lo-25
Equal ratio of material
Incorporate with top
6-8 inches of soil. Do not use where acid-soil plants (aealea, rhododendron, etc.) are to be grown.
Broadcast uniformly on surface soil.
Can be worked into soil or used as a mulch.
Thoroughly water and drain mixes several times before planting to prevlnt salt injury to f’snts.
Conservation planting up tc 450
Incorporate with top
6 inches of soil. Use maximum rate only where excessive growth for several months following establish- ment is desirable.
For each inch beyond 6 inches of incorporation, add 1,000 pounds per 1,000 square feet on soils where groundwater nitrogen will not be increased.
Broadcast screened or unscreened compost uniformly on surface after seeding; unscreened is more effective.
- 43 -
Table 25 (cont.)
Establishment (Soil incorporation)
(metric tons per hectare)
Sod production, incorporated with soil
Sod production, unincorporated soil with
Source: Adapted from Hornick et al. (1979).
Incorporate with top
4-6 inches of soil.
Uee lower rate on relatively fertile on infertile soil and higher rate soil.
Broadcast uniformly on sur- face before seeding small reeded species (bluegrass) after seeding large seeded rpecies (fescues). or
Broadcast uniformly on sur- face. On cool-season grasses apply higher rate in fall or lower rate in fall and again in early spring.
Incorporate with top 4-6 inches of soil.
Apply uniformly to surface.
Irrigate for germination and establishment.
- 44 -
Application Rates for Sewage Sludge Compost in the First of Use Based on N or P Fertilizer Recommendations
Remarks N-based fertilizer recoamendat ions
P-based fertilizer recommendations
(tons compost per hectare)
Nursery crops and ornamental8
(shrubs and trees 1
Establishment loo-380 35-100 Incorporate with top
6-8 inches of soil. not use where acid-soil plants (azalea, rhodo-
Do dendron, etc.) are to be grown. Broadcast uniformly on surface soil.
Can be worked into soil or used as a mulch.
Conservation planting up to 500 n.r,
Mulch 17-40 n.r.
Incorporate with top 6 inches of soil. Use maximum rate only where excessive growth for several months follow- ing establishment is desirable. For each inch beyond 6 inches of incorporation, add 22 tons per acre on soils were groundwater nitrogen will not be increased.
Spread screened or unscreened compost uni- formly on surface after seeding; unscreened is effective,
- 45 -
Table 26 (cont.)
Barley, oats, rye, wheat
N-based fertilizer recommendat ions
P-based fertilizer recommendations
(tons compost per hectare)
Remarks incorporate into soil l-2 weeks before plant- ing or in previous fall.
Incorporate into soil l-2 weeks before plant- ing. Supplemental potash may be required depending on soil test.
Legumes can be grown in rotation with corn, oats, or other nitrogen-requiring crops.
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, using
25 pounds per acre of soluble nitrogen fertilizer when needed.
Broadcast uniformly on surface in fall or early spring 1 year after incorporated application.
- 46 -
Table 26 (cont.)
N-baaed fertilizer recommendations
P-based fertilizer recowsendations
(tons compost per hectare)
Incorporate with top
4-6 inches of soil.
Use lower rate on rela- tively fertile soil and higher rate on infertile soil.
Spread uniformly on surface before sec- ding small seeded species
(btuegrass) or after seeding large seeded species
Spread uniformly on surface. On cool- season grasses apply higher rate in fall or lower rate in fall and again in early spring.
Incorporate with top
4-6 inches of soil.
Sod production, incorporated with soil
Establishment 55-165 7-17
Rototill into surface l-2 weeks before planting or in previous fall.
Rate is for years after initial garden estab- liehment. Rototill into surface l-2 weeks before planting or in previous fall. n.r. = not recommended.
Adapted from Hornick et al. (1979).
- 47 - n'f!mOIMmXYpoB EVALUATIMG TllEE~CPBASIBILITYOF M)-CCHPOSTIW:
In developing countries the waste stream is relatively higher in organic matter than that of industrialized countries.
Since compost is derived only from the organic wastes, it would seem that developing countries have a relative advantage in the production of compost. In addition, domestic solid waste in developing countries contains few, if any, toxic materials which minimizes the risks of recycling them in the domestic solid waste to the land in the form of compost. The purpose of this chapter is to present and analyze the e_conomic parameters underlying will be done by presenting the fundamental co-composting information operations.
This needed to assess the viability financial of co-composting, followed by development of hypothetical models in and then economic terms, along with a discussion of the differences between them. The models will then be computerized and results and sensi- tivity analysis presented. The methodology followed conforms to World Bank guidelines for project economic analysis.
Analysis is being limited to co-composting domestic solid waste with night soil, although with minor modif icationa it would be applicable compost operations using domestic solid waste or sludge separately. composting of domestic solid waste would be more closely correlated to
Direct to the figures presented here, since the night soil component is relatively small
(less than soil/sludge,
10 percent of total inputs). Direct compost ing of night however, requires the use of a bulking agent or organic amendment to reduce its moisture content.
(For a detailed description composting, see Shuval et al. 1981.) Co-composting utilizes solid waste to serve as a bulking agent for the night soil. of night the soil domestic
COMPOSITION OF WASTE AND VALUE OF RESOURCES RECOVERED
The hypothetical models developed in this chapter assume a typical composition of solid waste for developing countries, which limits the capital requirements for equipment such as hammermills or rasps (to grind incoming domestic solid waste) by the waste composition (highly organic) and the use of a manual picking or sorting process. The specifics of the waste stream and its need for size reduction would vary for each municipality.
Typical domestic solid waste generation rates for developing countries that will be used as the basis for these models are 0.3 kilograms/person/day of domestic solid waste with a moisture content of 50 percent and a density of 250-400 kilograms per cubic meter and 1.5 liters of night soil/person/day with a solids content of 3 percent.
The quantity of night soil that can be processed by the co-composting operation depends on the moisture content of the material
This chapter was written by World Bank staff economists Frederick Wright and
Edward F. Quicke.
- 48 - to be composted; this should be no greater than 55 percent.
The anal ysi 8 assumes fresh night soil is collected and used by the co-composting operation, which severely percent solids), limits dried the amount used. sewage sludge
The uae of pit
(lo-20 percent latrine solids), sludge (20-25 or dewatered sludge would allow a greater population base to be handled. lower moisture liquid human waste would change the analysis
The use of a slightly by increasing the amount of compost increased solids but would have little produced if in direct any impact proportion to on compost-processing the costs.
Local conditions will determine the source of liquid material for the co-composting operation.
For the purposes of modeling, the domestic solid waste composition as given in table 27 has been assumed.
Table 27. Domestic Solid Waste Composition
X Domestic solid waste*
Plastic and rubber
Inerts, ash, rejects, etc.
* Moisture content of 50 percent, density of
Domestic solid waste composition and quantities generated are subject to wide variations as shown in chapter 1, table 1, and depend a great deal on the local collection/scavenging system. Waste composition and quantity also vary according to season (higher ash content in winter, higher moisture levels during wet season, etc.) and source (industry, economic level, etc.). areas, the waste stream may consist almost entirely of organic material,
In many the recoverable material of any value having been removed by scavengers before collection and delivery to the composting plant. Because variations in compo- sition could have a substantial impact on the operating viability of a composting system, waste composition must be determined prior to consideration of compoeting as a waste management option.
Variations in quantities of waste may also effect the capacity need for alternative disposal utilization of the co-composting operation or the systems , particularly where co-composting opera- tions are uaed for a siguificant portion of the waste stream.
The moisture content of the domestic solid waste is very important when co-composting is done, since the lower the domestic solid waste moisture the greater the
- 49 - amounts of night soil (3 percent solids) or sewage sludge (lo-20 percent solids) that can be disposed of.
The domestic solid waste collection system is not being analyzed here but plays a very important role and should be examined when composting as a disposal option is considered. is only possible on the organic material, the inert
Since composting material (including metals, glass, plastics) needs to be sorted out if good quality compost is to be made.
The percentage of available materials recovered will not approach
100 percent of their content in the domestic solid waste unless sophisticated recovery technologies recovery coefficients are used. Table 28 illustratea
(for manual sorting) eatimated reasonable resource from the available literature.
Table 28. Resource Recovery Coefficients
(ferrous) and rubber
The remainder consists of compostable material
(most of the unreclaimed paper and some textiles also fall in this category) and rejects.
The rejects (comprising mainly inert material such aa construction unrecovered recyclable materials) must be disposed waste of in an appropriate and man- ner -- a sanitary such as construction landfill, for example -- or some other recycling technology land reclamation fill or waste-derived building blocks where feasible. composting
Therefore, is the landfilling of rejects vi11 be done. in many cases the appropriate site for the co- site, where sorting and separation and disposal
For modeling purposes, the US dollar equivalent prices for recovered materials will be assumed as given in table 31.
Table 29. Recovered Material Values
(ferrous) and Rubber (mixed)
* Prices are ex-plant.
- 50 -
The actual prices received for recovered materials are relatively unstable and highly dependent on the local market (rural, availability, etc.). In addition, these materials industry, transport tend to be bulky and transport costs constitute a high percentage of the end users coat.
Also, the size of the composting operation has some bearing on prices for recovered materials.
A amall-scale plant would only be able to offer material users significant quantities after a perins of time, whereas a large facility would be in a better position to negotiate a long-term sales contract. investing in a composting/resource recovery plant, detailed estimates
Prior to must be made of the local market (quantity and price) for recovery materials. Table
30 estimates the value of recovered materials from one ton of waste, based on the assumed waste composition (table 291, resource recovery coefficients
(table 301, and material valuea (table 31).
Table 30. Recovered Materials,
Revenue/Ton of Domestic Solid Waste
Domestic solid waste content kg
Recovery coeff. x
Quantity recovered kg
Aa can be seen, the gross revenue generated for moat items is rather small (particularly for textiles, metals, and glass) and one might assume it is not economical to recover them (recovery, of course, depends on local labor costs and potential compostable materials. markets).
Therefore, then become rejects (requiring
Yet, they disposal) except would if for still not the paper, need sorting recovered these and would and sold, are not and a significant percentage of the end cost has to be invested for both recycling and co-composting.
The other revenue-generating
(value) of c ompost is also sensitive item will to local be the compost. conditions patterns (vegetables or other high value crops), soil condition,
The price such as cropping availability of alternative soil conditioners (such as livestock wastes or crop residues), and costs of agricultural water). inputs (for example, inorganic fertilizers
Other potential buyers of compost include greenhouses and horticul- and tural plant nursery operations (as a substitute for other more expensive
- 51 - growing media, such as peat moss), land reclamation projects (atrip mining or landfill cover), and public works (parks, landscaping, etc.).
The amount of carpost produced depends on the quantity of compostable material, content of volatile solids, and its initial and final moisture con- tent.
Particle size, moisture content, aa well as the carbon/nitrogen ratio
(the mixing of night soil or sewage aludge with the compoatable part of the domestic solid waste generally improves the C/N ratio) and oxygen content are the critical factors affecting the speed of the composting process and the quality of the finished compost.
A review of the available literature indicates a aubstantial varia- tion in the yield of compost, particularly from soiid waste,
For example, the research done by the TVA at Johnson City indicates a 20-30 percent reduction in total solids (after removal of noncompostables) for municipal waste com- post.
Other sources show reductions in solids as low as 10 percent (Flintoff) and as high as 50-55 percent, reports make specific reference again based on total to reduction in compostable volatile solids.
Other solids and show values ranging from 42 percent (Net0 and Stentiford) up to 62 percent
(Diaz). Still others report yields of compost based on the total waste stream, with figures ranging from 37-50 percent !Eqr);
Other factors that compound the problem of comparing these compost yields are the variations in waste composition, maturity. the final moisture content, and the
Before a decision is made on the economic viability degree of compost of composting, the yield of the proposed co-composting plant needs to be estimated based on trials that utilize the local waste atream.
For modeling purposes and 80 kilograms of night soil- l/t he input/output balance for one ton of waste is as presented in table 31.
The compost product, in addition to being a soil conditioner, have some value as a low-grade fertilizer with analysis closely correlated would to the waste input. Typical N (nitrogen), P (phosphate), and
(potassium) values for municipal waste and night soil compost are 1.3, 0.9, 1.0, respectively; however, wide variations nature of the nitrogen, much of it exist. Because ia unavailable for of the unmineralized immediate plant use
(typically, only 10 percent is available in the first year) and therefore acts much like a low-grade, elow-release fertilizer. The major value of compost is derived from its organic content which improves soil texture.
Improved soi 1 structure increases water retention capabilities resulting in either greater yields ability or lower to provide micronutrients, irrigation and/or requirements. improve utilization and enhance
(thought to be a function of slower leaching). using compost on food crops is the crop that
Other benefits come from compost’s of plant nutrients, particularly utilization waste-derived of artificial
One point fertilizers of caution co-compost
L/ The 80 kg of night soil (3% solids) added after the separation step raises the moisture content of the compoatable material to 55%. Use of pit latrine wastes or sewage sludge at 20% solid would be 140kg and increase the amount of compost to 360kg/l ton domestic solid waste.
- 52 -
Table 31. Material Balance P r
1 Ton Domestic Solid Waste a
Loss of volatited solids and water
1080 a. Assumed to have an initial moisture content of
50%. b. Rejects consist of inerts (excluding ash and fines), and unrecovered metals, glass and plastics. c. Quantity of compost produced is based on 700 kg of compostable material at 50% moiature plus 80 liters of night soil at 3% solids. During the composting process 33% of total solida are consumed and the final product has a 30% moisture content for a total weight reduction of
57%. when sewage sludge is used) may contain heavy metals (lead, cadmium, nickel, zinc, mercury) which would limit the acceptable application in the majority of urban areas in developing countries rates.
However, the potential percentage of heavy metals is negligible.
In order to preaent a wide range of composting alternatives, four different scale base case models of one nonreactor windrow, will be developed and analyzed. cornposting
The descriptions of system, the the 3- and 50- ton-per-day plants are from Flintoff (1976) for India, and the 150- and 300- ton-per-day from consultants’ work done for the recently appraised Egypt Solid
Waste Management project. Interpolation of physical components was also done as a cross check to get a degree of consistency across the four hypothetical base case modela. Financial prices ussd are based on the consultants’ for Bgypt . It should be explicitly understood that, while efforts report have been made to be realistic, these base case models are hypothetical and should be used with caution, although attempts have been made to make them as realistic as possible. methodology
Their main purpose is to allow the reader to work through the using data from his or her specific situation.
A description of these four base case models is given below in table 32.
- 53 -
Table 32. Description
D of Base Case Models
3 tans/8-hour input), day (Domestic entirely solid manual/windrow-sty waste e operations on an unpaved site of 500 m 1 , with storage tank (night soil) and a manual rotary screen (waste from 10,000 people and night soil from 160 people or sludge from 1,900 people).
50 tons/B-hour day, using a 2 ha paved site, conveyors, separator, windrow-style operations with rotary screen, ballistic storage tank (night soil), front-end loader, tractor and trailers
(waste from 160,000 people and night soil from 2,500 people or sludge from
150 tons/lb-hour operation day, windrow-style using a 18.5 ha paved site with weigh bridge, storage tank (night soil), civil works, conveyors, shredding drums, magnetic separator, baler windrow turning hydraulic machine (l), frontend loaders (2), tipper trucks (4), workshop, laboratory generator, and bagging line (waste from 500,000 people and night soil from 8,500 people or sludge from 93,000 people).
300 tons/l6-hour day, using a 25 ha site, same description as in C with two times equipment and throughput.
In addition to these windrow (periodic-turning) systems, there are at least two other viable co-cornposting systems suited for conditions in developing countries, systems. such as the
These were described static in some detail aerated pile, in chapter 3. and reactor
The basic input/output relationships are the same for all co-composting systems.
For the static aerated pile there would be minor changes in capital costs
(suction fans and process controls but no windrow turning equipment) and reduced operating costs (less turning). For the enclosed reactor systems, the capital and operating costs would increase dramatically land requirements (only for the cornposting, not maturation). but have lower
Analyses of these additional sensitivity analysis co-composting that options makes changes will in both be approximated eapital using and operating costs as outlined in chapter same for all models and technologies.
3, table 8. The physical parameters (waste input, recovery rates, and compost production) operating are the
CAPITAL AND OPERATING COSTS
Base case investment costs for the four windrow models are detailed in table
Models A and B could be constructed in less than one year, while the larger models would require a two-year construction period.
Staffing and operating coefficients are given in tables 34-36.
Estimated Capital Costs (Base Case)
(thousands of US$)
Fences and gates
Cornposting area building
Paving to roads and
Storage tank (night soil)
Conveyors and feeding assembly
Bagging plant- b/
Installation & Engineering
Training and Tech. Asst.
1311.0 a. Either tipper trucks or tractors and trailers. b. Used for fine-grade compost only.
- 55 -
Table 34. Estimated Staffing Requirements (base case)
* Nanagement staff includes some or all of the duties; supervisor, mechanical engineer, accountant, maintenance engineer, electricians and lab technicians.
Table 35. Miscellaneous Base Case Operating Requirements (units/year)
Electricity kw-hr ) liters)
Water (thousands of m3)
Fuel (thousands of liters)
Lubricant (thousands of of
Table 36. Financial Input Prices (base case)
1.6 US t/kw-hr
2.3 US t/m3
20 US L/liter l.POUS$/liter
Maintenance costs are estimated at 2 percent/year of total equipment costs.
Average financial wage rates used for the base case analysis are
$1,62O/person/year for management and $1,25O/person/year for labor.
These rates, as with other input prices, would of course vary from country to country and should be adjusted to the specific location being studied. operating cost parameters are listed in table 37.
- 56 -
Operating Cost Estimate (base case)
(thousands of US$/year)
Fringe benefits @ 25percent 2.0
Overtime 25percent 2.0
Total Plant Running Costs
2.0 l l
Management of the co-cornposting operation should be stressed, parti- cularly since the handling of pathogens is involved.
Proper training record keeping is essential to production of good quality hygienic compost. and
LAND VALUE AND LANDFILL REQUIREMENTS COSTS
The plant must also bear the cost of reject material
(amounting to at least 119 kilograms/ton domestic solid waste input). disposal
These costs will include transport
(including land), and operating to a sanitary costs. landfill facility,
For base case modeling its capital purposes the land price for both the landfill
$25,00O/hectare (nearby urban areas). and the composting
Transport facility is assumed at cost to the landfill is being assumed at a nominal US$l.O/ton of rejects (i.e., the compost plant is close to the landfill and transport equipment from the plant will be used). Typical densities for rejects, which consist primarily of inorganic waste (stones and building materials such as concrete, brick, etc.), are relatively higher
(approximately sanitary landfill
30 percent) than generally landfilled wastes. Assuming the depth is 3 meters (excluding thickness of cover material), and the rejects have a compacted density of 0.67 tons/cubic meter, each ton of rejects therefore requires l/2 square meters of land area. For without the project case a reasonable density for compacted landfilled composting/resource recovery, i.e., without project) waste is 0.5 tons/cubic
(without meter which would require 0.67 square meters of land area per ton. landfill operating costs have been estimated at US$2.43/ton
(including costs of equipment, civil works, and operations) excluding land. It is worth noting that the landfilled rejects, because of their low organic content, would
- 57 - create a landfill that did not produce methane gas.
This can either be considered a plus or a minus depending on long-term management of the landfill
(reduced risk of explosion, or lost income potential from gas recovery).
Also, for the same reasons, there should be fewer rodent and odor problems associated with the landfilling of rejects and it should be possible to use them for land reclamation (swamp, coastal) activities, which would result in almost total elimination of landfill requirements.
In addition, rejects are of very low value, they should not attract scavengers since to the the landfilling site.
Landfill disposal or a give-away program may also be required for the poorer fully quality compost used for landfill if it cannot be marketed.
Compost has been success- cover and surface reclamation of sanitary landfills in place of soil. For modeling purposes compacted compost is estimated to require transport
0.55 square and landfill meter of land operations per would ton (depth of 3 meters). be approximately
Costs for the same as for rejects.
All of the base case model assumptions (quantities and prices) are subject to a fairly high variation, and should be modified to reflect the circumstances the analysis, of any specific sensitivity project environment under review.
As part of tests will be performed to vary assumptions systematically for individual and groups of line items in the models. The intent will be to determine general viability of cornposting and highlight the key parameters.
The base case models have been developed using Lotus 123 (a popular personal computer spreadsheet) which can be modified easily to reflect particular situations.
OTHER FACTORS AFFECTING FINANCIAL COSTS AND REVENUES
In addition to the basic quantitative capital/operating parameters and prices outlined earlier, the planner must consider several other items, a few of which are discussed here.
Transport distances to the compost facility systems for domestic solid waste and night soil collection
(or landfill) and local are a major cost of any waste management scheme. These costs are not being addressed here since it is assumed that the collection costs are almost equal regardless of the final disposal method.
This is not to say that collection options should not be examined.
For example, for domestic solid waste it is generally accepted that it is more economical to separate the recoverable materials at the source, prior to mixing with the general waste stream.
Source separation or widespread scavenging would reduce the recycling revenue of the compost plants to almost zero while having only a limited impact on operating costs since sorting of rejects (with no value) must still be carried out.
Another factor to consider is the type of domestic solid waste collection vehicle.
Com- pacting trucks are generally inadequate for the developing countries due to maintenance trucks difficulties for pit latrines, and the already high density of the waste.
Vacuum septic tanks or cess pools are often very effective since they limit the health risks involved in human handling and can discharge
- 58 - the human wastes to the cornposting consideration is the organisation stations, utilisation of capital, of plant the and labor). directly. collection
Still another process (transfer
All of these will depend a great deal on local conditions and practicesl The compost plant has been assumed to be located near the currently analyze the specific situation -- it used landfill. may be less
It expensive is important to locate to the compost plant either closer to the waste generation point (lower collection transport costs) or closer to the agricultural areas (lower transport costs for the compost).
The seasonality of the waste stream will also affect the viability the compost facility.
In general, of tvo elements pertain: (1) the volume of domestic solid waste and night soil , and (2) the composition
(moisture and ash content in particular).
The design capacity of the compost plant must allov for either adequate storage and processing flexibility (multiple shifts) to meet peak utilization loads or alternative disposal vi11 also have a significant systems. impact
The plant capacity on operating efficiency.
For the purposes of the four models, it is assumed that they average 80 percent of design capacity from the year after investments are completed, and only 50 percent during in the vaste final year of construction. stream and down-time
This figure allovs for variations for equipment and site maintenance.
Another seasonal factor would be the efficiency of the comporting process during the rainy season when the vindrovs may require temporary covers or more frequent turning. In areas with heavy rain seasons, a simple roof shelter may be built
(adding throughput). to the capital cost but maximieing the potential operating
It is typical of most waste disposal operations that they operate at a loss, which is true for almost all compost operations in both industralized and developing countries (depending of course on operating costs and the value of compost and recovered materials). This net composting operating cost of domestic solid vaste disposal is generally covered by charging a “tipping fee” for accepting the vaste from the collection system. The tipping fee (if set high enough) would make cornposting a viable activity for the privateeVsector.
A waste management planner would try to set the tipping fee as far as possible below the costs of alternative disposal (dumping, landfill, sanitary landfill, incineration, etc.), yet high enough to make composting financially viable.
For the purposes of the four f’ set at US$l.O/ton waste input,-
%@ ncial models, the initial and sensitivity tests will tipping fee will be carried be out to determine the level of tipping fee needed to run a financially posting facility.
If the municipality runs both the collection operations, viable com- and cornposting the tipping fee becomes a proxy for the estimated savings on landfilling costs and allows the municipality this case, one could substitute a collection to compare the alternatives. In fee that is then allocated to the collection/disposal operations for costs recovery. be compared vith the waste generator’s willingness
This fee, and ability of course, to pay. must
A/ This tipping fee would be extremely low in comparison with that found in some parts of the United States where landfills fees for landfills or incineration facilities are scarce and tipping can range up to US$30/ton, or even higher for certain wastes such as sewage sludge.
- 59 -
The marketability and price received for compost are probably the most important financial factors. compost is very crop- and location-specific.
As mentioned earlier,
In temperate the winter demand for or tropical monsoon climates, the land application of compost may be seasonally restricted and require site. storage capacity either at the application
Compost, due to its moisture retention abilities, demand for certain higher-valued and higher-risk area or cornposting is often in greater crops*
Moreover, the quality of the compost, that is, nutrients, impact on its price, Throughout particle the available sixe, and maturity, literature, has a great the need for a well-thought-out and executed compost marketing program is stressed.
Failure to market the compost adequately has been cited as the main cause for the failure of composting operations. In many areas, compost users will need to have its use and value demonstrated to them. The demonstration of composts agricultural usefulness may be dramatic in developing countries where farmers often cannot get or do not use fertilizers or manure since the potential for incremental yield increases from using compost would be more than in other regions of the world. For existing compost plants the range of prices is from
SO/ton (actually it is given away) up to a reported US$40/ton. This range of prices certainly covers different quality composts being used for different purposes.
For base case modeling purposes, it is assumed that there are four compost market outlets (table 38).
Table 38. Compost Markets and Prices (base case)
Landfill works cover
X of Production
These prices are assumed ex-plant and would of course depend greatly on local conditions and marketing efforts.
These four market outlets would not all get the same quality compost.
The last category, landfill cover, would include the poorer quality product and in some cases would not have a value of zero, since alternative transported landfill from a significant cover may have a value , particularly distance.
The horticulture if market it must be would only get the highest quality compost. landfill cover compost are included
Costs of transport and disposal as a cost in the models. for the
The financial factor most often overlooked by planners is the working capital requirements. Working capital
(minimum resource requirements for carrying breaks down operations), into: (1) and (2) permanent variable
(seasonal requirements for such things as unsold compost). For modeling purposes net working capital requirements are estimated at one month’s gross revenue and costed in the model at a 12 percent annual interest rate (i.e.,
1 percent of annual gross revenues).
- 60 -
FROM FINANCIAL COSTS/REVENUES TO ECONOXIC COSTS/BENEFITS
The basic thrust of project economic analysis is to determine if the co-composting process is a beneficial (productive, or lover cost disposal, waste management) use of scarce resources (capital,
There are several fundamental differences in this material, process and labor). from the financial accounting system -- the object here is to quantify the impact on the economy and not simply assess the financial operations. Considerations include the
“economic” nonquantifiable cost of labor, transfer payments, and other external and effects of the project in terms of the economic costs and benefits.
The most significant adjustment to the financial base
model comes from the use of “shadow prices,” or economic conversion factors, which attempt to adjust imperfect financial market prices to their true economic values.
These financial prices often include government transfer payments, such as taxes, subsidies, and quotas , and are adjusted through their exclusion and through the use of international (free trade) border prices.
The economic valuation of goods that are not usually traded internationally (e.g., recycled goods -- paper, glass, low-grade metals, tex- tiles; compost; labor) is less refined, and it is often impossible to estimate the correct economic exchange price.
Several valuation options exist. simplest would be to assume that the economic price equals the financial
(economic conversion factor = l.O), that is, assume a free market does exist.
Another option is to value these goods in terma of other traded goods; for example, the recycled materials can be valued based on the energy saved -- the oil equivalent -- through their use in the production process. For the compost, vith more research, estimates could be made of its value in terms of reduced agricultural inputs, such as soil conditioners, fertilizer, and
increased production of internationally traded agricultural products
(vheat, corn, fruits, method -- tradable vegetables, etc.), or both. Uhen using the latter
saved or incremental tradable goods produced -- the analysis benefits. materials should
Examples include of the incremental incremental ccsts of real izing these costs include transport of recycled to the processing factory or transport and spreading for the camp09 t . methods. realistic.
There are several problems with either of these economic valuation
For each country/location a different approach might be more
Where there is already an active recycling trade, the use of market prices adjusted for macromarket imperfections makes the most sense. It is also vorth noting that many developing countries do not have internal sources for virgin materials and therefore have only two alternatives, importation or recycling. lated
In addition, conversion factor. many of these countries are extremely short of foreign exchange for imports.
This would argue for the relative economic advantages of recycling , which should be accounted for by a properly calcu-
The same is true for compost, but there will rarely be an active, significant
to be very difficult volume soil conditioner trade. to isolate the agricultural
In addition, it has value of compost vithin the extremely complex agroeconomic system, which includes sun, water,
- 61 - nutrients, soils, plant varieties, and farming methods.
However9 there have been numerous experiments that have conclusively shown increased yields, over a wide range, attributed to the use of compost. depends greatly on the existing conditions, with
The yield less impact impact of compost on high quality soils also facility and often very risky is large: resulting in dramatic to use market prices yield if increases the on poor soils. composting/resource
It is recovery an oversupply may be created and cause prices to fall. counted
It is also worth stressing here that economic benefits should not be twice.
For example, if the market price (adjusted by a conversion factor) is used to estimate economic value, savings or agricultural impact. This would one cannot be double also count counting the energy since the market price includes the consumers’ “economic” benefits of using the material or compost.
Nonquantified impacts include the project’s impact on land values and quality of life. The value of land near the compost plant may decline and values near the forgone landfill, which would now be smaller or more sanitary, may increase. particularly
Health and sanitation co-cornposting, when it benefits can result is compared with from cornposting, more traditional and waste disposal options such as open dumping of solid waste or direct land disposal of night soil , sludge and septage.
External environmental impacts of composting/resource recovery could possibly be of value. There are both positive effects -- reduced health water and soil pollution hazards and raw material needs, as well as improved soil structure resulting in less erosion -- and negative ones -- smell, leachate -- which depend on how well the cornposting operation composting facility is well designed and managed, it is is managed. expected
If the to have little if any negative impact on the environment and numercus benefits. Some of these benefits are captured elsewhere in the analysis in such things as recycled
Others are materials, not, less land such as improved for landfill, sanitation benefits are excluded from the analysis. these nonquantifiable benefits of camposting or the market value of compost. and health.
It should also be noted that may not accrue most of to the cornposting enterprise.
For any particular investment, there is also the consideration of sunk costs, for example, existing equipment. landfill operations,
For cornposting, this is not usually significant including since land and rejects would continue to be landfilled and it is unlikely that composting would handle the entire waste stream, more often being only a component in the overall vaste management scheme.
Another significant adjustment to the financial model is needed for labor.
The economic price of labor depends on the local demand curves, which in turn depend on the opportunities market supply-and- for alternative work and valuation assumption of leisure. is that skilled
For labor the is purpose in of relatively these short four models, supply, with the an economic conversion factor greater than 1.0, for example, 1.5* and that there
- 62 - is a relative surplus of unskilled labor, a factor of, say, 0.5 -- a typical situation in developing countries.
For the illustrative calculations below, capital cost estimates from the financial base case models will remain unchanged in the base case economic model a.
These costs were originally estimated in US dollars and therefore will serve as economic values ‘for our purposes.
As mentioned earlier, the labor costs for the base case economic models will be adjusted by factors of 1.5 and 0.5 for management and general labor, respectively. Fringe benefits and overtime will remain at 25 percent each, although there may be some small element of a transfer payment in the fringe benefits.
Other operating costs will be adjusted to reflect economic prices as discussed previously (table 39).
Table 39. Economic Input Prices (base case)
10 US ilyegr
2.9 US t/m
40 US t/liter
1.20 US t/liter an arbitrary
The base case financial
25 percent, price even though its for water economic has been adjusted value upward by is very difficult to estimate; in any case, it is a very small input. more significant
The price of water would be if it were used to value the compost’s agricultural input savings.
The base case economic models will value the recycled materials at the financial prices, which are rather conservative. The alternative valuation, energy saved, has been estimated for the United States (table 40). if the energy costs of mining the virgin ore are also included, the values of scrap in terms of energy savings increase. In many cases, these figures are misleading; for example, steel energy savings are dependent on the type of furnace, type of scrap, and end product. For glass the energy savings would be much greater if intact containers were recycled. of contamination in plastics greatly affect both
The type and amount the recycling options and energy savings. reprocessing,
For paper the quality thereby making it less valuable. of the fibers decreases during
- 63 -
Used to Process Virgin and Recycled Materials
Virgin ore Recycled material
(thousands of BTU/kg)
Source: Adapted from Hayes (1978).
5.7 t% 1
Assuming that the above figures are reasonable and that the marginal source of energy is imported oil, the approximate energy-based economic value of the recovered materials is shown in table 41.
Table 41. Recycled Material Valuation - Energy Based
Domestic solid waste
Plastics & rubber- b/
/1 Based on table 43 and World Bank Commodity Price Data.
/2 Calculations done as in table 32. value based on newsprint. a. No data available for rag recycling, b.
One half polyethelene.
Bxcept for glass, these energy-based valuations are higher than the financial prices and will only be used for a sensitivity test. This valuation would need adjustment for transport to the recycling plant and any processing overheads beyond the use of virgin materials. valuations
For the economic value of compost in the models, three alternative will be tested.
The compost’s economic value for a specific project area depends on its quality and ultimate use. As an upper value it is assumed that compost has value equivalent to peat, which is a
Recent peat export prices for Ireland have been about US$lO/ton,-
55 aded good. excluding transport which can be costly. small and is primarily sold to
The world the trade in. peat home garden or moss is relatively commercial nursery markets.
Compost should not be considered the full equivalent of peat moss.
Therefore, as an upper value of compost we will use the value of peat without any adjustment for transport, that is, US$‘lO/ton. structure
Compost is at its lowest value as a low-grade fertilizer; value is not included. costs were ignored. the soil
This would represent a floor on its value if the necessary transport and application
Approximate 1984 fertilioer prices are listed in table 42.
Urea (46 percent
TSP (46 percent
Muriate of potash ( i 0%
Based on a co-compost nutrient mix of 1.3, approximate value would be US$8.75/ton (igno=g
(N, P, K),- benefits
21 the includ- ing the slow-release nutrients). nature of the
The World Bank projections nitrogen and the for fertilizers value of in constant the micro- terms show that prices should rise by 37 percent for N, 12 percent for P, and 15 percent for U through 1995.
To keep the economic analysis simple, these as well as any other (energy, land) relative included in this analysis. increases
The fertilizer in economic value prices will needs to be reduced not be by the
A/ 50% moisture content fob costs 5 Irish pounds/300 liter bale. g/ If greater amounts of dried sewage sludge vere used, these nutrient values would be [email protected], but in any case they will vary depending on local waste compositioxL*
I- 65 - increased handling, transport, and application alent amount of inorganic fertilizer. This costs cost compared with is estimated the equiv- at US$2.75/ton which, when deducted, gives a low-end economic value for compost of US$6.0/ton ex-factory.
As a realistic base case value for the compost, a conservative estimate was to be used of yield increases and inputs saved that were attributable this valuation realistic to compost. Because of the many factors method is probably the least certain affecting but would crop yield, be the most economic value. For example, typical net incomes for field crops in the developing countries range between US$200-500/ha, and up to US$l,200/ha for fruits and vegetables.
The reasonable application rate of compost for vegetable crops can be estimated from the figures presented in chapter 5, table 24 and amounts to 50-100 tons every 2 to 4 years. If we assume that 25 tons/ha of compost per year allows net income to increase approximately
US$500-600/ha (switching from field crops to vegetables), ture value would be US$20-24/tan. From this figure the upper we must deduct agricul- transport from the plant and application costs. A compost value of US$ZO/ton will be used as a proxy in the base case.economic models.
This value is very subjective in that it is a substitute for input savings on fertilizer, soil conditioners, and water, which accrue over a period of years; the value of increased crop yields, which depend on the local cropping patterns, soil conditions, to achieve these benefits. etc;
For areas and the transport/application with badly overexploited costs soils and/or shortages or lack of fertilizer inputs, the yield response from using compost could be dramatic and therefore specific locations.
There is its a lack economic of data value may on the be much higher benefit of in compost resulting from the improvement of the physical structure of soil, and this may be a constraint on the increased demand for, and value of, compost.
The market outlets for compost will remain the same for the economic analysis but prices will be equal remain at zero. for all but landfill cover (lowest quality), which will landfill,
The base case economic values for other cost factors miscellaneous operating unchanged from the financial models. expenses, and working capital, will such as remain
RESULTS FROM HYPOTHETICAL MODEL CALCULATIONS
The computer model developed (using Lotus l-2-3) takes the form of a simple line-item budget covering a 2O-year period.
All of the parameters discussed in this chapter are included. equipment in year 10, with no salvage value.
The models assume replacement of
There is no. provision for re- sale of the land, or re-use of the landfill.
The base case models are built up from the financial price ass\lmptions adjusted by a factor that is set to 1, for the financial analysis, and set to the shadow economic conversion factor for the economic analysis.
These factors can readily be substituted to adapt any “base case” situation also some standard input/output to a particular operating investment coefficients situation.
There are composition
- 66 - and density
-- and four sets (one for each base case model) of physical parameters as described in this chapter.
Capital investments are assumed to take one year for models A (3 tons per day) and B (50 tons per day) with a 50 percent capacity utilization reached in that year.
For the larger models C (150 tons per day) and D (300 tons per day) investments occur over a two-year period (50 percent each year) with a SO percent capacity utilization in year 2. For the remainder of the 20 years, capacity utilization is 80 percent. investments,
Since this chapter is not intended to evaluate the financing investments. no calculation has been included for funding the initial capital of
Analysis indicators the hypothetical models. are calculated
The first at two stages is based on the “net or bottom with project” lines
(with), in which represents the compost facility would be a good indicator if the private operations sector including were running tipping fee and the composting plant but had no responsibility
“net incremental” (incr ) , which for the landfill. takes into account
The second indicator the benefits is the of reduced landfill (without project) and excludes the tipping fee (transfer
The latter situation would be typical of a situation payment). where the operations -- composting municipality. and landfill -- are run by the same entity,
Both bottom lines are calculated for the financial that is, and economic factors, although the “net with” is not really meaningful for the economic analysis.
The incremental bottom line is more relevant, even in the financial model, if the compost plant is to be run by the municipal government.
The indicators calculated for each hypothetical model include internal rate of return (IRR), net present value (NPV) per ton of domestic solid aaste, which is the cashflow NPV at 12 percent divided by the discounted
(at 12 percent) amount of waste processed (NPV/ton). This last indicator adjusts the models to a consistent used in calculating the context of this average analysis incremental it unit gives for costs comparison for utility an indication and is traditionally rate setting. In of the average cost incurred for each ton of waste processed by the co-composting operation. that
The results for the hypothetical co-composting forgone landfill
(including recovery is benefits not a financially are of recyclable counted. materials) base case financial worthwhile
It will models indicate operation even if the seems clear not reduce that co-composting the cost of waste management and more likely would only increase the financial management on municipalities. burden of waste
The base case economic analysis has similar implications and shows that co-composting is likely to be a higher cost waste management alternative than sanitary landfill. See table 43 for the base case financial results and table 44 for the base case economic results.
Sensitivity analysis on the hypothetical financial base case indicates that either the compost or the recycling revenues would need to increase by a factor of 4-S times for the composting plant
(with) to break
Recycled materials compost
Wet With Project
Table 43. Base Case Results -- Financial
NPV(12X)$/Toa Domestic Solid Waste Processed
Table 44. Base Case Results -- Economic
NPV(12X)$/Ton Domestic Solid Waste Processed
Internal Rate of Return%
- 68 - even (IRR = 12% or NPV/ton
[ 12X] = 0) at a 12 percent discount rate. The increase in either compost or recycled revenues required would be somewhat less -- approximately three to four times as high received a tipping fee equal to the forgone landfill
-- if costs the compost of about plant
(i.e., net incremental 1. A tipping fee of 14-20 US$/ton (equivalent to the net with project Loss) would be required for the plant to break even finan- cially at a 12 percent discount rate. The required increase in total reve- nues -- compost plus recycled materials -- would need to more than double from the base case for the “with project” to have a 12 percent rate of return.
Sensitivity on compost revenues in the hypothetical economic base case indicates that the use of a peat-based valuation (US$70/ton) would make
The use of the N-P-K valuation for compost results in about valuation a US$4/ton decrease for recycled in materials
NPV from the makes significant economic base case.
Energy impact on the economic base case, decreasing waste processing costs about US$7/ton in PV from the base case l
The substitution of sewage sludge for night soil would raise compost production and revenues about 7 percent.
Table 45 outlines the results of adjusting the base economic models to approximate the aerated pile and an enclosed reactor system (Model A is excluded since it is using manual processing).
Table 45. Alternative Technologies
-- Results (Economic Values)
NP'J (12%) $/ton Domestic Solid Waste Processed
(incr ) pi&
-4 a. Investment costs (excluding iand) up 60X, operating costs up 20X, Land for plant down 20%. b. Investment costs up 20% for model B and down 20% for models C & D (to reflect the addition of fans to all models and deletion of windrow-turning machines in models C & D), operating costs down 20%.
- 69 -
The reactor option is much more costly; the aerated pile costs, however, are slightly worse for labor-intensive model B and slightly better for models C & D by about US$4/ton in NPV terms than the base case economic models.
The potential advantage process is somewhat more controLLed.in of the aerated pile terms of uniform system temperature is that the achieved, which is critical in destroying the pathogens in the night soil sludge and septage and thus removing them from the environment. should be investigated as the system of lowest cost
The aerated piie when considering system co- cornposting.
Sensitivity of the economic models to Land pricing was also tested.
There was a marginal impact of higher Land prices on the models’ indicators for the with or incremental bottom lines since land is a relatively minor component of the compost plant net with project
, and increased costs there are offset by increased benefits (Landfill impact of land prices forgone) was seen in the widening in the without. of the difference
The real between the net with and net incremental indicators. The relative land valuation might
. in the situation where sanitary Landfill available within a reasonable distance to the waste source. options are no longer
Sensitivity tests on a combination of factor:3 out.
These are intended to demonstrate the potential cost were also carried effectiveness of co-composting in specific local situations that might be more favorable than assumed for the base case analysis. These sensitivity for Model A - 3tpd economic base case in table 46 below. results are presented
Table 46. Sensitivity Tests - Multiple Change
Model A - 3tpd - Economic
X Change from Base Case
Line Item Changes
Reduced Landfill costs (without project)
IRR - incremental
NPV/Ton - incremental (12%)
+ 3.0 4~1.6
Prom the illustrative calculations done here one may conclude that, if local conditions correspond to any of these sensitivity scenarios, further detailed investigation is warranted. However, any significant investment in composting should be done only after detailed analysis of potential markets and a commitment has been made to actively market the compost and recovered recyclables.
Many other sensitivity tests have been carried out and a copy of the
Lotus 1-2-3 template can be made on diskettes (one S-1/4” IBM format required) sent in by interested persons.
A short user’s manual will also be provided on the diskette explaining the structure of the template.
There are customized menus that allow the selection of model size, economic or financial prices
(factors), investments, as well as various sensitivity operating and maintenance, tests for IRR and NPV/PV on recycled materials, sales, compost sales, percent, tipping fee
+200 percent, and without project
(-100 percent, -50 percent, +lOO
+400 percent, +SOO percent).
A custom menu for printing the assumptions, or results, is also included.
For those readers familiar with the Lotus 123, any of the assumptions outlined in this chapter can, of course, be changed to allow for analyses of specific situations:
(1) where compost values (prices) may be higher than the base case assumptions because of, for example, scarce or poor quality land, large horticulture industry, or shortages of inputs;
(2) where a subset of the domestic solid waste collected may not require sorting prior to co-composting, as in produce markets; or (33 where sanitary landfill of domestic solid waste is not an option such as when there exists a high water table or scarcity of land and co-composting is thought to be a cost-effective component of the waste management.
- 71 -
Refuse collection, treatmmsnt, and disposal im one of the major problems facing urban planner8 and operator8 in auny developing countries today, in addition to the problems ammociated with inadequate treatment and
Unmightly pile8 of wamte, drains clogged with refumc and night soil,
filled with human and domemtic
meptic tank mludge duaped in the open are all examplem of
in which the urban environment is being polluted today in many citiem and towns of the developing world. City dwellarm are being exposed to dimeamem transmitted theme by pathogens present in
to the nuimancem produced by the
ituation. Further- more, the volume of wamte being produced im rapidly increaming with the influx of rural dwellerr into the urban environment. wamte management
fart becoming a priority countricm that are rapidly growing in mite.
Indeed, proper refume and human in army citiem in developing
In the preceding chapter8 , co-compomting of garbage with human wastes
been described in detail through both a review of the literature and economic and financial
models, with dimcummion centering on the following the robumtnemm of the aerobic comporting
the variety of available compomting
the possibilities of to-compomting different the effectiveness of efficient dimeame-causing organimmm comporting
in destroying the many usem of compost the economics of different-mized comporting mymtemm.
The choice of co-composting am a wamte treatlaent alternative for garbage and human wamte mumt be conridered in the light of other existing treatlaent alternatives dumping of mludge. much am landfilling, incineration, and the ocean uiatenke
Before deciding to compost, the planner mot consider and review meverai bamie faetorm aiready de scribed in previoum chapters. iafotlution on the wamte material; transport of the
and the compost that
produced ; aurrketing of the product; the conmtruction, operation, and coats; the location and land requitemntm of the plant: and the type of plant that would be moat muitable for producing comport under local conditions. If the decimion im taken to conmider comporting
an option for
- 72 - waste treatment and aunagcment, the the
theme factors will play in ensuring
of a comporting operation must be
Sow of the more significant elements are reiterated below,
It is important to determine the nature and composition of the wastes to be composted.
Such basic information will be of use later when the time
to choose an appropriate composting system.
Furthermore, it is useful to know how the collection of theme wastes would fit
the overall waste
Banagement system (e.g., landfilling and incineration) and if there are already waste-recycling activities to which this could be added, such
of garbage for recyclablea or scavenging and biogas opera- tions.
a mwket for any compost that might be produced?
horticulturists in the city outskirts who would use it to
the quality and productivity of their crops.
Maybe the public
sector is involved in a landscaping program, or perhaps there is badly eroded topsoil
sandy and/or clay soils that could be reclaimed for productive use.
The financial waste is dependent on a well-developed
production. viability of co-composting garbage and human market that is willing to pay
Next, we ask about the type of plant, taking into consideration possible location, availability of trained technical staff and manual labor, and financial resources to cover capital and operating costs, in order to determine which myrtem would be most appropriate for the city. Economic and financial feasibilitiem will be of importance in considering involved for a specific system.
The planner may often find that the costs
simple windrow or forced aeration establishment
will best suit and will be therefore most effectively the capabilities of the run.
There is aLso the consideration of the potential for manufacture nationally, requirement for foreign exchange components. thus reducing the
PILOT SCALE COMPOSTING
Once the waste materials and composting system have been identified, it is useful, if a
operation is being planned, to start with a pilot plant.
firet, the prospective operators will become familiar with the
second, it wiL1 serve
good public relations exercise to produce small amounts of compost for
or as mamples
- 73 -
BENEFITS AND JUSTIFICATION tion?
There what benefits accrue from the separation/compost are those that can be readily quantified, need for sanitary Landfill of garbage and recovrring such as reducing materials for opera- industry, the which often obviate importation
For specific waste management or mining activities, of Llimilar the industrial careful materials. integration of composting operations should allow for more efficient savings of which can easily be quantified collection and used to offset networks, the cost the of compogting. benefits
In addition, it should be relatively simple to demonstrate the of compost in terms of improved soil productivity, measured as increased yields and/or reduction of other inputs (fertilizers and water), and easier tillage. This can easily be carried out in a controlled trial using compost produced locally on a trial basis for two or three cropping seasons perhaps at the pilot compost plant.
Other benefits, longevity of the soil, in the environment, and the improved aesthetic quality of the surroundings, are difficult to quantify but are of importance in ensuring adequate mainte- nance of the environment. such as the effect of compost on the quality and the reduced health risk of having pathogenic material
There are many examples in the world where the high costs of environ- mental degradation are plainly seen with hindsight but were not quantified at a time when something could have been done to prevent them.
The valuation of productive soils in the future may be much greater than we now can quantify and, with hindsight, composting may eventually look more attractive.
Situations in which the economic models will show that composting is economically viable or the least-cost waste management alternative are quite site-specific. Where landfilling of waste is very costly due to high land values or high transport costs, composting may become the Least-cost alter- native for waste management. Often the composting plant can be Located in much a way as to reduce collection and landfill costs, both of which should be included as benefits when evaluating tives. The marketability for least-cost the compost waste is the other management critical alterna- benefit, At the present time horticultural nurseries in peri-urban areas and desert land reclamation areas offer the best economic returns.
It is possible, however, that the economic benefits from improved soil structure are considerably greater report than has been generally does not attribute appreciated, although the analysis in this any specific economic value to such improvement, simply because there is a lack of empirical field data from which to quantify economic returns. Were such quantification to be available, it is Likely that the models prepared for this report would show that composting is also economically attractive under ather conditions.
To embark on a large compo;;rting operation is to embark on a Long-term activity which ensures both the improvement of soil for agricultural purposes, at a time when increased food production is so important, and the conversion of waste materials into resources.
OTHRR NETNODS OF CPCOHPOSTIlG MITE SWACB SLUDGE AUD BIGHT SOIL
SEWAGE SLUDGE AND NIGHT SOIL COMPOSTED WITH BARR
The composting of sludge and night soil together with bark is carried out in course, both reactor and nonreactor on the availability systems. The use of bark depends, of of the material (for example, on the location of a wood-processing plant in the vicinity or within easy transport distance).
Table A-l describes some of theme systems.
In all cases, the temperatures achieved during the composting period would indicate adequate pathogen removal. In compost plants where bark is used a-8 a bulking agent, odor control does not appear to be a problem, possibly because of the odor- absorbing properties treated with pesticides, of the bark. Problems can occur if the wood ham been since they may persist in the compost.
SEWAGE SLUDGE AND NIGHT SOIL COMPOSTED WITH STRAW
Straw is a waste material that is readily composted with sewage sludge in reactor as well as nonreactor systems. The examples described in table A-2 are of both types (though mainly the Latter).
The use of straw in composting is common in farming communities but is not Limited to them. As table A-2 indicates, a windrow compost product can be ready within 4 months of starting the process.
Forced aeration would speed up the composting process.
The Beltsville aerated static documented and reviewed in the literature pile composting process is well
(see, for example, Nurizzo 1981).
The windrow method of composting sludge with wood chips is also well documented. The two processes are similar in terms of product quality but the windrow method appears to be more suitable for digested than for raw sewage sludge.
The forced aeration process is also used for composting night soil
(Patterson and Rogers 1979; Shuval, Gunnerson, and Julius 1981).
Night soil end bark
Sludge end bark
-we, sludge, end bark
Raw deretered sewage s I udge end berk
Dewetered sewage sludge end berk tend recycled wPost)
- 76 -
Table A-l. Colposting of Sludge and Night Soil with Bsrk
WY bmar toi let open baskets
W i ndrows
Verticei reactor with 10 levels
Bark was added to night soil in dry toilets et the rate of 4 parts bark to 1 part night soil.
Tefsperetures of over 60° C were achieved.
Bark end sludge (end other wastes) were mixed together end conposted to produce w&ebe,w a market- able product.
Dewetered digested sewage sludge was mixed with bark (1:3) end -posted in large besksts that could be easily stacked.
Temperatures of up to 75’ C were ette i ned . The retention time in the baskets was 9-12 weeks followed by 3-4 weeks maturation in piles to produce wRindekcepost.w
Dewetered sewage sludge (25 percent solids) mixed with bark (1:3) and composted in wlndrows for at least 21 days.
In general, tempere- tures of 50-75’ C are mein- telned for et least half of this time, although it is less in the winter.
Dewatered sludge (22-25 per- cent solids) is mixed with bark (2:l) and fed into a
IO-level reactor. Retention time Is 50 days end ntove- ment from level to level through traps in floor occurs every 3 days. Tw- peretures are usually mein- talned et 70° C or higher for about 10 days end over
50 ’ C more than 15 days.
Wesner f 1978 1,
(19801, Tebessren et al. (1981)
Raw dewstored sewkge sludge end strew
Raw dewetered sewage sludge end strew
Digested sludge and strew
S-age sludge end strew
Table A-2. CarpostIng of Sludge end Night Soil with Strew
W i ndrows
WI ndrows eiaist w i ndron
(Full-scale plant.) experimental
The sewage sludge
(25-30 percent sol ids) was mixed with strew (1:l volume) end composted in windrows, which were turned regularly (8 times) for 3 months.
At the end of this time the compost was reedy for use.
55-60° C were regularly achieved even in some of the colder glonths.
Experiments. The sludge
(21.8 percent sol ids) was mixed with strew et a ratio of (28:l). Temperatures of
55-62’ C were maintained in windrout, which were turned once weekly for 3 months (in earlier stages there were problems with fly control 1.
Exper i ment .
Digested sludge was mixed with strew et a ratio of
1:1.25 in windrows for 6 weeks during which tempere- tures of 65-70’ C were ech loved as above, except the retlo of mixture was
1:s of sludge to straw.
The strew is chopped and mixed with the sewage sludge and then sprayed a windrow. out into
Bldlingmeier end Tebesaren
Streuch, Berg, end Fleischle
Bidl lngmeier and
Isusterer (1979 1
- 78 -
Table A-2 (cont.)
Sewage sludge and strew
Dewatered sewage sludge is mixed with chopped strew (end/or other bulking agents) end fed into the reactor, which has a reten- tion time of 34 days.
Bidl ingma ler and Dicke #I (1980)
Sewage sludge and wood chips (rindrow)
Table A-3. Description of the Deltsville end Windrow Cumposting
Aerated Static Pile
Process description Reference
Sewage sludge and wood chips (aerated pile)
Night sol I (toi let wastes 1, paper, waod chips (aerated
Dlgested sewage sludge is mixed with wood chips (1:3 volume ratio) in windrows 1.8 meters high and 2.1 meters wide. The windrows are turned daily for et least 2 weeks, then they are spread outp dried, end cured for
30 days. The wood chips are screened out for reuse.
Raw sewage sludge(22 percent solids) is mixed with wood chips, and then transferred to a composting pad consisting of wood chips spread over perforated piping. Air is drawn through the pipe into a compost filter, The pile is mainteined for 21 days followed by screening end drying. Tempera- tures of 55’ C are achieved throughout the pi le.
The night soil is mixed with paper end wood chips on a concrete pad end then transferred to the can- posting pad, which is a bed of wood chips covering a perforated
Air is drawn through the pipe into a compost filter. The pile is mrinteined for 21 days at temperatures of 60’ C for most of this time. The compost is then cured for 30 days.
- 79 -
The two processes using sewage sludge are described briefly in table
with a process using night soil (from chemical toilets). It
be noted that it is not essential to use only wood chips in the
Beltsville process; other organic bulking agents (for example straw,
Detailed experiments carried out on pathogen
the Beltsville efficient at aerated pile process have shown it to be
the pathogen content of the product (Burge,
Barsh, and Millner 1977; Burge and Millner 1980).
materials have been composted together with sewage sludge and night soil.
Some of these are described in table A-4 to show the versatility of the process. sludge
night soil. effects on pathogen control. animal wastes are composte.1 together with
As noted in chapter 3, this should have no adverse
Table A-4. Rethods of Cunposting Sewage Sludge with Other Bulking Agents
Process Description Reference
Biolnist w I ndrow
The mixture w I ndrow . is sprayed out onto a
Sludge, mush- roam wastes, poultry wastes, organic bulking en* w
Raw sewage sludge end sewdust end recycled c-P=*
Kneer bioreac- tor (EN system)
BAV bioreac- tor
The mixture is retained in the reec- tor for 14 days. Temperatures of
60-85’ C are maintained for most of this time.
Then the raw compost is matured for 6-8 weeks in a windrow.
Cawatered raw sewage (25 percent solids) is mixed with sawdust and return compost (50, 10, end 40 percent, respectively) and fed into a cylindrical reactor, which is open at the top. Retention time is
3 days. This is followed by 6-8 weeks of maturation in windrows.
Temperatures of 75-80’ C are reached.
Bidlingmaier and Tebasaran
Tabesaran et al.
Table A-4 (cont.)
Ran semage sludge and peat, straw lignite.
Raw sewage sludg8 and sawdust and recycled f=P=t .
Swego sludge end p8et
Sewage sludge end rice hulls end recyci8d capost kwage sludge end shrsdded papsr
Sewage s I udg8 end ssrdust
BAV bioreac-- tor
WSiS bioreac- tor
As abov8, except mixture is 1:l.
Biohum process w i ndrow
Feirf ield digester reactor
Trlge process eel I reactor
The dewstored sewage sludge cent solids) and recycled
(25 per- is rpixed with sawdust compost and fed into a closed cylindrical reactor, mhere it is retained for lo-14 days.
The raw materiels are mixed together end ccmposted in a w I ndrow .
The digested s8wage sludge is mixed with rice hulls end finished compost
(1:l:l volume) and fed into a trough where it is composted for 2 weeks by forced aeration end turning.
This Is followed by l-2 months of meturet ion.
Temperatures reach up to 7o” c.
Dewetered sewage sludge Is mixed * with shredded paper end fed into a reactor. The retention tlme is
7 devs anr! temeeretures reach
70° C during rhls time.
The sewage sludge (15-20 percent solids) is mixed with sawdust at a retio of 1:s wt end fed into a vertical reactor consisting of four cells. The retention time is
12-15 days and t8mperetures of
70-80’ C are achieved. Metura- tion occurs in piles fin a shed)
In which tecnperetures often reach so0 C.
Bldlingmaier and Bickei
Bidtingmeier end Tebassren
Tebaseren et al.
- 81 -
Table A-4 (cont.)
Sewage sludge and sawdust
(and other bulking materiel)
Water hysc 1 nth , night soil, rice strew
Night soil rice husks, grass cutt i rigs, briquette c i ndsr
WI ndrow/ pi ies
Windrows eerat ion by ver I ous methods
The windrows are turned for 3 months and then sold es a product ‘Grow
Rich.” The contents of the windrows are dewatered sewage sludge (30 per- cent solids) end sawdust et weight ratios 80:20.
The maximum tempere- ture achieved Is 74’ C.
Experiment. Night soil, water hyacinth, end fin some cases) rice strew were mixed end com- posted in piles for 2-3 months.
Temperatures of 43-64’ C were maintained for et least 8 days in the coolest parts of the piles.
Night soil is mlxed with different amounts of rice husks, grass cut- tlngS, or briqU8tt8S Of cinder into w I ndrows.
These era aerated by various fII8thOdS.
Temperatures of up to 70° C are achieved end
HO0 C maintained for et least
Poipresert et al.
Kim end and Bee
- 82 -
SENAGE SLUDGE MD NIGHT SOIL COMPOSTED
WITHOUT THE ADDITION OF BULKING AGENTS
The processes described in table A-S indicate some of the ways in which sewage sludge or night soil can be composted without the addition of any bulking agents .
In all the examples given, the sludge has to be dewatered before being mired with the recycled compost. (If night soil is used instead, some dewatering may also be required.)
The temperatures camposting in the examples given here should be sufficient relatively pathogen-free achieved to during ensure a product if they are maintained for almost all the retention time and are kept uniform throughout the reactor.
Table A-5. Uethods of Composting Sewage Sludge end Night Soil Alone
Process Description Reference
Sewage sludge and recyclad capost
Dlgasted sewage sludge and recycled compost
(also same sawdust 1
Sewage sludge end recyc I8d compost
Dewatered sludge cake was successfully composted in a laboratory scale reactor in which temperatures of 60-70° were maintained.
D8WOt8r8d digested sewage sludge (20-25 percent solids)
IS mixed with recycled CU8pOSt in a vertical reactor for 14 days.
Temperatures of 60-70’ C are reached. The air drawn out of the reactor is passed into en activated sludge tank. MetUra- ration of ccnnpost takes place for
6 weeks in windrows.
The sludge end recycled compost are added to a slowly rotating drum (which is stopped at night). The retention time is 24 hours followed by a P-week maturation period in a windrow. Temperatures of 60-75’ C are attained.
Beeder ( 1979)
Bidi ingme ier
Bid1 ingme lier and Bicke ‘I
Table A-5 (cont.1
Dawetered tswege sludge end r8cyc I ed compost
Sewage s I udge fdewetsred 1 end recycled capost
Dawetered sewage sludga end r8CyClbd caapost
Raw or digested sewage sludg8 end recyc I8d capost
W 1 ndrow
Roed i ger
Ferment- techn i
(Pi lot plant) k
Forced eeret ion through fermenter
The sewage sludge is mixed with recycled compost et a ratio of 3:2 end deposited es a windrow, which Is turned by a cueposter for 4 weeks. This is followed by 30 days of metu- ration.
The sewage sludge is mixed with recycled compost and put in a vertical reactor.
The retention tlma is 4-6 days, efttr which the compost is put in J dryer for a further
4-6 days; it is then pelleted end stored for sale.
Tempere- tures of over 65’ C are attained in the reactor.
The sewage sludge end recycled compost are mixed end ground and fed into the fermenters, where the mixture is OOrOt8d and turned.
The retention tlm8 is 10 days end temperatures of up to 7S” C are attained. The compost is then graded end begged.
The dewetered sludge is mixed with recycled compost and fed into a vertical reactor consisting of two levels.
Retention time is 7-9 days, during which t8mperatures of
65-70’ C are r88Ch8d end malnteined.
Tebeseran et al.
Bidlingmeier end end Tebaseren
- 64 -
Table A-5 (cont.)
Raw sludge and recycled
Digested or condi- tiowd sludge and recyc 1 ed compost
Pel lets in piles
The dewatered sludge (60 percent moisture) Is mixed with finished compost three parts to two and the mixture is laid as a windrow over a bed of straw on a con- crete floor having an aera- tion-and-drainage systam. A
Cubey cunposter is used to mix the motorists, The retention tima is 4 weeks, followed by 50 days of curing. Temperatures resch 76’ C during this time.
The sludge is dewatered and passed through a mincer to make pellets. These are piled for up to 8 weeks after mixing with recycied ccmpost.
- 85 -
E. coli kfycobac- terium tuberculosis
Table B-l. Survival of Bacterial Pathogens during Cornposting
Refuse/sludge in reactor
Refuse/sludge in windrow
Refuse/sludge in reactor
15 days days days
12 days days
Dewa t ered raw sludge and wood chips in windrow
Refuse and sludge in drum
Night soil and 29 rubbish in
40 pile, aerobic and anaerobic
Raw sludge, digested s Ludge
14 days days days days days days
Burge et al.
(cont. ) and
- 86 -
Salmonella dub1 in
Refuse and sludge in windrow
Refuse and sludge in reactor,
H20, 15 square centimetera
Refuse and sludge in windrows
Activated and primary sludge windrow
Refuse compost 55
Refuse and sludge in windrows
Sewage sludge 50-70 and wood chips
Refuse and sludge windrow
8 days l-5 weeks
Survival high x
65 2 weeks
Knoll (19591, quoted Wiley
Epstein et al.
- 87 -
S. sef tenburg
Feces and garbage windrow
Refuse and sludge in reactor,
48’ C to HZO, 15 centimeters
Refuse and sludge in windrow
Night soil and garbage
S. typhi- murium
Refuse and sludge
Sh. dysen- teriae
- not stated.
17 hours l-3 days
Savage, Chase, and MacMillan
Savage et sl.
Chinese Academy of Sciences
Golueke et al.
Feachem et al.
- 88 -
Bacterio- ehage f2
Survival of Viral Pathogens during Cornposting
Sewage sludge and grass, sewage sludge and refuse
Sewage sludge and wood chips, sewage sludge and wood chips turned once
2 weeks and 70 days
Raw sludge and wood chips, digested sludge and wood chips
Coliphage f2 Sludge and wood chips
Poliovirus 1 Sewage sludge mesophi- lit
Poliovirus 1 Refuse and sludge
Cramer, and Burge
Burge et al.
Gaby (1975) Poliovirus type 2
Sludge and refuse mix
- not stated.
- 89 -
Table B-3. Survival of Protozcel P&hogens during Cornposting
Vegetable matter and feces
Refuse and sludge
7 weeks days days
- 90 -
Survival of Helminthic Pathogens during
Ascaris Night soil lumbricoides and garbage ova
Ascaris Feces and lumbricoides vegetable ova matter, soil ash
Ascaris lumbticoides ova
Ascaris lumbricoides ova
Garbage and night soil
Hookworm ova Night soil
N.americanus Night soil
- not stated.
LOS days days
Academy of Sciences
- 91 -
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