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Newsletter and Technical Publications
<Municipal Solid Waste Management>

Sound Practices
Composting

1.4.2 Sound technical options

Composting in industrialized, transition, and developing countries

The process of composting is similar in all areas of the world, but there are practical differences in industrialized, transition, and developing countries. The main differences relate to the waste stream to be composted, the agricultural traditions relating to production and use of compost, and the physical infrastructure of the built and natural environment. In relation to composting, transition countries are more like industrialized countries in relation to their infrastructure, but more like developing countries in relation to their waste streams.

Siting and scale of composting

General siting considerations
Most compost systems require open land for establishing and manipulating compost piles. In many ways, the kinds of land and sites available dictate the choice of composting system. Sound practice in siting for facilities other than backyard bins includes:

  • selection of a site with suitable access for the form of transportation;
  • availability of a buffer area between the site and nearby land users, to minimize the nuisance of waste and compost odors;
  • appropriate soil for absorption or collection of leachate; and
  • the possibility of placing the compost in a building, in cases where there is a need to control climate or a greater need to buffer the surrounding environment.

Backyard composting
Backyard composting can be both an individual strategy for management of household kitchen and garden wastes and a formal strategy for the management of the organic waste stream in a region. The Source Book discussion refers only to the second aspect. Backyard composting represents the smallest scale of composting and is a sound approach when:

  • a significant number of households have individual or collective yards or gardens, and there is enough room for a compost pile;
  • composting is culturally familiar to most people; and
  • the waste stream to be composted contains primarily vegetable matter, since it is easier to control rodents and insects when little animal matter is present.

 

Organic Farmer in Tokyo
This organic farmer in Tokyo collects the garden waste of neighbors and food wastes from restaurants, and even grinds up restaurant chopsticks for his compost heap.
(credit: Chris Furedy)

Decentralized neighborhood-, block-, or business-scale composing
The next larger scale for composting is the neighborhood-, block-, or business-scale composting site. Such facilities can provide a waste management opportunity to a small group of people at a relatively low cost. Small-scale composting uses the wastes of a number of households, shops, or institutions; the composting is done on unused land, beside community gardens, or in parks. This may be called multi-source or decentralized composting, in contrast to backyard composting, where the wastes are from one source. These sites, which usually process less than five tons of waste per day, can be smaller than municipal sites and generally reduce the need for movement of compostable materials.

Sound practice for siting neighborhood composting sites requires that they:

  • be accessible to all who want to use them;
  • be clearly designated with signs that all users and non-users can read or interpret;
  • be sited with the agreement of the surrounding land users;
  • have adequate fencing or control to prevent their becoming an open dump; and
  • have appropriate soil to absorb leachate.

For neighborhood compost piles to work, there must usually be a compost monitor or supervisor within the user community who takes responsibility for maintaining order and cleanliness. Sound practice generally requires backup from the municipal government in terms of technical and logistical support for removal of undesired items or turning of the piles.

Decentralized composting on the village and community scale
Composting is clearly a sound practice for management of compostable waste streams at the village or community scale. Centralized composting of this type, whether privately or publicly developed, must come under the jurisdiction of the municipal or community authorities, who accept responsibility for its operation. These facilities will generally be in the range of 2 to 50 tons per day, depending on the size of the community and the proportion of compostable materials in the waste stream.

Siting is important, and sound practice requires that the compost operation follow the siting guidelines listed above for neighborhood composting. At this scale, it may also be necessary for the site to accommodate more turning, processing, screening, and storage of the compost than at smaller scales.

Centralized composting at the municipal scale
Centralized composting refers to composting of animal and plant wastes from multiple sources, where the wastes are transported from several points to a facility that can receive 10 to 200 tons per day.

Municipal-scale composting plants receive wastes from a single jurisdiction, usually a city, sometimes including associated suburbs or squatter settlements. Municipal-scale centralized plants are distinguished from regional facilities by differences in scale, management, financing, and siting. At this scale, sound practice for siting of the compost facility in industrialized countries must usually be a formal process that includes:

  • a technical assessment of the area, soil, and geographic attributes of potential sites;
  • the involvement of engineering and design professionals in site selection and design;
  • environmental assessment of the potential sites;
  • a formal evaluation and selection process to involve all stakeholders,
  • a formal remediation or compensation program to minimize and/or compensate for nuisance effects of traffic, odor, leachate, and noise at the composting site;
  • a separate collection and/or pre-processing system to ensure that only desired materials actually enter the compost system itself, with appropriate attention to the role of waste pickers or the informal sector in pre-processing and recovery of non-compostables; and
  • a formal system for using and/or marketing the finished compost.
Compost Windrow
Turning a compost windrow with a front loader. Waste pickers have removed non-organics.
(credit: Chris Furedy)

Centralized composting at the regional scale
Centralized regional composting facilities generally have a design capacity of more than 50 tons per day, and as much as 1,000 tons per day. In addition to the siting and design requirements cited above, sound practice for regional scale composting includes:

  • a siting process that takes into account the equity effects of siting a compost plant for many jurisdictions within the boundaries of one of them. A frequent strategy here is to distribute the sites for landfill, compost plant, and incinerator (if part of the system) between different municipalities.
  • agreements between the participating municipalities or jurisdictions for siting, design, financing, operations, maintenance, environmental compliance, and billing for services;
  • enforceable protocols for the quality and composition of the compostable materials delivered to the facility, since a failure of separation from any one source can contaminate the compost for all participating jurisdictions;
  • agreements between the jurisdictions for use, take-back, and marketing of the finished compost;
  • waste delivery agreements and commitments from the various participating jurisdictions; and
  • designated routes for delivery of compostables.

Composting at landfill and incinerator sites
Particularly in developing countries, but increasingly in industrialized countries as well, composting facilities may be located at landfill sites. This allows separately collected organics or yard wastes to be processed at the landfill. Siting is simplified or rolled into the landfill siting process.

Sound practice here differs in industrialized and developing countries. In industrialized countries, sound practice will usually require that the composting operations be separate from the landfill, have their own scale or separate entrance, and that the resulting compost be split between low-quality product used in landfill operations as daily and final cover, and high-quality for other uses.

In developing countries, where the waste stream has a sufficiently high proportion of organic materials, wastes may be left to decompose at the landfill or dump. In such cases of Ònatural composting,Ó sound practice requires a clear decision about the role of decomposition processes in landfill management, including a decision whether or not to remove the top layers of material once they are partially decomposed, either for further composting or for use in agriculture, and whether to allow farmers to remove compost from the landfill or dump.

Waste stream and separation protocols

Waste stream of industrialized, transition, and developing countries
Industrialized and transition countries have more mature urban infrastructure, and a more clear separation between urban and rural food production practices. Developing countries tend to have more agriculture and horticulture within urban limits, providing a ready market for compost as either a soil amendment or a fertilizer, depending on its organic and nutrient content. Developing and transition countries tend to have a higher proportion of vegetable and animal wastes, sometimes as high as 90%. When non-compostable materials are recovered by waste picking, source separation, or pre-processing at a compost facility, these waste streams are highly compostable.

People in industrialized and transition countries are also more likely to keep their yard wastes separate, while in developing countries these are likely to be mixed with other household wastes.

Yard waste composting
The composting of yard wastes at almost any scale is a simple aerobic process. The carbon-nitrogen ratio of yard wastes allows them to be composted without difficulty, although in many climates the moisture and air levels must be managed. Water must be added in many temperate climates, while in rainy climates the material requires drying, frequent aeration, covering, or the addition of paper or woody materials to reduce moisture content.

Sound practice in preprocessing of yard wastes, if required at all, is usually limited to shredding or chipping of larger woody wastes. For most yard wastes, sound practice dictates composting in active windrows (large, elongated piles which are watered and turned to maintain adequate levels of oxygen and moisture).

In temperate climates, collection and composting of the annual leaf fall from deciduous trees and bushes represents a significant logistical and operational task for municipal governments. Sound practice, as in any composting operation, integrates the set-out and collection requirements with the composting process, to make sure that what gets collected can be composted. For example, after a number of frustrated attempts to achieve leaf composting with plastic bags, many North American municipal governments now require leaves from the autumn leaf fall to be set out in compostable paper bags.

Kitchen waste and source-separated organics
Vegetable and animal wastes from kitchens in industrialized and transition countries represent a highly compostable stream, but one which requires more careful management than yard waste. In these countries, kitchen wastes are only compostable if they are separated from mixed household or commercial waste and held for collection (or backyard composting) in a separate container. In developing countries, kitchen wastes represent such a large percentage of overall household waste that it may be thought that separate containers are not necessary. This becomes problematic if more contaminants enter the waste stream.

Depending on culinary traditions, the carbon-nitrogen ratio of kitchen wastes may be ideal for composting, or it may be too high in nitrogen (protein, from meats, dairy products, and certain green vegetables). Too high a protein content can complicate the composting activity and lead to unpleasant odors. One sound practice to minimize this is to restrict composting to only vegetable materials. While increasing the ease of management, this decreases the fertilizer value of the resulting compost.

The addition of yard waste to kitchen waste streams generally increases the carbon level and decreases the moisture content, improving compostability.

European biowaste composting. Northern European countries, in particular Denmark, Germany, and the Netherlands, have developed a particularly sound practice in their system approach to composting of separate kitchen and yard waste, which they call Òbiowaste.Ó This practice entails the use of a modular in-vessel composting system, followed by a period of composting, either in (a) aerated static piles (piles that are not turned, but that instead use forced aeration to bring oxygen to the waste) or (b) active windrows. In either case, several months of curing are needed prior to processing for market. The finished biowaste compost can be sold for a mix of agricultural, horticultural, and civil engineering uses, ranging from application on farmland to highway berms.

Kitchen waste composting versus animal feeding in a wastemanagement system. There are many viable systems to feed kitchen waste to animals or to collect it for livestock feeding. In terms of the waste management hierarchy, this represents a higher use of kitchen wastes than composting, as more of the nutrient value is productively used. (There are, however, considerable health risks in feeding wastes to animals.)

Whenever a compost system is being planned, it is important to evaluate the extent to which compostables are already being diverted to animal feed. Municipal authorities are sometimes unaware of these processes. If people need their kitchen wastes for animals they are unlikely to cooperate with centralized composting systems. In developing countries, disruption or replacement of animal feeding systems with composting does not usually represent sound practice.

Wet waste
A variation on the composting of kitchen wastes is to identify and separately collect a wet waste stream for composting. This approach was tried in the late 1970s and early 1980s in Europe and rejected in favor of the biowaste systems, which deliver higher quality compost. Designation of wet-dry systems for collection is not considered a sound practice.

Mixed solid waste
Composting of mixed solid waste is a controversial topic. In industrialized and transition countries, the waste stream is generally too diverse and contains too many metals and plastics to allow mixed-waste composting to be considered a sound practice. Technical approaches to mixed-waste composting have relied heavily on mechanical pre-processing and separation systems. These have generally failed to operate or to produce either a clean stream of compostables or marketable recyclables. In developing countries, the waste stream contains high levels of organic wastes, since the main non-compostables are not thrown out or are picked out prior to final disposal. The resulting waste stream is highly compostable, and composting it using low-technology can be a sound practice, especially when urban and peri-urban agriculture provides a strong demand for the resulting compost.

Wastewater sludge and human fecal matter
Wastewater sludge, septage, and human fecal matter are high-nitrogen materials that can be aerobically composted under certain circumstances. They are high in moisture, sometimes actually liquid, and composting can only work if they are combined with carbon sources such as wood or paper and bulking agents, such as chipped wood or rubber, which are dry and maintain air spaces in the compost piles.

Anaerobic digestion of these materials can also work, and is a sound practice on farms in industrialized countries. It is operationally more difficult than aerobic composting. Alternatively, sludges can be left to dry into cakes which may be used as fertilizer (but see cautions, below).

Sound practice in handling these materials requires adequate attention to the health and safety of the workers and surrounding environment. The use of shoes and gloves, and the provision of facilities for washing after work, are important elements of sound practice. Government guidelines for safe composting of these materials often requires that each batch of compost be allowed to ÒcookÓ at temperatures of 50Ð55¡C for three or more days.

The main problem with composting of wastewater sludge is that the wastewater usually includes both industrial and residential discharges. In most countries, wastewater from urban sources may include metals and contaminants that affect the quality and safety of the resulting compost. This can result in a situation where the compost is too contaminated and must be landfilled, at a high cost.

Sound practice in composting these materials is almost always dependent on the presence of an industrial wastewater pre-treatment regimen, and on careful monitoring of the compost.

Manures and animal wastes
Manures and animal wastes have been composted for centuries. Manures are high in nitrogen, but most bedding materials are carbon sources, so manures bedded on straw, wood, plant wastes, or paper are easy to compost. Most manure composting begins with a hot aerobic phase, which is followed by a slow vermicomposting (worm culture) phase. Manure composting produces excellent fertilizer that is important for sustainable agriculture.

Separation and collection systems

In most developing countries, lack of economic and environmental motivation means that it will be very difficult, if not impossible, to explicitly promote source separation of compostable materials. Nevertheless, since the success of composting systems and the quality of the compost depend heavily on the materials that are composted, a separate collection system for compostables would facilitate the production of high-quality compost. Community collection bins for compostables are one possibility and may, under certain circumstances, be easier to implement than household collection of compostables. To date, success is reported primarily for the collection of organic wastes from large food markets.

Support for or enhancement of existing materials recovery systems, both formal and informal, will enhance the compostability of the urban waste streams.

Sound compost technologies and technical options

All composting processes consist of bacteriological decomposition of the waste materials. The differences in the systems described here relate to the management of that biological process, to its speed and temperature, and to the strategies for controlling moisture and aeration, and not to the decomposition process itself.

Technical aspects of the composting process
Volume reduction in composting. All true composting processes result in volume reduction, since the action of the bacteria transforms materials into steam and gases, while insects and microorganisms also feed on the organics. Additional volume reduction occurs due to removal of non-compostables during pre-processing or final screening, in addition to the moisture loss and volume reduction during composting itself. Thus a 100-ton-per-day facility will produce only 30 - 50 tons of compost per day.

Duration of composting. Composting is completed when the compostable mate-rials have been completely converted to humus. Stability of compost can be tested by re-wetting the material and observing if it heats up again, which indicates that there are still uncomposted materials in the pile. Most aerobic composting systems include a period of active composting, generally from 21 to 60 days, and a period of curing, generally from 6 to 24 months.

Composting can be accelerated by intensive aeration and inoculation of the piles with suitable bacteria. More land is required when the period of composting is longer because the throughput of wastes is slower. In places where land for siting is scarce, sound practice may entail selection of more intensive management practices instead of more extensive land use.

Small-scale composting of animal wastes
Composting and digestion of bones is carried out as a small industry in some developing countries. It can produce ingredients in the manufacture of fertilizer, animal feed, and glues. The traditional methods of sun-drying, breaking up bones manually, composting in pits (sometimes with the addition of household organics), and steam digestion carry various health risks, and cannot be considered a sound practice.

Small-scale aerobic composting of animal wastes, including manures, hide scrapings, and tannery and slaughterhouse wastes can also produce fertilizers, but carry some pathogenic risks. All of these types of small enterprises generate leachate and associated bad odors, and are typically associated with poor working conditions and risks to worker health, but may be profitable and provide subsistence income. Sound practice could include introducing technical and health improvements, rather than eradicating the activities themselves.

Coordinated backyard compost systems
Backyard composting generally consists of household-level aerobic decomposition of household organic garden and kitchen wastes, with the resulting compost being used in the yard itself. Close proximity of yards to each other in many neighborhoods in both industrialized and developing countries implies a need for management of the compost for vector and odor control, including periodic aeration or turning.

In recent years, a number of governments in industrialized countries have treated backyard composting as a means of waste reduction, since the materials which are composted remain at home and do not enter the municipal waste stream. Sound practice in organized backyard composting systems includes the following:

  • government purchase or subsidy of backyard composters, which contain the waste, prevent animal raiding, and facilitate aerobic conditions; and
  • an intensive program of public education, usually including the visit of a volunteer or paid trainer to each individual household.

Such backyard composting and mulching programs, which have operated successfully in Northern Europe, North America, Australia, and New Zealand, are much less costly to a community than centralized compostable collection programs. They have participation rates approaching 30%, with significant results in terms of wastes diverted from the municipal waste stream.

Particularly in developing countries, rodents and vectors are a concern in cities with high pest populations. Consequently, municipal health officers frequently advise against backyard composting, and in some places it is prohibited by the health code. The screens on vermicompost pits in Bangalore to keep out rodents are a visible reminder to the public of the need for careful management of backyard and neighborhood composting.

Pre-processing
Pre-processing is a technical component of almost all composting systems above the level of backyard composting. Pre-processing is usually necessary to create the conditions for bacterial action.

Pre-processing consists of three separate types of operations:

  • separation or removal of oversize, non-compostable, or dangerous materials;
  • size reduction, through chipping, grinding, or shredding, to create many small particles suitable to sustaining bacterial action; and
  • blending and compounding, to adjust the carbon-nitrogen ratio, moisture content, or structure of the materials to be composted.

Mechanical pre-processing is often the most costly part of a composting system, as well as the most vulnerable to breakdown. For this reason, sound practice in composting involves minimizing pre-processing to the greatest extent possible by pre-selecting the waste streams to be composted through source separation and separate collection.

Windrow and active pile systems
A sound, simple form of composting involves building piles of compostables. The piles, called windrows, form the basic environment for compost bacteria and other organisms to perform decomposition. Important considerations in planning windrows include:

  • the size of the windrows, which must be of sufficient mass to allow for heat build-up. The composition of the wastes and the climate are the two primary determinants of windrow size.
  • the shape of the windrows, which is related to the type of aeration that is used and the type of equipment used to aerate;
  • whether the windrows are open or covered, which depends on the climate and the moisture content of the waste; and
  • the spacing of the windrows, which is dependent on the size of the site and type of equipment used.

Active pile systems require manual or mechanical turning of the windrows, with crews using shovels or rakes, or with equipment such as a bulldozer, tractor, or windrow turning machine. Turning aerates the piles, blends the materials, brings about additional size reduction, and prevents excessive buildup of temperature to the point of spontaneous combustion. In developing countries, waste pickers may be allowed to work over the windrows to remove recyclables and pieces of wood, as was done in a windrow system in Kathmandu in the early 1990s.

An active pile system:

  • has relatively high land use requirements;
  • uses a varied amount of labor, depending on whether turning is manual or mechanical;
  • has low capital cost and low-to-moderate operating cost;
  • can be developed without purchase of specialized equipment. Mechanical turning can be done with loaders or bulldozers, which are present in almost any municipal public works vehicle fleet.
  • requires limited site infrastructure;
  • imposes very limited requirements for site modification;
  • may use a variety of compostable materials; and
  • may well release odors during turning early in the composting cycle. A large buffer zone between the composting plant and neighboring residences may be needed, especially if the windrows are infrequently turned.

Windrow turning machines. Specially designed windrow turning machines have been developed in the US, Asia, and Europe. These vary in size from a wildcat tractor attachment to the very large scarab-type turner, which straddles the windrows. The ones built in India are low cost and work effectively with the waste stream. They may provide an opportunity for South-South technology transfer, although the problems associated with imported technology persist: the need to train repair persons and to obtain spare parts.

Windrow turning machines allow for production of a more uniform compost. They decrease labor costs but increase the capital costs of active pile systems. They may increase land requirements, as the design of turning machines limits the size of the piles and imposes pile spacing requirements. Compared to bulldozers, however, specialized windrow turning machines are more effective in aerating windrows and may therefore be a cost-effective alternative.

 

Locally Designed Windrow in New Delhi
There is a variety of locally designed windrow turning machines, like this one in New Delhi.
(credit: Chris Furedy)

Static pile systems
Static pile composting systems represent another option for sound technical practice. However, they have higher capital costs than active pile systems and are used more frequently in sludge composting than in composting of biowaste or yard waste.

In static pile composting systems, the windrows are not turned. Instead, they are aerated continuously or periodically using blown air systems. Static piles typically require a site with aeration channels built into the pad on which the piles sit. Piles are built over this channel, and a network of perforated piping is introduced during placement into piles of the materials to be composted. During composting, air is blown or drawn by pipe systems driven by electric or gas motors through the static piles to provide aeration.

In-vessel systems
The use of in-vessel systems represents a sound technical approach to composting in circumstances which can sustainably accommodate a higher-technology approach. In an in-vessel system, much of the composting process is carried out indoors or inside a vessel a large, enclosed chamber in which mechanical mixing and/or forced aeration are performed where moisture, air, and temperature can be controlled to create the optimal conditions for composting.

Almost all in-vessel systems require a residence time (time physically in the vessel) of 3-30 days, followed by a period of 21 to 180 days of active composting in an active or static pile. Once the active composting is completed, the material is stored in piles or windrows for curing for up to two years.

In-vessel systems offer protection from weather conditions, better odor control, and shorter periods of active processing, but they are expensive to build and operate. Their status as a sound practice for developing countries is open to question, especially since equipment and parts typically have to be imported and paid for with foreign exchange.

They may represent a sound practice for industrialized or transition countries, or for industrialized areas of developing countries, for specific, at least partially source-separated waste streams and as part of an integrated waste management strategy.

Common variations on in-vessel systems include:

Modular in-vessel systems. Modular in-vessel systems represent the best practice in most cases where in-vessel composting is desired. These systems have a series of smaller vessels or divisions within the vessel. The modules can generally be purchased separately or added on to the system later. They are also set up to compost more than one waste stream at a time.

Two variations on modular systems represent particularly sound practice. The agitated bay system uses a vessel divided into a series of bays or stalls, which are turned by an overhead agitator. Residence time in an agitated bay system is usually 10-21 days. The second type of modular system uses multiple closed boxes, each up to 20 meters in length. From the outside, they resemble trailer bodies. Inside, the walls contain a forced aeration and temperature control system. Residence time in the vessels ranges from 5 to 30 days, depending on the available land for final composting or curing.

Modular systems have moderate capital costs and low-to-moderate operating costs. They control odor and leachate very well. Modular systems are a sound approach in densely populated areas where siting is difficult and land is scarce.

 

Rotary Style Composting Plant in Bangkok
This rotary-style composting plant in Bangkok was remodeled from an older system.
(credit: Somchitt Trivichien)

Drum or "Dano-type" systems. In drum systems, compostables are introduced into a rotating horizontal drum for a relatively short residence time, followed by a long period of active-pile composting. These systems are called Dano-type systems after the original Danish design, now no longer protected by patent. The large metal drums are up to 30 meters long and may be divided into separate chambers. Some have trommel screens in the first chamber to remove designated materials during composting. Dano-type systems require a large amount of land for the active pile composting.

Tower systems. In tower systems, the compostable material is introduced into a vertical tower and composted under forced aeration. Some tower systems also mechanically turn or agitate the material during its residence. Residence time in tower systems is typically 2-5 weeks, and composting is essentially complete when the material is removed to curing piles.

Tower-type systems offer more odor control during composting and require much less land, since the period of active composting takes place in the vessel. They represent a particularly sound practice for sludge composting or co-composting of sludge and yard wastes.

Field composting and using compost from dumps
The most widespread form of composting and use of compost from urban wastes in the world today results from the delivery of fresh garbage to farms by collection crews, the removal of compost from dumps by nearby farmers, and the conversion of old dump land into farms.

The best known example of garbage farming is at CalcuttaÕs Dhapa dump, where the municipality leases out dump land for vegetable farming. The combination of dirt, dust, organics, human and animal feces, and ash in CalcuttaÕs garbage produces a fertile growing medium that requires no additives; the dump is in a wetland and there are numerous ponds between the ridges of garbage that provide water.

At BeijingÕs main dump, the authority has provided sifting machines to encourage farmers to remove compost and thereby extend the life of the dump.

In Yangon, Myanmar, the City Development Corporation allows small enterprises to mine the oldest inner-city dump (now closed) for metals (materiel dating from World War II) and screen the compost. In this way they hope to gradually remove the hill of compost so that land can be available for redevelopment. The remaining dump land is farmed in the growing season.

These largely undocumented and informal practices in many places throughout the developing world use valuable organic matter and help in waste reduction. However, they carry a risk of bacterial, glass, or chemical contamination which can present health hazards during the work of gardening or in the consumption of the crops in some places. At old dumps in cities with low levels of industry, the subsurface compost probably contains few heavy metals and would likely pass tests for use in farming.

If land, compost, and crops are monitored and judged safe for use, these traditions of natural composting and garbage farming could be regarded as sound practices for many places. Given uncertainties about quality and contamination, these practices can be endorsed as sound practice if soil and product testing is done regularly, or in places like Yangon where there is little industry. Sound practice over the long term will necessitate improving the practices themselves, rather than supplanting them and displacing their beneficiaries.

 

Use of Organic Municipal Wastes Through Urban Farming
The most extensive use of organic municipal wastes is through urban farming on old dump sites. This neighborhood dump that served a low-income area received mostly organic materials and was easily converted into a small vegetable farm.
(credit: Ben van Bronckhorst)

There is a need for assistance to developing countries in adequate testing and long-term monitoring, and in advice on crops that may be safely grown on old garbage dumps or on composted garbage removed from them. Sound practice improvements to garbage farming include:

  • development, distribution, and guided use of testing tools to check the soil, compost, and crops for contaminants;
  • promotion of deposit-refund schemes for some potential contaminants (e.g., batteries);
  • support and enhancement of recovery to remove dangerous or toxic materials from the garbage prior to dumping (which would require paying people to do this);
  • education of farmers and the public. The use of solid waste on peri-urban farms, a major practice in China, requires intensive education in composting techniques and regulation to prevent direct application to soil.
  • monitoring for parasites and other forms of contamination. Chinese authorities have not in general managed to monitor and control the practice sufficiently except within the boundaries of big cities.

Promising innovations
Centralized vermicomposting. Vermicomposting, also called vermiculture or worm composting, is a relatively cool but aerobic composting process in which certain varieties of redworms and earthworms can be used to break down organic materials. Worms mechanically break down compostables and partially decomposed materials by eating them, and biochemical decomposition occurs via bacteria and chemicals in the wormsÕ digestive system. Vermiculture requires considerable labor and careful control of composting conditions, including temperature, moisture, and the mix of ingredients. Its successes to date are limited to relatively small-scale or pilot programs.

The use of vermicomposting in centralized or village-scale composting systems is currently being explored in pilot projects. Considerable work was done in Manila in the 1970s but the markets for the resulting worm castings did not develop.

Vermiculture can be carried out by small-scale enterprises, in a cottage-industry manner. Worms are easily affected by impuri- ties, so the organic wastes should be source-separated domestic wastes, or from markets. Vermiculture produces a superior fertilizer-type product. However, there is not yet enough information to indicate whether sufficient markets exist to absorb worm castings on a scale that would significantly contribute to municipal waste reduction.

Vermiculture does not necessarily kill all pathogens. In particular, some viruses and parasites can survive the process. Therefore, if the input materials present a high risk of containing pathogens, the finished product could still contain pathogens. This may be of particular concern in developing countries, where wastes used in vermicomposting may not be source-separated.

Anaerobic digestion. Anaerobic digestion is an approach to composting which shows promise as a sound practice in industrialized countries. A number of facilities in France and Belgium appear to be capable of composting mixed waste under pressure and are recovering both compost and methane gas.

Most anaerobic systems include pre- processing similar to that in centralized aerobic systems, followed by conveyance of the compostables to a large pressurized tank or vessel. Water must usually be added as anaerobic bacteria generally require a liquid or semi-liquid environment.

Sound marketing approaches

Marketing of compost
Effective marketing of the compost is important to sound practice. In industrialized countries, compost is ordinarily considered to be a soil amendment, rather than a fertilizer, because of its relatively low nutrient value. It is considered to have value as a soil conditioner for dense or sandy soils, assisting all soils to retain moisture, synthetic fertilizers, and natural nutrients. It is useful in regulating soil temperature and in preventing erosion. Compost has been known to inhibit destructive agricultural diseases and pests.

While sound practice in composting systems depends heavily on marketing of compost, this does not necessarily require that composting make a profit. Marketing may include any type of beneficial use, ranging from use in roads and parks to give-away programs for residents.

Market development
Because compost from municipal waste materials is not precisely a fertilizer, the market for it in agriculture and horticulture is sometimes more potential than real. Virtually every instance where composting has become part of an MSWM system has benefited from the active development of compost markets and the setting of compost standards. These market development activities are essential elements of sound practice.

To date, Europe is the only area of the world with clear and enforceable compost quality standards, and with a history of government intervention to stimulate and support compost markets. The European emphasis on compost marketability has led its development from mixed waste composting to composting of source-separated biowaste. This has had an enormous effect on compost quality far larger than policy makers imagined.

 

Elements of market development
  • government stimulation of the compost market
  • compost and land application standards
  • compost use in the public sector
  • compost as daily or final landfill cover

Government stimulation of the compost market. Government action to stimulate the market has been significant and has included:

  • use of compost in public works projects, including some high-profile demonstration projects in parks and gardens;
  • giving compost away to garden centers and businesses;
  • specifying that government contractors use compost in government-funded construction projects;
  • requiring that nurseries supplying plantings to the government use compost;
  • supporting the price of compost, either for a short period or in cases where such support is justified based on an analysis of overall MSWM plans or requirements;
  • removing or modifying subsidies on chemical fertilizers that compete with compost;
  • providing technical assistance to composting facilities on quality control; and
  • providing free or low-cost testing of compost for its nutrient value or for suspected contaminants.

The French Association for Energy and Environment, now called ADEME (formerly ANRED) provides nearly a textbook example of how government-supported intervention essentially created composting practice in France. The program was based on three concepts:

  • the development of new markets;
  • a quality assurance program to farmers to encourage the use of compost; and
  • a program of paid technical assistance to selected municipal composting technologies to improve compost operations and resulting compost quality.

Compost and land application standards. The second critical element in sound marketing approaches is the establishment of compost and land application standards and guidelines. The European Union is far ahead of all other countries and regions in its compost standards program, which identifies three grades of compost ranging from acceptable to very high quality based on levels of heavy metals.

Land application standards connect the compost itself to its use in agriculture and allow or limit compost use on various crops. It is essential to give farmers confidence that compost is safe for use, and that they will not be penalized at a later date.

Compost use in the public sector. The successful development of compost systems to date has almost always involved heavy participation of the public sector in using compost in public works projects. This is a win-win strategy, as it tends to reduce costs and increase effectiveness of public works expenditures while illustrating the value of compost for greening and landscaping. Its effect is enhanced by signs that bring the use of compost to the attention of the public.

Compost as daily or final landfill cover. Another use of dump compost is as cover for fresh deposits of MSW, in cases where other cover material is scarce or expensive to transport to the dump. Landfill cover is an excellent use of lower quality compost or compost with large particles in it.

The use of compost as cover for landfills has been important in some places, since the compost substitutes for soil that would otherwise have to be excavated, purchased, and transported.

Compost quality control
The assurance of compost quality from within the composting and waste management system is very important for sound marketing practice.

The first element in quality control is controlling the inputs to the composting process. In industrialized countries, quality control rests upon clear and enforceable source separation protocols, combined with sound collection practice and pre-processing. In developing countries, where source separation is unlikely, manual pre-processing and post- processing is required to ensure the quality of the compost produced. Market wastes make particularly good input for composting operations.

Sound management of the composting process itself is also essential to ensuring the nutrient value of the compost. Process control, moisture control, aeration, and temperature all contribute to the biological processes.

Table of Contents

  • Brochure
  • IETC Brochure


  • International Year of Forests
  • International Year of Forests


  • World Environment Day
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  • UNEP Campaign
  • UNite to Combat Climate Change