COMPOSTING

Municipal Solid Waste

To date, success in composting MSW to produce a marketable product is quite rare. Facilities for large-scale composting of MSW are encountering engineering and process control problems (Allen, 1992). Increased application of the technology may depend on research to identify the causes of those problems and engineering development work to find better solutions to operational problems.

Mechanical processing, either before or after composting, has been a major technical barrier to successful MSW operations because some systems are inappropriately designed (CRSI, 1989). Many appear to be designed to minimize initial capital cost or to minimize O&M costs. Operating experience sometimes indicates the need for significant modifications of such plants (CRSI, 1989).

Troublesome problems with odor have been reported at some plants. Biofiltration is used for odor control at some composting facilities, but it requires relatively large areas and sophisticated operational control, and performance is frequently poor. The fate of odoriferous compounds absorbed in the biofilter is not well known.

Yard Waste

Some communities are quite restrictive about the types of yard waste they will accept for composting. Such restrictions are apparently required because of the equipment that the communities have chosen. The influence of such barriers to public participation has not been well characterized.

Markets

Municipal Solid Waste

MSW-derived compost fares worse than composts derived from sewage sludge, manure, and yard waste in the competition for available markets (Hammer, 1992). Acceptance of MSW derived compost will require a clearer understanding of appropriate uses for it. Solutions to that problem might include:

• A better rationale for setting standards
• A better understanding of the effects of contaminants on land and crops
• Greater product consistency.

Data on the following important topics were limited, unreliable, or unavailable:

• The impact of curbside collection programs, particularly of household hazardous waste, on the quality of compost products
• Concentrations of toxics and pathogens in compost made from yard waste (CRSI, 1989)
• The effect of metals and chemicals in the compost on the food chain (CRSI, 1989).

No data on emissions from collection of composting were found. Once compost is made and applied to land, it may undergo only aerobic decomposition; if so, it would release little methane. No studies of any emissions from compost in use were found.

Municipal Solid Waste

No quantitative information was found for the following subjects:

• Amounts and identity of volatile organic compounds (VOCs) released during composting and curing
• Specific emissions volatile solvents that were discarded in MSW, during composting
• Emissions from treatment of leachate.

Little information is available about the nature and effectiveness of programs for curbside collection and composting of yard waste. Missing data include:

• Emissions released during composting and curing
• Disposition of the product, including quantities used as daily landfill cover or otherwise disposed of as waste
• The long-term environmental impacts of the eventual products of MSW composting in various applications.

The benefits and costs of composting programs have been examined less carefully than those of other components of MSW management strategies because composting has been a small-scale contributor to the field. Given the increasing popularity of composting, a thorough evaluation seems overdue.

The value of composting of either yard waste or MSW to an overall management strategy is difficult to evaluate because limited data are available on:

• Energy requirements
• Transportation requirements and emissions
• Percentage of the compost produced that is beneficially used.

Less Commonly Used Technologies

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