The number of U.S. composting programs increased by 40% in 1990, to about 1,400 altogether. At least 500 of these programs compost only leaves on a seasonal basis (Glenn and Riggle, 1991). Such programs are more common in the Northeast than in other regions.
No estimates of the total tonnage of yard waste composted were found. However, yard waste constitutes 18-20% of MSW nationwide. The percentage varies between 0% and 40% from community to community, depending on socio-economic factors, land use (size of lots), age of the community, mix of residential and commercial buildings, and so forth (Deyle and Hanks, 1991; ).
For composting mixed MSW, the United States has 16 operating plants with a total combined design capacity of 2,050 tons per day (Apotheker, l991a). Another 11 plants (with a combined capacity of 1,900 tons per day) are under construction (Apotheker, l991a). Most of the MSW composting facilities have small capacities; 11 of the 15 operating facilities have capacities of less than 100 tons per day (Glenn and Riggle, 1991). The largest U.S. facility is the 600 ton per day plant mentioned in the preceding subsection (Apotheker, l991a). That facility is the first U.S. operation to adopt composting technologies that have been widely and successfully used in Europe (Apotheker, l991a). It is still in the start-up stage, and no evaluations of its performance have been published (Apotheker, l991a).
Applications and Markets
No estimates of the amount of compost produced as part of MSW management programs have been published. There is, however, an apparent limit on the total amount that could be used. One source suggests that about 60 tons per acre per year is the maximum acceptable level for agricultural use, although larger quantities are acceptable for sod use (Rigo, 1991). More detailed information is provided in Appendix G.
The products of composting facilities are often difficult to sell, or even to distribute free of charge. Compost produced from yard waste is a more marketable product than compost made from mixed MSW (Hammer, 1992). Typically, compost from MSW competes with compost derived from sewage sludge and sawdust (Humber, 1991), or with manure (Hammer, 1992). These competing products have a higher fertilizer nutrient value than the MSW compost (Humber, 1991). A study of yard waste compost prices reported a range of $0 to $25 per ton for the compost (Deyle and Hanks, 1991).
Use of compost made from MSW is made more difficult because many states have no standards for compost content; without standards, consumers often fear using a waste-derived product (Hammer, 1992). A consortium of U.S. university and government researchers have proposed nationwide U.S. standards, but others have been unable to reach agreement on what standards would be appropriate (Hammer, 1992). Canadian and European standards are ten times more restrictive with respect to some metals than the proposed U.S. standards (Hammer, 1992). All the mixed MSW composting facilities operating in 1991 for which testing data are available are reported to meet the proposed U.S. standards (Hammer, 1992).
Apparently, no state or federal agency has yet proposed standards for determining when a compost product has been "stabilized" (a stable, or "finished" compost can be stored without releasing objectionable odors, and it does not inhibit plant growth). No formal system of grading has been introduced to measure nitrogen-phosphorus-potassium content, particle size and uniformity, contaminants such as glass and plastic, and pathogens, pesticides, and toxics, if any.
MSW compost is frequently used for landfill cover. In that application, it substitutes for "earthen materials" (FR, l991j). For example, of the 37,000 tons of compost made from MSW in the Delaware Reclamation Plant in 1990, 500 tons were sold, and the rest went to landfill. (see Appendix G. page G-ll). The new federal guidelines for daily cover (FR, l991j) call for 6 inches of "earthen materials," but the regulation is based on performance, not material (Cassidy, 1991). As long as the cover controls disease vectors, fire, odors, blowing litter, and scavenging, it is likely to be a permissible exception to the regulation (FR, l991k). However, because compost used as daily landfill cover is not intended to promote plant growth (the daily cover will be covered with more MSW) or improve the soil, it has little special value in this application; furthermore, compost may be no more effective in decreasing landfill volume than shredding MSW, which eliminates the need for daily cover (see also CRSI, 1989). The use of compost in the final closure landfill cover may be beneficial.
A separate segment of the industry composts sewage sludge at more than 100 installations. In some sludge composting operations, MSW is a useful additive to increase air circulation in the composting piles.
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