Compost stability

Compost stability is defined by its biological property of microbial activity, measured by respirometric methods focusing on oxygen uptake, carbon dioxide evolution, and heat output. Stability tests predict odor potential and depend on some measurement of respiration rate. Dissolved oxygen (DO) meter respirometry takes advantage of improvements in the Clark-type polarographicprobe used to measure oxygen partial pressure in a closed system. The DO meter was used to determine the rate of oxygen uptake of municipal solid waste (MSW) compost samples loaded into 55 gallon pilot-scale reactor vessels equipped with temperature feedback control. During the first 2 weeks, the compost was turned every 3 to 4 days and amended with water to maintain 50% moisture in the organic matter. Thereafter, it was turned once per week for 2 more weeks. Samples were collected upon each turning. Each successive set of samples showed a decrease in activity, although differences in stability were not detected after 13 days. The volatile organic matter decreased from 79% to 64% over the composting period.