Stability indexes for municipal solid waste compost

Compost was prepared from the organic fraction of the municipal solid waste stream, using a windrow process. Stability was defined using rather simple tests. The pH was acidic at the beginning and stabilized near a neutral range. Electrical conductivity (EC) dropped and stabilized near a value of approximately 50 percent of the initial reading. The drop in EC was not due to leaching but to decomposition of organic acids. Another sensitive index was NH4 concentration. It decreased sharply from initial levels of a few hundred ppm to a stable value of about 50 ppm. The stability point as determined by simple chemical analyses of the aqueous extract of the compost correlated well with the decrease of the organic matter decomposition rate.