Enzyme Activities as Indicators of Municipal Solid Waste Compost Maturity

Composts of municipal solid waste in a commercial scale facility were assayed for enzymatic activities over time. The main enzymes assayed in this study were alkaline phosphatase, acid phosphatase, endo-cellulase, glucosidase, and lipase (C10). The biomass was measured by using lipid phosphate as a measure of the amount of cellular membranes, and metabolism was measured by the amount of 14C-acetate incorporated into the lipid phosphate pool. All tests followed steady trends which show promise for use as possible stability and maturity indicators. Cellulase activity appears to be a good indicator of stability. The lipase activity appears to be a good indicator of compost maturity. A simple test strip (Api-Zyme from Api Analytab Products, Plainview, New York) was also used and compared to the standard enzyme assay methods. Api-Zyme and standard methods gave comparable results. The use of specific enzymatic activities presents an inexpensive and fast method, which may be combined with others, to predict a composts' stability and possible maturity status based on microbial activity.