Aerobic and anaerobic digestion of processed municipal solid waste. Effects of retention time on cellulose degradation

Effective disposal of municipal solid wastes (MSW) through biological processes must focus on the maximal reduction in bulk. Since cellulose is a major component in processed municipal solid waste, biological treatment processes must result in near complete degradation of the polymer. Specific cellulose degradation rates were determined for aerobic and anaerobic digestion systems fed a high cellulose, processed MSW feed, while maintaining optimum nutrient levels, mesophilic temperature (37 degree C), and a pH of 7.0-7.4. Reducing the retention time resulted in reduced cellulose conversion for both aerobic and anaerobic systems with similar trends. Anaerobic retention times of less than 12 d resulted in unstable digestion, with increased volatile fatty acid pools and decreases in pH. Reducing aerobic retention times below 8 d dramatically reduced cellulose conversion without unstable digestion conditions or volatile fatty acid accumulation.