An anaerobic/aerobic process for solid waste composting

This research evaluated an innovative anaerobic/aerobic process for the treatment of the organic fraction of municipal solid waste (OFMSW). The complete experimental set-up includes a combination of an acidogenic batch reactor and a methanogenic filter. The effluent from the acidogenic reactor was fed into the methanogenic reactor through a holding/recycling tank. The experimental study was conducted by altering the operating conditions, including input total solids (TS), number of batch reactors in series, biomass seeding ratio (BSR), effluent recycle rate, solid waste retention time (SWRT), and pH in the holding/recycling tank. Operating conditions of the methanogenic filter were kept constant throughout the study. The substrate was introduced into the combined system by routinely alternating the batch feed to the acidogenic reactor. The optimum operating conditions, in terms of the highest TS and TVS destruction and the greatest methane production, were determined. The system was operated in a constant-temperature room at 35°C;At the end an operating period, or half SWRT, the digested wastes was removed from the acidogenic phase. In the meanwhile, free liquid was drained into the holding/recycling tank. Air at a temperature of 25°C was then pumped into the drained acidogenic reactor at a controlled rate to initiate aerobic composting, and, simultaneously, to dry the digested solid wastes;The system achieved a volatile solids destruction averaging 53% (90.4% of the biodegradable fraction of the solid wastes). The system produced a methane yield averaging 0.227 m[superscript]3/kg (3.64 ft[superscript]3/lb) of TS added to the system. Aerobic polishing reduced the moisture content of the composted residue to less than 5% and produced an odor-free product;These laboratory studies indicate that the anaerobic/aerobic approach has much to offer, as compared with aerobic composting. With the anaerobic/aerobic approach, solids destruction was equivalent to that normally achieved by aerobic composting. However, the anaerobic approach has the advantage of producing significant quantities of a valuable fuel (methane). Also, the process was operated in totally sealed reactors, avoiding release of the odors commonly associated with aerobic composting operations. The aerobic polishing step results in a product that is stable, low in moisture, and odor free