High-solids anaerobic digestion of mixed municipal and industrial waste

Laboratory studies on dry anaerobic digestion of mixture of paper, kitchen food waste, and sewage sludge have demonstrated the optimum performance at total solids (TS) at the range of 30-35% TS. The thermophilic process (at 55 degrees C) was found to be superior to a mesophilic (35 degrees C) one, both in terms of volatile solid (VS) reduction and specific gas production, but was somewhat less stable at short mass retention times (MRT). The efficiency of total volatile solids destruction and the decrease in the oxygen demand were found to be proportional to the product of the mass retention time and temperature (d.degrees C). Pilot studies, conducted on a mixture of sewage sludge, mixed paper, food waste, and solids from a potato processing conducted on site in Portage la Prairie, Manitoba, Canada, have demonstrated the feasibility of running the process at loads exceeding 9 kg TS/m(3).d and producing biogas at 140 m(3) of wet solids fed to the composter. The residual oxygen demand per unit mass of the dry compost was 20 mg O2/g.h, which indicated a need for aerobic postcuring of the anaerobically produced compost.