HIGH-SOLIDS ANAEROBIC-DIGESTION OF MIXED MUNICIPAL AND INDUSTRIAL-WASTE

Laboratory studies on dry anaerobic digestion of mixture of paper, kit chen food waste, and sewage sludge have demonstrated the optimum perfo rmance at total solids (TS) at the range of 30-35% TS. The thermophili c 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 re tention times (MRT). The efficiency of total volatile solids destructi on 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 pape r, food waste, and solids from a potato processing conducted on site i n Portage la Prairie, Manitoba, Canada, have demonstrated the feasibil ity of running the process at loads exceeding 9 kg TS/m(3).d and produ cing biogas at 140 m(3) of wet solids fed to the composter. The residu al oxygen demand per unit mass of the dry compost was 20 mg O2/g.h, wh ich indicated a need for aerobic postcuring of the anaerobically produ ced compost.