Sludge management using the biodegradable organic fraction of municipal solid waste as a primary substrate

An innovative anaerobic composting process has been used to manage wastewater treatment plant sludges using the biodegradable organic fraction (BOF) found in municipal solid waste (MSW) as a primary substrate. Three different types of wastewater treatment plant sludges (primary, thickened activated, and digested) were commingled with a simulated biodegradable organic fraction of municipal solid waste and used as a feedstock. Digester performance was evaluated for each feedstock under similar retention times, a constant total solids content, and a constant C:N ratio. Additional aspects of the process which have been analyzed include volume reduction, air emission, and humus characteristics. Results obtained indicate that stable and robust digestion was achieved using organic loading rates of 6.5-8 g biodegradable volatile solids per kilogram active reactor mass per day. Under these organic loading rates, methane gas production rates as high as 0.36 m(3)/kg biodegradable volatile solids added per day were obtained, gassifying approximately half the dry mass of the feedstock. Substrate volume reduction through the process was similar to 65-69% as compared with the same quantities of sludge and MSW in a well-compacted landfill. The emissions produced from anaerobic digestion and aerobic biodrying are found to have no adverse effect on human heath and the environment. The humus produced is a fine, odorless, and pathogen-free material with metal pollutant concentrations well below the ''clean sludge'' standards specified by EPA Part 503 of the U.S. Environmental Protection Agency (U.S. EPA).