Anaerobic Digestion of Municipal Solid Waste

Anaerobic digestion of classified municipal solid waste is a proposed disposal method for the mushrooming quantities of solid waste. To determine the suitability of anaerobic digestion to Los Angeles area wastes, a two-year pilot-scale study was conducted. A survey of a Southern California community was made to determine typical municipal waste composition. Municipal solid waste with characteristics conforming to survey results was classified using the Cal Recovery Process to provide a feedstock for digestion. Four 50-gal (0.19‐m3) digesters were operated at organic loading rates from 0.065 lb VS cu ft-day-0.25 lb VS cu ft-day (1.04kg/m3⋅day). Feed concentration ranged from 2.6%-8% VS and hydraulic retention time ranged from 15-30 days. Feed solids were composed of 80% classified municipal solid waste and 20% primary sludge. Results of the experimental investigation showed that gas containing 55%-60% methane can be produced at a rate of 7.0 cu ft-9.0 cu ft gas lb-VS applied (0.44m3‐0.56m3/kg⋅VS applied). The highest gas production rate was obtained at the lowest digester loading rates. Digester mixing ability appeared to be the controlling process variable. No chemicals for pH control or nutrients were required to maintain normal process operation.