Thermal energy interchange during anaerobic methane fermentation of waste organic substrates.

An experimental calorimeter-type anaerobic fermentation system was developed to evaluate the extent of thermal energy interchange during anaerobic digestion of waste organic solids at 36 C. Results over a period of 184 days indicated that the energy released during conversion of the waste substrate was utilized primarily for the production of CH(4) and that any excess released as heat during normal digestion was not sufficient to overcome heat losses from the system. The more exothermic response observed during retarded digestion was attributed to the accumulation of volatile acids and associated reduction in gas yields. After combustion of the CH(4) produced during digestion, between 2,370 and 3,950 kcal per lb of volatile solids converted per day was available for heating the process and maintaining optimal temperature conditions.