Thermophilic Anaerobic Digestion Using an Induced Bed Reactor

Abstract

An induced bed reactor (IBR) was developed at Utah State University (USU) to apply high-rate anaerobic digestion techniques to high-suspended-solids content substrates (6% to 12% total solids) such as food waste and dairy manures. This technology has been successfully implemented at multiple full-scale installations in the U.S. and Canada as a waste treatment and energy production technology. A 58 L bench-scale reactor was operated at 55C with three organic loading rates and three corresponding hydraulic retention times using a dextrose/yeast extract substrate at 30.6 g L-1 COD. Influent and effluent streams were monitored for solids composition, gas quality and quantity, and chemical oxygen demand (COD). Residence time distribution (RTD) was determined using step input tracer studies with rhodamine WT and lithium tracers. The IBR was successfully operated at thermophilic temperatures for 180 days, demonstrating a COD removal rate of 64% and a robust thermophilic culture. Under the conditions studied, the IBR exhibits complete mix behavior with no mechanical energy input. Development of a granulated sludge bed comprising a settled sludge volume of 120 mL L-1 was evident. Further work should be done to determine conditions required for improved solids retention and thus improved performance.