Performance of the Induced Bed Reactor Anaerobic Digester at Mesophilic and Thermophilic Temperatures

Abstract

The induced bed reactor (IBR) was developed at Utah State University (USU) to apply high-rate anaerobic digestion techniques to high-suspended-solids content substrates (3% to 12% total solids) such as food waste and dairy manures. This technology has been successfully implemented at full-scale multiple installations in the U.S. and Canada as a waste treatment and energy production technology. The objective of this study was to provide a baseline understanding of the performance of the IBR at a range of temperatures and loading rates. Bench-scale reactors (58 L volume) were operated at 35C, 45C, and 55C under three organic loading rates and three corresponding hydraulic retention times for each reactor using a dairy manure starter culture and a dextrose/yeast extract substrate at 30.6 g L-1 COD. Influent and effluent streams were monitored for parameters including solids composition, VFAs, gas quality and quantity, and chemical oxygen demand (COD). Results were integrated with those from a previously published study on operation of the IBR at thermophilic temperatures (55C). The IBRs were successfully operated for over 180 days, demonstrating a peak COD removal rate of 89% at 35C. Development of granulated sludge beds comprising settled sludge volumes of 500 mL L-1 (35C), 250 mL L-1 (45C), and 120 mLL-1 (55C) was evident. Operational data regarding reactor performance in terms of COD, VFAs, and biogas are reported. The IBR was demonstrated to operate at all three temperature levels, although the 45C reactor was susceptible to process upset, and the 55C reactor produced consistently poor-quality gas compared to the other reactors.