Mesophilic anaerobic digestion of corn thin stillage: a technical and energetic assessment of the corn-to-ethanol industry integrated with anaerobic digestion

BACKGROUND: The purpose of this study was to reduce the VS (volatile solid) and recover energy (methane) from thin stillage through mesophilic anaerobic digestion in corn-ethanol plants. The performance of a continuously stirred tank reactor (CSTR) with different hydraulic retention times (HRTs) was evaluated in this study. RESULTS: The results show no differences in volatile solid (VS) destruction (82-83%) in the reactor with HRTs ranging from 25 to 40 days. The maximum volumetric methane production rate of 1.41 L L-1 day(-1) was produced at 25-day HRT, whereas the maximum methane yield of approximately 0.63 L CH4 g(-1) VSfed (0.77 L g(-1) VSremoved) was achieved with HRTs between 30 and 40 days. Simulation results using a kinetic model indicate that the reactor needs to be operated for longer than 23 days in order to achieve 80% of maximum methane yield. The techno-economic potential of a corn-ethanol facility to produce an estimated 57% energy recovery using mesophilic anaerobic digestion has long been overlooked. A corn-ethanol plant integrated with mesophilic anaerobic digestion increases the net energy balance ratio from 1.26 to 1.80. CONCLUSION: Mesophilic anaerobic digestion complements the corn-ethanol business so that the sustainable energy obtained from corn recovery is made more lucrative and renewable. (C)c 2011 Society of Chemical Industry