Effect of inoculum/substrate ratio on mesophilic anaerobic digestion of bioethanol plant whole stillage in batch mode

摘要

A study of anaerobic digestion of whole stillage from a dry-grind corn ethanol plant was conducted to evaluate the possibility of replacing fossil fuel input of large ethanol plants by using ethanol residues as digester feedstock. The effect of inoculum to substrate ratio (ISR) on biogas/methane production rates and ultimate yields was evaluated in mesophilic batch digesters. A first order kinetic model was evaluated for both volatile solids (VS) and total chemical oxygen demand (TCOD) removals. The results demonstrated that in an ISR range of 3.67-0.46 g/g on VS basis, kinetic constants (k) for both VS and TCOD removals decreased significantly, indicating an initial reactor overloading or substrate inhibition. However, despite the slower biodegradable rates from the reactors with ISRs of 0.46 and 0.92, none of the reactors experienced a chronic substrate inhibition. At the highest organic loading (ISR of 0.46 g/g), degradation was complete in 15-16 days. Biochemical methane potential assays indicated significant digestion potential (691-788 mL biogas and 401-458 mL CH_4 per g VS_(added) at 0℃, 1 atm) with organic removals between 76% and 94% in batch mode. Future studies will verify the anaerobic digestion potential of full-strength whole stillage at larger scale.