Performance Optimization of Anaerobic Continuous Stirred-Tank Reactor Operating on Distillery Spent Wash

Abstract

In order to better understand the performance, anaerobic treatment of spent wash with very high chemical oxygen demand (COD) (110,000–140,000 mg/L) and biochemical oxygen demand (BOD) (55,000–65,000 mg/L) was studied on a full-scale continuous stirred-tank reactor (CSTR). Under variable organic loading rates (OLRs), optimum conditions for maximum COD removal and biogas generation were found to be OLR=60,000–65,000 kg COD/day, hydraulic retention time (HRT)=22–17 days, and volatile fatty acids (VFA) to alkalinity ratio of around 0.12. Maximum COD removal efficiency was found to be around 71% when operated in the pH range of 7–8 with stable temperature of 37°C–38°C with biogas conversion coefficient of 0.4. These figures are particularly significant when operating the anaerobic biodigesters for treatment of spent wash and to produce biogas as an energy source. An anaerobic CSTR can successfully be employed for the treatment of distillery spent wash, but postmethanation effluent still contains a high COD concentration and needs to be treated further to meet the pollution norms and standards.