Biomethanation of Distillery Wastewaters in Fluidised-Bed Bioreactor and Mathematical Modelling

Abstract

An anaerobic three-phase fluidised-bed reactor (FBR) was used to treat distillery wastewaters for biogas generation using actively digested aerobic sludge from a sewage plant. The optimum digestion time was 8 h and optimum initial pH of feed was 7.5. The optimum temperature of feed was 40°C, optimum feed flow was 14 L/min and maximum organic loading rate (OLR) was 39.513 kg COD m−3 h−1. The OLRs were calculated on the basis of chemical oxygen demand (COD) inlet in the bioreactor at different flow rates. The maximum methane (CH4) concentration was 63.56% (v/v) of the total biogas generation at optimum biomethanation process parameters. The maximum biogas yield rate was 0.835 m3/kg COD m−3 h−1 with maximum CH4 yield rate (63.56% v/v) of 0.530 m3/kg COD m−3 h−1 at optimum digestion parameters. The maximum COD and biological oxygen demand (BOD) reduction of the distillery wastewaters were 76.82% (w/w) and 81.65% (w/w), respectively, with maximum OLR of 39.513 kg COD m−3 h−1 at optimum conditions. The optimisation of these parameters enabled stable functioning of the process and allowed the application of high loading rates. This study deals with mathematical modelling of the experimental data on biomethanation and suggests model equations relating kinetic parameter (rate constant k) and maximum specific growth rate μmax with respect to COD (substrate) removal. The mathematical modelling is also analysed for hydrodynamic pressure δp vs. feed flow u and hydrodynamic pressure δp with respect to CH4 gas yields.