PERFORMANCE OF UASB REACTOR TREATING HIGH OIL & GREASE PET FOOD WASTEWATER UNDER CRITICAL LOADING CONDITIONS

Pet food industrial wastewater contains very high concentration of oil and grease (O&G) which is difficult to treat biologically. In this study, anaerobic treatability of pet food wastewater was evaluated in a mesophilic (35°C) upflow anaerobic sludge blanket (UASB) reactor without any pretreatment with the ultimate goal of establishing critical loading criteria. The reactor was seeded with sludge from a full-scale anaerobic digester treating ethanol wastewater and was started with acetate based synthetic wastewater. Subsequently, it was fed with diluted wastewater for over 160 days. The feed flow rate was at 2 L/d to maintain a long HRT of 5 days, which allowed for better destruction of COD and O&G. The foam produced by anaerobic process was removed manually every week.Overall COD removal efficiencies of 90-98% were achieved at feed COD of 25 g/L and O&G of 20 g/L (OLR of 14 kgCOD/m3.d). Approximately 10 L/d of biogas (67% methane) was produced initially but increased to 15-20 L/d. Mass balances on COD and O&G indicated that about 74% of the COD and 54% of the O&G were removed through biodegradation and the rest were removed with foam. It was found that the reactor operation is feasible at O&G loadings of less than 0.5 gO&G/gVSS.d, which is about 3 times higher than literature (Hwu et al, 1998). However, the sludge characterization showed that due to long chain fatty acids (LCFA) inhibition, the biological activity of the sludge was reduced and caused the reactor to collapse on day 163. Moreover, at failure, 70% of the sludge was washed out.