Comparative Evaluation of Aerobic and Anaerobic Treatment of High Oil and Grease Rendering Wastewater

This study evaluated and compared the performance of a conventional activated sludge system to a batch anaerobic digestion system dealing with high oil and grease (O& 50,000-66,000 mg/L) wastewater with COD and BOD levels as high as 100,000 mg/L and 80,000 mg/L respectively. The use of biosurfactants for treatment was also examined. Batch laboratory experimental results and pilot-scale data are presented. The aerobic biodegradation rate was about 10 times faster than that of anaerobic digestion. More than 90% of soluble COD (SCOD) can be removed at a contact time of 5 days treating dissolved air flotation (DAF) pretreated wastewater. Furthermore, the biosurfactant affected a significant increase in the COD anaerobic degradation rate for the raw wastewater. The performance of the on-site pilot-scale system attests to the viability of the activated sludge process for the treatment of the waste. A soluble COD removal efficiency of 91% in the effluent was obtained as well as 97-99% removal of BOD, with effluent SBOD as low as about 10 mg/l. Oil and grease concentrations in the final effluent averaged at 15 mg/l.