Immobilized biological method for anaerobic biodegradation of carbohydrate and protein in wastewater

Abstract

Aerobic activated sludge processes for treatment of domestic wastewaters consume energy intensely. Anaerobic processes are much more energy-efficient but are prone to washout of anaerobic biomass when operating at short hydraulic retention time. In this study, we use an immobilized biomass to overcome the barrier and investigate the anaerobic biodegradation of two major domestic wastewater components, carbohydrates and protein, and the production of methane from which. The anaerobic experiments were operated at hydraulic retention times of 1 to 24 h and temperatures at 35 °C, 25 °C, and 15 °C. The anaerobic immobilized bio-plates reactor (AnIBPR) treated a synthetic wastewater with sucrose at 1000 mg/L of chemical oxygen demand (COD) and completely converted the carbohydrate to methane. Soluble COD removal was 78.2% even at low temperature of 15 °C. Methane recovery efficiencies were found to be 90%, 86%, and 74% at 35 °C, 25 °C, and 15 °C, respectively. Enhanced degradation of protein (1000 mg/L as COD) was observed in the presence of added carbohydrate, resulting in significant removals of both carbohydrate and protein with methane recovery efficiencies from 78% to 55%. The AnIBPR converted 83% of the carbohydrate to methane at HRT of 1 h and slightly longer for protein alone to methane. For domestic wastewaters, the presence of carbohydrates is likely to enhance and not suppress the hydrolysis/acidogenesis of the co-existing protein during COD removal and methane generation. The AnIBPR shows potential for enhanced domestic wastewater treatment particularly in tropical regions. • The AnIBPR retains high biomass (35 ∼ 42 g/L) for anaerobic wastewater treatment. • The AnIBPR achieves methane yields at 0.04 L/g COD and recovery at 90% to 74%. • The AnIBPR removes 83% of COD and convert to methane at 80% recovery in 1-h HRT. • The AnIBPR achieves 90% removal of total protein at HRT of 12 h. • The presence of carbohydrates enhanced anaerobic biodegradation of protein.