Effect of microwave pretreatment on semi-continuous anaerobic digestion of sewage sludge

Sewage sludge is a waste produced worldwide in wastewater treatment plants (WWTP) that constitutes a major environmental and health problem. Although anaerobic digestion has become a widely used method for the management and treatment of sewage sludge, the biomethanization of this waste leads to low biodegradability and low methane production. Microwave pretreatment under fixed conditions of 20 × 106 J/kg TS (Total Solids) and 700 J/s has been described as an interesting alternative in order to improve the feasibility of the anaerobic digestion of sewage sludge. In this study at laboratory scale, the semi-continuous anaerobic digestion of raw sewage sludge and pretreated sewage sludge were compared in terms of organic loading rate (OLR), biodegradability and methane production. The main results were found to be OLR up to 2.80 × 10−5 kg TVS (Total Volatile Solids)/m3·s, 70% biodegradability and a 20% improvement in methane yield compared to sewage sludge without pretreatment. Higher loads led to free ammonia accumulation, increase of pH values and system destabilization.