Effect of ultrasonic pretreatment on the semicontinuous anaerobic digestion of waste activated sludge with increasing loading rates

Anaerobic digestion (AD) is the most widely used method to stabilize and recover energy from waste activated sludge (WAS). However, AD of sludge results in a low biogas yield. Ultrasonic pretreatment (USp) is the most effective sludge disintegration technology and has elicited interest to increase the biodegradability and improve the efficiency of the AD. This study investigated the influence of USp on the semicontinuous AD of WAS as a strategy to increase its performance. During an experiment lasting 90 days, 0.8-L digesters were semi continuously fed under different conditions: raw sludge and sonicated at 15000, 25000 and 35000 kJ/kg TS (total solids); and an increase of the organic loading rate (OLR) from 1 to 3 kgVS/m(3).(1, for 30 days each. The maximum biogas rate (0.218 L/d) was reached at 25000 kJ/kg TS and 3 kgVS/m(3).d. The highest VS removal efficiency