Influence of ultrasonically enhanced pretreatment on characteristics and anaerobic digestion of waste activated sludge

Ultrasonic pretreatment was applied to disintegrate waste activated sludge (WAS) and its effects on sludge characteristics and anaerobic digestion were examined. The WAS was subjected to three energy densities and then was anaerobically digested after ultrasonic pretreatment at 1.5 W/mL for 30 min. Results show that soluble COD of WAS increases linearly with both sonication time and energy density. When the WAS is sonicated at 0.8 and 1.5 W/mL for 30 min, soluble COD is increased by a factor of 4.7 and 6.0, respectively. Decreases of pH, alkalinity and particle size are also observed for the sonicated WAS. When the sonicated sludge is anaerobically digested, total COD removal is increased by 13.5%. At a sonicated sludge dosing rate of 5%, the anaerobic digester can reach steady state within 10 days and the daily biogas production is increased by 57.9% in comparison with the feed of raw sludge.