Assessment of Waste-Activated-Sludge Pretreatment by Ultrasound and Applicability of Biodegradability Indicators

Waste-activated sludge (WAS) samples that were generated over a range of solids residence times (SRTs) under controlled operating conditions were employed in bench-scale sonication tests to characterize the impact of physical pretreatment processes on WAS anaerobic digestion and to assess the applicability of indicators for characterizing WAS digestibility. Physical, chemical, and biochemical analyses were conducted on raw and pretreated WAS samples and the results were compared to those obtained in biochemical methane potential (BMP) and biochemical acid potential (BAP) tests. The solublization responses indicated that the materials that were solublized were affected by the WAS SRT and sonication level. Despite differences in solublization responses, BMP tests revealed that sonication only marginally increased the ultimate biodegradability of the sludges. NH4 responses from the BMP tests and volatile fatty acids (VFAs) responses from the BAP tests were found to be indicative of the impact of sonication on the rate of hydrolysis and acidification/ammonification. Both responses suggested an increase in the rate of hydrolysis, which is typically the rate-limiting process in WAS digestion. DOI: 10.1061/(ASCE)EE.1943-7870.0000657. (C) 2013 American Society of Civil Engineers.