Effect of digester F/M ratio on gas production and sludge minimization of ultrasonically treated sludge.

Sludge pretreatment by mechanical, chemical or thermal methods before anaerobic digestion has been applied to increase the digestability of excess sludge. Pretreatment processes rely on their ability to disrupt cell membranes and to release organic materials from the cells into the aqueous phase. Pretreatment by mechanical disintegration has grown rapidly in recent years in parallel with the advances in technology. Ultrasonic sludge disintegration -one of the most commonly used mechanical pretreatment methods- enables the occurrence of cavitation bubbles for the break-up of microorganism cells to extract intracellular materials. The purpose of this study was to conduct disintegration experiments to optimize sonication parameters and to operate subsequent batch anaerobic digesters to examine the effect of food to microorganism ratio (F/M) in sonicated and unsonicated samples. Results showed that high sonication powers and longer treatment times were effective in sludge disintegration in terms of soluble chemical oxygen demand release. Sonicated sludge digested in batch reactors with higher initial F/M ratio caused higher methane generations, higher sludge reductions and had better dewatering characteristics.