Pretreatment of Sewage Sludge by Low-frequency Ultrasound

The key point of waste activated sludge (WAS) pretreatment is to rupture the cell wall for allowing the release of intracellular matter that acts as a bioavailable substrate in anaerobic digestion processes. In this regard, ultrasonic irradiation has been one of the most effective tools owing to the unique properties of ultrasound to produce extreme conditions in heterogeneous liquids such as waste activated sludge. The present study investigates the impact of short-frequency ultrasound on disintegration, biodegradability and dewatering characteristics of sewage sludge by monitoring soluble chemical oxygen demand (sCOD), dissolved organic carbon (DOC), soluble proteins, total dissolved nitrogen, particle size and dewaterability of raw and sonicated sludge samples to optimize the operating parameters. The results showed that short wave ultrasound is a highly effective method of WAS treatment, because it provides high degrees of disintegration and biomass transfer from sludge solids to the aqueous phase, thus resulting in enhanced biodegradability.