Effect of pretreatment methods on breaking up bacteria and solubilization of organic substances in waste activated sludge

The efficiency of treating waste activated sludge (WAS) by biologic methods is connected with efficiency of digesting the organic substances in WAS. In order to enhance the digestion rate of WAS, it needs to be pretreated. In this study, the effects of several pretreatment methods, including thermal, alkaline, ultrasonic and combined methods, on the solubilization of chemical oxygen demand (COD), carbohydrates and DNA in WAS were investigated. It was found that the process of thermal pretreatment was the best in breaking up bacteria, and the effects of thermal pretreatment were related to the efficiency of heat transfer in the sludge. Ultrasonic pretreatment was the best in disintegration of WAS, and ultrasonic effects occurred more easily in extracellular polymeric substance (EPS). Alkaline pretreatment could reduce WAS well, and it could accelerate the hydroxylation of carbohydrates.