Respirometric characterization of the soluble COD fractions after ultrasonic activated sludge disintegration

Excess sludge treatment and disposal is currently a major challenge in wastewater treatment plants due to associated high costs and environmental regulation factors. Sludge disintegration technology (e.g., ultrasonic sludge disintegrators), can result in a significant reduction of the excess sludge produced in both municipal and industrial wastewater treatment plants when integrated as a solubilisation step in the sludge recycle of the activated sludge plant. For modelling the process of ultrasonic sludge disintegration, knowledge about the release of soluble COD (sCOD) and soluble Kjeldahl nitrogen (sKN) as a function of the applied specific ultrasonic energy (ES, kJ/kg DS) provides insufficient information to result in a successful sludge disintegration model that is consistent with existing IWA Activated Sludge Models (ASM). In the research proposed in this paper, it was shown that respirometric data can be used to characterize the different COD fractions that are released and converted during the ultrasonic treatment of waste activated sludge. From the experiments it was concluded that the ultrasonically released COD in the supernatant liquid consists for approximately 70% of slowly biodegradable COD (XS), mainly in the form of colloidal particulate material, 20% of readily biodegradable COD (SS), and a remaining part of inert soluble COD (Si). Based on the performed COD fractionation experiments, also a saturation-based solubilisation model was proposed that is compatible with existing ASMs and that describes the ultrasonic sludge disintegration as a function of the specific energy (ES).status: publishe