Conditions for effective ultrasonic disintegration of activated sludge suspension

Abstract

Low-frequency and high energy sonication were used in the experiments on ultrasonic disintegration of activated sludge. Selected operational parameters of sonication were monitored and analyzed. The transformation of solids into a dissolved form by application of ultrasounds was analyzed on the base of changes in the concentrations of carbon, nitrogen and phosphorus. The scope of the research included determination of a five-day biochemical oxygen demand and rate constant of decomposition, which parameters indirectly represented the biodegradability of product of activated sludge disintegration. The study showed that the propagation of ultrasonic wave was highly disintegrating factor, generating a product of the characteristics of concentrated organic solution. By sonication of activated sludge the dissolved phase was enriched particularly in significant amounts of nitrogen and phosphorus. These elements could disturb the processes that require additional source of carbon, thus application of sonication for generation of easily available of organic carbon may seem less feasible. It seems more appropriate application of sonication to reduce the excess sludge through sludge disintegration and biological conversion. For optimum ultrasonic disintegration of activated sludge was considered sonication time 1200 s, which corresponded to the acoustic energy 170 kJ and specific energy 36 MJ/kgTS. In view of obtained values of the rate constant of decomposition, it was found that the disintegration of sludge required energy sonication in excess of 22 MJ/kgTS. Determination of potential applications of activated sludge subjected to sonication still requires further investigations that would use system for biological wastewater treatment. This would be the most reliable way to prove the suitability of activated sludge sonication in wastewater treatment technologies.