Effects of Low Frequency Ultrasonic Irradition on the Anaerobic Sludge Treatment Process

The management of waste activated sludge is one of the most problem in the operation of wastewater treatment plants. Consequently, the concept of sludge minimization was studied extensively in recent years to solve the problem of the large amount of sludge. Additionally,several conventional methods that were used for the solution of the problem, some new techniques are also under development. One of these techniques is ultrasound, which is defined as sound waves produced in a wide frequency range over the range audible by humans. In the literature, it was demonstrated that the efficiency of physical, chemical, and biological processes of sewage treatment increases with the specific degree of the frequency and dosage of ultrasound by the formation of small cavitation bubbles. The study aimed to investigate changes in the physical properties of waste active sludge and determine the anaerobic decomposition dynamics, following the use of ultrasound irradiation. pH, TS, TVS, DCOD, DDCOD, rheological measurements were conducted for waste activated sludge samples, which were exposed to ultrasonic intensity for different periods, to determine the effectiveness of ultrasonic radiation. After the samples were exposed to ultrasonic radiation, anaerobic batch reactors were operated at two different temperatures, at 25 ºC and 35 °C, for a period of 30 days. Biogas production in reactors were measured every 24 hours on a regular basis. Finally, pH, TS, TVS, DCOD were analyzed to determine the dynamics of the anaerobic decomposition. The results demonstrated that DCOD and DDCOD increased by 58% and 27%, while TS and TVS were decreased by 21% and 30%, respectively as the ultrasonic power and time increased. As a result, removal of TS, TVS and DCOD and the formation of biogas in the anaerobic reactors increased with ultrasonic cavitation, depending on the reactor operating conditions and the character of raw waste activated sludge.