Effect of Ultrasound in Improving Dewatering and Stabilization of Anaerobic Digested Sludge

In biological wastewater treatment large quantities of sludge are produced. This sludge is highly putrescible.For disposal and safe usage should be stabilized. The anaerobic digestion is a standard technique for stabilization. Due to the rate imiting step of sludge hydrolysis, anaerobic degradation is a slow process with high digestion time. Due to high retention time and sludge dewatering problem, application of methods to reduction of retention time and remove of limitation and is necessary. The ultrasonic wave due to increase of enzymatic activity can be reduction time of hydrolysis that limiting step in aerobic digestion. In this survey the samples of sludge were the anaerobic digestion from south Tehran wastewater treatment. Ultrasonic frequency used are 35 and 131 kHz and duration time are 15 , 30,60 and 90 min.Total solids,volatile solids,pH,temperature , total COD, SCOD and settleable solids are measured.The result show that the application of ultrasonic wave increased SCOD and temperature and decrease VS,pH and settleable solids.The rate of VS reduction in 35 kHz at time 15, 30,60 and 90 min are 40,29.3,39.7 and 46.2 percent and in the 131 kHz are 45.4,12.76,30.55and 18.34 percent respectively.Application of ultrasonic wave in frequency 131 kHz to decrease of VS and increase of dewatering of sludge more effective than the 35 kHz at the low sonication time and the most performance are in the 15 min and 131 kHz frequency.