Optimization of Irradiation Cycle for Enhancement of Biological Treatment of Wastewater by Low Intensity Ultrasound
低强度超声波强化污水生物处理中超声辐照周期的优化选择

This work aims to optimize one of the critical technological parameters--ultrasound (US) irradiation cycle for utilizing the low intensity ultrasound to enhance biological wastewater treatment. The aerobic activated sludge from domestic wastewater treatment plant was used for this study as an experimental material. Oxygen uptake rate (OUR) and 2, 3, 5-triphenyl tetrazoliumchloride-dehydrogenase activity (TTC-DHA) were determined to indicate the changes of biological activity (within 48 h) after US irradiation at 0.3 W/cm2 in irradiation time of 10 min. The activity of sludge took 8 h after irradiation to reach peak level, and the enhancement effects induced by US faded away 24 h after irradiation. In addition, 8 h and 24 h were used as irradiation cycle respectively to carry out repeated US treatment. Results showed that when 8 h cycle was used, sludge activity decreased quickly after second US irradiation, and after third US exposure, sludge activity decreased even less than 50% of the control. When 24 h was used as the irradiation cycle, sludge activity increased after each US irradiation, but the extent of each increase declined with the increase of the number of US exposure. In consideration of US equipment costs and stability of treatment effects, 8 h should be selected as the US irradiation cycle and each time we can expose only a part of activated sludge in the biological reactor to avoid the decrease of sludge activity induced by repeated US treatment. The paper also analyzed the mechanism of biological activity enhancement by US according to above phenomena.