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

为了对低强度超声波强化污水生物处理的重要工艺参数———超声辐照周期进行优化,采用城市污水处理厂的好氧活性污泥为试验材料,以好氧呼吸速率(Oxygen Uptake Rate,OUR)和TTC-脱氢酶活性(2,3,5-triphenyl tetrazoliumchloride-dehydrogenase activity,TTC-DHA)为指标,研究了频率35kHz、强度0.3W/cm²的超声波辐照10min后0～48h污泥活性的变化规律,发现超声辐照处理后8h污泥活性达到最大值,24h后超声波的强化作用基本消失.随后分别以8h和24h为超声辐照周期,进行了反复超声辐照处理试验.结果表明,当采用超声辐照周期为8h时,第2次超声辐照后污泥的活性就开始明显下降,3次辐照后污泥的活性下降到对照的一半;当采用超声辐照周期24h时,每次超声辐照后污泥活性依然有所升高,但是随着超声辐照次数增加,其升高的幅度逐渐降低.考虑到设备投资及处理效果稳定性,应采用8h的超声处理周期,每次只处理反应器内一定比例的污泥以避免反复超声引起的污泥活性下降.根据上述现象分析了低强度超声波改善污泥活性的机理.

Optimization of Irradiation Cycle for Enhancement of Biological Treatment of Wastewater by Low Intensity Ultrasound

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.