Purification of Waste Water Containing Surfactant by Photo-catalytic Oxidation and Ultrasonic Treatment

为了开发新的废水处理工艺，采用光催化-超声氧化降解表面活性剂，在光催化降解过程中，总有机碳（TOC）浓度显著降低后，再进行超声处理。超声辐照使TOC浓度略有下降。然而，TOC去除效率达不到100%。在光催化-超声联合降解过程中，表面活性剂的降解速率随着搅拌速度的增加而降低。在较低的搅拌速度下，TiO_2光催化剂颗粒可能会在驻波波的波节处局域化。加入适量玻璃微珠的催化剂悬浮液经26 kHz超声波辐照后，发现催化剂颗粒与玻璃微珠发生了团聚和沉淀。用Brant-Hiedemann理论解释了玻璃微珠加入量对催化剂颗粒团聚的影响。再分散后的催化剂仍保持与原催化剂相同的光催化活性。根据以上结果，我们提出了一种新的废水处理复合工艺。该工艺由两个罐组成。一种是带有低压汞灯和高频超声波发生器的分解槽。另一种是带有低频超声波发生器的回收罐。废水在分解槽中处理后流入回收槽，在回收槽中通过低频超声波的照射分离光催化剂颗粒。分离出的颗粒返回到分解槽。

In order to develop the new process for the waste water treatment, the decomposition of surfactant was carried out by using the photo-catalytic and sonolytic oxidations.For the consecutive process, that is, after the concentration of total organic carbon (TOC) was considerably decreased with the photo-catalytic process, ultrasonic process was applied. The TOC concentration was slightly decreased by ultrasound irradiation. However, the TOC removal efficiency of 100% was not reached. It must be that the decomposition of TOC hardly progresses since the TOC concentration was too low.For the combined process of the photo-catalysis and the sonolysis, the decomposition rate of surfactant decreased with the stirring speed. In the case of the lower stirring speed, the particles of the TiO_2 as photo-catalyst may be localized at the nodes of standing wave. Therefore, the apparent reactivity of catalyst decreases.The aggregation and precipitation of the catalyst particles with glass beads were found when the ultrasonic at 26kHz was irradiated to the suspension of catalyst added the appropriate amount of glass beads. The dependency of the amount of added glass beads on the aggregation of the particles can be explained by the theory of Brant-Hiedemann.The precipitates of the catalyst particles were re-dispersed by the irradiation of ultrasonic at 200kHz. The re-dispersed catalysts still held the same photo-activity as the raw catalysts.From the above results, we propose a new hybrid process for waste water treatment. The process consists of two tanks. One is a decomposition tank with a low-pressure mercury lamp and an ultrasonic generator of high frequency. Another is a recovery tank with a ultrasonic generator of low frequency. Waste water is treated in the decomposition tank and flows into the recovery tank where the photo-catalyst particles are separated by the irradiation of ultrasonic at low frequency. Separated particles are returned to the decomposition tank.