College of Biological and Environmental Engineering, Zhejiang University of Technology, Hangzhou 310032, China.
J Environ Sci (China). 2012;24(10):1777-84. doi: 10.1016/s1001-0742(11)61021-8.
The photodegradation of gaseous dichloromethane (DCM) by a vacuum ultraviolet (VUV) light in a spiral reactor was investigated with different reaction media and initial concentrations. Through the combination of direct photolysis, O3 oxidation and HO* oxidation, DCM was ultimately mineralized into inorganic compounds (such as HCl, CO2, H2O, etc.) in the air with relative humidity (RH) of 75%-85%. During the photodegradation process, some small organic acids (including formic acid, acetic acid) were also detected and the intermediates were more soluble than DCM, providing a possibility for its combination with subsequent biodegradation. Based on the detected intermediates and the confirmed radicals, a photodegradation pathway of DCM by VUV was proposed. With RH 75%-80% air as the reaction medium, the DCM removal followed the second-order kinetic model at inlet concentration of 100-1000 mg/m3. Kinetic analysis showed that the reaction media affected the kinetic constants of DCM conversion by a large extent, and RH 80% air could cause a much lower half-life for its conversion. Such results supported the possibility that VUV photodegradation could be used not only for the mineralization of DCM but also as a pretreatment before biodegradation.
在螺旋反应器中，通过真空紫外（VUV）光对不同反应介质和初始浓度的气态二氯甲烷（DCM）进行光降解研究。通过直接光解、O3 氧化和 HO*氧化的结合，DCM 最终在相对湿度（RH）为 75%-85%的空气中被矿化为无机化合物（如 HCl、CO2、H2O 等）。在光降解过程中，还检测到一些小分子有机酸（包括甲酸、乙酸），且中间产物比 DCM 更易溶解，为后续生物降解提供了结合的可能性。基于检测到的中间产物和确定的自由基，提出了 VUV 光降解 DCM 的途径。在 RH 为 75%-80%的空气作为反应介质的情况下，在入口浓度为 100-1000mg/m3 的情况下，DCM 的去除遵循二级动力学模型。动力学分析表明，反应介质在很大程度上影响了 DCM 转化的动力学常数，而 RH 为 80%的空气会使 DCM 的转化半衰期大大降低。这些结果支持了 VUV 光降解不仅可用于 DCM 的矿化，而且可作为生物降解前的预处理的可能性。
