Department of Chemical and Biological Engineering, The University of British Columbia, Vancouver, Canada.
Water Sci Technol. 2011;63(7):1427-33. doi: 10.2166/wst.2011.321.
Vacuum-UV (VUV) photoinduced degradation of the herbicide 2,4-D was studied. A flow-through VUV photoreactor was used (i) in batch mode to study the kinetics of degradation and (ii) in continuous mode under steady state to analyze the potential utilization of this process in commercial applications. In both cases, the reactants were recycled to minimize diffusive resistances. Experimental results from the batch studies showed that the initial degradation rate of 2,4-D in ultrapure water was independent of the initial concentration of the herbicide. However, a reduction in the reaction rate was obtained over the course of the treatment, largely due to the formation of 2,4-D partial oxidation by-products which compete with 2,4-D molecules for HO (scavenging effect). Increases in water alkalinity reduced 2,4-D degradation rate as a consequence of the scavenging of HO by carbonates and bicarbonates. The degradation of 2,4-D in raw surface waters was also investigated. A noticeable reduction in the degradation rate was observed because of the presence of NOM and alkalinity, both being known HO scavengers. Additionally, the presence of inorganic species/ions that absorb VUV may also have contributed to the reduction of the overall degradation rate. High conversions were obtained in the continuous system. At a residence time of 25 seconds, conversions of 97% and 65% were achieved for inlet herbicide concentrations of 1 and 10 mg L(-1), respectively. Under these conditions, the received dose of 185 nm radiation was 44.8 mJ cm(-2).
真空紫外（VUV）光诱导除草剂 2,4-D 的降解研究。采用流动式 VUV 光反应器（i）在分批模式下研究降解动力学，（ii）在稳态下连续模式下分析该过程在商业应用中的潜在应用。在这两种情况下，反应物都被回收以最小化扩散阻力。批处理研究的实验结果表明，2,4-D 在超纯水中的初始降解速率与除草剂的初始浓度无关。然而，在处理过程中，反应速率会降低，这主要是由于 2,4-D 的部分氧化副产物的形成，这些副产物与 2,4-D 分子竞争 HO（清除作用）。水的碱度增加会降低 2,4-D 的降解速率，这是由于碳酸盐和碳酸氢盐对 HO 的清除作用。还研究了 2,4-D 在天然地表水中的降解情况。由于存在 NOM 和碱度，这两种物质都是已知的 HO 清除剂，因此观察到降解速率明显降低。此外，可能会吸收 VUV 的无机物质/离子的存在也会导致整体降解速率降低。在连续系统中获得了高转化率。在停留时间为 25 秒的情况下，当入口除草剂浓度分别为 1 和 10 mg/L(-1)时，转化率分别达到 97%和 65%。在这些条件下，185nm 辐射的接收剂量为 44.8 mJ cm(-2)。
