Department of Civil and Mineral Engineering, University of Toronto, 35 St. George Street, Toronto, Ontario, M5S 1A4, Canada.
Department of Civil and Mineral Engineering, University of Toronto, 35 St. George Street, Toronto, Ontario, M5S 1A4, Canada.
Water Res. 2019 Sep 15;161:448-458. doi: 10.1016/j.watres.2019.06.033. Epub 2019 Jun 13.
The photolysis of chlorine by UV light leads to the formation of the hydroxyl radicals (OH) as well as reactive chlorine species (RCS) that can be effective as advanced oxidation processes (AOPs) for water treatment. Much of the research to date has been done at laboratory- or bench-scale. This study reports results from a model that demonstrates that the relative effectiveness of the UV/Cl AOP compared to the more traditional UV/HO AOP is a function of optical path length. As such, the relative effectiveness of the two treatment options evaluated at small scale may not reflect the relative performance at full-scale, making results previously obtained at small-scale potentially less scalable. This study therefore compares the performance of UV/Cl to UV/HO at a full-scale water treatment plant, using sucralose and caffeine as spiked surrogates for contaminants that are reactive solely to OH radicals, and to both OH and RCS, respectively. pH was varied between 6.5 and 8.0. The results demonstrated that when using a medium pressure UV lamp, UV/Cl might lead to approximately twice the production of OH radicals as UV/HO at pH 6.5 when using the same molar oxidant concentration, but adding chlorine to the UV reactor at pH 8.0 had a negligible impact on OH radical concentration in comparison to UV alone. The study also confirmed previous small-scale results that RCS can be a major contributor to UV/Cl treatment for compounds such as caffeine that are susceptible to RCS, with UV/Cl effective at both pH 6.5 and 8.0 for such compounds. Disinfection byproducts were monitored, with adsorbable organohalide (AOX) formation increasing by approximately 10 μg-Cl/L due to chlorine photolysis, but only at pH 6.5 and not at pH 8.0. This implies that UV/Cl might increase AOX mostly due to reaction between OH and organic precursors to make them more reactive with chlorine, and not due to RCS. The formation of specific DBPs of current or emerging regulatory interest was minimal under all conditions, except for chlorate. Chlorate yields were in the order of 6-18% of the photolysed chlorine.
紫外光（UV）光解氯气会生成羟基自由基（OH）和活性氯物种（RCS），这些物质可用作水处理的高级氧化工艺（AOP）。迄今为止，大部分研究都是在实验室或台架规模进行的。本研究报告了一个模型的结果，该模型表明，与更传统的 UV/HO AOP 相比，UV/Cl AOP 的相对有效性是光程的函数。因此，在小尺度下评估的两种处理选择的相对有效性可能无法反映全规模的相对性能，这使得以前在小尺度下获得的结果可能不太具有可扩展性。因此，本研究在一个全规模的水处理厂中比较了 UV/Cl 和 UV/HO 的性能，使用三氯蔗糖和咖啡因作为仅对 OH 自由基有反应以及分别对 OH 和 RCS 有反应的污染物的加标替代物。pH 值在 6.5 到 8.0 之间变化。结果表明，当使用中压 UV 灯时，在相同摩尔氧化剂浓度下，当 pH 值为 6.5 时，UV/Cl 可能导致 OH 自由基的生成量约为 UV/HO 的两倍，但在 pH 值为 8.0 时向 UV 反应器中添加氯对 OH 自由基浓度的影响与单独使用 UV 相比可以忽略不计。该研究还证实了以前在小规模上的结果，即 RCS 可能是对易受 RCS 影响的咖啡因等化合物的 UV/Cl 处理的主要贡献者，对于此类化合物，UV/Cl 在 pH 值为 6.5 和 8.0 时均有效。监测了消毒副产物，由于氯光解，可吸附有机卤化物（AOX）的形成增加了约 10μg-Cl/L，但仅在 pH 值为 6.5 时增加，而在 pH 值为 8.0 时则没有增加。这意味着 UV/Cl 可能会增加 AOX，主要是由于 OH 和有机前体之间的反应，使它们更容易与氯反应，而不是由于 RCS。在所有条件下，除了氯酸盐外，当前或新兴监管关注的特定 DBP 的形成都很少。氯酸盐的产率为光解氯的 6-18%。
