Department of Civil and Environmental Engineering, Stanford University, 473 Via Ortega, Stanford, CA, 94305, United States.
Research & Development Department, Orange County Water District, 18700 Ward Street, Fountain Valley, CA, 92708, United States.
Water Res. 2019 Nov 1;164:114939. doi: 10.1016/j.watres.2019.114939. Epub 2019 Jul 31.
Advanced oxidation using UV/free chlorine and UV/chloramines are being considered as alternatives to UV/HO for treatment of reverse osmosis (RO) permeate in treatment trains for the potable reuse of municipal wastewater. This pilot-scale comparison of the three advanced oxidation processes (AOPs) evaluated three factors important for selecting among these alternatives. First, the study characterized the speciation of oxidants serving as the source of radicals within the AOPs to facilitate process modeling. Kinetic modeling that included consideration of the chloramines occurring in RO permeate accurately predicted oxidant speciation. Modeling of the UV/free chlorine AOP indicated that free chlorine is scavenged by reactions with ammonia and monochloramine in RO permeate, such that oxidant speciation can shift in favor of dichloramine over the short (∼30 s) timescale of AOP treatment. Second, the order of efficacy for degrading the target contaminant, 1,4-dioxane, in terms of minimizing UV fluence was UV/free chlorine > UV/HO ≫ UV/chloramines. However, estimates indicated that the UV/chloramines and UV/HO AOPs could be similar on a cost-effectiveness basis due to savings in reagent costs by the UV/chloramines AOP, provided the RO permeate featured >3 mg/L as Cl chloramines. Third, the study evaluated whether the use of chlorine-based oxidants within the UV/free chlorine and UV/chloramines AOPs enhanced disinfection byproduct (DBP) formation. Even after AOP treatment and chloramination, total halogenated DBP formation remained low at <15 μg/L for all three AOPs. DBP formation was similar between the AOPs, except that the UV/free chlorine AOP promoted haloacetaldehyde formation, while the UV/HO and UV/chloramines AOPs followed by chloramination increased chloropicrin formation. However, total DBP formation on a toxic potency-weighted basis was similar among the AOPs, since haloacetonitriles and haloacetamides were the dominant contributors and did not differ significantly among the AOPs.
采用 UV/自由氯和 UV/氯胺的高级氧化工艺（AOP）正被视为替代 UV/HO 的方法，用于处理市政污水回用处理厂中的反渗透（RO）产水。本研究采用中试规模对比了这三种高级氧化工艺（AOP），评估了在这些替代方案中选择的三个重要因素。首先，本研究对作为 AOP 中自由基来源的氧化剂的形态进行了特征描述，以方便进行工艺建模。动力学模型包括对 RO 产水中存在的氯胺的考虑，能够准确预测氧化剂的形态。UV/自由氯 AOP 的建模表明，自由氯会与 RO 产水中的氨和一氯胺发生反应而被消耗，因此在 AOP 处理的短（约 30s）时间尺度内，氧化剂的形态可以向二氯胺转变。其次，就最小化紫外线照射量而言，1,4-二恶烷作为目标污染物的降解效果顺序为 UV/自由氯>UV/HO>UV/氯胺。然而，根据估计，如果 RO 产水中的有效氯胺含量>3mg/L，则 UV/氯胺和 UV/HO AOP 在成本效益方面可能相似，因为 UV/氯胺 AOP 可以节省试剂成本。第三，本研究评估了 UV/自由氯和 UV/氯胺 AOP 中使用含氯氧化剂是否会增强消毒副产物（DBP）的形成。即使经过 AOP 处理和氯胺化，所有三种 AOP 的总卤代 DBP 形成仍保持在低水平，<15μg/L。三种 AOP 的 DBP 形成情况相似，除了 UV/自由氯 AOP 促进卤代乙醛形成，而 UV/HO 和 UV/氯胺 AOP 随后进行氯胺化会增加三氯硝基甲烷的形成。然而，根据毒性加权基础，AOP 之间的总 DBP 形成情况相似，因为卤代乙腈和卤代乙酰胺是主要贡献者，并且在 AOP 之间没有显著差异。
