The University of Queensland, Advanced Water Management Centre, Queensland, 4072, Australia.
The University of Queensland, Advanced Water Management Centre, Queensland, 4072, Australia; ICRA, Catalan Institute for Water Research, Scientific and Technological Park of the University of Girona, H(2)O Building, Emili Grahit 101, 17003 Girona, Spain; ICREA, Catalan Institute for Research and Advanced Studies, 08010, Barcelona, Spain.
Water Res. 2017 May 1;114:113-121. doi: 10.1016/j.watres.2017.01.038. Epub 2017 Jan 23.
Chlorine demand of a water sample depends on the characteristics of dissolved organic matter (DOM). It is an important parameter for water utilities used to assess oxidant and/or disinfectant consumption of source waters during treatment and distribution. In this study, model compounds namely resorcinol, tannic acid, vanillin, cysteine, tyrosine, and tryptophan were used to represent the reactive moieties of complex DOM mixtures. The reactivity of these compounds was evaluated in terms of Cl demand and electron donating capacity (EDC). The EDC was determined by mediated electrochemical oxidation (MEO) which involves the use of 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) as an electron shuttle. The Cl demand of readily oxidizable compounds (resorcinol, tannic acid, vanillin, and cysteine) was found to correlate well with EDC (R = 0.98). The EDC values (mol e/mol C) of the model compounds are as follows: 1.18 (cysteine) > 0.77 (resorcinol) > 0.59 (vanillin) > 0.52 (tannic acid) > 0.36 (tryptophan) > 0.19 (tyrosine). To determine the effect of pre-oxidation on EDC, ozone was added (0.1 mol O/mol C) into each model compound solution. Ozonation caused a general decrease in EDC (10-40%), chlorine demand (10-30%), and UV absorbance (10-40%), except for tyrosine which showed both increased UV and EDC. Before and after ozonation, 24 h disinfection byproduct (DBP) formation potential tests (Cl residual = 1.5 mg/L) were conducted to evaluate the use of EDC for DBP formation prediction. The results indicate that there was no significant correlation between the EDC of the model compounds and the formation potentials of adsorbable organic chlorine, trichloromethane, and trichloroacetic acid. This suggests that while EDC correlates with Cl demand, chlorine consumption may not directly translate to DBP formation because oxidation reactions may dominate over substitution reactions. Overall, this study provides useful insights on the reactions of ABTS and HOCl with model DOM compounds, and highlights the potential application of MEO for rapid determination of Cl demand of a water sample.
水样的氯需求取决于溶解有机物（DOM）的特性。它是供水公司用于评估源水在处理和分配过程中氧化剂和/或消毒剂消耗的重要参数。在本研究中，使用间苯二酚、没食子酸、香草醛、半胱氨酸、酪氨酸和色氨酸等模型化合物来代表复杂 DOM 混合物的反应部分。根据氯需求和电子供体能力（EDC）来评估这些化合物的反应性。EDC 通过介导电化学氧化（MEO）来确定，该方法涉及使用 2,2'-联氮-双（3-乙基苯并噻唑啉-6-磺酸）（ABTS）作为电子穿梭体。易氧化化合物（间苯二酚、没食子酸、香草醛和半胱氨酸）的氯需求与 EDC 密切相关（R=0.98）。模型化合物的 EDC 值（mol e/mol C）如下：1.18（半胱氨酸）>0.77（间苯二酚）>0.59（香草醛）>0.52（没食子酸）>0.36（色氨酸）>0.19（酪氨酸）。为了确定预氧化对 EDC 的影响，向每个模型化合物溶液中添加臭氧（0.1 mol O/mol C）。臭氧化普遍导致 EDC（10-40%）、氯需求（10-30%）和紫外吸光度（10-40%）降低，除了酪氨酸，其紫外吸光度和 EDC 均增加。臭氧化前后进行 24 小时消毒副产物（DBP）生成潜力测试（Cl 残留=1.5 mg/L），以评估 EDC 用于 DBP 生成预测的使用情况。结果表明，模型化合物的 EDC 与可吸附有机氯、三氯甲烷和三氯乙酸的生成潜力之间没有显著相关性。这表明，虽然 EDC 与氯需求相关，但氯消耗可能不会直接转化为 DBP 生成，因为氧化反应可能超过取代反应。总的来说，本研究提供了关于 ABTS 和 HOCl 与模型 DOM 化合物反应的有用见解，并强调了 MEO 用于快速测定水样氯需求的潜在应用。
