Dichloramine (NHCl₂) naturally exists in reverse osmosis (RO) permeate due to its application as an antifouling chemical in membrane-based potable reuse treatment. This study investigated mechanisms of background NHCl₂ hydrolysis associated with the generation of oxidative radical species in RO permeate, established a kinetic model to predict the oxidative capacity, and examined its removal efficiency on trace organic contaminants in potable reuse. Results showed that NHCl₂ hydrolysis generated transient peroxynitrite (ONOO^–) and subsequently dissociated into hydroxyl radical (HO^•). The maximal HO^• exposure was observed at an RO permeate pH of 8.4, higher than that from typical ultraviolet (UV)-based advanced oxidation processes. The HO^• exposure during NHCl₂ hydrolysis also peaked at a NH₂Cl-to-NHCl₂ molar ratio of 1:1. The oxidative capacity rapidly degraded 1,4-dioxane, carbamazepine, atenolol, and sulfamethoxazole in RO permeate. Furthermore, background elevated carbonate in fresh RO permeate can convert HO^• to carbonate radical (CO₃^•–). Aeration of the RO permeate removed total carbonate, significantly increased HO^• exposure, and enhanced the degradation kinetics of trace organic contaminants. The kinetic model of NHCl₂ hydrolysis predicted well the degradation of contaminants in RO permeate. This study provides new mechanistic insights into NHCl₂ hydrolysis that contributes to the oxidative degradation of trace organic contaminants in potable reuse systems.

中文翻译：

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膜淡化渗透物中的二氯胺水解：饮用水再利用应用中氧化能力的机理见解和影响


二氯胺 (NHCl ₂ ) 天然存在于反渗透 (RO) 渗透液中，因为它在基于膜的饮用水回用处理中用作防污化学品。本研究研究了背景 NHCl ₂ 水解与 RO 渗透液中氧化自由基物质生成相关的机制，建立了预测氧化能力的动力学模型，并检验了其对饮用水回用中痕量有机污染物的去除效率。结果表明，NH4Cl ₂ 水解产生瞬时过氧亚硝酸盐（ONOO ^– ），随后解离为羟基自由基（HO ^• ）。在 RO 渗透液 pH 值为 8.4 时观察到最大 H2O ^• 暴露，高于典型的基于紫外线 (UV) 的高级氧化工艺。 NHCl ₂ 水解过程中 H2O ^• 暴露也在 NH ₂ Cl-to-NHCl ₂ 摩尔比为 1:1 时达到峰值。氧化能力快速降解 RO 渗透液中的 1,4-二恶烷、卡马西平、阿替洛尔和磺胺甲恶唑。此外，新鲜 RO 渗透物中背景升高的碳酸盐可以将 H2O ^• 转化为碳酸盐自由基 (CO ₃ ^•– )。 RO 渗透物的曝气去除了总碳酸盐，显着增加了 H2O ^• 暴露，并增强了痕量有机污染物的降解动力学。 NHCl ₂ 水解动力学模型很好地预测了RO渗透水中污染物的降解。这项研究为 NHCl ₂ 水解提供了新的机制见解，该水解有助于饮用水再利用系统中痕量有机污染物的氧化降解。