Reactive Nitrogen Species Are Also Involved in the Transformation of Micropollutants by the UV/Monochloramine Process
Reactive Nitrogen Species Are Also Involved in the Transformation of Micropollutants by the UV/Monochloramine Process
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活性氮也参与紫外线/一氯胺工艺对微污染物的转化
DOI：
10.1021/acs.est.9b01212
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发表时间：
2019-10-01
影响因子：
11.4
通讯作者：
Fang，Jingyun
中科院分区：
文献类型：
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作者：
Wu，Zihao;Chen，Chunyan;Fang，Jingyun
UV/一氯胺(NH_2Cl)工艺是水处理中一种新兴的高级氧化工艺，它是通过NH_2Cl的紫外光解产生的自由基来实现的。以布洛芬(IBP)和萘普生(NPX)为代表性微污染物，研究了UV/NH2ClAOP对微污染物的降解作用。在这个过程中发现了羟基自由基(HO·)和氯原子(Cl·)，并且意外地发现，活性氮物种(RNS)在微污染物的转化中也起着重要的作用。电子顺磁共振(EPR)分析证实了·NO和HO·的产生。在pH 6.0~8.6范围内，HO·、Cl·和·NO的浓度基本不变，导致IBP和NPX的基于UV通量的准一级速率常数(k‘)略有变化，分别为1.65×10-3和2.54×10-3cm2/mJ。对于IBP，在pH为7，50μM-NH_2Cl时，RNS对K‘的相对贡献率为27.8%，高于Cl·(6.5%)，但低于HO·(58.7%)。对于NPX，RNS对K‘的相对贡献率为13.6%，低于Cl·(23.2%)和HO·(46.9%)。HO·、Cl·和·NO的浓度随着NH_2Cl投加量的增加而增加。天然有机物(NOM)和碳酸氢盐的水基质组分可清除HO·、Cl·和RNS。5 mg/L能使IBP和NPX的K‘分别降低66.9%和57.6%，而2 mM小苏打由于CO3·-对NPX降解的贡献，使IBP的K’降低了57.4%，NPX的K‘增加了10.5%。在UV/NH_2Cl降解IBP和NPX的过程中，检测到含有亚硝基、羟基和氯基的产物，表明氮氧化物自由基(·NO)以及HO·和Cl·的作用。UV/NH2Cl处理的样品中三氯硝基甲烷的生成被强烈地促进，进一步表明RNS在这一过程中的重要作用。本研究首次证明了RNS参与了微污染物在UV/NH_2Cl中的转化。
The UV/monochloramine (NH2Cl) process is an emerging advanced oxidation process (AOP) in water treatment via radicals produced from the UV photolysis of NH2Cl. This study investigated the degradation of micropollutants by the UV/NH2Cl AOP, with ibuprofen (IBP) and naproxen (NPX) selected as representative micropollutants. Hydroxyl radical (HO•) and chlorine atom (Cl•) were identified in the process, and unexpectedly, we found that reactive nitrogen species (RNS) also played important roles in the transformation of micropollutants. The electron paramagnetic resonance (EPR) analysis proved the production of•NO as well as HO•. The concentrations of HO•, Cl•, and•NO in UV/NH2Cl remained constant at pH 6.0–8.6, resulting in the slightly changed UV fluence-based pseudo-first-order rate constants (k′) of IBP and NPX, which were about 1.65 × 10–3and 2.54 × 10–3cm2/mJ, respectively. For IBP, the relative contribution of RNS tok′ was 27.8% at pH 7 and 50 μM NH2Cl, which was higher than that of Cl•(6.5%) but lower than that of HO•(58.7%). For NPX, the relative contribution of RNS tok′ was 13.6%, which was lower than both Cl•(23.2%) and HO•(46.9%). The concentrations of HO•, Cl•, and•NO increased with the increasing NH2Cl dosage. Water matrix components of natural organic matter (NOM) and bicarbonate can scavenge HO•, Cl•, and RNS. The presence of 5 mg/L NOM decreased thek′ of IBP and NPX by 66.9 and 57.6%, respectively, while 2 mM bicarbonate decreased thek′ of IBP by 57.4% but increased thek′ of NPX by 10.5% due to the contribution of CO3•–to NPX degradation. Products containing nitroso-, hydroxyl-, and chlorine-groups were detected during the degradation of IBP and NPX by UV/NH2Cl, indicating the role of nitrogen oxide radical (•NO) as well as HO•and Cl•. Trichloronitromethane formation was strongly enhanced in the UV/NH2Cl-treated samples, further indicating the important roles of RNS in this process. This study first demonstrates the involvement of RNS in the transformation of micropollutants in UV/NH2Cl.