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典型PPCPs在氯氧化及紫外/氯工艺中的降解与转化规律研究
论文作者:童鞋论文网  论文来源:www.txlunwenw.com  发布时间:2019/9/11 8:35:42  

摘要:近年来,药品及个人护理产品(PPCPs)在水环境的各个区域被频繁检出。由于水环境中的PPCPs对人体健康具有潜在威胁,从而引起人们的广泛关注。环境中残留PPCPs能够进入饮用水处理系统,威胁饮用水水质安全。

氯消毒是一种应用广泛的传统消毒工艺,几百年来在防止水生疾病,保障饮用水水质安全方面承担着重要作用。但过程中产生的氯代消毒副产物通常对人体有害。优化氯氧化工艺,分析氯消毒副产物的毒性是目前氯氧化工艺的重要研究方向。紫外/氯工艺作为一种新型高级氧化技术,对于控制水中消毒副产物的产生具有重要研究意义。使用紫外与氯消毒联用工艺降解水中痕量污染物PPCPs,逐渐引起人们的广泛关注。

本研究对典型PPCPs有机防晒剂二苯甲酮-9(BP9)在氯消毒过程中的氧化反应进行研究,考察BP9初始浓度、余氯初始浓度、溶液pH值和氨氮浓度对反应的影响,探究BP9氯氧化降解机理,识别氯氧化反应产物,评估其生态风险。结果表明,在BP9初始浓度5 mg·L-‍1、余氯初始浓度5 mg·L-1的条件下,90 s内BP9去除率达到91.3%,符合准一级反应动力学。降解速率常数随着BP9初始浓度及氨氮浓度增加而减小,随余氯初始浓度增大而增大,中性条件下有利于BP9氯氧化反应。基于高效液相色谱质谱联用仪(HPLC-MS/MS)和气相色谱质谱联用仪(GC-MS)解析出7种中间产物,提出可能降解路径。发光细菌毒性分析和ECOSAR软件预测均表明,BP9氯氧化反应生成了比母物质毒性更高的中间产物,对饮用水水质安全造成潜在风险。

此外,本研究对药物类典型PPCPs对乙酰氨基酚(AAP)和诺氟沙星(Nor)在紫外/氯工艺中的反应进行研究,考察污染物初始浓度、余氯初始浓度、紫外光强、溶液pH值和氨氮浓度对反应的影响,探究AAP和Nor在紫外/氯工艺中降解机理,识别降解产物反应路径,评估其生态风险。研究表明,紫外/氯工艺是一种有效去除水中AAP和Nor的水处理工艺。两种物质降解过程均符合准一级反应动力学。与单一紫外或单一氯氧化相比,紫外光和次氯酸钠的联用明显加速了降解过程。另外,紫外/氯工艺的反应速率常数随游离氯初始浓度和紫外光强的增加而增加,随污染物初始浓度增加而减小。强酸性和弱碱性条件有利于AAP降解,弱碱性条件利于Nor降解。根据前线轨道理论,AAP苯环上的C5位置可能是HO•和Cl•最易攻击的活性位点,N5是Nor反应活性最强的位点。在紫外/氯降解AAP过程中鉴定出12种AAP中间产物,其中7种是由超高效液相色谱飞行时间质谱联用仪(UPLC-Q-TOF)数据得出,5种是通过GC-MS得出;在Nor降解过程中使用UPLC-Q-TOF鉴定出30种降解中间产物。活性自由基参与了一系列反应,包括氯化反应、羟基化反应和脱羧反应。发光细菌毒性试验和ECOSAR预测均表明,在降解过程中AAP和Nor反应液的急性毒性没有降低。因此,需要进一步评估紫外/氯工艺的生态风险,以确保饮用水水质的安全。

Currently, pharmaceuticals and personalcare products (PPCPs) cause wide public concern due to their frequentoccurrence in aquatic environment and the potential risks posing to humanhealth. PPCPs are detected in high prevalence environments. The residuals ofPPCPs are continuously emitted into the drinking water sources, threatening thesafety of drinking water quality.

Chlorination is a widely used traditionaldisinfection process, that has played an important role in preventing aquaticdiseases and ensuring the safety of drinking water for hundreds of years.However, chlorine by-products are generally harmful to humans. Optimizing thechlorination and analyzing the toxicity of chlorine by-products are importantresearches. The UV/chlorine process, as a new advanced oxidation technology,has important significance in controlling the production of disinfectionby-products. Degradation PPCPs by the combination of UV and chlorine hasgradually attracted widespread attention.

Chlorination of a typical PPCPsbenzophenone-9 (BP9) was studied. The effect of initial BP9 concentration,initial residual chlorine, pH value, and ammonia concentration on the reactionwere also investigated. The degradation mechanism and the ecological risk werefurther discussed. The results indicated that, BP9 removal could reach 91.3% in90s under the conditions of initial BP9 concentration 5 mg·L-1, initialresidual chlorine 5 mg·L-1. BP9 chlorination process obeyed thepseudo-first-order kinetics. The degradation rate decreased with the increaseof initial BP9 concentration and ammonia nitrogen concentration, whileincreased with the increase of initial residual chlorine. Neutral conditionsare favorable for BP9 chlorination. Seven intermediates were identified byHPLC-MS/MS and GC-MS, and possible degradation pathways were also proposed.Luminescent bacteria experiment and ECOSAR prediction both showed thatintermediates produced in BP9 chlorination have higher toxicity than the parentcompound, which pose a potential risk to drinking water safety.

The removal of acetaminophen (AAP) andnorfloxacin (Nor) in aqueous solution by the UV/chlorine process wereevaluated. The effect of the initial contaminant concentration, chlorine dose,pH value, and UV intensity on the reaction were also investigated. Thedegradation mechanism and the ecological risk were further discussed. Theresults indicated that degradation both fitted pseudo-first-order kinetics.Compared with UV alone or dark chlorination, the combination of UV and chlorinesignificantly accelerated the degradation process. The degradation waspositively affected by chlorine dose and UV intensity, while negativelyaffected by the initial contaminant concentration during the UV/chlorineprocess. Strong acidic and weak alkaline conditions were favorable for AAPdegradation. And weak alkaline conditions were favorable for Nor degradation.The frontier orbital theory analysis shows that the C5 position in the benzenering of AAP is likely to be the first site attacked by HO• and Cl• radical toform the products. N5 position of Nor is likely to be the most reactiveposition. During the AAP degradation by the UV/chlorine process, sevenintermediates of AAP were identified by Q-TOF, and five transformation productswere detected based on GC-MS. Thirty intermediates were identified by Q-TOFduring Nor degradation. The active radicals participate in a series ofreactions, including hydroxylation, decarboxylation, and chlorination.Luminescent bacteria experiment and ECOSAR prediction both revealed that acutetoxicity of AAP and Nor degradation could only be partially reduced. Ecologicalrisks during the UV/chlorine process need to be further evaluated.

关键词:PPCPs;氯氧化;紫外/氯工艺;影响因素;中间产物;风险评价

PPCPs; Chlorination; UV/chlorine process;Influencing factors; Intermediates; Risk assessment

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