|Alternative Title||Transformation of water quality in drinking water distribution system with sequential disinfection of UV and Cl2|
|Place of Conferral||北京|
|Keyword||饮用水 Uv/cl2消毒 管网水质 生物膜 反硝化菌 Drinking Water Uv/cl2 Disinfection Distribution System Water Quality Biofilm Nitrate Reducing Bacteria|
|Abstract|| 饮用水处理过程中，传统的氯消毒在控制管网中微生物生长的同时会增加消毒副产物（DBPs）的生成风险。近年来，紫外（Ultraviolet，UV）消毒逐渐引起人们关注。通常情况下紫外和氯联合应用于饮用水消毒。了解紫外与氯（UV/Cl2）联合消毒对管网水质转化的影响对饮用水水质安全保障具有重要意义。本论文以北方某自来水厂地表水和地下水为研究对象，采用环状生物膜反应器模拟管网，系统研究了 UV/Cl2联合消毒的饮用水管网中水质及微生物群落结构变化情况，主要研究内容和结果如下：|
从水库底泥中提取天然有机物（NOM），根据亲疏水性的不同分级成腐殖酸（HA）、富里酸（FA）和富里酸亲水（FAHPI）部分，以市售 HA和 FA作为对照，通过高效凝胶色谱（HP-SEC）、红外光谱（FT-IR）表征以及氯消耗实验确定 NOM 中氯反应活性位点，研究低（中）压紫外照射对 NOM中反应活性位点及后续 DBPs 生成的影响。研究结果表明底泥中提取的疏水性 HA的氯反应活性基团是芳环、甲基、愈创木基木质素基团，DBPs的生成以三氯甲烷（TCM）为主；而底泥中提取的 FA和 FAHPI的氯反应活性基团是酚羟基，DBPs的生成以二氯乙酸（DCAA）为主。UV照射可以降低NOM疏水性和TCM生成量，增加 NOM亲水性和 DCAA生成量。相同剂量的中压 UV照射对NOM结构及DBPs生成的影响较低压紫外照射大。
以地表水为研究对象，通过扫描电镜（ SEM）、X-射线衍射（XRD）、电化学、定量PCR（qPCR）和焦磷酸测序Pyrosequencing）等分析方法，表征管网腐蚀、管垢物相结构、管垢生物膜中微生物群落结构特征，探讨采用UV/Cl2联合消毒强化腐蚀层形成的地表水管网中管网腐蚀及微生物群落结构特征。结果表明，UV/Cl2消毒管网中，UV预处理可以减少氯消毒管网中氯消耗，并抑制拉森指数升高带来的管网出水铁释放和浊度增加。定量 RCR、焦磷酸测序和主成份分析结果表明UV预处理可以诱发氯消毒管网管垢生物膜中反硝化菌Dechloromonas sp.成为优势菌，微生物驱动的铁氧化还原循环进一步抑制UV/Cl2消毒管网的腐蚀，而单独 Cl2消毒管网中分泌铁载体的微生物抑制腐蚀效果较反硝化菌低。
以地下水和地表水为研究对象，通过定量PCR（qPCR）和焦磷酸测序（Pyrosequencing）分析，表征管网进出水及管垢生物膜的微生物群落结构及条件致病菌分枝杆菌（Mycobacterium sp.）含量变化。研究结果表明不经过低氯生物膜培养阶段，UV与高浓度氯抑制管网中总细菌及铁循环菌生长，管网生物膜对腐蚀抑制作用减弱，腐蚀速率加快。消毒剂可以有效控制管网出水中条件致病菌分枝杆菌（Mycobacterium sp.），但对管垢生物膜中分支杆菌抑制效果不明显。
|Other Abstract|| Chlorination has been considered as a cost-effective approach for inactivating waterborne pathogens in drinking water treatment (DWT), However, chlorine reacts with natural organic matter (NOM) to form a variety of toxic disinfection by-products (DBPs). Recently, ultraviolet irradiation has gained increasing application as a primary disinfectant in DWT, followed by chlorination. While effects of UV/Cl2 treatment on the transformation of water quality in drinking water distribution system (DWDS)are unclear. In this scenario,annular reactors (ARs) were installed to simulate the DWDS, with the carbon-filtered water and ground water as the raw water. Tranformation of water quality in DWDS with UV/Cl2 disinfection were systematically investigated. The main conclusions were as follows.|
(1) UV effects on NOM structure and subsequent DBPs formation
Sediment-derived humic acid (HA), fulvic acid (FA) and hydrophilic fraction of fulvic acid (FAHPI) samples were utilized in UV irradiation followed by chlorination, with the commercial humic substances for comparison. High performance size exclusion chromatography (HP-SEC),fourier transform infrared spectroscopy (FT-IR) and chlorine decay were utilized to characterize the reactive groups toward chlorine. UV effects on the reactive groups of NOM and subsequent DBPs formation were evaluated. It was found that FA and FAHPI samples mainly consisted of ester, phenolic hydroxyl and aromatic ketone groups, among them,phenolic hydroxyl groups were highly reactive with chlorine, forming dichloroacetic acid (DCAA) during chlorination. While HA samples mainly contained aromatic, methyl and guaiacyl lignin groups, which were reactive toward chlorine, forming trichloromethane (TCM). UV irradiation eliminated the aromatic, methyl and guaiacyl lignin groups, depressing TCM formation during post-chlorination and increased phenolic hydroxyl groups, enhancing subsequent DCAA formation. Medium pressure UV light generally exerted greater impacts on NOM structures and subsequent DBPs formation than corresponding low pressure UV light did.
(2) Effects of UV/Cl2 treatment on DBPs transformation in drinking water distribution system
Annular reactors (ARs) equipped with cast iron coupons were installed to simulate the DWDS. THM4 and HAA5 concentrations in influents and effluents of AR with UV/Cl2 and AR with Cl2 were monitored. Excitation emission matrix (EEM), electrochemistry analysis and pyrosequencing were used to characterize the orgnic matters in influents and effluents of ARs, corrosion rate and biological community in biofilms. It was found that both THM4 and HAA5 concentration in effluents of two ARs were decreased as compared with that in influents at different running stages. At stage I, corrosion rate and DBPs reduction ratio in the AR with UV/Cl2 were higher than that in the AR with Cl2, while corrosion rate and DBPs reduction ratio in the AR with Cl2 were higher than that in the AR with UV/Cl2 at stage II. Pyrosequncing resutls showed that relative abundance of dehalogenating bacteria in the biofilm of AR with Cl2 was higher than that in the biofilm of AR with UV/Cl2at different running stages. Reduction of DBPs was influenced by both the biological and chemical porcesses in DWDS.
(3) Characterization of corrosion and biological community in corrosion-reinforced surface water DWDS with UV/Cl2 disinfection
Surface water was used to simulated the DWDS. Scanning electron microscopy (SEM), X-ray diffraction (XRD), electrochemistry analysis, realtime fluorescent quantitative-PCR (qPCR) and pyrosequencing were utilized to characterize the corrosion rate, corrosion scales and biological commuinty of bioflims in the AR with UV/Cl2 and AR with Cl2. It was found that UV pretreatment not only reduced the required initial chlorine dose, but also inhibited the iron release and turbidity of effluents resulting from the increase of the Larson-Skold Index (LI) of drinking water. It was verified that UV/Cl2 disinfection denitrifying functional bacteria advantage in the biofilm of corrosion scales in drinking water distribution system. Principal component analysis indicated that the nitrate-reducing bacteria (NRB) Dechloromonas exhibited the greatest corrosion inhibition by inducing the redox cycling of iron to enhance the precipitation of iron oxides and formation of Fe3O4 in the AR with UV/Cl2, while the rhizobia Bradyrhizobium and Rhizobium, and the NRB Sphingomonas, Brucella producing siderophores had weaker corrosion-inhibition effect by capturing iron in the AR with Cl2.
(4) Characterization of corrosion and biological community in DWDS with UV/Cl2 disinfection under physical running condition
Ground water and carbon-filtered surface water was used to simulated the DWDS. Realtime fluorescent quantitative-PCR (qPCR) and pyrosequencing were utilized to characterize total bacteria, opportunistic pathogen and biological communities in the influents, effluents and biofilm of two ARs.It was found thatsequential disinfection with UV and high chlorine prevented the accumulation of biomass within the AR, preventing the formation of protective layer, resulting higher corrrosion rate in the AR with UV/Cl2 than that with Cl2 alone. In addition, disinfectant could better control Mycobacterium sp. (opportunistic pathogen) in bulk water than that in biofilms.
|朱莹. 紫外与氯联合消毒的饮用水管网水质转化研究[D]. 北京. 中国科学院研究生院,2015.|
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