|Alternative Title||The mechanism of O3-BAC and disinfection processes controlling the regrowth of opportunistic pathogens in the drinking water distribution systems|
|Place of Conferral||北京|
|Keyword||条件致病菌,饮用水输水管网,生物膜,腐蚀产物,Qpcr Opportunistic Pathogens, Drinking Water Distribution Systems, Biofilms, Corrosion Products, Qpcr|
饮用水管网中病原微生物二次增长问题已经越来越受到人们的关注。输水管网中存在生物膜、腐蚀产物、悬浮颗粒物、松散沉积物，这些物相为病原微生物提供了理想的生存场所。当水质等因素扰动时，生物膜、腐蚀产物等中的病原菌可能会脱落、释放进入管网水体，甚至迁移到水龙头，从而对饮用水产生二次污染，产生潜在感染风险。传统病原菌的研究往往关注肠道病原菌如大肠杆菌（Escherichia coli），肠球菌（Enterococcus），伤寒杆菌（Typhoid bacillus）等，而条件致病菌（Opportunistic pathogens，OPs）作为饮用水管网系统中的特殊病原菌，其二次增长及在管网中的分布研究在国内研究还较少。基于此，本研究通过实际管网条件致病菌调查、实验室模拟管网研究、纯菌实验，对条件致病菌在饮用水中分布特征和不同消毒工艺消毒效果进行了相关研究，主要研究结果如下：
3. 以氯消毒（Cl2）为对照，研究UV/Cl2组合工艺对地下水输水管网条件致病菌影响。研究表明：在相同的余氯下，UV/Cl2管网出水中条件致病菌含量低于Cl2，说明UV/Cl2能够更有效控制管网水中条件致病菌的增长。UV/Cl2管网和Cl2消毒管网中的腐蚀产物、生物膜、松散沉积物中的条件致病菌含量没有显著差异（p>0.05），这表明腐蚀产物、生物膜、松散沉积物中的条件致病菌对UV/Cl2工艺的抵抗性较强。Spearman拟合分析发现管网出水、生物膜、腐蚀产物、松散沉积物中的条件致病菌之间存在一定的相关性，说明这些物相中条件致病菌存在一定的微生态关系。管网水样16S rRNA Illumina HiSeq测序表明UV、Cl2、管网均能影响水中微生物群落组成。UV/Cl2进水中微生物多样性低于单独氯消毒管网进水，经过管网后，两管网出水中微生物生物多样性趋于接近。
4. 采用纯菌实验，对比研究条件致病菌P. aeruginosa和指示菌E. coli不同消毒工艺下的灭活特性。（1）紫外及紫外联合消毒（UV/Cl2，Cl2/UV，UV/H2O2，UV/H2O2/Cl2）表明：E. coli对紫外的抗性为P. aeruginosa的1.24倍。悬浮颗粒物能够显著降低紫外消毒效果，且对P. aeruginosa的降低程度大于E. coli。吸附6 h后，P. aeruginoas和E. coli吸附到颗粒物上菌数分别占总菌数94.93%和65.35%，说明P. aeruginosa更容易粘附在悬浮颗粒物上。UV和Cl2，Cl2与UV之间没有观察到协同消毒效应，而UV/H2O2与Cl2之间存在一定协同消毒效应，且对E. coli的协同应大于对P. aeruginosa。光复活/暗复活实验表明，在相同的灭活率下，E. coli的光/暗修复率大于P. aeruginosa；UV/H2O2能有效抑制P. aeruginosa和E. coli光/暗修复。（2）单独氯消毒表明：在高浓度氯时，P. aeruginosa和E. coli都能被氯快速灭活。但是在低浓度氯时，P. aeruginosa氯抗性高于E. coli。悬浮颗粒物能明显降低两种菌的灭活效率，且P. aeruginosa灭活速率降低幅度更大。PI染色和SEM表明在氯消毒过程中P. aeruginosa和E. coli细胞膜被破坏。
The regrowth of pathogens in drinking water distribution systems (DWDS) has been drawn attention. The biofilms, corrosion products, suspended particles, and loose deposits typically exist in DWDS, which could be the ideal realms for the pathogens. The pathogens inhabiting the biofilms and corrosion products may be detached, released, and transferred to the water-taps when their stabilities are disturbed by the water, causing potential pollution and health risks. Previous studies of pathogens are mainly focused on the intestinal pathogens like Escherichia coli, Enterococcus, and Typhoid bacillus et al. However, as the emerging pathogens, opportunistic pathogens (OPs) are limited studied in China, especially for its regrowth and occurrence in the DWDS. Based on this, this study systematically studied the distribution of OPs in DWDS and the impact of different disinfection processes on OPs through OPs survey, simulated DWDS and pure bacteria experiments. The followings are the results of this study.
(1) A total of 44 tap-water samples from 11 taps were sampled to investigate the OPs and FLA of tap-water in a northern city of China. Results demonstrated average gene copies of Legionella spp. and Mycobacterium spp. were significantly higher than Aeromonas spp. (p<0.05). Legionella spp. and Mycobacterium spp. were 100% (44/44) positively detected while P. aeruginosa and Aeromonas spp. were 79.54% (35/44) and 77.27% (34/44) positively detected, demonstrating Legionella spp. and Mycobacterium spp. were resistant OPs in the tap water. Legionella pneumophila was only detected in 4 samples (4/44). No Mycobacterium avium and Naegleria fowleri was detected in any of the samples. Acanthamoeba spp. was 95.45% (42/44) detected. Average gene copies of target OPs (except P. aeruginosa) were highest in summer among four seasons (p<0.05), suggesting the seasonal prevalence of OPs. Average gene copies of OPPPs in the taps of low-use-frequency were relatively higher than taps of high-use-frequency but the difference was not significant for some OPPPs (p>0.05). Spearman correlation analysis demonstrated the number of OPs were negatively correlated with chlorine concentrations (rs=-0.311 to -0.710, p<0.05). However, no significant correlations between the number of OPs and AOC, BDOC, and turbidity were found (p>0.05). Moderate positive correlations were observed between the target microorganisms (rs=0.319-0.785, p<0.05) through Spearman correlation analysis, demonstrating some potential microbial interactions existed between them.
(2) Effects of O3-BAC-Cl2 process on the OPs in the DWDS inoculated with surface water were studied, with single Cl2 and O3-Cl2 disinfection acting as controls. Results showed the AOC, BDOC, and HPC in the BAC-filter column decreased with the depth. In addition, the decrease extent of organic matters and HPC from the top-middle of BAC-filter was relatively bigger than middle-bottom. The OPs in the biofilms of BAC-filter were reduced with the increasing of depth, which could be due to the reduction of nutrients and the microbial competition along the BAC-filter. O3-BAC-Cl2 process could reduce the number of OPs in the effluents of DWDS. However, the effects of O3-BAC-Cl2 controlling the OPs in the biofilms and corrosion products were not apparent, demonstrating the resistance of OPs in the biofilms and corrosion products.
(3) Effects of UV/Cl2 on the OPs in the DWDS inoculated with groundwater were studied, with single Cl2 acting as control. Results showed that the number of OPs in the efffluents of UV/Cl2 was less than Cl2 with the same chlorine residual, demonstrating UV/Cl2 could more effectively control the regrowth of OPs in the water. The number of OPs distributed in the biofilms, corrosion products, and loose deposits of UV/Cl2 and Cl2 was not significant different (p>0.05), demonstrating the OPs in the biofilms, corrosion products, and loose deposits were resistant to UV/Cl2 process. Some correlations between OPs were found in the effluents, biofilms, corrosion products, and loose deposits, suggesting some potential microbial interactions existed in the DWDS. 16S rRNA Illumina HiSeq analysis demonstrated UV, Cl2, and DWDS could influence the microbial community composition. The microbial diversity in the influents of UV/Cl2 was lower than Cl2. However, after flowing through the DWDS, the microbial diversity in the effluents of UV/Cl2 and Cl2 tended to be similar.
(4) Effects of different disinfection processes on the OPs P. aeruginosa and indicator bacteria E. coli were studied with pure bacteria experiments. (1) UV and UV-based disinfection (UV/Cl2，Cl2/UV，UV/H2O2，UV/H2O2/Cl2). E. coli was 1.24 times the UV-resistance of P. aeruginosa. Suspended particles could obviously reduce the efficiency of UV disinfection and the reduction of P. aeruginosa was greater than that of E. coli. After 6 h of attachment, the number of P. aerugionsa and E. coli adsorbed on the particles accounted for 94.93% and 65.35% of the total bacteria respectively, suggesting P. aeruginosa adhered more easily to suspended particles. No synergistic disinfection effect was observed between UV and Cl2, Cl2 and UV. However, there was a certain synergistic disinfection effect between UV/H2O2 and Cl2, and the synergy for E. coli was greater than for P. aeruginosa. Photoreactivation/dark repair experiments showed that the photo- and dark-repair rate of E. coli was greater than that of P. aeruginosa at the same inactivation rate. UV/H2O2 could effectively inhibit P. aeruginosa and E. coli photo/dark repair. (2) Single Cl2 disinfection. Both P. aeruginosa and E. coli could be rapidly inactivated by chlorine at high concentrations of chlorine. However, P. aeruginosa had higher chlorine resistance than E.coli at low concentrations of chlorine. When suspended particles were present, the inactivation rate of the two strains was significantly reduced, and the inactivation rate of P. aeruginosa was reduced more significantly. PI staining and SEM showed that cell membranes of P. aeruginosa and E. coli were destroyed during chlorine disinfection.
|刘丽忠. O3-BAC及消毒工艺对饮用水管网条件致病菌生长控制机理[D]. 北京. 中国科学院生态环境研究中心,2018.|
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