管网中土霉味致嗅物卤代苯甲醚的生物甲基化生成与调控机制研究

In recent years, it is common that the finished water quality reach the drinking water standard. However, there is off-flavor in tap water for a long term in China and at abroad, which make people distrust the water quality even panic. Haloanisoles, as an earthy-musty odorant, is continually detected in tap water. The proposer’s previous studies have shown that haloanisoles were easily produced by disinfection by-products halophenol biomethylation. However, the specific biological mechanisms and process are unclear. The annular reactor (AR) will be used to simulate the real water supply pipeline in this proposal. The spatio-temporal distribution of haloanisoles will be studied under different biofilm structures, water quality factors and hydraulic conditions. The main microorganisms promoting biomethylation and O-methyltransferase will be screened and evaluated using high-throughput sequencing method and so on. The chemical structure characteristics of some dominate precursor and methyl donor with high biological potential will be analyzed. We will research on the key environmental conditions and important factors during 2-3 kinds of preponderant bacteria or fungi producing O-methyltransferase and promoting haloanisoles formation. After that, we will also build the kinetics model and dynamic pathway of odorants formation under the reaction of residual chlorine and biofilm. On the basis of the research, the mechanisms of haloanisoles formation by biomethylation will be demystified. In addition, the characteristics and key factors of musty-earthy odorants formation in distribution system will also be investigated. These results of the study will be helpful to predict the risk of taste and odor compounds formation and prevent the off-flavor pollutants occurring in tap water.

国内外自来水普遍存在出厂水质达标，而龙头水长期有异味的矛盾，造成民众对水质安全的不信任甚至恐慌。卤代苯甲醚是一类龙头水中检出率较高的土霉味致嗅物，申请人前期研究表明经生物甲基化易由消毒副产物卤代酚产生，但具体生物作用机制与过程尚不明确。本项目拟采用环状生物膜反应器（AR）模拟供水管道，研究不同生物膜结构、水质因素和水力条件下卤代苯甲醚的时空分布规律；采用高通量测序等手段筛选和鉴定促进生物甲基化的主要微生物和氧甲基转移酶，分析具有高生物化潜能的主导前体物和甲基供体的化学结构特征；研究2-3种优势细菌/真菌产生氧甲基转移酶和促进卤代苯甲醚生成的关键环境条件及控制因素；建立余氯和生物膜作用下致嗅物产生的动力学模型和动态生成路径。经研究揭示生物甲基化产生卤代苯甲醚的本质，明确土霉味致嗅物在管道中的产生规律及制约因素，为预测致嗅物的生成风险和从根本上抑制龙头水异嗅异味的产生提供理论依据。

近年来供水管网引发的嗅味问题受到了密切关注，成为我国饮用水品质保障中一项亟需解决的科学问题。卤代苯甲醚（HA）是一种新兴的土霉味致嗅物，主要由微生物甲基化作用生成。然而，其生成机制尚不明确，导致无法有效控制饮用水嗅味。因此，本项目研究了管网内微生物生成HA的规律和机理，利用中试管网和环形反应器（AR）模拟实际供水管道，探究了不同因素对管网内2,4,6-三氯苯甲醚（TCA）生成的影响，对比了不同种类HA生成量和揭示反应前后微生物的变化规律；比较了不同细菌的HA生成能力、O-甲基化特点及在实际管网内的分布；研究了饮用水中氯和金属离子对HA细胞内外分布的影响和内在机制；基于宏转录组测序，识别了生物膜内潜在卤代酚甲基转移酶（HPOMT）的种类。.研究结果表明：（1）球墨铸铁管生成的2,4,6-TCA最多，最大生成量为385ng/L；温度上升和流速增加可促进2,4,6-TCA的生成；余氯对2,4,6-TCA生成的抑制率为38.8%~47.1%。（2）筛选出8株细菌，其中伴熊鞘氨醇单胞菌主要生成TCA和TBA，而摩拉维亚假单胞菌易生成DCA和MCA。S-腺苷甲硫氨酸是产嗅细菌主要的甲基供体。（3）2,3,6-TCA主要位于细胞内（87.4%~96.0%）。余氯可抑制总2,3,6-TCA的生成，但增加了胞外的浓度；Ca2+, Mg2+ 及低浓度的Fe3+和Zn2+能促进2,3,6-TCA的生成；高浓度Fe3+和Zn2+及Cu2+, Mn2+对2,3,6-TCA的生成有抑制作用。除了影响HPOMT活性，金属离子还能改变质膜完整性和调节SAM循环过程来影响HA的生成和分布。（4）经宏转录组测序，发现了5种HPOMT，主要来自硝基还原假单胞菌和阿氏肠杆菌。.本项目解决了HA在供水管网中如何产生，如何被抑制等机制不明的科学问题，为提出控制管网中异嗅异味的产生和保障饮用水品质的方案和技术提供了理论依据。