典型污染物包覆层中氯仿的沿程生物转化机制

为明晰氯仿（CF）在包覆层中的降解过程，构建了模拟覆盖层系统（SLCS），并结合高通量测序技术首次系统分析了CF在SLCS中的沿程生物转化机制，结果表明，覆盖层可根据氧气含量分为有氧区（0~20cm）、缺氧区（20~40cm）和无氧区（>40cm）.高通量测序分析表明，有氧区的优势菌为甲烷氧化菌，其中I型菌Methylobacter（甲基杆菌属）及Ⅱ型菌Methylosinus（甲基弯菌属）居多，缺氧区甲烷氧化菌的相对丰度为13%左右，缺氧和无氧区中Anaeromyxobacter（厌氧粘细菌属）成为了优势CF厌氧降解菌.CF在有氧、缺氧和无氧条件下均有效降解.在缺氧和无氧区，CF经厌氧还原脱氯转化为二氯甲烷，部分二氯甲烷在Dehalobacter（脱卤素杆菌属）作用下产生乙酸盐、H₂和CO₂.在有氧区，其余二氯甲烷通过甲烷氧化菌共代谢降解.改变进气口通量发现，SLCS对甲烷的去除率与通量呈负相关关系（R²=0.80），但甲烷氧化速率与通量呈正相关关系（R²=0.90）.与甲烷类似，SLCS对CF的去除率与进气口通量呈负相关关系（R²=0.86），但降解速率与进气口通量呈正相关关系（R²=0.89）.此外，进气口通量的增加对CF好氧共代谢降解的促进作用大于厌氧还原脱氯降解.该研究对氯代烃类污染物的降解提供了新的基础，对该类污染物的原位生物修复提供了理论依据.

The biotransformation mechanism of chloroform in landfill cover

It is important to deeply understanding the degradation mechanism of chloroform (CF) along the depth of a soil layer. In this study, the simulated landfill cover system (SLCS) was set up and biotransformation mechanism of CF was firstly investigated by the method of diversity sequencing. The results showed that the landfill cover was divided into three zones along the depth, aerobic zone (0~20cm), anoxic zone (20~40cm) and anaerobic zone (>40cm), based on the oxygen content. The analysis of diversity sequencing revealed that methanotrophs were dominant bacteria in aerobic zone, including type I methanotrophs Methylobacter and type Ⅱ methanotrophs Methylosinus. While Anaeromyxobacter was the dominant bacteria for CF biodegradation by reductive dechlorination in anoxic and anaerobic zone. In addition, the relative abundance of methanotrophs in the anoxic zone was about 13%. These results suggested that CF was firstly degraded effectively in aerobic, anoxic and anoxic zone. Previous studies reported that CF can be degraded into dichloromethane reductive dechlorination in the anoxic and anaerobic zone, and part of dichloromethane would be transformed into acetate, H₂ and CO₂ due to the activity of Dehalobacter, which agreed with this study. The metabolic product dichloromethane was then completely degraded by through co-metabolism by methanotrophs in aerobic and anoxic zone. Moreover, the relationship between biodegradation capacity and gas flux was also studied. With the change of inlet flux, there was a negative correlation between methane removal efficiency and flux (R²=0.80), while the positive correlation was found between methane biodegradation rate and flux (R²=0.86). Similarly, CF biodegradation efficiency decreased with increase of inlet gas flux (R²=0.86), while biodegradation rate increased with increase of inlet gas flux (R²=0.89). Therefore, aerobic co-metabolism contributed more in in removal of CF than reductive dichlorination. These results provided theoretical basis for in situ bioremediation of chlorinated aliphatic hydrocarbons pollutants.