典型功能层带-填埋场覆盖层中四氯化碳代谢机制及功能微生态响应

Transformation mechanism of carbon tetrachloride and the associated micro-ecology in landfill cover, a typical functional layer zone

垃圾填埋场是四氯化碳(carbon tetrachloride, CT)污染的重要来源,明晰覆盖层功能层带中CT的转化机制对其污染控制尤为重要。本研究通过构建模拟覆盖层系统,开展了CT沿程生物降解及微生态研究。覆盖层理化特性分析表明,长期生物氧化使覆盖层形成了稳定存在的厌氧层(>45 cm)、缺氧层(15–45 cm)和好氧层(0–15 cm)功能层带,各特征层带氧化还原电位、微生物群落结构差异显著,为CT降解提供了生物资源和有利条件。降解结果显示,CT在厌氧层和缺氧层脱氯产生氯仿(chloroform,CF)和二氯甲烷(dichloromethane,DCM)及氯离子(Cl–),副产物在30 cm处浓度最大,好氧层中CF和DCM迅速发生好氧降解;CT降解速率为13.2–103.6μg/(m2·d),随填埋气通量增大而增大。多样性测序结果表明,不同层带功能菌属差异显著,中慢生根瘤菌(Mesorhizobium)为好氧层CT潜在降解菌属,硫杆菌(Thiobacillus)和间孢囊菌(Intrasporangium)为厌氧层和缺氧层潜在功能菌属;覆盖土中6种脱氯菌属和18种甲烷氧化菌分别负责CT厌氧转化和CF与DCM的好氧降解,缺氧层可同时发生厌氧脱氯和好氧转化过程。降解机理分析可知,通过调控手段实现包气带的厌氧层-缺氧层-好氧层稳定存在对全氯代烃的无害化去除十分重要,增大缺氧层范围可强化全氯代烃去除。研究结果为填埋场中氯代污染物的去除提供了理论指导。

Landfill is one of the important sources of carbon tetrachloride(CT) pollution, and it is important to understand the degradation mechanism of CT in landfill cover for better control. In this study, a simulated landfill cover system was set up, and the biotransformation mechanism of CT and the associated micro-ecology were investigated. The results showed that three stable functional zones along the depth, i.e., aerobic zone(0–15 cm), anoxic zone(15–45 cm) and anaerobic zone(>45 cm), were generated because of long-term biological oxidation in landfill cover. There were significant differences in redox condition and microbial community structure in each zone, which provided microbial resources and favorable conditions for CT degradation. The results of biodegradation indicated that dechlorination of CT produced chloroform(CF), dichloromethane(DCM) and Cl– in anaerobic and anoxic zones. The highest concentration of dechlorination products occurred at 30 cm, which were degraded rapidly in aerobic zone. In addition, CT degradation rate was 13.2–103.6 μg/(m2·d), which decreased with the increase of landfill gas flux. The analysis of diversity sequencing revealed that Mesorhizobium,Thiobacillus and Intrasporangium were potential CT-degraders in aerobic, anaerobic and anoxic zone,respectively. Moreover, six species of dechlorination bacteria and eighteen species of methanotrophs were also responsible for anaerobic transformation of CT and aerobic degradation of CF and DCM,respectively. Interestingly, anaerobic dechlorination and aerobic transformation occurred simultaneously in the anoxic zone in landfill cover. Furthermore, analysis of degradation mechanism suggested that generation of stable anaerobic-anoxic-aerobic zone by regulation was very important for the harmless removal of full halogenated hydrocarbon in vadose zone, and the increase of anoxic zone scale enhanced their removal. These results provide theoretical guidance for the removal of chlorinated pollutants in landfills.