Microcosm experimental study on microbial degradation of trichloroethylene in contaminated groundwater

Volatile chlorinated hydrocarbons such as trichloroethylene have become one of the most highly detected organic pollutants in groundwater of China. In order to enrich the theoretical support of bioremediation of groundwater polluted by chlorinated hydrocarbons in China, the aquifer sediments and groundwater samples were collected from a chlorinated hydrocarbons contaminated site in Beijing. The effects of different concentrations of sodium acetate, sodium lactate and lactic acid on the removal of trichloroethylene under anaerobic conditions were preliminarily investigated by the microcosm experiments. Combined with the analysis of the intermediate products and the change of microbial diversity in each anaerobic system, the reaction mechanism was elaborated. The results showed that under the anaerobic condition, the removal rate of trichloroethylene in the system of 1.0 g/L sodium acetate was the highest, and the degradation rate was 94.5%. The test system with sodium acetate could maintain neutral pH and low redox potential for a long time, and at the same time, it could achieve the highest TOC degradation rate. Only cis-1,2-dichloroethylene was detected in the intermediates of anaerobic degradation on the 30th day of the reaction. It was inferred that the main mechanism of biodegradation of trichloroethylene under the anaerobic condition was hydrogenolysis. In the microcosm system, the dominant microbes at the phylum level contained Proteobacteriae and Firmicutes, which were potential high-efficiency biodegradable bacteria for chlorinated hydrocarbons. The qPCR results showed that the total amount of bacteria increased greatly in each reaction system, and a high level of tceA was detected in each sample (about 10⁶-10⁷copies/L), suggesting that the hydrogenolysis of TCE might be carried out under the function of tceA.