Bioremediation effect on key microorganisms and targeted pollutants in the chlorinated ethenes contaminated groundwater in south taiwan

Chlorinated ethenes are one group of pollutants commonly found in the soil and groundwater contaminated sites. In-situ bioremediation using anaerobic dehalogenation is a promising method for the treatment of chlorinated ethenes. To understand the feasibility and efficiency of in-situ anaerobic bioremediation, a SybrGreen-qPCR method was employed to quantify the abundances of two key microorganisms in the samples collected in a chloroethenes contaminated site in south Taiwan in 2013 and 2015. The results showed that in the hotspots of the site, chlorinated ethenes were reduced by 90% within 2 years. In addition, chloroethenes were found to re-distribute caused by the combined effect of groundwater flow and degradation of the chemicals. The results of microbial analysis showed that genus Desulfitobacterium increased from 10² ~ 10⁴ Copies/L groundwater detected in the first seven months after bioremediation to 10⁴ ~ 10⁷ Copies/L groundwater after 26 months of the treatment. Moreover, genus Dehalococcoides abundance was observed to increase by 3 times after the treatment, with ~10⁷ Copies/L groundwater. The observation indicates that bioremediation could effectively enrich the two functional microbes, and may cause the reduction of chloroethenes in the hot spot of the contaminated site. However, when bioremediation is applied for groundwater remediation, attention should be paid to the transformation of chloroethenes and transport of the contaminants with groundwater flow in the site.