Assessment of Biodegradation in Natural Attenuation Process of Chlorinated Hydrocarbons Contaminated Site: An Anaerobic Microcosm Study

In this study, the anaerobic microcosm systems under in-situ conditions were constructed using the soil and the groundwater collected at a former pesticide manufacturing site. The in-situ natural attenuation potential was evaluated and its relationships with the geochemistry conditions and the microbial communities were carefully explored. The site was heavily contaminated with chlorinated hydrocarbons (CHCs) including perchloroethylene (PCE) and 1,2-dichloroethane (1,2-DCA). The 0 ~ 20 mV redox conditions measured in both the heterogeneous soil and the groundwater favored a series of CHCs biodegradation correlated processes. The significant contributions of biodegradation processes to the attenuation of CHCs were confirmed by comparing the PCE and 1,2-DCA degradations as accompanied with Cl− accumulation rates between the unsterilized microcosms and the sterilized controls. The 16S rRNA gene based denaturing gradient gel electrophoresis (DGGE) analysis revealed the distinct shifts of microbial community compositions in the soil and the groundwater microcosm systems during the incubation. The Shannon-Winner index analysis further suggested the decrease and the increase of microbial diversities in the soil and the groundwater samples, respectively. The dominant species mainly associated with phylum Proteobacteria, Firmicutes, and Actinobacteria. The recovered genera Geobacter, Streptomyces, and Acetoanaerobium associated 16S rRNA gene sequences confirmed the in-situ biological dechlorination potentials of CHCs. In summary, this study revealed high biological attenuation potentials with the suitable redox conditions for the studied actual CHCs contaminated site and indicated the high probability of the in-situ natural attenuation approach for CHCs contaminated site remediation.