Field test of a bioaugmentation agent for the bioremediation of chlorinated ethene contaminated sites.

Chlorinated ethenes are toxic compounds that were widely used in the past, and their improper handling and storage caused notable pollutions worldwide. In situ bioremediation by reductive dechlorination of bacteria is a cost-effective and ecologically friendly way to eliminate these pollutions. During the present study, the efficiency of a previously developed bioaugmentation agent combined with biostimulation was tested under field conditions in contaminated soil. Furthermore, the preservation of dechlorinating ability was also investigated in a long-term experiment. Initially, aerobic conditions were present in the groundwater with possible presence of anaerobic micro-niches providing habitat for Brocadia related anammox bacteria. "Candidatus Omnitrophus" was also identified as a dominant member of community then. Significant changes were detected after the biostimulation, anaerobic conditions established and most of the dominant OTUs were related to fermentative taxa (e.g. Clostridium, Trichococcus and Macillibacteroides). Dominant presence of vinyl-chloride coupled with the lack of vinyl-chloride reductase gene was observed. The most notable change after the bioaugmentation was the significant decrease in the pollutant quantities and the parallel increase in the vcrA gene copy numbers. Similar to post-biostimulation state, fermentative bacteria dominated the community. Bacterial community composition transformed considerably with time after the treatment, dominance of fermentative-mainly Firmicutes related-taxa decreased and chemolithotrophic bacteria became abundant, but the dechlorinating potential of the community remained and could be induced by the reappearance of the pollutants even after 4 years.