Anaerobic Dechlorination of Pentachlorophenol (PCP) Coupling with Fe(III) Reduction.

Essentially, the anaerobic transformation of chlorinated organic pollutants in anaerobic soil is a microbial dechlorinated respiration induced electron transfer metabolic process, during which the chlorinated organic pollutants serve as electron acceptors. This process is largely regulated by the coordination and competition of the other available electron acceptors that are naturally abundant in soil, such as Fe(III). To illustrate the relationship between the dissimilatory Fe(III) reduction and the anaerobic transformation of chlorinated organic pollutants, laboratory experiment has been done through anaerobic pure and bacterial suspension culture, respectively. In pure culture, an iron reducing bacterium Clostridium beijerinckiiZ was isolated from a paddy soil, and testified capable of dechlorinating pentachlorophenol (PCP) directly; and the anaerobic transformation of PCP by C. beijerinckii Z could also be accelerated by simultaneous reduction of Fe(III). In bacterial suspension culture, two kinds of bacterial suspension (PCP domesticated consortium vs. iron reducing consortium) were compared for their ability of reductive transformation of PCP in the presence or absence of ferrihydrite minerals. Results showed that irrespective of consortium type, the presence of ferrihydrite minerals can promote the reduction of PCP in anaerobic conditions. Additionally, in the absence of ferrihydrite minerals, the transformation rates of PCP was in the order of PCP domesticated consortium > iron reducing consortium; while this order was opposite in the presence of iron oxides. This suggested that the reductive transformation of PCP by iron reducing consortium could be facilitated when coupling with the reduction of iron oxides. Therefore, our findings give evidences regarding the role of Fe(III) reducing bacteria in dechlorinating PCP, either by directly using PCP as electron acceptor to transform PCP, or by using Fe(III) as electron acceptor and coupling iron redox cycling with reductive dechlorination of PCP through the biochemical electron transfer, in anaerobic paddy soils.

Acknowledgments: This research was financially supported by the National Natural Science Foundation of China (41322006, 41090284), the National High Technology Research and Development Program of China (863 program, no. 2012AA06A203), the Fundamental Research Funds for the Central Universities, and Zhejiang University K.P.Chao’s High Technology Development Foundation.