Enhanced anaerobic biodegradation of PCBs in contaminated sediments using hydrogen

Anaerobic biodegradation of Polychlorinated biphenyls (PCBs) by addition of hydrogen to enhance the indigenous microbial activity in contaminated sediments was examined. Hydrogen was either provided directly to the sediments or generated indirectly by anaerobic corrosion of zerovalent iron. The effect of different concentrations of hydrogen generated on the reductive dechlorination process was analyzed.; Microcosm experiments were performed on contaminated sediments obtained from Lake Hartwell and Lake Michigan for a period of 12 months. Environmental factors, microbial populations and PCB concentrations in all three sediments were quite different. The experiments revealed that the system amended with the lowest iron dosage of iron (0.05g Fe per 12.5g wet sediment) achieved significant enhancement in terms of biodegradation of PCBs when compared to other forms of enhancements as well as natural biodegradation. Elevated concentrations of hydrogen, hydroxide anion and hydrogen sulfide anion resulting from the amendment of large quantities of zerovalent iron or hydrogen to sediment could increase microbial activity of other microbial population like methanogens and sulfate reducers to compete for the electron donor with dehalorespirers. This research shows that when a mixed microbial consortium is present in contaminated sediments, PCB dechlorination can be stimulated by continuous addition of low concentrations of hydrogen to enhance known dechlorinators; these Dehalococcoides-like microbes are suspected to be present in the sediments considered. Addition of controlled amounts of microscale iron metal to sediments has the potential to be developed as an efficient and cost effective technology for remediation and destruction of PCBs in contaminated sediments by providing a continuous source of electron donor for anaerobic biodegradation.