Performance of a pilot-scale packed bed reactor for perchlorate reduction using a sulfur oxidizing bacterial consortium.

A novel sulfur-utilizing perchlorate reducing bacterial consortium successfully treated perchlorate (ClO4⁻) in prior batch and bench-scale packed bed reactor (PBR) studies. This study examined the scale up of this process for treatment of water from a ClO 4⁻ and RDX contaminated aquifer in Cape Cod Massachusetts. A pilot-scale upflow PBR (∼250-L) was constructed with elemental sulfur and crushed oyster shell packing media. The reactor was inoculated with sulfur oxidizing ClO4⁻ reducing cultures enriched from a wastewater seed. Sodium sulfite provided a good method of dissolved oxygen removal in batch cultures, but was found to promote the growth of bacteria that carry out sulfur disproportionation and sulfate reduction, which inhibited ClO4⁻ reduction in the pilot system. After terminating sulfite addition, the PBR successfully removed 96% of the influent ClO4⁻ in the groundwater at an empty bed contact time (EBCT) of 12 h (effluent ClO4⁻ of 4.2 µg L(-1)). Simultaneous ClO4⁻ and NO3⁻ reduction was observed in the lower half of the reactor before reactions shifted to sulfur disproportionation and sulfate reduction. Analyses of water quality profiles were supported by molecular analysis, which showed distinct groupings of ClO4⁻ and NO3⁻ degrading organisms at the inlet of the PBR, while sulfur disproportionation was the primary biological process occurring in the top potion of the reactor.

Reductive dechlorination of 2-chlorophenol by Anaeromyxobacter dehalogenans with an electrode serving as the electron donor.

Electrodes poised at potentials low enough to serve as an electron donor for microbial respiration, but high enough to avoid the production of hydrogen, have been proposed as an alternative to the use of soluble electron donors for stimulating the bioremediation of chlorinated contaminants and/or metals. However, this form of respiration using pure cultures of microorganisms has only been reported in Geobacter species. To further evaluate this bioremediation strategy studies were conducted with Anaeromyxobacter dehalogenans, which has previously been reported to reductively dechlorinate 2-chlorophenol to phenol with acetate as the electron donor. Anaeromyxobacter dehalogenans could oxidize acetate with electron transfer to a graphite electrode poised at a positive potential, demonstrating its ability to directly exchange electrons with electrodes. Anaeromyxobacter dehalogenans attached to electrodes poised at -300 mV versus standard hydrogen electrode reductively dechlorinated 2-chlorophenol to phenol. There was no dechlorination in the absence of A. dehalogenans and electrode-driven dechlorination stopped when the supply of electrons to the electrode was disrupted. The findings that microorganisms other than Geobacter species can accept electrons from electrodes for anaerobic respiration and that chlorinated aromatic compounds can be dechlorinated in this manner suggest that there may be substantial potential for treating a diversity of contaminants with microbe-electrode interactions.