3. Alkyl halide remediation via bioaugmentation with halorespiring bacteria
Anaerobic transformation of chlorinated solvents using dehalorespiring bacteria has been demonstrated to offer significant kinetic and energetic (less biomass needed) advantages over cometabolic dechlorination reactions. Researchers associated with the CME are collaborating on a project aimed at harnessing this catabolic process to demonstrate its potential application in groundwater remediation efforts. The site is a perchloroethylene (PCE)-contaminated aquifer in Oscoda, Michigan, which has shown historical evidence for PCE and TCE dechlorination in the field, resulting in the accumulation of predominantly cis- and trans-dichloroethenes (DCEs).
The specific objectives of this project are to (i) evaluate in situ halorespiration activity using aquifer material and enriched organisms derived thereof, (ii) assess the effectiveness of biostimulation and bioaugmentation approaches to enhance dechlorination activity in batch and column configurations, (iii) address scaling issues to transfer the technology to the field.
Microcosm studies with aquifer samples obtained from discrete depths and in the presence of a range of electron donors, including lactate, indicated that the extent of dechlorination increased with depth (Figure 1). Enrichments from deep aquifer samples (ethene production) exhibited halorespiration activity, based on the following criteria: (i) activity could be transferred, (ii) the electron donor fraction diverted to energy production (fe) was 0.65-0.7, and (iii) low H2 treshold concentrations. Subsequently, amplified 16SrDNA from aquifer material indicated the presence of genes similar to a known halorespirer, Desulfuromonas sp. strain BB1 (Figure 2), and a halorespiring (PCE-DCE) strain (designated BRB1) was isolated.
The column studies (inoculated with D. strain BB1) showed that not only was this strain able to colonize aquifer solids, but it also rapidly dechlorinated the added PCE to cis-DCE, indicating that strain BB1 or BB1-like organisms are suitable organisms for bioaugmentation. Batch studies indicated that bioaugmentation with strain BRB1 significantly enhances dechlorination activity at low inoculum densities (0.5 to 5% tested in batch) in the presence of lactate. Further studies with a Bachman aquifer enrichment able to dechlorinate DCE to ethene are conducted concurrently with biomass scaling experiments to aid in designing the pilot test, which is scheduled to be initiated in May 2000.
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