Bioaugmentation of an Aerobic Culture Capable of Chlorinated Solvent Cometabolism to a Subsurface Test Zone

A butane-utilizing culture able to cometabolize chlorinated aliphatic hydrocarbons (CAHs) was bioaugmented into an aquifer test zone at Moffett Federal Airfield, CA. Microcosm bioaugmentation tests conducted with groundwater and aquifer solids collected from the test site indicated a strong potential for viability of the bioaugmented culture in the site subsurface. Microcosms bioaugmented with the butane-utilizing culture were able to degrade aqueous concentrations of 1,1-dichloroethylene (1,1-DCE) up to 1 mg/L and could successfully transform mixtures of 1,1-DCE, 1,1,1-trichloroethane (TCA) and 1,1-dichloroethane (DCA) when fed butane. T-RFLP analyses showed the presence of bioaugmented organisms within the microcosms throughout the 10-month test period. An isolate from the butane-utilizing culture was grown in batch bottles containing mineral media and a butane-in-air headspace. Approximately 4 g dry weight of culture was harvested and bioaugmented to the field site. The site consisted of two parallel well legs, each with an injection well, two fully penetrating monitoring wells containing solid support media, three groundwater monitoring wells and an extraction well. One well leg was bioaugmented with the isolate and the other was used as an indigenous control leg. A mixture of 1,1-DCE, TCA and DCA (~50 ug/L, 135 ug/L and 150 ug/L respectively) was continuously pumped through both well legs with alternate pulses of dissolved oxygen and butane. Fifty percent removal of 1,1-DCE occurred within one day in the bioaugmented leg; however, it took about 6 days to achieve complete butane utilization and 1,1-DCE removal to below 2 ug/L. During this period DCA and TCA were reduced by 70- 90 percent and 30-50 percent respectively. When the butane/oxygen pulses were changed from a 1-hr cycle to a 24-hr cycle 1,1-DCE removal fell to 50 percent and DCA and TCA concentrations increased to influent levels. Upon returning to short pulse cycles, 1,1-DCE removal efficiency returned to 95 percent while DCA and TCA were not effectively transformed. Groundwater microbial samples obtained 1 m from the injection well did not show the presence of the bioaugmented organism. Butane uptake was observed in the non-bioaugmented leg after about 14 days of butane addition, but no CAH transformation was observed. Butane oxidation without CAH transformation continued through the period of longer pulse cycles; however, upon return to the shorter pulse cycles 1,1-DCE removal efficiencies similar to those obtained in the bioaugmented leg were achieved without significant removal of DCA or TCA. Comparison of initial groundwater microbial samples showed no significant differences between the two legs. Microbial analyses are ongoing and a second field season will begin in September 2002 to assess TCA transformation ability upon re-bioaugmentation of the site.