An In Situ Bioreactor for Treatment of Contaminated Groundwater 

Katherine C. Key and Kerry Sublette (University of Tulsa), Brett Baldwin (Microbial Insights), Ed Sullivan (Whitman Companies) 

Bacteria capable of degrading hydrocarbons are ubiquitous in the environment because hydrocarbons are natural products that have been present in the environment in high concentrations for millions of years. This is not true of chlorinated hydrocarbons. The evolutionary origin of organisms like Dehalococcoides which are capable of reductive dechlorination of PCE and TCE to ethane is uncertain.  Some chlorinated compounds occur naturally but at concentrations far lower than concentrations found in TCE and PCE plumes and from the standpoint of evolution TCE and PCE have been in the environment at these concentrations for only a short time. The result is that Dehalococcoides spp. are not uniformly found to occur in TCE and PCE plumes and not uniformly distributed within a given plume.  We are developing a new approach to the problem of the nonuniform distribution of halorespiring organisms in a PCE or TCE plume. We are building on existing Bio-Sep bead technology which is currently being successfully used commercially as a forensic tool for characterizing subsurface microbial  ecology. The ability of the Bio-Sep bead material to be rapidly colonized by the active components of a groundwater microbial community make it an ideal material to serve as an immobilization matrix for an in situ bioreactor to first collect and concentrate native, active Dehalococcoides cells from an actively dechlorinating part of a TCE or PCE plume and then transfer these indigenous dechlorinators to a less active part of the plume. Bacteria form biofilms in the interior of Bio-Sep beads but the association with the beads is dynamic with cells continually being captured and released from the beads. Therefore, an in situ bioreactor containing a dense culture of Dehalococcoides cells will release these cells when transferred to a new groundwater monitoring well. The in situ bioreactor can also be subjected to a continuous injection of nutrients from a surface source to maintain the growth and reproduction of the bacteria and therefore result in the continuous release of these organisms into the well environment.  Dehalococcoides will then be transported into the aquifer matrix by groundwater flow and potentially through chemotactic movement of the cells. An initial field test of this approach will be presented.