Electrokinetic transport of bacteria

The remediation field is in need of a simple, safe, and cost-effective technology that directly treats contaminants sorbed to aquifer solids. In the absence of an indigenous microbial population competent to degrade the contaminants of concern, bioaugmentation, or injecting competent degradative bacteria into the subsurface has been investigated. A major problem encountered with bioaugmentation is the limited dispersion of bacteria injected into contaminated aquifers: bacteria often adhere strongly to solid surfaces. In the absence of a strong hydrogeological gradient the organisms remain localized at the origin of injection, resulting in fouling of wells and inadequate dispersion of degradative bacteria. The ability to directionally transport bacteria away from injection sites and into zones of contamination would be advantageous to bioaugmentation approaches used for in-situ remediation. Bench-scale model aquifers were used to test electrophoresis as a tool for bacterial dispersion in situ. Preliminary studies with several strains demonstrated that the net negative surface charge of bacteria in a solution at neutral pH caused electrokinetic transport of the cells through sand towards the anode in a de electric field. Subsequent experiments were conducted in a variety of porous media with a trichloroethylene (TCE) degrading, adhesion-deficient variant of Burkholderia cepacia G4 (1CB). 1CB was directionally transported through sand, soil, and aquifer sediment at rates ranging from 1.6 to 6cmh depending upon the porous media tested, over distances up to 0.4m. Transport of the wild-type G4 through sand and sediment in response to a hydraulic gradient is severely retarded in relation to the adhesion-deficient 1CB, whereas electrokinetic transport rates are identical for the two strains. Experiments performed with TCE-contaminated sediment suggest that 1CB retains its ability to degrade TCE during electrokinetic transport. (C) 1997 Elsevier Science B.V.