Electrokinetic transport of PAH-degrading bacteria in model aquifers and soil
An investigation of the mobility, viability, and activity of polycyclic aromatic hydrocarbon (PAH) degrading bacteria in an electric field is presented. Bench-scale model aquifers were used to test electrophoresis and electroosmosis as potential mechanisms for bacterial dispersion in contaminated sites. Glass beads, alluvial sand from Lake Geneva, and historically polluted clayey soil were used as packing materials. The green-fluorescent protein labeled PAH-degrading bacteria Sphingomonas sp. L138 and Mycobacterium frederiksbergense LB501TG were used as test organisms because of the known differing physicochemical surface and adhesion properties of the corresponding wild-type strains. No adverse effects of the electric current on bacterial viability and PAH-degradation were observed in the system chosen. Up to 90% of the weakly negatively charged and moderately adhesive cells of strain L138 were transported by electroosmosis, whereas 0-20% were transported by electrophoresis. By contrast, poor electrokinetic transport of strongly charged and highly adhesive cells of M. frederiksbergense LB501TG occurred in the different model aquifers. Treatment of bacteria with the nonionic surfactant Brij35 resulted in up to 80% enhanced electrokinetic dispersion of both strains. Our findings demonstrate that electroosmosis may be a valuable mechanism to transport bacteria in the subsurface with transport efficiencies heavily depending on the retention of the bacteria by the solid phase.