Effect of Aquifer Heterogeneity on the Transport and Activity of Functional Dechlorinating Bacteria under an Electric Field

Electrokinetic-enhanced bioremediation (EK-Bio) is an alternative strategy for remediating trichloroethylene (TCE)-contaminated low-permeability aquifers. However, the influence of aquifer heterogeneity, commonly found under field conditions, on the transport and activity of functional dechlorinating bacteria under an electric field is not clear. In this study, heterogeneous column experiments were conducted to observe bacterial transport and TCE degradation, and supplementary batch incubation experiments were conducted to assay the activity of the bacteria from different zones of the columns. Results show that TCE in the heterogeneous columns could be effectively and completely biodechlorinated by EK-Bio. The EK transport of functional dechlorinating bacteria (i.e., obligate organohalide-respiring bacteria (OHRB) Dhc) was facile in sandy fillings and could be hindered by the clayed fillings at the cathode side of the injection point. The relative abundance of versatile OHRB was significantly increased in all media. Biodechlorination activity was high in all of the injection points and clayed fillings. Sandy media exhibited a high biodechlorination activity only at the cathode side of the injection points. Mixed layers of clay/sand fillings showed a high biodechlorination activity. Complete biodechlorination was more favorable in clayed fillings than in sandy fillings, even with a lower Dhc relative abundance. Special care must be paid to the design and application of the EK-Bio process in heterogeneous aquifers.