Transportation and augmentation of the deposited soil bacteria in the electrokinetic process: Interactions between soil particles and bacteria

Abstract The use of electrokinetic (EK) phenomena can facilitate bioaugmentation by enhancing the mobility and redistribution of deposited soil bacteria through heterogeneous soil. In this research, batch treatments (T1-T6) were used to assess the characteristics of bacterial transportation and proliferation under a weak electric field (1 V/cm). The strain Bacillus cereus was mainly transported toward the cathode by electro-osmosis flow (EOF). The bacterial transport efficiency was 1.07 × 107 CFUs/mL from days 0–9 when deionized water was used as the electrolyte solution and was elevated by 46% when EOF was enhanced with 0.010 mol/L NaHCO3 solution containing 0.04 mol/L Na2SO4. However, in all treatments, bacterial transport efficiency decreased by 70%-95% after 9 days. The bacterial transport efficiency was closely related to the EOF effective action distance (ED) which narrowed as soil and bacterial properties changed after the EK process. Correspondingly, the bacteria in soil were transformed from loose-bound to tight-bound status due to the deepened secondary minimum depth of XDLVO interaction energy after EK treatment. In addition to bacterial transportation, the electric field stimulated the proliferation of bacteria to achieve higher counts by promoting bacterial adhesion and facilitating fluid contact between ions, dissolved organic carbon, and bacteria. The stimulatory effect of electric field on bacteria was stronger than the transportation effect of the electric field on bacteria. Improvements in both bacterial migration and proliferation contributed to bioaugmentation under EK conditions. Near-cathode sections (S3, S4) are optimal for bacterial augmentation under the EK treatment for a long duration.