Bioremediation of diesel-contaminated soil by bacterial cells transported by electrokinetics

The electrokinetic technology was applied in bioremediation for the purpose of supplying a Pseudomonas strain capable of degrading diesel to contaminated soil bed, and their biodegradation of diesel was carried out after a desired cell distribution was obtained. Electrokinetic injection of the strain was made possible because the cells acted as negatively charged particles at neutral pH, and thus the cells were transported with a precise directionality through the soil mostly by the mechanism of electrophoresis and in part by electroosmosis. A severe pH change in the soil bed was formed due to the penetration of electrolysis products, which was harmful to the cell viability and cell transport. To achieve a desirable cell transport and distribution, the control of pH in soil bed by a recirculating buffer solution in electrode chambers was essential during the application of an electric field. The judicious selections of electrolyte concentration and conductivity were also important for achieving an efficient electrokinetic cell transport since a higher electrolyte concentration favored the maintenance of pH stability in soil bed, but lowered electrophoretic mobility on the other hand. With electrolyte solution of pH 7 phosphate buffer, a 0.05 M concentration showed a better cell transport than 0.02 M and 0.08 M. The cells under pH 8 were transported more efficiently, and even more cell distribution was obtained, compared to the cells under pH 7 or pH 9 in a given time period. Up to 60% of diesel was degraded in 8 days by the Pseudomonas cells, which were distributed electrokinetically under the conditions of pH 8 (1,800 muS/cm, a mixture of phosphate and ammonia buffers) and 40 mA in a soil bed of 15 cm length.