Electrokinetic biosparging of toluene in groundwater

Electrolysis of water occurs when electrokinetic techniques are used to remediate contaminated soils and groundwater. Under an electric field, generation of hydrogen and oxygen gases, and hydroxyl and hydrogen ions, occurs at the electrodes. By orienting electrodes vertically, oxygen has been generated at the base of aqueous solutions and saturated soil specimens, which then rises in the form of fine bubbles through the overlying media. Three sets of experiments were performed to explore the ability of this oxygen flow to encourage removal of dissolved-phase toluene by both sparging and biosparging. Low electric currents of 10 to 50 mA were found to be sufficient to generate appreciable quantities of oxygen. These, in turn, were found to stimulate more rapid growth of bacteria (Pseudomonas putida mt-2) in uncontaminated aqueous media with and without the presence of gravel. In addition, bubble generation was found to cause abiotic removal of the volatile toluene in coarse-grained soils (sand and gravel) but not in fine-grained sand. Finally, removal of toluene from aqueous solution was achieved through the combined action of sparging and enhanced biodegradation (biosparging).