A process using air/ozone injected in a pulsing manner (C-Sparging™) demonstrated reduction of MTBE from over 1000 ppb to less than 100 ppb in less than 40 days. The rate of decay shown by weekly monitoring during and after treatment was a ten-fold reduction, monitored in wells located 3 to 7 meters from the injection point.
The process consists of three parts: First, fine bubbles with a high surface-to-volume ratio are injected into the saturated zone to extract dissolved MTBE from contaminated groundwater. Second, ozone contained within the bubble and thin film around the bubble reacts extremely rapidly to decompose MTBE into simple products, alcohols, acetate and formate. Third, the residual oxygen from the reaction encourages bioremediation which consumes the breakdown products, converting them to carbon dioxide and water.
Soil type at the site was gravelly sands with the water table level at 2 to 3 meters. Contamination extended vertically 1 to 3 meters deep. The Spargepoints
® were installed at a depth of 10 meters. Results were monitored by three indicators in groundwater samples from monitoring wells: 1) VOC removal, analyzed by certified laboratory; 2) dissolved oxygen (DO) field determinations; 3) oxidation-reduction potential (ORP) field determinations.
Groundwater samples showed an immediate rise in concentration of MTBE and benzene due to agitation of the groundwater and capillary pores by the fine bubbles, stripping adsorbed fractions, followed by a progressive drop in concentration. Concentrations of MTBE in monitoring wells placed at 3 and 4 meters from the Spargepoint® rose to 1300 and 550 ppb before converging to less than 100 ppb, for a removal efficiency of 99.9% and 99.8% respectively after 5± weeks. Benzene rose to a high of 4300 ppb before dropping to below 700 ppb, for 99.8% efficiency after 5± weeks.
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