Advances in Groundwater Treatment to Remove Mtbe

We have developed two significant modifications to conventional airstripping of MTBE from contaminated groundwater. The first modification involves application of thermodynamic principles to improve by at least a factor of three the overall mass transfer efficiency, obtaining very high removal efficiencies, using a combination of higher operating temperatures (40-60 C) and vacuum pressures (from 0.3 to 0.6 atm) in the system. Higher temperatures and lower operating pressures increase the stripping factor by increasing both Henry's constant and the mass transfer coefficient. These process improvements allow the removal of much less volatile compounds like polyaromatic hydrocarbons (PAHs) and hexachlorobenzene (HCB), or more soluble compounds like methyl tert-butyl ether (MTBE) from contaminated water, increasing the operational range of the stripping unit. Waste heat from an internal combustion engine is used to increase water temperature. The engine supplies the vacuum and uses the gas-phase pollutants as supplementary fuel. These results have also been applied to removal of these compounds from contaminated groundwater using hollow fiber membranes. Contaminated water is passed through the inside of the fiber, with a vacuum applied to the outside of the membrane. The membrane's hydrophobic properties selectively allow the transfer of organics through the membrane while retaining water inside the fiber, for differential pressures up to 1 MPa (150 psi), based on capillary entry pressure. The hollow fiber membrane construction provides a very high surface area for mass transfer from the water to the gas phase. Much lower volume of gas is generated using this stripping method compared to conventional airstripping, reducing the size of treatment units. Increased water temperature and high vacuum result in high removal efficiencies, using very compact units for water treatment. Reprint from: Proceedings of the 31 Mid-Atlantic Industrial and Hazardous Waste Conference, University of Connecticut, Storrs, CT. June 20-23, 1999