Treatment of Groundwater Contaminated with Chlorinated Hydrocarbons

The ground water aquifer underneath a chemical manufacturing plant in Southeast Texas has been contaminated with the leachate from its landfill. There are 17 major chlorinated hydrocarbon contaminants found in the groundwater with concentrations ranging from 1 ppm to 1200 ppm. An air-stripping unit followed by a thermal catalytic oxidation unit is currently operating on-site to remove all of the chlorinated compounds from the contaminated groundwater. Because one of the contaminants, Bis(2-chloroethyl)ether (DCEE), has a fairly low Henry’s law constant, a high air flow rate is employed in the stripping unit in order to improve the overall stripping efficiency. This high air flow rate has caused maintenance problems in the air-stripping unit and a higher energy consumption in the thermal catalytic oxidation unit. Also, the effluent from the air stripping unit still contains a fair amount of DCEE which may require further treatment before being discharged into the receiving stream in the event of a tighter effluent permit A photo-chemical oxidation unit was set up to study the feasibility of using UV/H 2 O 2 to destroy DCEE. Kinetics and factors which may affect the effectiveness of DCEE oxidation were investigated. The oxidation of 1,2-Dichloroethane (DCA), 1,1,2- Trichloroethane (TCA), and 1,1,2,2-Tetrachloroethane (TetCA) were also studied because they have the most significant concentrations in the contaminated groundwater. The information gathered from the oxidation of these three compounds will be used to determine whether the UV/peroxidation process can be used as an alternative treatment process for the contaminated groundwater. The stoichiometric ratio of DCEE to H 2 O 2 is 1:10 for the complete oxidation of DCEE. Under this condition, over 99% of the DCEE at an initial concentration of 220 ppm was oxidized after 10 minutes of irradiation. Several volatile oxidation intermediates were observed at the early stage of the oxidation process; however, nearly all of the by-products were not detected after 30 minutes of irradiation. No by-products of high molecular weights were ever observed even at very low H 2 O 2 doses The results from the oxidation of 1,2-DCA, 1,1,2-TCA, and 1,1,2,2-TetCA indicated that these compounds are much more recalcitrant to the UV/peroxidation process than DCEE. Stoichiometic amounts of H 2 O 2 for the complete oxidation of chloroethanes were always required in order to prevent the formation of high molecular weight compounds.