In Situ Catalytic Groundwater Treatment Using Palladium Catalysts and Horizontal Flow Treatment Wells

摘要

The EPA estimated in 1996 that of 8,336 Department of Defense (DoD) sites needing cleanup, approximately 70% had contaminated groundwater, mostly from chlorinated solvents such as trichloroethylene (TCE) and tetrachloroethylene (PCE). Because TCE and PCE are mobile and refractory in aquatic environments, there is significant need for efficient treatment methods. Palladium (Pd) catalyzed reductive dechlorination transforms chlorinated ethylenes and other volatile organic compounds (VOCs) into their respective saturated hydrocarbons or lesser chlorinated analogues. With hydrogen gas as the reductant, the process is selective requiring only small quantities of hydrogen to remove contaminants to below regulatory limits. For some VOCs the dechlorination reaction occurs rapidly, even in water under ambient temperature, pressure and pH. The process can be utilized to efficiently treat water contaminated with reactive chlorinated contaminants. A one-pass catalytic process has many advantages, mainly that contaminants are destroyed instead of being transferred to another medium (e.g., air or activated carbon), thus avoiding generating a secondary waste stream. The technology is particularly favorable for treating water contaminated with high concentrations (>1 mg L-1) of chlorinated ethylenes and is therefore suited for source control.