There are currently between 500,000 and 2.5 million leaking underground fuel storage tanks in the United States. Soluble organic compounds that enter the groundwater from these tanks can be a major hazard to public health and the environment. Two contaminate classes are of particular concern: (1) BTEX fuel additives consisting of benzene, ethyl benzene, toluene, and three isomers of xylene, and (2) fuel oxygenates, particularly methyl tert-butyl ether (MTBE). Both BTEX and MTBE have acute and long-term toxic effects, and may be carcinogenic. Given these risks to human health, considerable federal and private resources are being expended to remove these compounds from contaminated groundwater sites throughout the country. Its unique chemical characteristics (e.g., high water solubility and polarity) make MTBE more difficult to remove from contaminated groundwater than BTEX. Although MTBE can be treated with granular activated carbon (GAC), it diminishes the bed life of GAC by over 75% compared to BTEX. Also, unlike BTEX, MTBE is generally resistant to microbial degradation. Various other remediation methods have been investigated in an attempt to find an effective, economical method to remove MTBE, including phytoremediation, soil vapor extraction, multiphase extraction, air sparging, membranes (reverse osmosis), ozonation, and photocatalytic oxidation (PCO). This project will employ proprietary photoelectrocatalytic oxidation (PECO) devices to completely remove MTBE from contaminated groundwater. In PECO, an electrode is coated with a TiO2-based photocatalyst that is irradiated with UV light. A potential of 1 to 5 V is applied between the photoanode and a cathode to minimize recombination of photogenerated electrons and holes and improve the efficiency of the system. Flow- through PECO prototypes will be used in replicate laboratory experiments to evaluate the effects of NaCl concentration, initial MTBE concentration, and competing contaminants (e.g., BTEX) on the degradation kinetics, and degree of mineralization of MTBE and its expected reaction by-products. Compounds will be measured by TOC and GC-MS. Additional larger commercial-scale PECO units will be fabricated and tested at actual MTBE-contaminated sites to evaluate the effectiveness and costs of MTBE remediation by PECO. Based on the results of these evaluations, additional trials and studies will be designed in Phase 2 for remediation of other problem organic contaminants. A particular interest will be determining the economic viability of employing PECO as the first stage of a two-stage PECO/GAC treatment system.
The fuel additive methyl tert-butyl ether (MTBE), and other organic carcinogens associated with gasoline (e.g, BTEX), can enter the nation's drinking water from leaking underground fuel storage tanks, fuel spills, and in the course of normal use. To alleviate these environmental health risks, a highly efficient, and cost-effective photoelectrocatalytic oxidation technology has been developed to remove organic pollutants from water. This project will test the utility of this technology for treating MTBE contamination, both as a stand-alone treatment and as the first stage of a two-stage treatment process in which granular activated carbon is used to polish the water.
