A Photoelectrocatalytic Device for Removing MTBE from Water

描述（由申请人提供）：目前在美国有50万到250万个泄漏的地下燃料储罐。从这些储罐进入地下水的可溶性有机化合物可能对公众健康和环境构成重大危害。有两类污染物特别值得关注：(1)由苯、乙苯、甲苯和三种二甲苯异构体组成的BTEX燃料添加剂，以及(2)燃料含氧物，特别是甲基叔丁基醚（MTBE）。BTEX和MTBE都有急性和长期的毒性作用，并可能致癌。鉴于这些对人类健康的风险，联邦和私人正在花费大量资源从全国受污染的地下水中清除这些化合物。其独特的化学特性（例如，高水溶性和极性）使MTBE比BTEX更难从受污染的地下水中去除。虽然MTBE可以用颗粒活性炭（GAC）处理，但与BTEX相比，它使GAC的床层寿命减少了75%以上。此外，与BTEX不同，MTBE通常耐微生物降解。为了找到一种有效的、经济的方法来去除MTBE，人们研究了各种其他的修复方法，包括植物修复、土壤蒸汽萃取、多相萃取、空气喷射、膜（反渗透）、臭氧化和光催化氧化（PCO）。该项目将采用专有的光电催化氧化（PECO）装置从受污染的地下水中完全去除MTBE。在PECO中，电极上涂有二氧化钛基光催化剂，用紫外光照射。在光阳极和阴极之间施加1至5 V的电位，以尽量减少光生电子和空穴的复合，提高系统的效率。流动式PECO原型将用于重复实验室实验，以评估NaCl浓度、初始MTBE浓度和竞争污染物（例如BTEX）对降解动力学、MTBE矿化程度及其预期反应副产物的影响。化合物将通过TOC和GC-MS进行测定。将在实际的MTBE污染地点制造和测试其他更大的商业规模的PECO装置，以评估PECO修复MTBE的有效性和成本。根据这些评估的结果，将在第二阶段设计更多的试验和研究，以修复其他有问题的有机污染物。特别关注的是确定采用PECO作为两级PECO/GAC处理系统的第一阶段的经济可行性。

DESCRIPTION (provided by applicant): 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. PUBLIC HEALTH RELEVANCE: 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.