A Photoelectrocatalytic Device for Removing MTBE from Water

描述（由申请人提供）：目前在美国有50万至250万个泄漏的地下燃料储存罐。从这些水箱进入地下水的可溶性有机化合物可能对公共健康和环境造成重大危害。两种污染物类别特别值得关注：（1）BTEX燃料添加剂，由苯、乙苯、甲苯和二甲苯的三种异构体组成，以及（2）燃料含氧化合物，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。考虑到这些对人类健康的风险，正在花费大量的联邦和私人资源，从全国各地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）使得MTBE比BTEX更难从被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的床寿命缩短了75%以上。此外，与BTEX不同，MTBE通常对微生物降解具有抗性。已经研究了各种其他修复方法，试图找到一种有效的，经济的方法来去除MTBE，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）设备，以完全去除受污染的地下水中的MTBE。在PECO中，电极涂覆有用UV光照射的基于TiO 2的光催化剂。在光阳极和阴极之间施加1至5V的电势，以使光生电子和空穴的复合最小化并提高系统的效率。流通型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MTBE及其预期反应副产物的降解动力学和矿化度的影响。将通过TOC和GC-MS测量化合物。将在实际的MTBE污染场地制造和测试额外的较大商业规模的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。特别感兴趣的是确定采用PECO作为两级PECO/GAC处理系统的第一级的经济可行性。 公共卫生相关性：燃料添加剂甲基叔丁基醚（MTBE）和其他与汽油相关的有机致癌物（例如BTEX）可以通过泄漏的地下燃料储存罐、燃料泄漏和正常使用过程进入国家的饮用水。为了减轻这些环境健康风险，开发了一种高效、低成本的光电催化氧化技术来去除水中的有机污染物。该项目将测试该技术在处理MTBE污染方面的效用，既作为独立处理，也作为两阶段处理过程的第一阶段，其中颗粒活性炭用于抛光水。

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.