OCR Text |
Show Abstract There has long been interest in utilizing photochemical methods for the detoxification of hazardous organic materials. Unfortunately, classical, low temperature (i.e., ambient or near ambient) photochemical processes are either too slow or fail to completely mineralize the targeted wastes to be practical for wide spread use. Researchers at the University of Dayton Research Institute have recendy developed a photothermal process that overcomes the problems previously encountered with photochemical detoxification techniques. Specifically, it has been demonstrated that elevated temperatures (i.e., >200°C) increases the intensity of light absorption by typical hazardous organic chemicals, and that the spectral region of absorption broadens, and shifts towards the visible portion of the electromagnetic spectrum. This results in a far greater potential for air toxics to absorb near ultraviolet radiation than was previously thought. It has also been shown elevated temperatures significantly increase the rate of photothermal reactions, making this process a viable technique for the destruction of air toxics. In this paper the authors will discuss the theoretical foundation for the photothennal detoxification process, and present a summary of the work in progress to develop a Photothermal Detoxification Unit (PDU) which will include examples of high temperature absorption spectra, and the results from actual trials with a Laboratory Scale Photothermal Detoxification Unit (LS-PDU). Introduction The scientific literature is replete with studies concerning photochemical reactions of hazardous organic materials.fi-5] However, the majority of these studies address naturally occurring photochemical reactions in atmospheric and aquatic systems to study the fate of pollutants in the environment as the result of exposure to natural sunlight.[6,7] It has been suggested that photolysis based processes hold potential for treating hazardous organic wastes.[8,9,10,l 1] Most of the techniques currently in use involve photoinitiation of chemical oxidation by additives such as hydrogen peroxide. [10] Relatively recently it has been recognized that the rate of many photochemical reactions may be accelerated at elevated temperatures.[12-18] This has led to the development of a process for hazardous waste destruction in which concentrated solar radiation is used as an energy source providing both intense thermal energy and near ultraviolet ( U V ) radiation capable of inducing rapid photochemical destruction of high molecular weight compounds. [12-17] More recently, w e have begun to develop a high-temperature photochemical (i.e., photothennal) treatment technology which makes use of more conventional sources of heat and U V radiation. This effort has been undertaken as a new initiative with the support of the U.S. Environmental Protection Agency's Emerging Technology Program. Specifically, this new effort will develop a detailed design for a prototype Photothennal Detoxification Unit (PDU) for use in processing the effluent from soil vapor extraction (SVE) and thermal desorption (TD) operations. 1 III-19 |