다양한 고급산화공정을 이용한 2-chlorophenol의 분해특성 연구

Abstract

Chlorophenols, found in aqueous systems and hazardous waste sites, exhibit a considerable water solubility, strong odor and taste, and high toxicity. Industrial activities, drinking water chlorination and partial degradation of phenoxy pesticides are the contributing sources of chlorophenols. As one of chlorophenols, 2-chlorophenol (2-CP) which is widely used in paper, pulp, pesticide, and herbicide industries, is very toxic and poorly biodegradable pollutant. Also 2-CP is one of the EPA (Environmental Protection Agency) priority pollutants. Trace toxic by-products such as PAHs, dioxins, and furans are frequently found in the incineration of 2-CP and considered carcinogens or mutagens. There are several treatment alternatives available for treatment of chlorophenols. The biological oxidation process is the common option due in part to its cost-effectiveness and versatility in handling a wide variety of organic pollutants. But the biological treatment is effective only in low concentrations of the organics and has the generally long retention time. Thermal destruction, for example, incineration, is another effective choice for the treatment of wastes containing high concentrations of chlorophenols. However this process has some disadvantages that the considerable energy is required to heat and vaporize the water mass before specific organic pollutants are destroyed and it can lead to the formation of new toxic organic materials. Activated carbon adsorption and air-steam stripping can be accepted for treatment of wastes containing chlorophenols, but activated carbon adsorption produces spent carbon as a waste by-product, and air-steam stripping creates an air pollutant problem. Therefore, it is most favorable to examine destructive technologies for the treatment of toxic organic pollutants including chlorophenols, and advanced oxidation processes (AOPs) are possible technologies. The photo-Fenton process, usually known as one of AOPs which are designed to generate hydroxyl radicals (HO), represents an attractive alternative for treatment or pretreatment of chlorophenols. The photo-Fenton process utilizes a combination of hydrogen peroxide (H₂O₂) and ferrous ions (Fe₂+) in the presence of UV radiation. The first step of the process is the Fenton process, represented by equation (1). Fe₂++ H₂O₂ → Fe₃+ + OH- + OH· (1) In the presence of UV radiation, the ferric ions (Fe₂+) produced in the Fenton process are converted back to ferrous ions (Fe₂+), as known in equation (2), with formation of an additional equivalent of hydroxyl radical. Fe₃+ + H₂O → Fe₂+ + H+ + OH· (2) The hydroxyl radicals formed in these two reactions react with organic species (RH) present in the system, promoting their oxidation, as indicated in equation (3). OH + RH → H₂O + R· (3) The pH of the solution has a considerable influence on the reaction rate. At pH values higher than four, iron ions precipitate out of the solution in the form of hydroxides. The optimum pH for the photo-Fenton process is typically in the range of pH 3.0～3.5, where Fe(OH)₂+ is the predominant iron species present in the solution. In the present study, the degradation characteristics of 2-CP by the Fenton process and the photo-Fenton process were studied. The degradation efficiency of 2-CP in aqueous solution was investigated as a function of initial pH, Fenton reagent concentration and initial concentration of 2-CP. Also, reaction intermediates of 2-CP by Fenton process and photo-Fenton process were identified, respectively.