Study On Photodegradation Of Dimethyl Sulfide By Microwave Discharge Electrodeless Lamp

Dimethyl sulfide (DMS) is one of the eight ordorous substances in the first batch of key monitoring provisions in China, mainly from the anaerobic fermentation process, such as sewage treatment plant, landfill, paper mill and livestock production plant. It is characterized by negative hedonic character and very low odour threshold values (OTV,0.6-40ppb), high toxicity, which is seriously harmful to health, especially nervous centralis and blood circulatory system. DMS is reactive in the troposphere that can be oxidized with irradiation, or by O3,-OH and other radicals to be SO2and methanesulfonic acid (MSA), ultimately be changed to NSS-SO42-(non sea salt sulfate), which contributes directly to the formation of acid precipition. And dimethyl sulfide in the stratosphere can be oxidized or photolysis to aerosol, speeding chlorine formation and ozone destruction.In this paper, we built up a small microwave-assisted photodegradation experimental platform using a self-made microwave discharge electrodeless lamp (MDEL) as illuminant to degrade dimethyl sulfide at various process parameters, media and active radicals. And the effects on the removal efficiency were investigated systematically. The byproducts were analyzed to reveal the photodegaradation mechanism by MDEL.First the MDEL, which was made of quartz and filled with mercury and argon gas, was characterized. This lamp showed mainly atomic Hg emission lines at253.7nm and185nm. Its radiation at185nm accounted for21%of the total UV output in this study, compared with conventional mercury lamp of7%. The UV output power was up to1000W·m-1, thirty times over that of conventional mercury lamp.Direct photolysis and indirect photo-oxidation by the induced O(1D) and HO-were the main oxidation forms for DMS degradation, where (1D) induced oxidation played a dominating role.The results of continuous microwave photocatalytic degradation of DMS showed that, at the microwave output power of1000W, removal efficiency of DMS in the air atmosphere was94.3%with the initial H2S concentration of20ppm, the gas residence time of10s and RH of20%. And the removal efficiency of H2S increased with increasing microwave output power or the gas residence time, and decreased with increasing initial DMS concentration.DMS photodegradation proceeded towards total mineralization with formation of CO2, and SO42. It also gave rise to the formation of several reaction intermediates as CH3OH, H3CS(O)CH3and H3CS(O)2CH3(and most probably CH4, HCHO, H3CSSCH3) with better water solubility. Besides, DMS could be removed by the radiation of MDEL in the air atmosphere with TiO2film-coated reactor, or TiO2/AC filled reactor. The efficiency was higher than that of the microwave photolysis degradation in a relatively short time. With the illumination time growth, the degradation rate decreased due to catalyst deactivation.