Excimer Uv Light Source And The Degradation Of Effluents

The paper reported the study of the planar and cylindrical Xe₂*. KrBr*, KrI* excimer ultraviolet (UV) light sources. The optimized discharge parameters were determined, and then the lamps were used to degrade organic pollutants without addition of oxidants. The results showed that direct photolysis of pollutants by excimer UV radiation supplied a new way to degrade wastewater and waste air.The 172 nm vacuum-UV intensity and efficiency of the Xe₂* excimer lamp depended on many parameters including applied voltage, frequency, and gas pressure as well. The 172 nm radiation intensity increased with increasing of the applied voltage or frequency while the radiation efficiency had a maximum value. Both the radiation intensity and efficiency had a maximum value when the pressure was changed. The optimized parameters of the lamp were found to be: voltage 4 kV, frequency 20 kHz, pressure 280 torr while the radiation power of the lamp was 25.4 mW (equal to photon flow of 2.2 ×10^-6 einst min^-1).KrBr* excimer lamp provided an intense narrow band UV radiation at 207 nm, whose intensity increased with the total gas pressure at first, and then decreased with further increasing of gas pressure. It was found that in the presence of He and Ar buffer gas, the results differed from the simple mixtures of krypton and bromine. Ar gas had a negative effect on the KrBr* excimer emission while He gas contributed to increase all the emission intensity produced by the KrBr* excimer lamp. The optimized parameters of the lamp were found to be: voltage 5 kV, frequency 20 kHz, total pressure 300 torr, Br₂ pressure 10 torr, buffer gas He pressure 20 torr while the radiation power of the lamp was 3 mW (equal to photon flow of 3.1 ×10^-7 einst min^-1).The excimer radiation at 191 nm generated by the KrI* excimer lamp was very weak and less dependant on gas pressure due to predissociation which was confirmed by the strong emission of atomic iodine line at 183 nm.The photodegradation of organic dye in aqueous solution was achieved by 172 nm radiation emitted from the Xe₂* excimer lamp without addition of oxidants. The influence of reaction equipment, additives, dye structure and initial concentration on the efficiency of decolorization and chemical oxygen demand (COD) was investigated. It was found that the quantum yield was higher in the case that the solution served as one electrode of the lamp. Dissolved oxygen in the solution contributed to theincrease of the decolorization rate and COD removal rate while KC1 added as HO^· radical scavenger decreased the efficiency of the decolorization and COD removal. Dye structures could influence the decolorization rate. The dye decolorization followed pseudo-first order kinetics under all reaction conditions. The degradation was mainly attributed to the impact of HO^· radicals produced by water absorbing 172 run radiation. Major intermediates detected were aromatic compounds, some low weight by-products, several organic acids and inorganic ions by LC-MS, GC-MS and IC.The photodegradation of organic dye C.I. Acid Red 213 (AR-213) was achieved by 207 nm radiation emitted from the KrBr* excimer lamp without addition of oxidants at different initial pH value. A strong pH dependence of the dye degradation was observed. Precipitates were found to be generated when the irradiated solution of initial acidic pH was adjusted to alkaline pH and they would disappear again when the solution was readjusted to acidic condition. The efficiency of COD removal was greatly increased after the filtration of precipitates. The same phenomenon was also observed for other kinds of dyes. Direct photolysis was the mainly pathway in degradation of AR-213 dye for both 02-saturated and N₂-saturated solution. The intermediates formed were due to the cleavage of azo bond, opening of ring group, combination between organic radicals and formation of adducts. That the direct photodegradation of organic compounds by 207 nm radiation supplied an alternative way to treat wastewater.The photodegradation of carbon disulfide was achieved by 172 nm radiation emitted from the cylindrical Xe₂* excimer lamp at atmospheric condition. It was found that the degradation rate of carbon disulfide decreased with increasing of initial concentration and the flow rate. Moisture in the air contributed to increase the degradation rate. The degradation mechanism by 172 nm radiation was discussed.