Applied Basic Research On Photo-Catalytic Treatment VOCs Vapor Of High-salt Wastewater Evaporation Process

High-salt wastewater is a kind of wastewater that is produced in industrial production.It is often treated with multi-effect evaporation technology,especially MVR technology.Secondary steam containing volatile organic compounds(VOCs)with high-humidity is generated in the application of MVR technology,and the pollution problem of benzene-based VOCs is more prominent.Therefore,it is necessary to optimize the treatment process of high-salt wastewater by combining treatment methods of VOCs.Adsorption and photocatalytic oxidation(PCO)are common methods for the treatment of VOCs with low concentration.In order to fully utilize the synergistic interaction between these two methods,toluene was selected as the target pollutant.TiO2 was uniformly loaded onto the activated carbon by impregnation method,and it was used as the catalyst.Microwave electrodeless lamp(MEDL)which is able to emit light with the wavelength of 185 nm+254 nm was used as the light source to investigate the factors and mechanism of the degradation of toluene by microwave electrodeless photocatalytic oxidation(MEDL-PCO).The key factors to affect the activity of the catalyst are the adsorption performance of activated carbon and the crystal form and loading of photocatalyst TiO2 as well as its dispersion on the carrier.In this paper,the carrier was modified with hydrochloric acid and nitric acid.It was shown that the oxygen-containing functional groups on the surface of activated carbon modified by hydrochloric acid or nitric acid were increased through FTIR,Boehm and XPS characterization,which could promote the adsorption of toluene by activated carbon.What’s more,the structure and properties of the catalyst were analyzed by means of BET,SEM and XRD,to investigate the effect of different preparation conditions on the morphology and structure of the catalyst.The results showed that the optimum process for the preparation of catalyst(TiO2/AC)is:over-distillation with atmospheric pressure,the immersion time with 6h,the calcination temperature with 400℃.Under the optimized conditions,the catalyst obtained has a large specific surface area,and the TiO2 crystal form is anatase phase dispersed evenly on the carrier.The degradation efficiency of toluene by MEDL-PCO was greatly affected by the amount of catalyst,residence time,relative humidity and oxygen concentration.Then,the degradation rate of toluene under different working conditions was investigated by the catalyst activity evaluating device.The results showed that 3g was the optimum dosage of the catalyst,and the degradation of toluene gas by MEDL-PCO was promoted with the increase of residence time,relative humidity and oxygen concentration,which proved that the system is suitable for the removal of toluene VOCs produced during the evaporation of high-salt wastewater.The amount of reactive oxygen species(ROS)produced determines the degradation efficiency by MEDL-PCO.In this paper,the effect of relative humidity and oxygen concentration on the total amount of ROS and the amount of hydroxyl radical(·OH),superoxide radical(·O2-)and singlet oxygen(1O2)were investigated by DPCI oxidation-extraction spectrophotometry(OEP)and quenching method.As a result,the increase of relative humidity and oxygen concentration can increase the yield of ROS,and the increase of humidity can promote the production of hydroxyl radical(·OH),and the increase of oxygen can promote the production of ROS such as O2-and 1O2.The mechanism of toluene degradation by MEDL-PCO was investigated by XRD,FTIR,XPS and GC-MS.It was found that the crystal form of the catalyst had no significant changes after the reaction,and some aromatic groups were adsorbed on the surface,and the adsorption oxygen content was improved.Finally,the degradation mechanism of toluene is complicated,which is presumed to be mainly composed of methyl oxidation and benzene ring opening.