Study On Photodegradation Of PAEs In Water By Vacuum UV Based On Interlayer Photoreactor

Water is the source of life.However,with the development of society,we are facing a serious problem of drinking water pollution.Many studies have shown that phthalate esters（PAEs）,which is widely used in industry,has been frequently detected in drinking water sources.The content of PAEs in the effluent of many water purification plants or water supply network in China can not be ignored.The conventional water purification process has limited effect on the removal of PAEs,so it is of great significance to find a new and efficient water treatment process for the control of PAEs in drinking water.The advanced oxidation process based on vacuum ultraviolet has an efficient effect on the removal of refractory organic compounds in water,and it is a new technology that has attracted much attention in the field of water purification in recent years.In addition,UV technology has high scene flexibility,so it has good prospects.In this paper,a new interlayer VUV photoreactor was constructed with typical PAEs,dimethyl phthalate（DMP）and diethyl phthalate（DEP）,as target pollutants.In this system,the influencing factors and mechanism of DMP and DEP degradation were studied,and the energy consumption of the degradation process was evaluated.First of all,on the basis of the most commonly used annular photoreactor,the influence of reactor parameters（hydraulic radius）on the degradation effect was discussed.The VUV photoreactor was improved and its operation parameters were optimized.The results show that the interlayer VUV photoreactor can better solve the problem of mass transfer from the target pollutant to the reaction zone,and has a better effect on the removal of DMP and DEP.It can improve the irradiation efficiency of low pressure mercury lamp.The greater the output power of 185 nm irradiation,the better the degradation effect of pollutants.The circulating flow rate in the interlayer VUV photoreactor system has little effect on the degradation of DMP and DEP.On the interlayer VUV photoreactor,the effects of water quality on the degradation of DMP and DEP were discussed,and the energy consumption of degradation was evaluated.The results showed that p H had little effect on the degradation of DMP and DEP in the range of 3-9.The degradation effect decreased with the increase of initial concentration of DMP and DEP.The degradation rate of DMP and DEP increased with the increase of temperature（5^°C-25^°C）,but there was no obvious change when the temperature continued to rise（25^°C-35^°C）.HCO₃^-and NO₃^-in water showed inhibitory effect on the degradation of DMP and DEP,while SO₄^2-had no obvious effect.Taking tap water as the application scenario,the degradation efficiency has decreased.Using electrical energy per order（EE/O）to evaluate the energy consumption.The EE/O of interlayer VUV photoreactor system is smaller than that of annular photoreactor system.Finally,the degradation mechanism of DMP and DEP was discussed.The results show that the hydroxyl radical generated in the system plays an important role in the degradation.The second-order reaction rate constants of two kinds of PAEs with hydroxyl radical were calculated to be:k _DMP,·OH=4.65×10⁹M^-1s^-1,k _DEP,·OH=2.80×10⁹M^-1s^-1,respectively.Compared with the annular photoreactor system,the interlayer VUV photoreactor system has higher steady-state concentration of hydroxyl radicals,higher H₂O₂ formation rate and higher H₂O₂ formation concentration.The degradation process of two kinds of PAEs in interlayer VUV photoreactor is alkyl chain breaking and benzene ring opening.In addition,hydroxylated derivatives and benzene substitutes may be formed in the degradation process of DMP.