Study On The Degradation Of Typical Trace Organic Pollutants In Water By Over-flow UV/chlorine Proces

The increasing occurrence of trace organic contaminants in nature water has brought new challenges to aquatic ecological protection and water quality security.The UV/chlorine and VUV/UV/chlorine processes are one of the most efficient technologies to degrade these contaminants in water,but they are susceptible to p H,contaminant and oxidant concentrations,and water matrices.Existing relevant researches are mostly carried out in batch reactors or under batch mode with the contaminants being completely mixed with reactive species.By contrast,practical UV-AOPs are usually operated in flow-through reactors where the extent of mixing is different,which may affect the kinetics and mechanism of contaminants degradation.The main purpose of this study was to investigate the degradation of contaminants in flow-through UV/chlorine reactors and to evaluate the applicability of the steady-state approximation（SSA）model.Meanwhile,the effects of water matrices and reactor configuration on the degradation kinetics and energy consumption of contaminants were investigated.Finally,the degradation of a contaminant in flow-through reactors is promoted by enhancing the light field and flow field.Firstly,the degradation of high-concentration atrazine（ATZ）,sulfamethoxazole （SMX）and metoprolol（MET）in a flow-through UV/chlorine reactor under different water matrices was investigated.The results showed that the degradation processes could be well fitted by the pseudo-first-order kinetics（R²≥0.97）with the order of rate constants following SMX>MET>ATZ.The low UV transmittance of the reaction solutions and the limited extent of mixing in the flow-through reactor resulted in poor applicability of the steady-state approximation model in predicting the degradation rates of the contaminants.Compared with in deionized water,the degradation rate of ATZ in tap water was slightly decreased,while those of SMX and MET were increased significantly.It can be obtained from the analysis of individual water matrix that,the reason for the latter is that the generation of ClO^·and CO₃^·–was promoted respectively with Cl^–and HCO₃^–,while the UV photolysis-dominated degradation pathway of ATZ made it less affected.The E_EO results implied that the energy consumption in real water was expected to be further reduced by increasing the oxidant concentration appropriately.Based on the generation of disinfection by-products（DBPs）and toxicity assessment,future research needs to focus on the degradation efficiency of ATZ itself and the generation of trichloromethane（TCM）during the degradation of MET.Secondly,the influence of reactor configurations on the degradation of contaminants by flow-through UV/chlorine process was explored after reducing the concentrations of pollutants and oxidants in equal proportions.The degradation fitted well with pseudo-first-order kinetics（R²>0.92）,and the optimized SSA model was roughly applicable with the predictions deviated within 47%.UV photolysis here stood as the major degradation pathway for ATZ while the non-radical processes（UV photolysis and chlorination）played a dominant role in SMX degradation as the reactor internal diameter increased.The degradation rates were reduced to varying extents with water matrices where the effect of dissolved organic matter（DOM）was most prominent（as large as 73.6%）.Although a reactor with the larger internal diameter resulted in reduced degradation rate constants on account of the decreased average fluence rate,the lower energy efficiency was also achieved.The E_EO values of micropollutants degradation by UV/chlorine fell in the range of 0.04–1.80 kWh m^–3 order^–1 in deionized water and under different water matrices.The acute toxicity was observed to be higher after UV/chlorine treatment in tap water due to complex water matrices,but still stayed low in general.Finally,the degradation of ATZ in flow-through reactors was enhanced by optimizing the light and flow fields.The degradation rate of ATZ in the UV/chlorine process was increased due to the enhanced UV photolysis by the increase of fluence rate.The degradation of ATZ by the VUV/UV and VUV/UV/chlorine processes still fitted well with pseudo-first-order kinetics（R²>0.90）,and the degradation rate was significantly improved due to the enhanced radical oxidation.The addition of baffles in the reactor can improve the extent of mixing,thereby promoting the degradation of ATZ by radicals.E_EO analysis showed that in a reactor with a smaller internal diameter,the VUV/UV process was preferred to achieve the purpose of efficient and economical ATZ degradation.This study demonstrated the potential application of the UV/chlorine process in terms of effective micropollutants removal,energy consumption and toxicity variations,and the VUV/UV and VUV/UV/chlorine processes can enhance the degradation of refractory trace organic contaminants（e.g.,ATZ）,which will help promote the engineering application of the above processes.