Reduction Of Typical DBPs In Drinking Water By Iodide-Assisted UV/S(Ⅳ) Process:Efficiency And Mechanism

Chlorine disinfection applied in drinking water treatment have avoided human from risk caused by pathogenic microorganisms,but disinfection by-products(DBPs)are generated due to the reaction of chlorine and DBP percusors(e.g.,natural organic matters).The strategies for DBPs control in drinking water include sourcewater protection,enhancing removal of DBP percusors,optimizing the disinfectant or disinfection paramneters.However,these three control strategies aim to keep the concentration of DBPs in effluent of drinking water plants below the guideline of health standards,limmted method is available for dealing with the DBPs generated in the water distribution system.Household water treatment(HWT)facility,locating at the user terminal,can futher clean pollutants before they flow out from the tap and thus is expected to reject these DBPs.Unfortunately,the typical HWT technologies,such as membrane filtration and activated carbon adsorption,remove DBPs ineffeiciently due to the DBPs’ low molecuer weight and polarity of some DBPs.Therefore,this article proposes iodide-enhanced UV/S(Ⅳ)advanced reduction process(ARP)combined with typical house water process to remove DBPs,for the purpose of providing an economical and efficient integrated echnology for accessing safe drinking water.The typical DBPs,such as bromate(BrO3-),monochloroacetic acid(MCAA),chloroform(TCM),were selected as the model compounds to study the efficiency and mechanism of DBPs removal by UV/S(Ⅳ)/KI process.To investigate its application potential,the UV/S(Ⅳ)/KI process was also tested by treating real waters.The results indicate that the UV/S(Ⅳ)/KI process showed a high removal efficiency for the selected DBPs.For example,under the conditions of pH=9.2,temperature=20±1℃,and dissolved oxygen=7.0mg·L-1,the degradation rate of bromate is 2.35μM·min-1,which is much better than those reported in previous studies.The degradation of BrO3-was proved to be dominated by eaq-reduction which made a 77.4%contribution.In this system,S(Ⅳ)not only acted as a precursor of eaq-,but also acted as a shielding agent of active iodine species(RIS)and regenerant agent of I-(precursor of eaq-),while I-played a role similar to a homogeneous catalyst.In addition,we found that bicarbonate(HCO3-),nitrate(NO3-),humic acid(HA),and other strong electron acceptors in drinking water will compromise the reduction capacity of UV/S(Ⅳ)/KI process.To solve the problem of efficiency declining of DBPs removal by UV/S(Ⅳ)/KI process for real waters,we attempted to optimize this process by increasing the hydrated electron yield and manipulating dominating radical.The results showed that converting the dominating radical from eaq-to CO2·-is not feasible while replacing the UV254 lamp with a vacuum ultraviolet lamp(VUV)succeded.The later increased the hydrated electron yield,which made the bromate reduction efficiency by VUV/S(Ⅳ)/KI process increase to 2.43 times of that by UV/S(Ⅳ)/KI process.Besids,the VUV/S(Ⅳ)/KI process exibited a high removal efficiency for halogenated organics.The higher the halogenation degree,the faster the degradation rate.The efficiency and economics of the VUV/S(Ⅳ)/KI process combined with a typical HWT process(microfiltration+activated carbon adsorption+ultrafiltration)were also studied.The results illustrated that typical HWT process alone can not effectively remove DBPs in real water while the removal efficiency can be significantly improved by the combined process.We also found that the combined process mainly did not increase the biological toxicity of treated water.Futhermore,the cost of selected DBPs VUV/S(Ⅳ)/KI process of in real water is 0.0076 ￥·m-3.In summary,the typical HWT process combined with VUV/S(Ⅳ)/KI process is promising as an alternative control technology of DBPs in drinking water.