Study On The Transformation Characteristics Of Typical Organic Iodine Compounds By Ultraviolet-initiated AOPs

Disinfection by product（DBPs）produced during drinking water disinfection has a potential great threat to water safety and the emerging high toxic iodinated disinfection by-product（I-DBPs）is the focus of attention in the field of environment.Recently,UV-integrated advanced oxidation process（UV-AOPs）has attracted much attention as a promising technology for efficient removal of refractory organic iodine sources in aqueous phase.For this reason,this paper takes two typical organic iodine compounds Iopamidol（IPM）and Levothyroxine Sodium（LTX）as research objects and intends to explore the degradation kinetics of common UV-AOPs,which is UV/Cl₂,UV/H₂O₂ and UV/NH₂Cl.The photodegradation of IPM and LTX can be well described by pseudo-first-order model and the removal efficiency ranked in descending order of UV/Cl₂>UV/H₂O₂>UV/NH₂Cl>UV.This synergistic effect can be attributed to the different free radical species generated in each system.The best working condition parameter for removal is that the UV strength is 9.76 m W cm^-2,the dosage of oxidant is 1000μM and the removal rate is more than 99%under such parameter.However,the p H behaviors exhibited quite differently.For IPM,p H=7.0 is the optimal in UV/Cl₂ and UV/NH₂Cl followed by acid and base,the solution p H increases and decreases obviously in UV/H₂O₂.For LTX,the order of k_obsin UV and UV/NH₂Cl is p H5.0>p H6.0>p H7.0>p H8.0>p H9.0,k_obs has an obvious maximum at p H 7.0 at chloramination.It also has an energetically effect on the degradation of IPM and LTX in the actual background water,specifically:in the presence of Cl^-,the UV/Cl₂degradation of IPM k_obs remains unchanged while the UV and UV/NH₂Cl process of LTX slightly increases the degradation of k_obs;when the HCO₃^-exist,the degradation of k_obs by UV and UV/NH₂Cl of LTX decreases slightly.In the background of NOM,the k_obs of LTX decreased significantly and the value of k_obs in the degradation of UV and chloramination was pure water>raw water>FA>HA,which is different between UV/NH₂Cl process.The efficiency of the photodegradation system was evaluated by empolying the kinetic model combined with the concept of electrical energy per order（EE/O）as the index of energy demand.The order of EE/O is UV>UV/NH₂Cl>UV/H₂O₂.The high concentration oxidant and UV intensity are beneficial to reduce the energy consumption and improve the economic benefit.Pretreatment of IPM by UV/Cl₂ and UV/NH₂Cl clearly enhanced the production of classical DBPs and iodo-trihalomethanes（I-THMs）during subsequent oxidation while UV/Cl O₂ and UV/H₂O₂exhibited almost elimination effect.In this paper,the degradation efficiency of typical organic iodine compounds in different UV-AOPs and the law of I-DBPs formation and control reduction were compared,so as to provide a theoretical basis for the popularization and application of UV-AOPs in drinking water treatment in China.