Comparative Study On The Performance Of UV Peroxides For The Removal Of Refractory Organic Pollutants

In this study,three UV-based advanced oxidation processes,UV/peroxymonosulfate（UV/PMS）,UV/peroxydisulfate（UV/PDS）,and UV/hydrogen peroxide（UV/H₂O₂）,were compared for different degradation kinetics of target pollutants.In view of the purpose of comparing the removal efficiency of three oxidation systems for different active contaminants,Benzoic acid（BA）,nitrobenzene（NB）and trichloromethane（TCM）with different secondary reaction rate constants with hydroxyl radical（HO^·）and sulfate radical(SO₄^·-)were selected as target pollutants.In view of the discussion on the degradation efficiency of antibiotics,trimethoprim（TMP）and enrofloxacin（EFX）,which widely exist in water sources,were selected as target pollutants.The removal kinetics of these five organic pollutants by three UV/peroxide systems were compared under pure water and actual water background conditions.The formation of bromate and chlorate in uv/peroxide system was further studied.First of all,in the pure water system,the removal efficiency of five target pollutants by UV/H₂O₂,UV/PMS and UV/PDS systems under different p H conditions was compared.Furthermore,the effects of inorganic carbon and natural organic matter（NOM）,the main free radical capture agents in water,on the decontamination efficiency of three UV/peroxide systems were studied.The results show that under acidic and neutral conditions,the decontamination effect of UV/H₂O₂ on BA degradation is better than that of UV/PDS and UV/PMS,and the effect of UV/PDS on TMP and EFX is better than that of UV/H₂O₂ and UV/PMS,while the effect of UV/H₂O₂ and UV/PMS on NB is better than that of UV/PDS.Under alkaline conditions,the degradation efficiency of BA,NB,TMP and EFX by UV/PMS was the highest,and that of TCM by UV/PDS was the highest under all p H conditions.Bicarbonate ions,carbonate ions,and NOM had significant inhibitory effects on all three oxidation systems.The inhibitory effect of NOM on the decontamination efficiency of UV/H₂O₂ was the greatest and the inhibitory effect on the UV/PDS process was the least.However,bicarbonate and carbonate had the greatest inhibitory effect on the UV/PDS process.Secondly,the concentrations of bromate and chlorate in UV/H₂O₂,UV/PMS,UV/PDS systems were monitored,and the formation pathways of bromate and chlorate in UV/PMS and UV/PDS systems were also analyzed.Among the three oxidation systems,the concentration of bromate and chlorate in UV/PDS is the highest and small amount of bromate and chlorate were found in UV/PMS,but not in UV/H₂O₂.In UV/PMS and UV/PDS systems,the formation of hypobromic/hypochlorite and bromate/chlorate is mainly through the oxidation of HO^·and SO₄^·-and secondary free radicals Br^·/Cl^·and Br₂^·/Cl₂^·.However,the formation of bromate/chlorate in UV/PMS system is less than that in UV/PDS system because PMS captures some free radicals.Finally,under the background of surface water and tap water,the removal efficiency of BA,TMP and EFX and the consumption of peroxide in UV/H₂O₂,UV/PMS and UV/PDS systems were compared.The results show that the removal rate of mixed drugs in tap water is lower than that in ultrapure water,and the removal rate of mixed drugs in surface water is lower than that in tap water and ultrapure water.The UV/H₂O₂ system was the best for pollutant removal in the surface water background,however,H₂O₂ was the least consumed and PMS was the most consumed among the three oxidants.Under the background of tap water,the UV/PDS system has the best removal effect of pollutants and among the three oxidants,the consumption of H₂O₂ is the least,and the consumption of PMS is the largest.And no bromate and chlorate were detected in the three systems in tap water.