Photocatalysis Sulfite Technologies On Pharmaceutical Degradation And Bacteria Sterilization

The society development leads to the increasing consumption of pharmaceutical and personal care products(PPCPs).They are usually discharged into the sewage system through human/animal excretion,illegally emission and wrong disposal.However,the performance of traditional wastewater treatment plants on such pollutant removal is generally unsatisfactory,leading to the rising water pollution and therefore seriously threatening the ecosystem and human health.A large number of studies have proved that Advanced Oxidation Process(AOP)could effectively degrade most organic pollutants in aquatic solutions.In the past,ultraviolet(UV)/sulfite under anaerobic conditions was usually regarded as an Advanced Reduction Process(ARP).This study found that in the presence of oxygen,UV/sulfite could also be used as an AOP.Therefore,this paper mainly investigated the oxidation degradation mechanism of organic pollutants by UV/sulfite and Fe(III)was introduced to improve the oxidation potential of UV/sulfite.Furthermore,the application of the improved system in the sterilization and disinfection were explored.In this study,the oxidation degradation of a typical iodinated contrast agent,iopamidol(IPM),by UV/Na2SO3 at pH 7 was first investigated.Herein,the oxysulfur radicals(including sulfate radical(SO4·-)and sulfite/peroxomonosulfate radicals(SO3·-/SO5·-))played important roles on IPM degradation.The increment of pH enhanced the contribution of SO4·-(from 11.3%to 19.8%)on IPM removal.Besides,some water quality parameters(i.e.,Cl-,I-and natural organic matter)investigated here exhibited inhibitory effect on IPM removal.Three inorganic iodine species(i.e.,I-,reactive iodine species and 103-)were detected during oxidation degradation of IPM by UV/Na2SO3.The transformation products(TPs)by various reactive species were further distinguished.The acute toxicity assay of Vibrio fischeri indicated that TPs by UV/Na2SO3 were less toxic than that by direct UV photolysis.Furthermore,under neutral conditions,the degradation of metoprolol(MTP)as the target compound,by the UV/Na2SO3 with oxygen as an AOP and that without oxygen as an ARP was comparatively studied herein.The MTP degradation by both processes followed the pseudo-first-order law with comparable reaction rate constants of 1.2×10-3 s-1 and 1.5×10-3 s-1,respectively.Scavenging experiments demonstrated that both eaq-and H.played a crucial role in MTP degradation by the UV/Na2SO3 as an ARP,while SO4-was the dominant oxidant in the UV/Na2SO3 AOP.The degradation kinetics of MTP by the UV/Na2SO3 as an ARP and AOP shared a similar pH dependence with a minimum rate obtained around pH 8.The benzene ring and ether groups of MTP were proposed as the major reactive sites for both processes based on molecular orbital calculations by density functional theory.The similar degradation products of MTP by the UV/Na2SO3 process as an ARP and AOP indicated that eaq-/H·and SO4·-might share similar reaction mechanisms,primarily including hydroxylation,dealkylation,and H abstraction.However,the toxicity of treated solution by UV/Na2SO3 as an ARP was weaker than that as an AOP.The introduction of Fe(Ⅲ)could enhance the oxidation potential of UV/Na2SO3.Exiperiment results indicated that the addition of Fe(Ⅲ)could increase the degradation efficiency of CBZ from<30%to 62%.In certain range of concentrations,the addition of the reaction reagent(i.e.,Fe(Ⅲ),Na2SO3)promoted CBZ degradation.By means of scavenging experiments and kinetic model fitting,it was found that CBZ degradation was attributed to the contribution of SO3·-and SO4·-.The contribution rate of SO4·gradually increased from 37%at pH 5.6 to 61%at pH 7.96,while that of SO3·-showed the opposite trend.The dissolved oxygen seriously inhibited CBZ degradation by hindering the conversion of SO32-to active species(especially SO4·-).Although the complexing agents improved the stability of Fe(Ⅲ),it slowed down the binding of Fe(Ⅲ)with SO32-and thus inhibited CBZ degradation.Finally,CBZ was decomposed by UV/Na2SO3/Fe(III)system via hydroxylation and aldehydation.Finally,the application of solar/Na2SO3/Fe(Ⅲ)system in sterilization and disinfection was further investigated,where Escherichia coli(E.coli)was selected as the target microorganism.The reactive species,including HO·and O2·-,played an important role on E.coli inactivation.The appropriate increment of reaction reagents(i.e.,Fe(Ⅲ)and Na2SO3)enhanced E.coli inactivation.However,the increasing pH,anaerobic environment and the complexing agent inhibited E.coli inactivation.Besides,solar/Na2SO3/Fe(Ⅲ)system showed good performance on Staphylococcus Aureus(as the prokaryotic microorganism)inactivation but poor performance on Candida Albicans(as the eukaryotic microorganism)inactivation.