Bisulfite And Nitrilotriacetic Acid In Situ Promote The Formation Of Intermediate Manganese And Its Degradation Of Sulfamethoxazole

Antibiotics,a kind of emerging pollutants,have potential threat to human health and ecosystem.Meanwhile,sulfamethoxazole（SMX）is one of the highest frequency and concentration of antibiotics detected in water environment of China.If the residual SMX in water environment is not properly treated,it will cause serious harm to human health and ecological environment.With the production of intermediate-valence manganese（Mn（III）,Mn（V）,Mn（VI））and SO₄^·-,bisulfite（HSO₃^-）combined with permanganate（KMn O₄）is an effective means to enhance the degradation of organic pollutants by KMn O₄.In addition,the complexing agent can not only enhance the oxidative organic pollutants of KMn O₄,but also accelerate the oxidation of Mn（II）.Therefore,in this paper,SMX was selected as the main target pollutant to explore the degradation efficiency of permanganate/bisulfite（PM/BS）system.As one of complexing agent,nitrilotriacetic acid（NTA）was introduced to construct Mn（Ⅱ）/NTA/BS and PM/NTA/BS systems,further investigating the formation of intermediate manganese and the degradation of SMX.The main research contents and results are as follows:（1）The degradation of SMX in wastewater by PM/BS system was studied.The results showed that 80%SMX was removed within 10 s in PM/BS system,while no obvious SMX degradation was observed in PM or BS alone system within 300 s.Reactive manganese species（RMn S,Mn（Ⅲ）,Mn（V）and Mn（VI））,sulfate radical(SO₄^·-)and hydroxyl radical（^·OH）formed in PM/BS system all played a role in accelerated degradation of SMX.Due to the loss of RMn S,SMX degradation was significantly inhibited with the increase of p H.The best[BS]:[PM]ratio for SMX removal was 7.5:1-10:1.Presence of Cl^-,HCO₃^-or natural organic matter（NOM）significantly inhibited the degradation of SMX.Based on the detected transformation products,two degradation pathways of SMX by PM/BS,namely N-S bond cleavage and amino oxidation,were proposed.（2）The degradation efficiency,influencing factors and reaction mechanism of Mn（Ⅱ）/NTA/BS on SMX were studied.The results showed that the addition of NTA enhanced SMX removal in Mn（Ⅱ）/BS under neutral conditions.UV-vis absorption spectra of reaction solution showed that stable Mn（Ⅲ）was produced,while alcohol inhibiting and the relative rate methods ruled out the possibility that^·OH and SO₄^·-were the main active species for SMX degradation in Mn（II）/NTA/BS system.Therefore,it was inferred that Mn（Ⅲ）was the primary reactive species.At p H=5.6～9.5,Mn（Ⅱ）/NTA/BS could greatly degrade SMX.Dissolved oxygen participated in the reaction process in the system,and the reduction of its concentration would inhibit the autocatalytic stage,thus affecting the removal of SMX.Due to the complexing ability with Mn（II）,HCO₃^-and fulvic acid（FA）were not conducive to the autocatalytic stage,making it difficult to start the reaction.Four intermediates were detected during the degradation of SMX in Mn（Ⅱ）/NTA/BS system,and the possible degradation pathways were speculated as N-S bond breaking,hydroxylation,amino oxidation and coupling reaction.（3）The degradation of SMX by NTA enhanced PM/BS system was systematically studied.The results showed that NTA can stabilize the production of RMn S in this system,and induced the reduction product Mn（Ⅱ）to regenerate Mn（Ⅲ）again,promoting the continuous degradation of SMX in the system under neutral conditions.At p H=7.0,the degradation of SMX in PM/NTA/BS system presented two stages,which were the rapid reaction stage of 10s before the reaction and the continuous reaction stage of 290 s after the reaction,respectively.The effect of NTA dosage mainly showed in the continuous degradation stage.Appropriate amount of NTA could stabilize the RMn S and reduce the generation of Mn O₂,while excessive amount might compete with SMX for RMn S.The p H of SMX degradation in PM/BS system was broadened by the introduction of NTA and the promoting effect is most obvious at p H=7.0.Consistent with PM/BS system,the reduction of dissolved oxygen would inhibit the degradation of SMX.Cl^-,HCO₃^-and FA inhibited the degradation of SMX in PM/NTA/BS system,while Fe³⁺was in favor of SMX degradation.Five products were detected in the degradation process of SMX by PM/NTA/BS system,suggesting that the degradation pathways include N-S bond breaking,hydroxylation reaction,amino oxidation,coupling reaction and N-O bond breaking.