Effect And Mechanism For The Sulfamethoxazole Removal In Water By Enhanced KMnO₄ Oxidation By Phenolic Compounds

Very recently,frequent detection of sulfamethoxazole（SMX）in aquatic environment arouses people’s concern on their potential risks to environment and health.Although the concentrations of SMX in the environment is low,its potential risk to ecological balance and human health is high.Due to the poor and slow biodegradability,a large proportion of SMX can not be eliminated in conventional wastewater treatment plants.Thus,it is urgent to develop efficient methods towards SMX degradation.KMnO₄,a cheap and convenient oxidant,showed sluggish reactivity toward SMX.Phenolic compounds in the aqueous environment could accelerate the transformation of contaminants by KMnO₄.Therefore,this paper,the strengthening effect,reaction mechanism,and reaction path of SMX removal by KMnO₄ in the presence of phenolic compounds was explored.Meanwhile,the acute toxicity of the reaction system was evaluated.The study showed that SMX had hardly any degradation by KMnO₄.But an astonishing degradation of SMX by KMnO₄ could be observed in the presence of CAT.Furthermore,more phenolic compounds were explored in our work,experiment result indicated that 4-methylcatechol（4mCAT）and protocatechuic acid（PRO）also could enhance the SMX removal by KMnO₄ in different extent.During the reaction,phenolic compounds were oxidized and transformed to a class of important intermediates―quinone compounds,which were identified by UV spectrometer.The reaction products were identified by HPLC/electrospray ionization quadrupole time-of-flight（QTOF）mass spectrometer（HPLC/ESI-QTOFMS）,the result proved that the 1,4-nucleophilic addition between SMX and quinone compounds occurred,which resulted in the reduction of SMX.In addition,filtration experiments proved that quinone compounds could be generated in oxidation of phenolic compounds by KMnO₄ or MnO₂ from consumption of KMnO₄,and KMnO₄played a major role in this process.Take CAT for example,some common influencing factors on the SMX removal in KMnO₄/phenolic compounds system was explored in the study.The pH value have significant influence on the SMX removal,the best effect was observed at pH 7.With the increase of CAT and SMX concentration,the extent of SMX loss also increased.In a certain range,The SMX removal efficiency also increase with increase of the KMnO₄ concentration,and it decrease as the KMnO₄ concentration further increase.Ca²⁺had negligible effect on SMX remove and Zn²⁺showed the ability to accelerate on the reaction,indicating that Zn²⁺could catalyze this reaction.The acute toxicity of system was evaluated by measuring the decrease in the bioluminescence of Photobacterium phosphoreum.It was found that the acute toxicity of addition product was lower than that of SMX.This can be attributed to the substitution of amino group on the benzene ring of SMX,which affects the biological activity of SMX.It was found that MnO₂ also contributed to the oxidation of phenolic compounds,so we prepared colloidal MnO₂ and verified effect of SMX removal by MnO₂ in the presence of phenolic compounds.CAT,4mCAT,PRO,syringic acid（SRY）,and syringaldehyde（SRYLD）could enhance the SMX removal by MnO₂ in different extent.The quinone compounds also can be generated in oxidation of phenolic compounds by MnO₂.Identification of reaction products indicated that the1,4-nucleophilic addition between of SMX and quinone compounds occurred when CAT,4mCAT,or PRO was present,the 1,2-nucleophilic addition between of SMX and quinone compounds occurred when SRY was present.The highest SMX removal efficiency was observed at pH 5.The SMX removal efficiency increased with the increase of CAT or MnO₂ concentration.With the increase of SMX concentration,The SMX removal efficiency decreased and actual SMX loss increased.