次氯酸钠对磺胺二甲氧嗪的降解与风险评价

Degradation and risk assessment of sulfadimethoxine during sodium hypochlorite disinfection process

自来水原水中新兴污染物的存在对饮用水水质安全提出新的挑战。采用氯消毒对典型磺胺类抗生素磺胺二甲氧嗪(Sulfadimethoxine,SDM)进行降解研究,考察余氯初始浓度、pH值、氨氮(NH4-N)等因素对降解的影响,探究SDM氯氧化降解机理,评估其生态风险。结果表明:在SDM初始浓度为15μmol/L、余氯初始浓度为60μmol/L的条件下,120 s内SDM去除率达到95.9%,降解过程符合准二级反应动力学。反应速率常数随着余氯初始浓度增大而增大,随着NH_(4)^(+)-N浓度增大而减小,背景阴离子Cl^(-)、NO_(3)^(-)、SO_(4)^(2-)对反应影响甚微,HCO_(3)^(-)、CO_(3)^(2-)对反应有抑制作用,中性条件下有利于SDM氯氧化反应。基于高分辨质谱HRMS Orbitrap解析出9种降解中间产物,降解过程中发生氯代反应、脱甲基反应和羟基加成反应等。在消毒过程中,SDM的完全去除并不意味着生态风险的有效削减,对饮用水水质安全构成潜在风险。

The presence of emerging contaminants in the raw water puts forward new challenges to drinking water treatment process.The chlorination of typical sulfonamides antibiotic sulfadimethoxine(SDM)in the sodium hypochlorite disinfection process was studied.The chlorination effects,including the initial concentration of residual chlorine,the pH value of the solution,ammonia concentration,and the inorganic anions,were also investigated.The mechanism of SDM chlorination was explored and the ecological risk was further assessed.The results showed that,under the conditions of the initial SDM concentration 15μmol/L,the initial concentration of residual chlorine 60μmol/L,the SDM removal reached high up to 95.9%in 120 s.The degradation process conformed to the pseudo-second reaction kinetics.The constants of degradation rate decreased with the increasing ammonia concentration,and increased with the initial concentration of residual chlorine.Background anions Cl^(-),NO_(3)^(-),SO_(4)^(2-)had marginal effects on the reaction while HCO3-and CO32-had inhibition effects on the reaction.SDM chlorination can be improved under neutral conditions.Nine degradation intermediates are identified by using high-resolution mass spectrometry HRMS Orbitrap.The degradation process covers chlorination,demethylation and hydroxyl addition reactions.The complete removal of SDM does not imply an effective reduction of ecological risk during disinfection process which poses a potential risk to the safety of drinking water quality.