Triclosan(TCS)is a broad-spectrum antimicrobial agent that was widely used in various pharmaceutical and care products.TCS is not easily degraded in the natural environment and is persistent and bio-accumulative,which can have adverse effects on plants,animals and the human endocrine system.Therefore,the study of TCS removal in soil and groundwater media has significant theoretical implications for groundwater remediation in China.In this paper,the Mn(Ⅱ)/Na2SO3 system was constructed to degrade TCS,and the efficacy,mechanism and influencing factors of this system to degrade TCS were investigated in detail.By batch experiments,free radical inhibition experiments,electron paramagnetic resonance experiments,and degradation product analysis experiments,the main active oxides for TCS degradation were identified,and the effects of environmental factors on the efficiency of the Mn(Ⅱ)/Na2SO3 system for TCS degradation were investigated.Finally,the factors influencing the removal of TCS by manganese oxides in soil and groundwater media were investigated,and the degradation products of TCS in soil media under the action of manganese oxides were determined.The main findings were as follows:(1)The degradation of organic pollutant TCS in solution by the oxidation system of Mn(Ⅱ)-activated sulfite was investigated,and the results showed that the degradation efficiency of 10μmol·L-1 TCS reached about 75%in the reaction of 200μmol·L-1 Mn(Ⅱ)and 200μmol·L-1 Na2SO3 for 24 h under the coexistence conditions,and the degradation efficiency of TCS was proportional to the Mn(Ⅱ)concentration.Unlike from the conventional transition metal element activated sulfite degradation pollutants,the free radicals(SO4·-and SO5·-)generated in the Mn(Ⅱ)/Na2SO3 system were not the direct active oxides for TCS degradation,while the generated manganese oxides were the direct active oxides for TCS degradation,a result that was verified by The inhibition of TCS degradation in the presence of free radical quencher conditions was verified to be in high agreement with the inhibition of manganese oxide generation.In addition,the degradation products of TCS after 24 h of TCS reaction were characterized by liquid-phase mass spectrometry,and it was found that the degradation products of TCS in the Mn(Ⅱ)/Na2SO3 system were dominated by oligomers(dimers and trimers),which were mainly generated through the single-electron transfer process between manganese oxides and TCS.(2)The effects of environmental factors on the efficiency of the Mn(Ⅱ)/Na2SO3 system in degrading TCS were investigated,and the following conclusions were obtained:p H has a strong influence on the degradation of TCS by the Mn(Ⅱ)/Na2SO3 system,and TCS has a significant degradation effect in the range of p H 6.0-6.5,and both acidic(p H 5.0)and weakly basic(p H8.0-9.0)will completely inhibit the degradation of TCS;the 10μmol·L-1 iron ions significantly promoted the efficiency of the Mn(Ⅱ)/Na2SO3 system in degrading TCS within 1 h of reaction,but then significantly inhibited the degradation of TCS;high concentrations of both humic acid and anions inhibit the degradation of TCS by quenching free radicals;the degradation efficiency of the Mn(Ⅱ)/Na2SO3 system in the actual water environment were verified,and the results showed that the degradation efficiency of the system was only 20%for TCS in surface water samples and up to 60%for TCS in groundwater samples under the same conditions.(3)The degradation effects of manganese oxide in simulated contaminated soil and groundwater for TCS removal were investigated,and the results showed that:the degradation efficiency of manganese oxide in soil and groundwater for TCS was mainly influenced by the p H value of soil and groundwater,and it had a high degradation effect under acidic conditions.The degradation rate of TCS increased with the increase of manganese oxide addition,and its degradation kinetic constant was proportional to the concentration of manganese oxide.In addition,the degradation rate of TCS increased with the increase of Mn O2 addition,and its degradation kinetic constant was proportional to the concentration of Mn O2.The rapid release of Mn(Ⅱ)from the soil with the reaction indicated that the degradation reaction was a redox reaction.The organic acids had different effects on the degradation efficiency of TCS in soil,with the increase of organic acid concentration,the degradation efficiency of oxalic acid and citric acid changed from promoting to inhibiting,while that of tartaric acid changed from inhibiting to promoting.The degradation products of TCS in soil were analyzed and found that the degradation products were mainly dimers,and the main reaction pathway was that the phenolic hydroxyl group of TCS was deprived of one electron by manganese oxide. |