| Chloramphenicol?CAP?,a chloro-nitro-aromatic antibiotic,is a broad-spectrum antibiotic with excellent antibacterial properties and strong stability.Therefore,it is widely used in the treatment of human and animal diseases.At present,chloramphenicol is widely detected in environment.Chloramphenicol can lead to fatal bone marrow suppression and aplastic anemia.But,it is difficult to remove it effectively by conventional water treatment process.In addition,when chloramphenicol is treated with chlorine disinfection,it's easily attacked to form a halogenated acetamide disinfection by-product,dichloroacetamide?DCAc Am?,which is a highly toxic and cytotoxic haloacetamide disinfection by-product and seriously harmful to human health.In this paper,a new advanced oxidation process was applied to remove chloramphenicol and a comparative study with ozone and ozone/hydrogen peroxide on the process was made.The degradation intermediates of chloramphenicol were detected by liquid chromatograph/mass spectrometer?LC/MS?and the reaction path was speculated.In addition,by observing the trend of DCAc Am production during the chlorination disinfection after O3,O3/H2O2 and O3/PMS pretreatment,more comprehensive theoretical guidance is provided for the practical application of O3/PMS process.The O3/PMS system includes three oxide species:O3,HO·and SO4·-.By means of competitive kinetics,the rate constants of the second order reaction between chloramphenicol with O3,HO·and SO4·-was determined as follows:0.291M-1s-1?2.27×109M-1s-1?1.02×108M-1s-1.The results reflected the removal degree of chloramphenicol by each oxide species.The degradation efficiency of chloramphenicol in O3/PMS system is closely related to the dosage of PMS and some water quality parameters such as:p H,coexisting ions and natural organic matter.With the increase of PMS dosage,the decomposition of ozone and the reduction efficiency of chloramphenicol were increased.The increase of p H value significantly improved the degradation rate of chloramphenicol and shortened the reaction time to reach stability.The effect of carbonate on chloramphenicol degradation was divided into two stages:at lower concentration,it had no effect on chloramphenicol degradation.However,when the concentration reached a certain value,carbonate obviously inhibited chloramphenicol degradation.Similar to carbonate effect,the degradation effect to chloramphenicol by natural organic matter could also be divided into two stages:at lower concentration,natural organic matter could obviously promote ozone decomposition and chloramphenicol removal,but when natural organic matter was in higher concentration,it completely hindered the degradation of chloramphenicol.The chloramphenicol degradation was promoted by the addition of chloride ions.But with the increase of chloride concentration,the promoting effect was gradually weakened.The carbonate concentration and pH of the groundwater selected in the experiment are both high,whose effect on hydroxyl radical is more obvious than sulfate radical.Therefore,the inhibition of chloramphenicol degradation was more evident in the O3/H2O2 system in real water.By comparing and analyzing the products produced through the degradation process of chloramphenicol with the five-kind oxidation systems:O3,O3/TBA,O3/H2O2,O3/PMS and O3/PMS/TBA,we could conclude that because there are many kinds of oxides in O3/PMS system and many oxidation modes work together,it produced the most products.By comparing the effect of the five pre-oxidation systems?O3,O3/TBA,O3/H2O2,O3/PMSandO3/PMS/TBA?on the formation of dichloroacetamide?DCAc Am?during chloramphenicol chlorination,it could be concluded that with the increase of the concentration of NaCl O,the amount of DCAc Am was increased.Besides,when the NaCl O concentration was 0.1m M,except for O3 and O3/H2O2,the formation of dichloroacetamide in the other three groups of preoxidation system was higher than the system with chlorination only.When the concentration of Na Cl O was 0.5m M,the formation of dichloroacetamide in the other four preoxidation systems except O3/H2O2 system was higher than that the system with chlorination only.What's more,it was worthwhile to note that natural organic compounds had a significant inhibition effect on the formation of DCAc Am.In the O3,O3/H2O2 system,the addition of natural organic compounds lessened the DCAc Am production to less than 0.2?M,and the amount of DCAcAm in the five preoxidation systems was smaller than that in the system with chlorination only. |
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