| In recent years,antibiotics as a new class of environmental pollutants have been widely concerned by researchers at home and abroad.Although its concentration is relatively-low in the environment,its potential environmental problems cannot be ignored due to its continuous investment and persistence in the ecosystem.Chloramphenicol is a kind of common antibiotics.Although national regulations have been banned,but still able to detect its traces in the river,groundwater,sewage treatment plants and other water environment.This shows that the traditional water treatment process has a limited effect on its removal.Therefore,it is necessary to develop a new and efficient advanced treatment process.Advanced Oxidation Process(AOPs)consists of a series of similar but different chemical processes designed to address pollution problems in water,air and soil.In the past few decades,AOPs has been widely used in many subject areas,such as the understanding of basic principles,the elaboration of dynamics and mechanisms,the development of new materials,the development and application of membranes.In the water treatment industry.AOPs have attracted extensive attention from researchers due to their high efficiency,cleanliness,mild reaction conditions,no secondary pollution,and complete degradation of pollutants.AOPs are mainly produced by free radicals(HO.or SOS-and other reactive groups),which in turn oxidize and degrade pollutants,which are usually highly oxidizing.The use of transition metal Fe(?)ions to catalyze the generation of free radicals by oxidants is a common mode in AOPs.However,Fe(?)ions have a strong dependence on pH.At the same time,the cyclic conversion of Fe(?)/Fe(?)during the reaction is also an important factor affecting the progress of AOPs reaction,and the use of Fe(?)ions in large quantities may also be Cause secondary pollution of metal ions.Therefore,the Fe(?)ion-based AOPs system needs to be optimized.At present,some studies have shown that some carboxylic acids may have an important influence on the solubility of Fe(?)ions due to special chemical functional groups.At the same time,the corresponding iron-carboxylate complex can promote the cyclic conversion of Fe(?)/Fe(?)under a certain wavelength of light irradiation.Therefore,in combination with the above-mentioned problems in the natural environment and industry,this study uses advanced oxidation technology based on photochemistry,and visible light synergizes with Fe(?)ions to activate the hydrogen persulfate system(Vis/Fe(?)/PMS)to degrade chloramphenicol simulated wastewater.The effects of visible light,initial pH,Fe(?)dosage,oxidant dosage,common inorganic ions on chloramphenicol degradation were investigated.At the same time,due to the slow regeneration rate of Fe(?)ions and the strict requirement of reaction pH in the system,the team added four different complexing agents(citric acid,oxalic acid,tartaric acid.EDTA)to the system to investigated their effects on the advanced oxidation process.By measuring the final degradation of chloramphenicol and the evolution of Fe(?)ions.oxidants and reactive radical species in the degradation process,the effects and mechanisms of different complexing agents on the degradation of chloramphenicol in Vis/Fe(?)/PMS system were speculated to provide theoretical basis for relevant research.According to the experimental results,the following conclusions were drawn:(1)The degradation experimental results show that Vis/Fe(?)/PMS system has excellent performance on the degradation of chloramphenicol,and the degradation process follows pseudo-first-order kinetic model.Under the experimental conditions,the optimum combination of the substances involved in the oxidation process is as follows:initial chloramphenicol concentration is 0.01mM.initial oxidant concentration is 0.2mM,initial Fe(?)concentration is 0.1mM,initial pH of the system is 3.After 60 minutes,the degradation rate of chloramphenicol reached 93%.(2)Free radical identification experiments showed that HO-and SO4·-"existed simultaneously in Vis/Fe(?)/PMS system,and both of them promoted the degradation of chloramphenicol.(3)Complexation experiments showed that the four complexing agents can promote the degradation of chloramphenicol in the Vis/Fe(?)/PMS system at low concentrations.Among them,the promotion effect of oxalic acid is the most significant.The reason is that oxalic acid itself has a simple structure,and the iron oxalate complex itself has excellent photochemical activity,which not only greatly promotes the regeneration of Fe(?)ions,but also may generate other active substances with strong oxidizing properties;citric acid and Tartaric acid has the same number of functional groups,and its structure and molecular weight are relatively close,both of which show low concentration promotion and high concentration inhibition;EDTA is a strong complexing agent of traditional iron,although it has more carboxylic acid functional groups,but due to molecular weight The huge and corresponding chemical structure is stable and therefore mostly manifests as inhibition.Comprehensive analysis shows that the mechanism of the complexing agent may be related to complexing agent concentration,steric hindrance effect and molecular weight.(4)Degradation products and mineralization experiments show that Vis/Fe(?)/PMS has a good mineralization effect on chloramphenicol.When the initial concentration of chloramphenicol is 0.1mM,the initial concentration of oxidant is 2 mM,and the initial concentration of Fe(?)is 1 mM,the mineralization rate of chloramphenicol reaches 53.7%after 12 hours of reaction.Moreover,the addition of oxalic acid can significantly increase the mineralization rate of chloramphenicol in the pre-reaction period,but the oxalic acid is gradually decomposed during the reaction process,and the promoting effect is weakened.At the same time,the formation of chloride,nitrate,formate and oxalate ions was detected in the system.Finally,by comparing the effects of four complexing agents on the degradation of chloramphenicol in the Vis/Fe(?)/PMS system,the recommended order of complexing agents was:oxalic acid,citric acid,tartaric acid,EDTA. |
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