Removal Efficiency And Mechanism Of Tetracycline And Amoxicillin In Recharged Influent During Soil Aquifer Treatment

Water pollution,water shortage and groundwater over-exploitation are the main environmental concerns recently,and how to efficiently obtain cheap reused water resource become a hotpot.With the increasing use of antibiotics,the presence of trace amounts of antibiotics has been widely detected in the sewage treatment plants.Although the concentration of those antibiotics detected always ranged from ng/L to g/L,it still causes security risks on the reusing of water.Soil aquifer treatment(SAT)exhibited a high efficiency in removal of various pollutants,was a barrier before the reuse of water.In this paper,the removal efficiency and mechanism of two different antibiotics,tetracycline(TC)and amoxicillin(AMO),were studied by laboratory simulating SAT system.To choose the target antibiotics,the methods of the weighted score of persistent pollutants was used,and the parameters of dosage(exposure level),migration and environmental ecotoxicity used as the screening indicators,establish the screening system,and ultimately filter the target antibiotics are TC and AMO.The adsorption characteristics of TC and AMO in three typical soils represented by loess,black soil and kaolin were studied,and the parameters of initial concentration,adsorption time,p H,temperature,soil organic matter and soil redox potential were evaluated.At the same time,the adsorption kinetics and adsorption thermodynamics of TC were clarified.The results showed that the adsorption capacity of TC was the best in black soil,the saturated adsorption capacity was 85 mg/g,the adsorption capacity of loess on AMO was 92 mg/g in the three,and the acid p H was favorable for loess,black soil and kaolin The adsorption capacity of TC and AMO is decreased when the organic matter in the soil is removed,such as the adsorption capacity of TC in the black soil,and the adsorption capacity of TC is decreased from 106 mg/g to 94 mg/g,which decreased by about 10%.The adsorption kinetics simulation showed that the adsorption of TC on black soil was better simulated by the first order reaction kinetics equation.The adsorption kinetics of TC on loess and kaolin compare with the quasi-second order kinetic equation,the adsorption kinetics of AMO is more suitable for quasi-second order kinetics equations.The adsorption of TC on loess and clay satisfies the Langmuir adsorption isotherm,that is,the adsorption process of the loess to the TC is monomolecular adsorption.The Freundlich equation,which is used to characterize the competitive adsorption,is more suitable for the adsorption of TC.Langmuir adsorption isotherm can be very good for three kinds of soil adsorption AMO thermodynamic simulation.Simulated SAT system exhibited a relatively higher TC removal rate of 94%,with an effluent concentration of 3 ?g/L.The removal rate of AMO is about 91.5 %.TC was mainly adsorbed and degraded in the soil layer with depth of 0~50 cm,and 65% of the total soil removal effect on TC was observed.Correspondingly,64% of AMO was removed in 50-100 cm soil layer.This indicated that TC preferentially adsorbed by surface soil with higher relative oxygen content,while AMO is easily degraded in the relatively anaerobic environment.The removal efficiency of TC was 68% in the aerobic condition,while the removal rate of nitrate was reduced by nearly 7% in the case of nitrate reduction and sulfuric acid reduction.The degradation rate of AMO was about 52% under the condition of anaerobic and nitric acid reduction,and the degradation rate of AMO was less than 50% under aerobic and sulfuric acid reduction conditions.The residuals of TC and AMO in the simulated SAT system were analyzed.The results showed that the residue of TC in the surface soil was the least,which is about 6.7 ?g/g,and it is 13.2 ?g/g and 25.8 ?g/g at 50 cm and 100 cm.The contents of AMO in the three soil layers were reduced to 26.8 ?g/g,20.0 ?g/g and 13.4 ?g/g for 60 days after the reactor was stopped for 60 days.The degradation pathway of TC in the simulated SAT system is mainly epimerization.At the same time,the carbocyclic ring of TC may be destroyed under weakly alkaline conditions,and the inactivated aldehydrate is formed.AMO is in microbial related enzyme The cleavage of the amide carbocyclic ring occurs,and the carboxyl group after ring opening may undergo decarboxylation and further degrades.