Study On The Degradation Efficency Of Levofloxacin In Water By Activated Persulfate

Levofloxacin（LVX）is a broad-spectrum fluoroquinolone antibacterial drug,which is mass-produced and used because of its high antibacterial effect,safe use and wide application range.However,LVX is biologically toxic and inhibitory,belongs to refractory organic matter,and has certain biological activity after being discharged from the body,which is easy to cause water pollution and harm to human health and ecological environment.Therefore,it is urgent to find an efficient method to degrade LVX.At present,advanced oxidation technology based on sulfate radicals（SO₄^-·）has attracted much attention in the research of treatment of refractory organic compounds.In this study,LVX was used as the target pollutant,the advanced oxidation method of peroxodisulfate（PDS）was used to degrade LVX by Fe²⁺activated PDS and external field effect（thermal field and electric field）combined with Fe²⁺activated PDS.The oxidation efficiency of pollutants under different influencing factors was explored,and determined the optimal reaction conditions.The main research contents and results are as follows:（1）In the Fe²⁺/PDS system,the effects of PDS concentration,Fe²⁺concentration,LVX concentration,and initial p H on the degradation of LVX were investigated.The results show that with the increase of Fe²⁺concentration,PDS concentration and initial concentration of LVX within a certain range,the degradation effect of pollutants is better,and the best under the condition of unadjusted p H.The optimum reaction conditions:[Fe²⁺]₀=0.2 mmol/L、[PDS]₀=2 mmol/L、[LVX]₀=5 mg/L、unadjusted p H（6.87）,the reaction will degrade 68.94%after 60 min.Among the background components of water,Cl^-can promote the degradation of LVX in a short time;while HCO₃^-can promote the degradation of LVX in a low concentration and a short time,but with the increase of concentration,the degradation process is inhibited;NO₃^-、H₂PO₄^-and natural organic fulvic acid（FA）also have inhibitory effect on the degradation of LVX,the higher the concentration,the stronger the inhibitory effect.Exploring the free radicals in the system found that SO₄^-·and·OH are the main free radicals.According to the mechanism,it is speculated that the degradation path of LVX may be de-piperazinyl and de-quinolone,F atom and aromatic ring hydroxylation,demethylation alkylation and carboxylation reactions.（2）In the heat/Fe²⁺/PDS system,the effects of PDS concentration,Fe²⁺concentration,temperature,LVX concentration and initial p H on the degradation of LVX were investigated.The results show that the higher the temperature,the better the degradation effect,but the improvement of the degradation effect is not obvious above 60℃.The degradation effect was the best under the condition of unadjusted p H,and the worst under the condition of strong acid and strong alkali.The optimum reaction conditions:[Fe²⁺]₀=0.2 mmol/L、[PDS]₀=2 mmol/L、[LVX]₀=5 mg/L、unadjusted p H（6.87）、T=60℃,the degradation efficiency of LVX was 93.25%when the reaction reached 30 min.Through activation energy analysis,it was found that the second-order reaction rates at different temperatures were in good agreement with the Arrhenius equation,and calculated to obtain Ea=48.52 k J/mol.（3）In the EC/Fe²⁺/PDS system,the effects of electrolyte concentration,current intensity,Fe²⁺concentration,PDS concentration,initial p H,LVX initial concentration and electrode spacing on the degradation of LVX were investigated.The results show that the increase of electrolyte concentration,current intensity,Fe²⁺concentration,PDS concentration and LVX initial concentration within a certain range can promote the degradation of pollutants,the degradation of pollutants is better with the decrease of the electrode spacing,and the best under the condition of unadjusted p H.The optimum reaction conditions:[Na₂SO₄]₀=0.2 mol/L、EC=0.7 A、[Fe²⁺]₀=0.1 mmol/L、[PDS]₀=2 mmol/L、[LVX]₀=5 mg/L、h=2.5 cm、unadjusted p H（5.73）,the degradation efficiency of LVX was 92.43%when the reaction reached 30 min.The kinetic fitting results show that the variation process of LVX concentration with time in EC/Fe²⁺/PDS system is more in line with the second-order reaction kinetic model（R²>0.98）,the rate constant is 0.0760 mg^-1.L.min^-1,and the kinetic equation is y=0.0760x+0.0382.