Investigation Of Ferrate-catalyzed Ozone Oxidation On Fluoroquinolone Antibiotics

Fluoroquinolones（FQ）antibiotics are widely used and frequently detected in municipal wastewater and surface waters.The conventional sewage treatment technology only alter their existing status,rather than completely degrade them.A variety of advanced oxidation technologies represented by catalytic ozonation have become effective means to deal with the recalcitrant pollutants.We propose a multi-stage oxidation technology of potassium ferrate/ozone.It combines the oxidation ability of potassium ferrate and ozone;and makes full use of the synergistic effect of potassium ferrate’s flocculation and ozone’s catalysis;and indicates promising potential in the treatment of aqueous fluoroquinolone antibiotics.In this experiment,the secondary effluent from a sewage treatment plant of pharmaceutical factory and synthetic simulated water containing ciprofloxacin were used as research samples.The catalytic effect of potassium ferrate reduction product on ozone was verified.Based on this,a multistage oxidation system of potassium ferrate combined with ozone was established.The degradation effect and mechanism of multi-stage oxidation on fluoroquinolone antibiotics were investigated.The effect of potassium ferrate reduction products on ozone decomposition was studied by detecting the change of ozone concentration in water.After separating the residual potassium ferrate reduction products in the solution,the indexes including dissolved organic carbon（DOC）,ultraviolet absorption(UV₂₅₄),and fluorescent organicswere analyzed to present the role of potassium ferrate reduction products in the stage of ozone treatment.The catalytic effect of potassium ferrate on ozone was compared and verified.The effects of potassium ferrate dosage,ozone concentration,and pH on the multistage oxidation system on ciprofloxacin were investigated.By adding HCO₃^-and PO₄^3-as representitive anions,the impact on treatment was explored,as well as the effect of common coagulants(Fe²⁺,Fe³⁺)on multistage oxidation system.Based on the results of the influencing factors,the optimal conditions were selected to investigate the composition of ciprofloxacin after being treated by potassium ferrate alone,ozone alone,and combined treatment,to infer the potential degradation pathway of ciprofloxacin by the multi-stage oxidation system.The major results of the relevant studies are as follows.（1）The potassium ferrate reduction products accelerated the decomposition of ozone in water.Based on the experiment with potassium ferrate alone,the potassium ferrate reduction product increased the removal of DOC by 14.9%and UV₂₅₄ by 29.03%during the subsequent ozone treatment process.Potassium ferrate effectively catalyzed ozone and improved the ability of ozone to oxidize refractory organic matters.（2）With the increasing dosage of potassium ferrate（10,30,60,90 mg/L）,the catalytic ozonation effect of potassium ferrate reduction products was enhanced.The increasing concentration of ozone gas strengthened the treatment effect of the multistage oxidation system to a certain extent.Under the condition of initial pH=3,the optimal mineralization rate（37.98%）was obtained by potassium ferrate treatment alone;The effect of ozone treatment alone was improved with the increase of pH;The combined treatment effect of potassium ferrate and ozone was significantly better than other two treatment methods,and the maximum mineralization rate was 50.29%under the condition of initial pH=5.The treatment effect of potassium ferrate,after fullly reduced,combined with ozone was better than that of synchronic potassium ferrate and ozone treatment.（3）HCO₃^-had a slight inhibitory effect on the oxidation of potassium ferrate and the multi-stage oxidation system;PO₄^3-significantly inhibited the oxidation of potassium ferrate and the multi-stage oxidation system;Fe²⁺and Fe³⁺significantly intensified the effect of potassium ferrate treatment alone and slightly the effect of the multi-stage oxidation system.（4）A total of 12 intermediate products of the ciprofloxacin degradation process were detected by a Fourier transform ion cyclotron resonance mass spectrometry.The molecular structures of these 12 products were deduced,and the pathways of multi-stage oxidative degradation of ciprofloxacin were inferred as defluorination,hydroxyl addition,hydration,decarboxylation,and ring-opening reaction.