Degradation Of Norfloxacin In Water Using Persulfate Activated By Reduced Biochar-supported Nano Zero Valent Iron/nickel

Norfloxacin?NOR?is the third generation of quinolones,which has the characteristics of broad spectrum,high efficiency and low toxicity,and is widely used in medical and aquaculture industries.However,only a small number of antibiotics can be absorbed by organisms,most of them are excreted in the form of raw drugs from feces or urine and enter the environment.In recent years,more and more researchers have detected the residual norfloxacin in water.Although the concentration of norfloxacin in the environment is low,the residual norfloxacin in the environment may pose a great threat to the environment.Therefore,it is particularly important to find an efficient method for the treatment of norfloxacin.Sulfate radical?SO₄^-·?has the advantages of strong oxidation ability,fast reaction speed and multiple activation modes.Porous material supported zero-valent iron has high stability and good dispersion.It can be used to activate persulfate to effectively degrade norfloxacin in the environment.In this study,biochar-supported nano-zero-valent iron-nickel?BC@nZVI/Ni?was synthesized by liquid-phase method and characterized.The degradation kinetics and reaction mechanism of BC@nZVI/Ni activated persulfate?PS?system for norfloxacin wastewater degradation were discussed.The effects of initial concentration of antibiotics,PS dosage,BC@nZVI/Ni dosage,initial pH value,temperature,humic acid?HA?,inorganic anions on the degradation of norfloxacin?NOR?were investigated.The intermediate products of NOR degradation were determined and the possibility was speculated.The main degradation pathway.The main conclusions are as follows:?1?BC@nZVI/Ni was characterized by scanning electron microscopy?SEM?,X-ray diffraction?XRD?and X-ray photoelectron spectroscopy?XPS?.SEM characterization showed that nZVI/Ni did not agglomerate and dispersed on the biochar.XRD spectra confirmed the existence of zero-valent iron,and part nano-zero-valent iron oxidized into other valent iron ions.XPS spectra showed the existence of iron,nickel and hydroxyl and carboxyl groups in BC@nZVI/Ni and biochar,of which Fe0 accounted for about 10.9%of the total iron content.?2?Under the same dosage,BC@nZVI/Ni/PS system had better degradation effect on NOR than PS,BC,BC@nZVI/Ni,BC/PS,BC@nZVI/Ni/PS system.When the BC@nZVI/Ni dosage was 0.2g/L,the PS concentrate was 0.4mM,90%NOR was completely eliminated within 20min at 303K,indicating that BC@nZVI/Ni could successfully activate PS to degrade NOR.The reaction kinetics of NOR in different systems showed that the degradation of NOR accorded with the Quasi-First-Order kinetic model in the first 20 minutes,and the reaction rate of BC@nZVI/Ni/PS system was the fastest.?3?The effects of different factors?different ratio of iron to carbon,initial concentration of NOR,concentration of PS,dosage of BC@nZVI/Ni,pH,temperature and HA?on the degradation of NOR were discussed.In the experiment of different iron-carbon ratio,the lower iron-carbon ratio will cause the agglomeration of nano zero-valent iron/nickel,and the higher will affect its active site.when the mass ratio of carbon to iron is 5:1,the biochar loaded with nano zero-valent iron/nickel has the best effect.In the initial concentration of NOR?5-20mg/L?experiment,the removal rate of NOR decreased gradually with the increase of NOR concentration.Under different PS concentration?0-1mM?and BC@nZVI/Ni dosage?0-0.4g/L?,NOR removal increased at first and then decreased,and 0.6mM PS and 0.2g/L BC@nZVI/Ni were the best dosage.In addition,pH and temperature also have great influence on the degradation,alkalinity will inhibit the degradation of NOR,the addition of biochar improves the degradation range of NOR;with the increase of temperature,the high temperature pyrolysis of PS greatly increases the degradation rate of NOR;the existence of HA and SO₄^2-,NO₃^-will inhibit the degradation of NOR,the presence of Cl^-and HCO₃^-will slightly promote the degradation of NOR.?4?The main free radicals involved in the reaction were analyzed by electron paramagnetic resonance?EPR?and free radical quenching experiments.it was proved that under acidic and neutral conditions,sulfate radical was the main free radical,and under weak alkaline conditions,some sulfate radicals react with hydroxyl ions in the solution to form hydroxyl radicals,which play a major role in alkaline conditions.By studying the concentration change of Fe???and Fe???in solution,the mechanism of PS activation in the presence of BC@nZVI/Ni composites was proposed.?5?It is speculated by Ultraflex MALDI-TOF/TOF spectrometry that norfloxacin can be degraded by defluorination decarboxylation and piperazine ring opening under the action of sulfate radical and hydroxyl radical.