Research On Degradation Of Naproxen In Aqueous Solution By Persulfate Activated With Zero Valent Iron

In recent years,pharmaceuticals and personal care products(PPCPs),as a new type of organic pollutants,have been frequently detected in sewage treatnent plant influents and effluents as well as various natural aqueous environment,and have obtained growing interest.Naproxen(NAP)is a kind of non-steroidal anti-inflammatory drugs,and it is also one of the most frequently detected PPCPs in the aquatic environment.Naproxen is difficult to be degraded by microorganisms in the natural environment,while it is easy to accumulate in living organisms through the food chain,which brings non-negligible harm to the ecological environment and human health.However,the conventional water treatment technologies are not ideal.Therefore,it is of great significance to seek a fast,green and efficient water treatment technology for the degradation of PPCPs such as NAP.Advanced oxidation technology(AOPs)has been proved to be an effective method for degradation of refractory organic pollutants due to its strong oxidation ability,fast reaction speed,low selectivity and high degradation efficiency.In this paper,the advanced oxidation technology of zero valent iron(ZVI)activated with persulfate(PS)was selected to degrade NAP in aqueous solution.A series of studies were carried out about the influence of key parameters and water background components on NAP degradation efficiency.The contribution of various reactive oxygen species on NAP degradation was explored through the kinetic model.This paper also investigates the oxidation products and reaction mechanism of NAP in ZVI/PS system.This study provides theoretical basis and comprehensive evaluation for the application of ZVI/PS advanced oxidation technology in the degradation of organic pollutants such as NAP.Comparative experimental results showed that the ZVI/PS system can effectively degrade NAP,and the NAP removal rate was 93.5%,which was 33.4%higher than the Fe2+/PS system,besides,the degradation of NAP in the ZVI/PS system was fitted with pseudo-first-order kinetic model.The experimental results of influencing factors showed that the solution pH has a significant effect on the degradation efficiency of NAP,and the apparent reaction rate constant(kobs)decreased with the increase of the initial solution pH(3.0?11.0).Increasing the PS concentration(100?500 ?M)could increased NAP degradation efficiency.The value of kobs increased with the increase of ZVI dosage(0.25?1.50 ?M).The concentration of target pollutant NAP(5?25 ?M)increased,which leads to the decrease of NAP degradation rate in ZVI/PS system.Moreover,the background composition of water also affects the degradation of NAP.The existence of HCO3-,NO3-and NOM had negative influence on NAP removal,while Cl-exhibited a slightly positive impact on the NAP transformation.The addition of ammonia can significantly improve the removal of NAP by ZVI/PS system under neutral and alkaline conditions.Compared to its counterpart without ammonia,the degradation rates of NAP by ZVI/PS were increased from 23.1%(pH 7)and 18.1%(pH 9)to 100%and 36.6%,respectively.The application range of effective pH of the system was broadened,and the ability of ZVI/PS system to resist the impact of background components was strengthened by ammona.Finally,the mechanism of degradation of NAP by ZVI/PS system was studied.Radical scavenging experiments and the electron spin resonance(ESR)study proved that both sulfate radical(SO4·-)and hydroxyl radical(HO·)participate in the NAP degradation.The second order rate constants for NAP reacting with SO4·-and HO· at pH 5 were(5.64±0.73)×109 M-1 s-1 and(9.05±0.51)×109 M-1 s-1,respectively.In addition,based on the detected nine intermediates via UPLC-QTOF-MS/MS,the pathways of NAP degradation in ZVI/PS system was proposed,and the degradation process mainly includes hydroxylation,demethoxylation,carbon-carbon double bond oxidative cleavage,decarboxylation,intramolecular polymerization dehydration,and single bond cleavage.