Efficiency And Mechanism Of Ferrate/Peroxymonosulfate System In Degrading Ibuprofen In Water

Pharmaceuticals and personal care products（PPCPs）include antibiotics,pesticides,anti-inflammatory agents,fungicides,cosmetics,etc.Because they are continuously discharged into the natural environment,various harmful ingredients are frequently detected in the natural environment.The general structure of these refractory pollutants is stable,not easily degraded,has specific environmental toxicity,and poses a potential threat to the ecological environment and human health.It has attracted widespread attention in recent years.Ibuprofen（IBP）is a common non-steroidal anti-inflammatory drug with frequent daily use and significant emissions.Through gradual accumulation,it will cause irreversible damage to animals and plants.IBP is a kind of PPCPs that are frequently detected in the environment,and it is difficult to completely remove them by conventional treatment methods in sewage treatment plants.Therefore,it is urgent to develop an efficient and green water treatment technology to degrade PPCPs.In this paper,ferrate（Fe（Ⅵ））and peroxymonosulfate（PMS）systems are used to degrade IBP in water.The influencing factors,mainly including the initial p H of the IBP solution,the dosage of PMS,the dosage of Fe（VI）,the initial dosage of IBP and the natural organic matter on the degradation of IBP in Fe（Ⅵ）/PMS systems are investigated.The active species of Fe（Ⅵ）/PMS system were identified,and the degradation mechanism and path of IBP were analyzed.Meanwhile,the application of Fe（Ⅵ）/PMS system in actual water bodies and the degradation of other pollutants are also studied.Through comparative experiments,it is found that the removal rate of IBP by Fe（VI）or PMS oxidation system alone is 19.8%and 22.1%,respectively.In comparison,the removal rate of IBP by Fe（VI）/PMS system is 92.8%,increasing by about 70%.According to the experimental data,a kinetic model was established to obtain the reaction rate constants of Fe（VI）,PMS,and Fe（VI）/PMS systems.The different initial p H values of the solution will affect the types of active species in the Fe（VI）/PMS system,thereby affecting the final removal rate and degradation rate of IBP.In the p H range（5-9）,the removal rate of IBP is higher than 85%,but under the conditions of p H=3 and p H=11,the removal rate of IBP is only 68.85%and 48.5%.The increase in the dose of PMS 0.3 m M-0.7 m M increases the amount of activated hydrogen persulfate（HSO₅^-）,which can generate more free radicals,and the removal rate and degradation rate of IBP will increase accordingly.Increasing the dosage of Fe（VI）（0.15 m M-0.35 m M）can activate PMS to generate more free radicals.It can also create more high-active intermediate iron,promoting IBP degradation,and both the IBP removal rate and reaction rate increase.The dosage of Fe（VI）/PMS is unchanged,changing the initial concentration of pollutant IBP from 5μM to 50μM,the removal rate dropped from 94.8%to 70.75%of the reaction rate also decreased.The increase of PMS and Fe（VI）dosage can increase the mineralization degree of IBP.Still,the highest TOC removal rate is 53.95%,which shows that the formation of intermediate products affects the complete mineralization of IBP.The presence of natural organic matter（NOM）inhibits the degradation of IBP by the Fe（VI）/PMS system.When the NOM concentration is 1-50 mg/L,the removal rate of IBP drops from 85.35%to 40.3%.After testing the degradation reaction of the system,the iron content in the solution reached the standard required for drinking water.In this article,the degradation mechanism of IBP by Fe（VI）/PMS system was studied.Through chemical quenching experiments and electron spin resonance spectroscopy（EPR）identification,SO₄^·-and HO^·were produced in the Fe（VI）/PMS system.The specific compound generated by the probe compound methyl phenyl sulfoxide reaction and the intermediate valence iron proves that there is also the medium valence iron Fe（IV）.Nine intermediate products of IBP degradation were detected by gas chromatography-mass spectrometry（GC-MS）.After analysis,the degradation path of IBP in the Fe（VI）/PMS system was proposed.The degradation process mainly includes hydroxylation,demethylation,decarboxylation,single bond cleavage,intramolecular polymerization,and dehydration.To explore the efficiency of Fe（VI）/PMS system remove other pollutants,Fe（VI）/PMS was used to treat atrazine（ATZ）and naproxen（NAP）,and the removal rate was above 95%.Fe（VI）/PMS was used to degrade the IBP under the background of tap water and Songhua River.It was found that the inorganic ions and natural organic matter in the water have an inhibitory effect on the removal of IBP.By increasing the oxidant dosage,a removal rate of IBP more than90%.A prediction model of the IBP removal rate and the required oxidant dosage in the water treatment has also been established.The dosage of oxidant needed can be predicted according to the p H of raw water and IBP removal requirements to achieve high efficiency and cost-saving.This study clarified the efficiency of Fe（VI）/PMS system to degrade IBP and defined the influence of a single factor on IBP removal.The mechanism of action of free radicals and intermediate valence iron in the process of IBP is clarified.By degrading other types of pollutants and using the actual water environment as the background to degrade IBP,the IBP degradation model is established to provide an experimental reference basis and theoretical support for applying the Fe（VI）/PMS system in the actual water environment.