Treatment Of Polycyclic Aromatic Hydrocarbons In Wastewater By Ferroferric Oxide Supported Nano Zero Valent Iron Fenton-like Method

Polycyclic aromatic hydrocarbons（PAHs）have attracted extensive attention from scholars all over the world due to their wide distribution and high toxicity.In this paper,several common PAHs（naphthalene（Nap）,phenanthrene（Phe）and pyrene（Pyr））were selected as target pollutants,and self-made Fe₃O₄-nZVI composites were used as catalysts to study the treatment effect of Fenton-like technology on PAHs simulated wastewater.The effect of different factors（H₂O₂ concentration,initial PAHs concentration,Fe₃O₄-nZVI dosage,p H and temperature）on the degradation of typical PAHs in Fe₃O₄-nZVI Fenton-like system were investigated,and the degradation products of PAHs were analyzed by Gas chromatography-Mass spectrometry（GC-MS）.The possible degradation mechanisms and pathways of PAHs in Fe₃O₄-nZVI Fenton-like system were explored.This study provided a reference and basis for the treatment of PAHs and other polluted wastewater.Fe₃O₄-nZVI materials were prepared by co-precipitation and liquid-phase reduction method,and characterized by Scanning electron microscope-X ray energy spectrum analyzer,X-ray diffraction analyzer,Photoelectron spectrometer and Vibration sample magnetometer.The characterization results showed that the obtained nanomaterial Fe₃O₄-nZVI was spherical and aggregated into chains with a particle size of 50-200 nm.The material contained 64.27%Fe,16.53%O,11.47%C,7.45%B and 0.29%S.The nZVI in Fe₃O₄-nZVI existed in an amorphous state.The material had high crystallinity.The saturation magnetization value was105.52 emu/g,indicating that the obtained Fe₃O₄-nZVI composite material had the possibility of magnetic recycling and reuse.Single factor experiments showed that five factors,which are H₂O₂ concentration,initial PAHs concentration,Fe₃O₄-nZVI dosage,p H and temperature,had significant effects on the degradation of PAHs by Fe₃O₄-nZVI Fenton-like method.With the increase of H₂O₂concentration,the degradation rate of Nap increased continuously,while the degradation of Phe and Pyr first increased with the increase of H₂O₂ concentration,and then showed a significant downward trend.The degradation rate of PAHs decreased with the increase of its initial concentration,and first increased and then decreased with the increase of Fe₃O₄-nZVI dosage,p H and temperature.Under the optimum reaction conditions（the H₂O₂ concentration for Nap,Phe and Pyr was 15,10,10 mmol/L,respectively,the initial concentration of PAHs was 20mg/L,the dosage of Fe₃O₄-nZVI was 0.6 g/L,and the p H was 3,25℃）,the degradation rates of the three PAHs could reach 96.79%,98.64%and 98.10%,respectively.After four repeated experiments,the degradation effects of the three PAHs remained above 85%.The quenching reaction proved that·OH was the dominant free radical in Fe₃O₄-nZVI Fenton-like system,which could significantly promote the degradation of organic pollutants.In the Fe₃O₄-nZVI Fenton-like system,various intermediate products were detected during the degradation process of Nap,Phe and Pyr.According to the products formed by the system,it was speculated that the degradation pathway of Nap might have two stages.The first stage was the hydrogen substitution reaction on the benzene ring.The second stage was the oxidation,chain scission reaction and complete mineralization of the quinone group on the side ring.As for Phe,there might be four degradation pathways.The first was the hydrogen substitution reaction of·OH at the 9 and 10 sites.The second was that the·OH radical might attack the 4position in addition to the 9 and 10 sites.The third was that the 2 and 3 positions of phenanthrene were oxidized to generate quinones.The fourth was that the phenanthrene was isomerized to generate anthracene in the system,and then hydrogen substitution reaction occured at the 9 and 10 positions of anthracene.Based on the above results,it could be confirmed that Fe₃O₄-nZVI Fenton-like method had obvious degradation effect on PAHs.The research results would provide reference and basis for the treatment of wastewater polluted by PAHs,or other persistent organic pollutants（POPs）.