Enhance Degradation Of Polycyclic Aromatic Hydrocarbons With Persulfate Activation By Nano Zerovalent Iron

Polycyclic aromatic hydrocarbons（PAHs）are a type of persistent organic pollutants commonly found in the environment.They are highly toxic,persistent,bioaccumulative,and long-distance migration.In recent years,with the rapid development of human society,the content of PAHs discharged into the natural world has increased year by year,and eventually deposited in soil and groundwater through atmospheric deposition and rainfall.In order to remove polycyclic aromatic hydrocarbons in soil quickly and efficiently,in-situ chemical oxidation technology has been developed.Activated persulfate technology is widely used because of its high safety,ease of transportation and storage,and high degradation efficiency.Fe²⁺is the most commonly used activator because of its high content,cheap and non-toxic properties.However,excess Fe²⁺reacts with sulfate radicals to cause unproductive consumption,reduce degradation efficiency and increase costs.Therefore,This article uses nano zerovalent iron as a slow release activator to solve this problem.In this paper,modified nano zerovalent iron（nZVI）was prepared using PEG-4000 as a dispersant,it is then used to activate persulfate to degrade PAHs.During the reaction process,the concentration ratio of the two was optimized,and the effects of different initial pH on the degradation of phenanthrene were explored,and the morphology and composition of the n ZVI before and after the degradation reaction were explored,and the degradation mechanism was further explored.The results showed that the diameter of nZVI particles modified with PEG-4000（as a dispersant）was evenly distributed between 50-100 nm,and had a typical shell-core structure.The modified nZVI also had a certain degradation effect of polycyclic aromatic hydrocarbons.The degradation of phenanthrene is the best under the neutral condition and the concentration of nZVI and oxidant persulfate is 1:1.And after 24 hours,the maximum degradation rate of phenanthrene is 58%.Cockroaches also have significant degradation effects with degradation rates of 52.9%and 51%,respectively.It was found that this degradation system can exert its degradation effect over a wide range of initial pH values.When the initial pH value was 3,the highest degradation rate of phenanthrene reached 73%.The study of the morphology a nd composition of n ZVI before and after the degradation reaction found that during the process of pollutant degradation,n ZVI was consumed,the content of Fe⁰ decreased,and the surface was partially passivated.In the nZVI-PS system,the results of electron paramagnetic resonance and radical quenching experiments consistently demonstrated that both sulphate radicals and hydroxyl radicals exist simultaneously in the degradation process of phenanthrene,and they act together to oxidize.Based on the above research,it can be determined that n ZVI activated persulfate technology has a significant effect on the degradation of polycyclic aromatic hydrocarbons.This study will provide effective reference techniques for the application of polluted water bodies and soil remediation.