Study On Photodegradation Of Phenanthrene In Aeolian Sand

With industrial development, the deposition of polycyclic aromatic hydrocarbons(PAHs) increased every year, which brings a serious threat to the safety of soil. Photodegradation reaction has an important influence on the migration behavior of PAHs in soil. It can reduce not only the content of PAHs in soil surface, but also reduce the risk of groundwater pollution. In this study, aeolian sand in blow-sand region of Northern Shaanxi was chosen as typical soil and phenanthrene(Phe) as typical pollutant of PAHs. The effects of light source, aeolian sand, initial concentration of pollutants and other environmental conditions were investigated and the photocatalytic degradation mechanism of Phe in Aeolian sand was established. In addition, explored the product and proposed reaction pathways of Phe in aeolian sand.The results obtained were as follows:(1)Research to the impact of various factors on photodegradation indicated:(1) The type of light source would affect phenanthrene photodegradation. The Phe degradation effect was different due to different bands. Under the same conditions, the ability of Phe photodegradation of ultraviolet(UVA, UVB, UVC) was UVC> UVA> UVB.(2) The rate of phenanthrene degradation increases as the light radiation intensity increases.(3)Among three UV lighting systems, the law of the impact of initial concentration of pollutents on photodegradation was substantially the same, that is, the degradation rate increased as the concentration increased; when up to a certain concentration, the rate decreased as the concentration increased.(4) Photodegradation rate substantially increased with the increasing of p H value, which meant an alkaline environment was more suitable for Phe photodegradation in aeolian sand.(5) Phe degradation rate increased as the temperature increased.(6) The higher the moisture content of aeolian sand was, the higher the rate of phenanthrene photodegradation would be.(7) Appropriate amount of humid acid in aeolian sand could promote Phe photodegradation. However, if the concentration of humid acid was too high, it would suppress photodegradation.(2)The process of Phenanthrene photodegradation in aeolian sand met the first-order kinetics model. The photodegradation rate constant of Phe in UVA, UVB, UVC were 0.204?0.121?0.645d-1.(3)The analysis of photodegradation mechanism showed that ·O2- played a major role in Phe degradation of natural light in aeolian sand. During the process of photodegradation, unsaturated carbon-hydrogen bond on benzene ring was destroyed.(4)Pathways of Phenanthrene degradation in aeolian sand can be divided into three types:(1) Phe turned into an isomers—anthracene, which had higher chemical activity after receiving the light. It could not only conduct the addition reaction, but also could react with oxygen free radical and generate peroxides; then macromolecular compounds further transformed into small molecule organic compound.(2) Phe was oxidized directly by oxygen free radicals on its position 9,10 keys, and then transformed into small molecule organic compound.(3) The 9,10 keys of Phe firstly reacted with organic matter, then was oxidized by oxygen free radicals into carbonyl compounds, then further transformed into small molecule organic compound.This research further reveals the photodissociation process of PAHs in soil, especially the aeolian sand, which would deepen our comprehension on migration, conversion and ultimate destination of PAHs in unsaturated zone. Our study will also have a better scientific value and clinical significance to the degradation of organic pollutant by light energy or advanced light oxidation technology for future.