| Polycyclic Aromatic Hydrocarbons (PAHs) are a class of persistent organic pollutants in the environment. Most PAHs have carcinogenic, teratogenic and mutagenic effects, can through different media ecological cycle accumulate in environment and in organisms, there are a huge potential or direct harm. Phenanthrene (PHE) is a typical tricyclic PAHs, has negative B area and positive K area, which maybe the cause of carcinogenic of PAHs. As its low molecular weight and simple structure, it has become the typical substance for the environmental scientist to study PAHs.So far, the main processes of phenanthrene degradation were physical process, chemical process, and biological process, et cetera. Physical treatment of PHE is only transferred in different environment media, can not be fundamentally eliminated PHE from the environment. Biological treatment is a better way to degradate PHE because of its low costs, high efficiency, no secondary pollutant. But, biological treatment often takes a long time and there are regional differences, apply scope are very restrictive. Chemical treatment, especially advanced oxidation treatment, has a high efficient and a short treatment time, has no big environmental requirements. But the cost is very high. In view of this, the thesis put forward to use the light source and add some auxiliary substances to photochemical degradation of PHE, in order to reduce processing costs and achieve better treatment effect.The thesis studied the photochemical degradation treatment method of PHE. Firstly, the PHE photochemical degradation pathway in the water environment has been studied by different oxygen atmospheres (aerobic-anaerobic), which can prove the photodegradation is directly or indirectly. Next, through literature review to choose the initial PHE concentration, pH, HA concentration, Cl-concentration, NO3-concentration, H2O2 concentration, six influencing factors to study the process of photodegradation on PHE. Finally, based on the results of single factor experiment to have a furthermore study about the interaction between selected factors. Concluded as follow:As different light sources and different oxygenated conditions were considered in the photodegradation experiment, the results showed that under the aerobic conditions, ultraviolet light source irradiation,180 min, the removal rate of PHE is the best. So choose these conditions as the basic conditions for subsequent experiments.It has been founded in the photodegradation pathway experiments of PHE that under aerobic conditions the photo-oxidation process is the main cause of the degradate of PHE. Direct photodegradation and sensitized photodegradation also took part in the photodegradation process. While in anaerobic environment, the photodegradation process of PHE is mainly through direct photodegradation. There are active oxygen species 1O2, · OH took part in the entire photogegradation process.In the single factor experiments, the results showed that degradate rate of PHE can be inhibited with the increase of initial concentration of PHE. It has a little effect on the degradate rate of PHE with the increase of pH values, the removal rate become relatively smooth fluctuations. It can be promote the photodegradation of PHE with the increase of nitrate ions concentration and chloride ions concentration. Increasing HA concentration, phenanthrene photodegradation efficiency has also been reduced, HA play an inhibitory effect. With increasing concentrations of H2O2, PHE photodegradation efficiency became increases but then decreases.In central composite experimental design four factors and five levels experiment, the interaction effects of different factors (PHE initial concentration, HA concentration, H2O2 concentration, Cl- concentration) on PHE have been studied. The results show that the four factors are significant factors of photodegradation process of PHE, and the affecting order is HA concentration> PHE initial concentration> H2O2 concentration> Cl- concentration. After multivariate experiment optimization results in initial PHE concentration 2.8μM, HA Omg/L, H2O2 concentration 0.05mM, Cl- concentration 0.5M, the photodegradation efficiency up to 52.75%. |
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