The Study Of Migration And Transformation Of PAHs (Phenanthrene) In Vadose Zone

PAHs is a strong inert hydrocarbons, widely exist in the atmosphere, water and soil. In recent years a large number of studies show that the air,soil, water and the organisms have been polluted by PAHs. Biological experiments of toxicity indicate that PAHs is hard to degradation, which has a certain residual in the environ ment. and PAHs have Bioaccumula~ tion and "carcinogenic, teratogenic, mutagenic", which posed a potential threat to the human health and ecological environment.Wastewater irrigation as a measure of saving water resource plays a indispensable part in our economic development. The history of Zhangshi wastewater irrigation region in Shenyang city traces back to more than fifty years ago. As long as the agricultural use of sewage water for irrigation has led to area pollution of the surface soil and water. Natural environmental pollution is getting worse. The soil, surface water and groundwater pollution survey in Zhangshi wastewater irrigation region found that PAHs pollution is very serious. PAHs pollutions of surface water and soil is particularly conspicuous on the region's social and ecological sustainable development. Local area has been very serious, which directly threat to the local agricultural production and farmers living environment.Soil vadose zone is a multiphase environment, and it's not only the basis of all organisms, but also one of the sink to the environmental pollutants. The majority of PAHs in environment residue in the soil. PAHs in the environment largely depends on the behavior of polycyclic aromatic hydrocarbons in soil migration and conversion behavior. The soil adsorption and degradation not only reduced the activity and volatile mobile of PAHs, but in the air and groundwater residues of PAHs is also a certain influence. The soil organic matter and the microbial are the most important factors affect the impact of PAHS pollutants in the soil relocation and transformation.In this paper, using the phenanthrene as a target pollutants, taking static experiment and indoor column dynamic simulation experiment method, research the static adsorption, the adsorption and desorption dynamics behavior of the phenanthrene in soil. Static experiment analyze the phenanthrene soil adsorption and desorption behavior quantitatively and its adsorption and desorption curves was confirmed. Through research the adsorption behavior of phenanthrene in soil, scientific analysis of PAHs affect adsorption and desorption behavior, determine the impact factors of PAHs adsorption and desorption behavior. Through Soil column dynamic simulation of PAHs in the soil vadose Zone migration, adsorption and microbial degradation, discuss the main movement to transform of PAHs in the soil vadose zone. In the indoor soil column experiment, The vadose zone soil is loaded in diameter 9cm plexiglass column according the sequence of the level in soil, simulating the process of PAHs pollution into the soil vadose zone in a natural state under two different flow patterns. Through discussions of the adsorption, the proliferation and microbial degradation in the Vadose Zone, study the migration and transformation rule of PAHs, and the possibility of groundwater pollution. Conclusion of the study are as follows:Soil organic matter content of the vadose zone is the main factors which control soil layers'adsorption capacity of PAHs. Phenanthrene adsorption isotherm is linear in the low concentration range, and is within a degree of non-linear in high concentrations. Soil particle size in the vadose zone influence the adsorption and desorption of PAHs. The adsorption of phenanthrene in the soil layers can be fitted Linear equation and Freundlich equation. The adsorption kinetics of phenanthrene in soil can be fitted Lagergren two level adsorption rate equation.Static adsorption kinetics results showed that the majority process of adsorption and desorption of phenanthrene are rapid stage, rapid adsorption stage in 8h reached equilibrium, the desorption process to achieve balance within 2h. the amount of phenanthrene released in Desorption process is small, and the majority of residue is in the soil. The adsorption and desorption process is not reversible process, the physical adsorption can be desorption.We researched the migration and transformation of phenanthrene in vadose zone by the indoor column dynamic simulation experiment. Longitudinal dispersion coefficient(D),adsorption coefficient (Kd) and retardation factor were abtained through curve fitting and parameter estimation. The results indicate that the migration and transformation of phenanthrene in vadose zone were due to dispersion, adsorption and biodegradation. The adsorption is reperesented by Linear Law, which adsorption coefficient (Kd) was 0.134 L/g和0.201 L/g differently in continuous water supply way and intermittent water supply way. Adsorption kinetics of continuous water supply colume can be used Lagergren two level adsorption rate equation, the adsorption capacity in vadose zone is 476.19μg/g when phenanthrene adsorption of soil reach adsorption balance. Longitudinal dispersion coefficient(D) is 0.00498m2/d in the experiment. Then calculate chemistry mobility in different water supply ways. In the end, draw a conclusion that the time which phenanthrene penetrate the vadose zone vertically into groundwater is 38.4a and 58.7a. the results of dynamic soil column experiments match successfully with study area conditions.