Study On Natural Attenuation Rate And Its Influencing Factors In Aeration Zone Of Benzene Series

Benzene series and alkanes,as representative substances in VOCs,are more volatile in soil and groundwater and reach the ground to cause vapor intrusion.Therefore,they have been the focus of environmental circles in recent years.The natural attenuation technology based on soil particles and microorganisms in the aeration zone has attracted much attention in the environmental industry because of its advantages of green and harmless,low cost and less environmental disturbance.This paper studies the reaction rate and removal rate of natural adsorption and biodegradation of benzene series and alkanes in several representative regions of China.Through headspace oxygen monitoring,soil physical and chemical properties characterization and microbial community analysis,the adsorption of VOCs by soil particles and the biodegradation of VOCs by indigenous microorganisms in a closed system were studied,and the natural attenuation potential of several soils was analyzed by comparing several soil conditions.In addition,this paper studies the effects on the natural attenuation rate and natural attenuation removal rate of pollutants by changing the ambient temperature,soil moisture content and soil particle size.The experimental results show that the aeration zone environment can adsorb and biodegrade benzene series and alkanes under aerobic conditions,and the reaction conforms to the pseudo first-order reaction.By monitoring the O2 concentration and the number of microorganisms before and after natural attenuation,the indigenous microorganisms in the aeration zone produce aerobic biodegradation of pollutants.Among the four representative soils in China(black soil,loess,laterite and sand),black soil has stronger adsorption capacity than other soils because of its acidic,large specific surface area and high content of organic matter.In addition,due to the existence of Bacillus,phenylbacillus,unclassified bacterium kd4-96,blastococcus and Streptomyces in black soil,it has a certain biodegradation ability.By comparing the natural attenuation and removal rates of VOCs in several soils,it is concluded that the natural attenuation capacity of several soils from high to low is: black soil > loess >laterite > sand.The maximum theoretical adsorption capacity of black soil,loess and laterite was obtained by fitting the adsorption isotherm model.When the ambient temperature rises(5-35 ℃),the natural attenuation ability of the aeration zone will be reduced,resulting in steam intrusion;Among the several moisture contents used in this paper,when the soil moisture content is 14%,the natural attenuation ability of soil reaches the strongest;With the decrease of soil particle size and the increase of porosity,the natural attenuation ability of aeration zone will be enhanced.