Study On Environmental Chemical Behavior And Influence Factors Of BTEX In Soil

Benzene series (BTEX) are important soil contaminants, which can causethreat to human health by entering the food chain through plant uptake andaccumulation, or contaminate underground water through seepage，and then affecthuman health directly or indirectly through irrigation or drinking. Therefore, it is ofgreat significance for us to systematic assess the soil capacity of pollutants and choosereasonable technology to control soil and groundwater contaminated by BTEX. Atpresent, the research of BTEX in soil has turned to dynamic experiment，whichstudied on multiple components, multiple variable factors instead of single targetpollutants or single factor. These researches are more realistic to environmentalconditions and thus become the major study trend. This paper mainly focused on thepetrochemical contaminated soil in arid areas of Xinjiang. Four kinds of benzeneseries (BTEX) including benzene, toluene, ethylbenzene and xylene were selected astarget pollutants, and the headspace GC-MS technology were used to analyze theconcentration of BETX in samples. Static adsorption experiments and adsorptionkinetics experiments were carried out to study the characteristics, mechanisms as wellas influence factors of BTEX sorption on soil. Column experiments were used tostudy vertical migration and distribution of BTEX in soil after leakage andcontaminated the top of soil. L9(34) orthogonal experiment was used to study theremoval ability of BTEX by plant. The major conclusions of this thesis were asfollows:(1) Gas chromatography-mass spectrometry with static headspace extraction（HS-GC/MS） was used to determine benzene series (BTEX) in soil.In order to getthe optimal analysis condition, several affecting parameters of HS were studied indetail, such as equilibrium temperature，equilibrium time and, addition amount ofmatrix modifying solution, recoveries and precisions were also studied. Resultsshowed that5.00mL of matrix modifying solution with equilibrium temperature at45℃and equilibrium time at10minutes were the best condition for headspaceprocedure. Under the optimized conditions, the correlation coefficients between BTEX concentrations and peak areas were in the range of0.996-0.999. The spikedrecoveries for benzene, toluene, ethylbenzene, and xylene were81.46%,86.70%,94.45%and99.9%, respectively. The relative standard deviation RSD （n=6） were6.62%,5.43%,4.51%and4.28%. Limit of detection and quantification of the methodwere0.127,0.0911,0.0764,0.204μg/kg and0.424,0.303,0.254,0.681μg/kg,respectively.(2) Sorption behaviors of benzene serial materials （BTEX） at lowconcentrations in arid soil were systematically investigated. Effects of soil organicmatter, pH and salinity of solution were analyzed. Results showed the adsorptionequilibrium was established within48h. The adsorption isotherms of BTEX on soilsignificantly fit to Henry linear adsorption model. Soil organic matter content is themain factor in the adsorption process. The pH value influence on adsorption processwas no regular. Soil adsorption capacity of BTEX decreased with the salinity solutionor temperature increasing.(3) One-dimensional soil column device was used to simulate verticalmigration and distribution of the target contaminants in the soil after the BTEXleakage on ground. Experimental results demonstrated average rate of migration were1.95,2.54,4.01cm/h when the leakage volume of10,30and50mL, respectively.The dynamics characteristics of BTEX migration fit well to the second orderexponential equations, and the maximum leakage distance was proportional to theleakage volume.(4) Different initial concentrations of BTEX solution leaching soil columnwas used to investigate the distribution of BTEX migration with differentconcentration in soil. The effects of the leaching method, pH value of leachingsolution and the salinity on BTEX migration were discussed by using the home-madeBTEX contaminated soil. Results showed that leaching solution concentration ofBTEX, benzene, toluene, ethylbenzene, xylene in different soil column increasedfirstly and then decreased. The largest residues of BTEX in soil indicated no obviouseffects of pH value on migration when the surficial soil was polluted, so was thesalinity. Dripirrigation was beneficial to reduce the residues of BTEX in soil. (5) Scindapsus aureus was selected as the research object and L9(34)orthogonal experiment was used to study removal of BTEX by plant. Temperature,treatment time, and biomass of Scindapsus aureus were used to evaluate the BTEXremoval efficiency. Results showed that Scindapsus aureus weight was the primaryfactor of the removal effect, temperature and exposure time take the second and thirdplaces respectively. BTEX removal ability of Scindapsus aureus increased with theincrease of the weight.