Study On Natural Attenuation Of Diesel In The Underground Environment

Study on Natural Attenuation of Diesel in the Underground EnvironmentPetroleum provides impetus for economic development and is closely related to people's life. Petroleum often leak or discharge when it is in the extraction, transportation and refining process, which causes serious environment contamination. Diesel is more widely used in the petroleum products. Now, there are various problems that soil and groundwater are contaminated by diesel, which poses a direct threat to the production and living of people. Natural attenuation can remediate petroleum-contaminated water and soil by physicochemical and biological condition of petroleum-contaminated site and natural attenuation ability of petroleum hydrocarbons. Determine the concentration reduction, toxicity and migration of petroleum hydrocarbons by monitoring the plume of groundwater. It is significant to the controlling and remediation of petroleum-contaminated groundwater and soil through studying the natural attenuation mechanism and its feasibility of application in the petroleum-contaminated underground environment.This thesis summarized the domestic and international study of natural attenuation based on the hydrogeology and groundwater dynamics theories. A series simulate experiments were conducted by using the hydrogeology research methods and interdisciplinary knowledge according to site-specific hydrogeological conditions. We studied natural attenuation mechanism in different media of vadose zone, analyzed the affection of depth, lithology of the media and moisture content to the natural attenuation, and discussed the migration and transformation of diesel contaminants and natural attenuation in the aquifer.In the experiments on natural attenuation mechanism of diesel in vadose zone, the results showed that:(1) Adsorption exited both in fine sand and clay. Adsorption equilibrium time of diesel sewage by fine sand and clay were 24h. Through the adsorption isotherm equation of Langmuir, we calculated theoretic adsorption quantity of diesel sewage respectively was 234 mg·kg-1 and 430 mg·kg-1.(2) In the beginning of the experiment, adsorption and other mechanical roles mainly affected the migration of organic pollutants. (3) In the process of natural attenuation of diesel, volatilization had the main effect on the removing of TPH. In the diesel polluted sand, the first-order attenuation kinetics equations of volatilization were respectivelyρ(TPH)=25.48e-0.0221x andρ(TPH)= 25.48e-0.0109x.(4) When the adsorption reached saturation, biodegradation increased gradually and the removal of organic pollutants was obvious at the end of experiment. In the diesel polluted sand, the first-order attenuation kinetics equations of biodegradation were respectively p (TPH)=25.48e-0.0027x andρ(TPH)=25.48e-0.0051x.(5) The natural attenuation efficiency of diesel pollutants in the clay was higher than in the fine sand. The soil particles were finer, the ability of blocking was stronger.In the influencing factor experiments on natural attenuation of diesel in vadose zone, the results showed that:(1) Depth and moisture content of medium were important factors in affecting the efficiency of diesel degradation. In the same medium conditions, the moisture content of the medium was greater, the biological activity was stronger and the efficiency of biological degradation was higher.(2) The particles of medium were finer, the adsorption of pollutants on the surface was better, the growth of biological activity was faster and its degradation ability of diesel was higher. The natural attenuation ability of diesel in the vadose zone were:fine sand>medium sand>coarse sand.(3) Volatilization and biodegradation were important factors in affecting natural attenuation of diesel in vadose zone. Volatilization decreased as the depth of vadose zone, and biodegradation enhanced as the time.In experiments on natural attenuation of diesel in aquifer, the results showed that:(1) During the experiment, plume was formed as the center of diesel leaking port in the aquifer, and it migrated with the groundwater flowing. It expanded constantly until ninetieth day, when the plume area of each pollutant was the largest, and the plume was stable.(2) The migration ability of BTEX and naphthalene was different in the aquifer. Naphthalene migrated the fastest, and the pollution area was largest. Benzene migrated the slowest, and the pollution area was the smallest. (3) In the 60 days which the pollution source was cut off. TPH, BTEX and naphthalene showed a downward trend with time. At the end of the experiment, natural attenuation efficiency of each pollutant was more than seventy percent, which showed natural attenuation was an effective repair method to the diesel-contaminated groundwater.