Volatilization Of BTEX In Underground Environment And The Influence To Air Sparging

With the development of modern civilization, the industrial process is also developing at an unprecedented rate. The petroleum industry as a support of contemporary industrial development is overwhelming. BTEX are common components of petroleum, and the petroleum industry may lead to serious pollution during a series of courses such as mining, transport, storage and processing. Due to their toxicity and the"carcinogenicity- mutagenicity-teratogenicity", BTEX can lead to a direct threaten to surrounding environment and people's health once the groundwater is polluted. Currently, petroleum contamination on soil and groundwater pollution exists prevalently in the world, how to control, treat and rehabilitation has caused attention all over the world.The processes of BTEX natural attenuation in the groundwater include dilution, convection, dispersion, physical adsorption, volatilization and a series of biogeochemical processes. BTEX are volatile organic compounds, so volatilization is one of the main functions to remove subsurface BTEX. Therefore, the study of the law of volatilization underground, a variety of factors affecting the volatilization and the quantificational study of the volatile removal rate under different conditions have important theoretical significance to air sparging (AS). Based on the study of factors affecting BTEX volatilization, the influence of these factors to the removal effect of AS was studied, which could give guide to the engineering practice.Based on the research domestic and abroad, a series of simulation experiments were conducted to study the volatilization of BTEX underground; made quantificational research to study the affection of BTEX initial concentration and ambiance elements volatilization; analyze the relation between these elements and volatile removal rate; determine the best operating condition by comparing experiments; under the best condition study the influence of the elements affecting volatilization to AS.In experiments on subsurface BTEX volatilization, aqueous BTEX and BTEX on media were analyzed and calculated respectively. The results showed that:(1) The concentration of organic compounds in the water had an important impact on volatilization. When the initial concentration of BTEX in groundwater was high, the concentration remaining after evaporation also relatively rapid decayed. On the contrary, when the initial concentration of BTEX decreased, the attenuation of residual concentration after volatile experiment became slow. The initial concentration of BTEX and volatile removal rate fitted logarithmic dependency relation. The fitting equation were YB(%) = 5.3741Ln(C0) + 58.715, YT(%) = 15.78Ln(C0) + 2.2679, YE(%) = 25.792Ln(C0) - 23.597, YX(%) = 37.957Ln(C0) - 52.099. With the initial BTEX concentrations in groundwater increased, volatile removal rate increased significantly, and changes in the lower concentration became more apparent. Thus, for high concentration BTEX contaminated sites it is suitable to adopt the methods promoting BTEX volatilization for rapid treatment and rehabilitation.(2) The vadose zone thickness was one of the most significant ambient factors impacting the volatilization of BTEX, which depended on the relation between the capillary region and the vadose zone. When the capillary zone is thinner and entirely belongs to the capillary region, the volatilization of BTEX in groundwater is much easier. Most have a high volatile rate of over 80%, and hardly change with the thickness of vadose zone. After the thickness of vadose zone is greater than the capillary region range, volatilization is inhibited obviously, and even no volatilization while thickness is 15cm higher than capillary region. (3) Another important factor that impacted BTEX volatilization was ambient temperature. In the range of experimental temperature, BTEX removal rate of volatilization and temperature present logarithmic dependence. The fitting equation were YB(%) = 48.681Ln(T) - 62.250, YT(%) = 24.072Ln(T) + 18.125, YE(%) = 37.125Ln(T) - 23.736, YX(%) = 28.738Ln(T) - 6.7729.(4) Volatilization of BTEX also changed with the soil type of vadose zone and aquifer, the greater the average particle size of media, the greater the removal rate was, and both of them present linear positive correlation between.In experiments on the factors impacting AS, concentration of BTEX in aqueous were measured and calculated, the results showed that:(1) Due to the good volatilization of BTEX, under the condition of continuous aeration and aeration flow 0.15m3/h, the removal rate was up to 95%. However, there was tailing phenomenon in the last phase of the experiment.(2) Comparing with continuous aeration, the removal rate was not so different when the intermittent aeration was used. However, the removal efficiency increased which could save the energy in actual projects and reduce the workload of significance. As to the adoption to actual projects, the specific operating conditions under different sites need specific analysis. In this experiment, medium sand was used as aquifer media, and the best removal rate appeared under the aeration rate of 0.15m3/h and intermittent aeration with cycle of 2h.(3) The factors influence volatilization such as the thickness of vadose zone, soil type of aquifer and soil type of unsaturated zone would also influence the repairing effect of AS. When the vadose zone media were medium sand, fine sand and clayey, AS removal rate of benzene were 86.7%, 55.2% and 46.2% individually. When the aquifer media was fine sand, AS removal rate of benzene was 37.5%, which was 51.4% lower than that in medium sand. It meant when the soil type of vadose zone or aquifer media was finer and the size was smaller, the AS removal rate of BTEX was lower and the rehabilitation effect became worse.