| Air sparging is a high-efficiency,low-cost and low-energy in-situ remediation technology of contaminated sites.However,when geological conditions of contaminated sites are complex,such as the influences of soil layering and fine-grained soil content,traditional air sparging technologies often have poor remediation effects such as tailing and other issues.Therefore,the study of surfactant foam enhanced air sparging under complex geological conditions is of important engineering application and scientific research value.Based on the National Key Research And Development Program(No.2018YFC1802300)and the National Natural Science Foundation Project(No.41672280,41877240),this paper focuses on typical volatile organic compounds(VOCs),and all the research is based on indoor one-dimensional soil column test,two-dimensional model box test and surfactant foam.Properties and foam stability,migration of surfactant foam in two-dimensional space and effects on groundwater properties,foaming surfactant enhanced air sparging remediation effect and complex geological conditions combined with surfactant and thickener to guide airflow enhancement experimental research on air sparging remediations are experimentally studied.Main research results achieved in this paper are listed as follows:The effects of surfactant type,concentration of surfactant solution,air sparging flow rate on foaming properties of surfactant solution and foam stability were investigated by laboratory tests.The results show that both surfactants SDBS and Triton X-100 have good foaming performance and foam stability.The maximum foaming height of SDBS solution is39cm,and the maximum foaming height of Triton X-100 solution is 72cm.The half-life of the SDBS solution foam is 850s,and the maximum half-life of the Triton X-100 solution is2580s.Under the same air sparging flow rate and different concentration of surfactant solution,when the concentration of SDBS solution increased from 0.2 CMC to 2.0 CMC,the ultimate foaming height increased with the increase of air sparging flow rate from 2cm to37cm;Triton The concentration of Triton X-100 solution increased from 1.0 CMC to 2.0CMC,and the ultimate foaming height increased from 34 cm to 46 cm.When the concentration of surfactant SDBS solution was 0.2-0.8 CMC,the foam half-life increased with the air sparging flow rate.Through indoor two-dimensional model test,the relationship between air sparging of foamed surfactant on air sparging affected zone,air sparging pressure and flow rate,gas phase saturation,horizontal and longitudinal migration of surfactant foam in two-dimensional sandbox,Speed and effects on groundwater properties including surface tension and dissolved oxygen.The test results show that under the different air sparging pressures,the area of the air sparging affected zone increases with the increase of air sparging pressure;the relationship between air sparging pressure and flow rate is:Q=a*P+b(a>0,b<0),and the correlation coefficient R~2 of linear fitting is greater than 0.92;the gas phase saturation is proportional to the air sparging pressure,and the glass beads are 0.5-1 mm,1-2 mm,2-3 mm,3-4 mm,when the air sparging pressure is 10-30 kPa,the gas phase saturation of the foamed surfactant after 1 h is from 3%to 37%,6%to 28%,and 11%to 60%,respectively.And21%-69%;for the glass beads of the same particle size,the longitudinal migration distance of the foam front is proportional to the air sparging pressure at the same time,and the longitudinal migration distance of the foam front increases with the increase of the air sparging pressure,and the glass bead size 0.5-1mm,1-2mm,2-3mm,3-4mm,respectively,when the air sparging pressure is from 10-30kPa,the longitudinal migration distance of the foam front is from 8.00-40.00cm,2.04-40.00cm,11.04-40cm and 27.79-40cm;in the two-dimensional sand box,under different air sparging pressures,glass beads of different particle sizes,the horizontal and longitudinal average migration velocity v of the foam is exponentially related to the time t,and the functional relationship is v=a*exp(b*t)+c;After air sparging of foaming surfactant,the surface tension of the aqueous solution in the flask under different air sparging pressures generally increases from bottom to top and from the middle to the sides;after foaming the surfactant for 1 hour The dissolved oxygen in the sandbox under different air sparging pressures generally increases from bottom to top and from the middle to the sides.In the same air sparging pressure and glass beads of different particle sizes,the larger the particle size of the glass beads,the higher the dissolved oxygen value and dissolve.Taking MTBE as a typical volatile organic pollutant,through indoor experiments,the effects of conventional air sparging and foaming surfactant air sparging on the concentration of MTBE in the next-dimensional sand column were studied.The experiment found that during the aerated process of one-dimensional sand column and air sparging of foamed surfactant,the concentration of MTBE solution at the bottom of the sand column decreased the fastest,and the concentration of MTBE solution in the middle of the sand column decreased moderately,while the top of the sand column The concentration of MTBE solution is the slowest.When the air sparging flow rate is 0.5L/min,the concentration of MTBE solution obtained by foaming surfactant air sparging at 3 sampling points is higher than that of conventional air sparging.When the air sparging flow rate is 1L/min,and the air is continuously injected for 4h,the MTBE concentration at the bottom of the sand column is lower than the MTBE concentration at the time of conventional air sparging when the foamed surfactant is aerated,but in general,the middle part of the sand column and sand during conventional air sparging The MTBE concentration in the upper part of the column is lower than the MTBE concentration in the air sparging of the foaming surfactant.When the air sparging flow rate is 1.5,2,2.5 L/min,the air is continuously injected for 6 hours,and the bottom of the sand column and the sand column are aerated when the foaming surfactant is aerated.The concentration of MTBE in the middle is lower than the concentration of MTBE in the conventional air sparging.Under the same air sparging pressure at the same time,the normalized MTBE tail gas concentration in the conventional air sparging process is smaller than the normalized MTBE tail gas concentration in the foamed surfactant air sparging.Through two-dimensional model tests,the use of thickener(SCMC)and surfactant(SDBS)in saturated sand and glass beads to study the gas flow law during groundwater air sparging.The test found that when aerating in a homogeneous saturated sand layer,the gas flow will first move upwards first.When a low-permeability zone is encountered above the gas flow,the gas will collect under the low-permeability zone.When the gas is collected to a certain extent,priority is given.Moving in the horizontal direction,the airflow channels are also distributed on both sides of the low-permeability zone,and the airflow moves upward through the channels on both sides of the low-permeability zone;in addition,studies have shown that using 10g/L SCMC solution on both sides of the low-permeability zone and at low The 0.6 g/L SDBS solution in the permeate zone and the lower zone can effectively direct the gas flow through the low permeability zone because the surfactant reduces the surface tension of the low permeability zone and the liquid below it,reducing the gas entry pressure.The thickener,on the other hand,increases the viscous resistance of the liquid on both sides of the low permeability zone,and the combination of the two promotes the passage of gas through the low permeability zone. |
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