Laboratory Experimental Research On Remediation Of MTBE-Contaminated Saturated Sand By Surfactant-Enhanced Air Sparging

In-situ air sparging is a cost-effective and efficient technology for remediation of groundwater saturated zone contaminated by volatile organic compounds. However, the zone of influence is usually narrow and the remediation effect is not good due to the limitation of the contamiant characteristics and geological conditions of the site in the practice of conventional air sparging. Therefore, mechanism and effect study of a practical and effective technology of enhanced air sparging is of important scientific and engineering significance. Financially supported by the National Natural Science Foundation of China (41330641,41272311) and based on saturated sands contaminated by volatile organic compound methyl tert-butyl ether (MTBE),1-D and 2-D laboratory model tests as well as physical and chemical mechanism experiments were performed, through which the mechanism, air flow behavior and removal effect of Sodium dodecyl benzene sulfonate (SDBS) enhanced air sparing is systematically studied. The main achievements are summarized as follows:1. Through physical and chemical mechanism experiments of surfactant-enhanced air sparging, the influences of pH value and salinity on the surface tension of SDBS solution and solubilization and desorption of MTBE induced by SDBS are studied. Test results indicate that when SDBS concentration is below its critical micelle concentration the surface tension increases slightly with the increase of pH value. When the salinity is lower than 15%o, the surface tension of SDBS solution decreases significantly with the increase of salinity. When the the concentration of SDBS solution is relative low, the solubilization increase and desorption effects of MTBE are much poor. But if the SDBS concentrations are greater than 200 mg/L and 500 mg/L respectively, the functions of solubilization and desorption begin to take effect.2. The air flow behaviors including relationship between air flow rate and air pressure, saturation degree of air phase, air flow pattern, radius of influence and number of air flow channels are systematically studied through 1-D and 2-D laboratory mode tests of surfactant-enhanced air sparging. Experimental results indicate that the introduction of surfactant decreases the minimum incoming air sparging pressure, and the air flow rate of foam-based surfactant-enhanced air sparging (FSEAS) is lower than that of conventional air sparging (CAS) and surfactant solution-enhanced air sparging (SSEAS) at the same pressure. The introduction of surfactant can significantly increase the air phase saturation degree and radius of influence, and the number of air flow channels also can be increased to some extent. Such enhancement effects of surfactant in coarse sands (2.0-4.0 mm) are beeter than in fine sands (0.5-1.0 mm). Basically, the surfactant has little influence on the air flow pattern, but the bubble size in coarse sands (2.0-4.0 mm) is decreased, and many micro bubbles arise. The air flow behavior of SSEAS is generally better than that of FSEAS, but latter way is much more suited to field practice.3. Laboratory model tests on remediation of MTBE contaminated saturated sand by SDBS enhanced air sparging are conducted to study the removal process and effect of contaminants. Test results indicate that the removal rate of FSEAS is higer than that of CAS under the condition of both 1-D and 2-D laboratory model tests. The effect of remediation enhancement of surfactant in coarse sands (2.0-4.0 mm) is better than in fine sands (0.5-1.0 mm). Under the condition of 1-D model test, the lumped-parameter KLa gradually decreases from bottom to the top of sand column at any kind of sparging test. In addition, the KLa of surfactant influcened region in FSEAS is higher than that of CAS for the same position. Under the condition of 2-D model test, the MTBE contaminants may migrate to the surrounding originally clean area due to the limted zone of influence for single sparging well and the groundwater disturbance by air flow injection.4. Based on the theory of multiphase flow, the leakage, migration of Benzene and the following air sparging process are numerically simulated by TOUGH2 with the consideration of surfactant enhancement. Research results indicate that decrease of surface tension will increase the radius of influence, air phase saturation degree and removal rate of contaminant, which will significantly improve the effect of contamiant removal.