Study on mechanisms and effect of surfactant-enhanced air sparging.

In an attempt to enhance the effectiveness of air sparging, two sets of experiments were designed to investigate the mechanisms and effect of surfactant-enhanced air sparging (SEAS). The first set was performed at different surface tensions and with different kinds of surfactants (sodium dodecyl benzene sulfonate and Tween-80 [Uniqema Americas LLC, Wilmington, Delaware]), which were added into the contaminated aquifer of different media (particle distribution size = 0.25 to 0.5 mm and 5 to 10 mm). The results indicated that the air saturation in the aquifer increased rapidly at an early stage, then the increase of air saturation slowed down with the increase of airflow rate. The air saturation of medium sand increased with the decrease in water surface tension, and maximum air saturation was achieved at a surface tension of approximately 5 x 10(-2) N/m (50 dyn/cm), which was considered to be the optimum surface tension for air sparging enhancement in the medium sand aquifer. The increase of air saturation in gravel was the result of the increase of foamability and foam stability. The second group of experiments is about the removal of chlorobenzene from the medium sand aquifer. The experiments indicated that chlorobenzene removal by SEAS was more complete and efficient than that of conventional air sparging technology. However, the increase of removal rate and the decrease of lingering concentration by SEAS was not significant, with a further decrease in the surface tension when the surface tension dropped to 5.04 X 10(-2) N/m (50.4 dyn/cm).