SURFACTANT-ENHANCED AIR SPARGING: LABORATORY EVALUATION OF PERFORMANCE

Air sparging is a subsurface remediation technology for the removal of volatile organic compounds (VOCs) from contaminated groundwater. The effectiveness of air sparging is limited by many factors but mainly by the slow removal of contamination that is not proximal to the primary channels of air flow induced during the injection of air into the contaminated saturated zone. As a consequence, contaminant removal rates typically drop by orders of magnitude after sparging systems have removed contamination in direct contact with the sparge bubbles/channels approaching rates that appear to be limited by the aqueous diffusion of the contaminant.Air sparging performance can be enhanced by increasing the distribution of air in the sparge zone, creating more channels or air bubbles and by inducing localized water movement between air channels. In an attempt to enhance the effectiveness of air sparging, laboratory experiments were conducted to evaluate the benefits of using surfactants to lower the interfacial tension between water and air in the sparge zone and thereby promote increased contact between the flowing gas phase and the contamination. This is accomplished due to the formation of additional air channels in progressively smaller pore spaces following the introduction of surfactant. The increase in air contact with the contamination results in an increase in mass removal rates. The evaluations of the effects of the surfactant were performed in laboratory experiments designed to compare the mass removal rates of conventional air sparging to surfactant-enhanced air sparging. The evaluations were conducted under one-dimensional flow conditions in a glass column packed with sand and contaminated with measured masses of trichloroethylene, introduced as a nonaqueous phase liquid. Several trials of each experiment were performed in an attempt to obtain reproducible results. The results indicated that the injection of a surfactant slug resulted in a two-order magnitude reduction in the number of gas pore volumes flushed to achieve 90% mass removal.The potential for improving the cost effectiveness of air sparging by means of slug introduction of surfactants appears promising as it may result in substantial operational, maintenance, and monitoring cost savings as a consequence of reduced remediation time.