Modelling the role of surfactant and biodegradation in the remediation of aquifers with non-aqueous phase contaminants

The strong sorption of hydrophobic contaminants poses a serious challenge to the development of remediation technologies. Their low solubilities in water limit the applicability of treatment technologies such as pump-and-treat. Their dissolution by surfactants is a promising approach for circumventing this difficulty. The solubilized contaminant is subsequently irrigated onto a vegetated zone and mineralized. A two-zone model is developed for a system in which the contaminant is flushed from the aquifer with an aqueous surfactant solution and applied to vegetated soil. The model takes into account dissolution, sorption and biodegradation of the contaminant in the aquifer zone under the assumption that local equilibria prevail. It also takes into account sorption, mineralization and plant uptake in the rhizosphere zone assuming that mineralization obeys Monod kinetics. Model simulation was performed to determine the effects of surfactant and oxygen concentrations in enhancing contaminant removal from the aquifer and to evaluate the number of flushings required to reduce the concentrations of contaminant to desired levels. The results indicate that surfactant appreciably reduces the number of flushings by increasing the solubilization of contaminant. Increasing oxygen concentration enhances contaminant degradation. The model predicts an optimistic outcome because of the assumptions imposed; it is expected that the actual number of flushings will be larger than predicted.