Utilization of predispersed solvent extraction for removal and enzymatic degradation of chlorinated solvents in ground water

Abstract

The feasibility of applying a recently developed liquid-liquid extraction method termed Predispersed Solvent Extraction (PDSE) in an ex situ pump-and-treat system to remove trace amounts of dissolved chlorinated solvents like perchloroethylene (PCE) and trichloroethylene (TCE) from contaminated ground water has been investigated. In PDSE, the solvent is comminuted into globules with diameters ranging from submicron to 100 microns, and stabilized by a surfactant film prior to contact with the aqueous feed. These stabilized globules, termed oil-core aphrons (OCAs), disperse readily in water since water is the continuous phase in systems where the oil-water phase ratios can be as high as 9. Due to their fine particle size and large surface area, high extraction mass-transfer rates are achieved with minimal mixing. OCA phase separation from water can be expedited with microbubble foam flotation. Experiments in this investigation focused on PDSE process development for this groundwater remediation application. Distribution coefficients for PCE and TCE in possible OCA solvents were determined experimentally and agree with published calculated values. Various surfactant/solvent OCA formulations using the aforementioned solvents were examined with emphasis on creating a weakly stable dispersion which would maximize extraction efficiency yet destabilize sufficiently to permit rapid flotation with minimum losses in the raffinate. Accelerating phase separation, hence solvent recovery, through dispersion chemical destabilization with salts, coagulants, and flocculants at varied pH was examined with and without microbubble flotation. The presence of OCAs in the aqueous phase reduced vapor phase concentrations of PCE as much as 96% and was assessed through apparent Henry's Law constants. TCE concentrated in dodecane OCA extract was degraded with a CO-dehydrogenase enzyme complex to cis 1,2-dichloroethylene, trans 1,2-dichloroethylene, and 1,1-dichloroethylene, and vinyl chloride as a possible means of destroying TCE dissolved in the extract. Based on the implications of these experiments, the development of a PDSE ex situ pump-and-treat system appears technically feasible and a conceptual process layout has been provided.