Use of cosolvent for DNAPL mass depletion in source zones and its impact on the plumes
Cosolvents have been used in remediation of source zones at sites contaminated with non-aqueous phase liquid (NAPL), because of their ability to increase the solubility of NAPL constituents. Upon depletion of NAPL mass from the treated zone, complete recovery of cosolvent is generally required considering the possible toxicity to the indigenous microbial communities from chemicals used as cosolvent. Since cosolvent flushing involves enhanced extraction of NAPL mass, additional above ground treatment of waste fluids is required. The laboratory research conducted in this thesis focused on ways to eliminate these two needs. First, a biofriendly cosolvent, ethyl lactate (EL), was found to be very efficient in recovering DNAPL mass in source zone. The residual amount of EL not only poses no harm to indigenous microbial population in a DNAPL contaminated site, but also serves as electron donor to promote the microbial dehalogenation of chlorinated contaminants, such as perchloroethylene (PCE) and trichloroethylene (TCE) in the down gradient plume. Therefore, the flushing agent, EL, can be left behind at low concentrations to facilitate biodegradation in the plume. Secondly, the option of coupling a cosolvent with a chemical oxidant, potassium permanganate, to destroy contaminant in situ, was examined. Tertiary butyl alcohol (TBA) and acetone are two cosolvents that have the capacity to enhance solubility of PCE dramatically and while also being relatively recalcitrant toward oxidation by permanganate, therefore are suitable for use in cosolvent-enhanced in-situ permanganate oxidation. The reaction kinetics between PCE and permanganate are lowered in the presence of either TBA or acetone, probably due to preferential solvation. Nonetheless, the enhanced solubility of PCE with TBA or acetone resulted in an overall improved PCE destruction efficiency, as indicated by the experiments with the presence of free phase PCE, both in the batch reactor, and under aqueous flow condition in the one-dimensional column and the two-dimensional flow chamber. Overall, the experiments conducted in this research confirmed the two ways of using cosolvent to deplete DNAPL mass: (1) to increase DNAPL recovery efficiency through cosolvent-flushing with a biofriendly compound to benefit the afterward biodegradation in the plume, and (2) to increase in-situ chemical oxidation efficiency by increasing DNAPL solubility.
Rao, Purdue University.
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