Development and Optimization of Targeted Nanoscale Iron Delivery Methods for Treatment of NAPL Source Zones

摘要

This project was designed to develop and evaluate innovative nanoscale zero valent iron (nZVI) technologies for application to the treatment of dense nonaqueous phase liquid (DNAPL) source zones. An integrated research program, that combined multi-scale laboratory experiments with mathematical modeling, was undertaken: to investigate the transport and reactivity properties of commercially available nZVI systems; to develop and refine novel nZVI encapsulation formations with superior potential for source zone remediation; and to develop laboratory validated mathematical models for prediction of the delivery and effectiveness of these nZVI systems for DNAPL source zone treatment. A number of processes were identified which will tend to limit the effectiveness of aqueous slurry nZVI injection for in situ DNAPL mass transformation, even under the most favorable conditions. These processes include pore clogging (and associated injection pressure increases), groundwater flow bypassing of the treated zone, DNAPL mobilization, unfavorable iron to DNAPL mass ratios, and reaction limitations due to dissolution mass transfer. Column transport experiments demonstrated the superior injection and mobility performance of biodegradable micro-emulsion nZVI formulations. However, reactivity studies suggest that emulsification will tend to slow aqueous phase reactions and to promote contaminant solubilization. Controlled emulsion partitioning to the NAPL may offer promise for sustained in situ reaction, but further research is needed to address reaction limitations due to low water solubility in the DNAPL. The trapping number concept and a model based upon modified clean bed filtration theory were successfully implemented to reproduce experimental observations of nZVI injection, transport, and reaction.