Published: June 16, 2011 r2011 American Chemical Society 6102 dx.doi.org/10.1021/es200577n | Environ. Sci. Technol. 2011, 45, 6102–6109 ARTICLE pubs.acs.org/est Polymer-Modified Fe 0 Nanoparticles Target Entrapped NAPL in Two Dimensional Porous Media: Effect of Particle Concentration, NAPL Saturation, and Injection Strategy Tanapon Phenrat, †,‡,§ Fritjof Fagerlund, §,3 Tissa Illangasekare, § Gregory V. Lowry, †,||, * and Robert D. Tilton ||,^, * Center for Environmental Implications of Nanotechnology (CEINT) and † Department of Civil & Environmental Engineering, ) Department of Chemical Engineering, and ^ Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213-3890, United States ‡ Department of Civil Engineering, Naresuan University, Phitsanulok, Thailand, 65000 § Center for Experimental Study of Subsurface Environmental Processes, Colorado School of Mines, Golden, Colorado 80401, United States 3 Department of Earth Sciences, Uppsala University, Villav € agen 16, 75236 Uppsala, Sweden b S Supporting Information ’ INTRODUCTION Reactive metallic or bimetallic nanoscale zerovalent iron (NZVI) particles are used for in situ remediation of chlorinated organic compounds in the form of dense nonaqueous phase liquids (DNAPLs) in contaminated groundwater and soil. 1,2 Subsurface DNAPLs, which only slowly dissolve, can persist as a long-term source of groundwater contamination. NZVI is often injected with the intention of rapidly dechlorinating entrapped DNAPL to decrease the source mass and strength, and shorten the time for meeting remediation goals. 1,3 Over the past decade, substan- tial advances in NZVI synthesis and characterization, 4À9 under- standing NZVI reactivity and longevity, 10À12 understanding effects of surface modification on NZVI mobility in porous media, 13À21 and field scale evaluations 8,22À24 have been made. However, after initial indications of the surface activity of polymer-modified NZVI at NAPL/water interfaces, 25 little research progress has been made toward delivery of NZVI to NAPL source zones 26 even though source zone targeting would be a unique feature that could make in situ NAPL remediation by NZVI more effective than passive remediation techniques. Delivering NZVI to the DNAPL/water interface where aqu- eous phase DNAPL concentrations are at their highest can potenti- ally increase the rate of dechlorination and the efficient usage of Received: February 19, 2011 Accepted: June 1, 2011 Revised: May 29, 2011 ABSTRACT: Polymer-modified nanoscale zerovalent iron (NZVI) particles are delivered into porous media for in situ remediation of nonaqueous phase liquid (NAPL) source zones. A systematic and quantitative evaluation of NAPL targeting by polymer-modified NZVI in two-dimensional (2-D) porous media under field-relevant conditions has not been reported. This work evaluated the importance of NZVI particle concentration, NAPL saturation, and injection strategy on the ability of polymer-modified NZVI (MRNIP2) to target the NAPL/water interface in situ in a 2-D porous media model. Dodecane was used as a NAPL model compound for this first demonstration of source zone targeting in 2-D. A driving force for NAPL targeting, the surface activity of MRNIP2 at the NAPL/water interface was verified ex situ by its ability to emulsify NAPL in water. MRNIP2 at low particle concentration (0.5 g/L) did not accumulate in or near entrapped NAPL, however, MRNIP2 at moderate and high particle concentrations (3 and 15 g/L) did accumulate preferentially at entrapped NAPL, i.e., it was capable of in situ targeting. The amount of MRNIP2 that targets a NAPL source depends on NAPL saturation (S n ), presumably because the saturation controls the available NAPL/water interfacial area and the flow field through the NAPL source. At effective S n close or equal to 100%, MRNIP2 bypassed NAPL and accumulated only at the periphery of the entrapped NAPL region. At lower S n , flow also carries MRNIP2 to NAPL/water interfaces internal to the entrapped NAPL region. However, the mass of accumulated MRNIP2 per unit available NAPL/water interfacial area is relatively constant (∼0.8 g/m 2 for MRNIP2 = 3 g/L) from S n = 13 to ∼100%, suggesting that NAPL targeting is mostly controlled by MRNIP2 sorption onto the NAPL/water interface.