NIRT: Targeted Delivery and Microbial Interactions of Polymer-Functionalized Nanoparticles for Groundwater Source-Zone Remediation (BES ) 1,2 Robert D. Tilton, 3 Gregory V. Lowry, 4 Krzysztof Matyjaszewski and 5 Edwin G. Minkley; Departments of 1 Chemical Engineering, 2 Biomedical Engineering, 3 Civil & Environmental Engineering, 4 Chemistry and 5 Biological Sciences, Carnegie Mellon University, Pittsburgh, PA An environmental problem When Dense Nonaqueous Phase Liquids (DNAPL), such as chlorinated solvents, are released into groundwater, they pose a significant environmental and public health hazard. DNAPL distributes both as residual saturation and as a plume of dissolved contaminants. Conventional “pump and treat” remediation methods require multiple wells to pump groundwater from the plume to the surface for chemical treatment, leaving the residual saturation source behind to continually replenish the plume. Plume treatment strategies, such as pump and treat or permeable reactive barriers, have been estimated to require as much as a century to meet cleanup goals. The method being developed here will target the chemical treatment to the residual saturation zone in situ. Drawing from: Heiderscheidt, Jeffrey L. DNAPL source zone depletion during in situ chemical oxidation (ISCO): Experimental and modeling studies. Ph.D. Dissertation. Colorado School of Mines, Golden, CO. (2005) A nanotechnology solution: nanoscale zero valent iron (NZVI) particles for in situ source zone remediation. NZVI Engineering Objectives Requirements: High reactivity and long lifetime Mobility in groundwater Minimal risk of disrupting natural microbial communities Desirable Features: Accumulation in source zone Synergism with natural dechlorinating microbes A---Aggregation B---Straining C---Attachment D---NAPL Targeting NZVI: “Reactive Nanoiron Particles” (RNIP supplied by Toda Kogyo USA) Fe 0 Fe 3 O 4 Trichloroethylene (TCE) Acetylene H+H+ H2H2 Fe 0 Fe 3 O 4 Immobility in porous media: A major problem with NZVI for in situ remediation. 20 µm Need to control NZVI aggregation and deposition: NZVI surface modification is necessary. Designing Polyelectrolyte Surface Modifiers to Inhibit NZVI aggregation Inhibit NZVI adhesion to mineral and natural organic matter (NOM) surfaces Promote source zone accumulation Electrosteric repulsions inhibit NZVI aggregation… …and adhesion to soil grains and negatively charged NOM Quartz Crystal Microgravimetry shows that all of the PSS-containing polymers prevent NZVI adhesion to quartz (and NOM). Bare NZVI Buffer: 1 mM NaHCO 3 All polymer modifiers used: Adsorbed mass (<0.3 mg/m 2 ) ~ 180 mg/m 2 equivalent to Sedimentation curves show that adsorbed copolymers improve NZVI colloidal stability. Sand column studies demonstrate that copolymers enhance NZVI mobility. Practical concentration for field application Nominal pore water velocity 1 mm/s With PMAA 42 -PMMA 26 -PSS 462 PMAA 48 -PMMA 17 -PSS 650 modified NZVI: 10 times less reactive than unmodified NZVI, but still reactive enough TCE t 1/2 ≈ 6 days (at 2 g/L) for the lowest activity modified particles Polymer-modified NZVI remains reactive. Fe 0 Fe 2+ 2 e - 2 H 2 O H OH - Fe 0 Oxidation H 2 Production and pH Increase Fe 0 Fe 2+ 2 e - R-Cl +H 2 O R-H + OH - + Cl - Fe 0 Oxidation Abiotic Dechlorination H2H2 2 e - 2 H + R-Cl +H 2 O R-H + OH - + Cl - Microbial Reductive Dehalogenation Synergism? Microcosm studies are underway to investigate NZVI interaction with dechlorinating microbes. Anchor block: poly (methacrylic acid) (PMAA n ) Hydrophobic block: poly (methyl methacrylate or butyl methacrylate) (PMMA m or PBMA m ) Hydrophilic block: poly (styrene sulfonate) (PSS p )