An environmental problem

1. Abiotic Dechlorination Fe0 Oxidation Fe0 R-Cl +H2O 2 e- Fe2+ R-H + OH- + Cl- R-Cl +H2O H2 2 e- R-H + OH- + Cl- 2 H+ Microbial Reductive Dehalogenation 20 µm Sand column studies demonstrate that copolymers enhance NZVI mobility. Nominal pore water velocity 1 mm/s With PMAA42-PMMA26-PSS462 Practical concentration for field application Buffer: 1 mM NaHCO3 All polymer modifiers used: Adsorbed mass (<0.3 mg/m2) Synergism? equivalent to Bare NZVI ~ 180 mg/m2 NIRT: Targeted Delivery and Microbial Interactions of Polymer-Functionalized Nanoparticles for Groundwater Source-Zone Remediation (BES-068646) 1,2Robert D. Tilton, 3Gregory V. Lowry, 4Krzysztof Matyjaszewski and 5Edwin G. Minkley; Departments of 1Chemical Engineering, 2Biomedical Engineering, 3Civil & Environmental Engineering, 4Chemistry and 5Biological Sciences, Carnegie Mellon University, Pittsburgh, PA A nanotechnology solution: nanoscale zero valent iron (NZVI) particlesfor in situ source zone remediation. An environmental problem Fe0 Oxidation 2 H2O 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) Fe0 2 e- Fe2+ H2 + 2 OH- 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 H2 Production and pH Increase • A---Aggregation • B---Straining • C---Attachment • D---NAPL Targeting NZVI: “Reactive Nanoiron Particles”(RNIP supplied by Toda Kogyo USA) Immobility in porous media: A major problem with NZVI for in situ remediation. Fe0 Trichloroethylene (TCE) Fe3O4 Fe0 Polymer-modified NZVI remains reactive. Fe3O4 Acetylene PMAA48-PMMA17-PSS650 modified NZVI: 10 times less reactive than unmodified NZVI, but still reactive enough TCE t1/2≈ 6 days (at 2 g/L) for the lowest activity modified particles H+ H2 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 Anchor block: poly (methacrylic acid) (PMAAn) Electrosteric repulsions inhibit NZVI aggregation… …and adhesion to soil grains and negatively charged NOM Microcosm studies are underway to investigate NZVI interaction with dechlorinating microbes. Hydrophobic block: poly (methyl methacrylate or butyl methacrylate) (PMMAm or PBMAm) Hydrophilic block: poly (styrene sulfonate) (PSSp) Sedimentation curves show that adsorbed copolymers improve NZVI colloidal stability. Quartz Crystal Microgravimetry shows that all of the PSS-containing polymers prevent NZVI adhesion to quartz (and NOM).