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

An environmental problemWhen 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)

Fe0

Fe3O4

Trichloroethylene(TCE)

Acetylene

H+H2

Fe0

Fe3O4

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

water

mineral surface

water

water

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).

Time (min)

0 10 20 30 40 50 60 70 80

f

(Hz)

-500

-400

-300

-200

-100

0

Bare NZVI

Buffer: 1 mM NaHCO3

All polymer modifiers used:Adsorbed mass (<0.3 mg/m2)

~ 180 mg/m2

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 PMAA42-PMMA26-PSS462

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

Polymer-modified NZVI remains reactive.

Fe0

Fe2+

2 e-

2 H2O

H2 + 2 OH-

Fe0 Oxidation

H2 Production and pH Increase

Fe0

Fe2+

2 e-

R-Cl +H2O

R-H + OH- + Cl-

Fe0 Oxidation Abiotic Dechlorination

H2

2 e-

2 H+

R-Cl +H2O

R-H + OH- + Cl-

Microbial Reductive Dehalogenation

Synergism?

Microcosm studies are underway to investigate NZVI interaction with dechlorinating microbes.

Anchor block: poly (methacrylic acid) (PMAAn)

Hydrophobic block:poly (methyl methacrylate or butyl

methacrylate)(PMMAm or PBMAm)

Hydrophilic block:poly (styrene sulfonate) (PSSp)