Reactive Nanoparticles for In Situ Groundwater Remediation: Optimizing the Benefits and Mitigating the Risks with Surface Coatings

Transcription

1 Reactive Nanoparticles for In Situ Groundwater Remediation: Optimizing the Benefits and Mitigating the Risks with Surface Coatings Gregory V. Lowry, Tanapon Phenrat, Yueqiang Liu, Hye-Jin Kim, Navid Saleh, Robert Tilton, Krzysztof Matyjaszewski Carnegie Mellon University Tissa Illangasekare Colorado School of Mines R OECD July 16, 2009

2 Nanoparticle-based Treatment Strategy for Groundwater Contaminants Requires 1. Rapid and prolonged reactivity 2. Mobility for emplacement 3. Target specificity 4. Cost-effective Treatment 5. Low risk Goal: Degrade contaminants in source area

3 Conceptual Model of DNAPL Source Zone Treatment NZVI Injection Plume Concentration MCL How many injections? How long between them? NO ACTION SOURCE REMOVAL POST REMOVAL Cost-effectiveness relies on effective emplacement and selectivity of NZVI for contaminant.

4 Contaminants are reduced Reactive Fe 0 Nanoparticles Nano Fe 0 is oxidized Fe 0 TCE Acetylene Fe 3 O 4 Fe 0 Fe 0 Fe 3 O 4 H 2 H + Fe 3 O 4 Lifetime depends on oxidant loading, ph, and potentially on microbial activity H + is reduced Liu et al, (2005) ES&T 39, 1338 Liu and Lowry, (2006) ES&T, 40 (19) 6085 Liu, et al., (2007) ES&T

5 RNIP Not All NZVI is the Same Fe 0 core Fe 3 O 4 shell FeOOH Fe 0 Fe 0 /Fe 3 O 4 Intensity (a.u.) (a) (b) Crystalline (220) (311) (110) (222) (400) (422) (511) (440) (200) Fe(B) Fe 0 core Borate shell (c) (degree) Amorphous Fe 2+ + BH 4- Fe 0 /FeB x /Na 2 B 4 O 7 10 nm Liu et al, (2005) ES&T 39, 1338; Liu et al, (2005) Chem. Mat. 17(21); ;Nurmi et al. (2005) ES&T 39, 1221.

6 Differences in Reactivity with TCE Fe(B) RNIP Faster Reaction k obs =1.4 x 10-2 L hr -1 m -2 Saturated Products Slower reaction k obs =3 x 10-3 L hr -1 m -2 Unsaturated Products *Iron Filings k=10-3 to 10-4 L hr -1 m -2 Liu, et al., Environ. Sci. & Technol. 2005, 39,

7 Nano Effect Unit Cell dimension of BCC Fe 0 ~0.29 nm 1nm crystals means ~4 3 unit cells (64 atoms) per crystallite? Strained structure and high excess surface area/edge sites. Images from Nurmi et al. (2005) ES&T 39, 1221.

8 NZVI Reactive Lifetime Depends on ph Fe 0 2H Fe 2 H 2 ~2 weeks ph=6.5 ~9 months ph 8.0 Liu and Lowry, (2006) Environ. Sci. Technol., 40 (19) 6085

9 TCE Concentration Affects Fe 0 Utilization Efficiency Small effect of TCE concentration on reactivity Use in source zone increases Fe 0 efficiency Liu, et al., (2007) ES&T

10 Estimated Cost of Treatment using NZVI Economics 0 2 Fe Fe 2 e TCE n e m H products 3 Minimum: 4e - (2 Fe 0 )/TCE : 0.85:1 (by mass) - For Acetylene, n=4 For Ethene, n=6 For Ethane, n=8 Acetylene Assuming $50/kg Fe 0 Cost: $44/kg TCE (acetylene) $66/kg TCE (ethene) $88/kg TCE (ethane) TCE transformation by RNIP

11 Measured TCE degraded/mass of Fe 0 Product Fe 0 / TCE degraded Product Fe 0 / TCE degraded H :1 MRNIP I 28:1 MRNIP II 121:1 RNIP 27:1 EHC 1000:1 * RNIP-R 17:1 * Z-Loy 30:1 *Z-Loy and RNIP-R were prepared using 100 mg/l TCE instead of 50 mg/l TCE which may improve the selectivity for TCE for those NZVI. Phenrat et al., (2008) Battelle Conf.

12 Nanomaterial Mobility in Porous Media A---Aggregation B---Straining C---Deposition D---NAPL Targeting Depends on: Chemical ph, ionic strength, ionic composition, surface coating Physical flow velocity, particle/aggregate size, heterogeneity Lowry, G. V. (2007). Groundwater Remediation Using Nanoparticles. In Environmental Nanotechnology: Applications and Impacts of Nanomaterials. Eds. M. Wiesner and F. Bottero, McGraw-Hill, New York, NY, 2007 p

13 F=10-5 (~80 mg/l) Aggregation makes emplacement difficult 1-min Nanoiron sedimentation in 1 mm Na Aggregation I t crit 4 mg/l 25 micron 9-min t= 156 t = mg/l t = 294 d p ~45 mm 470 mg/l 25 micron 35-min Sedimentation I Sedimentation II t = 1, mg/l 1130 mg/l d p ~120 mm 25 micron Phenrat T., et al., (2007) ES&T 41, 284.

14 Polymer Modified Reactive Nanoiron (NZVI) Fe 0 /Fe 3 O 4 (RNIP) + O H O n O m O SO 3 H p M n =2000 M n =5700 M n =8340 Liu, Y., et al., (2005) ES&T 39, Nurmi, J., et al., (2005) EST 39, PMAA-PMMA-PSS RNIP Modifier Apparent z potential (mv) Average Dia (nm) Bare RNIP PMAA 48 -PMMA PSS 650 PAP (MW=2.5k) -51.7± ±18.6 PSS (MW=70k) -48.9± ±16.6 Saleh et al., 2005 Nano Lett

15 Role of Surface Modifiers on Aggregation, Transport, Reactivity, and Toxicity Inhibits Aggregation Inhibits Deposition Charge Stabilization Promotes Selectivity water solvent Saleh et al., 2005 Nano Lett Decreases Toxicity -- Bacteria Steric Stabilization Li et al. ES&T (in prep) water solvent

16 Modifiers Inhibit Aggregation Aggregation I t crit PSS70K Polymers inhibit aggregation and provide a stable fraction PSS1M CMC90K Sedimentation I Sedimentation II Bare No apparent trend with MW Saleh, N. et al. (2005). Nano Lett. 5 (12) Saleh, N. et al., (2007) Environ. Eng. Sci. 24 (1) p Phenrat, et al., (2008) J Nanopart. Res. 10 p

17 Configuration of Adsorbed Homopolymer Low concentration of adsorbed polymer RNIP RNIP RNIP High concentration of adsorbed polymer RNIP d M Important parameters: Adsorbed mass and layer thickness (d)

18 Ohshima s Model d M RNIP Parameters: d-layer thickness N-charge density in layer 1/l softness parameter CMC90K CMC700K H. Ohshima, M. Nakamura and T. Kondo, Colloid Polym. Sci. 270 (1992) Phenrat, et al. (2008) J Nanopart. Res. Vol. 10 p PSS70K PSS1M

19 Agglomeration (and deposition) Occurs in a Secondary Minimum Attraction due to V vdw +V M R NI P R NI P V osm is strong repulsive force and results in secondary minimum Repulsion due to V ES +V osm + V elas V elas V ES V osm V T PSS70K Need to consider: V elas, V osm due to polyelectrolyte V vdw V M Secondary minimum Phenrat, et al. J Nanopart. Res. Vol. 10 p

20 How long does coating remain on particles? Coating?? Time Does coating desorb? What is the time scale? What is the behavior after desorption of coating? Kim et al., 2009 ES&T

21 Very Slow Desorption of Polymers (t 1/2 ~years) Ln(C/C 0 ) rapid slow Time (day) PSS1M PSS70K Poly(styrenesulfonate) Ln(C/C 0 ) Polyaspartate 0.00 rapid slow PAP10K PAP2.5K Time (day) Kim et al., 2009 ES&T

22 Polymer-modified Particles Respond to NAPL Avoids mineral surfaces water solvent Targets DNAPL: PMMA shrinks in water and extends in DNAPL

23 TCE NAPL Targeting Polymer-modified nanoiron emulsifies TCE Saleh et al., 2005, Langmuir 21, Self-assemble at the DNAPL/water interface Unmodified and PSSmodified particles do NOT emulsify TCE Saleh, et al. Nanolett. 2005, 5 (12) 2489.

24 Coatings Affect Reactivity C C H C C H C C H C C H C C H C C H Tail C C C C H H C C H C C C C H H C C H C C H RNIP Train Loop C C H Phenrat et al., 2009 ES&T 43 (5), pp 1507 d PSS70K-Modified NZVI Region I: Site blocking Region II: Site blocking and mass transfer limitation

25 Coatings Decrease OS response by CNS Microglia to NZVI, BUT. Bare Aged Magnetite PAP-coated Phenrat et al. (2009) ES&T 43 (1)

26 Polyaspartate-coated NZVI Entered the Neuron Cell Nucleus N27 Neurons PAP-coated nanoparticles Phenrat et al. (2009) ES&T 43 (1)

27 Conclusions and Remaining Challenges Surface modifiers MUST be considered when assessing transport and toxicity of particles Adsorbed mass and extended layer conformation Market Potential Need realistic in situ costs of treatment using NZVI (e.g. $/kg DNAPL removed) Feasibility depends on iron type and site geochem. Risks to Environment & Health Exposure to Fe 0 may pose risk Fully oxidized NZVI show no toxicity (for ROS endpoints used) Bactericidal effects are mitigated by oxidation Exposure risks to humans is low

28 Conclusions and Remaining Challenges Safe and Responsible Development Organic surface coatings reduce risks to human health and ecosystem caveat that one coating increased uptake into neurons Transport (exposure potential) depends on coating type and groundwater velocity Challenges No adequate demonstration of emplacement techniques or effectiveness of treatment Will depend on NZVI type, ph, oxidant loading, contamination architecture Cannot measure where reactive NZVI is emplaced A well controlled and highly instrumented field pilot is needed to obtain realistic cost information

29 Measuring effect of NZVI on PCE mass emission Back of tank Flow direction Treatment Zone#1 P4 P7 P9 Flow direction MRNIP2 reactive R2 zone covers Port 6 to Port 8 (P6-P8) R1 PCE Source

30 Nanoparticle Transport is Affected by NZVI Heterogeneity 1m Flow

31 Questions?

32 Transport of Fe 0 Nanoparticles in Porous Media Inlet Monolayer of sand Outlet 1 1/2 Micro-fluidic PDMS cell Saleh, N. et al., (2007) Environ. Eng. Sci. 24 (1) p

33 In Situ Targeting Challenges Nanoiron trajectory at different porewater velocities Flow velocities: (2.6-13m/day) Residence time: 1-10 s Contacting particles with TCE remains a challenge SERDP project investigating methods to improve mixing Baumann et al. 2005

34 Summary of Reactivity Studies Not all NZVI is created equally Reaction rates and products are different Reactive lifetime depends on type of NZVI and site geochemistry Nano effect observed for one type of NZVI Use in a source zone should provide more efficient use of Fe 0

35 Mechanistic understanding of adsorbed polyelectrolyte effect on aggregation Approach 3 types of modifiers (PSS, PAP, CMC) Measure surface excess, G (mg/m 2 ) Monitor sedimentation over time Indicates degree of aggregation

36 Measured Layer Properties Modifier M w D P Γ d 1/λ ψ DON * ψ 0 * (kg/mole) (--) (mg/m 2 ) (nm) (nm) (mv) (mv) PSS 70k ±0.3 67±7 37±1 2.1± ±0.1 PSS1M CMC90K CMC 700K 1,000 4, ± ± ± ±3 0 49±1 1.7± ±3. 2 9± ± ± ±1.5 40± ±1 4.2± ±0.1 PAP2.5K ±0.2 40±12 24±1 5.1± ±0.2 PAP 10k ±0.3 44±13 26±1 4.5± ±0.2 Steric Repulsions Phenrat, Tilton, and Lowry, J Nanopart. Res. 10 p

37 Surface Excess and Layer Thickness Determine Ability to Stabilize NZVI Against Agglomeration PSS70K PAP10K PAP2.5K CMC700K CMC90K Bare Phenrat, et al. J Nanopart. Res. Vol. 10 p

38 Adsorbed Polymeric Layer Thickness and Fe 0 Content Affect Emplacement The greater the adsorbed layer thickness, the greater the ZOI Role of electrosteric stabilization The greater the Fe 0 content, the smaller the ZOI Role of magnetic attraction

39 Estimating ZOI from COMSOL Based Simulation: Effect of Injection Rate The greater the NZVI injection rate, the larger the ZOI Influence of Shear on Detachment and Disaggregation