Injection of Stabilized Zero-Valent Iron Nanoparticles for Treatment of Solvents in Source Zones

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1 Injection of Stabilized Zero-Valent Iron Nanoparticles for Treatment of Solvents in Source Zones Zhong (John) Xiong, PhD, PE; Peter Bennett, PG; Dawn Kaback, PhD, AMEC Geomatrix, Inc. Dongye (Don) Zhao, PhD, Auburn University

2 Chlorinated Solvents in Groundwater at DoD Sites solvents are most widespread groundwater contaminants affecting ~5,000 DoD sites, other federal, and commercial for example, TCE detected at 852 NPL sites cleanup cost: >$750 billion over 30+ years can t treat to MCL with pump and treat at most sites

3 In Situ Remediation Technologies Can Provide Improved Solutions Granular zero-valent iron (ZVI) has been used primarily in permeable reactive barriers (PRBs) ZVI has excellent reductive dechlorination capability PRBs often used to treat dilute plume, at property boundaries, etc. Deeper applications require injection in wells or boreholes rather than trenching Permeable Reactive Barrier - ZVI

4 ZVI Can Treat a Variety of Contaminants Source: Lehigh University Organic solvents (TCE, PCE, PCBs) Pesticides (DDT, lindane) Fertilizers (nitrate) Heavy metals (Cr, As, Pb) Explosives (TNT, RDX) Radioactive materials (U, Tc)

5 Recent ZVI Advances Broader applications beyond PRBs source zone treatment with delivery through injection points or wells Particle Performance Advancements Iron coated with a metal catalyst such as Pd, Ni, or Cu Particle size reduced to nanoscale to improve reactivity Nanoscale ZVI (nzvi) coated with stabilizers to prevent agglomeration and precipitation of particles Source: gnet.myweb.hinet.net/

6 Effect of Particle Size on Reaction Rate Specific Surface Area (m 2 /g) = Surface Area (m 2 ) πd 2 6 = Mass (g) ρπd 3 /6 ρd = d (nm) ,000 1,000,000 Assuming ρ= 7.8 g/l SSA (m 2 /kg) 769,231 76, dc dt = - k SA a s C ZVI C C contaminant conc. k SA rate constant a s SSA C ZVI conc. of iron Johnson et al., Environmental Science and Technology,1996 The greater the surface area, the higher reaction rate

7 Nano-scale ZVI (nzvi) Advantages for Source Zone Treatment High surface area High reaction rates Facilitates in-situ delivery Diffusion in soil/sediment pores Source: W.-X., Zhang, Lehigh University Source: cgr.ese.ogi.edu/iron/

8 nzvi Performance Issue: Agglomeration and Precipitation Fisher Scientific Non-stabilized nzvi

9 Stabilization of nzvi Particles Can Prevent Agglomeration and Precipitation O OH H O R H O H (c) Stabilizers: Polyelectrolytes (e.g. CMC, PSS), NOM, guar gum, etc. Mechanisms: Electrostatic stabilization and steric stabilization O OH H 2 C O O H 2 C C O H H (b) O Fe Fe H OH O H 2 C O O H 2 C C O (a) = CMC OH H CMC = carboxymethyl cellulose H OH Source: He, F. and Zhao, F., Environmental Science and Technology, 2007

10 Transmission Electron Microscope (TEM) Images of nzvi Particles Non-Stabilized CMC-Stabilized Source: Xiong, Z., Zhao, D., Pan, G., Water Research, 2007

11 Lab Testing of nzvi Reactivity C/C Non-stabilized Fe-Pd CMC-Stabilized Fe-Pd Starch-Stabilized Fe-Pd Control Chlorine, mg/l Cl as TCE-Cl Cl - Cl - +TCE-Cl Control Time, min Time, min Fe = 0.1 g/l; Pd = 0.1 mg/l; Starch or NaCMC = 0.2% (w/w); Initial TCE = 50 mg/l. Fe-Pd with starch: 37x faster; with CMC: 74x faster.

12 Field Testing of Stabilized nzvi Injection for Treatment of Solvents in Groundwater Two field demonstrations completed California Alabama Third demonstration project underway at DoD Site (Hill AFB) Field sampling completed Laboratory testing ongoing Field injections planned for Summer and Fall 2010

13 Field Test 1: Treatment of TCE in groundwater nzvi prepared in field from common chemicals to ensure freshness and reactivity of particles, and maintain low cost Push-pull test conducted in existing well To injection pump 90-gallon nanoparticle suspension

14 Field Test 1 Demonstrated that Particles Remained in Suspension Recovered slurry of ZVI nanoparticles (0.33 g/l) from a push-pull test Remarks: Slurry remains dark ZVI nanoparticles remain fully suspended

15 ethene, ethane (umol/l) Field Test 1: Stabilized nzvi demonstrated TCE dechlorination, producing daughter products C*Br time since midpoint of injection (minutes) ethene ethane 1-C*Br

16 Field Test 2: Treatment of TCE and PCBs in groundwater The field test site and equipment for field preparation and injection of CMCstabilized Fe-Pd nanoparticles A sample bucket of the CMCstabilized Fe-Pd suspension taken from the reactor

17 Field Test 2: TCE was significantly reduced in downgradient monitoring wells Concentrations of TCE, PCE, cis-dce, VC, and PCB 1242 in groundwater over time C/C PCB 1242 PCE TCE cis-dce VC C/C PCB 1242 PCE TCE cis-dce VC Time, days MW-1 (5 feet downgradient of the injection well) Time, days MW-2 (10 feet downgradient of the injection well).

18 DoD nzvi Demonstration Project AFCEE BAA Project Field demonstration of green, stabilized Fe-Pd nanoparticles to treat chlorinated solvents in soil and groundwater Project Profile: Project Start/Finish: September 2009/September 2011 Location of demonstration: Hill AFB, UT OU2 contains 2 unlined trenches where TCE was disposed of from 1967 to 1975 (~45,000 to 50,000 gallons) Demonstration site contains high concentrations of TCE in the groundwater as a small hotspot (21.5 mg/l) in 2009

19 Technical Objectives Test the feasibility (mobility and reactivity) of using stabilized nanoparticles for degrading chlorinated solvents under AF field conditions Quantify the effects of field environmental conditions, soil type, and properties on process effectiveness and validate benchscale experimental data Determine appropriate operating conditions, i.e., injection pressure, superficial liquid velocity (SLV), and iron dosage Generate field-scale process cost and performance data for general end-user acceptance

20 Technical Approach Stabilized Fe-Pd bimetallic nanoparticles using green and low-cost starch and cellulose (CMC) as a stabilizer will be prepared on-site and injected into the target volume to treat chlorinated solvents in groundwater and soil This project is evaluating the following: Can the particles be easily delivered into the subsurface and be effectively dispersed in the target zone? Can the particles treat chlorinated solvents in soil and groundwater? Can the particles be prepared and injected in a system that is cost effective? through laboratory testing using soil and groundwater from the demonstration site and field testing at the demonstration site

21 Site Plan Demonstration Area

22 Proposed Well Layout

23 Schematic Cross Section of Hill AFB, OU2

24 Geologic Cross Section of the Demonstration Area

25 Sample Depth (feet above mean sea level) Sample Depth (feet below ground surface at SB-1) Concentrations of Volatile Organic Compounds (VOCs) in Soil 4665 approximate water table depth interval with sand seams SB-1 PCE SB-1 TCE SB-2 PCE SB-2 TCE SB-3 PCE SB-3 TCE Concentration (mg/kg) Note: 1. The soil samples were collected on November 18, 2009 with Geoprobe Dual-Tube system following EPA Method Abbreviations: 1. PCE = tetrachloroethene 2. TCE = trichloroethene

26 Groundwater Level (feet below ground surface) Groundwater Purging Test Results Pumping rate = 0.38 L/min Pumping rate = 0.28 L/min Pumping rate = 0.40 L/min Pumping rate = 0.40 L/min Pumping rate = 0.40 L/min Pumping rate = 0.38 L/min Pumping rate = 0.38 L/min Pumping rate = 0.21 L/min Pumping rate = 0.21 L/min Notes: Time (minutes) 1. The purging test data were collected on November 18, 2009 with a peristaltic pump and an electric sounder. 2. The groundwater level was 16.4 feet below ground surface before purging. 3. The purging test was carried out in the existing well U2-085 (screen interval: feet below ground surface). 4. The pumping rates were measured by filling an one-liter bottle and recording the time with a stopwatch.

27 Status of Laboratory Testing Completed characterization of site soil and groundwater Investigating methods for field measurement of nzvi Hydrogen Production Method Spectrophotometric Method Filtration Method ConductingTreatability Tests Prepared optimized CMC-stabilized nanoparticles Completed batch tests to evaluate TCE degradation Conducting column tests to further evaluate TCE degradation and delivery and distribution of nanoparticles and biodegradation of stabilizer

28 Laboratory Testing Summary of Results Site groundwater and soil characterization TCE is the main chlorinated contaminant in groundwater with a concentration of 14.3 mg/l ph = 7.81, TOC = mg/l, alkalinity = 711 mg/l, electrical conductivity = 1.2 mmhos/cm The hydraulic conductivity of the unconfined aquifer is ~1 foot per day Investigating a method for field measurement of nzvi Spectrophotometric method can be used to measure solid particle concentration in a suspension, but can t distinguish nzvi from iron oxide A filtration method with 100 nm (pore size) membrane filter is being investigated A method measuring volume of hydrogen gas produced by acidifying the nzvi suspension is being investigated Treatability Test TCE is completely removed from site groundwater within three hours with nzvi = 0.34 g/l, Pd/Fe = 0.1% by weight, CMC = 0.16% by weight

29 Plans for Field Testing Design basis for nanoparticle injection Total mass of TCE in the test area is estimated to be approximately 102 g A total of 5,220 g of nanoparticles are planned to be injected, which is 30 times greater than what is needed to react with 102 g TCE based on a stoichiometric calculation Three rounds of injection are planned, each spaced one month apart to address potential TCE rebound Planned well installation Four demonstration wells (DW-1 through DW-4) are to be installed in the vicinity of existing wells U2-085 and U2-084

30 Field Testing.. Baseline testing and groundwater sampling Slug tests Baseline groundwater sampling On-site preparation and injection of nanoparticles Iron-palladium bimetallic nanoparticles Groundwater will be recirculated between upgradient injection well and downgradient extraction well Pressure injection may be used to enhance particle delivery Injection monitoring Post-injection groundwater and soil monitoring Post-injection monitoring will be conducted for one month after each of the first two injection events and three additional monitoring events will be conducted one month, five months, and one year, respectively, after the end of the third injection event.

31 Questions?