1 In-Situ Treatment of Groundwater with Non-aqueous Phase Liquids December 10-12, 2002, Chicago, IL Scott G. Huling, Ph.D., P.E. USEPA Robert S. Kerr Environmental.

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In-Situ Treatment of Groundwater with Non-aqueous Phase Liquids

December 10-12, 2002, Chicago, IL

Scott G. Huling, Ph.D., P.E.USEPA Robert S. Kerr Environmental

Research Center, Ada OK

In-Situ Fenton Oxidation: A Critical AnalysisFundamental ChemistryBench-scale Treatability StudiesField-scale Applications (pilot- or full-scale)Fate and Transport Issues

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Fenton and Related ReactionsH2O2 + Fe+2 Fe+3 + OH- + ·OH (1)

H2O2 + Fe+3 Fe+2 + ·O2- + 2 H+ (2)

·O2- + Fe+3 Fe+2 + O2 (3)

·OH + Contaminant Products (CO2, Cl-, etc.) (4)Scavenging reactions n

i=1 ki

·OH + ni=1 Si products of scavenging rxn (5)

Nonproductive reactions2 H2O2 + reactants O2 + 2 H2O (6)

Miscellaneous optimum pH 3-4; metals mobility;

exothermic; stabilizers

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Potential Limitations of Fenton Oxidation

1. Non-productive reactions2. Scavenging3. Low reaction rates4. Insufficient Fe5. pH adjustment 6. Oxidant, iron, acid, stabilizer transport7. O2(g) production8. Undesirable reaction byproducts9. Enhanced volatilization and transport

10. Unreactive target compounds

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Cross-section of hazardous waste spill/release

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Bench-scale Treatability Study Objectives

High Priority1. Proof of concept – quantify extent of

oxidation given potential limitations2. Determine reaction byproducts3. Metals mobility

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Bench-scale Study Guidelines

1. Components: soil, ground water, reagents 2. Capture and quantify losses from the reactor3. pH change4. Monitoring parameters: target, byproducts,

metals 5. Control6. Establish pre-, post-oxidation concentrations 7. Perform pre-, post-oxidation mass balance

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Field-Scale Application Guidelines

1. Injectate volume vs. pore volume target area 2. H2O2 concentration 3. pH adjustment4. Pulse injection of Fe(II) and H2O2

5. Injection strategy

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H2O2 Reaction, Subsurface Transport[H2O2(t)] / [H2O2]O = exp(–KH2O2 R2 π Z η / Q)

(After, Clayton, 1998)

Flow, well spacing, pH

0

0.2

0.4

0.6

0.8

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1.2

0 0.2 0.4 0.6 0.8 1 1.2

Radial Distance (m)

C (t

) / C

0

12 L/min

4 L/min

kH2O2 = -0.91/hr

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Other Chemical Reagents

Reactions/interactions

Fe(II) - precipitation, complexation, oxidationAcid - consumed by acid neutralizing capacity Stabilizers (H2O2, Fe(II)) - precipitation,

complexation, oxidation

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K = 100 ft/day

K = .0001 ft/day

K = 0.1 ft/day

Diffusion

Advection

Avg. K = 10 ft/day

K = .01 ft/day

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Non-ideal Conditions Need to be Considered

Preferential pathways - greater rate of transport and oxidant delivery occurs through high conductive zones

Lower permeability zones - diffusion dominated transport << H2O2 reaction

Multiple applications

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Transport Issues

Representative volume Heat and O2(g) released - impact

Pneumatic transport of ground water Decreased DNAPL visc., increased mobilityDNAPL evaporationVolatilization of DNAPL componentsThermal desorption from the solid phaseEnhanced H2O2 decomposition

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Ground waterflow

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SVE is a Complimentary Technology to Fenton Oxidation

Capture/treat/dispose volatiles SVE may already be part of the remedyMinimize the transport/uncontrolled lossMinimize potential exposure pathwaysVent wells for deeper systems

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Performance Monitoring

Preferred monitoring parameters:target compound - aqueous (rebound: long

term vs. immediate), solidreaction byproducts - aqueousMetals - aqueousH2O2 - aqueous

Off-gas, soil gas samplesEstablish sentry wells

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… performance monitoringGround water monitoring

Low priority - limited value for performance evaluation

CO2

DOTOC CODConductivityORPTemperature

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Effects of ISFO on Natural Attenuation?

1. H2O2 - antiseptic, heat 2. Heterogeneity - microniches, preferential pathways3. Improvement in post-oxidation biodegradation4. Microbial sensitivity5. Population changes6. Toxicity response

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Health and Safety

Heat released O2(g) released + Flammable vaporsEnhanced volatilization Accumulation of vapors (buildings, utilities)

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Conclusions

Hydroxyl radical – strong oxidantPotential limitationsNumerous parameters influence success/failureMonitoring parameters/approach – key to successful

performance evaluationEnhanced transport processesRecognize/capture volatile emissions

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Scavenging Analysis

Target contaminant oxidation reaction: k OH + C reaction byproducts

Scavenger oxidation reaction: ki

OH + Si reaction byproducts

Reaction rate equations: D[C]/dt = k OH [C] D[Si]/dt = iki OH [Si]

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Relative Reaction Rates

Relative rate of reaction (RR) between OH and Si, and OH and C

RR = (iki [OH] [Si]) / (k [OH] [C])

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Example 1

[TCE ] = 450 g/L (3.42×10-6 M); k = 4.2×109 L/mol-s [Cl-] = 1250 mg/L (3.52×10-2 M); k = 4.3×109 L/mol-

s[CO3

2- ] = 150 mg/L (2.5×10-3 M); k = 3.9×108 L/mol-s[·OH] assume 10-15 M

RR = 10,600

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Example 2

[PCE ] = 4.15 mg/L (2.5×10-5M); k = 2.6×109 L/mol-s [Cl-] = 45 mg/L (1.27×10-3M); k = 4.3×109 L/mol-s[H2O2]= 50% , 500,000 mg/L (1.47×101M); k = 2.7×107 L/mol-s[·OH] assume 10-15 mol/L

RR = 6,180