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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 Analysis Fundamental Chemistry Bench-scale Treatability Studies - PowerPoint PPT Presentation
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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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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
1
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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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