treatment technologies in-situ soil vapor extraction (s) solidification/stabilization (s) soil...
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Treatment Technologies
In-Situ Soil Vapor Extraction (s) Solidification/Stabilization (s) Soil Flushing (s) Electrokinetic Separation (s) Bioventing (s) Enhanced Bioremediation (s,gw) Phytoremediation (s,gw) Chemical Oxidation (s,gw) Thermal Treatment (s, gw) Monitored Natural Attenuation
(s,gw) Air Sparging (gw) Bioslurping (s,gw) Dual Phase Extraction (s,gw) In-Well Air Stripping (gw) Passive/Reactive Treatment Walls
(gw)
Ex-Situ Biopiles (s) Landfarming (s) Slurry Phase Biological Treatment (s) Chemical Extraction (s) Soil Washing (s) Solidification/Stabilization (s) Incineration (s) Thermal Desorption (s) Excavation, Retrieval, and Off-Site (s) Chemical Reduction/Oxidation (s,gw) Bioreactors (gw) Constructed Wetlands (gw) Adsorption/Absorption (gw) Advanced Oxidation Processes (gw) Air Stripping (gw) Granulated Activated Carbon (GAC)
(gw)
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Groundwater Remediation Approaches 1990s Technologies:
Air Sparging/Soil Vapor ExtractionTwo-Phase Extraction (Bioslurping)Permeable Reactive BarrierHRC-ORC (Enhanced Bioremediation)
“New Millenium” Methods:Air/Ozone SpargingIn-well Air StrippingPhytoremediationIn situ Thermal TreatmentChemical Oxidation
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Air Sparging / Ozone Injection
Air sparging = air blown into groundwater
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Air Sparging / Ozone Injection
Advantages:Active, in-situ treatment of groundwater CVOCsOff-the-shelf system for pilot studiesNo ex-situ groundwater treatment or discharge
Limitations:Short-circuiting to surface or adjacent wellsVariable conductivity can impact effectivenessRequires electrical powerCan have high O&M/equip replacement costs
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In-well Air Stripping Also “GW circulation
wells” (GCW) Dual casing and screen
allow air to be blown in and stripped water to be recirculated
Stripped VOCs captured by vacuum extraction system
VOCs in air need treatment (GAC?)
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In-well Air Stripping
Advantages:Captures most VOC vaporsRadius of influence 3-5 times > sparge wellsWorks in deep aquifers
Limitations:Recovered vapors may need treatmentWorks only for VOCs and a few SVOCs
Clayey horizons will limit recirculationSusceptible to iron bacteria and scaling
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Phytoremediation
GroundwaterTransport Out
GroundwaterTransport In
Plant Exposure(Dissolved Phase)
Degradation in Groundwater
Foliar DepositionDegradation in
PlantAccumulation in Plant Tissue
Surface Emissions
Transpiration
Degradation inRhizosphere
Volatilization from
Groundwater
Plant Exposure(Vapor Phase)
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Phytoremediation Applicability:
Will not work below root zone (trees <20 ft) Advantages:
Works for most metals, VOCs, and SVOCsCan control erosion and gw flowGood for chemicals in shallow perchedaquifers
Limitations:Slow when new compared to active methodsPlants die in toxic groundwater
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In Situ Thermal Treatment
Thermally enhanced SVE technology using hot-air/steam or electrical resistance (SPEH)/ electromagnetic/ radio frequency heating (RFH)
Stripped SVOCs and VOCs captured by SVE
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In Situ Thermal Treatment
Advantages:Can enhance poor soil conditionsWorks in high moisture/poor soil conditionsCan treat SVOCs, VOCs, fuels, pesticides
Limitations:Recovered vapors need treatmentCan be self-limiting (soil too dry)High O&M costs
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In-Situ Chemical Oxidation (ISCO)
Strong oxidizers can degrade chlorine bond
Strong oxidizers used for TCE: KMnO4, H2O2, ozone, Fenton’s reagent
Chem-ox potentially applicable to TCE at many sites with shallow groundwater KMnO4 pilot test for TCE
in groundwater at Warren AFB
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Contaminants Treated by ISCO
BTEX MTBE TPH 1,1,1-TCA DCA PCE TCE DCE vinyl chloride
1,4-dioxane PAHs carbon
tetrachloride chlorinated
benzenes phenols munitions (RDX,
TNT, MHX) PCBs
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In-Situ Chemical Oxidation Advantages:
Faster removal time than HRC/ORCMCLs reached in days, not yearsExpensive equipment not needed to injectNo O&M cost after last injection
Limitations:Very high CVOC concentrations may not degrade Multiple treatments if high Fe, CO3 and SO4
Chemicals more expensive than air or ozone
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Five Major Oxidants
Permanganate (KMnO4 or NaMnO4)
Peroxide (H2O2)
Persulfate (S2O82-)
Ozone (O3)
Percarbonate (CO32-)
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Permanganate Chemistry
Electron transfer reaction
PCE Oxidation4KMnO4 + 3C2Cl4 + 4H2O
6CO2 + 4MnO2(s) + 4K+ + 12Cl- + 8H+
TCE Oxidation2KMnO4 + C2HCl3 2CO2 + 2MnO2(s) + 3Cl- + H+ + 2K+
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Permanganate Application
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Peroxide
Hydrogen peroxide alone is an oxidant unable to degrade most contaminants before
decomposition 2H2O2(aq) 2H2O + O2(g)
kinetically slow
Addition of ferrous iron dramatically increases oxidative strength
H2O2 + Fe2+ “Fenton’s Reagent”
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Fenton’s Reagent Application
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Persulfate Chemistry
Direct oxidation through electron transfer:
3NaS2O8 + C2HCl3 + 4H2O 2CO2 + 9H+ + 3Cl- + 3Na+ +
6SO42-
Sulfate free radical reactions Chain-initiating Chain-propagating Chain-terminating
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Persulfate Application
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Ozone Chemistry
Two types of reactions direct oxidation by O3
indirect oxidation, OH radical
Indirect oxidation is faster Radical reactions
Chain-initiating Chain-propagating Chain-terminating
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Ozone Application
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Percarbonate
Proprietary product, RegenOxTM
Similar to Fenton’s Reagent, though Less exothermic Longer lasting No gas production
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Oxidant Comparison
Permanganate
(potassium)
Fenton’s Reagent
Persulfate Ozone
Strength 1.7 volts 2.8 and 1.8 volts
2.5 and 2.0 volts
2.8 and 2.1 volts
Contaminants Treated
Short list – ethenes, munitions; no TCA, BTEX?
Long list – BTEX, MTBE, ethenes, TCA and 1,4-dioxane
Moderate list – BTEX, ethenes, TCA and 1,4-dioxane; limited data
Moderate list – BTEX, MTBE, ethenes; no TCA or 1,4-dioxane unless H2O2 combo
SOD Reactivity
high low low low
Handling Issues
-chemical-dust
- chemical- explosion- pressure
- chemical - chemical- explosion
Ease of Injection
Easy - one solution, no off-gas
Difficult – 2 solutions, off-gas
Moderate – 2 solutions, no off-gas
Moderate – sparge system, no liquids
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Oxidant Comparison
Permanganate
(potassium)
Fenton’s Reagent
Persulfate Ozone
Persistence Long (direct) Short (OH radical)
Long (direct)Short (SO4 radical)
Short (OH radical)
Residuals MnO2 solid oxygen SulfateSulfuric acid
oxygen
Oxidant Cost
$1.60 - $2.00/lb
$0.59/lb (traditional)$4.00/lb (modified-chelate)
$1.08/lb (alone)$1.26/lb (iron chelate)
System costs: $2K to $26K/lb ozone
Predictability
Difficult Difficult Difficult Difficult
Regulatory Acceptance
Yes (UIC waiver)
Yes (UIC waiver)
Yes (UIC waiver)
Yes (UIC waiver)
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Delivery Methods
Direct push drilling and injection Well injection Gravity fee or pressure inject Continuous drip injection Hydraulic fracturing with solid
emplacement
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Important Considerations
Choose oxidant based on site-specific conditions Thoroughly characterize site geology Thoroughly characterize contaminant distribution Pay close attention to delivery method used (and
the potential for good distribution)