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)

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

Air Sparging / Ozone Injection

Air sparging = air blown into groundwater

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

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?)

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

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)

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

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

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

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

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

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

Five Major Oxidants

Permanganate (KMnO4 or NaMnO4)

Peroxide (H2O2)

Persulfate (S2O82-)

Ozone (O3)

Percarbonate (CO32-)

Permanganate Chemistry

Electron transfer reaction

PCE Oxidation4KMnO4 + 3C2Cl4 + 4H2O

6CO2 + 4MnO2(s) + 4K+ + 12Cl- + 8H+

TCE Oxidation2KMnO4 + C2HCl3 2CO2 + 2MnO2(s) + 3Cl- + H+ + 2K+

Permanganate Application

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”

Fenton’s Reagent Application

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

Persulfate Application

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

Ozone Application

Percarbonate

Proprietary product, RegenOxTM

Similar to Fenton’s Reagent, though Less exothermic Longer lasting No gas production

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

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)

Delivery Methods

Direct push drilling and injection Well injection Gravity fee or pressure inject Continuous drip injection Hydraulic fracturing with solid

emplacement

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)