Remediation of soils containing chlorinated solvents

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Remediation of soils containing chlorinated
solvents
Eduardo SáezDepartment of Chemical and
Environmental Engineering, The University of
Arizona, Tucson, AZ
Phoenix, 6 March 2008
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Trichloroethylene (TCE)
Perchloroethylene (PCE)
Cl
Cl
Cl
Cl
CC
CC
Cl
H
Cl
Cl
Degreasing solvent Machine cleaning Airplane
cleaning Before 1970s Coffee
decaffeination Vegetable oil extraction
Degreasing solvent Dry cleaning
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Toxicity (TCE and PCE)
Type 2A carcinogen (probable human carcinogen)
Central nervous system depressant
Liver and kidney damage
Increased chance of miscarriage
Maximum contaminant limit 5 ppb (drinking water)
Occupational exposure standards (inhalation)
250-2500 ppb (odor threshold for TCE 28000 ppb)
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1 ppb 1 part per billion
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Soil Vapor Extraction (SVE)
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Why does SVE work?
TCE and PCE (and other organics that are usually
encountered with them) are Volatile Organic
Compounds (VOCs) At 20?C, 1 m3 of atmospheric
air can hold a maximum of 17 g of water 380 g
of TCE 203 g of PCE
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Other Remediation Options
Thermal remediation (enhanced SVE) In situ
processes Bioremediation Flushing
(surfactants) In situ oxidation (injection of
permanganate, etc.) Permeable reactive barriers
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Park-Euclid Plume
Yellow contours represent PCE concentration in
groundwater from 100 ppb to 1 ppb
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Granular Activated Carbon (GAC) Adsorption
Released into atmosphere
GAC Column

• Common Remediation Technology
• Requires SVE
• Downside
• Non-destructive
• High restoration/disposal cost

Vadose Zone
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Catalytic Removal
Released into atmosphere

• Proposed Remediation Technology
• Requires SVE
• Destructive Technology

Pt/Rh Catalyst
Vadose Zone
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Catalytic Destruction of PCE Options
CO2
Oxidation
Cl
Cl
CC
C2H6 (ethane)
Cl
Cl
Hydrogenation
Other products Cl2, HCl
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Oxidation
Concern production of dioxins
MCL 0.03 ppt (drinking water)
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Catalytic Converter

• Commercially available catalyst
• Noble metal/metal oxide combinations (Pt/Rh and
  Pd/Rh with Al2O3 and/or Ce2O3 )
• 3 way catalytic converter
• 1981
• 2CO O2 ? 2CO2
• HC O2 ? CO2 H2O
• NOx ? N2 O2

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Process Aspects

• Problems
• Oxidation production of dioxins and furans
• Hydrogenation (reduction) catalyst poisoning
• Solution
• Use both oxidation/reduction conditions at the
  same time
• ? Hydrogenation requires hydrogen
• Solution
• Use common hydrocarbons (i.e. propane) as
  alternative

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Field Process Flow Diagram
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Field Extended Operation

• 100 Lpm Flow Rate
• SVE Gas
• 2 C3H8 (vol)
• 0.2 s Residence Time
• 520 oC Catalyst Temperature

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Conclusions

• Pt/Rh 3-way catalysts can effectively destroy
  PCE, TCE in gas streams
• Alternative to non-destructive technologies
• Short-chain alkanes are effective alternatives to
  H2 for hydrogenation
• Propane provides the best combination of
  effectiveness and cost
• Harmless products (ethane, some methane, CO2)