Biodegradation Processes for Chlorinated Solvents

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Biodegradation Processes for Chlorinated Solvents
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Dehalogenation

• Stripping halogens (generally Chlorine) from an
  organic molecule
• Generally an anaerobic process, and is often
  referred to as reductive dechlorination
• RCl 2e H gt RH Cl
• Can occur via
• Dehalorespiration (anaerobic)
• Cometabolism (aerobic)

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Dehalorespiration

• Certain chlorinated organics can serve as a
  terminal electron acceptor, rather than as a
  donor
• Confirmed only for chlorinated ethenes
• Rapid, compared to cometabolism
• High percentage of electron donor goes toward
  dechlorination
• Dehalorespiring bacteria depend on
  hydrogen-producing bacteria to produce H2, which
  is the preferred primary substrate

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Reductive Dechlorination ofChlorinated Ethenes

• CCl CCl PCE
• CHClCCl TCE
• CHClCHCl 1,2 DCE
• CH CHCl VC

2
2
2
2
H
Ethylene CH CH
CO Carbon dioxide
2
2
2
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Added Danger

• Dechlorination of PCE and TCE should be
  encouraged, but monitored closely
• The dechlorination products of PCE are more
  hazardous than the parent compound
• DCE is 50 times more hazardous than TCE
• Vinyl Chloride is a known carcinogen

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Cometabolism

• Fortuitous transformation of a compound by a
  microbe relying on some other primary substrate
• Generally a slow process - Chlorinated solvents
  dont provide much energy to the microbe
• Most oxidation is of primary substrate, with only
  a few percent of the electron donor consumption
  going toward dechlorination of the contaminant
• Not all chlorinated solvents susceptible to
  cometabolism (e.g., PCE and carbon tetrachloride)

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Cometabolic Transformations ofChlorinated
Aliphatic Hydrocarbons (CAHs)

• CCl CHCl Cl C CHCl
  CO , Cl ,H O

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Classification System for Chlorinated Solvent
Plumes

• Type 1 Anaerobic due to anthropogenic carbon
• Type 2 Anaerobic due to naturally occurring
  carbon
• Type 3 Aerobic due to no fermentation
  substrates

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Dechlorination Zones
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Natural Attenuation
Will it work for Chlorinated Solvents?
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Natural Reductive Dechlorination

• Natural dechlorination of solvents in aquifers
  with rich organic load and low redox potential
• Not frequently found
• Many chlorinated solvent plumes located in low
  organic load, aerobic aquifers

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Natural Attenuation
Not fast enough Not complete enough Not
frequent enough to be broadly used for some
compounds, especially chlorinated solvents
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Enhanced Bioattenuation

• Engineered system to increase the intrinsic
  biodegradation rate to reduce contaminant mass
• Usually addition of electron acceptors (oxygen,
  nitrate, sulfate) or electron donors (organic
  carbon, hydrogen)
• Could involve bioaugmentation - adding the
  catalyst for bioattenuation

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Enhanced Bioattenuation of Chlorinated Solvents

• Inadequate electron donor concentrations
• Determine methods of adding electron donors

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In Situ Biodegradation of Chlorinated Solvents
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Enhanced Bioattenuation
Petroleum Chlorinated Technology
Hydrocarbons Solvents (e acceptor) (e
donor) Liquid Delivery Oxygen Benzoate
Nitrate Lactate Sulfate Molasses Carbohydra
tes Biosparge Air (oxygen) Ammonia Hydrogen
Propane Slow-release Oxygen Hydrogen
(ORC) (HRC)
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Selective Enhancement of Reductive Dechlorination

• Competition for available H2 in subsurface
• Dechlorinators can utilize H2 at lower
  concentrations than methanogens or
  sulfate-reducers
• Addition of more complex substrates that can only
  be fermented at low H2 partial pressures may
  provide competitive advantage to dechlorinators

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Electron Donors

• Alcohols and acids
• Almost any common fermentable compound
• Hydrogen apparently universal electron donor, but
  no universal substrate
• Laboratory or small-scale field studies required
  to determine if particular substrate will support
  dechlorination at particular site

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Electron Donors
Acetate Hydrogen - Pickle liquor Acetic
acid biochemical Polylactate esters Benzoate
electrochemical Propionate Butyrate gas
sparge Propionic acid Cheese whey Humic acids
- Sucrose Chicken manure naturally occurring
Surfactants - Corn steep liquor Isopropanol
Terigitol5-S-12 Ethanol Lactate Witconol
2722 Glucose Lactic acid Tetraalkoxsilanes Hydroc
arbon Methanol Wastewater contaminants
Molasses Yeast extract Mulch
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Electron Donor Demand

• Theoretical demand for 1 g PCE 0.4 g COD
• Must use many times more substrate due to
  competition for electron donors
• Minimum of 60 mg/L TOC to support dechlorination
  beyond DCE in microcosm studies in Victoria, TX
  soils (Lee et al., 1997)

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Electron Donor Technology in Field-Scale Pilots
Electron Electron Site Reference Donor
Acceptor Benzoate CO Victoria, TX Beeman et al
1994 Beeman 1994 Acetate NO Moffett Air
Field, CA Semprini et al 1992 Schoolcraft,
MI Dybas et al 1997 Yeast Extract SO
/CO Niagara Falls, NY Buchanan et al
1995 Methanol / ? FAA facility, OK Christopher
et al 1997 Sucrose Tergito15-S-12 SO Corpus
Christie, TX Lee et al 1995 Witconol
2722 Methanol ? Breda, Netherlands Spuij et al
1997
2
3
2
4
4
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Electron Donor Technology in Field-Scale Pilots
Electron Electron Site Reference Donor
Acceptor Lactic acid ? Watertown, MA ABB
Environmental Lactate Fe Dover AFB,
DE Grindstaff 1998 Benzoate / Lactate
/ ? Pinellas, Fl US DOE 1998 Methanol Molasses
? Eastern PA Nyer et al 1998 Molasses ? Willi
amsport, PA Nyer Suthersan 1996
3
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Engineered Delivery Systems

• Air injection into vadose zone - venting /
  bioventing
• Air injection into ground water - air sparging /
  biosparging
• Gas, other than air, injection into ground water
  - ammonia, hydrogen, propane
• Slow release into ground water - ORC, HRC
• Liquid addition - infiltration or injection
  wells, surfactant / cosolvent flush
• Recirculation - extraction / reinjection systems,
  UVB wells, pump and treat

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Hydrogen Sparging
Promotes in situ biodegradation - Minimize
hydrogen gas entering unsaturated zone
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Hydrogen Releasing Compound (HRC )

• A food grade polylactate ester slowly degraded to
  lactic acid
• Lactic acid metabolized to acetic acid with
  production of hydrogen
• Hydrogen drives reductive dechlorination

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Hydrogen Releasing Compound (HRC )

• A moderately flowable, injectable material
• Facilitates passive barrier designs
• Slow hydrolysis rate of lactic acid from ester
  keeps hydrogen concentration low, may favor
  reductive dechlorination over methanogenesis

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Hydrogen Releasing Compound (HRC )

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HRC Application

• Delivery Systems - bore-hole backfill or
  injection via direct-push technologies
• Designs for Barriers and Source Treatment
• 1. Upgradient 1
  2 3 4
• barrier
• 2. Series of
• barriers
• 3. Downgradient
• barrier
• 4. Grid of HRC
• injection points

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Substrates for Bioattenuation of CAHs (Lee et al,
1997)
any substrate that will yield hydrogen under
fermentative and/or methanogenic conditions will
... support dechlorination of PCE to DCE if the
microbial population is capable of ... the
dechlorination reaction biotransformation of
DCE to VC and ethene ... not ... universal and
may require specific substrates or enrichment
strategies
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Substrates for Bioattenuation of CAHs (Lee et al,
1998)
No substrate that reliably supports complete
dechlorination at all sites has been identified
to date.
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Limitations for Applicationof Bioattenuation
Technologies

• Delivery of materials to the subsurface (contact)
• Bioavailability of the contaminants
• Toxicity of contaminants
• Threshold substrate concentration

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Contact in the Subsurface
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Toxicity of Trichloroethylene
Air or water in contact with oily phase may
exceed toxic limit for microorganisms TCE
gt 6 mg/L in water (30 reduction 1.8 mg/L
Moffett field) gt 2 mg/L in air
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Maximum Solvent Concentrations for Reductive
Dechlorination
Solvent Concentration Reference (mg/L) PCE
50 Smatlak et al 1996 cis-DCE 8.0 Haston et
al 1994 VC 1.9 - 3.8 DiStefano et al
1991 DCM 66 Freedman Gossett
1991 TCA 100 Galli McCarty 1989
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What We Dont Know

• Should you use a slow, controlled release or
  large/small periodic dosing of electron donor?
• Is it redox reduction or electron donor addition
  that triggers reductive dechlorination?
• Under field conditions, does competion for
  hydrogen exist between dechlorinators,
  methanogens, and sulfate reducers? Does it
  matter?

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Prognosis?
Electron Donor Technology for engineered
bioattenuation of CAHs will equal the impact of
Electron Acceptor Technology on
bioremediation of HCs