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Biodegradation Processes for Chlorinated Solvents Cive 7332 Lect 6

Biodegradation Processes for Chlorinated Solvents Cive 7332 Lect 6. Stripping halogens (generally Chlorine) from an organic molecule Generally an anaerobic process, and is often referred to as reductive dechlorination R–Cl + 2e – + H + ––> R–H + Cl – Can occur via

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Biodegradation Processes for Chlorinated Solvents Cive 7332 Lect 6

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  1. Biodegradation Processes for Chlorinated SolventsCive 7332Lect 6

  2. Stripping halogens (generally Chlorine) from an organic molecule Generally an anaerobic process, and is often referred to as reductive dechlorination R–Cl + 2e– + H+ ––> R–H + Cl– Can occur via Dehalorespiration (anaerobic) Cometabolism (aerobic) Dehalogenation

  3. 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 Dehalorespiration

  4. CCl =CCl PCE CHCl=CCl TCE CHCl=CHCl 1,2 DCE CH =CHCl VC H H H Reductive Dechlorination ofChlorinated Ethenes 2 2 2 2 H Ethylene CH = CH CO Carbon dioxide 2 2 2

  5. 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 Added Danger

  6. Fortuitous transformation of a compound by a microbe relying on some other primary substrate Generally a slow process - Chlorinated solvents don’t 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) Cometabolism

  7. CCl =CHCl Cl C CHCl CO , Cl ,H O NADH, O 2 CO , H O Primary Reaction CH 2 2 4 O MMO - 2 2 2 2 NADH, O Secondary Reaction 2 Cometabolic Transformations ofChlorinated Aliphatic Hydrocarbons (CAHs)

  8. 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

  9. Dechlorination Zones

  10. Natural Attenuation Will it work for Chlorinated Solvents?

  11. 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

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

  13. 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

  14. Enhanced Bioattenuation of Chlorinated Solvents • Inadequate electron donor concentrations • Determine methods of adding electron donors

  15. Electron Donor Addition To: • Treatment • Treatment / Recycle • Recycle Injection Well Recovery Well Nutrient Addition (if necessary) DNAPL In Situ Biodegradation Zone In Situ Biodegradation of Chlorinated Solvents

  16. Enhanced Bioattenuation Petroleum Chlorinated Technology Hydrocarbons Solvents (e– acceptor) (e– donor) Liquid Delivery Oxygen Benzoate Nitrate Lactate Sulfate Molasses Carbohydrates Biosparge Air (oxygen) Ammonia Hydrogen Propane Slow-release Oxygen Hydrogen (ORC) (HRC)

  17. 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

  18. 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

  19. 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 Hydrocarbon Methanol Wastewater contaminants Molasses Yeast extract Mulch

  20. 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)

  21. 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 4 2 4

  22. 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 ? Williamsport, PA Nyer & Suthersan 1996 3+

  23. 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

  24. Blower Hydrogen gas Vapor Treatment SVE Well DNAPL Tiny Bubbles Hydrogen Sparging Promotes in situ biodegradation - Minimize hydrogen gas entering unsaturated zone

  25. 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

  26. 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

  27. Hydrogen Releasing Compound (HRC ) ®

  28. 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

  29. 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”

  30. Substrates for Bioattenuation of CAHs (Lee et al, 1998) “No substrate that reliably supports complete dechlorination at all sites has been identified to date.”

  31. Delivery of materials to the subsurface (contact) Bioavailability of the contaminants Toxicity of contaminants Threshold substrate concentration Limitations for Applicationof Bioattenuation Technologies

  32. Methane Oxygen Sorption / Desorption 10 1 0.1 Dissolution Contact in the Subsurface

  33. Toxicity of Trichloroethylene Air or water in contact with oily phase may exceed toxic limit for microorganisms TCE: > 6 mg/L in water (30% reduction = 1.8 mg/L; Moffett field) > 2 mg/L in air

  34. 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

  35. What We Don’t 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?

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

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