The basic science of anaerobic bioremediation Dan Leigh PG, CHG June 4, 2013 Introduction: Dan Leigh – Licensed geologist and hydrogeologist – Walnut Creek, CA – Applying bioremediation for > 25 yrs – Applying anaerobic bioremediation of chlorinated organics for >20 yrs – Currently working on development of biogeochemical processes occurring during anaerobic bioremediation – [email protected] – 925.984.9121 Basic Science of Anaerobic Bioremediation 2 FMC provides a wide range of products for application of anaerobic bioremediation, biogeochemical and abiotic degradation EHC® Solid organic substrate with microscale ZVI EHC-L ® Liquid organic substrate with soluble Fe(II) ® ® EHC with sulfur source for biogeochemical EHC-M metals treatment ® Emulsified Lecithin Substrate for ELS enhancement of anaerobic bioremediation ® Solid organic substrate with ZVI for Daramend treatment of contaminated soils http://environmental.fmc.com/solutions Basic Science of Anaerobic Bioremediation 3 Presentation outline • Basic concepts of biological and geochemical processes – Respiration, fermentation, co metabolism – Electron donors and acceptors – Biotic and abiotic anaerobic degradation pathways of chlorinated ethenes – Processes for stimulating anaerobic bioremediation of chlorinated organics • Significant site conditions not conducive to anaerobic bioremedation and how to overcome them – Inappropriate or insufficient bacteria – High dissolved oxygen – Low pH – High sulfate concentrations • Biogeochemical degradation • Summary Basic Science of Anaerobic Bioremediation 4 Contaminants that can be degraded by anaerobic processes • Chlorinated solvents such as PCE, TCE, TCA, DCA, CCl4, chloroform and methylene chloride • Chlorobenzenes including di- and tri-chlorobenzene • Energetic compounds such as TNT, DNT, HMX, RDX, nitroglycerine and perchlorate. • Most pesticides including DDT, DDE, dieldrin, 2,4-D and 2,4,5-T • Nitrate compounds • Petroleum hydrocarbons This presentation focuses on biological and geochemical processes that occur during the in situ anaerobic degradation of chlorinated ethenes. Basic Science of Anaerobic Bioremediation 5 Bioremediation is a natural and sustainable remediation process. Bioremediation utilizes the life processes of organisms to reduce the concentration, mass, mobility or toxicity of contaminants. – Yeast, fungi, bacteria or plants are stimulated to degrade toxic substances. – The primary processes include respiration and fermentation. – Not a new technology – • e.g. wastewater treatment – Improvements to bioremediation approaches are being developed. Basic Science of Anaerobic Bioremediation 6 Basic concepts of biological and geochemical processes • Several biological processes occur during anaerobic bioremediation including: – Respiration: Aerobic and Anaerobic – Fermentation – Co-metabolism • Abiotic processes can be integrated, or occur naturally, which enhance biological degradation processes. • Biotic and abiotic anaerobic degradation processes occur in distinct, identifiable pathways. Basic Science of Anaerobic Bioremediation 7 Respiration processes Eating and breathing Electron Electron Organism Donor Acceptor Respiration Aerobic Respiration Aerobic Respiration Basic Science of Anaerobic Bioremediation 8 Aerobic and anaerobic respiration • Aerobic respiration – Molecular oxygen (O2) is the only electron acceptor used in the process • Anaerobic respiration – Any inorganic electron acceptor (other than oxygen) is used in the respiration process • NO3, Mn(IV), As(V), Fe(III), SO4, CO2 • Cr(VI), ClO4 Basic Science of Anaerobic Bioremediation 9 Respiration Biologically Mediated Oxidation - Reduction Work Growth Light bulb Protein Synthesis Motors Reproduction Resistor Electron Donor Electron Acceptor Negative Positive Reduced Oxidized O CnHn Fe(II) 2 Fe (III) NO HNO2 3 H2S SO4 As(III) As(V) CO H2 2 Mn(II) Mn(IV) Basic Science of Anaerobic Bioremediation 10 Eh range for various electron acceptors 2- + - 3+ 0 Chromium (VI ) Cr2O7 + 14H + 6e 2Cr +7H O (Eh = +1330) 1000 2 Transfer Anaerobic + - 0 Aerobic Oxygen O2 + 4H + 4e 2H2O (Eh = +820) - + - 0 Electron Anaerobic Nitrate 2NO3 + 12H +10e N2(g) + 6H2O (Eh = +740) + - 0 Arsenic (V) H3AsO4 + 2H +2e H3AsO3 + H2O (Eh = +559) + - Manganese (IV) MnO2(s) + HCO3 +3H + 2e MnCO3 (s) + 2H20 500 (Eh0 = +520) Redox Potential (Eh0) in Millivolts @ pH = 7 and T = 250C 0 Iron - - 0 - FeOOH(s) +HCO3 + 2H+ e FeCO3 + 2H2O (Eh = 50) Sulfate SO 2- + 9H+ + 8e- 0 - 4 HS- + 4H2O (Eh = 220) Decreasing Amount of Energy Released During During Released of Energy Amount Decreasing + - 0 - -250 Methanogenesis CO2 + 8H + 8e CH4 + 2H2O (Eh = 240) Basic Science of Anaerobic Bioremediation 11 Anaerobic respiration and chlororespiration Electron Electron Biota Donor Acceptor Respiration Mn(IV) NO3 AnaerobicAerobic Fe(III) RespirationRespiration SO4 CO2 Chlororespiration Basic Science of Anaerobic Bioremediation 12 Eh range for cholorinated ethene degradation 2- + - 3+ 0 Chromium (VI ) Cr2O7 + 14H + 6e 2Cr +7H O (Eh = +1330) 1000 2 Transfer Anaerobic + - 0 Aerobic Oxygen O2 + 4H + 4e 2H2O (Eh = +820) - + - 0 Electron Anaerobic Nitrate 2NO3 + 12H +10e N2(g) + 6H2O (Eh = +740) + - 0 Arsenic (V) H3AsO4 + 2H +2e H3AsO3 + H2O (Eh = +559) + - Manganese (IV) MnO2(s) + HCO3 +3H + 2e MnCO3 (s) + 2H20 500 (Eh0 = +520) Redox Potential (Eh0) in Millivolts @ pH = 7 and T = 250C 0 Iron FeOOH(s) +HCO - + 2H+ e- 0 - 3 FeCO3 + 2H2O (Eh = 50) Range for Effective PCE TCE Chlorinated Ethene Degradation TCE DCE (chlororespiration) DCE VC Sulfate SO 2- + 9H+ + 8e- 0 - 4 HS- + 4H2O (Eh = 220) VC Ethene Decreasing Amount of Energy Released During During Released of Energy Amount Decreasing ↓ + - 0 - -250 Methanogenesis CO2 + 8H + 8e CH4 + 2H2O (Eh = 240) Basic Science of Anaerobic Bioremediation 13 Many organisms generate energy by fermentation rather than respiration • Fermentation refers to the conversion of sugar to acids, gases and/or alcohol using yeast or bacteria. • Fermentation does not use an electron transport chain (e.g. O2, NO3, Mn(IV), SO4, CO2) as does respiration. • Fermentation uses a reduced carbon source (e.g., cellulose, lecithin, lactose, sugars). – to generate volatile fatty acids ((VFAs) e.g. lactic, acetic, propionic, valeric, butyric acids) – and gases (e.g. H2, CO2, CH4) • H2 is used by dechlorinating bacteria to generate energy by sequentially reducing chlorinated organics. Basic Science of Anaerobic Bioremediation 14 A note about co-metabolic oxidation The microbial breakdown of a contaminant in which the contaminant is oxidized incidentally by an enzyme or cofactor that is produced during microbial metabolism of another compound is called aerobic/anaerobic co-metabolism. – Co-metabolic oxidation applies respiration processes: • Electron donor: (e.g., methane, ethane, ethene, propane, butane, toluene, phenol, ammonia) PLUS: electron acceptor (e.g, O2, SO4) – Enzymes generated to degrade food source also fortuitously degrades CEs or other contaminants. – The degrading organism does not gain energy from the contaminant degradation. – The presence of electron donor may inhibit contaminant degradation. Co-metabolism can be a challenge to apply. – Often requires substantial engineering effort – It is difficult to identify co-metabolic degradation in the aquifer – May not be an efficient use of substrate Basic Science of Anaerobic Bioremediation 15 Dechlorinating bacteria • Several organisms capable of partially dechlorinating chlorinated organics. • Only organism confirmed to dechlorinate DCE and VC to ethene is Dehalococcoides (Dhc). • Dhc uses H2 as the electron donor in dechlorination process. Basic Science of Anaerobic Bioremediation 16 Biological Reductive Dechlorination of Chlorinated Ethenes ORP 0 - 50 H HCl HCl H H ClH HCl H H ClH HCl H C C C C C C H H H ClH H H H ClH - 150 Cl HCl H Cl HCl H cis Ethene1,2TCEPCEVC -DCE transEthenePCETCEVC 1,2 -DCE 1,1EthenePCETCEVC - DCE - 200 - 250 Basic Science of Anaerobic Bioremediation 17 β elimination (abiotic) pathway Fe Fe Fe 0 0 0 Hydrogenolysis Hydrogenation II II II Cl Cl Cl H H H C C C C C C Cl Cl Cl Cl Cl Cl DichloroacetylenePCE ChloroacetyleneAcetyleneTCE AcetyleneDCEEtheneEthane Basic Science of Anaerobic Bioremediation 18 Some Hypothesized Reaction Pathways Biotic Abiotic PCE PCE TCE TCE Dichloroacetylene Cis 1,2-DCE Trans 1,2-DCE 1,1-DCE, trans 1,2-DCE, cis1,2-DCE VC Chloroacetylene VC Ethene Ethene Acetylene Ethane Ethane CO2, CH4,H2O CO2 , CH4 , H2O α-elimination Hydrogenolysis β-elimination Hydrogenation Basic Science of Anaerobic Bioremediation 19 Biological and abiotic degradation processes appear different when measuring standard analytical parameters Anticipated change in CE molar concentration Biological Degradation Abiotic Degradation (Chlororespiration) (β elimination) Concentration Concentration Time Time PCE TCE DCE VC Ethene Total Basic Science of Anaerobic Bioremediation 20 Generating anaerobic bioremediation processes Enhanced anaerobic bioremediation is conducted by providing whatever is limiting the complete degradation process. Electron Electron Organism Chlororespiration Donor Acceptor Need appropriate organism and electron donor (H2) to degrade CEs Other supplements can be made to further enhance the anaerobic process. – Chemical reductants (e.g. ZVI, ferrous iron) – Nutrients Additional supplements can be made to enhance synergistic effects. – Sulfate – Iron Basic Science of Anaerobic Bioremediation 21 Anaerobic reductive dechlorination is stimulated by providing an electron donor to the organisms Various substrates