Contaminant Bioremediation

Transcription

1 Contaminant Bioremediation Petroleum hydrocarbons, chlorinated solvents, metals and radionuclides Dr. Al Cunningham Center for Biofilm Engineering Montana State University Bozeman MT USA Natural Attenuation of Petroleum ydrocarbons in Soil and Groundwater Dr. Al Cunningham Center for Biofilm Engineering Montana State University Bozeman 1

2 Fuel ydrocarbon Constituents C 3 C 2 C 3 C 3 C 3 Benzene Toluene Ethylbenzene o-xylene 3 C C 3 C O C 3 C 3 MtBE -C -C -C -C -C -C -C -C- Octane Natural Attenuation Observed reduction in contaminant concentration with migration from source (in soil and groundwater). Includes physical, chemical & biological processes (advection/dispersion, sorption, biotransformation, volatilization) Or dilution, phase partitioning, & destruction 2

3 MNA reduces C and C* For petroleum hydrocarbons the biotransformation process proceeds by: Growth-Promoting biological oxidation of organic compounds. Electrons transferred from electron donors (organic contaminants) to electron acceptors. i.e. (O 2, NO 3-,Fe(III), SO 4-2,CO 2 ) 3

4 Biotransformation fundamentals Organic Carbon Microbial Cell O2 Molecule NO3- SO4- - e- e- Fe3+ Nutrients CO2 Oxidation-reduction If O2 is the electron acceptor Aerobic biotransformation If NO3- (or other) is electron acceptor Anaerobic biotransformation (Aerobic) Organics + Oxygen = CO2 + 2O + new cells (Anaerobic) Organics + NO3- = N2 + CO2 + 2O + new cells Energy Available from Electron Acceptor Processes Electron Acceptor Fe +3 O 2 G o (kj/mol mineralized) Toluene Benzene NO , Mn +4 ~ ~ SO CO

5 Water Chemistry in Biodegradation Reactions Aerobic Respiration of Benzene C O 2 7 CO O red text is measurable constituent Water Chemistry in Biodegradation Reactions Anaerobic Respiration of Benzene Denitrification - C NO N CO O Iron Reduction C Fe(O) Fe CO O red text is measurable constituent 5

6 Water Chemistry in Biodegradation Reactions Anaerobic Respiration of Benzene Sulfate Reduction C SO S + 6 CO O Methanogenesis C O + x CO C CO 2 red text is measurable constituent Oxidation of Petroleum ydrocarbons via Methanogenesis A two-step process involving fermentation and respiration: Step 1) BTEX compounds are fermented by fermentative bacteria to compounds such as acetate and hydrogen. C O 3C 3 COO (Fermentation of Benzene) 6

7 Fermentation. Fermentation is a unique reaction in that it requires no external electron acceptors because the organic compound being degraded acts as both an electron donor and electron acceptor. During fermentation, organic compounds are converted to innocuous compounds such as acetate, water, carbon dioxide, and (most important) dissolved hydrogen through a series of internal electron transfers catalyzed by microorganisms. Oxidation of Petroleum ydrocarbons via Methanogenesis Step 2) By-products (hydrogen and acetate ) used as primary substrates by fermentative and respirative bacteria to produce methane, CO 2 and water. 3C 3 COO 3C 4 + 3CO 2 (Fermentation of acetate) CO 2 3C O (Oxidation Of ydrogen) 7

8 Biodegradation Component of MNA Garrison Fuel Release 8

9 Garrison Fuel Release Garrison Fuel Release 9

10 Garrison Fuel Release Garrison Fuel Release 10

11 Garrison Fuel Release Garrison Fuel Release 11

12 Garrison Fuel Release Garrison Fuel Release 12

13 Garrison Fuel Release Garrison Fuel Release 13

14 Garrison Fuel Release Garrison Fuel Release 14

15 Garrison Fuel Release Relative Importance of Electron Acceptor Processes at 25 Air Force Sites Methanogenesis 39% Aerobic Respiration 10% Denitrification 14% Sulfate Reduction 29% Iron (III) Reduction 8% Source: Wiedemeier et al.,

16 Natural Attenuation of Chlorinated Solvents in Soil and Groundwater Dr. Al Cunningham Center for Biofilm Engineering Montana State University Bozeman Common Chlorinated Solvents Perchloroethene (PCE) 1,1,1-Trichloroethane (TCA) C=C C C Trichloroethene (TCE) C=C 1,1-Dichloroethane (DCA) 1,1-Dichloroethene (DCE) C=C C C 16

17 Degradation Processes for Chlorinated Solvents Abiotic Degradation: ydrolysis 1,1,1-TCA C C + 2 O C C + O Less Chlorine -faster hydrolysis half-life: days- months More Chlorine -slower hydrolysis -half-life: years 17

18 For Chlorinated Solvents the biotransformation process proceeds by: Growth-promoting biological reduction of organic compounds (halorespiration). The organic compound is used as an electron acceptor during reductive chlorination. Dehalorespiration or halorespiration is the term used to describe reductive dechlorination caused by microorganisms that utilize chlorinated compounds as electron acceptors. Dissolved hydrogen is used as the electron donor. Biodegradation: halorespiration e - acceptor PCE TCE C C C C e - donor e - + Microorganism 18

19 YDROGEN PRODUCTION ydrogen, 2 is needed to drive biodegradation d of chlorinated solvents 2 is produced by fermentation of petroleum hydrocarbons and other fermentable substrates Fermentation. Fermentation is a unique reaction in that it requires no external electron acceptors because the organic compound dbeing degraded d dacts as both an electron donor and electron acceptor. During fermentation, organic compounds are converted to innocuous compounds such as acetate, water, carbon dioxide, and (most important) dissolved hydrogen through a series of internal electron transfers catalyzed by microorganisms. 19

20 ydrogen Concentration in alorespiration 20 2 Conc. (nm/l) Methanogenesis Sulfate Reduction Iron, Manganese Reduction Range of activity for halorespiration Nitrate Reduction Degradation Processes for Chlorinated Solvents 20

21 Biodegradation: Aerobic Respiration e - donor C VC C e - acceptor O O O e - Ethene C C Microorganism alorespiration vs. Other Degradation Processes For Ethenes 1 = step in halorespiration process Alternative Degradation g Mechanisms 21

22 alorespiration vs. Other Degradation Processes For Ethanes 1 = step in halorespiration process Alternative Degradation Mechanisms alorespiration vs. Other Degradation Processes For Methanes 1 = step in halorespiration process Alternative Degradation Mechanisms 22

23 Degradation Processes for Chlorinated Solvents Cometabolism Cometabolism is a process by which contaminants (especially chlorinated solvents) are degraded by an enzyme that is fortuitously produced by organisms for other purposes. As a result the organism receives no known benefit from the degradation of the compound. 23

24 Chlorinated Solvent Biodegradation Summary Biodegradation initiated by halorespiration Rates are faster for more highly chlorinated compounds Rates can be modeled using first order decay ydrolysis is major abiotic (chemical) mechanism for degradation Biodegradation Processes for Chlorinated Solvents Compound alorespiration Aerobic Oxidation Anaerobic Oxidation Aerobic Cometabolism Anaerobic Cometabolism PCE X X TCE X X X DCE X X X X X Vinyl Chloride X X X X X 1,1,1-TCA X X X 1,2,-DCA X X X X Chloroethane X X Carbon Tetrachloride X X Chloroform X X X Methylene Chloride X X X 24

25 Natural Attenuation of Chlorinated Solvents Type 1 Environment: Anaerobic (anthropogenic carbon) Carbon fermented to produce hydrogen for alorespiration (low ORP, DO, nitrate, sulfate Elevated Fe(II), methane) Fuel spills, landfills etc. Rapid, extensive degradation of highly chlorinated compounds (PCE, TCE, TCA, CT) Solvent Plume Characteristics Change with Redox high redox low redox 25

26 Natural Attenuation of Chlorinated Solvents Type 2 Environment: Anaerobic (natural carbon) Swamps, Wetlands, high organic carbon soils Possibly slower biodegradation rates for highly chlorinated compounds Natural Attenuation of Chlorinated Solvents Type 3 Environment: Aerobic (no fermentation) Well oxygenated ground water, little organic matter No halorespiration, PCE, TCE, TCA, CT will not degrade Very long dissolved phase plumes Natural attenuation due to advection/dispersion sorption, hydrolysis (TCA only). Elevated Chloride concentration (due to hydrolysis) for TCA, possibly for CT but not for PCE, TCE 26

27 Data Supporting Natural Attenuation If halorespiration is occurring (Type 1&2 Environments): Presence of daughter products (DCE, VC, Ethene) Concurrent attenuation of fermentable carbon Chloride concentrations are elevated Methane is being produced Fe(II) is being produced Solvent Properties Solvent Structure Specific Gravity Methanes Vapor Pressure (mm g) Water Solubility (mg/l) enry's Law Constant (atm*m 3 /mol) Methyl chloride C Methylene chloride C Chloroform C Carbon tetrachloride C Ethanes Chloroethane C 2 C ,1-Dichloroethane C 2 C ,2-Dichloroethane C 2 C ,1,1-Trichloroethane C 3 C ,1,2-Trichloroethane C 2 C ,1,2,2-Tetrachloroethane C 2 C T 1,2,2,2-Tetrachloroethane th C 2 C Pentachloroethane C 3 C exachloroethane C 3 C Ethenes Vinyl Chloride C 2 =C ,1-Dichloroethene C 2 =C cis-1,2-dichloroethene C=C trans-1,2-dichloroethene C=C Trichloroethene C=C Tetrachloroethene C 2 =C

28 Abiotic Degradation alf-lives Natural Attenuation Where to learn more... On the Web: EPA Monitored Natural Attenuation Guidance Document EPA Attenuation Models: In Print: Wiedemeier, T.., et al Natural Attenuation of Fuels and Chlorinated Solvents in the Subsurface. John Wiley and Sons, Inc. Alleman, B.C., and A. Leeson Natural Attenuation of Chlorinated Solvents, Petroleum, and Other Organic Compounds. Battelle Memorial Institute. 28

29 Bioremediation of Metals and Radionuclides Dr. Al Cunningham Center for Biofilm Engineering Montana State University Bozeman MCL or Inorganic MCLG 1 Chemicals (mg/l) 2 TT 1 (mg/l) 2 Arsenic none Chromium (total) Copper 1.3 TT 8 ; Action Level=1.3 Lead zero TT 8 ; Action Level=0.015 Mercury (inorganic) Selenium Metals and radionuclides Current Drinking Water Standards* National Primary Drinking Water Regulations * 1 MCL or Radionuclides MCLG1 (mg/l) 2 TT 1 (mg/l) 2 Uranium as of 12/08/03: zero National Secondary Drinking Water Regulations as of 12/08/03: 30 ug/l Contaminant Secondary Standard Iron 0.3 mg/l Manganese 0.05 mg/l Silver 0.10 mg/l 29

30 Footnotes for tables on previous slide 1 Definitions: Maximum Contaminant Level (MCL): The highest level of a contaminant that is allowed in drinking water. MCLs are set as close to MCLGs as feasible using the best available treatment technology and taking cost into consideration. MCLs are enforceable standards. Maximum Contaminant Level Goal (MCLG): Level of contaminant in drinking water below which there is no known or expected risk to health. MCLGs allow for margin of safety & are non-enforceable public health goals. Maximum Residual Disinfectant Level (MRDL): ighest level of disinfectant allowed in drinking water. Convincing evidence that addition of a disinfectant is necessary for control of microbial contaminants. Maximum Residual Disinfectant Level Goal (MRDLG): The level of a drinking water disinfectant below which there is no known or expected risk to health. MRDLGs do not reflect the benefits of the use of disinfectants to control microbial contaminants. Treatment Technique: A required process intended to reduce the level of a contaminant in drinking water. 2 Units are mg/l unless otherwise noted. Milligrams per liter are equivalent to parts per million. 3 The Safe Drinking Water Act requires EPA to revise the existing 50 parts per billion (ppb) standard for arsenic in drinking water. On January 22, 2001, EPA published a new standard for arsenic in drinking water that requires public water supplies to reduce arsenic to 10 ppb by U.S. Environmental Protection Agency Administrator Christie Whitman announced March 20, 2001 that t EPA will propose to withdraw the pending arsenic standard d for drinking water that was issued on January MCLGs were not established before the 1986 Amendments to the Safe Drinking Water Act. Therefore, there is no MCLG for this contaminant. 8 Lead and copper are regulated by a Treatment Technique that requires systems to control the corrosiveness of their water. If more than 10% of tap water samples exceed the action level, water systems must take additional steps. For copper, the action level is 1.3 mg/l, and for lead is mg/l. Metal/radionuclide reduction and precipitation Some microorganisms, called Dissimilatory Metal Reducing Bacteria or DMRB, can use metals and radionuclides as terminal electron acceptors. This is an enzymatic process and is termed dissimilatory metal reduction. It is also sometimes called direct metal reduction Other microorganisms can reduce metals indirectly Other microorganisms can reduce metals indirectly through non-enzymatic mechanisms, usually involving a reaction between a microbial end product and the metal 30

31 Remediation Concept: Metals such as Cr(VI) and radionuclides such as U(VI) are relatively e soluble and hence mobile in ground water. Through a process called dissimilatory metal reduction these and other metals/radionuclides can be (microbially) reduced to Cr(III) and U(IV) both of which are relatively insoluble and precipitate from solution in the form of metal/radionuclide complexes. This remediation strategy does not destroy the metal/radionuclide but rather removes it from groundwater by way of deposits which are (hopefully) stable indefinitely. Cr(VI) reduction mechanisms DMRB Bacteria generate energy through electron transport Electron source biotic Bacteria e- + Cr(VI) Cr(III) Organic matter Reduced d metal (Fe(II) (Abiotic) Electron sink e- + Cr(VI) Cr(III) Electron sink 31

32 In Situ Groundwater Treatment - DMRB e - Donor Immobilization scenario 32

33 Metals/Radionuclides Known to be Reduced via Dissimilatory Microbial Reduction Cr(VI) Fe(III) U(VI) Mn(IV) Se(VI), (IV), (0) Tc(VII) g(ii) Cu(II) Co(III) Pd(II) Np(V) Pu(IV) Mo(VI) V(V) Au(III), (I) Ag(I) Bacterial Cr(VI) Reduction The ability of bacteria to reduce Cr(VI) is a widespread trait across a number of chemotrophic and phototrophic bacterial genera including: Pseudomonas Bacillus Enterobacter Deinococcus Desulfovibrio Desulfotomaculum Achromobacter Rhodopseudomonas Rhodobacter Shewanella Micrococcus Streptomyces Microbacterium Escherichia Pantoea 33

34 Bacterial U(VI) Reduction Microbes that reduce U(VI) to U(IV) include: Deinococcus radiodurans Desulfotomaculum reducens Desulfovibrio baculatum/desulfuricans/ vulgaris Geobacter metallireducens Pyrobaculum islandicum Shewanella alga Shewanella putrefaciens Thermus sp. Microbial mats containing Oscillatoria (sorption) and Rhodopseudomonas and an unidentified SRB (enzymatic reduction) Bacterial U(VI) Reduction A number of short chained organic acids and hydrogen can serve as C & E sources for U(VI) reduction Early literature suggests that biological U(VI) reduction is due to biogenically produced sulfide. In soils and groundwaters more current data suggest that enzymatically catalyzed dissimilatory metabolism is responsible for most biological U(VI) reduction in these environments As with Cr(VI), many physiologically diverse mechanisms seem to exist for U(VI) reduction. These include cytochrome c3 reduction by D. vulgaris 34

35 Conclusions Many bacteria across a wide number of genera possess the physiological capability to reduce one or more of a variety of metals/radionuclides via dissimilatory metabolism These bacteria are ubiquitous and often occur in both contaminated and pristine environments The intrinsic metal reduction capabilities of these organisms greatly affect natural mineral deposition and in contaminated environments can be used as mechanisms to immobilize and concentrate a variety of metals and radionuclides. 35