Bioremediation -contaminants (Ch. 14)

1. Bioremediation-contaminants (Ch. 14) Joonhong Park May 27, 2014

2. History of Hazardous Chemicals Synthetic detergents (Germany during World War II): Poor Biodegradability of Branched Alkyl Benzene Sulfonate (ABS) [Figure 14.1] Pesticides: Silent Spring (Rachel Carson, 1962) Polychlorinated biphenyls (PCBs) and halogenated hydrocarbon: probably cause about half of the environmental problems attributable to organic pollution in the world (Tiedje et al., 1993) Natural occurring pollutants: BTEX (benzene, toluene, ethlybenzene, xylene), polycyclic Aromatic Hydrocarbons (PAHs), dioxins, heavy metals, radioactive matters/rays, asbestos etc. Recalcitrant to Microbial degradation of Chemicals

3. Factors causing molecular recalcitrance Martin Alexander (1965) described factors causing organic compounds to resist biodegradation in the environment, which he termed “molecular recalcitrance”: • A structural characteristic of the molecule prevents an enzyme from acting • The compound is inaccessible, or unavailable. • Some factor essential for growth is absent • The environment is toxic • Requisite enzymes are inactivated. • The community of microorganisms present is unable to metabolize the compound because of some physiological inadequacy.

4. Molecular Structure Relationship between enzyme activation site and the chemical structure of a pollutant (cf. Quantitative Structure-Activity Relationship) Electronic, hydrophobic and steric effects Henry’s constant, KH: volatilization Octanol-water partitioning constant, Kow: hydrophobicity, sorption Solubility, Cs: bioavailability

5. Bioavailability NAPL Phase Or SOM C-NAPL C-SOM water Bacterium C-water What if the aqueous concentration is lower than “threshold” for Microbial biodegradation ?

6. Contaminant availability for biodegradation Two phenomena limiting substrate availability for biodegradation • Strong sorption to surfaces • Formation of a nonaqueous phase Limited substrate availability is bad for biodegradation of a contaminant while is good for biodegradation when the compound is toxic to microorganisms.

7. Light NAPL (non-aqueous phase liquid) contamination Tank LNAPL residual Vapor from LNAPL Capillary fringe LNAPL Free Phase Water table Dissolved LNAPL (plume) Groundwater Flow

8. Dense NAPL contamination Vapor from NAPL NAPL residual Capillary fringe Water table Dissolved NAPL (plume) Clay Layer Groundwater Flow Direction LNAPL Free Phase Groundwater Flow Bedrock

9. Relative ease of cleaning-up of contaminated aquifers as a function of contaminant chemistry and hydrogeology (1=easiest; 4 = the most difficult) Contaminant chemistry Strongly sorbed, dissolved (degrades/volatilizes) Strongly sorbed, dissolved Separate Phase LNAPL Separate Phase DNAPL Mobile, Dissolved (degrades/ Volatilizes) Mobile, Dissolved Hydrogeology Homogeneous, single layer 1 1-2 2 2-3 2-3 3 Homogeneous, multiple layer 1 1-2 2 2-3 2-3 3 Heterogeneous, single layer 2 2 3 3 3 4 Heterogeneous, multiple layer 2 2 3 3 3 4 Fractured 3 3 3 3 4 4

10. Microorganism presence Even though a contaminant is known to be readily biodegradable, the absence of a suitable microbial population may be a limiting factor. Bioaugmentation: - addition of biodegradation populations into contaminated fields. - The survival of foreign microbes in new environment is questionable. • Genetically modified organisms cannot be released into fields. (Genetically modified indigenous microbes? Digging contaminated soil into a field to be treated? Are they acceptable?)

11. Categories of environmental contaminants Hydrocarbons: BTEX (low FW), PAHs (high FW) Oxygenated hydrocarbons: alchohols, ketones, ethers, MTBE Halogenated aliphatics: chlorinated ethenes, chlorinated ethanes (highly chlorinated vs. low chlorinated) Halogenated aromatics: PCBs, chlorinated dioxins, chlorinated dibenzofurans (highly chlorinated) and other low chlorinated halogenated aromatics Nitroaromatics: TNT, RDX, HMX Metals: Cr. Cu, Ni, Pb, Hg, Cd, Zn etc. Nonmetals: As, Se Oxyanions: nitrate, (per)chlorate, phosphate Radionuclides See Table 14.1 and Table 14.2

12. Energy Metabolism versusCometabolism Energy Metabolism: Respiration and Catabolism of a Pollutant => Resulting in Microbial Growth => sustainable biodegradation Cometabolism: Fortuitously biodegraded => Little Microbial Growth => May not be sustainable

13. Absence of physiologically significant compounds Electron donor. Electron acceptor (e.g. oxygen limitation is common). Inducing agent (e.g. presence of toluene is needed to induce toluene oxygenase expression) Carbon, nitrogen and phosphorus sources Trace metals (e.g. Fe is needed for oxygenase)

14. 60 0.25CO2 + H+ + e- = (1/24)C6H12O6 + 0.25H2O (Glucose/CO2) 50 40 H+ + e- = 0.5H2 (Hydrogen/H+) Electron Donors 30 1/6CO2 + H+ + e- = (1/12)CH3CH2OH + 0.25H2O (Ethanol/CO2) 20 1/8CO2 + 1/8 HCO3- + H+ + e- = 1/8 CH3OO- + 3/8H2O (Acetate/CO2) 10 0 ∆Go’ (kJ/e- eq) 1/8 CO2 + H+ + e- = 1/8 CH4 + 0.25H2O (methane/CO2) -10 -20 1/8 SO42- + 19/16H+ + e- = 1/16 H2S + 1/16 HS-+0.5H2O (sulfide/sulfate) -30 -40 Electron Acceptors ½ CCl2CCl2 + ½ H+ + e- = ½ CHClCCl2 + ½ Cl- (PCE) -50 -60 1/5 NO3- + 6/5H+ + e- = 1/10 N2 + 3/5H2O (N2/Nitrate) -70 Fe3+ + e- = Fe2+ (Fe[II]/Fe[III]) -80 1/4O2 + H+ + e- = 0.5H2O (H2O/O2)

15. S-min, CSTR and PFR PFR CSTR S(mg/L) S-min Travel Time through a Reactor

16. Scope and characteristics of contaminants • Category of Contaminants

17. Degree of Halogenation vs. Biodegradation 가장 산화됨 Cl H Cl Cl Cl H C C C C C C Cl Cl H H Cl H Tetrachloroethene (Perchloroethene, PCE) cis-Dichloroethene (cDCE) monochloroethene (vinyl chloride, 발암물질) Cl H H H Cl C C H C C C C Cl Cl Cl H H H Trichloroethene (TCE, Cs = 1,100 mg/L) ethene trans-Dichloroethene (tDCE) 가장 환원됨

18. Aerobic degradation Sorption Reductive dechlorination Sorption onto Subsurface Material Degradation Rate Monochlorinated Polychlorinated 0.25 4 Degree of Chlorination

19. Biodegradability The apliphatic and aromatic hydrocarons are readily biodegradable by a range of aerobic bacteria and fungi. The key is that molecular O2 is needed to activate the molecules via initial oxygenation reactions. Evidence of anaerobic biodegradation of aromatic hydrocarbons is growing. Anaerobic biodegradation rates are slower than aerobic rates, but they can be important when fast kinetics are not essential. Most halogenated aliphatics can be reductively dehalogenated, although the rate appears to slow as the halogen substituens are removed. Highly chlorinate aromatics, including PCBs, can be reductively dehalogenated to less halogenated species. Lightly halogenated aromatics can be aerobically biodegraded via initial oxygenation reactions. Many of the common organic contaminants show inhibitory effects on microorganism growth and metabolism. Due to their strongly hydrophobic nature, many of the inhibitory responses are caused by intereactions with the cell membrane. In some cases, intermediate products of metabolism can be more toxic than the original contaminant.

20. Scope and characteristics of contaminants • Organic compounds - most often amenable to bioremediation - the most detected in groundwater - Many of them are hydrophobic (log Kow >1) and less soluble (solubility < 10,000 mg/l) Ex. PAH, PCB => Significance? - Some are volatile (KH > 10-3 atm-m3/mol)

21. Mixtures of organic compounds - In many instances, the original contamination was a mixture of related components that co-exist normally in a commercial product • PCBs (Arochlor1242 has 42% chlorine overall but contains biphenyl congeners having 1 through 6 Cl substituents with 80% having 3, 4, or 5 Cl substituents) • PAHs (in tars, asphalts, and petroleum sludges) • Various petroleum distillation fractions

22. Hydrocarbon composition of gasoline components • (Hill and Moxey, 1960) 4 4 4 4 2 1 2 1 1 1 5 3 3 5 3 3 5 Thermal-cracked Catalytic reformed Catalytic cracked Straight-run 1: n-alkanes 2:alkenes 3: aromatics 4:isoalkanes 5:cycloalkanes Troublesome BTEX: benzene (2-5% v/v), toluene(6-7% v/v), ethylbenzene(5% v/v), and xylenes (6-7% v/v) => their relatively high solubility causes them to be the prime water pollutants among the compounds in gasoline. More complications – Additives: antiknock compds, antioxidants, metal deactivator, Antirust agent, antipreignition agents, upper cylinder lubricants, alcohols, and oxygenates (MTBE => a big problem!)

23. Mixtures created by codisposal - A common situation of codisposal: the mixture of organic and inorganic materials in sanitary landfills and in their leachates Freeze and Cherry, 1979; Rittmann et al., 1994

24. Mixtures created by codisposal -Volatile and nonvolatile organic compounds and trace metals found in groundwater at an air force base (US, CA) - Chemical-manufacturing facilities: long-term, mixture, very low solubility sludges, unacceptable products, other residues => “gumbo” Pitra and McKenzie, 1990; Rittmann et al., 1994

25. Mixtures created by codisposal • US Department of Energy (DOE) sites are unique in that the contamination of the subsurface often involves complex mixtures of organic and inorganic chemicals, including short- and long-lived radionuclides (USDOE, 1990) • The degree of complexation with the chelators controls the mobility of the radionuclides, while the biodegradation of the chelators is affected by their complexation to the heavy metals.