Bioremediation -contaminants (Ch. 14). Joonhong Park May 27, 2014. 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)
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Bioremediation-contaminants (Ch. 14)
May 27, 2014
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
Factors causing molecular recalcitrance
Martin Alexander (1965) described factors causing organic compounds to resist biodegradation in the environment, which he termed “molecular recalcitrance”:
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
What if the aqueous concentration is lower than “threshold” for
Microbial biodegradation ?
Two phenomena limiting substrate availability for biodegradation
Limited substrate availability is bad for biodegradation of a contaminant while is good for biodegradation when the compound is toxic to microorganisms.
Light NAPL (non-aqueous phase liquid) contamination
Vapor from LNAPL
Dissolved LNAPL (plume)
Dense NAPL contamination
Vapor from NAPL
Dissolved NAPL (plume)
Groundwater Flow Direction
Relative ease of cleaning-up of contaminated aquifers as a function of contaminant chemistry and hydrogeology (1=easiest; 4 = the most difficult)
Strongly sorbed, dissolved
Strongly sorbed, dissolved
single layer 1 1-2 2 2-3 2-3 3
multiple layer 1 1-2 2 2-3 2-3 3
single layer 2 2 3 3 3 4
multiple layer 2 2 3 3 3 4
Fractured 3 3 3 3 4 4
Even though a contaminant is known to be readily biodegradable, the absence of a suitable microbial population may be a limiting factor.
- addition of biodegradation populations into contaminated fields.
- The survival of foreign microbes in new environment is questionable.
(Genetically modified indigenous microbes? Digging contaminated soil into a field to be treated? Are they acceptable?)
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
See Table 14.1 and Table 14.2
Energy Metabolism: Respiration and Catabolism of a Pollutant => Resulting in Microbial Growth => sustainable biodegradation
Cometabolism: Fortuitously biodegraded => Little Microbial Growth => May not be sustainable
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)
0.25CO2 + H+ + e- = (1/24)C6H12O6 + 0.25H2O (Glucose/CO2)
H+ + e- = 0.5H2 (Hydrogen/H+)
1/6CO2 + H+ + e- = (1/12)CH3CH2OH + 0.25H2O (Ethanol/CO2)
1/8CO2 + 1/8 HCO3- + H+ + e-
= 1/8 CH3OO- + 3/8H2O (Acetate/CO2)
1/8 CO2 + H+ + e- = 1/8 CH4 + 0.25H2O (methane/CO2)
1/8 SO42- + 19/16H+ + e-
= 1/16 H2S + 1/16 HS-+0.5H2O (sulfide/sulfate)
½ CCl2CCl2 + ½ H+ + e- = ½ CHClCCl2 + ½ Cl- (PCE)
1/5 NO3- + 6/5H+ + e- = 1/10 N2 + 3/5H2O (N2/Nitrate)
Fe3+ + e- = Fe2+ (Fe[II]/Fe[III])
1/4O2 + H+ + e- = 0.5H2O (H2O/O2)
Travel Time through a Reactor
(vinyl chloride, 발암물질)
(TCE, Cs = 1,100 mg/L)
Sorption onto Subsurface Material
Degree of Chlorination
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.
- 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)
- In many instances, the original contamination was a mixture of related components that co-exist normally in a commercial product
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!)
- 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
-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