Limits to Petroleum Degradation Name the 3 most common things that most often limit in situ petroleum hydrocarbon degradation Nitrogen Phosphorus Oxygen

Oxidation/Reduction Reactions Hydrocarbon biodegradation is essentially an oxidation/reduction reaction Hydrocarbon is oxidized and Electron acceptor is reduced hydrocarbon + electron acceptor + microorganisms + nutrients  carbon dioxide + microorganisms + waste products Electron acceptors include: O2, NO3-, iron oxides (Fe(OH)3), SO42-, H2O

Aerobic Degradation Aerobic bacteria use O2 as their terminal electron acceptor Water saturated with air contains 6 – 12 mg/L dissolved O2 Complete conversion of hydrocarbons to CO2 and H2O requires ~3 mg/L of O2 for each 1 mg/L hydrocarbon Maximum of 12 mg/L dissolved O2 = maximum 4 mg/L hydrocarbon degradation Unlikely to have saturated dissolved O2

Organic Chemistry polycyclic aromatic hydrocarbon monocyclic aromatic hydrocarbons primary alkane biphenyl type benzenoid ring organohalide nitro compound

plume: a continuous emission from a point source of contamination that has a starting point and a noticeable pathway

Typical hydrocarbon plume undergoing natural attenuation

BTEX Benzene, Toluene, Ethylbenzene, Xylene Volatile monoaromatic hydrocarbons Commonly found together in crude petroleum and petroleum products such as gasoline Major cause of environmental pollution LUSTs: leaking underground storage tanks ~35% of 1.4 million gas storage tanks in the US are leaking

Biocatalysis/Biodegradation Database http://umbbd.msi.umn.edu/ Microbial biocatalytic reactions and biodegradation pathways primarily for xenobiotic, chemical compounds.

Aerobic BTEX Degradation Pseudomonads: chemoorganotrophs, aerobic, rod-shaped bacteria Important genera are: Pseudomonas, Burkhoderia, and sometimes Xanthomonas Isolated from the environment Some are pathogenic 1968: strain of Pseudomonas putida isolated grew on ethylbenzene, benzene, and toluene toluene dioxygenase!

Toluene Dioxygenase -Catalyzes over 108 reactions 1. Monocyclic aromatics 2. Fused Aromatics 3. Linked aromatics 4. Miscellaneous

Anaerobic BTEX Degradation Wide variety of microorganisms Denitrifiers, example is Thauera aromatica Iron Reducers Sulfate reducers, examples are Desulfovibrio, Desulfobacter Methanogens Usually requires a consortium

What might FOOTPRINTS be??? Field Studies Crude oil study in MN in 2000 Buried oil pipeline ruptured in 1979 = 3200 barrels of oil spilled into subsurface Growth of aquifer microbial populations (dominated by aerobes, iron reducers, methanogens) Biodegradation caused a number of FOOTPRINTS near the plume = geochemical changes What might FOOTPRINTS be???

Chlorinated Solvents