2. What are petrochemicals?
โข Chemicals derived from petroleum or natural gas
โข Major petrochemicals are acetylene, benzene,
ethane, ethylene, methane, propane, and
hydrogen
โข A huge variety of products are made with
petrochemicals
โข Including plastics, soaps, pharmaceuticals, fertilizers,
pesticides, detergents,
3. ๏One of the major environmental problems
caused by HCS:
๏ Resulting from activities of petrochemical
industry.
๏Accidental releases of petroleum products
๏HCS belong to the family of carcinogens and
neurotoxic organic pollutants
๏Main cause of water and soil pollution
๏Accumulation of pollutants in living cells may
cause death or mutations
๏Their removal is necessary
4. Degradation of HCS
โข Several methods are utilized
Chemical degradation
Biodegradation
๏ง Biodegradation involve
Microbial remediation( effective method)
Bacterial degradation
Fungal degradation
Phytoremediation (by using plants)
5. Microbial Degradation of Petroleum
Biodegradation of HCS is a complex process depending on:
โข the nature
โข Amount of the hydrocarbons present
Petroleum HCS divided into four classes:
โข The alephatics
โข The aromatics
โข The asphaltenes (phenols, fatty acids, ketones, esters, and
porphyrins),
โข And the resins (pyridines, quinolines, carbazoles,
sulfoxides, and amides
Contโฆ.
Hydrocarbons
6. The susceptibility of HCS to microbes can be
ranked:
โข Linear alkanes
โข Branched alkanes
โข Small aromatics cyclic alkanes
โข High molecular weight (PAHs)
Contโฆ
7. Natural mechanism for degrading HCS:
โข by bacteria, yeast, and fungi
โข Mix population of these microbes are more
efficient
โข Bacteria are the most active agents in
petroleum degradation
8. Enzymes and microbes Participating in
Degradation of HCS
Enzymes Substrates Microorganisms References
Soluble Methane
Monooxygenases
C1โC8 alkanes alkenes and
cycloalkanes
Methylococcus
Methylomonas
McDonald et
al.
Particulate Methane
Monooxygenases
C1โC5 (halogenated) alkanes
and cycloalkanes
Methylobacter
Methylococcus
McDonald et
al.
AlkB related
Alkane
Hydroxylases
C5โC16 alkanes, fatty acids,
alkyl benzenes, cycloalkanes
Pseudomonas
Burkholderia
Rhodococcus
Mycobacterium
Jan et al.
Eukaryotic P450 C10โC16 alkanes, fatty acids Candida maltosa
Candida tropicalis
Yarrowia lipolytica
Iida et al
Bacterial P450
oxygenase system
C5โC16 alkanes, cycloalkanes Caulobacter
Mycobacterium
Iida et al
Dioxygenases C10โC30 alkanes Acinetobacter sp. Maeng et al
10. โข Biosynthesis of cell biomass occurs from the
central precursor metabolites, for example,
โข acetyl-CoA, succinate, pyruvate.
โข Other mechanisms are
โข Attachment of microbial cells to the substrates
โข Production of biosurfactsants
11. Biodegradation of Petroleum compounds
11
Petroleum compounds are categorized into 2 groups
โข Aliphatic hydrocarbon e.g. alkane, alcohol,
aldehyde
โข Aromatic hydrocarbon e.g. benzene, phenol,
toluene, catechol
โข H.C. (substrate) + O2 H.C.-OH + H2O
โข H.C. (substrate) + O2 H.C.
O
H
O
H
monooxyge
nase
dioxygenase
17. โข under nitrate-reducing condition : Nitrate-reducing
17
bacteria couple the oxidation of org. cpd. with
water to the exergonic reduction of nitrate via
nitrite to N2
OH OH O
Metabolic
pool
3H2 H2O
H2
COOH
CH3
18. Factors Influencing Petroleum HCS
Degradation
A number of limiting factors affect the
biodegradation of petroleum HCS
โข Chemistry of HCS
โข Physiological factors
โข Nutrients
20. conclusion
โข Cleaning up of petroleum HCS is a real world problem.
โข It depends on the indigenous microorganisms to transform or
mineralize the organic contaminants.
โข Microbial degradation process aids the elimination of spilled
oil from the environment after critical removal of large
amounts of the oil by various physical and chemical methods.
โข This is possible because microorganisms have enzyme systems
to degrade and utilize different hydrocarbons as a source of
carbon and energy.
โข Therefore, based on the present review, it may be concluded
that microbial degradation can be considered as a key
component in the cleanup strategy for petroleum
hydrocarbon remediation