Biodegradation of petrochemicals

KHUDA BAKHSH

FA14-R02-002

COMSATS ABBOTTABAD

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What are petrochemicals?

• Chemicals derived from petroleum or natural gas

• Major petrochemicals are acetylene, benzene, ethane, ethylene, methane, propane, and hydrogen

• A huge variety of products are made with petrochemicals

• Including plastics, soaps, pharmaceuticals, fertilizers, pesticides, detergents,

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

Degradation of HCS

• Several methods are utilized

Chemical degradation

Biodegradation

Biodegradation involve

Microbial remediation( effective method)

Bacterial degradation

Fungal degradation

Phytoremediation (by using plants)

Biodegradation of HCS is a complex process depending on:• the nature • Amount of the hydrocarbons presentPetroleum HCS divided into four classes:• The alephatics• The aromatics• The asphaltenes (phenols, fatty acids, ketones, esters, and

porphyrins), • And the resins (pyridines, quinolines, carbazoles,

sulfoxides, and amidesCont….

Microbial Degradation of Petroleum Hydrocarbons

The susceptibility of HCS to microbes can be ranked:

• Linear alkanes

• Branched alkanes

• Small aromatics cyclic alkanes

• High molecular weight (PAHs)

Cont…

Natural mechanism for degrading HCS:

• by bacteria, yeast, and fungi

• Mix population of these microbes are more efficient

• Bacteria are the most active agents in petroleum degradation

Enzymes and microbes Participating in Degradation of HCS

Enzymes Substrates Microorganisms References

Soluble MethaneMonooxygenases

C1–C8 alkanes alkenes and cycloalkanes

MethylococcusMethylomonas

McDonald et al.

Particulate MethaneMonooxygenases

C1–C5 (halogenated) alkanes and cycloalkanes

MethylobacterMethylococcus

McDonald et al.

AlkB relatedAlkaneHydroxylases

C5–C16 alkanes, fatty acids, alkyl benzenes, cycloalkanes

PseudomonasBurkholderiaRhodococcusMycobacterium

Jan et al.

Eukaryotic P450 C10–C16 alkanes, fatty acids Candida maltosaCandida tropicalisYarrowia lipolytica

Iida et al

Bacterial P450oxygenase system

C5–C16 alkanes, cycloalkanes CaulobacterMycobacterium

Iida et al

Dioxygenases C10–C30 alkanes Acinetobacter sp. Maeng et al

Mechanism of Petroleum HCS Degradation

• Biosynthesis of cell biomass occurs from the central precursor metabolites, for example,

• acetyl-CoA, succinate, pyruvate.

• Other mechanisms are

• Attachment of microbial cells to the substrates

• Production of biosurfactsants

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Biodegradation of Petroleum compounds

Petroleum compounds are categorized into 2 groups

• Aliphatic hydrocarbon e.g. alkane, alcohol, aldehyde

• Aromatic hydrocarbon e.g. benzene, phenol, toluene, catechol

• H.C. (substrate) + O2 H.C.-OH + H2O

• H.C. (substrate) + O2 H.C.O

HO

H

monooxyge

nase

dioxygenase

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Straight chain

aliphatic H.C.

compounds

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Cyclic aliphatic

H.C.

compounds

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Aerobic degradation

of aromatic compounds

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Anaerobic degradation

Under nitrate-reducing bacteria

Sulfate-reducing bacteria

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• under nitrate-reducing condition : Nitrate-reducing 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

CH3

COOH

Factors Influencing Petroleum HCS Degradation

A number of limiting factors affect the biodegradation of petroleum HCS

• Chemistry of HCS

• Physiological factors

• Nutrients

• Temperature range.

conclusion• Cleaning up of petroleum HCS is a real world problem.

• It depends on the indigenous microorganisms to transform or mineralize the organic contaminants.

• 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.

• This is possible because microorganisms have enzyme systems to degrade and utilize different hydrocarbons as a source of carbon and energy.

• 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