Biodegradation Petroleum

8/12/2019 Biodegradation Petroleum

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Natural vs. Anthropogenic

Domestic waste Herbicides/pesticidesPaper Plastics

Acid mine drainage DetergentsOil Chlorinated solventsMetals

Points of concern:

1. natural vs. anthropogenic

Cl

OH

Cl

O – CH2 - COOH Cl

Cl

There are many different organic contaminants that are spilled into theenvironment.

2. quantity added or spilled

- carrying capacity or self purification



Extent of problem

• 300 million metric tons/yr

• > 1,200 Superfund sites

• Cleanup costs estimated to exceed 1 trillion $



In most cases there are two steps required for biodegradation:

1) uptake and transport of the contaminant into the cell and 2) metabolism.Compounds with low solubility and/or high sorption are not in the aqueous

solution surrounding the cell and therefore their uptake is limited.

Example:

Compound Solubility (mg/L) Biodegradation in 5 days

C7H16 2.93 complete

C16H34 0.0063 ~ 64%

C40H82 very, very low ~ 5%

Factors affecting biodegradability

1. Bioavailability

low water solubilitysorption



A

B

C

D

Hydrocarbon phase

Aqueous phase

How do microbes increase bioavailability in the environment?

A - Uptake of solubilized hydrocarbonB – Uptake of hydrocarbon at the oil-water interfaceC – Uptake of dispersed droplets of oil

D –

Production of biosurfactants to increase the oil-water interfacial area

Scenario –an ocean oil spill



2. Genetic makeup - lack of appropriate degrading genes

Each step in a biodegradation reaction is catalyzed by an enzyme. If theappropriate enzymes are not present, biodegradation will not occur. Sinceeach enzyme is encoded by a gene, the genetic makeup of the microbial

population is a critical factor in determining whether biodegradation willoccur.

3. Contaminant structure (steric hindrance or unusual functional groups)

The presence of the following structures generally inhibit biodegradation

unusual atoms (halogens) R - CH2 - Cl

aromatic ring systems

high molecular weight -(CH2 – CH2 – CH2 – CH2)n-

branching R - C - CH3

CH3

CH3



Increasing biodegradation rate (mg/g sludge dry solids/ hr)

94.8 55.0 55.0 25.0 13.9

COO- CH3 OH Cl NO2

How different substituents influence biodegradation of phenol



2,2,5,5-tetramethylhexane

CH3 - C - CH2 - CH2 - C - CH3

CH3

CH3

CH3

CH3

CH3 – CH2 – CH2 – CH2 – CH2 – CH3

vs.

hexane

Given a pair of structures you should be able to predict which of

the pair will degrade more rapidly.



Benzene

Benzo(a)pyrene

vs.



CH2 - COOH

Cl

Cl

CH2 - COOH

Cl

Cl

Cl

2, 4- D

2, 4, 5 - T

vs.



ethanol

TCE

CH3 - CH2 - OH

C = CH

ClCl

Cl

vs.



4. Environment (biotic and abiotic)

• moisture content (too much limits oxygen availability, too little

inhibits microbial activity in general)

• oxygen (required for rapid biodegradation processes)

• pH (extremes limit microbial activity)

• nutrient availability (includes mineral nutrients and organic matter) • competition (are the microbes of interest active, do added microbes

survive?)

All of these need to be with acceptable ranges to allow optimal

biodegradation activity.



Biodegradation terminology

Transformation - any single biodegradation step in a pathway is a transformationreaction. A transformation can result in partial or complete detoxification of acontaminant or can create a compound even more toxic than the parentcompound.

Mineralization - the parent compound is completely degraded to CO2, new cellmass, and water. This is a highly desirable result for toxic contaminants.

Cl

Cl

N NH - CH

CH 3 CH 3

CH 3 - CH 2 - NH N N

Atrazine transformationproduct is notdegraded further

Cl

Cl

N NH - CH

CH 3

CH 3 N

N H

CH 3 - CH 2 -NH2

+ mineralization

CO2 + cell mass + H2O



Biodegradation terminology (cont.)

Cometabolism - Sometimes an enzyme can act nonspecifically on a

substrate leading to a transformation reaction that does not provideenergy to the microbe. A good example is oxidation of TCE bymethane-utilizing microbes.

lack of enzyme specificity detoxification

OH



Biosynthesis - partial or incomplete degradation can also result inpolymerization or synthesis of compounds more complex and stablethan the parent compound.

Cl NH2 Cl

Cl NH Cl

– C – CH2 – CH3

=

O

Propanil

Abiotic/biotic polymerization Binding to humus

Cl N Cl

Cl = N Cl

Cl N Cl

= N Cl

Cl Cl

N

H

tetrachloroazobenzenedichloroanilino - trichloroazobenzene

– C – CH2 – CH3

= OHO

CO2 + cell mass + H2O

Mineralization



CH3 – (CH2 – CH2 )n – CH3 Aliphatics:

Alicyclics:

Aromatics:

OH

Biodegradation pathways

Most contaminants can be categorized into one of three structure types, allcommonly found in petroleum products. Some contaminants contain a

combination of these structures.

Note to instructors: No actual pathways are presented in this slide show.You will have to decide what pathways (aerobic and anaerobic) you want

to present.



Bioremediation

For successful and cost-effective bioremediation, there need to be degradingmicrobes, adequate bioavailability, and suitable environmental conditions. For

petroleum spills, there are normally degrading microbes present so the issuesbecome bioavailability and environmental conditions.

In ocean oil spills, access to the oil is limited to the surface area between the oil-water interface. In general oxygen is not limiting but as shown below, nitrogenand phosphorus are limiting.

1. oil alone 0

2. oil + microorganisms 53. oil + micro. + P 5-10

4. oil + micro. + N 5-10

5. oil + micro. + N + P 75

Treatment in seawater % biodegradation

From Atlas and Bartha studying degradation constraints in an oil spill:



In the subsurface, the most limiting factor is generally oxygen. Therefore,

addition of oxygen is one of the most common approaches to cleanup ofsubsurface contamination.

In addition, nutrients such as N and P may be added.

In some cases, natural activities are fast enough to control the contaminantplume. This is called intrinsic bioremediation or natural attenuation. This

approach is desirable because it requires only monitoring of the contaminantplume. Must address the questions:

In subsurface terrestrial environments, there are many options. These includeboth in situ and ex situ treatment.

Is intrinsic activity fast enough?

Will the plume impact human or ecological health?



If a more aggressive approach is required, there are several optionsavailable:

In situ treatments

• Bioventing

• Air sparging

• Permeable reactive barriers

Ex situ treatments

• Biofiltration

• Soil vapor extraction and treatment

• Groundwater extraction and treatment



In situ bioremediation in the vadose zone and groundwater. Nutrient andoxygen are being pumped into the contaminated area to promote in situprocesses. Water is being pumped to the surface for ex situ treatment in anaboveground bioreactor. Following treatment, an injection well is returning thecontaminant-free water to the aquifer.

Example 1



Bioventing and biofiltration in the vadose zone. Air is slowly drawn through thecontaminated site (bioventing) which stimulates in situ aerobic degradation.Volatile contaminants removed with the air can be treated biologically using abiofilter as shown or by adsorption on activated carbon, or by combustion.

Example 2



Bioremediation in groundwater by air sparging. Air is pumped into thecontaminated site to stimulate aerobic biodegradation Volatile contaminantsbrought to the surfaced are treated by biofiltration, activated carbon, orcombustion.

Example 3

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Biodegradation Petroleum

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