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Friday, October 31, 2008

BIOREMEDIATION

 Bioremediation is the use of biological processes to remove contaminants from the environment

 Decontamination through biological agents such as microbes, plants and fungi usually occurs naturally in the environment but is often slow
 Bioremediation uses naturally occurring bacteria and fungi or plants to degrade or detoxify substances hazardous to human health and/or the environment

 There are 2 Types of Microorganisms
 Biostimulation
 Bioaugmentation
How does bioremediation work?
 The majority of bioremediation involves a redox reaction that detoxifies the contaminant

 However the reaction can be expedited by improving the environmental conditions in one of the following ways depending on what the limiting factor is
These factors are,

Cont..
Limiting factors

 Adding an electron acceptor
 Adding an electron donor
 Adding a limiting nutrient
 Increasing the bioavailability of the contaminant.
 Stimulating the production of a specific enzyme
Major Types of Bioremediation
1.In situ Bioremediation
In situ treatment means that remediation occurs directly at the site of the contaminant
2.Ex situ Bioremediation
Ex situ treatment requires that the contaminant be transported elsewhere
Cont….
Ex-situ -Bioremediation
 Slurry-phase
 Soil combined with
water/additives in tank, microorganisms, nutrients,
oxygen added
Advantages of Ex-situ Bioremediation

 Easier to control

 Used to treat wider range of contaminants and soil types

 Faster

In-situ Bioremediation
 Biostimulation - stimulates biological activity.
 Bioventing (Inject air/nutrients into unsaturated zone – good for midweight petroleum, jet fuel)
 Biosparging (Inject air/nutrients into unsaturated and saturated zones)
 Bioaugmentation - Inoculates soil with microbes.


Advantages of In-situ Bioremediation
 Less expensive

 Creates less dust

 Less possibility of contaminant release into environment

 Good for large volumes

Ex-situ treatment
 Is the better understood and developed approach to bioremediation, though recently in-situ is gaining much attention.
In-situ treatment
 Is usually more advantageous than
Ex-situ since it requires less equipment and labor and has a lower cost and environmental impact.
How Contamination Occurs
 Oil Leaks from Ships

 Use of Agricultural Chemicals

 Industrial Wastes

 Domestic Wastes

 Laboratory Wastes



Contamination Transport
 Spills or leaks sink into soil or water
 Get transported by water movement

Classes of contaminants biodegraded
Natural Bioremediation
 Natural strains have biodegradative capability

 Can use In-situ populations

 Need to increase total population by adding substrates
 Contaminated sites often very low nutrient
 Contain mixed populations of bacteria

Bioremediation Strategies
(Role of Bacteria)

 Increase substrates detoxified
Ralstonia metallidurans
Deinococcus radiodurans
 Increase rate of detoxification

 Increase access to hydrophobic contaminants



Toxin Digesting Reactions

 Denitrification 2NO3− + 10e− + 12H+ → N2 + 6H2O

 Manganese MnO2 + 2e− + 4H+ → Mn2+ + 2H2O

 Iron III reduction Fe(OH)3 + e− + 3H+ → Fe2+ + 3H2O

 Sulfate reduction SO42− + 8e− +10 H+ → H2S + 4H2O

 Fermentation 2CH2O → CO2 + CH4
Composting
 The high temperatures prevalent during composting, combined with the high nutrient contents of decomposing organic matter such as manure, and the heavy microbial load of the compost system efficiently stimulate the biodegradation of hydrocarbon contamination
Surfactants
 Extractions can be performed on the contaminated soil by adding surfactants in order to leach the hydrocarbons from the soil matrices
Rhizosphere Effects

 The rhizosphere soil has a greater degradation capability for contaminants than does soil without plant roots.
How Bacteria Access Contaminants
Conditions that favor Bioremediation
 Temperature

 Water

 Nutrients

 C:N ratio

 Oxygen in sufficient quantity
Uses of Bioremediation
 Oil spill

 Soil Pollution

 Agricultural practices


 The biggest spill ever occurred during the 1991 Persian Gulf war when about 240 million gallons spilled from oil terminals and tankers off the coast of Saudi Arabia.

Bioremediation of the Exxon Valdez Alaskan oil spill
 Exxon Valdez supertanker ran aground in 1989 resulting in the spillage of about 11 million gallons of crude oil in Alaska.
How Bioremediation uses in Oil Spill.
 The biodegradation by indigenous microorganisms can population could rapidly biodegrade the aliphatic and aromatic fractions of crude oil

 The microbial community completely mineralized them to CO2 and H2O

Soil Bioremediation
 The introduction of substances or biological organisms into the soil, resulting in a change of the soil quality, which is likely to affect the normal use of the soil or endangering public health and the living environment
Agricultural Chemicals
 Fertilizer Pesticides
 Weedcides
Advantages of bioremediation
 Natural process and therefore perceived as an acceptable waste treatment process for contaminated soil

 Many compounds can be transformed to harmless products

 Complete destruction of target pollutants is possible.
Disadvantages of bioremediation
 Limited to those compounds that are biodegradable

 Sometimes the products of biodegradation are more toxic or persistent than the parent compounds

 Biological process are highly specific

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