Bioaugmentation is the introduction of a group of natural microbial strains or a genetically engineered variant to treat contaminated soil or water.

Usually the steps involve studying the indigenous

Endemic (ecology)

Endemism is the ecological state of being unique to a defined geographic location, such as an island, nation or other defined zone, or habitat type; organisms that are indigenous to a place are not endemic to it if they are also found elsewhere. For example, all species of lemur are endemic to the...

 varieties present in the location to determine if biostimulation

Biostimulation

Biostimulation involves the modification of the environment to stimulate existing bacteria capable of bioremediation. This can be done by addition of various forms of rate limiting nutrients and electron acceptors, such as phosphorus, nitrogen, oxygen, or carbon...

 is possible. If the indigenous variety do not have the metabolic capability to perform the remediation process, exogenous

Exogenous

Exogenous refers to an action or object coming from outside a system. It is the opposite of endogenous, something generated from within the system....

 varieties with such sophisticated pathways are introduced.

Bioaugmentation is commonly used in municipal wastewater treatment to restart activated sludge bioreactors. Most cultures available contain a research based consortium of Microbial cultures, containing all necessary microorganisms (B. licheniformis

Bacillus licheniformis

Bacillus licheniformis is a bacterium commonly found in the soil. It is found on bird feathers, especially chest and back plumage, and most often in ground-dwelling birds and aquatic species ....

, B. thurengensis

Bacillus thuringiensis

Bacillus thuringiensis is a Gram-positive, soil-dwelling bacterium, commonly used as a biological pesticide; alternatively, the Cry toxin may be extracted and used as a pesticide. B...

, P. polymyxa

Paenibacillus polymyxa

Paenibacillus polymyxa is a Gram-positive bacterium used as a soil inoculant in agriculture and horticulture. It is capable of fixing nitrogen....

, B. sterothemophilus

Bacillus stearothermophilus

Bacillus stearothermophilus is a rod-shaped, Gram-positive bacterium and a member of the division Firmicutes. The bacteria is a thermophile and is widely distributed in soil, hot springs, ocean sediment, and is a cause of spoilage in food products. It will grow within a temperature range of 30-75...

, Penicillium sp., Aspergillus sp., Flavobacterium, Arthrobacter, Pseudomonas, Streptomyces, Saccaromyces, Triphoderma, etc.). Whereas activated sludge systems are generally based on microorganisms like bacteria, protozoa, nematodes, rotifers and fungi capable to degrade bio degradable organic matter.

Bioaugmentation of chlorinated solvents

At sites where soil and groundwater are contaminated with chlorinated ethenes, such as tetrachloroethylene

Tetrachloroethylene

Tetrachloroethylene, also known under its systematic name tetrachloroethene and many other names, is a chlorocarbon with the formula Cl2C=CCl2. It is a colourless liquid widely used for dry cleaning of fabrics, hence it is sometimes called "dry-cleaning fluid." It has a sweet odor detectable by...

 and trichloroethylene

Trichloroethylene

The chemical compound trichloroethylene is a chlorinated hydrocarbon commonly used as an industrial solvent. It is a clear non-flammable liquid with a sweet smell. It should not be confused with the similar 1,1,1-trichloroethane, which is commonly known as chlorothene.The IUPAC name is...

, bioaugmentation is used to ensure that the in situ microorganisms can completely degrade these contaminants to ethylene

Ethylene

Ethylene is a gaseous organic compound with the formula . It is the simplest alkene . Because it contains a carbon-carbon double bond, ethylene is classified as an unsaturated hydrocarbon. Ethylene is widely used in industry and is also a plant hormone...

 and chloride

Chloride

The chloride ion is formed when the element chlorine, a halogen, picks up one electron to form an anion Cl−. The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides. The chloride ion, and its salts such as sodium chloride, are very soluble in water...

, which are non-toxic. Bioaugmentation is typically only applicable to bioremediation of chlorinated ethenes, although there are emerging cultures with the potential to biodegrade other compounds including chloroethane

Chloroethane

Chloroethane or monochloroethane, commonly known by its old name ethyl chloride, is a chemical compound with chemical formula , once widely used in producing tetraethyllead, a gasoline additive...

s, chloromethane

Chloromethane

Chloromethane, also called methyl chloride, R-40 or HCC 40, is a chemical compound of the group of organic compounds called haloalkanes. It was once widely used as a refrigerant. It is a colorless extremely flammable gas with a minorly sweet odor, which is, however, detected at possibly toxic levels...

s, and MTBE

Methyl tert-butyl ether

Methyl tert-butyl ether, also known as methyl tertiary butyl ether and MTBE, is an organic compound with molecular formula 3COCH3. MTBE is a volatile, flammable, and colorless liquid that is immiscible with water. It has a minty odor vaguely reminiscent of diethyl ether, leading to unpleasant taste...

. The first reported application of bioaugmentation for chlorinated ethenes was at Kelly Air Force Base

Kelly Air Force Base

Kelly Field Annex and is a former United States Air Force facility located in San Antonio, Texas. In 2001, the runway and land west of the runway became "Kelly Field Annex" and control of it was transferred to the adjacent Lackland Air Force Base, part of Joint Base San Antonio...

, TX (Major et al., 2002).

Bioaugmentation is typically performed in conjunction with the addition of electron donor (biostimulation) to achieve geochemical conditions in groundwater that favor the growth of the dechlorinating microorganisms in the bioaugmentation culture.

Sources

• Andrea Leeson, Bruce C. Alleman, Pedro J. J. Alvarez, Victor S. Magar (Hrsg.): Bioaugmentation, biobarriers, and biogeochemistry: the Sixth International In Situ and On-Site Bioremediation Symposium. San Diego, California, June 4-7, Battelle Press 2001, Band 6, ISBN 1574771108.
• Donald Lee Wise (Hrsg.): Bioremediation of contaminated soils. CRC Press, 2000, ISBN 0824703332.