Public Services and Procurement Canada
Biodegradation by methanotrophs is an in situ technology that allows transformation of chlorinated compounds by indigenous methanotrophic microorganisms for the treatment of contaminated groundwater and soil. Methanotrophs are aerobic bacteria that use methane (CH4) as a source of carbon and energy.
Methanotrophic bacteria produce the enzyme methane mono-oxygenase that oxidizes methane and transform various chlorinated compounds. Methanotrophs can therefore cometabolize chlorinated compounds in the presence of methane and oxygen (final electron acceptor). Cometabolism is the fortuitous transformation of a contaminant (such as TCE) by a microorganism without the organism directly benefiting from the transformation. For cometabolism to occur, an appropriate primary substrate (such as methane) must be present to serve as a source of carbon and energy for the microorganism that performs the contaminant transformation. Dissolved or gaseous nutrients, such as soluble fertilizers, may also be injected into the contaminated matrix.
The presence of methane in the environment is necessary for the development and growth of methanotrophs. If methane concentrations are too high, competition for the active site of the methane mono-oxygenase will favour the oxidation of methane. If not enough methane is present, the chlorinated compound will initially be degraded quickly, but will slow down as the contaminant is not a source of energy for the organism. Methane and oxygen injections are required to enhance the biodegradation of halogenated organic compounds. Dissolved or gaseous nutrients, such as soluble fertilizers, may also be injected into the contaminated matrix.
The oxidation of chlorinated compounds produces chlorinated epoxides that are unstable in water and quick to breakdown. Subsequent transformations are catalyzed by methanotrophic or other types of bacteria.
Methanotrophic biodegradation projects may include:
Tests examining the effect of temperature change on hydraulic conductivity and
establishing the zone of freezing with a pilot scale tubing system are recommended to
properly design the full-scale containment system.
In situ methanotrophic biodegradation is potentially applicable to remote northern sites where impediments to material transport and injection equipment mobilization can be overcome. Cold temperatures can hamper biodegradation and microbial activity may only occur during the summer months, thus treatment time may take several years. Microbial activity may be possible in deep soil as temperatures (below permafrost) are relatively constant over the course of the year.
Follow-up monitoring may be required to verify that the remediation objectives as well as applicable regulations are met once the groundwater system normalizes; after stimulation is withdrawn and excess biomass dies off.
Vinyl chloride, a toxic compound which can be produced during reductive dehalogenation of certain chlorinated compounds, is not produced by methanotrophic cometabolism. Laboratory or pilot scale studies, as well as strict control of injected materials are typically required.
Installation of a vapour extraction system to collect all gas emissions may be required where bioventilation or biosparging is used.
Application examples are available at these addresses:
The use of methanotrophs in the biodegradation of chlorinated solvents has been demonstrated as an effective remediation strategy. Mineralization of 90% of TCE was observed at a contaminated site located, at Savannah River, USA, after the injection of gaseous methane, oxygen and nutrients. As with all remediation technologies, the efficacy and time required for remediation is dependent upon several factors, including the type and concentration of contaminants, the microbiological population and activity and the physical and chemical conditions of the contaminated site.
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Composed by : Karine Drouin, M.Sc., National Research Council
Updated by : Karine Drouin, M.Sc., National Research Council
Updated Date : April 1, 2008
Latest update provided by : Marianne Brien, P.Eng., Christian Gosselin, P.Eng., M.Eng., Golder Associés Ltée
Updated Date : March 22, 2019