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Landfill Methane Biofilters

Methane, a potent greenhouse gas, is generated in landfills by the anaerobic decomposition of deposited organic waste after oxygen has been depleted. Although net release is mitigated in cover soil by methanotrophs (which oxidise methane and use it as a carbon source) landfills remain a significant anthropogenic source of methane

Within a landfill, the initial period of anaerobic conditions witnesses high levels of methane production, followed by a long tail-off as the organic waste is used up. The high concentration of methane initially produced is relatively easy to eliminate, with burning for electricity generation a popular option. However, the tail-off period (which can last over a hundred years) results in substantial net production of low concentrations of methane that are too dilute to support combustion and consequently far harder to manage.

To mitigate the release of landfill gas containing low methane concentrations, Norfolk County Council are trialling a custom-made methane biofilter. Effectively a large bioreactor containing methanotrophs through which landfill gas can be directed and stripped of methane. This biofilter is designed to harness and improve the methane oxidising potential of resident methanotrophic bacteria.

The aim of this project is to investigate the methanotroph community in the biofilter and to identify key players involved in methane consumption. By isolating and characterising representative methanotrophs, potential physiological limitations to methane oxidation can be identified and then tested in a lab scale replica of the biofilter matrix. Findings will be fed back into biofilter design and management to improve both the efficiency and consistency of methane oxidation.

This is being approached as three broad questions: “Where?” “Which?” and “How?”

Where is most methane oxidation occurring?

Which are the most active methanotrophs?

How can biofilter design and operation be optimised for improved methane removal?

Both culture-independent and culture-dependent techniques are being used to achieve these goals: DNA-Stable Isotope Probing and amplicon sequencing provides the identity of active methane oxidisers while more traditional isolation techniques are being used to retrieve key methanotrophs from the biofilter.

The Norfolk County Council biofilter at Strumpshaw closed landfill