This paper describes a project in which a horizontal flow reedbed has been used to achieve removal of dissolved methane from leachate draining from an old closed landfill site in the UK Midlands, by means of biological oxidation. The bed has performed very well indeed, although extreme rainfall conditions during early 2014 caused flows of up to 160m~3/d that were more than double maximum design values. Later in that year, concentrations of dissolved methane reached 3.8mg/l, twice the design values of 2mg/l, and breakthrough of methane to levels of 0.7mg/l was noted for a short period, until methane levels in leachate returned to design values of 2mg/l/. Prevention of iron accumulation in the bed by use of a Header Tank settlement arrangement is discussed, but the design adopted has great potential for adption at many similar old and closed landfill sites.
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