Case Studies of Methane Stripping Trials
When we started designing these plants we carried out a variety of trials at different landfills. The data from these trials has formed the basis for our process designs ever since. However, on occasions we do still encounter unusual sites, and for these sites a trial is still undertaken before commencing the detailed process design.
On this page we discuss the trials, and provide case study information for two of our first full scale MSP sites.
Methane Stripping Site Trials
Methane removal rates of up to 99.4% were achieved reliably during the trials discussed below. It was noted that allowing effluents from the final tank to stand for a further 10 minutes, resulted in the reduction of dissolved methane concentrations, as very small entrained bubbles were lost from the liquid surface.
The aeration and methane stripping process had no significant effect on any major chemical characteristics of the leachate, although the precipitation of small amounts of a ‘hardness’ scale on the inside of each reactor was evident, and must be taken into account within a full-scale design. This scaling did not result in significant reductions in ions of calcium, magnesium or iron.
No significant reduction in ammoniacal-N took place.
Case Studies of Full Scale Methane Stripping Plants
Results from the trials have formed a reliable basis to design a number of full-scale treatment plants.
Red Moss Methane Stripping Plant, Manchester
One such plant, representing a state-of-the-art solution in 1999, is Red Moss MSP, designed and commissioned by Enviros Aspinwall. Red Moss is a large, substantially above-ground landfill site in Horwich, near Bolton. The site is now closed, but was operated by Greater Manchester Waste Disposal Authority until the mid 1990s. As part of extensive restoration works recently completed, a methane stripping plant was designed and constructed to provide pre-treatment of leachate, prior to discharge into the public sewer. The plant was designed to treat up to 1000 m3/day, to a standard of less than 0.14 mg/l of dissolved methane.
Commissioned in March 1999, the plant’s typical operating results are presented in Table 1.
Kendal Fell Methane Stripping Plant
An example of the smaller plant was constructed and commissioned at a site in the Lake District. Kendal Fell landfill occupies a former limestone quarry to the western edge of Kendal. First operated by Econowaste Ltd, it was then taken over and operated by Hanson Waste Management from 1993. Since then it was operated by successor company Greenways and WRG, and the site contains about one million tonnes of waste.
The sensitivity of the aquifer dictated that the base of the site be double HDPE lined, with an intermediate leak detection layer. The quarry sides are vertically lined with a patented HDPE and rock gabion system, incorporating a gas collection layer. The site has been completed to final levels, and a final synthetic capping layer has been applied.
Leachate egress represents a potential risk to groundwater quality, therefore, leachate is collected from site and treated prior to discharge to an adjacent sewer. The volumetric limit at the sewer is 175 m3/day, and the discharge consent again sets a limit of 0.14 mg/l for dissolved methane. Recent improvements to the leachate management system at the site included the construction of a new methane stripping plant, in early 2000 (see Figure 5), to ensure that consent limits are routinely met – a robust treatment technology operating with minimal requirement for supervision.
Such methane stripping pre-treatment plants are rapidly becoming more common, as water companies recognise the dangers involved in dissolved methane within leachates pumped to sewer. It is unlikely that discharge of raw leachates into public sewers, without such pre-treatment to remove dissolved methane, will either provide adequate safeguards, or enable typical consent limits to be achieved with any degree of confidence. Data such as those discussed,
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Figure 3. Reductions achieved during trials on the 5 landfill sites
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Table 1: Red Moss methane stripping plant. Typical operating results March 1999.
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Sampling point
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Dissolved methane (mg/l)
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Raw leachate
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9.980
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Aeration tank 1
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4.610
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Aeration tank 2
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1.840
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Aeration tank 3
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0.486
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Aeration tank 4
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0.133
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Aeration tank 5
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0.102
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Final effluent
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0.095
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(consented
limit)
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(0.140)
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(NB: Since closure and restoration capping of the landfill in 2003 reduced flows to those capable of alternative disposal, this plant has been moved to another landfill by WRG.)
ENVIROS Consulting is an independent UK environmental consultancy.
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