International Review of Waste Management Policy - Department of ...

etween 0.1 to 5 l CH4/m 2*h, so that a mean value of 3 l CH4/m 2*h seems realistic.
Even if one considers the potential influence of temperature, water content, and the
varying gas qualities, it seems entirely probable, therefore, that such a layer would be
able to oxidise a very high proportion of methane from the landfill gas emanating from
MBT-treated wastes. Early trials suggest that a gas oxidation layer of about 120 cm
combined with a gas distribution layer of 50 cm is suitable. 1228 Fugitive emissions of
methane are therefore minimal in this case.
The positive effects on landfill behaviour of pre-treatment can only be realised if the
landfill is adapted to the conditions presented by the waste. Landfill gas capture is
not necessary (the low flux makes this technically infeasible, as was previously
discussed in Section 63.2.1.2) and therefore no energy is generated from the landfill
gas.
We have effectively modelled two landfills. In the first, we keep the characteristics of
the landfill the same as for general mixed waste. All that changes is that the gas
generation from the treated waste is low. However, as part of a more general
‘landfilling of waste’, we assume that in these situations, any gas emitted is treated
as though it was coming from untreated waste.
In the medium- to long-term, we would expect, particularly with the pre-treatment
guidelines enforced, that landfill cells would be designed for primarily treated waste.
In this case, we have modelled a second landfill kin which there is no gas capture in
the conventional sense, where an active cover layer is depleted, and where, in line
with the evidence cited above, 90% of the remaining methane emitted is oxidised by
the landfill cover layer.
63.2.1.6 Summary of Assumptions - Climate Change Impacts of Landfill
Table 63-6 summarises our assumptions with regard to the management of landfill
gas for untreated waste. These landfill gas capture assumptions result in total climate
change impacts of €79.80 per tonne of untreated waste to landfill if the high external
costs are assumed, or €63.06 if the lower damage costs are applied. The totals
include emissions associated with energy used at the landfill (although these are
insignificant in comparison to the direct emissions from the process).
Management and Landfill Symposium. S Margherita di Pula, Caligari, Italy, 4-8 October 1999. pp 409-
418.
1228 Humer, M.; Lechner, P.: Design of a landfill cover layer to enhance methane oxidation - results of a
two year field investigation. In: Christensen, T.H.; Cossu, R.; Stegmann, R. (Eds): Proc. Sardinia 2001,
8. Int. Waste management and Landfill symposium, Vol. 2, 541-550, Cagliari, 2001.
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International Review of Waste Policy: Annexes