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

instantaneous collection rates for permanently capped landfilled waste can be as
high as 90%, capture rates may be much lower during the operating phase of the
landfill (35%) or when the waste is capped with a temporary cover (65%). 1220 In
addition, gas collection is technologically impractical towards the end of the site’s life.
The Intergovernmental Panel on Climate Change (IPCC) has recently stated that
lifetime gas capture rates may be as low as 20%. 1221 We would consider, however,
that landfills in the UK are somewhat better engineered than in the general (global)
case, although a recent report by the European Environment Agency uses the IPCC
figure. 1222
We have assumed a landfill gas capture of 50% as our central assumption. Results
obtained assuming 20% of the landfill gas is captured are also presented for
sensitivity analysis.
Our model assumes that waste which has been pre-treated (e.g. through an aerobic
stabilisation process) will behave differently in landfill with respect to the generation
of landfill gas, and that pre-treated wastes will therefore ultimately require a different
form of gas management in landfill. The landfill of pre-treated waste is discussed in
Section 63.2.1.5.
63.2.1.3 Energy Generated from Landfill Gas
Energy is generated from a variable proportion of the recovered gas. At times of high
flux, emissions can be greater than the capacity of the engines and thus a proportion
of the gas must be flared. At times of low flux, i.e. towards the end of the site lifetime,
emissions may be too small for the gas engines to function effectively. In such a
situation, the usual practice of the landfill operator is to flare the gas.
LQM carried out a survey of landfill operators to estimate the total flare capacity
across UK landfills. 1223 They noted within their analysis that:
991
There are difficulties in ascertaining the actual volumes of LFG burnt as
detailed records, if they exist at all, will be held by individual site operators. It
is rare to find a flow stack with a flow measurement device installed, even
though the capital cost of such a device is relatively small.
1220 K. Spokas, J. Bogner, J.P. Chanton, M. Morcet, C. Aran, C. Graff, Y. Moreau-Le Golvan and I. Hebe
(2006) Methane Mass Balance at 3 Landfill Sites: What is the Efficiency of Capture by Gas Collection
Systems? Waste Management, 5, pp515-525
1221 IPCC (2007) Climate Change 2007: Mitigation. Contribution of Working Group III to the Fourth
Assessment Report of the Intergovernmental Panel on Climate Change (B. Metz, O.R. Davidson, P.R.
Bosch, R. Dave, and L.A. Meyer (eds), Cambridge University Press, Cambridge, United Kingdom and
New York, NY, USA., pp 600.
1222 M. Skovgaard, N. Hedal, A. Villanueva, F. Andersen and H. Larsen (2008) Municipal Waste
Management and Greenhouse Gases, ETC/RWM Working Paper 2008/1, January 2008.
1223 Land Quality Management (2003) Methane Emissions from Landfill sites in the UK, Final Report
for Defra, January 2003.
International Review of Waste Policy: Annexes