10.3.2 Landfill CH4: regional trends
Landfill CH4 has historically been the largest source of GHG emissions from the waste sector. The growth in landfill emissions has diminished during the last 20 years due to increased rates of landfill CH4 recovery in many countries and decreased rates of landfilling in the EU. The recovery and utilization of landfill CH4 as a source of renewable energy was first commercialized in 1975 and is now being implemented at >1150 plants worldwide with emission reductions of >105 MtCO2-eq/yr (Willumsen, 2003; Bogner and Matthews, 2003). This number should be considered a minimum because there are also many sites that recover and flare landfill gas without energy recovery. Figure 10.5 compares regional emissions estimates for five-year intervals from 1990–2020 (US EPA, 2006) to annual historical estimates from 1971–2002 (Bogner and Matthews, 2003). The trends converge for Europe and the OECD Pacific, but there are differences for North America and Asia related to differences in methodologies and assumptions.
A comparison of the present rate of landfill CH4 recovery to estimated global emissions (Table 10.3) indicates that the minimum recovery and utilization rates discussed above (>105 MtCO2-eq yr) currently exceed the average projected increase from 2005 to 2010. Thus, it is reasonable to state that landfill CH4 recovery is beginning to stabilize emissions from this source. A linear regression using historical data from the early 1980s to 2003 indicates a conservative growth rate for landfill CH4 utilization of approximately 5% per year (Bogner and Matthews, 2003). For the EU-15, trends indicate that landfill CH4 emissions are declining substantially. Between 1990 and 2002, landfill CH4 emissions decreased by almost 30% (Deuber et al., 2005) due to the early implementation of the landfill directive (1999/31/EC) and similar national legislation intended to both reduce the landfilling of biodegradable waste and increase landfill CH4 recovery at existing sites. By 2010, GHG emissions from waste in the EU are projected to be more than 50% below 1990 levels due to these initiatives (EEA, 2004).
For developing countries, as discussed in the previous section (10.3.1), rates of landfill CH4 emissions are expected to increase concurrently with increased landfilling. However, incentives such as the CDM can accelerate rates of landfill CH4 recovery and use in parallel with improved landfilling practices. In addition, since substantial CH4 can be emitted both before and after the period of active gas recovery, sites should be encouraged, where feasible, to install horizontal gas collection systems concurrent with filling and implement solutions to mitigate residual emissions after closure (such as landfill biocovers to microbially oxidize CH4—see section 10.4.2).