Figure 10.2: Pathways for GHG emissions from landfills and wastewater systems:

Figure 10.2a: Simplified landfill CH4 mass balance: pathways for CH₄ generated in landfilled waste, including CH₄ emitted, recovered and oxidized.

Note: Not shown are two longer-term CH₄ pathways: lateral CH4 mitigation and internal changes in CH₄ storage (Bogner and Spokas, 1993; Spokas et al., 2006) Methane can be stored in shallow sediments for several thousand years (Coleman, 1979).

Figure 10.2b: Overview of wastewater systems.

Note: The major GHG emissions from wastewater – CH₄ and N₂O – can be emitted during all stages from sources to disposal, but especially when collection and treatment are lacking. N₂O results from microbial N cycling under reduced aeration; CH₄ results from anaerobic microbial decomposition of organic C substrates in soils, surface waters or coastal zones.