Landfill
Decomposition gases

Rotting food and other decaying organic waste create decomposition gases, especially CO and CH from aerobic and anaerobic decomposition, respectively. Both processes occur simultaneously in different parts of a landfill. In addition to available O, the fraction of gas constituents will vary, depending on the age of landfill, type of waste, moisture content and other factors. For example, the maximum amount of landfill gas produced can be illustrated a simplified net reaction of diethyl oxalate that accounts for these simultaneous reactions:

4 C H O + 6 H O → 13 CH + 11 CO

On average, about half of the volumetric concentration of landfill gas is CH and slightly less than half is CO. The gas also contains about 5% molecular nitrogen (N), less than 1% hydrogen sulfide (H S), and a low concentration of non-methane organic compounds (NMOC), about 2700 ppmv.

Landfill gases can seep out of the landfill and into the surrounding air and soil. Methane is a greenhouse gas, and is flammable and potentially explosive at certain concentrations, which makes it perfect for burning to generate electricity cleanly. Since decomposing plant matter and food waste only release carbon that has been captured from the atmosphere through photosynthesis, no new carbon enters the carbon cycle and the atmospheric concentration of CO is not affected. Carbon dioxide traps heat in the atmosphere, contributing to climate change. In properly managed landfills, gas is collected and flared or recovered for landfill gas utilization.
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