家庭や企業から出る有機性廃棄物は、埋立地に埋められた後も分解を続けます。

READING

Organic waste from homes and businesses continues to decompose after it is buried in landfills. Because little oxygen reaches material deep inside a landfill, microorganisms break it down under conditions that produce methane. This gas is a powerful greenhouse gas, and it can keep forming for many years after waste has been deposited. If no collection system is installed, methane may escape through the soil and into the atmosphere, increasing emissions from the waste-management sector.

Uncontrolled methane creates risks beyond its contribution to climate change. As more gas is released from buried waste, landfills can become an important source of greenhouse-gas emissions, making national climate targets harder to achieve. Methane can also move through spaces inside the landfill and accumulate in enclosed areas. At high concentrations, it is highly flammable, so a spark can cause fires or explosions that threaten workers and nearby communities. Managing the gas is therefore important both for environmental protection and for site safety.

One response is to install networks of wells and pipes that collect landfill gas before it escapes. The captured methane can then be burned as fuel or used to generate electricity, reducing direct emissions while producing useful energy. However, collecting all of the gas is difficult because waste is unevenly distributed and continues to settle over time. Some methane can escape from areas that the collection system does not reach effectively. Adding equipment to older landfills can also be expensive because these sites may not have been designed for gas recovery. If the amount of methane available for energy production is too small, the income from selling fuel or electricity may not cover installation and operating costs. As a result, recovery systems can reduce landfill emissions, but they may be less practical at some existing sites.