1. Waste Disposal: MSW is collected and deposited in landfills, where it undergoes compaction and burial.
2. Anaerobic Conditions: Once in the landfill, the organic waste decomposes under anaerobic (oxygen-deprived) conditions. This anaerobic environment promotes the growth of methanogenic bacteria, which thrive in the absence of oxygen.
3. Methane Production: Methanogenic bacteria break down organic matter through a series of biological reactions known as anaerobic digestion. This process produces methane (CH4) as a byproduct, along with carbon dioxide (CO2) and small amounts of other gases.
4. Gas Migration: As methane is generated, it migrates through the landfill's porous materials and reaches the atmosphere. It can escape through vents, cracks, and other openings in the landfill cover.
Methane is a particularly harmful GHG due to its high global warming potential (GWP). In the short term, methane is approximately 28-36 times more effective at trapping heat in the atmosphere compared to carbon dioxide. Although methane persists for a shorter period (around 12 years) in the atmosphere compared to carbon dioxide, its impact on global warming is significant.
When comparing methane to other gases like carbon monoxide (CO) or carbon dioxide (CO2) released during the burning of waste, here are some key differences:
1. Global Warming Potential: Methane has a significantly higher GWP compared to carbon monoxide or carbon dioxide. For example, methane's GWP over a 100-year timeframe is about 28-36 times higher than carbon dioxide, while carbon monoxide has a negligible GWP.
2. Persistence: Methane has a shorter atmospheric lifetime compared to carbon dioxide. Carbon dioxide can remain in the atmosphere for hundreds to thousands of years, contributing to long-term climate change. In contrast, methane breaks down relatively quickly over approximately 12 years, but its impact during that time is more potent.
3. Toxicity: Carbon monoxide is highly toxic and can cause severe health effects in humans and animals when present in high concentrations. Carbon dioxide, while not directly toxic, contributes to climate change and can cause indirect harm through its impact on the environment. Methane, though not toxic, is a powerful greenhouse gas and plays a significant role in global warming.
Therefore, the emission of methane gas during the decomposition of municipal solid waste in landfills is a significant concern due to its high global warming potential. While carbon monoxide and carbon dioxide are also released during waste burning, methane stands out as a particularly harmful gas in terms of its contribution to climate change. Reducing methane emissions from landfills is crucial for mitigating the impact of greenhouse gases on the environment.