Which of the following is dominantly released during the third stage (anaerobic) of decomposition in municipal landfill?

Correct option is D

The decomposition of municipal waste in a landfill occurs in four primary stages. The third stage of decomposition is known as the methanogenic (anaerobic) stage, where methane (CH₄) and carbon dioxide (CO₂) are the dominant gases produced.
Stages of Decomposition in Landfills:
1. Initial Stage (Aerobic Phase):
· Organic matter decomposes in the presence of oxygen, producing carbon dioxide (CO₂) and water.
2. Transition Stage (Facultative Anaerobic Phase):
· Oxygen depletes, and facultative anaerobes start producing acids such as acetic acid and other intermediate compounds.
3. Methanogenic Stage (Anaerobic Phase):
· Anaerobic bacteria break down organic matter into methane (CH₄) and carbon dioxide (CO₂). This is the dominant phase for methane production.
4. Final Stage:
· Stabilization occurs with reduced gas production and minimal biological activity.
Methane is the primary gas released during the third stage of landfill decomposition. It is a potent greenhouse gas that poses both environmental challenges and potential as an energy source when captured and utilized properly.
Information Booster 1. Methane Production:
· Landfills are one of the largest sources of methane emissions globally.
· Methane can be captured and converted into energy (landfill gas recovery).
2. Environmental Impact:
· Methane is 25 times more potent than carbon dioxide in trapping heat over a 100-year period.
· Proper management of landfill gas reduces greenhouse gas emissions.
3. Waste Decomposition Rates:
· Decomposition depends on factors like moisture, temperature, and waste composition.
4. Landfill Gas Composition:
· Typical gases: 45-60% methane and 40-55% carbon dioxide.
· Trace gases: Ammonia, hydrogen sulfide, and volatile organic compounds (VOCs).
5. Gas Recovery Systems:
· Modern landfills use gas collection systems to minimize emissions and harness methane for energy.
Additional Knowledge · Ammonia (Option a):
· Released during the early anaerobic stages due to the breakdown of nitrogen-containing organic materials.
· Aldehyde (Option b):
· Produced during the initial aerobic phase due to incomplete oxidation of organic matter.
· Acetic Acid (Option c):
· Forms in the transition stage as intermediate organic acids accumulate before being converted to methane.
· Methane (Option d):
· Produced during the third (methanogenic) stage by methanogenic bacteria under anaerobic conditions.
Key Points:
· Methane is a significant by-product of landfill waste decomposition.
· Capturing methane reduces emissions and can be an energy resource.