Which of the following gases are dominantly released during the second phase of decomposition in a municipal landfill?

Correct option is B

During the second phase of decomposition in a municipal landfill, the dominant gases released are ammonia, hydrogen, and carbon dioxide. This phase is known as the acidogenic phase, where the breakdown of organic matter by acid-forming bacteria produces volatile fatty acids, along with gases like ammonia (NH₃), hydrogen (H₂), and carbon dioxide (CO₂).
Explanation:
The decomposition process in a landfill occurs in four phases:
1. Phase 1 (Aerobic Phase):
· In the presence of oxygen, bacteria break down organic matter, producing carbon dioxide (CO₂) and water (H₂O).
2. Phase 2 (Acidogenic Phase):
· Oxygen is depleted, and anaerobic conditions prevail.
· Acid-forming bacteria produce gases like ammonia, hydrogen, and carbon dioxide as they break down complex organics into simpler acids.
3. Phase 3 (Acetogenic Phase):
· Acetogenic bacteria convert fatty acids into acetic acid, hydrogen, and carbon dioxide.
4. Phase 4 (Methanogenic Phase):
· Methane-producing bacteria generate methane (CH₄) and carbon dioxide (CO₂).
Information Booster:
1. The second phase of landfill decomposition is characterized by acid production and the release of ammonia, hydrogen, and carbon dioxide.
2. Ammonia (NH₃) results from the breakdown of nitrogen-rich organic matter.
3. Hydrogen (H₂) is produced during the breakdown of acids by bacteria.
4. Carbon dioxide (CO₂) is a by-product of anaerobic respiration.
5. Understanding landfill gas composition helps in managing landfill emissions and energy recovery.
6. Proper gas management reduces environmental hazards such as explosions and greenhouse gas emissions.
Additional Knowledge:
· (a) Carbon dioxide and water:
· Released during the initial aerobic phase when oxygen is present.
· (b) Ammonia, hydrogen, carbon dioxide:
· Produced during the second (acidogenic) phase as complex organics decompose.
· (c) Methane and carbon dioxide:
· Predominant in the methanogenic phase (fourth phase).
· Methane (CH₄) is a key landfill gas and a potent greenhouse gas.
· (d) Ammonia, hydrogen, and methane:
· Not all these gases are produced together in the second phase; methane appears later during methanogenesis.
Key Points:
1. Landfill decomposition occurs in four distinct phases.
2. Second phase gases include ammonia, hydrogen, and carbon dioxide.
3. Proper landfill gas management mitigates environmental impact.
4. Methane is captured during later phases for energy production.
5. Monitoring landfill emissions helps in pollution control and safety.