Gas formation in the sludge blanket is caused by which process?

• A. Nitrification
• B. Aerobic digestion
• C. Methanogenesis
• D. Denitrification

Answer: (D)

Gas formation in the sludge blanket happens from anaerobic digestion by methanogens, a process called methanogenesis. In the absence of oxygen, the microbial community breaks down organic matter and produces methane-rich biogas (mostly methane with some CO2). This gas production is characteristic of anaerobic systems like a sludge blanket in UASB or other anaerobic digester configurations.

Nitrification is an aerobic oxidation of ammonia to nitrite and nitrate and does not produce methane. Aerobic digestion uses oxygen to break down organics and yields CO2 and biomass, not methane. Denitrification removes nitrate by reducing it to nitrogen gas under anoxic conditions, which can generate gas, but the primary gas associated with the sludge blanket itself in anaerobic digestion is methane from methanogenesis.