Which gas is produced by anaerobic digestion and is toxic?

• A. Methane
• B. Hydrogen Sulfide
• C. Carbon Dioxide
• D. Oxygen

Answer: (B)

Anaerobic digestion produces biogas mainly composed of methane and carbon dioxide, but sulfur-containing compounds can be transformed into hydrogen sulfide, which is toxic even at low concentrations. Methane is primarily a flammable gas, not acutely toxic at typical exposure levels, and carbon dioxide, while it can cause asphyxiation in extremely high concentrations, isn’t considered a toxin in normal conditions. Oxygen isn’t produced in this process. So, the gas produced by anaerobic digestion that is toxic is hydrogen sulfide.