Which gas is listed as a toxic product of anaerobic digestion?

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

Answer: (B)

Gases from anaerobic digestion include methane, carbon dioxide, and hydrogen sulfide. Hydrogen sulfide is the toxic gas. It forms when sulfur-containing compounds in the feedstock break down, and at higher concentrations it can irritate and then paralyze the respiratory system, with a tendency to accumulate in confined spaces since it’s heavier than air. Methane is flammable and can cause asphyxiation by displacing air, but it isn’t inherently toxic. Carbon dioxide can also cause asphyxiation in enclosed spaces, but it isn’t the toxic gas specifically associated with anaerobic digestion. Oxygen isn’t produced in this process.