Which trace contaminants may be present in biogas produced by anaerobic digestion?

• A. Hydrogen Sulfide And Moisture
• B. Ammonia Only
• C. Oxygen
• D. Neon And Argon

Answer: (A)

Biogas from anaerobic digestion commonly carries two important trace contaminants: hydrogen sulfide and moisture. Hydrogen sulfide comes from sulfur-containing compounds in the feedstock and the activity of sulfate-reducing bacteria. It is corrosive to metal surfaces, toxic at high concentrations, and responsible for the rotten-egg odor, so it must be removed or controlled. Moisture, or water vapor, is always present and can condense in pipelines and equipment, leading to corrosion, rust, and operational problems; drying and condensate management are essential to protect the system.

Oxygen isn’t a typical contaminant in digested biogas because the process is anaerobic, though small leaks can introduce it. Neon and argon are inert atmospheric gases and aren’t produced in meaningful amounts by anaerobic digestion. Ammonia can occur in some systems, but the most routinely encountered contaminants to manage are hydrogen sulfide and moisture.