Energy recovery from biogas is becoming more common, but the processes are hampered with the presence of hydrogen sulfide (H₂S).  Biogas is a mixture of methane and carbon dioxide (CO₂) and is often contaminated with toxic quantities of H₂S.  Sources of biogas are: municipal landfills that produce landfill gas (LFG); wastewater treatment plants; industrial plants; and large scale livestock farms.  The H₂S levels can range between 200-5000 ppmv from municipal facilities to over 30,000 ppmv from industrial facilities.

Hydrogen sulfide (H₂S) itself has an offensive odor of "rotten eggs" at concentrations as low as 50 parts per billion by volume (ppbv) and is toxic at concentrations above 100 parts per million by volume (ppmv). H₂S is a health and safety hazard, and when combined with carbon dioxide (CO₂) and water vapor (H₂O), corrodes plant equipment such as boilers and piping, and can ruin power-generating equipment.