Degan’s System – Draco I – Commercial iron sponge for scrubbing hydrogen sulfide from the gas. Methane and carbon dioxide are odorless. The trace of H2S provides most of the odor of raw biogas. Removing this trace of highly odorous (rotten eggs) and poisonous gas can leave the biogas odorless, which means leaks are far more difficult to detect. Fortunately, H2S easily oxidizes/burns to odorless sulfur dioxide.