Hydrogen sulfide (H2S) is a colorless gas that is immediately recognizable for its “rotten egg smell”. H2S is found in biogas, with concentrations in dairy manure-derived biogas generally varying from 600 to sometimes over 7,000 ppm. In addition to its characteristic smell, H2S is also corrosive, flammable, poisonous, and heavier than air; the last two make H2S a particularly dangerous gas from a human health perspective.