The most common inorganic gases found in water are carbon dioxide (CO2), methane (CH4), hydrogen (H2), hydrogen sulfide (H2S), ammonia (NH3), carbon disulfide (CS2), sulfur dioxide (SO2), oxygen (O2) and nitrogen (N2). In addition, many different organic gases in water arise from biodegradation of organic matter. Of these dissolved inorganic and organic gases, those with an offensive odor generally contain N and/or S combined with H, C, and/or O, such as H2S, NH3, CS2 and SO2.
Hydrogen sulfide (H2S), from anaerobic reduction of sulfate (SO42-) by bacteria.
SO42- + organic matter + SRB –> S2- + H2O + CO2 + SRB growth
S2- + 2H2O <–> OH– + HS– + H2O <–> H2S(g) + 2OH–
S2- + H2O <–> HS– + OH–
HS– + H2O <–> H2S(aq) + OH–
is usually the most prevalent odor in aerobic natural waters and sewage. Sulfate enters natural waters from sulfate minerals and aerobic decomposition of organic material; it is formed in domestic wastewater by the aerobic biodegradation of sulfur-containing proteins. In addition to H2S, other disagreeable odorous compounds may be formed by anaerobic decomposition of various organic materials.
Eugene R. Weiner. Application of Environmental Aquatic Chemistry. A Practical Guide. Third edition. CRC Press