Biological conversion of hydrogen sulfide into elemental sulfur

Currently, hydrogen sulfide is removed from process gas streams by a series of reactions at high temperature to produce elemental sulfur in Claw, Stretford or other processes. These physicochemical processes have high intrinsic capital and operating costs often are restricted by contaminants, and do not effectively remove all the H2S. As an alternative, the anaerobic, photosynthetic bacterium, Chlorobium thiosulfatophilum, has been demonstrated to convert hydrogen sulfide to elemental sulfur in a single step at atmospheric conditions. The autotrophic bacterium uses CO2 as the carbon source. Energy for cell metabolism is provided by incandescent light and the oxidation of H2S. A bench scale study has been performed in a CSTR equipped with a sulfur separator. Optimum process conditions have beet achieved to maximize cell growth and elemental sulfur production. Near total conversion of H2S is achieved in a retention time of a few minutes. High concentrations of H2S or organics do not affect the culture. Sulfur recovery by settling is very efficient and near theoretical yields of sulfur are achieved. Economic projections indicate that sour gas can be desulfurized for $ 0.08-0.12/MSCF.