Microbial Reduction of Sulfur Dioxide with Anaerobically Digested Municipal Sewage Biosolids as Electron Donors

A concentrated stream of sulfur dioxide (SO 2 ) is produced by regeneration of the sorbent in certain new regenerable processes for the desulfurization of flue gas. We have previously proposed that this SO 2 can be converted to elemental sulfur for disposal or byproduct recovery using a microbial/Claus process. In this process, two‐thirds of the SO 2 ‐reducing gas stream would be contacted with a mixed culture containing sulfate‐reducing bacteria (SRB), where SO 2 would act as an electron acceptor with reduction to hydrogen sulfide (H 2 S). This H 2 S could then be recombined with the remaining SO 2 and sent to a Claus unit to produce elemental sulfur. The sulfate‐reducing bacterium, Desulfouibrio desulfuricans , has been immobilized by coculture with flocforming heterotrophs from an anaerobic digester, resulting in a SO 2 ‐reducing floc that may be collected from the effluent of a continuous reactor for recycle by gravity sedimentation. The carbon and energy source for these cultures was anaerobically digested municipal sewage solids. The maximum specific activity for SO 2 reduction in these cultures, in terms of dry weight of D. desulfuricans biomass, was 9.1 mmol of SO 2 /h. g. The stoichiometry with respect to the electron donor was 15.5 mg of soluble COD/mmol of SO 2 reduced.