MICROBIAL REDUCTION OF SULFUR-DIOXIDE WITH ANAEROBICALLY DIGESTED MUNICIPAL SEWAGE BIOSOLIDS AS ELECTRON-DONORS

A concentrated stream of sulfur dioxide (SO2) is produced by regenerat ion of the sorbent in certain new regenerable processes for the desulf urization of flue gas. We have previously proposed that this SO2 can b e converted to elemental sulfur for disposal or byproduct recovery usi ng a microbial/Claus process. In this process, two-thirds of the SO2-r educing gas stream would be contacted with a mixed culture containing sulfate-reducing bacteria (SRB), where SO2 would act as an electron ac ceptor with reduction to hydrogen sulfide(H2S). This H2S could then be recombined with the remaining SO2 and sent to a Claus unit to produce elemental sulfur. The sulfate-reducing bacterium, Desulfovibrio desul furicans, has been immobilized by coculture with floc-forming heterotr ophs from an anaerobic digester, resulting in a SO2-reducing flee that may be collected from the effluent of a continuous reactor for recycl e by gravity sedimentation. The carbon and energy source for these cul tures was anaerobically digested municipal sewage solids. The maximum specific activity for SO2 reduction in these cultures, in terms of dry weight of D. desulfuricans biomass, was 9.1 mmol of SO2/h . g. The st oichiometry with respect to the electron donor was 15.5 mg of soluble COD/mmol of SO2 reduced.