BIODESULFURIZATION OF FLUE-GASES AND OTHER SULFATE SULFITE WASTE STREAMS USING IMMOBILIZED MIXED SULFATE-REDUCING BACTERIA/

Sulfur dioxide (SO2) is one of the major pollutants in the atmosphere that cause acid rain. Microbial processes for reducing SO2 to hydrogen sulfide (H2S) have previously been demonstrated by utilizing mixed cu ltures of sulfate-reducing bacteria (SRB) with municipal sewage digest as the carbon and energy source. To maximize the productivity of the bioreactor for SO2 reduction in this study, various immobilized cell b ioreactors were investigated: a stirred tank with SRB flocs and column ar reactors with cells immobilized in either kappa-carrageenan gel mat rix or polymeric porous BIG-SEP beads. The maximum volumetric producti vity for SO2 reduction in the continuous stirred-tank reactor(CSTR) wi th SRB flocs was 2.1 mmol of SO2/(h.L). The kappa-carrageenan gel matr ix used for cell immobilization was not durable at feed sulfite concen trations greater than 2000 mg/L (1.7 mmol/(h.L)). A columnar reactor w ith mixed SRB cells that had been allowed to grow into highly stable B IG-SEP polymeric beads exhibited the highest sulfite conversion rates, in the range 16.5 mmol/(h.L) (with 100% conversion) to 20 mmol/(h.L) (with 95% conversion). The average specific activity for sulfite reduc tion in the column, in terms of dry weight of SRB biomass, was 9.5 mmo l of sulfite/(h.g). In addition to flue gas desulfurization, potential applications of this microbial process include the treatment of sulfa te/sulfite-laden wastewater from the pulp and paper,petroleum, mining, and chemical industries.