Analysis of immobilized cell bioreactors for desulfurization of flue gases and sulfite/sulfate-laden wastewater

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 cultures of sulfate-reducing bacteria (SRB) with municipal sewage digest as the carbon and energy source. To maximize the productivity of the SO2-reducing bioreactor in this study, various immobilized cell bioreactors were investigated: a stirred tank with SRB flocs and columnar reactors with cells immobilized in either kappa-carrageenan gel matrix or polymeric porous BIO-SEP(TM) beads. The maximum volumetric productivity for SO2 reduction in the continuous stirred-tank reactor (CSTR) with SRB flocs was 2.1 mmol SO2/h.l. The kappa-carrageenan gel matrix used for cell immobilization was not durable at feed sulfite concentrations greater than 2000 mg/l or at sulfite feed rate of 1.7 mmol/h.l. A columnar reactor with mixed SRB cells that had been allowed to grow into highly stable BIO-SEP polymeric beads exhibited the highest sulfite conversion rates in the range of 16.5 mmol/h.l (with 100% conversion) to 20 mmol/h.l(with 95% conversion). In addition to flue gas desulfurization, potential applications of this microbial process include the treatment of sulfate/sulfite-laden wastewater from the pulp and paper, petroleum, mining, and chemical industries.