Analysis of immobilised cell bioreactors for desulfurisation of flue gases and sulfite/sulfate laden wastewater

Abstract

Sulfur dioxide (SO2) is one of the major pollutantsin the atmosphere that cause acid rain. Microbialprocesses for reducing SO2 to hydrogen sulfide(H2S) have previously been demonstrated byutilizing mixed cultures of sulfate-reducing bacteria(SRB) with municipal sewage digest as the carbon andenergy source. To maximize the productivity of theSO2-reducing bioreactor in this study, variousimmobilized cell bioreactors were investigated: a stirredtank with SRB flocs and columnar reactors with cellsimmobilized in either κ-carrageenan gel matrix orpolymeric porous BIO-SEPTM beads. Themaximum volumetric productivity for SO2reduction in the continuous stirred-tank reactor (CSTR)with SRB flocs was 2.1 mmol SO2/h·l. Theκ-carrageenan gel matrix used for cellimmobilization was not durable at feed sulfiteconcentrations greater than 2000 mg/l or at sulfite feedrate of 1.7 mmol/h·l. A columnar reactor withmixed SRB cells that had been allowed to grow intohighly stable BIO-SEP polymeric beads exhibited thehighest sulfite conversion rates, in the range of16.5 mmol/h·l (with 100% conversion) to20 mmol/h·l (with 95% conversion). In addition toflue gas desulfurization, potential applications of thismicrobial process include the treatment ofsulfate/sulfite-laden wastewater from the pulp and paper,petroleum, mining, and chemical industries.