Sulfur dioxide from flue gas was converted into sulfate after the absorption of alkaline solutions. Haloalkaliphilic microorganisms have been used in reducing sulfate to decrease expenses and avoid sulfide inhibition. The effects of different COD/SO42- ratios and hydraulic retention times (HRTs) on the sulfate removal efficiency and bacterial community were investigated in model experiments. Ethanol showed better performance as an electron donor than lactate. The optimum COD/SO42- ratio and HRT were 4.0 and 18 h, respectively, with respective sulfate removal efficiency and rate of 97.8 +/- 1.11% and 6.26 +/- 0.0710 g/Ld. Sulfide concentrations reached 1603 +/- 3.38 mg/L. Based on denaturing gradient gel electrophoresis analysis of 16S rDNA, the major sulfate-reducing bacterium (SRB) was Desulfonatronovibrio sp., which was only detected at a COD/SO42- ratio of 4.0 using ethanol as an electron donor. Different HRTs had no significant effect on the band corresponding to this species. PCR results show that methane-producing archaea (MPA) were from the acetoclastic methanogenic family Methanosarcinaceae. Quantitative real-time PCR did not demonstrate any significant competition between SRB and MPA. The findings of this study indicate that sulfate reduction, nitrate reduction, and sulfide oxidization may occur in the same bioreactor. (C) 2014 Elsevier B.V. All rights reserved.