Thermophilic sulfate and sulfite reduction with methanol in a high rate anaerobic reactor

Thermophilic sulfite and sulfate reduction offers good prospects as part of an alternative technology to conventional off-gas desulfurization technologies. Thermophilic sulfate and sulfite reduction with methanol as the sole carbon and energy source for the sulfate reducing bacteria was studied in lab-scale Expanded Granular Sludge Bed (EGSB) reactors operated at 65 °C and pH 7.5. At a hydraulic retention time (HRT) of 4 hr, sulfite and sulfate elimination rates of up to 0.22 mol-S.l -1 .day -1 (100% elimination) and 0.15 mol-S.l -1 .day -1 (80% elimination), respectively, were achieved. Sulfite and sulfate reduction accounted for 85–90% of the electrons released during degradation of methanol. In addition, 10–13% and 1–2% of the consumed methanol was converted to acetate and methane, respectively. Acetate was not utilized as electron donor for sulfate reduction. Acetate production seemed to be linearly correlated to the amount of sulfite and sulfate reduced. Sulfite disproportionating activity of the sludge was demonstrated by the simultaneous appearance of sulfide and sulfate in batch tests with sulfite. However, sulfite disproportionation rates were 4 times lower than sulfate reduction rates with methanol. The results clearly demonstrate that methanol can be efficiently used as electron and carbon source to obtain high sulfite and sulfate elimination rates in thermophilic bioreactors.