Thermophilic sulfate and sulfite reduction with methanal ina high rate anaerobic reactor

Thermophilic sulfite and sulfate reduction offers good prospects as part of an alternative technology to conventional off-gas desulfurization technolo gies. Thermophilic sulfate and sulfite reduction with methanol as the sole carbon and energy source for the sulfate reducing bacteria was studied in l ab-scale Expanded Granular Sludge Bed (EGSB) reactors operated at 65 degree sC and pH 7.5. At a hydraulic retention time (HRT) of 4 hr, sulfite and sul fate 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 achieve d. Sulfite and sulfate reduction accounted for 85-90% of the electrons rele ased during degradation of methanol. In addition, 10-13% and 1-2% of the co nsumed methanol was converted to acetate and methane, respectively. Acetate was not utilized as electron donor for sulfate reduction. Acetate producti on seemed to be linearly correlated to the amount of sulfite and sulfate re duced. Sulfite disproportionating activity of the sludge was demonstrated b y the simultaneous appearance of sulfide and sulfate in batch tests with su lfite. However, sulfite disproportionation rates were 4 times lower than su lfate reduction rates with methanol. The results clearly demonstrate that m ethanol can be efficiently used as electron and carbon source to obtain hig h sulfite and sulfate elimination rates in thermophilic bioreactors.