Biotreatment process is widely used to treat high-strength sulfate-laden organic wastewater. By applying molasses wastewater as the sole organic carbon source and sodium sulfate as the electron acceptor in an acidogenic sulfate-reducing reactor, the electron flows of sulfate-reducing bacteria (SRB), the physiological metabolic pathways and products of SRB, the population dynamics of SRB, and the effect of sulfide production on hydrogen production were examined under different chemical oxygen demand/sulfate (COD/SO 42-) ratios. The results showed that the number of electrons flowing to SRB was reduced when the COD/SO42- ratio increased and, hence, improved the sulfate removal rate. SRB was also the consumer of hydrogen and volatile fatty acids (VFAs) produced by acidogenic bacteria. The metabolic activities of SRB resulted in 45%-82% acetic acid in the terminal liquid products in the acidogenic reactor. The SRB also maintained a low-level hydrogen partial pressure by transferring hydrogen among microbial populations and guaranteed high performance stability in the acidogenic reactor. Copyright © 2007 American Chemical Society.