The effect of sulfate reduction on the acidogenic phase was investigated using anaerobic chemostat systems at 35°C. Sucrose (10,000 mg COD/l) was used as the sole organic substrate. Chemostat systems were maintained at hydraulic retention times (HRTs) of 2, 4, 6, 8 and 10 h. The sulfate concentration in the substrate was increased to 0 (control), 600, 1200 and 2400 mg/l. Sulfate reduction occurred even at an HRT of 2 h, while the hydrogen production rate evidently decreased with increasing sulfate concentration at HRTs of 2 and 4 h. Hydrogen was a key electron donor for the sulfate-reducing bacteria (SRB). The sulfate removal efficiencies were over 90% at sulfate concentrations of 600 and 1200 mg/l at HRTs of longer than 8 h. No inhibition in the degradation of sucrose was observed although the free-H2S concentration was up to 99 mg S/l. Hydrogen-consuming and lactate-consuming SRB were maximally enumerated at 108 and 109 MPN/ml at a sulfate concentration of 2400 mg/l and an HRT of 2 h. The SRB were enumerated at 105 to 107 MPN/ml even in the absence of sulfate. The results of this study showed that SRB could grow under acidogenic condition, and almost sulfate could be removed in the acidogenic phase.
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