Effect of sulfate on intermediate production and degradation in thermophilic metanogenic process was investigated using four CSTRs fed with starch or shochu waste as organic matters. The CSTRs were operated as semi-continuous manure, one time of feeding for 3-4 days, at 55°C, pH 7, 1.2kg/m
3/day of CODcr volumetric loading rate, and 25-33 days of HRT. The “St-7” reactor and “St-S” reactor were fed with starch at different initial sulfate level, that is, 33mgS/L and 100mgS/L respectively. The “Sh-7” reactor and “Sh-S” reactor were fed with shochu waste with 33mgS/L and 100 mgS/L of sulfate respectively. As the results, St-7 marked higher VFA and hydrogen partial pressure than Sh-7 in each feeding. Hydrogen partial pressure was increased up to 10
2-10
3 Pa in St-7, whereas it was suppressed lower 10
1 Pa in Sh-7. As to reactors St-S and Sh-7, the Gibbs free energy (ΔG') for propionate degradation were kept minus, and propionate degradation was occurred in the early stage of their fermentation. On the other hand, St-7 had unfavorable condition to propionate degradation, and beginning of the degradation was delayed. Sulfate-reducing bacteria act as a hydrogen consumer in the all of reactor. It was revealed biodegradation of propionate could be enhanced by the maintenance of low hydrogen pressure such as 10 Pa, and sulfate-reducing bacteria have effectiveness to achieve that condition.
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