Prevention of substrate and product inhibitions by using a dilution strategy during dark fermentative hydrogen production from molasses.

Substrate and product inhibitions have a significant effect on dark fermentative hydrogen gas production. Particularly, rapid formation of volatile fatty acids leads to fast pH decreases shifting the metabolic pathway. Therefore, controlling volatile fatty acid accumulation has great importance in maintaining effective hydrogen production. In this context, a dilution strategy was applied to regulate volatile fatty acids levels within the desired concentration range. A three-factor Box-Behnken statistical experiment design was established to assess the effects of dilution time, dilution percentage and initial COD concentration on hydrogen formation yield and rate. Highest hydrogen yield (7.7 mL H 2 /mL reactor) and rate (21. 47 mL H 2 /h or 9.38 mmol/L reactor.h) were achieved when 85 gCOD/L containing fermentation media was diluted with a percentage of 130 of the initial working volume at the 3rd hour of the fermentation period. Moreover, this strategy enabled to start fermentation with 55 g glucose/L. Image 1 • Hydrogen production was improved with a proper dilution of dark fermentation media. • Dilution conditions were assessed by Box-Behnken statistical experiment design. • Negative effects of substrate and product inhibitions were reduced significantly. • Dilution strategy enabled to ferment high sugar-containing molasses. [ABSTRACT FROM AUTHOR]