Role of xylose from acidic hydrolysates of agave bagasse during biohydrogen production

This study compares the H2 production from glucose, xylose, and acidic hydrolysates of Agave tequilana bagasse as substrates. The fermentation was performed in a granular sludge reactor operated in two phases: (1) model substrates (glucose and xylose) and (2) acidic hydrolysates at 35 °C, pH 4.5 and a hydraulic retention time of 5.5 with glucose (10 g L−1) and xylose (12 g L−1). A sequencing batch reactor was used to acclimate the biomass between the glucose and xylose continuous fermentation (with a mixture of xylose-glucose) and acidic hydrolysates. During the discontinuous acclimating step, the xylose/glucose ratio increment negatively affected the H2 productivity. Although the continuous H2 production with xylose was negligible, the co-fermentation with glucose (88–12%) allowed H2 productivity of 2,889 ± 502 mL H2 L−1d−1. An acidic hydrolysate concentration of 3.3 gcarbohydrate L−1 showed a 3-fold higher H2 productivity than with a concentration of 10 g L−1. The results indicated that xylose, as the only substrate, was challenging to metabolize by the inoculum, and its mixture with glucose improved the H2 productivity. Therefore, the low H2 productivity with hydrolysates could be related to the presence of xylose.