According to previous experiment in our laboratory, the maximum H2 yield was 0.59 to 0.66 mol H2 /
mol glucose in a 120 h batch process, if applying a heat shock pre-treatment and a specific mix of
nutrients [17]. Figure 3 shows the yields of H2 for each pre-treated sample. The best performances were
as follow: MW5min@ 800W+pH4 and BES 8mM by means of 0.96 and 0.88 mol H2/mol glucose
respectively; WB 90°C +pH4 and BES 7mM by means of pH of 0.62 and 0.52 mol H2/mol glucose
respectively; CHCl3 (0.10%) be means of 0.34mol H2/mol glucose. The rest of the pre-treatments showed
a low performance, in comparison to Blanc 1 and Blanc 2. In order to achieve the highest possible H2
yield, glucose has to be fermented to acetate. In addition, it has been reported [7, 18,19] that H2 is not
produced in propionate fermentation, rather in butyrate and acetate-ethanol fermentation, especially after
a pre-treatment, which enhance the formate production. Therefore, butyrate-acetate fermentation has been
appointed by several researchers as the main pathways followed by the bacteria for bio-H2 production,
due to its potential to change to butanol production (H2 is directly consumed or it production is inhibited).