et al. (2013) also showed that the high stirring velocity could enhance the hydrogen transfer from the liquid phase and therefore increase the hydrogen production.
Fig. 3 shows the material balance in the combination bioprocess of solid-state fermentation and fermentative hydrogen production from food waste (mass ratio of 4%). The best hydrogen yield
(39.14 ml H2/g food waste or 219.91 ml H2/VS added) was achieved at food waste mass ratio of 4%. It was observed from Table 6 that the result obtained from this study is comparable or higher than the other reported studies. Part of the reason for higher hydrogen yield obtained from this study could be simply due to the degradative capability of the microbial inoculum relative to the form of the substrate. Obviously, more hydrogen yield could be achieved using glucose solution (food waste hydrolysate) rather than direct food waste solid as substrate. Furthermore, other different reported pretreatments could solubilize part of the starch contained in the food waste,while a large amount of starch remained in the solid phase (Gioannis et al., 2013). In this study, the starch conversion efficiency of food waste could reach 82.8–87.2% by using enzymatic hydrolysis within 24 h. Thus, the fermentability of food waste could be improved by
enzymatic hydrolysis that increases the accessibility of the starch in the food waste hydrolysate. Furthermore, there is around 224 mg/L of FAN generated in the food waste hydrolysate which may be compared to 3.56 g yeast extract (Leung et al., 2012).Therefore, it demonstrated that the proposed combination bioprocess could effectively accelerate the hydrolysis rate, improve raw material utilization and enhance hydrogen yield.