The effect of reduced pressure and glucose concentration on hydrogen and volatile fatty acid yield: The role of homoacetogenesis

In this study, the influence of headspace pressure (HP; 20?100 kPa) and organic loading rate (OLR; 10?30 g/L) on H2 and volatile fatty acid (VFA) yield were investigated. The experiments were carried out in the semicontinuous mode, the main products in VFAs were ethanol and butyrate, which accounted for more than 75%. More than 79% generated H2 was consumed through homoacetogenesis pathway when HP was 100 kPa, and lowing HP could effectively promote the accumulation of H2 (increased by at least 2 times). Even though consumed H2 through homoacetogenesis was related to OLR and HP, the lower HP was more likely to reduce this part H2 consumption, especially under 10 g/L condition. As for acid production rate, both OLR and HP have a significant effect (p < 0.05). Maximum acid production rate was 489.86 mg-COD/g-CODdegrade?d- 1when OLR was 20 g/L and HP was 40 kPa.