Strategy of controlling the volumetric loading rate to promote hydrogen-production performance in a mesophilic-kitchen-waste fermentor and the microbial ecology analyses

The kitchen waste was chosen as a high solid (42 g L−1 of volatile suspended solid, VSS) and high organic (107 g L−1 of chemical oxygen demand) feedstock for operating a 3-L mesophilic fermentor. The greatest specific hydrogen production rate ( r H 2 ) was observed in Stage 3 as 3.4 L-H2 L−1 day−1 with a volumetric loading rate (VLR) of 100 g-COD L−1 day−1; the highest hydrogen yield was observed in Stage 2 as 96 mL-H2 g−1 of influent VSS with a VLR of 46 g-COD L−1 day−1. In Stages 1 (with a VLR of 27 g-COD L−1) and 2, the sum of Butyrivibrio fibrisolvens and Clostridium proteoclasticum is dominant, but in Stage 3, Olsenella genomosp, became dominant and constituted 44% of the entire population. The dependence of VLR and r H 2 could be regressed as a linear equation of r H 2 = ( 2.83 VLR + 40.5 ) × 10 - 2 .