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(H2)) was observed in Stage 3 as 3.4 L-H(2) 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-H(2) 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(H2), could be regressed as a linear equation of r(H2), = (2.83 VLR + 40.5) x 10(-2). (C) 2011 Published by Elsevier Ltd.