The objective of the present study was to evaluate the influence of the carbon/phosphorus (C/P) ratio (300-1100) on hydrogen production and the control of homoacetogenesis in four anaerobic fluidized bed reactors with fixed carbon/nitrogen ratios of 100, 150, 200, and 250. The reactors were fed glucose (5000 mg L-1) at the hydraulic retention time (HRT) of 8 h. Low production of acetic acid attributed to homoacetogenesis was observed in all reactors (<29 % of total metabolite production) at C/P ratios between 500 and 1100, with no occurrence at the C/P ratio of 300. Thus, the effect of HRT (8 to 1 h) on hydrogen production was evaluated at a C/P ratio of 300. The highest values of hydrogen yield (1.76 mol H-2 mol(-1) hexose) and hydrogen production rate (13.81 H-2 day(-1) L-1) were observed for a C/N/P ratio of 100/0.5/0.3 at HRTs of 8 and 1 h, respectively. The maximum hydrogen production was attributed to butyric acid production. The decrease in the HRT caused an increase in acetic acid and ethanol production. Molecular analysis identified the presence of Ethanoligenens sp. and Clostridium sp., which were related to the production of hydrogen, ethanol, butyric acid, and acetic acid. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.