The production of hydrogen in an anaerobic fluidized bed reactor (AFBR) was evaluated under different organic loading rates (OLRs) with the addition of 1 g L−1 sodium bicarbonate for pH control. Expanded clay was used as the support material for microbial attachment. Two AFBRs were operated with glucose concentrations of 10 and 25 g L−1 and a hydraulic retention time (HRT) decreasing from 8 to 1 h at a controlled temperature of 30°C. A linear correlation was observed between the hydrogen production rate (HPR) and the OLR, except for the reactor operated with 25 g L−1 glucose. The maximum HPR of 1.58 L h−1 L−1 was obtained with an HRT of 1 h, and the maximum H2 yield of 1.32 mol H2 mol−1 glucose was obtained with an HRT of 2 h, in the reactor operated with 10 g L−1 glucose
