This work presents a simple heuristic approach to maximize the hydrogen production rate (HPR) using an on-line optimization strategy in a continuous stirred tank reactor. An initial investigation of the relationship between the organic loading rate (OLR) and HPR was used to propose the objective function of a nonlinear optimization problem, subject to a limited range of hydraulic retention times (HRTs) and a maximum productivity standard deviation. The inlet flow was the optimized variable while the influent substrate concentration was fixed at a constant value. The results showed a maximum HPR of 25.4 L H-2/(L d), reached for an optimal OLR of approximately 100 g COD/(L d) and an HRT of approximately 4 h. Following the optimization strategy, the specific HPR was increased from 7.52 to 16.35 L H-2/(gVSS d). The hydrogen yield increased from 1.8 to 2.32 mol H-2/mol glucose, representing an improvement of 29%. Finally, during the optimization period, the specific hydrogen production rate increased from 3.3 to 16.35 L H-2/(gVSS d), which suggested that the substrate was used by hydrogen-producing biomass rather than by other competing microorganisms. (C) 2015 Elsevier Ltd. All rights reserved.