Although a novel anaerobic down-flow structured bed reactor has shown feasibility and stable performance for a long-term compared to other anaerobic fixed bed systems for continuous hydrogen production, the volumetric rates and yields have so far been too low. In order to improve the performance, an operation strategy was applied by organic loading rate (OLR) variation (12-96 g COD L (1) d (1)). Different volumetric hydrogen rates, and yields at the same OLR indicated that the system was mainly driven by the specific organic load (SOL). When SOL was kept between 3.8 and 6.2 g sucrose g (1) VSS d (1), the volumetric rates raised from 0.1 to 8.9 L H-2 L (1) d (1), and the yields were stable around 2.0 mol H2 mol (1) converted sucrose. Furthermore, hydrogen was produced mainly via ethanol-type fermentation, reaching a total energy conversion rate of 23.40 kJ h (1) L (1) based on both hydrogen and ethanol production. (C) 2015 Elsevier Ltd. All rights reserved.