A high-rate hydrogen production process able to produce H(2) at a maximum rate of 15 L/L/h was successfully developed by the Feng Chia University (FCU) biohydrogen research team. This highly efficient hydrogen fermentation system includes a 400 L pilot-scale system constructed for determining scale-up operation parameters for commercializing the bioH(2) production technology. The pilot-scale system is composed of a feedstock tank, mixing system, fermentor, gas/liquid separator and automatic control system. The fermentor is fed with sucrose (20 g COD/L) and operated at 35 degrees C. A batch strategy is used for system start-up. The fermentor was first operated in a batch mode for two days and then switched to a continuous-feeding mode (HRT 12 h) for one month. During the continuous operation, pH notably affected H(2) production efficiency and bacterial community. For the first 14-day operation, the H(2) production rate increased from 0.017 to 0.256 L/L/h with a pH variation from 5.0 to 7.0. The DGGE results indicate the presence of two Clostridium species (namely, Clostridium butyricum and Clostridium pasteurianum) in the fermenter. Stable hydrogen production rate was obtained at pH 5.5-6.0 when C. pasteurianum became dominant in the mixed culture. Crown Copyright 2009 Published by Elsevier Ltd on behalf of Professor T. Nejat Veziroglu. All rights reserved.