Hydrogen production from beverage industry wastewater (20 g/L-hexose equivalent) using an immobilized cell reactor with a continuous mode of operation was studied at various hydraulic retention times (HRT, 8-1.5 h). Maximum hydrogen production rate (HPR) of 55 L/L-d was obtained at HRT 1.5 h (an organic loading of 320 g/L-d(hexose equivalent)). This HPR value is much higher than those of other industrial wastewaters employed in fermentative hydrogen production. The cell biomass concentration peaked at 3 h HRT with a volatile suspended solids (VSS) concentration of 6.31 g/L (with presence of self-flocculating Selenomonas sp.), but it dropped to 3.54 gVSS/L at 1.5 h HRT. With the shortening of HRT, lactate concentration increased but the concentration of the dominant metabolite butyrate did not vary significantly. The Clostridium species dynamics was not significantly affected, but total microbial community structure changed with respect to HRT variation as evident from PCR-DGGE analyses. Analysis of energy production rate suggests that beverage wastewater is a high energy yielding feedstock, and can replace 24% of electricity consumption in a model beverage industry. (C) 2015 Elsevier Ltd. All rights reserved.