A novel continuous mixed immobilized sludge reactor (CMISR) containing activated carbon as support carrier was used for fermentative hydrogen production from molasses wastewater. When the CMISR system operated at the conditions of influent COD of 2000-6000 mg/L, hydraulic retention time (HRT) of 6 h and temperature of 35 degrees C, stable ethanol type fermentation was formed after 40 days operation. The H-2 content in biogas and chemical oxygen demand (COD) removal were estimated to be 46.6% and 13%, respectively. The effects of organic loading rates (OLRs) on the CMISR hydrogen production system were also investigated. It was found that the maximum hydrogen production rate of 12.51 mmol/h L was obtained at OLR of 32 kg/m(3) d and the maximum hydrogen yield by substrate consumed of 130.57 mmol/mol happened at OLR of 16 kg/m(3)d. Therefore, the continuous mixed immobilized sludge reactor (CMISR) could be a promising immobilized system for fermentative hydrogen production. (C) 2012 Elsevier Ltd. All rights reserved.