Biohydrogen production in an anaerobic fluidized granular bed bioreactor was strongly dependent on temperature and effluent recycle rates. At 45 degrees C as the effluent recycle rate was increased from 1.3 to 3.5 L/min, the total H(2) output for the bioreactor increased from 10.6 to 43.2 L/h. Volumetric H(2) productivity also increased from 2.1 to 8.7 L H(2)/L/h. At 70 degrees C as the effluent recycle was increased from 1.3 to 3.5 L/min, the total H(2) output for the bioreactor increased from 13.8 to 73.8 L/h. At 70 degrees C volumetric H(2) productivities increased from 2.8 to 14.8 L H(2)/L/h as the effluent recycle rate was increased from 1.3 to 3.5 L/min. At 45 degrees C % H(2) was 45% and reached 67% at 70 degrees C. Maximum hydrogen yields at 45 degrees C were 1.24 and 2.2 mol H(2)/mol glucose at 70 degrees C. (C) 2011 Elsevier Ltd. All rights reserved.