Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he Optimization of hydrogen production in a granule-based UASB reactor Bai-Hang Zhao a , Zheng-Bo Yue a , Quan-Bao Zhao a , Yang Mu a , Han-Qing Yu a,Ã , Hideki Harada b , Yu-You Li b a Department of Chemistry, University of Science & Technology of China, Hefei 230026, China b Department of Civil Engineering, Tohoku University, Sendai 980-8579, Japan article info Article history: Received 24 November 2007 Received in revised form 6 March 2008 Accepted 7 March 2008 Keywords: Granule Hydrogen Optimization Response surface methodology (RSM) Upflow anaerobic sludge blanket (UASB) reactor abstract Hydrogen production from sucrose in a granule-based upflow anaerobic sludge blanket (UASB) reactor was optimized through employing response surface methodology (RSM) with a central composite design in this study. The individual and interactive effects of influent sucrose concentration (S in ) and hydraulic retention time (HRT) on anaerobic hydrogen production were elucidated. Experimental results show that a maximum hydrogen yield of 1.62 mol-H 2 /mol-hexose was obtained under the optimum conditions of S in 14.5 g/L and an HRT 16.4 h. The hydrogen yield was individually dependent on S in and HRT, while their interactive effect on the hydrogen yield was not significant. Throughout the experiments the hydrogen content fluctuated between 25.9% and 50.0%, but free of methane. Ethanol, acetate and butyrate were the main aqueous products and their yields all correlated well with S in and HRT, indicating a mixed-type fermentation in this UASB reactor. & 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. 1. Introduction Hydrogen has attracted increasing worldwide attention as a clean energy source due to the following advantages: clean, efficient with a high energy yield (122 kJ/g), renewable, and no generation of toxic byproducts [1]. Physical, chemical and biological processes have been used for hydrogen production. Among them, hydrogen production through anaerobic fer- mentation is particularly attractive because hydrogen can be produced from renewable organic matters [2]. Most of experiments on hydrogen production from various types of wastewater have been carried out with an anaerobic con- tinuous-flow stirred tank reactor (CSTR) at laboratory [3–5]. However, the CSTR is unable to retain a high level of biomass for hydrogen production due to its intrinsic structure. This might lead to a decrease in the hydrogen production capability and system stability [6]. For example, the sus- pended-growth hydrogen-producing biomass in a CSTR is sensitive to the fluctuation of operating parameters such as retention time, pH and temperature [7]. A significant variation of environmental parameters often leads to a failure of a hydrogen-producing CSTR [1]. To overcome this problem, an upflow anaerobic sludge blanket (UASB) reactor with separate reaction and settlement regions is desirable. The main feature of the UASB reactor is the retention of a large amount of anaerobic granules [8]. Compared to sludge flocs, sludge granules have good settling ability and can resist to the fluctuation of operating parameters [9]. Anaerobic hydrogen production is a complex process and is effected by many factors [10], e.g., hydraulic retention time ARTICLE IN PRESS 0360-3199/$ - see front matter & 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2008.03.008 Ã Corresponding author. Fax: +86 551 3601592 E-mail address: hqyu@ustc.edu.cn (H.-Q. Yu). INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 33 (2008) 2454– 2461