Effect of temperature on continuous hydrogen production of cellulose S.I. Gadow a,b , Yu-You Li a,c, *, Yuyu Liu a a Dept. of Environmental Science, Graduate School of Environmental Studies, Tohoku University, Sendai 980-8579, Japan b Dept. of Agric. Microbiol., National Research Center, Dokki, Cairo, Egypt c College of Environmental Science and Municipal Engineering, Xian University of Architecture and Technology, No. 13 Yanta Road, Xi’an 710055, China article info Article history: Received 5 April 2012 Received in revised form 24 April 2012 Accepted 25 April 2012 Available online 15 June 2012 Keywords: Bio-hydrogen Cellulose Temperature Dark fermentation Continuous mode CSTR abstract The effect of temperature on the hydrogen fermentation of cellulose was evaluated by a continuous experiment using a mixed culture without pretreatment. The experiments were conducted at three different temperatures, which were mesophilic [37  2  C], ther- mophilic [55  2  C] and hyper-thermophilic [80  2  C], with an influent concentration of cellulose of 5 g/l and a hydraulic retention time [HRT] of 10 days. A stable hydrogen production was observed at each condition. At 37  2  C, the maximum hydrogen yield was 0.6 mmol H 2 /g cellulose. However, at 55  2  C and 80  2  C, the maximum hydrogen yields were 15.2 and 19.02 mmol H 2 /g cellulose, respectively. While 26% of the biogas was methane under the mesophilic temperature, no methane gas was detected under both the thermophilic and hyper-thermophilic temperatures. The results show that operational temperature is a key to sustainable bio-hydrogen production and that the thermophilic and hyper-thermophilic conditions produced better results than mesophilic condition. Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. 1. Introduction Even though research on biological H 2 production has been carried out over a quarter century [1], hydrogen is produced almost entirely from fossil fuels such as natural gas and naphtha. In such processes, the same amount of CO 2 as that formed from combustion is released [2]. Besides being an environmentally friendly fuel, producing only water upon combustion, H 2 has an energy yield of 142 kJ/g, 2.75 times higher than that of any hydrocarbon [3]. In the direct bioconversion of cellulose to hydrogen, the precise role that temperature has on the stability of hydrogen production from cellulose remains unclear at this stage. Two temperatures that have been commonly used in the literature: the mesophilic and thermophilic conditions. It has been reported that mesophilic anaerobic bacteria are not capable of utilizing cellulose effectively. While, in order to hydrolyze the cellulose so that it can generate H 2 by mesophilic anaerobic bacteria, exogenous cellulose enzymes need to be added to the culture [4]. Since ther- mophilic anaerobic bacteria can effectively utilize cellulose, they have great potential for H 2 production using cellulose without the addition of exogenous cellulose [5]. In just the last few years, a group of bacteria have been discovered that have the remarkable property of growing near and above 100  C [6]. Under hyper-thermophilic anaerobic conditions, * Corresponding author. Lab of Urban and Regional Environmental Systems, Graduate School of Environmental Studies, 6-6-11 Aoba, Sendai 980-8579, Japan. Tel.: þ81 22 795 4867; fax: þ81 22 795 7465. E-mail address: yyli@epl1.civil.tohoku.ac.jp (Y.-Y. Li). Available online at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 37 (2012) 15465 e15472 0360-3199/$ e see front matter Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2012.04.128