Thermophilic biohydrogen production from energy plants by Caldicellulosiruptor saccharolyticus and comparison with related studies Galina Ivanova a , Ga ´bor Ra ´ khely a,b , Korne ´l L. Kova ´cs a,b, * a Department of Biotechnology, University of Szeged, H-6726 Szeged, Hungary b Institute of Biophysics, Biological Research Center, Hungarian Academy of Sciences, Szeged, Hungary article info Article history: Received 28 January 2009 Received in revised form 13 February 2009 Accepted 15 February 2009 Available online 5 April 2009 Keywords: Extreme thermophile Hydrogen production Energy plants Caldicellulosiruptor saccharolyticus Sweet sorghum Wheat straw Maize biomass Bagasse Silphium abstract Air-dried samples of sweet sorghum, sugarcane bagasse, wheat straw, maize leaves and silphium were utilized without chemical pretreatment as sole energy and carbon sources for H 2 production by the extreme thermophilic bacterium Caldicellulosiruptor saccharolyticus. The specific H 2 production rates and yields were determined in the batch fermentation process. The best substrate was wheat straw, with H 2 production capacity of 44.7 L H 2 (kg dry biomass) 1 and H 2 yield of 3.8 mol H 2 (mol glucose) 1 . Enzymatically pretreated maize leaves exhibited H 2 production of 38 L H 2 (kg dry biomass) 1 . Slightly less H 2 was obtained from homogenized whole plants of sweet sorghum. Sweet sorghum juice was an excellent H 2 source. Silphium trifoliatum was also fermented though with a moderate production. The results showed that drying is a good storage method and raw plant biomass can be utilized efficiently for thermophilic H 2 production. The data were critically compared with recently published observations. ª 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. 1. Introduction Sugarcane, sweet sorghum, wheat, maize and their byprod- ucts, for instance, are currently subjects of studies concerning their ability to serve as substrates for biofuels’ production. One of the advantages using such material as biomass for biofuel production is that these plants are short-rotation crops. Some relatively new and less well-studied energy crops, e.g. Silphium trifoliatum, have considerable potential as they re-grow from their rhizome after each harvest, which allows multiple harvests without the need to re-plant. Maize and sorghum silage can serve both as energy plants and as fodder, while sugarcane, sweet sorghum syrup, corn and wheat starch are used in the food industry. The leftover biomass, however, is mostly unexploited and poses a disposal problem. Abbreviations: BGS, sugarcane bagasse; CFU, colony forming unit; E, extract; PML, pretreated maize leaves; PWS, pine wood shavings; RB, residual biomass; SSC, sweet sorghum concentrate 65  Bx; STR, Silphium trifoliatum leaves; SSJ, sweet sorghum juice; SSP, sweet sorghum plant (Sorghum bicolor); TC, total carbon; TOC, total organic carbon; UML, untreated maize leaves; WST, wheat straw. * Corresponding author. Department of Biotechnology, University of Szeged, H-6726 Szeged, Kozepfasor 52, Hungary. Tel.: þ36 62 544351; fax: þ36 62 544352. E-mail address: kornel@brc.hu (K.L. Kova ´ cs). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he 0360-3199/$ – see front matter ª 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2009.02.082 international journal of hydrogen energy 34 (2009) 3659–3670