Fermentative hydrogen production with xylose by Clostridium and Klebsiella species in anaerobic batch reactors Sandra I. Maintinguer*, Bruna S. Fernandes, Iolanda C.S. Duarte, Nora Ka ´ tia Saavedra, M. Angela T. Adorno, M. Bernadete A. Varesche Department of Hydraulics and Sanitation, School of Engineering of Sa ˜o Carlos, University of Sa ˜o Paulo, Av. Trabalhador Sa ˜o-carlense, 400, 13566-590 Sa ˜o Carlos, SP, Brazil article info Article history: Received 6 April 2011 Received in revised form 8 July 2011 Accepted 22 July 2011 Available online 23 August 2011 Keywords: Mesophilic conditions Xylose 16S rRNA Klebsiella sp. Clostridium sp. abstract Hydrogen production was obtained from low concentrations of xylose metabolized by heat treated inoculum obtained from the slaughterhouse wastewater treatment UASB reactor installed in Brazil. The molecular biological analysis Clostridium and Klebsiella species, recognized as H 2 and volatile acid producers, in addition to Burkholderia species and uncultivated bacteria. The assays were carried out in batch reactors: (1) 630.0 mg xylose/L, (2) 1341.0 mg xylose/L, (3) 1848.0 mg xylose/L and (4) 3588.0 mg xylose/L. The following yields were obtained: 3% (0.2 mol H 2 /mol xylose), 8% (0.5 mol H 2 /mol xylose), 10% (0.6 mol H 2 /mol xylose) and 14% (0.8 mol H 2 /mol xylose), respectively. The end products obtained were acetic acid, butyric acid, methanol and ethanol in all of the anaerobic reactors. The concentrations of xylose did not inhibit microbial growth and hydrogen production. This suggested that low concentrations of xylose should be added to wastewater to produce hydrogen. Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. 1. Introduction Biohydrogen is a promising alternative energy source [1]. The hydrogen gas generated in wastewater treatment by biological processes can be used as an alternative energy source. Waste- waters are raw materials that do not incur production costs [2]. Mixed anaerobic cultures obtained from sewage sludge can be used for fermentative hydrogen production because they contain a variety of hydrogen-producing bacteria [3]. Several compounds, such as glucose, hexose isomers and polymers as starch or cellulose, have different production levels of hydrogen per mole of organic substrate, depending on the fermentative pathway and end products. Diverse wastewater from agriculture, wood processing and the paper industry may contain xylose [1,3]. Most of studies are related with glucose, and sucrose as substrate source by mixed cultures and a very little attention have been given to xylose fermentation though it has been reported as a suitable substrate source for bio- hydrogen production [4]. Xylose is a common and abundant sugar obtained from the hydrolysis of lignocellulosic materials, in particular, hemicellulose. Hydrolysis of lignocellulose materials produces sugars composed mainly of xylose, which accounts for 35e45% of the total product composition [1]. Fermentative hydrogen production from hexose, glucose and sucrose is well studied [1,5,6e8]. In contrast, fermentative hydrogen production of xylose (i.e. pentose) is less well studied [1,3]. The following xylose degradation pathways may result during the fermentative process of hydrogen gas production: (1) consumption of xylose and generation of acetic acid and (2) * Corresponding author. Tel.: þ55 1633738357; fax: þ55 1633739550. E-mail addresses: mainting2008@gmail.com, mainting@sc.usp.br (S.I. Maintinguer), varesche@sc.usp.br (M.B.A. Varesche). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 36 (2011) 13508 e13517 0360-3199/$ e see front matter Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2011.07.095