Combined hydrogen and ethanol production from sugars and lignocellulosic biomass by Thermoanaerobacterium AK 54 , isolated from hot spring Margret Audur Sigurbjornsdottir, Johann Orlygsson ⇑ University of Akureyri, Faculty of Natural Resource Sciences, Borgir at Nordurslod, 600 Akureyri, Iceland article info Article history: Received 11 July 2011 Received in revised form 12 October 2011 Accepted 13 November 2011 Available online xxxx Keywords: Ethanol Hydrogen Hot spring Thermoanaerobacterium Hydrolysate Lignocellulose abstract Combined biohydrogen and bioethanol (CHE) production from monosugars, polymeric carbohydrates and hydrolysates made from various lignocellulosic biomasses was investigated by strain AK 54 , a saccharo- lytic, thermophilic ethanol and hydrogen producing bacterium isolated from a hot spring in Iceland. Opti- mum growth conditions for the strain were between pH 5.0–6.0 and at 65 °C. As determined by full 16S rRNA analysis, strain AK 54 belongs to the genus Thermoanaerobacterium, most closely affiliated with Ther- moanaerobacterium aciditolerans (99.0%). Effect of increased initial glucose concentration on growth and end product formation was investigated and good correlations were observed between increased sub- strate loadings and end product formation of up to 50 mM where clear inhibition was shown. The ability to utilize various carbon substrates was tested with positive growth on xylose, glucose, fructose, man- nose, galactose, sucrose and lactose. The major end products in all cases were ethanol, acetate, lactate, hydrogen and carbon dioxide. By lowering the partial pressure of hydrogen during glucose degradation, the end product formation was directed towards hydrogen, acetate and ethanol but away from lactate. Hydrogen and ethanol production from hydrolysates from biomass (7.5 g L 1 (dw)); cellulose, newspaper, grass (Phleum pratense), barley straw (Hordeum vulgare), and hemp (Cannabis sativa L), was investigated. The biomass was chemically (acid/alkali) and enzymatically pretreated. The highest ethanol production was observed from cellulose hydrolysates (24.2 mM) but less was produced from lignocellulosic bio- masses. Chemical pretreatment of biomass hydrolysates increased hydrogen and ethanol yields substan- tially from barley straw, hemp and grass but not from cellulose or newspaper. The highest hydrogen was also produced from cellulose hydrolysates or 6.7 mol-H 2 g 1 TS pretreated with alkali (12.2 mol-H 2 g 1 glucose equivalents) but of the lignocellulosic biomass, highest yields were from grass pretreated with base (4.9 mol-H 2 g 1 TS). Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Currently, the world’s energy demand is focused on the use of fossil fuels which are inevitably depleting [1–3]. Fossil fuels have the big disadvantage that they are high in sulfur, nitrogen and metal content and its burning results in extensive amount of SO 2 and NO x emissions to the atmosphere. Additionally, CO 2 is released which is considered to have undesirable climatic consequences. Energy con- sumption is growing at rising rates at the same time, leading to increased interest of renewable alternatives to fossil-based fuels. Biohydrogen and bioethanol are promising CO 2 neutral types of biofuels since they are derived from renewable sources [4–6]. Biohy- drogen has a great potential as a clean, renewable energy carrier with higher energy content as compared to hydrocarbon fuels and water as the sole end product after combustion [7–9]. Production of bioethanol as fuel has increased in recent years; in 2005 around 54.2 billion liters of ethanol was produced, mostly from sugar (Brazil) and starch (USA) [5]. Techniques used today for bioethanol production depend on limited supply of raw material leading to interest in fermentation of lignocellulosic biomass (e.g. wood, straw and grasses), namely second generation ethanol production [10,11]. Production of biohydrogen and bioethanol through microbial fer- mentation are well known processes but thermophiles have many advantages compared to mesophilic microorganisms concerning fast growth rates and their ability to degrade a broad variety of sub- strates. Furthermore, many thermophiles produce fewer types of undesired end products compared to mesophiles [12,13]. High val- ues of hydrogen produced per mol of glucose utilized have been re- ported by the hyperthermophiles Caldicellulosiruptor saccharolyticus and Thermotoga elfii; 3.3–4.0 mol-H 2 mol carbohydrate [14,15] and by enrichment culture isolated from Icelandic hot spring; 3.2 mol-H 2 mol-glucose 1 in semi-continuous batch reactor and 2.10 mol-H 2 mol-glucose 1 in batch culture [16,17]. The highest ethanol yield reported is for the thermophilic bacteria Thermoanaerobacter ethanolicus; 1.9 mol-EtOH mol-glucose 1 degraded [18] but several strains are capable of yields reaching 1.5 mol-EtOH mol-glucose 1 [19]. 0306-2619/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.apenergy.2011.11.035 ⇑ Corresponding author. Tel.: +354 4608511; fax: +354 4608998. E-mail address: jorlygs@unak.is (J. Orlygsson). Applied Energy xxx (2011) xxx–xxx Contents lists available at SciVerse ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy Please cite this article in press as: Sigurbjornsdottir MA, Orlygsson J. Combined hydrogen and ethanol production from sugars and lignocellulosic biomass by Thermoanaerobacterium AK 54 , isolated from hot spring. Appl Energy (2011), doi:10.1016/j.apenergy.2011.11.035