Lignocellulosic ethanol: From science to industry L. Viikari a , J. Vehmaanpera ¨ b , A. Koivula c, * a University of Helsinki, Department of Applied Chemistry and Microbiology, P.O. Box 27, FI-00014 Helsinki, Finland b ROAL Oy, P.O. Box 57, FI-05201 Rajama ¨ki, Finland c VTT Technical Research Centre of Finland, P.O. Box 1000, FI-02044 VTT, Espoo, Finland article info Article history: Received 12 December 2011 Received in revised form 9 May 2012 Accepted 14 May 2012 Available online 6 June 2012 Keywords: Ethanol Lignocelluloses Trichoderma reesei Enzymes Cellulases Hydrolysis abstract Lignocellulosic raw materials, not competing with food production, can provide environ- mental, economic, and strategic benefits for the production of biofuels. The cost of biomass-based biotechnical ethanol production has been recently reduced significantly, mainly due to advances in the conversion techniques; i.e. by improved enzymes and new yeast strains. Conversion of the cellulosic components into fermentable sugars is, however, still the major technological and economical bottleneck in the production of fuels or other high-volume commodity products from cellulosic biomass. Especially, the enzy- matic hydrolysis still forms a major cost factor. The targets for reducing the costs of biotechnical conversion processes of lignocelluloses to ethanol can be divided into three categories: the costs of enzymes, the costs of produced sugars and the costs of ethanol production. The efficiencies of individual enzymes can be improved by designing enzymes with optimal domain structures and binding properties, and with higher specific activity, lower end-product inhibition and higher thermal stability, as well as by optimizing the production processes. The cost of the enzymatic hydrolysis is dependent on the efficiency, yield and costs of the pretreatment, synergistic action of cellulases and accessory enzymes, as well as on the needed amount of externally added enzymes. The costs of ethanol production are further affected by the yield, concentration and production rate of ethanol. This work reviews the major bottlenecks in the conversion process, as well as highlights recent approaches to overcome these problems. ª 2012 Elsevier Ltd. All rights reserved. 1. Introduction Among potential alternative bioenergy resources, lignocellu- losics have been identified as the prime source of biofuels and other value-added products. Lignocelluloses from agricul- tural, industrial and forest sources account for the majority of the total biomass present in the world and compose a vast renewable resource. Lignocellulosic raw materials, not competing with food production, can provide environmental, economic, and strategic benefits for the production of fuels. Ambitious goals have been set for biofuels in most parts of the world, including those of the U.S. Department of Energy Office with a scenario for supplying 30% of the gasoline demand with biofuels by the year 2030, and the European Union with a vision of 10% of the EU’s transportation fuels deriving from biofuels by 2020. Today, the main aim is not only to replace fossil fuels by any biofuel but to review the greenhouse gas emission saving thresholds. Thus, the political timetables concerning the use of lignocellulosic raw materials for production of ethanol and other biofuels bring challenges to * Corresponding author. Tel.: þ358 40 720 7158. E-mail address: Anu.Koivula@vtt.fi (A. Koivula). Available online at www.sciencedirect.com http://www.elsevier.com/locate/biombioe biomass and bioenergy 46 (2012) 13 e24 0961-9534/$ e see front matter ª 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.biombioe.2012.05.008