Research Paper Pretreatment of wheat straw using steam, steam/acetic acid and steam/ethanol and its enzymatic hydrolysis for sugar production Samyar Zabihi, Roozbeh Alinia, Feridun Esmaeilzadeh*, Jamshid Fathi Kalajahi Chemical and Petroleum Engineering Department, Shiraz University, Shiraz, Iran article info Article history: Received 9 February 2009 Received in revised form 22 September 2009 Accepted 18 November 2009 Published online 19 January 2010 Wheat straw is a suitable raw material for ethanol production, since it has a high cellulose content. In the bioconversion of lignocellulosic materials to ethanol, pretreatment of the material prior to enzymatic hydrolysis is essential to obtain high overall yields of sugar and ethanol. The objective here is to find additives which increase the efficiency of the sugar production. The pretreatment of wheat straw by steam explosion soaked with acetic acid or ethanol prior to the pretreatment was investigated by varying the temperature (180–225)  C and the retention time (3–60 min). The results showed that the pretreatment of wheat straw by steam explosion with soaked with acetic acid or ethanol was more effective than that by steam explosion alone. Additionally, the pretreatment of wheat straw by steam explosion at 210  C and 10 min, by steam/acetic acid at 220  C and 8 min and by steam/ethanol at 220  C and 5 min resulted in the best overall yield of reducing sugar which was found to be 177.3 g kg 1 on dry solids (DS) basis, 244.1 g kg 1 DS, and 264.3 g kg 1 DS, respectively. ª 2009 IAgrE. Published by Elsevier Ltd. All rights reserved. 1. Introduction Ethanol, a clean and renewable energy source, which can be produced through fermentation from renewable biomass, has drawn much attention from the government and researchers (Sun and Cheng, 2002). In many countries, including the USA, wheat straw is an abundant by-product from wheat production. The average yield of wheat straw is 1.3–1.4 kg kg 1 of wheat grain (Montane et al., 1998). Based on the data from Food and Agriculture Organization (FAO), 63.5 million tonnes of wheat were produced in the USA in 2003 with a world production of 556.3 million tonnes (Saha et al., 2005). In Iran the average production of wheat straw is 13–14 million tonne per annum. Cellulose, the major frac- tion of lignocellulosic biomass, can be hydrolysed to reducing sugar by cellulase enzymes. This hydrolysis can be influenced by porosity (accessible surface area) of lignocel- lulosic biomass, cellulose fibre crystallinity, and lignin and hemicellulose content. A pretreatment process is therefore essential in order to remove lignin and hemicellulose, reduce cellulose crystallinity, and increase the porosity of the materials (Karimi et al., 2006). Steam explosion is the most commonly used method for pretreatment of lignocel- lulosic materials (Sun and Cheng, 2002). Steam explosion essentially includes both physical and chemical pretreat- ments which effectively catalyze the depolymerisation of * Corresponding author. E-mail addresses: zabihi_samyar@yahoo.com (S. Zabihi), aliniaroozbeh@yahoo.com (R. Alinia), esmaeil@shirazu.ac.ir (F. Esmaeilzadeh), zeglda@shirazu.ac.ir (J.F. Kalajahi). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/issn/15375110 biosystems engineering 105 (2010) 288–297 1537-5110/$ – see front matter ª 2009 IAgrE. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.biosystemseng.2009.11.007