Alkaline peroxide pretreatment of rapeseed straw for enhancing bioethanol production by Same Vessel Saccharification and Co-Fermentation Pinar Karagöz a,b , Indre V. Rocha a , Melek Özkan b,⇑ , Irini Angelidaki a,⇑ a Department of Environmental Engineering, Technical University of Denmark, Miljoevej 113, 2800 Kongens Lyngby, Denmark b Department of Environmental Engineering, Gebze Institute of Technology, 41400 Kocaeli, Gebze, Turkey article info Article history: Received 6 June 2011 Received in revised form 12 September 2011 Accepted 21 October 2011 Available online 4 November 2011 Keywords: Rapeseed straw Bioethanol Co-fermentation Same Vessel Saccharification and Fermentation (SVSF) abstract Alkaline peroxide pretreatment of rapeseed straw was evaluated for conversion of cellulose and hemicel- lulose to fermentable sugars. After pretreatment, a liquid phase called pretreatment liquid and a solid phase were separated by filtration. The neutralized pretreatment liquids were used in a co-fermentation process, with Saccharomyces cerevisiae and Pichia stipitis. The solid fraction was used for simultaneous saccharification and co-fermentation process in the same vessel. The effects of various operating vari- ables were investigated. Pretreatment with 5% (v/v) H 2 O 2 at 50 °C for 1 h was found to be the optimal pretreatment combination with respect to overall ethanol production. At this condition, 5.73 g ethanol was obtained from pretreatment liquid and 14.07 g ethanol was produced by co-fermentation of solid fraction with P. stipitis. Optimum delignification was observed when 0.5 M MgSO 4 was included in the pretreatment mixture, and it resulted in 0.92% increase in ethanol production efficiency. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Dwindling petroleum sources, increasing demands for energy and threatening climatic changes have put urgent pressure to the search for alternative energy sources and development of sustain- able renewable energy technologies. There has been considerable interest in finding cheap renewable sources to produce green and environmentally friendly bio-fuels. Since biomass energy is already a part of the global carbon cycle, the use of fuel ethanol can signif- icantly reduce the net carbon dioxide emissions once it replaces fossil fuels (Li et al., 2009). Lignocellulosic agricultural residues are promising raw materials for bioethanol. As they are residues and wastes, they do not compete with primary food production. Currently only the seeds of rapeseed straw are utilized for produc- tion of biodiesel, while the straw parts are unutilized. Utilization of the rapestraw for bioethanol production has been suggested in a newly proposed biorefinery concept (Luo et al., 2010). Lignocellulosic material consists of lignin and the carbohydrate polymers cellulose and hemicelluloses. Lignocellulosic materials are rigid structures, requiring efficient pretreatment in order to re- lease the carbohydrates from their lignin association and make the cellulose and hemicelluloses more accessible to enzymatic attack. Subsequently, the carbohydrate polymers need to be hydrolyzed for releasing the single sugar units and make them accessible for fermentation. Minimization of loss of sugars and energy consump- tion and increasing enzymatic digestibility are common targets for all types of pretreatments (Petersen et al., 2009). Since different lignocellulosic materials have different physico-chemical charac- teristics, it is necessary to adopt suitable pretreatment technolo- gies based on the lignocellulosic biomass characteristics of each raw material (Alvira et al., 2010). Different pretreatment methods including biological, chemical, physical and physicochemical, have been developed for lignocellu- losic waste pretreatment. Among all pretreatment methods steam, dilute acid, alkaline and oxidative pretreatment methods have been widely employed. In oxidative pretreatment, an oxidizing compound like hydrogen peroxide or peracetic acid is added to the biomass (Hendriks and Zeeman, 2009). As compared to alkali pretreatment, alkaline peroxide treatment is more effective in lig- nin solubilization (Chen et al., 2008) and improving of crop residue digestibility (Talebnia et al., 2010). Gould (1984) demonstrated the use of H 2 O 2 for delignification with a maximum pH of 11.5. Fur- thermore, Taherzadeh and Karimi (2008) reported that no furfural or HMF (inhibitory sugar degradation products) were detected in pretreatment liquid obtained with alkaline peroxide pretreatment which favors the fermentation step in an ethanol production. For an optimal production of ethanol from lignocellulosic hydrolysates obtained from enzymatic saccharification, maximum amount of sugar release and conversion of all fermentable sugars to ethanol is desired. Saccharomyces cerevisiae, the most widely used yeast for ethanol production, cannot convert xylose (Talebnia 0960-8524/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2011.10.075 ⇑ Corresponding authors. Tel.: +90 2626053222; fax: +90 2626053205 (M. Özkan), tel.: +45 45251429; fax: +45 45932850 (I. Angelidaki). E-mail addresses: mozkan@gyte.edu.tr (M. Özkan), iria@env.dtu.dk (I. Angel- idaki). Bioresource Technology 104 (2012) 349–357 Contents lists available at SciVerse ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech