Research paper Delignification of rapeseed straw using innovative chemo-physical pretreatments M. Brahim a, b, * , S. El Kantar a , N. Boussetta a , N. Grimi a , N. Brosse b , E. Vorobiev a a Sorbonne Universites-Universite de Technologie de Compiegne, Unite Transformations Integrees de la Matiere Renouvelable e EA 4297, Centre de Recherches de Royallieu, BP 20529, 60205 Compiegne Cedex, France b Universite de Lorraine-Faculte des Sciences et Technologies, Laboratoire d’Etudes et de Recherche sur le Materiau Bois e EA 4370, Boulevard des Aiguillettes, BP 70239, 54506 Vandœuvre-Les-Nancy cedex, France article info Article history: Received 25 July 2016 Received in revised form 19 September 2016 Accepted 26 September 2016 Keywords: Rapeseed straw Microwaves Ultrasounds High-voltage electrical discharges Enzymatic hydrolysis Delignification abstract Rapeseed straws are recoverable lignocellulosic biomass for second generation bioethanol production. Therefore, a pretreatment step is recommended in order to increase accessibility of enzymes to sugars. As a pretreatment step in this study, several innovative technologies have been performed in order to investigate their efficiency for delignification and enzymatic hydrolysis purposes: microwaves (MW), high voltage electrical discharges (HVED) and ultrasounds (US). As a key processing parameter, different levels of energy input were studied MW (1832e7328 kJ/kg), US (916e3664 kJ/kg) and HVED (204 e814 kJ/kg) corresponding to a treatment duration range of 10e40 min. Treatment temperature (60 e90  C) and medium alkalinity (0.125e0.5 M) impact was also investigated and optimized based on sugar and soluble lignin contents in black liquor, and lignin removal yields. Delignification yields increased from 28.3%, 28.6% and 31.2% for 10 min of treatment to 38.4%, 41.5% and 42.3% for 40 min of treatment, respectively for MW, US and HVED. However, in order to achieve the same efficiency the energy required by HVED is 9 times and 4.5 times less than that required by MW and US respectively. Treatment temperature also revealed to be important as sugars yields increased by 41.6% when tem- perature increased from 60  C to 90  C for HVED and the optimal medium alkalinity was found to be 0.3 M. Finally, better enzymatic hydrolysis yields were obtained and correlated to better delignification performances improving material accessibility. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction Disadvantages of fossil fuels such as emissions of greenhouse gases, result in several environmental problems, health issues and safety hazards [1]. Therefore, a lot of interest is currently focused on renewable resources. In first generation biorefineries, agricultural products such as corn, sugar cane and molasses are employed as feedstock [2]. However, for better consumers' perception, non-food raw materials should be used. Lignocellulosic biomass mainly composed by cel- lulose, hemicellulose and lignin, is the most suitable feedstock for the second generation of biorefineries. It can be supplied from various sources of low cost such as industrial wastes, wood and agricultural residues [3]. Rapeseed straws are an example of agri- cultural residue with low economic value, traditionally used for animal feeding. The rapeseed straw contains 64.0% of holocellulose and 26.4% of acid insoluble lignin [4]. Other components of rape- seed straw such as waxes ash, and organic acids are also presented but in minor quantities [5]. Production of bioethanol from ligno- cellulosic biomass is usually performed in two stages. First, the cellulose was hydrolyzed into reducing sugars and then the sugars were fermented by yeasts or bacteria into ethanol. To achieve high yields of fermentable sugars after enzymatic hydrolysis, the ligno- cellulosic biomass should be pretreated [4]. The objective of the pretreatment is to remove part of the lignin and hemicellulose coatings. This improves the accessibility of enzymes to cellulose during enzymatic hydrolysis [6]. Different conventional methods are used for the fractionation of rapeseed straw. Alkali pretreatments with sodium hydroxide [7], peroxide pretreatment [8] and aqueous ammonia [9] have been investigated, but these treatments have the inconvenient to be time * Corresponding author. Universit e de Technologie de Compi egne, Unit e Trans- formations Int egr ees de la Mati ere Renouvelable, Centre de Recherches de Royal- lieu, BP 20529, 60205 Compi egne Cedex, France. E-mail address: marwa.brahim@utc.fr (M. Brahim). Contents lists available at ScienceDirect Biomass and Bioenergy journal homepage: http://www.elsevier.com/locate/biombioe http://dx.doi.org/10.1016/j.biombioe.2016.09.019 0961-9534/© 2016 Elsevier Ltd. All rights reserved. Biomass and Bioenergy 95 (2016) 92e98