Eco-friendly dry chemo-mechanical pretreatments of lignocellulosic biomass: Impact on energy and yield of the enzymatic hydrolysis Abdellatif Barakat a,⇑ , Santi Chuetor a , Florian Monlau b , Abderrahim Solhy c , Xavier Rouau a a INRA, UMR 1208 Ingénierie des Agropolymères et Technologies Emergentes 2, place Pierre Viala, F-34060 Montpellier, France b Star Agro Energy Research Group, University of Foggia, Via Napoli, 25 Foggia, Italy c MAScIR Foundation, INANOTECH, VARENA Center, Rabat Design, Rue Mohamed El Jazouli, Madinat Al Irfane, 10100 Rabat, Morocco highlights  Innovative dry NaOH chemo-mechanical pretreatment was developed.  Dry (TS dry ) and dilute (TS dilute ) NaOH chemo-mechanical pretreatment were compared.  TS dilute consumed higher amounts of water and energy compared to TS dry .  Energy efficiency obtained for TS dilute was 0.417 kg glucose kW h 1 and 0.888 for TS dry . article info Article history: Received 22 March 2013 Received in revised form 6 June 2013 Accepted 4 July 2013 Keywords: Lignocellulosic biomass biorefinery Dry pretreatment Size reduction Energy efficiency abstract In this study, we developed an eco-friendly dry alkaline chemomechanical pretreatment of wheat straw without production of waste and liquid fractions with objective to save energy input, to decrease the environmental impact and to increase enzymatic hydrolysis. Wheat straw was pretreated with NH 3 , NaOHAH 2 O 2 , NH 3 AH 2 O 2 and NaOH at high materials concen- tration (5 kg/L) equivalent to biomass/liquid ratio of 1/5 (dry chemomechanical) and at low materials concentration (0.2 kg/L) equivalent to biomass/liquid ratio of 5/1 (dilute chemomechanical). Untreated and chemical treated wheat straw samples were subjected to grinding and milling following by enzy- matic hydrolysis with commercial cellulases. NaOH and NaOHAH 2 O 2 dry chemomechanical pretreatments were found to be more effective in decreasing the particle size and energy consumption and increasing the surface area. However, alkaline dilute-chemomechanical treatments consumed higher amounts of water (5 L water/1 kg biomass) and energy compared to dry-chemomechanical treatments. In point of fact, the lowest energy efficiency obtained was 0.417 kg glucose kW h 1 for dilute-chemomechanical treatments compared to 0.888 kg glucose kW h 1 glucose kW h 1 for dry-chemomechanical treatments. Alkaline dry-chemomechanical pretreatments approach appears more attractive and efficient in terms of glucose, energy efficiency and environmental impact, compared to conventional alkaline chemome- chanical pretreatments. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction The pretreatment of lignocellulosic biomass prior to enzymatic attack is an essential step in order to increase cellulose and hemi- celluloses accessibility and biodegradability [1,2]. Application of pretreatment steps allows modifying the supramolecular struc- tures of cellulose–hemicellulose–lignin matrix, thereby changing the natural binding characteristics of lignocellulosic materials and increasing the holocelluloses accessibility for enzymatic or biological action. A large number of pretreatment methods have been developed until now [3–7]. Some chemical, physico-chemical, physical and mechanical pretreatments are known to be effective, but that these methods have some disadvantages in terms of energy consumption or energy input, corrosion of processing tools, introduction of inhibiting effects, the number of separation and purification steps, etc. The performance of pretreatments step mainly depends on the energy input and output and the environmental impact. The cur- rent use of a high amount of water, solvents are in part responsible for the cost of pretreatment steps in lignocellulose biorefineries and a negative environmental impact [2]. The mechanical pretreatments allow in an improved depoly- merization of saccharides during hydrolysis and improved total 0306-2619/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.apenergy.2013.07.015 ⇑ Corresponding author. Tel.: +33 0 4 99 61 25 81; fax: +33 0 4 99 61 30 76. E-mail address: barakat@supagro.inra.fr (A. Barakat). Applied Energy 113 (2014) 97–105 Contents lists available at SciVerse ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy