Pretreatments are crucial to achieve efficient conversion of lignocellulosic biomass to soluble sugars. In this light, switchgrass was subjected to 13 pretreatments including steam explosion alone (195 degrees C for 5, 10 and 15 min) and after impregnation with the following catalysts: Ca(OH)(2) at low (0.4%) and high (0.7%) concentration; Ca(OH)(2) at high concentration and higher temperature (205 degrees C for 5, 10 and 15 min); H2SO4 (0.2% at 195 degrees C for 10 min) as reference acid catalyst before steam explosion. Enzymatic hydrolysis was carried out to assess pretreatment efficiency in both solid and liquid fraction. Thereafter, in selected pretreatments the solid fraction was subjected to simultaneous saccharification and fermentation (SSF), while the liquid fraction underwent anaerobic digestion (AD). Lignin removal was lowest (12%) and highest (35%) with steam alone and 0.7% lime, respectively. In general, higher cellulose degradation and lower hemicellulose hydrolysis were observed in this study compared to others, depending on lower biomass hydration during steam explosion. Mild lime addition (0.4% at 195 degrees C) enhanced ethanol in SSF (+28% than steam alone), while H2SO4 boosted methane in AD (+110%). However, methane represented a lesser component in combined energy yield (ethanol, methane and energy content of residual solid). Mild lime addition was also shown less aggressive and secured more residual solid after SSF, resulting in higher energy yield per unit raw biomass. Decreased water consumption, avoidance of toxic compounds in downstream effluents, and post process recovery of Ca(OH)(2) as CaCO3 represent further advantages of pretreatments involving mild lime addition before steam explosion. (C) 2016 Elsevier Ltd. All rights reserved.