Four lignocellulosic biomasses, water hyacinth, rice straw, mango leaves and spruce were pretreated by ionic liquid (IL) to enhance anaerobic digestion. The effect of pretreatment conditions, such as alkyl chain length of IL, temperature, time and operation cycle on lignocellulosic composition, structure and biogas production was evaluated. The enhancement of biogas production by [C(4)mim]CI pretreatment at 120 degrees C for 2 h decreases in the order of water hyacinth > spruce > rice straw > mango leaves. Higher methane production of regenerated rice straw and mango leaves could reach 233 and 125 mL/g carbohydrates under 140 degrees C or 2 h and 140 degrees C for 8, respectively. Furthermore, the technology of aqueous biphasic systems was developed to recovery IL, and the recovery rate of ILs was in the range of 543-94.6%. (C) 2013 Elsevier Ltd. All rights reserved.