Enhancement of anaerobic digestion of grass by pretreatment with imidazolium-based ionic liquids.

In this work, the toxicity of imidazolium-based ionic liquids (ILs) and the enhancement of high-solid anaerobic digestion by pretreatment were studied. Compared with [Bmim]Cl, [Bmim]OAc and [Bmim]BF4, [Bmim]PF6 had the highest toxicity. When the mass ratio of [Bmim]PF6 to grass was higher than 1:10, biogas was not produced within 30 days. The ability to remove lignin and hemicellulose followed the sequence of [Bmim]OAc, [Bmim]Cl, [Bmim]BF4 and [Bmim]PF6. The crystallinity index of grass pretreated with [Bmim]OAc, [Bmim]Cl, [Bmim]BF4 and [Bmim]PF6 reduced by 73.83%, 54.44%, 17.52% and 7.47%, respectively. The pretreatment with ILs enhanced the methane yield of grass by reducing crystallinity and particle size. The grass pretreated with [Bmim]OAc had the highest methane yield, about 221 mL/g volatile solids, due to its good lignin removal ability and relative low toxicity. After 10 times recycling, the cumulative methane yield of grass pretreated by recycled [Bmim]OAc decreased by 11.95%.