BACKGROUND Bacterial nanocellulose (BNC) is a versatile biomaterial, however its production at industrial scale is not cost-effective due to the high cost of culture media. Sweet sorghum bagasse (SSB) is an annually renewable agricultural residue with little or no value and could even cause haze if burned. The proposed approach is the first to use SSB to produce BNC by means of pretreatment of green solvent ionic liquid (IL) for promoted enzymatic saccharification due to the recalcitrant lignocellulose structure of SSB. But the questions, 'Which is the best IL' and 'Are there any negative effects' need answers. RESULTS Six kinds of ILs were first compared in detail and showed diverse inhibition of cellulase and bacterial culture with changing IL concentration. Inhibition by IL of cellulase and BNC production could be removed completely by thorough washing. The results showed that three ILs, [AMIM]OAc, [EMIM]Fmt and [EMIM]OAc, had higher dissolving capacity and strong enhancement of cellulase saccharification of SSB. The fermentable sugar yield from SSB was enhanced by more than 7.5 times after [EMIM]Fmt-pretreatment at biomass loading of 20%. The highest productivity of 0.71 g L-1 d(-1) of crude BNC was obtained after cultivation with the hydrolysate of [EMIM]Fmt-pretreated SSB.CONCLUSION The results demonstrated a new approach to produce BNC by biorefining lignocellulosic waste SSB, which could provide the following potential benefits: better utilization of the agricultural residual SSB than burning, which causes haze and air pollution, improving economic benefits of SSB for farmers, and decreasing the production cost of BNC. (c) 2018 Society of Chemical Industry