Sustainable bioethanol and value-added chemicals production from paddy residues at pilot scale

Biorefineries from paddy residues (rice straw and rice husk) have a high potential to satisfy human society’s need for sustainable fuel and chemical production. Biorefinery systems should be created in a sustainable and eco-friendly manner, accompanying the safe disposal of waste stream produced during processing. This study developed a pilot-scale biorefinery, whose bioethanol production from rice straw was an integrated recovery system for lignin, silica, and nutrient recovery. The recovery yield of silica and lignin from the black liquor of alkaline pretreatment was up to 96%, and the lignin purity reached 79% without the existence of carbohydrate fiber. After the recovery, the final liquid waste mainly contained inorganic matters and has a potential to be reused in the acidification step. The distillation residue was a nitrogen source for simultaneous saccharification and fermentation equivalent to corn steep liquor with the final ethanol concentration of 1.6 wt% in 160 h. The new process can be considered as a zero-waste biorefinery model. The material flow indicated that more valued products produced by the simple method increase the profits of this process. Also, the energy efficiency of the process was 0.53 that demonstrated the process’s economy and sustainability. The proposed system was feasible to foster the sustainable integration of local agricultural development and biomass industry shortly.