Sequential mild acid and alkali pretreatment of rice straw to improve enzymatic saccharification for bioethanol production

Sequential pretreatment using different NaOH concentrations (0.5%, 1.0%, 1.5%, w/w) and 1% H2SO4 (w/w) was evaluated as a strategy for effective hydrolysis of rice straw. The efficiency of sequential NaOH and H2SO4 (SNA) pretreatment against sequential H2SO4 and NaOH (SH) was assessed. SH pretreated biomass attained more sugar yield compared to SNA pretreated biomass. The sugar yields from pretreated biomass improved with increasing NaOH concentration in both SH and SNA treatments. The maximum sugar release of 40.6 mg/ml (83.2% efficiency) was obtained from SH pretreated biomass when the stage 2 alkali treatment was performed at 1.5% w/w NaOH. The non-detoxified hydrolysate from this biomass was fermented with 96.8% efficiency.