Effects of reduced severity of ammonium sulfite pretreatment on bamboo for high cellulose recovery

In this study, the conditions for the pretreatment of bamboo by ammonium sulfite to achieve high cellulose recovery were investigated and optimized. To obtain higher cellulose recovery under low-severity pretreatment conditions such as ammonia sulfite concentration, pretreatment time and pretreatment temperature, three-factor and three-level experiments were designed by the Box–Behnken design based on response surface methodology. The results showed that the cellulose recovery yield after 48 h enzymatic hydrolysis could reach 58.36–59.87%; moreover, the recovered cellulose was pretreated with 20% ammonium sulfite at 150 °C for 6 h, and the obtained yield was in agreement with the predicted yield (58.87%). It was about 13-fold higher than that of the untreated bamboo (4.41%). Pretreatment temperature and ammonia sulfite concentration are significantly important factors than pretreatment time in the design space for achieving high cellulose recovery. Moreover, SEM analysis of the pretreated bamboo substrate under optimized conditions illustrated that the biomass surface had become more rough and porous after pretreatment.