In the case where solids were not separated post-pretreatment, the whole slurry were pH adjusted to 5.0 with NaOH.
For pretreatment reaction conditions a central composite design (CCD) incorporating variables of temperature, time and acid concentration was employed to define the optimum pretreatment process. Each independent variable was assessed at five coded levels (2, 1, 0, 1, 2) (Table 1).