These results indicated that the optimal WBY dosage was 15% for the four pre-treatments. As discussed above the reducing sugar yield of the 20% WBY could be increased by a higher concentration of NaOH in pre-treatment 1. For the other pre-treatments the results suggest that 15% WBY might display enough specific surface area to subject to erosion before hydrolysis and the 20% WBY might be too viscous for the physical processes to work as efficient as that for lower concentrations. Changing the settings used in the instruments such as shear input, ultrasonication or microwave ower may assist in increasing the reducing sugar yield of the 20% WBY after hydrolysis. The highest reducing sugar yield ob- tained from ultrasonication (29.19%) was almost six times higher than that obtained from the untreated WBY (4.15%), followed by NaOH treatment (28.29%), high speed homogenizer (13.33%) and microwave treatment (13.01%). Although WBY treated by 0.1 M NaOH (pre-treatment 1) and ultrasonication (pre-treatment 3) had the similar reducing sugar yield, the best pre-treatment time of ultrasonication (40 min) was obviously shorter than that of 0.1 M NaOH pre-treatment (30 h). Furthermore ultrasonication without harsh chemicals used could reduce the environmental impact. Therefore, it can be concluded that ultrasonication in combination with mild acid hydrolysis was the most effective pre-treatment to improve the reducing sugar yield of WBY with an optimal dosage of 15% and a best pre-treatment time of 40 min.