3. Results and discussion
3.1. Composition of rice straw hydrolysate
The composition of each rice straw hydrolysate was shown in Table 1. In the dilute acid hydrolysate, the xylose monomer was the major sugar at a concentration of 32.5 g/L, which is twice as high as the glucose concentration. In addition, the glucose was the dominant partition of monosaccharide in the enzymatic hydrolysis hydrolysate. Either the glucose concentration 66.2 g/L or the total sugar concentration 80 g/L was higher than that in dilute acid hydrolysate significantly. The trace concentration of cellobiose was generated during enzymatic hydrolysis due to β-glucosidase inhibited from the accumulation of glucose. The lignocellulosic degradation product such as acetic acid, HMF and furfural are also released into hydrolysate after feedstock with a pretreatment and have been demonstrated to show a negative effect on ethanol fermentation[3]. Although a lot of detoxification methods have been developed to remove these potential inhibitors, the overliming process is still considered as the most economical methods and showed a capacity to remove the furan-derived compounds effectively. With overliming detoxification, the concentration of furfural was down to 0.15 g/L and below in the dilute acid hydrolysate, and HMF was not detectable. However, acetic acid is unable to be taken off via this detoxification method.