2.3. Preparation of rice straw hydrolysate
The rice straw material was performed using twin-screw extruder accomplished with follow-up hot water extraction. The sliced rice straw was first introduced into the twin-screw extruder at 50% solid content with 3% (w/w) of dilute sulfuric acid. The straw fed was squeezed with 130°C of temperature at 50 rpm and then transferred to a hot water extraction reactor. The straw squeezed in the extraction reactor was further mixed with steam and sustained for 30 min at 160°C of reaction temperature with a nearly 30% of solid content in the end of extraction operation. Under the circumstances the xylose released from the conversion of hemicelluloses and dissolved into aqueous phase as the acid hydrolysis hydrolysate. The solid residues and hydrolysate were then separated by filtration. Afterward, the effluent was treated with overliming method as detoxification process and the details were described elsewhere. The remaining solid residue was then stored until to the use of enzymatic hydrolysis later. The solid residue after dilute acid pretreatment was transferred to 1 L hydrolysis reactor until 1% dry matter (DM). The enzyme loading was set at 6.5 FPU/g DM using a commercial cellulase, Celluclast