Control of pH by CO 2 Pressurization for Enzymatic Saccharification of Ca(OH) 2 -Pretreated Rice Straw in the Presence of CaCO 3

The aim of this study was to investigate the effect of pH control by CO 2 pressurization on the enzymatic hydrolysis of herbaceous feedstock in the calcium capturing by carbonation (CaCCO) process for fermentable sugar production. The pH of the slurry of 5 % (w/w) Ca(OH) 2 -pretreated/CO 2 -neutralized rice straw could be controlled between 5.70 and 6.38 at 50 °C by changing the CO 2 partial pressure ( p CO 2 ) from 0.1 to 1.0 MPa. A mixture of fungal enzyme preparations, namely, Trichoderma reesei cellulases/hemicellulases and Aspergillus niger β-glucosidase, indicated that pH 5.5-6.0 is optimal for solubilizing sugars from Ca(OH) 2 -pretreated rice straw. Enzymatic saccharification of pretreated rice straw under various p CO 2 conditions revealed that the highest soluble sugar yields were obtained at p CO 2 0.4 MPa and over, which is consistent with the expected pH at the p CO 2 without enzymes and demonstrates the effectiveness of pH control by CO 2 pressurization.