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

Abstract

The aim of this study was to investigate the effect of pH control by CO2 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/CO2-neutralized rice straw could be controlled between 5.70 and 6.38 at 50 degrees C by changing the CO2 partial pressure (pCO(2)) from 0.1 to 1.0 MPa. A mixture of fungal enzyme preparations, namely, Trichoderma reesei cellulases/hemicellulases and Aspergillus niger beta-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 pCO(2) conditions revealed that the highest soluble sugar yields were obtained at pCO(2) 0.4 MPa and over, which is consistent with the expected pH at the pCO(2) without enzymes and demonstrates the effectiveness of pH control by CO2 pressurization.