High Solid-Loading Pretreatment/Saccharification Tests with CaCCO (Calcium Capturing by Carbonation) Process for Rice Straw and Domestic Energy Crop, Erianthus arundinaceus

Abstract

The CaCCO process (Park et al., 2010), a sugar platform for herbaceous lignocellulosics, was modified and evaluated for fermentable-sugar recovery in solution, using rice straw (RS) as well as stems and leaves of Erianthus arundinaceus (ER), one of the strategic energy crops in Japan. Continuous wet milling of a mixture of feedstock, water and Ca(OH)₂, with a weight ratio of 3/7/0.3, was adopted, not only to evaluate the applicability for wet feedstocks, but also for simultaneous Ca(OH)₂ mixing with the milled feedstocks. We also applied low temperatures of 95-100°C for the alkali pretreatment to save energy. Enzymatic-saccharification tests were performed for the pretreatment slurries from 10 kg feedstocks for 72 h at 40°C under a CO₂-pressurized atmosphere at 0.9 MPa with high-solid loadings of 28.4% (w/w) for RS and 27.8% (w/w) for ER. These tests successfully solubilized 80.6% (RS) and 68.1% (ER) of the total glucose- and xylose residues in the solids. Following centrifugation, the solubilized-sugar concentrations in the recovered solutions were 16.9% (w/v) for RS and 15.5% (w/v) for ER. Thus, we demonstrated that the CaCCO process could be a simple and flexible platform for preparation of dense sugar solutions from dry- and wet feedstocks, which could stimulate a new agricultural bio-industry for vitalizing rural areas.