Calcium-Capturing-by-Carbonation (CaCCO) process as a simple and flexible sugar platform for herbaceous lignocellulosics in rural areas

The supply of fermentable sugars from agricultural wastes and/or energy crops in rural areas is expected to generate an off-the-grid system for new bio-industry. We evaluated the CaCCO process, a sugar platform 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. We adopted continuous wet milling of a mixture of feedstock, water and Ca(OH)₂, not only for flexible application of the process for wet feedstocks, but also for simultaneous Ca(OH)₂ mixing with the milled feedstocks. Low temperatures below 100^oC were applied to save energy for the alkali pretreatment. Then, we performed CO₂-pressurization of the pretreatment slurries for both neutralization and pH control during the saccharification. With the aid of a pilot scale (100 L), CO₂-pressurizing saccharification reactor, the pretreatment slurries were hydrolyzed with enzymes for 72 h at 40^oC, 0.9 MPa with high-solid loadings of 28%(w/w). These tests 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 above 15% (w/v). The solutions were readily fermented to various valuables: fuel ethanol, bacterial cellulose, an enzyme preparation, yeast cells and a microbial pigment. Thus, the CaCCO process could be a simple and flexible platform for preparation of dense sugar solutions, which could stimulate a new agricultural bio-industry for vitalizing rural areas.