Tuesday, April 20, 2010
8-21

CaCCO process: A novel carbohydrate platform for bioconversion of herbaceous lignocellulosic biomass

Ken Tokuyasu, Riki Shiroma, Muhammad Imran Al-Haq, and Jeung-yil Park. Food Resource Division, National Food Research Institute, National Agriculture and Food Research Organization, 2-1-12 Kannondai, Tsukuba, 305-8642, Japan

Alkali pretreatment is advantageous over other pretreatment technologies for herbaceous lignocellulosic biomass in that lignin and side chains of xylan can be removed from solid biomass, facilitating the subsequent enzyme saccharification of cellulose and xylan in the pretreated solid. However, the alkali processes have problems of the release of carbohydrates, such as a part of xylan and sucrose, in solution, resulting in a low carbohydrate recovery after a solid-liquid separation step. This problem becomes more obvious in the case of rice straw containing significant amounts of sucrose and starch.
In this study, we developed a novel lime pretreatment process [CaCCO process; calcium capturing by carbonation (CO2)] without the subsequent solid-liquid separation step. In CaCCO process, CaCO3 remains in the vessel during saccharification and fermentation. Even though the pH after carbonation was about 6, no significant decrease in glucose- and xylose-liberation activities of commercial enzyme preparations could be observed. In the presence of CaCO3 Saccharomyces cerevisiae and Pichia stipitis unaffectedly fermented liberated monosaccharides into ethanol. In addition, we established a novel wet-preservation method for herbaceous feedstocks through the use of lime. Although it has been found that lime pretreatment at ambient temperature is effective for herbaceous feedstocks, the pretreatment still has the same problem as mentioned above. We combined the wet-preservation method with CaCCO process, and confirmed its high pretreatment efficiency. Since there have been no robust, environmentally-friendly methods of biomass preservation, the CaCCO process could newly provide us with a robust way for efficient preservation and pretreatment of herbaceous feedstocks.