8-82: Enzymatic saccharification of rice straw pretreated using TiO2/UV for bioconversion to ethanol

Rice straw is a lignocellulosic biomass that is a renewable organic substance and alternative source of energy. Presently, rice straw was pretreated in a novel manner using TiO₂/UV system and the pretreated rice straw was hydrolyzed using Accellerase 1000™. Hydroxyl radicals (OH^·) can degrade lignin and carbohydrates. UV irradiation of TiO₂ solution, hydroxyl radicals producing system, was investigated for its ability to oxidize rice straw. The optimal conditions for TiO₂/UV pretreatment were found to be: TiO₂ concentration (0.1%, w/v), irradiation time (120 min), UV lamp type (UVC, 254 nm). Under these conditions, the cellulose saccharification was 346.68 mg glucose/g rice straw (81.41% of theoretical) and hemicelluloses saccharification was 55.08 mg xylose/g rice straw (25.91% of theoretical). These results show that UV irradiation of the TiO₂ solution is an efficient pretreatment method to enhance rice straw digestibility. The fermentation of enzymatic hydrolysates containing 10.5 g/L glucose and 3.21 g/L xylose with Pichia stipitis produced 3.94 g/L ethanol with corresponding yield of 0.39 g/g rice straw. Also, the final ethanol concentration was about 1.37%, which is 75.1% of the stoichiometric and fermentation efficiency yields. For the first time, TiO₂/UV system was developed for the pretreatment for saccharification of lignocelluloses. It is a potential pretreatment method for enabling ethanol production from lignocelluloses.