Glucose production from liquid-ammonia soaking of rice straw for ethanol production

Abstract

Rice straw is a plentiful agricultural by-product after rice harvesting in Thailand. Although it can be used as animal feeds, its abundance necessitates the elimination before next cultivation; thus, farmers usually removeit by fire. Due to its characteristics, i.e. high cellulosecontent, rice straw is considered as an attractive feedstockfor cellulosic ethanol production. However, the presence of lignin in its structure may limit enzymatic hydrolysis of sugar production. In this work, rice straw was soaked with liquid ammonia (28%, v/v) at a ratio of 1: 10 (g biomass:ml liquid ammonia), 60 °C for 7 days in order to remove lignin. Based on dry weight basis, the pre-treated solid contained 45.2% glucan, 20.9% xylan and 10.1% lignin, a value corresponded to about 80% in lignin reduction.The commercial fungal cellulase preparation was applied to the pre-treated solid. After 24-h incubation, thecellulase loading of 100 FPU/ g substrate released glucose 210 mg/ g substrate, corresponded to 53% conversion of glucan to glucose. In addition, ethanol production by simultaneous saccharification and fermentation using the same enzyme loading to 1.5% (w/v) pre-treated rice straw gave 0.32% (w/v) ethanol. Thus, liquid ammonia soaking is one of good choices for rice straw pre-treatment to enhance glucose releasefor ethanol production.