Efeito do pré-tratamento com hidróxido de amônio na sacarificação de bagaço de cana-de-açúcar e sabugo de milho e produção de etanol 2G

Abstract

The pretreatment of lignocellulosic biomass is a fundamental step in the production of second- generation (2G) ethanol. In this study, sugarcane bagasse (SBC) and corn cobs (CC) were pretreated with 28–30% ammonium hydroxide (NH₄OH) to break down the biomass for subsequent saccharification and alcoholic fermentation. The pretreatment promoted high delignification, reaching 65.50% for SBC and 73.50% for CC, with preservation of the polysaccharide fraction. The pretreated solid fractions were subjected to enzymatic hydrolysis with different substrate loads (10 to 30%), using 12.5 FPU/g of cellulose from the commercial Cellic CTec3 cocktail. Batch hydrolysis fed with 30% biomass resulted in higher concentrations of total reducing sugars (TRS) compared to the conventional batch process (10%), reaching 65.15 g/L in pretreated bagasse (SBCT) and 70.18 g/L in pretreated cob (CCT). In addition, low concentrations of acids and inhibitors were detected in the hydrolysates, demonstrating the effectiveness of this pretreatment. The hydrolysates obtained in the fed-batch process had high levels of fermentable sugars, containing 43.75 g/L of glucose and 18.12 g/L of xylose in SBCT, and 41.63 g/L of glucose and 18.75 g/L of xylose in CCT, respectively. After fermentation, the highest ethanol yields were obtained with the ST hydrolysate, with 19.20 g/L (Yp/s of 0.49 and Qp of 0.87), using Saccharomyces cerevisiae Y904, and 26.34 g/L with the pentose-fermenting yeast. Spathaspora passalidarum Y7204 (Yp/s of 0.44 and Qp of 0.73). Although the co- cultures showed promising results, aspects such as metabolic synergism, competition for substrates, and catabolic repression by glucose still require investigation. These results demonstrate the efficiency of pretreatment with NH₄OH as a low-cost method with low inhibitor formation, highlighting the potential of pretreated hydrolysates for 2G ethanol production.