Estudo do pré-tratamento do bagaço de caju com peróxido de hidrogênio alcalino para a produção de etanol

Abstract

Alkaline H2O2 pretreatment (AHP) and enzymatic saccharification were evaluated for conversion of cashew apple bagasse (CAB) cellulose and hemicellulose to fermentable sugars. First, the effects of the concentration of hydrogen peroxide at pH 11.5, the biomass loading and the pretreatment duration performed at 35 °C and 250 rpm were evaluated after the subsequent enzymatic saccharification of the pretreated biomass using a commercial cellulase enzyme with low load. The CAB used in this study contained 20.56 ± 20.19% cellulose, 10.17 ± 0.89% hemicellulose and 35.26 ± 0.90% lignin. The pretreatment resulted in a reduced lignin content in the residual solids. The best condition pretreatment from CAB was obtained with alkaline hydrogen peroxide (4.3% v/v H2O2), pH 11.5, 35 °C, 5% w/v CAB for 6 h, these solids were named of CAB-AHP. After, the effect of the combination of four commercial enzymes were evaluated. The combination of the enzymes, cellulase complex and β-glucosidase, on the proportion of 0.61:0.39 with load of 30 FPU/gCAB-AHP and 66 CBU/gCAB-AHP, respectively, was found to achieved high monomeric sugar release. The higher sugar yield was in the assays with 4 gcellulose/100 mL obtained glucose yield of 511.68 mg/gCAB-AHP (36 g/L) and xylose yield of 237.8 mg/gCAB-AHP (13 g/L). The liquid obtained after hydrolysis enzymatic was used in separate hydrolysis and fermentation (SHF) process with Saccharomyces cerevisiae, Kluyveromyces marxianus ATCC 36907 and K. marxianus CCA510 at 30 ºC and 150 rpm. The ethanol concentration was similar for all microorganism (approx 15 g/L). However the yeast S. cerevisiae showed higher productivity. Also, the solid fraction obtained of pretreatment was used in the study of simultaneous saccharification and fermentation (SSF). SSF was conducted using cellulose complex enzyme (30 FPU/gCAB-AHP) and β-glucosidase enzyme (66 CBU/gCAB-AHP) at 45 ºC and 150 rpm and evaluated the yeasts K. marxianus ATCC 36907 and K. marxianus CCA510. The ethanol concentration in SSF from CAB-AHP using K. marxianus ATCC36907 reached 18 g/L with 48 h, corresponding to an ethanol yield of 98% based on cellulose content. The results show that alkaline hydrogen peroxide is effective for the pretreatment of CAB and this solid can be used on the ethanol production by SSF.