Produção de etanol por sacarificação e fermentação simultânea da fibra de caju pré-tratada com peróxido de hidrogênio alcalino

Abstract

This work studies the ethanol production from cashew apple fiber pretreated with alkaline hydrogen peroxide (FC-PHA) by a Simultaneous Saccharification and Fermentation (SSF). The effects of solids loading (4.52, 6.79, 9.05 e 10.0 gFC-PHA/100 ml) and temperature (37, 40, 45 e 50 °C) in batch SSF processes were evaluated. These experiments were realized with Kluyveromyces marxianus ATCC 36907 (5 g/L) and enzymatic complex Cellic CTec 2 (30 FPU/gFC-PHA) in Erlenmeyers of 250 ml with 100 ml of SSF medium (sodium citrate buffer 100 mM pH 4.8, supplemented with 1 g/L yeast extract and 1 g/L ammonium sulfate) at 150 rpm for 72 h. Then, prehydrolysis effects in SSF process were evaluated. Two prehydrolysis times (12 h and 24 h) were studied. It was the on study effect ten feeding strategies were investigated for fed-batch SSF mode operation. A study of enzyme loading (30 FPU/gFC-PHA, 25 FPU/gFC-PHA, 15 FPU/gFC-PHA e 10 FPU/gFC-PHA) was carried out in order to obtain an economic process in large scale process. The ethanol production wasalso performed in 1L Bioreactor with 750 ml of medium and using 15 FPU/ gFC-PHA of enzyme loading. This work also presents the characterization of lignin obtained from the liquor resulting from the pretreatment of cashew apple fiber with alkaline hydrogen peroxide. Results showed that batch-SSF report in an ethanol yield of 83.84 % and an ethanol concentration of 21.0 ± 0.48 g/L in processes conducted at 45 ºC and 10 % of solids loading (FC-PHA). However, the addition of prehydrolysis stage prior to Batch-SSF did not improve the ethanol yields that were 66.54 % and 60.23 % for PSSF 12 h and 24 h respectively. The hygroscopic property of FC-PHA does not allow the increasing of solids loading in the SSF processes. Therefore, ten strategies was study and the maximum ethanol production was29.7 ± 0.84 g/L after 48 h of fermentation obtained with the solid feeding of 10% FC-PHA at the beginning of the processes supplemented with 4% FC-PHA after 24 h. The study of ethanol production using different enzymatic charges does not show any significant differences on experiments with 30 e 15 FPU/gFC-PHA. Therefore, it was followed for bioreactor assays the enzyme loading of 15 FPU / gFC-PHA. Batch ethanol production in bioreactor with 10% (FC-PHA) showed an ethanol yield decrease of 18.48%. Feeding strategies were also evaluated in a bioreactor with ethanol production of 21.71 ± 0.07 g/L after 48h of fermentation and an efficiency of 61.92%. The same experiment was reproduced in shaker and showed an ethanol production 26.88% higher. The results indicate that the cashew apple fiber pretreated with alkaline hydrogen peroxide could be used as substrates for ethanol production in fed-batch SSF and the extracted lignin from black liquor generated during the pretreatment showed characteristics similar to those cited in the literature.