Repeated-batch simultaneous saccharification and fermentation of cassava pulp for ethanol production using amylases and Saccharomyces cerevisiae immobilized on bacterial cellulose

Reusing biocatalysts and repeated-batch process are promising approaches for the reduction of time and costs of a fermentation process. The present study investigated the use of alpha-amylase, glucoamylase, and cells of Saccharomyces cerevisiae immobilized on bacterial cellulose (BC) in repeated-batch simultaneous saccharification and fermentation (SSF) process for ethanol production from cassava pulp (CP). Ratio between the immobilized alpha-amylase and glucoamylase, and concentration of CP were optimized to achieve high CP saccharification efficiency, and the immobilized enzymes and cells were reused for four times in five consecutive batches of SSF. The optimum ratio between immobilized alpha-amylase and glucoamylase, and CP concentration were 75:25 by mass, and 60 g/L, respectively, yielding 0.74 g(glucose)/g(CP) (80% hydrolysis efficiency). Repeated-batch SSF gave an overall ethanol yield of 0.28 g/g(CP), and an ethanol production rate of 0.27 g/h, whereas a batch SSF gave a yield of 0.3 g(ethanol)/g(CP) and a production rate of 0.036 g(ethanol)/h. The results reported in this study revealed the applicability of BC as a supporting material for enzymes and cells immobilizations, and the feasibility of the repeated-batch SSF process in ethanol fermentation.