Bioconversion of Cassava Stem to Ethanol Using Aspergillus fumigatus and Saccharomyces cerevisiae

Cassava stem was bioconverted to ethanol using microorganisms. First, cassava stem was pretreated by in ways, alkaline solution alone (ASA), microwave treatment combined with alkaline solution (MTCAS), and ultrasonic treatment combined with alkaline solution (UTCAS). The compositions of cassava stem pretreated by different methods were analyzed, and the results showed that the cassava stem pretreated by MTCAS was more suitable for saccharification and subsequent ethanol production. The pretreated cassava stem was subjected to simultaneous saccharification and ethanol production using Aspergillus fumigatus and Saccharomyces cerevisiae. Response surface methodology was used to optimize various process parameters including fermentation temperature, initial pH, fermentation time, rotational speed and substrate concentration. A bioconversion yield of 70 mg/g was obtained at the optimum conditions of fermentation, viz, temperature 35 degrees C, initial pH 5.6, fermentation time 132 h, rotational speed 155 rpm, and substrate concentration 4.6 wt%. An experiment under optimum conditions confirmed the model predictions. The results suggest that pretreatment with MTCAS and simultaneous fermentation with A. fumigatus and S. cerevisiae would be a good choice for the bioconversion of lignocellulosic biomass to bioethanol. Considering the cost advantage, using microbial fermentation instead of pure enzyme hydrolysis is more advantageous in 2nd generation bioethanol production.