Development of yeast aerobic granules for long-term continuous bioethanol production from rice straw hydrolysate

For the first time application of aerobic granulation technology has been demonstrated for bioethanol production. A reactor was fabricated for ethanol production from rice straw hydrolysate (RSH) using Saccharomyces cerevisiae aerobic granules. The yeast granules were developed within 4-6 days by alternate aerobic mixing phase and settling phase without airflow of 8 h and 4 h, respectively. These yeast granules were found to produce ethanol (34.42 g/L) from pure glucose (80 g/L). A column filter was designed using activated charcoal, silica, cotton, and concrete aggregate to eliminate toxic impurities from RSH. Compared to unfiltered RSH, the filtered one was found to be more effective in ethanol production. A maximum of 16.18 g/L ethanol was produced from filtered RSH containing 10 g/L reducing sugar supplemented with pure glucose (40 g/L). It was possible to continuously run the process for more than 60 days. This study for the first time demonstrates continuous bioethanol production for an extended period by repeated use of yeast in the form of novel aerobic granules. This new concept has the potential to improve bioethanol production efficiencies of existing biorefineries.