Bioethanol production from taro waste using thermo-tolerant yeast Kluyveromyces marxianus K21

• Bioethanol production from taro waste medium using Kluyveromyces marxianus K21.
• Corn gluten meal can be used as an organic nitrogen source.
• Simultaneous saccharification and fermentation (SSF) was recommended.
• The scaling-up experiment in a 5 L bioreactor was performed.
• A 94.2% theoretical ethanol yield was obtained.

In the present study, evaluation and optimization of taro waste (TW), which was mainly composed of taro peels that contain many starch residues, as the main carbon source in medium were studied. The flask studies showed the optimal medium was using 170 g/L of TW which is about 100 g/L of glucose and 9 g/L of CGM as alternative nitrogen source. Simultaneous saccharification and fermentation (SSF) exhibited higher bioethanol productivity toward separation hydrolysis and fermentation (SHF). The optimal condition of SSF was 5% of Kluyveromyces marxianus K21 inoculum at 40 °C resulting in the maximum ethanol concentration (48.98 g/L) and productivity (2.23 g/L/h) after 22 h of cultivation. The scaling up experiment in a 5 L bioreactor demonstrated that K21 can still maintain its capability. After 20 h of cultivation, 43.78 g/L of ethanol (2.19 g/L/h of productivity) was achieved corresponding to a 94.2% theoretical ethanol yield.