Operational strategies for producing bioethanol in a continuous single-stage reactor

Novel strategies to facilitate the transition from batch to continuous simultaneous saccharification and fermentation were studied in this work. Implementing these strategies in bioethanol production plants to change production to a continuous mode will avoid large modifications in the process configuration. Therefore, experiments were carried out in a single-stage reactor applying strategies that favour a priori viability of yeast and stability of the process. The effects of (a) hydraulic residence time (HRT), (b) anaerobic and microaerobic operation, (c) inoculation strategy and (d) growth inhibition due to high ethanol concentrations were evaluated. The highest ethanol concentration (6.3 % w/w) was achieved during anaerobic operation, with reinoculations every 3–4 days and an HRT of 60 h; however, the processes suffered severe instability under these conditions. The greatest productivity and stability of the process was achieved using periodic microaeration and an HRT of 36 h (0.169 % ethanol weight/h), overcoming the result obtained during batch operation (0.128 % ethanol weight/h).