Microaeration enhances productivity of bioethanol from hydrolysate of waste house wood using ethanologenic Escherichia coli KO11

This is the first study showing the successful application of waste house wood (WHW) to the pilot-scale production of bioethanol by hydrolysis using diluted acid and fermentation using the ethanologenic recombinant Escherichia coli KO11. The major sugars in the WHW hydrolysate were glucose, mannose and xylose; the percentages were approximately 35%, 35% and 20% (w/w), respectively. In anaerobic fermentation using a 5-l reactor in which the oxygen transfer rate (OTR) was 0 mmol/(l·h), KO11 consumed only 25% of the xylose in the WHW hydrolysate over the examined fermentation time of 100 h; however, hexoses such as glucose and mannose were consumed completely. Microaeration at an OTR of 4 mmol/(l·h) enhanced the xylose utilization ratio of KO11 to 100%, at which the ethanol concentration was 35.4 g/l and the ethanol yield was 0.42, although the maximum ethanol concentrations were 28.8 and 26.6 g/l at OTRs of 0 mmol/(l·h) and 15 mmol/(l·h), respectively. Moreover, this microaerobic fermentation at OTR of 4 mmol/(l·h) was applied to 1000-l scale bioethanol production using the WHW hydrolysate. The xylose utilization ratio reached 100% and the ethanol yield was determined to be 0.45 for a 63-h fermentation, which were comparable to those obtained from the laboratory-scale fermentation.