3.3.1. Optimization of kLa
As indicated by the results shown in Fig. 2, oxygen supply levels have a significant impact on 1-butanol production. Therefore, kLas were examined and optimized. Because kLa values are used to scale up from laboratory scale to pilot scale or production scale bioreactors, optimization of kLa is one of the important factors for designing the industrial production process.
As shown in Fig. 4, kLas clearly affect growth, glucose consumption, and metabolite production. 1-Butanol productivity increased with increasing kLa up to 76.6 ± 1.2 h−1 and decreased thereafter. At a kLa of 76.6 ± 1.2 h−1, 1-butanol was produced in a linear manner from 8 to 20 h of cultivation. A titer of 6.03 g L−1 was achieved, correlating with a yield of 0.147 g (g glucose)−1 and a productivity of 0.251 g L−1 h−1 at 24 h, when the initial 40 g L−1 glucose was exhausted. Growth, glucose consumption rate, and butyric acid production increased whereas acetic acid production decreased with increasing kLa.