Influence of aeration on bioethanol production from ozonized wheat straw hydrolysates using Pichia stipitis.

The influence of aeration on ethanol production by Pichia stipitis was studied in wheat straw hydrolysates subjected to ozone pretreatment for the first time. In a first stage, different aeration rates ranging from 0.03 to 0.50 L air/min, which corresponds to a volumetric oxygen transfer coefficient from 1.1 to 9.6 h(-1), were applied to model glucose/xylose substrates. The most promising value was found to be 3.3 h(-1) (0.1 L air/min) leading to better xylose utilization, an ethanol yield of 0.40 g ethanol/g sugars and complete depletion of sugars at 72 h. In a second stage, the effect of aeration was analyzed in ozonized wheat straw hydrolysates. Sugars were completely depleted at 96 h and ethanol yield reached a value of 0.41 g ethanol/g sugars. The addition of controlled oxygen (K(L)a=3.8 h(-1)) enhances the efficiency of the process causing an increase of 29.1% in ethanol production and a considerable reduction of 42.9% in fermentation time as compared to non-aerated hydrolysates.