Evaluation of the inline stripping of ethanol during cyanobacteria cultivation in a bubble column bioreactor
¹ University of Applied Sciences Upper Austria, Faculty of Engineering, Department of Bio & Environmental Technology, Stelzhamerstr. 23, AT4600 Wels, Austria
² University of Calabria, Via P. Bucci, IT87036 Rende (CS), Italy
Cyanobacteria are oxygenic phototrophic microorganisms capable of photosynthesis. In this redox reaction driven by light energy, carbon dioxide and water are converted into chemical energy in form of carbohydrates and oxygen. The output of this process is restricted by product inhibition from the bioethanol. Here, we evaluate a method of ethanol stripping in a bubble column for perspective use for determination of ethanol production rate of engineered cyanobacteria. The knowledge about the amount of condensation and recovery rate combined with HPLC measurement for ethanol determination can be used to specify the real amount of produced ethanol (absolute) by cyanobacteria in the used bioreactor. Stripping and recovery rate are depending on several parameter like flow rate, initial ethanol concentration, condensation temperature etc. Due to the high influence of these parameters they have to be supposed to be static regarding to the degrees of freedom.
To evaluate the system different ethanol concentration were testet for stripping and determination of recovery rate. As the stripping rate was much higher compared to the ethanol production rate with our Synechococcus elongatus PCC 7942 the medium was spiked with ethanol to varying concentrations of 0.5, 1 and 2% v/v. It could be shown that ethanol could be removed quantitavely. Removal rates of 97 98% were reached with initial ethanol concentrations of 5 g L-1 to 20 g L-1. The results demonstrated determination of ethanol in the exhaust air stream and quantitavely recollection by cultivating engineered Synechococcus elongatus in bubble column bioreactors.