Evaluation of the inline stripping of ethanol during cyanobacteria cultivation in a bubble column bioreactor

A. Jäger¹,*, C. Nicoletti² and K. Krennhuber¹

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
*Correspondence: a.jaeger@fh-wels.at

Abstract:

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.

Key words:

bioethanol, bubble column bioreactor, cyanobacteria, inline down-streaming, stripping

New constructs for ethanol production via cyanobacteria

F. Pfannerer¹, K. Krennhuber¹, A. Jäger¹ and H. Kahr¹*

¹University of Applied Sciences Upper Austria, R&D, Franz-Fritsch-Straße 11,
AT 4600 Wels, Austria
*Correspondence: Heike.Kahr@fh-wels.at

Abstract:

Alternatives to fossil fuels must be developed due to several already known reasons. Bioethanol can be an attractive energy concept. Bioethanol gasoline hybrid fuel can be used by most internal combustion engines. First and second generation bioethanol production is already available – here agricultural crops or residues are utilised. There are controversial discussions about these bioethanol production methods – the food versus fuel debate, cost and energy efficiency. Alternative advanced bioethanol production must be established with competitive production costs. Photosynthetic prokaryotes like cyanobacteria are attractive organisms for this purpose – these prokaryotes are fast growing organisms and utilize solar energy and CO₂. But these prokaryotes must be genetically manipulated for ethanol production. In this study transformation was performed using homologous recombination to introduce the pyruvate decarboxylase (pdc) and alcohol dehydrogenase B (adhB) genes of Zymomonas mobilis into the photosynthetic prokaryote Synechococcus elongatus PCC 7942 genome. These cyanobacteria grow in fresh water and seawater or even in wastewater. Both genes were expressed under the control of the strong constitutive promoter of psbA1 gene (encoding photosystem II protein D1). Various cloning strategies were done. Each construct was transformed successful in Synechococcus elongatus PCC 7942 and the potential bioethanol production was determined with HPLC. Only one construct produces bioethanol at detectable level. Diverse reactors and scale up steps were done to increase the bioethanol production. Anyhow further cloning strategies must be implemented to improve the production rate to achieve an effective bioethanol production from Synechococcus elongatus PCC 7942.

Key words: