Development and evaluation of an oscillatory baffled reactor for biological applications

• Main Author: Tröger, Claudia Natalie
• Published: University of Newcastle upon Tyne 2011
• Subjects: 660.284292
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.580659

Oscillatory baffled reactors (OBRs) are a form of plug flow reactor, in which tubes fitted with orifice plate baffles have an oscillatory motion superimposed upon the net flow of the process fluid. The interaction of the baffles with the oscillatory motion of the fluid generates uniform mixing and enhanced transport rates, whilst maintaining conditions approximating plug flow. Unlike conventional tubular reactors, where a minimum Reynolds number must be maintained, the tube-side mixing is independent of any net flow, potentially allowing long residence times to be achieved in a reactor of greatly reduced length-to-diameter ratio leading to much more compact designs. This suggests a niche application in converting long reactions from batch to continuous processing. Fermentations show characteristically long residence times. Therefore, they could be intensified in an OBR. Since one major advantage of the OBR is its highly uniform, controllable mixing, which can be used to enhance gas-to-liquid mass transfer, it should be suitable for biological reactions. Fed-batch or continuous fermentation is a second advantage, as it should minimise substrate and product inhibition. Lower, more uniform shear rates than in a stirred tank reactor would be an additional advantage for processing shear-sensitive cells. Previous research has shown that the OBR can provide higher biomass concentrations and greater gas-liquid mass transfer than conventional fermenters. In this work two different fermentation systems were studied. Firstly, as a benchmark experiment, the fermentation stage of the beer production process was investigated in order to determine any relative advantages of using the OBR. Secondly, the production of biopolymers, namely polyhydroxyalkanoates (PHA), by Pseudomonas putida KT2442 was studied. Biopolymers are biodegradable polymers made from renewable resources. They can be made from plants or by microorganisms. P. putida is one such microorganism. Under nutrient limitation and carbon excess it produces polyhydroxyalkanoates (PHA), which are linear polyesters, to store carbon as energy resource. PHAs are biodegradable and are used in the production of bioplastics. The production of biopolymers from microorganisms is currently not cost-effective, because of expensive substrates, low yields and complex downstream processing. Therefore, intensification of PHA production to achieve higher yields in smaller, more efficient equipment at lower capital costs would be an advantage. The parameters investigated in the two systems were agitation rate and temperature. The main result of the beer fermentation was that beer could be successfully produced in the OBR with a significant reduction in time-to-completion to a fifth of that of a conventional beer fermentation. This was achieved at 37 ± 1 °C and an oscillatory Reynolds number (Reo) of 300. For the biopolymer production it was demonstrated that PHA can be produced in the OBR. The fermentation temperature and agitation rate resulting in the highest optical density (OD) and PHA yield in this parameter space were determined as 30 ± I °C and an oscillatory Reynolds number of 300 respectively. It was also demonstrated that using an OBR can lead to higher OD (10.8 vs 7.32) and dry cell weight (3.75 g/L vs 2.4 g/L) than in a comparable conventional stirred tank reactor.