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Science is Wonder-ful! BioRapid in the 'European Researcher's Night'

Inhomogeneities appear along the height of industrial scale bioreactors. They are expensive and difficult to handle. Therefore, scale-down approaches try to mimic large-scale bioprocesses, thus decreasing the price of optimization experiments and the working volumes. The demonstration was performed for more than 1500 attendants, where the big majority were very young biochemical engineers :) .

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The first drawback that faces scale-up from lab scale is the limitation in the power of mixing, which leads to limitations in mass transport. This in turn, causes the appearance of alternating micro-environmental conditions, to which cells are continuously exposed. In order to study the consequences of these heterogeneous conditions on the cell status, scale-down bioreactors were designed, e.g. an aerated stirred tank reactor (STR) connected to a non-aerated plug flow reactor (PFR), to which feed is added. Here we present the principle with a homogenous reactor connected to a bulb condenser, which acts as PFR.

The reactor contains yellow colored sugar dissolved in water, whilst the feed comprises a red sugar aqueous solution. Once the feed (red) is mixed with the yellow water, gravity induces a gradient of colors along the height of the bulb condenser. When the liquid returns to the homogenous reactor (mostly yellow), the color changes again to the original one. The method presented here applied to biotechnology, results in a system that mimics the industrial scale: the typical aerobic cells under study are grown in the homogenous reactor (STR), sparged with oxygen, whilst the feed is typically the carbon source. Thus, (i) a zone of the bioreactor with high substrate availability and low dissolved oxygen concentration (i.e. the feed zone in a fed-batch experiment, simulated in the PFR) and (ii) a homogeneous bulk zone of the bioreactor, in which the substrate concentration is limited (simulated in the STR) are simulated at the lab scale. A system like this is usually called

A system like this is usually called two-compartment reactor (Two-CR), where the variable location of the feeding and the sparger, as well as the profile of the feeding, enables to study the influence of various conditions at distinct residence times of the cells opposed to these gradients. In order to mimic the real case more closely, where also a zone with both low carbon source and low oxygen availability is observed, a second PFR without a feeding port but of same dimensions can be added to the system, thus achieving the three zones in one system and leading to the Three-CR system. In our European project, called Biorapid, we are working with anaerobic lactic acid bacteria, which consume lactose and produce lactic acid. Unlike the vast majority of microorganisms, we are not investigating carbon source and oxygen availability gradients, but pH gradients. Under too acidic conditions, these cells stop growing, so it is critical to control the pH in the whole reactor. As it happens with the carbon source and the oxygen availability, in the large-scale, pH gradients also appear due to longer mixing times. We are using the scale-down approach described here in order to investigate the effect of variable pH values around cells on their physiological activity and size.

Last modified: Thu, 27 Oct 2016 19:56:16 BST