9 Oct 2018 Practical 1: Operation of an Automated Fermentation System Introduction: The purpose of this practical is to be familiar with the basic operation of a fermentation system. The system investigated in this practical involved the fermentation of yeast cells (saccharomyces cerevisiae). In order to have successful and sufficient growth of cells in a bioreactor, the following factors must be considered in the design of the reactor: 1. Reactor configuration: stirred or air driven 2. Reactor size 3. Processing conditions: Control of pH, temperature, oxygen, substrate, sterilization. 4. Mode of operation: Batch/ fed batch / continuous fermentation / combination of all. The mixing of the contents in the bioreactor should ensure that the solution is homogenous. It should reduce non-uniformities in fluids by eliminating concentration gradients. Mixing can be done by using impellers with baffles or by aeration. With an impeller, a vortex can form in the solution. Baffles are put on the side of the bioreactor to prevent this. When mixing by aeration, bubbles are produced from a sparger and as the bubbles move to the top of the solution, they mix the contents of the bioreactor. Aeration is usually used for much larger bioreactors where the cost of running impellers would be too much because of the heat they generate. A cooling coil would be necessary to keep the contents of the reactor at a suitable temperature. Aeration is also used for cells which lack cell walls like animal cells or some bacterial cells. They are more delicate. It does not use shear force to mix and cause the cells to break. Most fermentations are carried out using aseptic conditions. This is very important for slow growing cultures that require more time. The longer it takes for the culture to grow, the more time it must spend in the bioreactor. And thus, the longer the process must run for, the more likely that bacterial contamination can occur. Industrial fermenters are designed for in situ steam sterilisation have a minimum number of internal structures. Crevices and stagnate areas are avoided. These could cause a build-up of bacteria. Gaps or cracks are also avoided. All entry points of stirred also must be sealed to prevent bacteria from entering the bioreactor. The materials used to make the fermenter are also important. They must be non-toxic, non-reactive and they must withstand the high temperatures for sterilisation. Glass can be used for small bioreactor vessels with a capacity of less than 30L or for a vertical sight glass in a larger bioreactor. Glass is smooth, non-toxic, corrosion proof and transparent. Stainless steel allows the use electropolishing instead of mechanical polishing. Mechanical polishing involves using abrasives. This should be avoided in cleaning a bioreactor as it causes small crevices to form, which may house bacterial cells. Copper and copper-containing material must be avoided in the fermenter construction because of its toxic effect of cells. There are 4 main modes of operation. They all have a significant effect on substrate conversion in process reliability