Downstream Processing Using Membrane Technology

Membrane filtration is a very gentle separation technique and can be used at low temperatures. This makes it suitable for liquids that contain micro-organisms and/or are heat sensitive, which is often the case in liquids processed in the field of biotechnology. However, one drawback is that these liquids are often very complex, which is a disadvantage when using membrane technology as it makes the process difficult to optimise regarding both process parameters and cleaning. This thesis deals with different aspects of membrane filtration and how membranes can be applied in different stages of the downstream processing. The work presented in this thesis covers downstream processing in the production of lactic acid from fermented wheat starch. In this process microfiltration and ultrafiltration are used to remove micro-organisms and proteins from the broth. Finally, water-splitting electrodialysis is used to convert the sodium lactate produced during the fermentation to lactic acid and sodium hydroxide. The use of sub-critical flux when separating micro-organisms from lactic-acid-containing fermentation broth has also been studied. Part of the work deals with the retention of proteins in microfiltration membranes and how this is affected by pH, ion strength and membrane material. Two different proteins, bovine serum albumin and protein A have been studied