Biosurfactants are naturally occurring amphiphiles with potential for use as alternatives to traditional petrochemical and oleochemical surfactants. The unique properties of biosurfactants, including their biodegradability and tolerance of a wide range of temperature and pH, make their use in a range of novel applications attractive. Currently the wider ultilisation of biosurfactants is hindered by a lack of economically viable production routes, with downstream processing presenting a significant challenge. This thesis presents an investigation into the production of HFBII, a hydrophobin protein, using an adsorptive bubble separation technique called foam fractionation for in situ recovery of the biosurfactant. The effects of foaming on the production of HFBII by fermentation were investigated at two different scales. Foaming behaviour was characterised in standard terms of the product enrichment and recovery achieved. Additional specific attention was given to the rate at which foam, product and biomass overflowed from the fermentation system in order to assess the utility of foam fractionation for HFBII recovery. HFBII was expressed as an extracellular product during fed batch fermentations with a genetically modified strain of Saccharomyces cerevisiae, which were carried out with and without antifoam. In the presence of antifoam HFBII production is shown to be largely unaffected by process scale, with similar yields of HFBII on dry matter obtained. More variation in HFBII yield was observed between fermentations without antifoam. In fermentations without antifoam a maximum HFBII enrichment in the foam phase of 94.7 was measured with an overall enrichment of 54.6 at a recovery of 98.1%, leaving a residual HFBII concentration of 5.3 mg L-1 in the fermenter. It is also shown that uncontrolled foaming reduced the concentration of biomass in the fermenter vessel, affecting total production. This series of fermentation experiments illustrates the potential for the application of foam fractionation for efficient in situ recovery of HFBII, through simultaneous high enrichment and recovery which are greater than those reported for similar systems. After the suitability of foam fractionation was demonstrated a novel apparatus design was developed for continuously recovering extracellular biosurfactants from fermenters. The design allows for the operating conditions of the foam fractionation process, feed rate and airflow rate, to be chosen independently of the fermentation parameters. Optimal conditions can then be established for each process, such as the aeration rate required to meet the biological oxygen demand of the cell population. The recirculating foam fractionation process was tested on HFBII producing fermentations. It is shown that by using foam fractionation to strip HFBII from fermentation broth in situ the amount of uncontrolled overflowing from the fermenter was greatly reduced from 770.0 g to 44.8 g, compared to fermentations without foam fractionation. Through optimisation of the foam column operating conditions the proportion of dry matter retained in the fermenter was increased from 88% to 95%, in contrast to a dry matter retention of 66% for fermentation without the new design. With the integrated foam fractionation process a HFBII recovery of 70% was achieved at an enrichment of 6.6. This work demonstrates the utility of integrated foam fractionation in minimising uncontrolled foaming in fermenters whilst recovering an enriched product. This integrated production and separation process has the potential to facilitate improved biosurfactant production, currently a major barrier to their wider use.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:548670 |
| Date | January 2011 |
| Creators | Winterburn, James |
| Contributors | Martin, Peter ; Saiani, Aline |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://www.research.manchester.ac.uk/portal/en/theses/production-of-biosurfactant-by-fermentation-with-integral-foam-fractionation(e4bd51dc-f31f-468a-81d4-d1a512d7b5a2).html |
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