Monitoring of fermentation processes using novel on-line techniques

  • Melissa Black

Student thesis: Doctoral Thesis


Biotechnology processes are crucial to the pharmaceutical and many other industries including the oil industry. These processes are often complex and poorly understood and hence frequently developed and operated sub-optimally. There are many techniques that could be used to monitor and improve these processes including infrared spectroscopy, acoustic monitoring and refractive index measurements. Novel probes have been designed by Bioinnovel and Stratophase that have the potential to monitor these processes using these techniques. This work investigates these new probes to monitor Xanthomonas campestris and Escherichia coli fermentations and the use of infrared to monitor a X. campestris fermentation which has not previously been studied.From the work investigating the use of infrared monitoring of a X. campestris fermentation it was shown to be possible to model the fermentation using a combination of off-line reference analyses. Mid-infrared off-line monitoring produced a PLS model which could monitor the glucose consumption within the fermenter using the 980 -1200 cm-1 region. The root mean squared error of calibration (RMSEC) of this model was 2.78 g/L over a measured glucose concentration range of 0-35 g/L. A model was also built to monitor the xanthan production of these fermentations using the same region. The RMSEC of this model was 2.78 g/L over a measured glucose concentration range of 0-25 g/L. The error associated with these models are higher than desired because of poor reference analysis as well as difficulties of the overlapping peaks of xanthan and glucose in this region.The Bioinnovel acoustic monitoring probe was first characterised to identify the optimal experimental conditions. Model analyte solutions of agar, starch, glycerol and xanthan were analysed and a relationship between the concentration of the solution and the velocity of the acoustic wave was identified. These velocities were in good agreement with the literature for example pure glycerol's measured velocity was 1914 ms-1 (Std. dev 2.19 ms-1) in comparison to the literature value of 1904 ms-1. To explore potential combination of acoustic and rheological properties, the rheological characterisation of model xanthan was carried out including viscosity measurements of 0-2% wt./v xanthan solutions. The viscosity of the solutions increases as the concentration increases therefore it may be possible in the future to combine velocity measurements with the viscosity measurements with further experiments. Throughout the experiments with the Bioinnovel probe potential improvements for the probe design were noted.The refractive index probe designed by Stratophase was used to monitor an E. coli fermentation. First the probe was characterised and off-line analysis demonstrated the potential to monitor certain analytes within the fermentation broth such as glucose and biomass. These experiments found the Bragg wavelength shift increased as the concentration of the analytes increased for example the wavelength shift of 2.5 g/L was measured as 5.50 pm and of 15 g/L was measured as 73.41 pm. When the probe was used to analyse the fermentation samples off-line the combination of the changes in the Bragg wavelength (decrease of 66 pm over 12 hours) were as expected after the model solution analysis, the decrease of the glucose concentration playing the largest part in the change in Bragg wavelength. However, on-line analysis proved difficult as the probe fouled due to biomass on the sensor window and the probe itself did not always survive the autoclaving process due to the high temperature and pressure conditions.
Date of Award15 Jan 2018
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SupervisorAlison Nordon (Supervisor) & Brian McNeil (Supervisor)

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