Abstract for presentation at Chemeca 2005

A New Quantitative Risk Model of a Fermenter for Friday 13th Syndrome

  • Mr Rohit Patil, Food Research Group, School of Chemical Engineering, The University of Adelaide, Adelaide, SA 5005, Australia, Australia
  • Dr KR (Ken) Davey, Food Research Group, School of Chemical Engineering, The University of Adelaide, Adelaide, SA 5005, Australia, Australia
  • Mr Ben Daughtry, SARDI Food Safety Research, Adelaide, SA 5065, Australia, Australia

    • In the food and pharmaceutical industries plant failure can be costly - and sometimes catastrophic to public health with survival of unwanted pathogenic micro organisms in the plant or product. Not all plant failure can be attributed to human error. Novel application of Quantitative Risk Assessment (QRA) has led researchers to the notion of Friday 13th Syndrome (Davey and Cerf 2003) - i.e. the unexpected failure of well-operated plant. Here, a new mathematical model for a general fermentation based on Monod kinetics for Escherichia coli is synthesised that incorporates both variability in micro organism growth characteristics together with the effect of chance - to predict the likelihood of unexpected failure. Failure is defined as fermenter washout. Fermentation of E. coli is one of the most widely used unit operations worldwide. Simulations of continuous operation of the fermenter are performed using a Microsoft Excel(TM) spreadsheet with an add-in @Risk (pronounced at risk) version 4.5 (Palisade Corporation) with 100,000 iterations from Monte Carlo sampling of model parameters. Results underscore that the combined effect of small variability in growth characteristics (µmax, Yx/s and Ks) of the micro organism has a highly significant effect on destabilising a well-operated fermenter - and sometimes can lead to a catastrophic failure. The exciting prospect of developing robust fermenter operation from applying insights from this approach is briefly discussed.

    Conference Organiser - ICMS Pty Ltd