Dynamic multi-point measurement of foam behaviour for a continuous fermentation over a range of key process variables

摘要

Formation of excessive foam can cause a number of problems during fermentation processing,for example,it can lead to 'foam out' and subsequent contamination.Antifoam is commonly added to control foaming,but this can affect mass transfer and can add significantly to process costs.Furthermore,there is a tendency to run fermentations at below maximal working volume to ensure foam containment;this obviously has cost implications.Methods for measuring and controlling foam formation are currently relatively simplistic and are not based on a thorough understanding of foam formation and stability behaviour.Foams are complex gas-liquid dispersions whose characteristics depend on solution properties and process conditions,principally,for an impeller driven fermenter,gas flow rate and impeller speed.In this paper,dynamic multi-point measurements of conductance across a foam phase formed during a continuous Pseudomonas sp.fermentation are reported for a range of process regimes in which the only variables were gas flow rate,gas composition and impeller speed.Foam behaviour is characterised in terms of foaming frequency,a steady state conductance,liquid distribution through the foam phase and foam formation rates.The dependence of these parameters on process variables is described.Two different types of foam behaviour are identified.On the basis of this analysis suggestions are made for developing strategies to minimise foam formation or to minimise antifoam additions.