Integrated recirculating foam fractionation for the continuous recovery of biosurfactant from fermenters

Abstract

A novel foam fractionation design has been developed for continuously recovering extracellular biosurfactants from fermenters. The apparatus 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 fed batch fermentations producing the hydrophobin protein HFBII. It is shown that by using foam fractionation to strip HFBII from fermentation broth in situ the amount of uncontrolled overflow from the fermenter was greatly reduced from 770 g to 44.8 g, compared to previous 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 dry matter retention of 66% for fermentation without the new design. With the integrated foam fractionation process an HFBII recovery of 70% was achieved at an enrichment of 6.6. This study demonstrates the utility of integrated foam fractionation in minimising uncontrolled foaming in fermenters whilst recovering an enriched product.