Competitive continuous fermentations with selective recycle

An inclined settler is used to partially separate desired cells from undesired cells in the product stream of a competitive continuous fermentation on the basis of differences in sedimentation velocities owing to differences in floc-forming capabilities. A stream that is enriched in the desired cells is then selectively recycled to the bioreactor. Experiments with nonsegregating yeast cultures and segregating bacterial cultures have demonstrated that maintenance of the slower-growing strains is achievable using selective recycle, whereas washout of these strains by the faster-growing competing strains occurs in the absence of selective recycle. These results are in good agreement with theoretical predictions.