Foam-free rhamnolipid production using an integrated membrane-stirrer system

Abstract

Rhamnolipids are biosurfactants that tend to cause strong foaming, making microbial production in an aerated stirredtank fermenter challenging. The continuous removal of rhamnolipids from the cultivation broth via in situ liquid-liquid extraction can remedy this foam challenge, and thereby supports long-term cultivation and production. However, for efficient processing and stable phase separation, a specialized apparatus is required. In this study, the novel multiphase loop reactor, which is a modified airlift reactor with an internal loop enabling continuous in situ liquid-liquid extraction, was designed and adapted to produce rhamnolipids with a recombinant bacterium, Pseudomonas putida KT2440. The initially designed multiphase loop reactor showed a low oxygen transfer rate, unable to meet the oxygen demand of the whole-cell biocatalyst, resulting in inefficient growth and production. A re-design of the sparger via 3D printing enableda high oxygen supply allowing rhamnolipid production at key performance indicators that matched stirred-tank reactor cultivations. Advantageously, the multiphase loop reactor allowed stable and constant phase separation and solvent removal enabling continuous cultivation in the future. Concluding, the successful use of the multiphase loop reactor for rhamnolipid synthesis is presented, highlighting its potential to become a new platform technology for intensified bioprocessing.