Development of a foam adsorption method for the fermentative production and recovery of rhamnolipids

Rhamnolipids are one of the most researched biosurfactants. They exhibit physical properties which are superior to their synthetic counterparts. However, the biotechnological production of this biosurfactants is cost-intensive, mostly due to downstream processing. Therefore an intensification of the downstream process is considered in this work. Foam adsorption, a novel separation method, is applied for intensification of the fermentative production and recovery of rhamnolipids. Firstly, the proof of principle of this novel hybrid separation method is presented, where the foam separation process and adsorption process effects are enhanced. Further on, foam adsorption method is developed for its application as an in situ separation method for the whole broth processing. An integrated process is concepted and an automated adsorption unit is built up for the purpose of integrated rhamnolipid processing. Finally, an in situ fermentation process is performed in an external configuration with direct contact between the rhamnolipid-enriched fermentation foam phase and the packed adsorption bed. Based on the hydrophobic-hydrophobic interactions, the rhamnolipid separation occurs upon the contact with the adsorbent bed, resulting in burst of the foam and the depletion of the rhamnolipids from the fermentation medium. The producing microorganism, Pseudomonas putida EM383, is also enriched in the foam phase, but the flagella-free strain does not bind or accumulate in the adsorption column. Biomass is recycled back into the bioreactor along with the rest of the fermentation broth. After 82 h of fermentation in an integrated process, 15.5 g of rhamnolipids were purified by in situ adsorption and further solvent evaporation at 96% purity, suggesting 73 mg L-1 h-1 volumetric productivity at 0.05 g g-1 yield of rhamnolipids on glucose. Developed rhamnolipid processing enables continuous and complete separation of rhamnolipids from the fermentation system, at the volumetric productivities and yields that are comparable to the values of the reference production system.