Foam adsorption as an ex situ capture step for surfactants produced by fermentation

- Adsorbent characteristics for efficient rhamnolipid adsorption are described.
- Rhamnolipid adsorption from a foam phase has been demonstrated.
- Fermentation with simultaneous separation of rhamnolipid was conducted by foam adsorption.

In this report, a method for a simultaneous production and separation of a microbially synthesized rhamnolipid biosurfactant is presented. During the aerobic cultivation of flagella-free Pseudomonas putida EM383 in a 3.1 L stirred tank reactor on glucose as a sole carbon source, rhamnolipids are produced and excreted into the fermentation liquid. Here, a strategy for biosurfactant capture from rhamnolipid enriched fermentation foam using hydrophobic-hydrophobic interaction was investigated. Five adsorbents were tested independently for the application of this capture technique and the best performing adsorbent was tested in a fermentation process. Cell-containing foam was allowed to flow out of the fermentor through the off-gas line and an adsorption packed bed. Foam was observed to collapse instantly, while the resultant liquid flow-through, which was largely devoid of the target biosurfactant, eluted towards the outlet channel of the packed bed column and was subsequently pumped back into the fermentor. After 48 h of simultaneous fermentation and ex situ adsorption of rhamnolipids from the foam, 90% out of 5.5 g of total rhamnolipids produced were found in ethanol eluate of the adsorbent material, indicating the suitability of this material for ex situ rhamnolipid capture from fermentation processes.