Abstract
Biosurfactants offer environmental as well as health benefits over traditionally used chemical surfactants and heterologous production from engineered microorganisms has been demonstrated, offering containable as well as scalable production of these alternative chemicals. Low product titers and cost intensive downstream processing are the main hurdles for economical biosurfactant production at industrial scales. Increased biosurfactant concentrations are found in the liquid fraction of the foam formed during fermentation of producing microbes. Adsorption of biosurfactants from foam fractions in cultivations may offer a simple concentration and purification method which could enable their cost-effective production. Here, foam adsorption was applied as an in situ method for separation of the rhamnolipid biosurfactants during fermentation of Pseudomonas putida EM383. An integrated process was designed to capture the produced rhamnolipids on hydrophobic adsorbent in packed bed units while minimizing the impact of adsorption on the productivity of the system by recirculating cell-containing collapsed foam flow-through back into the reactor vessel. A stable rhamnolipid production by P. putida EM383 on glucose was performed coupled to this adsorption strategy for 82 h, after which no remaining rhamnolipids were found in the cultivation broth and 15.5 g of rhamnolipids could be eluted from the adsorbent. Rhamnolipid yield from glucose feed was 0.05 g g−1, when up to 2 g L−1 glucose pulse feeding was applied. After solvent evaporation, a product purity of 96% was obtained. The results indicate that the integrated adsorption method can be efficient for simultaneous production and recovery of rhamnolipid biosurfactants from microbial fermentations.
Highlights
Biosurfactants are thought to be efficient alternatives and possible enhancers of chemically synthesized surface active agents, as they are in comparison biodegradable, less toxic, more effective at extreme temperature and pH values, and can be produced from renewable resources (De et al 2015)
No differences in biomass growth or overall rhamnolipid production were observed between fermentations with and without integrated foam adsorption and glucose concentrations during the fermentation were similar in both fermentations
Rhamnolipid production was observed after 12 h of the cultivation in both fermentation systems, indicating a partially growth-associated rhamnolipid production as already described for heterologous P. putida (Wittgens et al 2011)
Summary
Biosurfactants are thought to be efficient alternatives and possible enhancers of chemically synthesized surface active agents, as they are in comparison biodegradable, less toxic, more effective at extreme temperature and pH values, and can be produced from renewable resources (De et al 2015). The most common practice in the foam destruction is the use of antifoam chemicals and mechanical foam breaking devices. These steps add to the complexity as well as cost of the downstream process and are insufficient for foam destruction in vigorously foaming biosurfactant systems (Winterburn and Martin 2012). Research efforts regarding biosurfactant production processes have been directed towards development of more effective downstream processes. For this reason, there is an interest in utilizing controlled foaming in biosurfactant fermentation systems through the application of foam separation techniques (Chen et al 2006a). Foam fractionation is a process whereby dissolved or colloidal material is selectively adsorbed on the surface of rising bubbles and is partially segregated by the foam (Lemlich 1972)
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