As a consequence of end-product cytotoxicity, conventional biofuel production processes remain predominantly confined to dilute fermentation conditions which in turn constitute ineffectual feeds for downstream separation and purification1, leading to economically-unviable bioprocesses2. To overcome such limitations, we have developed a toolbox of techniques for the in situ recovery of biofuel products, including Expanded Bed Adsorption (EBA). Here, for the first time, we describe the design and application of an EBA process for the recovery of free fatty acid (FFA) biofuels. Continuous up-flow of the culture medium supports expansion of the adsorbent (ion-exchange or hydrophobic resins) bed while permitting Synechocystis sp. to pass through the interparticle region. We have systematically screened and characterized a library of commercial resins, comparing Free Fatty Acid (FFA) adsorption capacity, ease of desorption, and re-usability. Fouling due to competitive adsorption of biomass, proteins, and anion species was also investigated. A bench scale EBA column operating in conjunction with a photobioreactor (PBR) has been developed and its ability to achieve in situ FFA recovery evaluated with respect to such parameters as flow rate, loading time, and FFA desorption. These experimental results are compared to the predictions of a mechanistic model.
1. Straathof, A.J. Auxiliary phase guidelines for microbial biotransformations of toxic substrate into toxic product. Biotechnology progress 19, 755-762 (2003).
2. Schugerl, K. & Hubbuch, J. Integrated bioprocesses. Current opinion in microbiology 8, 294-300 (2005).
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