REVIEW In situ product removal in fermentation systems: improved process performance and rational extractant selection Julian T. Dafoe • Andrew J. Daugulis Received: 16 August 2013 / Accepted: 30 September 2013 / Published online: 20 October 2013 Ó Springer Science+Business Media Dordrecht 2013 Abstract The separation of inhibitory compounds as they are produced in biotransformation and fermenta- tion systems is termed in situ product removal (ISPR). This review examines recent ISPR strategies employ- ing several classes of extractants including liquids, solids, gases, and combined extraction systems. Improvement through the simple application of an auxiliary phase are tabulated and summarized to indicate the breadth of recent ISPR activities. Studies within the past 5 years that have highlighted and have discussed ‘‘second phase’’ properties, and that have an effect on fermentation performance, are particular focus of this review. ISPR, as a demonstrably effective processing strategy, continues to be widely adopted as more applications are explored; however, focus on the properties of extractants and their rational selection based on first principle considerations will likely be key to successfully applying ISPR to more challenging target molecules. Keywords Absorption Á Adsorption Á Biocatalysis Á Extractive fermentation Á Ionic liquids Á Reactive extraction Á Product removal (in situ) Introduction The incorporation of an extractant phase for in situ product removal (ISPR) of inhibitory fermentation and biotransformation molecules is a powerful tool to alleviate the effect of high aqueous-phase con- centrations of target molecules, improving bioreactor productivity. Such a processing configuration has been termed a ‘‘two-phase partitioning bioreactor’’ (TPPB) reflecting the presence of distinct aqueous and sequestering phases, as well as the fact that the target molecule will differentially partition between these two phases. In addition to reducing toxic product concentrations, ISPR can be applied to shift unfavourable reaction equilibria, reduce the number of downstream processing steps, favour the accumu- lation of an intermediate in multistep reaction systems, and prevent product losses due to degrada- tion or volatility. The affinity of a target molecule for the extractant phase is measured by the distribution (partition) coefficient at equilibrium, while selectivity is mea- sured by the distribution coefficient towards the target molecule relative to another species, which can be another fermentation product molecule, or water itself. An auxiliary phase possessing a high distribution coefficient is desirable to minimize the amount of sequestering phase required, which has economic consequences throughout the design, extraction, recovery, and recycling aspects of a bioprocess. Selectivity towards the target molecule relative to J. T. Dafoe Á A. J. Daugulis (&) Department of Chemical Engineering, Queen’s University, Kingston, ON K7L 3N6, Canada e-mail: daugulis@chee.queensu.ca J. T. Dafoe e-mail: Julian.dafoe@chee.queensu.ca 123 Biotechnol Lett (2014) 36:443–460 DOI 10.1007/s10529-013-1380-6