Enhancing Nonionic Surfactant-Mediated Butyric Acid Extraction through Fermentation Medium Salt Augmentation

Nonionic surfactant (NIS)-mediated extraction offers a promising approach to recover volatile organic acids like butyric acid from fermentation broths but often suffers from poor phase separation and selectivity. This study examines how salt type, concentration, and their interaction influence butyric acid recovery and distribution or partition coefficient (K_p) in an Ecosurf EH-3 NIS system. Results show that higher salt concentrations generally enhanced extraction of the acid with anion identity exerting the strongest effect, complemented by cation contributions, consistent with the Hofmeister series. Notably, FeSO₄·7H₂O and KH₂PO₄ exhibited synergistic salting-out effects. Response surface analysis identified optimal abiotic conditions (0.67 M KH₂PO₄ and 0.28 M FeSO₄·7H₂O), achieving 92.60% recovery and a K_p of 6.70. However, biotic tests revealed that moderate salt levels (0.20 M KH₂PO₄ and 0.05 M FeSO₄·7H₂O) best maintained Clostridium tyrobutyricum viability while delivering 70.97% butyric acid recovery, a K_p of 4.25, and a selectivity of 4.91, demonstrating the potential of salt augmentation for integrated fermentation-extraction systems.