High-value medium-chain fatty acid production from food waste condensate via chain elongation during syngas fermentation: Selective recovery and real-time wettability using a supported liquid membrane contactor

This study presents an integrated approach combining syngas fermentation with supported liquid membrane contactors (SLMCs) for the selective recovery of medium-chain fatty acids (MCFAs) from food waste condensate (FWC). The process aims to valorize short-chain fatty acids (SCFAs) produced during syngas fermentation into high-value MCFAs and recover them efficiently using SLMCs. Polyvinylidene fluoride (PVDF) membranes impregnated with organic extractants, including tertiary amine (TOA) and tertiary phosphine oxide (TOPO), were evaluated for their MCFA transport performance and interfacial stability. Among them, the TOPO-filled PVDF membrane (TOPO 50) exhibited the highest selectivity, achieving an octanoic acid recovery of 88.1 %, while the acetic acid recovery remained low at 2.76 %. This selectivity was attributed to favorable hydrophobic and hydrogen bonding interactions between TOPO and MCFAs. Furthermore, real-time optical coherence tomography (OCT) revealed that TOPO 50 maintained structural integrity during 12 h of operation, showing only an 8.0 % porosity loss and a 5.3 % reduction in water contact angle, whereas the pristine PVDF membrane experienced severe wetting with an 86 % porosity loss.