Medium-Chain Fatty Acids Recovery from Synthetic Organic Waste Streams Using Supported Liquid Membranes
Hiroki Fukuda, Jongho Lee
Abstract
Medium-chain fatty acids (MCFAs) derived from organic waste have been recognized as a high-value biochemical, but their selective separation from the waste remains a challenge. Here, we demonstrate facile and selective MCFA recovery from synthetic organic waste streams using supported liquid membranes (SLMs). SLMs were fabricated by filling a nonpolar solution of trioctylphosphine oxide (TOPO) in dodecane into microporous, hydrophobic substrates. An acidic solution containing ethanol, short-chain fatty acids (SCFAs), and MCFAs was prepared as a feed stream to mimic the effluent of MCFA-producing anaerobic bioreactors. We demonstrated >90% recovery of MCFAs while ethanol and SCFAs were effectively rejected. A trade-off relation was found between recovery and selectivity, modulated by the partition coefficient of the fatty acids into the membrane liquid. MCFA recovery increased with a higher TOPO concentration or temperature due to the enhanced complexation of MCFAs by TOPO. Conversely, the selectivity of MCFAs over SCFAs increased with a lower TOPO concentration or temperature, owing to the larger contrast in partition coefficients of SCFAs and MCFAs, at the cost of reduced recovery rates. Tuning the partition coefficient even allowed for selective separation among MCFAs. Our study highlights the potential of SLMs for producing high-value biochemicals from organic waste.