Volatile fatty acids permeation through nanofiltration and reverse osmosis membranes

This work presents a comprehensive experimental and modeling framework to describe and predict the volatile fatty acids (VFA) permeation in commercial polymeric nanofiltration (NF) and reverse osmosis (RO) membranes. The permeation behavior was evaluated using single‐ and multicomponent VFA solutions under varying feed concentration, pH, and transmembrane pressure. Permeate flux increased with increasing pressure and decreasing feed concentration, pH, and aliphatic chain length. The RO membrane exhibited significantly higher rejection (50%–90% at pH 3 and 90%–100% at pH 6) compared to the NF membrane (approximately 0% at pH 3 and up to 40% at pH 6), while the latter provided higher permeate flux. All experimental results were described using the solution‐diffusion model coupled with boundary layer model. The findings suggest that selective fractionation of VFA is limited by intrinsic transport and solute losses, whereas concentration via RO operated at pH above the acids' pK a is more feasible.