Separation of lactic acid from fermentation broth by cross flow nanofiltration: Membrane characterization and transport modelling Original Research Article

A dynamic mathematical model was developed for a flat sheet cross flow nanofiltration membrane module for separation of lactic acid from fermentation broth. The model developed with extended Nernst-Planck approach included pH effects during Donnan exclusion of lactate ions through Henderson–Hasselbalch equation. The most relevant structural characteristics (pore radius, porosity to thickness ratio and membrane charge density) of the membranes were completely determined by comparison and convergence of the model-predicted and experimental data on flux and rejection using standard solute-solvent systems as well as actual fermentation broth. Thus the pore sizes of the investigated three nanofiltration membranes NF2, NF3 and NF20 were determined as 0.57 nm, 0.55 nm, and 0.54 nm respectively. Through the modelling and experimental investigation the best membrane (NF2) that could retain and recycle more than 90% sugars while allowing more than 70% lactic acid to permeate could also be selected. Finally refined model could very well predict transport of lactic acid through nanofiltration membranes operated in flat-sheet cross flow module as evident in very small relative error (< 0.1) and the value of overall correlation coefficient (R2) of greater than 0.980.