Modelling the microfiltration of lactic acid fermentation broths and comparison of operating modes

This paper deals with the first unit operation of the downstream process for the production of lactic acid: the clarification of fermentation broths by cross-flow microfiltration. Microfiltration experiments conducted under constant transmembrane pressure and under constant permeate fluxes (higher and lower than the critical flux) were represented by the resistance in series model in which the membrane resistance, the adsorption resistance, the bacteria cake resistance and the soluble compounds concentration polarisation resistance were taken into account. The different operating modes were compared in terms of two industrial interest criteria: the productivity and fouling rates. Higher productivities were obtained during constant transmembrane pressure runs whereas the lowest fouling rate was observed during the run conducted with a constant permeate flux lower than the critical flux. However, this fouling was mainly due to adsorption and solute components concentration polarisation. Key words: Microfiltration; Fermentation broths; Productivity; Fouling rate; Constant pressure; Constant flux

The clarification of the lactic acid fermentation broth was modelled by the resistance in series law in which the membrane resistance, the adsorption resistance, the bacteria cake resistance and the soluble compounds concentration polarisation resistance were taken into account. In all cases, the resistances due to adsorption and solutes concentration polarization dominated. We found that constant transmembrane pressure mode was preferable for the batch microfiltration, unless the clarification is coupled to another unit operation which requires a constant feed flow rate. ss — Steady state — Initial