Separation and Concentration of Lactate from Cassava Fermentation Broth by Reverse Osmosis

Abstract

A reverse osmosis experiment was performed to separate and concentrate lactate from cassava fermentation broth.Pure lactic acid and ammonium lactate solutions were also used as model solutions. The influence of operating conditions, including feed velocity, transmembrane pressure and feed concentration, on the filtration properties (permeate flux, rejection and osmotic pressure) were studied. The concentration factor of lactic acid during batch operation of reverse osmosis was also evaluated. In the laminar flow regime, permeate flux increased with increasing of feed velocity due to concentration polarization of the solute on the membrane surface. However, the permeate flux was not affected by feed velocity in the turbulent regime. Permeate flux and rejection increased with transmembrane pressure and decreased with feed concentration due to higher osmotic pressure. At a transmembrane pressure of 5.5MPa and an initial feed velocity of 0.7 m/s, lactic acid in the model solutions could be concentrated from three to six times; however, the concentration factor in fermentation broth only reached two. The degree of concentration increase of lactic acid was affected by the presence of medium and residual sugar in the fermentation broth, as both may contribute to the increase of osmotic pressure and also polarize the concentration effect that occurs on the membrane surface.