Recovery of lactic acid from fermentation broth using electrodialysis

Abstract

Two-stage electrodialysis was studied for its application to lactic acid recovery from fermentation broth. Suitable ion exchange membranes for this purpose were selected by using a newly designed membrane-fouling test procedure, and then with the selected membranes two-stage electrodialysis was carried out: recovery of sodium lactate from fermentation broth (desalting electrodialysis) and acidification of the purified sodium lactate (water-splitting electrodialysis). Membrane-fouling tests were carried out with a 0.5 N NaCl solution, model solutions, and fermentation broth. Among the membranes tested(Tokuyama Co., Japan), CMS, CMB and CM-1 as cation exchange membranes, and AM-1 as anion exchange membrane showed relatively low electrical resistances to be selected. Desalting electrodialysis was operated in a constant-current and a subsequent constant-voltage modes, and the switching point was predetermined from limiting current density measurement data. The limiting current density was proportional to lactate concentration up to 10 g/L for the combination of CM-1 and AM-1, but it could not be found beyond this level. The relationship between the electrical resistance of membrane stack and the lactate concentration was identified. The amount of water transferred due to electroosmosis which caused volume changes in the feed and permeate solution was experimentally determined also. For three possible combinations of cation exchange and anion exchange membranes selected by the fouling tests, desalting electrodialysis was carried out with fermentation broth. The electrodialyzer consisting of CMS and AM-1 showed the most desirable performance in terms of glucose rejection and hardness removal. The lactate recovery and the glucose rejection were as high as 99% and 84%, respectively, and the magnesium and calcium ion rejection were as high as 71% and 44%, respectively. Such low rejections of magnesium and calsium ions suggested that an additional ion exchange step woul...