Production processes of fermented organic acids targeted around membrane operations: design of the concentration step by conventional electrodialysis

Organic acids are increasingly used for various industrial applications. Th eir production is mainly achieved by fermentation. Precipitation or extract ion stages, which generate big amount of effluents, are then traditionally used to get the acid in a suitable form. To lower the impact on the environ ment, the implementation of cleaner operations are investigated. In this co ntext, a complete process targeted around membrane operations for clarifica tion, concentration and conversion was studied. The present paper is devote d to the study of the concentration step, carried out by conventional elect rodialysis (EDC). A model, based on the description of the solute and solut ion fluxes through the membranes is developed. Dedicated procedures are pro posed to determine the different contributions, i.e. electromigration and d iffusion, to these fluxes so as to feed the model. This approach is then ap plied to the concentration of sodium lactate solutions. The preponderance, of electromigration is thus demonstrated as well as the existence of a maxi mum achievable concentration, the predicted value of which is confirmed exp erimentally. Comparison between EDC of sodium and ammonium lactate solution s shows that the counter ion has negligible influence on the transport of l actate. The influence of the membrane characteristics is also drawn from co mparison with previously published results. Finally, the predictions of the model are compared with the experimental results concerning the concentrat ion of a fermentation broth and a good agreement is stated. The approach pr oposed in this paper can be used as well to design EDC concentration of any other organic acid salt than lactate. (C) 2001 Elsevier Science B.V. All r ights reserved.