Mathematical modeling of transport phenomena and quality changes of fish sauce undergoing electrodialysis desalination

Abstract

Despite many existing attempts on modeling electrodialysis (ED) desalination, no work has so far modeled the effect of water transport due to osmosis across the membranes on the quality changes of such a highly concentrated product as fish sauce during the desalination. In this study, a model taking into account the effect of water transport due to the osmotic pressure and electric potential is proposed. Coupled mass and momentum transport equations, along with appropriate initial and boundary conditions, were numerically solved using the finite element method through COMSOL Multiphysics™ version 4.3. The predictability of the model was compared with that of the model neglecting water transport. The model was capable of predicting the evolutions of the salt concentration and volume as well as the quality changes, in terms of the total nitrogen concentration, total amino nitrogen concentration, total aroma concentration and total change of color, of fish sauce undergoing ED desalination at both laboratory and pilot scales. The model was validated against the experimental results and noted to satisfactorily predict the evolutions of the salt concentration as well as volume of the diluate (fish sauce) and concentrate solutions at both scales; quality changes were also well predicted. The effect of neglecting the water transport during ED on the various predicted values was also illustrated. When water transport was not considered, the evolutions of the salt concentration of both the diluate and concentrate solutions as well as the changes of all quality attributes were not adequately predicted.