2000 Volume 26 Issue 6 Pages 816-822
The authors carried out nanofiltration of skim milk and analyzed the salt rejection data using the extended Nernst-Planck equation.
The following observed rejections of major constituents in salts were obtained. Na and K: 50 to 60%, Cl: -5 to 15%, Ca, Mg and P: >97%. It is considered that since Ca and Mg are mostly combined with phosphate and citrate in milk, they were rejected by a sieving effect, thus producing high rejections. Electroneutrality in permeate, and no-electric-current condition in solute flux are observed, respectively.
In the subsequent analysis, the authors used a set of proposed assumptions, 1) a complete rejection of solute except Na, K and Cl by the membrane, 2) existence of a fixed charge in skim milk due to impermeable ions of proteins, etc. Rejection of Na, K and Cl calculated from the analysis are in good agreement with those of the experimental data.