The results of a detailed experimental and theoretical study of the rejection of single salts and multi-electrolyte mixtures by a loose ceramic TiO2 (SCT Membralox(R)) membrane at the borderline between ultra- and nanofiltration (NF) are compared with similar results obtained using a tighter organic nanofilter (NF200). Theoretical ion rejection predictions for multi-electrolyte solutions are obtained by solving numerically the hindered transport extended Nernst-Planck (ENP) ion flux equations using our computer simulation program, NANOFLUX, which incorporates electrostatic, steric, and hydrodynamic interactions and a new choice for ion size (bare crystal, or Pauling, radius). We find that, depending on the operating conditions, the looser ceramic nanofilter does not necessarily perform less well than the tighter organic one. We also examine how well the rejection of multi-electrolyte mixtures can be predicted by hindered electro-transport theory (HETT), using a database of single salt results, over a wide range of relative salt mole proportions and pH. Finally, we propose a combined experimental and theoretical method for characterizing, simulating, and optimizing the performance of charged nanofilters using the computer program NANOFLUX. (C) 2003 Elsevier Science B.V. All rights reserved.