Comparison between diafiltration and concentration operation modes for the determination of permeation coefficients of humic substances through ultrafiltration membranes

The permeation of theoretical mixtures of organic compounds through ultrafiltration (UF) membranes was simulated through the application of available mathematical models for the permeation of each single solutes. The simulations were performed for both concentration and diafiltration operation modes and the mixtures' permeation coefficients were calculated. The results of those simulations put into evidence that mixture permeation coefficients calculated from the variation of the retentate concentration are lower than those calculated from the variation of the permeate concentration, but they are relatively independent of the UF operation mode. A sample of fulvic acids was then submitted to sequential UF, through a series of membranes, by both operation modes. The mixture permeation coefficients were calculated from the variation of the permeate concentration and statistical similar values were obtained from both operation modes, as predicted by simulations. However, concerning the total percentage of organic matter losses, large differences were observed between the methods. (C) 2001 Elsevier Science B.V. All rights reserved.