The paper presents the results of tests carried out on selected membranes, SEPA (Osmonics Inc., USA). The efficiency of membrane water softening was evaluated on the basis of permeate flux and the physicochemical analysis of raw water and permeate. The transport-separation properties of the membranes were determined using (a) the model solutions of NaCl and MgSO_4 and (b) the natural waters of high degree of hardness. The performed tests indicate that the DS-5-DK and DS-3-SE membranes may be applied to the softening of water for drinking and household purposes. The model based on the extended Nernst-Planck and the Donnan equations has been quantitatively fitted to the experimental data. The obtained values of model parameters indicate that in the case of RO membranes a mechanism other than the Donnan exclusion is responsible for the high retention of ions. The membrane filtration modelling will be performed in the next stage of project.
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