Study of monovalent ion selectivity of anion-exchange membranes: effect of surface modification and applied voltage

Today, reduction of nitrate content is a great challenge not only in potable water production but also in food industry, especially in dairy products. In many applications, it is neither necessary nor desirable to remove all present ions from treated solution but, e.g., only as said nitrate. Nowadays, attention is paid to electrodialysis as a promising technique for selective demineralization. In this work, we deal with selectivity adjustment of heterogeneous anion-exchange membranes (AEMs) AM(H)-PES (MEGA, Czech Republic) using surface modification with polymer film based on perfluorosulphonic acid. In the next step, the influence of applied voltage on course of electrodialysis was investigated. For individual AEMs the batch desalination process of mixed equimolar solution containing NaNO3, NaCl, NaH2PO4 and Na2SO4 was evaluated as well as selective transport of individual anions. The measurements suggest that there was a time extension in the case of modified AM(H)-PES. With respect to selectivity, all AEMs show slight decline of selectivity eventually unchanged values with higher applied voltage besides to lower voltage. Any AEM appeared to have no selectivity for same charged ions with similar size, regardless of applied voltage. However, it was confirmed that it is possible to increase somewhat the selectivity of monovalent and divalent ions as well as selectivity of H2PO4- and Cl- or NO3- by voltage lowering.