Abstract
The creation of monovalent selective ion exchange membranes benefits the desalination of surface waters by removing interfering monovalent ions while preserving polyvalent ionic nutrients. Studies of a promising method of layer-by-layer adsorption of polymers for the creation of monovalent selective coatings note a significant effect of the number of formed layers and of the nature of the external layer on the properties of the resulting membranes. This article reports the changes in properties of layer-by-layer coated heterogeneous membranes occurring at increasing numbers of layers that are attributed to the supposed intermixing of polymers between the layers, namely dependence of limiting current densities determined from i-V curve, enhanced electroconvection that was attributed to the appearing electrical heterogeneity of the surface, and the decreasing monovalent selectivity in electrodialysis of mixed NaCl + CaCl2 solution (from 1.33 to about 1) between the samples with five and six to eight layers of polymers.
Highlights
Agriculture is the largest consumer of water, accounting for about 70% of global freshwater withdrawals
This means that ionic nutrients required for the normal functioning of living organisms, such as Ca2+, Mg2+, SO42− and PO43− are removed together with undesirable monovalent ions such as Na+ and Cl−, which can lead to nutrient deficiencies [11]
Modified membranes based on the MK-40 heterogeneous membrane were created, containing a homogenizing layer of perfluorosulfone material LF-4SC and adsorbed layers of polyallylamine and sodium polystyrene sulfonate
Summary
Agriculture is the largest consumer of water, accounting for about 70% of global freshwater withdrawals. Water can be purified or desalted using a number of membrane technologies [3,4,5,6,7]; there are new designs for membranes for metal removal from wastewater [8] and there are membrane technologies that could aid in recuperation of energy for desalination process [9], but the disadvantage is that widely used membrane technologies, including reverse osmosis, nonselectively reduce the total mineralization [10] This means that ionic nutrients required for the normal functioning of living organisms, such as Ca2+, Mg2+, SO42− and PO43− are removed together with undesirable monovalent ions such as Na+ and Cl−, which can lead to nutrient deficiencies [11]. Selective demineralization using selective electrodialysis carried out using monovalent selective membranes was proposed [13] for agricultural producers with high requirements for water quality, such as greenhouses
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