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The reagent-free electromembrane process of removing carbonates, bicarbonates, and carbonic acid from softened natural carbonate water using an electrodialysis synthesizer EDS-01 with a two-cell unit cell formed by a bipolar membrane and a cation-exchange membrane has been studied. MB-2M membranes modified with an ionopolymer containing phosphoric acid groups catalytically active in a water-splitting reaction have been used as bipolar membranes, while heterogeneous membranes Ralex CMH (Mega a.s., Czech Republic) have been used as cation-exchange membranes. The decarbonization process has been carried out in two stages. At the first stage, a reagent-free correction of pH of the solution treated has been carried out. The value of pH in acid compartments has been adjusted to be 2.5-4.0. At the second stage, this solution has been deaerated with air purified from carbon dioxide. For a quantitative description of the process, a previously developed model has been adapted to describe the electrodialysis process with bipolar and cationexchange membranes. It is shown that the electrodiffusion transfer of anions through the cation-exchange membrane and bipolar membrane is practically absent, and the change in the concentrations of carbonate ions, bicarbonates, and carbonic acid is due to the quasi-equilibrium chemical reactions. The deaeration of acidified softened water reduces the total carbon content from 5 to 1 mmol/L. The decarbonization of softened water is accompanied by a decrease in the concentration of sodium cations and total mineralization. With an EDS-01 electrodialysis synthesizer performance of 100 L/h, the specific energy consumption is in the range from 0.16 to 6.12 kW h/m 3 depending on the current density.

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