Selectable ion concentrations with electrolytic ion exchange

An apparatus to treat an influent solution comprising ions to obtain a selectable ion concentration in an effluent solution, the apparatus comprising:

• (a) an electrochemical cell comprising:
• (i) a housing comprising first and second electrodes;
• (ii) a water-splitting ion exchange membrane positioned between the first and second electrodes, the membrane comprising (i) a cation exchange surface facing the first electrode, and (ii) an anion exchange surface facing the second electrode;
• and
• (iii) an influent solution inlet and an effluent solution outlet with a solution channel therebetween, the solution channel allowing the influent solution to flow past both the anion and cation exchange surfaces of the water-splitting ion exchange membrane and thereby form the effluent solution;
• (b) an ion sensor to measure an ion concentration in the influent solution, at least partially influent solution, or effluent solution, and generate an ion concentration signal;
• (c) a variable voltage supply to maintain the first and second electrodes at a plurality of different voltage levels;
• and
• (d) a controller to receive the ion concentration signal from the ion meter and send a control signal to the variable voltage supply to adjust the voltage level applied to the first and second electrodes in response to the ion concentration signal to achieve a predefined ion concentration range in the effluent solution.

A method of treating an influent solution comprising ions to control the concentration of ions in an effluent solution, the method comprising:

• (a) flowing the influent solution past both anion and cation exchange surfaces of a water-splitting ion exchange membrane to form the effluent solution;
• (b) maintaining a time averaged electric field across the cation and anion exchange surfaces of the water-splitting membrane;
• and
• (c) varying the strength of the time averaged electric field to control the ion concentration of the effluent solution.