Water production for coffee brewing by electrodeionization

A resin-wafer electrodeionization (RW-EDI) apparatus for purifying water for coffee brewing, the apparatus comprising:

• a cathode;
• an anode;
• a plurality of porous solid resin wafer exchange units arranged in a stack between the cathode and the anode, each unit comprising a monovalent-selective cation exchange membrane, an anion exchange membrane, and an ion exchange resin wafer between the cation-exchange membrane and the anion-exchange membrane, the resin wafer being in contact with the cation exchange membrane and the anion exchange membrane;
• and
• an air distributor adapted and arranged to aerate water flowing inside the resin wafers during use, or to aerate water flowing out of the resin wafers during use;
• wherein:
• each resin wafer comprises a fused porous mixture of a cation exchange resin (CER) and an anion exchange resin (AER);
• each resin wafer exchange unit in the stack is oriented such that the cation exchange membrane faces the cathode and the anion exchange membrane faces the anode;
• each resin wafer exchange unit in the stack is spaced from an adjacent resin wafer exchange unit to thereby defining an ion concentrate chamber between the anion exchange membrane of one resin wafer exchange unit and the cation exchange membrane of the adjacent resin wafer exchange unit;
• and the ion concentrate chambers are in fluid flow connection with each other;
• the cathode is separated from the resin wafer exchange unit adjacent to the cathode by a first bipolar ion exchange membrane, and the anode is separated from the resin wafer exchange unit adjacent to the anode by a second bipolar ion exchange membrane;
• each resin wafer comprises (a) a water inlet at a first end thereof adapted to introduce water to be purified from a water reservoir into the resin wafer and to flow through the wafer, (b) a water outlet at an opposite end thereof to direct a flow of partially deionized water out of the resin wafer and back into the reservoir to be recirculated through the resin wafers one or more times by a pump adapted to distribute water from the water reservoir into the resin wafers, and (c), either (i) a first air inlet at the first end of the resin wafer adapted to introduce air from the air distributor into the resin wafer and to flow through the resin wafer with the water to be purified, and an air outlet at the opposite end of the resin wafer to direct a flow of partially CO2-depleted air out of the resin wafer along with the flow of partially deionized water, or (ii) a second air inlet adapted and arranged to introduce air from the air distributor into the partially deionized water flowing out of the resin wafer;
• wherein optionally, the water inlet also serves as the first air inlet;
• and optionally, the water outlet also serves as the air outlet;
• the water inlets of the resin wafers are in fluid flow connection with each other, and the water outlets of the resin wafers are in fluid flow communication with each other;
• the apparatus is vented to maintain air pressure within the apparatus at ambient atmospheric pressure;
• and
• wherein, when in use, water to be purified is pumped through the resin wafers to presaturate the wafers with the water to be purified and to fill the ion concentrate chambers;
• and the reservoir is filled with the same water to be purified;
• next, an electrical potential is applied across the anode and the cathode by a direct current power source and water is pumped from the reservoir into the resin wafers through the water inlets;
• water flows out of the porous resin wafers through the water outlets, and back into the reservoir for recirculation through the resin wafers;
• at the same time, the water flowing through the resin wafers from the reservoir is aerated by the air distributor either inside the resin wafers or after the water exits the resin wafers;
• the electrical potential creates an electric field that drives a flow of anions into the ion concentrate chambers toward the anode and drives a flow of monovalent cations into the ion concentrate chambers toward the cathode;
• consequently, an ion concentration increases in water that is present in the ion concentrate chambers, and water flowing through the resin wafers is partially deionized, and retains calcium and carbonate ions;
• and carbon dioxide present in the air of the aerated water dissolves and ionizes to automatically adjust the pH of the water being recirculated through the resin wafers to a value suitable to maintain a desired calcium carbonate alkalinity in the water present in the reservoir for use in coffee brewing;
• and recirculation of the water is halted when the desired calcium carbonate alkalinity is achieved in the water present in the reservoir.