It can produce treated water equivalent to distilled water through a reverse osmosis membrane from raw water that has passed through the pretreatment system and is most often applied to water treatment systems these days. In general, the principle of osmosis is the principle of equilibrium by diffusion of a low-concentration liquid toward a high-concentration solution. On the contrary, the principle is to remove ions in the water by artificially applying high pressure and reverse osmosis to use the high-concentration solution at a low concentration. The semi-permeable membrane allows only tiny atoms, water, small organic molecules, and gas to pass through.

EDI is a membrane separation deionization system that continuously and uniformly produces pure water through electrical regeneration using an ion exchange membrane, ion exchange resin, and direct current power. Unlike the existing pure water system using only ion exchange resin, it does not undergo a chemical regeneration process and can be used continuously without generating wastewater. Ions are selectively removed by passing them through a cation exchange membrane and an anion exchange membrane, and the cation/anion exchange resin is used between each exchange membrane as a medium to increase the ion exchange rate. RO-produced water is used as a source, and the presence of CO2 in the inflow water may affect the quality of the produced water, so a membrane degasifier is selectively used for pretreatment.

To obtain ultrapure water, it is usually installed additionally on the back of EDI or 2B3T+MB, and mixed-bed resin is used. If there are Sio2 regulations on the treated water quality, an anion resin tower can be additionally configured in front of the mixed bed resin tower.The RO + EDI + polisher system has a high initial installation cost but has a small site area. It can obtain high-purity produced water, and its process is the most preferred these days. ※ The composition of pure water and ultrapure water systems may vary depending on raw water quality and overall conditions.

The raw water that has passed through the pretreatment system passes through the cation tower, decarboxylation tower, anion tower, and mixed bed tower in that order to obtain high-quality pure water. The cation tower adsorbs cations in water and releases H+ through an H+-based cation exchange resin. The adsorbed cations are reduced to H+ ions during regeneration by injecting 5%–10% HCl or 5% H2SO4.The decarboxylation tower degasses the CO2 gas generated in the cation tower and releases it into the air. In the anion tower, anions in water are adsorbed, and OH is released through an OH-based anion exchange resin. The adsorbed anions are reduced to OH-based anion exchange resin during regeneration by injecting 5%–10% NaOH.In a mixed bed tower, water quality of higher purity than 2B3T can be obtained by mixing H+-based cation exchange resin and OH-based anion exchange resin inside the tower. The regeneration method uses HCl and NaOH inside the tower to reduce them to H+ and OH- ions.The 2B3T+MB system is mainly used for large-capacity pure water production and can continuously produce pure water through regeneration. ※ The composition of pure water and ultrapure water systems may vary depending on raw water quality and overall conditions.