Continuous, chemical-free production of High Purity and Ultra Pure Water
Advanced Electro Deionization (EDI) technology is typically implemented downstream of Reverse Osmosis (RO) equipment and is used to produce High Purity and Ultra Pure Water. As the successor to more traditional Ion Exchange resin systems, environmentally friendly EDI systems now set the standard for demineralized water production. Consuming only electricity, EDI equipment can operate continuously, making pure product water of consistent quality, without chemical waste. The systems have a very limited footprint and frequent maintenance is not required.
Companies constantly focus on reducing operating costs, improving efficiency and eliminating the use of hazardous chemicals in the workplace. For High Purity and Ultra Pure Water production EDI strongly supports these goals and many thousands of systems have been installed over 30 years, operating successfully in many environments and applications.
The Electro Deionization process uses ion exchange resins, ion-selective membranes and an applied DC electrical current to remove ions, such as salts, acids and bases. Weakly ionized materials, like dissolved silica, carbon dioxide, boron and some organics are also removed.
Most EDI modules are built with membranes that are permeable to either cations or anions, in an alternating sequence. The spaces between them act as liquid flow compartments, each with an inlet and an outlet. Dependent on the polarity of the ion exchange membrane and its orientation to a cathode or anode, an individual compartment either depletes the water of ions (product water) or accumulates ions (reject water).
To facilitate ion transfer in low ionic strength solutions, the dilute compartments and the concentrate compartments are filled with ion exchange resins. In an EDI module, a part of the feed flow, approximately 5% of the volume, continuously washes out the ions from the concentrate compartments. This concentrate outlet, also called the reject stream, is recirculated upstream of the RO system to be recovered, while the dilute compartments deliver purified product water.
Unlike traditional Ion Exchange resin systems, EDI needs no chemical regeneration. All EDI devices producing ultrapure water operate in electro-regeneration mode, in which the resins are continuously regenerated by H+ and OH- ions, released by the electrically-induced dissociation of water molecules.
For more than 20 years, Pure Water Group has worked with EDI – designing, constructing and supplying EDI systems to extract the very best from this technology. Our EDI systems can achieve up to 99,9 percent salt removal, reduce the levels of individual ionic species to parts-per-billion or even parts-per-trillion levels, and produce ultrapure water with a resistivity of 10 to 18 MegOhm.cm (0,1 to 0,055 microSiemens/cm conductivity).
But outstanding water quality alone is often not the only goal. In our experience, the importance of recycling water has grown steadily, particularly in industries such as power generation and semiconductor fabrication, where huge quantities of pure water are required. Since the EDI concentrate (or reject) stream contains the feed water contaminants at 5-20 times higher concentration, it can usually be recycled back to the RO pretreatment. The recycle option increases the total plant recovery and so minimizes overall water consumption.