FAQs on Electrochemical Water Treatment Systems
Editorial Note: Our colleagues in the Water Quality Association developed, for state drinking water programs, the following information about electrochemical water treatment systems.
The water treatment industry is constantly driven to find more sustainable solutions to treatment problems. Cation exchange water softeners and Reverse Osmosis systems are very effective but raise discharge and efficiency concerns. But electrochemical water treatment systems are emerging as a potential solution because they efficiently reduce both hardness and TDS, without the use of salt. The technology goes by several names and you might have heard it referred to as Continuous Electrolytic Deionization (CEDI), Capacitive Deionization (CAP DI), Electrically Regenerated Ion Exchange.
Ok, it has lots of fancy names, how does it work?
Electrochemical water treatment systems utilize electricity to induce the removal of dissolved contaminants in the water. Positively charged contaminants such as calcium, magnesium, sodium, lead and uranium are called cations. Negatively charged contaminants such as chlorides, nitrates, nitrites, sulfates and fluorides, are called anions. The introduction of a negatively charged electrode, or cathode, into the water will cause positively charged cations to move towards it. Electrochemical water treatment systems take advantage of this property by combining the electrode with ion exchange membranes.
Ion exchange membranes allow either only cations or anions through. No water passes through these membranes: Only the dissolved contaminants pass. Using charged membranes then, treated product water is left behind on the other side of the membrane. The product water can then be released to a storage tank where it is collected for use.
To prevent scaling, the system will periodically flush the concentrate zone to drain, and a chemical cleaning cycle may also be used every 6-12 months. Even with the flushing and cleaning cycles, these systems operate at a relatively high efficiency rate of around 80%.
What are the operational requirements?
Electrochemical systems operate at relatively low voltages, with residential units available that can plug into any household outlet. The typical operating cost of a residential unit is about $40 to $50 dollars per year for a family of four. These systems can also operate on wells without the use of a booster pump.
That all sounds great but what do these electrochemical systems remove?
Basically anything that is ionized when dissolved in water will be reduced. A typical target for the product water would be <5 grains per gallon of hardness and <150 ppm of total dissolved solids, but they are not practical if your aim is to produce soft water with <1 grain of hardness.
There is always a catch, what other limitations does this technology have?
Each system is unique and in order to completely understand the limitations of a specific system you must consult with the manufacturer. Pre-treatment to remove potentially harmful sediment, chlorine, iron and silica is often recommended.
