How Reversed Electrodes are Used for Hard Water Treatment?

How Reversed Electrodes are Used for Hard Water Treatment?

In water treatment process, calcium and magnesium deposits build-up on the cathode. Over time, the deposits can cause increases in the operating cell voltage, thus decreasing cell efficiency.

Various techniques have been proposed for the removal of the cathode scale deposits from hard water treatment systems. The technique of polarities of the electrodes are periodically reversed in the hard water treatment system is used commercially though it has its own challenges (shorter lifetimes depending on conditions applied). It is cost effective, has little or no downtime for cleaning purposes, and has the ability to withstand corrosion problems.

In the current reversal application, usually, two or more electrodes are introduced into the water system to be disinfected. A DC voltage is applied on the electrodes with periodic polarity reversal to clean the cathode of the hard water scales deposited on it. The scale deposits are thin films of hydroxides and /or compounds of calcium and/or magnesium that form on the cathode during the disinfection and chlorination (water-electrolysis) process. During the water-electrolysis, the film scale deposits (consisting mainly of Ca(OH)2, CaCO3, and Mg(OH)2) forms on the cathode surface due to the local increase in pH caused by the evolution of hydrogen.

However, the pH on the anode surface decreases due to the evolution of oxygen. This technique is used for the removal of cathode scale deposits by periodically reversing the polarity of the electrodes. When the polarity of the electrodes is reversed, the former cathode with scale deposits acts as the anode and, with continued electrolysis, a local pH decrease at the anode surface occurs. This leads to the dissolution of the scale deposits on the anode surface.