Why Dimensionally Stable Anodes are the Best Electrode Material for Water Disinfection?

Why Dimensionally Stable Anodes are the Best Electrode Material for Water Disinfection?

If electrochemical disinfection is applied to drinking water, industrial water, seawater, or other solute-containing water, its effect is mainly based on the electrochemical production of hypochlorite and/or hypochlorous acid from the chloride content of the water. The hypochlorous acid and hypochlorite concentrations are usually termed “free chlorine” or “active chlorine”.

Where there is a low chloride concentration in the water to be treated (as in drinking water) the current efficiency of the electrode material for the production of free chlorine is crucial; it should be as high as possible. Very great differences have been found in the efficiency of free chlorine production between different electrode materials at low chloride concentrations.  

An important aspect in choosing the appropriate electrode material is electrode lifetime. Although electrode lifetime has been improved where electrode polarity remains constant, frequent polarity change between anode and cathode is still problematic in this regard. Because of the formation of calcareous deposits at the cathode during electrolysis in water containing calcium and magnesium ions, polarity reversal is necessary to clean the cathode surface of these deposits at regular intervals. The alkaline pH in the vicinity of the cathode leads to the precipitation of calcium carbonate (CaCO3) and magnesium hydroxide (Mg(OH)2). On reversing the polarity, the former cathode acts as an anode and the scaling is removed due to the acidic anodic pH.  

But polarity reversal reduces electrode lifetime. This is especially true for IrO2 or mixed IrO2/RuO2 electrodes. The shortest lifetime of the electrodes tested was observed for the RuO2-coated titanium electrodes, followed by IrO2-coated electrodes. Mixed IrO2/RuO2-coated electrodes had the longest lifetime under the experimental conditions. These materials are all clearly outperformed by platinized titanium electrodes, which are still running seemingly unaffected after nearly eight years.  

It can be seen that DSA type electrode materials clearly outperform diamond and Pt electrodes, which are therefore not generally applicable as anodes for water disinfection based on the electrochemical production of free chlorine.