Rethinking electrochemical oxidation of bisphenol A in chloride medium: Formation of toxic chlorinated oligomers

Overevaluation of Electro-oxidation for Chemical Oxygen Demand Removal Using a Boron-Doped Diamond Anode: The Roles of Various Electrogenerated Oxychlorides and Countermeasure

“…Among various anode materials, BDD electrodes are currently regarded as the state-of-the-art anode for EO owing to their high efficiencies in • OH yield, extreme stability under anodic polarization, corrosion resistance, and commercial availability. , More favorably, their performance in terms of COD removal can be further improved by the reactive chlorine species such as Cl • ( E Cl • / Cl − 0 = 2.4 V NHE ), Cl 2 •– ( E Cl 2 • prefix− / Cl − 0 = 2.0 V NHE ), and ClO • ( E ClO • / Cl − 0 = 1.5–1.8 V NHE ), which were in situ-formed via both direct anodic oxidation and • OH-mediated indirect oxidation of Cl – , an ion ubiquitously found in most wastewaters . Given the above perspective, Cl – has an important effect on the BDD applied in wastewater treatment. − However, Cl – can be also converted into undesirable inorganic oxychloride anions (denoted as ClO x – , x = 1 to 4, for convenience) at very high concentration via multistep oxidation on the BDD surface, such as ClO – , ClO 2 – , ClO 3 – , and ClO 4 – (Table S1), − the maximum contaminant level (MCL) of which is stipulated by the U.S. Environmental Protection Agency (EPA) because of health concerns and ecosystem safety. , The electrogeneration of these oxychlorides has gained extensive attention during BDD utilized for COD removal from Cl – -laden wastewaters. For example, oxychlorides including approximately 45 mM ClO 3 – and 5 mM ClO 4 – were electrochemically produced in the 120 min BDD-treated urine wastewater containing 100 mM Cl – at 93 mA cm –2 .…”