What happens to inorganic nitrogen species during conductive diamond electrochemical oxidation of real wastewater?

• Nitrate is the main intermediate in the CDEO of nitrogen-containing organics.
• Ammonium is not formed by organic oxidation but by cathodic reduction of nitrates.
• Ammonium removal is related to the breakpoint chlorination reaction.

This work describes the oxidation of caffeine, metoprolol, SMX and progesterone in real wastewater in terms of inorganic nitrogen speciation and help clarify the mechanisms that affect inorganic nitrogen species as final products. In synthetic solutions containing ammonium or nitrate ions, it has been confirmed that reduction of nitrates is a very favored process while oxidation of ammonium is negligible. Role of chloride is demonstrated to be important in the formation of chloramines, as well. These results allow the clarification of the production of nitrates as main products of the oxidation of organic chemicals and the occurrence of ammonium and chloramines in the reaction media, as well as the depletion of nitrogen by gaseous nitrogen production. Results are of a great relevance to interpret the mechanisms proposed in the literature for the treatment of organic wastes by conductive diamond electrochemical oxidation.