Near-complete atrazine mineralization in an electro-Fenton-born-doped diamond electrochemical system

The complete mineralization of atrazine beyond dealkylation and dechlorination is still difficult and advanced oxidation technologies are being tested. In this work, we used the electro-Fenton (EF) process, with a carbon-felt cathode and either boron-doped diamond (BDD) or Pt as the anode, to investigate atrazine degradation and mineralization in aqueous solution. The experiments were carried out in an undivided electrochemical cell filled with a solution containing atrazine, Fe2+ and Na2SO4 as the supporting electrolyte. Disappearance of atrazine was pseudo-first order. Applied current densities of 2, 10, and 20 mA cm-2 (based on the 25 cm2 geometric BDD area) completely eliminated the parent herbicide after 40, 20 and 10 min in the EF-BDD system, respectively, while 50, 30, and 15 min were required for the EF-Pt system. The most interesting one was the nearly complete mineralization realised with BDD (97.06 % total organic carbon (TOC) removal after 8 h at 40 mA cm⁻²) in com­parison to EF-Pt (81.03 %) and EF-BDD (96.29 %) and anodic oxidation with BDD (96.29 %). Desethylatrazine, deisopropylatrazine, hydroxyatrazine and desethylhydroxyatrazine were detected as early intermediates by chromatographic monitoring, followed by detection of the presence of cyanuric acid, carboxylic acids, and finally inorganic ions. Cyanuric acid TOC removal reached 77 % after 3 h in EF-BDD, while EF-Pt achieved only 4.2 % after 10 h at the same applied current; EF-BDD achieved almost 90 % mineralization of cyanuric acid after 10 h. The absolute rate constant of the reaction between cyanuric acid and hydroxyl radicals was 1.53´10-8 M-1 s-1. These results show that homogeneous Fenton chemistry, combined with the high oxidation power of the BDD anode, is key to achieving near-complete atrazine mineralization despite the cyanuric-acid bottleneck.