Electro-Fenton and photoelectro-Fenton degradation of the antimicrobial sulfamethazine using a boron-doped diamond anode and an air-diffusion cathode

The degradation of sulfamethazine was tested by electro-Fenton (EF) and photoelectro-Fenton (PEF) using a cell with a boron-doped diamond (BDD) anode and an air-diffusion cathode. The main oxidant of this antimicrobial was hydroxyl radical (OH) formed at the BDD surface from water oxidation and in the bulk from Fenton's reaction between added Fe2+ and generated H2O2 at the cathode. Optimum conditions for both treatments were pH 3.0 and 0.5 mM Fe2+. PEF with UVA radiation was more powerful, allowing an almost total mineralization. EF also gave a large mineralization by the high oxidation ability of OH. The increase in current density enhanced the degradation rate of both processes, but consuming more specific charge and lowering mineralization current efficiency. Higher drug contents yielded greater efficiencies. Sulfamethazine decayed following a pseudo-first-order kinetics, more rapidly in PEF, and its constant rate rose at higher current density and lower drug content. 4,6-Dimethyl-2-pyrimidinamine, catechol, resorcinol, hydroquinone and p-benzoquinone were detected as aromatic intermediates. Oxalic, oxamic and mainly formic acids were accumulated in EF, disappearing more rapidly in PEF due to the additional photolysis of their Fe(III) complexes by UVA light. Organic N was mineralized as NH4+ ion, along with a smaller proportion of NO3- ion.