Mineralization of sulfanilamide by electro-Fenton and solar photoelectro-Fenton in a pre-pilot plant with a Pt/air-diffusion cell

•Up to 94% mineralization of sulfanilamide by solar photoelectro-Fenton with a Pt/air-diffusion cell.•Poor degradation by comparative electro-Fenton due to accumulation of carboxylic acids.•Catechol, resorcinol, hydroquinone and p-benzoquinone as aromatic intermediates.•Maleic, fumaric, acetic, oxalic and oxamic acids as carboxylic acids.•Release of sulfate and ammonium ions, as well as nitrate ion in much lesser extent.

The mineralization of sulfanilamide solutions at pH 3.0 was comparatively studied by electro-Fenton (EF) and solar photoelectro-Fenton (SPEF) using a 2.5 L pre-pilot plant containing a Pt/air-diffusion cell coupled with a solar photoreactor. Organics were primordially oxidized by hydroxyl radical (OH) formed from Fenton’s reaction between H2O2 generated at the cathode and added Fe2+ and/or under the action of sunlight. A mineralization up to 94% was achieved using SPEF, whereas EF yielded much poorer degradation. The effect of current density and Fe2+ and drug concentrations on the degradation rate, mineralization current efficiency and energy cost per unit DOC mass of EF and/or SPEF was examined. The sulfanilamide decay always followed a pseudo first-order kinetics, being more rapid in SPEF due to the additional generation of OH induced by sunlight on Fe(III) species. Catechol, resorcinol, hydroquinone and p-benzoquinone were identified as aromatic intermediates. The final solutions treated by EF contained Fe(III) complexes of maleic, fumaric, oxamic and mainly oxalic acids, which are hardly destroyed by OH. The quick photolysis of Fe(III)-oxalate complexes by sunlight explains the higher oxidation ability of SPEF. The N content of sulfanilamide was mainly mineralized as NH4+ ion and in much lesser extent as NO3- ion, whereas most of its initial S was converted into SO42- ion.