Paired electrocatalytic H₂O₂-persulfate activation for sulfamethoxazole mineralization in a filter-press cell using BDD and air diffusion electrodes

This paper deals with the paired electrocatalytic H2O2-persulfate (H2O2-PS) activation to yield SO4 center dot- and center dot OH for the antibiotic sulfamethoxazole (SMX) mineralization. A filter-press cell with a boron-doped diamond (BDD) anode and a gas diffusion cathode (GDE) was used to form the PS (through the anodic oxidation (AO) of sulfate) and H2O2 (via oxygen reduction reaction, ORR). Bulk electrolysis in the flow cell reached accumulation values of 1.48 mM PS and 4.80 mM H2O2 in 100 mM Na2SO4 at pH 3, with current density and mean linear flow velocity of j = 10 mA cm(-2), and u = 39.5 cm s(-1). On the other hand, the influence of the initial sulfate concentration 50 <= CSO42- <= 500 mM), applied current density (5 <= j <= 15 mA cm(-2)), initial PS and SMX concentrations (0 <= C-PS <= 1 mM, 5 <= C-SMX <= 20 mg L-1) was systematically addressed on the H2O2-PS process performance. The best trial achieved the total abatement of 20 mg L-1 of SMX in a 100 mM Na2SO4 + 0.5 mM PS at pH 3, u = 39.5 cm s(-1), and j = 10 mA cm(-2). Lastly, a degradation pathway of SMX was proposed in which most of the by-products consisted of short-chained carboxylic acids and ammonium. Scavenger tests revealed that the degradation of SMX is provoked by center dot OH (68.3 %), SO4 center dot- (3.9 %), and other oxidants (27.8 %).