Assessment of 4-Aminoantipyrine Degradation and Mineralization by Photoelectro-Fenton with a Boron-Doped Diamond Anode: Optimization, Treatment in Municipal Secondary Effluent, and Toxicity

4-Aminoantipyrine (4-AA), a persistent metabolite of dipyrone found in natural water, has been treated in 100 mL of aqueous 0.050 M Na2SO4 solutions at pH 3.0 by photoelectro-Fenton (PEF) with a 4 W UVA lamp. The assays were performed in a cell equipped with a boron-doped diamond (BDD) anode and an air-diffusion cathode for H2O2 generation. The formation of an unstable Fe(III)-4-AA complex with 1:2 molar ratio was evidenced. A 2(4) central composite design was used to assess the effect of four independent variables on PEF performance. The optimized conditions for 62.5 mg L-1 4-AA were: current density of 77.5 mA cm(-2) and 47.75 mg L-1 Fe2+, yielding 99% 4-AA degradation at 7 min, and 45% 4-AA mineralization with 3.2% mineralization current efficiency at 130 min. Slightly slower degradation and similar mineralization were obtained under these conditions when 4-AA was spiked into a municipal secondary effluent, showing a low influence of natural organic matter on PEF. The initially high acute toxicity determined using Artemia salina was largely diminished upon PEF treatment.