Comparative degradation of the diazo dye Direct Yellow 4 by electro-Fenton, photoelectro-Fenton and photo-assisted electro-Fenton

► Fast decolorization of Direct Yellow 4 solutions by electro-Fenton and photoelectro-Fenton. ► Almost total mineralization by the more powerful photoelectro-Fenton. ► Photo-assisted electro-Fenton potent as and more economic than photoelectro-Fenton. ► Maleic, oxalic and oxamic acids as generated carboxylic acids. ► Higher release of NH4+ than NO3 ion, but initial N mainly lost as volatile N-compounds.