The treatment of highly recalcitrant and non-biodegradable solutions of 1 mM of o-toluidine has been comparatively treated by different water treatment technologies based on Fenton's reaction: conventional Fenton process, electro-assisted Fenton process and electro-assisted photo-Fenton process. The pollutant was mainly oxidized by the homogeneous (OH)-O-center dot released in situ by the Fenton's reaction. The electro-assisted photo-Fenton technology demonstrated better performance due to the faster electro-regeneration of iron(II) and the coupled photolysis of several by-products such carboxylic acids attaining complete o-toluidine removal in 60 min of treatment. The study of the biodegradability enhancement after the treatment achievieng values near to 0.4 of BOD5/COD ratio assessed the feasible application of electro-assisted photo-Fenton process as pre-biological treatment. In addition, a reaction pathway for o-toluidine mineralization by electro-assisted photo-Fenton's reaction is proposed. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.