AbstractIn the present work, treatability studies were carried out with oil refinery wastewater (effluent from the secondary treatment) using electrooxidation (EO) process employing two mixed oxide anodes: SnO2–RuO2–IrO2|Ti and IrO2–Ta2O5|Ti. Both electrodes' performance were compared by their capacity to generate active chlorine in a synthetic solution and organic matter mineralization of a sample with an average phenol (C6H6O) concentration of 100 mg L−1. Before degradation experiments, surface analysis, and linear sweep voltammetry tests were performed. SnO2–RuO2–IrO2|Ti anode yielded higher active chlorine, reaching an average concentration of 340 mg L−1 at 90 min of electrolysis and 25 mA cm−2. On the other hand, IrO2–Ta2O5|Ti anode only generated an average concentration of 200 mg L−1 at 90 min and 40 mA cm−2. Regarding the degradation experiments, SnO2–RuO2–IrO2|Ti anode showed the highest dissolved organic carbon removal, ranging from 26% to 40%. In addition, through a three‐dimensional excitation–emission matrix fluorescence analysis, it was possible to elucidate the degradation of C6H6O and some possible polycyclic aromatic hydrocarbons present in the effluent. The results suggested that 65%–90% of the hydrocarbons and C6H6O present in the effluent were degraded with the SnO2–RuO2–IrO2|Ti anode applying 25 mA cm−2 within the first 30 min of electrolysis, reaching almost 99% degradation at 90 min. The EO process using SnO2–RuO2–IrO2|Ti can be an alternative for tertiary treatment of oil refinery wastewater for degradation and mineralization of the remaining organic matter of secondary effluents (biological processes) via active chlorine species.