BACKGROUND: Fenton and photo-Fenton processes were explored as photochemical pre-treatments to improve the biodegradability of wastewater containing atrazine, a commercial pesticide. The effects of H2O2, Fe3+ and irradiation level on the degradation processes were studied and the optimal conditions determined. RESULTS: Fenton and photo-Fenton oxidation systems were able to remove 85 and 100% of atrazine, respectively, in a 120 min period. These processes produced a biocompatible solution, removing 100% of the initial biorecalcitrant compound; however, cyanuric acid remained in the effluent after the chemical oxidation treatment due to the stability of the N-heterocyclic ring of this acid. Nevertheless, it was found that the cyanuric acid remaining from the photo-oxidative process can be removed by means of an anaerobic treatment. CONCLUSIONS: The results obtained in this work indicate that a coupled photo-Fenton-biological treatment system is a feasible method to achieve the complete mineralization of biorecalcitrant pollutants such as atrazine. (C) 2015 Society of Chemical Industry