Photochemical-biological treatment of a real industrial biorecalcitrant wastewater containing 5-amino-6-methyl-2-benzimidazolone

5-amino-6-methyl-2-benzimidazolone (AMBI), used in the manufacture of dyes, was characterised as a biorecalcitrant compound by means of different biod egradability tests. In order to enhance the biodegradability of this import ant pollutant, the application of Advanced Oxidation Process (AOPs) as a pr etreatment was explored. Some experiments were addressed to find the most e fficient AOP. The systems H2O2/hv, TiO2/H2O2/hv, Fe3+/hv, Fe3+/H2O2 and Fe3 +/H2O2/hv were compared. The photo-Fenton system was the most efficient and the optimal conditions (AMBI, Fe3+, H2O2 concentrations) for the degradati on of AMBI were found. During the photo-Fenton degradation, experiments wer e also made to obtain information concerning the evolution of: (a) organic carbon and initial compound concentration; (b) the oxidation state; (c) the toxicity; (d) the biodegradability; and (e) the chemical nature of the int ermediates. These analyses show that the solution resulting from the treatm ent of AMBI is biologically compatible and complete mineralisation can be p erformed by biological means. A combined photochemical (Fenton) and biologi cal flow reactor for the degradation of AMBI was successfully operated in c ontinuous mode at laboratory scale, 100% of the initial concentration of AM BI and 80.3% of Dissolved Organic Carbon (DOC) were removed in 3.5 hours of total residence time. Finally, some field experiments under direct sunligh t carried out at the Plataforma Solar de Almeria, Spain, demonstrated that this solar catalytic system is an effective treatment for this kind of indu strial wastewater.