This work is proposing a design strategy for an industrial combined solar photo-Fenton/aerobic biological system for the decontamination of wastewater polluted with commercial pesticides. The two possibilities.(photo-Fenton/bio and Bio/photo-Fenton) of the combined system were evaluated (using different analytical tools and bioassays, mainly DOC, COD, toxicity and biodegradability) in pilot plant and the most successful was scaled-up. Photo-Fenton (20 mg/L of Fe(2+)) was carried out in compound parabolic collectors (CPC) at an initial DOC of 500 mg/L (100 mg/L of each commercial pesticide). The biological pilot reactor was an Immobilized Biomass Reactor (IBR) filled with polypropylene Pall Ring supports colonized by activated sludge. The industrial plant has a total collector surface of 150 m(2), total photo reactor volume of 1060 L and the scaled-up biological treatment plant (also an IBR) consists basically of two IBRs (1230 L each). The photo-Fenton treatment at pilot plant scale was able to reduce toxicity (from 96% to 50% of inhibition) and increase biodegradability (from 50% to 95%) of the wastewater and the most suitable point for combining it with the biological treatment was after the total elimination of the active ingredients. The efficiency of the combined photo-Fenton/bio system in terms of mineralization was 94%, of which 35.5% corresponds to the AOP and 58.5% to the aerobic biological treatment. The combination Bio/photo-Fenton was not successful. The efficiency of the industrial-scale combined system (photo-Fenton/bio) was 84%, 35% corresponding to the photo-Fenton treatment and 49% to the biological stage. (C) 2010 Elsevier B.V. All rights reserved.