A combined strategy of a photo-Fenton pretreatment followed by a Sequencing Batch Biofilm Reactor (SBBR) was evaluated for total C and N removal from a synthetic wastewater containing 200 mg L−1 of the antibiotic Sulfamethoxazole (SMX). Photo-Fenton reaction was performed with two different H2O2 concentrations (300 and 400 mg L−1) and 10 mg L−1 of Fe2 + . The pre-treated effluents with the antibiotic intermediates as sole carbon source, together with a nutrients solution, were used as feed for the biological reactor. The SBBR was operated under aerobic conditions to mineralize the organic carbon and the hydraulic retention time (HRT) was optimized down to 8 hours. Then, an anoxic denitrification stage of 24 hours of HRT was added right after the aerobic stage of the same duration in order to remove the NO3 generated along the chemical–biological treatment. TOC, COD and SMX concentrations together with O2 uptake rate (OUR) profiles were monitored in purpose of assessing the performance of the system. NO3, NH4+ and total N concentrations were analyzed to find out the fate of N contained in the initial SMX molecule. A start up strategy resulted in the correct formation of a biofilm over the volcanic support. The total TOC removals achieved with the combination of the chemical and the biological processes were 75.7 and 87.7% for the low and the high H2O2 concentration pretreatments respectively. Practically all N present in the SMX solution was eliminated in the SBBR when the aerobic–anoxic strategy was used.

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