A novel biological treatment system was developed for the treatment of piggery wastewater under tropical conditions. It incorporated three consecutive sponge-based floating biofilters. This Upflow Anaerobic/Anoxic/Aerobic Floating Filter (UA3FF) system was shown to effectively deal with carbonaceous and, particularly, nitrogenous matter. The rationale proposed for the processes occurring in anoxic-aerobic reactors was discussed in the light of the concept of nitritation-denitritation rather than nitrification-denitrification. The N-related microbial communities manipulated by changing DO concentration and hydraulic retention time affected a considerable increase in the total and specific N-removal (69% and 0.6 kg N m-3 filter media per day, respectively) as compared to data reported elsewhere. Fluorescence In Situ Hybridization and PCR amplification of ammonia monooxygenase (amoA) gene were used to study interrelationships between N-related microbial groups in the system. Operational behavior and performance of the reactors were interpreted in terms of microbiological data. The N-removal efficiency of the biological UA3FF system was compared with a combined biological/physico-chemical system based on (a) biological anaerobic pretreatment followed by (b) chemical precipitation (CP) and (c) air stripping. Both systems were scrutinized as to operational advantages and costs. The treatment options could produce effluent of high quality (150 mg COD l-1, 90 mg total-N l-1) amenable for the subsequent treatment at the municipal facilities. However, biological treatment system was superior to the combined system by a factor of 20 as far as costs are considered.
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