An operational procedure is presented which enables biological phosphorus removal to be performed using a set of five submerged high rate biofilters. The new process was developed using an upflow biofilter with floating filter media, originally conceived to perform nitrification and denitrification of wastewaters (Biostyr-ND). Anaerobic contact periods were introduced in the functioning periods of the biofilters under continuous feed, ensuring alternating anaerobic/aerobic conditions (A/O) on the fixed biomass. The selection of phosphate-removing bacteria in the biofilm was verified by the efficiency of P removal (60 - 70%) and by the high concentrations of total P in the sludge removed from the system during backwash (≈ 3.4 % Pt/TSS). The activity of the autotrophic nitrifying bacteria was not affected by the alternating A/O conditions reached values close to 1 kg N-NH4/m3d. An improvement in the denitrification process was observed due to carbon storage during anaerobic contact.

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