An innovative fixed-film mobile bed bioreactor for high-rate denitrification of wastewaters has been developed and tested. This reactor, called the Mixazur® enables a high denitrification efficiency due to high kinetics. These properties are combined with a very simple system, particularly due to the choice of a suitable mineral granular support for bacterial growth, enabling a very low filling ratio. This low filling ratio, usually smaller than 5% vol., offers a sufficient surface area for fixed-film development, easily moved by a simple mechanical agitation with low energy consumption (< 30 W/m3 of reactor). The experimental study showed that this reactor can achieve an eliminated loading rate of 0.6 kg NOx-N/m3 of reactor per day at a removal efficiency more than 80% and at water temperatures between 13 and 20°C. The separation of a denitrifying biomass in a specific pre-denitrifying bioreactor led to a development of a very active biofilm with denitrification rates as high as 10 mg NOx-N/g MLVSS.h at 18°C. The scale-up of this system does not need any sophisticated wastewater inlet distribution system, any additional material/biomass separation device and any recirculation loop for maintaining a constant fluidization velocity. Moreover, the reactor is characterized by its low-cost equipment, continuous operation and by auto-regulation of both biofilm thickness and activity due to a controlled shear stress and by an overall easy operation. The first full-scale facility, for 1200 p.e., using this system has been operating since 1996.

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