Patent ID: 8382984

Claim:
A process for purifying wastewater via a biological treatment that uses a set of microorganisms that have different metabolic spectra, in order to remove carbon and nitrogen, or even phosphorus, a portion of the microorganisms being fixed to movable solid supports and constituting a fluidized fixed biomass, wherein: another portion of the microorganisms is free for an activated sludge type treatment; a first non-aerated treatment zone ( 1 a , 21 a ) is provided, followed by a second aerated treatment zone ( 1 b , 21 b ); the treated effluent is subjected to a solid/liquid separation via flotation at a rate greater than 10 m/H; and a portion of the sludge recovered by flotation is recirculated to the activated sludge treatment, this recirculation being controlled so that the SM concentration of the effluent subjected to the liquid/solid separation remains compatible with the flotation used and remains between 0.3 g/L and 1.5 g/L.