Abstract: The invention is a biological process for purifying waste water in order to produce an effluent with a low content of carbon and of oxygenated nitrogen compounds. The process includes an initial step of mixing the waste water in a biological reactor with activated sludge to denitrify the resulting mixture. Then, air is introduced into the mixture to form an anoxic sludge thereby directly oxidizing carbon present in the anoxic sludge and removing carbon therefrom, simultaneous with the denitrification. The anoxic sludge is clarified to separate it from a denitrified intermediate effluent. The clarified anoxic sludge is recycled to the biological reactor.

Abstract: This method measures the soluble phosphorus concentration in the treated water for at least two different places of the treatment line: at the intake of the secondary clarification step to obtain a measurement P1 and at the outlet of the treatment line to obtain a measurement P2, the measurement P1 determining the amounts of the product precipitating the phosphorus in the liquor of at least one of the tanks in which the anoxic or aerobic steps are carried out upstream of the secondary clarification. The measurement P2 is continuously compared to the measurement P1 so as to detect a possible salting out of the phosphorus at the level of the secondary clarification. When the difference between these two measurements (.DELTA.P1-P2) is noted, one of the two following measures occurs: supplementary injection of the precipitating product, before the secondary clarification, or modification of the flow rate of recirculation of the sludge of the clarification step towards the first anaerobic step.

Abstract: Process for the treatment of liquid effluents, such as waste water, for the purpose of removal of carbon, nitrogen and phosphorus pollution using an activated sludge, according to which the effluent, after having been subjected to mechanical pretreatments, is brought into contact with the activated sludge. The effluent/activated sludge mixture is the subjected to clarification/settling in order to separate the treated water from the thickened sludge, the latter then being recycled at the head of the aeration treatment and the excess sludge being continuously discharged. An inert material of inorganic origin is injected into the activated sludge, this material being immediately and homogeneously dispersed in the activated sludge, in order to create a mixed culture containing both, and in a single bacterial floc, free heterotrophic species and autotrophic species partially fixed on the particles of the said material within the floc.

Abstract: Process for the biological treatment of water using a biological reactor containing a culture of microorganisms, immobilized on a granular support material, according to which an expendable powdery material is injected into the said reactor, said process being performed so as to ensure a self-selection and a self-regulation of the support material of the particle size necessary for the biological process.