Sequencing batch facility and method for reducing the nitrogen content in waste water

A process for the treatment of effluents containing nitrogen in the form of ammonium, using chemical oxidation and reduction reactions in a sequencing batch reactor (1), the process comprising:

• a feed step (2), during which a volume of effluents to be treated is introduced into the reactor (1),
• at least one first aeration step (10), during which oxygen or air is injected into the reactor (1) for a partial oxidation of the ammonium to give nitrites and/or nitrates,
• a second anoxic step (20), during which, by interrupting the injection of oxygen or air, nitrogen gas is produced,
• a settling step (30), during which sludge is deposited at the bottom of the reactor (1) to form a sludge bed, and content of the reactor clarifies at the surface thereof,
• a draining step (40), during which a clarified fraction of the content of the reactor is evacuated,
• said draining step (40) and feed step (2) taking place simultaneously,
• wherein during the feed step (2), the volume of effluents to be treated is introduced at less than 1 m from the bottom of the reactor (1),
• wherein during the draining step (40), the clarified fraction of the content of the reactor is evacuated at a predefined evacuation level (42) at the surface of the content of the reactor,
• and wherein the level of the content of the reactor is kept substantially constant during the draining step (40) and feed step (2).