Method and unit for the purification of wastewater with aerobic granular sludge

A unit for the biological purification of wastewater, comprising a reactor with a first compartment (2) and a second compartment (4) that communicate with each other in the lower part, the wastewater to be treated arriving in the first compartment, the second compartment containing aerobic granular sludge and being at atmospheric pressure, and a means for injecting oxygen-containing gas being provided in the lower part of the second compartment, wherein:

• the reactor is a sequential batch reactor;
• the first compartment (2) is closed at the upper part and may be isolated from the atmosphere;
• vacuum means (3) and pressurizing means (7) are placed in the non-immersed upper zone of the first compartment (2);
• means (8, 8b) for injecting and distributing the wastewater to be treated are positioned in the lower zone in the second compartment (4),
• the reactor being designed to operate according to a cycle comprising two phases, namely:
• an anaerobic first phase during which:
• the first compartment (2) is filled under vacuum with wastewater to be treated,
• then the pressure in the first compartment is suddenly brought back to atmospheric pressure in order to rapidly discharge a volume of wastewater to be treated into the second compartment (4) in which no injection of oxygen-containing gas takes place and
• the above two operations are repeated several times in order to introduce and distribute a sufficient volume of effluent in pulsed sequential mode in the second compartment (4), the biological reactions being carried out in an anaerobic medium with the pulsed expanded sludge bed (5) under the effect of the hydraulic stress of the feed;
• an aerobic second phase during which:
• the feed of wastewater to be treated is stopped,
• an injection of oxygen-containing gas takes place in the second compartment (4), the biological reactions being carried out in an aerobic medium with sludge stirred under the effect of the gas injection,
• the gas injection is stopped and the granular sludge left to rapidly settle and
• the treated wastewater is extracted from the second compartment after which another cycle starts.