Introduction of AAO/A2O Process

The traditional Activated Sludge Process is the earliest Sewage Treatment Solution, which has high efficiency in removing organic matters. The harm of water eutrophication is becoming more and more serious,the removal of nitrogen and phosphorus is included in the goal of sewage treatment, so the improved AO Process and AAO Process of activated sludge method appear.

There are two kinds of AO Process, one is Anaerobic-Aerobic Process for phosphorus removal, and the other is Anoxic-Oxic Process for nitrogen removal.

AAO is the abbreviation of Anaerobic-Anoxic-Oxic.AAO Process is both nitrogen and phosphorus removal process.　

AAO Process Flow

Anaerobic Reactor,where raw sewage and phosphorus containing return sludge discharged from the sedimentation tank enter at the same time. The main function of this reactor is to release phosphorus, while some organics are ammoniated;

Anoxic Reactor,the primary function is denitrification. Nitrate nitrogen is sent from the aerobic reactor through internal circulation. The circulating mixed liquid volume is large, generally 2Q (Q is the flow of raw sewage);

OXic Reactor—-Aeration Tank, this reaction unit is multifunctional, where BOD removal, nitrification and phosphorus absorption are carried out. The mixed liquid with a flow of 2Q returns to the anoxic reactor from here.

The Sedimentation Tank is used to separate sludge from water. Part of the sludge returns to the anaerobic reactor and the supernatant is discharged as treated water.

AAO Process Characteristics

1. The organic combination of anaerobic, anoxic and aerobic environmental conditions and different microbial communities can simultaneously remove organic matters, nitrogen and phosphorus.
2. In the process of simultaneous deoxidation, phosphorus removal and organic matter removal, this process is the simplest, and the total hydraulic retention time is also less than other similar processes.
3. Under the alternate operation of anaerobic anoxic aerobic, filamentous bacteria will not multiply in large numbers, and SVI will not produce sludge bulking in general.
4. The phosphorus content in sludge is high, generally more than 2.5%.
5. The effect of nitrogen and phosphorus removal is affected by the fact that the reflux of mixed liquor is smaller than that of wood, and the effect of phosphorus removal is affected by D0 and nitric oxygen entrained in the returned sludge, so the efficiency of nitrogen and phosphorus removal is unlikely to be high.

AAO biological nitrogen and phosphorus removal process is a combination of traditional activated sludge process, biological nitrification and denitrification process and biological phosphorus removal process.It is a commonly used Sewage Treatment Solution, which can be used for secondary sewage treatment or tertiary sewage treatment, as well as reclaimed water reuse, with good nitrogen and phosphorus removal effect. The treatment efficiency of this process can generally reach: BOD5 and SS are 90%~95%, total nitrogen is more than 70%, and phosphorus is about 90%.

#QDEVU #WATERTREATMENT #WASTEWATERTREATMENT #SEWAGETREATMENT