AAO Technology (Anaerobic - Anoxic - Oxic) (Wastewater Treatment Plant, Vietnam)


AAO (Anaerobic - anaerobic - aerobic) is a commonly used technique. AAO treatment, including pretreatment, biological treatment, biological and chemical post-treatment (after coagulation, sludge treatment, etc.). Pretreatment of wastewater in order to place the oil, ammonia, etc., to create conditions for the biological treatment. Biochemical biochemical post-treatment effluent is further processed to the emission standards, while isolated from the sludge filter press treatment. Optimization of pretreatment are: 1 ammonia treatment. The main source of water and biochemical ammonia wastewater. Ammonia treatment in de-NH3, ammonia wastewater containing a certain amount of fixed ammonium salt, so by adding a certain amount of 40% NaOH solution, so that the fixed ammonia ammonium volatile separated into free ammonia, to reduce Biochemical NH3-N content. 2 heavy waste oil processing. In order to reduce the oil content of biological water, to transform the device to the addition of tar, high-efficiency filter's porous ceramic filters, oil removal efficiency of 60%. 3 light oil, suspended oil processing. Of light oil, suspended the oil problem, install the belt in the degreasing **** oil skimming machine, the oil slick to bond and rely on a continuous rotating pulleys toppled the oil collection **** into the biochemical system which reduces the oil content of the sewage . 4 sub-standard sewage treatment. Installed in the regulation of pool pumps, sewage sent to the mechanization of the excessive ammonia settler, so that re-treatment of sewage, the sewage water to ensure 100% qualified biochemistry. After the optimization of biological treatment is mainly: in order to prevent excessive water ****, in the final effluent after coagulation and sedimentation **** installation of an activated carbon filter, the use of quartz sand filter and activated carbon adsorption of suspended particles of sewage, to the purpose of reducing ****. Above process optimization measures in the country implemented a new plant at Nanjing Iron and optimize the effluent COD decreased after the 25mg / l, SS reduced the 20mg / l, reduced **** content of 0.33mg / l, significantly increased the AAO effect of biochemical treatment.


An adaptation of the A/O process . It is an activated sludge process that can achieve nitrification, denitrification andbiological phosphorus removal as well as BOD removal. The three stage process involves an anaerobic zone of about one hour retention followed by an anoxic zone of similar size and finally an aerobic (oxidation) zone of 4 to 6 hours retention ( see Figure A.1). In the process the third zone is used for BOD removal and nitrification. The recycle from the end of the third (aerobic) zone back to the inlet of the second (anoxic) zone results in the nitrate being mixed with the wastewater in the anoxic zone and the nitrate is denitrified to nitrogen gas. The return activated sludge from the sedimentation tank is fed back to the start of the anaerobic zone. The first zone is required in order to obtain biological phosphorus removal. The percent removal can be in excess of 95% for nitrogen and 90% for phosphates.


AAO technology is a common process used by municipal wastewater treatment plants for nitrogen and phosphorus removal and is carried out by a combination of an anaerobic tank, anoxic tank and oxic tank.

The process can be divided into three stages as follows:

Firstly, the wastewater and the external returned sludge flows into the anaerobic tank with the agitator set to prevent sedimentation of material suspended in the wastewater. Secondly, the wastewater flows into the anoxic tank aerators with agitators set to control aeration. Thirdly, the wastewater flows into the oxic tank where BOD5 in the wastewater undergoes further decomposition by aerobic bacteria present in the tank.