Applicable conditions of aao process

A-A-O biological denitrification and phosphorus removal process is a combination of traditional activated sludge process, biological nitrification and denitrification process and biological phosphorus removal process. In this process, BOD, SS and nitrogen and phosphorus in various forms will be removed together.

The system's activated sludge, the bacterial flora is mainly composed of nitrifying bacteria, denitrifying bacteria and phosphorus polymerization bacteria, specialized anaerobic and general specialized aerobic bacteria are basically eliminated by the process.

In the aerobic section, the nitrifying bacteria will convert the ammonia nitrogen in the influent stream and the ammonia nitrogen from organic nitrogen into nitrate through biological nitrification;

In the anoxic section, the denitrifying bacteria will convert the nitrate brought by the internal reflux into nitrogen through biological denitrification, which will escape into the atmosphere, so as to achieve the purpose of denitrification;

In the anaerobic section, the phosphorus-aggregating bacteria will release phosphorus, and absorb easily degradable organic matter such as low-grade fatty acids; while in the aerobic section, the phosphorus-polymerizing bacteria over-absorb phosphorus and remove phosphorus through the discharge of residual sludge.

Disadvantages of AAO process:

The requirements of nitrogen removal and phosphorus removal for external environmental conditions are contradictory, nitrogen removal requires lower organic load and longer sludge age, while phosphorus removal requires higher organic load and shorter sludge age, which is often difficult to trade-off;

Because of the anaerobic zone is in the front, the nitrate in the refluxed sludge has a negative impact on the anaerobic zone;

Since The anoxic zone is located in the middle of the system, denitrification in the allocation of carbon sources in a disadvantageous position, thus affecting the system's denitrification effect;

Because of the existence of internal circulation, the conventional process system discharged in the residual sludge actually at least a small portion of the complete phosphorus release, phosphorus absorption process, the rest is basically not anaerobic state and directly from the anoxic zone into the aerobic zone, which is unfavorable for the system to remove phosphorus.