A2/O process (focusing on denitrification and phosphorus removal)

A2/O process (focusing on denitrification and phosphorus removal)

Introduction:

A2/O process is the abbreviation of Anaerobic-Anoxic-Oxic, which is the abbreviation of anaerobic-anoxic-aerobic biological denitrification and phosphorus removal process. The treatment efficiency of this process can generally reach: BOD5 and SS are 90% to 95%, total nitrogen is more than 70%, and phosphorus is about 90%. It is generally suitable for large and medium-sized urban sewage treatment plants that require denitrification and phosphorus removal. However, the capital construction and operation costs of the A2/O process are higher than those of the ordinary activated sludge process, and the operation and management requirements are high. Therefore, for the current national conditions in my country, this process is only used when the treated sewage is discharged into a closed water body or a slow-flowing water body to cause eutrophication, thereby affecting the water supply source.

Process characteristics:

1. Advantages:

high pollutant removal efficiency, stable operation, and good resistance to shock loads. Good sludge settling performance. The organic combination of three different environmental conditions, anaerobic, anoxic, and aerobic, and different types of microbial flora can simultaneously have the functions of removing organic matter, denitrification and phosphorus removal. The denitrification effect is affected by the size of the mixed liquor return ratio, and the phosphorus removal effect is affected by the DO and nitrate oxygen entrained in the return sludge, so the denitrification and phosphorus removal efficiency cannot be very high. In the process of simultaneous deoxygenation, dephosphorization and removal of organic matter, this process flow is the simplest, and the total hydraulic retention time is also less than other similar processes. Under anaerobic-anoxic alternating operation, filamentous bacteria will not multiply in large numbers, SVI is generally less than 100, and sludge swelling will not occur. The phosphorus content in the sludge is high, generally more than 2.5%.

2. Disadvantages:

The reaction tank volume is larger than the A/O denitrification process. The sludge internal recirculation volume is large and the energy consumption is high. The cost of using it in small and medium-sized sewage plants is relatively high. The economic benefits of biogas recovery and utilization are poor. Sludge leachate requires chemical phosphorus removal.