AO high-efficiency nitrogen and phosphorus removal system

The invention discloses an anaerobic-oxic (AO) high-efficiency nitrogen and phosphorus removal system. The AO high-efficiency nitrogen and phosphorus removal system is provided with a secondary sedimentation tank which is communicated with a sewage outflow end of a biological tank, wherein a first-level anoxic zone, an anaerobic zone, a first-level oxic zone, a second-level anoxic zone, a second-level oxic zone, a third-level anoxic zone, a third-level oxic zone, a fourth-level anoxic zone and a fourth-level oxic zone are arranged in the biological tank from sewage inflow to sewage outflow inturn; the secondary sedimentation tank comprises a sewage outflow port and a sludge reflux pipe; the sludge reflux pipe is communicated with the first-level anoxic zone in the biological tank, and isused for injecting reflux sludge into the first-level anoxic zone; sewage is injected from the upper sides of the first-level anoxic zone, the second-level anoxic zone, the third-level anoxic zone and the fourth-level anoxic zone from a sewage inflow port through pipelines respectively; stirrers which ensure that sediments are not generated in mixed liquid are arranged in the anoxic zones and theanaerobic zone from the first level to the fourth level; and the amount of the sewage which is injected into the first-level anoxic zone, the second-level anoxic zone, the third-level anoxic zone andthe fourth-level anoxic zone is 0 to 40 percent of inflow rate. By the AO high-efficiency nitrogen and phosphorus removal system, the concentration of the sludge in the subsequent levels is improved,the volume of the biological tank is reduced, and engineering investment is saved.