Step-feed multi-stage AO+MBR (Anoxic/Oxic+Membrane Biological Reactor) nitrogen and phosphorus removal system

The invention discloses a step-feed multi-stage AO+MBR (Anoxic/Oxic+Membrane Biological Reactor) nitrogen and phosphorus removal system. The step-feed multi-stage AO+MBR nitrogen and phosphorus removal system comprises a multi-stage AO biological reaction tank constructed by an anaerobic tank, a first-stage anoxic zone, a first-stage aerobic zone, a second-stage anoxic zone, a second-stage aerobic zone, a third-stage anoxic zone, a third-stage aerobic zone, a fourth-stage anoxic zone and a fourth-stage aerobic zone which are communicated in sequence, and an MBR tank, wherein sewage injection ports of the anaerobic tank, each of the second-stage anoxic zone, the third-stage anoxic zone and the fourth-stage anoxic zone is connected with a sewage inflow pipe through an electric sewage regulating valve and a sewage flow meter arranged on a water inlet pipeline; each stage of aeration pipeline of each of the first-stage aerobic zone, the second-stage aerobic zone, the third-stage aerobic zone and the fourth-stage aerobic zone is connected with a main air pipe through an electric air regulating valve; a dissolved oxygen concentration determination probe is arranged at the tail end of each of the first-stage aerobic zone, the second-stage aerobic zone, the third-stage aerobic zone and the fourth-stage aerobic zone; the MBR tank is provided with a sewage outflow port and a sludge outlet; and the sludge outlet is connected with the sludge injection port of the anaerobic tank. The nitrogen and phosphorus removal efficiencies of the system are increased.