Sewage treatment device based on pre-denitrification

The sewage treatment device comprises a sewage tank, an anoxic tank, an aerobic tank and a sedimentation tank, the sewage tank, the anoxic tank, the aerobic tank and the sedimentation tank are sequentially communicated, sewage in the sedimentation tank flows back to the anoxic tank through a return pipe, sludge in the aerobic tank flows back to the anoxic tank, and the anoxic tank is communicated with the anoxic tank. The sewage tank is arranged above the anoxic tank; and a self-driven stirring mechanism is arranged in the anoxic tank. Potential energy of sewage is converted into kinetic energy for driving the blades, the stirring blades can be driven to rotate to mix sludge and sewage without an external power supply, and the problems that cables of the external power supply of stirring machinery are abraded and potential leakage hazards exist are solved; meanwhile, the driving cover and the first stirring shaft and the second stirring shaft which are coaxially arranged are used for stirring the anoxic tank