System and method for constant water level sequential batch type sewage treatment system with continuous variable volume

The invention discloses a system and a method for constant water level sequential batch type sewage treatment system with continuous variable volume. The method includes continuously injecting sewage into a constant water level variable volume adjusting area to enable an adjustable volume area to float on the liquid level in separation mode, injecting water to a constant water level variable volume reaction area through a distribution pump, injecting water to a constant water level variable volume water quality stabilizing area through a constant water level water decanting device and a waterdecanting pump, enabling supernate after reaction to be discharged into the supernate of the a constant water level variable volume water quality stabilizing area on the other side of the constant water level variable volume reaction area, pass through a smoothing clearing area and finally pass through an inclined plate clearing area and continuously discharging purification water equivalent withpreprocessing feeding wate