Method and device for controlling the biological process in waste-water treatment plants

A method and a device for continuously controlling the supply of oxygen to waste waters in the oxidation tank of a biological purifying plant, wherein the waster waters flowing continuously are subjected to aeration by blowing pressurized air. The method provides for substantially continuous regulation of the flow rate of air blown into the waste waters with at least a first control level which substantially continuously modifies the set point of the concentration of dissolved oxygen in the waste waters.