WASTEWATER TREATMENT DEVICE, WASTEWATER TREATMENT METHOD, WASTEWATER TREATMENT SYSTEM, CONTROL DEVICE, CONTROL METHOD, AND PROGRAM

Biological treatment is performed with respect to water to be treated flowing in a plurality of aerobic tanks 2a to 2d that constitute a reaction tank 2. Air is supplied to the reaction tank 2 from air diffuser units 6a to 6d respectively provided in the respective aerobic tanks 2a to 2d, to aerate the water to be treated. A nitrate meter 7 is provided on an inflow side of the aerobic tank 2c, which is a desired position along the flow of the water to be treated in the reaction tank 2, to measure a nitrate concentration. The nitrate meter 7 supplies a measurement value of the nitrate concentration to the control unit 9. The control unit 9 supplies a control signal to gas supply-amount control units 10a to 10d so that the nitrate concentration falls within a predetermined range of the nitrate concentration to be controlled, and controls a gas supply amount from the air diffuser units 6a to 6d to the water to be treated for each of the air diffuser units 6a to 6d or collectively in the air diffuser units 6a to 6d.