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

When 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, the water to be treated is aerated by air diffuser units 6a to 6d. A nitrate meter 7 is provided on an inflow side of the aerobic tank 2c, which is a desired position along a flow of the water to be treated in the reaction tank 2 to measure a nitrate concentration, and an ammonia meter 11 is provided near an outflow side of the reaction tank 2 to measure an ammonia concentration. A control unit 9 supplies a control signal to gas supply-amount control units 10a to 10d so that both the nitrate concentration and the ammonia concentration fall within respective predetermined ranges based on the values of the nitrate concentration and the ammonia concentration, 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.