An orbital wastewater treatment system includes a tank assembly, at least one impeller, a flow-diversion mechanism, an actuator, optionally at least one sensor disposed in the tank assembly, and a control unit. The tank assembly has an anoxic zone and an aerobic zone and passages between the two zones. The impeller is disposed in the tank assembly for aeration and for moving mixed liquor under process about the tank assembly. The flow-diversion mechanism is disposed at least one of the passages between the aerobic and the anoxic zone. The actuator is operatively connected to the gate for regulating the flow state or configuration thereof in response to a signal generated by the control unit at least partially pursuant to a predetermined schedule and/or at least partially in accordance with input from the sensor.