Abstract: An orbital wastewater treatment system includes a tank assembly, at least one impeller, at least one flow-diversion mechanism, at least one actuator, optionally at least one sensor disposed in the tank assembly, and a control unit. The tank assembly has three treatment zones and pairs of passages between the first zone and the second zone and between the second zone and the third zone. The impeller disposed in the tank assembly moves mixed liquor under process about the tank assembly. Multiple flow-diversion mechanisms disposed at the passages between the zones of each pair control process conditions pursuant to a predetermined schedule and/or at least partially in accordance with input from the one or more sensors.