A wastewater treatment system having a tank, a rotatable surface aerator and an elongate draft tube is presented. The elongate draft tube is at least partially submerged beneath the liquid and is rotated about its longitudinal axis for orbitally moving the liquid through the tank in a fixed direction. The rotatable surface aerator is coupled to the proximal end of the draft tube and is at least partially immersible into the liquid. The system further can provide an anoxic zone. A process for treating wastewater is also provided.