The Sequencing Batch Reactor is a fill-and-draw activated sludge system. Each tank in the SBR system is filled with wastewater during a discrete period of time and then operated in a batch treatment mode. After treatment, the mixed liquor is allowed to settle for a predetermined amount of time and then the clarified supernatant is withdrawn from the tank. During treatment, sedimentation, and withdrawal, the wastewater flow is either directed to another SBR tank in the system, as in a multiple tank configuration, or to a storage tank configuration where it is drawn for treatment after the supernatant withdrawal has been completed. One modification of the SBR process, the intermittent cycle extended aeration system (ICEAS), operates on the principle of continuous feed as in a continuous-flow activated sludge system, but with intermittent withdrawal as in the SBR system. With the exception, therefore, of the ICEAS, an SBR system is comprised of either a storage tank and an SBR tank or a minimum of two SBR tanks to accommodate a continuous inflow of wastewater to the treatment plant.