The Continuously Sequencing Reactor is a Biological Nutrient Removal (BNR) system utilizing continuous flow in a single basin. It sequences through the 3 process phases required for BNR – Oxic, Anoxic and Anaerobic – in one basin. The 3 phases do not occur at the same time in the basin. They occur sequentially – one after the other, repetitively, over time. During the Oxic phase, the entire basin is Oxic (i.e. aerobic).