The secondary tube settlers are designed on low overflow rate and are provided after the SAFF reactor to enable separation of solids. A steep slope is provided in the secondary tube settler to eliminate the need of scrapper mechanism. A part of the sludge is recalculated to the SAFF reactor in order to maintain MLSS levels and a part is sent to the Sludge Collection Tank. Overflow of Secondary Tube Settler is sent for Tertiary Treatment.