After preliminary treatment, the waste water flows by gravity to the next process known as Secondary Treatment. Secondary treatment is a biological treatment process designed to remove nitrogen, phosphorus, organics, and other different types of bacteria contained in living systems. Our secondary treatment process consists of four aeration tanks and five blowers (only two run at any one time, providing oxygen to the aeration tanks), and three secondary clarifiers for settling. A large portion of the settled sludge is recirculated to the head of the aeration tanks. This recirculated sludge is known as Return Active Sludge, or 'RAS'. A smaller portion recirculated sludge is wasted to the head of the plant which allows us to control our mixed liquor suspended solids (MLSS) concentration, and is known as Waste Activated Sludge, or 'WAS'.
Next step ... Tertiary Treatment