Sewage Treatment Plant - Equalization Tank

Equalization Tank

The sewage from the bar screen chamber and oil, grease and grit trap comes to the equalization tank. The equalization tank is the first collection tank in an STP.

Its main function is to act as buffer: 

To collect the incoming raw sewage that comes at widely fluctuating rates, and pass it on to the rest of the STP at a steady (average) flow rate.

During the peak hours, sewage comes at a high rate. The equalization tank stores this sewage, and lets it out during the non-peak time when there is no/little incoming sewage.

1 The inlet pipe 

2 The sewage is collected in the tank. 

3 The raw sewage lift pumps

4 The delivery pipe takes the sewage to the aeration tank.

5 The coarse bubble diffusers are short length of tubes that have holes at regular spacing. They release large bubbles in the tank to lightly aerate the sewage, and also to agitate the mix continuously.

6 Compressed air comes though this air supply pipeline. 

Operation And Maintenance Considerations

• Keep air mixing on at all times
• Ensure that the air flow/ mixing is uniform over the entire floor of the tank. Adjust the placement of diffusers and the air-flow rate as needed.
• Keep the equalization tank nearly empty before the expected peak load hours 
• Check and clean clogged diffusers at regular intervals.

RAW SEWAGE LIFT PUMPS

1 There are two identical pumps. Controls ensure that only one pump can run at a time.

2 Both pumps have independent suction pipes. 

3 The delivery pipes from both pumps are combined in a T-shaped header. 

4 The bypass pipeline returns the excess sewage back to the tank.

5 Valves

Operation And Maintenance Considerations

• Switch between the main and standby pump every 4 hours (approximately).
• Check oil in the pump every day; top up if necessary
• Check motor-to-pump alignment after every dismantling operation
• Check condition of coupling and replace damaged parts immediately
• Check for vibrations and tighten the anchor bolts and other fasteners
• Check condition of bearings, oil seals, mechanical seal and replace if necessary
• Completely drain out oil and replace a fresh as per manufacturer’s recommendation