Sedimentation Tanks Maintenance and Tips

Maintenance

Cleaning the Sedimentation Tanks

The sedimentation tanks should be cleaned occasionally so that experimental results aren't affected by build-up.

• Plug the pipes going to the sed tanks or shut down the pilot plant so that no water is running to the sed tanks.
• Open the drains on the bottoms of the tanks and let the water and sludge drain out.
• While there's still some water in the tank, place the cleaning pump in the tank and drain out the sludge at the bottom of each tank. (Use an extension cord if the pump's power cord can't reach the tank on the right.)

• Hose down the sides and bottoms of the tanks.
• For a thorough cleaning, gently remove the effluent launder and clean sludge off the inside and outside.
• Replace the tubes leading to turbidimeters when they start to look dirty.

Cleaning Turbidimeters

See Turbidimeter Maintenance.

Tips

Determining the height of the sludge blanket

As of early November '08, there's no set way to check the height of the sludge blanket. ("Height" refers to the top of the mass of sludge in the tank.) One way to find the top of the sludge blanket is to shine a flashlight into the tank from the top. Let the beam hit one of the walls and check where it's visible from the outside. Move the beam down and watch the spot of light move down until it stops moving even when you're moving the flashlight. This spot is the top of the sludge blanket. (Since the sludge blocks light, the spot of light is visible only until the beam hits the top of the sludge blanket.)

Lowering the Sludge Blanket with Lamella in the Tank

This can take a while. The sed tank must be carefully drained in intervals when trying to lower the sludge blanket.

1. Open the valve a little. Very dirty water should flow out.
2. Let water flow until the water is more clear than brown.
3. Open the valve a little more and do the same.
4. Repeat 1-3 carefully until the water opening the valve further would seem to make the velocity too high. (Pulling sludge out of the tank too fast could disturb the blanket a little. Just use your judgment.)
5. Repeat this process every few minutes. If the water coming out is very clear as soon as you open the valve, wait longer between draining periods. (Waiting some time between drainings seems to allow more sludge to flow into the outflow pipe at the bottom of the tank.)