Sedimentation Tanks Maintenance and Tips

Maintenance

Tank Drainage Manifold

A tank drain system was designed to drain in 30 minutes (Q ~drain~ = 20 L/min. The design is similar to the effluent launder except this manifold is located at the bottom of the tank.

By the same method as was used for the tank effluent manifold the manifold diameter was determined to be 1.905cm (0.75") and the orifice diameter is 0.3572cm (9/64").
* The available head for the sludge ports is the total water depth (84.455cm or 33.25") minus the head loss in the manifold and minus the velocity head at the end of the manifold.
* Kminor was assumed to be 0 in the manifold and 1.0 for the pipe entrances and exits.
* The constant for the determining orifice diameter was found to be 0.63
*Qratio = 0.90
* 15 orifices were assumed to provide a similar layout to the effluent manifold.
The hole size in the drain manifold was increased to 1/4" to allow for faster tank drainage.

Cleaning the Sed Tanks

The sed tanks should be cleaned occasionally so the 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 manifold and clean sludge off the inside and outside.
• Replace the tubes leading to turbidimeters when they start to look dirty.

Cleaning Turbidimeters

Turn off the both the turbidimeter and the pump that is pumping to that turbidimeter. Unscrew the top of the turbidimeter. Gently lift out the inside apparatus. Holding the bottle with a KimWipe, unscrew the bottle and remove it. Clean the bottle with distilled water, making sure to remove any buildup inside. Replace the bottle and screw in the top.
It is important that there are no fingerprints on the bottle that goes inside the turbidimeter. Wipe any fingerprints or other marks off with a KimWipe.

• Replace the tubes leading to turbidimeters when they start to look dirty.
  

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.)

Draining the sed tank on the left

As of November '08, the sed tank on the left (lamella tank) drains very messily. To keep water from spraying on the floor, hold a 90 degree elbow over the opening of the drain so that water flows through the elbow. This allows to direct the water flow. If you need to be able to see the effluent, hold the elbow so that the other end is facing up. Water will flow part of the way up and back down. (If you hold it right, you won't be splashed.)

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.)