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

Cleaning Turbidimeters

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.)