overflow pipes design for wastewater 3

[drogones12]

Hi guys,

what are the other methods for designing overflow pipes for a existing septage tank who has .017MGD? I have used water distribution model and autoCad. what are the main concerns?

 

[bimr]

One would think such an overflow pipe would be considered a bypass around treatment. Bypasses are generally illegal.

 

[jgailla]

I'm glad you've used computer modeling to do something which should be figured out from first principles.
Try doing something by hand.
A computer can give you any answer you want.

 

[drogones12]

Hi bimr,

It is not a bypass pipe. my boss want the pipe installed because the sensor alarm and antomated septage transfer pump sometime fail on us, and when they do that we will have permit issues because of the spilling raw wastewater out of the septage tank. Due to all the concerns, we want to install pipes right under the sensor and connect to the inflow raw wastewater manhole, so the septage wastewater will still go through all the treatment process. Is it still illegal? any suggestions will be appreciated.

Hi jgailla,

Thank you. I would need to compute the hydraulic by hand if we don't have the GEM 8 model software.

Jason Li

 

[dicksewerrat]

I'd use the Manning's equation. Jow far is it to the intake MH? What kind of slope can you get on the pipe?

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[bimr]

There should not be any issues. I recommend that you use an 8-Inch pipe and you can install the pipe at the minimum slope (0.28%) for a gravity sewer. If you expect solids in the overflow, you can increase the slope.

For best results, use an upturned elbow as the entrance to the overflow pipe. That will allow you to set an overflow level with accuracy.

An overflow entrance that consists of a pipe through the wall will not function as well hydraulicly and allows a larger overflow range between pipe invert and maximum overflow level.

Install a vent on the 8-Inch sewer after it goes through the tank wall to ensure gravity flow.

 

[drogones12]

Hi dicksewerrat,

I haven't done the physical measure yet, GIS data is not very accurated for our plant at this point, our slope will be pretty smooth since the elevation of the intake manhole and the septage is not to much diffenrent. we might need pumps. I will post some number. Thank you

Hi Bimr,

Thank you again

 

[drogones12]

Hi guys,

As I've stated above, this septage unit treats about average .017MGD of wastewater. Should I still use this number to calculate the diameter of the overflow pipes?

 

[bimr]

From your previous posts, I assume that you are inquiring about a septage handling facility at a wastewater treatment plant.

The flow of 0.017MGD is an average flow over 24 hours. Your overflow needs to be sized for a peak flow, not an average flow. It is hard to say what that peak flow is because it depends on how fast the septage material is being discharged from trucks as well as the level that exists in the septage holding tank.

You also have to balance the potential organic loading on your treatment plant if your overflow is too large. The ability to handle the organic load from the septage tank will depend somewhat on the size of your treatment plant.

There is also a consideration regarding pipe cleaning. Most sewer cleaning firms don't have sewer cleaning equipment for pipes smaller than 8-Inch size.

 

[drogones12]

Hi dicksewerrat,

Back to my septage facility pipe design project, the elevation at the entrance is 246' and the manhole is 235'. The path about 86' from the tank to the manhole horizontally. If I use Manning equation, How do I find the S since I have to consider the minor loss on the elbows and valve? I would think S=elevation head/path=246-235/86, is that right?

 

[bimr]

That is the correct method for the slope.

Changes in direction in gravity sewers are made using manholes. The slope carries through the manhole. Elbows and valves are not used.

 

[dicksewerrat]

An 8 inch pipe will handle every thing you need. Seperate question. If you can use gravity to put the sewage into the plant, why are you using a pump?

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[drogones12]

Hi Dicksewerrat,

Pump will not be necessary for this project. I wasn't sure if I had enough elevation head to satisfy 2ft/s of flow speed. Thank you