Intermittant use of a sanitary force main

[TJWard]

Hi All,

I'm working on the design of a sanitary force main for a new stadium. The stadium will be used intermittently and could potentially have +/- 1 month between uses....

Sewage would be sitting in a plastic force main (possibly SDR 21) and pump station (possibly 304 stainless steel) for this duration.

The force main runs essentially flat however we're adding air release valves to vent any gases which build up in the main. We're planning on venting the pump station with use of a carbon filter and using a grinder pump to break up solids.

What other issues should I be looking out for? Can sewage sit for this duration of time without issue?

Thanks for any advice offered

 

[RWF7437]

My recollection is that sanitary sewage goes septic in about 3 to 4 hours. It appears you may need to flush this force main periodically with fresh water using, of course, an air gap to prevent back siphonage.

good luck

 

[bimr]

Tour some of the newer stadiums. My understanding is that the new stadiums are using low water use urinals. That should help your design.

You should not overly concern yourself with the sewage sitting in the forcemain. Make sure you have at least 3.5 ft/sec velocity so that the forcemain will resuspend solids on pump startup. Make the sewer and discharge outlet corrosion proof. PVC or lining.

Do a google search on "stadium big flush". That startup testing for testing.

 

[sjohns4]

As mentioned before, keep the velocity up. If there is no likelyhood the flow will increase, I would use the smallest FM as possible to keep the velocity as high as reasonablly possible and minimize the liquid required to to flush the FM. You might want to consider adding a pig launcher at the PS.

Use as much PVC / HDPE as possible. If you have to use DIP anywhere be sure and spec a lining such as 401 protecto ceramic. Also, if you're using a concrete wetwell I'd look at a lining such as Sherwin-Williams Surflex or Duramar lining systems. Gas from septic sewer will destroy concrete or typical cement lining used in DIP.

If it's a submersible station use stainless steel guide rails. Keep the pumps submerged at all times and during the low flow periods to keep them out of the H2S gas.

Suggust to the owner normal operating procedure should be to fill the pump station with clear water and allow to cycle enough to flush the FM at least 1.5 times. This could be as simple as leaving a faucet run a few days. That said, I'd be willing to bet that would be forgotten in the next year or two, so do the owner a favor and follow the other advice I mentioned above.

 

[TJWard]

Great, I dont see any critical problems provided we pay careful attention to the material selection and the O&M procedures.

Thanks for the help