Desnity of liquid contained in a sewage treatment plant? 4

normal water is about 62 lb/ft3, so 70 lb/ft3 could account for "sludge and whatever" ... and why would you doubt what the internet tells you ? (smile)

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

Because 70lb/ft3 feels lighter, I have no experience of sewage so need to confirm it.

That should be something you get from the people doing the functional design, not from the internet.

I can't find it cited anywhere, but my understanding is that the unit weight of the sludge is very close to the unit weight of water. I think it's something like 65pcf versus water's 62.4pcf.

I think that 70pcf would be a conservative number.

I've done several WWTP designs in the last 6-7 years; and we do not account for a separate sludge weight. Nothing has fallen down yet.

Also, is your tank above ground or embedded in the ground? If embedded, then the controlling loading is usually the in-situ earth pressures; which are significantly more than water or sludge.

My points are ;

-The following unit weights suggested at (Design of Liquid Retaining Concrete Structures (by J.P. Forth, A.J. Martin )

Water= 10.0 kN/m3

Raw sewage= 11.0 kN/m3

Digested sludge aerobic= 10.4 kN/m3

Digested sludge anaerobic= 11.3 kN/m3

Sludge from vacuum filters= 12.0 kN/m3


- The max. unit wt is for Sludge from vacuum filters and 12.0 kN/m3.
You may perform structural design assuming density 62 lb/ft3 ( except sludge tank), provided that the maximum level of the liquid would be the height of the tank/ overflow weir and the appropriate load factor is used . The load factor will compansate the density variation.


My opinion



I cannot give you the formula for success, but I can give you the formula for failure..It is: Try to please everybody.

@JoelTXCive
Thank you for your useful feedback. It is a sewage treatment plant within a basement, some external walls are in contact with soil. Some are internal walls having nothing on the other side. I needed density for these internal walls.

@HTURKAK
Thank you very much, I really needed some book reference too.