Enviro Question

[owillis28]

I am posting a question for a NCEES Environmental question # 504. For some reason I can't post to the environmental section.

When the calculate the specific gravity of the primary sludge, where to the 1.32 and 1.0 come from? I understand where the 4 and 96 in the denominator (actually they are the numerators in the denominator, if that makes any sense?

Could someone point me in the right direction? I did find some information in the CERM manual on page 30-12 (Quantities of Sludge), but it seems to be dealing with fixed solids content and volatile solids content.

Ahhhhhhhhhhhhhhhhhh!

owillis

 

[Guest]

I don't recall the CERM having a table for this, but from Metcalf & Eddy TABLE 12-7 entitled, "Typical data for the physical characteristics and quantities of sludge produced from various wastewater treatment operations and processes," provides the following:

Treatment operation/process, specific gravity of sludge solids, specific gravity of sludge, dry solids (lb/103 gal) per range and typical.

So, primary sedimenation has Gs = 1.4 and activated sludge Gs = 1.25

The way I see it, the author took the average value between the two processes.

JR

 

[owillis28]

Same problem, different question

1. What is the equation the author used to find the volume of the primary sludge?

2. In my solution, I ended up with 6.1 MGD. I do not understand the units that were used in coming up with their answer.

8.34 (lbm*L)/(mg*MG)

-OR-

8.34 lbm(of water)/gal(of water) - Can you use this conversion since we are dealing with sludge? Maybe the product of all the numbers in the denominator allows us to use this conversion.

-OR-

Maybe I am way off!

Ahhhh

owillis

 

[Cheese]

I got out of an environmental class yesterday and have the following comments.

1) Instructor just gave us the SG of sludge = 1.03

2) You are dealing with biosolids which (as can seen from above) are almost = water, thus 8.34lbm/gal should work.

I still don't understand how to convert all these units though.

Anyone got this one figured out?

Thanks,

Cheese

 

[RIP - VTEnviro]

Whenever I saw a problem that required a specific gravity or density for activated sludge, I just assumed it was the same as water. Most unthickened sludge is just a couple percent solids anyway.

When all else fails on a problem and you don't know the equation, start looking at what you're given and the units they're in. If you know what units you need, you can generally figure out a way to get there using what you got and canceling out terms.