Env Exam Prep Problem 26 JUL 2007

[Guest]

The following following characteristics and assumptions are provided for an aerated grit chamber:

• Detention time of peak flow rate = 4.0 min
• Designed hourly average flow for WWTP = 10 MGD
• Assume two (2) chambers will be used
• Assume depth-to-width ratio = 1.5:1.0
• Assume 5 std ft3/min for air supply
• Assume that 7 ft3 of grit is produced for every 1 MGD of flow

Determine the following design elements:

a) Peak hourly flow;

B) Volume of grit chamber;

c) Size of rectangular chamber;

d) Necessary air supply; and

e) Average volume of grit generated.

Answers to follow ....

JR

 

[RIP - VTEnviro]

I always liked these problems. You can't just plug and chug into an equation but actually have to look at it and apply the math on your own.

Sadly I have no interest in working problems at this hour, and I'm half drunk, so I'll attempt this brain teaser in the morning.

 

[RIP - VTEnviro]

Whadaya think?

 

[Guest]

^^^ My results are slightly different ... same methodology:

A. Q = 10 MGD * 3.0 = 30 MGD

B. Vol = 5568 ft3 (different due to peaking factor)

C. Each Chamber = 10-ft x 15-ft x 33-ft (based on volume)

D. Air needed = 5 ft3/min-ft * 33-ft = 165 ft3/min (slightly tricky there, but that is how my problem read)

E. Volume of grit = 70 ft3/d

Not bad all-in-all B)

JR

 

[RIP - VTEnviro]

Assume 5 std ft3/min for air supply

You didn't say 5 scfm/min/ft!! Hence my confusion!!

:dunno: