What is the detention time in hours for a clarifier with an inner diameter of 112.2 ft and a water depth of 10.33 ft if the flow rate is 7.26 MGD?

• A. 1.5 hr
• B. 2.52 hr
• C. 3.0 hr
• D. 4.0 hr

Answer: (B)

To determine the detention time in hours for a clarifier, we first need to calculate the volume of the clarifier and then use the flow rate to find the detention time.

1. Calculate the volume of the clarifier:

The volume ( V ) of a cylindrical clarifier can be calculated using the formula:

[

V = \pi \times \left( \frac{D}{2} \right)^2 \times H

]

where ( D ) is the inner diameter and ( H ) is the water depth.

Given:

• Inner diameter, ( D = 112.2 ) ft

• Water depth, ( H = 10.33 ) ft

First, calculate the radius (( r )):

[

r = \frac{D}{2} = \frac{112.2}{2} = 56.1 \text{ ft}

]

Now calculate the volume:

[

V = \pi \times (56.1)^2 \times 10.33 \approx 3.14159 \times 3154.61 \times 10.33 \approx