Question

A city is to install rapid sand filters downstream of the clarifiers. The design loading rate is selected to be 160 m^3/ (m^2.d). The design capacity of the water works is 0.35 m^3/s. The maximum surface per filter is limited to 50 m^2 and find out the normal filtration rate?

(a) 154.3 m^3/(m^2.d)

(b) 154.6 m^3/(m^2.d)

(c) 155.6 m^3/(m^2.d)

(d) 155.3 m^3/(m^2.d)

I had been asked this question during an online exam.

My query is from Filtration in chapter Unit Operations of Bioprocess Engineering

Answer 1

The correct choice is (a) 154.3 m^3/(m^2.d)

For explanation I would say: Select four filters .

The surface area for each filter is, a = 189 m^2/4 = 47.25 m^2

We can use 7 m×7 m or 6 m×8 m or 5.9 m×8 m (exact)

If a 7 m×7 m filter is installed, the normal filtration rate is

V = Q/A = (0.35 m^3/s×86,400s/d)/(4×7 m×7 m) = 154.3 m^3/(m^2.d)