A rapid sand filter is required to treat the flow of 0.50 m 3 /se
| A rapid sand filter is required to treat the flow of 0.50 m3/sec. The filtration rate is 120 m3 per day per m2 of filter area. Each filter is washed for 5 minutes every 24 hours at a wash rate of 15 mm per second per m2 of filter area. The filter remains out of operation for a total interval of 30 minutes per day. Calculate the minimum number of filters required if the area of each filter is 50 m2.
A. 6
B. 7
C. 8
D. 9
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Right Answer is: C
SOLUTION
Total water to be filtered every day = 0.5 × 60 × 60 × 24
∴ Maximum flow rate = 43200 m3/day
Filtration rate per m2 = 120 m3 per day
∴ Actual water filtered per day \(= 120 \times \frac{{23.5}}{{24}} = 117.5{\rm{\;}}{{\rm{m}}^3}{\rm{\;per\;day}}\)
Rate of backwashing = 15 mm per second per m2
∴ The volume of water required for backwashing = 15 × 10-3 × 5 × 60
∴ The volume of backwash water per m2 = 4.5 m3 per day
∴ Net water filtered per m2 per day = 117.5 – 4.5 = 113 m3/day/m2
∴ Number of filters required \(= \frac{{43200}}{{113 \times 50}} = 7.64 \approx 8\)