GATE Civil Engineering (CE) 2018 Shift 1 Solved Paper

Question : 38 of 65

Marks: +1, -0

A rapid sand filter comprising a number of filter beds is required to produce

99 {MLD}

of potable water. Consider water loss during backwashing as

5 \%

, rate of filtration as

6.0

{m} \/ {h}

and length to width ratio of filter bed as

1.35

. The width of each filter bed is to be kept equal to

5.2 {m}

. One additional filter bed is to be provided to take care of break-down repair and maintenance. The total number of filter required will be

Solution:

Total water to be filtered

=99 × 1.05 {MLD}

=103.95 {MLD}

(Addition of

5 \%

to be used for backwashing)

\;{L}/{B}=1.35 \;\;

where

B=5.2 {m}

∴ \;\; L=7.02 {m}

∴

Surface area of each filter

=36.504 {m}^{2}

Total surface area required

=\;{\;\text " Discharge through filter "\;}/{\;\text " Rate of filtration "\;}=\;{10.3 .95 × 10^{3}}/{6 × 24}

=721.875 {m}^{2}

Total no. of working units required

=\;{721.875}/{36.504}=19.77

filters

=20

filters
1 unit is to added as standby, thus total no. of units required

=21

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