A water filtration unit is made of uniform-size sand particles of 0.4 mm diameter with shape factor of 0.84 and specific gravity of 2.55. The depth of the filter bed is 0.70 m and the porosity is 0.35. The filter bed is to be expanded to a porosity of 0.65 by hydraulic backwash. If the terminal settling velocity of sand particles during during backwash is 4.5 cm/s, the required backwash velocity is

A water filtration unit is made of uniform-size sand particles of 0.4

1.	A water filtration unit is made of uniform-size sand particles of 0.4 mm diameter with shape factor of 0.84 and specific gravity of 2.55. The depth of the filter bed is 0.70 m and the porosity is 0.35. The filter bed is to be expanded to a porosity of 0.65 by hydraulic backwash. If the terminal settling velocity of sand particles during during backwash is 4.5 cm/s, the required backwash velocity is
A.	0.69 cm/s
B.	6.35 × 10-3 m/s
C.	5.79 × 10-3 m/s
D.	0.75 cm/s
Answer» C. 5.79 × 10-3 m/s

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