The percentage of filtered water, which is used for backwashing in rapid sand filters, is about______________?

A. 0.2 to 0.4
B. 0.4 to 1.0
C. 2 to 4
D. 5 to 7

Assertion A: Slow sand filters are more efficient in removal of bacteria than rapid sand filters. Reason R : The sand used in slow sand filters is finer than that in rapid sand filters. Select your answer based on the coding system given below?

A. Both a and r are true and r is the correct explanation of a
B. Both a and r are true but r is not the correct explanation of a
C. A is true but r is false
D. A is false but r is true

The effective size of sand particles used in slow sand filters is_______________?

A. 0.25 to 0.35 mm
B. 0.35 to 0.60 mm
C. 0.60 to 1.00 mm
D. 1.00 to 1.80 mm

In water treatment, rapid gravity filters are adopted to remove_______________?

A. Dissolved organic substances
B. Dissolved solids and dissolved gases
C. Floating solids and dissolved inorganic solids
D. Bacteria and colloidal solids

The alum, when added as a coagulant in water_______________?

A. Does not require alkalinity in water for flocculation
B. Does not affect ph value of water
C. Increases ph value of water
D. Decreases ph value of water

Alum as a coagulant is found to be most effective when pH range of water is______________?

A. 2 to 4
B. 4 to 6
C. 6 to 8
D. 8 to 10

The detention period and overflow rate respectively for plain sedimentation as compared to sedimentation with coagulation are generally_______________?

A. Less and more
B. Less and less
C. More and less
D. More and more

The settling velocity of a particle in a sedimentation tank increases if______________?

A. Particle size is decreased
B. The surface area of tank is increased
C. The depth of tank is decreased
D. None of the above

Percentage of bacterial load that can be removed from water by the process of plain sedimentation is about_______________?

A. 10 to 25
B. 50
C. 75
D. 100

The length of rectangular sedimentation tank should not be more than_______________?

A. B
B. 2b
C. 4b
D. 8b