24 - 48 hours

10-12 days

2-3 months

1-2 year

less than that of slow sand filters

in between the filtration rate of slow sand filters and rapid sand filters

greater than that of rapid sand filters

equal to that of slow sand filters

to increase the filtration slow sand filters capacity of

to increase the filtration rapid sand filters capacity of

for isolated buildings like pools, hotels etc swimming

all of the above

(i) and (ii)

(ii) and (iii)

(i) and (iv)

(ii) and (iv)

removal of turbidity

removal of hardness

killing of disease bacteria

complete sterilisation