True about slow sand filter is -: (A) Occupies less space, (B) More expensive, (C) Requires longer duration, (D) Sand size 0.4-0.7 mm
Answer is C. Option A - wrong, slow sand filter occupy more space Option B - wrong, it is less expensive Option C - correct, rate of filtration is very slow (2-3m.g.a.d.) hence takes longer time Option D - wrong, effective sand size in slow sand filter is 0.2-0.3 mm (PARK TB 25th edition pg 773)