Question

In a filtration plant, water is filtered using layers of

• A. sand and clay
• B. clay and fine gravel
• C. sand and fine gravel
• D. sand, fine gravel and medium gravel

Answer 1

The correct option is D

sand, fine gravel and medium gravel

Filtration plant consists of a layer of sand, fine gravel and medium sized gravel and this creates pores of varying sizes.
Diameter of a grain of fine sand is approximately 0.1 millimetre, so only particles with diameters less than 0.1 millimetre would pass through the fine sand layer.