Q.17 Which one of the following impurities is easiest to remove from waste
water?

1. Bacteria

2. Colloids

3. Dissolved solids

4. Suspended solids

Ans. (d) Three types of impurities are found in wastewater, suspended particles (solids). colloidal impurities and dissolved material (inorganic and organic) like calcium, ammonia, toxic material, phosphate. calcium and nitrate.

Out of them suspended solids like sand silt and clay impurities are easily removed, in sewage treatment plants.