Which one of the following impurities is easiest to remove from wastewater?
a. Bacteria
b. Colloids
c. Dissolved solids
d. Suspended solids
The answer is option (d) Suspended solids.
Explanation: Suspended solids can be removed by sedimentation and decantation. Dissolved solids can be removed by evaporation of water which is an energy-intensive process. Removal of colloids needs centrifugation. Removal of bacteria involves the use of bactericidal agents. Hence, (d) is the correct option.