Question

Which of the following impurities is easiest to remove from wastewater?
A. Bacteria
B. Colloids
C. Dissolved solids
D. Suspended solids

Answer 1

Hint: In wastewater treatment, first of all larger particles are separated out by filtration or sedimentation. It is easily visible and so easy to remove from the water. Cleanliness of water is very essential as impurities in water could lead to many infectious diseases.

Complete answer: Wastewater consists of various types of impurities. For e.g. some impurities will be in the form of suspended solids, some will be in the colloid form and certain bacteria, protozoa, etc. can also be present in the wastewater. During the treatment of wastewater, suspended solids like sand, small stones, etc. can be easily removed either by filtration or sedimentation. Since suspended solids are bigger in size and more in weight, so it settles down and the water can be poured into another container. Microscopic bacteria which are present in water and are not visible. It can only be removed by using a desirable disinfectant. In order to remove colloids and other dissolved impurities, special filtration and purification techniques are required. The technology which is used to cleanse water is called a wastewater treatment system. Many bacteria, protozoa, etc. that feed on organic matter are used in wastewater treatment as this water contains organic matter like garbage.
Hence, the correct answer is option D.

Note: Colloids are smaller particles dissolved in any substance (wastewater) and these particles are microscopic. Examples of a colloidal solution are foam, milk, aerosol (small liquid or solid particles dispersed in gas). The dispersed substance is known as a colloid. In aerosol, liquid or solid particles are colloids.