What is the correct sequence of steps followed from initial to last during water treatment process?

(A) Coagulation

(B) Filtration

(C) Screening

(D) Sedimentation

Choose the correct answer from the options given below:

The correct answer is (C), (D), (A), (B).

Here is the step-by-step explanation of the water treatment process sequence:
1. Screening (C): This is the first step in the water treatment process. In this stage, large floating and suspended debris such as leaves, twigs, plastic bottles, and paper are removed by passing raw water through metal bars or screens. This prevents damage to the downstream equipment and pumps.
2. Sedimentation (D): After screening, water is allowed to sit in large basins. The flow of water is slowed down, which allows heavier suspended particles, silt, and sand to settle at the bottom of the tank under the influence of gravity. This settled material is called sludge and is removed periodically.
3. Coagulation (A): Coagulation (often followed by flocculation) is then introduced to remove finer colloidal particles that do not settle easily by gravity alone. Chemicals called coagulants (such as alum) are added to the water, neutralizing the electrical charges of the fine particles so that they stick together to form larger, heavier clumps called flocs.
4. Filtration (B): Finally, the water is passed through filters consisting of layers of sand, gravel, and sometimes activated carbon. This step removes the remaining fine particles, flocs, and many micro-organisms that did not settle during the sedimentation and coagulation stages.

Therefore, the correct chronological sequence of these steps is Screening ⇒ Sedimentation ⇒ Coagulation ⇒ Filtration, which corresponds to the sequence (C), (D), (A), (B).