What is the correct sequence of the following drinking-water treatment…
2024
What is the correct sequence of the following drinking-water treatment processes, from the initial stage to the final stage?
A. Filtration
B. Disinfection
C. Pre-settling of large, readily settleable particles under gravity
D. Flocculation
Answer: C. C, D, A, B — ConceptA water-treatment train is ordered by the size of the impurities and the mechanism used to remove them. Pre-settling can remove large, readily…
- A.
A, B, C, D
- B.
A, B, D, C
- C.
C, D, A, B
- D.
C, D, B, A
Show answer & explanation
Correct answer: C
Concept
A water-treatment train is ordered by the size of the impurities and the mechanism used to remove them.
Pre-settling can remove large, readily settleable particles before finer treatment. Flocculation then aggregates smaller suspended particles, filtration removes the aggregates, and disinfection provides the final microbial barrier.
Application
Pre-settling of large particles under gravity (C) comes first because readily settleable solids can be removed before finer treatment.
Flocculation (D) then brings the remaining fine suspended particles together into larger flocs.
Filtration (A) follows to retain the flocs and fine particles in the filter medium.
Disinfection (B) is performed after physical clarification to inactivate disease-causing microorganisms.
Cross-check
The two sequences beginning with filtration postpone coarse-particle removal. The sequence C, D, B, A places disinfection before filtration. Keeping physical removal before microbial inactivation yields C, D, A, B.
Therefore, the correct sequence is C, D, A, B.