Consider the following unit processes commonly used in water treatment; rapid mixing (RM), flocculation (F), primary sedimentation (PS), secondary sedimentation (SS), chlorination (C), and rapid sand filtration (RSF). The order of these unit processes (first to last) in a conventional water treatment plant is
1
PS → RSF→ F→ RM→ SS→ C
2
PS → F→ RM→ RSF→SS→ C
3
PS → F→ SS→ RSF→RM→ C
4
PS → RM→ F→SS→RSF→ C