Raw water enters the sedimentation tank where coagulant makes fine particles clump into heavier floc that settles under gravity (Stokes' law). Clarified water then passes down through a layered sand/gravel filter bed, and finally chlorine is dosed to inactivate remaining pathogens before the water leaves clean.
v = (2/9) * (ρp - ρf) * g * r² / μ (Stokes settling velocity)
Filtration efficiency ↑ with media depth (deeper bed = more contact time)
Pathogen removal ↑ with chlorine dose × contact time (CT concept)
- Flow rate — faster flow reduces settling and contact time, raising residual turbidity.
- Coagulant dose — more coagulant speeds particle settling in the sedimentation tank.
- Filter media depth — a deeper bed traps more particulate, further cutting turbidity.
- Chlorine dose — higher dose (glowing green stage) increases pathogen inactivation.
This is the same coagulation → sedimentation → filtration → disinfection train used by real municipal drinking-water plants worldwide.