Breakpoint Chlorination Curve Interpretation

B) Chlorine is first consumed by demand, then free chlorine residual rises, then free chlorine is destroyed at the breakpoint, and only after the breakpoint does combined residual increase.

This reverses the key idea: chloramines (combined residual) form before free chlorine dominates. The breakpoint is where combined residual is being destroyed, not where free chlorine is being destroyed; after breakpoint, free residual increases with dose.

C) Chloramine formation is the initial demand region, then demand ends at the breakpoint, and the dip occurs because free chlorine is converting to more chloramines after the breakpoint.

Chloramine formation is not the same as the initial demand region; the initial region is where chlorine is being consumed and little residual is measured. The dip is not caused by free chlorine converting to more chloramines after breakpoint; it occurs as chloramines are oxidized on the way to achieving free residual.

D) Free chlorine residual appears immediately at low doses, then chloramines form after the breakpoint, and the dip occurs because ammonia demand increases as dose increases.

Free residual typically does not appear immediately when ammonia or other demands are present; early chlorine is tied up meeting demand and forming combined residual. Chloramines generally form before the breakpoint, not after, and the dip is due to chloramine destruction rather than an increasing ammonia demand with higher dose.