Formation of combined chlorine (chloramine) as a stable disinfection residual. Precise Cl:N molar ratio control prevents formation of toxic dichloramine or trichloramine.
Coefficient of Variation (CoV) ≤0.05 at Cl:N reaction point. Separate mixer required for ammonia injection — cannot use same mixer as chlorine dosing. Cl:N molar ratio must be 4.5–5:1 by mass throughout cross-section. pH 7.5–9 for monochloramine speciation.
Preferred MOC: 316SS standard. Avoid copper and brass alloys (ammonia attack). FRP for higher ammonia concentrations.
Two separate mixers: chlorine mixer first, contact pipe, then ammonia mixer downstream. Ammonia mixer minimum 5D upstream of residual measurement. Non-return valve on ammonia injection line.