Treatment process
Chloramination
Chlorine combined with ammonia to form monochloramine — a weaker but far more persistent disinfectant, used to maintain a residual across large distribution networks with less by-product formation.
Key facts
- Scale
- Municipal
- Treatment stage
- Disinfection
How it works
Ammonia is dosed after chlorine at a controlled chlorine-to-nitrogen ratio. The resulting monochloramine decays slowly, sustaining a residual across networks where free chlorine would disappear.
What it removes — and what it does not
| Row | Removes | Does not remove |
|---|---|---|
| 1 | Maintains a protective residual over long network residence times | Cryptosporidium |
| 2 | Suppresses biofilm regrowth | It is a much weaker primary disinfectant than free chlorine and is not used alone for primary disinfection |
Trade-offs
- Forms fewer trihalomethanes but can form nitrosamines, notably NDMA
- Nitrification within the network if ammonia is over-dosed
- Highly toxic to fish and must be removed before aquarium use
- Damages some dialysis and food-processing equipment unless removed
Related intelligence
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Sources
- World Health Organization — Guidelines for Drinking-water Quality. Public but restricted · CC BY-NC-SA 3.0 IGO
- NSF International / American National Standards Institute — NSF/ANSI drinking water treatment unit standards. Public but restricted · Publisher terms — public access, reuse not clearly granted
- American Water Works Association — AWWA standards, water audits and utility benchmarking. Public but restricted · Publisher terms — public access, reuse not clearly granted