The Multi-Barrier Disinfection Strategy
No single disinfection technology is optimal for every pathogen and every plant condition. Chlorine is highly effective against bacteria but weak against Cryptosporidium. UV inactivates Cryptosporidium and Giardia but leaves no residual. Chloramines provide long-lasting residual in the distribution network but slower primary disinfection. Best-in-class utilities combine technologies to cover every pathogen class while controlling DBPs.
A modern multi-barrier program typically includes:
- Primary disinfection — UV, ozone, or free chlorine at the plant to achieve required log-inactivation of bacteria, viruses, and protozoa.
- Secondary disinfection — Chloramines or low-level free chlorine to maintain a measurable residual throughout the distribution system.
- DBP control — pH adjustment, ammonia dosing for chloramine formation, and source-water management to keep trihalomethanes (THMs) and haloacetic acids (HAAs) below regulatory limits.
