CLmaster: closed-loop control of chlorine and chloramine disinfection
CLmaster is a machine-learning based real-time control system for chlorine disinfection. It controls the dosing of sodium hypochlorite and, for chloramination, aqueous ammonia, so that the disinfection target is met continuously as flow, ammonia and chlorine residual change. It sends its setpoints to the plant's SCADA system using the standard OPC protocol.
The disinfection target
The target is CT: the product of the total chlorine residual and the modal contact time. In California, Title 22 sets a CT of 450 mg·min/L for disinfected tertiary recycled water. CLmaster adjusts the chemical doses to hold CT at the target rather than above it.
Why conventional dosing is inefficient
Chlorine dosing is usually controlled with fixed dosing tables, fixed chlorine-to-ammonia ratios or PID loops. These do not follow real-time changes in flow, chlorine decay, and ammonia or organic load, so operators dose conservatively to be certain of compliance. Conservative dosing means higher chemical use and more disinfection byproducts.
How CLmaster works
- CT as the control target. Doses are adjusted to hold CT at the target as flow and contact time change.
- Coordinated dosing. Sodium hypochlorite and aqueous ammonia are controlled together, so that the chlorine-to-ammonia ratio stays in the range that forms monochloramine.
- Process history. The control uses the recent history of doses and residuals, so it accounts for chemical already in transit and avoids overcorrection.
- Safe limits. Dose limits and limits on the rate of change keep every adjustment within safe bounds.
Building on stable ammonia
At Pomona, machine-learning ammonia-based aeration control (The Water Research Foundation Project 5148) made the effluent ammonia more stable and allowed aqueous ammonia addition for chloramination to be reduced or eliminated. Stable ammonia makes precise control of the disinfection chemicals possible. CLmaster and DO/Nmaster are designed to work together.
Operators keep authority
Operators can override CLmaster at any time. Every reading is checked before it is used; faulty readings are detected and not acted on, and operators are alerted. If sensors fail, control returns to the operators.
Instruments
CLmaster uses chlorine and ammonia analyzers, flow measurement and the existing chemical feed pumps. These can be bought from any supplier; Ekster & Associates sells none of them, but provides recommended performance specifications.
Current project
Full-scale work on The Water Research Foundation Project 5385, "Machine Learning Meets Disinfection: Full-Scale Wastewater Chloramination Control for Compliance and Cost Savings", began in October 2026 at the Pomona Water Reclamation Plant of the Los Angeles County Sanitation Districts. Carollo Engineers leads the project; Ekster & Associates is co-principal investigator and leads the development of the machine-learning models and the controller. Results will be published when they have been measured.