Chloramination Control in Drinking Water

What is chloramination?

Chloramination is a secondary disinfection process by which chlorine (Cl2) and ammonia (NH3) are combined to produce chloramines, a persistent disinfectant used to maintain a residual in a long distribution system . The residual chloramine aids in preventing post microbial growth in the distribution system.

The residual chloramine aids in preventing post microbial growth in the distribution system. If free chlorine is used as the secondary disinfectant, it often dissipates, leaving the distribution system with no measurable residual.

Another advantage of chloramination is unlike free chlorine, the chloramine compound’s reaction with precursors to form trihalomethanes (THM’s) is extremely slow. This leaves little to no measurable THM’s, even after extended contact times.

What Are Trihalomethanes -THMs?

THM’s are suspected carcinogens. Because of their link to cancer, Maximum Contaminant Levels (MCL) have been established. MCL’s of 80 micrograms per liter (μg/l) THM’s are currently regulated, with stricter levels (60μg/l THM) to be implemented very soon.

The Disinfectants and Disinfection By-Products rule (D/DBP) committee has determined that chloramination is an effective means of reducing reactions with precursors that contribute to the formation of THM’s.

Automatic Chloramination Control

Three chloramine compounds are formed in the chloramination process: monochloramines, dichloramines and trichloramines. Out of these, the desired chloramine compound is monochloramine since it contributes little or nothing to taste and odor in the final product.

Reliability in chlorine dosing is essential for proper chloramine formation. One of the most reliable methods of chloramination control is accomplished by optimizing the use of a continuous online microprocessor-based chlorine analyzer. The chlorine analyzer is used to measure the combined chlorine residual for chlorine dosing control.

To produce the desired monochloramine, the chlorine to ammonia ratio must be maintained at three to four parts chlorine to one-part ammonia. (The ammonia is usually dosed before the chlorine for proper THM control). This ratio can be controlled by pacing the ammonia feed on the chlorine feed, thus controlling the proper ratio of chlorine to ammonia.

MICROCHEM ® 450 Controller

De Nora Water Technologies MicroChem® 450 controllers are microprocessor-based, setpoint controllers designed for use in water treatment plant operations. The MicroChem® unit accepts both flow and residual signal as inputs. Digital displays provide immediate access to all setup and operating information.

Chloramination is an effective method for secondary disinfection and THM control. Future regulations on THM reduction merit the use of chloramines for water treatment. The De Nora Water Technologies MicroChem® 3 residual analyzer and MicroChem® 450 controller are reliable instrumentation for chlorine and ammonia dosing and chloramination control.