Chloramine is widely used by municipal water suppliers to maintain disinfection throughout water distribution networks. Although this disinfectant helps control microbial growth, activated carbon is commonly used to solve this problem, but successful chloramine treatment involves more than installing a carbon filter. The carbon must have suitable surface activity, the water must receive adequate treatment, and the resulting water must meet the requirements of the downstream process.
This article examines chloramine removal from a water-quality perspective, explains how activated carbon changes the chemistry of treated water, and outlines how to evaluate whether a carbon treatment system is suitable for your application.
Why Is Chloramine Harder to Remove
Chlorine and chloramine are both water disinfectants, yet their properties differ greatly. Free chlorine exists as hypochlorous acid (HOCl) and hypochlorite (OCl⁻). Chloramine forms when chlorine reacts with ammonia; monochloramine (NH₂Cl) is the primary form adopted by municipal water systems.
Their key distinction is stability. Chloramine lasts far longer than free chlorine, keeping residual disinfection across distribution networks, but this stability also makes it harder to remove.
Industrial facilities need to identify the exact disinfectant species and required removal level, rather than only checking for chlorine. A carbon filter effective for free chlorine often fails for chloramine.
Testing incoming water for free chlorine, combined chlorine, or a mixture is critical before selecting a carbon medium.
What Happens When Chloramine Is Removed
Understanding the outlet-water composition is essential when selecting a treatment process.
1. Chloramine Concentration Decreases
The primary objective is to reduce the chloramine residual to the level required by the application.
For a reverse osmosis system, the acceptable residual depends on the membrane manufacturer’s requirements. For aquariums or other sensitive applications, the target must account for the tolerance of the organisms or process involved.
There is no universal outlet concentration suitable for every application. The required limit should be established before the filter is designed.
2. Chloride May Remain in the Treated Water
Chloramine decomposition can convert its chlorine component into chloride ions. Chloride remains dissolved in water and is not ordinarily removed by a standard activated carbon filter.
This matters when a process requires control of dissolved salts. If the application has a strict chloride specification, the complete treatment train must be evaluated rather than assuming that carbon filtration removes all chlorine-containing species.
3. Ammonia or Ammonium May Remain
Ammonia is an important consideration because it may be produced during chloramine decomposition.
Depending on the water pH, ammonia can exist as un-ionized ammonia (NH₃) or ammonium ions (NH₄⁺). The relative proportions change with pH and temperature.
In some applications, the residual amount may be acceptable. In others, particularly systems sensitive to ammonia or nitrogen compounds, an additional treatment stage or a separate ammonia-control strategy may be required.
For this reason, a chloramine-removal test should not automatically be treated as proof of ammonia removal.
4. Other Water Quality Parameters May Remain Unchanged
Activated carbon treatment is not a universal purification process. Dissolved salts, hardness, and many inorganic ions are not reliably removed by conventional activated carbon.
If the final application requires low conductivity, low hardness, or a specific ionic composition, additional processes such as reverse osmosis or ion exchange may be needed.
The treatment objective should therefore be defined in terms of the complete water-quality specification, not a single disinfectant measurement.
How to Choose Right Activated Carbon
Conventional granular activated carbon can remove chloramine, yet its reaction rate may be insufficient for short contact times or strict water quality requirements. Catalytic activated carbon is engineered with specialized surface properties to accelerate chloramine breakdown and is the preferred choice when chloramine reduction is the primary goal.
When sourcing carbon, confirm whether it is standard or catalytic grade and review chloramine removal test data instead of relying only on general adsorption indices such as iodine number.
| Parameter | Catalytic Activated Carbon (Chloramine Grade) |
|---|---|
| Mesh Size | 8×30 / 12×40 mesh |
| Iodine Number (ASTM D4607) | 850–1000 mg/g |
| Hardness / Abrasion Number | ≥93% |
| Moisture Content | ≤5 wt% |
| Ash Content | ≤7 wt% |
| Bulk Density | 0.46–0.54 g/cm³ |
| pH Working Range | 6.0–8.5 |
| Temperature Range | 5–40 ℃ |
Activated Carbon Application
Reverse Osmosis Systems
Certain reverse osmosis membranes, especially many thin-film composite polyamide membranes, are vulnerable to oxidants. Reducing chloramine upstream can help protect the membrane, provided the treatment system is designed for the incoming water and the membrane manufacturer’s requirements.
Monitoring should confirm that the carbon stage provides the necessary protection under actual operating conditions.
Aquariums and Aquaculture
Chloramine residuals can harm fish and other aquatic organisms. Activated carbon can help treat incoming water, but ammonia released during chloramine decomposition must also be considered.
Where ammonia is a concern, the overall water preparation process should include suitable verification and any additional treatment necessary for the species and operating conditions.
Food and Beverage Manufacturing
Some manufacturing processes require water with controlled disinfectant residuals to protect product quality or downstream equipment. Activated carbon may form part of the purification system, subject to applicable product-contact, hygiene, and water-quality requirements.
Commercial and Industrial Water Purification
Hotels, commercial buildings, laboratories, and industrial facilities may use activated carbon where municipal chloramine residuals interfere with a downstream process.
The correct design depends on the required outlet quality, flow demand, and whether the application also requires control of organic contaminants, taste, odor, or other water-quality parameters.
Frequently Asked Questions
Is a high iodine number enough to guarantee chloramine removal?
No. Iodine number describes adsorption behavior for a specific test substance. It does not directly measure catalytic activity toward chloramine. Application-specific test results are needed.
Will activated carbon remove both chloramine and ammonia?
Activated carbon can decompose chloramine, but ammonia may remain in the treated water. If ammonia removal is required, the treatment system should be designed and tested for that additional objective.
Does chloramine removal also reduce chloride?
Not necessarily. Chloride can be produced during chloramine decomposition and generally remains dissolved in the water. Conventional activated carbon is not a reliable method for removing chloride ions.
How can I determine the right carbon bed size?
The bed volume should be selected based on the required outlet quality, flow rate, validated contact-time requirements, and product performance data. A preliminary hydraulic calculation is useful, but testing and system design are needed before final sizing.
Conclusion
Activated carbon can provide effective chloramine control, but a successful treatment system must address more than the disinfectant itself. The carbon surface must support the necessary reactions, the filter must provide suitable operating conditions, and the treated water must meet the requirements of the downstream process.
For demanding applications, catalytic activated carbon is often the most appropriate starting point. Nevertheless, its suitability should be confirmed through relevant performance data and verification under actual operating conditions.
Need help selecting activated carbon for chloramine treatment?
Share your inlet-water analysis, target outlet quality, flow rate, and filter specifications with our team. We can help evaluate suitable carbon grades and identify the information needed to develop a reliable treatment solution.
