Chloramination is the process of adding chloramines – a group of chemical compounds that contain chlorine and ammonia – to drinking water for microbial inactivation.

The particular type of chloramine used in drinking water treatment is called monochloramine (chemical symbol NH₂Cl), which is mixed into water at levels that inactivate microbes but results in the water still being potable. Monochloramine is an oxidant and biocide. Chloramine levels up to 4 milligrams per liter (mg/L) or 4 parts per million (ppm) are considered acceptable levels in drinking water.

To meet EPA standards intended to reduce disinfection by-products, some water treatment plants are switching from chlorine to chloramine. Chloramine can last longer in the water pipes and produces fewer disinfection by-products.

Advantages of monochloramine over chlorine include:

• More chemically stable & stays longer in the water distribution network

• Generates much lower levels of regulated disinfection byproducts (DBPs)

• Less noticeable impact on the taste & odor of the water

Chloramines have corrosive properties that can damage metal pipes and, over time, degrade rubber, such as O-rings, gaskets, and seals. As a result, chloramines can damage process equipment such as downstream membranes.

Chloramines can also cause aggravation of skin conditions and irritation of the eyes and sinuses. Chloramines leave water with an undesirable metallic or chemical taste. From brewing beer to coffee, chloramines will offset the flavor profile of any beverage into which it is introduced.

There are several options for successful chloramine reduction:

Carbon Adsorption/Filters can be performed with many types of carbon, but granular activated carbon (GAC) is the form most commonly used.

For removal of monochloramine, catalytic carbon is preferred, as standard activated carbon is less efficient. Chloramines are significantly harder to remove than free chlorine and require an extended period of contact with activated carbon (referred to as empty bed contact time (EBCT)).

In cases where the prevention of microbiological contamination is critical, such as in pharmaceutical or semiconductor facilities, steam or hot water sanitizable filter vessels are required.

Catalytic carbon is more effective at reducing monochloramines than standard activated carbon.

The use of carbon tends to come with additional challenges and costs such as:

• backwashing & sanitization to prevent biogrowth

• wasted backwash and displacement water (negative impact to “net zero” directives)

• larger footprint, often n+1 designs for continuous operation

• filtration media replacement costs

• high total cost of ownership and high maintenance

Chemical dechlorination reactions occurring from sulfites, bisulfites, or metabisulfites can also reduce chloramines. Sodium metabisulfite is commonly used for chemical dechlorination. However, introducing chemicals into the water increases the loading to downstream processes such as membranes, thus increasing the cleaning frequency or reducing the flux of the membranes.

These reducing agents react with oxygen in the air and water and must be reconstituted frequently due to loss of solution strength. This method also requires a significant footprint, occupying valuable factory space, which may be particularly important for skid mounted equipment.

Ultraviolet light is an effective way to reduce chloramines. This method uses ultraviolet energy to turn free chlorine and chloramines into inorganic compounds such as chloride, nitrite, and nitrate ions.

Both medium-pressure (polychromatic) and low-pressure (monochromatic)UV solutions are used for chloramine reduction. However, low-pressure UV lamps utilize a fraction of the energy compared to medium-pressure lamps.

UV provides several economic and non-economic benefits over carbon and reducing chemicals when it comes to dichlorination. Some of these benefits include:

• Lower total cost of ownership (Capex and Opex)

• Low footprint solution

• No biofouling potential, no additional dissolved solids loading on downstream processes

• No wasted water for backwash or hot water sanitization, easier to transition to net-zero emissions

• Reduced maintenance and labor requirements

• Continuous operation

Based on current studies and installations, no known or measureable toxic byproducts are generated from chloramine reduction using UV technology.