Chlorine & Chloramines Reduction

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.

Low-pressure lamps can emit UV radiation only at a wavelength of 253.7 nm. In contrast, medium-pressure UV systems emit a wide range of wavelengths within the germicidal UV range, ranging from 200 to 600 nm. The term “pressure” refers to the vapour pressure of mercury in the lamp.

Beyond inactivating pathogens, low-pressure UV can reduce monochloramine (NH₂Cl) through a process called photolysis. In this process, the monochloramine molecule is ideally suited to absorb the UV output from a low-pressure lamp, which leads to the efficient breakdown of monochloramine. Low-pressure UV systems typically cost significantly less than medium-pressure systems, both in capex and opex. Low-pressure UV lamps operate at a lower temperature than medium-pressure lamps and therefore last longer and use less energy - requiring less frequent replacement of bulbs. All of this contributes to a much more affordable system compared to medium-pressure UV.

Another advantage that comes with less energy, less heat, and longer lamp life is that low-pressure UV can better handle intermittent flow. Medium-pressure systems require constant flow, as the lamps release a lot of heat (medium-pressure UV lamps have wall temperature of 700 to 900C). This usually means the lamps have a shorter useful lifespan. Cooling is necessary, and if water is not constantly flowing, it can shorten the lifespan of the lamps even more. This contributes to higher operating costs.

Perhaps the most important disadvantage of medium-pressure UV compared to low-pressure UV is its cost. With energy requirements of approximately 6x higher than low-pressure for the same level of monochloramine reduction, this leads to a higher opex. In addition, with medium-pressure systems expensive to purchase and operate (energy) and expensive to maintain (lamp cleaning and replacement), this leads to a higher total cost of ownership compared to low-pressure systems.

Yes. Operating installations exist today using ultraviolet (UV) technology with low-pressure lamps to reduce chloramines in water. UV is a robust, versatile, reliable approach to address numerous requirements in industrial water applications, including chloramine reduction. UV treatment is an increasingly popular dechlorination technology with none of the above drawbacks of carbon or chemicals. Using UV treatment with low-pressure lamps for both free chlorine and/or combined chlorine (chloramines) reduction results in low levels of harmless byproducts.

The UV dosage required for dechlorination depends on a number of factors including the pH, initial and desired chloramine concentration and background level of organics. Given the selection of right UV solution is a confluence of multiple factors and variables, it is recommended to have an in-depth techno-commercial discussion before selection of UV for a pharmaceutical or a beverage plant.

Note that the typical UV dose for reduction of chloramines are several times higher than that for normal microbial inactivation. As a result, membranes stay cleaner longer because the dose for dechlorination is so much higher than the normal dose used if dechlorination was not the goal. Additional benefits of using UV for dechlorination are:

• High levels of UV disinfection
• Elimination of the safety hazards associated with handling chemicals
• Elimination of risk of biofouling and introducing microorganisms into RO (via GAC or injection of neutralizing chemicals); and
• Small footprint
• Easier to meet Net Zero goals without “wasted” water and energy for backwashing and hot water sanitization
• Overall improved water quality at point of use

UV reactors designed for chloramine treatment are generally easy to install and operate (two plumbing connections per unit and one electrical hook-up). They are equipped with a user-friendly operator interface, alarm and system status indication and designed for ease of maintenance (typically requiring only annual lamp changeout).

Typical UV system components include:

• A stainless steel UV reactor
• UV lamps that are properly secured inside quartz sleeves, easing installation, replacement, and maintenance
• Quartz sleeves with sufficiently high transmission rates to deliver the UV energy produced by UV lamps
• Intensity sensors to monitor the UV intensity passing through the water. These sensors can be connected to alarm systems to alert the operator in case of low UV intensity. The operator usually has easy access to these sensors for necessary installation, replacement, calibration, and maintenance
• Electronic ballasts

Multiple factors, such as pH (Palin, 1950), quantum yield, UV dose, UVT of water, and UV wavelength, affect monochloramine reduction. The literature-reported range for UV dose per log (90%) removal with low-pressure Hg lamps, emitting UV at 253.7 nm, is 3600 to 4000 mJ/cm². Given the selection of right UV solution is a confluence of multiple factors and variables, it is recommended to have an in-depth techno-commercial discussion before selection of UV for a pharmaceutical or a beverage plant.