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, 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.

Monochloramine is a low molecular weight, uncharged inorganic compound, formed through the reaction of free chlorine (HOCl/ClO^–, pK_a=7.54) with free ammonia (NH₄⁺/NH₃, pK_a=9.25).

          At pH ~7–8:

NH₄⁺ + HOCl ® NH₂Cl + H₂O + H⁺

NH₄⁺ + ClO^–  ® NH₂Cl + H₂O

Historically, most public water supplies have been treated with chlorine to satisfy the standards set by the Safe Drinking Water Act of 1974. The U.S. Environmental Protection Agency (EPA) allows drinking water treatment plants to use chloramine and chlorine to treat drinking water. Research shows that chloramine and chlorine both have benefits and drawbacks.

Although chlorine treatment is a highly effective method of microbial inactivation, it also has certain disadvantages. Residual chlorine is toxic to many kinds of aquatic life. Moreover, the reaction of chlorine with organic materials in the water can lead to formation of carcinogenic trihalomethanes and organochlorines. These compounds can cause stress cracks in stainless steel, alter and damage active pharmaceutical agents, or lead to undesirable by-products.

To meet EPA standards intended to reduce disinfection by-products, some water treatment plants are switching 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

Chloramine has been used to treat drinking water in the United States since 1929. In 1998, an EPA survey estimated 68 million Americans were drinking water treated with chloramine. Several major U.S. cities, such as Philadelphia, San Francisco, Tampa Bay, and Washington, D.C., use chloramine to disinfect drinking water. Chloramine is recognized for microbial inactivation in drinking water as an effective alternative to chlorine.

Chloramines have corrosive properties that can damage metal pipes and, over time, degrade rubber, such as O-rings, gaskets, and seals. Chloramines can also cause aggravation of skin conditions and irritation of the eyes and sinuses.

Chloramines leave water with an undesirable metallic or chemical tang. From brewing beer to coffee, chloramines will offset the flavor profile of any beverage into which it is introduced.

• Adsorption dechlorination can be performed with many types of activated carbon, but granular activated carbon (GAC) is the form most commonly used in large water treatment filters.

For removal of monochloramine, catalytic carbon is preferred, as other carbon filters tend to be less efficient. Chloramines are significantly harder to remove than chlorine and require an extended period of contact with the 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 water treatment systems, steam or hot water sanitizable filter vessels are required.

• Chemical dechlorination, reactions occurring from sulfites, bisulfites, or metabisulfites, can also reduce chlorine. Sodium metabisulfite is commonly used for chemical dechlorination. Chemical reduction prevents a microbiological breeding ground from being introduced upstream of the rest of the water treatment systems.

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 another effective way to reduce chlorine/chloramine. This is a high intensity treatment that uses ultraviolet light to turn free chlorine and chloramines into inorganic compounds such as chloride, nitrite, and nitrate ions
  • Both polychromatic (medium pressure) and monochromatic (low pressure) UV solutions are used for chlorine and chloramine reduction.

• Catalytic carbon is significantly more effective at reducing monochloramines than other carbon solutions.

  Chloramines require an extended period of contact with the 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 water treatment systems, steam or hot water sanitizable filter vessels are required.

  Use of carbon tend to come with additional challenges and costs such as:

  • backwashing & sanitization
  • larger footprint
  • filtration media replacement costs

   

Ultraviolet (UV) technology is a highly effective method of reducing chloramines in water. Trojan Technologies pioneered the technology of chloramine reduction utilizing UV light in the pre-membrane filtration or RO make-up water stream.

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.