Information Sheet 1.4
Disinfection with chloramine
Disinfection should not be compromised to control disinfection by-products
General description
Chloramines are formed when chlorine and ammonia are added to water:
NH3 + HOCl

NH2Cl + H2O
monochloramine
NH2Cl + HOCl

NHCl2 + H2O
dichloramine
NHCl2 + HOCl

NCl3
+ H2O
nitrogen trichloride (trichloramine)
There are three types of chloramines; monochloramine, dichloramine and trichloramine with
production of the three types dependent on pH and the ratio of chlorine to ammonia.
Monochloramine is the preferred choice because it is the most stable and produces the lowest
tastes and odours. Dichloramine is a stronger disinfectant than monochloramine but is less stable
and produces distinctive odours. Trichloramine is the least stable and produces offensive odours.
Formation and stability of monochloramine is favoured at Cl2/NH3 ratios of 3 to 5 (with 4
typically used) and a pH above 8 (UWRAA 1990, USEPA 1999).
The primary reason for using monochloramine rather than chlorine is its much greater
persistence. In Australia chloramination has provided persistent residuals through very long
drinking water pipelines (>100kms) and provides protection against growth of free-living
organisms such as Naegleria fowleri (UWRAA 1990).
Performance validation
There is a reasonable amount of published information (Wolfe et al 1984; USEPA 1991) on the
effectiveness of preformed monochloramine (that is, monochloramine that is formed off-site)
against viruses, protozoa and bacteria (USEPA 1991, LeChevallier and Au 2004). However,
there are gaps in the available data, particularly on the difference between effectiveness of
preformed monochloramine versus the effectiveness of monochloramine that is produced in the
field.
Preformed monochloramine is a much weaker disinfectant than chlorine, with Ct1 values 20-200
fold higher than for free chlorine (USEPA 1991). While inactivation results for monochloramine
produced in the field are better than those for preformed monochloramine (Wolfe and Olson
1985, UWRAA 1990, USEPA 1999), Cts remain much higher than those for chlorine.
1
Ct refers to the product of concentration measured as mg/L and time measured in minutes
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The USEPA reported Cts for 99% inactivation of Giardia and viruses at 15oC of 1000 mg/L.min
and 428 mg/L.min respectively (US EPA 1999). Cts for 99% inactivation of Aeromonas,
Salmonella and heterotrophic bacteria were less than 100 mg/L.min (USEPA 2006). Field results
have shown that monochloramine is very effective in reducing N. fowleri, E. coli, Aeromonas
spp, heterotrophic plate count bacteria and fungi in drinking water supplies (UWRAA 1990).
Table IS1.5.1 provides a summary of Ct value ranges for the 99% inactivation of various
microorganisms by chloramine. The Ct values should be considered as indicative only, and
suitable safety factors should be applied to ensure adequate disinfection.
Table IS1.5.1 Examples of Ct values for 99% (2 log) inactivation of various
microorganisms by chloramine 1,2,3
Microorganism
Preformed Chloramine Ct value
(mg/L.min)
Reference
Escherichia coli
95-180
LeChevallier and
Au 2004
Enteric viruses
428 (for viruses in general) (15oC)
USEPA 1999
1000 (15oC)
USEPA 1999
Giardia
Cryptosporidium
7200 (25oC) (4)
Korich et al 1990
o
Notes: (1) Temperature is 5 C unless stated.
(2) pH is within range of 6-9 unless stated.
(3) The values in the table are based on published values and should be viewed as the
minimum values necessary to achieve effective disinfection
(4) The Ct value for Cryptosporidium is for a 1 log reduction
The important conclusion to draw from Table IS1.5.1 is that chloramines require a much higher
Ct than chlorine to inactivate microorganisms. Therefore, for distribution systems where
chloramine is going to be used, the need for much greater Cts will be an important consideration
(i.e. water needs to be held in the pipe network and/or tanks for longer to allow sufficient time
for effective disinfection).
Given that the chloramination process will be a critical control point (CCP), other important
issues that will need to be considered to ensure the effectiveness of the process are:

establishing target criteria (section 3.4.2) and critical limits for the chloramination process

preparing and implementing operational procedures (section 3.4.1) and operational
monitoring (section 3.4.2) for the process

preparing corrective action procedures (section 3.4.3) in the event that there are excursions in
the operational parameters
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
undertaking employee training (section 3.7.2) to ensure that the chloramination process
operates to the established target criteria and critical limits
Water quality considerations
The influence of pH on the effectiveness of disinfection appears to be variable (UWRAA 1990,
USEPA 1999, Cromeans et al 2010) and could depend on the target organism. Varying the pH
will influence the species of chloramine present and this could impact on the effectiveness of
disinfection. The target range for pH during chloramination is 8.5  0.2.
As for chlorine, disinfection times are reduced at higher temperatures (USEPA 1999, Kahler et al
2011). Monochloramine appears to remain effective at high turbidities but inactivation rates
decrease as turbidities increase (UWRAA 1990).
Practical considerations
Chloramines are formed by the addition of either liquefied anhydrous ammonia or aqueous
ammonia (UWRAA 1990, USEPA 1999), either before or after chlorine dosing. The addition of
ammonia first reduces the production of chlorinated disinfection by-products but it also reduces
initial inactivation by reducing the contact time between the free chlorine and the treated source
water.
Chloramination has a long history of use and was introduced in Brisbane in 1935. Robust and
reliable dosing and monitoring equipment is available. Reliable field kits for measuring residuals
within the distribution system are also available; these kits generally measure concentrations of
chloramines as total chlorine. There have been reports of false free chlorine readings with tabletbased methods (UWRAA 1990). The DPD-Ferrous titrimetric method is less prone to false
readings (see monochloramine Fact Sheet).
Persistence
Persistence is the principal advantage of chloramination, and it has been used successfully to
produce disinfectant residuals through long pipeline systems exceeding 100kms in length.
Persistence can be reduced by nitrification, particularly at the ends of distribution systems.
Nitrification is caused by bacterial oxidation of ammonia to nitrite, and nitrite to nitrate (Cunliffe
1991). Nitrifying bacteria are naturally-occurring sediment and biofilm organisms. Nitrification
can accelerate chloramine decay, and at the ends of distribution systems can lead to complete
loss of residual and the replacement of chloramines with oxidised nitrogen (nitrate and nitrite). A
number of factors have been associated with nitrification including detention times, excess
ammonia (low chlorine:ammonia ratios) and low chloramine residual. The common practice to
reduce the likelihood of nitrification is maintaining minimum chloramine residuals of 1.5-2 mg/L
(Cunliffe 1991, USEPA 1999).
By-products
Chloramination generally reduces chlorinated DBPs, including THMs, but does not eliminate
them. A similar range of DBPs will be produced, as when chlorine is used, particularly when
chlorine is added before the ammonia (WHO 2000). In addition, chloramination is associated
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with production of higher concentrations of nitrosamines, including NDMA (see NDMA Fact
Sheet).
Guideline values have been developed for a number of disinfection by-products (see Chapter 10
and associated Fact Sheets). Whilst every effort should be taken to minimise the formation and
concentration of disinfection byproducts this should never be done in a manner that compromises
disinfection as poor microbiological quality represents a greater and more immediate risk to
human health than short term exposure to disinfection byproducts (Hrudey 2009).
Application
Chloramination is used in drinking water supplies where persistence is a key advantage and can
be particularly useful in long or complex distribution systems that have extended detention times.
It has been particularly effective in reducing the occurrence of Naegleria fowleri in systems
incorporating long above ground pipelines, and has also been shown to reduce the occurrence of
Legionella in buildings (Flannery et al 2006).
In conjunction with other disinfectants, such as chlorine or ultraviolet (UV) light, chloramines
can also be used as a secondary (or booster) disinfectant to provide persistent residuals within the
distribution system.
Operational monitoring
There is a variety of equipment available to continuously monitor concentrations of chloramines
in drinking water. It is common practice to undertake continuous monitoring of free and/or total
chlorine residual, with remote monitoring and alarm systems being applied at drinking water
treatment plants. However, operational monitoring has been more heavily focussed on
monitoring chloramine concentrations/residuals rather than Cts.
Where chloramination is used as the primary disinfectant, due to the relatively high Cts required
to inactivate microbial pathogens, it is important to determine the minimum Cts before the first
customer in the drinking water distribution system. This is often done by calculating minimum
Cts at maximum flow rates.
Due to the influence of pH on the formation and stability of monochloramine, where possible,
the pH of the water at the point of disinfection should also be monitored on a continuous basis.
References
Cunliffe DA (1991) Bacterial nitrification in chloraminated water supplies Applied and Environ.
Micro 57: 3399-3402
Cromeans TL, Kahler AM, and Hill VR. (2010). Inactivation of Adenoviruses, Enteroviruses,
and Murine Norovirus in Water by Free Chlorine and Monochloramine. Applied and Environ.
Micro 76: 1028-1033
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Flannery B, Gelling LB, Vugia DJ, Weintraub JM, Salerno JJ, Conroy MJ, Stevens VA, Rose
CE, Moore MR, Fields BS, and Besser RE. (2006) Reducing Legionella colonization of water
systems with monochloramine. Emerging Infectious Diseases 12: 588-596
Hrudey S. (2009) Chlorination disinfection by-products, public health risk tradeoffs and me.
Water Research 43: 2057-2092.
Kahler AM, Cromeans TL, Roberts JM, Hill VR. (2011) Source water quality effects on
monochloramine inactivation of adenovirus, coxsackievirus, echovirus, and murine norovirus.
Water Research 45:1745-51.
Korich DG, Mead JR, Madore MS, Sinclair NA and Sterling CR (1990) Effects of ozone,
chlorine dioxide, chlorine, and monochloramine on Cryptosporidium parvum oocyst viability.
Applied and Environ Micro. 56, 1423-1428.
LeChevallier MW and Au K-K (2004) Water treatment and pathogen control. World Health
Organization, Geneva.
USEPA (1991) Guidance manual for compliance with the filtration and disinfection
requirements for public water systems using surface water sources. USEPA Washington DC
USEPA (1999)Alternative disinfectants and oxidants guidance manual. USEPA Washington DC
USEPA (2006) The effectiveness of disinfectant residuals in the distribution system. USEPA
Washington DC
Urban Water Research Association of Australia (UWRAAA) (1990) Chloramination of water
supplies. UWRAAA, Melbourne Australia.
World Health Organization (WHO) (2000) Disinfectants and disinfection by-products.
Environmental Health Criteria 216. WHO, Geneva.
Wolfe, R.L., N.R. Ward, and B.H. Olson. 1984. “Inorganic Chloramines as Drinking Water
Disinfectant: A Review.” J. AWWA. 76(5):74-88
Wolfe RL. and Olson BH. (1985). Inability of laboratory models to accurately predict field
performance of disinfectants, p. 555-573. In R. L. Jolley, R. J. Bull, W. P. Davis, S. Katz, M. H.
Roberts, and V. A. Jacobs (ed.), Water chlorination: chemistry, environmental impact and health
effects, vol. 5. Lewis Publishers, Inc., Chelsea, Mich.
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