# ![](media/image1.wmf)Chloramines

The disinfectant potential of chlorine-ammonia compounds or chloramines
was identified in the early 1900s. The potential use of chloramines was
considered after observing that disinfection by chlorine occurred in two
distinct phases. During the initial phase, chlorine reducing compounds
(i.e., demand) cause the rapid disappearance of free available chlorine.
However, when ammonia was present bactericidal action was observed to
continue \[even though free chlorine residual was dissipated\]. The
subsequent disinfection phase occurs by the action of the inorganic
chloramines.

## Chloramines Chemistry

Chloramines are formed by the reaction of ammonia with aqueous chlorine
(i.e., HOCl). Initially, chloramines were used for taste and odor
control. However, it was soon recognized that chloramines were more
stable than free chlorine in the distribution system and consequently
were found to be effective for controlling bacterial regrowth. As a
result, chloramines were used regularly during the 1930s and 1940s for
disinfection. Due to an ammonia shortage during World War II, however,
the popularity of chloramination declined. Concern during the past two
decades over chlorinated organics (e.g., THM and HAA formation) in water
treatment and distribution systems, increased interest in chloramines
because they form very few disinfection byproducts (DBPs).

### Equilibrium, Kinetic, and Physiochemical Properties

Chloramines are formed from the reaction of chlorine and ammonia. The
mixture that results may contain monochloramine (NH~2~Cl), dichloramine
(NHCl~2~), or nitrogen trichloride (NCl~3~). When chlorine is dispersed
in water, a rapid hydrolysis occurs according to the following reaction:

$\text{Cl}_{2} + H_{2}O \rightarrow \text{HOCl} + H^{+} + \text{Cl}^{-}$

The equilibrium constant (K~eq~) at 25^o^C is 3.94 x 10^4^ M^-1^ for
this reaction. In dilute solutions at pH greater than 3, the forward
reaction is essentially complete. Hypochlorous acid (HOCl) is a weak
acid that dissociates as follows:

$\text{HOCl}Û\text{OCl}^{-} + H^{+}\text{pK}_{a} = 7\text{.}6$

Relative proportions of HOCl and OCl^-^ are dependent upon pH. Both of
the chlorine species in the above reaction are powerful oxidants,
capable of reacting with many substances present in water. In aqueous
solutions with pH 7.0 to 8.5, HOCl reacts rapidly with ammonia to form
inorganic chloramines in a series of competing reactions (White, 1992).
The simplified stoichiometry of chlorine-ammonia reactions are as
follows:

$\text{NH}_{3} + \text{HOCl} \rightarrow \text{NH}_{2}\text{Cl} + H_{2}O$
(monochloramine)

$\text{NH}_{2}\text{Cl} + \text{HOCl} \rightarrow \text{NHCl}_{2} + H_{2}O$
(dichloramine)

$\text{NHCl}_{2} + \text{HOCl} \rightarrow \text{NCl}_{3} + H_{2}O$
(nitrogen trichloride)

These competing reactions, and several others, are primarily dependent
on pH and controlled to a large extent by the chlorine:ammonia nitrogen
(Cl~2~:N) ratio. Temperature and contact time also play a role. Figure
6-1shows the typical relationships between the chloramine species at
various Cl~2~:N ratios for pHs ranging from 6.5 to 8.5. This figure
shows that monochloramine is predominately formed when the applied
Cl~2~:N ratio is less than 5:1 by weight. As the applied Cl~2~:N ratio
increases from 5:1 to 7.6:1, breakpoint reaction occurs, reducing the
residual chlorine level to a minimum. Breakpoint chlorination results in
the formation of nitrogen gas, nitrate, and nitrogen chloride. At
Cl~2~:N ratios above 7.6:1, free chlorine and nitrogen trichloride are
present. Figure 6-2 shows the relationship between chloramine species as
the pH changes (Palin, 1950). The Figure shows that dichloramine becomes
a dominant species at low pH.

[]{#_Ref396018230
.anchor}![](media/image2.wmf){width="6.242361111111111in"
height="3.185416666666667in"}

Figure 6-1. Theoretical Breakpoint Curve

To avoid breakpoint reactions, utilities should maintain a Cl~2~:N ratio
between 3 and 5 by weight. A ratio of 6 is actually optimum for
disinfection, but it is difficult to maintain a stable operation at that
point in the breakthrough curve. Therefore, a Cl~2~:N ratio of 4 is
typically accepted as optimal for chloramination.

Furthermore, over a period of a day or so, without any modification of
pH or Cl~2~:N ratio, monochloramine will degrade slowly to dichloramine
to a ratio of 43 percent NH~2~Cl to 57 percent NHCl~2~. Dichloramine is
relatively unstable in the presence of HOCl; therefore, pure solutions
of this form of monochloramine are difficult to generate and maintain.

![](media/image3.wmf){width="4.518055555555556in"
height="4.311111111111111in"}

Source: Palin, 1950.

[]{#__RefHeading___Toc450036326 .anchor}Figure 6-2. Distribution Diagram
for Chloramine Species with pH

## Generation

Chloramines are formed by the reaction of hypochlorous acid and ammonia
according to the equations described in Section 6.1. Table 6-1
summarizes the theoretical doses of chlorine and ammonia based on these
formulas. Monochloramine is the preferred chloramine species for use in
disinfecting drinking water because of taste and odor problems
associated with dichloramine and nitrogen trichloride. To ensure that
these compounds are not formed, common practice was to limit the
chlorine to ammonia ratio to 3:1. However, because of problems such as
nitrification and biofilm growth, which can be caused by excess ammonia,
current practice is to use a Cl~2~:N ratio in the range of 3:1 to 5:1,
with a typical value of 4:1.

[]{#__RefHeading___Toc450036317 .anchor}Table 6-1. Chlorine Dose
Required for NH~3~ - Cl~2~ Reaction

  --------------------------------------- -------------------------------
  **Reaction**                            **mg Cl~2~/mg NH~3~**

  Monochloramine (NH~2~Cl)                4.2

  Dichloramine (NHCl~2~)                  8.4

  Nitrogen Trichloride (NCl~3~)           12.5

  Nitrogen (N~2~)                         6.3

  Nitrate (NO~3~)                         16.7

  Free residual reaction                  9
  --------------------------------------- -------------------------------

Source: AWWA and ASCE, 1990.

The rate of reaction of monochloramine formation is sensitive to pH.
Table 6-2 shows the calculated reaction times for monochloromine
formation at 25°C, and at a chlorine:amonia ratio of 3:1 (White, 1992).

[]{#__RefHeading___Toc450036318 .anchor}Table 6-2. Time to 99 Percent
Conversion of Chlorine to Monochloramine

  -------------------------------- --------------------------------------
  **pH**                           **Time (seconds)**

  2                                421

  4                                147

  7                                0.2

  8.3                              0.069

  12                               33.2
  -------------------------------- --------------------------------------

### Chlorine Feed Facilities

Table 6-3 summarizes commonly used methods of chlorine addition,
including their safety precautions and costs.

[]{#__RefHeading___Toc450036319 .anchor}Table 6-3. Methods of Chlorine
Addition

  ----------------------------------------------------------------------------
  **Method**     **Description**           **Safety precautions** **Costs**
  -------------- ------------------------- ---------------------- ------------
  Gaseous        Gas delivered in          Gaseous chlorine is    The cost per
  chlorine       containers ranging in     classified by the      pound of
                 size from 150 lb          Uniform Fire Code as   liquid
                 cylinders to 90 ton rail  an oxidizing, highly   chlorine is
                 cars. One ton cylinders   toxic, compressed gas. in the range
                 are commonly used. Feed   New gaseous chlorine   of \$0.08 to
                 equipment consists of     facilities should be   \$0.20 per
                 solution water            designed with          pound
                 pump/ejector to create    enclosures and air     depending on
                 vacuum and automatic      scrubbers to capture   the quantity
                 orifice control to meter  and neutralize any gas purchased.
                 the gas. Gas can be drawn that leaks. Risk       
                 directly from storage     management prevention  
                 container or be generated plans should be        
                 by an evaporator from     prepared. Personnel    
                 liquid withdrawn from the safety equipment and   
                 container. A schematic of training should be     
                 gaseous chlorine feed     provided for           
                 system is shown in        operators.             
                 Figure 6‑3.                                      

  Sodium         Sodium hypochlorite can   Hypochlorite solution  Typical
  hypochlorite   be purchased bulk in      is toxic and           chemical
                 quantities ranging from   classified as          cost is
                 55 gal drums to 4,500 gal hazardous. Storage     \$0.60 to
                 truck loads. Bulk loads   facilities should be   \$1.00 per
                 can be stored in          designed with          pound Cl~2~.
                 fiberglass or plastic     secondary containment. 
                 tanks. Solution is fed                           
                 directly into the process                        
                 stream. A schematic of                           
                 typical hypochlorite feed                        
                 system is shown in Figure                        
                 6-4.                                             
  ----------------------------------------------------------------------------

### Ammonia Feed Facilities

Ammonia feed facilities can be located on-site at the water treatment
plant or at remote locations in the distribution system (Dennis et al.,
1991). Most ammonia feed facilities use either gaseous (anhydrous
ammonia) or liquid (aqueous) ammonia. Though anhydrous ammonia is a gas
at ambient temperature and pressure, it is commonly stored and
transported as a liquid in pressure vessels. In this phase, ammonia is
highly soluble in water. Storage facilities and handling equipment
should be kept dry (Dennis et al., 1991).

![](media/image4.wmf){width="6.243055555555555in"
height="3.472916666666667in"}

[]{#_Ref396019666 .anchor}Figure 6-3. Gaseous Chlorine Feed System

![](media/image5.wmf){width="6.243055555555555in" height="3.625in"}

[]{#__RefHeading___Toc450036328 .anchor}Figure 6-4. Hypochlorite Feed
System

#### Anhydrous Ammonia

Anhydrous ammonia is stored in portable cylinders or stationary tanks.
Portable cylinders are similar to chlorine cylinders and are available
in 100, 150, and 800 lb sizes (Dennis et al., 1991). The cylinders are
rated for a minimum service pressure of 480 psi. Stationary tanks are
typically 1,000 gallon vessels that can be used on-site. These tanks are
refilled by tanker trailers. The storage tanks can be located indoors or
outdoors. Since each tank has a minimum working pressure of 250 psi
(valves and fittings on the tanks are rated for 300 psi), a tank stored
outdoors should have protection from extreme temperatures (greater than
125°F and less than 28°F) (Dennis et al., 1991). In warmer climates, an
outdoor tank should be painted white and protected from sunlight. In
colder climates, the tank should be wrapped with heat tape to prevent
impairment of the ammonia vaporization.

Anhydrous ammonia is applied using an ammoniator. An ammoniator is a
self-contained modular unit with a pressure reducing valve, gas flow
meter, feed rate control valve, and miscellaneous piping for controlling
the flow of ammonia. Automatic paced ammoniators are available. An
evaporator is used when large quantities of ammonia gas are needed. An
anti-siphon valve or check valve should be used to prevent water from
entering the ammoniator.

Anhydrous ammonia is usually applied by direct feed or solution feed.
The direct feed method is typically used when the process stream has a
low pressure and the ammonia feed rate is less than 1,000 lb per day
(i.e., maximum rated feed capacity). Ammonia is drawn from the storage
tank under high pressure (e.g., 200 psi), and injected directly into the
process stream at a low pressure of 15 psi. The tank pressure is first
reduced by a pressure reducing valve to approximately 40 psi, and then
by another pressure reducing valve in the ammoniator. Typical
application points are at open channels and basin facilities. Figure 6-5
is a schematic of a direct anhydrous ammonia feed system.

[]{#_Ref396019886 .anchor}The solution feed method is typically used
where direct feed systems are not adequate (e.g., ammonia feed rate is
greater than 1000 lb/day or where the process stream pressure is high)
(Dennis et al., 1991). This type of application is similar to the
chlorine vacuum feed system. The supply tank pressure is reduced by a
pressure reducing valve to create a vacuum. An eductor is used to
withdraw ammonia from the ammoniator where the ammonia is dissolved into
a side water stream and pumped into the process stream. Solution feed
ammoniators are available up to 4,000 lb/day capacities and can operate
at discharge pressures up to 100 psi (Dennis et al., 1991). Softened
water (i.e., hardness less than 29 mg/L as CaCO~3~) is required for the
carrier stream. Otherwise, the ammonia addition will precipitate scale
that may plug the eductor and application point. Figure 6-6 shows a
schematic of a solution feed system.

#### Aqueous Ammonia

Aqueous ammonia is produced by dissolving anhydrous ammonia into
deionized or softened water. This form of ammonia is shipped in cargo
trucks or polyethylene lined steel drums. Plastic drums are not
recommended since they tend to lose their shape under the slight
pressure exerted by the aqueous ammonia. Aqueous ammonia is stored in
low pressure tanks, typically steel or fiberglass. Since excessive
temperatures will cause ammonia gas to vaporize, each storage tank
should be equipped with a water trap or ammonia scrubber to keep vapors
from escaping to the atmosphere.

![](media/image6.wmf){width="6.175694444444445in"
height="3.0340277777777778in"}

Source: Montgomery, 1985.

Figure 6-5. Anhydrous Ammonia Direct Feed System

[]{#_Ref396019900
.anchor}![](media/image7.wmf){width="6.229861111111111in"
height="3.7006944444444443in"}

Source: Montgomery, 1985.

Figure 6-6. Anhydrous Ammonia Solution Feed System

Aqueous ammonia feed systems are similar to other liquid chemical feed
systems. They require a storage tank, chemical metering pump, relief
valve, pulsation dampener, flow meter, and backpressure valve.
Typically, the feed pumps are positive displacement or progressive
cavity type metering pumps. The feed pumps should be placed fairly close
to the storage tank to minimize chances of ammonia vaporization in the
piping (Dennis et al., 1991). The pump should be designed to compensate
for changes in ambient temperatures, different aqueous ammonia
solutions, and changes in the chlorine-to-ammonia ratio (Skadsen, 1993).
When aqueous ammonia is applied to water, complete mixing is required
for the ammonia to react with chlorine in the water to reduce the
formation of dichloramine and nitrogen trichlorine. Figure 6-7 shows a
schematic of an aqua ammonia feed system.

Metropolitan Water District of Southern California (MWDSC) uses aqueous
ammonia at its chloramination facility. Ammonia is stored in unlined
tanks and pumped to the ammoniator with progressive cavity pumps. During
startup of its aqueous ammonia feed system, MWDSC experienced complete
pump failures. Based on MWDSC's experience, EPDM rotors with adequate
quality chromed finish stators are recommended for progressive cavity
pumps. A mechanical seal is also recommended instead of a packing box to
reduce the possibility of ammonia leaks (Skadsen, 1993). MWDSC also
later installed special blow-offs and strainers in the feed pump suction
line to reduce plugging at the magnetic flow meters. The pump problems
prior to startup led MWDSC to install an alternative, redundant ammonia
feed system. A pressurized system was designed to feed aqueous ammonia
by pressurizing the ammonia tanks and by-passing the pump.

[]{#_Ref396034569
.anchor}![](media/image8.wmf){width="6.207638888888889in"
height="2.7881944444444446in"}

Source: Montgomery, 1985.

Figure 6-7. Aqua Ammonia Feed System

A 5.5 gpm flexible impeller centrifugal pump with a recirculation loop
back to the storage tank regulates the back pressure on the by-passed
feed pump. This alternative, redundant method proved to be reliable and
economical. In addition, it provided a stable feed rate and required
little maintenance (Skadsen, 1993).

#### Piping and Valving

For anhydrous ammonia, the typical piping materials for both direct and
solution feed systems are stainless steel, PVC, and black iron (Dennis
et al., 1991). Stainless steel or black iron pipe is used in the high
pressure (i.e., greater than 15 psi) portions of the feed system. PVC
pipe is used only in the low pressure portion of the feed system, after
the ammoniators.

For aqueous ammonia, PVC piping should be used due to the corrosive
nature of aqueous ammonia (Dennis et al., 1991).

#### Safety Provisions for Chloramine Generation Facilities

A chloramination facility should include some safety provisions to
prevent the formation of nitrogen trichloride and the vaporization of
ammonia at ambient temperatures. The possible formation of nitrogen
trichloride at a chloramination facility should be considered when
selecting sites for the ammonia and chlorine storage facilities.

Dennis et al. (1991) provides detailed information about safety
provisions for chloramine facilities. Chlorine gas and ammonia gas
should never be stored in the same room. The ammonia gas application
points should be located at least 5 feet away from chlorine feed
solution lines. Anhydrous ammonia is lighter than air, so any leaking
vapor will rise quickly. Under pressure, anhydrous ammonia is a liquid.
Great amounts of heat are absorbed when the pressurized liquid reverts
to a gas. If the storage tanks and/or chemical feed equipment are
installed indoors, ventilation and vapor detection devices should be
located at high points in the room. The ventilation rates will vary
depending on the appropriate regulatory agency's requirements.
Typically, a minimum of 6 room volume changes per minute is recommended.

Ammonia gas storage tanks should be protected from direct sunlight or
direct sources of heat (i.e., greater than 125^o^F) to avoid pressure
increases in the tank (Dennis et al., 1991). Otherwise, ammonia gas may
be released into the atmosphere through the pressure relief valves. In
warm regions, outdoor tanks should be covered with a shelter or
outfitted with a temperature control sprinkler system. Where fugitive
emissions of ammonia are a concern, fume control may be required. If the
accidental release from a storage container is a concern, an emergency
scrubber system similar to a chlorine gas scrubber system should be
considered.

## Primary Uses and Points of Application

Monochloramine is used in drinking water treatment for disinfection and
nuisance organism control. Points of application are based on treatment
objectives and contact time disinfection requirements.

### Primary Uses

#### Disinfection

The primary use of monochloramine in water systems is as a secondary
disinfectant for maintaining a residual in the distribution system.
Chloramines are a good choice for secondary disinfectant because of the
following potential benefits:

-   Chloramines are not as reactive with organics as free chlorine in
    forming THMs.

-   The monochloramine residual is more stable and longer lasting than
    free chlorine or chlorine dioxide, providing better protection
    against bacterial regrowth in systems with large storage tanks and
    dead-end water mains.

-   The monochloramine residual has been shown to be more effective in
    controlling biofilms because of its superior ability to penetrate
    the biofilm. Controlling biofilms also tends to reduce coliform
    concentrations and biofilm induced corrosion.

-   Because chloramines do not tend to react with organic compounds,
    many systems will experience less incidence of taste and odor
    complaints when using chloramines.

Water systems in Indiana and Virginia found that conversion from free
chlorine to monochloramine as the secondary disinfectant significantly
reduced coliform concentrations in the distribution system (Norton and
LeChevallier, 1997).

The normal dosage range for monochloramine is in the range of 1.0 to 4.0
mg/L. The minimum residual of monochloramine in the distribution system
is typically regulated at 0.5 mg/L (Texas Natural Resource Conservation
Commission). For prevention of nitrification in a distribution system, a
minimum monochloramine dosage of 2.0 mg/L is recommended (Norton and
LeChevallier, 1997).

#### Nuisance Organism Control

Cameron et al. (1989a) investigated the effectiveness of monochloramine
to control the Asiatic clam in both the juvenile and adult phases. The
adult Asiatic clam was found to be much more resistant to monochloramine
than the juvenile form. Monochloramine was found to be the most
effective for controlling the juvenile Asiatic clam in terms of LT~50~
(time required for 50 percent mortality). Monochloramine doses used to
control the juvenile Asiatic clam range from 1.2 to 4.7 mg/L. Further
research showed that the effectiveness of monochloramine increased
greatly as the temperature increased (Cameron et al., 1989b).

### Points of Application

The formation of monochloramine can be accomplished by first adding
ammonia and then chlorine, or vice versa. Ammonia is added first where
formation of objectionable taste and odor compounds caused by the
reaction of chlorine and organic matter are a concern. However, most
drinking water systems add chlorine first in the treatment plant in
order to achieve the required concentration and contact time (CT) to
meet EPA's SWTR disinfection requirements. Typically, the point of
ammonia addition is selected to "quench" the free chlorine residual
after a target period of time based on optimizing disinfection versus
minimizing DBP formation.

Because the germicidal effectiveness of monochloramine is a factor of
200 less than for free chlorine, extremely long contact times are
required for monochloramine to meet EPA disinfection CT requirements.
Therefore, if ammonia is added first, a means of ensuring that CT
requirements are met must be developed.

#### Impact on Other Treatment Processes

Monochloramine addition impacts other processes at the water treatment
facility. These impacts include:

-   Ammonia used in the chloramination process can provide nutrient
    ammonia for nitrifying bacteria growth in the distribution system,
    which can cause increased nitrate levels in the finished water where
    systems do not normally test for nitrate.

-   Imbalances in chlorine and ammonia concentrations (in greater than
    an 8 to 1 ratio) can cause breakpoint chlorination reactions to
    occur when encountered in distribution system

-   Monochloramine addition upstream of filters will reduce biological
    growth on filters. This has a favorable impact on the filters by
    keeping them clean and reducing the backwash frequency. It also has
    the undesirable impact of reducing BDOC removal in the filters when
    the filters are run in a biological mode.

The reader is referred to EPA's *Microbial and Disinfection Byproduct*
*Simultaneous Compliance Guidance Document* (expected to be available in
1999) for additional information regarding the interaction between
oxidants and other treatment processes.

## Pathogen Inactivation and Disinfection Efficacy

Chloramination of drinking water has been practiced in the United States
for nearly 80 years. In addition to achieving disinfection, chloramines
have been used by the Denver Water Department for controlling tastes and
odors since 1918 (Hazen and Sawyer, 1992). Chloramination has also been
found to provide a more stable residual in water distribution system.
However, because of its relatively weak disinfecting properties for
inactivation of viruses and protozoa pathogens, it is rarely used as a
primary disinfectant, and then only with long contact times.

### Inactivation Mechanisms

The mechanisms by which chloramines inactivate microorganisms have been
studied to a lesser degree than chlorine. A study of inactivation of *E.
coli* by chloramines concluded that monochloramine readily reacts with
four amino acids; cysteine, cystine, methionine and tryptophan (
Jacangelo et. al, 1987) . The mechanism of inactivation for chloramine
is therefore thought to involve inhibition of proteins or protein
mediated processes such as respiration. Jacangelo further concluded that
because of the inconsistency in rate of inactivation monochloramine
should have "multiple hits" upon bacterial cells before cell death.

Few studies have been performed to determine the mechanism for viral
inactivation. The initial site for destruction of bacteriophage f2
involved the RNA fragment (Olivieri et al., 1980). However, the primary
mechanism for poliovirus inactivation by chloramines involved the
protein coat (Fujioka et al., 1983). Similar to free chlorine, the
mechanism of viral inactivation by chloramine may be dependent on
factors such as virus type and disinfectant concentration.

### Environmental Effects

Several studies have been performed to determine the effect of pH,
temperature, and organic and inorganic compounds on the disinfection
effectiveness of chloramines. Following is a summary of the affect these
parameters have on pathogen inactivation.

#### pH

The effect of pH on disinfection has more to do with the organism than
with the disinfectant; however, pH also impacts disinfection efficiency
by controlling the chloramine species distribution. Studies have
indicated that the disinfection efficacy of monochloramine and
dichloramine are not equal. One study showed that the bactericidal
properties of dichloramine were superior to that of monochloramine
(Esposito, 1974). However, pH may be a compounding factor because
changes in pH may alter the physiological response of the organism (Hoff
and Geldreich, 1981). Other studies have shown that monochloramine is
superior to dichloramine with regard to virucidal ability (Dorn, 1974;
Esposito, 1974; Olivieri et al., 1980). Some evidence suggests that
solutions containing approximately equal concentrations of
monochloramine and dichloramine may be more microbiocidal than those
containing only monochloramine or dichloramine (Weber and Levine, 1944).

#### Temperature

Similar to most of the disinfectants discussed in this report, the
bactericidal and viral inactivation efficiency of chloramine increases
with increasing temperature. Moreover, the efficiency dramatically
decreases under conditions of high pH and low temperature. For example,
the inactivation of *E. coli.* is approximately 60 times slower at pH
9.5 and temperatures of 2 and 6^o^ C than at pH 7 and temperatures
between 20 and 25^o^C (Wolfe et al., 1984). Similar results were
obtained for poliovirus 1 inactivation (Kelley and Sanderson, 1958).

#### Organic Nitrogen and Other Compounds

In addition to ammonia, free chlorine reacts with organic nitrogen
compounds to form a variety of organic chloramines. These organic
chloramines are undesirable byproducts because they exhibit little or no
microbiocidal activity (Feng, 1966). Studies have indicated that
chlorine binds to amine-containing compounds more rapidly than to
ammonia (Weil and Morris, 1949; Morris, 1967; Margerum et al., 1978) and
that chlorine can be transferred from inorganic chloramines to
amine-containing compounds (Margerum et al., 1978; Isaac and Morris,
1980)

Several other reactions may occur which divert chlorine from the
formation of chloramines. These reactions can include oxidation of iron,
manganese, and other inorganics such as hydrogen sulfide (Hazen and
Sawyer, 1992).

### Disinfection Efficacy

Chloramines are relatively weak disinfectants for virus and protozoa
inactivation. As a consequence, it is extremely difficult to meet the
SWTR CT criteria for primary disinfection of *Giardia* and viruses using
chloramines because very long detention times are needed. However, given
the ability of chloramines to provide a stable residual, this form of
disinfection appears to be feasible for secondary disinfection
protection against microbial growth in distribution systems. The
following paragraphs describe the disinfection efficiency of chloramines
in terms of bacteria, virus, and protozoa inactivation.

#### Bacteria Inactivation

A series of comprehensive experiments was initiated in the mid 1940s to
determine the relative bactericidal effectiveness of free chlorine and
inorganic chloramines. Results from these experiments showed
conclusively that under relatively demand-free, laboratory-controlled
conditions, free chlorine inactivated enteric bacteria much faster that
chloramines (Wattie and Butterfield, 1944). In this experiment, a
monochloramine concentration of 0.3 mg/L required 240 minutes of contact
time for 3-log inactivation of *E. coli* whereas exposure to 0.14 mg/L
free Cl~2~ required only 5 minutes to achieve the same level of
inactivation at the same temperature and pH.

#### Virus Inactivation

According to reports written by Kabler et al. (1960) and the National
Research Council (1980), all studies conducted prior to 1944 that
compared virucidal potency of free and combined chlorine were inaccurate
because the experiments failed to clearly differentiate between free and
combined forms of chlorine and because high-chlorine-demand water was
used in the experiments.

The majority of the experiments conducted after the mid-1940s has shown
that inorganic chloramines require much higher concentrations and
considerably longer contact times than free chlorine to achieve
comparable levels of virus inactivation. Experiments showed that contact
times between 2 and 8 hours were required at concentrations between 0.67
to 1.0 mg chloramines to achieve greater than 2-log inactivation of
poliovirus 1 (Mahoney and MK500), poliovirus 2 (MEF), poliovirus 3
(Sackett), coxsackievirus B1, and coxsackievirus B5 (EA 80) (Kelley and
Sanderson, 1958 and 1960). In contrast, 0.2 to 0.35 mg/L free Cl~2~
required 4 to 16 minutes of contact time to achieve comparable levels of
inactivation under the same conditions.

#### Protozoa Inactivation

Of the three predominant forms of pathogens (i.e., bacteria, viruses,
and protozoan \[oo\]cysts), studies have shown that protozoan
\[oo\]cysts are usually the most resistant to all forms of disinfection.
Studies have indicated that free chlorine is a more effective
disinfectant than chloramines for \[oo\]cyst inactivation (Chang and
Fair, 1941; Chang, 1944; Stringer and Kruse, 1970). Chloramine
concentrations of 8 mg/L were required for 2-log inactivation of
*Entamoeba histolytica* cysts whereas only 3 mg/L of free chlorine was
required to obtain the same degree of inactivation (Stringer and Kruse,
1970). Contact times for both disinfectants were 10 minutes.

#### CT Values

CT values for achieving *Giardia* cyst and virus inactivation using
chloramines are shown in Table 6‑4 and Table 6-5, respectively. Values
contained in these tables were obtained from the *Guidance Manual for
Compliance with Filtration and Disinfection Requirements for Public
Water Systems Using Surface Water Sources* (AWWA, 1991).

CT values shown in Table 6-4 are based on disinfection studies using in
vitro excystation of *Giardia lamblia*. CT values shown in Table 6-5
were based on data using preformed chloramines at pH 8. No safety factor
was applied to laboratory data used to derive the CT values shown in
Table 6-4 and Table 6-5 since chloramination conducted in the field is
more effective than using preformed chloramines, since monochloramine
tends to degrade with time and some free chlorine is present when
forming chloramines which enhances the inactivation process.

[]{#__RefHeading___Toc450036320 .anchor}Table 6-4. CT Values for
*Giardia* Cyst Inactivation Using Chloramines

  ------------------ --------------- ----------- ----------- ----------- -----------
                     **Temperature                                       
                     (°C)                                                
                     (mg•min/L)**                                        

  **Inactivation**   **5**           **10**      **15**      **20**      **25**

  0.5-log            365             310         250         185         125

  1-log              735             615         500         370         250

  1.5-log            1,100           930         750         550         375

  2-log              1,470           1,230       1,000       735         500

  2.5-log            1,830           1,540       1,250       915         625

  3-log              2,200           1,850       1,500       1,100       750
  ------------------ --------------- ----------- ----------- ----------- -----------

Source: AWWA, 1991.\
Values shown in this table are based on a pH range between 6 and 9.

[]{#__RefHeading___Toc450036321 .anchor}Table 6-5. CT Values for Virus
Inactivation Using Chloramines

  ------------------ --------------- ----------- ----------- ----------- -----------
                     **Temperature                                       
                     (°C)                                                
                     (mg•min/L)**                                        

  **Inactivation**   **5**           **10**      **15**      **20**      **25**

  2-log              857             643         428         321         214

  3-log              1,423           1,067       712         534         356

  4-log              1,988           1,491       994         746         497
  ------------------ --------------- ----------- ----------- ----------- -----------

Source: AWWA, 1991.

## DBP Formation

The effectiveness of chloramines to control DBP production depends upon
a variety of factors, notably the chlorine-to-ammonia ratio, the point
of addition of ammonia relative to that of chlorine, the extent of
mixing, and pH.

Monochloramine (NH~2~Cl) does not produce DBPs to any significant
degree, although some dichloroacetic acid can be formed from
monochloramine and cyanogen chloride formation is greater than with free
chlorine (Jacangelo et al., 1989; Smith et al., 1993; Cowman and Singer,
1994). The inability to mix chlorine and ammonia instantaneously allows
the free chlorine to react before the complete formation of chloramines.
In addition, monochloramine slowly hydrolyzes to free chlorine in
aqueous solution. Therefore, halogenation reactions occur even when
monochloramine is formed prior to addition in the treatment process
(Rice and Gomez-Taylor, 1986). The closer the chlorine:ammonia ratio is
to the breakpoint, the greater the formation of DBPs (Speed et al.,
1987). In addition to controlling the formation of DBPs, chloramination
results in lower concentrations of a number of the other specific
organic halides generated from free chlorine, except for cyanogen
chloride (Krasner et al., 1989; Jacangelo et al., 1989). Increased
production of cyanogen chloride is observed when monochloramine is used
as a secondary disinfectant instead of free chlorine.

The application of chloramines results in the formation of chlorinated
organic material, although it occurs to a much lesser degree than from
an equivalent dose of free chlorine. Little is known about the nature of
these byproducts, except that they are more hydrophilic and larger in
molecular size than the organic halides produced from free chlorine
(Jensen et al., 1985; Singer 1993).

## Status of Analytical Methods

### Monitoring of Chloramines

There has been little development of analytical procedures for selective
determination of monochloramines (Gordon, et al., 1992). Typically, the
methods used for chlorine residual measurement are adapted for
chloramine measurement. The DBPR promulgated on December 16, 1998 (63 FR
69390) establishes three analytical methods that are acceptable for
measuring residual chloramines (combined chlorine). These methods are
presented in 40 CFR § 141.131(c) and include:

-   Amperometric Titration (Standard Method 4500-Cl D and ASTM Method D
    1253-86);

-   DPD Ferrous Titrimetric (Standard Method 4500-Cl F); and

-   DPD Colorimetric (Standard Method 4500-Cl G).

    If approved by the State, systems may also measure chloramines by
    using DPD colorimetric test kits.

#### Amperometric Titrations

The amperometric titration method is utilized extensively in water
treatment laboratories (Gordon, et al., 1992). This method capable of
differentiating the three most common forms of chlorine, namely
chlorine/hypochlorous acid/hypochlorite ion, monochloramine, and
dichloramine, as long as the combined forms are not present in
concentrations greater than about 2 mg/L (as Cl~2~). For higher
concentrations, dilution of the samples is required, but differentiation
is still possible (Aoki, 1989).

The amperometric titration method is a standard of comparison for the
determination of free or combined chlorine. This method is not greatly
affected by common oxidizing agents, temperature variations, turbidity,
and color (Standard Methods, 1995). Amperometric titration requires a
greater degree of skill than colorimetric methods. The differentiation
of free chlorine, monochloramine, and dichloramine is possible by
control of potassium iodide (KI) concentration and pH during the
analysis.

Several methods are commonly used to measure chlorine species utilizing
the amperometric titration including forward and back titration (Gordon,
et al., 1992). The lower limit of detection of these methods varies
depending on the instrumentation used and type of water sample analyzed.
The lower limit of detection for commercial amperometric titrating
equipment is about 30 μg/L as Cl~2~ (Sugam, 1983).

Table 6-6 shows the working range, expected accuracy and precision,
operator skill level required, interferences, and current status for
amperometric method monochloramine analysis comparison.

#### Colorimetric Methods

Over the years, numerous colorimetric methods have been developed to
measure free and combined chlorine in aqueous solutions (Gordon, et al.,
1992). Not many of these methods would be recommended as the method of
choice. Two of the colorimetric methods listed in Standard Methods
(1995), are DPD methods. In addition, the colorimetric LCV method
modified by Whittle and Lapteff (1974) can be used to measure free and
combined chlorine species.

The DPD methods (ferrous titration and colorimetric) are operationally
simpler for determining free chlorine than the amperometric titration
(Standard Methods, 1995). Procedures are given for estimating separate
monochloramine and dichloramine fractions, as well as combined chlorine
fractions.

The LCV method modified by Whittle and Lapteff modifies the discontinued
Standard Method for LCV. The maximum chlorine concentration that can be
determined by this modified procedure, without dilution of the sample,
is 10 mg/L as Cl~2~ (Whittle and Lapteff, 1974).

See Table 6-6 for the working range, expected accuracy and precision,
operator skill level required, interferences and current status for
colorimetric method monochloramine analysis comparison.

### Disinfectant Interferences

Interferences to free chlorine may impact the measurement of
monochloramine since the methods use the free chlorine level in the
determination of monochloramine. Many strong oxidizing agents interfere
in the measurement of free chlorine in all monochloramine methods,
including bromine, chlorine dioxide, iodine, permanganate, hydrogen
peroxide, and ozone. However, the reduced form of these compounds (i.e.
bromide ion, chloride ion, iodide ion, manganous ion, and oxygen) do not
interfere. Reducing agents such as ferrous compounds, hydrogen sulfide,
and oxidizable organic matter generally do not interfere (Standard
Methods, 1995).

[]{#__RefHeading___Toc450036322 .anchor}Table 6-6. Characteristics and
Comparisons of Monochloramine^a^ Analytical Methods

  -------------- ----------- ------------ ------------ ------------ ------------------- ----------- --------- ------------- -------------
  **Type of      **Working   **Expected   **Expected   **Skill      **Interferences**   **pH        **Field   **Automated   **Current
  Test**         Range       Accuracy (±  Precision (± Level^b^**                       Range**     Test**    Test**        Status**
                 (mg/L)**    %)**         %)**                                                                              

  Amperometric   0.1 - 10    NR           0 - 10       2            dichloramine,       pH          Yes       Yes           Recommended
  Titration,                                                        nitrogen            dependent                           
  Forward                                                           trichloride,                                            

  Amperometric   0.1 - 10    NR           NF           2            dichloramine,       pH          Yes       Yes           Recommended
  Titration,                                                        nitrogen            dependent                           
  Back                                                              trichloride,                                            

  Colorimetric   0.01 - 10   NR           2 - 7        1            dichloramine,       Requires    No        No            Recommended
  DPD Ferrous                                                       nitrogen            buffer                              Lab Test
  Titration                                                         trichloride,                                            
                                                                    oxidizing species                                       

  Colorimetric   0.01 - 10   NR           5 - 75       1            dichloramine,       Requires    Yes       No            Recommended
  DPD                                                               nitrogen            buffer                              Field Test
                                                                    trichloride,                                            
                                                                    oxidizing species                                       
  -------------- ----------- ------------ ------------ ------------ ------------------- ----------- --------- ------------- -------------

Source: Gordon et al., 1992.

Notes: ^a^ Little actual work has been carried out on selective
determination of chloramines. The values reported are from extrapolated
studies that had objectives other than the selective determination of
chloramines.

> ^b^ Operator skill levels: 1 = minimal, 2 = good technician, 3 =
> experienced chemist. NR = Not reported in literature cited by
> referenced source.

#### Amperometric Titrations

The amperometric titration methods are unaffected by dichloramine
concentrations in the range of 0 to 9 mg/L as Cl~2~ in the determination
of free chlorine. Nitrogen trichloride, if present, may react partially
as free chlorine. The amperometric method will measure organic
chloramines as free chlorine, monochloramine, or dichloramine, depending
upon the activity of chlorine in the organic sample (Standard Methods,
1995). Dichloramine may also interfere with the measurement of both
monochloramine and free chlorine (Marks, et al., 1951). The presence of
iodide ion can be a severe problem if the titrator glassware is not
washed carefully between determinations (Johnson, 1978).

Manganese dioxide, a common interference in most chlorine analytical
procedures, does not interfere in the amperometric measurement of free
chlorine (Bongers et al., 1977). However, because of its reaction with
iodide ion, added during analysis, manganese dioxide does interfere with
the amperometric measurement of combined forms of chlorine such as
monochloramine (Johnson, 1978).

#### Colorimetric Methods

Sample color and turbidity may interfere in all colorimetric procedures.
In the DPD colorimetric methods, high concentrations of monochloramine
interfere with free chlorine determination unless arsenite or
thioacetimide are added. In addition, the DPD methods are subject to
interference by oxidized forms of manganese unless compensated for by a
blank (Standard Methods, 1995). The DPD methods are unaffected by
dichloramine concentrations in the range of 0 to 9 mg/L as Cl~2~ in the
determination of free chlorine. Nitrogen trichloride, if present, may
react partially as free chlorine. The extent of this interference in the
DPD methods does not appear to be significant (Standard Methods, 1995).

In the LCV colorimetric method, Whittle and Lapteff (1974) reported that
dichloramine did not interfere with the monochloramine measurement.

### Chloramine Monitoring for Systems Using Chloramines

Pursuant to 40 CFR §141.132(c)(1), community water systems and
non-transient non-community water systems that use chloramines, must
measure the residual disinfectant level at the same points in the
distribution system, at the same time, and at the same frequency (based
on population served) as total coliforms are sampled, as specified in 40
CFR §141.21. These systems may use the results of residual disinfectant
concentration sampling conducted under §141.74(b)(6)(i) for unfiltered
systems or §141.74(c)(3)(i) for systems which filter, in lieu of taking
separate samples. No reduced monitoring allowances exist for these
systems.

Compliance with the MRDL of 4.0 mg/L (as chlorine) is based on a running
annual arithmetic average, computed quarterly, of monthly averages of
all samples collected by the system under §141.132(c)(1). If the average
quarterly averages covering any consecutive four-quarter period exceeds
the MRDL, the system is in violation of the MRDL and must notify both
the public, pursuant to §141.32, and the State, pursuant to §141.134.
Where systems switch between the use of chlorine and chloramines for
residual disinfection during the year, compliance is determined by
including together all monitoring results of both chlorine and
chloramines in calculating compliance.

## Operational Considerations

The purpose of this section is to address operational considerations in
the use of chloramines in drinking water treatment. Specifically, the
following topics are addressed below: the conversion of chloramination
from chlorination; the potential operational impacts from chloramination
disinfection; and special considerations for chloramination facilities.
For a more detailed discussion of chloramine disinfection, refer to
"Optimizing Chloramine Treatment" by Kirmeyer et, al. 1993.

### Conversion to Chloramination from Chlorination

#### Planning

Project planning and preparation are essential to ensure an efficient
changeover, maintain a dependable and safe system, and preserve the
public confidence in the water purveyor (Skadsen, 1993). Planning and
preparation should consider the following aspects:

-   Raw water composition and suitability to chloramination;

-   Treatment plant and distribution system attributes and monitoring
    program;

-   Employee training;

-   Public notification and education; and

-   Environmental affects from chloraminated water.

#### Preliminary Analysis

A bench scale study is necessary to identify the water characteristics
and to determine if chloramination is suitable. White (1992) describes
some of the study objectives and variables to consider. The reaction
time to form free chloramine residuals varies for each water source
since the reaction rate between chlorine and ammonia nitrogen depends on
the water's temperature and pH of the water. The reaction rate is also
affected by the chlorine and ammonia nitrogen concentrations. To
properly control the reaction time between chlorine and ammonia, the
study should use different chlorine:ammonia nitrogen ratios, ammonia
feed doses, and contact times.

The amount of ammonia required for chloramine residual disinfection
depends on the following factors (Dennis et al., 1991):

-   Organic nitrogen in the water;

-   Ammonia residual desired in the distribution system; and

-   Chloramine residual type and concentration required in the
    distribution system.

If there is organic nitrogen in the untreated water, the amount of
supplemental ammonia required should be carefully determined by
subtracting the background ammonia from the desired dose. The dose
should also consider the amount of ammonia residual desired in the
distribution system. For residual disinfection, approximately 1 to 2
mg/L of ammonia is required (Dennis et al., 1991).

For each specific water, a breakpoint curve should be developed to
determine the chloramine residual type required. Monochloramine
residuals are preferred for most water distribution systems.
Dichloramine and nitrogen trichloride residuals may cause taste and odor
problems when concentrations exceed 0.8 mg/L or 0.02 mg/L, respectively.
Monochloramines are primarily formed when the theoretical chlorine to
ammonia dose ratio is less than 5 to 1 (by weight ratio) and the pH is
greater than 7.0 (Dennis et al., 1991). The chloramine residual
concentration leaving the treatment plant will vary depending on the
size of the distribution system and the chloramine demand exerted by the
system. Typical chloramine residuals range from 1 to 4 mg/L (Dennis et
al., 1991).

#### The Metropolitan Water District (MWDSC)

MWDSC of Southern California converted from free chlorine to chloramine
disinfection in 1985 to assist its 27 member agencies in complying with
the EPA's total trihalomethane regulation. MWDSC serves approximately 15
million people and operates five treatment plants, with a combined
capacity of 1,670 MGD. Raw water is taken from two sources: the Colorado
River and California state project water.

Prior to the changeover, MWDSC performed extensive investigations into
the chemical, microbiological, and engineering aspects of chloramine
disinfection. To prepare for the changeover, MWDSC coordinated the
efforts among its treatment plants, distribution system reservoirs,
laboratory personnel, and management. A formal request for approval to
use chloramines as a disinfectant was submitted to the California State
Department of Health Services. Next, a series of workshops was held on
the engineering, chemical, and microbiological aspects of chloramine
disinfection. MWDSC also prepared a manual for the type of
chloramination application method and ammonia form selected. Information
in the manual included the feed equipment information, project
specifications, piping layouts, preliminary analysis, and safety and
maintenance issues.

It was essential to notify specific sectors of the public that could be
affected by the use of chloramines. MWDSC made its customers aware of
the changeover and kept them apprised of the options for preventing
adverse reactions through an extensive notification program that
involved state and county health departments, appropriate interest
groups, and the media.

### Potential Operational Impacts from Chloramination Disinfection

#### Pretreatment

Ammonia in excess of the required chlorine can promote the growth of
nitrifying bacteria in filter beds (i.e., rapid sand filters) (White,
1992). The excess ammonia acts as a nutrient and causes the growth of
nitrifying bacteria, which convert the excess ammonia to nitrates and
nitrites. Excessive levels of nitrate in drinking water have caused
serious illness and sometimes death in infants under six months of age.
The symptoms include shortness of breath and blueness of skin \[40 CFR
§141.32(e)(20)\]. Prior to designing a chloramination facility, the
amount of ammonia naturally occurring in the raw water should be
determined. The required ammonia dosage would then be based on the
anticipated naturally occurring ammonia levels.

A chloramine residual concentration should also be maintained in the
discharge stream from the filters. An adequate residual concentration
would be between 0.5 to 1 mg/L chloramine (White, 1992).

#### Nitrification

Nitrification in chloraminated drinking waters is usually partial.
Partial nitrification occurs when the chloraminated water has excess
ammonia present in the distribution system (Skadsen, 1993). Partial
nitrification can have various adverse effects on water quality,
including a loss of total chlorine and ammonia residuals and an increase
in heterotrophic plate count (HPC) bacteria concentration. The excess
ammonia encourages the growth of nitrifying bacteria that convert
ammonia to nitrates. An intermediate step in this conversion results in
a small amount of nitrite being formed. Research has shown that a
chlorine demand of 5 mg/L is exerted by 1 mg/L of nitrite (Cowman and
Singer, 1994). The nitrites rapidly reduce free chlorine, accelerate
decomposition of chloramines, and can interfere with the measurement of
free chlorine (Skadsen, 1993). Valentine (1998) found that the decay of
monochloramine was increased (from a second order rate constant of 0.07
to 0.106) by the presence of 0.5 mg/L of nitrite. If nitrification
episodes are allowed to continue, very low (or zero) total chlorine
residual concentration levels may occur. Loss of chlorine residual
allows an increase in HPC bacteria and potentially increases in total
coliforms and may result in a positive sample (Cowman and Singer, 1994).
Additional information on nitrification can be found in (Kirmeyer et,
al. 1995), "Nitrification Occurrence and Control in Chloraminated Water
Systems."

**Factors.** Several possible factors have been implicated as
contributing to nitrification. These factors include low
chlorine-to-ammonia ratio, long detention times, and temperatures
(Cowman and Singer, 1994). Though some articles noted that low
monochloramine dosages may lead to nitrification, other research has
reported nitrification occurring at monochloramine concentrations
greater than 5.0 mg/L (Cowman and Singer, 1994). Nitrifying bacteria are
relatively more resistant to disinfection by monochloramine than free
chlorine (Cowman and Singer, 1994). The optimum conditions for
nitrification would be a water system with free-ammonia, a pH of 7.5 to
8.5, a water temperature of 25 to 30^o^C, and a dark environment.
Nitrifying bacteria exhibit slow growth and have been found in higher
numbers in the sediment of distribution systems than in the biofilm
(Cowman and Singer, 1994).

If the water reservoirs in the distribution system are covered, partial
nitrification may occur (White, 1992). Nitrification occurred in two of
MWDSC's covered reservoirs (Garvey and Orange County reservoirs) after
the changeover. Approximately 10 weeks after the changeover from
chlorine to chloramine, water quality degradation was occurring in the
Garvey Reservoir. MWDSC increased the amounts of free chlorine added to
the plant effluent to maintain a 1.5 mg/L monochloramine residual at the
reservoir effluent and the chlorine to ammonia ratio was increased from
3:1 to 4:1 to decrease the amount of excess ammonia in the water. These
changes were more effective than the flushing programs for the
distribution system, which only helped temporarily.

**Control Measures.** Nitrification may pose a potential problem for any
utility using monochloramine as a disinfectant (Cowman and Singer,
1994). Thus, nitrification should be carefully assessed and controlled.
Nitrification may be controlled by monitoring at strategic locations
throughout the distribution system for monochloramine and dichloramine
residuals (White, 1992).

The chloramine free residual stability is increased throughout the
distribution system when there is increased control of microbial
contaminants and decreased bacterial concentrations in the raw water to
acceptable levels. Recommended approaches to prevent and control
nitrification in the distribution system include (Cowman and Singer,
1994):

-   Decreasing the detention time;

-   Increasing the pH;

-   Decreasing the temperature;

-   Decreasing TOC concentrations;

-   Increasing chloramines residual;

-   Increasing the chlorine-to-ammonia ratio; and

-   Decreasing the excess ammonia concentration.

For the distribution system, the system should be evaluated to identify
the low-flow or dead-end sections. The detention times in the system
should be operationally minimized (Skadsen, 1993). For reservoirs, those
with single inlet-outlet configurations should especially be carefully
monitored and operated (Skadsen, 1993).

MWDSC stresses the importance of developing nitrification strategy
control measures. In particular, a comprehensive monitoring program
should be established to alert personnel to implement control measures
when required. To control nitrification, MWDSC developed a control
strategy where the reservoirs and distribution system were first sampled
for nitrite levels (Skadsen, 1993). MWDSC also decreased the detention
times in reservoirs and distribution systems, especially during warmer
weather, which helped to keep nitrite levels down.

The chloramination operation was modified to add more chlorine to the
reservoir inlet and increase the chlorine-to-ammonia ratio from 3:1 to
5:1 at the plant effluent. The initial 3:1 ratio corresponded with a 1.5
mg/L monochloramine residual and 0.2 mg/L excess ammonia. At these
concentrations, the agencies receiving the water had the flexibility of
blending the chloraminated water with chlorinated water or adding more
chlorine to those sections of the system with long detention times.
Increasing the ratio further to 5:1 controlled the nitrification problem
by decreasing the amount of free ammonia in the distribution system.
Operating at a 5:1 ratio requires more monitoring since an overdose of
chlorine can reduce the chloramine residual.

A survey of chloramine users in the United States was conducted in June
1991. This survey showed that the chlorine to ammonia ratio varied from
3:1 to 7:1 (Dennis, et al, 1991). The chloramine residual varied from
0.8 mg/L to 3 mg/L (Dennis, et al, 1991). Table 6-7 shows the results
from this survey. The agencies surveyed reported excellent results with
secondary chloramine disinfection (Dennis et al, 1991). EPA is in the
process of collecting and evaluating chloramine use in the United States
as part of the Information Collection Rule (ICR), but until those data
are available, the 1991 survey appears to be the most recent national
survey of chloramine use.

Each year, MWDSC also added chlorine past the breakpoint to allow a free
residual for 30 days. The ideal locations for breakpoint chlorination
are at the distribution reservoirs and interconnections. The increased
chlorine oxidizes any nitrite and nitrifying bacteria and eliminates the
excess ammonia in the distribution system. For larger water systems,
MWDSC recommends maintaining chlorination stations throughout the
distribution system. Both fixed and mobile chlorinators may be used.
Mobile chlorinator units are self-contained and trailer-mounted with
evaporators, chlorinators, generator, a booster pump for transport
water, and chlorine injectors. They are designed to draw liquid chlorine
directly from a 17-ton chlorine trailer and to inject a chlorine
solution into the distribution system or reservoir.

Since nitrifying bacteria were found in higher numbers in the sediments
of the distribution system than in the biofilm, flushing sediment from
the system will help to control nitrification. The addition of a
disinfectant (i.e., free or combined chlorine) is required to remove
nitrification.

At the Indiana American Water Company, the distribution system is
temporarily converted back to free chlorine for scheduled flushing (Lyn
et al., 1995). Utilities should evaluate their flushing program to avoid
consumer complaints with inappropriate flushing techniques.

#### Taste and Odor

If the chlorine to ammonia-nitrogen ratios are between 3:1 and 5.5:1,
disagreeable tastes and odors should be evaluated at the consumer tap
(White, 1992).

Fishy tastes and odors (e.g., from source waters and return washwater
from the washwater treatment system) can be controlled by a 1-hour
contact time with free-chlorine residual of 2 mg/L prior to the addition
of ammonia (Dennis et al., 1991). This prechlorination eliminates the
fishy taste and odor but may increase the THM concentrations at the
plant effluent.

[]{#__RefHeading___Toc450036323 .anchor}Table 6-7. Survey of Chloramine
Users in the United States

+---------+--------+--------+-------+---------+----------+-----------+
| **A     | **Tre  | **Type | *     | **Chl   | **NH~3~  | **Nitr    |
| gency** | atment | of     | *Chlo | oramine | I        | ification |
|         | Capa   | Amm    | rine: | R       | njection | Control   |
|         | city** | onia** | Am    | esidual | Point**  | Str       |
|         |        |        | monia | (       |          | ategies** |
|         |        |        | Nit   | mg/L)** |          |           |
|         |        |        | rogen |         |          |           |
|         |        |        | ra    |         |          |           |
|         |        |        | tio** |         |          |           |
+=========+========+========+=======+=========+==========+===========+
| City of | 730    | Anh    | 5:1   | 2.1 -   | Pr       | None      |
| Dallas, | mgd;   | ydrous |       | 2.3     | esedimen |           |
| TX      |        |        |       |         | ta-tion, |           |
|         | 3      |        |       |         | Post-fi  |           |
|         | plants |        |       |         | ltration |           |
+---------+--------+--------+-------+---------+----------+-----------+
| City of | 600    | A      | 3:1   | 0.8 -   | Post-fil | None      |
| Denver, | mgd;   | queous |       | 1.0     | tration, |           |
| CO      |        | (30%)  |       |         | prior to |           |
|         | 3      |        |       |         | chlorine |           |
|         | plants |        |       |         | addition |           |
+---------+--------+--------+-------+---------+----------+-----------+
| Indian  | 176    | Anh    | 3:1   | 1.5 -   | Post-fi  | Increase  |
| apolis, | mgd;   | ydrous | v     | 2.0     | ltration | ratio in  |
| Water   |        |        | aries |         |          | summer    |
| Co., IN | 4      |        |       |         |          |           |
|         | plants |        |       |         |          |           |
+---------+--------+--------+-------+---------+----------+-----------+
| Mia     | 300    | Anh    | 5:1   | 2.7 -   | 10 ft    | 2 weeks   |
| mi-Dade | mgd;   | ydrous |       | 3.0     | after    | free      |
| Water   |        |        |       |         | chlorine | chlorine  |
| Aut     | 3      |        |       |         | flash    | every     |
| hority, | plants |        |       |         | mix      | November  |
| FL      |        |        |       |         |          |           |
+---------+--------+--------+-------+---------+----------+-----------+
| City of | 305    | Anh    | 5:1   | 0.8 -   | Post-fi  | None      |
| Mil     | mgd;   | ydrous |       | 0.9     | ltration |           |
| waukee, |        |        |       |         |          |           |
| WI      | 2      |        |       |         |          |           |
|         | plants |        |       |         |          |           |
+---------+--------+--------+-------+---------+----------+-----------+
| City of | 530    | A      | 3:1   | 2.0     | Post-fi  | None      |
| Philad  | mgd;   | queous |       |         | ltration |           |
| elphia, |        | (30%)  |       |         |          |           |
| PA      | 3      |        |       |         |          |           |
|         | plants |        |       |         |          |           |
+---------+--------+--------+-------+---------+----------+-----------+
| City of | 225    | Anh    | 7:1   | 1.8     | 70 ft    | None      |
| Po      | mgd    | ydrous |       |         | do       |           |
| rtland, |        |        |       |         | wnstream |           |
| OR      |        |        |       |         | of       |           |
|         |        |        |       |         | chlorine |           |
|         |        |        |       |         | in       |           |
|         |        |        |       |         | conduit  |           |
+---------+--------+--------+-------+---------+----------+-----------+
| Orleans | 300    | Anh    | 3:1   | 2.0 -   | Pre-fi   | None      |
| Parish, | mgd;   | ydrous |       | 2.5     | ltration |           |
| LA      |        |        |       |         |          |           |
|         | 2      |        |       |         |          |           |
|         | plants |        |       |         |          |           |
+---------+--------+--------+-------+---------+----------+-----------+
| St.     | 360    | A      | 4:1   | 2.5     | Co       | None      |
| Louis   | mgd;   | queous |       |         | ncurrent |           |
| Co.     |        | (30%)  |       |         | with     |           |
| Water   | 4      |        |       |         | chlorine |           |
| Aut     | plants |        |       |         | at flash |           |
| hority, |        |        |       |         | mix,     |           |
| MO      |        |        |       |         |          |           |
|         |        |        |       |         | post-fi  |           |
|         |        |        |       |         | ltration |           |
+---------+--------+--------+-------+---------+----------+-----------+

Source: Dennis et al.,1991.

### Special Considerations for Chloramination Facilities

#### GAC Filters with Ammonia Addition

The Ann Arbor Water Treatment Plant in Michigan is a 50 mgd lime
softening plant that draws its water from the Huron River (80 to 90
percent) and ground water (10 to 20 percent). When chloramination is
applied to the river water, the chlorine is injected into the raw water
line immediately before ammonia is applied. The total chlorine feed
averages 3.3 mg/L with an average demand of 2.0 mg/L for the river
water.

Evidence of nitrification occurred immediately after a change in
treatment from sand to GAC filtration. Prior to the change to GAC, the
treatment plant had successfully used monochloramine as both a primary
and a final disinfectant. Nitrification was not evident. The GAC
received an application of approximately 1.3 mg/L ammonia. This input of
ammonia to the filters constituted a nutrient source that allowed
nitrifying bacteria to become established and proliferate. The GAC
particles have been observed to harbor nitrifying bacteria and
nitrification has been observed in GAC beds. Higher nitrifying bacteria
levels have been observed in other filter beds as compared with source
water. The GAC effluent also showed pronounced seasonal peaks in HPC
bacteria from May to July, and percent total coliforms positive from
July to August. These seasonal peaks are most probably temperature
related. During periods of nitrification, GAC effluent HPC bacteria
concentration was steadily decreasing while in the distribution system,
HPC bacteria were increasing.

#### Organic Nitrogen

Concentrations of organic nitrogen and ammonia nitrogen as low as 0.3
mg/L may interfere with the chloramination process. The monochloramine
residuals will hydrolyze with the organic nitrogen to form
organochloramines, which are nongermicidal. This reaction would take
about 30 to 40 minutes. After the monochloramine residuals disappear,
free ammonia nitrogen reappears. Free ammonia nitrogen is a powerful
biological nutrient. Its presence promotes biological instability in
that portion of the distribution system. Biological instability usually
results in foul tastes and odors plus dirty and/or colored water at the
consumers tap (White, 1992).

The free chlorine residual or chloramine residual method may be used to
clean an area with biological instability. Of the two methods, the free
chlorine residuals method is superior (White, 1992). Free chlorine
residuals restore distribution system stability quicker (i.e., a few
days for free chlorine versus weeks for chloramines), the clean-up
process can be monitored, and the clean-up is complete when the free
chlorine residual concentration reaches 85 percent of the free chlorine
concentration.

Based on their conversion to chloramination experience, MWDSC recommends
that utilities employing chloramines for disinfection monitor for total
organic nitrogen levels. When levels are high, the amino acid fraction
is also likely to rise. This rise may impair the chloramination
disinfection efficiency if high levels of organic nitrogen are not
detected.

#### Mixing

Mixing at the point of application greatly affected the bactericidal
efficiency of the chloramine process. When the pH of the water is
between 7 and 8.5, the reaction time between ammonia and chlorine is
practically instantaneous. If chlorine is mixed slowly into the
ammoniated water, organic matter, especially organic matter prone to
bleaching with chlorine solution, may react with the chlorine and
interfere with chloramine formation (White, 1992).

#### Blending Waters

When chlorinated water is blended with chloraminated water, the
chloramine residual will decrease after the excess ammonia has been
combined and monochloramine is converted to dichloramine and nitrogen
trichloride. The entire residual can be depleted. Therefore, it is
important to know how much chlorinated water can be blended with a
particular chloraminated water stream without significantly affecting
the monochloramine residual. Blended residual curves should be developed
for each specific blend.

#### Corrosion

Chloramination and corrosion control can limit bacterial biofilm
development in the distribution system. If optimum corrosion of iron
pipes is not controlled, the chloramination efficiency may be impacted.
Corrosion inhibitors with higher phosphate concentrations may reduce
corrosion rates (Lyn et al., 1995).

#### Formation of Nitrogen Trichloride

If water in the distribution system tends to form nitrogen trichloride,
the finished water should be subjected to post-aeration, which readily
removes nitrogen trichloride (White, 1992). Nitrogen trichloride is also
readily destroyed by sunlight (White, 1992).

#### Human Health and the Environment

Users of kidney dialysis equipment are the most critical group that can
be impacted by chloramine use. Chloramines can cause methemoglobinemia
and adversely affect the health of kidney dialysis patients if
chloramines are not removed from the dialysate water. Chloramines can
also be deadly to fish. The residuals can damage the gill tissues, enter
the red blood cells, and cause an acute blood disorder. Chloramine
residuals should be removed from the water prior to the water contacting
any fish. As such, fish hobbyists should be notified, along with pet
stores and aquarium supply establishments.

## Summary

### Advantages and Disadvantages of Chloramine Use

The following list highlights selected advantages and disadvantages of
using chloramines as a disinfection method for drinking water
(Masschelein, 1992). Because of the wide variation of system size, water
quality, and dosages applied, some of these advantages and disadvantages
may not apply to a particular system.

**Advantages**

-   Chloramines are not as reactive with organics as free chlorine in
    forming DBPs.

-   The monochloramine residual is more stable and longer lasting than
    free chlorine or chlorine dioxide, thereby providing better
    protection against bacterial regrowth in systems with large storage
    tanks and dead end water mains. However excess ammonia in the
    network may cause biofilming.

-   Because chloramines do not tend to react with organic compounds,
    many systems will experience less incidence of taste and odor
    complaints when using chloramines.

-   Chloramines are inexpensive.

-   Chloramines are easy to make.

**Disadvantages**

-   The disinfecting properties of chloramines are not as strong as
    other disinfectants, such as chlorine, ozone, and chlorine dioxide.

-   Chloramines cannot oxidize iron, manganese, and sulfides.

-   When using chloramine as the secondary disinfectant, it may be
    necessary to periodically convert to free chlorine for biofilm
    control in the water distribution system.

-   Excess ammonia in the distribution system may lead to nitrification
    problems, especially in dead ends and other locations with low
    disinfectant residual.

-   Monochloramines are less effective as disinfectants at high pH than
    at low pH.

-   Dichloramines have treatment and operation problems.

-   Chloramines must be made on-site.

### Summary Table

Table 6-8 summarizes the considerations for the use of chloramine.

[]{#__RefHeading___Toc450036324 .anchor}Table 6-8. Summary of Chloramine
Disinfection

+--------------+-------------------------------------------------------+
| **Con        | **Description**                                       |
| sideration** |                                                       |
+==============+=======================================================+
| Generation   | Chloramines are generated by the sequential addition  |
|              | of chlorine (hypochlorous acid) and ammonia at a      |
|              | Cl~2~ to NH~3~ ratio ranging from of 3:1 to 5:1.      |
|              | Either chlorine or ammonia may be added first.        |
|              | Chlorine is normally added first to act as the        |
|              | primary disinfectant and after 10 to 30 minutes,      |
|              | ammonia is added to prevent further formation of      |
|              | DPBs.                                                 |
|              |                                                       |
|              | The most common methods of chlorine addition include  |
|              | gas feed using a dilution water eduction system or    |
|              | direct feed of bulk hypochlorite solution (12 percent |
|              | typical commercial strength).                         |
|              |                                                       |
|              | The most common ammonia feed facilities include       |
|              | anhydrous ammonia fed either directly or via a        |
|              | dilution water eduction system or direct feed of bulk |
|              | aqua ammonia solution (20 percent typical commercial  |
|              | strength).                                            |
+--------------+-------------------------------------------------------+
| Primary uses | Monochloramine is used primarily as a secondary       |
|              | disinfectant to provide a residual in the             |
|              | distribution system. It is used where elevated DBPFP  |
|              | levels in the treated water can cause high levels of  |
|              | DBP formation in the distribution system if free      |
|              | chlorine is used as the secondary disinfectant.       |
|              | Monochloramine has been found to be more effective    |
|              | than free chlorine in controlling biofilms and        |
|              | coliform bacteria in systems with long detention      |
|              | times due the lower decay rate of chloramine.         |
|              | Monochloramine will have much less tendency to react  |
|              | with organics present and hence will form less taste  |
|              | and odor causing compounds.                           |
+--------------+-------------------------------------------------------+
| Inactivation | At pH 7 and below, free chlorine is 200, 200, 50, and |
| efficiency   | 2.5 times more effective in inactivating bacteria,    |
|              | viruses, spores, and cysts respectively than          |
|              | monochloramine.                                       |
+--------------+-------------------------------------------------------+
| Byproduct    | Monochloramine substantially reduces the DBP          |
| formation    | formation but still forms some DBPs.                  |
+--------------+-------------------------------------------------------+
| Limitations  | Monochloramine is increasingly being used as a        |
|              | secondary disinfectant to provide a residual in       |
|              | distribution systems because of its lower decay rate  |
|              | then free chlorine and lesser tendency to form DBPs.  |
|              |                                                       |
|              | Caution should be used in using monochloramine in     |
|              | distribution systems where water sources using free   |
|              | chlorine residual are also used. High Cl~2~ to N      |
|              | ratios can occur where waters using different         |
|              | residuals combine leading to the possible formation   |
|              | of taste and odor causing dichloramine and nitrogen   |
|              | trichloride. In some cases the residual maybe         |
|              | completely removed by the breakpoint reaction.        |
+--------------+-------------------------------------------------------+
| Point of     | Monochloramine is normally generated at the treatment |
| application  | facility with the addition of ammonia to chlorinated  |
|              | water. Ammonia is normally added prior to the pumping |
|              | into the distribution system. In some cases, ammonia  |
|              | is added prior to the clearwell to minimize formation |
|              | of DBPs by free chlorine residual.                    |
+--------------+-------------------------------------------------------+
| Special      | Nitrification and generation of bacterial growths can |
| co           | occur if the Cl~2~ to N ratio is too low and          |
| nsiderations | conditions exist for the growth of nitrifying         |
|              | bacteria. A minimum residual of 2.0 mg/L of           |
|              | monochloramine has been found effective in            |
|              | controlling nitrification in most systems.            |
+--------------+-------------------------------------------------------+

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Chloramines [6-1](#chloramines)

6.1 Chloramines Chemistry [6-1](#chloramines-chemistry)

6.1.1 Equilibrium, Kinetic, and Physiochemical Properties
[6-1](#equilibrium-kinetic-and-physiochemical-properties)

6.2 Generation [6-3](#generation)

6.2.1 Chlorine Feed Facilities [6-4](#chlorine-feed-facilities)

6.2.2 Ammonia Feed Facilities [6-5](#ammonia-feed-facilities)

6.3 Primary Uses and Points of Application
[6-10](#primary-uses-and-points-of-application)

6.3.1 Primary Uses [6-10](#primary-uses)

6.3.2 Points of Application [6-11](#points-of-application)

6.4 Pathogen Inactivation and Disinfection Efficacy
[6-12](#pathogen-inactivation-and-disinfection-efficacy)

6.4.1 Inactivation Mechanisms [6-12](#inactivation-mechanisms)

6.4.2 Environmental Effects [6-12](#environmental-effects)

6.4.3 Disinfection Efficacy [6-13](#disinfection-efficacy)

6.5 DBP Formation [6-15](#dbp-formation)

6.6 Status of Analytical Methods [6-16](#status-of-analytical-methods)

6.6.1 Monitoring of Chloramines [6-16](#monitoring-of-chloramines)

6.6.2 Disinfectant Interferences [6-17](#disinfectant-interferences)

6.6.3 Chloramine Monitoring for Systems Using Chloramines
[6-19](#chloramine-monitoring-for-systems-using-chloramines)

6.7 Operational Considerations [6-20](#operational-considerations)

6.7.1 Conversion to Chloramination from Chlorination
[6-20](#conversion-to-chloramination-from-chlorination)

6.7.2 Potential Operational Impacts from Chloramination Disinfection
[6-22](#potential-operational-impacts-from-chloramination-disinfection)

6.7.3 Special Considerations for Chloramination Facilities
[6-25](#special-considerations-for-chloramination-facilities)

6.8 Summary [6-27](#summary)

6.8.1 Advantages and Disadvantages of Chloramine Use
[6-27](#advantages-and-disadvantages-of-chloramine-use)

6.8.2 Summary Table [6-28](#summary-table)

6.9 References [6-29](#references)

Table 6-1. Chlorine Dose Required for NH~3~ - Cl~2~ Reaction
[6-3](#__RefHeading___Toc450036317)

Table 6-2. Time to 99 Percent Conversion of Chlorine to Monochloramine
[6-4](#__RefHeading___Toc450036318)

Table 6-3. Methods of Chlorine Addition
[6-4](#__RefHeading___Toc450036319)

Table 6-4. CT Values for *Giardia* Cyst Inactivation Using Chloramines
[6-15](#__RefHeading___Toc450036320)

Table 6-5. CT Values for Virus Inactivation Using Chloramines
[6-15](#__RefHeading___Toc450036321)

Table 6-6. Characteristics and Comparisons of Monochloramine^a^
Analytical Methods [6-18](#__RefHeading___Toc450036322)

Table 6-7. Survey of Chloramine Users in the United States
[6-25](#__RefHeading___Toc450036323)

Table 6-8. Summary of Chloramine Disinfection
[6-29](#__RefHeading___Toc450036324)

Figure 6-1. Theoretical Breakpoint Curve [6-2](#_Ref396018230)

Figure 6-2. Distribution Diagram for Chloramine Species with pH
[6-3](#__RefHeading___Toc450036326)

Figure 6-3. Gaseous Chlorine Feed System [6-5](#_Ref396019666)

Figure 6-4. Hypochlorite Feed System [6-6](#__RefHeading___Toc450036328)

Figure 6-5. Anhydrous Ammonia Direct Feed System [6-7](#_Ref396019886)

Figure 6-6. Anhydrous Ammonia Solution Feed System [6-8](#_Ref396019900)

Figure 6-7. Aqua Ammonia Feed System [6-9](#_Ref396034569)