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

## Objective of this Manual

Chlorine is, by far, the most commonly used disinfectant in the drinking
water treatment industry (Sawyer et al., 1994). Today, chlorine is used
as a primary disinfectant in the vast majority of all surface water
treatment plants, being used as a pre-disinfectant in more than 63
percent and as a post-disinfectant in more than 67 percent of all
surface water treatment plants (USEPA, 1997). This manual is organized
to provide technical data and engineering information on disinfectants
that are not as widely used as chlorine. Also, where applicable, this
document describes the use of these disinfectants as oxidants and any
associated implications.

The U.S. Environmental Protection Agency (EPA) encourages utilities to
examine all aspects of their current disinfection practices to identify
opportunities to improve the quality of the finished water without
reducing microbial protection. The objective of this guidance manual is
to describe alternative disinfectants and disinfection techniques that
may be used to comply with both the Stage 1 Disinfectants and
Disinfection Byproducts Rule (DBPR) and Interim Enhanced Surface Water
Treatment Rule (IESWTR) and highlight advantages and disadvantages of
their use.

EPA is not recommending that utilities employ the disinfectants and
oxidants discussed in this manual, nor is it advocating that utilities
switch from one disinfectant or oxidant to another. EPA acknowledges
that selection of the most appropriate disinfection technique is a
site-specific decision best left to utility personnel and state
agencies. Utilities should use this guidance as an information resource
to assist in the selection of appropriate disinfectants and disinfectant
schemes to meet their specific goals. Extensive bench and/or pilot scale
testing and a thorough review of regulatory requirements should precede
changes to disinfection practice. Systems should refer to the Guidance
Manual for Compliance with the Filtration and Disinfection Requirements
for Public Works Systems Using Surface Water Sources (AWWA, 1991) to
ensure disinfectant schemes meet regulatory log inactivation
requirements. Utilities should also refer to EPA\'s *Disinfection
Profiling and Benchmarking Guidance Manual* (currently in production) to
ensure compliance with the new regulatory requirements of the IESWTR.

This chapter presents a brief discussion of the background and
regulatory context of alternative disinfectants, including an overview
of the disinfection profiling and benchmarking approach to evaluate
disinfection efficiency. In addition, a decision-making framework is
provided that utilities can employ to assess the applicability of
various disinfectants and disinfection strategies for individual
systems. Chapter 2 presents an overview of disinfection, including the
use of chlorine, with the next six chapters of this manual devoted to
each of the following alternative disinfectants and oxidants:

-   ***Chapter 3*** - Ozone (O~3~);

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-   ***Chapter 4*** - Chlorine dioxide (ClO~2~);

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-   ***Chapter 5*** - Potassium permanganate (KMnO~4~);

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-   ***Chapter 6*** - Chloramine (NH~2~Cl);

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-   ***Chapter 7*** - Ozone/hydrogen peroxide combinations
    (O~3~/H~2~O~2~); and

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-   ***Chapter 8*** - Ultraviolet radiation (UV).

For each disinfectant, this guidance manual describes the chemistry
specific to the disinfection or oxidation process, generation, primary
uses and points of application, disinfection byproduct (DBP) formation,
pathogen inactivation and disinfection efficacy, the status of
analytical methods for residual monitoring, and operational
considerations. Chapter 9 provides similar information regarding the use
of combined disinfectants. A summary of existing disinfectant usage in
the United States is provided in Appendix A. Cost estimates for the use
of alternative disinfectants are provided in Appendix B.

## Background

The most important use of disinfectants in water treatment is to limit
waterborne disease and inactivate pathogenic organisms in water
supplies. The first use of chlorine as a continuous process in water
treatment was in a small town in Belgium in the early 1900s (White,
1992). Since introduction of filtration and disinfection at water
treatment plants in the United States, waterborne diseases such as
typhoid and cholera have been virtually eliminated. For example, in
Niagara Falls, NY between 1911 and 1915, the number of typhoid cases
dropped from 185 deaths per 100,000 population to nearly zero following
introduction of filtration and chlorination (White, 1986).

In 1974, researchers in the Netherlands and the United States
demonstrated that trihalomethanes (THMs) are formed as a result of
drinking water chlorination (Rook, 1974; Bellar et al., 1974). THMs are
formed when chlorine or bromide reacts with organic compounds in the
water. EPA subsequently conducted surveys confirming widespread
occurrence of THMs in chlorinated water supplies in the United States
(Symons et al., 1975; USEPA, 1978). THMs and other DBPs have been shown
to be carcinogenic, mutagenic, etc. These health risks may be small, but
with the large population exposed, need to be taken seriously.

As a result of DBP concerns from chlorine, EPA, as well as the water
treatment industry, placed more emphasis on the use of disinfectants
other than chlorine. Some of these alternative disinfectants, however,
have also been found to produce DBPs as a result of either reactions
between disinfectants and compounds in the water or as a natural decay
product of the disinfectant itself (McGuire et al., 1990; Legube et al;
1989). These DBPs include:

-   Halogenated organics, such as THMs, haloacetic acids, haloketones,
    and others, that are produced primarily as a result of chlorination.

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-   Organic oxidation byproducts such as aldehydes, ketones, assimilable
    organic carbon (AOC), and biodegradable organic carbon (BDOC), that
    are associated primarily with strong oxidants such as ozone,
    chlorine, and advanced oxidation; and

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-   Inorganics such as chlorate and chlorite, associated with chlorine
    dioxide, and bromate, that is associated with ozone, and has also
    has been found when chlorine dioxide is exposed to sunlight.

As documented in this manual, the type and amount of DBPs produced
during treatment depends largely on disinfectant type, water quality,
treatment sequences, contact time, and environmental factors such as
temperature and pH.

When considering the use of alternative disinfectants, systems should
ensure that the inactivation of pathogenic organisms is not compromised.
Pathogens pose an immediate critical public health threat due to the
risk of an acute disease outbreak. Although most identified public
health risks associated with DBPs are chronic, long-term risks, many
systems will be able to lower DBP levels without compromising microbial
protection.

## Regulatory Context

Pursuant to requirements of the Safe Drinking Water Act (SDWA)
Amendments of 1996, EPA is developing interrelated regulations to
control microbial pathogens and disinfectant residuals and disinfection
byproducts in drinking water. These rules are collectively known as the
microbial/disinfection byproducts (M-DBP) rules and are intended to
address complex risk trade-offs between the desire to inactivate
pathogens found in water and the need to reduce chemical compounds
formed as byproducts during disinfection. The rules are being
promulgated in two phases.

As part of the first phase, the Stage 1 DBPR and the IESWTR were
promulgated on December 16, 1998 (63 FR 69390 and 63 FR 69478,
respectively). The Stage 1 DBPR applies to all community water systems
(CWS) and non-transient, non-community water systems (NTNCWS) that treat
their water with a disinfectant for either primary or residual
treatment. The IESWTR amends the Surface Water Treatment Rule (SWTR) and
includes new and more stringent requirements to control waterborne
pathogens including specifically the protozoan *Cryptosporidium.* The
IESWTR applies to all public water systems that use surface water, or
ground water under the direct influence of surface water as defined at
40 CFR, Part 141, Subpart H[^1], and that serve at least 10,000 people.

Three future rules, also included in phase one include the Long-Term 1
Enhanced Surface Water Treatment Rule (LT1ESWTR), the Ground Water Rule
(GWR), and the Filter Backwash Rule (FBR). Each of these rules are
planned for promulgation in November 2000. The LT1ESWTR will address
pathogen inactivation and removal requirements for Subpart H systems
serving fewer than 10,000 people. The GWR will specify appropriate
disinfection techniques, including the use of best management practices
(BMPs) and source control measures. The FBR will set a standard for
filter backwash recycling for all public water systems regardless of
size.

The second phase, consisting of the Stage 2 DBPR and the Long-Term 2
ESWTR, will be promulgated in the year 2002 and will revisit the
regulations for the formation of DBPs for all systems and the
inactivation and removal of pathogens for surface water systems,
respectively.

The projected dates for future M-DBP regulatory activities are
summarized in Table 1-1.

[]{#__RefHeading___Toc448641910 .anchor}Table 1-1. Key Dates for
Regulatory Activities

  ----------------- -----------------------------------------------------
  **Date**          **Regulatory Action**

  November 2000     Promulgate Long-Term 1 Enhanced Surface Water
                    Treatment Rule

  November 2000     Promulgate Ground Water Rule

  November 2000     Promulgate Filter Backwash Rule

  May 2002          Promulgate Stage 2 Disinfectants and Disinfection
                    Byproduct Rule

  May 2002          Promulgate Long-Term 2 Enhanced Surface Water
                    Treatment Rule
  ----------------- -----------------------------------------------------

Concurrent with the M-DBP rules, in May 1996, EPA promulgated the
Information Collection Rule (ICR) to obtain data on source water
quality, byproduct formation, and drinking water treatment plant design
and operations. The ICR applies to Subpart H systems serving more than
100,000 people and ground water systems serving more than 50,000 people.
EPA intended to use data from the ICR to address completely the complex
trade-offs between chronic DBP health risks and acute pathogenic health
risks, but delays in promulgation of the ICR eliminated this potential
data source for use in the IESWTR. Until the ICR data are analyzed in
detail, EPA cannot fully address the issue of DBP and pathogenic risk
trade-offs.

National Primary and Secondary Drinking Water Regulations, published in
40 CFR Parts 141 and 143, respectively, limit the amount of specific
contaminants and residual disinfectants and classes of these compounds
that are delivered to users of public water systems. These limits are
expressed as follows:

-   **Maximum Contaminant Level Goals (MCLGs).** MCLGs are
    non-enforceable health goals for public water systems. MCLGs are set
    at levels that, in the EPA Administrator's judgment, allow no known
    or anticipated adverse effect on the health of persons to occur and
    that allow an adequate margin of safety.

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-   **Maximum Residual Disinfectant Level Goals (MRDLGs).** As with
    MCLGs, EPA has established MRDLGs for disinfectants at levels at
    which no known or anticipated adverse effects on the health of
    persons occur and that allow an adequate margin of safety. MRDLGs
    are non-enforceable health goals based only on health effects and
    exposure information and do not reflect the benefit of the addition
    of the chemicals for control of waterborne microbial contaminants.

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-   **Maximum Contaminant Levels (MCLs).** MCLs are enforceable
    standards set as close to the MCLGs as technically and economically
    feasible.

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-   **Maximum Residual Disinfectant Levels (MRDLs).** MRDLs are similar
    to MCLs. MRDLs are enforceable standards, analogous to MCLs, that
    recognize the benefits of adding a disinfectant to water on a
    continuous basis and of addressing emergency situations such as
    distribution system pipe ruptures. As with MCLs, EPA has set the
    MRDLs as close to the MRDLGs as feasible.

In November 1979, the EPA set an interim MCL for Total THMs (TTHMs) of
0.10 mg/L as an annual average for systems serving at least 10,000
people. This standard was based on the need to reduce THM levels due to
suspected carcinogenicity. Since then, EPA has developed and promulgated
standards for numerous contaminants. As of the December 16, 1998 DBPR
promulgation, MCLGs, MCLs, MRDLGs, and MRDLs are as presented in Tables
1-2 through 1-4. As included in these tables, the December 16, 1998
Stage 1 DBPR:

-   Lowered the existing MCL for TTHMs from 0.10 mg/L to 0.080 mg/L;

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-   Extended the MCL for TTHMs to all size systems;

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-   Requires enhanced coagulation or enhanced precipitative softening
    for certain systems;

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-   Established MRDLs and MRDLGs for chlorine, chloramine, and chlorine
    dioxide;

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-   Established MCLs for haloacetic acid (five) (HAA5), bromate, and
    chlorite, and

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-   Established MCLGs for eight disinfection byproducts.

Further, the SWTR of 1989 requires 3.0-log inactivation for *Giardia*
cysts and 4.0-log inactivation for viruses in surface water supplies. To
meet these goals, the SWTR established treatment requirements for
filtration and disinfection. As shown in Table 1-5, these goals can be
met using various treatment schemes that include filtration and
disinfection. The IESWTR requires a 2.0 log removal of *Cryptosporidium*
for Subpart H systems serving at least 10,000 people.

[]{#__RefHeading___Toc448641911 .anchor}Table 1-2. Primary Drinking
Water Regulations Related to Microbiological Contaminants

  --------------- ---------- ---------- ------------- -------------------- ---------------------
  **Compound**    **MCLG\    **MCL\     **Potential                        **Sources of Drinking
                  (mg/L)**   (mg/L)**   Health                             Water Contamination**
                                        Effects**                          

  *Giardia        Zero       TT^1^                    Gastroenteric        Human and animal
  lamblia*                                            disease              fecal waste

  *Legionella*    Zero       TT                       Legionnaire's        Common bacteria in
                                                      disease              natural waters; can
                                                                           proliferate in water
                                                                           heating systems

  Heterotrophic   N/A        TT                       Indicates water      
  Plate Count                                         quality,             
                                                      effectiveness of     
                                                      treatment            

  Total Coliform  Zero       \< 5.0%^2^               Indicates potential  Human and animal
                                                      presence of          fecal waste
                                                      gastroenteric        
                                                      pathogens            

  Turbidity       N/A        TT                       Indicates water      Particles from storm
                                                      treatment failure    runoff, discharges
                                                      and pathogens in     into source water,
                                                      drinking water       and erosion

  Viruses         Zero       TT                       Gastroenteric        Human and animal
                                                      disease              fecal waste
  --------------- ---------- ---------- ------------- -------------------- ---------------------

> Source: AWWA Internet, 1997.
>
> ^1^TT = Treatment technique requirement in lieu of MCL as established
> in 40 CFR §141.70.
>
> ^2^ No more than 5.0 percent positive if \>40 samples/month. No more
> than 1 positive if \<40 samples/month \[40 CFR §141.63(a) \].

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Table 1-3. Primary Drinking Water Regulations Related to Disinfection
Byproducts

  -----------------------------------------------------------------------------------
  **Compound**           **MCLG\    **MCL\     **Potential       **Sources of
                         (mg/L)**   (mg/L)**   Health Effects**  Drinking Water
                                                                 Contamination**
  ---------------------- ---------- ---------- ----------------- --------------------
  Bromate                Zero^3^    0.010^4^   Cancer            Ozonation byproduct

  Bromodichloromethane   Zero^3^    see TTHMs  Cancer, liver,    Drinking water
                                               kidney, and       chlorination and
                                               reproductive      chloramination
                                               effects           byproduct

  Bromoform              Zero^3^    see TTHMs  Cancer, nervous   Drinking water
                                               system, liver and ozonation,
                                               kidney effects    chloramination, and
                                                                 chlorination
                                                                 byproduct

  Chlorite               0.8^3^     1.0^4^     Hemolytic anemia  Chlorine dioxide
                                                                 disinfection
                                                                 byproduct

  Chloroform             Zero^3^    see TTHMs  Cancer, liver,    Drinking water
                                               kidney,           chlorination and
                                               reproductive      chloramination
                                               effects           byproduct

  Dibromochloromethane   0.06^3^    see TTHMs  Nervous system,   Drinking water
                                               liver, kidney,    chlorination and
                                               reproductive      chloramination
                                               effects           byproduct

  Dichloroacetic Acid    Zero^3^    See HAA5   Cancer and other  Drinking water
                                               effects           chlorination and
                                                                 chloramination
                                                                 byproduct

  Haloacetic Acids^1^    N/A        0.060^4^   Cancer and other  Drinking water
  (HAA5)                                       effects           chlorination and
                                                                 chloramination
                                                                 byproduct

  Trichloroacetic Acid   0.3^3^     See HAA5   Possibly cancer   Drinking water
                                               and reproductive  chlorination and
                                               effects           chloramination
                                                                 byproduct

  Total                  N/A        0.08^4^    Cancer and other  Drinking water
  Trihalomethanes^2^                           effects           chlorination and
  (TTHMs)                                                        chloramination
                                                                 byproduct
  -----------------------------------------------------------------------------------

Source: 63 *FR* 69390 (12/16/98)

^1^ HAA5 is the sum of the concentrations of mono-, di-, and
trichloroacetic acids and mono-and dibromoacetic acids.

^2^ Total Trihalomethanes are the sum of the concentrations of
bromodichloromethane, dibromochloromethane, bromoform, and chloroform.

^3^ Finalized on December 16, 1998 (63 FR 69390) as established in 40
CFR §141.53.

[]{#_Ref396703235 .anchor}^4^ Finalized on December 16, 1998 (63 FR
69390) as established in 40 CFR §141.64

Table 1-4. Primary Drinking Water Regulations Related to Residual
Disinfectants

  ---------------------- ------------------------ ------------------------
  **Disinfectant**       **MRDLG^3^\              **MRDL^4^\
                         (mg/L)**                 (mg/L)**

  Chlorine^1^            4 (as Cl~2~)             4.0 (as Cl~2~)

  Chloramine^2^          4 (as Cl~2~)             4.0 (as Cl~2~)

  Chlorine Dioxide       0.8 (as ClO~2~)          0.8 (as ClO~2~)
  ---------------------- ------------------------ ------------------------

> ^1^ Measured as free chlorine\
> ^2^ Measured as total chlorine

^3^ Finalized on December 16, 1998 (63 *FR* 69390) as established in 40
CFR §141.54.

^4^ Finalized on December 16, 1998 (63 *FR* 69390) as established in 40
CFR §141.65

[]{#__RefHeading___Toc448641914 .anchor}Table 1-5. Log
Removal/Inactivation through Filtration and\
Disinfection Required Under the SWTR

  ------------------------------------- ---------------- ----------------
  **Process**                           ***Giardia*      **Virus**
                                        cysts**          

  ***Total log removal/inactivation     ***3.0***        ***4.0***
  Required***                                            

  Conventional sedimentation/filtration 2.5\             2.0\
  credit\                               0.5              2.0
  Disinfection inactivation required                     

  Direct filtration credit\             2.0\             1.0\
  Disinfection inactivation required    1.0              3.0

  Slow sand filtration credit\          2.0\             2.0\
  Disinfection inactivation required    1.0              2.0

  Diatomaceous earth credit\            2.0\             1.0\
  Disinfection inactivation required    1.0              3.0

  No Filtration\                        0.0\             0.0\
  Disinfection inactivation required    3.0              4.0
  ------------------------------------- ---------------- ----------------

> Source: AWWA, 1991.
>
> Note: Some instances may require higher than 3 and 4 log removal.
> Also, some states may reduce removal filtration process.

### Disinfection Profiling and Benchmarking

The IESWTR establishes disinfection benchmarking as a procedure
requiring certain PWSs to evaluate the impact on microbial risk of
proposed changes in disinfection practice. It is designed to facilitate
utilities and States working together to assure that pathogen control is
maintained while the provisions of the Stage 1 DBPR are implemented.
This procedure involves a PWS charting daily levels of pathogen
inactivation for a period of at least one year to create a profile of
inactivation performance. The PWS then uses this profile to determine a
baseline or benchmark of inactivation against which proposed changes in
disinfection practices can be measured.

Systems are required to prepare a disinfection profile if either TTHM or
HAA5 levels are at least 0.064 or 0.048 mg/L, respectively, as an annual
average. These levels, equal to 80 percent of the MCLs established for
these compounds by the Stage 1 DBPR, are intended to include most
systems that will modify their disinfection practices to comply with the
Stage 1 DBPR. To determine applicability, systems that collected TTHM
and HAA5 data under the ICR must use the results of the last 12 months
of ICR monitoring unless the State determines there is a more
representative data set. Non-ICR systems may use existing TTHM and HAA5
data, if approved by the State, or must conduct TTHM and HAA5 monitoring
for four quarters. This monitoring must be completed no later than 15
months after promulgation of the IESWTR (i.e., by March, 2000).
Alternatively, systems can elect to forgo this monitoring if they
construct a disinfection profile.

A disinfection profile consists of a compilation of daily *Giardia
lamblia* log inactivations (plus virus inactivations for systems using
either chloramines or ozone for primary disinfection) computed over a
period of at least one year. It is based on daily measurements of
disinfectant residual concentration(s), contact time(s), temperature,
and pH. The profile may be developed using up to 3 years of existing
(i.e. grandfathered) data, if the State finds the data acceptable.
Systems having less than 3 years of acceptable grandfathered data are
required to conduct one year of monitoring to create the profile. This
monitoring must be complete within 27 months of IESWTR promulgation
(i.e., by March, 2001). The disinfection benchmark is equal to the
lowest monthly average inactivation level in the disinfection profile
(or average of low months for multi‑year profiles).

Any system required to develop a disinfection profile under the IESWTR
that decides to make a significant change to its disinfection practice
must consult with the State prior to making the change. Significant
changes in disinfection practice are defined as: 1) moving the point of
disinfection, not including routine seasonal changes, 2) changing the
type of disinfectant, 3) changing the disinfection process, and 4) other
modifications designated as significant by the State. As part of the
consultation process, the system must submit to the State the following
information: a description of the proposed change; the disinfection
profile for Giardia lamblia (and, if necessary, viruses) and benchmark;
and an analysis of how the proposed change will affect the current
levels of disinfection. In addition, the State is required to review the
disinfection profile a part of its periodic sanitary survey.

For more information on disinfection profiling and benchmarking, refer
to EPA's *Disinfection Profiling and Benchmarking Guidance Manual*
(expected to be available in 1999).

## Use of Disinfectants as Chemical Oxidants

Most disinfectants are strong oxidants and/or generate oxidants as
byproducts (such as hydroxyl free radicals) that react with organic and
inorganic compounds in water. While the primary focus of this manual is
disinfection, many of the disinfectants described in this manual are
also used for other purposes in drinking water treatment, such as taste
and odor control, improved flocculation, and nuisance control. Because
DBPs are produced irrespective of the intended purpose of the oxidant,
it is important to also address uses of disinfectants as oxidants in
water treatment. These additional uses are described in more detail in
Chapter 2.

## How Chlorine is Addressed in this Guidance Manual

This guidance manual does not provide as broad a discussion of chlorine
and chlorination practices as it does for the capabilities and uses of
alternative disinfectants. There are two reasons EPA has taken this
approach: 1) the goal of this manual is to provide technical and
engineering information to utilities and the states on alternative
disinfectants and oxidants, about which there is less comprehensive
information than for chlorine; and 2) a great majority of utilities
already use chlorine, in a wide variety of applications, for which there
exists a wealth of literature on chlorine's uses and performance
capabilities. Summarizing this large body of knowledge in this guidance
is neither practical nor necessary.

This manual is not an EPA endorsement of alternative disinfectants nor
is it a recommendation for utilities to switch from chlorine to an
alternative disinfectant. Rather, this manual provides technical and
engineering information to assist local professionals in making
treatment decisions. EPA believes that utility and state program
personnel are best able to select disinfectants and design a
disinfection scheme, based upon site-specific conditions, that meets
operational and regulatory constraints. EPA does not require the use of
chlorine or any other specific disinfectant for site-specific uses.
Again, local professionals are best suited to select disinfectants to
address the unique water treatment challenges posed by their source
water and plant infrastructure.

EPA recognizes that, at the present time, chlorination is an important
and central component of most water treatment regimes in this country.
As such, a summary of the uses and capabilities of chlorine is provided
in Section 2.7 of this manual. Section 2.7 also contains an extensive
reference list for additional information on chlorination.

## A Summary of Alternative Disinfectant Properties

Subsequent chapters in this manual discuss several disinfectant
alternatives available to a water supplier. Table 1-6 summarizes the key
technical and regulatory considerations associated with the use of the
various disinfectants for selecting the most appropriate disinfectant.
The table provides some broad guidelines to provide a framework for
decision making. The ratings in Table 1-6 are based on a typical
disinfectant application. Thus, even though chlorine is considered to be
prone to THM formation, the table does not address the degree or amount
of THMs produced. Similarly, more than 2-log inactivation can be
achieved for some disinfectants, but the high dose required may not make
it a reasonable application, and in that case, would be identified in
the table as not able to achieve 2-log inactivation.

The following key issues are addressed in Table 1-6:

-   **THMs, oxidized organics, and halogenated organics are produced.**
    Halogenated organics are formed when chlorine or ozone (in the
    presence bromide ion) is used, while oxidized organics occur in the
    greatest concentration when a strong oxidant is used. The production
    of DBPs depends on the amounts and types of precursors in the water.

-   **Inorganic byproducts are produced.** Inorganic byproducts include
    chlorate ion, chlorite ion, and bromate ion associated with chlorine
    dioxide and ozone.

-   **MRDLs are required for some disinfectants.** Note that this
    requirement must be balanced with the requirement to maintain a
    residual in the distribution system. For most disinfectants, such as
    chlorine, the MRDL is relatively high and will generally not create
    a problem.

-   **Lime softening impacts are noted.** The high pH treatment during
    lime softening has an impact on chlorine, chloramines, and UV.

-   **Turbidity impacts UV disinfection and ozonation.** Ozone may
    interfere with coagulation and settling. As such, it is recommended
    that ozonation be placed after settling but before filters to
    minimize turbidity impacts.

-   **Inactivation requirements are divided into those achieving more or
    less than 2-log inactivation.** This differentiation is to identify
    the feasibility of achieving high inactivation at modest doses. For
    example, while chlorine can achieve 3-log *Giardia* cyst
    inactivation, the CT requirement for 3-log inactivation of 100 to
    more than 300 mg-min/L will require high chlorine doses and/or long
    contact times. However, 4-log virus inactivation is achievable with
    a CT of 15 to 60 mg·min/L for most temperatures.\
    \
    Recently there has been some reports of 2-log and higher
    *Cryptosporidium* oocyst inactivation with UV, using a system that
    concentrates the oocysts on a filter and then allows extended
    exposure to UV to doses as high as 8,000 mW·s/cm^2^. This type
    application is considered experimental at this time.

-   **Applicability as a secondary disinfectant represents the ability
    of the disinfectant to maintain a residual in the distribution
    system.** Only chlorine, chlorine dioxide, and monochloramine
    provide residual disinfection in the distribution system. Chlorine
    dioxide is limited to systems with smaller distribution systems
    because the total chlorine dioxide dose that can be applied is
    limited by the production of chlorate ion and chlorite ion.

-   **Operator skill provides general guidance to the amount of operator
    attention and maintenance required.** All of the disinfectants can
    be placed on automatic control to limit the amount of operator
    attention. The operational attention is rated based on the
    complexity of the disinfectant application. Therefore, permanganate,
    which is a simple chemical feed system with few mechanical elements,
    is rated 1 (low attention), while peroxone which include both ozone
    systems and hydrogen peroxide feed systems, is rated 5 (high
    attention).

-   **All chemical disinfectants are judged to be applicable to small
    and large utilities.** Modular units of the technologies can cover a
    large range of flows. Ozone and chlorine dioxide generators are
    available with small and large capacities. Chlorine and chemical
    feed systems have been used successfully in all applications. Most
    UV water treatment facilities are less than 200 gpm in capacity.

Key elements in the decision making process relate to the water source
(i.e., ground or surface water) and existing treatment configuration
(including filtration) because these factors have a significant impact
on the degree of log removal required during disinfection. Water quality
has a large impact on the potential for DBP BOM formation.

[]{#__RefHeading___Toc448641915 .anchor}Table 1-6. Summary of
Disinfectant Properties

[]{#__RefHeading___Toc448641916 .anchor}(Based on Typical Disinfectant
Application)

  ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  **Condition**             ![](media/image2.wmf){width="0.2513888888888889in"   ![](media/image3.wmf){width="0.2513888888888889in"   ![](media/image4.wmf){width="0.2513888888888889in"   ![](media/image5.wmf){width="0.2513888888888889in"   ![](media/image6.wmf){width="0.2513888888888889in"   ![](media/image7.wmf){width="0.2513888888888889in"   ![](media/image8.wmf){width="0.2513888888888889in"
                            height="1.2513888888888889in"}                       height="1.2513888888888889in"}                       height="1.2513888888888889in"}                       height="1.2513888888888889in"}                       height="1.2513888888888889in"}                       height="1.2513888888888889in"}                       height="1.2513888888888889in"}
  ------------------------- ---------------------------------------------------- ---------------------------------------------------- ---------------------------------------------------- ---------------------------------------------------- ---------------------------------------------------- ---------------------------------------------------- ----------------------------------------------------
  Produce THM with TOC      y                                                    s                                                    n                                                    n                                                    y                                                    s                                                    n

  Produce oxidized organics s                                                    y                                                    s                                                    s                                                    n                                                    y                                                    s

  Produce halogenated       y                                                    s                                                    n                                                    n                                                    y                                                    s                                                    n
  organics                                                                                                                                                                                                                                                                                                                                                

  Produce inorganic         n                                                    s                                                    y                                                    n                                                    n                                                    s                                                    n
  byproducts                                                                                                                                                                                                                                                                                                                                              

  Produce BOM               s                                                    y                                                    s                                                    n                                                    n                                                    y                                                    n

  MRDL applies              y                                                    n                                                    y                                                    n                                                    y                                                    n                                                    n

  Lime softening impacts    y                                                    n                                                    n                                                    n                                                    y                                                    n                                                    y

  Turbidity impacts         n                                                    s                                                    n                                                    n                                                    n                                                    s                                                    y

  Meet *Giardia* - \<2.0    y                                                    y                                                    y                                                    n                                                    n                                                    n                                                    n
  log                                                                                                                                                                                                                                                                                                                                                     

  Meet *Giardia* - \>2.0    n                                                    y                                                    y                                                    n                                                    n                                                    n                                                    n
  log                                                                                                                                                                                                                                                                                                                                                     

  Meet *Crypto* - \<2.0 log n                                                    y                                                    y                                                    n                                                    n                                                    n                                                    n

  Meet *Crypto* - \>2.0 log n                                                    y                                                    n                                                    n                                                    n                                                    n                                                    n

  Meet Virus - \<2.0 log    y                                                    y                                                    y                                                    n                                                    n                                                    n                                                    y

  Meet Virus - \>2.0 log    y                                                    y                                                    y                                                    n                                                    n                                                    n                                                    y

  Secondary disinfectant    y                                                    n                                                    s                                                    n                                                    y                                                    n                                                    n

  Operator skill (1=low;    1                                                    5                                                    5                                                    1                                                    2                                                    5                                                    3
  5=high)                                                                                                                                                                                                                                                                                                                                                 

  Applicable to large       y                                                    y                                                    y                                                    y                                                    y                                                    y                                                    n
  utilities                                                                                                                                                                                                                                                                                                                                               

  Applicable to small       y                                                    y                                                    y                                                    y                                                    y                                                    y                                                    y
  utilities                                                                                                                                                                                                                                                                                                                                               
  ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

y = yes, n = no, s = sometimes

The following sections describe each of these phases.

## Selecting a Disinfection Strategy

This section presents general guidance that can be used to assess the
applicability of various disinfectants or combination of disinfectants
to select an appropriate disinfection strategy. Because the selection of
an appropriate strategy depends on site-specific conditions unique to
each water supply system, final selection of a strategy should be made
with appropriate technical guidance (e.g., engineering study/evaluation
or bench or pilot scale testing of alternatives). Selecting the most
appropriate disinfectant strategy for water treatment requires a balance
among three key driving forces:

-   **Providing water free of pathogens.** Since the SWTR, the
    regulatory focus for pathogen removal focused on coliform bacteria,
    heterotrophic plate counts, *Giardia* cysts, *Legionella*, and
    viruses. Recently, the focus has been expanded to include
    *Cryptosporidium* oocyst removal and inactivation, especially due to
    its resistance to chlorine.

-   **Avoiding the production of disinfection byproducts (DBPs).**
    Trihalomethanes (THMs), other halogenated organics, ozone DBPs,
    oxidation byproducts, and some disinfectant residuals present a
    health risk and must be limited in drinking waters. DBP precursor
    removal through process optimization or enhanced coagulation is the
    first step in DBP control.

-   **Requiring residual disinfectant to maintain the bacteriological
    quality in the water as it is distributed to customers to control
    regrowth.** The potential for DBP formation increases with extended
    contact between DBP precursors and residual disinfectants.

When changing disinfectants or oxidants water providers should consult
with their primacy agencies. The impact of the change should consider
the impact on disinfection credit using disinfection profiling and
benchmarking techniques as summarized in Section 1.3.

### Disinfection Strategy Evaluation

The selection of a disinfection strategy, as presented below, is
affected by the following:

-   Effectiveness of the current disinfection system;

-   Need to change disinfectants;

-   Selection of an alternative disinfectant; and

-   Primary and secondary disinfection requirements.

    As used in this guidance, primary and secondary disinfection are
    defined as follows:

    **Primary disinfection:** The first (i.e., primary) disinfectant
    used in a treatment system, with the primary objective of the
    disinfectant being to achieve the necessary CT (i.e., microbial
    inactivation).

    **Secondary disinfection:** The second disinfectant used in a
    treatment system, with the primary objective of the disinfectant
    being to maintain the disinfection residual through the distribution
    system.

For discussion, the approach to select a disinfection strategy is
divided into three phases:

-   Evaluate the current primary disinfection practice

-   Select a primary disinfectant

-   Select a secondary disinfectant.

#### Evaluate the Current Primary Disinfection Practice

Figure 1-1 presents the decision making process used to determine
whether the present primary disinfectant can meet disinfection and
byproduct requirements. The key decision points in Figure 1-1 include:

-   **Meet current microbial inactivation limits.** Microbial limits are
    defined by the primary drinking water standards shown in Table 1-2.
    The regulated indicators of pathogens include *Giardia lamblia*,
    *Legionella*, HPC, total coliform turbidity, and viruses. The
    disinfectant must be capable of meeting the inactivation
    requirements for disinfection. If not, the plant must determine if
    the current disinfectant can meet the microbial inactivation
    requirements solely through process modifications. A process
    modification may be to move the application point, increase dose,
    increase contact time, or adjust pH. If not, a new disinfectant may
    be needed. In some instances, a PWS may opt to improve its current
    microbial inactivation even though the PWS is meeting current
    microbial limitations. In these instances, an evaluation is
    necessary to ensure that any process modifications to improve
    inactivation will still provide compliance with the microbial
    limits.

-   **Meet current DBP limits.** A second set of limits imposed on
    disinfectant usage are DBP requirements. The DBP limits are
    established in the Stage 1 DBP rule (See Table 1-3 and Table 1-5).
    To meet these limits on a consistent basis under normal varying
    water quality conditions, 80 percent of the MCL serves as an action
    level that requires a change in treatment practice. Similar to
    microbial inactivation, some PWSs may desire to improve current DBP
    protection, thus requiring evaluation of these modifications. By
    optimizing existing treatment processes, the production of DBPs can
    be reduced. Optimization may include pretreatment optimization
    (i.e., coagulation, filtration, etc.) or process modifications such
    as moving the point of disinfection. Enhanced coagulation is
    required by the Stage 1 DBP rule. Where process modifications are
    contemplated, the PWS must ensure that both microbial inactivation
    and DBP formation comply with applicable regulatory requirements. If
    optimized treatment cannot meet DBP and microbial requirements, a
    new disinfectant may be needed.

#### Select a Primary Disinfectant

If it is determined that a new disinfectant is required or desired for
better public health protection, the second phase in the decision
process (Figure 1-2) addresses the factors concerning selection of a
primary disinfectant. This decision requires knowledge of the following
three key components:

-   **TOC concentration.** A high TOC concentration indicates a high
    potential for DBP formation. In these cases, the decision tree will
    favor those disinfectants that will not produce DBPs or will produce
    the least amount of DBPs. Note that precursor removal and enhanced
    coagulation are used to reduce TOC during treatment optimization as
    indicated in Figure 1-1. "High TOC" quantifies the potential to
    produce DBPs and is defined as a condition meeting one of the
    following criteria:

```{=html}
<!-- -->
```
-   TOC exceeds 2 mg/L;

-   TTHM exceeds MCL (0.08 mg/L under Stage 1 DBPR); or

-   HAA5 exceeds MCL (0.06 mg/L under Stage 1 DBPR).

![](media/image9.wmf)

[]{#__RefHeading___Toc448641917 .anchor}Figure 1-1. Flow Diagram to
Evaluate Current Disinfection Practices

-   **Bromide ion concentration.** The reactions of strong oxidants
    (ozone and peroxone) with bromide ion to produce hypobromous acid
    and bromate ion, precludes their usage with waters containing high
    concentrations of bromide ion. High bromide ion is defined as
    concentrations exceeding 0.10 mg/L.

-   **Filtered versus non-filtered systems.** The use of ozone or
    ozone/peroxide for unfiltered systems without the benefit of
    biofiltration to reduce ozonation byproducts and BOM is strongly
    discouraged.

#### Select a Secondary Disinfectant

The selection of a secondary disinfectant depends on the selected
primary disinfectant. Figure 1-3 identifies three decision points for
secondary disinfectants:

-   **Assimilable organic carbon (AOC) concentration.** AOC is produced
    when a strong oxidant (e.g., ozone) is used as primary disinfectant
    in the presence of high TOC water. High AOC is defined as
    concentrations exceeding 0.10 mg/L after filtration. In these cases,
    additional biological or GAC treatment should be considered to
    stabilize the finished water and prevent regrowth in the
    distribution system.

-   **DBP formation potential (DBPFP).** The DBPFP serves as an
    indication of the amount of organic byproducts that could be
    expected to form in the distribution system if chlorine is used.
    Because DBP formation continues in the distribution system, the DBP
    content at the plant effluent should be limited. A high DBPFP is
    defined as a water meeting one of the following criteria:

```{=html}
<!-- -->
```
-   TTHM seven-day formation exceeds the MCL (0.08 mg/L under Stage 1
    DBPR); or

-   HAA5 seven-day formation exceeds the MCL (0.06 mg/L under the Stage
    1 DBPR).

    **• Distribution system retention time.** In a large distribution
    system, booster stations may be required to maintain the
    disinfection residual. Since chlorine dioxide has an upper limit for
    application, its usage may not be feasible if relatively high doses
    are required to maintain a residual in the distribution system. A
    distribution system retention time is considered high if it exceeds
    48 hours.

![](media/image10.wmf)

[]{#__RefHeading___Toc448641918 .anchor}Figure 1-2. Flow Diagram to
Narrow Selection of a New Primary Disinfectant

![](media/image11.wmf)

[]{#__RefHeading___Toc448641919 .anchor}Figure 1-3. Flow Diagram to
Narrow Selection of a New Secondary Disinfectant

###  Summary

The approach outlined above serves as a basis to evaluate the need for
and to select the most appropriate alternative disinfectants for
drinking water systems. The approach is general enough to cover the
likely outcomes of the inactivation requirements and DBP formation.
However, in some cases, site-specific conditions may dictate a different
approach. It is important to consult with the primacy agency whenever a
change in treatment is considered. Remember that the IESWTR requires
certain PWSs to use disinfection profiling and benchmarking procedures
when proposing changes to disinfection practices. In addition, some of
the decisions may lead to a situation where additional treatment will be
required. For example, filtration may be needed to reduce the
disinfectant dose and limit DBP formation in cases of high TOC and high
bromide ion levels. In those instances, bench scale or pilot studies may
be required to select the most appropriate disinfectant.

## References

1.  AWWA (American Water Works Association). 1991. *Guidance Manual for
    Compliance with the Filtration and Disinfection Requirements for
    Public Works Systems Using Surface Water Sources*.

2.  AWWA Safe Drinking Water Advisor - Library on Internet (1997).

3.  Bellar, T.A, J.J. Lichtenberg, and R.C. Kroner. 1974. "The
    Occurrence of Organohalides in Chlorinated Drinking Water." *J.
    AWWA*. 66(12): 703-706.

4.  Legube, B., J.P. Croue′, J. De Latt, and M. Dore′. 1989. "Ozonation
    of an Extracted Aquatic Fulvic Acid: Theoretical and Practical
    Aspects." *Ozone Sci. Eng*. 11(1): 69-91.

5.  McGuire, M.J., D.W. Ferguson, and J.T. Gramith. 1990. Overview of
    Ozone Technology for Organics Control and Disinfection. Conference
    proceedings, AWWA Seminar on Practical Experiences with Ozone for
    Organics Control and Disinfection, Cincinnati, OH.

6.  Rook, J.J. 1974. "Formation of Haloforms during Chlorination of
    Natural Water." *Water Treatment and Examination*. 23(2): 234-243.

7.  Sawyer, C.N., P.L. McCarty, L. Parkin, and G.F. Parkin. 1994.
    *Chemistry for Environmental Engineering*, fourth edition. McGraw
    Hill, Inc., New York, NY.

8.  Symons, J.M., T.A. Bellar, J.K. Carswell, J. DeMarco, K.L. Kropp,
    G.G. Robeck, D.R. Seeger, C.J. Slocum, B.L. Smith and A.A.
    Stevens. 1975. "National Organics Reconnaissance Survey for
    Halogenated Organics." *J. AWWA*. 67(11): 634-647.

9.  USEPA (U.S. Environmental Protection Agency). 1997. *Community Water
    System Survey - Volume II*. Detailed Survey Result Tables and
    Methodology Report. EPA 815-R-97-001b.

10. USEPA. 1978. National Organics Monitoring Survey (NOMS). Technical
    Support Division, U.S. Environmental Protection Agency, Office of
    Drinking Water. Cincinnati, OH.

11. White, G.C. 1992. *Handbook of Chlorination and Alternative
    Disinfectants*. Vol. 3. Van Nostrand Reinhold Co. New York, NY.

12. White, G.C. 1986. *Handbook of Chlorination*. Van Nostrand Reinhold
    Company, New York, NY.

Introduction [1-1](#introduction)

1.1 Objective of this Manual [1-1](#objective-of-this-manual)

1.2 Background [1-2](#background)

1.3 Regulatory Context [1-3](#regulatory-context)

1.3.1 Disinfection Profiling and Benchmarking
[1-7](#disinfection-profiling-and-benchmarking)

1.4 Use of Disinfectants as Chemical Oxidants
[1-8](#use-of-disinfectants-as-chemical-oxidants)

1.5 How Chlorine is Addressed in this Guidance Manual
[1-8](#how-chlorine-is-addressed-in-this-guidance-manual)

1.6 A Summary of Alternative Disinfectant Properties
[1-9](#a-summary-of-alternative-disinfectant-properties)

1.7 Selecting a Disinfection Strategy
[1-11](#selecting-a-disinfection-strategy)

1.7.1 Disinfection Strategy Evaluation
[1-12](#disinfection-strategy-evaluation)

1.7.1.1 Evaluate the Current Primary Disinfection Practice
[1-12](#evaluate-the-current-primary-disinfection-practice)

1.7.1.2 Select a Primary Disinfectant
[1-13](#select-a-primary-disinfectant)

1.7.1.3 Select a Secondary Disinfectant
[1-15](#select-a-secondary-disinfectant)

1.7.2 Summary [1-17](#summary)

1.8 References [1-18](#references)

Table 1-1. Key Dates for Regulatory Activities
[1-4](#__RefHeading___Toc448641910)

Table 1-2. Primary Drinking Water Regulations Related to Microbiological
Contaminants [1-6](#__RefHeading___Toc448641911)

Table 1-3. Primary Drinking Water Regulations Related to Disinfection
Byproducts [1-6](#_Ref401037486)

Table 1-4. Primary Drinking Water Regulations Related to Residual
Disinfectants [1-7](#_Ref396703235)

Table 1-5. Log Removal/Inactivation through Filtration and Disinfection
Required Under the SWTR [1-7](#__RefHeading___Toc448641914)

Table 1-6. Summary of Disinfectant Properties
[1-11](#__RefHeading___Toc448641915)

(Based on Typical Disinfectant Application)
[1-11](#__RefHeading___Toc448641916)

Figure 1-1. Flow Diagram to Evaluate Current Disinfection Practices
[1-14](#__RefHeading___Toc448641917)

Figure 1-2. Flow Diagram to Narrow Selection of a New Primary
Disinfectant [1-16](#__RefHeading___Toc448641918)

Figure 1-3. Flow Diagram to Narrow Selection of a New Secondary
Disinfectant [1-17](#__RefHeading___Toc448641919)

[^1]: Subpart H systems are defined as public water systems supplied by
    a surface water source or by a ground water source under the direct
    influence of surface water.