# PEROXONE (OZONE/HYDROGEN PEROXIDE)

Advanced oxidation processes generate highly reactive hydroxyl free
radicals to oxidize various compounds in the water. As discussed in
Chapter 3, hydroxyl radicals are produced during the spontaneous
decomposition of ozone. By accelerating the ozone decomposition rate,
the hydroxyl radical concentration is elevated, which increases the
oxidation rate. This procedure increases the contribution of indirect
oxidation over direct ozone oxidation as discussed in Chapter 3.

Several methods have been used to increase ozone decomposition and
produce high concentrations of hydroxyl radicals. One of the most common
of these processes involves adding hydrogen peroxide to ozonated water,
a process commonly referred to as peroxone.

The Metropolitan Water District of Southern California (MWDSC) conducted
extensive research into the use of peroxone to control organics and
oxidize taste and odor compounds (e.g., geosmin and 2-methylisoborneol
\[MIB\]) while providing sufficient levels of molecular ozone to
guarantee CT values and primary disinfection. While this chapter focuses
on peroxone as a disinfectant, similar results are expected from other
advanced oxidation processes such as ozone plus UV, ozone at high pH,
hydrogen peroxide plus UV, and other combinations.

A key issue with the use of peroxone as a disinfection process is that
the process does not provide a measurable disinfectant residual. It is
therefore not possible to calculate CT similar to the use of other
disinfectants. While no credit can be given for hydroxyl free radicals
because it cannot be measured directly, some credit may be considered
for any detected ozone in peroxone systems. Peroxone does provide
pathogen inactivation, as discussed in this chapter, but equivalent CT
values or methods of calculating equipment CT credits have not been
established at the date of publication of this guidance document.

## Peroxone Chemistry 

The ozone decomposition cycle is similar to that discussed in Chapter 3.
However, the added hydrogen peroxide or ultraviolet radiation
accelerates the decomposition of ozone and increases the hydroxyl
radical concentration. By adding hydrogen peroxide, the net production
of hydroxyl free radicals is 1.0 mole hydroxyl radical per mole ozone.

Similar to the discussion of ozone in Chapter 3, oxidation in the
peroxone occurs due to two reactions (Hoigné and Bader, 1978):

-   Direct oxidation of compounds by aqueous ozone (O~3(aq)~); and

-   Oxidation of compounds by hydroxyl radicals produced by the
    decomposition of ozone.

The two oxidation reactions compete for substrate (i.e., compounds to
oxidize). The ratio of direct oxidation with molecular ozone is
relatively slow (10^-5^-10^7^M^-1^sec^-1^) compared to hydroxyl radical
oxidation (10^12^-10^14^M^-1^sec^-1^), but the concentration of ozone is
relatively high. On the other hand, the hydroxyl radical reactions are
very fast, but the concentration of hydroxyl radicals under normal
ozonation conditions is relatively small.

A key difference between the ozone and peroxone processes is that the
ozone process relies heavily on the direct oxidation of aqueous ozone
while peroxone relies primarily on oxidation with hydroxyl radical. In
the peroxone process, the ozone residual is short lived because the
added peroxide greatly accelerates the ozone decomposition. However, the
increased oxidation achieved by the hydroxyl radical greatly outweighs
the reduction in direct ozone oxidation because the hydroxyl radical is
much more reactive. The net result is that oxidation is more reactive
and much faster in the peroxone process compared to the ozone molecular
process. However, because an ozone residual is required for determining
disinfection CT credit, peroxone may not be appropriate as a
pre-disinfectant.

The peroxone process utilizes oxidation by hydroxyl radicals. The
oxidation potential of the hydroxyl radical and ozone are as follows:

$\text{OH} + e^{-} \rightarrow \text{OH}^{-}$ *E^0^* = +2.8*V*

$O_{3} + 2H^{+} + 2e^{-} \rightarrow O_{2} + H_{2}O$ *E^0^* = +2.07*V*

$O_{3} + H_{2}O + 2e^{-} \rightarrow O_{2} + 2\text{OH}^{-}$ *E^0^* =
+1.24*V*

In addition to having an oxidation potential of hydroxyl radical higher
than ozone, the hydroxyl radical is also much more reactive approaching
the diffusion control rates for solutes such as aromatic hydrocarbons,
unsaturated compounds, aliphatic alcohols, and formic acid (Hoigné and
Bader, 1976).

### Oxidation Reactions

Because the radical oxidation is much more effective than direct
oxidation with ozone, it has been used extensively to treat difficult to
oxidize organics such as taste and odor compounds and chlorinated
organics (e.g., geosmin, MIB, phenolic compounds, trichloroethylene
\[TCE\], and perchloroethylene \[PCE\]).

Neither ozone nor peroxone significantly destroys TOC. Peroxone will
oxidize the saturated organics and produce byproducts similar to those
found in ozonation; namely, aldehydes, ketones, peroxides, bromate ion,
and biodegradable organics (MWDSC and JMM, 1992). However, with
peroxone, the biodegradibility of the water (not the organic compounds)
increases, rendering "a portion of the TOC" amenable to removal in
biologically active filters.

Peroxone has found a niche in oxidizing difficult-to-treat organics,
such as taste and odor compounds including geosmin and MIB (Pereira et
al., 1996; Ferguson et al., 1990). In addition, peroxone and other
advanced oxidation processes have been shown to be effective in
oxidizing halogenated compounds such as 1,1-dichloropropene,
trichloroethylene, 1-chloropentane, and 1,2-dichloroethane (Masten and
Hoigné, 1992; Aieta et al., 1988; Glaze and Kang, 1988). Hydroxyl
radicals will react with all these compounds plus refractory aliphatics
such as alcohols and short-chain acids (Chutny and Kucera, 1974).

The optimum peroxide:ozone dose ratio to maximize hydroxyl radicals'
reaction rate can be determined for a specific oxidation application.
For instance, the optimum peroxide:ozone dose ratio for TCE and PCE
oxidation in a ground water was determined to be 0.5 by weight (Glaze
and Kang, 1988). Tests showed that TCE required lower ozone dosages for
the same percentage removal compared to PCE.

LADWP conducted pilot studies and operated a 2,000 gpm full scale AOP
demonstration plant in 1995. The peroxide:ozone dose ratio used was 0.5
to 0.6. Ground water containing up to 447 mg/L TCE and 163 mg/L PCE was
treated to below the respective MCLs. However, bromate ion was formed in
excess of the 0.010 mg/L MCL (Karimi et al., 1997).

### Reactions with Other Water Quality Parameters

As with ozone alone, pH and bicarbonate alkalinity play a major role in
peroxone effectiveness (Glaze and Kang, 1988). This role is primarily
related to bicarbonate and carbonate competition for hydroxyl radical at
high alkalinity and carbonate competition for hydroxyl radical at high
pH levels. Also, excessive peroxide can also limit the formation of the
hydroxyl radical and reduce the effectiveness of peroxone.

Turbidity alone does not appear to play a role in peroxone effectiveness
nor does peroxone appear to remove turbidity. Tobiason et al. (1992)
studied the impact of pre-oxidation on filtration and concluded that the
pre-oxidation did not improve effluent turbidities, but did appear to
increase filter run times because of lower head loss or delayed
turbidity breakthrough. Filter effluent turbidities were similar for
no-oxidant and pre-oxidant trains.

### Comparison between Ozone and Peroxone

The key difference between ozone and peroxone is in the primary
oxidation mode; that is, direct oxidation or hydroxyl radical oxidation.
The reactivities of these compounds create a different effect in the
reactions with water constituents and, thus, disinfection effectiveness.
Table 7-1 summarizes the key differences between ozone and peroxone as
they relate to their application in drinking water treatment.

[]{#__RefHeading___Toc450036124 .anchor}Table 7-1. Comparison between
Ozone and Peroxone Oxidation

  ------------------------------------------------------------------------
  **Process**       **Ozone**                  **Peroxone**
  ----------------- -------------------------- ---------------------------
  Ozone             "Normal" decomposition     Accelerated ozone
  decomposition     producing hydroxyl radical decomposition increases the
  rate              as an intermediate product hydroxyl radical
                                               concentration above that of
                                               ozone alone.

  Ozone residual    5-10 minutes               Very short lived due to
                                               rapid reaction.

  Oxidation path    Usually direct aqueous     Primarily hydroxyl radical
                    molecular ozone oxidation  oxidation.

  Ability to        Excellent                  Less effective.
  oxidize iron and                             
  manganese                                    

  Ability to        Variable                   Good, hydroxyl radical more
  oxidize taste and                            reactive than ozone.
  odor compounds                               

  Ability to        Poor                       Good, hydroxyl radical more
  oxidize                                      reactive than ozone.
  chlorinated                                  
  organics                                     

  Disinfection      Excellent                  Good, but systems can only
  ability                                      receive CT credit if they
                                               have a measurable ozone
                                               residual.

  Ability to detect Good                       Poor. Cannot calculate CT
  residual for                                 value for disinfection
  disinfection                                 credit.
  monitoring                                   
  ------------------------------------------------------------------------

## Generation

The peroxone process requires an ozone generation system as described in
Chapter 3 and a hydrogen peroxide feed system. The process involves two
essential steps: ozone dissolution and hydrogen peroxide addition.
Hydrogen peroxide can be added after ozone (thus allowing ozone
oxidation and disinfection to occur first) or before ozone (i.e., using
peroxide as a pre-oxidant, followed by hydroxyl radical reactions) or
simultaneously. Addition of hydrogen peroxide following ozone is the
best way to operate, however a system cannot obtain a CT credit unless
the ozone residual is sufficiently high.

There are two major effects from the coupling of ozone with hydrogen
peroxide (Duguet et al., 1985):

-   Oxidation efficiency is increased by conversion of ozone molecules
    to hydroxyl radicals; and

-   Ozone transfer from the gas phase to the liquid is improved due to
    an increase in ozone reaction rates.

The most efficient operation is to add ozone first to obtain CT
disinfection credit, followed by peroxide for hydroxyl radical
oxidation.

Ozonation can be described as occurring in two stages. In the first
stage, ozone rapidly destroys the initial oxidant demand present,
thereby enhancing the ozone transfer rate into solution from the gas
phase. Addition of hydroxyl free radicals to the first stage should be
minimized since the hydrogen peroxide competes with ozone-reactive
molecules (i.e., initial demand) for the ozone present. In the second
stage, organic matter is oxidized, taking place much slower than in the
first stage. Adding hydrogen peroxide during the second stage makes it
possible to raise the overall oxidation efficiency, since the reaction
of hydrogen peroxide with ozone produces hydroxyl radicals enhancing
chemical reaction rates. In practice, the addition of hydrogen peroxide
to the second stage of ozonation can be achieved by injecting the
hydrogen peroxide into the second chamber of an ozone contactor (Duguet
et al., 1985). The most efficient operation is to use ozone first to
obtain CT credit and peroxone second for micropollutant destruction.

Energy consumption of the peroxone process includes that for ozone
generation and application, plus for metering pumps to feed peroxide.
The peroxide addition step does not require any more training from an
operator than any other liquid chemical feed system. Systems should be
checked daily for proper operation and for leaks. Storage volumes should
also be checked daily to ensure sufficient peroxide is on hand, and to
monitor usage.

## Primary Uses and Points of Application

Peroxone is used for oxidation of taste and odor compounds, and
oxidation of synthetic organic compounds. Peroxone is also used for the
destruction of herbicides (e.g., atrazine), pesticides, and VOCs.
Peroxone is applied at points similar to ozone for oxidation. Addition
of ozone first and hydrogen peroxide second is the better way to
operate. Alternatively, hydrogen peroxide can be added upstream of
ozone.

### Primary Uses

#### Taste and Odor Compound Oxidation

Peroxone is used to remove taste and odor causing compounds because many
of these compounds are very resistant to oxidation, even
ozone-oxidation. More recently, significant attention has been given to
tastes and odors from specific compounds such as geosmin,
2-methyliosborneol (MIB), and chlorinated compounds. Studies at MWDSC
demonstrated the effectiveness of peroxone to remove geosmin and MIB
during water treatment (Ferguson et al., 1990; Ferguson et al., 1991;
Huck et al., 1995).

#### Synthetic Organic Compound Oxidation

Peroxone and other advanced oxidation processes have been shown to be
effective in oxidizing halogenated compounds such as 1,1-dichloropropene
(DCPE), TCE, 1-chloropentane (CPA), and 1,2-dichloroethane (DCA) (Masten
and Hoigné, 1992; Aieta et al., 1988; Glaze and Kang, 1988). The
hydroxyl radicals formed react with all these compounds plus refractory
aliphatics, such as alcohols and short-chain acids (Chutny and Kucera,
1974).

### Points of Application

The peroxone process is applied at points similar to ozone for oxidation
as discussed in Chapter 3. Importantly, peroxone addition should be
after settling and prior to biological filtration. It is important to
add hydrogen peroxide after the initial ozone demand is consumed to
avoid hydroxyl free radical competition with the initial ozone demanding
constituents.

#### Impact on Other Treatment Processes

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

-   The use of hydroxyl free radicals generates BDOC, which can cause
    biological growth in distribution systems if not reduced during
    biologically active filtration. When peroxide addition is placed
    before filters, it impacts the filters by increasing biological
    growths and increasing backwash frequency (depending on the level on
    BDOC produced).

-   Hydroxyl free radicals are strong oxidants that interfere with
    addition of other oxidants, such as chlorine, until the ozone
    residual is quenched.

-   The oxidation of iron and manganese by hydroxyl free radicals
    generates insoluble oxides that should be removed by sedimentation
    or filtration. This also may impact the filters by increasing the
    load on the filters and increasing backwash frequency.

The reader is referred to the *Microbial and Disinfection Byproduct
Simultaneous Compliance Guidance Document* (currently in production) for
additional information regarding the interaction between oxidants and
other treatment processes.

## Pathogen Inactivation

Both peroxone and other advanced oxidation processes have been proven to
be equal or more effective than ozone for pathogen inactivation.
Disinfection credits are typically described in terms of CT
requirements. Because peroxone leaves no measurable, sustainable
residual, calculation of an equivalent CT for disinfection credit is not
possible unless there is measurable ozone residual.

### Inactivation Mechanism

Experiments have indicated that long contact times and high
concentrations of hydrogen peroxide are required for bacteria and virus
inactivation (Lund, 1963; Yoshe-Purer and Eylan, 1968; Mentel and
Schmidt, 1973). Achieving a 99 percent inactivation of poliovirus
required either a hydrogen peroxide dose of 3,000 mg/L for 360 minutes
or 15,000 mg/L for 24 minutes. Based on these results, when the
combination of ozone and hydrogen peroxide is used, the primary cause
for pathogen inactivation is attributed to ozone, specifically the
mechanisms associated with the oxidation of pathogens by direct ozone
reaction and hydroxyl radicals.

As described in Chapter 3, the mode of action of ozone on microorganisms
is poorly understood. Some studies on bacteria suggest that ozone alters
proteins and unsaturated bonds of fatty acids in the cell membrane,
leading to cell lysis (Scott and Lesher, 1963; Pryor et al., 1983),
while other studies suggest that ozone may affect deoxyribonucleic acid
(DNA) in the cell (Hamelin and Chung, 1974; Ohlrogge and Kernan, 1983;
Ishizaki et al., 1987). Virus inactivation was reported to be related to
the attack of the protein capsid by ozone (Riesser et al., 1977). Little
information was found discussing the mode of action of ozone on
protozoan oocysts. However, a few researchers have suggested that ozone
causes the oocyst density to decrease and alters the oocyst structure
(Wickramanayake, 1984; Wallis et al., 1990).

The debate continues regarding the primary mode of action for hydroxyl
free radicals. Some researchers believe that ozone disinfection is a
result of direct ozone reaction (Hoigné and Bader, 1975; Hoigné and
Bader, 1978), while others believe that the hydroxyl radical mechanism
for disinfection is the most important mechanism (Dahi, 1976; Bancroft
et al., 1984). Studies using ozone-hydrogen peroxide have shown that
disinfection of *E. coli* is less effective as the peroxide to ozone
ratio increases to above approximately 0.2 mg/mg (Wolfe et al., 1989a;
Wolfe et al., 1989b). The decrease in disinfection was believed to be
cause by lower ozone residuals associated with higher peroxide to ozone
ratios, which indicates that direct ozone reaction is an important
mechanism for pathogen inactivation.

### Environmental Effects

Although the chemistry of the peroxone process is still not completely
understood, optimal production of the hydroxyl radical appears to depend
on the pH, ozone concentration, ratio of hydrogen peroxide to ozone,
contact time, and water composition (Glaze et al., 1987).

#### Competing Chemical Reactions

One disadvantage of the peroxone process is that it involves radical
intermediates that are subject to interference from substances that
react with hydroxyl radical, decreasing the effectiveness of the
process. Alkalinity, bicarbonate, and pH play a major role in the
effectiveness of hydroxyl free radicals. This effect is primarily
related to bicarbonate competition for hydroxyl radical at high
alkalinity and carbonate competition for hydroxyl radical at pH levels
higher than 10.3 (see Chapter 3). Lowering the alkalinity prior to the
application of the peroxone process may be necessary for water that has
a high bicarbonate level. In addition to carbonate and bicarbonate,
organic constituents of humic substances have also been found to react
with the hydroxide radical (Glaze, 1986).

#### Ratio of Hydrogen Peroxide and Ozone

A study conducted at MWDSC indicated that the performance of peroxone is
greatly dependent upon the peroxide:ozone ratio (Wolfe et al., 1989b).
Results from previous studies at MWDSC suggested that the optimal ratio
for disinfection was less than or equal to 0.3. One of the primary
objectives of the 1989 study was to optimize further the process for
disinfection by altering peroxide:ozone ratios and contact times.
Results from the study indicated that peroxone at a 0.2 ratio of
peroxide:ozone was comparable to ozone for disinfection of indicator
organisms and *Giardia muris* cysts, and that at higher ratios,
disinfection decreased because ozone decreased.

### Disinfection Efficacy and Pathogen Inactivation

Recent studies have indicated that the disinfection effectiveness of
peroxone and ozone are comparable (Wolfe et al., 1989b; Ferguson et al.,
1990; Scott et al., 1992). A study conducted by Ferguson et al. (1990)
compared the pathogen inactivation capability of peroxone and ozone
using MS-2 and f2 coliphages as well as *E. coli.* and heterotrophic
plate count (HPC) bacteria. The f2 and MS-2 coliphages were comparable
in their resistance to ozone and peroxone. No differences in the amounts
of MS-2 or f2 inactivation were apparent when the peroxide:ozone ratio
was varied from 0 to 0.3. Results of the *E. coli.* and HPC studies
showed that peroxone and ozone also had comparable results in regards to
bacteria inactivation.

Table 7-2 lists CT values derived for inactivation of *Giardia muris*
cysts by ozone and peroxone from another study conducted by MWDSC. The
contact times used for calculating the CT values were based on 10% and
50% breakthrough of tracer compounds in the contactor. Ozone
concentrations used for CT were based on the ozone residual and half of
the residual and dose. The results of this study suggest that peroxone
is slightly more potent than ozone based on the fact that CT values for
ozone were greater than for peroxone. However, because ozone decomposes
more rapidly in the presence of hydrogen peroxide, higher ozone dosages
may be necessary with peroxone to achieve comparable residuals.
Moreover, the use of ozone residuals to calculate CT products for
peroxone may not take into account other oxidizing species that may have
disinfectant capabilities.

[]{#__RefHeading___Toc450036125 .anchor}Table 7-2. Calculated CT Values
(mg•min/L) for the Inactivation of *Giardia muris*

+-------------+-------------+-------------+-------------+-------------+
| **Ina       | **Ozone**   | **Ozone**   | **Pe        | *           |
| ctivation** |             |             | roxone^b^** | *Peroxone** |
|             | **C~        | **C~        |             |             |
|             | 1~T~1~^a^** | 2~T~2~^a^** | **C~        | **C~        |
|             |             |             | 1~T~1~^a^** | 2~T~2~^a^** |
+-------------+-------------+-------------+-------------+-------------+
| 90%         | 1.6         | 2.8         | 1.2         | 2.6         |
+-------------+-------------+-------------+-------------+-------------+
| 99%         | 3.4         | 5.4         | 2.6         | 5.2         |
+-------------+-------------+-------------+-------------+-------------+

Data obtained from Wolfe et al., 1989b. Results at 14^o^C.

^a^ C~1~, ozone residual; C~2~ (ozone dose + ozone residual)/2; T~1~ and
T~2~ time (in minutes) to reach 10 percent and 50 percent breakthrough,
respectively

^b^ The H~2~O~2~/O~3~ ratio for all results was 0.2.

## Disinfection Byproducts

The principal byproducts associated with peroxone are expected to be
similar to those for ozonation and are listed in Table 3-9. Additional
DBPs could form from reactions with hydroxyl radicals. Peroxone does not
form halogenated DBPs when participating in oxidation/reduction
reactions with NOM. However, if bromide ion is present in raw water
halogenated DBPs may be formed. Similar to ozone, the principal benefit
of using peroxone for controlling THM formation appears to be that it
eliminates the need for pre-chlorination and allows lower doses of free
chlorine or chloramines to be applied later in the process train after
precursors have been removed by coagulation, sedimentation, and/or
filtration and at lower doses. But peroxone does not reduce the DBPFP.

Based upon studies and findings involving peroxone, there is no
beneficial lowering of THMs as long as free chlorine is utilized as a
secondary disinfectant, unless the application of peroxone allows
chlorine to be applied later in the process train to water containing
reduced precursor concentrations. The MWDSC study found that the use of
peroxone/chlorine resulted in THM concentrations 10 to 38 percent
greater than the use of ozone/chorine. However, the THM concentrations
of waters disinfected with peroxone/chloramines and ozone/chloramines
were similar (Ferguson et al., 1990).

The use of peroxone as a primary disinfectant and chloramines as a
secondary disinfectant can successfully control halogenated DBP
formation if bromide ion is not present and adequate CT credit can be
established. As with ozone, bromate ion formation is a potential concern
with source waters containing bromide ions. The oxidation reaction of
bromide ion (Br^-^) to hypobromite ion (BrO^-^) and bromite ion
(BrO~2~^-^) and subsequently to bromate ion (BrO~3~^-^) occurs due to
direct reaction with ozone, intermediate reactions can also occur
through hydroxide radical mediated mechanisms if bromide is not present
and adequate CT credit can be established (Pereira et al., 1996).

In general, peroxone produces more bromate ion than ozone when similar
ozone residuals (CT credits) are achieved (Krasner et al., 1993). On the
other hand, when the ozone dosage is kept constant, peroxone has tended
to produce comparable amounts of bromate ion as ozone. Although peroxone
produces hydroxyl radicals that can increase bromate ion formation,
hydrogen peroxide may also reduce the hypobromite ion (produced
initially during the ozonation of bromide) back to bromide ion.

A study by MWDSC evaluated the effectiveness of peroxone to control
taste and odor, DBPs, and microorganisms (Ferguson et al., 1990). In
attempting to optimize the hydrogen peroxide to ozone ratio
(H~2~O~2~:O~3~) and the contact time for the source water, the study
found pre-oxidation of source waters followed by secondary disinfection
with chloramines was an effective strategy for controlling
concentrations of THMs and other DBPs. The study found that the two
source waters disinfected with peroxone, with free chlorine as the
secondary disinfectant, resulted in THM concentrations ranging from 67
to 160 μg/L. Conversely, using chloramines as a secondary disinfectant
resulted in THM concentrations consistently below 3.5 μg/L (Ferguson et
al., 1990).

However, if a short free chlorine contact time is applied after
biological filtration and before ammonia addition to inactivate
heterotrophic plate count bacteria in the effluent of the biologically
active filter---THMs and other DBPs will be formed at higher
concentrations than from post chloramination alone. Depending on the TOC
and bromide ion concentration of the water, as well as the pH of
chlorination, temperature, and reaction time, between 2 and 28 µg/L of
TTHMs have been formed in experiments conducted at MWDSC (personal
communication, 1998).

Bromate formation in conventional ozonation, and advanced oxidation
processes combining ozone and hydrogen peroxide, were recently
investigated at five water treatment plants in France. The source water
bromide ion concentrations ranged from 35 to 130 μg/L. Bromate ion
formation during the ozonation step varied from less than 2 to 42 μg/L.
In general, advanced oxidation results in greater bromate ion
concentrations when compared with conventional ozonation, provided the
same ozone residual is maintained for both processes. However, lower
concentrations of bromate ion result if the ozone dosage is kept
constant between the two processes and the hydrogen peroxide dosage is
increased (von Gunten et al., 1996). To reduce bromate ion formation
potential, the proposed ozone contactor at Stone Canyon Filtration Plant
includes three ozone application points instead of two (Stolarik and
Christie, 1997). Thus, when peroxone is used for obtaining CT credit,
more bromate ion may form than during ozonation. However, if peroxone is
only used for micropollutant destruction, less bromate ion may form than
when ozone is used.

## Status of Analytical Methods

Hydrogen peroxide in solution reacts with ozone to ultimately form water
and oxygen. Consequently, the simultaneous presence of both oxidants is
accepted as being only transient (Masschelein et al., 1977). Chapter 3
summarizes ozone analytical methods that can be used for ozone/hydrogen
peroxide disinfectant residual monitoring. This section will present the
status of analytical methods for hydrogen peroxide only.

### Monitoring of Hydrogen Peroxide

Standard Methods (1995) does not list procedures for measuring hydrogen
peroxide. Gordon et al. (1992) list several methods for hydrogen
peroxide analysis including:

-   Titration methods;

-   Colorimetric methods; and

-   Horseradish peroxidase methods.

Table 7-3 shows the working range, expected accuracy and precision,
operator skill level required, interferences and current status for
hydrogen peroxide analysis.

#### Titration Methods

Two titration methods are available for the analysis of hydrogen
peroxide; namely, iodometric and permanganate. Precautions for the
iodometric titration include the volatility of iodine, interferences by
metals such as iron, copper, nickel, and chromium, and fading titration
end points (Gordon et al., 1992). Organic and inorganic substances that
react with permanganate will interfere with the permanganate titration.

Titration of hydrogen peroxide with permanganate or iodide ion is not
sufficiently sensitive for determining residual concentrations
(Masschelein et al., 1977).

#### Colorimetric Methods

The most widespread method for the colorimetric determination of
hydrogen peroxide is that based on the oxidation of a Titanium (IV) salt
(Masschelein et al., 1977). A yellow complex is formed and measured by
absorption at 410 nm. On a qualitative basis, ozone and persulfates do
not produce the same colored complex.

The oxidation of the leuco base of phenolphthalein is used as a
qualitative test for hydrogen peroxide (Dukes and Hydier, 1964).
Sensitivity and precision of the method is sufficient in the range
between 5 and 100 μg/L. This low working analytical range makes this
method impractical for measuring hydrogen peroxide residual levels.
Also, the instability of the color obtained makes the method less
suitable for manual use. No interference data are available, but it is
expected that other oxidants would interfere (Gordon et al., 1992).

The oxidation of cobalt (II) and bicarbonate in the presence of hydrogen
peroxide produces a carbonato-cobaltate (III) complex (Masschelein et
al., 1977). This complex has absorption bands at 260, 440, and 635 nm.
The 260 nm band has been used for the measurement of hydrogen peroxide.
A detection limit of 0.01 mg/L has been reported (Masschelein et al.,
1977). Optical interferences are caused by 100 mg/L nitrate and 1 mg/L
chlorite ions. Other oxidizing agents do interfere with this method as
will any compound with an absorption at 260 nm (Gordon et al., 1992).

[]{#__RefHeading___Toc450036126 .anchor}Table 7-3. Characteristics and
Comparisons of Hydrogen Peroxide Analytical Methods

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

  Iodometric        \> 10       5               5               2            Oxidizing Species   Acidic    Yes       No            Currently
  Titration                                                                                                                        Used

  Permanganate      0.1 - 100   5               5               2            Oxidizing Species   Acidic    Yes       No            Currently
  Titration                                                                                                                        Used

  Colorimetry,      0.1 - 5     NR              NR              2            Ozone               Acidic    Yes       No            Not
  Titanium IV                                                                                                                      Recommended

  Colorimetry,      0.005 - 0.1 NR              NR              2            Ozone               Neutral   Yes       Yes           Not
  Leuco Base of                                                                                                                    Recommended
  Phenolphthalein                                                                                                                  

  Colorimetry,      0.01 - 1    NR              NR              2            Ozone               Neutral   Yes       Yes           Not
  Cobalt                                                                                                                           Recommended
  III/HCO~3~^-^                                                                                                                    

  HRP^b^            10^-8^ -    NR              NR              2            Other Peroxides,    4.5 - 5.5 No        Yes           Currently
                    10^-5^                                                   Ozone                                                 Used
  ----------------- ----------- --------------- --------------- ------------ ------------------- --------- --------- ------------- -------------

Notes:

> ^a^ Operator Skill Levels: 1 = minimal, 2 = good technician, 3 =
> experienced chemist
>
> NR = Not reported in literature cited by referenced source.
>
> Adapted from Gordon et al., 1992
>
> ^b^ This method can not be used in real peroxone-treated waters where
> the hydrogen peroxide concentration is significantly higher.

#### Horseradish Peroxidase Methods

Several methods incorporate the chemical reactions between peroxidase
and hydrogen peroxide. Horseradish derived peroxidase (HRP) is used most
often. The scopoletin procedure is one of the more widely accepted
fluorescent methods of low levels of hydrogen peroxide utilizing HRP
(Gordon et al., 1992). Again, no information is available on potential
interference.

#### Summary

In general, the analytical procedures for hydrogen peroxide in drinking
water are impacted by other oxidizing species such as ozone. Three of
the methods are currently used, but not recommended for disinfectant
residual measurement (Table 7-3). The scopoletin HRP method is the most
promising, although additional study of potential interferences is
required (Gordon et al., 1992).

## Operational Considerations

Peroxide is a strong oxidant and contact with personnel should be
avoided. Secondary containment should be provided for storage tanks to
contain any spills. Dual containment piping should be considered to
minimize the risk of exposure to plant personnel. Storage containers may
explode in the presence of extreme heat or fire.

### Process Considerations

The impacts of the peroxone process are similar to those described for
ozone in Chapter 3. Because an additional oxidant is added to the water,
the tendency to transform organic carbon compounds to a more
biodegradable form may be increased with the addition of peroxide.

### Space Requirements

The metering pumps used to add peroxide should be housed with adequate
space around each pump for maintenance access. These pumps are generally
not very large, so space requirements are not significant.

The storage area can range from small where peroxide is obtained in
drums, to large tank farms if plant flow is great. As mentioned
previously, secondary containment should be provided. Peroxide has a
lower freezing point than water. Housing or heat tracing should be
provided for storage tanks and exterior piping if extended periods with
temperatures below freezing are anticipated.

### Materials

Peroxide can be stored in polyethylene drums or tanks. The specific
gravity is 1.39 for 50 percent peroxide, which should be considered in
the design of the tank walls. Acceptable pipe materials for peroxide
include 316 stainless steel, polyethylene, CPVC, and Teflon. Gaskets
should be Teflon because natural rubber, Hypalon and EPDM are not
resistant to hydrogen peroxide. Metering pumps heads should be
constructed of peroxide resistant materials.

Hydrogen peroxide is purchased from chemical suppliers and is
commercially available in 35, 50, and 75 percent strengths. Peroxide is
supplied in drums or in bulk by tankcar. Price depends on strength and
quantity.

Peroxide can be stored onsite, but deteriorates gradually over time even
when stored correctly. Peroxide deteriorates rapidly if contaminated and
with heat or exposure to certain materials. Peroxide is added to the
water with metering pumps to accurately control dose. Pumps should be
designed to prevent potential air binding of peroxide off-gas. Multiple
pumps should be provided for redundancy. As with any chemical added to
water, adequate mixing should be provided.

## Summary

### Advantages and Disadvantages of Peroxone Use (Ozone/Hydrogen Peroxide)

The following list highlights selected advantages and disadvantages of
using peroxone as a disinfection method for drinking water. 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**

-   Oxidation is more reactive and much faster in the peroxone process
    compared to the ozone molecular process.

-   Peroxone is effective in oxidizing difficult-to-treat organics, such
    as taste and odor compounds.

-   Peroxone processes have been shown to be effective in oxidizing
    halogenated compounds.

-   The tendency to transform organic carbon compounds to a more
    biodegradable form may be increased with the addition of peroxide.

-   Pumps used to house peroxide are not very large; so space
    requirements are not significant.

**Disadvantages**

-   Peroxide is a strong oxidant and contact with personnel is extremely
    dangerous.

-   Peroxide can be stored onsite, but deteriorates gradually even when
    stored correctly.

-   Peroxone as a disinfection process does not provide a measurable
    disinfectant residual. It is therefore not possible to calculate CT
    similar to the use of other disinfectants.

-   Peroxone's ability to oxidize iron and manganese is less effective
    than that of ozone.

### Summary Table

Table 7-4 summarizes the considerations relative to peroxone
disinfection considerations.

[]{#__RefHeading___Toc450036127 .anchor}Table 7-4. Summary of Peroxone
Disinfection Consideration

  -----------------------------------------------------------------------
  **Consideration**     **Description**
  --------------------- -------------------------------------------------
  Generation            Because of its instability, ozone must be
                        generated at the point-of-use. Hydrogen peroxide
                        is purchased from chemical suppliers. Hydrogen
                        peroxide can be stored onsite, but is subject to
                        deterioration.

  Primary uses          Primary use includes chemical oxidation. As an
                        oxidizing agent, peroxone can be used to remove
                        SOC pollutants and increase the biodegradability
                        of organic compounds. Peroxone is an effective
                        disinfectant but its CT credit has not been
                        established. It is highly reactive and does not
                        maintain an appreciable residual for CT credit
                        calculations. Peroxone may be difficult to use
                        for disinfection because it is highly reactive
                        and does not maintain an appreciable ozone
                        residual level.

  Inactivation          Peroxone is one of the most potent and effective
  efficiency            germicides used in water treatment. It is
                        slightly more effective than ozone against
                        bacteria, viruses, and protozoan cysts.

  Byproduct formation   Peroxone itself does not form halogenated DBPs;
                        however, if bromide is present in the raw water
                        or if chlorine is added as a secondary
                        disinfectant, halogenated DBPs including bromate
                        may be formed. Other byproducts include organic
                        acids and aldehydes.

  Limitations           Ideally, ozone should be used as a primary
                        disinfectant prior to peroxone treatment.

  Point of application  For disinfection, peroxone addition should be
                        after ozonation. Ozone contact should precede
                        addition of hydrogen peroxide. For oxidation,
                        peroxone can be added prior to
                        coagulation/sedimentation or filtration depending
                        on the constituents to be oxidized.

  Special               Ozone generation is a relatively complex process.
  considerations        Storage of LOX for ozone generation is subject to
                        building and fire codes. Ozone is a highly toxic
                        gas and the ozone production and application
                        facilities must be monitored for ambient ozone.
                        Hydrogen peroxide is a hazardous material
                        requiring secondary containment for storage
                        facilities.
  -----------------------------------------------------------------------

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7\. PEROXONE (OZONE/HYDROGEN PEROXIDE)
[7-1](#peroxone-ozonehydrogen-peroxide)

7.1 Peroxone Chemistry [7-1](#peroxone-chemistry)

7.1.1 Oxidation Reactions [7-2](#oxidation-reactions)

7.1.2 Reactions with Other Water Quality Parameters
[7-3](#reactions-with-other-water-quality-parameters)

7.1.3 Comparison between Ozone and Peroxone
[7-3](#comparison-between-ozone-and-peroxone)

7.2 Generation [7-4](#generation)

7.3 Primary Uses and Points of Application
[7-5](#primary-uses-and-points-of-application)

7.3.1 Primary Uses [7-5](#primary-uses)

7.3.2 Points of Application [7-6](#points-of-application)

7.4 Pathogen Inactivation [7-6](#pathogen-inactivation)

7.4.1 Inactivation Mechanism [7-6](#inactivation-mechanism)

7.4.2 Environmental Effects [7-7](#environmental-effects)

7.4.3 Disinfection Efficacy and Pathogen Inactivation
[7-8](#disinfection-efficacy-and-pathogen-inactivation)

7.5 Disinfection Byproducts [7-9](#disinfection-byproducts)

7.6 Status of Analytical Methods [7-10](#status-of-analytical-methods)

7.6.1 Monitoring of Hydrogen Peroxide
[7-10](#monitoring-of-hydrogen-peroxide)

7.7 Operational Considerations [7-13](#operational-considerations)

7.7.1 Process Considerations [7-13](#process-considerations)

7.7.2 Space Requirements [7-13](#space-requirements)

7.7.3 Materials [7-13](#materials)

7.8 Summary [7-14](#summary-1)

7.8.1 Advantages and Disadvantages of Peroxone Use (Ozone/Hydrogen
Peroxide)
[7-14](#advantages-and-disadvantages-of-peroxone-use-ozonehydrogen-peroxide)

7.8.2 Summary Table [7-15](#summary-table)

7.9 References [7-16](#references)

Table 7-1. Comparison between Ozone and Peroxone Oxidation
[7-4](#__RefHeading___Toc450036124)

Table 7-2. Calculated CT Values (mg•min/L) for the Inactivation of
*Giardia muris* [7-8](#__RefHeading___Toc450036125)

Table 7-3. Characteristics and Comparisons of Hydrogen Peroxide
Analytical Methods [7-12](#__RefHeading___Toc450036126)

Table 7-4. Summary of Peroxone Disinfection Consideration
[7-15](#__RefHeading___Toc450036127)