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Hydrogen peroxide
Disinfection And Health Effects
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Most people know hydrogen peroxide as a
compounds that bleaches hair. It can also be used for water disinfection.
Louis Jacque Thenard discovered hydrogen
peroxide in 1818.
Hydrogen peroxide consists of oxygen and hydrogen atoms. These can be found everywhere on earth.
Hydrogen peroxide contains a combination of two hydrogen
atoms and two oxygen atoms.
In the environment, hydrogen peroxide can be found in
very low concentrations.
Gaseous hydrogen peroxide is produced by photo chemical
reactions in the atmosphere surrounding the earth. It can also be found in
water in small quantities.
Peroxide is a chemical compound that contains
the peroxide ion (O22-).
The peroxide ion consists of a single bond between two oxygen atoms: (O-O)2-.
It is a strong oxidiser.
Hydrogen peroxide has the chemical formula H2O2 and
the following structural formula: H-O-O-H
The hydrogen peroxide molecule contains one extra oxygen
atom, compared to the more stable water molecule.
The bond between the two oxygen atoms, the so-called
peroxide bond, is broken while two H-O radicals are formed. These radicals
quickly react with other substances, while new radicals are formed and a chain
reaction takes place.
Hydrogen peroxide solutions look like water and can be
dissolved in water unrestrainedly. At high concentrations these solutions give
off an irritating, acidic smell.
Hydrogen peroxide is inflammable. At low temperatures it
becomes solid.
The amount of hydrogen peroxide in the solution is expressed in
weight percentage.
For water treatment, concentrations of 35 or 50 %
hydrogen peroxide are used.
Selectivity
Hydrogen peroxide is used for different
applications, because it is very selective. By changing the reaction conditions
(temperature, pH, dose,
reaction time and the addition of a catalyser),
hydrogen peroxide will attack different pollutions.
Corrosiveness of hydrogen
peroxide
The corrosiveness of process water due to
hydrogen peroxide depends on the amount of dissolved oxygen that is produced.
Oxygen corrodes iron-containing metals. The amount of iron and the pH are a
greater influence on corrosiveness than the concentration of hydrogen peroxide
is.
Destruction of hydrogen
peroxide
Hydrogen peroxide can disintegrate during
transport. Oxygen and heat are released. Hydrogen peroxide itself is
inflammable, but the oxygen can enhance the inflammation of other substances.
In diluted solutions, the heat is absorbed by water. In
concentrated solutions, the temperature of the solution is increased,
accelerating hydrogen peroxide destruction.
The rate of destruction is multiplied with 2,2 for every
10 °C of rise in temperature. The alkalinity and presence of pollutions also
accelerate the destruction of hydrogen peroxide.
For the production of hydrogen peroxide, special
catalysers are used to make sure that hydrogen peroxide is not destroyed by
pollutants in the water.
Since 1880, hydrogen peroxide is a commercial
product. It was first produced in the United Kingdom by burning barium salt (Ba), which produced barium peroxide (BaO2).
Subsequently the barium peroxide was dissolved in water
and hydrogen peroxide was produced. Since the 19th century the production of
hydrogen peroxide has largely increased. Nowadays about half a billion
kilograms are produced annually.
When hydrogen peroxide comes in contact with flammable
substances, such as wood, paper, oil or cotton (cellulose), spontaneous
ignition may occur.
When hydrogen peroxide is mixed with organic matter, such
as alcohols, acetone and other ketones, aldehydes and glycerol, heavy
explosions may occur.
When hydrogen peroxide comes in contact with substances,
such as iron, copper, chromium, lead, silver, manganese, sodium, potassium, magnesium, nickel, gold, platinum, metalloids, metal oxides or metal salts, this may
result in powerful explosions. This is why hydrogen peroxide is usually
transported in diluted form.
The oldest known application of hydrogen
peroxide was bleaching straw hats, which were fashionable in the beginning of
the twentieth century.
From 1920 to 1950, hydrogen peroxide was produced through
electrolysis. This method produced pure hydrogen peroxide.
Nowadays, self-oxidation processes are used to produce
hydrogen peroxide. During these processes, hydrogen is the raw material.
Versatility of hydrogen
peroxide
Hydrogen peroxide is versatile. It can be
used for many applications. It can be used in all media; air, water, waste
water and soils. It is sometimes used combined with other agents, to enhance
and accelerate processes.
Hydrogen peroxide is most commonly used to remove
pollutants from waste water and from air. It contests bacterial growth (for
example bio fouling in water systems) and it can enhance bacterial growth (for
example bio remediation of polluted soils and ground water) through oxygen addition.
It can also be used to treat pollutions that can be
easily oxidized (for
example iron and sulphides) and pollutions that are difficult to
oxidise (for example dissolved solids, gasoline and pesticides).
Finally, it can be used to bleach paper, textile, teeth
and hair or to produce food, minerals, petrochemical substances or washing
powder.
In pure form, hydrogen peroxide is used as an oxygen
provider to drive Russian submarines.
Hydrogen peroxide is a strong oxidiser. It is
more powerful than chlorine (Cl2), chlorine dioxide (ClO2) and potassium permanganate (KMnO4).
Through catalysis, hydrogen peroxide can be converted
into hydroxyradicals (OH).
The oxidation potential of hydrogen peroxide is just
below that of ozone.
Table 1: Oxidation potentials of various oxidisers
Oxidiser
|
Oxidation potential
|
|
|
3,0
|
hydroxyradicals
|
2,8
|
|
|
2,1
|
hydrogen peroxide
|
1,8
|
potassium permanganate
|
1,7
|
|
|
1,5
|
|
|
1,4
|
Most hydrogen peroxide applications consist
of hydrogen peroxide injection into flowing water. No other chemicals or
equipment are required.
This application is used to control biological growth, to
add oxygen, to remove chlorine residues and to oxidize sulphides, sulphites,
metals and other easily oxidized materials. The suitability of hydrogen
peroxide for these applications is influenced by pH, temperature and reaction
time.
Catalytic hydrogen peroxide
Pollutions that are not easily oxidized,
require hydrogen peroxide activation by catalysers (iron, manganese or other metalloids). These
catalysers can also be
used to enhance hydrogen peroxide reactions, which would otherwise take hours
or days.
What are advanced oxidation
processes?
Advanced oxidation processes are a new
development in the field of hydrogen peroxide disinfection. These processes
produce reactive oxygen radicals, without the interference of metal catalysers.
Examples are the combination of hydrogen peroxide
with ozone (peroxone) or Ultra Violet Light. The result of these methods is far-reaching oxidation
of difficultly degradable substances, without the production of residues or
sludge.
These methods are used worldwide for groundwater
treatment, for drinking water and process water treatment and for organic
matter disinfection and removal from industrial wastewater.
Among other applications, hydrogen peroxide
is used as a disinfectant. It is used to treat inflammation of the gums and to
disinfect (drinking) water.
It is also used to combat excessive microbial growth in
water systems and cooling towers.
In the United States, hydrogen peroxide is used more and
more frequently to treat individual water supplies. It is used to prevent the
formation of colors, tastes, corrosion and scaling by pollution degradation
(iron, manganese, sulphates) and micro-organism degradation.
Hydrogen peroxide reacts very fast. It will than
disintegrate into hydrogen and water, without the formation of byproducts.
This increases the amount of oxygen in water.
The disinfection mechanism of hydrogen peroxide is based
on the release of free oxygen radicals:
H2O2 → H2O + O2
Pollutions are decomposed by free oxygen
radicals, and only water remains. Free radicals have both oxidising and
disinfecting abilities. Hydrogen peroxide eliminates proteins through
oxidation.
Peroxides such as hydrogen peroxide (H2O2),
perborate, peroxiphosphate and persulphate, are good disinfectants and
oxidisers. In general these can adequately remove micro-organisms. However,
these peroxides are very unstable.
Perborates are very toxic. Peracetic acid (PAA) is a
strong acid. It can be very aggressive in its pure form. Stabilised
persulphates can be used to replace chlorine for waste water treatment.
In the 1950's, hydrogen peroxide was first
used for drinking water disinfection in Eastern Europe. It is known for its
high oxidative and biocidal efficiency. Hydrogen peroxide has not been used
often for drinking water disinfection, but it's popularity seems to increase.
It is often used combined with ozone, silver or UV.
The application of peroxides for disinfection
and water treatment are limited. Recently, more stable forms have been
developed, which can be used for application in swimming pools.
Hydrogen peroxide disinfection requires a high dose. The
main disadvantage is the small disinfecting and oxidising ability of hydrogen
peroxide at active concentrations (tens of milligrams per litre), which are
required for swimming pool disinfection.
Another problem is the quick decomposition of hydrogen
peroxide in water and the presence of oxygen radicals. Through stabilizer
addition, the decomposition of hydrogen peroxide is delayed and the
disinfection ability can be maintained.
Compared with chlorine, bromine, ozone and other disinfectants, hydrogen peroxide is not
a very powerful disinfectant.
Swimming pools disinfection by hydrogen peroxide is not
allowed, unless it is used in combination with other disinfectants (UV, ozone,
silver salts or ammonia quart salts). Hydrogen peroxide improves the
disinfection ability of other disinfectants.
Hydrogen peroxide can be used for cooling
tower water disinfection, when it is combined with other disinfectants.
Peracetic acid (CH3COOH, PAA) can also be used for cooling tower
water disinfection.
Hydrogen peroxide can be used for
dechlorination, in other words to remove residual chlorine. Residual chlorine
forms corrosive acids when it is oxidised by air or condensates on process
systems.
When chlorine reacts with hydrogen peroxide, hydrogen
peroxide falls apart into water and oxygen. Chlorine gas hydrolyses into
hypochlorous acid (HOCl), which subsequently ionises into hypochlorite ions
(OCl).
Cl2 + HOCl + H+ +
Cl
HOCl + H+ + Cl
After thaT, hydrogen peroxide reacts with
hypochlorite:
OCl- + H2O2 (g)
-> Cl- + H2O + O2
The reaction between hydrogen peroxide and hypochlorite
takes place very quickly. Other organic and inorganic substances cannot react
with hypochlorite.
Advantages: Contrary to other chemical
substances, hydrogen peroxide does not produce residues or gases. Safety
depends on the applied concentration, because hydrogen peroxide is completely water
soluble.
Disadvantages: Hydrogen peroxide is a
powerful oxidizer. It reacts with a variety of substances. It is therefore
diluted during transport, as a safety measure. However, for hydrogen peroxide
disinfection, high concentrations are required.
Hydrogen peroxide slowly decomposes into water and
oxygen. An elevation of temperature and the presence of pollutions enhance this
process.
The concentration of hydrogen peroxide in a solution slowly decreases. This is
caused by the following reaction:
2 H2O2 → 2 H2O + O2
This is a redox reaction. Hydrogen molecules partly function as
reductors
and partly as oxidizers.
Is hydrogen peroxide efficient?
The efficiency of hydrogen peroxide depends
on several factors, such as pH, catalysers, temperature, peroxide concentration
and reaction time.
Exposure to hydrogen peroxide takes place
through inhalation of damp or mist, through food uptake and through skin or eye
contact.
Hydrogen peroxide can irritate the eyes, skin and mucous
membranes.
Exposure of the eyes to concentrations of 5%
or more can result in permanent eye damage.
Tests with laboratory animals from the American
International Agency on Cancer Research (IARC) show that hydrogen peroxide can
be carcinogenic to animals.
Laboratory tests with bacteria show that hydrogen
peroxide is mutagenic; it changes and damages DNA.
When humans inhale hydrogen peroxide, it causes lung
irritation. Skin exposure causes painful blisters, burns and skin whitening.
Organs that are extra susceptive to hydrogen peroxide
exposure are the lungs, the intestines, the thymus, the liver and the kidneys.
The effects of chronic exposure on humans are unknown.
Effects on reproduction and development are not demonstrated so far.
For disinfection, hydrogen peroxide can be
combined with other agents. For example peracetic acid and peroxone.
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In fact, it was previously
thought to be a good and healthful substance. 
Part of the reason mercury is
extremely toxic is because it can enter the body through inhalation, ingestion
or skin absorption. 
Mercury has no value to the
human body and is best thought of as poison. The effects of mercury exposure
vary depending on the form and level of exposure.
Breast milk can become
contaminated and in utero exposure to mercury has been attributed to an
increase in neural tube defects. 
Lead 
.
