The link between
water quality and health has been known since
the early ages. Clear water was considered
clean water. Swamp areas were associated with
fever.
Disinfection has been applied for centuries.
Two basic rules dating back to 2000 B.C. state
that water must be exposed to sunlight and
filtered with charcoal and that impure water
must be purified by boiling the water and than
dipping a piece of copper in the water seven
times, before filtering the water.
Descriptions of ancient civilizations were
found about boiling water and water storage in
silver jugs. To realize water purification
copper, silver and electrolysis were applied.
Disinfection has been applied for several
decades. However, the mechanism has been known
for only one hundred years.
In 1680 Anthony van Leeuwenhoek developed the
microscope. His discovery of microorganisms
was considered a curiosity. It took scientists
another two hundred years before they started
using the microscope to distinguish
microorganisms and other pathogens.
The first multiple filter was developed in
1685 by the Italian physician Lu Antonio Porzo.
The filter consisted of a settling unit and a
sand filtration unit. In 1746 the French
scientist Joseph Amy received the first patent
for a filter design, which was applied in
households by 1750. The filters consisted of
wool, sponges and charcoal.
For the past centuries humans have suffered
from diseases such as cholera and the plague.
The origin of these diseases was
misinterpreted. It was said that the diseases
were a devine punishment or were caused by
impure air or the alignment of the planets.
In 1854 a cholera epidemic caused many deaths
in the city of London. John Snow, an English
doctor, discovered that the cholera epidemic
was caused by a contaminated water pump, He
prevented a spread of the epidemic by closing
down the contaminated water pump. After that
scientists have performed bacteriological
studies to research the development, existence
and identification of microorganisms and the
removal of microorganisms from drinking water.
In the nineteenth century the effect of
disinfectants, such as chlorine, was
discovered. Since 1900 disinfectants are
largely applied by drinking water companies to
prevent the distribution of diseases and to
improve water quality.
When we open the
tap, clean tasty water flows out. Water
undergoes several purification steps before it
flows from taps.
Water that is used for drinking water
production contains water molecules and a
large variety of other substances. One of the
properties of water is that it easily
dissolves other substances. Water that falls
to earth during rain showers dissolves
substances, particles and gasses such as
oxygen, which can be found in air.
Contaminants that are present in air also
dissolve in rain water. When surface water
flows on earth it also dissolves several
different substances, such as sand particles,
organic matter, microorganisms and minerals.
Water that settles into the ground and becomes
groundwater often contains large amounts of
dissolved minerals, as a result of contact
with soils and rocks. Human activities, such
as agriculture and industrial waste and sewer
water discharge cause a number of pollutants
to enter the water.
Water
purification has largely developed in the past
century. Drinking water disinfection has
decreased the number of outbreaks of
waterborne diseases, such as cholera and
typhoid.
In developing countries there is usually not
enough clean drinking water or sewerage. In
these countries waterborne diseases cause many
people to be ill or to die, mainly fragile
groups such as young children, elderly people
and people with a weakened immune system (AIDS
patients and organ transplant receivers).
The larger part of pathogenic microorganisms
is removed by means of water treatment
techniques, such as coagulation, flocculation,
settling and filtration. To increase drinking
water safety disinfection is applied as a
final treatment step.
There are several different disinfectants,
which either kill or deactivate pathogenic
microorganisms. Examples of disinfectants are
chlorine containing substances, peroxide,
bromine, silver-copper, ozone and UV. All
disinfectants have benefits and drawbacks and
can be used for water disinfection depending
on the circumstances.
Besides drinking water disinfection,
disinfection may also be applied in swimming
pools and cooling towers. Water disinfection
is a very important factor for these
applications.
Swimming pools contain a large variety of
contamination, which originates largely from
swimmers. The contamination contains
microorganisms, among other things.
To prevent contagion of swimmers by pathogenic
microorganisms, swimming water must be
disinfected. Swimming pool water is often
circulated. Before the water is returned to
the swimming pool it is purified. The
purification includes disinfection.
Cooling towers are used to cool down process
water. After that the water can be reused.
Within cooling towers circumstances are ideal
for growth and multiplication of
microorganisms. Bio film development is a
mayor problem in cooling towers, because this
promotes corrosion and blocks the system.
Another problem in cooling towers, as well as
ventilation systems, is the development of
legion Ella bacteria. These bacteria spread
through aerosols and can cause legionnaires
disease. This is a very serious disease that
resembles pneumonia. Many countries now have
legal standards, determining that the
development of legion Ella bacteria in cooling
towers should be prevented by the disinfection
of cooling water.
In the early seventies it was discovered that
disinfection byproducts can form during water
disinfection by means of chemical
disinfectants. When this was discovered
research started on the development and health
effects of these byproducts. Today there are
legal standards indicating maximum levels of
disinfection byproducts in drinking water.
Methods to lower the concentration of
disinfection byproducts in drinking water have
also been researched.
Water
disinfection means the removal, deactivation
or killing of pathogenic microorganisms.
Microorganisms are destroyed or deactivated,
resulting in termination of growth and
reproduction. When microorganisms are not
removed from drinking water, drinking water
usage will cause people to fall ill.
Chemical
inactivation of microbiological contamination
in natural or untreated water is usually one
of the final steps to reduce pathogenic
microorganisms in drinking water. Combinations
of water purification steps (oxidation,
coagulation, settling, disinfection,
filtration) cause (drinking) water to be safe
after production. As an extra measure many
countries apply a second disinfection step at
the end of the water purification process, in
order to protect the water from
microbiological contamination in the water
distribution system. Usually one uses a
different kind of disinfectant from the one
earlier in the process, during this
disinfection process. The secondary
disinfection makes sure that bacteria will not
multiply in the water during distribution.
Bacteria can remain in the water after the
first disinfection step or can end up in the
water during back flushing of contaminated
water (which can contain groundwater bacteria
as a result of cracks in the plumbing).
Disinfection
commonly takes place because of cell wall
corrosion in the cells of microorganisms, or
changes in cell permeability, protoplasm or
enzyme activity (because of a structural
change in enzymes). These disturbances in cell
activity cause microorganisms to no longer be
able to multiply. This will cause the
microorganisms to die out. Oxidizing
disinfectants also demolish organic matter in
the water, causing a lack of nutrients.
