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Microorganisms |
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Microorganisms can be found commonly in
nature. Invisible to bare eyes,
microorganisms are present in soils,
air, food and water. Before humans are
born, we are free from microorganisms.
Through consumption of food and air we
are exposed to microorganisms soon after
we are born. The microorganisms will
remain present on and in our bodies.
Most microorganisms are harmless and
will contribute to a number of vital
processes in the human body, such as the
metabolism. But there are also
microorganisms which can cause disease
or which are harmful to people with low
resistance to disease.
Pathogenic microorganisms in the water
have a number of specific properties
which distinguish them from chemical
contaminants. They are living organisms.
They are not dissolved in water, but
they will coagulte or attach to colloids
and solids in water. |
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Types of pathogenic microorganisms |
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Pathogenic
microorganisms in drinking water can be
divided up into three types: bacteria,
viruses and parasitic protozoa. Bacteria
and viruses can excist in both surface
water and groundwater, whereass
parasitic protozoa can be found mainly
in surface water. |
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Bacteria |
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Bacteria
are single-cell organisms, shaped like a
sphere, spiral or rod. They can excist
as individual bacteria or in bacterial
chains, bundles or pairs. Bacteria are
the most abundant lifeform on earth.
They are between 0,4 and 14 μm in length
and about 0,2 to 12 μm in width.
Consequentially they can only be viewed
under a microscope. Bacteria feed on
fluid nutrients. They can reproduce by
means of DNA replication, causing a
bacteria to split into two independent
cells. In ideal circumstances this
process taken about 15 to 30 minutes.
Some types of bacteria can form spores.
These spores contain a protective layer
which is heat resistant and can protect
bacteria from a lack of moist and food.
Bacteria play a role in various
processes. Some bacteria breack down
organic matter and play an important
ecological role, other assist in the
human metabolism. |
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Viruses |
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Viruses
are organisms which can cause infections
and which only reproduce in living host
cells. When viruses excist outside host
cells, they are inactive. Viruses
contain a protective shell. They are
shaped like a spear, sphere or wire and
they are so small (between 0,02 and 0,09
μm) that they can slip through filters
which capture bacteria.
Contrary to bacteria and parasitic
protozoa, viruses contain only one type
of nucleic acid (RNA or DNA). They
cannot reproduce, but instead take over
the metabolism of the host cell and make
sure the DNA is copied in the host cell,
causing new viruses to develop. |
Three different types of viruses |
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Contrary to bacteria, viruses are not
naturally present in the human body.
When people are infected with a virus it
usually leaves the body through
secretion. When secreation takes place
water can be contaminated with viruses.
When the water is not thoroughly
disinfected, other people can be
infected with viruses. |
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Parasitic protozoa |
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Parasitic
protozoa are single-cell organisms. They
have a very complex metabolism and feed
on solid nutrients, algae and bacteria
which are present in multiple-cell
organisms, such as humans and animals.
Multiplication take place through
splitting of the cells. Various types of
parasitic protozoa are spread in
sleeping, protected form as a cyste or
oocyste. Oocysts of Cryptosporidium and
cysts of Giardia can be found in waters
throughout the world as a consequence of
fecal pollution. As cysts the pathogens
are resistant to chlorine disinfection.
Parasitic protozoa can be removed by
means of filtration or chlorine dioxide
application. |
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The odds of infection |
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The odds
of infection depend upon the type of
pathogen, the way in which it is
transferred, the infective dose and
persistence of the microorganism, and
the resistance of the person that is
infected.
The infective dose means the number of
microorganisms that need to enter te
body before the disease occurs. This
dose is very low for viruses and
parasitic protozoa. The persistence of a
microorganism depends upon the viable
time of the microorganism, when it is
not present in a human host. Bacteria
are commonly the least persistent
microorganisms, and protozoic cysts are
the most persistent ones.
Young children, elderly people and sick
people have a lower resistance to
disease and are therefor more fragile.
When a person is infected the pathogens
multiply within the host, causing the
risk of illness to rise. Not every
person that is infected with a pathogen
falls ill. People that do become ill
will spread a disease easily, mainly
through secretion. |
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Secretion and sewer water |
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When water
flows through a certain area, it
collects all kinds of substances and
gives these off in other areas.
Microorganisms also enter the water. The
larger part of microorganisms which
cause waterborne diseases originate from
human or animal feaces.
One drop of feaces contains millions of
microorganisms. In the faeces of cattle
there can be millions of E. Coli
bacteria , Giardia cysts and
Cryptosprodium spores. |
E.-Coli-Bacteria |
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In chicken
faeces pathogenic bacteria such as
Salmonella and Campylobacter can be
present. When fertilizers are applied to
land, rain can cause bacteria to rinse
out te surface water or groundwater,
causing the microorganisms to
contaminate water. |
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Cryptosporidium spores |
Giardia cysts |
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Sewer or waste water cannot be
discharged into the environment
untreated. The larger part of
purified waste water ends up in
rivers, lakes and oceans.
Sometimes heavy rainfall can cause
sewer systems to flood, causing
untreated water to end up in
surface water or groundwater. Not
every country purifies water
before it enters surface or
groundwater. Mainly developing
countries lack sanitary
facilities. The water can
contaminate water that is used for
drinking water purposes, causing
the risk of infection with
diseases carried by waterbone
microorganisms to become very
high. this is a particular risk
when drinking |
Legionella-Bacteria |
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water is
not treated at all. When septic tanks
are used for waste water treatment,
pathogenic microorganisms can
contaminate surface water and
groundwater sources. |
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Not all pathogenic microorganisms in
water originate from faeces. Legionella
(figure 5) can be found commonly in
water and easily multiplies in the water
distribution system. There are also
other pathogenic microorganisms that can
be found commonly in surface water. |
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Pollutants in swimming pools |
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The water
in public swimming pools contains
microorganisms and unwanted substances,
which derive from the skin and excretion
products of swimmers. Swimmers cause
many pollutants to enter the water, such
as bacteria from saliva, excretion
products, pollution from swimwear, skin
tissue, sebum, sweat, nose and throat
saliva, hairs, cosmetics and ammonia
(NH3). Vouching for clean swimming pool
water through constant refreshment is
often too expensive. Furthermore, this
does not solve the problem of pollutants
that remain on swimming pool walls. The
water is recicled, causing pollutant and
pathogen concentrations to increase.
Microorganisms will multiply and this
causes the risks of contagion to
increase. |
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Dissolved pollutants |
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Swimming
pool water contains dissolved
pollutants, such as urine and sweat and
other excretion products of swimmers.
Sweat and urine largely consist of
water, ammonia and ureum. These
substances also contain kreatine,
kreatinine and amino acids. The
components of sweat and urine are not
harmful for human health. However, when
these products react with disinfectants
in the water, such as chlorine, unwanted
reaction products can be formed which
consist mainly of chloramines.
The water can contain dissolved
pollutants that derive from
disinfectants and cleansing agents that
are used to clean swimming pools.
Dissolved pollutants are largely removed
by oxidation. This means that pollutants
are decomposed by chemicals. Substances
that are not or partly decomposed during
the oxidation process and oxidation
products are removed from the
circulation system by gradual
refreshment of swimming pool water. |
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Health effects of
swimming pool pollutants |
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Swimmers
are susceptive to pathogenic
microorganisms in swimming pool water.
As a result of cooling and water uptake,
the resistance of the mucous membranes
of swimmers can weaken, causing them to
become more susceptive to pathogens in
swimming pool water and air, and even to
pathogens that are present in their own
bodies. Microorganisms that enter the
water through excretion by swimmers can
cause a large variety of conditions.
Most pathogenic microorganisms cause
diarrhoea or skin rashes. Certain
microorganisms can cause serious
symptoms, such as paralysis, brain
inflammation, heart inflammation,
jaundice, fevers, vomiting, diarrhoea
and respirational or eye infections.
Pathogenic mciroorganisms that can be
found in swimming pool water are
bacteria, viruses and parasitic
protozoa. Young children, elderly people
and people with damaged immune systems
are more susceptive to infections caused
by these species and will fall ill more
easily. People that have an untreated
form of cancer may also suffer from
lower resistance to waterborne diseases.
Not every person that is infected will
fall ill, but hen or she can still cause
contagion of other people.
In developing countries, the number of
people with damaged immune systems is
increasing, as a result of an increase
in the number of AIDS patients in the
last 20 years. |
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Disinfection of
swimming pool water |
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Micro-organisms polluted swimming pools.
Every swimmer adds 1.000.000 to
1.000.000.000 microorganisms to the
water. The water itself contains
microorganisms, as well. After oxidation
a disinfectant must be added to the
water to kill pathogenic microorganisms. |
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Demands on
disinfectants |
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Disinfectants used for swimming pool
water disinfection must meet certain
demands. They should be harmless and
non-irritating to swimmers and
attendants. They must be active in small
concentrations and remain their activity
for a long time.
Contrary to drinking water
disinfectants, disinfectants for
swimming pool treatment must be active
in the pool itself, because pollutions
and pathogenic micro-organisms are
constantly added to the water. Therefore
the water has to maintain a residual
disinfectant concentration. The
disinfectant must be easily traced and
measured and should be safe to use. |
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Disinfection methods for swimming
pool water |
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In some
countries, sodium hypochlorite is used
for both oxidation and disinfection of
swimming pools. When it is added to
water, sodium hypochlorite increases the
pH value. It is better to use chlorine
as a disinfectant and an oxidizer at a
pH value of 6,5. Often, acid is added to
lower the pH value. |
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