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WATER FAQS

W hat is w at er purif ication?

Water purification generally means freeing water from any kind of impurity itcontains, such as contaminants or micro organisms.Water purification is not a very one-sided process; the purification process containsmany steps. The steps that need to be progressed depend on the kind of impuritiesthat are found in the water. This can differ very much for different types of water.

I n which way s is polluted wat er treate d?

Settling

Before the purification process begins some contaminants, such as oil, can be settledin a settling tank. They can then be removed easily, after they have reached thebottom of the tank.

Removal of dangerous microorganisms

Often polluted water has to be freed from microorganisms. The water is thandisinfected, usually by means of chlorination.

Removal of dissolved solids

Microorganisms are not only a threat to water; they can also be an advantage when

it comes to water purification processes. They can convert harmful contaminants toharmless substances. This biological purification process usually takes a long timeand it is only used for water that is polluted with contaminants that themicroorganisms, usually bacteria, can convert.

Physical/ chemical techniques

When treatment by microorganisms is not an option we often use different treatmenttechniques, called physical/ chemical treatment techniques. Chemical treatmentoften deals with the addition of certain chemicals, in order to make sure that thecontaminants change structure and can then be removed more easily. Fertilizerssuch as nitrates are removed this way. Removal of contaminants can also be donethrough more difficult specific chemical processes. It takes a lot of education to fully

understand these purification steps. Physical treatment usually deals with purificationsteps such as filtration.

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Water pollution treatment process

More detailed descriptions ofwater purification steps are available here

How can bacteria be removed from wa ter?

Bacteria and other microorganisms are removed from water through disinfection.This means that certain substances are added to kill the bacteria, these are calledbiocides. Sometimes disinfection can also be done with UV-light.

What is aerobic w ater treat ment?

When bacteria are used for water purification there are two sorts of transfer; one ofthese is aerobic transfer. This means, that bacteria that are oxygen dependent areconverting the contaminants in the water. Aerobic bacteria can only convertcompounds when plenty of oxygen is present, because they need it to perform anykind of chemical conversion. Usually the products they convert the contaminants toare carbon dioxide and water.

What is anaerobic w ater trea tm ent?

When bacteria are used for water purification there are two sorts of conversion; oneof these is anaerobic transfer. This means, that bacteria that are NOT oxygendependent are converting the contaminants in the water. Anaerobic bacteria can onlyconvert when oxygen levels are low, because they use other sorts of substances toperform chemical conversion. Anaerobic bacteria do not just develop carbon dioxideand water during conversion, but also methane gas. This can be used to keep themachinery that supports the purification going. The anaerobic conversion of asubstance requires more steps than aerobic conversion, but the final result is oftenless satisfactory. After anaerobic conversion usually aerobic bacteria (bacteria thatdo use oxygen) still need to finish the process, because the water is not cleanenough yet.

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How are fert i lizers rem oved from w ater?

Fertilizers such as phosphate are removed through addition of another chemical,

usually iron. The substances than become solid precipitates, that can be filteredfrom the water.

The removal of ammonium and nitrates is a little bit more complicated; it is apurification process that takes both aerobic and anaerobic conversion to removethem.In the aerobic conversion stage there are two bacterial species involved.Nitrosomonas bacteria that convert ammonia to nitrite and Nitrobacter bacteria thatconvert nitrite to nitrate after that.Although nitrate does not represent a direct health threat to most fish, high levelsare still undesirable. Apart from encouraging abnormal extensive algal growth, it isnow believed that high nitrate levels are implicated in some fish diseases. Thismeans that the process cannot be stopped here.The anaerobic bacteria take over; they convert nitrate to atmospheric nitrogen gas.This process only occurs in the absence of oxygen. The first stage is the reverse ofthe nitrification process, it converts nitrate back to nitrite. The second stage ofdenitrification converts nitrite to nitrogen gas (N2). This gas can be freely releasedinto the atmosphere without causing environmental damage.

W hat is microbiology?

Microbiology is the scientific field that is occupied with the study of microscopicorganisms, commonly known as microorganisms.

What are microorganisms?

All living creatures consist of cells. Cells are very small basic units of life. They arethe smallest structures capable of basic life processes, such as taking in nutrientsand expelling waste. Cells can only be made visible by microscopes.Microorganisms are organisms that usually consist of one single cell. Because of this,they are often referred to as "single-celled organisms". They are so small, thathumans cannot visualize them. We can only see them through microscopes, by whichthe cells are greatly enlarged.

At first, microorganisms were not seen as a separate kind. Microorganisms thatcarried out photosynthesis (see carbon cycle) were classified in the plant kingdom,and microorganisms that ingested food were placed in the animal kingdom. However,

in the 19th century, scientists had identified a wide variety of microorganisms withdiverse cell structures, very specific internal structures, and specific reproductivepatterns that made them realize these organisms did not belong to the plant oranimal kingdom.

W hat k inds of m icroorganisms are t here?

Microorganisms are divided up by their cell characteristics, in the same way as plantsand animals. There are two kinds of (micr) organisms. The first kind is the eukaryoticorganism (protista). Most organisms are eukaryotic, which basically means that thecells they consist of contain nucleuses and other internal parts, surrounded bymembranes. The second kind of microorganisms is the prokaryotic organism

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(monera). Prokaryotic cells are surrounded by a membrane, but they contain nonucleus or other internal parts (organelles), contrary to eukaryotic cells.

Monera and protists

The monera are bacteria and cyanobacteria. They are single-celled prokaryoticmicrorganisms, as was mentioned earlier. Bacteria are very important for otherorganisms, because they break down organic matter. During this process nutrientsare formed, which are reused by plants and animals. Some of the bacteria that liveon earth can cause disease, but most of them are quite useful as they aid animals inthe decomposition of food in their bodies. Bacteria differ from other types of cells inthe fact that they do not have a nucleus. With plants and animals this is where theDNA (genetic information) can be found. With bacteria the genetic material floatswithin the cell. They reproduce by first copying their DNA and than performing celldivision. Bacteria also lack membrane-bound organelles, such as mitochondria, thecell structures involved in energy metabolism.

Bacterial cells are so small that scientists measure them in units called micrometers(m), a millionth of a meter. An average bacterium is about one micrometer long.Bacteria know several different kinds of subdivisions, such as spherical (coccus) androd-shaped (bacillus) bacteria.

Spherical bacteria Rod-shaped bacteria

The protists are single-celled eukaryotic microorganisms, as mentioned earlier.Examples are amoebas, diatoms, algae and protozoa. These can be a danger tohuman and animal health, as certain protists can cause diseases, such as malariaand sleeping sickness. There are a wide variety of protists, and they inhabit manydifferent environments; fresh water, seawater, soils, and the intestinal tracts ofanimals, where they perform crucial digestive processes.Many species of protists can produce their own nutrients by the process ofphotosynthesis and many protists can also move around on their own accord.Protists vary greatly in size and shape; the green alga Nanochlorum is only 0.01 mmlong, but giant kelps can grow to 65 m or more in length.

W hich m icroorganisms in w ate r cause diseases?

Sometimes microorganisms that cause health effects can be found in drinking water.However, as drinking water is thoroughly disinfected today, disease caused bymicroorganisms is rarely caused by drinking water.People that swim in swimming pools will find that the water they swim in isdisinfected with either chlorine, ozone, UV or chlorine dioxide. But there are peoplethat swim outside in surface water every year. These are the people that are most

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susceptible to bacterial infections and infections caused by other microorganisms,because microorganisms often enter surface water through industrial discharge andanimal excrements. When you are an outside swimmer, you always have to be

careful and read the signs placed by the waterside, because the water you areswimming in may be infected, for example with botulism.There are various bacteria and protozoa that can cause disease when they arepresent in surface water.

Bacteria are not only known to cause disease when they enter a human bodythrough food, surface water may also be an important source of bacterial infection.In this table you can see various bacteria that can be found in surface water, and thediseases they cause when swallowed in large amounts, along with the symptoms.

Bacteria Disease/ infection Symptoms

Aeromonas Enteritis Very thin, blood- and

mucus-containing diarrhoeaCampylobacter jejuni Campilobacteriose Flue, diarrhoea, head- and

stomachaches, fever,

cramps and nausea

Escherichia coli Urinary tract infections,

neonatal meningitis,

intestinal disease

Watery diarrhoea,

headaches, fever, homiletic

uraemia, kidney damage

Plesiomonas shigelloides Plesiomonas-infection Nausea, stomachaches and

watery diarrhoea,

sometimes fevers,

headaches and vomiting

Salmonella Typhoid fever FeversSalmonellosis Sickness, intestinal cramps,

vomiting, diarrhoea and

sometimes light fevers

Streptococcus (Gastro) intestinal disease Stomachaches, diarrhoea

and fevers, sometimes

vomiting

Vibrio El Tor (freshwater) (Light form of) Cholera Heavy diarrhoea

Protozoa can accumulate in certain body parts, after they have penetrated a humanbody. The accumulations are called cysts.

Because of their parasitic nature, protozoa can cause various diseases. In this tableyou can see various protozoa that can be found in surface water, and the diseasesthey cause when swallowed in large amounts, along with the symptoms.

Microorganism Disease Symptoms

Amoeba Amoebic

dysentery

Severe diarrhoea, headache, abdominal pain,

chills, fever; if not treated can cause liver

abscess, bowel perforation and death

Cryptosporidium

parvum

Cryptosporidiosis Feeling of sickness, watery diarrhoea,

vomiting, lack of appetite

Giardia Giardiasis Diarrhoea, abdominal cramps, flatulence,

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belching, fatigue

Toxoplasm

gondii

Toxoplasmosis Flu, swelling of lymph glands

With pregnant women subtle abortion and

brain infections

How do we el iminate harm ful microorganisms from w ater?

To eliminate harmful microorganisms from water we tend to use disinfectants.Examples of disinfectants are chlorine, UV, ozone (O3) and chlorine dioxide(ClO2). There are several different advantages and disadvantages to the variousdisinfection techniques, as shown on our disinfection page. Chemicals that areharmful to certain types of microorganisms are often used to eliminate them. Thesechemicals are known as biocides, because they are mortal to microorganisms.

How can m icroorganisms be m ade useful during w ater treat ment ?

Microorganisms can be used to decompose contaminants in wastewater. This kind ofwater treatment is called biological water treatment. During biological watertreatment microorganisms break down organic matter, nitrates and phosphates. Thisis a brief explanation of how these biological water treatment processes work.

Removal of organic matter

Biological water purification is performed to lower the organic load of dissolvedorganic compounds. Microorganisms, mainly bacteria, do the decomposition of thesecompounds. There are two main categories of biological treatment: aerobictreatment and anaerobic treatment. Aerobic water treatment means decomposition

of organic matter by bacteria that need oxygen during the decomposition process.Anaerobic water treatment means decomposition of organic matter bymicroorganisms that do not use oxygen.In aerobic systems the water is aerated with compressed air (in some cases merelyoxygen), whereas anaerobic systems run under oxygen free conditions.

Removal of ammonium and nitrates

The removal of ammonium and nitrates is quite complex. It is a water treatmentprocess that takes both aerobic and anaerobic conversion to remove thecontaminants.In the aerobic conversion stage there are two bacterial species involved. Firstly,Nitrosomonas bacteria convert ammonia to nitrite. Secondly, Nitrobacter bacteriaconvert nitrite to nitrate. These two processes together are commonly known as thenitrification process.

After that, the anaerobic bacteria take over. These bacteria convert nitrate toatmospheric nitrogen gas. This process is called denitrification. Denitrification isaccomplished with many anaerobic bacteria, such as Achromobacter, Bacillus andPseudomonas. The first stage of denitrification is the reverse of the nitrificationprocess, it converts nitrate back to nitrite. The second stage of denitrificationconverts nitrite to nitrogen gas (N2). This gas can be freely released into theatmosphere without causing environmental damage.

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