Difference between revisions of "Water treatment options"

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m (New page: ==Jargon== pH - a measure of the acidity of the water. Most fresh water sources have a pH of 6-8. The ocean's pH is ~8.3. A pH above 7 is considered preferable because enteric pathogens ...)
 
 
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== Jargon ==
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pH - a measure of the acidity of the water. Most fresh water sources have a pH of 6-8.  The ocean's pH is ~8.3. A pH above 7 is considered preferable because enteric [[pathogens]] prefer a pH below 7.
  
==Jargon==
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Enteric Pathogen - diseases which attack the digestive system such as Typhoid and Cholera
pH - a measure of the acidity of the water. Most fresh water sources have a pH of 6-8. The ocean's pH is ~8.3. A pH above 7 is considered preferable because enteric pathogens prefer a pH below 7.
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 +
Sedimentation - passing the water through a very calm, pond like structure so that the solids will settle out.
 +
 
 +
Coagulation - using chemicals such as [[allum]] to accelerate sedimentation.
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 +
Turbidity - the cloudiness of the water
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 +
NTU - a measure of turbidity
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 +
== Intake Design ==
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One of the most often neglected elements in the water treatment system is the intake.  The intake must be diesigned to limit the amount of dirt and debris taken into the system to reduce problems downstream.
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* Intake channels which do not face upstream are preferable.
 +
* Fast flowing water will carry more dirt and debris, so seek natural sedimentation basins within the stream.
 +
* When designing the intake, keep in mind that it must be accessed for maintenance.
 +
* Custom made perforated pipes and drums can help preserve water quality.
 +
* Placing the intake .5m below the water surface can avoid algae growth.
 +
* Avoid suctioning sediments from the lake/river bottom.
  
Enteric Pathogen - diseases which attack the digestive system such as Typhoid and Cholera
+
== Suspended Solids Removal ==
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Suspended Solids Removal is typically the most difficult element of the water treatment process.  There are 2 primary methods of suspended solids removal, sedimentation and coagulation and flocculation.
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====Sedimentation====
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The easiest way to remove suspended solids is through sedimentation.If it is possible to let the water sit for a period of time, or pass slowly through a tank, heavier particles can settle out. See [[Sedimentation (water treatment)]]{{w|Sedimentation (water treatment)}}.  Also, if the sedimentation period lasts days to weeks, sedimentation can also have the effect of killing off bacteria. If the water is relatively clear, this step may not be important. Or if the water is turbid (cloudy) but the solids do not settle out easily, this step may be of little use.
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A simple test of the efficacy of sedimentation involves, taking a jar of the water and allowing it to sit after being mixed.  If the [[supernatant]]{{w|supernatant}} water is less than 5NTU after 6-8 hours, then either filtration or coagulation must be employed. 
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INSERT SOME METHOD FOR DETERMINGING SEDIMENTATION TANK SIZE AND CONTACT TIME
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When designing sedimentation tanks, special care should be taken to ensure that inlets and outlets produce minimal disturbance.
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====Coagulation and Flocculation====
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Frequently, the suspended solids will not settle out in a reasonable period of time and sedimentation alone will not work.  If this is the case, a two step process of coagulation and flocculation is employed.
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==== Filtering ====
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A [[water filter]] is important as pathogens and other contaminants are mostly attached to particles in the water. This step is sometimes skipped if the water is very clear. 
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*[[Slow sand filters]]{{w|Slow sand filters}}
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*[[clay pot filters]]{{w|clay pot filters}}
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*[[ceramic water filters]]{{w|ceramic water filters}}
  
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== Disinfection ==
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Disinfection is the backbone of water treatment and required to inactivate pathogens such as viri and bacteria.  Filtration is typically employed so that the disinfection phase is more effective.
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*Boil the water for 10 minutes.
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*[[Solar water disinfection]]{{w|Solar water disinfection}}
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*Chlorine or iodine.
  
==Contaminants==
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== Removing arsenic ==
{| class="prettytable"
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In cases of arsenic contamination the [[Sono arsenic filter]]{{w|Sono arsenic filter}} should be considered. As it contains sand and charcoal, the filter should also be effective against other impurities. Arsenic containing water is typically groundwater and thus should not usually contain significant pathogens. Iron and manganese oxides can offer a cheap method of removing low levels of arsenic from water. The oxides are able to adsorb arsenic ions and remove them from solution.
| Contamination types
 
| Contamination Agents
 
| Comments
 
  
|-
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== See also ==
| Physical
 
| Particles and suspended solids
 
| It is common to experience large seasional variance in quantity of particles and suspended solids.  When choosing intake location, consideration of the natural features such as flood terracing should be made to optimize the placement of the intake
 
|-
 
| Biological
 
| Faecal waste
 
| Faecal contamination is detected via the methods described in [[Water Quality Field Testing]] and approprate treatment methods determined based on those results.  Common diseases spreat through Faecal contaminataion include cholera and typhoid fever.
 
|-
 
|
 
| Algae
 
| Algae can result in bad taste.  It is difficult to remove with [[coagulants]] and can speed up deterioration of sand filters.  [[Bankside filtration]] can help to avoid these problems
 
|-
 
| Chemical
 
| Minerals, soil type
 
| High salinity (due to the presense of Sodium ions) is treated with expensive procedures such as [[reverse osmosis]] and [[distillation]].  pH (due to the presence or lack of Hydrogen ions) must also be considered as its levels influence coagulant and chlorine dosages and contact times
 
  
The pH and salinity of different sources can vary, even though the sources may be in a close proximity. pH is an important factor where treatment involves the addition of coagulants (alum etc) as the quantity to be added is influenced by pH, as is the contact time for chlorine.
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* [[Water supply and purification for emergencies]]
|-
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* [[Solar water disinfection]]
|
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* [[Decreasing turbidity to optimize solar water disinfection]]
| Industrial effluents
 
| In a number of situations industrial or agrochemical pollution can be very marked. As the removal of such contamination requires high technology solutions, it is generally not possible to reliably achieve this during an emergency without use of more expensive and complex treatment plants. A check to ensure that insect larvae and fish life flourish in the water source can provide an indication of quality, e.g. by keeping fish in the header tank''. ''
 
  
Look for signs of agricultural activities, empty chemical sacks etc. to establish if there is a potential for chemical contamination. Rivers and streams are more likely to be “self cleansing” than ponds and lakes.  
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== References ==
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http://www.oxfam.org.uk/resources/downloads/emerg_manuals/water_treatment.pdf
  
|}
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[[Category:Water treatment]]

Latest revision as of 09:50, 1 May 2012

Jargon[edit | edit source]

pH - a measure of the acidity of the water. Most fresh water sources have a pH of 6-8. The ocean's pH is ~8.3. A pH above 7 is considered preferable because enteric pathogens prefer a pH below 7.

Enteric Pathogen - diseases which attack the digestive system such as Typhoid and Cholera

Sedimentation - passing the water through a very calm, pond like structure so that the solids will settle out.

Coagulation - using chemicals such as allum to accelerate sedimentation.

Turbidity - the cloudiness of the water

NTU - a measure of turbidity

Intake Design[edit | edit source]

One of the most often neglected elements in the water treatment system is the intake. The intake must be diesigned to limit the amount of dirt and debris taken into the system to reduce problems downstream.

  • Intake channels which do not face upstream are preferable.
  • Fast flowing water will carry more dirt and debris, so seek natural sedimentation basins within the stream.
  • When designing the intake, keep in mind that it must be accessed for maintenance.
  • Custom made perforated pipes and drums can help preserve water quality.
  • Placing the intake .5m below the water surface can avoid algae growth.
  • Avoid suctioning sediments from the lake/river bottom.

Suspended Solids Removal[edit | edit source]

Suspended Solids Removal is typically the most difficult element of the water treatment process. There are 2 primary methods of suspended solids removal, sedimentation and coagulation and flocculation.

Sedimentation[edit | edit source]

The easiest way to remove suspended solids is through sedimentation.If it is possible to let the water sit for a period of time, or pass slowly through a tank, heavier particles can settle out. See Sedimentation (water treatment)W. Also, if the sedimentation period lasts days to weeks, sedimentation can also have the effect of killing off bacteria. If the water is relatively clear, this step may not be important. Or if the water is turbid (cloudy) but the solids do not settle out easily, this step may be of little use.

A simple test of the efficacy of sedimentation involves, taking a jar of the water and allowing it to sit after being mixed. If the supernatantW water is less than 5NTU after 6-8 hours, then either filtration or coagulation must be employed.

INSERT SOME METHOD FOR DETERMINGING SEDIMENTATION TANK SIZE AND CONTACT TIME

When designing sedimentation tanks, special care should be taken to ensure that inlets and outlets produce minimal disturbance.

Coagulation and Flocculation[edit | edit source]

Frequently, the suspended solids will not settle out in a reasonable period of time and sedimentation alone will not work. If this is the case, a two step process of coagulation and flocculation is employed.

Filtering[edit | edit source]

A water filter is important as pathogens and other contaminants are mostly attached to particles in the water. This step is sometimes skipped if the water is very clear.

Disinfection[edit | edit source]

Disinfection is the backbone of water treatment and required to inactivate pathogens such as viri and bacteria. Filtration is typically employed so that the disinfection phase is more effective.

Removing arsenic[edit | edit source]

In cases of arsenic contamination the Sono arsenic filterW should be considered. As it contains sand and charcoal, the filter should also be effective against other impurities. Arsenic containing water is typically groundwater and thus should not usually contain significant pathogens. Iron and manganese oxides can offer a cheap method of removing low levels of arsenic from water. The oxides are able to adsorb arsenic ions and remove them from solution.

See also[edit | edit source]

References[edit | edit source]

http://www.oxfam.org.uk/resources/downloads/emerg_manuals/water_treatment.pdf