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Water treatment options

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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 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

Suspended Solids Removal

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

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)DEPRECATED TEMPLATE - PLEASE USE {{W}} INSTEAD..) 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.

Coagulation and Flocculation

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

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

  • Slow sand filtersDEPRECATED TEMPLATE - PLEASE USE {{W}} INSTEAD.
  • clay pot filtersDEPRECATED TEMPLATE - PLEASE USE {{W}} INSTEAD.
  • ceramic water filtersDEPRECATED TEMPLATE - PLEASE USE {{W}} INSTEAD.

Disinfection

Disinfetion 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.

  • Boil the water for 10 minutes.
  • Solar water disinfectionDEPRECATED TEMPLATE - PLEASE USE {{W}} INSTEAD.
  • Chlorine or iodine.


Removing arsenic

In cases of arsenic contamination the Sono arsenic filterDEPRECATED TEMPLATE - PLEASE USE {{W}} INSTEAD. 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.

References

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