Water Treatment "Part 15": Filtration process.

Water is filtered by running it through filters, which are typically constructed of sand and may also include granular activated carbon. Getting rid of suspended contaminants including clay, iron, and ammonium lumps as well as some dangerous bacteria and viruses is the aim of this procedure. There are many types of filtration, some of which are: slow filtration, quick filtration, and filtration under relatively high pressure. Each of these filtration techniques has a different filter thickness. However, rapid sand filtration is the most widely used filtering method and is used in nearly all water treatment plants.

Slow sand filter room

Chemical and biological disintegration processes that occur within the filter surface:

Particles whose sizes exceed the size of the filter pores stay on the surface when the water flows through the filtration surface. This can cause the filtration surface to clog up because of the large concentrations of suspended particles. It should be mentioned that it is essential to prevent methane from dissolving into the surface of the filter and to do it sooner rather since it can lead to obstruction and filter failure due to the haphazard growth of biodegradable bacteria.
Chemical reactions that occur inside the filter surface result in the removal of manganese and the transformation of iron (II) to iron (III), forming lumps that may be eliminated.

4Fe2+ + O2 + 2H2O + 8HCO3- ====== 4Fe(OH)3 + 8CO2

If a decline in performance is noticed, the filter should be backwashed since the blockage of the pores during the filtering process might cause the filtration speed to decrease.

Use of activated charcoal in filters:

To increase the efficiency of the sand filter's ability to remove pollutants, activated charcoal is utilized. This material aids in the removal of both mineral and organic contaminants.
One benefit of activated charcoal is that it lasts a very long time before needing to be replaced. Its ability to adsorb organic chemicals that are dissolved in water is also crucial for the process of making drinking water.​

References:

• [Introduction to Water Chemistry (Pollution- Treatment- Analysis). Dr. Nasser Al-Hayek. Publication of the Higher Institute for Applied Sciences and Technology (HIAST). Syrian Arab Republic, 2017.]
• Taparhudee, Wara (2002). "Applications of Paddle Wheel Aerators and Diffused-Air System in Closed Cycle Shrimp Farm System" (PDF). Witthayasan Kasetsart (Sakha Witthayasat). 36: 408–419. Retrieved 26 April 2020.
• Unsafe water kills more people than war, Ban says on World Day". UN News. 22 March 2010. Retrieved 10 May 2018
• Raymond Desjardins- Livre: Le traitement des eaux- 2éme edition- Ecole Polytechnique de Montréal- 1997- ISBN 2-553-00643-8
• Drinking Water Treatment- EDX- Delft University of Technology.
• Book- Drinking Water: Principles and Practices- by Hans J C Van Dijk (Author), Jasper Q J C Verberk (Author), Peter J De Moel.