Posted by on Saturday, December 17, 2011 Under: Coagulation & Filtration
Coagulation is an important process in the swimming pool water treatment process. It helps to remove very small particles from the pool water. In a conventional swimming pool sand filter, the size of the gaps between the sand grains (pores) are around 70 microns. As the filter begins to trap particles, the size of the pores decreases. This is known as 'filter ripening'. When the filter is fully ripened, it will be capable of trapping particles the size of around 5 - 10 microns. The size of cryptosporidium cysts are about 5 microns, bacteria is around 1 - 5 microns, and colloidal matter can be as small as 0.1 micron. 
Even with a ripened filter, some of the pollution is too small and will pass through the filter. This is why coagulation is so important. This pollution has to be removed, especially cryptosporidia as it is not going to be killed by the chlorine in the pool. We need to add a coagulant, which works by causing the small particles to bind together to form what are known as flocs. The flocs are typically 20 - 50 microns, so will be large enough to become trapped in the filter. The most common coagulants used in swimming pool water treatment are:

  • Polyaluminium Chloride (PAC)
  • Polyaluminium Sulpho-silicate (PASS)
  • Aluminium Sulphate (Kibbled Alum)
  • Sodium Aluminate
  • Iron Chlorides
  • Iron Sulphates  

In : Coagulation & Filtration 

Tags: "coagulation" "cryptosporidia" "flocs" "filter ripening"