How is Cryptosporidium removed from raw water?

As Cryptosporidium is a protozoa which is pathogenic to humans measuring only 4 – 6 µm in diameter and are highly resistant to disinfection using chlorine then they are more commonly removed by conventional treatment processes such as coagulation, clarification, media (sand) and membrane filtration. Other treatment regimes include Ozone (O3) and Ultra Violet (UV) irradiation. Ozone and UV treatment do not actually kill the oocysts but inactivate the DNA thus disabling their ability to reproduce.

Given the dimensions of Cryptosporidium oocysts effective removal cannot be guaranteed by filtration alone. It is necessary to add a coagulant chemical to raw water that will ensure that the smaller particles, which can be up to several hundred times smaller than the grains of sand in the filter media, bind together through electro-chemical force attraction, forming what is known as floc. These larger floc particles can then be more effectively removed by the filtration process.

Micro-Filtration (MF) and Ultra-Filtration (UF) membranes are very effective at removing particles between 0.1µm - 10µm (MF) and 0.001µm – 0.1µm (UF). These filtration techniques are often used where the source water coming into a water treatment works is already of a high quality and will not require initial clarification. The disadvantage is that only high quality raw water will be effectively treated as membrane filters would become quickly blocked should the water be have high colour or turbidity.


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