5.9.2 Ultrafiltration (UF)
This employs membranes with smaller pores (0.001–0.02 μm) than those for microfiltration and utilises much greater pressure (up to 3000 kPa). An atomic mass unit is 1/12 of the mass of a neutral atom of the most abundant isotope of carbon, i.e. I.66X 10−27 kg.
Commonly, the membranes are made of polysulphone, polyacrylonitrile, polyamide and cellulose acetate. Inorganic ceramic membranes are also used. Owing to its ability to remove very small particles, UF is mainly used for the separation of macromolecules, allowing molecules with a mass of 1000 atomic mass units (amu) to pass through the membrane. UF is used as protection against Cryptosporidium by one water company in the south-east of England.
It is also used in the removal of bacteria and viruses for food processing waters and for the removal of colour and humic substances from drinking water in small upland supplies.