Membrane filtration
Membrane filtration has been around for years. In the 60's, reverse osmosis was the privileged solution for water desalination. In the 80's, nanofiltration was used to soften and decolour water. In the 90's, the municipal market was an avid user of ultrafiltration and microfiltration to treat it's drinking water. They are distinct because they act as a physical barrier to the microorganisms and they can be cleaned with a backwash.
They became popular because certain microorganisms, like the cryptosporidium, showed a greater resistance the a primary disinfectant like chlorine. Water control authorities also defined the limits for the use of chemical products
For all these reasons, the water treatment industry searched for alternate methods of safely disinfecting water without the use of chemicals. The membrane filtration system was chosen.
The efficient removal of particles and suspended colloids in the water characterize ultrafiltration. The ultrafiltration membranes are defined by the size of their pores. Generally, membrane pores can measure 0,1 to 0,2 microns; certain membranes have pores that measure 0,005 micron.
The size of a bacteria is between 0,1 and 10 microns. The size of some microorganism, like giardia or cryptosporidium, is between 1 to >10 microns and the size of a virus can vary from 0,01 to 0,1 micron.
The ultrafiltration membrane pores usually measure about 0,02 microns. As you can see, they are a very good barrier against bacteria and microorganism but cannot stop virus that measures less then 0,02 microns. The USEPA, an organisation recognized by the drinking water industry, suggests that you complete the membrane disinfection process with a UV disinfection process to guarantee a secure drinking water. The ultrafiltration system is used in the residential markets.