Smaller Than You Think—Reverse Osmosis Membranes

Reverse osmosis coupled with a nanofiltration or ultrafiltration membrane is very effective in blocking the tiniest particles in water, making them a prime choice in water treatment systems. Just how small are the particles that can be blocked by reverse osmosis filtration systems?

To say that reverse osmosis can trap things invisible to the naked eye is too ambiguous. There are dozens of things that exist below 40 microns, the threshold for unassisted human vision. Reverse osmosis can prevent particles as small as 0.0001 microns from passing through. At this range, a reverse osmosis membrane can effectively block:


Considered the smallest viruses known to man, parvoviruses are spherical pathogens with a diameter of 18 nanometers or 0.018 microns. One strain, parvovirus B19, can cause erythema infectiosum, popularly known as the fifth disease. Human parvovirus in contaminated water can likewise cause gastroenteritis, more commonly known as “stomach flu”.


Some lead pipes remain in household plumbing (typically homes built before the 1980s) despite laws that have prohibited their use for years. Untreated water can contain traces of lead and other unwanted metals. At just 0.1 to 0.7 microns wide, lead particles can be trapped with reverse osmosis membranes.


Reverse osmosis systems were widely used to control the radiation leak from the Fukushima Daiichi nuclear power plant following the disastrous Tohoku earthquake. Alone, it can remove radioactive materials like uranium (230 pm or 0.00023 microns) and radium (200 pm or 0.0002 microns).


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