According to the Encyclopedia of Separation Science, Membrane filtration is a type of filtration that uses a very thin filter medium where the particles to be separated are usually large compared to the pore size characteristic of the membrane. Particles larger than the membrane’s pores are rejected on the surface and do not get a chance to get to pass through the filter.
There are generally three types of membrane filtration: 1) Reverse osmosis, with an impermeability of membrane at less than 0.001 μm (micro meters or one nanometer), 2) Ultrafiltration, at 0.001–0.1 μm, and 3) Microfiltration, at 0.1–10 μm. Membrane filtration depends of the pore size to successfully separate particles it seeks to filter.
In the case of water, these “particles” are also called contaminants and are in the form of dissolved solids, bacteria, viruses, protozoa, and other physical, chemical, biological, or radiological substance or matter. At certain heightened levels, these contaminants make the water truly unsafe to drink. This happens naturally sometimes due to environmental or geological factors, and other times due to calamities, both natural or man-made.
Among the smallest impurities are viruses such as SARS, Hepatitis A, and Rotavirus measuring at more than 0.02 μm.
The case of water unavailability or contamination is much prevalent in many areas around the world that the cost of water becomes much higher than average or the frequency of disease reaches epidemic levels. Luckily, the World Health Organization is able to certify a number of innovative solutions that address this problem.