What is nanofiltration?

When you think of nanotechnology, you may think of an imperceptible, self-replicating microplague come to wipe out the human race (as in the Michael Crichton novel). Or you may consider the ever-decreasing size of technology. But a form of nanotechnology performs another function: Nanofiltration removes harmful particles from our drinking water every day.

Nanofiltration came to prominence in the 1970s and 1980s as an alternative to reverse osmosis, ultrafiltration, and microfiltration. These forms of water filtration were not totally effective at removing particles of all sizes, however. As filter technology improved, ie, as more technical, advanced membranes were designed, smaller-sized grains were able to be filtered out. By the end of the 1980s, nanofiltration technology had developed such that it filtered out adulterants from water that other filtration technologies could not. This article on nanofiltration says, for instance,

The key difference between nanofiltration and reverse osmosis is that the latter retains monovalent salts (such as sodium chloride), whereas nanofiltration allows them to pass, and then retains divalent salts such as sodium sulphate. Robert Peterson, in his Foreword to Elsevier's Nanofiltration – principles and applications, describes reverse osmosis (especially in the water treatment business) as the main course, the steak perhaps, of a meal, whereas nanofiltration “is like the wine menu … an opportunity for creativity and exploration”.

The key to the development of nanofitraltion technology has been creating better and better filtration technologies. Nanofiltration is a liquid phase membrane separation process; it separates inorganic and organic substances from solution in a liquid. Nanofiltration separates these substances by running them through a membrane under pressure (a smaller amount of pressure than what would normally be used for reverse osmosis, as well). Great advances in nanofiltration generally occurs due to the creation of better membrane technologies. Presently, many nanofiltration systems use an inorganic material; ceramic is an especially popular material.

Ceramics have excellent corrosive-resitance and feature an excellent range of control over their porosity. Ceramic membranes have the advantage of being fully capable of functioning in very high or very low pH environments. Ceramic nanofiltration has industrial applications in the food and dairy sector, chemical processing, pulp and paper industry, and textiles. However, the predominant use of nanofiltration is of course in fresh, process, and waste water filtration.

A growing use of ceramics in nanofiltration is with field of nanofiber media. Nanofibers are made of synthetic materials that are spun into fibers whose diameters range from 10 μm to 100 nm. Advances in spinning techniques have enabled water filtration manufacturers to better utilize ceramic technology. Such ceramic nanofilters feature the high density and durability of ceramics with the capability of removing contaminants to below 0.1 μm. Using ceramics in water filtration technology has increased the robustness and safety of our water supply. And as manufacturers of technical ceramics find ways to decrease cost, we will only see ceramics’ influence in water filtration technology increase.