Nanofiltration uses membranes that remove panicles and molecules hundreds of times smaller than ultrafilters, down to a molecular weight of about 1000. They are produced the same way as ultrafilters-rolled-up membrane cylinders with netting spacers-but the design also includes a “reject” stream that directs most of the water to waste before it can become so concentrated that it causes clogging. This produces a “tangential flow” pattern that is less conducive to clogging. That means there are three plumbing connections for nanofilters: inlet, outlet product water, and outlet waste water. This is inefficient in terms of wasting a lot of water, but highly efficient in terms of saving money on premature replacement of expensive membrane cartridges.
Nanofiltration can be used alone to purify many water supplies without using any other equipment or chemicals, because it can remove all particles of all sizes: all colloids, all types of micro