Reverse osmosis and nanofiltration
Reverse osmosis is the most selective membrane technology and it removes all dissolved mineral salts in water, whereas the nanofiltration membrane, which has slightly larger pores, can separate the different components of a fluid on the basis of their size.
Both of these performing technologies require clear raw water (< 1 NTU), so that pretreatment stages are often necessary (sand filtration or ultrafiltration).
The energy consumption of reverse osmosis and of nanofiltration has considerably decreased during the last twenty years. For seawater desalination, thanks to efficient energy recovery systems, reverse osmosis now requires less than 3 kWh per m3 produced drinking water.
