The cut-off value varies between 0.1 and 0.001 micron. At an operating pressure of 1.5 bars the effluent (possibly prefiltered) is pushed through the membrane from the outside to the inside (Out/In) or from the inside to the outside (In/Out). Backwashing is necessary to maintain the membrane’s permeability. Many types of UF membranes exist varying in technology (stuffing method, hollow fiber, flat…) and materials (polysulfone, PVDF (polyvinylidene fluoride), ceramic,…).

This technology gets rid of dissolved pollutants in (monovalent and polyvalent ions, such as heavy metals, organic compounds including pesticides, micropollutants), colouring agents, wastewater, surface water, brackish water, as well as groundwater odour. The fluid is forced through a semi-permeable membrane with a cut-off value range of 0.1 to 10nm at a pressure of 5 to 20 bars. Nanofiltration is a good choice compared to reverse osmosis (RO) if you want to limit energy consumption, opt for a more robust technology and limit the need for additional stages of treatment such as remineralization

Osmosis is the natural process by which molecules of a solvent go from the least to the most concentrated solution. Applying a sufficient pressure reverses the natural movement of the fluid. Therefore it is the water with the highest pollution content that goes through the semi-permeable membrane with a pore size no larger than 1nm in diameter. Thus ions including salt, pesticides and other organic compounds, colouring agents, bacteria, viruses and microalgae are trapped.