Illustrasjon: Suspended solids
In NF membranes, the pores are between 0.001 and 0.01 µm. The pores are so small that several mechanisms occur simultaneously during filtration: Separation based on size and shape, solubility and diffusion in the membrane material itself and effects of the surface properties of the membrane - mainly the membrane charge. Pressure is the driving force for the separation. Nanofiltration plants are operated at 8-40 bar, based on how dense the membrane is.
Nanofiltration can be used to produce low salinity water for use in the prevention and treatment of fish parasites, such as lice and AGD.
NF can also be used to produce low salinity water as intake water for RAS (Resirculating Aquaculture Systems) plants, especially for post-smolt production. Intake water with the desired salinity can be produced directly from sea water, no freshwater source is needed. The sulphate content is greatly reduced by nanofiltration, which can prevent H2S formation. At the same time, release of metals by mixing sea water and fresh water is avoided, and the filtration provides increased biosecurity.
Water quality low salinity water
Salinity: 3-22 ‰
NaCl: 2900-21900 mg / l
Ca2 +: 5-50 mg / l
Mg2 +: 3-50 mg / l
SO42-: <15 mg / l
Suspended solids, parasites, bacteria, virus: ≈ 0
Prevention and treatment of fish parasites
Intake water for land-based aquaculture facilities
Intake water for post-smolt production