With many water-borne contaminants, if a membrane becomes Irreversibly scaled, or fouled, it cannot be cleaned and must be replaced.
In addition, colloidal and particulate contaminants can also adhere to the membrane surface and cause fouling.
If a buildup of salts and minerals in the feed-water to a membrane occurs continuously, dissolved substances can precipitate and form a solid film, fouling the surface of the membrane. This waste brine stream is necessary to flush salts and minerals away from the membrane to prevent them from accumulating and fouling the membrane surface. Desalination devices that use membrane elements (for example: RO or NF) always create two streams of water as the water exits the element: desalinated product water (which has passed through the membrane), and a waste brine (that has flowed across the membrane surface). Generally speaking, RO membranes used for residential and commercial water treatment applications remove all dissolved solids by approximately 98%, while nanofilter membranes remove divalent ions (hardness components: calcium and magnesium) by approximately 90% and monovalent ions (sodium chloride) by approximately 50%. Therefore, nanofilter membranes require much less pressure to pump water across the membrane because hydraulic driving force does not have to overcome the effect of osmotic pressure derived from monovalent ions. It is the monovalent ions that create osmotic pressure that requires the moderate to high pressures necessary to pump water through an RO membrane. An NF membrane allows a high percentage of monovalent ions such as sodium and chloride to pass through, while it retains a high percentage of the divalent ions. An NF membrane produces soft water by retaining the hardness creating divalent ions present in water. However, nanofiltration is relatively new in the field of water treatment technology. based on the following technologies: activated carbon for organic removal: ultraviolet light disinfection: ion exchange for hardness removal (water softening), and membrane desalination such as reverse osmosis (RO) or nanofiltration (NF). Traditionally, water is purified or treated through a variety of available water treatment devices designed both for communal and for point-of-use applications, e.