Paanimart Blog » How to Choose RO Membrane and Filters for RO water purifier
NF delivers slightly coarser filtration than RO, with the ability to remove particles as small as 0.002 to 0.005 μm in diameter. NF is a relatively recent technology that was developed mainly for potable water generation. NF removes harmful contaminates, such as pesticide compounds and organic macromolecules, while retaining minerals that RO would otherwise remove. Nanofiltration membranes are capable of removing larger divalent ions such as calcium sulfate, while allowing smaller monovalent ions such as sodium chloride to pass through.
What is nanofiltration?
While RO and NF are both membrane technologies that use a semipermeable medium to remove certain ions and particles from a liquid stream, they can be distinguished based on the size of particulates that each is able to remove. Comparatively, RO and NF are capable of removing finer contaminants than microfiltration and ultrafiltration, with applications including the removal of: • hardness • heavy metals • nitrates • organic macromolecules • radionuclides • sulfates • total dissolved solids (TDS) Nanofiltration, however, delivers slightly coarser filtration than RO, with the ability to remove particles as small as 0.002 to 0.005 μm in diameter, including pesticide compounds and organic macromolecules, while retaining minerals that RO would otherwise remove; nanofiltration membranes are capable of removing larger divalent ions such as calcium sulfate, while allowing smaller monovalent ions such as sodium chloride to pass through. Because of its filtration properties, nanofiltration is often used to: • concentrate and demineralize valuable byproducts, such as metals from wastewater • generate potable drinking water • remove nitrates SHARE THIS E-BOOK: • remove pesticides from ground or surface water • soften water .
What type of membrane should you use?
Membrane configurations can vary, but mostly spiral wound and hollow fiber membranes are used. The quality and overall efficiency of the unit can depend on the type of membrane chosen, which can include: Hollow fiber; more suitable for low-solid liquid streams, these membranes are constructed of thousands of hollow fibers that resemble spaghetti and can be efficiently kept clean with occasional backwashing and clean-in-place (CIP) technology. Plate and frame; these membranes are placed on top of plate-like structures that collect solids on the inside of the supporting plate. These have low packing densities and can be less efficient than other filtration methods, but they are generally easy to use and clean. Typically used on solutions difficult to filter. They are also among the lower-cost membranes but higher-cost systems. Spiral-wound; spiral-wound membranes are among the commonly used. They are composed of flat sheets of membrane between meshlike spacers that are wound around a central tube (this tube collects the permeate after filtration) and placed within a casing. They are relatively compact and can be used in high-volume applications with low suspended solids. Tubular; several tube-like membranes are placed within a pipe/shell, and as the stream is passed through the tubes, it transfers the permeate to the pipe/shell side. These can be less permeable with a lower packing density and are generally used for hard-to-treat streams, such as those with high TDS, TSS, and oils, greases, and fats.