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Reverse Osmosis Information

Types of Membranes

NF MEMBRANES
NF, Nanofiltration, membranes are frequently referred to as water softening membranes because they have good rejection of the calcium and magnesium salts that form the bulk of hardness. Most typically the nanofilter element will be a "low rejecting" version of an RO membrane. Sodium chloride rejection will usually be in the 60 to 80 % range. The membrane is usually more variable than RO membrane in roll to roll performance specifications, but individual element performance consistency within a roll is quite good. The same constraints that apply to TFC RO elements will apply to NF membranes, e.g. no chlorine in the feed. NF membranes are not stock items, but made to order. We therefor have to require a minimum order to justify manufacturing elements. The minimum order will vary by spiral size, but will be usually equivalent to one roll of membrane. The NF membrane would be available in any of our standard or custom size elements. Please call to discuss your requirements, and applications.

UF MEMBRANES
UF, Ultrafiltration, is another type of membrane frequently found in a spiral element configuration. The membrane is used for separating molecular size compounds and colloids. The membranes are characterized by a molecular weight cutoff number that will signify the molecular size for approximately 90% retention. In general materials with higher molecular weight will be retained much better while smaller compounds will pass through the membrane into the permeate stream. Water and ions usually pass through the membrane with little or no hindrance. The membranes are used in cutoff ranges from 1000 to 100,000. Either the retentate or permeate or both may be a final product. The diversity of feed stocks, as well as requirements for cleaning and sanitization make it necessary to have many different styles of elements as well as types of membrane material. At this time Osmotik does not have adequate space or personnel to manufacture UF elements in-house. It may be possible for us to subcontract manufacturing or distribute product made by others in conjunction with sales of our own products. Be sure to discuss your full range of filtration requirements when discussing reverse osmosis or nanofiltration requirements.

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