Reverse osmosis and nanofiltration

Description and fields of application

Using reverse osmosis (RO) it is possible to remove extremely small sized particles, larger molecules as well as ions from the process water. In contrast to the micro and ultrafiltration, there the pore size defines the limits of separation; RO using special membranes involves a diffusive mechanism so that separation efficiency is dependent on solute concentration as well as on flux rate and working pressure. The latter has to be very high since it has to overcome the osmotic pressure building up between both sides of the membrane.

GTWE offers reverse osmosis systems for desalinization in different fields of industrial application:

  • Cooling water
  • Boiler feed water
  • Production water
  • Waste water treatment
  • Feed water for dilution or refilling of long distance heat pipelines

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Nanofiltration (low pressure reverse osmosis)

Nano filtration (NF) is a technology ranging somewhere in between Ultrafiltration (UF) and RO having a pore size of about one nanometer. However in case of NF the membrane is rated by molecular weight cut-off rather than pore size. The operating pressure of a NF system is much lower than that of a RO one. Therefore NF systems are often called “low pressure reverse osmosis” or “loose reverse osmosis” systems.

A special feature of the NF-membrane is its ion selectivity:  monovalent ions pass the membrane a lot easier than multivalent ions like sulfate or carbonate. This may be used to reclaim unconsumed acids coming from an etching or cleaning process. However its typical area of operation is the separation of fluids, the removal of ions and the mechanical filtration with extremely small pores.

Scaling and antiscalant

If concentration of solutes rise during operation of a RO or NF system above a certain limit (solubility limit) crystallization of that component happens leading to a blocking of the membrane. Using a antiscalant (also known as scale inhibitors) the crystallization can be suppressed for a while.

Our experts will pick the adequate antiscalant for your application.