Water treatment semipermeable membrane, (reverse) osmosis

In the simplest definition, a semipermeable membrane is said to exist when the membrane allows the solvent, but not the solute, to pass through. More generally, only molecules below a certain molar mass or colloids or particles below a certain size are allowed to pass through.

Reverse osmosis or reverse osmosis is a physical membrane technology process for concentrating solutes in liquids, using pressure to reverse the natural osmosis process. The medium in which the concentration of a particular substance is to be reduced is separated by a semipermeable membrane from the medium in which the concentration is to be increased. The latter is subjected to a pressure that must be higher than the pressure created by the osmotic demand to balance the concentration. This allows the molecules of the solvent to migrate against their "natural" osmotic propagation direction. The process pushes them into the compartment where solutes are less concentrated.

Reverse osmosis with a semi-permeable membrane is used for desalination and partial desalination for various industrial and commercial applications, boiler feed water, cooling water treatment and drinking water treatment. This involves desalination of seawater and brackish water, further partial desalination of well water to remove heavy metals, nitrate, sulfate, fluoride, boron and organic contaminants.

Basics about antiscalants

The crystallization or precipitation of ions in the membranes must be prevented. This can be achieved by adding antiscalants. Antiscalants are polymeric compounds based on phosphates or polymers that enclose the crystallites that form and thus prevent crystalline precipitates from forming on the membrane.

Dr. Nähring Water Treatment GmbH has various FreeFlow antiscalants in its portfolio, depending on requirements:

  • Antiscalant against precipitation of calcium carbonate
  • Antiscalant against precipitation of calcium sulfate
  • Antiscalant against precipitation of barium sulphate
  • Antiscalant against precipitation of strontium sulfate
  • Antiscalant against precipitation of calcium phosphate
  • Antiscalant against precipitation of calcium fluoride

Metals such as iron, aluminum and manganese can also be stabilized by dosing antiscalants.

Nevertheless, cleaning of the membrane by using membrane cleaners may remain necessary.

Dr. Nähring Water Treatment GmbH is offering various Mem and Memobrane cleaners in its portfolio, depending on requirements: Solid membrane cleaners of the Mem product line, liquid membrane cleaners of the Memobrane product line.

 

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