SEAWATER MEMBRANE

⏳Estimated reading time: 5 minutes⏳

Membranes are used to perform reverse osmosis, which consists of applying pressure to salt water and passing it through a semipermeable membrane that releases water with a high salt concentration on the outside and water without salts suitable for consumption through an internal opening, having eliminated even viruses and bacteria in this process.

Each membrane must be inserted into a hermetically sealed container that can withstand a maximum pressure of approximately 1000 PSI or 70 bar. Under optimal operating pressure, reverse osmosis will occur between 58 and 60 bar. It's important to note that seawater in the Mediterranean has a salt concentration of around 37,000 ppm. Reverse osmosis used to obtain drinking water from seawater will reduce the salt concentration to approximately 300 ppm when the membrane is new. Operating at a pressure below 55 bar will result in a higher salt concentration in the produced water, as will membranes that are worn due to use or inadequate maintenance.

If membranes are used with seawater without subsequent periodic freshwater rinses (at weekly intervals), they will become unusable. When purchasing a marine water purifier or desalination system, ensure it has an automatic freshwater rinse system that activates when the reverse osmosis process is stopped. Some systems include a weekly timer for automatic rinsing.

Another important consideration is the containers for these membranes. Fiberglass containers are strongly recommended; stainless steel containers will eventually rust internally (remember that seawater is highly corrosive), and the rust particles will ultimately damage the membrane.

The membranes consist of an inner core of perforated polymer around which the microperforated polyamide is wound like a canvas. The quality of a membrane is determined by the density of the polyamide and, above all, by its grade, which must be polyamide S.

The most common membrane sizes used in a marine desalination system are 2.5” x 21” (6.35 cm x 53.34 cm) or 2.5” x 40” (6.35 cm x 101.6 cm). These are designated as 2521 or 2540. Seawater membranes are also available in 4” diameters with the same lengths, or in 8” diameters.

It is highly recommended that when replacing a membrane, the NBR O-rings should also be replaced, as this is the most seawater-resistant gasket material.

At DESSAL we have high quality membranes for the most common brands of water treatment plants on the market.