The membranes are used to carry out reverse osmosis, which consists of applying pressure on the salt water and making it pass through a semi-permeable membrane that derives the water with a high concentration of salt from the outside and the water through an internal hole. without salts suitable for consumption, having eliminated in this process even viruses and bacteria.
Each membrane must be inserted inside a hermetic container that supports a maximum pressure of about 1000 PSI or 70 bar. With optimum working pressure, osmosis will be carried out between 58 and 60 bar. It must be taken into account that seawater in the Mediterranean has a salt concentration of about 37,000 ppm. The osmosis carried out to obtain drinking water from seawater will convert this water to about 300 ppm when the membrane is new. If we work at a pressure lower than 55 bar, we will obtain a higher concentration of salts in the produced water, just as if the membranes are worn due to use or inadequate maintenance.
If the membranes are used with sea water without subsequent periodic rinsing with fresh water (rinsing interval of one week), these membranes will become unusable. It is necessary to take into account when buying a potabilizer or desalination plant for a boat that it has an automatic rinsing system with fresh water when stopping the osmosis process. There are systems that have a weekly timer for automatic rinsing.
Something else to consider are the containers for these membranes. It is strongly recommended that they be made of fiber, in the case of stainless steel containers these will end up oxidizing internally (remember that seawater is highly corrosive) and the oxide particles will end up damaging the membrane.
The membranes consist of an internal perforated polymer core in which the microperforated polyamide is rolled like a canvas. The quality of a membrane will be determined by the density of the polyamide and above all by its quality, which must be polyamide S.
The most commonly used membrane measurements in a boat desalination plant are 2.5”x 21” (6.35 cm x 53.34 cm) or 2.5” x 40” (6.35 cm x 101.6 cm). cm). The nomenclature for these first ones will be 2521 or 2540. There are also 4" diameter seawater membranes with the same length or 8" ones.
It is highly recommended that when replacing a membrane, NBR O-rings are also replaced, which 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.
