The use of a positive displacement pump to force seawater through a reverse osmosis membrane is appropriate because these pumps are designed to move fluids at a consistent flow rate and create the necessary pressure to overcome osmotic pressure. In reverse osmosis, particularly with seawater, high pressure (typically between 800 to 1200 psi) is essential to drive the water through the semi-permeable membrane, allowing freshwater to pass while rejecting dissolved salts and other impurities.
Positive displacement pumps achieve this by trapping a fixed amount of fluid and then forcing that same amount into the discharge pipe, effectively building up the pressure needed to facilitate the reverse osmosis process. This capability makes them particularly suitable for applications where high pressures are required, such as seawater desalination.
Other pump types are less effective for this specific application. Centrifugal pumps, while commonly used in various water treatment scenarios, struggle to generate the high pressures needed for reverse osmosis as their function is based on the speed of rotation to move liquid rather than creating a high-pressure environment necessary for overcoming osmotic pressure. Diaphragm pumps and piston pumps may also be used in specific contexts but do not provide the same efficiency or flow rate consistency required for large-scale seawater reverse osmosis systems.