Reverse Osmosis, simply called as RO, is a water purification method that removes ions, molecules and other larger particles from water using a semipermeable membrane. Desalination or removing salt from seawater is done by using reverse osmosis.
A solvent is forced into a region of low soluble concentration from a high solute concentration by applying pressure. This solution passes through a semipermeable membrane and while it does, unwanted particles and molecules are removed.
Usually, a single-pass seawater RO system has the following:
1. Intake – A pump at the source of water to be purified.
2. Pre-treatment – This stage involves removal of solids, sediments, carbonic acid from water, and dosing of oxidising biocodes to kill bacteria.
3. High-pressure pump – This allows the water to pass through the membrane. The pressure needed for seawater ranges from 800 to 1180 psi, and for brackish water, 225 to 376 psi.
4. Membrane – There is a pressure vessel with a membrane, allowing feed water to be pressed against the membrane. RO system membranes are made in a range of configurations and the two most common are spiral-wound and hollow-fiber.
5. Energy recovery – This is used to reduce the energy consumption.
6. Remineralisation and pH adjustment – desalinated water needs to be stabilized to protect downstream pipelines and storage by adding lime or caustic soda which prevents corrosion.
7. Disinfection – This secures secondary protection against downstream and membrane problems.