How Desalination Works
As the Earth's population continues to grow and develop, our limited freshwater resources become increasingly scarce, we are fortunate that Earth's oceans offer an alternative and can provide a sustainable supply of drinking water. Seawater can be cheaply and reliably converted into drinking water through a known process. like seawater reverse osmosis the process begins by drawing water from the ocean using wells located on the coast or using an intake structure located in the open ocean osmosis is a natural process where a solvent such as water passes through a semi-permeable barrier the the barrier or semi-permeable membrane allows some things to pass through it, but not others in nature, the direction of flow through the membrane is from a less concentrated solution, such as fresh water, to a more concentrated solution, such as seawater, until equilibrium is reached, reverse osmosis is when the opposite occurs by pressurizing the concentrated solution seawater we are able to force water molecules to pass from the salty seawater solution through membrane to fresh water to prevent reverse osmosis membranes from clogging with solid particles that may be suspended in seawater seawater is filtered before passing through ar through the membranes this is achieved by using multimedia filters that are tanks or containers that contain a series of granular materials in layers, these materials can be anthracite garnet sand pebbles and/or gravel that are assembled in layers, the filters remove twigs of sand, algae and other particles from seawater in some cases other types of membranes known as ultrafiltration and microfiltration membranes are used instead of multimedia filters to pre-treat seawater.
The filtered seawater then travels to cartridge filters that act as a second stage of filtration. The cartridge filter is used for seawater. made of a thread like synthetic material that is wound onto cartridges th These remove even smaller solid particles from seawater, such as fine sand and clay, before the seawater is passed to reverse osmosis membranes. High-pressure pumps increase the pressure of seawater up to 1,000 psi. The pressure must be high enough to overcome the natural osmotic pressure and the force of the water from the salt water side through the reverse osmosis membranes to the fresh water side the salt particles in the sea water are rejected so they do not pass through the membrane to the fresh water side and remain on the concentrated salt water side the reverse osmosis membrane can be thought of as a number of sealed sachets connected at their open ends to a tube there are spacers between each sachet which allow water to flow through the membranes the membrane sachets and spacers are then wrapped around the tube like an upside down paper towel roll The osmosis membranes are then encased in a fiberglass covering .
The membranes are connected end to end, usually six tons. o Seven membranes held together and housed in vessels that are built to withstand pressures up to 1200 psi As pressurized seawater enters the pressure vessel and flows across the membrane surface, water molecules are forced in and through the membrane envelopes, leaving the salt molecules behind, the desalinated water passes through the membrane and emerges at low pressure where it is collected in a tube and directed to one end of the pressure vessel the salt stream The concentrated salt that is rejected to flow through the membrane continues to pass through the membrane surface where it is collected separately, the concentrated salt stream retains about 55% of the total energy of the seawater stream that it was originally fed to the membranes to reduce the energy required to operate the reverse osmosis plant.
The pressurized concentrated streams are channeled to an energy recovery device here up to 98% of the energy from the concentrated salt stream is transferred to an equal volume of inco seawater extraction in an isobaric energy recovery device on energy recovery device significantly reduces plant operating costs by recovering energy from the concentrated salt stream and using it to pressurize 60% of the seawater that is fed to the membranes the concentrated salt stream will have about a salinity 60% higher than incoming seawater. The concentrated salt stream is sent back to the ocean through a brine disposal well or a device known as a brine outfall. returned to equilibrium with the ocean outfall location should not contain sensitive marine ecosystems in a properly designed brine outfall no noticeable increase in salinity can be detected within a few meters of the discharge exiting pressurized seawater of the energy recovery device has its pressure boosted by a small booster pump so that it is at the same pressure as the seawater coming out of the high pressure pump the boost is necessary as some pressure has been lost as As current travels through the reverse osmosis system, approximately 40% of the seawater entering the system is converted to drinking water during the reverse osmosis process.
Drinking water is further treated by adding calcium carbonate to improve taste and bringing the pH to a neutral range chlorine is also injected to provide sanitizing properties as the water travels from the plant reverse osmosis through distribution pipes to homes and businesses when proper conservation of natural water resources is practiced water reuse has been implemented and a water deficit still persists seawater reverse osmosis may offer an alternative sustainable with good management can provide vital water for coastal communities desalinated water supplies that are not susceptible to drought and other natural disasters can provide a clean and safe source of drinking water supply you you