Although ocean water desalination has been utilized for years, the technology has improved and become more efficient over the years. Early desalination relied on clay to extract fresh water from ocean water and then was replaced by boiling ocean water to capture the fresh water steam; this process is known as thermal distillation. Up until the 1960’s distillation was the primary method of turning salt water into fresh drinking water until the first Reverse Osmosis membrane was developed at the University of California Los Angeles (UCLA.).

The process of producing fresh water from ocean water consists of multiple steps.

Step 1.- Intake System.

Bring ocean water from the ocean to the desalination facility. This step requires an intake system to bring the water to the onshore facility. Several types of intake system exist including open ocean intakes, screened intakes, subsurface intakes and in some cases drawing spent ocean water from a once through cooling system from a near-by power plant. The intake system is a critical asset because with an operational intake water cannot be delivered to the plant. The intake itself is designed for marine protection and must be designed to inhibit growth that would clog up the intake pipes or facility. For more information on the intake systems please check out our Environmental Impacts tab.

Step 2.- Filtration.

Filter the raw ocean water through a filtration system to remove coarse material. This step requires the use of a filter to remove out shells, sand, particles and potentially red tide material that can damage or inhibit the desalination process downstream. These filters can be found in many forms including sand filters, plastic disk filters or even cloth filters.

Step 3.- Ultra Filtration.

Run the filtered water through Ultra Filtration (UF) membranes for removal of microscopic material in the ocean water. UF membranes are a low pressure membrane process (10-30 pounds per square inch-psi) for water treatment that is designed to remove turbidity causing particles including those comprised of suspended solids, bacteria, colloidal matter and proteins. The UF treatment effectively removes particles in the size range of less than 0.01 to 0.1 mm. Although the particle removal size is very small the water is still very salty and not ready for human consumption. Effective removal of these contaminants in the ocean water results in a filtrate well suited for further treatment by downstream Reverse Osmosis (RO).

Step 4.- Reverses Osmosis.

The UF filtrate water is then ready for the separation of the fresh water molecules and the salt and other dissolved compounds through the process known as Reverse Osmosis (RO.) The RO treatment removes 99.8% of all dissolved compounds in the ocean water. While the UF process removes particles in the water at rather low pressures, the RO unit requires much higher pressures (900-1100 psi) to overcome osmotic pressure of the ocean water. With such high pressures large pumps are needed to drive the process with a result of high energy costs. For more information about the energy required for desalination and Energy Recovery Devices (ERIs) check out our Energy Use tab.

Step 5.- Post Treatment.

Re-mineralize and polish the water for human consumption. Once the permeate water is collected from the RO units it is almost too pure to drink since all minerals that are needed for water stabilization have been removed through the process. The re-introduction of minerals is provided by running the water through a calcite filter or lime saturator followed by chlorine dosing for disinfection of any remaining pathogens to meet drinking water standards.

Step 6.- Brine Disposal.

With the fresh water ready for consumption, the RO reject water, also known as the brine, must be disposed of. Once the dissolved salt molecules are removed from the fresh water molecules the concentration is twice that of when it came in. This brine is disposed of utilizing an ocean diffuser system that creates rapid mixing as not to create a high salinity plume in the ocean. For more information about the brine diffusers and potential environmental impacts check out our Environmental Impacts tab.