From Ocean to Tap: How Desalination Works

The reverse osmosis building is the center of the desalination process, and the Carlsbad Desalination Plant. During this process, dissolved salt and other minerals are separated from the water, making it fit for consumption. The reverse osmosis building contains more than 2,000 pressure vessels housing more than 16,000 reverse osmosis membranes. The pressure vessels were provided by San Diego County-based Protec Arisawa, and Dow Water & Process Solutions produced the reverse osmosis membranes.

Reverse osmosis works by pushing water – under intense pressure – through semi-permeable membranes to remove dissolved salts and other impurities. These membranes act like microscopic strainers that allow only water molecules to pass through, leaving behind the salt, minerals and other impurities such as bacteria and viruses. In addition to the reverse osmosis membranes and pressure vessels, this building houses 144 state-of-the-art energy recovery devices produced by Energy Recovery, Inc. The energy recovery devices work by capturing the hydraulic energy created by the high-pressure reject stream of seawater produced during the reverse osmosis processes and transferring it into incoming seawater, without consuming any electrical power themselves.

These devices save the plant an estimated 146 million kilowatt-hours of energy per year, reducing carbon emissions by 42,000 metric tons annually – roughly equivalent to the annual greenhouse gas emissions from 9,000 passenger vehicles.