Subsea desalination - significant energy savings and greatly reduced environmental impact.

Seawater reverse osmosis (SWRO) is the dominant desalination technology in the world today. However, terrestrial SWRO is energy- and land intensive and more than 50% of the process is typically related to pre-treatment, not the RO process itself. Today's plants also have a negative impact on the local land and marine environment. This paper describes the design of a subsea SWRO system, Flocean, and its vast life-cycle benefits, including lower energy consumption, reduced cost of water, improved reliability, and enhanced environmental sustainability. Installed in water depths of 300-600 m, this approach brings several key advantages that result in significant cost and environmental savings through simplifications in design and operation: (1) In the disphotic zone from 200 m, less than 1% of sunlight reaches the system. This results in a high and consistent feed water quality as no plants grow and therefore there is significantly less life including algae and bacteria. Consequently, the need for pre-treatment is significantly reduced and, in some cases, even eliminated. (2) The system uses ambient hydrostatic pressure to reduce overall energy consumption by 30%-50%, even compared to modern SWRO systems with energy recovery systems. One of the many environmental benefits of the subsea desalination system is the brine discharge which has far less impact on marine life than current terrestrial SWRO systems. Access to high-quality, high-pressure feed water allows for chemical-free pre-treatment and low recovery operation without significant impact on the cost of water. The result is not only an energy-efficient system, but also a chemical-free brine that matches the salinity of the surrounding ocean. In addition, the brine is dispersed at deep sea in areas of low biological productivity. It all adds up to a green discharge product that is ideal for preserving the marine environment. The system was initially proven for oil and gas subsea water treatment applications and based on four decades of subsea technology experience in Norway. [ABSTRACT FROM AUTHOR]