Abstract
Over the past several decades, many improvements have been made in the design and operation of seawater reverse osmosis desalination systems (SWRO), including the intakes that provide feed water. The invention of the velocity-cap offshore intake system reduced the entrainment of fish due to their sensing of horizontal flow versus vertical flow. Use of passive screen intakes further lessened the environmental impacts of open-ocean surface intake systems by near elimination of impingement and a reduction in entrainment caused by the low inflow velocity and the small slot size of the screens. Further reduction of environmental impacts of intake systems can be achieved by careful location of the intake systems (away from sensitive marine areas such as estuaries). Subsurface intake systems in the form of conventional vertical wells produced high-quality feed water for small and medium capacity SWRO plants. Well intake systems force seawater to infiltrate through the seabed into a porous aquifer. The transport of the raw seawater in the aquifer results in a significant reduction in the raw water organic matter content. Relatively new well types, such as slant wells, horizontal wells, and radial collectors, have been introduced to provide feed water for SWRO facilities. Some types performed better than others and experimentation is still ongoing. Gallery intake systems were developed for use in a wider range of required capacities from medium to large. A major seabed gallery intake system was constructed in Japan and has produced a very high-quality feed water and other similar systems are being planned for construction. The concept of the self-cleaning beach gallery intake was developed and has not yet been installed for use in a medium or large capacity SWRO facility, but this intake design has high potential for success. Considerable additional research is merited on improving existing intake designs and creating new ones that can reduce SWRO operational costs by reducing the intensity of pretreatment.