Effects of Intake Depth on Raw Seawater Quality in the Red Sea
It has been suggested that using a deep open-ocean intake would improve feed water quality and would reduce the cost of SWRO water treatment by lessening membrane biofouling potential. The feasibility of developing deep intake systems for large-capacity SWRO plants located on the Red Sea was assessed. A bathymetric survey showed that the continental shelf along the Red Sea nearshore has a nearly vertical drop into deep water beginning at depths between 20 and 40 m. The vertical nature of the bathymetric profile and the issue of active seismicity make the development of a SWRO intake at a depth of greater than 100 m below surface a very risky venture along the Red Sea coast of Saudi Arabia. Detailed assessment of temperature and salinity with depth show a decrease of 5 °C and an increase of 1100 mg/L respectively over 90 m. Concentrations of algae, bacteria, total organic carbon, particulate and colloidal TEP, and the biopolymer fraction of natural organic carbon all showed declines in concentration. However, the general water quality improvements in reduced concentrations of organic matter were insufficient to reduce the intensity of pretreatment for an SWRO system. Overall, the Red Sea does not appear to be a good location for the use of deep SWRO intakes because of the structural risk of installing and maintaining an intake at near or below 100 m of water depth.
KeywordsNatural Organic Matter Alcian Blue Transparent Exopolymer Particle Transparent Exopolymer Particle Concentration Membrane Biofouling
Funding for this research was provided by the Water Desalination and Water Reuse and the Red Sea Centers at King Abdullah University of Science and Technology. The authors thank the ownership and staff at the Moya Bushnak Company for access to the SWRO facility with the deep intake and engineer Mohamed Arfin for allowing facility access and giving water sampling assistance. The authors thank the Center for Marine Operations and Research (CMOR) led by Dr. Abdulaziz Mohammed Al-Suwailem and the Red Sea Center for providing equipment of bathymetric surveying and the vessel and assistance in collection of offshore water quality data and samples.
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