Feasibility Analysis of a Seabed Filtration Intake System for the Shoaiba III Expansion Reverse Osmosis Plant

摘要

The ability to economically desalinate seawater in arid regions of theworld has become a vital advancement to overcome the problem onfreshwater availability, quality, and reliability. In contrast with the major capitaland operational costs for desalination plants represented by conventionalopen ocean intakes, subsurface intakes allow the extraction of high qualityfeed water at minimum costs and reduced environmental impact. A seabedfilter is a subsurface intake that consists of a submerged slow sand filter, withbenefits of organic matter removal and pathogens, and low operational cost.A site investigation was carried out through the southern coast of theRed Sea in Saudi Arabia, from King Abdullah University of Science andTechnology down to 370 kilometers south of Jeddah. A site adjacent to theShoaiba desalination plant was selected to assess the viability of constructinga seabed filter. Grain sieve size analysis, porosity and hydraulic conductivitypermeameter measurements were performed on the collected sedimentsamples. Based on these results, it was concluded that the characteristics atthe Shoaiba site allow for the construction of a seabed filtration system.A seabed filter design is proposed for the 150,000 m3/d Shoaiba IIIexpansion project, a large-scale Reverse Osmosis desalination plant. A filterdesign with a filtration rate of 7 m/d through an area of 6,000 m2 is proposed to meet the demand of one of the ten desalination trains operating at theplant. The filter would be located 90 meters offshore where hydraulicconductivity of the sediment is high, and mud percentage is minimal. The thinnative marine sediment layer is insufficient to provide enough water filtration,and consequently the proposed solution involves excavating the limestonerock and filling it with different layers of non-native sand and gravel ofincreasing grain size.An initial assessment of the area around Shoaiba showed similarsedimentological conditions that could lead into the application of comparableseabed filter design concepts to supply the entire feed water requirement ofthe plant. Considerations for the construction of a seabed filter should includetechnical feasibility and life cycle assessment, i.e. capital costs, operatingcosts and environmental impacts.