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

Abstract

The ability to economically desalinate seawater in arid regions of the world has become a vital advancement to overcome the problem on freshwater availability, quality, and reliability. In contrast with the major capital and operational costs for desalination plants represented by conventional open ocean intakes, subsurface intakes allow the extraction of high quality feed water at minimum costs and reduced environmental impact. A seabed filter is a subsurface intake that consists of a submerged slow sand filter, with benefits of organic matter removal and pathogens, and low operational cost. A site investigation was carried out through the southern coast of the Red Sea in Saudi Arabia, from King Abdullah University of Science and Technology down to 370 kilometers south of Jeddah. A site adjacent to the Shoaiba desalination plant was selected to assess the viability of constructing a seabed filter. Grain sieve size analysis, porosity and hydraulic conductivity permeameter measurements were performed on the collected sediment samples. Based on these results, it was concluded that the characteristics at the Shoaiba site allow for the construction of a seabed filtration system. A seabed filter design is proposed for the 150,000 m3/d Shoaiba III expansion project, a large-scale Reverse Osmosis desalination plant. A filter design 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 the plant. The filter would be located 90 meters offshore where hydraulic conductivity of the sediment is high, and mud percentage is minimal. The thin native marine sediment layer is insufficient to provide enough water filtration, and consequently the proposed solution involves excavating the limestone rock and filling it with different layers of non-native sand and gravel of increasing grain size. An initial assessment of the area around Shoaiba showed similar sedimentological conditions that could lead into the application of comparable seabed filter design concepts to supply the entire feed water requirement of the plant. Considerations for the construction of a seabed filter should include technical feasibility and life cycle assessment, i.e. capital costs, operating costs and environmental impacts.

Date of Award	Jun 2012
Original language	English (US)
Awarding Institution	Biological, Environmental Sciences and Engineering
Supervisor	Thomas Missimer (Supervisor)