Feasibility Analysis of a Seabed Filtration Intake System for the Shoaiba III Expansion Reverse Osmosis Plant Thesis by Luis Raúl Luján Rodríguez In Partial Fulfillment of the Requirements For the Degree of Master of Science King Abdullah University of Science and Technology Thuwal, Kingdom of Saudi Arabia June, 2012 2 The thesis of Luis Raúl Luján Rodríguez is approved by the examination committee. Committee Chairperson: Dr. Thomas Missimer. Committee Member: Dr. Gary Amy. Committee Member: Dr. Shahnawaz Sinha. 3 © June 2012 Luis Raúl Luján Rodríguez All Rights Reserved 4 ABSTRACT Feasibility Analysis of a Seabed Filtration Intake System for the Shoaiba Reverse Osmosis Plant Luis Raúl Luján Rodríguez 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 5 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. 6 ACKNOWLEDGEMENTS First and foremost, I would like to express my gratitude and appreciation to my thesis advisor Dr. Thomas Missimer for his continuous support and guidance. His patience, enthusiasm, and immense knowledge helped me at all times and made this research possible. I would also like to thank the rest of my committee members, Dr. Gary Amy and Dr. Shahnawaz Sinha for their excellent advice and generous time. I am honored to have this work revised by such a distinguished committee. I am grateful to the faculty, colleagues, and friends at the Water Desalination and Reuse Center for their encouragement, insightful conversations, and providing me with an excellent atmosphere to work in. Special thanks to Samer Al-Mashharawi who was exceptionally supportive and assisted me at every stage of this research. I am also indebted to express my gratitude to everyone who joined me in the long sampling trips that were needed, and all my friends for their caring support through the past months. Last but not the least, I would like to thank my family, for their unconditional support, love and encouragement throughout all years of my academic development. My father, mother and two brothers have always been my inspiration to become the best person I can be. 7 TABLE OF CONTENTS EXAMINATION COMMITTEE APPROVALS .............................................................................. 2 COPYRIGHT PAGE ............................................................................................................................... 3 ABSTRACT .............................................................................................................................................. 4 ACKNOWLEDGEMENTS ................................................................................................................... 6 TABLE OF CONTENTS ....................................................................................................................... 7 LIST OF FIGURES ............................................................................................................................... 10 LIST OF TABLES ................................................................................................................................ 13 Chapter 1: Introduction ......................................................................................................................... 14 Worldwide water problematic ...................................................................................................... 14 Seawater desalination ....................................................................................................................... 16 Research Objective: ............................................................................................................................ 19 Chapter 2: Literature Review .............................................................................................................. 21 Seawater intake systems .................................................................................................................. 21 Conventional open ocean intake designs .................................................................................. 22 Subsurface intakes .............................................................................................................................. 26 Wells ......................................................................................................................................................... 26 Radial (Ranney) collector well ....................................................................................................... 28 Horizontal wells ................................................................................................................................... 29 Slant wells .............................................................................................................................................. 30 Infiltration galleries ............................................................................................................................ 31 Seabed filtration ................................................................................................................................... 32 Slow sand filtration ............................................................................................................................ 37 8 Chapter 3: Methodology ........................................................................................................................ 40 Sampling trip ......................................................................................................................................... 40 Grain size distribution analysis ..................................................................................................... 42 Porosity determination ..................................................................................................................... 46 Hydraulic conductivity determination ....................................................................................... 47 Empirical equations ........................................................................................................................... 51 Hazen equation..................................................................................................................................... 52 Chapuis equation ................................................................................................................................. 53 Chapter 4: Results .................................................................................................................................... 54 Site description .................................................................................................................................... 54 Description of study area: ................................................................................................................ 56 Sediment description ......................................................................................................................... 58 Sediment sample collection ............................................................................................................ 62 Sieve grain size analysis results .................................................................................................... 64 Sediment uniformity .........................................................................................................................