Desalination Desalination y Process that removes dissolved minerals (including but not limited to salt) from seawater and brackish water y History y 1852: British patent on desalination device y 1928: First major commitment to desalination (Curacao, Netherlands Antilles) y 1938: First large‐scale desalination plant (Saudi Arabia) y WWII: Considerable desalination research by US (establishment of Office of Saline Water (OSW) and Office of Water Research and Technology (OWRT) y U.S desalination research funding: 1977 ‐ $144 million, 2000‐ $1.3 million Simplified Box Diagram for Desalination
Feedwater (seawater or brackish water)
Saline Water
Energy Brine Thermal, DESALTING Waste Electrical, DEVICE Discharge Solar, Wind
Fresh Water
Product World Desalination Capacity by Source of Water (June 1999)
Diagram of a Vapor Still
Major Desalting Processes y Thermal: y Multi‐stage flash distillation y Multiple‐effect distillation y Vapor compression y Membrane: y Electrodialysis y Reverse osmosis
Minor processes: freezing, membrane distillation, solar humidification
Boiling Temperature of Water at Different Pressures
Pressure (bar) Temperature (deg. C) 2 120 1 100 0.25 65 0.1 45
Multi‐stage flash distillation Advantages Disadvantages •Production of water with •Requires large energy input good quality (5 to 50 ppm •High maintenance tds) requirements •RO produces 10 to 500 •Larger space needed that RO ppm tds desalination plant •Leading technology for large‐•Most experience is from scale seawater distillation (in Middle East where energy use for 40 years) costs are less of a concern •Large amount of water necessary for production and cooling
Components of a Reverse Osmosis Plant Reverse Osmosis Advantages Disadvantages •Reduced energy costs •Sensitive to feedwater quality compared to distillation and requires extensive •Higher water recovery than feedwater treatment to limit distillation (45% for seawater) scaling and membrane fouling •In addition to removing salts, •Complicated feedwater RO processes also remove other pretreatment contaminants: organic molecules, viruses, bacteria, silica •Automation feasible
Proposed Kalaeloa Desalination Facility y Seawater reverse osmosis desalination facility y Undeveloped location previously part of Barber’s Point Naval Air Station y Water production expected by Spring 2004 y Produce 5 mgd freshwater from 12 mgd of source water y Supplement Oahu’s potable water supply y Will occupy 20 acres of land y Waste disposal through injection wells y Cost: $54 million (capital), $6.80 per 1000 gallons Proposed Location of Kalaeloa Desalination Facility