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Seawater Desalination: A sustainable solution to world water shortage


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Seawater desalination can provide a climate independent source of drinking water as stress on existing natural water supplies continues to increase with world population increasing disproportionately in urban centres and the impact of climate change. Jonathon Blesing, Technical Director, Aurecon, and Con Pelekani, Principal Process Engineer, SA Water, discuss the solutions delivered for the sustainable design and operation of SA Water’s Adelaide Desalination Plant.

Published in: Engineering

Seawater Desalination: A sustainable solution to world water shortage

  1. 1. Seawater desalination A sustainable solution to world water shortage Adelaide Desalination Plant Jonathon E. Blesing Technical Director, Aurecon Con Pelekani Principal Process Engineer, SA Water
  2. 2. • Mid 2013 7,095,217,980 est. • Growth rate 1.14% • Doubling period 61 years Where will the water come from? • Reduced wastage • Reduced pollution (increase availability) • Recycled water • Better stormwater management World population
  3. 3. All are dependent on natural rainfall, which is unlikely to change Conventional fresh water sources
  4. 4. Supply is reliant on: • Climatic conditions (seasonal, droughts) • Population concentration (pollution) • Excessive draw-off (increased salinity) Reduced pollution will increase availability Water storage (dams) can attenuate seasonal change No solution to an extended drought We still depend on rain Fresh water supply
  5. 5. Nature’s solution is not enough It’s not enough and it’s not reliable. We need an alternative source of water that is climate independent
  6. 6. Media reporting and common public perception often considers seawater desalination as: “…environmentally irresponsible and energy intensive, and described as a very expensive insurance policy for droughts necessary due to mismanagement of our natural resources, rather than a sustainable, environmentally responsible drinking water solution…” Seawater desalination – Common perception
  7. 7. To address these common perception issues and achieve a responsible and sustainable plant, the targets need to be: • Minimum impact on the marine, terrestrial or atmospheric environment • Minimum energy consumption • Minimum impact on local communities • Minimum cost – capital and operating A tough ask? Seawater desalination – sustainability
  8. 8. South Australian conditions • Driest state, driest continent • Adelaide 1.23M people • Reservoir capacity = 1 year • 40% to 90% from River Murray • River Murray also supplies NSW and Victoria and is a major food bowl
  9. 9. Climate impact Projections show Greater Adelaide would likely have a supply deficit by 2013 in extreme dry year events without a 100GL/a plant River Murray Drought Years
  10. 10. • Water security for Adelaide • Expand Mount Bold reservoir? • Stormwater reuse? • Wastewater recycling? • Seawater desalination? • How and where? Desalination Working Group
  11. 11. • Desalination plant at Port Stanvac • Capacity 50GL/year, expandable to 100GL/year • Maximum energy consumption <4.5kWh/kL • Low impact on marine environment • Positive impact on terrestrial environment • No impact on local community • Power from renewable energy source Recommendations
  12. 12. Concept design phase • Environmental Impact Statement • Detailed analysis of Gulf St Vincent • Detailed concept design prepared • Pilot Plant set up in December 2008 • Tenders called based on the detailed concept design Contract (Design/Construct) awarded to Adelaide Aqua consortium. January 2009 for 50GL/year plant (later extended to 100GL/year) – AUD$1.82b
  13. 13. Key Design Factors • Minimum environmental impact – intake system/outfall system • Energy efficient operation – minimum to maximum production • Minimum environmental impact during construction • Positive impact on local terrestrial environment • Minimal impact on local residential community • Power supply from renewable energy supply
  14. 14. Intake System
  15. 15. Intake System • 1.4km offshore • Deep water • Sandy seabed • 4.0m above seafloor • 100mm bar screen • Velocity 0.08m/sec through screen • Velocity 2.28m/sec in intake throat Minimal marine environmental impact
  16. 16. Outfall Diffusers
  17. 17. Outfall Diffusers • 1.1km off-shore • Four nozzles • Duckbill valves • Real time monitoring • No disturbance Minimal marine environmental impact
  18. 18. Outfall Diffusers Salinity variations • Salinity measured 100m from diffusers 0.4ppt to 0.9ppt above ambient • EPA limit 1.3ppt
  19. 19. Pre-treatment system disc filters • Intake screen in clear water • Band screens 3mm • Disc filters 100micron • Ultra filters 0.04micron (pore size)
  20. 20. Pre-treatment system ultra filters
  21. 21. The result • Silt density index (measured) – 2.4 average • Reduced fouling of RO membranes • Reduced clean-in-place and chemical usage • Reduced pumping cost • Increased life of membranes • Increased water recovery rate
  22. 22. Energy recovery – pressure exchange • 50% of raw seawater is normally rejected to sea but still at high pressure
  23. 23. Energy recovery – pressure exchange • 50% of raw seawater is normally rejected to sea but still at high pressure • Use pressure energy to draw more seawater and supply RO at high pressure
  24. 24. The result • 45% of RO pumping energy saved • 24,300kW across whole plant (at full capacity)
  25. 25. Energy recovery – gravity head • Main process plant at RL 52.0 • Pumping energy penalty from static head • 50% of seawater returned to sea • Two Francis Turbines recover energy from return pipes
  26. 26. The result • A hydro-power system generating 1,290kW at full production • Generated power supplied directly to the intake pumps
  27. 27. Permeate recovery • Unique arrangement of RO racks • First pass racks split (front/rear) • Second pass front – 2 stage • Second pass rear – 2 stage • First pass reject to energy recovery • Second pass reject recycled
  28. 28. Reverse Osmosis System
  29. 29. Reverse Osmosis System
  30. 30. Reverse Osmosis System
  31. 31. The result • All water passes through two membranes before transfer to remineralisation stage • Only first pass reject is returned to sea (via energy recovery) • Second pass reject is recycled saving pump energy • Average permeate recovery rate is 48.6% High recovery means less water pumped for given output
  32. 32. Other systems • 200kW solar panel array • Variable speed drive main pumping systems • Efficient operation from 30ML/day to 300ML/day
  33. 33. Specific energy consumption • SA Government specified 4.5kWh/kL maximum • Calculated SEC (based on design data) 3.6kWh/kL • Measured SEC 3.47-3.7kWh/kL
  34. 34. ADP – Site remediation Creek refurbishment
  35. 35. ADP – Site remediation Stormwater retention
  36. 36. Impact on local community • Landscaping shields the plant from outside view • Noise measurements at site boundary rear residential zone show plant is barely audible • No change to local traffic patterns • Construction phase of significant benefit to local industries • Buildings blend with local environment
  37. 37. Where does the ADP get its power from? • 20-year agreement with AGL to supply electricity • 100% from renewable sources
  38. 38. Cost to power the ADP 1-2 families How much is 3.6kWh/kL? 1-2 families refrigerators 3.6kWh/day 1.0kL/day
  39. 39. Cost to power the ADP Boeing 747 66MW cruising Hydrocarbon fuel No water ADP 45MW Renewable energy Water for 600,000 people ADP peak power demand is 45MW at full production
  40. 40. 120 Potable water production The ADP produces 300ML per day That’s 120 Olympic swimming pools OR…
  41. 41. Potable water production 2 x 25ML storage tanks 66m diameter x 8m high, filled 6 times per day
  42. 42. Environmental impact Will the desalination plant cause the global salinity in the gulf to rise?
  43. 43. Sustainable seawater desalination • Climate independent, inexhaustible supply of drinking water • Minimal impact on the marine, terrestrial or atmospheric environment • Low energy consumption • Able to run at low capacity when not required • Minimal impact on local community • Positive impact (remediation) on the site • Powered from renewable energy source
  44. 44. Adelaide Desalination Plant
  45. 45. Contact: Jonathon Blesing Technical Director +61 8 8237 9709 Read more on our website!