seawater desalination: a sustainable solution to world water shortage
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Seawater desalinationA sustainable solution to world water shortage
Adelaide Desalination Plant
Jonathon E. BlesingTechnical Director, Aurecon
Con PelekaniPrincipal Process Engineer, SA Water
• 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
All are dependent on natural rainfall, which is unlikely to change
Conventional fresh water sources
Supply is reliant on:• Climatic conditions (seasonal, droughts)• Population concentration (pollution)• Excessive draw-off (increased salinity)
Reduced pollution will increase availabilityWater storage (dams) can attenuate seasonal changeNo solution to an extended drought
We still depend on rain
Fresh water supply
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
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
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
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
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
• Water security for Adelaide• Expand Mount Bold reservoir?• Stormwater reuse?• Wastewater recycling?• Seawater desalination?• How and where?
Desalination Working Group
• 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
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
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
Intake System
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
Outfall Diffusers
Outfall Diffusers• 1.1km off-shore• Four nozzles• Duckbill valves• Real time monitoring• No disturbance
Minimal marine environmental impact
Outfall Diffusers
Salinity variations
• Salinity measured 100m from diffusers 0.4ppt to 0.9ppt above ambient
• EPA limit 1.3ppt
Pre-treatment system
disc filters
• Intake screen in clear water• Band screens 3mm • Disc filters 100micron • Ultra filters 0.04micron (pore size)
Pre-treatment system
ultra filters
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
Energy recovery – pressure exchange
• 50% of raw seawater is normally rejected to sea but still at high pressure
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
The result
• 45% of RO pumping energy saved• 24,300kW across whole plant (at full capacity)
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
The result
• A hydro-power system generating 1,290kW at full production
• Generated power supplied directly to the intake pumps
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
Reverse Osmosis System
Reverse Osmosis System
Reverse Osmosis System
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
Other systems
• 200kW solar panel array• Variable speed drive main pumping systems • Efficient operation from 30ML/day to 300ML/day
Specific energy consumption
• SA Government specified 4.5kWh/kLmaximum
• Calculated SEC (based on design data)3.6kWh/kL
• Measured SEC3.47-3.7kWh/kL
ADP – Site remediation
Creek refurbishment
ADP – Site remediation
Stormwater retention
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
Where does the ADP get its power from?
• 20-year agreement with AGL to supply electricity
• 100% from renewable sources
Cost to power the ADP
1-2 families
How much is 3.6kWh/kL?
1-2 families refrigerators
3.6kWh/day
1.0kL/day
Cost to power the ADP
Boeing 747 66MW cruising Hydrocarbon fuelNo water
ADP45MWRenewable energyWater for 600,000 people
ADP peak power demand is 45MW at full production
120Potable water production
The ADP produces 300ML per day
That’s 120 Olympic swimming pools OR…
Potable water production
2 x 25ML storage tanks 66m diameter x 8m high, filled 6 times per day
Environmental impact
Will the desalination plant cause the global salinity in the gulf to rise?
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
Adelaide Desalination Plant
