potable water production by means of desalination and other low-pressure membrane applications
DESCRIPTION
Appropriate Technologies Conference, Cape Town 3 & 4 September 2007. Potable water production by means of desalination and other Low-pressure Membrane applications. Water Wise. Society, my dear, is like salt water, good to swim in but hard to swallow. Arthur Stringer - PowerPoint PPT PresentationTRANSCRIPT
Water Technologies
Potable water production by means of desalination and other Low-pressure Membraneapplications
Appropriate Technologies Conference, Cape Town 3 & 4 September 2007
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Water Wise
Society, my dear, is like salt water, good to swim in but hard to swallow. Arthur Stringer
Water is the most neglected nutrient in your diet but one of the most vital. Kelly Barton
[Water is] the only drink for a wise man. Henry David
A chemical industry lobbying group defends its stand against strict water pollution laws. Spokeswoman Flo Brown elaborates: “The chemicals in the water act as a preservative, which extends the freshness period of the water by several decades. We think that’s a good deal for consumers.” (1970)
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Membrane Improvements
Costs have dropped by 50% in 20 years
Productivity has increased by 100%
Fouling resistant membranes
Chlorine Resistant, Low Pressure membranes
Increased membrane manufacturer competition
Membranes have become a commodity
Improved scale inhibitors
Improved energy efficiency of ancillary equip
Variable Speed Drives
Energy recovery
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Reverse Osmosis
How does it work?A
Leaf Growth
Air
Soil
Root System
Root Wall(semi-permeable Membrane)
Water
Nutrient
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Air
Soil
Root System
Root Wall(semi-permeable Membrane)
AmmoniumSulphate
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Air
Soil
Root System
Root Wall(semi-permeable Membrane)
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Fresh Water ConcentratedSalty Water
AppliedPressure
AppliedPressure
Reverse Osmosis
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What if the membranes fail?
Membrane degradation is slow
Routine cleaning maintains membrane condition
Ample time to source replacement membranes (good stock levels internationally)
Not a big issue, because:
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How long do RO membranes last?
End of membrane life is project specific (quality or quantity?)
3-7 years , but:
Type of pre treatment can increase life
Microfilter pre treatment - 5 years or more
Sand filter pre treatment - 3 years
Operating cost balance - Higher Pressure (energy) & frequent cleaning vs capital outlay?
You don’t need a full set - keep the best and replace the worst
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What about a project that was a disaster?
Failure to understand feed water
Change in feed water
Designer inexperience/lack of knowledge
Competitive tendering awards contracts to the company that “cut corners”
Poor commissioning
Inadequate pre treatment
Desalination failures occur because:
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Early failures of RO occurred in the first applications of a new technology
RO is now a mature technology
Failure causes are well understood and predictable
Correct design and sizing eliminates the potential for failure
DON’T PANIC
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Are they hard to maintain and operate?
Daily checks = 1/2hr
Weekly checks = 1hr
Daily monitoring can be done remotely
Cleaning a semi-automatic process every 3-6 months
No
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Design Issue – Pre treatment
Invest time & money to define the full range of feed conditions (algae, salts, pH, turbidity etc)
Opt for easy to treat water sources
Extremes of feed conditions must be the design basis for pre treatment
Choose pre treatment that gives stable treated water quality
Don’t experiment in remote locations
Give greater importance to proven technical solutions over price
“Poor Pretreatment is the No. 1 killerof RO Systems”
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Design Issue - Recovery
Aim for:
TDS < 2000mg/L 80-90%
TDS 2000-5000mg/L 70-80%
TDS 5000-10000mg/L up to 75%
Seawater (36000mg/L) 40-45%
Sparingly soluble salts may restrict further
DO make brine disposal the key driver for increasing recovery
DON’T use the lure of reduced operating cost as the driver for high recovery
Recommendations
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Typical water production costs for desalination plants and conventional water treatment plantsTypical water production costs for desalination plants and conventional water treatment plants
Range is for East Coast water (lowest cost), South Coast water and West Coast water (highest cost)5.80 – 8.30
Costing model
(5 Ml/d RO seawater desalination plant)
Range is for low TDS (2 000 mg/l)(lower cost) and high TDS (12 000 mg/l)(higher cost)2.40 – 4.90
(Costing model
(5 Ml/h RO groundwater desalination plant)
Range is for low TDS (2 000 mg/l)(lower cost) and high TDS (12 000 mg/l)(higher cost)5.30 – 9.40
Costing model
(15 m3/h RO groundwater desalination plant)
Cost includes electricity, labour, membrane replacement (every 5 years)
and pump maintenance.2.26
Boesmansriviermond
( 45 m3/h RO seawater desalination plant)
Relative high cost for management functions and transport due to remote location of the RO plant.7.81
Bitterfontein
(12 m3/h RO groundwater desalination plant)
Conventional water treatment plant. Cost includes purchase of raw water. 1.04
Withoogte
(72 Ml/d treatment plant)
Includes raw water costs (which include the new Berg River Water project) 1,05 – 1,25
City of Cape Town
(various plants)
Treatment plant includes ozonation and dissolved air flotation for treating
eutrophied water. Cost includesR 1.52/kl for purchase of raw water.
2.52Midvaal(250 Ml/d treatment plant)
Conventional water treatment plants. Cost includes purchase of raw water.2.53Rand Water (For 6 large water treatment plants, treating a total of
5 260 Ml/d)
Cost includes purchase of raw water.3.39Amatola Water(For 14 water treatment plants)
Notes Water production cost
(R/kl) Treatment System
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Low Pressure MEMBRANES
What are Low Pressure (LP) Membranes
How do they operate
Different LP Membrane Configurations
LP Membrane Applications
LP Membrane Market Acceptance and GROWTH
LP MEMBRANES INTRODUCTION
LP MEMBRANE OPERATION
LP MEMBRANE CONFIGURATIONS
LP MEMBRANE APPLICATIONS
LP MEMBRANE MARKET
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INTRODUCTIONFiltration Spectrum
Pressure > 5 Bar > 2 Bar > 0.5 Bar > 0.2 Bar
MOL WT < 100 < 1,000 < 100,000 < 1,000,000
MICRON < 0.001 0.001 to 0.01 to 0.1 to 1.0 to 0.01 0.1 1.0 10.0
LOW
PRESSURE
MEMBRANES
LP MEMBRANES INTRODUCTION
LP MEMBRANE OPERATION
LP MEMBRANE CONFIGURATIONS
LP MEMBRANE APPLICATIONS
LP MEMBRANE MARKET
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INTRODUCTIONTypical LP Membrane Surface
LP MEMBRANES INTRODUCTION
LP MEMBRANE OPERATION
LP MEMBRANE CONFIGURATIONS
LP MEMBRANE APPLICATIONS
LP MEMBRANE MARKET
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OPERATIONFiltration – Memcor Hollow fibre
FEED
FILTRATE
Feed water is outside
membrane
Filtered water flows through membrane to
the lumen
LP MEMBRANES INTRODUCTION
LP MEMBRANE OPERATION
LP MEMBRANE CONFIGURATIONS
LP MEMBRANE APPLICATIONS
LP MEMBRANE MARKET
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OPERATIONFiltration
Fouling on the surface of the membrane only
FEED
FILTRATE
LP MEMBRANES INTRODUCTION
LP MEMBRANE OPERATION
LP MEMBRANE CONFIGURATIONS
LP MEMBRANE APPLICATIONS
LP MEMBRANE MARKET
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OPERATIONBackwash method
Raw water remains outside
membrane
Filtrate is pushed
backwards through
membrane
Air scours outside of membrane
surface
LP MEMBRANES INTRODUCTION
LP MEMBRANE OPERATION
LP MEMBRANE CONFIGURATIONS
LP MEMBRANE APPLICATIONS
LP MEMBRANE MARKET
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LP MEMBRANE CONFIGURATIONS
LP MEMBRANES INTRODUCTION
LP MEMBRANE OPERATION
LP MEMBRANE CONFIGURATIONS
LP MEMBRANE APPLICATIONS
LP MEMBRANE MARKET
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LP MEMBRANE CONFIGURATIONS - Pressurised (Most Common)
Raw Water
Waste
TreatedWater
NoritHyflux
Memcor
Pall
FEATURES
Each membrane has own pressure vessel
Higher operating pressures
Easily packaged
LP MEMBRANES INTRODUCTION
LP MEMBRANE OPERATION
LP MEMBRANE CONFIGURATIONS
LP MEMBRANE APPLICATIONS
LP MEMBRANE MARKET
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LP MEMBRANE CONFIGURATIONS - Submerged
Raw Water
Waste
TreatedWater
Memcor Zenon
FEATURES
Membranes sit in Open Tank
Typically Low capital cost
Typically Low operating cost
Suited to Retrofit into existing Clarifiers/Sandfilters
LP MEMBRANES INTRODUCTION
LP MEMBRANE OPERATION
LP MEMBRANE CONFIGURATIONS
LP MEMBRANE APPLICATIONS
LP MEMBRANE MARKET
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LP MEMBRANE MARKETInstalled Capacity
EXPONENTIALGROWTH
WIDESPREAD MARKETACCEPTANCE
LP MEMBRANES INTRODUCTION
LP MEMBRANE OPERATION
LP MEMBRANE CONFIGURATIONS
LP MEMBRANE APPLICATIONS
LP MEMBRANE MARKET
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LP MEMBRANE MARKET GROWTH
LP MEMBRANE MARKETReasons for Growth
22%
2%
Superior performance vs traditional technologies
Declining fresh water sources or quality
More stringent regulatory requirements
Growing Market acceptance
LP MEMBRANES INTRODUCTION
LP MEMBRANE OPERATION
LP MEMBRANE CONFIGURATIONS
LP MEMBRANE APPLICATIONS
LP MEMBRANE MARKET
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LP MEMBRANE MARKET GROWTH
LP MEMBRANE MARKETTrend
22%
2%
Cost of Water
Cost of
Membranes
LP MEMBRANES INTRODUCTION
LP MEMBRANE OPERATION
LP MEMBRANE CONFIGURATIONS
LP MEMBRANE APPLICATIONS
LP MEMBRANE MARKET
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Potable Water Production
Typical Potable Water Quality:
Clean Turbid
Turbidity < 20 NTU < 100 NTU
Colour < 10 HCU < 100 HCU
Algae < 100 cells/mL < 104 cells/mL
Hardness < 200 mg/L < 200 mg/L
pH 6.0 - 8.5 6.0 - 8.5
Coagulant Nil < 20 mg/L
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Joyce Rd WPP - Tauranga, NZ
36 ML/d (9.5MGD) Pressurised Plant
Operational Dec ‘97
Highly variable feed water
LRV 5 (> 1 µm) filtrate quality
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Oropi Rd - Tauranga, NZ
Sister plant to Joyce Rd
32 ML/day (8.5MGD)
Expandable to 54ML/day
Commissioned June, 2002
Backwash recovery via clarifier
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Aqua 2000 - Bendigo, Vic
Capacity 126 ML/d (33 MGD)
Surface water (Colour 5 - 20 HCU)
Tight water quality targets:
Turbidity at each filter < 0.1 NTU
Particles at each filter < 10 particle/mL
Protozoa > Log 4 removal
THMFP < 80 g/L
Algae Toxins
Colour, Taste & Odour
Water Technologies
Thank you very much for your attention.