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Potable water production by means of desalination and other Low-pressure Membrane applications

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

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Potable water production by means of desalination and other Low-pressure Membrane applications

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  1. Appropriate Technologies Conference, Cape Town 3 & 4 September 2007 Potable water production by means of desalination and other Low-pressure Membraneapplications

  2. 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)

  3. 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

  4. Nutrient Water Root Wall (semi-permeable Membrane) Reverse OsmosisHow does it work? In Equilibrium • A Leaf Growth Air Soil Root System

  5. Air Soil Root Wall (semi-permeable Membrane) Root System Equilibrium Disturbed Ammonium Sulphate

  6. Osmosis Air Soil Root Wall (semi-permeable Membrane) Root System Returning to Equilibrium

  7. Applied Pressure Applied Pressure Reverse Osmosis Fresh Water Concentrated Salty Water

  8. What if the membranes fail? Not a big issue , because: • Membrane degradation is slow • Routine cleaning maintains membrane condition • Ample time to source replacement membranes (good stock levels internationally)

  9. How long do RO membranes last? 3-7 years , but: • End of membrane life is project specific (quality or quantity?) • 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

  10. What about a project that was a disaster? Desalination failures occur because: • 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

  11. DON’T PANIC • 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

  12. Are they hard to maintain and operate? No • Daily checks = 1/2hr • Weekly checks = 1hr • Daily monitoring can be done remotely • Cleaning a semi-automatic process every 3-6 months

  13. Design Issue – Pre treatment “Poor Pretreatment is the No. 1 killer of RO Systems” • 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

  14. Design Issue - Recovery Recommendations • 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

  15. Treatment System • Water production cost • (R/kl) • Notes • Amatola Water(For 14 water treatment plants) • 3.39 • Cost includes purchase of raw water. Conventional water treatment • Rand Water (For 6 large water treatment plants, treating a total of • 5 260 Ml/d) • 2.53 • Conventional water treatment plants. Cost includes purchase of raw water. • Midvaal(250 Ml/d treatment plant) • 2.52 • Treatment plant includes ozonation and dissolved air flotation for treating eutrophied water. Cost includesR 1.52/kl for purchase of raw water. • City of Cape Town • (various plants) • 1,05 – 1,25 • Includes raw water costs (which include the new Berg River Water project) • Withoogte • (72 Ml/d treatment plant) • 1.04 • Conventional water treatment plant. Cost includes purchase of raw water. • Bitterfontein • (12 m3/h RO groundwater desalination plant) • 7.81 • Relative high cost for management functions and transport due to remote location of the RO plant. Desalination plants • Boesmansriviermond • ( 45 m3/h RO seawater desalination plant) • 2.26 • Cost includes electricity, labour, membrane replacement (every 5 years) and pump maintenance. • Costing model • (15 m3/h RO groundwater desalination plant) • 5.30 – 9.40 • Range is for low TDS (2 000 mg/l)(lower cost) and high TDS (12 000 mg/l)(higher cost) • (Costing model • (5 Ml/h RO groundwater desalination plant) • 2.40 – 4.90 • Range is for low TDS (2 000 mg/l)(lower cost) and high TDS (12 000 mg/l)(higher cost) • Costing model • (5 Ml/d RO seawater desalination plant) • 5.80 – 8.30 • Range is for East Coast water (lowest cost), South Coast water and West Coast water (highest cost) Typical water production costs for desalination plants and conventional water treatment plants

  16. Low Pressure MEMBRANES LP MEMBRANES INTRODUCTION LP MEMBRANE OPERATION LP MEMBRANE CONFIGURATIONS LP MEMBRANE APPLICATIONS LP MEMBRANE MARKET • What are Low Pressure (LP) Membranes • How do they operate • Different LP Membrane Configurations • LP Membrane Applications • LP Membrane Market Acceptance and GROWTH

  17. INTRODUCTIONFiltration Spectrum LP MEMBRANES INTRODUCTION LP MEMBRANE OPERATION LP MEMBRANE CONFIGURATIONS LP MEMBRANE APPLICATIONS LP MEMBRANE MARKET LOW PRESSURE MEMBRANES MOL WT < 100 < 1,000 < 100,000 < 1,000,000 Pressure > 5 Bar > 2 Bar > 0.5 Bar > 0.2 Bar MICRON < 0.001 0.001 to 0.01 to 0.1 to 1.0 to 0.01 0.1 1.0 10.0

  18. INTRODUCTIONTypical LP Membrane Surface LP MEMBRANES INTRODUCTION LP MEMBRANE OPERATION LP MEMBRANE CONFIGURATIONS LP MEMBRANE APPLICATIONS LP MEMBRANE MARKET

  19. OPERATIONFiltration – Memcor Hollow fibre LP MEMBRANES INTRODUCTION LP MEMBRANE OPERATION LP MEMBRANE CONFIGURATIONS LP MEMBRANE APPLICATIONS LP MEMBRANE MARKET Feed water is outside membrane Filtered water flows through membrane to the lumen FEED FILTRATE

  20. FEED FILTRATE OPERATIONFiltration LP MEMBRANES INTRODUCTION LP MEMBRANE OPERATION LP MEMBRANE CONFIGURATIONS LP MEMBRANE APPLICATIONS LP MEMBRANE MARKET Fouling on the surface of the membrane only

  21. OPERATIONBackwash method LP MEMBRANES INTRODUCTION LP MEMBRANE OPERATION LP MEMBRANE CONFIGURATIONS LP MEMBRANE APPLICATIONS LP MEMBRANE MARKET Raw water remains outside membrane Filtrate is pushed backwards through membrane Air scours outside of membrane surface

  22. LP MEMBRANE CONFIGURATIONS LP MEMBRANES INTRODUCTION LP MEMBRANE OPERATION LP MEMBRANE CONFIGURATIONS LP MEMBRANE APPLICATIONS LP MEMBRANE MARKET

  23. LP MEMBRANE CONFIGURATIONS - Pressurised (Most Common) • 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 Treated Water Raw Water Waste Pall Hyflux Norit Memcor

  24. Treated Water Raw Water Waste Zenon LP MEMBRANE CONFIGURATIONS - Submerged • 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 Memcor

  25. LP MEMBRANE MARKETInstalled Capacity LP MEMBRANES INTRODUCTION LP MEMBRANE OPERATION LP MEMBRANE CONFIGURATIONS LP MEMBRANE APPLICATIONS LP MEMBRANE MARKET EXPONENTIALGROWTH WIDESPREAD MARKETACCEPTANCE

  26. LP MEMBRANE MARKETReasons for Growth LP MEMBRANES INTRODUCTION LP MEMBRANE OPERATION LP MEMBRANE CONFIGURATIONS LP MEMBRANE APPLICATIONS LP MEMBRANE MARKET LP MEMBRANE MARKET GROWTH • Superior performance vs traditional technologies • Declining fresh water sources or quality • More stringent regulatory requirements • Growing Market acceptance 2% 22%

  27. LP MEMBRANE MARKETTrend LP MEMBRANES INTRODUCTION LP MEMBRANE OPERATION LP MEMBRANE CONFIGURATIONS LP MEMBRANE APPLICATIONS LP MEMBRANE MARKET LP MEMBRANE MARKET GROWTH Cost of Membranes 2% 22% Cost of Water

  28. Potable Water Production

  29. 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

  30. 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

  31. 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

  32. Thank you very much for your attention.

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