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

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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AWA_Advanced Water Treatment Workshop

Water Technologies

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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Water Technologies

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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Water Technologies

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


AmmoniumSulphate

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Water Technologies

Air

Soil

Root System


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Water Technologies

Fresh Water ConcentratedSalty Water

AppliedPressure

AppliedPressure

Reverse Osmosis

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Water Technologies

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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Water Technologies

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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Water Technologies

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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Water Technologies

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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Water Technologies

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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Water Technologies

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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Water Technologies

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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Water Technologies

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 MEMBRANE MARKET

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INTRODUCTIONTypical LP Membrane Surface





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 MEMBRANE MARKET

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OPERATIONFiltration

Fouling on the surface of the membrane only

FEED

FILTRATE





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 MEMBRANE MARKET

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LP MEMBRANE MARKET

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Water Technologies

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 MEMBRANE MARKET

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Water Technologies

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 MEMBRANE MARKET

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Water Technologies

LP MEMBRANE MARKETInstalled Capacity

EXPONENTIALGROWTH

WIDESPREAD MARKETACCEPTANCE





LP MEMBRANE MARKET

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Water Technologies

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 MEMBRANE MARKET

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LP MEMBRANE MARKET GROWTH

LP MEMBRANE MARKETTrend

22%

2%

Cost of Water

Cost of

Membranes





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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Water Technologies

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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Water Technologies

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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Water Technologies

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.

Documents

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