4. membrane processes
DESCRIPTION
A semi-permeable membraneis a VERY THIN film thatallows some types of matterto pass through while leavingothers behindTRANSCRIPT
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MEMBRANE
PROCESSES
Ali Masduqi
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A membrane is a film
A semi-permeable membrane is a VERY THIN film that allows some types of matter to pass through while leaving others behind
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Advantages of membrane
technologies
1-The quality of the treated water is independent on the raw water quality
2-It produces high quality of treated water
3- physical and not a chemical process:
the solid/liquid phase separation & disinfection may be achieved without chemical addition
4- the amount of sludge is moderate
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Disadvantages of membrane
technologies
1-Fouling (colloids, solids, dissolved organicmatter, microorganisms)
2-Scaling (CaSO4, CaCO3, CaF2)
3- Microorganisms may also damage the material of the membrane
4- For reverse osmosis: hydrolysis of the membrane may ocur
cellulose acetate cellulose+acetate
5- Cost (expensive technologies)
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Colloids
Bacteria
Pollens Yeasts
Organic macromolecules
Organic compounds
Viruses Dissolved
salts
RO
NF
MF Sand filter
1 mm 0.1 mm 0.01 mm 0. 1 nm 0. 1 nm 10 mm 100 mm
hair visible to
naked eye
Red
globule Smallest
microorganisms
Polio
virus
UF
Membrane Classifications (Pore Size)
Microfiltration
Ultrafiltration
Nanofiltration
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10 100 1000 10000 100000
Total dissolved solid concentration mg/L
Ion exchange
Electrodialysis
Reverse osmosis
Freezing
distillation
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Membranes Classification (Driving Force)
Vacuum (Submerged Membranes)
• Compatible with higher solid concentration
• Can be used for retrofit
• High energy demand with air scouring
• Noise & evaporation concerns
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Membranes Classification (Driving Force)
Pressure (Canister Membranes)
• More compact design
• Cannot handle high solid concentration (> 100 NTU) for a substantial period of time
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Membranes Classification (Configuration)
Flat Sheet (Spiral-wound)
Mostly used in Reverse Osmosis
& Nanofiltration
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Membranes Classification (Configuration)
Tubular Membranes (OD > 3 mm)
Mostly used in Industrial MF
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Membranes Classification (Configuration)
Hollow Fiber Membranes (ID < 1.5 mm)
Mostly used in MF & UF
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Membranes Classification (Location of Membrane )
Inside-out Membranes
• Outside-In Membranes
Raw Water
Filtered Water
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APPLICATION OF MEMBRANE
TECHNOLOGIES IN
DRINKING WATER TREATMENT
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1-Microfiltration: mostly for industrial water treatment to reduce turbidity.
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2-Ultra filtration : mostly in industry
to separate macromolecules and to
reduce turbidity • PAC+ ultra filtration to remove :
- suspended solids.
- Organic matter.
- Micro pollutant.
- Taste and odors .
• Aeration +PAC+ ultra filtration to remove taste and odor
• Ultra filter membrane mainly applied at low pressure=10.5 kg/cm2
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3- nanofiltration
to remove:
- Suspended & dissolved matter .
- Micro pollutants
- Microorganisms
- T H M precursors
- Water softening
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4- electrodialysis • In Electrodialysis , the membrane allow ions to pass but not water. • The driving force is electrical current which carries the ions through the membrane. • By using stacks of alternate anion and cation permeable membranes ,it is possible to produce a treated and concentrate stream. The principle of Electrodialysis is illustrated on next figure:
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Source: Hall & Hyde, 1992
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Electrodialysis Uses electrical power to draw ions from
product water to the concentrate stream.
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5- reverse osmosis
The applied pressure is higher than the pressure for nanofiltration 10.5 -- 28.1 kg/cm2
- Mainly used to remove salt from seawater.
- It can be also applied to remove organic matter
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What is Osmosis
It is the transfer of water from regions of low
concentration to region of high one to
equilibrate between concentrations.
The process stops when hydrostatic pressure
on the high solute side counter acts the
osmotic pressure.
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REVERSE OSMOSIS Reverse osmosis consists of separating a solvent, such as water from a saline solution by the use of a semi permeable membrane and a hydrostatic pressure ( see this figure)
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Reverse Osmosis The Osmosis process can be reversed by applying high
pressure to the high concentration (source water, reject) side through a selective semi-permeable membrane.
Membranes develop from natural pig bladder to synthetic materials (polyamides-PA) membranes highly efficient at rejecting contaminants.
Membranes are made tough enough to withstand the greater pressures necessary for efficient operation .
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RO component and definition
RO membrane is one of the most important component in water treatment system.
RO is a process in which water is purified using ion exclusion semi-permeable membrane.
Reverse Osmosis is the reversing the Osmosis process
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Reverse Osmosis vs. Osmosis
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Type of reverse osmosis
Spiral wound
Tubular
Hollow fiber
See figures
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Source: http://twri.tamu.edu/reports/2002/2002-027/sr2002-027.pdf
Spiral wound
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Source: The Management and implementation Authority of the Man-Made River Project,
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Tubular Reverse Osmosis Equipment
Source: Reynolds & Richards, 1996
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Hollow-Fiber Reverse Osmosis Equipment
Source: Reynolds & Richards, 1996
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Source: http://twri.tamu.edu/reports/2002/2002-027/sr2002-027.pdf
Schematic of typical RO treatment system
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Pre-filters in RO systems
RO systems require a carbon pre-filter for the
reduction of chlorine (as mentioned before), which
can damage an RO membrane
A sediment pre-filter is required to ensure that fine
suspended materials in the source water do not
permanently clog the membrane.
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Comparing RO membranes
Disadvantages Advantages
Membrane
• Chlorine sensitive, requires
carbon pretreatment
• Little higher reject ratio
• Operate at wider pH
range
Thin film
membrane (TF)
• Not sensitive to chlorine
• Lower reject ratio
• Operate on less pH
range
Cellulose Triacetate
membrane (CTA)
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RO membrane performance
RO membrane performance is measured by
percent rejection.
Final product water quality can be measured
by either conductivity in micro-siemens/cm or
total dissolved solids (TDS) displayed as mg/L
or parts per million (PPM).
AAMI recommends both percent rejection and
water quality monitors be used
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