IntroductionIntroduction

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Reverse OsmosisReverse Osmosis

Principle of Reverse Principle of Reverse OsmosisOsmosis

The The phenomenon of osmosis occurs when phenomenon of osmosis occurs when pure water flows from a dilute saline solution pure water flows from a dilute saline solution through a membrane into a higher through a membrane into a higher concentrated saline solution.concentrated saline solution.

The phenomenon of osmosis, a semi The phenomenon of osmosis, a semi permeable membrane is placed between two permeable membrane is placed between two compartments “Semi permeable” means that compartments “Semi permeable” means that the membrane is permeable to some species the membrane is permeable to some species and not permeable to other.and not permeable to other.

Assume that, the membrane is permeable to Assume that, the membrane is permeable to water, but not salt.water, but not salt.

Place a salt solution in one compartment and Place a salt solution in one compartment and pure water in the other compartment.pure water in the other compartment.

The membrane will allow water to permeate The membrane will allow water to permeate through it to other side, But salt cannot pass through it to other side, But salt cannot pass through the membrane.through the membrane.

As a fundamental rule of nature, this system As a fundamental rule of nature, this system will try to reach equilibrium.will try to reach equilibrium.

The only possible way to reach equilibrium is The only possible way to reach equilibrium is for water to pass from the pure water for water to pass from the pure water compartment to the salt water compartment.compartment to the salt water compartment.

The Osmosis can cause a rise in the height of the The Osmosis can cause a rise in the height of the salt solution.salt solution.

This height will increase until the pressure of the This height will increase until the pressure of the column of water (Salt Solution) is so high that the column of water (Salt Solution) is so high that the force of this water column stops the water flowforce of this water column stops the water flow..

The equilibrium point of this water column The equilibrium point of this water column height in terms of water pressure against the height in terms of water pressure against the membrane is called Osmotic Pressure.membrane is called Osmotic Pressure.

If the If the forceforce applied to this column of water, applied to this column of water, the direction of water flow through the the direction of water flow through the membrane can be reversed.membrane can be reversed.

This is the basis of the term reverse osmosis.This is the basis of the term reverse osmosis. This Reversed flow produced a pure water from This Reversed flow produced a pure water from

the salt solution, Since the membrane is not the salt solution, Since the membrane is not permeable to salt.permeable to salt.

Two CompartmentsTwo CompartmentsA Semi-permeable membrane Placed in betweenA Semi-permeable membrane Placed in betweenConcentration Solution in Left side, Dilute Solution in Right SideConcentration Solution in Left side, Dilute Solution in Right Side

Dilute SolutionConcentrated Solution

Pressure

Equilibrium CaseEquilibrium CaseApplied Force in Concentration SideApplied Force in Concentration Side

How to use Reverse How to use Reverse OsmosisOsmosis

With a high pressure pump, Pressurized saline With a high pressure pump, Pressurized saline feed water is continuously pumped to the module feed water is continuously pumped to the module system.system.

With in the module consisting of a pressre With in the module consisting of a pressre vessel (housing) and a membrane element vessel (housing) and a membrane element the feed water will be split into a low saline the feed water will be split into a low saline product, Called (Permeate) and high saline product, Called (Permeate) and high saline brine, Called (Reject).brine, Called (Reject).

A flow regulating valve controls the A flow regulating valve controls the percentage of feed water that is going to the percentage of feed water that is going to the concentrate stream and the permeate which concentrate stream and the permeate which will be obtained from the feed.will be obtained from the feed.

A pressurized water flows into the vessel and A pressurized water flows into the vessel and through the channel between the spiral through the channel between the spiral winding of the element.winding of the element.

Up to seven element are connected together Up to seven element are connected together within pressure vessel.within pressure vessel.

The feed water becomes more and more The feed water becomes more and more concentrated and will enter the next element.concentrated and will enter the next element.

The permeate of each element will be The permeate of each element will be collected in the common permeate tube collected in the common permeate tube installed in the center of each spiral wound installed in the center of each spiral wound element and flows to a permeate collecting element and flows to a permeate collecting pipe outside of the pressure vessel.pipe outside of the pressure vessel.

VesselVesselFeedFeed

WaterWater

Feed Feed ValveValve

PermeatePermeate

WaterWater

Reverse Osmosis Reverse Osmosis ProcessProcess

Reverse Osmosis Reverse Osmosis ProcessProcess

Recovery (%) =Recovery (%) =Permeate FlowPermeate Flow

Feed FlowFeed Flow

Salt Passage (%) =Salt Passage (%) =Permeate Salt ConcentrationPermeate Salt Concentration

Feed Salt ConcentrationFeed Salt Concentration

Salt Rejection (%) =Salt Rejection (%) = 100 – Salt Passage100 – Salt Passage

Cross Flow Membrane Cross Flow Membrane FiltrationFiltration

There are four categories of cross flow membrane There are four categories of cross flow membrane filtration:filtration:

Micro filtrationMicro filtration

Ultra filtrationUltra filtration

Nano filtrationNano filtration

Reverse OsmosisReverse Osmosis

Micro Filtration (MF)Micro Filtration (MF)

Micro filtration removed particles in range of Micro filtration removed particles in range of approximately 0.1 to 1 micron.approximately 0.1 to 1 micron.

Suspended particles and large colloids are Suspended particles and large colloids are rejected while macromolecules and rejected while macromolecules and dissolved solids pass through mf.dissolved solids pass through mf.

Transmembrane pressure are typically 0.7 Transmembrane pressure are typically 0.7 bar (10 PSI).bar (10 PSI).

Ultra Filtration (UF)Ultra Filtration (UF)

Ultra filtration provide macromolecules Ultra filtration provide macromolecules separation for particles in theseparation for particles in the 20 to 1000 20 to 1000 Angstrom range (Up to 0.1 micron)Angstrom range (Up to 0.1 micron)..

All dissolved salt ands and smaller All dissolved salt ands and smaller molecules pass through the membrane.molecules pass through the membrane.

Items rejected by the membrane include Items rejected by the membrane include collide proteins, microbiological collide proteins, microbiological contamination and large organic molecules.contamination and large organic molecules.

Transmembrane pressure are typically 1 to 7 Transmembrane pressure are typically 1 to 7 bar (15 to 100 PSI).bar (15 to 100 PSI).

Nano Filtration (NF)Nano Filtration (NF) Nanofiltration refers to a specialty membrane Nanofiltration refers to a specialty membrane

process which rejects particles in the approximate process which rejects particles in the approximate size range of 1 nanometer (10 Angstrom).size range of 1 nanometer (10 Angstrom).

Organic molecules with molecular weight Organic molecules with molecular weight greater than 200-400 are rejected, Also greater than 200-400 are rejected, Also dissolved salt are rejected in the range of 20 dissolved salt are rejected in the range of 20 to 98%, Salts which have movement anions to 98%, Salts which have movement anions (eg. Sodium Chlorine, Calcium Chlorine), (eg. Sodium Chlorine, Calcium Chlorine), salts with divalent anions (Magnesium salts with divalent anions (Magnesium Sulfate) have higher rejections of 90 to 98%.Sulfate) have higher rejections of 90 to 98%.

Typical applications include removal of color Typical applications include removal of color and total organic carbon (TOC) from surface and total organic carbon (TOC) from surface water, removal Hardness or radium from well water, removal Hardness or radium from well water, Overall reduction of total dissolved water, Overall reduction of total dissolved solids (TDS) and Separation of organic from solids (TDS) and Separation of organic from inorganic matter specially food and inorganic matter specially food and wastewater applications.wastewater applications.

Items rejected by the membrane include Items rejected by the membrane include collide proteins, microbiological collide proteins, microbiological contamination and large organic molecules.contamination and large organic molecules.

Transmembrane pressure are typically 3.5 to Transmembrane pressure are typically 3.5 to 16 bar (50 to 225 PSI).16 bar (50 to 225 PSI).

Reverse Osmosis (RO)Reverse Osmosis (RO) Reverse Osmosis is the finest level of filtration Reverse Osmosis is the finest level of filtration

available.available. The RO membrane acts as a barrier to all The RO membrane acts as a barrier to all

dissolved salts and inorganic molecules, as dissolved salts and inorganic molecules, as well as organic molecules with a molecular well as organic molecules with a molecular weight greater than approximately 100 water weight greater than approximately 100 water molecular, rejection of dissolved salts in molecular, rejection of dissolved salts in typically 95 – 99 %.typically 95 – 99 %.

The application for RO are desalination of The application for RO are desalination of sea water recovery, food, beverage sea water recovery, food, beverage processing, biomedical separations, processing, biomedical separations, purification of home drinking water and purification of home drinking water and industrial process waterindustrial process water

Reverse osmosis is often used in the Reverse osmosis is often used in the production of ultra pure water for use in the production of ultra pure water for use in the semiconductor industry, Power industry semiconductor industry, Power industry (Boiler Feed Water) and medical / laboratory (Boiler Feed Water) and medical / laboratory applications.applications.

Utilizing Reverse osmosis prior to ion Utilizing Reverse osmosis prior to ion exchange (IX) dramatically reduces operating exchange (IX) dramatically reduces operating costs and regeneration frequency of the IX costs and regeneration frequency of the IX system.system.

Transmembrane pressure are typically 14 bar Transmembrane pressure are typically 14 bar (200 PSI) for brackish water, to 69 bar (1000 (200 PSI) for brackish water, to 69 bar (1000 PSI) for sea water.PSI) for sea water.

Range of filtration ProcessesRange of filtration Processes

Ionic Range Molecular Range Micro Molecular Micro Particle Range Macro Particle Range

Electron Microscopy Optical Microscopy Visible to Naked Eye

Human Hair

SandBlood CellsColloid

Proteins / EnzymesMetal ion

BacteriaVirus

Yeast Cells

Oil Emulsions

Reverse OsmosisReverse Osmosis

Nano-filtrationNano-filtration

Ultra-filtrationUltra-filtration

Micro-filtrationMicro-filtration

Particle FiltrationParticle Filtration

1010-3-3 1010-2-2 1010-1-1 11 1010 100100Micrometer

1010 101022 101033 101044 101055 101066Angstrom

Note: 1 Angstrom = 10-10 Meters = 10-4 Micron

Factors InfluencingFactors Influencing

With increasing effective pressureWith increasing effective pressure

The permeate flux will increaseThe permeate flux will increase

Permeate FluxPermeate Flux Salt RejectionSalt Rejection

PressurePressure

The permeate TDS will decreaseThe permeate TDS will decrease

Factors InfluencingFactors Influencing

With increasing TemperatureWith increasing Temperature

The permeate flux will increaseThe permeate flux will increase

Permeate FluxPermeate Flux Salt RejectionSalt Rejection

TemperatureTemperature

The salt passage will increaseThe salt passage will increase

Factors InfluencingFactors Influencing

With increasing Recovery ratioWith increasing Recovery ratio

The permeate flux will decreasingThe permeate flux will decreasing

Permeate FluxPermeate Flux Salt RejectionSalt Rejection

RecoveryRecovery

The salt rejection will decreasingThe salt rejection will decreasing

Factors InfluencingFactors Influencing

With increasing Feed Water Salt ConcentrationWith increasing Feed Water Salt Concentration

The permeate flux will decreasingThe permeate flux will decreasing

Permeate FluxPermeate Flux Salt RejectionSalt Rejection

Feed ConcentrationFeed Concentration

The salt rejection will decreasingThe salt rejection will decreasing