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Reverse Osmosis

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CONTENT

INTRODUCTION WHAT IS REVERSE OSMOSIS?

-Definition PRINCIPLE OF OPERATION TYPES OF MEMBRANES

-Basic three types:1.Cellulosic

2.Aromatic polyamide

3. Thin film composite

REVERSE OSMOSIS APPLICATIONS WHY REVERSE OSMOSIS? CONTAMINANT REDUCTION BY R.O. PROCESS BASIC CALCULATIONS REGARDING PERFORMANCE OF

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INTRODUCTION Before we will start about “REVERSE OSMOSIS” we must know about

Osmosis is the natural tendency of pure water with a low concentration of total dissolved solids (TDS) to travel through a semi-permeable membrane into a solution of higher TDS in order to balance the solute levels on both sides of the membrane.

The process of osmosis through semi-permeable membrane

was first observed in 1748 by Jean-Antoine Nollet. For the following 200 years, osmosis was only a

phenomenon observed in the laboratory. In 1949, the University Of California first investigated

desalination of seawater using semi-permeable membrane. So, Reverse osmosis is a membrane based demineralization technique used to

separate dissolved solids,such as ions,from solution (most applications involve water-based solutions)

Membranes in general act as selective barriers, barriers that allow some species(such as water) to selectively permeate through them while selectively retaining other dissolved species(such as ions).

Reverse osmosis offers an ideal method of water purification, by

rejecting most dissolved solids as well as suspended solids. 04/10/2023

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What is “Reverse Osmosis”?

Definition : Reverse Osmosis is a process in which pressure greater than the natural osmotic pressure is applied on the high concentration side of the membrane, forcing the water to travel through the membrane from the higher TDS to lower TDS chamber, thus ‘reversing’ the natural tendency of water flow.

Reverse Osmosis works on the same principle as osmosis, but in the reverse direction that is way it is called Reverse Osmosis.

  Reverse osmosis membranes also hold back suspended impurities;

such as, silt, colloidal particles and microorganisms by virtue of their ultra-fine pore size.

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Osmotic flow

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Principle Of Operation

Principle : Reverse osmosis is a basically membrane separation process to draw fresh water through a membranes from high TDS solutions such as seawater, brackish water, industrial effluent and other sources.

Water molecules from the low TDS solution migrate through the membrane into the high TDS solution Once the TDS concentrations in both chambers have reached equilibrium, the osmotic process stops as enough pressure has built up to stop the flow of water from one chamber to the other. This pressure is known as osmotic pressure.

Osmotic pressure can be predicted with Vant Hoff’s equation:

CRTWhere, C is the molar concentration of solute(mol/L) R is the universal gas constant (L*atm/mol*K) T is the absolute temperature.(K)

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Types Of R.O. Membranes

A reverse osmosis membrane must be freely permeable to water, highly impermeable to solutes, and able to withstand high operating pressures.

It should ideally be tolerant of wide ranges of pH and temperature and should be resistant to attack by chemicals like free chlorine and by bacteria. Ideally, it should also be resistant to scaling and fouling by contaminants in the feed water. There are three major types of reverse osmosis membranes:-

(1) Cellulosic (2) Fully aromatic polyamide (3) Thin film composite

The pore size for R.O membrane is around 0.0001 microns.

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1.Cellulosic Membranes:- Cellulose acetate (CA)membranes are

inexpensive and easy to manufacture

but suffer from several limitations.

Their asymmetric structure makes them susceptible to compaction

under high operating pressures, especially at elevated temperatures.

Cellulose acetate membranes are susceptible to hydrolysis(reaction

with water) and can only be used over a limited pH range (low pH 3

to 5 and high pH 6 to 8, depending on the manufacturers).

They also undergo degradation at temperatures above 35°C and

attack by bacteria.

Cellulose acetate(CA) membranes have a high water permeability but reject low molecular weight contaminants poorly.

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2.Aromatic polyamide membranes: Polyamide membranes have better resistance

to hydrolysis and biological attack than

cellulosic membranes.

They have better salt rejection characteristics

than cellulosic membranes.

They can be operated over a pH range of

4 to 11,extreme use of this range can cause irreversible membrane degradation.

They can withstand higher temperatures than cellulosic membranes.

as well as better rejection of water soluble organics.

3. Thin film composites: These membranes are made by forming a thin,

solute rejecting surface film on top of a porous

substructure.

In the thin film composites the water flux and solute

rejection characteristics are predominantly determined by the thin surface layer, whose thickness ranges from 0.01 to 0.1 micrometers.

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INDUSTRIAL WATER PURIFICATION

RURAL WELL WATER

PURIFICATION

MUNICIPAL WATER

PURIFICATION

MEDICAL DEVICE

MANUFACTURING

SEA WATERDESALINATION

WASTE WATER RECYCLING

BRACKISH WELL WATER

DESALINATION  

CAR-WASHES"SPOT-FREE RINSE"

FOOD PRODUCTSAnd

COSMETIC PRODUCTS

REVERSE OSMOSIS APPLICATIONS

LABORATORY WATER

PURIFICATION

BOTTLED DRINKINGWATER

PRODUCTION

PHARMACEUTICAL WATER

PURIFICATION

Reverse Osmosis Applications

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Why Reverse Osmosis? There are number of methods of water treatment ,for example ,media

filtration ,activated carbon filtration, water softening, & deionization . These methods of water treatment remove one impurity or a selected group of impurities from Contaminated water.

water being a universal solvent, it seldom contains one or more group of impurities.

The term water purification refers to leaving all kinds of impurities behind, regardless of their source or their nature. This is quite different than water treatment described above.

There are only three scientifically recognized methods of water purification.

o These are:- (1)Reverse osmosis[RO]

(2)Freeze-thawing

(3) Distillation 04/10/2023

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Contaminant reduction by R.O. process

By the RO process ,

(1) 93 to 99% reduction of Pb+2,(PO4)-3,Ag+,Zn+2, (SO4) -2,Cr+6,Fe+2,Mg+2 ions. (2) 90 to 98% reduction of SO2,Na+ ions. (3) 85 to 95% reduction of NO3- ions. (4) 70 to 80% reduction of arsenic. (5) also remove microbiological contaminants like viruses and bacteria.

After finishing the process the discharge water which containing this types of salts use in toilet &urinal flushing, make up water for cooling towers and water cooled condensers ,decorative fountains & washing purpose.

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Calculations regarding performance of reverse osmosis

There are some basic calculations that are used to judge the performance of an R.O. system. In order to accurately measure the performance of an R.O. system

we need the following operation parameters:

(1)Feed pressure

(2)Permeate pressure

(3)Feed conductivity

(4)Permeate conductivity

(5)Feed flow

(6)Permeate flow

1.Salt rejection in %:-

This equation tells how effective the RO membranes are removing contaminants. It does not tell you how each individual membrane is performing ,it tells about overall performing.

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The higher the salt rejection, the better the system is performing. A low salt rejection can mean that the membranes require cleaning or replacement.

2. %Recovery :- %Recovery is the amount of water that is being 'recovered' as good

permeate water.

Another way to think of Percent Recovery is the amount of water that is not sent to drain as concentrate, but rather collected as permeate or product water.

The higher the recovery % means less water to drain as concentrate and saving more permeate water.

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Thank you

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