Water Desalination and

Its Techniques

Presented By:

Partha Proteem Roy

PS4 Sekoni

SECOND TECHNICAL SEMINAR

AT PS3 JORHAT

Overview of Presentation

Introduction

Definition

Purpose of Desalination

Different Techniques of Water

Desalination

Future Technologies

Conclusion

Introduction

Economic expansion

Agriculture and food

Public health

Quality of life

Need of Fresh Water

Water Distribution

Sources of Fresh Water

Frozen Water: Fresh water source in form of ice bergs and glaciers.

Surface water: The water in a river, lake or fresh water wetland. Surface water is naturally replenished by precipitation and naturally lost through discharge to the oceans, evaporation, evapotranspiration and sub-surface seepage.

Under River Flow : The hyporheic zone often forms a dynamic interface between surface water and true ground-water receiving water from the ground water when aquifers are fully charged and contributing water to ground-water when ground waters are depleted. This is especially significant in karst areas where pot-holes and underground rivers are common.

Sources of Fresh Water

Ground water: It is located in the pore

space of soil and rocks. It is also water

that is flowing within aquifers below the

water table

Rainwater harvesting: It is the accumulation and deposition of rainwater for reuse before it reaches

the aquifer

Desalination: Different ways to

harness fresh water from saline water

to cater growing need of water due to

scarcity of fresh water.

Distribution of Precipitation

Definition

Water Desalination

Any of several processes that remove some amount of

salt and other minerals from saline water.

More generally, desalination may also refer to the

removal of salts and minerals

Purpose of Desalination

Why Desalination?75% of the Earth’s surface

is covered by water

97 % of that water is oceans

Only 1% is available for drinking

80 countries suffered from water

scarcity by the mid-1990s

1.5 billion people lack ready access

to drinking water

TDS

Total Dissolved Solids: It is a measure of the combined content of all

inorganic and organic substances contained in a liquid in

molecular, ionized or micro-granular (colloidal sol) suspended form.

Level of TDS (milligrams per litre) Rating

<300 Excellent

300-600 Good

600-900 Fair

900-1200 Poor

>1200 Unacceptable

Relative proportions of dissolved salts

in seawater

.

17Dr. Ola Abdelwahab

Elemental composition of seawater

Only six elements comprise about 99% of sea salts: chlorine (Cl-), sodium (Na+), sulfate (SO4

-2), magnesium (Mg+2), calcium (Ca+2), and potassium (K+). The relative abundance (large quantity) of the major salts in seawater are constant regardless of the ocean.

Only the amount of water in the mixture varies because of differences between ocean basins because of regional differences in freshwater loss (evaporation) and gain (runoff and precipitation).

The chlorine ion makes up 55% of the salt in seawater. Typically, seawater has a salinity of 35 parts per thousand.

18Dr. Ola Abdelwahab

Harmful Effects of drinking impure

water Vegetable Impurities: Peaty water, in the absence of a better supply, may

be used without much harm, but if the amount of solid matter is great it may even produce diarrhoea. Under this head we must include water containing germs, for although they generally get into the water from the excretions of animals, yet, as we know, they are vegetable in nature. Here we shall meet with the most dangerous kinds of water, causing many fatal epidemics.

Mineral Impurities: A moderate degree of hardness is not harmful, but if the hardness is great dyspepsia and constipation may result. Goitre seems to be due to the presence of magnesium limestone in the drinking water. Iron salts cause dyspepsia, constipation, and headache. Lead salts are especially dangerous, causing colic, paralysis, kidney disease, and sometimes death. These symptoms may occur when the amount of lead does not exceed one-tenth grain per gallon. Arsenic is dangerous and can cause cancer. Sodium causes cardiac disease. Fluoride causes crippling skeletal flourosis.

Natural Desalination: Water Cycle!

Major Stages

1. Evaporation

2. Condensation

3. Precipitation

4. Collection

Different Techniques of Water

Desalination

Membrane Technologies

Chemical Approaches

Thermal Technologies

Membrane Technologies

Pressure Driven

Microfiltration

Ultra filtration

Nano filtration

Hyper filtration

Electrical Driven

Electro-Dialysis

Electro-Dialysis Reversal

Membrane

Process

Applied Pressure

psi (kPa)

Minimum Particle

Size Removed

Application

(Type, Avg Removal Efficiency %)

Micro-filtration 4-70 (30-500) 0.1-3 µm - Particle/turbidity removal (>99%)

- Bacteria/protozoa removal (>99.99 %)

Ultra-filtration 4-70 (30-500) 0.01-0.1 μm - Particle/turbidity removal (>99 %)

- Bacteria/protozoa removal (>99.999 %)

- TOC removal (<20%)

- Virus removal/(partial credit only)

Nano-filtration 70-140 (500-1000) 200-400 daltons - Turbidity removal (>99%)

- Color removal (>98%)

- TOC removal (DBP control) (>95%)

- Hardness removal (softening) (>90%)

- Synthetic organic contaminant (SOC)

removal (500 daltons and up) (0-100%)

- Sulfate removal (>97%)

- Virus removal (>95%)

Hyper-Filtration 140-700 (1000-5000) 50-200 daltons - Salinity removal (desalination) (>99%)

- Color and DOC removal (>97%)

- Radionuclide removal

(not including radon) (>97%)

- Nitrate removal (85 to 95%)

- Pesticide/SOC removal (0 to 100%)

- Virus removal (>95%)

- As, Cd, Cr, Pb, F removal (40 to >98%)

Reverse Osmosis

Electrical Driven

Electro dialysis: It

utilizes electromotive

force applied to

electrodes adjacent

to both sides of a

membrane to

separate dissolved

minerals in water.

Electro Dialysis Reversal

Electrodialysis reversal (EDR) is a similar process,

except that the cation and anion reverse to routinely

alternate current flow.

Challenges for Membrane

Technologies Pressure Driven: Fouling and Scaling of membrane

Electric Driven: Limitation of TDS. Cost is proportional to

TDS (ideal for 4000 mg/L).

Chemical Approaches

Ion Exchange Technologies

It can best be described as the interchange of ions

between a solid phase and a liquid phase surrounding

the solid, chemical resins (solid phase) are designed to

exchange their ions with liquid phase (feedwater) ions,

which purify the water. It can be used in combination

with reverse osmosis.

Thermal Technologies

Solar Distillation

Multistage Flash

Multi Effect Distillation

Thermal Vapour Compression

Mechanical Vapour

Compression

Absorption Vapour

Compression

Pressure differences occur between two tanks as a fluid mixture is transferred between them. This drives the heat exchange for evaporation and condensation of saltwater to form potable water

Future Technologies

Electrodeionization (EDI)

Membrane Distillation (MD)

Freeze Separation (FS)

Capacitive Deionization (CD)

Rapid Spray Evaporation (RSE)

Freezing with Hydrates (FH)

Vacuum Distillation (VD)

Conclusion

Thank You