1. Desalination
A Perennial Future?

2. • “If we could ever competitively, at
a cheap rate, get fresh water from
salt water, that it would be in the
long-range interests of humanity
which would really dwarf any
other scientific
accomplishments.”
– John F. Kennedy in 1962

3. Introduction
• Desalination, for the past four decades, has been hailed as the
hope of mankind.
• Certain group of people believe that desalination is the only
answer for the increasing freshwater demand on a global
scale.

4. Geography of Desalination
• According to a recent report published by ‘Huntington
Beach Seawater Desalination Facility’- there are more
than 120 countries producing more than 3.5 billion
gallons of potable water every day using desalination
plants.
• The total number of plants amounts to a staggering
21,000 in which 50% of them use sea water and the rest
brackish water.
• They are prevalent in countries situated in the Persian-
Arabian Gulf, where there is acute scarcity of water.

5. Scope In India
• India too uses the desalination technologies to meet the
freshwater requirements of the people.
• If we shift the focus to Tamil Nadu, it is estimated that the
current water requirement is 1000 MLD (million liters per
day). Due to urbanization the city the demand tends to rise.
• Desalination plants in Minjur and Nemmeli, each provide 100
MLD whereas the plant at Pattipulam gives 200 MLD.
• Experts predict that if there are no desalination plants there
will be a shortage of 300 MLD in the next three years.
Therefore, this technology is considered an absolute necessity.

6. Methods employed in Desalination
Plants
• Sea water is converted into potable water using two
methodologies – Phase Change and Non-Phase Change.
• Here by phase change we mean the change in the state of
a particular substance. For example, the phase change
for water would be vapor when heated or ice when
cooled.
• Techniques like Electro-dialysis and Reverse Osmosis
fall under non-phase change process. Low Temperature
Thermal Desalination (LTTD) is a phase change process.

7. • The majority of desalination plants employ traditional
technologies like Reverse Osmosis and Electro-dialysis.
They produce around 300 MLD of water with a purity
level of 400- 500 PPM (Parts Per Million).
• The concept of Low Temperature Thermal Desalination
has been envisaged in the 1960’s. Though the complete
literature was known to the world, the implementation
has been absent. The National Institute of Ocean
Technology (NIOT) has developed and implemented a
process using this theory.
• Water derived from the LTTD method gives potable
water with salinity levels of 20-200 PPM, which is a
considerable achievement.

8. Working of Desalination Plant using
LTTD
• It is a known fact that the surface temperature of sea
water is around 28°C in the Indian conditions. The
temperature of the water decreases as the depth of the
sea increases.
• LTTD uses this temperature difference (technically
called ∆T) to establish an environment for desalination.

9. • The LTTD process contains a pressurized container
along with a condenser. The boiling point of water is
reduced from the original value (100° C) by applying
a pressure of 1013 millibar. The hot surface water is
passed into the pressurized container which turns
the water into vapor.
• It is then sent into a shell and tube condenser where
cold water from the depths is pumped to convert the
vapor back to water. This process is called flash
evaporation.
• The first of the LTTD desalination plants was set up
in Kavaratti, Lakshadweep by the National Institute
of Ocean Technology.

10. • In Reverse Osmosis the recovery rate is 45% which in
turn has some environmental repercussions like release
of hot water and brine discharge.
• “In the LTTD process, at a low temperature difference of
6° C, the recovery rate is very low. Depending on the
change in temperature we can increase or decrease the
amount of water recovered from the sea. This percentage
is usually in single digits. Though, the figure is small
environment will be safe as the brine discharge is
negligible. It is a renewable process with minimal stress
on the environment,” G.Venkatesan, Scientist of NIOT
who worked closely with the LTTD project.

11. • The post treatment process for the water obtained from
the LTTD is inexpensive. It is passed through limestone,
so that it attains the necessary nutrients and minerals.
This stage changes and balances the chemical structure
of water along with the pH level.
• “A trade-off has to be done. LTTD consumes higher
energy when compared to Reverse Osmosis and Electro-
dialysis. The only achievement is the protection of
environment.
I think some new technologies will eventually come and
reduce the consumption of LTTD,” adds Mr. Venkatesan.

12. The Disadvantages of Desalination
 Waste Disposal
• The process of desalination requires pretreatment and cleaning
chemicals, which are added to water before desalination to make
the treatment more efficient and successful.
• These chemicals include chlorine, hydrochloric acid and
hydrogen peroxide, and they can be used for only a limited
amount of time. Once they've lost their ability to clean the water,
these chemicals are dumped, which becomes a major
environmental concern.
• These chemicals often find their way back into the ocean, where
they poison plant and animal life.
Source: http://www.ehow.com/list_5961767_disadvantages-desalination.html

13.  Brine
• Brine is the side product of desalination. While the purified
water goes on to be processed and put into human use, the
water that is left over, which has a super saturation of salt,
must be disposed of.
• Most desalination plants pump this brine back into the
ocean, which presents another environmental drawback.
• Ocean species are not equipped to adjust to the immediate
change in salinity caused by the release of brine into the
area. The super-saturated salt water also decreases oxygen
levels in the water, causing animals and plants to suffocate.

14.  Health Concerns
• Desalination is not a perfected technology, and
desalinated water can be harmful to human health as
well.
• By-products of the chemicals used in desalination can
get through into the "pure" water and endanger the
people who drink it. Desalinated water can also be acidic
to both pipes and digestive systems.

15.  Energy Use
• In an age where energy is becoming increasingly
precious, desalination plants have the disadvantage of
requiring large amounts of power. Other water treatment
technologies are more energy efficient.

16. Vanishing Beaches of Tamil Nadu
----
A report on RO Desalination Plant
in Nemmeli district

28. Future Options of Desalination
• Desalination is process primarily done in developed
countries with enough money and resources. If
technology continues to produce new methods and
better solutions to the issues that exist today, there
would be a whole new water resource for more and more
countries that are facing drought, competition for water,
and overpopulation.
• Though there are concerns in the scientific world about
replacing our current overuse of water with complete
reliance on sea water, it would undoubtedly be at least an
option for many people struggling to survive or maintain
their standard of living.