Removing dissolved minerals from seawater through desalination could help address freshwater shortages but faces challenges. Over 15,000 desalination plants operate worldwide using methods like reverse osmosis or thermal distillation. However, desalination is energy intensive and produces toxic brine waste. New technologies aim to reduce energy usage and better handle brine, but challenges around cost and environmental impact remain.

2.  Removing dissolved minerals from
seawater, brackish groundwater, or
treated wastewater
—appears at first glance to be the ideal
answer to freshwater shortages. What
could be more attractive than
harnessing the planet’s seemingly
inexhaustible 1.34 quadrillion (that’s 15
zeros) megaliters of seawater?

3. Ocean Average Salinity (gms./lit)
Atlantic 35.4
Indian 34.8
Pacific 34.5
Brackish Waters 0.5 to 3

4.  Water for agriculture accounts to over 90% of water
use in India (Royal Academy of Engg 2012)
 By 2030, 2/3rds of the world population will be
suffering from water shortages (HSBC Optimised
Global Water Index, 2008)

6.  Over15,000 desalination plants in
operation worldwide, producing upto
55.6 cu.m. water a day (0.5% of global
reqmt)
 60% are located in the Middle East.
 Total world capacity is approaching 30
million m3/day of potable water
 The world's largest plant in Saudi Arabia
produces 128 Million Gallons a Day
(MGD) of desalted water.

7. • Multi Stage Flash Evaporation (MSF)
• Multiple Effect Distillation (MED)
Thermal • Vapor Compression Distillation (VCD)
• Low Temp. Thermal Desalination (LTTD)
• Solar Desalination
• Freezing (vacuum/ refrigerant)
Membrane • Reverse Osmosis (RO)
• Electrodialysis (ED or EDR)
• Forward Osmosis (FO)
• Ion Exchange (IEX)
Others
• Capacitive deionisation
• Solar thermal ionic Desalination

11. Intrinsically, the feed stream contains ..
 Dissolved solids
 Silt
 Algae
 Bacteria
 Various flora and fauna
 TEPs (Transparent Exopolymer Particles)
**TEP : Conc. : 20-5000 particles/ ml
Size: 0.002 to 0. 2 mm
Exist as amorphous blobs, clouds and sheets
 Hence, Pretreatment Method is generally a
customised form of Coagulation

15.  How it works
Separate saltwater and freshwater with a membrane that blocks salt
ions, and the freshwater rushes to the salty side by the natural process of
osmosis. Reverse osmosis (RO) uses hydraulic pressure to shove water
molecules in the opposite direction, with the membrane holding back the
salt.
Upside
Comparatively low energy cost.
Downside
Toxic brine; can’t completely filter potentially harmful substances like
boron, arsenic, lithium, and some pharmaceutical compounds. When
membranes become clogged, they must be scraped and bleached or they
stop working; cleaning, however, reduces the expensive membranes’
lifetime. Pretreating the water to remove the gunk slows the rate of fouling
but requires a lot of real estate.
Best for
Brackish groundwater, which contains on average only 3 to 5 grams of salt
per liter. RO is also increasingly being used to desalinate seawater, however.
 Energy trade-off
The pressure needed to push water through the membrane is proportional to
the water’s salinity. Higher pressure means higher energy cost. On
average, RO demands at least 3.5 MWh/ML produced from brackish water

16.  How it works
Capacitive deionization works without membranes. It filters impurities by
streaming the water between two charged electrodes. The electrodes
attract ions in the water, which stick to them, leaving freshwater. The
attached ions eventually clog the electrodes, but cleaning is easy:
Simply reverse the electrical polarity to flush the ions back out. Good
candidates for electrodes are advanced materials such as carbon
aerogel and mesoporous carbon.
 Upside
Easy to clean; requires less power. The process could theoretically go on
forever without changing electrodes.
 Downside
Works only for brackish water; in practice, electrodes can foul. Does not
mitigate toxic brine.
 Best for
Brackish water.
 Energy trade-off
Far less pressure means less energy.
 What’s next
This year, a test reactor will be unveiled in New Mexico, part of an
international project led by Campbell Applied Physics, in Rancho
Murieta, Calif., and several U.S. national laboratories.

18.  Adequate & Safe disposal of brine poses
a significant environmental challenge
 Brine Salinity depends upon:
Salinity of feedwater
Desalination Method
Recovery rate of plant
 Along with high salt levels, can contain
Mg, Pb, I as well as chemicals introduced
via urban & agril. runoff

19.  Reduce volume of brine to be
discharged and minimize the adverse
chemicals found therein.
 Usage of better artificial filters or even
natural filters, to reduce the amt. of
chemicals during the pre treatment
process


20.  Coastal Methods:
-Discharge to oceans
-Confined Aquifers
 Inland Methods:
-Deep well injection
-Evaporation Ponds
-Solar energy ponds
-Shallow Aquifer storage for future use

21.  There’s no definitive ans. to this Qs. Since
the Cost comprises of a no. of factors:
-Labor
-Chemicals
-Peripherals
-Maintenance
-Electricity
-Capital/Amortisation

22.  The plant has been constructed in the
New Jubail II Industrial Zone in the Saudi
Arabia, Kingdom’s Eastern Province.
 Provides 8,00,000 cu.m. of freshwater for
cities in the Eastern Province,
 Generates 2,750MW of electricity.
Freshwater produced by the $3.8 billion
desalination plant will be transported

24.  The Minjur desalination plant consists of 8,600 sea water
RO membranes, 248 pressure vessels, 23 pressure
exchangers, five high-pressure pumps, 16 pressure filter
vessels, electrical, automation and control systems, and a
1,200m of HDPE pipeline of 1,600mm diameter.
 The CMWSSB has laid a 33km pipeline with a cost of
INR930m ($20m) to carry the treated fresh water from
Minjur to Red Hills. The project also includes infrastructure
for the collection of seawater. A 110kV/22kV sub-station
has been set up by the Tamil Nadu Electricity Board for
uninterrupted power supply to the desalination plant.
 A thorough environmental impact study was conducted in
the planning stage.

25.  Chennai Water Desalination (CWDL) is
executing the project for the CMWSSB on a
design, build, own, operate and transfer
(DBOOT) basis.
 In September 2005, the CMWSSB signed a
bulk water purchase agreement (BWPA)
with CWDL to purchase water from the
Minjur desalination plant at a cost of
INR48.66/m³ ($1.03/m³). It will be sold to
industries at a rate of INR60/m³ ($1.27/m³).
 At the end of the 25-year agreement the
contract shall be renewed.

26.  As promising as the process sounds, there’s still a
price to pay. As long as the cost of desalination
continues to depend on the cost of energy, these
technologies won’t help much of the energy-starved
developing world that needs them the most.
Also, there is the problem of the toxic sludge
generated as a by product.
 Throwing the brine back into the ocean can kill fish
and smaller denizens of the food chain.
 Several contenders might make history of these
concerns. New methods in the pipeline reduce
desalination’s energy demands in innovative and
intriguing ways. Further off are technologies that
could turn desalination’s Achilles’ heel into a source
of strength: In the future, desalination might just be
powered by the very waste it filters out.

27.  http://www.fwr.org
 Desalination, with a grain of salt- A California
perspective, Cooleym, Gleick, Woolf
 Fundamentals of Water Desalination, Dessouky and Elsevier, 2002
 Desalination: A National Perspective, National Research Council
Committee on Adv. Desalination Tech., USA 2008
 http://www. Idadesal.org
 http://www.desline.com