Desalination plant

CONTENT
 What is Desalination?
 Desalination Technologies
 Advantages and Disadvantages
 Minjur and Nemmeli Desalination Plant
 Recent Updates
 List of Desalination Plants
 Desalination Plants in Minicoy and Agatti

Why Desalination?
 75% of the Earth’s surface is covered by water
 97.5% 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
Can we drink salt water?
 Small quantities are not harmful, but it is counterproductive (it just makes you more
thirsty!)
 Eventually, it can be dangerous, ultimately producing fatal seizures, heart arrhythmias
and kidney failure
Desalination refers to the process by which pure water is recovered from saline water using different
forms of energy. Saline water is classified as either brackish water or seawater depending on the
salinity and water source
DEFENITION:

The USGS Water Science School
What makes water saline?
What do we mean by "saline water?" Water that is saline contains significant amounts (referred
to as "concentrations") of dissolved salts. In this case, the concentration is the amount (by weight) of
salt in water, as expressed in "parts per million" (ppm). If water has a concentration of 10,000 ppm of
dissolved salts, then one percent of the weight of the water comes from dissolved salts.
Here are our parameters for saline water:
•Fresh water - Less than 1,000 ppm
•Slightly saline water - From 1,000 ppm to 3,000 ppm
•Moderately saline water - From 3,000 ppm to 10,000 ppm
•Highly saline water - From 10,000 ppm to 35,000 ppm
By the way, ocean water contains about 35,000 ppm of salt.
https://water.usgs.gov/edu/saline.html

Natural Desalination: Water Cycle!
Major Stages
1. Evaporation
2. Condensation
3. Precipitation
4. Collection

SIMPLIFIED FLOW CHART OF DESALINATION
PROCESS

Input Source of a Desalination plant
Source water for desalination can be marine or brackish surface water or highly mineralized
groundwater.
contamination by pathogenic viruses, bacteria and parasites and by a variety of chemical
contaminants from human activities.
Out put of a Desalination plant
 Brine water- Brine is the
concentrated salt water
that’s left after desalination.
 Fresh water

Drinking water quality standards for a Desalination Plants as per IS
10500:2012

BACTERIOLOGICAL STANDARDS
Water entering the Distribution system
Coli form count in any sample of 100 ml
should be Zero. A sample of the water entering
the distribution system that does not conform to
this standard calls for an immediate
investigation in to both the efficacy of the
purification process and the method of
sampling.
II. Water in the distribution system
•E.coli count in 100ml of any sample should be
zero.
•Coliform organisms not more than 10 per 100
ml in any sample.
•Coliform organisms should not be present in
100ml of any two consecutive samples or more
than 5% of the samples collected for the year.

The site, comprised of inland and offshore parts,
(i) must be located in a place where access and interconnections to the power supply grid, and to the
water supply networks are technically and economically feasible,
(ii) the area extent and shape must be the appropriate, so that civil, electrical, piping interconnections
and other works costs are minimized,
(iii) be suitably located in a marine environment where adequate quantity of feed water with a
reasonable good, uniform and steady quality of feed seawater is abstracted at a reasonable cost,
(iv) be at a location where the brine, backwash wastewater and other wastes are disposed without
environmental adverse effects,
(v) geologically and topographically are suitable for the construction and erection of the various
structures at reasonable costs,
(vi) environmental, town planning and rural planning regulations, law requirements and restrictions are
met,
(vii) the desalination plant shall have the social acceptance of the neighboring communities and other
authorities and finally
SITE SELECTION CRITERIA

• seawater intake system
• intake pumping station and seawater pipelines
• pretreatment plant
• intermediate treatment reservoirs
• brine discharge sub-system
• office and control building and storage areas and
• power supply sub-system.
A desalination project is usually made up of subsystems such as the

There are two main groups of processes which can be used to reduce the
concentration of dissolved solids in brackish or sea water.
1. Thermal processes
2. Membrane processes
Desalination Technologies

 The simplest example of a thermal process is distillation in which the heat is used to generate steam
from the sea water which is then condensed to form water with a low salinity which can be used for
domestic and industrial purposes or for irrigation.
 Owing to their high-energy requirements, thermal processes are normally used for seawater
desalination. Thermal processes are capable of producing high purity water and suited for industrial
process applications.
 Thermal processes account for 55% of the total production and their unit capacities are higher
compared to membrane processes.
There are three main desalination techniques which use the principle of desalination;
THERMAL DESALINATION
Multi-stage flash evaporation/distillation(MSF)
Multiple-effect evaporation/distillation(MED) also known as long-tube vertical distillation(LTV)
Vapour compression distillation(VCD)
http://www.barc.gov.in/publications/tb/desalination.pdf

A number of additional thermal process have also been proposed but have not yet been
exploited commercially;
Membrane distillation
Vapour reheat flash distillation
There are three thermal processes which use thermal energy to freeze and melt the ice
formed in the freezing stage;
Vacuum freezing
Secondary refrigerant freezing
Clathrate or hydrate formation process

The basic principle involved in the MSF process is to heat the sea water to about
90– 120°C using the heat of condensation of the vapour produced and
supplementing with external steam. The heated sea water is subsequently flashed
in successive stages maintained at decreasing levels of pressure.
The vapor produced is condensed and recovered as pure water. MSF can accept
higher contaminant loading (suspended solids, heavy metals, oil, grease, COD,
BOD etc.) in feed sea water.
It is capable of producing distilled quality product water good for power plants,
process industries and several other high purity applications.
Multi Stage Flash (MSF) Process

 MED plant has two or more effects. Each effect operates at a successively lower temperature and pressure.
The first effect is heated by low pressure steam (about 0.3 bar).
 Vapours are generated from the feed sea water in the first effect and directed to the second effect. Thus
vapours from the previous effect serve as the heat source to the succeeding effect for evaporating the brine.
Vapour from the last effect is condensed in the final condenser where sea water is used as the coolant. The
vapour produced in each effect is passed through the demisters to next effect.
 It is condensed inside the tubes transferring the latent heat to the brine falling outside the tube enabling a
portion of the brine to evaporate. Low temperature MED unit operates at about 65°C and therefore allows
the use of cheaper materials of construction due to less scaling and corrosion problems. MED is capable of
producing pure distilled water similar to MSF.
 The possibility of low temperature operation, low grade heat and waste heat utilization, low cooling water
requirement and low energy consumption have made MED an attractive alternative in recent years for sea
water desalination.
 Efficiency of MED plant can be improved by adding a vapour compressor.
 Mechanical Vapour Compressor (MVC) or Thermal Vapour Compressor (TVC) is used for this purpose
depending on site specific conditions.
Multi Effect Distillation (MED)

Membrane technologies are primarily used in the United States. These systems
treat the feed water by using a pressure gradient to force the water through
membranes.
The three major membrane processes are electrodialysis, electrodialysis
reversal, and reverse osmosis.
Membrane distillation is an emerging membrane-based desalination technology.
MEMBRANE TECHNIQUES
There are four membrane processes in current use:
Reverse osmosis(RO)
Electrodialysis(ED or EDR)
Electro-Deionisation (EDI)
Forward Osmosis(FO)

Electrodialysis and electrodialysis reversal
 The membranes used in electrodialysis are built to allow the passage of either positively or negatively
charged ions, but not both. Common ionic molecules in saline water are sodium, chloride, calcium, and
carbonate.
 Electrodialysis uses the driving force of an electrical potential to attract and move different cations
(positively charged ions) or anions (negatively charged ions) through the permeable membrane.
 The cations are attracted to the negative electrode, and the anions are attracted to the positive electrode.
When the membranes are placed so that some allow only cations to pass and others allow only anions to
pass, the process can effectively remove most of the salts from the water.
 The electrodialysis reversal process functions like the electrodialysis process; the only difference is that
in the reverse process, the charge of the electrodes is switched periodically.
 This reversal in flow of ions helps remove scaling and other debris from the membranes, which extends
the system’s operating life.

Reverse Osmosis (RO)
 RO is used for both brackish water and seawater desalination as well as for waste water treatment and water
recovery/reuse.
 A typical RO desalting plant consists of three sections, namely pretreatment section, membrane section and
post treatment section. Conventional pretreatment section typically consists of particulate filtration, micron
filtration and chemicals additions.
 Membrane section consists of membrane elements housed in pressure vessels through which pretreated
saline water is passed under pressure in excess of its osmotic pressure with the help of a high pressure pump
coupled with energy recovery device.
 The post treatment section consists of lime treatment for pH correction and chlorination for disinfection as
required to meet public health standards and to make the water noncorrosive to the water distribution
systems. Energy consumption depends on the salt content of the feed water. Development of RO
membranes of very high rejection, while maintaining high permeability, has potential to reduce the energy
consumption.
 Development of better energy recovery devices can further reduce the energy consumption.
 As the success of RO desalination hinges on the proper pre-treatment of the feed water, various membranes
could precede RO in order to selectively remove suspended solids (microfiltration), colloids/turbidity &
organics (ultrafiltration) and hardness and sulphates (nanofiltration).

Desalination Plants in Minicoy and Agatti, UT Lakshadweep
• PROCESS- LTTD ( low temperature thermal desalination)
• Earth System Science Organization (ESSO), through NIOT, has successful
demonstrated the 100 m3/day capacity land based desalination plant
• Six more desalination plant
1. Chetlat
2. Kiltan
3. Kadamat
4. Amini
5. Androth
6. kalpeni

• LTTD works on the principle of utilizing temperature gradient between two
water bodies to evaporate the warmer water at low pressure and condense
the resultant vapour with the colder water to obtain freshwater.
• The bathymetry around the islands allows availability of 350-380m water
depth within 400-1000m from the shore, for drawing water at 10-12°C.
• Warm surface sea water at about 28°C
Main components
• Flash chamber,
• Condenser,
• Pumps and Pipelines to draw warm and cold water,
• Vacuum pump to maintain the plant at sub-atmospheric pressures and
• Control system
Lttd (low temperature thermal desalination)

Ocean Thermal Gradient in coastal waters (NIO, Goa, 2000)
https://www.niot.res.in

MAJOR COMPONENTS https://www.niot.res.in

Process Equipment
• Flash chamber- 2.8m diameter & 5.2m height made of SS304L
• S-type demister pads- flash evaporation
• Shell & tube condenser- made of SS304L, 1.2m dia, 1120tubes of 0.019mdia for
condensing the vapour.
• Major part of plant piping was completed with HDPE ( High Density
polyethylene pipes)

Submarine pipelines
• Coolant water at 12°C
• Length 970m ( 220m
shallow and 750m deep)
• Agatti island has complex
topography.
• Flow rate -150kg/s
• Steel pipe- 220m length, dia
570mm, 10mm thickness
• HDPE pipe- 750m length, dia
630mm
• Flow velocity- 0.6m/s
• Every 12m section welded
https://www.niot.res.in

Shallow water region
• If HDPE pipes used in shallow water it needs to burried in soil or weighed
with concrete blocks
• Steel pipes subjected to corrosion
• Concrete blocks may not be required in case of steel pipes because of it’s
selfweight.
Deep water region
• HDPE pipes used to draw from deep ocean with 10-12°C at 350-400m
water depth.

Marine structures
Major components
• Sump
• Land to carry warm and cold water pipeline
• Plant structure
Sump
• Concrete structure
• At 5m water depth
• Dimension- 12.17m X 8.3m X 9.1m with two sets of pumps
1. 2 cold water pump
2. 2 warm water pump
• W
arm water drawn from 3m below MSL

Bridge
• To carry cold and warm water pipelines from sump
• Supported by gravity based concrete pier
• Length 100m to 250m
At agatti
• 240m long bridge
• 15spans each of 15m
• 14 piers
At minicoy
• 110m long bridge
• 4major span at 22m each

Plant building
• Flash chamber- Dry weight 80kN
approx
• Condenser- dry weight 120kN
approx
• Shell and tube condenser- 2.7kpa
• Fresh water generated in the
condenser

 An LTTD plant uses higher energy for its operation compared to the
membrane-based RO technology.
 LTTD is eco-friendly.
 It does not disturb the marine ecosystem
 There is no discharge of brine solution into the sea.
 LTTD does not necessitate storage of chemicals in the islands unlike RO.
 LTTD process does not require skilled labour for its operation.
 LTTD is a stand-alone technology.
ADVANTAGES

 As a drought proofing measure and to augment supply of water to Chennai City, CMWSS Board has set up a
100MLD capacity Seawater Desalination Plant on Design, Build, Own, Operate and Transfer (DBOOT) basis.
 CMWSS Board entered into Bulk Water Purchase Agreement (BWPA) with the Special Purpose Vehicle,
M/s. Chennai Water Desalination Limited (M/s. CWDL) for the purpose of setting up the Plant. This agreement
will be in force for a period of 25 years and during this period, CMWSS Board will purchase the water from
M/s. CWDL as per the terms and conditions stipulated in the BWPA. The asset will be transferred to CMWSS
Board after 25years. This plant was commissioned in July 2010.
 To convey the product water from the Desalination Plant to the Chennai City's water distribution network,
CMWSS Board developed the infrastructure facilities at an estimated cost of Rs.93.00 Crores including
Operation & Maintenance for a period of 5 years with the central assistance of Rs.87.80 Crores under
Jawaharlal Nehru National Urban Renewal Mission (JNNURM).
 The project envisages two stage pumping i.e., at plant site and at Madhavaram Booster Station and comprises
of various components such as Underground storage tanks, pipeline, pumping stations etc, The infrastructure
was dedicated to convey the product water from Kattupalli to the Chennai City.
MINJUR DESALINATION PLANT
http://www.chennaimetrowater.tn.nic.in/desalination.html

R.O. Membrane With Energy Recovery
System
Pipe Carrying Bridge Across Back
Water Canal
Gravity Settlers Filters
Under Ground Sump Cum Pump House

 As a drought proofing measure and to augment supply of water to the Southern parts of Chennai City, CMWSS
Board has set up a 100MLD capacity Seawater Desalination Plant on Engineering, Procurement and Contract
(EPC) basis.
 The Government of Tamil Nadu accorded Administrative Approval for the work of "Construction of 100 MLD
SWRO Desalination plant at Nemmeli" at a cost of Rs.914.42 Crore with GOI grant of Rs.871.24 Crore and
Rs.43.18 Crore from Go TN for this project
 CMWSS Board awarded the work of "Construction of 100MLD SWRO Desalination plant at Nemmeli and O&M
period of 7 years" to M/s.VA Tech Wabag Ltd., Chennai in consortium with IDE Technologies, Israel" This Plant
was commissioned in February 2013.
 To convey the product water from the Desalination Plant to the Chennai City's water distribution network,
CMWSS Board developed the infrastructure facilities at an estimated cost of Rs.145.61 Crores including
Operation & Maintenance for a period of 7 years
 The project envisages two stage pumping at plant site and at various intermediate Water Distribution Station in
Akkarai, Velachery, Pallipattu and Tiruvanmiyur to convey the product water from Nemmeli to the Chennai
City. About 10 lakh people are being benefitted by this project.
https://chennaimetrowater.tn.gov.in/desalination-
Nemmeli.html
DESALINATION PLANT AT NEMMELI

Some desalination facts
It is estimated that some 30% of the world's irrigated areas suffer from salinity
problems and remediation is seen to be very costly.
In 2002 there were about 12,500 desalination plants around the world in 120
countries. They produce some 14 million cubic meters/day of freshwater, which is
less than 1% of total world consumption.
The most important users of desalinated water are in the Middle East, (mainly
Saudi Arabia, Kuwait, the United Arab Emirates, Qatar and Bahrain), which uses
about 70% of worldwide capacity; and in North Africa (mainly Libya and
Algeria), which uses about 6% of worldwide capacity.
Among industrialized countries, the United States is one of the most important
users of desalinated water, especially in California and parts of Florida. The cost
of desalination has kept desalination from being used more often.
https://water.usgs.gov/edu/drinkseawater.html

LIST OF ADVANTAGES OF DESALINATION
1. It provides people with potable water.
This is perhaps one of the biggest and most important benefits of desalination. By
removing dissolved salts and other minerals from seawater, it can be turned to freshwater
that’s ideal for drinking. This can be a solution for many areas around the world that are
experiencing droughts, such as California and certain countries in the African continent.
2. It provides water to the agricultural industry.
Desalination doesn’t only produce potable water but also water that can be used for
irrigation, which is great for arid regions as well as areas that are going through drought.
Since they’ll have the chance to produce their own crops, they won’t be too dependent on
imports and they’ll get to improve their economy. They can also produce enough food for
their residents and keep hunger at bay.

List of Disadvantages of Desalination
1. It consumes a large amount of energy.
Opponents of desalination point out that it’s not a feasible solution to water supply problems
mainly because it requires so much energy. Reverse osmosis, meanwhile, uses a lot of energy to
overcome the natural osmosis process and remove large particles from seawater using a
semipermeable membrane.
2. It can be costly.
Desalination plants can be expensive to build because of the equipment and machines they
require and can range between $300 million to almost $3 billion. They can also be expensive to keep up
since, as mentioned above, they require a lot of energy to complete the desalination process. According
to studies, desalinated water is five times more expensive to harvest than freshwater, making it too
costly for the average consumer.

3. It can be harmful for the environment.
Desalination produces freshwater, but it’s also important to remember that it essentially removes
salt from seawater — salt that has to be disposed in one way or another. The problem with this is that
chlorine and other chemicals are often added to the water during processing and left behind with the brine
which, if dumped back to the ocean, brings with it many harmful substances that can destroy the marine
ecology.

 The Expert Appraisal Committee (EAC) of Ministry of Environment, Forests and Climate Change has recommended
grant of Coastal Regulation Zone (CRZ) clearance. At its 190th meeting on May 8, the EAC reconsidered the project
proposed by Chennai Metropolitan Water Supply and Sewerage Board (CMWSSB) at an estimated cost of
`3,912.16 crore. The project site falls in CRZ-3 and CRZ-4 area.
 This desalination plant, which is based on reverse osmosis process, should be tsunami-resistant for
which the plant site will be raised 6.5 metres above the last level affected by Tsunami.
http://www.newindianexpress.com/cities/chennai/2018/may/27/centre-clears-mega-
400-mld-desalination-plant-in-chennai

 deep sea site that is 40 km from the Ennore coast
 this plant will use indigenously developed low temperature thermal desalination (LTTD), which is an
environment-friendly technology.
http://www.newindianexpress.com/thesundaystandard/2017/
nov/18/tn-to-open-worlds-first-off-shore-desalination-unit

IIT-Madras sets up India’s 1st solar-powered desalination plant
U Tejonmayam| TNN | Updated: Mar 21, 2019, 09:16 IST
CHENNAI: The technology behind desalination plants may
appear simple extract seawater, remove salt, make freshwater but
operating such plants is power intensive and can also pollute the
environment through toxic brine (salts) effluents.
After it was realized that the solution to tackling water scarcity lay in
seawater and the Sun, a team has now set up the country’s first solar-
powered desalination plant, with a capacity to generate 10,000 litres of
freshwater a day, on 120sqm near Vivekananda Memorial at
Kanyakumari. The solar-powered lo- temperature flash desalination
system is locally available, time-tested and marries both technologies.
Plant set up near Vivekananda Memorial at
Kanyakumari`
https://timesofindia.indiatimes.com/city/chennai/iit-m-sets-up-indias-1st-solar-powered-desal-
plant/articleshow/68505168.cms

http://wes.wabagindia.com/docs/List%

 19744 The total number of desalination plants worldwide
 150 The number of countries where desalination is practiced
 More than 300 million, the number of people around the world who rely on desalinated water
for some or all their daily needs
INTERNATIONAL DESALINATION ASSOCIATION https://idadesal.org/
https://www.conservation.org/

REFERENCE:
Desalination From Beachapedia
The USGS Water Science School
Drinking water quality standards as per IS 10500:2012
Department of Atomic Energy Bhabha Atomic Research Centre Chemical
Engineering Group Desalination Division
Chennai metro water supply and sewerage (CMWSS)
International Desalination Association

Desalination plant

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