"Water, water, everywhere,
and all the boards did shrink;
Water, water, everywhere
Nor any drop to drink."
--Samuel Taylor Coleridge, The Rime of the Ancient Mariner
Hello coopsr and thanks for your question.
There are various methods of water Desalination. The majority of the
methods extract salt and minerals to obtain fresh water from seawater
or brackish water (water that is saltier than fresh water, but not as
salty as sea water) through the application of energy. The end product
is suitable for irrigation of agriculture or crops, hydration of
livestock and even human consumption.
What is considered ?Fresh Water??
Fresh water is water that contains minimal quantities of dissolved
salts, especially sodium chloride. Natural sources for freshwater are
lakes, streams, rivers, glaciers, and underground aquifers and
streams.
Water with a salt content of less than 0.5 parts per thousand (5000
ppm) and less than 0.03% ionic content is considered undesirable for
drinking and many industrial uses (World Health Organization e.g.
SBPC, 1995).
?Saltwater? is water found naturally in the ocean or seas and which
has high salinity content. Full strength seawater contains 35 parts of
salt, mainly sodium, for each 1000 parts water (salinity = 35 ppt)
equalling roughly 3%. Seawater contains various other substances and
minerals (for example - magnesium, potassium, calcium, chloride,
sulphate, hydrogencarbonate, and bromide).
For comparison the Great Salt Lake and the Dead Sea, both lakes, are
about 10 times saltier than seawater, partly due to the fact that the
Great Salt Lake, Dead Sea and other salt lakes have no outlets.
Dr. Allan R. Hoffman, Senior Analyst, U.S. Department of Energy (DOE)
comments on Desalination:
?There is broad agreement that extensive use of desalination will be
required to meet the needs of a growing world population. Energy costs
are the principal barrier to its greater use. Worldwide, more than
15,000 units are producing over 32 million cubic meters of fresh water
per day. 52% of this capacity is in the Middle East, largely in Saudi
Arabia where 30 desalination plants meet 70% of the Kingdom?s present
drinking water needs and several new plants are under construction.
North America has 16%, Asia 12%, Europe 13%, Africa 4%, Central
America 3%, and Australia 0.3%. The two most widely used desalination
technologies are reverse osmosis (RO; 44%) and multi-stage flash
distillation (MSF; 40%). Energy requirements, exclusive of energy
required for pre-treatment, brine disposal and water transport, are:
RO: 5,800-12,000 kWh/AF (4.7-5.7 kWh/m3) and MSF: 28,500-33,000 kWh/AF
(23-27 kWh/m3).?
In Spain ?The Environment Ministry has approved a ground-breaking
project by Spanish researchers that promises to solve the water
shortages that have become a serious problem in Spanish coastal areas.
The project consists of placing floating desalination plants out at
seas powered by wind turbines, allowing them to produce fresh water
with virtually no impact on the environment (joining wind and sea
forces). The project, which has received initial funding of ?12
million from the Ministry, will result in a first prototype being
produced within 18 months.?
http://www.marketnewzealand.com/MNZ/news/story/13572/12330.aspx
Israel built its first seawater distillation plant in 1965 to serve
the new Red Sea town of Eilat. Arab countries soon built even larger
plants for their desert communities. In the US Key West, Florida, was
the first North American city to be supplied drinking water from the
sea when its desalination plant opened in 1967.
The various methods for producing freshwater from seawater or Desalination are:
- Reverse Osmosis
- Distillation , known also as evaporation.
- Electro dialysis.
- Freezing methods.
- Mechanical Vapor Recompression (MVR).
The fundamentals of Reverse Osmosis
======================================
?Reverse osmosis, also known as hyperfiltration, is the finest
filtration known. This process will allow the removal of particles as
small as ions from a solution. Reverse osmosis is used to purify water
and remove salts and other impurities in order to improve the color,
taste or properties of the fluid. It can be used to purify fluids such
as ethanol and glycol, which will pass through the reverse osmosis
membrane, while rejecting other ions and contaminants from passing.
The most common use for reverse osmosis is in purifying water. It is
used to produce water that meets the most demanding specifications
that are currently in place.
Reverse osmosis uses a membrane that is semi-permeable, allowing the
fluid that is being purified to pass through it, while rejecting the
contaminants that remain. Most reverse osmosis technology uses a
process known as crossflow to allow the membrane to continually clean
itself. As some of the fluid passes through the membrane the rest
continues downstream, sweeping the rejected species away from the
membrane. The process of reverse osmosis requires a driving force to
push the fluid through the membrane, and the most common force is
pressure from a pump. The higher the pressure, the larger the driving
force. As the concentration of the fluid being rejected increases, the
driving force required to continue concentrating the fluid increases.
Reverse osmosis is capable of rejecting bacteria, salts, sugars,
proteins, particles, dyes, and other constituents that have a
molecular weight of greater than 150-250 daltons. The separation of
ions with reverse osmosis is aided by charged particles. This means
that dissolved ions that carry a charge, such as salts, are more
likely to be rejected by the membrane than those that are not charged,
such as organics. The larger the charge and the larger the particle,
the more likely it will be rejected?
http://www.gewater.com/library/tp/833_What_Is.jsp
?The reverse osmosis process contains several downsides which make it
an inefficient and ineffective means of purifying drinking water. The
small pores in the membrane block particles of large molecular
structure like salt, but more dangerous chemicals like pesticides,
herbicides, and chlorine are molecularly smaller than water (Binnie et
al, 2002). These chemicals can freely pass through the porous
membrane. For this reason, a carbon filter must be used as a
complimentary measure to provide safe drinking water from the reverse
osmosis process. Such chemicals are the major contaminants of drinking
water after municipal treatment.
Another downside to reverse osmosis as a method of purifying drinking
water is the removal of healthy, naturally occurring minerals in
water. The membrane of a reverse osmosis system is impermeable to
natural trace minerals. These minerals not only provide a good taste
to water, but they also serve a vital function in the body?s system.
Water, when stripped of these trace minerals, can actually be
unhealthy for the body.
Reverse osmosis also wastes a large portion of the water that runs
through its system. It generally wastes two to three gallons of water
for every gallon of purified water it produces. Reverse osmosis is
also an incredibly slow process when compared to other water treatment
alternatives?
http://www.historyofwaterfilters.com/reverse-osmosis-pc.html
Such a diagram of a Reverse Osmosis system can be found here:
http://www.searecovery.com/Graphics/desalinator/rograph.jpg
For practical purposes, reverse osmosis (RO) was commercialized in
1969. By January 1970, 208 electrodialysis units (with 6.2 mgd total
capacity) had been installed, including Coalinga, CA (1958), Buckeye,
AZ (1962), Port Mansfield, TX (1965), White Sands Missile Range, NM
(1969) and many others. In 1973, the Foss Reservoir Conservancy
decided to build a 3 mgd desalination plant.
Water Distillation:
=======================
Distilled water is water which has been heated to the boiling point
(212 degrees Fahrenheit or 100 degrees Centigrade) and converted to
steam.
The steam is then cooled and condensed back into liquid form as pure
water. Distillation kills biological contaminants such as bacteria,
parasites, cysts, and viruses, and removes organic and inorganic
chemicals, heavy metals, volatile gases, and other contaminants. The
water produced is pure and contains no solids, minerals, or trace
elements. Steam distillation is the only water purification method
that removes virtually all contaminants.
Distillation does not remove substances that have boiling points at a
lower temperature than water These substances are oils, petroleum,
alcohol and similar substances, which in most cases don't mix with
water.
Drawbacks are the high cost of energy required to mass produce distilled water.
Most desalination plants use "flash evaporation?. Seawater is first
heated, then pumped into a low-pressure tank. Since the boiling point
of water drops with the decrease in air-pressure, the water will
vaporize almost immediately, "flashing" into steam. The steam is then
condensed into fresh water.
?Solar power seems an efficient and environmentally friendly
alternative to traditional power. Though solar power can be effective
for distillation purposes, it works only with relatively small amounts
of liquid. Also, the time required for multiple distillations is much
greater when relying on solar power than when using traditional power
sources.
Distillation, like reverse osmosis, strips water of natural trace
elements. When these elements are removed from water, the hydrogen
composition becomes greater in proportion, making the water very
acidic. Several studies have proven that drinking distilled water,
stripped of minerals, can actually be harmful to the body system.
Long-term consumption of such de-mineralized water can result in
mineral deficiencies in the body. Though the removal of trace minerals
creates water that is ideal for use in photo or print shops, it
creates tasteless and even unhealthy drinking water.?
http://www.historyofwaterfilters.com/distillation-pc.html
Zoltan P. Rona MD MSc observed the health effects of drinking
different types of water for over 19 years and claimed that ?drinking
distilled water on a regular, daily basis is potentially dangerous.?
Dr. Masaru Emoto, Doctor of Alternative Medicine and Japanese water
researcher also performed extensive research on distilled water by
studying the crystallization processes and found that ?water that had
been distilled, polluted or passed through consumption had lost its
inner order. This leads to the realization that natural healthy water
carries an 'inner order' defining its nature and properties.?
http://miraculewater.com/WaterLibrary/Distilledwater.html
Electrodialysis Fundamentals
==============================
Electrodialysis was commercially introduce in the early 1960s.
When salt is dissolved in water, it splits into positive and
negatively charged ions. By running an electrical current through the
water you can draw these ions out.
Electrodialysis utilizes a membrane separation process that applies a
DC electrical current to move and separate dissolved minerals in
water. Cations and anions are displaced by an electric field through
selective membranes leaving drinking water. The separation of minerals
occur in individual membrane units called cells, which consist of a
cation selective membrane and an anion selective membrane. The
complete assembly of cells is called membrane stack.
electrodialysis plants for brackish water desalination make sense in
arid and semiarid regions. In such regions there is often an
inadequate water and energy supply infrastructure together with good
levels of solar radiation.
http://66.102.9.104/search?q=cache:VRK7fgjCsZ0J:www.rio3.com/proceedings/RIO3_103_P_de_Carvalho.pdf++Electrodialysis+desalination&hl=en
Walter Juda, Ph.D of Department of Chemical & Biological Engineering
at Tufts University is prominent in the field electrodialysis
equipment for water desalination. His ?track record includes founding,
and then harvesting, two businesses operating worldwide: Ionics,
involved in electrodialysis equipment for water desalination using
proprietary ion-exchange membranes, as well as Prototech Company,
involved in pollution control using proprietary catalysts and patented
noble metal chemistry, where he is Board Chairman (retired).?
http://ase.tufts.edu/chemical/facJuda.htm
Global Production of Desalinated Water figures for the global
production of desalinated water, by process and plant capacity. Can be
found here:
http://www.waterindustry.org/Water-Facts/de-sal-5.htm
Buckeye, Arizona has had all its water supplied by its own
electrodialysis-desalting plant since 1962.
http://www2.hawaii.edu/~nabil/buckeye.htm
Port Mansfield, Texas, also has an electrodialysis desalination
plant,located 80 miles west of Oklahoma City, it went on line in 1974.
At the time, it was the largest membrane desalination plant in the
world.
http://www.ionics.com/pdf/TP_500.pdf
A technical paper titled: ?Half a Century of Desalination with
Electrodialysis? can be found here:
http://www.ionics.com/pdf/TP_500.pdf
Freezing-Melting process for desalination of seawater
=======================================================
?The freezing method removes the fresh water, leaving concentrated
salt water behind. Salt waters have a certain critical temperature
which is a function of its salinity. When the salt water is reduced to
this temperature, ice crystals composed of fresh water are formed. It
is then possible to mechanically separate the ice crystals from the
solution and remelt them to get fresh water. This is the basic
principle on which freezing desalination methods are based on.
It is obvious that this method is not the most practical to use. It
can be easily demonstrated on a small-scale basis but when applied to
a large scale process, problems arise. The main problem lies in the
economical aspects of the initial capital costs and the maintenance
costs. The second problem is the thermodynamic efficiency relative to
upscaling the process.
Believe it or not, there are some advantages to this process. The
operating temperature of this type of process is obviously at or below
the freezing temperature of water. At these temperatures, scaling and
corrosion are greatly reduced. This is one of the drawbacks of other
conventional methods. Scaling is due to the buildup of precipitates
due to calcium, magnesium, bicarbonate, sulfate, sodium, and chlorine
ions in the water. The hard scale formed on the inside of the pipes
requires costly maintenance practices to remove. Corrosion of steel
pipes in contact with salt water is also increased with temperature.
Lower temperatures permit plastics and protective coatings on the
steel pipes to prevent corrosive attack. The thermodynamic efficiency
can also be increased due to the lack of heat exchangers required in
heat driven desalination processes.
There are several different methods for the separation of the ice
crystals from the liquid. The chosen method is dependent on the
characteristics of the ice crystals. Two items of concern are crystal
size and specific gravity. Filtration seems like it would be an
obvious approach but it is actually impractical. It requires a slow,
complicated filtration system and has not yet been applied to any
system. A wash-separation method is a more reasonable approach. It
takes the specific gravity into account. The solution flows up a
screened or perforated column and a floating column of ice crystals is
formed. Since the salt gets trapped in this ice column, it must be
counter-washed by process water.?
http://www.rpi.edu/dept/chem-eng/Biotech-Environ/Environmental/desal/freeze.html
Research in this area of Desalination is being conducted Dr. Shafiur
Rahman, Sultan Qaboos University, Sultanate of Oman,Dr. Mushtaque
Ahmed and Mr. Rashid Hamed Abdullah Al-Belushi, Sultan Qaboos
University, Sultanate of Oman and Dr. Xiao Dong Chen, The University
of Auckland, New Zealand:
?The main objective of the project is to identify the practical
limitations of the freezing-melting process for desalination of
seawater and suggest possible strategies to overcome the obstacles.
The major tasks of this project are the following.
1.Perform a thorough literature review to assess the current state of the art
in utilizing the freezing-melting process for desalination.
2.Identify the advantages and disadvantages of the freezing-melting
process relative to other desalination methods.
3.Identify the practical limitations of freezing-melting desalination
processes for commercial success and identify reasons why they did
not sustain in the market.
4.Assessment of the benefits of new approaches, such as combining freezing-
melting with reverse osmosis for desalination and perform analysis of new
approaches to develop possible alternatives to overcome the practical limitations.?
http://www.ewatermark.org/Watermark13/article2.htm
http://www.squ.edu.om/agr/depts/do/research/res-extprojects2003.html
Some major players in the field of water Desalination and Global Water Markets:
General Electric & Ionics, http://www.ionics.com/
===================================================
?GE Infrastructure, a unit of General Electric Company (NYSE: GE), and
Ionics, Inc. (NYSE: ION) announced today that they have signed a
definitive agreement for GE's acquisition of Ionics in an all cash
merger for $44 per share, valuing the transaction at approximately
$1.1 billion plus the assumption of existing debt. Ionics is a global
leader in desalination, water reuse & recycling, and industrial
ultrapure water services. Ionics will join GE Infrastructure?s Water &
Process Technologies business unit upon completion of the
transaction.?
http://www.ionics.com/aboution/pressrel/2004/11-24-04GEAcquisition.htm
Suez Lyonnaise des Eaux (which built the Suez Canal and had 1999
profits of $1.5 billion on sales of $32 billion).
=============================================================================
?French-based Suez was formed in 1997 by a merger between Compagnie de
Suez and Lyonnaise des Eaux. After the merger, the company?s name
became Suez Lyonnaise des Eaux and was subsequently shortened to Suez
in 2001. Suez?s water and wastewater business, which is run through
its subsidiary Ondeo, is the second largest in the world. Suez
provides water-related services to more than 115 million people
worldwide. Its other business areas are electricity, natural gas,
water and waste management. Suez also maintains interests in
television and broadband distribution. In 2001, Suez was ranked 99th
on Fortune?s Global 500, and in the same year it was ranked 19th in
the world among companies with the greatest international presence,
according to the United Nations World Investment Report. In the summer
of 2002, Suez merged its water and wastewater services into a division
called Suez Environment.?
http://www.publicintegrity.org/water/db.aspx?sid=db&par=6
http://www.lyonnaise-des-eaux.fr/
Vivendi SA
============
"Vivendi SA are referred to as the General Motors and Ford Motor
Company of the water world. Both are ranked among the 100 largest
corporations in the world by the Global Fortune 500."
http://www.publicintegrity.org/water/report.aspx?aid=59&sid=100
http://www.publicintegrity.org/water/db.aspx?sid=db&par=2
TSG Technologies, Inc.
========================
A wholly owned subsidiary of TSG Water Resources, Inc.
"TSG specializes in the design, construction, renovation, operation
and maintenance of water and wastewater treatment plants of all kinds,
but we have special expertise in water purification and wastewater
treatment utilizing membranes, including:
? Reverse osmosis (RO) desalination plants for water
? Membrane bioreactor (MBR) plants for wastewater"
http://www.tsgwater.com
Aquadyne. & the Jetwater process:
===================================
"JetWater is a modular plant that uses Mechanical Vapour Recompression
(MVR) to desalinate seawater and brackish groundwater or purify
industrial wastewater to produce pure, distilled water. This provides
a baseline product which enables blending with other water to meet
individual clients' specifications."
http://www.aquadyne.com.au/applications.php?PHPSESSID=a6da51c22c5424e61a815ecddde14ec7#what
Other Articles of Interest:
"Cholera and the Age of the Water Barons" is an intriguing article
regarding fears that mankind may be losing control of its most vital
resource to a handful of monopolistic corporations.
http://www.publicintegrity.org/water/default.aspx?sID=ch&rID=44&aID=44
?Water Privateers?:
http://www.thirdworldtraveler.com/Water/Water_Privateers_BG.html
Finally, please see also my colleague?s answer to a similar question
regarding ?What are the costs, issues, and complications on a small
scale of de-salinating water?:
http://answers.google.com/answers/threadview?id=227685
Please let me provide any clarifications you may deem necessary
Regards
Landog-ga
Sources:
http://www.answers.com/topic/desalination-1
http://www.answers.com/topic/freshwater
http://www.utdallas.edu/~pujana/oceans/why.html
http://wlapwww.gov.bc.ca/wat/wq/reference/glossary_2.html
http://encyclopedia.farlex.com/ocean
http://www.searecovery.com/Text/reverse_osmosis/whatro.html
http://www.searecovery.com
http://www.gewater.com
http://www.i4at.org/surv/distill.htm
http://www.historyofwaterfilters.com/distillation-process.html
http://miraculewater.com/WaterLibrary/Distilledwater.html
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