QUENCHING A GLOBAL THIRST
Japanese Researchers Help to Combat Water Shortages (June 26, 2003)
The world is currently facing a water crisis in the form
of water shortages, pollution, flood damage, and other problems. The urgent need
to solve these problems through cooperation by the whole international community
was brought into stark focus at the Third World Water
Forum, which was held in Japan in March. Water shortages, which the world
faces now and is predicted to face even more in the future, are a particularly
acute problem, and Japanese universities and companies are making a variety of
efforts to alleviate them. Their ideas include a method of generating electricity
and conducting desalination that takes advantage of temperature differences in
seawater; a special membrane for desalinating seawater; and a desalination filter
that uses sand at the bottom of the ocean. Japanese technology in these fields
is among the most advanced in the world, and there are high hopes for what these
research efforts may achieve.
|The Okinawa Prefecture Seawater Desalination Center (Okinawa Enterprise Bureau)
Exploiting Differences in Ocean Temperatures
According to surveys by international organizations, 97.5% of the Earth's water
is seawater, and no more than about 2.5% is freshwater. What is more, with most
freshwater held in glaciers, icebergs, and underground reservoirs, water that
can be used easily by humans, such as that in rivers and lakes, accounts for just
0.01% of the total. Meanwhile, the global population topped the 6 billion mark
in 2000 and is expected to reach 8 billion in 2025, of which 3.5 billion are likely
to face water shortages.
Mindful of these problems, Japanese universities and companies are stepping up
their efforts to research ways of harnessing water resources. One of the projects
attracting attention is a system under development at Saga University in Kyushu for desalinating seawater by taking advantage of differences
in ocean temperatures. This method of desalination is called the spray-flash method.
In it, a fine spray of warm surface seawater is sucked into the system, which
is depressurized to 0.05 atmospheres by a vacuum pump. In such low pressure the
boiling point of water drops to about 20 or 30 degrees Celsius, so the seawater
mist quickly evaporates into steam with its salt content removed. This steam is
cooled by cold deep-sea water and condenses into freshwater.
This method has been taken a step further by combining it with a form of electricity
generation that also uses differences in ocean temperature. This system involves
changing ammonia, which has a low boiling point, to gas by heating it with warm
water near the ocean surface and using this gas to power a turbine. The ammonia
is condensed back to its liquid form by cold deep-sea water, and the warm seawater
left over from the process is turned into freshwater using the spray-flash method.
There are plans to build a desalination plant using this system in Saudi Arabia.
The country already produces drinking water in desalination plants built by Japanese
firms that use heat generated by burning oil, and the idea is to use the warm
wastewater from these facilities in the system developed by Saga University. Under
the plan, spray-flash facilities will be constructed alongside three desalination
plants operating in Saudi Arabia.
The Saga University system is both cheap and environmentally friendly, and there
has been a flood of inquiries from dozens of countries afflicted by water shortages
in the Middle East and the South Pacific.
Companies Developing New Desalination Technology
In order to tackle water shortages, countries in the Middle East, Europe, and
elsewhere are stepping up efforts to desalinate seawater by filtering it through
special fine membranes. Plants for this purpose are underpinned by technology
developed by Japanese companies.
Major textiles maker Toray Industries Inc. has delivered a water-processing membrane to a seawater desalination
plant in the Caribbean nation of Trinidad and Tobago, and the plant started
operating in March 2002. This reverse osmosis membrane is made of a special polymer
called a polyamide, and what makes it special is its spiral configuration. With
holes just one two-millionth of a millimeter wide, it even filters out viruses
and bacteria. This system has been welcomed for its ability to produce 0.6 liters
of freshwater from one liter of seawater. The Trinidad and Tobago plant is the
largest facility of its kind in the world and can produce 136,000 tons of water
a day - enough to provide drinking water for 400,000 people.
This reverse osmosis membrane is the result of technology cultivated since the
days when Japan was known as a major textile producer and has proved its worth
domestically, too. The Okinawa Prefecture Seawater Desalination Center was completed
in 1997 and produces 40,000 cubic meters of drinking water per day, meeting 10%
of water demand on the prefecture's main island of Okinawa. Toray expects demand
for reverse osmosis membranes to rise and plans to increase its production capacity
by 150% from October 2002 levels by October 2003.
Meanwhile, major general contractor Obayashi Corp. recently started work on constructing Japan's largest seawater desalination
plant in Fukuoka Prefecture. The plant employs a system in which the water intake
is laid in sand at the bottom of the ocean. The deep-sea sand acts as a filter,
so there is no danger of the system sucking in fish eggs or fry. The plant is
due to be completed in 2005. Many other universities and companies are striving
to produce water resources, and the role of Japanese technology in international
water projects is sure to keep on growing.
Related Web Sites
Toray Industries Inc.
Copyright (c) 2004 Web Japan. Edited by Japan Echo Inc. based on domestic Japanese news sources. Articles presented here are offered for reference purposes and do not necessarily represent the policy or views of the Japanese Government.
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