According to the Securing Water for Food agency, between 2000 and 2050 water demand is expected
to increase 55 percent globally, meaning the number of people affected by water scarcity
will continue to grow.
By 2025, two-thirds of the world's population could be living
in severe water stress conditions.
Around the world, there is more salty groundwater than fresh, drinkable groundwater.
For example,
60 percent of India is underlain by salty water — and much of that area is not served
by an electric grid that could run conventional reverse-osmosis desalination plants.
To find solution for this drinking water issue in developing countries, USAID the U.S. Agency
for International Development had run a global competion for Desal prize.
The idea for the competition was to create a system that could remove salt from water
and meet three criteria: it had to be cost-effective, environmentally sustainable, and energy efficient.
The winners of the $140,000 first prize were a group from MIT and Jain Irrigation Systems.
The group came up with a method that uses solar panels to charge a bank of batteries.
The batteries then power a system that removes salt from the water through electrodialysis,
that means that dissolved salt particles, which have a slight electric charge, are drawn
out of the water when a small electrical current is applied.
Using the sun instead of fossil fuels to power a desalination plant isn't a totally new idea.
Larger solar desalination plants are being seriously investigated in areas where water
is becoming a scarce resource, including Chile and California.But the current technology
is expensive.
The MIT team's this new desalination technology "electrodialysis" is comparatively less expensive.
Both electrodialysis and reverse osmosis require the use of membranes, but the membranes in
an electrodialysis system are exposed to lower pressures and can be cleared of salt buildup
simply by reversing the electrical polarity.
That means the expensive membranes should
last much longer and require less maintenance.
In addition, electrodialysis systems recover
a much higher percentage of the water — more than 90 percent, compared with about 40 to
60 percent from reverse-osmosis systems, a big advantage in areas where water is scarce.
Researchers at MIT have designed a simple water filter by peeling the bark off a small
section of white pine, then inserting and securing it within plastic tubing.
It has always been my goal to develop technologies and methods towards a more sustainable, healthier,
and happier society.
About a Billion people on this planet lack
access to clean drinking water.
And, we recognized that this xylem tissue that conducts fluid
in plants could be used as a water filter.
So, how this works?
The xylem tissues in the
plants consist of these membranes which have these really tiny pores big enough to allow
water to flow through the xylem.
But they block the passage of larger particles.
So,
the xylem filters could be used to realize water purification devices that are simple
to use, safe, in order of magnitude cheaper than existing technologies, that would allow
it penetrate to the communities that today do not have access to clean drinking water.
We prepare our filter by simply taking a branch from pine tree, and cutting off a small section.
We took this branch mounted in a tube, flowed water which was contaminated with bacteria.
And, we found that this simple filter could remove 99.99% of bacteria from the water.
So, If you’ve run out of drinking water during a lakeside camping trip, there’s
a simple solution: Break off a branch from the nearest pine tree, peel away the bark,
and slowly pour lake water through the stick to get the safe drinking water.
This simple xylem filter can filter most types of bacteria, the smallest of which measure
about 200 nanometers.
However, the filter probably cannot trap most viruses, which are
much smaller in size.
Approximately 3 cm3 of sapwood can filter water at the rate of several liters per day,
sufficient to meet the clean drinking water needs of one person.
There are a number of water-purification technologies on the market today, although many come with
drawbacks: Systems that rely on chlorine treatment work well at large scales, but are expensive.
Boiling water to remove contaminants requires a great deal of fuel to heat the water.
Membrane-based
filters are expensive, require a pump, and can become easily clogged.
Right now, more than a million children die every year from water-borne diseases.
And,
this technology has the potential to make a difference.
A new research shows graphene can filter common salts from water to make it safe to drink
The new findings could lead to affordable desalination technology.
Graphene-oxide membranes have attracted considerable attention as promising candidates for new
filtration technologies.
Now the much sought-after development of making membranes capable of sieving common salts
has been achieved.
New research demonstrates the real-world potential of providing clean drinking water for millions
of people who struggle to access adequate clean water sources.
The new findings from a group of scientists at The University of Manchester were published
in the journal Nature Nanotechnology.
Previously graphene-oxide membranes have shown exciting potential for gas separation and
water filtration.
Graphene-oxide membranes developed at the National Graphene Institute have already demonstrated
the potential of filtering out small nanoparticles, organic molecules, and even large salts.
Until now, however, they couldn’t be used for sieving common salts used in desalination
technologies, which require even smaller sieves.
Previous research at The University of Manchester found that if immersed in water, graphene-oxide
membranes become slightly swollen and smaller salts flow through the membrane along with
water, but larger ions or molecules are blocked.
The Manchester-based group have now further developed these graphene membranes and found
a strategy to avoid the swelling of the membrane when exposed to water.
The pore size in the membrane can be precisely controlled which can sieve common salts out
of salty water and make it safe to drink.
As the effects of climate change continue to reduce modern city’s water supplies,
wealthy modern countries are also investing in desalination technologies.
Following the severe floods in California major wealthy cities are also looking increasingly
to alternative water solutions.
By 2025 the UN expects that 14% of the world’s population will encounter water scarcity.
This technology has the potential to revolutionise water filtration across the world, in particular
in countries which cannot afford large scale desalination plants.
It is hoped that graphene-oxide membrane systems can be built on smaller scales making this
technology accessible to countries which do not have the financial infrastructure to fund
large plants without compromising the yield of fresh water produced.
A solar-powered water harvester was constructed at the Massachusetts Institute of Technology
using a special material — a metal-organic framework, or MOF — produced at the University
of California, Berkeley.
This water harvester uses only ambient sunlight to pull liters of water out of the air each
day in conditions as low as 20 percent humidity, a level common in arid areas.
Rooftop tests at MIT confirmed that the device works in real-world conditions.
- Professor Yaghi, thank you very much for inviting us into your lab.
- It's a pleasure.
- I read that you've come up with a way to actually suck water out of the air and store
it.
- That's true.
We use materials called metal organic frameworks or MOFs and these are constructed from metal
ions that are in minerals and organic units.
Here you have the organic building unit and the other, of a metal ion.
And we mix them together and stir to make the metal organic framework or the MOF.
And once you remove the liquid, this is what you get.
And this is the material that is the MOF.
- So what does that powder look like close up?
- So if I zoom in on a granule of this solid, the structure does not look very much unlike
this.
The metal ion and the organic are linked together to make the framework that is the MOF and
it encompasses space, the liquid will bind to the framework, to the interior of the pores.
One-third of the world population live in arid regions where water is scarce, but that
air in those regions contains about 30% humidity.
These materials can take up the water from that atmosphere, concentrate it and deliver
liquid water using nothing but sunlight and the MOF. (marimba music) - So depending on
what kind of substance you want to attract and store, you actually change the kind of
metal and the kind of organic material?
- By using a longer organic unit, I can change the pore size.
By choosing a different metal, I can change the metal composition so I can do a different
kind of reaction absorbing different kinds of gases.
This MOF is a star for natural gas storage and if you put this in a natural gas tank,
you can store three times the amount of natural gas than without the MOF.
The purple one is very interesting because it traps carbon dioxide from the atmosphere
and also, from emissions in power plants to prevent carbon dioxide from reaching the atmosphere.
- It seems like this has been a revolutionary invention that could change so much into the
future.
- When I started doing this research in the early '90s, I was interested in the beauty
of molecules.
I was not necessarily interested in making the new materials going to solve the world's
problems, for a lot of problems facing societies such as water, such as carbon dioxide.
These are tremendous problems that are being investigated using MOFs worldwide and what
remains is really the wide-scale deployment of these to actually serve society.
As the availability of clean, potable water becomes an increasingly urgent issue in many
parts of the world, researchers are searching for new ways to treat salty, brackish or contaminated
water to make it usable.
Now a team at MIT has come up with an innovative approach that,
unlike most traditional desalination systems, does not separate ions or water molecules
with filters, which can become clogged, or boiling, which consumes great amounts of energy.
Instead, the system uses an electrically driven shockwave within a stream of flowing water,
which pushes salty water to one side of the flow and fresh water to the other, allowing
easy separation of the two streams.
According to the researchers, this approach is a fundamentally new and different separation
system.
Unlike most other approaches to desalination or water purification, this one performs a
“membraneless separation” of ions and particles.
Membranes in traditional desalination systems, such as those that use reverse osmosis or
electrodialysis, are “selective barriers”.
They allow molecules of water to pass through, but block the larger sodium and chlorine atoms
of salt.
Compared to conventional electrodialysis, “This process looks similar, but it’s
fundamentally different,”
In the new process, called shock electrodialysis, water flows through a porous material —in
this case, made of tiny glass particles, called a frit — with membranes or electrodes sandwiching
the porous material on each side.
When an electric current flows through the system,
the salty water divides into regions where the salt concentration is either depleted
or enriched.
When that current is increased to a certain point, it generates a shockwave
between these two zones, sharply dividing the streams and allowing the fresh and salty
regions to be separated by a simple physical barrier at the center of the flow.
Even though the system can use membranes on each side of the porous material, the water
flows across those membranes, not through them.
That means they are not as vulnerable
to fouling — a buildup of filtered material — or to degradation due to water pressure,
as happens with conventional membrane-based desalination, including conventional electrodialysis.
The underlying phenomenon of generating a shockwave of salt concentration was discovered
a few years ago by the Stanford University.
But that finding, which involved experiments with a tiny microfluidic device and no flowing
water, was not used to remove salt from the water.
The new system, by contrast, is a continuous process, using water flowing through cheap
porous media, that should be relatively easy to scale up for desalination or water purification.
One possible application would be in cleaning the vast amounts of wastewater generated by
hydraulic fracturing, or fracking