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Water Purification Innovations
10
Innovations in Water Purification
BY PATRICK J. KIGER
Food and shelter are
crucial for living, but nobody can survive for very long without water. That's
why, since the beginning of history, civilizations have lived near abundant
sources of H20.
But
it's not enough just to have plenty of it. The same water that gives life
can also make people sick or even kill them, if it contains dangerous
substances or disease-causing microbes.
And
since people use water for activities such as irrigating crops, washing and
waste disposal, sources of water close to a human population can easily become
contaminated [source: Hassan].
As
a result, humans have been trying to purify water for thousands of years. As
far back as 1500 B.C., Egyptians used the chemical alum to filter
suspended sediment out of their drinking water.
But
it wasn't until the late 1800s and early 1900s that scientists figured out that
microbes caused illnesses and that water could be treated with chlorine or
ozone to eliminate them [source: Environmental
Protection Agency].
While
the water that comes out of taps in most countries now is clean and safe, about
11 percent of the world's population -- 783 million people -- still doesn't
have access to potable water, according to a 2012 United Nations study.
So
scientists are developing new methods of obtaining water and purifying it. Here
are 10 of the most promising technologies.
10 Direct-Contact Membrane Desalination
If
we could tap the vast oceans as a source of drinking water, everyone would have
more than enough.
But
that means removing the salt, which is inefficient and costly using existing
technology.
That's
why a new process, developed by New Jersey Institute of Technology chemical
engineering professor Kamalesh Sirkar, has such dazzling promise.
In
Sirkar's direct-contact membrane distillation (DCMD) system, heated seawater
flows across a plastic membrane containing a series of hollow tubes filled with
cold distilled water.
The
DCMD's tubes have tiny pores, which are designed so that they can be penetrated
by the water vapor which collects on them, but not by salt.
The
vapor diffuses through the pores and is drawn off, to be condensed again into
liquid water.
According
to Sirkar, his system is extremely efficient -- it can produce 80 liters (21
gallons) of drinking water per 100 liters (26 gallons) of seawater, about twice
what existing desalination technology can produce.
One
potential downside of DCMD is that it requires a steady, inexpensive source of
heat in order to prevent the water temperature on either side of the membrane
from equalizing.
But
there's the possibility that DCMD systems could someday recycle waste heat from
shore-based factories and offshore oil drilling operations, making it a win-win
for everybody [source: Greenmeier].
9 Ceramic Water Filters
Clay
ceramic filters work in a fashion similar to the desalination technology
described in the previous section.
Basically,
water flows through clay that contains a lot of really tiny holes, which are
big enough to let water molecules though, but too small for bacteria, dirt, and
other bad stuff [source: Doulton USA].
The
first such device was developed by a British potter, Henry Doulton, back in the
early 1800s for purifying water drawn from the Thames, which was so
contaminated with raw sewage that cholera and typhoid were continual dangers [source: Brodrick].
Since
Doulton, other inventors have made improvements to his basic concept, such as
adding silver coatings to kill bacteria, so that today's ceramic filters do an
even better job of getting rid of dangerous pathogens.
The
really revolutionary development, though, is that humanitarian non-governmental
organizations have set up factories to make and give away large numbers of
inexpensive ceramic filters in the developing world.
A
2006 study found that Cambodians who used the simple filters, which are
portable and require no energy to run, reduced the incidence of diarrheal
disease by 46 percent, and E.coli contamination in their water by 95 percent
from 2003 rates [source: Resource Development International – Cambodia ]
One
drawback with these ceramic filters is the speed of filtration. The water seeps
out the clay filter at a rate of just 2 liters (2.11 quarts) per hour.
But
the process needs to be slow in to give the silver solution time to kill
pathogens. The filter also does not remove harmful chemicals like arsenic.
8 Herbal
Defluoridation
In
the U.S., water companies add a small amount of flouride -- between 0.8
and 1.2 milligrams per liter – to drinking water as a way to protect teeth
from decay.
But
in some parts of the world, including India, the Middle East and some African
countries, water already has a lot of naturally-occurring fluoride, and the
levels can be so high that they're dangerous to health.
In
one Indian village, for example, a naturally occurring level of 5 to 23
milligrams (.00017 to .008 ounces) per liter has caused residents to suffer
severe anemia, stiff joints, kidney failure and stained teeth [source: World Health Organization].
Fortunately,
Indian researchers offered a possible solution in a March 2013 International
Journal of Environmental Engineering article.
The
researchers have developed a filter system that uses a common medicinal herb,
Tridax procumbens, to absorb excess fluoride from drinking water.
The
plant, which has also been used to extract toxic heavy metals from water,
attracts fluoride ions when water passes through it at a temperature of about
27 degrees Celsius (80.6 degrees Fahrenheit).
The
filter potentially could provide an inexpensive, easy-to-use way of making
water safe in places where the supply contains excessive fluoride.
But
it also may be used by people in the U.S. and other countries who don't like
the idea of fluoride being added to their water [source: Science Daily].
7 'Super Sand'
Sand
and gravel have been used to purify water for thousands of years, and in 1804,
a Scotsman named John Gibb designed and built the first filter that strained
water through grains of sand to remove bigger particles of contamination.
His
technology worked so well that pretty soon, London and other big cities in
Europe were using it to make river water look clearer and taste better.
By
the late 1800s, scientists figured out that filtering made water safer to drink
as well, since the particles stopped by the filtering were the ones that helped
to transmit the microbes that caused water-borne diseases.
The
value of filtering was demonstrated in 1892, when the city of Hamburg, which
got its drinking water from the River Elbe, suffered a cholera epidemic that
killed 7,500 people, while the neighboring city of Altona, where water from the
same river was filtered, escaped almost untouched [source: Huisman and Wood].
But
recently, researchers have figured out how to coat sand grains with graphite
oxide to create "super sand" that reportedly can filter harmful
substances such as mercury from water five times as effectively as ordinary sand.
Work
continues to find ways to make super sand absorb even more contamination, and
eventually use it in developing countries where water supplies are dangerously
polluted [source: Science Daily].
6 Removing Arsenic
With Plastic Bottles
If
you've seen the 1940’s cinematic black comedy "Arsenic and Old Lace,"
in which a couple of well-meaning spinsters take it upon themselves to put
lonely old men out of their misery by giving them elderberry wine laced with
arsenic, you know that the latter substance is pretty bad stuff.
When
it contaminates drinking water, arsenic can cause bladder, lung and skin cancer,
as well as harm the nervous system, heart and blood vessels [source: National
Resources Defense Council].
Unfortunately,
almost 100 million people in developing countries today are exposed to
dangerously high levels of arsenic in their water, and they can't afford the
complex, expensive purification methods used in the U.S. to get rid of it.
However,
a new technology may offer a solution. Monmouth University (N. J.) chemistry
professor Tsanangurayi Tongesayi has developed an inexpensive arsenic-removing
system in which chopped-up pieces of ordinary plastic beverage bottles are
coated with cysteine, an amino acid.
When
the plastic pieces are added to water, the cysteine binds to the arsenic,
removing it and rendering the water drinkable.
In
tests, he's been able to take water containing dangerous arsenic levels of 20
parts per billion, and reduce it to 0.2 parts per billion, which meets the U.S.
Environmental Protection Agency's standard [source: Science Daily]
5 Salt for
Purification
In
impoverished countries where people can't afford to build expensive water
treatment plants, they sometimes rely upon a free resource – sunlight.
A
combination of heat and ultraviolet radiation from the sun will wipe out most
of the microbes that cause diarrhea, an ailment that claims the lives of 4,000
children in Africa every day.
One
complication: In order for the process to work, the water has to be clear,
which is a problem in rural areas where people get their water from rivers,
streams and boreholes that yield water filled with suspended clay particles.
But
Joshua Pearce, an associate professor of materials science and engineering at
Michigan Technological University, and colleague Brittney Dawney from Queens
University in Ontario have a solution.
In
a 2012 article in the Journal of Water, Sanitation and Hygiene for Development,
they proposed a solar disinfection regimen that first treats the water with a
process called flocculation, in
which a small amount of table salt is added to the water to draw out
the clay.
While
the resulting drinking water has higher levels of salt than Americans are used
to, it's still got less in it than Gatorade.
"I've
drunk this water myself,"
Pearce said in an interview. "If I
were somewhere with no clean water and I had kids with diarrhea, and this could
save their lives, I'd use it, no question" [sources: Science Daily, Dawney and Pearce].
4 The SteriPEN
For
travelers in developing countries, exposure to unsafe water can be a big risk.
Wouldn't it be great if you could just dip a magic wand into water and purify
it?
Now,
essentially, you can. A handheld device called the SteriPEN, marketed by
Maine-based company called Hydro Photon, uses ultraviolet light to
eradicate disease-causing microorganisms.
The
device employs the same purification technology used by bottled-water plants,
but it's been miniaturized, so that it weighs just 6.5 ounces (184 grams) and
fits into a backpack.
Stick
it into a liter of stream or pond water for 90 seconds, and voila -- it's safe
to drink [source: Stone].
Such
portable water purification systems can destroy bacteria, viruses and protozoa,
such as giardia and cryptosporidium, which can cause sickness [source: New York Times].
The
big market for SteriPENS is backpackers and travelers, but they're also used by
the U.S. military.
SteriPEN
also has donated some of the devices to game wardens who have to work in remote wilderness
areas where they don't have access to tap water [source: Stone].
One
caveat with ultraviolet purification: Water that's cloudy must be pre-filtered
first in order to remove particles that are in suspension [source: Centers for Disease Control and Prevention].
3 MadiDrop Ceramic
Water Purification Disks
Filters
are a convenient, inexpensive way to purify water in developing countries.
But
a University of Virginia-based nonprofit humanitarian organization called
PureMadi -- "Madi" is the Tshivenda South African word for
"water" -- has come up with an additional easy-to-use technology that
can purify a container of water simply by being immersed in it [source: Samarrai].
The
MadiDrop is a small ceramic disk, about the size of a hamburger patty,
which contains microbe-killing silver or copper nanoparticles.
Nanoparticles are basically really, really tiny objects
specially designed by scientists to behave as a single unit [sources: Samarrai, Mandal].
The
MadiDrop is cheaper, easier to use, and easier to transport than the larger
ceramic flowerpot filters (pictured on the first page) that PureMadi already is
making in an African factory, according to James Smith, a civil and
environmental engineer who is one of the project's leaders.
The
one downside, again, is that the MadiDrop doesn't remove suspended particles
that make water cloudy.
So
ideally, users will put water through a two-step purification process, by first
using the flowerpot filter to get rid of sediment and then eradicating the
microbes with MediDrop [source: Samarrai].
2 Toxin-Eating
Bacteria
Many
of us probably think of algae as that gross stuff that we have to clean out of
our fish tanks every now and then, but they can be a serious threat to health
as well.
Blooms
of blue-green algae, called cyanobacteria, are found in both fresh and salt
water throughout the world.
They
produce toxins called microcystins which
are easily ingested by people who drink, swim or bathe in water that's
contaminated with them.
Once
microcystins get into your body, they can attack your liver cells. That's
obviously not something that you want to happen.
Unfortunately,
conventional water treatment methods, such as sand filtration and chlorination,
don't get rid of these tiny menaces.
That's
why a new purification method developed by researchers at Scotland's Robert
Gordon University has so much promise.
The
researchers have identified more than 10 different strains of bacteria that
like to have microcystins for lunch, and are capable of metabolizing them so
that they break down into harmless, non-toxic materials.
If
the algae-killer bacteria are introduced into water sources, they should be
able to get rid of the microcystins and make the water safe to drink without
using any potentially harmful chemicals [source: Science Daily].
1 Nanotechnology
We've
already mentioned an innovative new device, the MadiDrop, which utilizes silver
or copper nanoparticles to kill bacteria.
But
nanotechnology -- that is, the engineering of really, really small objects and
structures, smaller than the width of a human hair -- has a lot more potential
to help clean up the world's drinking water.
Researchers
at India's D.J. Sanghvi College of Engineering say that filters fashioned from
carbon nanotubes and alumina fibers, for example, could be capable of
removing not just sediment and bacteria, but even traces of toxic elements such
as arsenic.
One
advantage of using nanofilters, as
they're called, is that they're more efficient than conventional water
filtration systems, and don't require as much water pressure. But even
though their pores are a lot smaller than conventional filters, they have a
similar or faster flow rate [source: Science Daily].
At
Massachusetts Institute of Technology, researchers are even looking at using
nanotechnology for desalination.
They're
experimenting with using sheets of graphene,
a form of carbon that's just a single-atom thick, to filter seawater.
With
nanotechnology, it's possible to create sheets filled with miniscule holes,
just a billionth of a meter thick, which can block particles of salt but allow
water molecules to pass through [source: Chandler].
Author's Note: 10 Innovations in Water Purification
I
grew up what used to be known as the Steel Valley in western Pennsylvania,
where the river that we depended upon for drinking water was polluted with
everything from heavy metals and acids from strip mines to raw sewage.
Yet
somehow, when it came out of our taps, the water looked crystal clear and
tasted OK. I always was puzzled about that, and wondered what elaborate
technology was required to render it potable.
Researching
this article was interesting to me, because I got to learn about both the
history of water purification, and what recent innovations may ensure that
people across the planet have access to clean water.
Patrick J. Kiger has written for HowStuffWorks since
2008 covering a wide array of topics, from history and politics to pop culture
and technology. He worked as a newspaper reporter for the Pittsburgh Press, and
the Orange County Register in California, where he covered one of the biggest
serial murder cases in U.S. history, and also as a staff writer at Baltimore
Magazine. As a freelancer, Patrick has written for print publications such as
GQ, Mother Jones and the Los Angeles Times, and on the web for National
Geographic Channel, Discovery News, Science Channel and Fast Company, among
others. In recent years, he's become increasingly interested in how
technological advances are altering urban life and the design of cities, and
has written extensively on that subject for Urban Land magazine. In his spare
time, Patrick is a longtime martial arts student and a fan of crime fiction,
punk rock and classic Hollywood films.
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