Friday, 22/11/2024 | 23:07 GMT+7
A desalination technology powered
by solar panels could provide enough clean, palatable drinking water to meet
the needs of India's water-deficient villages, MIT scientists say.
Sixty per cent 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.
An analysis by Massachusetts
Institute of Technology (MIT) researchers Natasha Wright and Amos Winter shows
that a different desalination technology called electrodialysis, powered by
solar panels, could provide enough clean, palatable drinking water to supply
the needs of a typical village.
Finding optimal solutions to
problems such as saline groundwater involves "detective work to understand
the full set of constraints imposed by the market," said Winter.
After weeks of field research in
India, and reviews of various established technologies, Winter said, "when
we put all these pieces of the puzzle together, it pointed very strongly to
electrodialysis" - which is not what is commonly used in developing
nations.
The factors that point to the
choice of electrodialysis in India include both relatively low levels of
salinity — ranging from 500 to 3,000 milligrammes per litre, compared with
seawater at about 35,000 mg/L - as well as the region's lack of electrical
power.
Such moderately salty water is
not directly toxic, but it can have long-term effects on health, and its
unpleasant taste can cause people to turn to other, dirtier water sources.
"It's a big issue in the
water-supply community," Winter said.
By pairing village-scale
electrodialysis systems with a simple set of solar panels and a battery system
to store the produced energy, an economically viable and culturally acceptable
system could supply enough water to meet the needs of a village of 2,000 to
5,000 people, researchers concluded.
They estimate that deployment of
such systems would double the area of India in which groundwater - which is
inherently safer, in terms of pathogen loads, than surface water - could
provide acceptable drinking water.
While many homes in India
currently use individual, home-based filtration systems to treat their water,
Wright and Winter concluded that village-scale systems would be more effective
- both because fewer people would be left out of access to clean water, and
because home-based systems are much harder to monitor to ensure effective water
treatment.
The study appears in the journal
Desalination.
Most organisations working to
improve clean-water access focus their attention on controlling known pathogens
and toxins such as arsenic, Wright said.
But her analysis showed the
importance of "what the water tastes like, smells like, and looks
like."
Even if the water is technically
safe to drink, that doesn't solve the problem if people refuse to drink it
because of the unpleasant salty taste, she said.
Electrodialysis works by passing
a stream of water between two electrodes with opposite charges.
Because the salt dissolved in
water consists of positive and negative ions, the electrodes pull the ions out
of the water, leaving fresher water at the centre of the flow, Winter said.
A series of membranes separate
the freshwater stream from increasingly salty ones.
Both electrodialysis and reverse
osmosis require the use of membranes, but those 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, Winter said.
In addition, electrodialysis
systems recover a much higher percentage of the water — more than 90 per cent,
compared with about 40 to 60 per cent from reverse-osmosis systems, a big
advantage in areas where water is scarce.
Having carried out this analysis,
Wright and Winter plan to put together a working prototype for field evaluations
in India.
Researchers said while this
approach was initially conceived for village-scale, self-contained systems, the
same technology could also be useful for applications such as disaster relief,
and for military use in remote locations.
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