Sep 10 2014 : Mirror (Pune)
Solar desalination for Indian villages
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A new initiative could create off-the-grid solar-powered desalination plants that could provide palatable drinking water to rural Indian communities with salty groundwater
Around the world, there is more salty groundwater than fresh, drinkable groundwater. For example, 60 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 reverseosmosis desalination plants.Now an analysis by Massachusetts Institute of Technology researchers 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.
The study, by Natasha Wright and Amos Winter, appears in the journal Desalination.
Winter explains that finding optimal solutions to problems such as saline groundwater involves “detective work to understand the full set of constraints imposed by the market.” After weeks of field research in India, and reviews of various established technologies, he says, “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 milligrams per liter, 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 longterm 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 says.
HOW IT WORKS
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, Winter says, leaving fresher water at the center of the flow. 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 says. 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 in January.
While this approach was initially conceived for village-scale, self-contained systems, Winter says the same technology could also be useful for applications such as disaster relief, and for military use in remote locations.
Susan Amrose, a lecturer in civil and environmental engineering at the University of California at Berkeley who was not involved in this work, says, Amrose adds, “The water scarcity challenges facing India in the near future cannot be overstated. India has a huge population living on top of brackish water sources in regions that are water-scarce or about to become waterscarce. A solution with the potential to double recoverable water in an environment where water is becoming more precious by the day could have a huge impact.”
The study, by Natasha Wright and Amos Winter, appears in the journal Desalination.
Winter explains that finding optimal solutions to problems such as saline groundwater involves “detective work to understand the full set of constraints imposed by the market.” After weeks of field research in India, and reviews of various established technologies, he says, “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 milligrams per liter, 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 longterm 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 says.
HOW IT WORKS
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, Winter says, leaving fresher water at the center of the flow. 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 says. 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 in January.
While this approach was initially conceived for village-scale, self-contained systems, Winter says the same technology could also be useful for applications such as disaster relief, and for military use in remote locations.
Susan Amrose, a lecturer in civil and environmental engineering at the University of California at Berkeley who was not involved in this work, says, Amrose adds, “The water scarcity challenges facing India in the near future cannot be overstated. India has a huge population living on top of brackish water sources in regions that are water-scarce or about to become waterscarce. A solution with the potential to double recoverable water in an environment where water is becoming more precious by the day could have a huge impact.”
