• Illustration: Christine Daniloff/MIT

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  • This map shows the salinity levels of the groundwater underlying India. Although the salinity levels found in most of this water is much lower than that of seawater and has little immediate effects on health, they can have long-term impact. The salinity can make the taste of the water so unpleasant that people will often opt to use surface water instead, even if surface water has more serious pathogens or toxins. Anything more than 480 milligrams of salt per liter (everywhere but the pictured light-blue areas) is considered objectionable in taste by most.

    This map shows the salinity levels of the groundwater underlying India. Although the salinity levels found in most of this water is much lower than that of seawater and has little immediate effects on health, they can have long-term impact. The salinity can make the taste of the water so unpleasant that people will often opt to use surface water instead, even if surface water has more serious pathogens or toxins. Anything more than 480 milligrams of salt per liter (everywhere but the pictured light-blue areas) is considered objectionable in taste by most.

    Courtesy of the researchers

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Sun-powered desalination for villages in India

Off-grid Indian communities with salty groundwater could get potable water through a proposed solar technique.

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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.

Now an analysis by MIT 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 MIT graduate student Natasha Wright and Amos Winter, the Robert N. Noyce Career Development Assistant Professor of Mechanical Engineering, 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. (For on-grid locations, the team found, reverse-osmosis plants can be economically viable.)

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 says.

Expanding access to safe water

By pairing village-scale electrodialysis systems — a bit smaller than the industrial-scale units typically produced today — with a simple set of solar panels and a battery system to store the produced energy, Wright and Winter concluded, 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. 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 says after consulting with nongovernmental organizations that work in the area, she 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.

Most organizations working to improve clean-water access focus their attention on controlling known pathogens and toxins such as arsenic, Wright says. 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 says.

At the salinity levels seen in India’s groundwater, the researchers found, an electrodialysis system can provide fresh water for about half the energy required by a reverse-osmosis system. That means the solar panels and battery storage system can be half as big, more than offsetting the higher initial cost of the electrodialysis system itself.

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 percent, compared with about 40 to 60 percent 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, “This paper raises the bar for the level and type of scientific rigor applied to the complex, nuanced, and extremely important problems of development engineering. … Solar-ED isn’t a new technology, but it is novel to suggest developing it for systems in rural India, and even more novel to provide this level of detailed engineering and economic analysis to back up the suggestion.”

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 water-scarce. 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 research was funded by Jain Irrigation Systems, an Indian company that builds and installs solar-power systems, and sponsored by the Tata Center for Technology and Design at MIT.

Topics: Research, Desalination, Solar, Water, Development, Mechanical engineering, India, School of Engineering


Wow..this is great..hope this technology launches soon in India..

How can I keep track of this project's progress?

I would appreciate contact info for the principal authors of this study. I got my start in the solar business over 30 years ago at MIT Lincoln Lab. I pioneered development of solar/ED technology. I am now actively involved in commercializing (financing) water supply projects in India. I believe that solar/ED is a viable approach for brackish water. I am very interested in connecting with the authors. Thank you

very great as early could serve Indian nation for remote villages

Interesting technology.
Dr.A.Jagadeesh Nellore(AP),India

Why the batteries? The advantage of solar desal over just solar power is the end product (water) itself provides an elegant and free storage. Does the additional cost of the batteries + additional panels to charge them + round-trip losses creates the most cost-effective solution? Why not just run the E.D. unit when the sun shines and store up water in a tank?

How much electricity would be required to desal per unit of water, say how much Watts per litre of output water fit for drinking ?

I am very keen to contribute to integration of Solar ED, particularly Solar PV integration. We at Sol2Sys provide complete systems solutions for Solar PV applications in India. Can I get contact details for the stakeholders at MIT?

While any study leading to wider use of solar power is welcome, readers should not be under the impression that this is the first time that solar ED has been considered for villages in India. Perhaps the MIT researchers are not aware that the Ministry of New and Renewable Energy (MNRE) of the Government of India had supported work in this area many yeas ago. I write with personal knowledge because I was heading the Indian solar energy programme in the Ministry for several years.

Firstly, we funded a large experimental solar powered ED unit (along with an RO unit as well) in a village in North Delhi. The project was implemented by the Delhi Energy Development Agency. About 14-15 years ago, we encouraged the Rajasthan Electronics and Instruments Ltd. (A photovoltaic module manufacturer) to design a PV system to power a small ED unit developed by a defense lab in Jodhpur, Rajasthan. We funded a pilot project to install 100 units in the villages of Rajasthan, a state known for its arid climate and scarce water resources. The project was completed but could not be expanded into a larger programme because the cost-effectiveness of this technology could not be established at that time (vis-a-vis other options such as solar stills) and also because REIL could not get a reliable vendor for the small ED systems.

The prices of PV modules have come down significantly in recent years, and it is possible that solar powered ED systems will turn out to be a good option for rural communities. If Wright and Winter are planning to "put together a working prototype for field evaluations", they may want to first contact REIL in Jaipur to learn from their experience.

-- Dr.E.V.R.Sastry
Former Adviser & Head. Solar Energy Group
Ministry of New and Renewable Energy, India

hi! I am a farmer & read this article in Agroone daily..i am to fed up with hard water in my farm , I have dutch roses in poly house & my water TDS is 1600ppm around.. I was thinking of RO unit , but as it costs in Lacks I was not able to purchase it. as soon as read the solar ED in news paper. I feel glad and just waiting for its launch in India.
Can anybody tell me how it works, or how much water the system will filter per hour. and what all system will cost as per hour liter capacity. as it will be working on solar , its great as we do have Light problems.

Great research with some great potential for parts of rural India, with potable water challenges. If you want to connect with Prof. Winter, his profile and contact info is in the "Related" panel to the right of the article above. This work may also have some great potential for smaller islands in the Caribbean, where climate change, rising sea levels, reduced and variable rainfall patterns could pose serious constraints to accessing potable water, both now and into the future.

Came up with this many years ago:
Might be of some use to some desalination crew somewhere.

Great Idea Please give the details

Its good indeed but i don't think this concept is needed now in india as reverse osmosis concept and some other researcher has given basic idea regarding this.

1: Just the solar panels would make it much cheaper for the Indian villages. The
coverage of people provided with drinking water would reduce to about 1/3 the
stated Nos of 2 K-5 K; These Nos would still more than No of people in
several Indian villages. With solar panel electrolysis process there may be
no need of RO.

2: Kindly provide details of design output power and approx cost
of the solar power panel and associated supply
system to cover the stated 2 K to 5 K persons. . Recent retail price of just
the Solar power panels in India ( Pune ) was of order of Rs 90 per Watt output
i.e. about US $ 1.5 per output watt.

3: Has MIT tried electrolysis of sea water? Kindly share the results of sea water desalination by electrolysis and analysis of the desalinated sea water. The analysis of
separated materials would help my comparison with local sample analysis results..

4: Has MIT tried using electrolytic process for cleaning polluted river water also? Can MIT share its outcome. This is one of the important current global and Indian needs. The expected river pollution could be both of chemical and bio origin .

How does this project address the issue of re-mineralization? It is a known problem that desalination can remove too much mineral content and actually make the water too sterile for farm use for instance.

What are the pressure and flow requirement of the desal system? I am referring to the feed water to the membrane(s). What kind of pump, motor, and membranes are being used?

Who do I contact to assist in commercializing this technology in Africa?

is this readily available cos i need a 300/400 lit per day

where can I buy this system

Utilising Sunlight and UV in the Sunlight,I have designed a cost effective Solar Disinfection system for Developing countries:


Dr.A.Jagadeesh Nellore(AP),India

Rural India is facing huge problem of salty water. MIT should work with Ministry of Panchayati Raj a Central Ministry of Govt. of India which conduct Capacity Building & Training Programme for Elected Representatives of Panchayats (Rural Local Bodies). It will provide plethora of information to researchers to solve the drinking water problems of rural areas.

In Gaza strip all water extracted from the aquifer is a saline water of TDS >4000 ppm.
This system can be applied to support farmers and vulnerable communities with frish water for all uses.
Is it possible to have further support and details of the proposed system in order to be adapted locally?

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