SINGAPORE — In the aftermath of earthquakes and tsunamis, one of the most desperate needs for survivors is often to have access to clean drinking water.
Desalination plants have long been essential to providing fresh water in places where natural supplies are lacking. Traditionally, two methods have been used to remove salt from water: thermal distillation, in which salt water is boiled and the purified vapor is collected; and membrane processes, like reverse osmosis and electrodialysis, in which water is forced through a semi-permeable membrane that acts as a microscopic strainer to filter out the salt crystals and other impurities.
More than 60 percent of all desalination plants worldwide use a membrane process, which typically consumes less energy than thermal distillation. Still, reverse-osmosis in particular remains very energy-intensive and usually requires huge plants to be economical.
Now, a Singapore company, memsys clearwater says it has developed a better technology that could revolutionize the economics of desalination. Called vacuum multieffect membrane distillation, it uses a relatively new process that combines thermal and membrane technologies, working in a vacuum so that the water boils at a much lower temperatures of 50 to 80 degrees Celsius (122 to 176 Fahrenheit) instead of the usual 100 degrees Celsius. It also comes in small, modular units suitable for use in disaster zones and remote communities.
In membrane distillation, steam from boiled seawater passes though a one-way permeable membrane, to be condensed on a cold surface and collected. The main advantage of membrane technology over reverse osmosis is that it does not require high pressure, said Adrian Yeo Piah Song, a researcher at the Nanyang Technological University in Singapore. Reverse osmosis needs large pumps and heavy-duty piping operating at high pressure. The supporting infrastructure makes it hard to install outside developed countries.
The new technology enhances efficiency by putting water through a cascade of membrane distillation processes working at progressively lower temperatures and pressures, recovering energy at each step to power the next.
“We have the first modular thermal separation process,” Götz Lange, managing director of memsys, said during an interview. “We didn’t change the thermal technology itself — you can’t change physics — we are just the first to put this advanced technology of thermal separation into a very tiny, cheap and reliable modular concept.”
After seven years of development, a small demonstration unit, powered by solar energy for extra sustainability, was installed last year at Marina Barrage, a dam completed in 2008 across the mouth of Marina Bay that has converted what is left of the old Singapore harbor after massive land reclamation, into a freshwater reservoir.
The demonstration unit has been designed for disaster relief. Able to fit in a 20-foot, or 6-meter, shipping container, it is completely mobile and runs on solar power so that it can operate without external infrastructure support. It can produce 1,000 liters, or 265 gallons, of fresh water a day. A key advantage of the technology is that it can use waste heat or solar-thermal energy to boil the water, Mr. Lange said.
“So far,” said Godart van Gendt, head of international distribution at memsys, “we already have 25 companies who have bought the technologies and are now doing research to apply the technology for their own purpose. They’re buying our unit and then they’re doing their research.
Customers include International Business Machines, which has been working for several years on ways to reduce overheating problems associated with concentrated photovoltaic systems. Those use mirrors or lenses to convert sunlight into electricity more efficiently than conventional flat panels. I.B.M. has developed a system that allows the heat to be recycled, and it is using memsys technology in a desalination project powered by waste heat from a concentrated photovoltaic generator.
“We have here two very nice-fitting technologies,” Mr. Lange said. “Concentrated photovoltaic is not quite ready yet, but when it is, it will be an absolutely brilliant fit with our technology. It will make effective use of the cooling energy for desalination and thereby make even better use of the solar energy.”
In Gran Canaria, one of the Canary Islands, memsys has supplied the core technology for a joint project with the Spanish water company Agbar, running on a mix of solar-thermal and grid-supplied power.
In Australia, a joint program with the National Center for Excellence in Desalination is planned to test the memsys technology on cleaning brackish groundwater at Tjuntjunjarra, in a remote corner of the state of Western Australia. The water there contains nitrates that exceed recommended levels for infants and pregnant woman. The tests will be part of a two-year research program using solar thermal and waste heat as energy sources.
Neil Palmer, the national center’s chief executive, said the technology seemed promising. Still, he cautioned, “there have not been enough trials of membrane distillation to make a call that it is cheaper than reverse osmosis, even if the energy for heating is free.”
He also said there were some concerns about “the potential high unit cost and the robustness of the technology for remote operation. That’s why we are doing the trial.”
Mr. Lange, the memsys managing director, said one advantage of his company’s process was that it could operate with the very high salt concentrations often found in saline groundwater, which technologies like reverse osmosis handle with difficulty. “You can treat such waters with special treatment methods but not on a small scale without being too expensive,” he said.
“ I don’t think we’re going into direct competition with reverse osmosis,” he said. “We solve problems where reverse osmosis comes to its limits. This will not replace reverse osmosis.”
“Whenever you have an easy environment and low salinity, reverse osmosis is, price-wise, very hard for us to compete with, at least for the next four to five years,” he added.
Investment costs for a reverse osmosis plant are about €700 to €2,000 per cubic meter of daily production capacity, or $3.75 to $10.75 a gallon. That is about half the present cost of the memsys technology, he said. Still, as it moves to commercial scale, Mr. Lange said, the costs will come down.
The technology potentially has wider applications beyond desalination, he said. At the Singapore Membrane Technology Center, memsys is studying modifications that would adapt it to treatment of water contaminated with oil, as in the Gulf of Mexico disaster last year.
