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The quest for a greener approach to desalinating water

Current methods for treating salt water to make it drinkable are energy-intensive, require harsh chemicals and produce waste – but new technologies that reduce the environmental impact of desalination are in the pipeline.


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As the world’s population continues to grow, the demand for fresh water is reaching unprecedented highs. One of the most popular ways to make fresh water is to desalinate the water that comes from the oceans covering 71 per cent of the Earth’s surface, but it is also possible to remove salt from brackish water in lakes, estuaries and industrial waste streams.

To meet the skyrocketing demand for fresh water, the desalination industry is growing rapidly: 6 million cubic metres per day of new desalination capacity came online in 2013, compared with just 4 million the year before, according to the International Desalination Association (IDA).  All told, the world is now producing more than 80 million cubic metres of desalinated water every day.

With that increased production comes rising concerns about the environmental impact. Desalination is an energy-intensive process that consumes electricity and heat, requires harsh chemicals, and produces waste in the form of brine, a highly-concentrated salty liquid that is often dumped back into oceans and streams, endangering wildlife. And when salt water is removed from the sea, fish and their eggs can end up as collateral damage, causing some environmentalists to worry about the impact of desalination plants on the natural food supply.

 

Good business case

Companies around the world are inventing new desalination technologies that could greatly reduce the impact on the environment. Many start-ups in this area have gained the support of giants such as General Electric, not to mention venture capitalists that are on the lookout for green investments. In the eight years ending in 2012, over $382 million was raised in venture money by 37 companies, to fund new desalination technologies, according the newsletter Global Water Intelligence.

“Reducing the environmental impact usually translates into a good business case,” says Helge Daebel, investment director for water at Emerald Technology Ventures in Zurich. “If you’re more energy efficient, which is good for the environment, it means that the operational expenditures [for desalination] are much lower. If you lessen your use of chemicals, the same can be said. We are continuously searching for opportunities there.”

There are two main techniques used to desalinate water, and both could benefit from green technologies. One is a thermal process that involves boiling salt water and then distilling fresh water by cooling the steam that is generated.

Another widely used method, reverse osmosis, uses semi-permeable membranes to separate the salt and other minerals from the water. This process of reverse osmosis is used to produce 60 percent of the world’s desalinated water, while thermal methods account for most of the rest, according to the IDA.

A number of companies are working on improving the membranes used in reverse osmosis, both to make the process more efficient and to reduce reliance on the chemicals that are used to clean them. UK-based Genesys International, for example, is developing several methods for reducing fouling that occurs when iron, aluminum and other minerals build-up on desalination membranes. The company’s latest innovation, Genairclean, uses tiny effervescent bubbles to agitate the scale build-up, making it easier to remove.

Cutting the use of chemicals

Ursula Annunziata, sales director at Genesys and vice president of the European Desalination Society, says about 20 desalination plants are now pilot testing Genairclean. Some report it reduces the amount of time required to clean the membranes and have cut back on the amount of chemicals used to combat fouling.

“One plant has gone down from cleaning every seven days to cleaning every six weeks,” Annunziata says. “And they could spread it out even longer.” Genairclean has won three awards for innovation in Europe since November.

Some companies are taking a hybrid approach, using membranes to improve thermal desalination processes. Since its formation in 2009, the US company Oasys Water, has raised $35 million in venture capital to develop a technology invented at Yale University. This is designed to produce fresh water from the waste water generated by oil and gas production - which can be up to five times as saline as sea water.

Oasys’s system filters the water through a membrane that traps the salt. It then heats the filtered water and transforms the resulting vapour into fresh water. But unlike traditional thermal desalination, the water does not need to reach boiling point, nor does it have to be run through high-pressure systems.

That cuts down on energy costs. “At a very low temperature, we can change the draw solution from a liquid to a vapour,” says Lisa Sorgini Marchewka, vice president of strategy and marketing for Oasys. “As compared to traditional desalination evaporators, we can use as much as 50 to 60 per cent less energy.” Oasys has been marketing its system since 2013 and has since installed it at desalination plants in Texas and China.

Resisting corrosion

Memsys, which has offices in Singapore and Germany, is also working on a hybrid thermal-membrane technology. The system uses hydrophobic membranes to separate vapour from salts, minerals, bacteria and viruses. It is also built in a modular fashion, with lightweight polymer-based materials that resist corrosion. And because it runs on low heat, it is so energy efficient it can be powered with diesel generators, waste heat from power plants, or solar heat, says Götz Lange, managing partner of Memsys. “That makes it suitable and economical for off-grid remote locations,” Lange says.

Lange estimates that traditional, large-scale reverse osmosis desalination plants require 3.5 kilowatt hours of energy per cubic metre of treated water. “For smaller systems that can go up to 7 or 8 kilowatt hours per cubic metre,” he says.  Thermal plants use about 1 or 2 kilowatt hours per cubic metre but they require ready access to heat sources.

GE is currently running trials of Memsys’s technology on water produced by shale and coal seam gas producers. GE has reduced the total energy and operating costs by using Memsys’s process instead of traditional evaporation technology, Lange says.

GE is also looking for ways to reduce the amount of water that is rejected during the desalination process, says Nauman Rashid, a marketing director for GE Power & Water in Dubai. The membranes traditionally used for reverse osmosis processes involving sea water, for example, typically hold back more than half of the water that passes through them, resulting in salty waste that is often pumped back into the ocean. “Environmentally there’s a concern that over a long period of time it can start to increase the salinity of the sea,” which could have a negative impact on ocean life, Rashid says. “Any technology that can reduce the amount of water that is rejected would be very welcome.”

Dealing with brackish water

For inland desalination plants that simply want to conserve as much water as they can, while also cutting down on waste, GE has developed a technology called electrodialysis reversal. The system uses electrical plates to desalinate brackish water, achieving a water recovery rate of up to 85 percent, Rashid says.

Another big green push in desalination is to expand the use of renewable power sources, particularly solar energy. “The primary reason is to change the carbon footprint so to speak, because you substitute a renewable for the fossil fuel,” says Leon Awerbuch, past president of IDA. Because sunlight is not plentiful everywhere, solar technologies are most appropriate in places like the Middle East and the American Southwest. And like other renewable sources, such as wind power, solar is often coupled with electric power, so there’s a backup for days when the sun doesn’t shine, Awerbuch says.

Using renewable energy to desalinate water may be environmentally sound, but it’s far from free, and that can present challenges. Erecting solar panels requires a large amount of land and up-front costs that may be difficult for some municipalities to fund, says Tom Pankratz, an independent desalination consultant in Houston, Texas, and a former IDA director. “Desalination is an energy-agnostic process - it doesn’t care where the electrons come from - but there’s a cost implication,” Pankratz says. “Renewables will increase the cost of desalination until they come down in price. There’s a lot of work going on to try to optimise this.”

Companies working in desalination are also pursuing other ways of greening the process. Some are developing entirely chemical-free methods. The Israeli firm IDE, for example, has developed Progreen, a reverse-osmosis “plant in a box,” which consists of modular pieces that desalination plant owners can assemble themselves, and that requires no chemicals.

Recyling brine   

As for reducing the impact on sea life, Pankratz says some new desalination operators are locating their plants far offshore, so they can draw sea water at the depths where fish are the least productive. And some companies are developing methods for recycling waste brine, by turning it into mineral-based products that can be used, for example, as industrial fillers.

Rashid says the demand for technologies that reduce the impact of desalination on the environment is rising around the world. In some countries, using less energy is about much more than being a good environmental steward and cutting the cost of desalination. “Any oil-exporting country that reduces its energy use isn’t just saving money, it’s saving fuel,” Rashid says. “That means it has more fuel to export. So anything we can do to reduce energy usage makes sense.”

On April 15, GE and Saudi Aramco launched the "ecomagination challenge" – a global competition to find innovative solutions that provide measurable and economically viable improvements to the process of seawater desalination.  Up to four $50,000 cash prizes will be awarded for the best ideas.  For more information: https://www.ninesights.com/community/ecomagination

Supported by GE.

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