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España, Technology for Life.

España, Technology for Life is a campaign to showcase Spanish tech businesses and sectors.

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Renewables

Desalination in Spain

Desalination in Spain

Environmental Challenges

When countries or municipalities propose new desalination plants, concerns about the environmental effects often arise in terms of energy consumption and the disposal of the residual brine. For every liter of water taken from the sea, less than half becomes desalted. The remaining brine has about twice the salinity of seawater and is usually returned to the sea.

"The brine could be a problem in theory, but it usually isn't," says Medina. "You have to study how resistant the marine life is to different levels of salinity, and you have to study the conditions of the sea in that area."

The effects of the brine on the surrounding flora and fauna in the sea depend on the specific marine life in the disposal area. The usual response is to pipe the outflow far enough from sensitive species that the water quickly disperses into the surroundings. This is carefully considered in all plans for new plants, and despite extensive research, there has not been a documented case of serious deleterious effect resulting from the disposal of brine.

At the same time, companies are aware of the need to mitigate the effect of brine on the surrounding seabed. Before the development of a plant begins, careful studies are done on the sensitivity of the local marine life. Various techniques to diffuse the brine may be employed. At times, desalination plants are built close to power plants, as is the case with the Carboneras plant. The brine from Carboneras is mixed with the cooling water of   the thermal power plant, diluting the brine to a percentage closer to that of the original seawater. Another option is to build a plant close to a wastewater treatment plant; many coastal treatment plants dispose of the residual freshwater directly into the sea, and the two may be mixed together.

"Many people think that desalination has sort of bad impact on the environment. This is exactly the contrary," says Corrado Sommariva, president of the European Desalination Society and divisional director of Mott Macdonald. "Because for instance one of the reasons for selecting desalination in Spain and in Australia was the preservation of some of the existing natural resources which would have been basically depleted if water transmission was implemented instead."

One of the main challenges that remains with the desalination process is the cost of the energy required to produce freshwater. Though different processes demand varying amounts of energy (desalting seawater with membranes requires the most, as it takes tremendous pressure to push the water through the membrane), it remains an issue in terms of cost and environmental issues, as nations around the world battle rising greenhouse gas emissions, such as those emitted by power stations.

In the last 30 years, the amount of energy required for desalination has fallen precipitously, and along with it the price. Decades ago it took approximately 12 kilowatt-hours of energy to produce one cubic meter of freshwater using RO technology; today it takes on average between 3 and 4 kilowatt-hours of energy. Even today, however, the cost of that energy makes up about 40 percent of the total cost to produce each cubic meter of water.

"We reached a technological maximum in the equipment performance. Any reduction in energy consumption" should come through improvements in the membranes and in how the system is configured, says Antonio Ordoñez, desalination technical director for Inima. "The way to reduce energy consumption is to reduce the pressure needed to separate salt from water".

Developments in new kinds of membranes or other tweaks in plant efficiency could help engineers continue to shave off small amounts of energy, reducing both the cost and the environmental impact.  

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