For some reason, it has become a popular assumption that water desalination consumes a great deal of energy, and is therefore problematic. Scientific analysis shows that this is not the case, and that the energy cost of desalination is not high.
Professor Rafi Semiat, director of the Grand Water Research Institute at the Technion Institute of Technology and an expert in desalination processes, has shown that the amount of energy now required for desalination is fairly low, and approaches the theoretical boundaries defined by the laws of thermodynamics.
Most of the energy in the desalination process based on reverse osmosis is required to generate high water pressure so that clean water will pass through the membranes (that extract heavy metals, nitrates, and other substances that are problematic in drinking water), while the salt concentrate is separated off. The desalinated water emerges at high pressure from the membranes, and companies in the filed have developed improvements that translate this pressure into energy that is fed back into the process, reducing the level of energy required for desalination.
A cubic meter of seawater can currently be desalinated at an energy cost of 2.2 kilowatt-hours. To that must be added the energy required to pump the seawater and the concentrate, so that in total the required energy is 3.7 kilowatt-hours per cubic meter. To put this in perspective, an electric bar heater on for an hour consumes 2 kilowatt hours, as do a washing machine and an air conditioner. A refrigerator operating for an hour consumes about 0.15 kilowatt-hours.
Another way of illustrating the amount of energy required for desalination is to compare with total family energy consumption. Professor Semiat makes this comparison in an article that appeared in the journal "Environmental Science and Technology". According to Semiat, if an average family used only desalinated water, its energy consumption would rise by just 3%.
This is a very encouraging figure in the light of the urgent need to save water and energy. For a family and for the country, it's a great deal easier to save on energy than on water.
A further comparison that needs to be made is with the cost of the alternative that is, the amount of energy we invest today in the water we consume. The energy required to pump water from Lake Kinneret from 210 meters below sea level to sea level is about 1.3 kilowatt-hours per cubic meter, and transporting a cubic meter of water 300 kilometers takes an amount of energy similar to that required for desalination. The geography of our country means that even using water from Lake Kinneret requires energy, and there are no free lunches.
To sum up, it is important that decision makers should have the true figures. The energy cost of desalination is not high in relation to the alternative and to domestic energy consumption.
The writer is an entrepreneur in cleantech and a marketing and business development consultant.
Published by Globes [online], Israel business news - www.globes.co.il - on July 9, 2009
© Copyright of Globes Publisher Itonut (1983) Ltd. 2009