Drops to drink

Singapore, a country with an extremely large amount of yearly rainfall, and a population of over 7000 people per square kilometer, is won of the most densely populated countries. Surprisingly though, water shortages have been plaguing the 5 million people living there. As we learned earlier in the summer, desalinization of water is a costly and slow process; however, the Singaporean government in collaboration with Siemens, a German engineering conglomerate have dedicated their time and money to making the process cheaper and efficient. Today, they claim to have created a method in Singapore which can "transform seawater into drinking water using less than half the energy required by the most efficient previous method." Most Ocean water starts out with around 3.5% salt and must be cut down to around 0.5% or less salt for human consumption. Usually the process of desalinization should take about 10 kilowatt-hours (kWh) of energy per cubic meter of seawater processed. This energy is used to heat the brine and partially evaporate the substance leaving you with newly condensed water vapor. Another process could use reverse osmosis, which utilizes special membrane to act as a sieve, passing on the water and filtering out the ions such as sodium chloride from the water. Reverse osmosis uses 4kWh per cubic meter of water to generate the pressure needed to maintain the sieve. The new system designed by Siemens only uses 1.8kWh per cubic meter and plans on lowering this energy even more to 1.5kWh. The process is called electrodialysis and works by utilizing a different membrane than reverse osmosis which actually passes the ions through membranes instead of water. Half pass positive ions and the other passes negatively charged ions. They alternate per channel so that when two electrodes flanking the system of each channel can pull the positively charged ions like in sodium and the other can pull the negatively charged ions like chloride. The result is a brine of sodium chloride which rises and is thrown away, while the water continues to go on to the same process a couple more times. By the end of the processes the water will have less than 1% salt concentration. This water is still not potable and must be employed an ion-exchange resin to lower the concentration to the drinkable amount of .5%. A full-scale plant in Singapore to produce water is being constructed now and will be finished in 2013.

http://www.economist.com/blogs/babbage/2011/07/desalination