Desalinate sea water using 50 percent less energy

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Instead of using reverse osmosis, which requires high-pressure pumps to force water through semi-permeable membranes, the Siemens engineers turned to electrochemical desalination. 

As a result of an R&D initiative that commenced in October 2008, a demonstration plant was built in Singapore to treat seawater to drinking water quality. The results show that the new process reduces desalting energy by over 50 percent compared to best available technology. The next step for Siemens is to set up a full-scale system in cooperation with Singapore's national water agency PUB by 2013.

However, to desalinate it for potable use is an extremely energy-intensive process. "Our new technology marks a revolution in seawater desalination," said Ruediger Knauf, Vice President of Siemens Water Technologies' Global R&D.

"The results of our pilot facility show that the new process not only functions in the laboratory but also on a larger scale in the field. Because of its high energy efficiency and thus good CO2 footprint, electrochemical seawater desalination can play a major role in regions suffering from freshwater shortages."

Since December 2010, the Siemens demonstration unit has been treating 50 m3 of seawater per day at a PUB facility in Singapore. The project goal was to produce World Health Organization standard drinking water quality from seawater, at the same time cutting energy consumption by half compared to current technologies.

Instead of using reverse osmosis, which requires high-pressure pumps to force water through semi-permeable membranes, the Siemens engineers turned to electrochemical desalination.

The process combines Electrodialysis (ED) and Continuous Electrodeionization (CEDI), both applying an electric field to draw sodium and chloride ions across ion exchange membranes and out of the water. As the water itself does not have to pass through the membranes, the process can be run at low pressure, and hence low power consumption.

The seawater is pre-treated with a self-cleaning disk filter, followed by Memcor ultrafiltration modules. The pilot desalination plant is composed of three ED units arranged in series to handle high concentrations of salt.

They are followed by three CEDI units assembled in a parallel flow configuration to remove smaller amounts of salt.

The energy demand of the whole process including pumping, pre-treatment, desalting, and post-treatment is less than half of what is used by the best available seawater desalination technologies today, which is typically between 3.4 to 4.8 kWh/m3.

Besides the energy savings, other advantages are low vibration and noise levels, improved safety, and only minimal pre- and post-treatment.

Setting up a pilot by 2013 is the next milestone in transitioning the electrochemical desalination technology to a viable product offering.