New desalination process can save energy, cut costs

Audrey Tan, The Straits Times AsiaOne 28 Nov 15;

The sea may surround Singapore but the costly process of turning seawater into potable water has been a major obstacle in purifying it for daily use.

But a new technology developed by American company Evoqua, with funding from Singapore's water agency PUB and the Economic Development Board, is paving the way for a more cost-effective desalination process.

The discovery - from a three- year pilot project started in 2010 at the PUB Variable Salinity Plant in Pasir Ris - uses half the amount of electricity required by conventional seawater reverse osmosis.

As a result, PUB told The Straits Times that it will roll out the Evoqua technology at its Tuas Water Reclamation Plant next year, with the capability to produce up to one million gallons of water a day.

PUB also hopes to further reduce the amount of energy needed for the process to just 1.5kWh for every cubic m of desalinated water.

The existing requirement using Evoqua technology is about 1.65kWh to 1.8kWh of electricity.

But with the conventional reverse osmosis method, 3.5kWh of electrical energy is usually needed.

The desalination process in reverse osmosis essentially involves pumping filtered seawater through a membrane with tiny pores under high pressure, to remove dissolved ions such as sodium, chlorine, calcium and sulphates.

On average, the concentration of these ions in seawater is about 3.5 per cent.

The goal is to reduce it to a level that meets drinking-water standards.

With the Evoqua technology, the ions are removed by a process known as electrochemical desalination.

These ions, which carry either a positive or negative charge, are eliminated from the water when they are attracted to electrodes of the opposite charge.

As a result, there is no need to pump the seawater through the tiny pores of a membrane under high pressure, thus saving on energy.

This energy-efficient method makes desalination a more viable and sustainable alternative for water- scarce Singapore.

Currently, Singapore uses 400 million gallons of water a day. The demand could almost double by 2060.

Up to one-quarter of the present demand is met by desalinated seawater. PUB hopes desalination can continue to supply the same proportion even in the long term when demand goes up.

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