Add salt as required: the recipe for fresh water

 作者:庞义     |      日期:2017-09-23 08:01:00
By Kate Ravilious Using desalination to slake the world’s thirst has been an uphill struggle, but now we’re learning to go with the flow STROLLING along Williamsons beach, a quiet strip of sand about 100 kilometres south-east of Melbourne, Australia, you would never guess that a monster lurks just behind the dunes. Nestled at the bottom of a 27-metre-deep pit is a 500-tonne mechanical giant that is about to begin burrowing under the beach and out to sea. In its wake the machine will leave a 4-metre-wide, 1.5-kilometre-long tunnel, the inlet for one of the world’s largest plants to turn seawater into drinking water. Australia is turning to desalination as fresh water in many parts of the country runs short following years of drought. It is not alone. Many countries are eyeing the oceans as a potential source of drinking water as populations grow and rainfall patterns change. Even the relatively rain-drenched UK now has its first large-scale desalination plant, opened earlier this year on the river Thames in east London. “Even the relatively rain-drenched UK has its first large-scale desalination plant, opened earlier this year on the river Thames in east London” Today’s desalination plants are unlikely to solve our looming water crisis, however. That’s because they have their own unquenchable thirst- for energy. It’s needed to drive reverse osmosis (RO), the process in which salty water is forced at high pressure through a membrane that lets water molecules through but blocks the salt. But now a number of researchers and start-up companies think they have a more energy-efficient alternative,