“Water, water everywhere, but not a drop to drink”. The line made famous by poet Samuel Taylor Coleridge provides a good description of the world’s water supply situation.
And his words have perhaps never been more relevant than today.
Around 70 percent of our planet’s surface is covered by sea water. Estimates vary, but the oceans contain about 1.5 quintillion (1,500,000,000,000,000,000) tons of the life-giving liquid – and there’s a lot more circulating in the air, in the ground and in our bodies. So you might imagine that providing sufficient water for the world’s population to survive and prosper isn’t much of a challenge.
The problem is, however, that some 98 percent of the planet’s water is salty. And of the remaining fresh water, only a relatively small proportion is readily available to use as drinking water or to supply other consumer, production or agricultural needs (lakes and rivers, for example, contain only around 0.035 percent of the planet's total water supply). To make matters worse, the pressures of climate change, population growth and increasing affluence are placing a heavy, growing burden on fresh water supplies.
More and more, therefore, the world’s local authorities, and industrial or agricultural producers are turning to sea water as a source. But going from salty to fresh water isn’t quite that easy.
Desalination in focus
Desalination is the process of producing drinking water and service water from seawater. It’s a process that doesn’t vary much around the world: Sea water is pumped from coastal inlet pipes, processed under high pressure through filters, then pumped onward, typically to reservoirs dotted around the landscape.
Torben Harlev Mai is an Application Manager at Denmark-based pump system manufacturer DESMI. DESMI provides industrial pumps for a wide variety of applications including desalination, with different models and capacities for water purification systems or reverse osmosis (RO) treatment. With more than 100 years in the field, DESMI centrifugal pumps have carved out a reputation around the world for high reliability, low maintenance costs and low NPSH (net positive suction head) values.
The powerful DESMI DSL double suction pump, for example, is ideally suited to seawater intake – and the company has a full range of pumps for brine, recirculation, backwash and transfer.
“It’s absolutely crucial to use highly efficient pumps at each stage of the desalination process,” says Torben. “That’s because it is very expensive to make water in this way. By comparison, pumping up and purifying groundwater uses around 2.7kWh of electricity per cubic meter. But for desalination, it’s 5 to 6 kWh – or double the energy consumption. And that’s not good for operating costs or for the environment.”.
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