Finding the right mix of minerals for purified water

Singapore is ramping up its desalination programme so that it can get even more fresh water from the sea.

This year, it opened its second desalination plant at Tuas, and desalinated sea water can now meet up to a quarter of the nation’s water needs.

After the salt and minerals are taken out of the sea water, however, it becomes very pure 

This super-pure water can leach minerals from metal water pipes, so minerals must be added before the water goes into the distribution networks - just enough to prevent damage to the pipes, but not so much that mineral deposits form in them.

Researchers are figuring out what minerals to add, how much and at what concentrations would be best for the pipes.

Currently, Singapore adds some calcium to its desalinated water and Newater to prevent pipe damage. In some countries, minerals such as calcium and magnesium are also added to drinking water for health reasons such as to keep bones strong 

Associate Professor Hu Jiangyong, deputy head of research at the National University of Singapore’s civil and environmental engineering department, together with colleagues and collaborators from national water agency PUB, compared various concentrations of calcium and magnesium in the water, based on what is added to desalinated water around the world.

They found that using calcium and magnesium together was better at preventing corrosion than calcium alone. But the exact ratio and amount need to be studied further, Prof Hu said.

The team also looked at three types of pipes - ductile iron and cast iron, which older distribution pipes are made of - and newer cement-lined ductile iron pipes.

They found cement-lined pipes were better at staving off corrosion than the older metal pipes.

Now they want to more closely simulate real-life conditions in tests, using segments of pipeline rather than just pieces of pipe wall, said Prof Hu.

“We hope to better understand the technical details and provide more technical information to the authorities,” she said.

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