Sustainable water softening with calcite

Dutch tap water is softened by water suppliers to protect your pipes and household appliances. Onno Kramer, water technologist at Waternet: "We did that with garnet sand. This was shipped in large ships from Australia to the Netherlands. Australian garnet sand has the ideal grain size, and lots of flats where calcium can stick to. But it is obviously a waste to have sand come from the other side of the world, contaminate it with calcium here and then throw it in the rubbish.

Onno: "I wondered: can we also soften water with something other than Australian garnet sand? I was thinking of grains of calcite. If we grind it just fine enough, will calcium in water stick to it as well as to garnet sand?" But experimenting with people's drinking water isn't easily done of course. Because an experiment can have unexpected outcomes. So Onno knocked on the door of the Chemical Engineering laboratory at the HU University of Applied Sciences Utrecht: "Can we make a setup at your place that works - in miniature - the same as Waternet's water softening process? And can we look for a more sustainable solution together?"

It proved a great success: not only do calcite grains work as well as garnet sand and are more durable, they are also much cheaper. Onno: "As the calcium in the water sticks to the calcite grains, you get bigger and bigger grains. When they get too big, we take them out of the water and have them ground up. Some of the new, small grains we use again for water softening. And some of it we don't need ourselves. We sell calcite that we have left over to the Calcite Factory, which supplies it to carpet manufacturers, for example, who use it to make a fire-resistant coating on carpets. Or to cosmetics brands, who use it in scrubs. That way, the process no longer costs us money, but actually yields benefits. Sustainably extracted calcite is in high demand. By producing this, we also help producers make more sustainable products. Thus, we have gone from polluter to calcite supplier."

"Innovative projects with partners like Waternet are very important to us," says researcher and lecturer Michiel van der Stelt. "We - as a knowledge institute - are ourselves looking for answers to sustainability questions. We translate that knowledge into education: together with Waternet, for example, we developed the Water Technology course. In addition, the assignments help our students gain hands-on practical experience. This experience will help students deal with innovation issues in their future jobs. And innovative professionals are badly needed."

Waternet's water softening process is now fully circular. Other processes, such as filtering, can still be improved. Will water treatment plants ever be fully circular? Yes, we are convinced of that. And together with these companies, we are committed to this in the coming years.

• Waternet

• Chemical Engineering Degree Programme (NL)

• The Innovation Lab Life Sciences & Chemistry