Ten years after Doris van Halem’s graduation, the ceramic pot filter has become a major hygiene intervention tool. The system is of a brilliant simplicity: a ceramic pot with tiny holes filters larger micro-organisms, such as bacteria, from the water. The pots are now manufactured in factories around the world, using local materials. The only drawback is that viruses, which account for various water-borne diseases, such as hepatitis, are not removed. But fortunately Van Halem discovered something else as well all those years ago.

The surprise finding

It happened as she was doing research for her graduation project with ceramic filters from Ghana, Cambodia and Nicaragua. The ceramic pots always contain a small amount of silver solution and Van Halem decided to compare  a number of filters, both with and without silver. “Silver has a magical image. It’s used in all sorts of products as a disinfectant., but we don’t know if that is actually true for viruses. I decided to get to the bottom of the mystery. And I found something very interesting.

The filters that had been in use for some time and had not been treated with silver, showed biofilm growth: organic material and bacteria that had adhered to the inside of the filter and had proliferated there. After a couple of months it turned out these filters were removing more viruses.” In TU Delft Waterlab Van Halem tried to test her surprise finding but it was winter and temperatures were too low. The trial didn’t work out. She decided to shelve her discovery until such time as it could be developed further. Thanks to a TU Delft Global Research Fellowship that time has come.

Tremendous impact

Van Halem has dedicated ten years of her life to helping developing countries through science and that makes her one of TU Delft Global’s more experienced project leaders. “I think I attach more importance to the relevance of my work than the average researcher. With globally oriented research one can make a big difference. Some academics look down a little on this type of work because the tropics are not an easy place to do top level research.

But once you understand the challenges – such as the more extreme conditions on the ground – you realise what a tremendous impact your work can have. And we have much to teach others along the way because Delft University is one of the leading centres of expertise when it comes to water purification."

Some advice

What would she say to people who are just starting out in the field? “All too often people think that once you have the right technology that’s it: problem solved. But it’s not just a matter of technology. Other factors come into play, such as changes in temperature or humidity and the fact that you can’t assume that the electricity supply will work 24 hours a day. It is vital to take the context and conditions on the ground into account early on and include that analysis in your research programme. It’s the kind of useful information which will save you from finding out what the effect of heat is, for example, two years after you have finished the programme.”


Published: November 2018


Elvin Karana, Ger Koper, Gertjan Medema and Katie Camille Friedma

Ceramic filters will be produced at local factories (Nicaragua)