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Research Zernike (ZIAM) Macromolecular Chemistry and New Polymeric Materials Loos Group

First PhD defence on Frisian campus: Extracting nutrients from the sewer

29 March 2016
Sewage treatment plant. Photo: Nationale Beeldbank

Potassium and ammonium are both vital nutrients in agriculture. As they are excreted through urine, waste water is an interesting source of these nutrients. During a joint PhD project at Wetsus and the University of Groningen, Anna Casadellà created a membrane that can be used to isolate potassium and ammonium from diluted urine. She will defend her thesis on 1 April 2016 in Leeuwarden, the first PhD defence at the University of Groningen/Campus Fryslân.

Fertilizers are important for agriculture, but fertilizer run-off can cause problems, such as algae bloom, in canals and lakes. Furthermore, some ingredients in fertilizer, like potassium and ammonium, are not always available. Therefore, a means to extract them at a water treatment facility would be a win-win solution. At Wetsus, the European centre of excellence for sustainable water technology, PhD student Anna Casadellà, a chemist interested in water technology, has worked to make this possible.


‘I have tested several approaches to selectively remove potassium and ammonium from waste water’, she explains. Finding substances that will bind these ions wasn’t the main problem. ‘There are several known products, but these are used only in a liquid phase.’ But that won’t work in a water treatment facility. ‘You need a membrane (with or without pores) that is selective for potassium and ammonium.’

Lots of cells have such selective membranes, but Casadellà had to make an artificial version. She set up a special synthetic lab at Wetsus, and worked closely with her PhD supervisor Katja Loos, professor of Polymer Chemistry at the University of Groningen.

Cheap zeolite

Casadellà studied the transport of the two nutrients and tested several options. In the end, a zeolite called clinoptilolite turned out to be the best option. ‘Mixed with polymer, it forms a membrane that can actually remove 60 percent of the potassium and 80 percent of the ammonium from diluted urine.’ As the zeolite is very cheap, these membranes could very well be a feasible option for water treatment plants. ‘My work is a proof of principle’, says Casadellà. ‘Implementation is the next step.’

Network organization

Casadellá’s PhD defence will be the first at the University of Groningen/Campus Fryslân. The Dean, Prof. Jouke de Vries, explains that many more will follow: ‘In 2011, 20 PhD students started their projects. All of them work at a Frisian knowledge institute with supervision from a Dutch university.’ A second round of projects was initiated in 2013, and a year later another 15 ‘Frisian’ PhD students started their projects. Several Dutch universities participated in the programmes initiated by what was then called University Campus Fryslân, a network organization of universities and several knowledge institutions in Fryslân.

University of Groningen/Campus Friesland’

‘But to move this Campus forward, we needed a university that would permanently associate itself withus’, says De Vries. Eventually, the University of Groningen stepped in. With funding from the province of Friesland, the municipality of Leeuwarden and the University of Groningen, the ‘University of Groningen/Campus Friesland’ officially started on 1 January of this year.

Historic Oranjezaal

‘The PhD defence will be in the historic Oranjezaal in Leeuwarden’s city hall, the seat of the municipal council. We hope that other PhD students from the programme will also defend their theses in Leeuwarden.’ It does require some organization: ‘Bringing the professors and the beadle from Groningen to Leeuwarden, for example.’ The PhD defence marks a return of university life to Friesland, which ended when the University of Franeker was closed in 1843. ‘The beadle’s staff from Franeker will be presented by the Mayor of that town. It is too fragile to use, but we plan to make a replica for use on our Campus.’


Anna Casadellà, who is from Spain, enjoyed her time in Friesland. ‘I am from Catalonia, which has a similar position in Spain as Friesland in The Netherlands’, she says with a broad smile. And she even understands quite a bit of Frisian. ‘The lab technicians often talked to me in Frisian.’ But otherwise, the Wetsus lab is a very international affair, she says. ‘It has been a great place to work.’

Anna Casadellà

Anna Casadellà studied Chemistry at the University of Girona and gained a Master’s in Water Science and Technology from the same university. After an internship at Wetsus, she was offered a PhD position there. Her thesis is titled: Ion-selective membranes for the recovery of ammonium and potassium . Her promotor is prof.dr. K.U. (Katja) Loos , department Macromolecular Chemistry & New Polymeric Materials of the University of Groningen. After defending her thesis, she will work for a short time as a volunteer with an NGO in the Dominican Republic, teaching water technology and hygiene. After this break, she wants to find work in this field.

Last modified:03 June 2021 11.18 a.m.
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