Fishing phosphate out of wastewater

Developing materials that can extract phosphate from wastewater is Louis de Smet’s mission for the next five years. The associate professor from the Laboratory for Organic Chemistry starts a research programme this month for which he has received an important European grant, the ERC Consolidator Grant.
Didi de Vries

Photo: Herman Kempers

Phosphate is an important nutrient for agriculture. ‘There are only a few phosphate mines in the world and those reserves are finite,’ says De Smet. Salvaging phosphate from wastewater is a good way of boosting the supplies. That is now mainly done with chemicals which cause phosphate precipitation. But because of the chemicals and the impure composition, the precipitate is not always suited for use in agriculture. De Smet wants to extract phosphate from wastewater with specially developed polymers which let some nutrients through and not others. The researcher is going to equip polymers with receptors which recognize specific nutrients. ‘See it as like tongs. If you adapt the shape of the tongs to a specific ion you can get the ions out of the wastewater through bonding.’ To this end de Smet adds the polymers to a porous electrode as an ultrathin layer. If a positively and a negatively charged electrode are placed in wastewater, positively charge ions bond with the negative electrode and the negative ions with the positive electrode. ‘The tongs will ensure that only the ion you want bonds with the electrode. Then you take the electrodes with bonded ions out of the wastewater and put them in clean water. If you reverse the electric field, the electrodes reject the ions and you get a solution containing only the nutrients you want.’

But this stage has not been reached yet. De Smet will be studying the polymers in the laboratory in the coming years. ‘Phosphate is the most complex ion we want to extract from wastewater. We are starting with relatively straightforward ions such as sodium and potassium. We’ll build up from there.’

De Smet will be supported by four PhD researchers. The first one started this week.

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