text Albert Sikkema photos Guy AckermansA proportion of the medication people take disappears down the toilet via their urine and faeces. The compounds get into the sewage and end up in the surface waters, where they create a problem, says Alette Langenhoff, who is leading the research on this issue within the Environmental Technology group. The medicine residues pose little threat to the health of humans — the concentrations in the drinking water are too low — but they do harm the environment. For example, oestrogen from contraceptive pills makes some fish change sex. And Indian vultures suffered kidney failure after they had fed on dead cows that had been treated with the painkiller diclofenac.
Manganese
That is why it is important to remove drug residues from wastewater. Water boards in particular are interested in technologies that enable this (see inset). Environmental Technology has 12 PhD candidates who are researching promising methods with funding from WUR, water boards, engineering consultancies, drinking-water companies, the research funding organization NWO and the European Union. Three of these students completed their PhD research in the past six months. Langenhoff explains their findings.
PhD candidate Wenbo Liu initially wanted to use bacteria to break down residual diclofenac in wastewater, but the results were disappointing. One plus point was that the control test that included manganese worked better than expected. Manganese ions with a positive charge (Mn4+) reacted with the diclofenac to produce harmless compounds. At the same time, the Mn4+ was reduced to Mn2+. Liu then investigated whether he could oxidize the manganese compounds back to Mn4+ with the help of bacteria, so as to create a circular purification system. Liu is now working on this as a postdoc in China. ‘It looks promising but it’s not yet an application,’ is Langenhoff’s assessment.
Marsh tubs
The second PhD candidate, Yujie He, built a lab model of a marsh system with aquatic plants and sediment. She then fed it with water containing a mix of seven medicine residues. Afterwards, she examined the biological processes in the artificial marsh. She discovered that UV breaks the medicine residues into smaller fragments. The medicine residues and breakdown products are then taken up by the aquatic plants, where enzymes convert them into harmless compounds. Meanwhile, bacteria in the water and sediment do the same with the drug residues that are still floating around freely.
The marsh system works, but it is still a black box, concludes Langenhoff. A new PhD candidate, Yu Lei, will now be testing marsh tubs with different plants and sediments to see precisely which plants and bacteria do the job. She hopes this will let her optimize the removal of medicine remains. The Vallei en Veluwe water board, one of the organizations funding the research, is supplying water from its purification plant for the tests on Wageningen campus. Langenhoff believes such a ‘constructed wetland’ would be suitable for the post-purification of water from a purification plant. ‘Such wetland systems already exist, for example for fixing nitrogen and phosphate, but we want to use them for medicine residues too.’
Our mash system works, but it is still al black box
Three-phase purification
The third PhD candidate, Arnoud de Wilt, tested a combination of biological and physical chemistry methods. First he used a biological reactor to filter organic waste from the wastewater. Then he used ozone to destroy the structure of the drug residues, followed by a third phase in which bacteria were used to break down the resulting fragments.
This project is also getting a follow-up. The financer Haskoning DHV, which has since taken De Wilt on as an employee, sees a future in it; the company wants to develop the process further and scale it up for practical application. The new WUR PhD candidate Koen van Gijn will now be examining how much ozone is needed, how fast the wastewater can be sent through the three-phase purification and how he can optimize the biological reactors.
Innovations
Langenhoff has spent the past six years on removing drug residues from water. This topic is unusual, she says, in that companies took the lead in funding the research and the government is now following. She expects the first effective and affordable systems for medicine decontamination to be on the market in five to ten years. And until then? ‘There are installations that can capture a lot of medicine residues using ozone and activated charcoal but they are expensive and inefficient. If we had to immediately convert all water purification plants to use these systems to prevent any medicine residues ending up in the surface water, the general public would have to foot the bill. That’s why our clients want innovation.’