“Recovering materials from feces and urine is our only hope.”

Human urine and feces are full of valuable substances such as phosphorus, nitrogen, carbon and minerals. “You can recover all this material,” says Annemieke ter Heine, who recently gave her inaugural lecture as professor of environmental technology at Wageningen University and Research. “But in practice this rarely happens. While we want to move towards a circular economy that focuses entirely on reuse.”

Ter Heijne develops technologies to recover materials from wastewater from households and industry. According to her, the fact that this rarely happens at all is partly due to infrastructure. Human feces now go through the sewer system to the wastewater treatment plant (WWTP). “Along the way, the concentration of all these materials becomes very dilute, in part because rainwater is often added. This makes recovery from wastewater treatment plants difficult. It is more efficient to do it closer to the source.”

Collect feces and urine from homes and offices?

“There have been a few initiatives for this purpose in the last ten or twenty years. For example, to collect feces and urine separately in neighbourhoods. Or to install vacuum toilets. But at the moment it remains limited to pilot projects. While residents with a vacuum toilet there Mostly positive about it We are. The barrier is not there. At the same time, I also see that building urine-fecal separation toilets or vacuum toilets in homes would require a completely different infrastructure than the sewers we have now. You can install them in new construction areas, but it is more difficult in existing buildings.

Ter Heine explains that until now, wastewater from households and industry has been largely purified using bacteria. For example, bacteria eat nitrogen and minerals, and then these substances largely disappear from the water. Bacteria settle in the sludge. The sludge is fermented in a separate facility, a process in which biogas is created. “This way you can generate energy from sludge,” says Ter Heine. The remaining sludge is then dried and incinerated. “Very low quality application,” says Ter Heijne.

Her predecessors have made important contributions to this joint purification process. “Gatzi Litinga laid the foundation for anaerobic purification, which is bacteria that extract all kinds of substances from wastewater in the absence of oxygen. This is now being used everywhere. The process of desulfurization of industrial waste streams using microorganisms has also been developed here.

Why are so few raw materials extracted from wastewater?

“Because you are dealing with these very dilute flows. But also because I think our society lacks vision around these kinds of solutions. There are many pilot projects, for example to recover phosphorus that is increasingly scarce, but it usually stays there. Building and testing new devices Restoring materials costs a lot of money and effort and causes teething problems. Money is limited. Ultimately, I think those who determine the strategy have different priorities.

How do you try to recover raw materials?

“We have a range of technologies available. They can be biological, chemical and physical, and we often make a combination of them. For example, in the case of physical separation, membranes are used to filter out certain substances. You can also use microorganisms, which are biological.

Before becoming a professor, you mainly worked on material recovery via bacteria, in combination with electrodes. Can you explain how that works?

“It arose from the idea of ​​extracting electricity from wastewater. In conventional wastewater treatment, oxygen is blown into tanks. Microorganisms transfer their electrons to oxygen, which turns into water. The transfer of these electrons provides microorganisms with energy that they can use, for example, to digest food. What we did was not supply oxygen, but an electrode, like in a battery. In this case it was the anode that absorbed the electrons. By combining the anode and cathode, we were able to generate electricity. I'm still amazed by this: that microorganisms eat our wastewater and produce electrons, which we can then use to generate electricity.

What about that technology?

“In our test setup, it worked like a charm. But as a whole the system was expensive. Wastewater treatment plants now have solar panels that efficiently and inexpensively generate electricity to power aeration, for example. In this case, the technology has not Which we have any difference. But we are also working on other purification processes with the same concept, which are microorganisms with electrodes. For example, you can use it to recover nitrogen from wastewater. And mercaptans, which are very smelly substances that are released during biofuel production .

Will material recovery become more popular?

“It's our only hope! Many materials will become rarer. Look at phosphorus. Or copper. Both are already on the European list of vital raw materials.

Will your techniques help with this?

“Technology alone is not enough. I can find it exciting, fun and valuable, but what matters is that it is put into practice. You need connection for that. With policy makers, businesses and the community.”

Last year a major project was launched to stimulate recovery. With parties from science, government and business. The barriers mentioned are many: regulations, cooperation, costs, knowledge.

“Something needs to be done in many areas at the same time. Then in the Netherlands we also want good education, good healthcare, defence, the eradication of poverty, and we have to address climate change. Someone needs to stand up and think about all these problems as a whole. This is a lot “I know. I'm looking too.”

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