Interview – Removing ‘forever chemicals’ from drinking water

Is it safe to drink water from the tap in Europe?

In EU countries, the tap water is safe to drink. The taste might differ among countries because the sources of the water are different, but it is safe. For example, in Denmark, where we are based, there is groundwater that is easy to abstract and treat. The water contains a lot of calcium, which makes it hard for kettles and other appliances, but it is safe to drink.

In other parts of Europe, they might use water from rivers, lakes or even from the sea. If the water comes from the rivers, you need to treat it more intensively and disinfect it to clear the pathogens. That can affect the taste of the water (which might taste of chlorine), but it still means that the water is safe to drink.  

Dr Zongsu Wei

Associate Professor and group leader for the Water Engineering Innovation Lab at Aarhus University in Denmark

What is the biggest threat when it comes to drinking water?

The global challenges for drinking water are pathogens, or bacteria, which are bad for human health. This is the case, for example, in many African countries, which don't have the sanitation systems to remove pathogens.

In Europe, water is treated to remove the pathogens. But threats might come from antibiotics in the water – from human consumption or from the animal farms. These antibiotics are harmful to the environment and can lead to antimicrobial resistant infections.

Another important, emerging threat is the contamination with PFAS, especially when it comes to drinking water wells which are located close to fire stations or airports. PFAS can be found in the foam used for extinguishing fires, so they can contaminate the surface waters, groundwater, rivers and lakes which are close to where the foams have been used. For the residents living close to these hotspots, the water can be dangerous, as they are likely to be exposed to high levels of PFAS from it.

But PFAS can also be found in most of the water sources because they are used in a variety of products: in the kitchen, carpet coatings, sofa coatings, the coating of your clothes and the containers for take-away food. PFAS have even been detected in the rain, dust and soil.

Are these forever chemicals, as they are called, dangerous for people?

Yes. Research has shown that they are a health risk, causing thyroid disease, liver damage and even kidney cancer. This is especially damaging for unborn children exposed through the mother’s diet during pregnancy, causing developmental problems.

Since these substances accumulate in the environment and in organisms, we need to find ways to remove them.

Can PFAS be removed from water?      

There are two methods: removal and degradation. To remove PFAS from the water you can use a simple filter for the bottles, made out of carbon, for example. When you pour the water through the filter, the PFAS stay behind. The problem is that when these filters are discarded, if not done properly, PFAS can be released to the environment again.

That is why the preferred method for removing PFAS from water is degradation; the destruction of the molecules. This can be achieved by applying high temperature or high pressure, boiling the water (like in a steam pot) or by burning the substances. But these methods are very energy-intensive and not environmentally friendly.

What we are researching in our lab is how to destroy these molecules at ambient temperatures and pressures by using light, electricity or ultrasound.

Most of the methods can’t destroy the PFAS molecules completely and the result is toxic intermediates. This is the reason why in our lab, we try to develop technologies that can completely degrade or destruct the PFAS.

Can these methods be applied at a large scale?

We have proven so far that we can do it in the lab at small scale. Recently, we have started working with water utility companies, like Aarhus vand and HOFOR, trying to upscale the technology. We think that in 3 to 5 years we would be able to apply these methods in the real world, not only in the lab. There are many research groups looking at PFAS degradation, but we are confident in our methods and our technology.

Your research group is also looking at water sustainability more broadly. What can you tell us about that?

Alongside climate change, water sustainability is one of the biggest issues we have to face. We need water for our everyday life. Water is used not only in households, but also in industry and agriculture. It needs to be treated before it is reintroduced into the water cycle.

In low-income countries, a lot of the wastewater is sent directly into the rivers, for example. These are issues that need to be taken on not only at individual level, but at community level, country level and even international level.

Regarding the use of water for green energy: if you want to produce green hydrogen, you need a lot of ultra-pure water. It takes a lot of energy to clean groundwater, or water from the lake or sea. And there needs to be a lot of water. So, if you use the groundwater, there won't be enough water for people to drink. If you use sea water, it will take a lot more energy to purify it. First, you need to make sure people have enough water to drink. There are competing priorities when we look at producing green fuel, and it depends on the country’s situation and water resources.