Water at risk: toxins leaking through sewage treatment (TT)

Thousands of biofilter plants have been installed in cities around the world to treat surface water. Now Swedish researchers see a risk that the technology could fail, and that toxic PFAS could flow right through.

– This is a big risk for us and for the environment, says researcher Ali Beryani at Luleå University of Technology.

PhD student Ali Beryani, together with the construction company NCC and researchers at Ohio State University, has examined 20 so-called biofilters in the United States.

Biofilter treatment is a relatively cheap and easy way to treat surface water, and is based on the same principle worldwide. Rainwater is collected and allowed to flow through a biofilter, which can be made of sand, for example. Dirt and pollutants remain in the filter before the water eventually flows into waterways.

But scientists have not yet known how good biofilters are at collecting the persistent chemicals PFAS. The potentially toxic highly fluorinated and persistent substances come from everything from firefighting foam to clothing and cars, and can travel with rainwater.

Beryani and his colleagues found a lot of PFAS in the biofilter systems, but not just at the top, where most of the pollutants accumulate, but in all layers. The fact that the molecules follow the water through the filter layers probably means that some of them follow the water into waterways and the environment.

In particular, the use of PFASs should be reduced because they are so difficult to purify. And if biofilters are to do a better job of dealing with persistent chemicals, the thousands of existing plants may need to be adapted. It may also be necessary to add substances that are better at absorbing PFASs, such as activated carbon or iron, or to review the type of sand used.

– In the next study I’m working on, we’ll be looking at exactly how effective additions can affect pollution, says Beryani.

– The solutions will probably be different in different places, depending on the types of PFAS present.

– They should be targeted, because there is not one kind that magically works for all pollutants, because there are so many different ones in surface water, he says.

The study has been published in the scientific journal Enviroment Science & Technology.