Slow sand filter removes 99.9% of nanoplastics from drinking water

— Cozine /

When it comes to providing safe drinking water, current filtration technologies do a great job, but the spread of plastic waste in the environment brings new threats. Researchers have designed a biologically active slow sand filter that eliminates almost all nanometer-sized plastic particles.

An invisible threat

In recent years, various studies have shown that microplastics (which measure less than 5 mm) accumulate everywhere, from the oceans to the highest reliefs in the world, including human organs. Notoriously difficult to spot due to their tiny size (just a few nanometers), their little brothers have been linked to stunted plant growth, abnormalities in shrimp and fish.

Scientists also consider plastic particles measuring between 1 nanometer and 20 micrometers to be respirable, while experiments in fruit flies have suggested they can alter the expression of genes associated with stress response and damage. oxidative.

While many questions remain about the effects of nanoplastics on our body, minimizing the risk of absorption is crucial. In the context of works published in the Journal of Hazardous Materialsresearchers from the Swiss Federal Institute for Water Development, Purification and Protection (Eawag) have studied different ways to remove these tiny particles from drinking water.

Three approaches to the test

Three approaches were tested: activated carbon filtration, ozonation (where ozone is injected into the water to treat and disinfect it) and slow sand filtration, involving a layer of gravel, sand and a biologically active layer on the surface, consisting of worms and bacteria. The latter form a biofilm which performs most of the decontamination.

Nanoplastics were tagged with the chemical element palladium and added to untreated water in considerable amounts, allowing their journey through these various processes to be tracked using a mass spectrometer. The team found that slow sand filtration proved to be by far the most effective, removing over 99.9% of the particles present.

Based on these results, the team says this filtration method would be effective at capturing high levels of nanoplastics for extended periods of time, noting that the top few centimeters of sand will occasionally need to be removed in order to prevent clogging of the biofilm.

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