Plastic popcorn: how microplastics can be caught in wastewater

Microplastics are everywhere. In the water, in the earth, in the air. Opinions differ on its harmfulness. However, it is accepted that microplastics have to come out of the environment again. One way to get your hands on microplastics before they enter the environment is through sewage treatment plants.

A non-profit green tech start-up from Karlsruhe called Water 3.0 has developed hybrid silica gels that use a physicochemical process to bind microplastic particles to their surface. They form fluffy clumps that look like popcorn. Hybrid silica gel acts as an adhesive on plastic particles. This microplastic popcorn floats on the surface of the water and can be easily fished with a sieve or sucked from the surface.

The longer the silica gel has to act, the larger the lumps will be. Researchers from Karlsruhe adapt the formulations of the hybrid silica gels to the respective wastewater. It should also be possible to bind other types of pollutants to silica gels and thus remove residues of drugs, pesticides or perfluorinated and polyfluorinated chemicals from the water.

Water 3.0.

A study by the “International Union for the Conservation of Nature” (IUCN) shows that there is theoretically a lot to be done for hybrid silica gels in wastewater treatment plants: about 35% of microplastics in the seas come from of our washing machines, so to speak. With each wash, the comfortable fleece sweater, running jersey and all other plastic laundry items lose fine fibers that the sewage dumps into the sewage treatment plant. There, up to 99% of the microplastics are filtered out in the first three stages of clarification – the rest, however, flow into the oceans. Some of the particles captured are also released into the environment: sewage sludge is still used as agricultural fertilizer. Phosphate enriched with sewage sludge is an essential but rare nutrient for cultivated plants.

For the WHO, she appreciates the dangers of microplastics in drinking water as low for humans. However, the European Commission concludes that the dangers posed by microplastics are very complex. For example, invisible microplastic particles bind poorly degradable environmental pollutants such as pesticides particularly well. Sea creatures ingest pollutant collectors and thus carry toxins into the food chain. However, there are no limit values ​​for microplastics in water yet.

With fine-pored membranes, galvanic deposition and coagulation processes – for example using ultrasound – microplastics could already be almost completely removed from the wastewater. However, wastewater treatment plants are expected to be widely converted for all of these processes. They are also greedy in energy and maintenance. With Wasser 3.0 technology, only a small amount of the hybrid silica gel solution needs to be added to the water to be purified. About 50 milliliters of hybrid silica gel slurry is sufficient for a 2000 liter test reactor.

The Wasser Method 3.0 has been tested in a long-term pilot test since the summer of this year. For twelve months, the Landau clean their municipal wastewater in a fourth purification stage with hybrid silica gels. The Wasser 3.0 team is already going further: it also considers its process as an option for cleaning industrial wastewater, rivers, lakes or the open sea.

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