Treatment plants cannot completely keep microplastics out of wastewater by conventional means. This is one of the results of a pilot study commissioned by the regional water association of Oldenburg and Ostfriesland, Germany (OOWV – Oldenburg-Ostfriesischer Wasserverband) and the Lower Saxony Water Management, Coastal Defence and Nature Conservation Agency (NLWKN - Niedersächsischer Landesbetrieb für Wasserwirtschaft, Küsten- und Naturschutz). The findings will be used to better protect flora and fauna in rivers and seas.
All plastic particles smaller than five millimetres are designated as microparticles. Microplastics have been included in the European Marine Strategy Framework Directive (MSFD) as an indicator of the status of marine waters.
Experts at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) examined wastewater and sewage sludge from twelve treatment plants in the region covered by the OOWV water board. “The study provides valuable findings about plastic residues that no one has obtained thus far. By applying state-of-the-art methods, it is now possible to specifically classify plastics, such as those used in toothpaste, cosmetics, fleece jackets and packaging, even in wastewater. For this reason the study is also relevant for legislators, manufacturers and industry,” explains OOWV Managing Director Karsten Specht.
To be able to detect and classify particles in wastewater as well as in sewage sludge, the researchers from the Alfred Wegener Institute employed micro-FTIR and ATR-FTIR spectroscopy. This involves using infrared radiation to set molecular bonds into oscillation. Depending on the method, the scientists press questionable particles onto a crystal for more detailed classification or place them on an aluminium oxide filter in order then to analyse them under a microscope. Through these methods it is possible to identify the plastics without a doubt and reliably differentiate them from natural materials.
However, whether the majority of the microplastic particles found can actually be traced back to cosmetic products, for example, or whether they stem from abrasion of items of daily use, cannot be determined at the present time,” says microbiologist Dr. Gunnar Gerdts, who analysed the samples at the Alfred Wegener Institute on Helgoland. “The results are surprising for us. The occurrence of microplastic particles varies considerably. There is an urgent need for further studies to enable comparability. And this not only applies to the wastewater of treatment facilities, but also in rivers that receive the wastewater. Currently there are neither valid findings on the pollution of German rivers with microplastics nor data on whether diffuse or rather point sources like treatment plants contribute to such pollution,” states Gerdts.
Almut Kottwitz, Permanent Secretary in the Lower Saxony Ministry of the Environment, Energy and Climate Protection, welcomes the pilot study: “Plastics have been in use in diverse form for over 60 years. However, no one has ever questioned what risks that entails. We now need a nationwide study on the input of microplastics into the food chain. The federal government has to provide the necessary research funds for that.”
Ute Schlautmann, the responsible department head at NLWKN explains: “The project enables us to take a big step forward in an issue that is important for the marine environment. From the water investigations in recent years we know about the pollution of rivers and coastal waters with plastic particles. Through this project we obtain for the first time concrete data on treatment plants as a possible input pathway. The results show that microplastics can be retained in treatment plants, but evidently not completely.” More far-reaching measurements are necessary, she adds, to be able to make more precise statements than was previously the case and obtain more exact quantitative estimates.
OOWV Department Manager Andreas Körner emphasises that additional studies are also necessary to determine further measures suitable for minimising the input of plastic particles into rivers and seas. “According to the study, we collect the majority of the microplastic particles by means of tertiary filtration, as we apply it in Oldenburg. Though this is a promising approach, the input of microparticles has to be avoided much earlier, i.e. during the production process,” explains Körner.
The drinking water system of five water works belonging to OOWV was also subjected to special scrutiny. AWI examined water samples from the production wells, the drinking water at the water works outlet and the drinking water in the water main as well as at the end consumer. The result showed no microplastic particles in the groundwater. And the number of particles per cubic metre in the drinking water was extremely low, i.e. a maximum of seven. In all likelihood, according to the scientists, the microplastics stem from abrasion of a seal or pipe. “This is substantiated by the outstanding quality of our drinking water,” says Managing Director Karsten Specht.