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A research team from Graz University of Technology, TU Wien and the Environment Agency Austria has developed a practical method to reliably determine microplastics in the inflow and outflow of wastewater treatment plants, and has demonstrated their high elimination performance.
The danger of microplastics for the environment and health has become increasingly recognised in recent years. They enter the water cycle via wastewater from households and rainwater discharged from impervious surfaces. Wastewater treatment plants are of particular importance here. A team led by Günter Gruber from the Institute of Urban Water Management and Landscape Water Engineering at Graz University of Technology (TU Graz) and Helmut Rechberger from the Institute of Water Quality and Resource Management at TU Wien, together with the Environment Agency Austria, have now been able to prove that wastewater treatment plants retain over 95 per cent of determinable microplastics. Together, the researchers have developed a standardised and practical method for determining microplastics in the inflow and outflow of wastewater treatment plants.
Sample-taking as a potential source of error
“There are now many studies on microplastics with a wide range of findings and results,” says Helmut Rechberger from TU Wien. “However, as there is still no standardised method for overall analysis, the results are difficult to compare. With the analysis methodology we have developed, comparable results can now be achieved.”
As part of the investigations, which were mainly carried out with the support of the City of Graz’s wastewater treatment plant, the TU Graz team dedicated itself to the difficult task of representative sampling and collection of solid samples. This process is considered one of the greatest potential sources of error, as microplastic particles vary greatly in size, density and behaviour in water. As a result, they are distributed very inhomogeneously in the wastewater flow; some particles float on the surface, others drift along the bottom and the rest are somewhere in between. For a representative measurement, large-volume 24-hour composite samples – 100 litres in the inlet and 1000 litres in the outlet – were required, which take into account the varying flowrates of wastewater produced over the course of the day.
Turbulence sought
In order to ensure good mixing, the team specifically sought out turbulent areas in the Graz wastewater treatment plant and took samples there over a period of 28 days, which they collected in stainless steel containers to avoid additional contamination. In preliminary tests, the research group also determined the ideal suction point, as the sample cannot be taken over the entire discharge depth. The researchers then validated this approach with further investigations at the Wiener Neustadt wastewater treatment plant.
The TU Wien team mainly dealt with the separation of solids, sample preparation and the implementation of one of the two analytical methods used to determine microplastics. A disc filter system was developed for this purpose, by which the sequential filtration (first with a mesh size of 20 µm, then 10 µm) of microplastic particles of large sample volumes enabled solid samples to be obtained. The Environment Agency Austria contributed a second method of analysis that can be used to determine not only the mass, but also the type of plastics and their concentrations.
High share of tyre abrasion
“It was exciting for us to see that plastic particles from tyre abrasion in particular were very prevalent in the inflow to the wastewater treatment plant,” says Günter Gruber. “The good news, however, is that our measurements have shown that wastewater treatment plants are a wonderful sink for microplastics. The mandatory thermal utilisation of sewage sludge from sewage treatment plants with a capacity of more than 20,000 population equivalents in Austria from 2033 will then make it practically harmless.”
This project was funded by the Federal Ministry of Agriculture, Forestry, Climate and Environmental Protection, Regions and Water Management (BMLUK) with a sum of 442,830 euros.
Contact at TU Graz:
Günter GRUBER
Ass.-Prof. Dipl.-Ing. Dr.techn.
TU Graz | Institute of Urban Water Management and Landscape Water Engineering
Phone: +43 316 873 8373
guenter.gruber@tugraz.at
Contact at TU Wien:
Helmut RECHBERGER
Univ.-Prof. Dipl.-Ing. Dr.techn. Dr.h.c.
TU Wien | Institute of Water Quality and Resource Management
Research Unit of Waste and Resource Management
Phone: +43 1 58801 22645
helmut.rechberger@tuwien.ac.at
https://www.bmluk.gv.at/themen/wasser/wasserqualitaet/abwasserreinigung/gebema.h... Further information on the project and the final project report (in German)
The samples were collected in stainless steel containers.
Source: Cajetan Beutle
Copyright: Beutle - TU Graz
The filters enabled solid samples to be collected.
Source: Günter Gruber
Copyright: Gruber - TU Graz
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