Sewage sludge, a byproduct of municipal wastewater treatment, has long been considered a valuable resource in agriculture, due to the rich nutrient content. When properly processed, it can be utilized as a fertilizer. However, sewage sludge also contains a lot of microplastics, which is a concerning issue.
Microplastics are small plastic particles less than 5 millimeters in size. They can originate from larger plastic items that break down over time or from plastic particles that are directly manufactured to be in this small size, for example in cosmetics. Microplastics are persistent in the environment and can be toxic due to the chemicals they release or absorb.
When sewage sludge is used on land, it can carry microplastics into the environment. This poses significant risks to ecosystems. Understanding microplastics in sewage sludge is essential for assessing their potential risks and setting regulations. However, studying microplastics in sewage sludge presents uncertainties.
In her dissertation, Maria Clara Lessa Belone investigated the uncertainties arising from the presence of sewage sludge during microplastic identification and from the possible degradation that polymers may undergo in sewage sludge before microplastic identification.
According to her, the presence of organic and inorganic matter of sewage sludge and the possible degradation of polymers before the analysis phase can make it incredibly difficult to distinguish microplastics from other particles. For example, polyamide, a widely used polymer in textile products, can be easily mistaken for organic material, such as nail, when analyzed using Raman spectroscopy. This technique is a common analytical technique used in microplastics research.
“Moreover, identifying rubber particles, which originate, for example, from car tires, have proven to be very challenging using the same technique. Current identification methods are often not comprehensive enough to handle the complex nature of sludge and microplastics. This creates gaps in our understanding of the true extent of microplastic contamination in sewage sludge”, she adds.
Maria Clara Lessa Belone is from Belo Horizonte, Brazil. She has completed her master’s degree at Tampere University where she has been working in Plastics and Elastomer Technology research group since October 2017.
Public defence on Thursday 19 June
The doctoral dissertation of MSc (Tech) Maria Clara Lessa Belone in the field of Materials Science titled Uncertainties in the Laboratory Analysis of Microplastics in Sewage Sludge: Insights into the Physicochemical Properties of Polymers and the Use of Raman Spectroscopy will be publicly examined at the Faculty of Engineering and Natural Sciences at Tampere University 12 o´clock on Thursday 19 June 2025 at Hervanta Campus, Festia, auditorium Pieni sali 1 (Korkeakoulunkatu 8, Tampere).
The Opponents will be Doctor Sebastian Primpke from Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Germany, and Docent Juliana Aristéia de Lima from RISE Research Institutes of Sweden. The Custos will be Professor Essi Sarlin from Faculty of Engineering and Natural Sciences at Tampere University.