University of Oulu

Asamoah, B.O.; Salmi, P.; Räty, J.; Ryymin, K.; Talvitie, J.; Karjalainen, A.K.; Kukkonen, J.V.K.; Roussey, M.; Peiponen, K.-E. Optical Monitoring of Microplastics Filtrated from Wastewater Sludge and Suspended in Ethanol. Polymers 2021, 13, 871.

Optical monitoring of microplastics filtrated from wastewater sludge and suspended in ethanol

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Author: Asamoah, Benjamin O.1; Salmi, Pauliina2; Räty, Jukka3;
Organizations: 1Department of Physics and Mathematics, University of Eastern Finland, P.O. Box 111, FI-80101 Joensuu, Finland
2Faculty of Information Technology, University of Jyväskylä, Mattilanniemi 2 (Agora building), P.O. Box 35, FI-40014 Jyväskylä, Finland
3Unit of Measurement Technology, MITY, University of Oulu, Technology Park, P.O.BOX 127, FI-87400 Kajaani, Finland
4Department of Biological and Environmental Science, University of Jyväskylä, Survontie 9C (YAC Building), P.O. Box 35, FI-40014 Jyväskylä, Finland
5Marine Management, Finnish Environment Institute (SYKE), Latokartanonkaari 11, FI-00790 Helsinki, Finland
6Department of Environmental and Biological Science, University of Eastern Finland, Kuopio Campus, P.O. Box 1627, FI-79211 Kuopio, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 1.4 MB)
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Language: English
Published: Multidisciplinary Digital Publishing Institute, 2021
Publish Date: 2021-05-18


The abundance of microplastics (MPs) in the atmosphere, on land, and especially in water bodies is well acknowledged. In this study, we establish an optical method based on three different techniques, namely, specular reflection to probe the medium, transmission spectroscopy measurements for the detection and identification, and a speckle pattern for monitoring the sedimentation of MPs filtrated from wastewater sludge and suspended in ethanol. We used first Raman measurements to estimate the presence and types of different MPs in wastewater sludge samples. We also used microscopy to identify the shapes of the main MPs. This allowed us to create a teaching set of samples to be characterized with our optical method. With the developed method, we clearly show that MPs from common plastics, such as polypropylene (PP), polyethylene terephthalate (PET), polystyrene (PS), and polyethylene (PE), are present in wastewater sludge and can be identified. Additionally, the results also indicate that the density of the plastics, which influences the sedimentation, is an essential parameter to consider in optical detection of microplastics in complex natural environments. All of the methods are in good agreement, thus validating the optics-based solution.

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Series: Polymers
ISSN: 2073-4360
ISSN-E: 2073-4360
ISSN-L: 2073-4360
Volume: 13
Issue: 6
Article number: 871
DOI: 10.3390/polym13060871
Type of Publication: A1 Journal article – refereed
Field of Science: 116 Chemical sciences
1172 Environmental sciences
215 Chemical engineering
Funding: The work is part of the Academy of Finland Flagship Programme, Photonics Research and Innovation (PREIN), decision 320166.
Copyright information: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (