A1 Journal article (refereed)
Particle balance and return loops for microplastics in a tertiary-level wastewater treatment plant (2021)

Salmi, P., Ryymin, K., Karjalainen, A. K., Mikola, A., Uurasjärvi, E., & Talvitie, J. (2021). Particle balance and return loops for microplastics in a tertiary-level wastewater treatment plant. Water Science and Technology, 84(1), 89-100. https://doi.org/10.2166/wst.2021.209

JYU authors or editors

Publication details

All authors or editors: Salmi, Pauliina; Ryymin, Kalle; Karjalainen, Anna K.; Mikola, Anna; Uurasjärvi, Emilia; Talvitie, Julia

Journal or series: Water Science and Technology

ISSN: 0273-1223

eISSN: 1996-9732

Publication year: 2021

Publication date: 31/05/2021

Volume: 84

Issue number: 1

Pages range: 89-100

Publisher: IWA Publishing

Publication country: United Kingdom

Publication language: English

DOI: https://doi.org/10.2166/wst.2021.209

Research data link: http://urn.fi/URN:NBN:fi:jyu-202009035741

Publication open access: Openly available

Publication channel open access: Open Access channel

Publication is parallel published (JYX): https://jyx.jyu.fi/handle/123456789/76137


Microplastics (MPs) from households, stormwater, and various industries are transported to wastewater treatment plants (WWTPs), where a high proportion of them are captured before discharging their residuals to watersheds. Although recent studies have indicated that the removed MPs are mainly retained in wastewater sludge, sludge treatment processes have gained less attention in MP research than water streams at primary, secondary, and tertiary treatments. In this study, we sampled twelve different process steps in a tertiary-level municipal WWTP in central Finland. Our results showed that, compared to the plant influent load, three times more MPs circulated via reject water from the sludge centrifugation back to the beginning of the treatment process. Especially fibrous MPs were abundant in the dewatered sludge, whereas fragment-like MPs were observed in an aqueous stream. We concluded that, compared to the tertiary effluent, sludge treatment is the major exit route for MPs into the environment, but sludge treatment is also a return loop to the beginning of the process. Our sampling campaign also demonstrated that WWTPs with varying hydraulic conditions (such as the one studied here) benefit from disc filter–based tertiary treatments in MP removal.

Keywords: water purification; waste water treatment; micro-litter; sewage sludge; sewage treatment plants

Free keywords: enzymatic purification; microplastics; reject water; return loop; wastewater sludge

Contributing organizations

Related research datasets

Ministry reporting: Yes

Reporting Year: 2021

JUFO rating: 1

Last updated on 2022-20-09 at 15:22