Sewage Derived Microplastic and Anthropogenic Fibre Retention by Integrated Constructed Wetlands

Abstract

AbstractHigh loads of microplastics and anthropogenic fibres can be discharged from wastewater treatment plants (WWTPs) into surface water bodies. Integrated Constructed Wetlands (ICWs) are potentially well suited to provide a cost-effective mitigation solution at small WWTPs where conventional treatment is prohibitively expensive. This study aimed to assess the microplastic and anthropogenic fibre retention efficiency of two ICWs (Northrepps and Ingoldisthorpe) in Norfolk (UK) over a 12-month period (2022–2023). Analysing a total of 54 water and 23 sediment samples, the findings revealed that Northrepps ICW received on average 349,920 (± 763,776) anthropogenic fibres day−1, with a retention rate of 99.3%. No seasonal variation was observed in retention efficiency. Ingoldisthorpe ICW intermittently received anthropogenic fibres in low concentrations, with an average of 9504 (± 19,872) day−1 and a retention rate of 100%. Microplastics and anthropogenic fibres were prevalent in sediment samples of the first cell of Northrepps ICW, averaging 10,090 items kg−1 dry sediment, while none were found at concentrations above the limit of detection in the second or third cell. Of the 369 fibres analysed by ATR-FTIR, 55% were plastic (dominated by polyester). Of the 140 suspected microplastic fragments analysed by ATR-FTIR, 73% were confidently identified as plastic (mostly polystyrene, polyethylene, or polypropylene). This study demonstrates how ICWs can effectively retain sewage effluent derived microplastics and anthropogenic fibres. However, the accumulation of plastic waste in ICWs may complicate long term management and their cost-effectiveness.