Microfibres and Microfragments in Sewage Sludge

Abstract

Wastewater sludge contains high concentrations of microplastics (MPs), which may pose environmental risks when sludge is applied to agricultural soils. This review examines recent advances in the characterization and quantification of MPs in sewage sludge, with a particular focus on microfragments and microfibres. A total of 153 references were analyzed, 107 of which were published after 2020. The review highlights the lack of standardized methods, which limits data comparability among sludge. Microfragments and microfibres are the predominant MP morphologies in sewage sludge, while polyethene and polypropylene are the most frequently detected polymers. Sludge matrices require pre-treatment to remove organic matter, and the most used method is peroxidation. Density separation is widely used to isolate MPs, although it may leave particles uncharacterized in residual solids. Finally, the most commonly used techniques for identifying MPs are FTIR and Raman spectroscopy. This review also considers emergent artificial intelligence-based technologies that deliver reliable results with reduced analysis time compared to traditional techniques.