Comparison of methodologies for microfiber analysis across different stages of wastewater from a textile dyeing company

Microfibers (MFs) — fibrous particles <5 mm in length, including both synthetic and natural fibers — from the textile industry pose growing environmental challenges, particularly through wastewater generated during production. This study presents a comprehensive comparison of analytical methodologies for detecting and characterizing MFs and MPs across four significant wastewater stages — underground water, inflow, outflow, and sludge — from an Italian textile dyeing factory. The novelty of this work lies in its integrated evaluation of sample-specific pretreatment strategies (no treatment, quick oxidative, and prolonged oxidative), filtration materials (stainless steel, aluminum oxide, and mixed cellulose ester membranes), and the use of two distinct micro-FTIR spectroscopy systems from different laboratories. This multifaceted approach enabled the identification of optimal workflows tailored to sample organic content and matrix complexity. Results showed that quick oxidative treatment is ideal for rapid processing, while prolonged treatment offers a more sustainable option. Single-step filtration proved to be the most practical and effective. The comparative micro-FTIR analysis revealed that polymer identification depends strongly on filter compatibility and instrument configuration. Inflow samples exhibited the highest MF concentration (825 MFs/L), and the wastewater treatment plant (WWTP) achieved a partial removal efficiency of 36.97%. The most common MF types were polyester, and cellulose-based materials (e.g., cotton, rayon and lyocell) with a notable presence of transparent and blue-fluorescent microfibers linked to fluorescent whitening agents. These findings not only highlight the variability of MFs and MPs pollution across wastewater stages but also provide a standardized analytical framework for environmental monitoring and regulatory assessment of microfiber emissions from industrial textile operations.