Sludge-Optimized Mass Quantification and Pilot Removal of Microplastics via Magnetic Capture and Microwave-Fenton Oxidation

Wastewater treatment plants (WWTPs) are important sources of microplastics (MPs) released into the environment, particularly through sewage sludge applied as agricultural fertilizer. Growing concern over this pathway highlights the need for reliable detection, quantification, and removal methods to support effective regulation and management. This study presents the development and validation of an innovative and sustainable methodology for the mass quantification and removal of MPs in wastewater and sludge. The method combines selective magnetic capture, microwave-assisted Fenton oxidation, and gravimetric analysis, enabling accurate MP determination without complex instrumentation. Analytical validation showed high performance, with an average recovery of 97.6% ± 3.0% (n = 3) and excellent reproducibility. Detected MPs were mainly polyester fibers, and sewage sludge contained an average MP concentration of 0.37% ± 0.07% w/w, underscoring its potential as a significant source of environmental contamination. The system achieved MP removal efficiencies of up to 50%, substantially reducing their release into soils and aquatic ecosystems, where MPs can accumulate in surface waters and drinking water sources. Overall, this work provides a robust, accessible, and scalable tool for monitoring MPs in wastewater treatment systems and supports the scientific basis for future regulatory frameworks. • The study addresses the growing concern about microplastics (MPs) in the environment, especially in wastewater treatment plants (WWTPs), which have been identified as major sources of MPs entering rivers, soils, and oceans. MPs are particularly concentrated in sludge, which is often applied in agriculture, thereby transferring pollution to soils and potentially into the food chain. The research emphasizes the urgent need for accurate and reproducible quantification methods to properly regulate and manage MPs. • Different strategies for MP detection and quantification in sludge were evaluated, including flotation, surfactant extraction, and advanced technology combining filtration, magnetic extraction, and selective oxidation. While flotation and surfactants showed moderate efficiency, the advanced method achieved the most accurate results, recovering more than 100% of spiked MPs due to the presence of background contamination. This method proved robust and reliable, as it was not influenced by particle size, shape, or density. • The experimental application of the advanced method to actual sludge samples from a WWTP revealed a concentration of approximately 0.37–0.39% MPs by weight in dehydrated sludge, mainly composed of polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET). These findings are consistent with results from similar international studies and highlight the relevance of mass-based quantification over particle counting, which often yields less reliable data. • The research also tested a pilot plant capable of continuously quantifying and removing MPs in the sludge line of the WWTP. The system, which uses a magnetic nanoparticle collector to capture MPs, achieved up to 50% removal efficiency. Extrapolated to full-scale operation, the plant could prevent more than 8 tons of MPs per year from being released into agricultural soils, significantly reducing environmental and health risks while promoting a circular economy approach. • In conclusion, the study demonstrates that advanced quantification technologies provide reliable tools for monitoring MPs in complex matrices such as sewage sludge. Moreover, pilot- scale removal systems show promising potential to mitigate MP emissions from WWTPs. These advancements directly contribute to achieving multiple UN Sustainable Development Goals, including protecting human health, improving water quality, reducing pollution, and preserving biodiversity on land and at sea.