Natural-based coagulants/flocculants for microplastics and nanoplastics removal via coagulation–flocculation: a systematic review

Abstract Microplastics (MPs) and nanoplastics (NPs) are emerging contaminants that can act as vectors for toxic pollutants, posing serious risks to aquatic ecosystems. Coagulation–flocculation–sedimentation (CFS) is a widely used technique for MPs and NPs removal, and natural-based coagulants/flocculants offer a more sustainable alternative to conventional chemicals. However, a comprehensive evaluation of their performance, mechanisms, and influencing factors remains lacking. This systematic review, conducted in accordance with the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines, critically assesses the applicability of plant, animal, and microbial-derived natural coagulants/flocculants for MPs and NPs mitigation in aquatic systems. These materials are applied either directly as substitutes for chemical coagulants, chemically modified, or as coagulant aids. Key coagulation mechanisms include charge neutralization, electrostatic patch, adsorption bridging, sweep flocculation and netting-bridging. Removal efficiency is governed by factors such as pH, dosage, interfering substances, stirring conditions, MPs and NPs properties, and temperature. Although natural-based materials demonstrate a promising potential for sustainable plastic remediation, challenges related to material variability and availability, storage stability, environmental impact and process scalability remain. Addressing these limitations is essential to advance their practical implementation and long-term viability in real water and wastewater treatment applications. Graphical abstract