Effective Removal of Microplastics and Nanoplastics with Cationic Cellulose Fibers in Wastewater Treatment

The ubiquitous contamination of water supplies by microplastics and nanoplastics is a growing global concern, posing significant risks to aquatic ecosystems and human health. Wastewater treatment plants serve as critical barriers to reducing the concentration of plastic contaminants before their release into natural environments. In this study, we introduce cationically functionalized cellulose fibers as bridging agents for enhancing the removal of microplastics and nanoplastics in coagulation–flocculation processes. Cellulose fibers are modified with quaternary ammonium groups via periodate-induced oxidation, and extensive characterization confirms their successful cationization. The addition of cationic fibers achieves near-complete removal (>99%) of 1 µm and 200 nm model microplastics and nanoplastics and 93% removal of 20 nm model nanoplastics from synthetic wastewater, significantly outperforming both unmodified fibers and conventional treatment (i.e., without fiber addition). Fluorescence microscopy of the settled flocs reveals a surface-enhanced removal mechanism of cationic fibers, driven by electrostatic interactions during floc formation. Fiber reusability tests conducted with fibers extracted from sludge show that high performance of cationic fibers is maintained, achieving 94% and 81% removal of 1 µm and 20 nm particles, respectively, after five consecutive reuse cycles. Furthermore, cationic fiber effectiveness for plastic removal is validated in microplastic- and nanoplastic-spiked municipal wastewater influent, demonstrating their practical applicability. This comprehensive assessment of functionalized cellulose fibers underscores their potential as a highly effective and sustainable approach for mitigating widespread plastic pollution with primary wastewater treatment.