Bio-inspired flocculation strategy for sustainable microplastic removal by co-precipitation synergy between extracellular organic matter (EOM) and Fe (III)

Coagulation has proven effective in removing microplastics (MPs) from water, yet existing studies indicate that using coagulants alone often yields unsatisfactory results. Therefore, developing sustainable flocculation technologies is crucial for efficient microplastic removal. In this study, microbial flocculants originated from algal extracellular organic matter (EOM) were used to enhance the effectiveness of the traditional flocculant ferric chloride (FeCl₃) for MP removal in marinr water. The PS flocculation efficiency of Fe (III)–EOM treatment achieved 90 %, which is 5 to 10 times higher than that of FeCl₃ treatment. Zeta potential, scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) analyses revealed that EOM significantly enhanced flocculation by facilitating charge neutralization and agglomeration adsorption. Additionally, reductions in total organic carbon (TOC), protein, total sugars and Fe concentration after flocculation in the Fe (III)–EOM system confirmed effective binding and co–precipitation of organic compounds in EOM with Fe (III). At 1 mmol/L Fe (III), the removal efficiency of TOC, total sugars, and proteins in the K1–EOM/S1–EOM systems reached 39 %/21 %, 47 %/40 %, and 10 %/18.7, respectively. Notably, the Fe (III)–EOM system significantly reduced residual iron levels to below 1 mg/L, which is significantly lower than that using FeCl₃ alone (29.1 mg/L). Therefore, the Fe (III)–EOM flocculation system demonstrates a high flocculation efficiency with low iron residue, providing a promising and sustainable solution for MP removal in water treatment.