Design and application of a polyacrylamide-grafted gelatin/biochar/Fe3O4 magnetic coagulant for microcystin-LR and turbidity co-removal: A case study with Yangtze River water.

This study presents a novel composite coagulant composed of polyacrylamide-grafted gelatin (PAM-g-gelatin), oak-derived biochar, and Fe₃O₄ magnetic nanoparticles for the efficient removal of turbidity and microcystin-LR (Mic-LR) from contaminated water. Comprehensive characterization using FTIR, BET, SEM, XRD, and EDX techniques confirmed successful synthesis and functional integration of the components, with a surface area of 27.596 m2/g. Experimental trials on Yangtze River water spiked with 300 μg/L Mic-LR and turbidity ranging from 0 to 30 NTU identified optimal operating conditions: 50 mg/L coagulant dosage, pH 8, and stirring at 400 rpm. Under these parameters, the composite achieved removal efficiencies of 88 % for Mic-LR and 94 % for turbidity. Improved performance in alkaline conditions was attributed to the increased ionization of functional groups such as -COOH and -NH₂, enhancing adsorption and floc formation. The synergistic role of biochar and magnetic particles contributed to better adsorption capacity, floc stability, and overall sustainability. Reusability tests showed high efficiency over four cycles, with slight performance reduction due to active site saturation. The coagulant also effectively removed Mic-RR (85.3 %) and Mic-YR (87.1 %), and maintained stable performance in complex water matrices, showing promise as a robust, cost-effective, and environmentally friendly solution.