Synthesis of water-soluble chitosan-grafted-polyethyleneimine as biocoagulant for river water treatment: Process...

This study investigates the synthesis of water-soluble chitosan-graft-polyethyleneimine (Cs-g-PEI) by graft copolymerization and its application as a biocoagulant for river water treatment. Structural characterization using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), proton nuclear magnetic resonance (¹H NMR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX) confirmed successful PEI grafting and improved solubility at neutral pH. The coagulation mechanism, primarily involves charge neutralization (neutralization of negatively charged particles by the cationic biocoagulant) and polymeric bridging (linking of particles by elongated polymer chains to promote aggregation), was supported by zeta potential and particle size analyses. Coagulation-flocculation performance was evaluated using river water from the Kerian River, Malaysia, with a focus on turbidity, total suspended solids (TSS), and chemical oxygen demand (COD) removal. Optimization using Response Surface Methodology (RSM) with Central Composite Design (CCD) identified optimal treatment conditions at 52.7 mg/L coagulant dosage and an initial pH of 5.0. Compared to conventional coagulants (aluminum sulfate and ferric chloride), Cs-g-PEI demonstrated superior removal efficiency, achieving up to 93.14 % turbidity, 91.35 % TSS, and 75.57 % COD, with minimal pH change in the treated water (from pH 5.0 to 5.1). Kinetic modeling indicated a second-order reaction behavior, with Cs-g-PEI achieving the fastest coagulation rate compared to aluminum sulfate and ferric chloride. These findings position Cs-g-PEI as a promising, environmentally friendly alternative to conventional coagulants, with strong potential for scalability, cost-effectiveness, and biodegradability in sustainable water treatment.