The efficient synthesis of bio-based anionic flocculants is crucial for sustainable wastewater treatment. However, existing bio-based flocculants often compromise between performance and eco-friendliness. This study developed a one-step method to synthesize low degree substitution citrated starch-grafted polyacrylamide (St-CA-PAM) as an eco-friendly alternative to synthetic flocculants. Citrated starch (St-CA) was prepared by esterification with citric acid, achieving a low degree of substitution (DS = 0.061), optimized for solubility and graft polymerization. The polyacrylamide grafting onto St-CA was also confirmed by Fourier Transform Infrared Spectroscopy (FTIR), Proton Nuclear Magnetic Resonance (¹H NMR), zeta potential (ZP), and intrinsic viscosity measurement. The presence of representative peaks in the ¹H NMR and FTIR spectra, indicating amide and carboxylic groups, confirmed the successful simultaneous modification, supported by the viscosity increase from 0.80 dl/g (St-CA) to 1.18 dl/g (St-CA-PAM). St-CA-PAM exhibited superior flocculation efficiency, achieving 90% turbidity removal (< 20 Nephelometric Turbidity Units (NTU)) at 10 ppm, significantly outperforming St, St-CA, and St-PAM, with optimal clarification (98%, 2.42 NTU) under alkaline conditions. The flocculation mechanism involved electrostatic patch effects and polymer bridging, forming large flocs (~ 850 nm) and enhancing sedimentation. Given its bio-based composition, low dosage requirements, and anionic nature, St-CA-PAM presents a promising, scalable, and sustainable alternative for wastewater treatment.

Keywords