Plasma-induced synthesis of chitosan-g-polyacrylamide and its flocculation performance for algae removal

Chitosan (CS)-g-polyacrylamide (PAM) is a highly efficient and environmentally friendly flocculant, which was synthesized through plasma-induced graft copolymerization of CS and acrylamide (AM). The effects of monomer concentration, AM:CS ratio, discharge power, discharge time, post-polymerization temperature, and post-polymerization time on the intrinsic viscosity, grafting ratio, and grafting efficiency of CS-g-PAM were investigated. The optimum conditions of graft copolymerization were as follows: 20% monomer concentration, 7:3 AM:CS ratio, 40 W discharge power, 90 s discharge time, 50°C post-polymerization temperature, and 24 h post-polymerization time. The structural characteristics of CS-g-PAM were characterized by Fourier-transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction. CS-g-PAM exhibited better flocculation efficiency than the commercially available PAM in both diatomite-simulated wastewater and low-turbidity algal water. The optimal turbidity removal efficiency for the diatomite-simulated wastewater was 99.9%, which was obtained with 6 mg L^-1 of CS-g-PAM at pH 11.0 and 250 s^-1 of velocity gradient. In low-turbidity algal water, the optimal removal efficiencies for chlorophyll-a, turbidity, and COD were 93.6%, 94.5%, and 98.2%, respectively.