An alternative strategy for enhanced algae removal by cationic chitosan-based flocculants

The water solubility and polymerizability of maleoyl chitosan (MCS) was significantly improved by introducing a maleoyl group into the chitosan chain and MCS is a promising monomer for preparing chitosan-based flocculants with good water solubility. In this study, MCS was grafted with acrylamide and diallyldimethylammonium chloride to prepared a cationic chitosan modified flocculant chitosan-graft-poly (acrylamide diallyldimethylammonium chloride) (PMAD) with excellent solubility by ultraviolet (UV)-induced copolymerization techniques. The effects of monomer concentration, the percentage of maleated chitosan, photoinitiator concentration and illumination time on the intrinsic viscosity, grafting efficiency and dissolution time of PMAD were investigated by single factor experiments. The optimal synthesis conditions were determined with monomer concentration 12.5%, MCS percentage 10%, cationicity 11.25%, photoinitiator concentration 0.3% and illumination time 120 min, proving that UV initiated method was benefited to improve water solubility of PMAD. PMAD prepared at the optimized condition has the optimal viscosity of 4,823.2 mg L–1, the grafting efficiency of 70.7% and the dissolution time of 75 min. At the same time, the synthesized products PMAD were characterized by infrared spectroscopy, scanning electron microscopy, H-nuclear magnetic resonance, thermogravimetric and X-ray diffraction techniques. The flocculation experiments of PMAD on algae-containing water showed that the flocculation performance of PMAD was remarkably higher than that of commercially available polyacrylamide and polyaluminum ferric chloride. The optimal removal rate of Chl a (81.2%), turbidity (94.9%), and algae cell concentration (99.7%) by PMAD was obtained at dosage of 40 mg L–1, pH value 8 and G value 500 s–1. The obtained zeta potential results proved that the main flocculation mechanism of PMAD was the function of adsorption bridging.