Polysaccharide-based green flocculants: A systematic and comparative study of their coagulation-flocculation efficiency

Abstract

Driven by the quest for greener flocculants, this study explores how cationized polysaccharides can enhance coagulation-flocculation efficiency, filling a gap in systematic comparative analyses. We introduce here a flocculation score which provides a robust framework for flocculation evaluation and comparison. Starch, chitosan, inulin, guar gum, pullulan, and hydroxyethyl cellulose were tested, both unmodified and modified with quaternary ammonium compounds. Promising results in coagulation-flocculation were observed compared to synthetic flocculants like cationic polyacrylamide (cPAM) and Poly(Diallyldimethylammonium Chloride) (pDADMAC). Advanced techniques such as AsFlFFF-MALS, NMR, PCD, rheology, SEM, image analysis, and zeta potential were used to thoroughly characterize these polysaccharides and their flocculation efficiency. Results revealed notable flocculation enhancement in kaolin suspension (model system) and industrial starch sludge with cationized polysaccharides over their unmodified counterparts. Key influencing factors -molecular weight, charge density, and viscosity- and their trends were identified, with higher charge densities notably enhancing flocculation particularly in kaolin suspensions, and higher molecular weight enhancing flocculation in industrial sludge. Chitosan emerged as the top unmodified polysaccharide, while cationic pullulan and starch were found to lead among modified polysaccharides. This study highlights eco-friendly cationized polysaccharides, providing insights for optimizing water treatment and a comparative analysis of six polysaccharides' intrinsic parameters and flocculation efficiency.