Screening of commercial natural and synthetic cationic polymers for flocculation of freshwater and marine microalgae and effects of molecular weight and charge density

Abstract

Twenty-five natural and synthetic cationic polymers of differentmolecular weightsand charge densitieswere evaluated for microalgae flocculation. Tanfloc is a naturallow molecular weight tanninpolymer whereas Zetag and Flopam are both synthetichigh!molecular weight polyacrylamide polymers. Five exponential concentrations (0.55,1.66, 5, 15 and 45 mg L-1) were tested for freshwater Chlorella vulgarisand marine Nannochloropsis oculata. All polymers were efficient (>90%at ≥ 1.66 mg L-1) for C. vulgaris. However,forN. oculata,only Tanfloc was effective. Charge density positively influenced flocculationdecreasing the required polymer dosage. Restabilisationwas observed only for synthetic polymers when overdosed. Natural polymers performed similarly for both species.In overall, Tanfloc SL and FlopamFO 4990 SH were the most efficientpolymers for microalgae flocculationthough Tanfloc is amore economic option (US$ 37 ton-1of biomass) and environmentally friendly than Flopam (US$ 171 ton-1of biomass).