Sustainable flocculation system for microalgae harvesting and dye-containing wastewater treatment: Chlorella vulgaris...

Biological molecules have the potential to precipitate soluble and suspended compounds in aqueous solutions. In this study, a bioflocculant was obtained from Chlorella vulgaris biomass by alkaline hydrolysis, and the resulting product was employed in both the harvesting of Chlorella sp. and the flocculation of systems containing dyes. The extraction procedure was optimized through a full factorial design, with the main bioflocculant fractions identified as proteins and polysaccharides. The bioflocculant significantly accelerated the microalgae harvesting process at pH 2 and 3 compared to self-flocculation, which performed better at pH > 4 due to cell's surface charges. At pH 3, a flocculation efficiency of >50 % was achieved within the first 20 min, with nearly 80 % cell removal within the first hour. The bioflocculant's performance was further evaluated using three reactive dyes with different chemical groups, all of which showed color removal greater than 80 %. Zeta potential analyses confirmed that charge neutralization and bridging effects were the main mechanisms driving the flocculation process. This novel approach to bioflocculant production and application presents a promising alternative for flocculation systems without compromising the further use of the precipitated materials.