An Investigation of the Impact of Flocculants on Process Optimization and Floc Properties in Chlorella vulgaris FACHB-15 Harvesting

This study systematically compared the harvesting efficiency and flocculation mechanisms of a bioflocculant (chitosan) and a chemical flocculant (Al2(SO4)3) for Chlorella cells. For the first time, the divergent mechanisms underlying floc structure formation between the two flocculants were elucidated by analyzing the EPS distribution and dynamic changes in microalgal surface functional groups. By optimizing critical operational parameters—including flocculant dosage, flocculation time, pH, and biomass concentration—the optimal dosages of chitosan and Al2(SO4)3 were determined as 0.5 mg/L and 90 mg/L, respectively. Under pH 6, both flocculants achieved over 99% flocculation efficiency within 30 min. Notably, at a dosage of 3 mg/L, chitosan-formed flocs exhibited denser structures, stronger adhesion, and a tendency to aggregate into spherical clusters compared to Al2(SO4)3-induced flocs. Beyond identifying ideal conditions for Chlorella flocculation, this work provides novel insights into the role of EPS and surface functional groups in flocculation mechanisms, offering both theoretical foundations and practical guidance for efficient microalgal harvesting. The findings hold significant implications for optimizing bioflocculant applications and advancing environmentally sustainable harvesting technologies.