A rapid, efficient and eco-friendly approach for simultaneous biomass harvesting and bioproducts extraction from microalgae: Dual flocculation between cationic surfactants and bio-polymer

Microalgal biomass harvesting and cell disruption are the main bottlenecks for downstream processing of microalgae such as high-value bioproducts extraction and biofuels production. In this study, we evaluated the performance of dual flocculation between cationic surfactants and bio-polymer of chitosan for simultaneous biomass harvesting and bioproducts extraction from Chlorella sorokiniana microalgae. First, the effects of individual natural flocculants of chitosan and two cationic surfactants: cetyltrimethylammonium bromide (CTAB) and dodecyltrimethylammonium bromide (DTAB) on biomass harvesting were studied. Next, the synergistic effect of dual flocculation between the cationic surfactants and chitosan on harvesting efficiency, time and flocculant dosage was investigated. Finally, we evaluated the potential of high value bioproducts extraction from microalgae after the individual and dual flocculation processes. Zeta potential analysis and microscopic images were employed to achieve mechanistic understanding. Maximum biomass harvesting efficiencies of 85 %, 88 % and 78 % were achieved using individual flocculants of chitosan, CTAB and DTAB, under their optimum dosages of 100, 400 and 4000 mg/L, respectively. A significant synergistic effect of dual flocculation between chitosan (C) and cationic surfactants on biomass harvesting efficiency (CTAB-C: 99 % and DTAB-C: 97 %), settling time (CTAB-C: 2 min and DTAB-C: 5 min) and optimum dosage of surfactants (CTAB-C: 100 mg/L and DTAB-C: 1000 mg/L) was observed. The synergistic effect was associated with multiple flocculation mechanisms of charge neutralization and bridging induced by cationic surfactants and chitosan, respectively. Furthermore, bioproducts recovery efficiencies of 12 %, 25 % and 15 % of cell dry weight were achieved for protein, carbohydrate and lipid, respectively by using dual flocculation of CTAB surfactant and chitosan at much lower dosage of 100 mg/L.