A high-performance and low-cost strategy to harvest saltwater Chlorella vulgaris using cationic polyacrylamide coupled with bentonite

In this study, a high-performance and low-cost strategy to harvest saltwater Chlorella vulgaris using cationic polyacrylamide (CPAM) combined with clay particles was developed. The optimal harvesting efficiency when using CPAM alone was only 75% at a dosage of 10 mg/L after 20 min. However, five types of common clay particles, including sodium bentonite (BE), kaolin, diatomite, attapulgite, and sepiolite, could improve the harvesting efficiency of CPAM, and BE showed the best synergistic effect due to its excellent charge patch and bridging adsorption. Further investigation indicated that the optimal process of harvesting microalgae occurred when CPAM was added first followed by BE (CPAM-BE), and the harvesting efficiency was above 94% with a settling time of 3 min and a pH range of 4–10 when 1 mg/L CPAM and 80 mg/L BE were added. The flocs formed by CPAM-BE settled better and exhibited better anti-shear and regrowth abilities than those formed by CPAM alone. In addition, CPAM-BE had no negative effects on lipid extraction and culture medium reusability, and BE could be reused.