Innovative and high efficiency harvesting process of Chlorella vulgaris by magnetic harvesting

This study explored the use of magnetic flocculation to harvest Chlorella vulgaris from synthetic wastewater by combining polyaluminium chloride (PAC), polyacrylamide (PAM), and Fe₃O₄ magnetic particles. The approach focused on finding the right conditions - e.g. pH, chemical dosages, mixing - to maximize algae recovery. PAC helped to destabilize the algae cells, PAM improved floc formation, and the magnetic particles enabled quick separation. Using these materials, the best recovery rate was over 90 %, achieved within 2 min under optimal conditions (pH 7-8, 1.25 mmol Al/L PAC, 2 g/L Fe₃O₄, and 1 mg/L PAM). Importantly, the Fe₃O₄ particles could be reused multiple times with no significant decrease in the efficiency of the process, which suggests this method could be cost-effective and sustainable. Presently a critical issue in the overall microalgae harvesting process is related to the detachment of the magnetic particles, which has not been previously attained with the required efficiency. Therefore to further improve the process, three detachment techniques were tested to recover algae biomass from the magnetic flocs. The alternating magnetic field method at pH 12 showed the highest success, removing nearly all algae within 10 min and working much better than the other tested methods like sonication or a steady magnetic field, or even all present existing methods. Overall, the results indicate that magnetic flocculation using this combination of materials and the final alternating magnetic field recovery method is a fast and reusable way to harvest microalgae. The overall system shows promise for practical use in wastewater treatment and biomass recovery.