Efficient microalgae harvesting: Synergistic flocculation and flotation with polyacrylamide and graphite electrolysis

Microalgae offer widespread applications, yet their harvesting remains challenging due to the limitations of conventional methods like centrifugation, filtration, and chemical flocculation, which often involve high energy costs, complex equipment, or environmental risks. This study investigated the efficiency of combining polyacrylamide (PAM) flocculation with electro-flotation to harvest Chlorella vulgaris , a widely cultivated microalgal species for biofuel production. The results demonstrated that PAM-electro-flotation significantly improved harvesting rates while reducing costs, with a PAM concentration of 5~10 mg L –1 and electrolysis at 30 A m –2 for 60 to 120 seconds being the most effective and energy-saving combination. At 10 mg L –1 PAM concentration, a 95% harvesting rate only needed 7.24×10 –5 kWh L –1 , while nearly 100% efficiency required around 4.97×10 –4 kWh L –1 . During electrolysis, phosphate concentrations decreased, and dissolved oxygen levels increased, supporting its potential for wastewater treatment. The method, utilizing nontoxic PAM and graphite electrodes, didn’t significantly affect microalgae photosynthetic efficiency (QY-24h > 0.65), especially at low PAM levels (≤5 mg L –1 ) and current densities (≤20 A m –2 ). Our study develops a PAM-electro-flotation system with optimal parameters, proving to be an efficient, environmentally friendly, cost-effective, and microalgae-safe method for microalgae harvesting. • A PAM-electro-flocculation system has been developed for microalgae harvesting. • PAM concentration of 5~10 mg L –1 and electrolysis at 30 A m –2 is most effective. • Nearly 100% harvesting efficiency requires around 4.97×10 –4 kWh L –1 . • The entire harvesting process only needs 60 to 120 seconds. • This method is safe for microalgal cells and can improve water quality.