Factors affecting microalgae harvesting efficiencies using electrocoagulation-flotation for lipid extraction

Microalgae harvesting is a relatively costly process in microalgae biodiesel production. In this study, electrocoagulation-flotation (ECF) was employed to harvest microalgae (Chlorella vulgaris). Higher current density achieved higher collection efficiency, but also resulted in higher energy consumption and increased levels of dissolved aluminium. At the same ratio of current density to initial cell density, collection efficiency decreased from 99.0% of 0.24 g L^-1 to 30.5% of 1.17 g L^-1 when the electrolysis time was 20 min. For stirring and aeration, the highest collection efficiency was 98.4%, obtained by stirring at 50 rpm for 20 min. This efficiency was nearly equal to the highest collection efficiency for aeration: 98.3% for 50 mL min^-1 aeration at 30 min. Acidic and neutral culture conditions were beneficial due to the positively charged aluminium species in the culture; higher collection efficiencies (more than 98%) occurred with pH levels of 5-7 after 20 min. The lowest energy consumption of 0.61 kW h kg^-1 was achieved at pH 5. In this research, ECF exhibited higher collection efficiency (99.4%) as compared to the 93.5% collection efficiency of chemical flocculation (Al₂(SO₄)₃).