Harvesting microalgae with electro-coagulation-flotation

Abstract

Microalgae is a promising candidate as a biofuel precursor because of its high lipid content and carbon fixation, but it need to decrease a cost owing to its high production cost. The electro-coagulation-flocculation which is a cheap microalgae harvesting technology should be approved to decrease a harvesting cost which comprises 20% of production cost. In this study, the performance of electro-coagulation-flocculation was measured using Nannochloropsis species which is proper to electro-coagulation-flocculation and Chlorella vulgaris which has high productivity. Nannochloropsis species was harvested 95% with 7.2 mA/$cm^2$ of current density for 10 minutes and Chlorella vulgaris was harvested 90% with 6 mA/$cm^2$ of current density for 15 minutes at 400ml ml harvest chamber. Nannochloropsis species was harvested 95% with same current density for 20 minutes and Chlorella vulgaris was harvested 90% with same current density for 45 minutes at 50 L harvest chamber. The performance of continuous electro-coagulation-flotation was measured using Chlorella vulgaris. It was harvested 90% with 6 mA/$cm^2$ of current density when the flow rate was below 15 ml/min, but the efficiency decreased at higher flow rate. Next, a hydrothermal treatment as a lipid extraction and hydrolysis of Chlorella vulgaris sample by electro-coagulation-flotation was compared with that of centrifugation to investigate side effects of electro-coagulation-flotation to downstream process. A hydrothermal treatment efficiency of sample by electro-coagulation-flotation was 65% which is same as efficiency of sample by centrifugation. And a hydrolysis efficiency of sample by electro-coagulation-flotation was 100% which is same as efficiency of sample by centrifugation. The aluminum concentration of the sample was 80 ppm. Next, Nannochloropsis species was harvested using triboelectric generator as different energy source of electro-coagulation-flotation instead of DC power supplier. It was harvested 90% in 60 hours by wind triboelectric generator using 10 m/s of wind.