Study on Flocculation Efficiency for Harvesting Nannochloropsis oculata for Biodiesel Production

Flocculation is one of the principal steps in biodiesel production from microalgae. Eight different flocculants were analysed for their efficiency of flocculation of marine microalga, Nannochloropsis oculata. Maximum flocculation was observed as 93.80 and 87.33% with FeCl3 and Fe2(SO4)3 at a concentration of 0.4 and 0.6g/L respectively at 180min. Zinc salts achieved second maximum efficient flocculation with ZnCl2 (0.6g/L) as 89.12% and ZnSO4 (0.8g/L) as 84.17% at 210 and 240 min respectively. Whereas salts of Aluminium showed flocculation efficiency of 85.46% with AlCl3 (0.6g/L) and 82.27% with Al2(SO4)3 (0.4g/L) at 210 and 240 min respectively. Magnesium salts showed less effect on flocculation though the incubation period was prolonged. As Iron salts exhibited complete cell lysis, even at lower concentrations, they were excluded from further study for flocculation. Effect of temperature, light and darkness were studied for Al salts and Zn salts, which showed that optimum temperature of 35C and light, are required for better flocculation. ZnCl2 showed ZnSO4, an efficient flocculation of 92.34 and 90.49% under illumination and under dark it was retarded to 83.14 and 80.14 % respectively; moreover cells remained intact on higher concentration and temperature. AlCl3 and Al2(SO4)3 showed efficiency of 88.49 and 85.91% under illumination but reduced to 74.77 and 68.79% respectively under darkness. Since structural instability is apparent with Al salts, Zinc chloride could be used as the efficient flocculant to flocculate Nannochloropsis oculata.