DISRUPTING AND HARVESTING OF MICROALGAE CELLS USING OZONE BUBBLES

Harvesting microalgae for biodiesel production has been a difficult process due to its small cell size. In the present study, harvesting process of Chlorella vulgaris was carried out by using ozonation to determine the optimized conditions for ozonation process, the effectiveness of ozonation in harvesting microalgae and plausible disruption of microalgae cell walls. The optimized ozonation conditions were found as follows: ozone concentration of 100% (45 g/m3), pH 6.0, ozonation for 30 minutes, ozone flowrate of 7.0 L/min and temperature of 40˚C. By utilizing the optimized conditions, it was found a 20% increment in overall sedimentation efficiency for microalgae at absorbance 1.5. In addition, the lipid yield attained was 38.5% higher than the conventional gravity sedimentation method. However, the optimized conditions did not produce a significant result for both sedimentation efficiency and lipid yield when microalgae with absorbance of 3.15 was used. Apart from that, zeta potential analysis showed that microalgae after ozonation claimed to have lower zeta potential value, resulting in instability and higher coagulation rate. SEM analysis was carried out to observe the cell morphology. Cell wall disruption and microalgae cell coagulation after ozonation were illustrated for both absorbance 1.5 and 3.15 in the SEM micrographs. The experimental data was found to be a good fit with pseudo-second-order kinetics model and an activation energy of 112.27 kJ/mol was determined using Arrhenius equation plot.