Combined Filtration and Flocculation for Chlorella vulgaris Harvesting

Background: The present study aims to explore the feasibility of using flocculation combined with filtration for microalgae harvesting, i.e., Chlorella vulgaris. This is important because mi-croalgae have small sizes and its broth is stable, which makes it difficult to be harvested. The afore-mentioned facts cause the harvesting cost to be relatively high and become the bottleneck of microal-gae processes. Objective: The objective of this research is to find the relation between microalgae concentration, chi-tosan dosing as a flocculant, and its filterability on membranes. Methods: Research was performed by first cultivating the microalgae in a lab-scale photobioreactor, followed by jar test, flocculation, and filtration experiment. Jar test flocculation was performed using chitosan and microalgae with different concentrations, by simply mixing it in a 100 mL bottle and ana-lyzing the results with UV Vis Spectroscopy. Filtration experiments were performed using lab-made polyvinylidene fluoride membrane, in a 100 mL dead-end filtration cell and in a 5 L tank for submerged filtration. During both filtration tests, filtration flux and fouling were monitored and compared. Results: Results showed that the chitosan concentration needed as a flocculant depends on the micro-algae biomass concentration. For the filterability tests, the results proved that flocculation with chi-tosan enhanced the filterability of the microalgae broth both in dead-end and submerged filtration mode. For the used biomass concentration of around 400 mg/L, the filterability test showed an opti-mum concentration of chitosan at 7.5 to 10 mg/L, which resulted in a higher filtration flux and lower irreversible fouling in the dead-end filtration and a higher critical flux in the submerged filtration set-up. Conclusion: This increased filterability allowed higher fluxes to be operated, thus resulting in a more efficient harvesting process.