Bioflocculation of Glagah strain consortium using Skeletonema costatum (Greville) cleve

Along with the increasing energy demand, microalgae-based renewable energy is currently being developed. One of the local Indonesian microalgae strains with high potential for biodiesel production is the Glagah strain consortium. Although biodiesel from microalgae is sustainable, the production costs are still relatively high, especially for harvesting (requires 25%–30% of total production cost). Bioflocculation is an alternative method of harvesting that employs inexpensive and environmentally friendly microorganisms as flocculant agents. Bioflocculant agents for floc formation may consist of diatoms with a high EPS output, such as Skeletonema costatum. Harvesting the local strain of S. costatum as a bioflocculant has not been the subject of extensive research on bioflocculation. This study determined the flocculation percentage, carbohydrate, lipid, and pigments content after harvesting Glagah strain consortium culture using S. costatum. The cultivation of Glagah strain consortium was carried out in Bold Basal Medium, then S. costatum in f/2 medium for seven days. Bioflocculation was performed by mixing S. costatum and Glagah strain consortium at 1:1, 1:2, and 1:4 ratios. The results showed that the addition of S. costatum to Glagah strain consortium culture increased the production of flocculation percentage, lipid, carbohydrate, and pigment content. The combining ratio of SG 1:2, on the other hand, resulted in the highest percentage of flocculation and a significant induction of biological materials, including carbohydrates, chlorophyll, and carotenoids. Then, the highest lipid content was produced in the mixing ratio of SG 1:1 cultivation.