Hydrodynamic cavitation for bacterial disinfection and medium recycling for sustainable Ettlia sp. cultivation. Issue 4 (August 2021) - Kim, Minsik
Abstract: Open cultivation systems are the most economic option for microalgal biomass production but their harvesting cost, bacterial invasion, and water usage are still deterring large-scale applications. Therefore, in this study, low-cost techniques for harvesting, bacterial disinfection, and medium recycling were sequentially implemented for Ettlia sp. For harvesting, the employed auto-flocculation harvested 96% of algae but was not able to remove bacteria that invaded during cultivation. For this reason, hydrodynamic treatment was applied as a bacterial disinfection method for medium recycling, and treated up to 100% of the bacteria in the supernatant. Afterward, the supernatant was replenished with nutrients and reused to grow microalgae. In medium-recycled cultivation, auto-flocculation recycled (AR) medium showed the highest final biomass concentration of 3.84 g L −1, while the centrifugation recycled (CR) medium and the fresh medium (FM) resulted in 3.78 and 3.67 g L −1, respectively. In addition, the lipid content of the AR group was highly increased to 20.4%, resulting in the highest lipid productivity of 0.11 g L −1 d −1 . Moreover, an analysis of fatty acid methyl ester compositions confirmed that 76.6% of lipid from the AR group were mainly composed of C16-C18, which are suitable for biodiesel. Consequently, the results showed that the implementation of low-cost techniques not only reduced process costs and water usage but also enhances both the biomass and lipid productivities of the species. Graphical Abstract: ga1 Highlights: Low-cost harvesting, bacteria control, and medium recycling were combined. Auto-flocculation harvested microalgae but left bacteria in the supernatant. Hydrodynamic cavitation disinfected bacteria with low-energy consumption. Biomass productivity of auto-flocculation recycled medium was slightly increased. Auto-flocculation recycled medium resulted in 1.6-fold higher lipid productivity.