Combined effects of nitrogen levels and Daphnia culture filtrate on colony size of Scenedesmus obliquus

Increased colony size facilitates the harvest of Scenedesmus cells from culture media; as such, factors that stimulate colony enlargement for production should be identified. This study aimed to investigate the combined effects of nitrogen levels and Daphnia culture filtrate on the colony size of Scenedesmus obliquus. Results showed that the colony formation of S. obliquus induced by Daphnia culture filtrate was promoted under low nitrogen levels. Colony size increased by approximately 50%-100%, which suggested that low nitrogen and zooplankton infochemicals synergistically affected the colony formation of S. obliquus. Furthermore, increased colony size and high settling velocities enhanced the suitability of populations for centrifugation and filtration; thus, these populations could be helpful for harvest. According to the results, addition of Daphnia culture filtrate at 3 days before S. obliquus was harvested could be useful. Therefore, the proposed method could be applied to facilitate efficient harvest of Scenedesmus biomass.