Effect of organic carbon to nitrogen ratio in wastewater on growth, nutrient uptake and lipid accumulation of a mixotrophic microalgae Chlorella sp.

This study investigated the biomass/lipid production, nutrient removal and fatty acid composition of an isolated mixotrophic microalga (Chlorella sp. G-9) cultured in simulated wastewater with different TOC/TN ratio. As the TOC/TN ratio of wastewater increased from 0 to 24, the growth rate of Chlorella sp. G-9 increased gradually, but did not increase further at 30. Nutrient removal was related to microalgae growth. In the wastewater with TOC/TN ratio of 24 and 30, 99.58% and 99.61% nitrogen was removed, respectively. In conditions of initial TOC/TN ratios of 24 and 30, Chlorella sp. G-9 could accumulate lipid as high as 35.3% and 36.5%, respectively. The corresponding lipid productivities were 34.2 and 32.6 mg L d, respectively, which were 13.7 and 13.0 times higher than those in photoautotrophic condition. Increasing the initial TOC/TN ratio of the wastewater could slightly increase the saturated degree in fatty acid, thereby improving the stability of biodiesel.