Fecitrate converted from Fe2O3 particles in coal-fired flue gas promoted microalgal biomass and lipid productivities

Highlights: • Na-Citrate was proposed to chelate FeCl₃ derived from Fe₂O₃ and HCl reactions. • Fe-Citrate gave much higher microalgal biomass and lipid productivities than FeCl₃, Fe-EDTA, Fe-DTPA and Fe-HEDTA. • A transmembrane absorption mechanism was proposed for Fe-Citrate and other Fe-chlates. • The maximum biomass and lipid productivities were obtained in 5 mg L⁻¹ Fe-Citrate medium. In order to reutilize Fe₂O₃ particles in flue gas from coal-fired power plant as a ferrum nutrient for improving microalgae growth, Na-Citrate was proposed to chelate FeCl₃ derived from Fe₂O₃ and HCl reactions to promote biomass and lipid productivities of Chlorella PY-ZU1. Fe-Citrate gave much higher biomass and lipid productivities than FeCl₃, Fe-EDTA, Fe-DTPA and Fe-HEDTA, because organic chelator prevented Fe³⁺ from depositing, lower stability constant resulted in easier dissociation of ferric chelate, smaller chelate facilitated Fe²⁺ (reduced from Fe³⁺) transportation through cell membranes. The biomass growth and photosynthetic capacity of Chlorella PY-ZU1 cultivated with Fe-Citrate (converted from Fe₂O₃ particles) medium were similar to those with commercial ferric ammonium citrate medium. The biomass and lipid productivities of Chlorella PY-ZU1 cultivated with 5 mg L⁻¹ Fe-Citrate medium were 1.30 and 1.72 times, respectively, higher than those with FeCl₃ growth medium.