Carbon dioxide fixation by algal cultivation using wastewater nutrients

Chlorella vulgaris was cultivated in wastewater discharged from a steel-making plant with the aim of developing an economically feasible system to remove ammonia from wastewater and CO₂ from flue gas simultaneously. Since no phosphorus compounds existed in wastewater, external phosphate (15.3-46.0 g m^-3) was added to the wastewater. After adaptation to 5% (v/v) CO₂, the growth of C. vulgaris was significantly improved at a typical concentration of CO₂ in flue gas of 15% (v/v). Growth of C. vulgaris in raw wastewater was better than that in wastewater buffered with HEPES at 15% (v/v) CO₂. CO₂ fixation and ammonia removal rates were estimated as 26.0 g CO₂ m^-3 h^-1 and 0.92 g NH₃₃ m^-3 h^-1, respectively, when the alga was cultivated in wastewater supplemented with 46.0 g PO₄³ m^-3 without pH control at 15% (v/v) CO₂.