Influence of exogenous CO₂ on biomass and lipid accumulation of microalgae Auxenochlorella protothecoides cultivated in concentrated municipal wastewater.

The effects of exogenous CO₂ on the growth and lipid accumulation of a local screened facultative heterotrophic microalgae strain Auxenochlorella protothecoides (UMN280) as well as nutrient removal from concentrated municipal wastewater stream (centrate) were examined in this study. A 12-day batch experiment was conducted with CO₂ aeration at three levels, namely, 0%, 1%, and 5% (v/v) CO₂ mixed with air, under light intensity of 60 μmol/(m² @@s). A two-stage growth pattern was observed. The first stage (first-fifth day) was dominated by heterotrophic growth in which organic carbon was the main carbon source. The second stage (6th-12th day) was dominated by autotrophic growth in which exogenous CO₂ had a positive effect on algal biomass accumulation. The addition of 5% CO₂ was better than that of 1% CO₂ on the biomass and lipid production. The uptakes of nutrients were similar between injection and no injection of CO₂, except on phosphorus removal which was affected by the acidification of CO₂.