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 mu mol/(m(2) @@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.