A photobioreactor was designed to evaluate the performance of a newly isolated thermo-tolerant microalga Desmodesmus sp. F2 in municipal wastewater under tropical outdoor conditions. The environmental parameters, levels of nutrients, and growth rates were monitored during the cultivations to elucidate the factors that contributed to accelerated growth after lag phase. Cultures bubbled with CO2-air had about 20% higher yields than the air-bubbled culture, and 2% of CO2 at a flux rate of 5 L/min was sufficient to reach this increased yield. In the cultures bubbled with CO2-air, the microalgal cells preferentially utilized ammonium and nitrate, while the air-bubbled culture made greater use of ammonium and organic nitrogen. In conclusion, the factors required for microalga Desmodesmus sp. F2 to achieve accelerated growth in tropical outdoor conditions include (1) 2% CO2 bubbling; (2) a level of ammonium higher than 100 mu M; and (3) a level of nitrate higher than 400 mu M. (C) 2012 Elsevier Ltd. All rights reserved.