Scenedesmus obliquus, Chlorella vulgaris, Chlorella kessleri and a natural Bloom were cultivated in batch experiments, under controlled conditions, in urban wastewater (WW) and synthetic wastewater (SW) under 5% CO2 in air, with the object of estimating their capacity for nutrient removal, carbon dioxide biofixation, and generation of valuable biomass. In both culture media, the Bloom (Bl) and Scenedesmus (Sc) showed higher final biomass concentration (dried weight, dw) than the other species; the maximum yield obtained was 1950 ± 243 mg L(-1) for Bl and the minimum 821 ± 88 mg L(-1) for Cv, both in synthetic wastewater. Maximum specific growth rate values do not show significant differences between any of the 4 strains tested (p ≤ 0.05), nor between the 2 culture media. A new homogeneous method of calculating productivities has been proposed. Nitrogen removal in all the reactors was higher than 90%, except for BlSW (79%), and for phosphorus, the removal was higher than 98% in all trials. Maximum CO2 consumption rates reached were 424.4 and 436.7 mg L(-1) d(-1) for ScSW and ScWW respectively.