Microalgae are emerging as one of the most promising long-term sustainable sources of renewable energy. Studies were conducted on two freshwater Chlorophytes, Chlorella vulgaris and Scenedesmus obliquus to evaluate heterotrophic growth rate and biomass productivity in filter-sterilized defined medium (BG 11) and municipal wastewater, both with varying concentrations of nitrogen (N). For each isolate, cultures were separately incubated in triplicate at room temperature with constant agitation on a shaker at 150 rpm for 9 days. In 0.25 mg N/L BG11 medium, the growth rate and biomass productivity of C. vulgaris were 0.28 day −1 and 3.5 g•L −1 , respectively. In wastewater, the same amount of N addition resulted in a higher growth rate 0.44 day −1 and associated biomass productivity of 4.96 g•L −1. Increasing N levels to 0.5 mg N/L in BG11 caused an increase in growth rate (0.37 day −1) and biomass productivity (4.28 g•L −1), while the increase in N in wastewater caused growth to decline to 0.32 day −1 with decreased biomass productivity of 2.19 g•L −1. A further increase in N to 1.0 mg N/L in BG11 caused an increase in the growth rate (0.43 day −1) and a decrease in biomass productivity (3.64 g•L −1), while in wastewater, growth rate and productivity of C. vulgaris were 0.32 day −1 and 2.31 g•L −1 , respectively. Overall, C. vulgaris grew faster and produced greater biomass than S. obliquus under comparable conditions. Based on high growth rate and biomass productivity of C. vulgaris, it could be a potential candidate for further consideration for simultaneous wastewater treatment and biofuel production.