Microalgae are among green trends for wastewater nutrient bioremediation, valuable biomass produc- tion, and CO 2 biofixation. Currently, limited information is available regarding combined effects of ni- trogen:phosphorus (N:P) ratio and CO 2 concentration on growth characteristics and nutrient removal capacity of Chlorella vulgaris cultivated in lagoon systems. The current work sought to address simple effects and interaction effects of various N:P ratios and CO 2 concentrations on growth kinetics of mi- croalgae, using samples taken from effluents of a domestic settling lagoon. The findings revealed that the medium supplemented with 16% CO 2 and N:P ratio of 10 was the most productive culture, gener- ating maximum biomass concentration, specific growth rate, biomass productivity, and CO 2 biofixation rate of 0.7900 g L −1 , 0.4170 d −1 , 0.08500 g L −1 d −1 and 0.1430 gCO 2 L −1 d −1 , respectively. Moreover, C. vulgaris adapted and grew well even under CO 2 levels as high as 24% in the wastewater. The microalga also demonstrated to uptake both nitrogen and phosphorous in the range of 70.0 0–95.0 0%. These obser- vations support the possibility of CO 2 bioremediation along with removal of nitrogen and phosphorous to below the most European restrictive limits for effluent discharges, while the increase in COD concen- tration caused by microalgae should be taken into account.

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