Influence of CO2 concentration and N:P ratio on Chlorella vulgaris-assisted nutrient bioremediation, CO2 biofixation and biomass production in a lagoon treatment plant

Abstract

Abstract Microalgae are among green trends for wastewater nutrient bioremediation, valuable biomass production, and CO2 biofixation. Currently, limited information is available regarding combined effects of nitrogen:phosphorus (N:P) ratio and CO2 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 CO2 concentrations on growth kinetics of microalgae, using samples taken from effluents of a domestic settling lagoon. The findings revealed that the medium supplemented with 16% CO2 and N:P ratio of 10 was the most productive culture, generating maximum biomass concentration, specific growth rate, biomass productivity, and CO2 biofixation rate of 0.7900 g L−1, 0.4170 d−1, 0.08500 g L−1 d−1 and 0.1430 gCO2 L−1 d−1, respectively. Moreover, C. vulgaris adapted and grew well even under CO2 levels as high as 24% in the wastewater. The microalga also demonstrated to uptake both nitrogen and phosphorous in the range of 70.00–95.00%. These observations support the possibility of CO2 bioremediation along with removal of nitrogen and phosphorous to below the most European restrictive limits for effluent discharges, while the increase in COD concentration caused by microalgae should be taken into account.