Potential of Chlorella vulgaris to abate flue gas

Abstract

The likely use of continuous cultures of Chlorella vulgaris for flue gas abatement was studied. Firstly, no pH-controlled photo-bioreactors were operated in order to understand the tolerance of this microalgae to high CO2 concentrations in the airstream. Thus, the effect in biomass productivity, CO2 fixation and biochemical composition of different percentage of pure CO2 (ranging 1–12%) in the air supply was investigated. When the inlet CO2 concentration varied from 1 to 10%, no statistical differences were found (ANOVA, p < 0.05) in the rate of carbon assimilation (0.6–0.8 g L−1 d). In all the cases, biomass presented a high content both proteins and lipids (40 and 25% respectively). However, when cultures were supplied with 12% of pure CO2 in the airstream, pH drastically dropped and cultures were not viable. Next, the potential use of CO2 contained in a simulated flue gas as a unique source of carbon was evaluated. Thus a mix of gases mimicking those presented in an exhausted stream of a power plant was used to aerate constantly the cultures. In this condition, cultures were only viable either when the simulated flue gas stream was diluted twelve times with air (resulting a constant supply of 1% CO2 in the airstream) or no diluted but being used by pulse to control the pH of the culture. In both cases, cultures achieved a steady state, rendering 0.7 and 0.9 g CO2 assimilated L−1 d−1 respectively. Biomass presented high content of proteins and lipids (40% respectively) in both conditions. These results suggest that the use of exhausted gases can make more economically feasible the production of microalgae and generate a valuable biomass rich in proteins and lipids.