Light-Dependent Biomass Response of Chlorella vulgaris Cultivated in BG-11 Medium Using a Tubular Photobioreactor

Cultivating microalgae, which photosynthesize, requires optimal light use while coping with the biological and technical limitations of illuminated reactors. In this paper, the effect of light on the biomass growth of Chlorella vulgaris in BG-11 medium in a laboratory-scale tubular reactor was studied using three different nominal levels of light exposure. The cultivation system consisted of vertically positioned transparent tubes and aeration, and BG-11 was selected after preliminary medium screening. Biomass concentrations recorded at 5,000, 10,000, and 15,000 lux were 1.50, 1.95, and 1.85 g/L, respectively. The intermediate treatment resulted in the highest amount of biomass when compared between the three different environments studied. As compared to 5,000 lux, the value at 10,000 lux was 0.45 g/L higher, which is an increase of 30.0%. An increment of illumination from 10,000 lux to 15,000 lux resulted in a decrease of 0.10 g/L (5.13% relative to the intermediate value). The values indicate a non-monotonic reaction within the tested range but do not prove photoinhibition, statistical significance, or causal mechanisms. However, because the irradiance measurements were done in terms of lux and not spectral photon flux density, extrapolation of this optimal value to other lighting sources is not easy. The results show that 10,000 lux is the most productive of the three tested levels of light in this particular case of culture setup and support more closely resolved experiments on lighting, optical attenuation, and cultivation efficiency.