Monitoring lipids profile, CO2 fixation, and water recyclability for the economic viability of microalgae Chlorella vulgaris cultivation at different initial nitrogen

The economic viability of microalgae as a bioenergy source depends on many factors. High CO2 fixing rate, improved lipids yield, and minimum water footprint are few key parameters. This study investigates the effect of four initial nitrogen concentrations (1-, 2-, 6-and 10-mM as nitrate) on lipids yield, their classification and composition, CO2 fixation rate, and water quality for further reuse after first cultivation. The initial 6 mM nitrate was found optimum for the growth and overall lipid productivity of Chlorella vulgaris. The maximum quantum efficiency (as Fv/Fm ratio) for algae decreases along with the cell growth profile and depletion of the initial nitrate concentration. CO2 fixation rate increased initially and peaked during exponential growth and then declined for the rest of the cultivation period. A higher CO2 fixation rate was recorded at 6 mM, and an overall fixation rate of CO2 was high at 6 mM. A higher total organic carbon (TOC) is produced in recycled water at a low nitrogen concentration of 1 and 2 mM. TOC changes during the cultivation period and with each reuse of water. Water was recycled twice successfully, while growth was inhibited during the 3rd cycle. Based on all these in-vestigations, 6 mM of initial nitrogen was found optimal at given growth conditions.

Automated summary

This study investigates the economic viability of microalgae as a bioenergy source, identifying 6 mM initial nitrate as optimal for the growth and lipid productivity of Chlorella vulgaris. The CO2 fixation rate increases initially and peaks during exponential growth, while water produces higher total organic carbon at low nitrogen concentrations.