Investigation of Effective Parameters on the Productivity of Biomass and Bio-cement as a Soil Improver from Chlorella vulgaris

In recent years, microalgae had attracted considerable attention for bio-cement production, as a soil improver, due to their ability to precipitate high levels of calcite, and Chlorella vulgaris is one of the most promising candidates. In this study, first, the effects of different types of nitrogen source and sodium bicarbonate and various concentrations of carbon dioxide on C. vulgaris microalgae were investigated in terms of biomass concentration, percentage of bio-cement precipitation, and productivity. Later, the Plackett-Burman method was applied to find the optimum amount of nutrition that highly influences microalgae growth and bio-cement production. Results showed that the growth rate and amount of biomass produced in the medium with nitrate as a source are much higher than in the medium with urea or ammonium. The biomass production of 504 mg/l and bio-cement productivity of 70% was obtained. Specific growth rate increases with increasing concentration of sodium bicarbonate (0.5-1 g/l) and the maximum growth rate are 0.96 d at 1 g/l sodium bicarbonate concentration. Also, increasing the concentration of carbon dioxide from 0.03% to 5% did not show much effect on the bio-cement precipitation. According to the results of culture medium optimization for both biomass and bio-cement productivity responses, only three components of the culture medium include calcium chloride, sodium nitrate, and sodium bicarbonate were effective. By applying optimum amounts of calcium chloride (0.4 g/l), sodium bicarbonate (2.5 g/l), and sodium nitrate (1 g/l) in the culture medium, the bio-cement efficiency reached 90.1% and the biomass productivity reached 490 mg/l.