Utilizing <i>Chlorella vulgaris</i> and In Situ Resources for Biomineralization-Driven Fabrication of Mars Bricks

This study explores the feasibility of fabricating calcium carbonate (CaCO3)-reinforced bricks using the carbonic anhydrase (CA) enzyme from Chlorella vulgaris biomass and resources available on Mars, such as carbon dioxide (CO2) and regolith. Microalgal biomass was cultivated under varying conditions: CO2 feed concentrations (0.04% or 5% v/v), human urine simulant dilution factors (UDFs) (61 or 121), and the presence of regolith extract (RE) in the nutrient medium. Results showed that CO2 and RE significantly influenced the production of microalgal biomass, which contained substantial CaCO3. The highest total biomass productivity (TBP) of 1.39 g/L-day was achieved in air-fed RE-containing media with UDF = 61, although this condition also yielded the most cell debris. In contrast, the most viable microalgal biomass (0.34 g/L-day) was produced in urine-only media with UDF = 61 supplemented with 5% CO2. For CaCO3 productivity, the highest (0.0164 g/L-day) was observed in RE-containing media (UDF = 61) with 5% CO2, despite having the lowest TBP (0.07 g/L-day). This CaCO3-rich microalgal biomass was used as the enzyme source for brick fabrication, resulting in bricks with a compressive strength of 542.83 psi. The low solubility of biomineralization-derived CaCO3 during enzyme extraction enhanced mineral availability in the bricks, improving the compressive strength and reducing the surface porosity. Although the highest brick compressive strength obtained in this work was lower than the recommended strength under reduced gravity (870 psi), the findings of this research indicate that Mars-based construction using in situ resources is feasible. Further optimization is essential to meet the structural demands of Mars’ habitats.