Biomass Production Potential of a Wastewater Alga Chlorella vulgaris ARC 1 under Elevated Levels of CO ₂ and Temperature

Abstract

The growth response of Chlorella vulgaris was studied under varying concentrations of carbon dioxide (ranging from 0.036 to 20%) and temperature (30, 40 and 50°C). The highest chlorophyll concentration (11 μg mL ^–1) and biomass (210 μg mL ^–1), which were 60 and 20 times more than that of C. vulgaris at ambient CO ₂ (0.036%), were recorded at 6% CO ₂ level. At 16% CO ₂ level, the concentrations of chlorophyll and biomass values were comparable to those at ambient CO ₂ but further increases in the CO ₂ level decreased both of them. Results showed that the optimum temperature for biomass production was 30°C under elevated CO ₂ (6%). Although increases in temperature above 30°C resulted in concomitant decrease in growth response, their adverse effects were significantly subdued at elevated CO ₂. There were also differential responses of the alga, assessed in terms of NaH ¹⁴CO ₃ uptake and carbonic anhydrase activity, to increases in temperature at elevated CO ₂. The results indicated that Chlorella vulgaris grew better at elevated CO ₂ level at 30°C, albeit with lesser efficiencies at higher temperatures.