Biomass Production Potential of a Wastewater Alga Chlorella vulgaris ARC 1 under Elevated Levels of CO2 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^oC). 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 CO₂ (0.036%), were recorded at 6% CO₂ level. At 16% CO₂ level, the concentrations of chlorophyll and biomass values were comparable to those at ambient CO₂ but further increases in the CO₂ level decreased both of them. Results showed that the optimum temperature for biomass production was 30^oC under elevated CO₂ (6%). Although increases in temperature above 30^oC resulted in concomitant decrease in growth response, their adverse effects were significantly subdued at elevated CO₂. There were also differential responses of the alga, assessed in terms of NaH¹⁴CO₃ uptake and carbonic anhydrase activity, to increases in temperature at elevated CO₂. The results indicated that Chlorella vulgaris grew better at elevated CO₂ level at 30^oC, albeit with lesser efficiencies at higher temperatures.