Carbon dioxide sequestration by Chlorella pyrenoidosa toward biomass and lipid production: an integrated multi-optimized management

The aim of this investigation was to evaluate the efficiency of unicellular microalga Chlorella pyrenoidosa cultivated in dairy industry wastewater for CO₂ sequestration and its influence on biomass and lipid production. For this purpose, three process parameters—CO₂ (2–10%), wavelength (420–680 nm), and temperature (20–50 °C)—were optimized using the central composite design (CCD) with response surface methodology (RSM). A total of twenty sets of experimental runs obtained by CCD were studied to optimize the process parameters for maximum biomass (mg L⁻¹), CO₂ fixation (mg L day⁻¹), and lipid yield (%). The highest biomass yield of 1.43 g L⁻¹ and maximum CO₂ fixation of 14.55 (mg L day⁻¹) were obtained with 5% CO₂, a temperature of 35 °C, and a wavelength of 520 nm. On the other hand, a maximum lipid yield of 34.21% was obtained with 5% CO₂, a temperature of 35 °C, and a wavelength of 420 nm. The most influential binary interaction among the selected variables for biomass production and CO₂ sequestration was found to be LED + Temp > CO₂ + Temp > CO₂ + LED. Meanwhile, the behavior of lipid content was highly influenced by the interaction of CO₂ + Temp > CO₂ + LED > LED + Temp. The highest degree of positive correlation was observed between biomass yield and CO₂. Fourier transform infrared spectroscopy (FTIR) reveals a strong signal at 1400–1700 cm⁻¹, confirming the existence of a carbonyl group (–COOR–).