Effect of differnt CO2 concentrations on Spirulina ULC 0444

Effect of CO₂ Concentrations on Spirulina platensis Growth and Bioproduct Analysis

This dataset investigates the effect of varying CO₂ concentrations on the growth, biomass productivity, and pigment production of three Arthrospira platensis strains (ULC 0444). The study evaluates the optimization of CO₂ as a carbon source for enhancing microalgae cultivation and productivity under controlled conditions.

Experimental Setup

Strains and Cultivation Mediumthe selected A. platensis strain (ULC 0444) was cultivated in Zarrouk medium with modifications to exclude NaHCO₃ and Na₂CO₃, allowing CO₂ to serve as the sole carbon source. Other essential nutrients (NaNO₃, K₂SO₄, Na₂HPO₄, MgSO₄) were added. The pH of the medium was adjusted to 9.5 using NaOH and HCl.

Experimental DesignA 10% inoculum (culture with OD750 = 0.2) was prepared and cultivated in transparent acrylic tubular reactors (10 cm diameter, 50 cm height). The reactors were aerated from the bottom with a mixture of CO₂ and atmospheric air. CO₂ concentrations (ambient air, 3%, 5%, and 10%) were provided by adjusting rotameters, ensuring a total airflow rate of 1000 mL·min⁻¹. Cultures were maintained at 25 ± 2 °C with continuous lighting at 50 μmol·m⁻²·s⁻¹ provided by red LED light.

Growth and Biomass AnalysisGrowth was assessed using OD750, and dry weight (DW) was determined using the formula:

DW = 9.9040 * OD + 0.7440

Biomass productivity was calculated as:

P = (Xf - Xi) / (tf - ti)

Pigment Extraction and QuantificationOn day 14, phycocyanin was extracted using freeze-thaw cycles in sodium phosphate buffer (50 mM, pH 7). Phycocyanin content (Cpc) was quantified spectrophotometrically using a Shimadzu UV-1280 UV-VIS Spectrophotometer at 652 nm and 615 nm:

Cpc = (A615 - 0.474 * A652) / 5.34

Extraction yield (Ypc) was determined as:

Ypc = (Cpc * VPBS) / DW

Lipid Extraction and FAME Analysis

Lipids were extracted using a methanol-chloroform-water method and transesterified for fatty acid methyl ester (FAME) analysis. Gas chromatography (Agilent 7820A) with a Flame Ionization Detector (FID) was used to quantify FAMEs. Calibration employed the Supelco 37 Component FAME Mix.

Biodiesel Property Evaluation

Key biodiesel properties were calculated using established formulas:

Degree of Unsaturation (DU):

DU = SUM(MUFAs + 2 * PUFAs)

Iodine Value (IV):

IV = SUM((N% * D * 254) / M)

Saponification Value (SV):

SV = SUM((N% * 560) / M)

Cetane Number (CN):

CN = 46.3 + (5458 / SV) - (0.225 * IV)

Long-Chain Saturation Factor (LCSF):

LCSF = (C16_0 * 0.1) + (C18_0 * 0.5) + (C20_0 * 1) + (C22_0 * 1.5) + (C24_0 * 2)

Cold Filter Plugging Point (CFPP):

CFPP = (3.1417 * LCSF) - 16.477

Higher Heating Value (HHV):

HHV = 49.43 - 0.015 * IV - 0.041 * SV

Oxidative Stability (OS):

OS = 117.9295 / C18p + 2.5905

Where:

DU: Degree of unsaturation

MUFAs: Monounsaturated fatty acids

PUFAs: Polyunsaturated fatty acids

N%: Proportion of each fatty acid

D: Number of double bonds

M: Molecular mass

C16_0, C18_0, etc.: Weight proportions of saturated fatty acids

C18p: Combined weight proportion of linoleic (C18:2) and linolenic acids (C18:3)