Optimizing growth conditions of Desmodesmus armatus NCIM 5583 for enhanced biodiesel production using CaO bionanocatalyst

Rising fuel security challenges can be addressed by utilizing potential and renewable energy feedstocks such as microalgae. This study focuses on biodiesel production from Desmodesmus armatus NCIM 5583 by optimizing biomass productivity and lipid content. Independent optimization experiments were performed to study key growth parameters, viz., light intensity, photoperiod, and NaNO₃ concentration. Growth conditions with 40 µmol/m²/s light intensity, 20 h L:04 h D photoperiod, and 0.25 g/L NaNO₃ concentration exhibited highest biomass productivity of 26.51 ± 1.1 mg/L d and lipid yield of 45.1 ± 0.16% (w/w). Further, CaO bionanocatalyst synthesized using waste eggshells were characterized using SEM, EDX, FT-IR, and XRD. The results from SEM and EDX confirmed the structural and elemental composition of bionanocatalyst with Ca and O as the main elements. XRD revealed the crystalline nature of CaO with a particle size of 28.74 nm. Lipid transesterification using the synthesized catalyst yielded 84 ± 0.2% (w/w) FAME and was analyzed using FT-IR, ¹H NMR, ¹³C NMR, and GC–MS. The results confirmed the presence of the methyl ester group, implying the conversion of microalgal lipids to biodiesel. The findings from this study demonstrate the potential of D. armatus for biodiesel production and the application of waste eggshells as transesterification catalysts.