Design, construction, and performance of a low-cost stainless-steel photobioreactor for enhanced microalgal biomass, lipid production, and biodiesel yield

The large-scale commercialisation of microalgae-based biodiesel is constrained by high capital and operational costs associated with photobioreactor systems. This study addresses this limitation through design, fabrication, and evaluation of a cost-effective 30 L stainless-steel stirred tank photobioreactor (SS-PBR) with integrated internal illumination for enhanced microalgal cultivation and biodiesel production. To enhance light dispersion, mass transfer, and culture stability, the reactor was built with locally obtained materials and fitted with mechanical agitation, controlled aeration, and inside LED lighting. Chlorella vulgaris and Scenedesmus obliquus , two native microalgal strains, were grown under carefully monitored circumstances. For S. obliquus and C. vulgaris , the SS-PBR attained maximum biomass concentrations of 9.92 ± 0.05 g L −1 and 7.55 ± 0.04 g L −1 , which translated into total biomass yields of 198.4 ± 1.0 g and 151.0 ± 0.8 g dry biomass per batch, respectively, with corresponding lipid contents of 58.48 ± 0.04% and 53.64 ± 0.07%. Biodiesel yields reached 99.48 ± 0.01% for S. obliquus and 96.54 ± 0.01% for C. vulgaris , with optimal productivity observed on day 6 of cultivation. Statistical analyses confirmed that cultivation time significantly influenced biomass growth, lipid accumulation, and biodiesel yield. Gas chromatography–mass spectrometry (GC–MS) analysis revealed fatty acid profiles dominated by C16–C18 chains with favourable saturated and monounsaturated compositions, while Fourier transform infrared (FTIR) spectroscopy confirmed functional group characteristics of high-quality biodiesel. The resulting fuel properties complied with international biodiesel standards. The developed SS-PBR demonstrated a substantially lower construction cost (∼USD 1500–1600) compared to conventional systems, while maintaining high productivity and operational efficiency. This study shows the potential of locally fabricated, internally illuminated photobioreactors as scalable and economically viable platforms for sustainable microalgae-based biodiesel production.