Optimizing Biodiesel Yield from Microalgae: A Comparative Study of Spirulina sp. and Nannochloropsis oculata Using KOH-Catalyzed In-Situ Transesterification

Abstract

The increasing demand for renewable fuels necessitates low-cost, high-yield biodiesel feedstocks. This study investigates biodiesel production from Spirulina sp. and Nannochloropsis oculata cultivated in 20% tofu wastewater, integrating waste valorization with sustainable biomass generation. Biodiesel was produced using in-situ transesterification, a single-step method that combines lipid extraction and conversion directly from wet biomass, with potassium hydroxide as a catalyst. The research aimed to optimize 2 key parameters: methanol-to-biomass ratio weight by volume (3:1 until 7:1 w/v) and reaction time (30-120 min). Wet biomass was reacted with methanol and 2% KOH under controlled stirring and temperature conditions (80 OC). The optimal conditions for highest biodiesel yields were obtained at a methanol-to-biomass ratio of 7:1 and 120-min reaction time: 12.5% for Spirulina and 17.5% for Nannochloropsis oculata. Kinetic analysis revealed solvent ratio significantly enhanced transesterification efficiency. Nannochloropsis oculata performed better at low ratios, Spirulina sp. at higher ratios, confirming biodiesel feasibility from tofu wastewater-based microalgae. Fourier Transform Infrared Spectroscopy (FTIR) spectra confirmed the presence of ester functional groups, while Gas Chromatography Mass Spectrometry (GCMS) analysis identified key fatty acid methyl esters such as methyl palmitate and methyl oleate. Nannochloropsis oculata biodiesel exhibited a greater proportion of saturated Fatty Acid Methyl Esters (FAMEs), indicating better fuel feedstock. Nannochloropsis oculata biodiesel exhibited higher saturated FAME content. These results establish the technical feasibility of this approach and underscore its potential contribution to future biofuel development. Nonetheless, comprehensive physicochemical and performance evaluations are required to fully validate its application as a commercial biodiesel alternative.