Employing microalgae cultivation on fruits and vegetable peel waste to produce biofuel, lutein, and biochar concurrently with an "Agro to Agro" algae biorefinery approach.

The aim of the current investigation is to explore the novel application of pumpkin, papaya, and orange peels as growth substrates for microalgae cultivation, with the overarching goal of advancing a sustainable "Agro to Agro" biorefinery paradigm. The research evaluates the integration of waste management practices into microalgal production, optimizing growth parameters to maximize output. Optimal concentrations of 2.8 mg L for orange peels, 35.5 mg L for papaya peels, and 35.5 mg L for pumpkin peels were identified, alongside a light intensity of 163.7 µmol m s and a nitrogen concentration of 0.8 g L. Under these conditions, Chlorella sorokiniana demonstrated peak biomass production of 3.16 g L, lipid productivity of 1.55 g L, and carotenoid productivity of 9.18 mg L, additionally, yielding significant amounts of palmitic acid (47.9%) and lutein. The study further explored the conversion of residual microalgae into biochar, with optimal pyrolysis conducted at 350 °C. The as-synthesized biochar was utilized effectively as a soil amendment for cultivating Vigna radiata. The present study underscores the viability of a closed-loop biorefinery approach, demonstrating the recycling of pumpkin, papaya, and orange peels as effective substrates for microalgae cultivation and subsequent biochar conversion for potential industrial applications. The promising results of the study advocate to the feasibility of this integrated model for sustainable future.