Valorization of Agricultural Industry Residues for Microalgae Production

Agricultural vegetable waste represents an underutilized feedstock for microalgal cultivation and high-value metabolite production. This study evaluated carrot residues as substrates for waste-derived growth media suitable for Chlorella sp. microalgae, using four pretreatment strategies: hydrothermal (120 °C, 3 h), enzymatic (45 °C, 3 h), and chemical (HCl, H₃PO₄). Hydrothermal pretreatment maximized dissolved organic carbon recovery (3.3-5.7 g/L) suitable for heterotrophic/mixotrophic growth but generated nutrient-poor media (NO₃⁻ 10-20 ppm; PO₄³⁻ 30-50 ppm). Enzymatic pretreatment preferentially mobilized macronutrients at 5-38-fold higher concentrations, enabling zero-supplementation, nutrient-complete media. Chlorella cultivation confirmed enzymatic pretreatment as the most reliable and universally applicable strategy (final biomass 0.60-0.88 g/L). Overall, these results establish a sustainable strategy for agricultural waste valorization through microalgal cultivation, directly applicable to food processing small-to-medium enterprises.