The valorization of agro-industrial waste streams represents a promising strategy for reducing production costs in microalgae biotechnology while promoting circular economy approaches. In this study, wastewater derived from fig jam processing was evaluated as an organic carbon source for mixotrophic cultivation of Limnospira (Spirulina) platensis. Cultures were grown under four conditions: a control medium and three concentrations of fig wastewater (FW) at 0.75%, 1.5%, and 3% (v v−1). The wastewater used in this study originates specifically from the washing and cleaning stages of dried fig processing, representing an early processing stream characterized by relatively high soluble sugar content and low thermal or chemical alteration. Biomass biochemical composition and bioactive compound production were investigated, including carbohydrates, proteins, lipids, photosynthetic pigments, polyphenols, antioxidant activity, and phycocyanin extraction yield and purity. The results showed that fig wastewater supplementation significantly influenced the metabolic profile of L. platensis. The highest protein content was obtained at 0.75% FW (44.90 ± 1.93 g 100 g−1 DW), whereas lipid accumulation increased with FW concentration, reaching 9.45 ± 2.30 g 100 g−1 DW at 3% FW. Antioxidant activity peaked at 1.5% FW (4.33 ± 0.43 μmol Trolox mg−1 DW), suggesting stimulation of oxidative stress response pathways under moderate organic supplementation. Pigment production showed different responses, with relatively stable chlorophyll and carotenoid contents but decreasing phycocyanin levels at higher FW concentrations. Phycocyanin yield decreased from 9.82 ± 1.00 g 100 g−1 DW in the control to 5.80 ± 0.22 g 100 g−1 DW at 3% FW, while purity values were highest at the highest FW concentration. These findings demonstrate that fig processing wastewater can be effectively used as an alternative organic substrate for mixotrophic Spirulina cultivation, enabling simultaneous wastewater valorization and production of biomass rich in proteins and bioactive compounds.
Franzoso et al. (Tue,) studied this question.