Valorization of Canteen Wastewater Through Optimized <em>Spirulina platensis </em>Cultivation for Enhanced Carotenoid Production and Nutrient Removal

The valorization of nutrient-rich institutional effluents represents a promising route for sustainable algal biotechnology. This study investigates the potential of canteen wastewater (CW) as an alternative culture medium for Spirulina platensis, integrating wastewater treatment with high-value carotenoid production. Growth performance, biochemical composition, and nutrient removal efficiencies were systematically evaluated under different CW dilutions and illumination intensities to determine optimal cultivation conditions. Spirulina cultured in 75% CW under 180 μmol photons m⁻² s⁻¹ achieved a biomass productivity of 0.071 g L⁻¹ day⁻¹, threefold higher than the synthetic BG-11 control (0.023 g L⁻¹ day⁻¹). Nutrient remediation exceeded 92% for nitrate and 89% for phosphate, reducing effluent concentrations below discharge limits. The resulting biomass was enriched in proteins (54.3% DW) and carotenoids (21.81 mg g⁻¹ DW), outperforming most reported wastewater-based systems. Mechanistic analysis attributed superior performance to balanced N:P ratios, moderated COD, and alleviation of ammonia toxicity at optimal dilution. This study provides the first integrated demonstration of Spirulina cultivation in canteen wastewater optimized for both bioremediation and carotenoid enrichment. The findings establish a circular bioeconomy framework for institutional wastewater management and support the transition toward sustainable, low-cost microalgal production systems.