Abstract

Abstract The high cost of specialized commercial media (e.g., Walne’s, Guillard’s, and Zarrouk’s) has limited the use of S. platensis as a valuable feed supplement for urban farming. This study explored a cost-effective alternative by investigating the use of commercial hydroponic compound fertilizers as a nutrient source and by determining the optimal pH for growth. Experiments were conducted in 5-liter bioreactors under semi-continuous cultivation. This study first evaluated the impact of increasing fertilizer dosages on biomass production and nutritional quality and then examined the effects of increasing pH (7.0 to 11.5), adjusted with baking soda. The results showed that an optimal fertilizer dosage of 0.74 g/L maximized biomass production at 0.12 g/L/day. However, crude protein content decreased from 53% at 0.4 g/L to 36% at 1.0 g/L, likely due to increased salt buildup in the culture medium. The pH of the culture medium markedly influenced biomass production and specific growth rate. Optimal biomass productivity for the pH series was observed to be 0.09 g/L/day within a baking soda concentration of 5.0 to 7.5 g/L (pH 9.0 to 10.0) with a predicted optimum of 5.83 g/L. These findings confirm the potential for developing a cost-effective Spirulina production system for urban farming. To ensure long-term sustainability, however, it is crucial to manage nutrient balance and sodium accumulation to prevent osmotic stress.

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