Investigating the Suitability of Remineralized Aquaponics Sludge for Microalgae Culture: Biomass Production and Nutritional Composition

Microalgae are promising resources for valuable products, and cultivating them requires a suitable culture medium to optimize growth and desired biochemical content. Aquaponic sludge, a byproduct of aquaponics systems, offers a sustainable and cost-effective alternative to conventional media by recycling waste and reducing environmental impact. This study aimed to compare the performance of standard BG-11 (Blue-Green 11) medium with remineralized sludge-water (RSW) and RSW supplemented with micronutrient solution (RSW+Mn) for cultivating Chlorella minutissima, Botryococcus braunii, and Haematococcus pluvialis. The highest specific growth rate (μ) of 0.097±0.011 was observed for C. minutissima in BG-11 medium, nearly 28% higher than in RSW medium. However, the highest dry biomass productivity (Pb ) of 0.012±0.011 was achieved by H. pluvialis in RSW+Mn medium, significantly 94% higher than in RSW medium. Additionally, the volumetric productivity of biomass (Qx ) for H. pluvialis in RSW medium was 0.045±0.017, nearly 50% higher than in BG-11 medium. The best doubling time (td) of 8.83±0.93 days was observed for H. pluvialis in RSW medium. Notably, C. minutissima cultured in RSW medium yielded the highest crude protein (55.77±1.81%) and total lipid (4.69±0.88%) contents. These results demonstrate that RSW medium can be tailored to achieve desired outcomes, such as optimizing growth rate or lipid content. This study highlights the potential of remineralized aquaponic sludge as a sustainable culture medium for microalgae, contributing to waste recycling and resource efficiency in aquaponics systems. Future studies should focus on optimizing RSW medium for large-scale cultivation of target microalgae species with specific biochemical profiles.