Scaling up the algal cultivation systems to commercial production is an essential step towards the biorefinery and circular bioeconomy concepts, meeting sustainable development goals (SDGs). The performance of the algal systems, regarding the biomass productivity and the associated biochemical composition, is improved by adapting the nitrogen-to-phosphorus (N/P) ratio of the culture medium. In this study, secondary-treated wastewater was used to cultivate microalgae Scenedesmus obliquus in pilot-scale circular ponds (3000 L) with N/P ratios of 4:1, 10:1, and 68:1, representing nutrient variability under natural (outdoor) environmental conditions. Based on the growth performance and macromolecule accumulation in the algal cells, the N/P ratio of 10:1 was selected to operate a raceway pond (300,000 L) for ensuring the scalability approach. Under this condition, the biomass concentration reached 0.98 ± 0.03 g/L, and the pollutant removal efficiencies (%) were ≈100 for NH₄⁺, 89.44 ± 3.98 for NO₃^-, and 79.01 ± 3.21 for PO₄^3-. Moreover, the metabolite contents (% of dry cell weight) of microalgae were 21.40 ± 1.86 for lipids, 33.40 ± 2.07 for proteins, and 18.66 ± 1.20 for carbohydrates. Microalgae production via outdoor open raceway ponds would meet multiple environmental (water, land, biodiversity, and greenhouse gases)-, economic (energy, investment, and industrialization)-, and social (awareness, and educational)-related SDGs. Hence, the study outcomes would contribute to the biomass conversion and biorefinery strategy, especially in developing countries.

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