Abstract
<title>Abstract</title> <p> This study evaluates the potential of two green microalgal strains, <italic>Chlorella sorokiniana</italic> and <italic>Scenedesmus obliquus</italic> , for the treatment of primary urban wastewater coupled with the production of value-added biomass. Cultivated in semi-continuous mode at a dilution rate of 0.3 day⁻¹, both species demonstrated high efficiency in removing nutrients and contaminants. Significant reductions were achieved for nitrates, ammonium, phosphates, and heavy metals (Fe²⁺, Cr, Ni²⁺and Cu²⁺) with removal efficiencies ranging from 19% to 100%. These results confirm that the treated effluent complies with regulatory standards for agricultural water reuse. Biochemical characterization revealed distinct metabolic profiles between the strains: <italic>C. sorokiniana</italic> was predominantly protein-rich (43.40% of dry weight), whereas <italic>S. obliquus</italic> exhibited a higher carbohydrate content (39.07%). Within a circular economy framework, aqueous extracts obtained via sonication were assessed for their biostimulant potential. <italic>C. sorokiniana</italic> extracts showed superior performance, increasing the germination index of watercress seeds by up to 135% at 0.5 g·L⁻¹. Additionally, this strain enhanced adventitious root formation in soybean by 129% and 218% at concentrations of 0.5 and 2.0 g·L⁻¹, respectively. It also exhibited cytokinin-like activity in cucumber cotyledons and uniquely promoted chlorophyll retention in wheat leaves. The results demonstrate that microalgae-based treatment of primary urban wastewater represents an effective and sustainable dual-purpose strategy. This approach enables efficient bioremediation for water reclamation while generating high-value biomass suitable for agricultural applications, thereby supporting the transition toward a bio-based circular economy. </p>