Phycoremediation of Dravyawati River (Jaipur): Simultaneous Wastewater Treatment and Biomass Generation Using Indigenous Algal Species

Rapid urbanization and unregulated industrial expansion in developing nations have intensified the degradation of freshwater ecosystems, with the Dravyawati River in Jaipur, Rajasthan, receiving untreated domestic sewage, industrial effluents, and agricultural runoff that elevate biochemical oxygen demand (BOD), chemical oxygen demand (COD), total nitrogen (TN), total phosphorus (TP), and total dissolved solids (TDS); since conventional physicochemical treatment technologies, though effective, entail high capital costs, energy demands, and secondary sludge generation, there is a pressing need for sustainable and resource-efficient alternatives, which this study addresses through the first systematic evaluation of indigenous microalgal consortia comprising Chlorella vulgaris, Scenedesmus obliquus, and Spirogyra sp. for simultaneous phycoremediation and biomass valorisation in the semi-arid urban river context of Jaipur. Water samples collected from three longitudinal transects of the Dravyawati River were subjected to phycoremediation in controlled 2-L photobioreactors at 25–32°C, pH 7–8.5, and 2000–5000 lux over a hydraulic retention time of 12 days, with pollutant removal efficiencies for TN, TP, BOD, COD, and TDS quantified at 3-day intervals using standard APHA methods, while biomass productivity was determined gravimetrically and biochemical composition (lipids, proteins, carbohydrates, chlorophyll) was characterised. The consortium achieved removal efficiencies of 83.6 ± 4.7% for TN, 78.9 ± 5.3% for TP, 76.4 ± 4.1% for BOD 5 , 78.2 ± 3.8% for COD, and 44.3 ± 3.4% for TDS, significantly outperforming all monoculture treatments, with Chlorella vulgaris demonstrating the highest individual removal performance among the single-species cultures; biomass yield reached 1.48 ± 0.12 g L -1 , corresponding to a biomass productivity of 0.123 ± 0.010 g L -1 d -1 in the consortium, with lipid content of 24.8–32.6%, protein content of 36.4–42.3%, and carbohydrate content of 18–26% across treatments, confirming applicability for bioenergy, biofertilizer, and nutraceutical value chains. These findings indicate that phycoremediation using locally adapted microalgae represents a scalable, cost-effective, and circular-economy-aligned strategy for urban river restoration in semi-arid India, with direct relevance to SDG 6 (Clean Water), SDG 11 (Sustainable Cities), and SDG 13 (Climate Action).