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Scenedesmus species, immobilized on alginate gel, was found effective in removing nitrate, atrazine, magnesium, phosphorus, zinc, oxadiazon, and triallate from groundwater in a continuous flow reactor. The laboratory‐scale experiments with synthetic groundwater, made of 8.8 mg/L NO3‐N and 90 µg/L atrazine, were performed at a hydraulic retention time of 7 days and the temperatures of 20 and 35°C. The highest uptake of nitrate and atrazine was observed at 20°C (97% and 70%, respectively). When tested in actual groundwater, 92% of nitrate, 100% of magnesium, 99.9% of phosphorus, and 92% of zinc were successfully removed at the end of 29 days’ treatment operations. The algal beads removed 100% of oxadiazon and triallate in the first 10 days, but some of the herbicides diffused back into the solution toward the end of the treatment process. Practitioner points Immobilized algae–alginate beads can remove nitrate, atrazine, oxadiazon, and triallate from groundwater in continuous flow reactor. The uptake rate of nitrate and atrazine is higher in room temperature (20°C). Same algae beads could be reused for herbicide uptake for the average of 10 days. The immobilized system is a natural sustainable alternative that can be used in groundwater pump and treat.

Mixing the Scenedesmus species with nanoclay and immobilizing in sodium alginate was evaluated as a sustainable treatment method for removing nitrate, atrazine, and metals from groundwater. Gel beads containing the hybrid mixture removed 100% of 10 mg/L N nitrate and 98% of 100 µg/L atrazine from synthetic groundwater in three days. The optimal amount of nanoclay was found to be 0.30 mg per bead. The experimental data fit well into a Freundlich adsorption isotherm and followed pseudo first-order kinetics. When tested in actual groundwater, 91% of nitrate and 100% of Cr, Se, and V were eliminated in three days without need for any nutrients or carbon source. Immobilizing algal beads embedded with nanoclay is a natural, low-cost alternative for groundwater treatment. The gel beads can be reused for at least two cycles without a compromise in performance. They are water-insoluble, easy to harvest, and offer high removal efficiency.

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