Microalgae-Immobilized Fe-CNF in an Activated Carbon Beads-Packed Photo-Modulated Bioreactor: Valorization of Nitrate-Enriched Water to Protein-Rich Biomass

Sequestration of nitrate-enriched water to intracellular proteins is an attractive route to producing value-added products from a bioresource. This study presents a novel strategy for the remediation of nitrate-enriched feedwater with the concomitant valorization to intracellular protein by immobilizingChlorella vulgarison iron (Fe)-carbon nanofiber (CNF)-modified activated carbon beads (ACBs) as the packing material in a photo-modulated bioreactor (PBR) operated under flow conditions. The sequestration of the feedwater produces protein-rich biomass via an ammonia generation pathway. CNFs augment the exposure of iron, an essential micronutrient for microalgae, as a dynamic biofilm at the bead surface. Reduction of nitrate to ammonia occurs in light, while the assimilation of ammonia to amino acids and proteins occurs in the dark. The effects of operating conditions, viz., photoperiods (0–24 h light–dark), nitrate concentrations (0.05–0.2 M), flow rates (0.5–2 cc/min), and the Fe-CNF/ACB amounts (10–50 g), on nitrate consumption, biomass production, and intracellular protein accumulation are determined. The results reveal a biomass yield of 2.6 mg/mL and protein concentration of 0.44 mg/mL under the optimized operating conditions. This study presents a translatable strategy for the generation of value-added products with potential water purification ability.