Continuous stirred tank reactor with recycled iron mixer for Fe(II)/chlorine-driven textile dyes oxidation: toward a sustainable continuous-flow process for micropollutants degradation

BACKGROUND

This study presents a novel and sustainable continuous-flow process for micropollutants degradation, using a lab-scale continuous stirred tank reactor (CSTR) equipped with a recycled iron mixer to drive Fe(II)/chlorine-induced oxidation. The recycled iron rod functions both as a mechanical stirrer and an in-situ source of Fe(II). The system's performance was evaluated by studding parameters such as chlorine flow rate (40–300 μL/s), submerged rod length (1–8 cm), rotation speed (0–500 rpm), dye concentration (5–40 mg/L), and pH (3–6).

RESULT

Maximum dye removal of 74% was achieved at pH 3, with higher chlorine flow rates, longer submerged rod length, and faster rotation speeds for an inlet dye concentration of 20 mg/L, while the reaction residence time did not exceed 45 s. Over 90% dye removal was observed at low concentrations (5 mg/L), and optimal performance occurred under acidic pH conditions. Higher pH values inhibited iron corrosion, quenching Fe(II) release and nullifying degradation. The matrix effect showed minimal impact with mineral water, while river and seawater reduced efficiency. Scavenger tests indicated ferryl species (Fe(IV)) as primary oxidant, while hydroxyl and chlorine radicals contributing less (10–20%). A comparison with a conventional Fe(II)/chlorine process showed that while the pre-dissolved Fe(II) system achieved higher conversion rates, the recycled iron system offered greater sustainability and operational simplicity through continuous Fe(II) generation.

CONCLUSION

This process provides a cost-effective, environmentally friendly, and efficient solution for micropollutant degradation in water matrices with light mineral and organic charges. © 2025 Society of Chemical Industry (SCI).