A comparative study on the degradation of ciprofloxacin in wastewater by iron-visible bismuth vanadate and iron-activated carbon systems: Mechanisms, efficiency, and ecotoxicity assessment

This study investigates the activation mechanisms of hydrogen peroxide by iron-visible bismuth vanadate (Fe 2+ /H₂O₂/BiVO₄/Vis) and iron-activated carbon (Fe 2+ /H₂O₂/AC) for ciprofloxacin (CIP) degradation. The Fe 2+ /H₂O₂/BiVO₄/Vis system achieved 99.8 % removal efficiency within 30 min at pH 2, while the Fe 2+ /H₂O₂/AC system demonstrated 99 % efficiency at pH 4. The optimum conditions were determined to be 25 mol/L H₂O₂ and 1.0 g/L catalyst dosage at pH 2 for the BiVO₄ system, and 200 mol/L H₂O₂ and 0.5 g/L catalyst dosage at pH 4 for the AC system. Scavenger experiments revealed that h + (non-radical holes) and • O₂ − were dominant in the BiVO₄ system, while • OH and 1 O₂ were primary in the AC system. Liquid chromatography high-resolution mass spectrometry identified by-products, confirming decarboxylation and piperazine ring opening as the primary degradation mechanisms. The electrical energy per order of magnitude (EEO) of the Fe 2+ /H₂O₂/BiVO₄/Vis system was 210 kWh·m −3 in 30 min. Ecotoxicity tests indicated that the degradation products are less harmful to aquatic organisms. Kinetic analysis revealed that the degradation process follows pseudo-second-order kinetics (R 2 = 0.93), while adsorption isotherms were best described by the Langmuir model (R 2 = 0.97). Both systems maintained over 90 % efficiency through five consecutive treatment cycles, demonstrating good stability and offering an effective alternative for treating contaminated wastewater. • Fe 2+ /H₂O₂/BiVO 4 /Vis and Fe 2+ /H₂O₂/AC systems effectively degraded CIP at acidic pH. • Scavenger tests confirmed • OH and • O₂ − as dominant radicals under acidic conditions. • LC-HRMS identified CIP degradation via decarboxylation & piperazine ring opening. • Fe 2+ /H₂O₂/BiVO 4 /Vis detected an EEO of 210 kWh·m −3 , showing reasonable energy efficiency. • Ecotoxicity tests identified risks to aquatic organisms from some by-products. • H₂O₂ levels, catalyst dose, & pH strongly affected degradation efficiency.