Optimization of ciprofloxacin removal from aqueous solutions using the TiO2/Fe3O4/UV process and toxicity assessment via resazurin reduction test

Ciprofloxacin (CIP) is a widespread environmental pollutant due to its high chemical stability and frequent presence in aquatic environments. Even at low concentrations, it poses serious risks to human health and ecosystems. This study aimed to optimize the photocatalytic degradation of CIP and evaluate the toxicity of the treated effluent from aqueous solutions. The experiments were conducted in batch mode using a 3 L photocatalytic reactor. Experimental optimization was performed using the Central Composite Design (CCD), considering pH, contact time, CIP concentration, and nanoparticle dose as variables. TiO 2 /Fe 3 O 4 nanocomposites were synthesized via the sol-gel method. Their structure, morphology, and elemental composition were analyzed using Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD (and Energy Dispersive X-Ray Spectroscopy (EDX). CIP residual concentrations were measured using High-Performance Liquid Chromatography )HPLC( according to the experimental design. Effluent toxicity was assessed using a resazurin colorimetric assay based on Escherichia coli activity. The results of the study showed that the synthesized nanoparticles were spherical, with a homogeneous size distribution below 100 nm, smooth surface morphology, and no observable aggregation, indicating successful synthesis of structurally stable and well-dispersed nanoparticles. Based on the CCD model, the optimal conditions were a contact time of 67.50 min, pH 7.50, an initial CIP concentration of 1 mg/L, and a nanocomposite dose of 255 mg/L. Under these conditions, CIP removal reached approximately 95%. ANOVA indicated that a second-order regression model with a high coefficient of determination (R 2 = 0.9895) best fit the data. The untreated CIP solution exhibited high toxicity toward E. coli , with a Half Maximal Effective Concentration (EC 50 ) of 1.30 mg/L. After photocatalytic treatment, EC 50 , 100% mortality concentration, and No Observed Effect Concentration (NOEC) in the treated effluent were 1.37, 2.27, and 0.92 mg/L, respectively; the reduction in toxicity was statistically significant ( p < 0.05). These results indicate that the synthesized TiO 2 /Fe 3 O 4 nanocomposite, combined with UV-C ) power = 125 W, intensity = 20 mW/cm 2 , λmax = 254 nm) radiation, is an effective and stable method for treating wastewater contaminated with antibiotics. The integration of effluent toxicity assessment with experimental modeling (CCD and statistical analysis) represents a novel aspect of this study. This approach has the potential to be scaled up for large-scale environmental applications and to ensure compliance with effluent discharge standards. However, several limitations, including dependence on operational conditions, the formation of potentially toxic intermediate compounds, and challenges in scalability, require further investigation.