Optimizing the removal of ciprofloxacin from aqueous solutions using an advanced oxidation process (TiO₂/Fe₃O₄/UVA) and evaluating toxicity via the biological reduction method of resazurin dye

Ciprofloxacin (CIP), due to its high chemical stability and widespread occurrence in aquatic environments, has emerged as a significant environmental pollutant. Even at low concentrations, it poses a serious threat to human health and ecosystems. Therefore, the present study aims to optimize the photocatalytic degradation of CIP and evaluate the toxicity of the treated effluent obtained from aqueous solutions. This experimental laboratory study was carried out in batch mode using a photocatalytic process in a reactor with an approximate volume of 3 liters. The optimization of experiments was conducted using the Central Composite Design (CCD). In this design, the variables pH, contact time, CIP concentration, and dose of nanoparticles (NP _S ) were investigated. TiO₂/Fe₃O₄ nanocomposites were synthesized using the sol-gel method. The structure, morphology, and elemental analysis of the TiO₂/Fe₃O₄ nanocomposites were evaluated using SEM, Fourier Transform Infrared Spectroscopy FTIR, and EDX analysis. In this study, the residual concentration of CIP was measured using a HPLC device according to the designed experimental runs. Additionally, the toxicity of the effluent was assessed using the resazurin colorimetric assay based on the bacterial activity of E. coli . The results obtained from this study showed that spherical nanoparticles with a relatively uniform size distribution and no aggregation were produced. Based on the CCD model, under the optimal experimental conditions, including a contact time of 85.76 min, pH of 7.7, an initial CIP concentration of 13.44 mg/L, and a nanocomposite dose of 289.64 mg/L, the removal efficiency of CIP reached approximately 95%. Additionally, the analysis of variance (ANOVA) showed that the second-order regression model with a very high coefficient of determination (R² = 0.9895) provided the best fit to the data. The toxicity assessment of the effluent from the reactor showed that the EC₅₀, 100% mortality concentration, and no observed inhibitory effect concentration (NOEC) for E. coli were 1.37, 2.55, and 0.92 mg/L, respectively. The results of this study showed that the synthesized nanocomposite, along with UV radiation, is an effective and stable option for treating wastewater contaminated with emerging pollutants such as antibiotics. It can be scaled up for large-scale applications in environmental protection and to ensure compliance with effluent discharge standards.