Response surface methodology optimization of trimethoprim degradation in wastewater using Eosin-Y sensitized 25%ZnFe2O4-g-C3N4 composite under natural sunlight

The present study investigated the degradation of trimethoprim using Eosin Y-sensitized ZnFe₂O₄-g-C₃N₄ photocatalyst under natural sunlight using a parabolic trough reactor. The photocatalyst performance was optimized for three independent variables: pollutant dosage (10–25 mg/l), catalyst dose (0.4–1.2 g/l), and solution pH (4–10). The central composite design (CCD) was used to generate the design matrix and the response surface for degradation and total organic carbon (TOC) removal as the responses. Multiple regression techniques for each response generated two quadratic polynomial models. The coefficient of determination (R²) for trimethoprim degradation and TOC removal was 0.99 and 0.96, respectively, and these models could explain the variability in response surface. The analysis of variance (ANOVA) revealed that the initial pollutant dose and catalyst dose were most significant (p < 0.05) in contributing to both degradation and TOC removal. The optimum parameters obtained by desirability function for pollutant concentration, pH, and catalyst concentration were 10 mg/l, 7.19, and 0.72 g/l. This yielded an optimum degradation and TOC removal of 89.52% and 49.12%, respectively. Validation studies using optimized conditions for single-factor experiments had negligible variation from the predicted values, with actual degradation and TOC removal being 87.02% and 46.33%, respectively. Considering the good predictability and validity of the models, Response Surface Methodology is a potential mathematical tool for modeling the photodegradation of different antibiotics in aquatic environments.