Tetracycline removal by a natural biosorbent: optimization by response surface methods employing DOE/FFD design of the experiment

This study utilised activated carbon, synthesised with H3PO4 as an active agent (referred to as C-H3PO4), as an adsorbent for the removal of tetracycline (TC), a commonly used pharmaceutical compound. The activated carbon underwent characterisation through SEM-EDS, FTIR, and XRD analyses. The C-H3PO4 particles were found to range in size from 63 to 50 µm and possessed acidic functions within a surface area of 590 mmol/g. To assess the adsorptive performance of C-H3PO4 in relation to tetracycline, several operational parameters were investigated, including contact time, temperature, pH, concentration of the pharmaceutical compound, and C-H3PO4 dosage. Optimal conditions were determined as follows: a pH of 2.8, a TC concentration of 15 mg/L, a temperature of 308 K, and an adsorbent dosage of 90 mg, utilising the design of experiments (DOE/FFD) for parameter optimisation. In addition, the analysis of variance (ANOVA) and three-dimensional surface plots were created to evaluate the interaction between the factors and the ideal conditions for removing tetracycline. The maximum adsorption capacity of C-H3PO4 onto TC was found to be 7.41 mg/g. The experimental data were best fitted using the pseudo-second-order and Freundlich models, suggesting a multilayer physisorption phenomenon.