Ampicillin removal by adsorption onto activated carbon: kinetics, equilibrium and thermodynamics

Pharmaceutical compounds are essential to preserve human and animal welfare, as well as to prevent illnesses. However, the elevated consumption of drugs, followed by incorrect disposal and inefficient wastewater treatment, may increase their environmental risk. In the case of antibiotics, such as ampicillin, some of the already known consequences are bacterial resistance and some toxic interactions with aquatic organisms. The scope of the present work is to investigate the removal of ampicillin through batch adsorption experiments onto granular activated carbon (GAC). The influence of pH and phase contact time were evaluated. Pseudo-first order, pseudo-second order and intraparticle diffusion models were adjusted to experimental data to determine process kinetics. In order to study adsorption equilibrium and thermodynamics parameters, isotherms at 298 K, 298 K and 308 K were constructed. The models of Langmuir, Freundlich and Sips fitted to experimental data. The best results (73% of removal, residual concentration 5.2 mg L^-1) were reached at pH 6 and 120 minutes of contact time. Pseudo-first order model better represented the adsorption kinetics (R² = 0.99), while the Langmuir equation suited well the experimental isotherms at 288 K and 298 K (R² = 0.998 and R² = 0.991) and the Sips equation better represented the system at 308 K (R² = 0.990). Thermodynamic parameters were estimated as ΔG° = -6,000 J mol^-1; -6,700 J mol^-1; -7,500 J mol^-1 at 288 K, 298 K and 308 K respectively, ΔH° = 14,500 J mol^-1 and ΔS° = 71.0 J mol^-1 K^-1. The results indicate that this process is spontaneous, efficient and potentially applicable in the removal of ampicillin from water.