Removal of carbamazepine, diclofenac and trimethoprim by solar driven advanced oxidation processes in a compound...

Contaminants of emerging concern (including pharmaceuticals) are not effectively removed by municipal wastewater treatment plants (WWTPs), so particular concern is related to agricultural wastewater reuse due to their possible uptake in crops irrigated with WWTPs effluents. Advanced oxidation processes (AOPs) and solar AOPs have been demonstrated to effectively remove pharmaceuticals from different aqueous matrices. In this study, an heterogeneous photocatalytic process using powdered nitrogen-doped TiO₂ immobilized on polystyrene spheres (sunlight/N-TiO₂) was compared to the benchmark homogenous AOP sunlight/H₂O₂ in a compound triangular collector reactor, to evaluate the degradation of three pharmaceuticals (carbamazepine (CBZ), diclofenac (DCF), trimethoprim (TMP)) in water. The degradation of the contaminants by sunlight and sunlight-AOPs well fit the pseudo-first order kinetic model (but for TMP under sunlight). High removal efficiency by solar photolysis was observed for DCF (up to 100%, half-life sunlight cumulative energy Q_S,1/2 = 2 kJ L^-1, half-life time t_1/2 = 32 min), while CBZ (32%, Q_S,1/2 = 28 kJ L^-1, t_1/2 = 385 min) and TMP (5% removal after 300 min) removal was poor. The degradation rate of CBZ, TMP and DCF was found to be slower during sunlight/H₂O₂ (Q_S,1/2 = 5 kJ L^-1, t_1/2 = 77 min; Q_S,1/2 = 20 kJ L^-1, t_1/2 = 128 min; Q_S,1/2 = 4 kJ L^-1, t_1/2 = 27 min, respectively) compared to sunlight/N-TiO₂ (Q_S,1/2 = 4 kJ L^-1, t_1/2 = 55 min; Q_S,1/2 = 3 kJ L^-1, t_1/2 = 42 min; Q_S,1/2 = 2 kJ L^-1, t_1/2 = 25 min, respectively). These results are promising in terms of solar technology upscale because the faster degradation kinetics observed for sunlight/N-TiO₂ process would result in smaller treatment volume, thus possibly perspective compensating the cost of the photocatalyst.