Application of adsorption and ozonation as quaternary treatment of WWTP effluent for the removal of contaminants of emerging concern: Results from laboratory scale experiments

European legislation introduces the need for quaternary treatment processes to reduce the risk associated with residual concentrations of Contaminants of Emerging Concern (CECs) present in the final effluent of Wastewater Treatment Plants. Among the various processes evaluated for this purpose, adsorption and ozonation have demonstrated the highest removal efficiencies. This study investigated the efficiency of these processes at laboratory scale, targeting four representative CECs commonly detected in wastewater: Carbamazepine (CBZ, antiepileptic), Sulfamethoxazole (SMX, antibiotic), 1H-Benzotriazole (BTR) and 5-Methyl-1H-Benzotriazole (MBTR) (corrosion inhibitors). Experiments were conducted under different operating conditions and treatment configurations. Overall, ozonation efficiently removed all the target CECs. CBZ and SMX exhibited similar reduction trends, achieving 90% removal within the first 5 min of treatment and complete removal after 15 min, at typical ozone dosages. MBTR was also effectively degraded but at a slower rate: the complete removal was observed only after 30 min. BTR required 60 min to reach a 50% concentration reduction. The removal patterns of these CECs in the mixture closely resembled those observed in the tests where they were present alone; only MBTR degradation rate decreased appreciably. Adsorption experiments, both in batch and continuous flow applications, revealed an inverse removal affinity: BTR>MBTR>>CBZ>SMX. The Freundlich isotherm model always provided the best fitting of the batch experimental data. The Freundlich constant, K_F, for benzotriazole compounds was significantly higher than for pharmaceuticals: 74.13 for BTR, 97.09 for MBTR, 18.90 for CBZ and 18.65 for SMX.

This study provides valuable insights into the comparative performance of ozonation and adsorption for CECs removal, offering critical data to support decision-making in the upgrading of wastewater treatment plants.