Degradation mechanisms of carbamazepine by δ-MnO2: Role of protonation of degradation intermediates.

Carbamazepine (CBZ), a widely used antiepileptic drug, is refractory to biological wastewater treatment. Rapid removal of CBZ is possible using synthetic manganese oxide (δ-MnO2) but the removal mechanisms require further investigation. In this study, CBZ degradation by δ-MnO2 was carried out at different pH to further explore the degradation mechanisms. Results show that CBZ degradation by δ-MnO2 was highly pH dependent, and rapid degradation occurred when pH <2.8. Based on the density functional theory calculations, increasing [H+] not only increased the reactivity of δ-MnO2, but also enhanced the secondary reactions of the intermediates. During the degradation process, protonation of CBZ degradation intermediates, instead of CBZ, played an important role. The overall kinetics of CBZ degradation was then described by the retarded first-order model. The initial rate (rinit) in the model between pH 2.0 and 6.2 was determined to be rinit = (2.41 ±â€¯0.51) × 10-3[CBZ]1.21[MnO2]1.07[H+]1.41. This is the first report revealing that protonation of intermediates from CBZ degradation can improve the CBZ oxidation by δ-MnO2. The pathways of CBZ degradation by δ-MnO2 were also proposed. The results of this study provide a new insight into the processing mechanism.

Plant uptake of diclofenac in a mesocosm-scale free water surface constructed wetland by Cyperus alternifolius.

This study aimed to assess the uptake of diclofenac, a widely used nonsteroidal anti-inflammatory pharmaceutical, by a macrophyte Cyperus alternifolius in a mesocosm-scale free water surface (FWS) constructed wetland. Quantitative analysis of diclofenac concentrations in water solution and plant tissues was conducted by high performance liquid chromatography analysis after sample pre-treatment with solid-phase extraction and liquid extraction, respectively. The FWS with Cyperus alternifolius obtained a maximum 69.3% diclofenac removal efficiency, while a control system without plant only had a removal efficiency of 2.7% at the end of the experiment period of 70 days. Based on mass balance study of the experimental system, it was estimated that plant uptake and in-plant conversion of diclofenac contributed about 21.4% of the total diclofenac removal in the mesocosm while the remaining 78.6% diclofenac was eliminated through biotic and abiotic conversion of diclofenac in the water phase. Diclofenac on the root surface and in roots, stems and leaves of Cyperus alternifolius was found at the concentrations of 0.15-2.59 µg/g, 0.21-2.66 µg/g, 0.06-0.53 µg/g, and 0.005-0.02 µg/g of fresh weight of plant tissues, respectively. The maximum bioaccumulation factor of diclofenac was calculated in roots (21.04) followed by root surface (20.49), stems (4.19), and leaves (0.16), respectively. Diclofenac translocation potentiality from root to stem was found below 0.5, suggesting a slow and passive translocation process of diclofenac. Current study demonstrated high potential of Cyperus alternifolius for phytoremediation of diclofenac in FWS and can be applied in other engineered ecosystems.