Improving ozonation to remove carbamazepine through ozone-assisted catalysis using different NiO concentrations

The carbamazepine (CBZ) abatement is herein evaluated using catalytic ozonation at different NiO concentrations as catalyst: 100, 300, and 500 mg L⁻¹, revealing its total destruction after 5 min of reaction either by conventional or catalytic ozonation. The NiO incorporation in the reactor does not increase the destruction rate, but the catalyst presence enhances the partial mineralization of the contaminant by conversion into oxalic and formic acids and the removal of total organic carbon (TOC) associated with the formation of oxidant species such as hydroxyl radical. Evidence for this behavior is the accumulation rate of the above acids which rise proportionally to the NiO concentration. The highest NiO concentration (500 mg L⁻¹) reached a maximum TOC removal of 79.2%, which exceeds by 50% the outcome of the conventional treatment. The accumulation-decomposition profiles of oxalic and formic acids suggest the occurrence of simultaneous reaction mechanisms (hydroxyl radicals and complex formations) on the catalyst during CBZ ozonation. According to XPS analysis, the presence of nitrogen species in the NiO-ozonated was attributable to byproducts of CBZ decomposition. The toxicity bioassay based on Lactuca sativa seeds demonstrate that ozonated samples attained similar plant germination than the reference substance (water) after 120 min of treatment. This result is comparable with or without the catalyst presence, indicating the formation of non-toxic accumulated byproducts at the end of the ozonation reaction.