Application of manganese oxides under anoxic conditions to remove diclofenac from water

This study focuses on the potential of applying manganese oxides (MnO₂) under anoxic conditions (absence of oxygen) to remove diclofenac (DFC). By investigating parameters that are important for application, including temperature, MnO₂: DFC molar ratio, and co-solutes, the DFC removal potential is evaluated in terms of efficiency and observed initial kinetics (k_obs,init). Four commonly-used kinetic models are compared in this study and the best fitting one is employed. Overall, DFC removal and k_obs,init both increase upon changing temperature from 10 to 30°C and both decrease after further increasing temperature to 40°C. Increasing the MnO₂: DFC molar ratio improves degradation, as this provides more reactive surface sites for DFC conversions. However, DFC removal does not further increase when increasing the MnO₂:DFC from 2200:1 to 8900:1. The presence of metal ions inhibits DFC removal, possibly because the ions adsorb onto the reactive sites at the MnO₂ surface and compete with DFC. Phosphate has a diverse effect on DFC degradation: low concentrations inhibit and high concentrations promote removal. The presence of humic acids significantly promotes diclofenac removal. These findings are a first step towards further developing pharmaceutical removal technology using MnO₂ under anoxic conditions.