The work performed includes the following findings:
1. Screening of the enhancement on micropollutant oxidation by the Mn(VII)-H2O2 oxidation compared to traditional Mn(VII) oxidation. In this part, a wide range of target micropollutants was screened for the enhanced oxidation in the Mn(VII)-H2O2 oxidation process compared to conventional Mn(VII) oxidation. HPLC-DAD was used to develop the corresponding analytical methods for various micropollutants. Both carbon- and nitrogen-based functional groups were investigated to check the possibility of enhancement on their abatement and to elucidate the moieties in micropollutants with complex structures which lead to an enhanced oxidation. By kinetic experiments with model compounds, the functional groups which lead to an enhancement could be elucidated.
2. Functional groups with enhanced oxidation by the Mn(VII)-H2O2 process. In this part, following the above study, functional groups with an enhanced oxidation by the Mn(VII)-H2O2 process were selected. Further experiments utilizing model compounds with these functional groups were performed for mechanistic investigations.
3. Evaluating the mechanisms for the enhanced abatement of micropollutants by the Mn(VII)-H2O2 process. The essential oxidative intermediate for the induction of the enhancement during the Mn(VII)-H2O2 oxidation process was found. A correlation between the electron density of the micropollutants and the extent of oxidation was established. The role of superoxide radical (O2•–), which is formed in this oxidation process, was elucidated.
4. Temperature and pH dependence of second-order rate constants of micropollutant oxidation by Mn(VII) oxidation. Phenolic compounds are important functional groups in micropollutants as well as in natural organic matter in water sources. Kinetic experiments were performed with phenolic compounds without and with different forms of substituents at various temperatures (10-40 oC) and pH (6.5-8.2) which covered the common temperatures and pH ranges in practical drinking water and wastewater treatment trains. Substitution effects were investigated in relation to activation energies of permanganate oxidation of phenols at various pH values.
5. Relationship between kinetic and thermodynamic parameters for micropollutant oxidation. Correlations between the kinetic and thermodynamic parameters for the oxidation of micropollutant by permanganate were established, with an emphasis on the pKa and temperature effects. The species-specific rate constants for the reaction of permanganate with protonated and deprotonated forms of phenols were considered based on the pH, the acid-base speciation of the micropollutant and the activation energy (Ea).
Overall, this project provides essential information on the enhancing character of the permanganate-hydrogen peroxide process, which is beneficial for water treatment plants that are already using permanganate oxidation. The permanganate-hydrogen peroxide process can be installed after permanganate oxidation by adding hydrogen peroxide to the residual permanganate, in order to enhance the removal of the micropollutants discovered in this project that are hard to be removed by permanganate oxidation alone. This project also shows the temperature effects of permanganate oxidation of micropollutants, and established novel correlations between kinetic and thermodynamic parameters. These data will be beneficial for scientists and engineers to optimize the dosage of oxidants adopted in real applications, to achieve a better micropollutant abatement efficiency at lower temperature or save costs by adding lower amounts of oxidants at higher temperatures.
Dissemination activities for this project include publication of two peer-reviewed SCI papers (to be finished), and the acknowledgement that this study was supported by the European Union’s Horizon 2020 research and innovation program Enhanced oxidation under the Marie Skłodowska-Curie grant agreement No 101022222 will be listed in the final publication of the two papers. They will both be open access for the benefits of the public. Presentations at international conferences were also made to benefit the scientists, engineers and stakeholders in the field of drinking water and wastewater treatment. At the conference 3rd IWA International Conference on Disinfection and DBPs, 27.06.2022–01.07.2022 Milan, Italy, a talk was given entitled ''permanganate reduction by hydrogen peroxide: formation of reactive manganese species and superoxide radical'' to disseminate the results of this project, with the European Commission acknowledged.
