In wastewater treatment, heterogeneous advanced oxidation processes (AOPs) are often evaluated by the degradation rate of pollutants, but this may overlook a problem: pollutants may not be completely mineralized but instead transfer and accumulate on the surface of the catalyst as degradation intermediates. Recently, the organic carbon transfer process (OCTP) proposed by Xing et al. in Nature Water indicates that partial degradation intermediates can mask active sites and lead to catalyst deactivation, but this deactivation is reversible. Based on this, we introduce OCTP as a question of where the carbon of heterogeneous AOPs goes, pointing out that the properties of the oxidant and the choice of the reaction path will determine whether the pollutants in the system move towards deep mineralization or surface accumulation, thereby affecting stability and long-term effectiveness. Based on this logic, we propose the index of catalyst regeneration extent (CRE) to quantify the recoverable effective life after cleaning and advocate designing corresponding strategies according to different situations.
Guo et al. (Sun,) studied this question.