Recent advances in bicarbonate-activated hydrogen peroxide system for water treatment

Due to the prominent performance under neutral or weak alkaline pH in water treatment, bicarbonate activated hydrogen peroxide oxidation system (BAP system) has gained increasing interest in recent years. To gain a better and comprehensive understanding of BAP system, this review summarized the developments of BAP system for water treatment in the following aspects: 1) the equilibrium properties and HCO4- formation in BAP system; 2) the in-situ generation of multiple reactive species and mechanisms in BAP systems, including the direct oxidation process without catalyst and enhanced oxidation process with homogeneous or heterogeneous catalysts. It summarized that the HCO4- with high reactivity, is the special species in BAP system. HCO4- and free radical species (O2-, OH, 1O2, and CO3-) are responsible for the direct oxidation depending on the pollutants. In the metal-BAP system, the metal-HCO3− complex also contribute to the decontamination in addition with the above reactive species. HCO3− exhibits multiple functions in BAP system, including participating in the generation of HCO4− and intermediate complex, providing pH buffer to stabilize the reactions, quenching OH to generate the long lifetime radical (CO3-), etc.. It makes BAP system show good performance in stabilizing the catalysis process and prolonging the lifetime of catalyst under neutral or weak alkaline conditions. BAP system is tended to be a clean, cost-effective, and efficient technology, which could further extend the application of H2O2-based AOPs. Finally, perspectives and future efforts needed for ongoing research on BAP system are proposed.