Generation, properties, and applications of singlet oxygen for wastewater treatment: a review

Contamination of drinking water sources with recalcitrant organic pollutants is a major health issue requiring advanced oxidation processes for the degradation of such pollutants. Here we review the use of advanced oxidation processes-based treatment of water, wastewater, and sludge, with focus on singlet oxygen production, reactivity mechanisms, and applications. Processes for single-oxygen production include photochemical production, decomposition of hydrogen peroxide, ozonides, endoperoxides, and sulfate radical-based advanced oxidation. Singlet oxygen is one of the main non-radical reactive oxygen species that are generated during advanced oxidation processes. It is less reactive but highly selective toward electron-rich organic compounds, compared to hydroxyl and sulfate radicals. When generated in large quantities, singlet oxygen can be the dominant reactive oxygen species responsible for the degradation of targeted pollutants. Singlet oxygen is less affected by water matrix components including dissolved organic matter and scavenging by anions.