Advances in the research on N and O dual isotope analysis of biological nitrogen removal performance

Biological denitrification is the most economical and effective way to meet the requirements of standard discharge of urban domestic sewage. However, the reaction mechanism of nitrogen (N) and oxygen (O) and the measurable total nitrogen loss cannot be accurately and quantitatively analyzed during the denitrification process. The new anaerobic ammonia oxidation (Anammox) technology makes the migration and conversion of N and O in the system more complex, and the mechanism of biological transformation is still unknown. In this study, the biological nitrogen removal system was divided into shortcut nitrification, full-range nitrification, shortcut denitrification, nitrous oxide (N2O) pathway distribution, and new Anammox technology. The reaction process was analyzed using the N and O dual isotope method to understand the reaction mechanism, and the theoretical technology was summarized in detail, combined with a mathematical model to explain the migration and transformation of N and O in the reaction system, and coupled with other isotope techniques (site preference (SP), C and S isotopes) to comprehensively describe the biological denitrification process. The insights gained in this study provide a reliable theoretical basis and analytical means for understanding the material changes in the actual biological wastewater treatment process. Additionally, the challenges and opportunities of using dual isotope technology to reveal the denitrification process are discussed.