Influencing factors of partial denitrification to enhance nitrogen removal and its coupled process application progress

As a front-end process for nitrogen removal, partial denitrification (PD) has been favored due to its advantages, such as high efficiency, low energy consumption, and low greenhouse gas emission. It has become a research hotspot in recent years. Partial denitrification coupled anammox process (PD/A) is a new biological nitrogen removal process, which not only plays an important role in the nitrogen cycle, but also holds high economic and practical value in terms of energy saving and environmental protection. The research status of PD process was introduced, and the influence of different inoculated sludge on PD process start-up was analyzed, based on existing research results. The magnetic effect, carbon source, C/N and iron-carbon ratio were reviewed to elucidate the mechanism of the influence of key factors on microbial community structure, key enzyme activity and cell metabolic pathways during enhanced nitrogen removal by PD process. The characteristics of different coupling forms of PD/A process were analyzed, and the research and application progress of the coupling process in treating practical wastewater such as municipal sewage, aquaculture wastewater and landfill leachate were summarized. Finally, the outlook of PD/A process in wastewater nitrogen removal treatment was prospected, and the potential engineering application scheme of PD/A process in landfill leachate treatment was proposed. It was considered that the key direction of future research was to overcome the influencing factors of PD and optimize the parameters of PD/A to enhance the efficiency and stability of the process.